Showing 1–50 of 51 results for author: Froula, D

Experimental demonstration of Flying-Focus enhanced Thomson scattering

Authors: E. Gerstmayr, C. Mariani, R. Fitzgarrald, M. VanDusen-Gross, C. Berger, Q. Chen, A. Di Piazza, M. S. Formanek, D. H. Froula, C. G. R. Geddes, A. J. Gonsalves, B. Greenwood, R. Jacob, A. Lu, A. McIlvenny, K. Nakamura, L. Obst-Huebl, J. P. Palastro, A. Picksley, K. Poder, D. Ramsey, H. G. Rinderknecht, G. Sarri, A. G. R Thomas, J. van Tilborg , et al. (1 additional authors not shown)

Abstract: We report the experimental demonstration of a spatiotemporally engineered "Flying-Focus" laser pulse for enhanced x-ray generation in relativistic Thomson scattering. A combination of longitudinal chromatic aberration, angular dispersion, and group delay dispersion was applied to an ultrashort relativistically intense laser pulse to control the motion of its focal point. Precise tuning of the grou… ▽ More We report the experimental demonstration of a spatiotemporally engineered "Flying-Focus" laser pulse for enhanced x-ray generation in relativistic Thomson scattering. A combination of longitudinal chromatic aberration, angular dispersion, and group delay dispersion was applied to an ultrashort relativistically intense laser pulse to control the motion of its focal point. Precise tuning of the group delay dispersion was used to match the velocity of the focus to the trajectory of a counterpropagating electron bunch, produced by a laser wakefield accelerator. This prolonged the Thomson scattering interaction while reducing nonlinear effects, leading to an enhanced x-ray yield. The approach has the potential to increase the spectral density and brightness of the x-ray beam by orders of magnitude compared to equivalent focusing without spatiotemporal control. This experiment establishes a new technique for structured-light control at high intensity, demonstrating the realization of dynamic intensity structures that enhance light-matter interactions and for the generation of ultra-bright radiation sources. △ Less

Submitted 17 July, 2026; originally announced July 2026.

Comments: 10 pages, 7 figures

Precision mapping of laser-driven magnetic fields and their evolution in high-energy-density plasmas

Authors: Lan Gao, PM Nilson, IV Igumenshchev, MG Haines, DH Froula, R Betti, DD Meyerhofer

Abstract: Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim$4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim$10$^{14}$ W$/$cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration… ▽ More Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim$4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim$10$^{14}$ W$/$cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations. △ Less

Submitted 9 July, 2026; originally announced July 2026.

Journal ref: Phys. Rev. Lett. 114, 215003 (2015)

Observation of Self-Similarity in the Magnetic Fields Generated by the Ablative Nonlinear Rayleigh-Taylor Instability

Authors: L. Gao, P. M. Nilson, I. V. Igumenschev, G. Fiksel, R. Yan, J. R. Davies, D. Martinez, V. Smalyuk, M. G. Haines, E. G. Blackman, D. H. Froula, R. Betti, D. D. Meyerhofer

Abstract: Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts… ▽ More Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts the time evolution of the number and size of the bubbles, linking the cellular magnetic field structures with the Rayleigh-Taylor bubble and spike growth. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Journal ref: Phys. Rev. Lett. 110, 185003 (2013)

Magnetic field generation by the Rayleigh-Taylor instability in laser-driven planar plastic targets

Authors: L Gao, PM Nilson, IV Igumenschev, SX Hu, JR Davies, C Stoeckl, MG Haines, DH Froula, R Betti, DD Meyerhofer

Abstract: Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim$4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim$10$^{14}$ W$/$cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration… ▽ More Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim$4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim$10$^{14}$ W$/$cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations. △ Less

Submitted 7 July, 2026; originally announced July 2026.

Journal ref: Phys. Rev. Lett. 109, 115001 (2012)

Mega-Gauss Plasma Jet Creation Using a Ring of Laser Beams

Authors: L. Gao, E. Liang, Y. Lu, R. K. Follet, H. Sio, P. Tzeferacos, D. H. Froula, A. Birkel, C. Li, D. Lamb, R. Petrasso, W. Fu, M. Wei, H. Ji

Abstract: Using 20 OMEGA laser beams at the Laboratory for Laser Energetics, University of Rochester, to irradiate a flat plastic target in a hollow ring configuration, we created supersonic cylindrical stable plasma jets with self-generated megagauss magnetic fields extending out to > 4 mm. These well-collimated magnetized jets possess a number of distinct and novel properties that will allow us to study t… ▽ More Using 20 OMEGA laser beams at the Laboratory for Laser Energetics, University of Rochester, to irradiate a flat plastic target in a hollow ring configuration, we created supersonic cylindrical stable plasma jets with self-generated megagauss magnetic fields extending out to > 4 mm. These well-collimated magnetized jets possess a number of distinct and novel properties that will allow us to study the dynamics, physical processes and scaling properties of astrophysical jets not feasible with other laboratory settings. The dimensionless parameters of these laboratory jets fall in the same regime as those of YSO jets. They will also provide new versatile laser-based platforms to study magnetized shocks, shear flows and other plasma processes under controllable conditions. △ Less

Submitted 6 July, 2026; originally announced July 2026.

Journal ref: The Astrophysical Journal Letters, 873:L11, 2019

Differentiable Programming for Plasma Physics: From Diagnostics to Discovery and Design

Authors: A. S. Joglekar, A. G. R. Thomas, A. L. Milder, K. G. Miller, J. P. Palastro, D. H. Froula

Abstract: Differentiable programming, enabled by automatic differentiation (AD), provides a robust framework for gradient-based optimization in computational plasma physics. While optimization is often only used towards design, we demonstrate that it can also be used for discovery and bridging the gap towards multi-scale modeling. We discuss four applications: (1) discovering novel nonlinear plasma phenomen… ▽ More Differentiable programming, enabled by automatic differentiation (AD), provides a robust framework for gradient-based optimization in computational plasma physics. While optimization is often only used towards design, we demonstrate that it can also be used for discovery and bridging the gap towards multi-scale modeling. We discuss four applications: (1) discovering novel nonlinear plasma phenomena, including a previously unknown superadditive wavepacket interaction regime, by optimizing differentiable kinetic simulations; (2) learning hidden variables that capture spatiotemporally non-local kinetic effects in fluid simulations, enabling hydrodynamic models to reproduce large Knudsen number physics typically requiring kinetic solvers; (3) accelerating Thomson scattering analysis by over $140\times$ while enabling extraction of velocity distribution functions with $\mathcal{O}(10^3)$ parameters; and (4) inverse design of spatiotemporal laser pulses that achieve target far-field behavior where full space-time coupling improves performance by $15\times$ over spatial or temporal optimization alone. These examples illustrate that differentiable programming not only accelerates existing design and inference workflows but enables qualitatively new capabilities, from algorithmic physics discovery to high-dimensional inference and design previously considered intractable. △ Less

Submitted 11 March, 2026; originally announced March 2026.

Comments: Invited submission to Physics of Plasmas

Laboratory observation of collective beam-plasma instabilities in a relativistic pair jet

Authors: J W D Halliday, C D Arrowsmith, A M Goillot, P J Bilbao, P Simon, V Stergiou, S Zhang, P Alexaki, M Bochmann, A F A Bott, S Burger, H Chen, F D Cruz, T Davenne, A Dyson, A Ebn Rahmoun, I Efthymiopoulos, D H Froula, J T Gudmundsson, D Haberberger, T Hodge, S Iaquinta, E E Los, G Marshall, F Miniati , et al. (15 additional authors not shown)

Abstract: We report on a measurement of collective behavior in a relativistic electron-positron pair plasma produced in the laboratory. Using the Fireball platform at CERN's HiRadMat facility, 440 GeV protons were used to generate an ultra-relativistic, charge-neutral electron-positron pair beam that propagated through an ambient RF discharge plasma. Magnetic-field amplification due to a beam-plasma instabi… ▽ More We report on a measurement of collective behavior in a relativistic electron-positron pair plasma produced in the laboratory. Using the Fireball platform at CERN's HiRadMat facility, 440 GeV protons were used to generate an ultra-relativistic, charge-neutral electron-positron pair beam that propagated through an ambient RF discharge plasma. Magnetic-field amplification due to a beam-plasma instability was diagnosed using a high-sensitivity Faraday-rotation probe, supported by detailed characterization of the diagnostic impulse response. The measured path-integrated magnetic field agrees quantitatively with predictions from particle-in-cell simulations. The results provide a critical benchmark for models of relativistic beam-plasma interactions in astrophysical contexts such as blazar jets and pulsar-wind nebulae. △ Less

Submitted 18 February, 2026; originally announced February 2026.

Comments: 7 pages, 4 figures

Spatiotemporal control of laser intensity using differentiable programming

Authors: Kyle G Miller, Tomas E Gutierrez, Archis S Joglekar, Amanda Elliott, Dustin H Froula, John P Palastro

Abstract: Optical techniques for spatiotemporal control can produce laser pulses with custom amplitude, phase, or polarization structure. In nonlinear optics and plasma physics, the use of structured pulses typically follows a forward design approach, in which the efficacy of a known structure is analyzed for a particular application. Inverse approaches, in contrast, enable the discovery of new structures w… ▽ More Optical techniques for spatiotemporal control can produce laser pulses with custom amplitude, phase, or polarization structure. In nonlinear optics and plasma physics, the use of structured pulses typically follows a forward design approach, in which the efficacy of a known structure is analyzed for a particular application. Inverse approaches, in contrast, enable the discovery of new structures with the potential for superior performance. Here, an implementation of the unidirectional pulse propagation equation that supports automatic differentiation is combined with gradient-based optimization to design structured pulses with features that are advantageous for a range of nonlinear optical and plasma-based applications: (1) a longitudinally uniform intensity over an extended region, (2) a superluminal intensity peak that travels many Rayleigh ranges with constant duration, spot size, and amplitude, and (3) a laser pulse that ionizes a gas to form a uniform column of plasma. In the final case, optimizing the full spatiotemporal structure improves the performance by a factor of 15 compared to optimizing only spatial or only temporal structure, highlighting the advantage of spatiotemporal control. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Comments: 15 pages, 5 figures, 4 tables

Suppression of pair beam instabilities in a laboratory analogue of blazar pair cascades

Authors: Charles D. Arrowsmith, Francesco Miniati, Pablo J. Bilbao, Pascal Simon, Archie F. A. Bott, Stephane Burger, Hui Chen, Filipe D. Cruz, Tristan Davenne, Anthony Dyson, Ilias Efthymiopoulos, Dustin H. Froula, Alice Goillot, Jon T. Gudmundsson, Dan Haberberger, Jack W. D. Halliday, Tom Hodge, Brian T. Huffman, Sam Iaquinta, G. Marshall, Brian Reville, Subir Sarkar, Alexander A. Schekochihin, Luis O. Silva, Raspberry Simpson , et al. (6 additional authors not shown)

Abstract: The generation of dense electron-positron pair beams in the laboratory can enable direct tests of theoretical models of $γ$-ray bursts and active galactic nuclei. We have successfully achieved this using ultra-relativistic protons accelerated by the Super Proton Synchrotron at CERN. In the first application of this experimental platform, the stability of the pair beam is studied as it propagates t… ▽ More The generation of dense electron-positron pair beams in the laboratory can enable direct tests of theoretical models of $γ$-ray bursts and active galactic nuclei. We have successfully achieved this using ultra-relativistic protons accelerated by the Super Proton Synchrotron at CERN. In the first application of this experimental platform, the stability of the pair beam is studied as it propagates through a metre-length plasma, analogous to TeV $γ$-ray induced pair cascades in the intergalactic medium. It has been argued that pair beam instabilities disrupt the cascade, thus accounting for the observed lack of reprocessed GeV emission from TeV blazars. If true this would remove the need for a moderate strength intergalactic magnetic field to explain the observations. We find that the pair beam instability is suppressed if the beam is not perfectly collimated or monochromatic, hence the lower limit to the intergalactic magnetic field inferred from $γ$-ray observations of blazars is robust. △ Less

Submitted 15 September, 2025; v1 submitted 10 September, 2025; originally announced September 2025.

Journal ref: Proc. Natl. Acad. Sci. 122 (2025) e2513365122

Path to a Single-Stage, 100-GeV Electron Beam via a Flying-Focus-Driven Laser-Plasma Accelerator

Authors: J. L. Shaw, M. V. Ambat, K. G. Miller, R. Boni, I. LaBelle, W. B. Mori, J. J. Pigeon, A. Rigatti, I. Settle, L. Mack, J. P. Palastro, D. H. Froula

Abstract: Dephasingless laser wakefield acceleration (DLWFA), a novel laser wakefield acceleration concept based on the recently demonstrated "flying focus" technology, offers a new paradigm in laser-plasma acceleration that could advance the progress toward a TeV linear accelerator using a single-stage system without guiding structures. The recently proposed NSF OPAL laser facility could be the transformat… ▽ More Dephasingless laser wakefield acceleration (DLWFA), a novel laser wakefield acceleration concept based on the recently demonstrated "flying focus" technology, offers a new paradigm in laser-plasma acceleration that could advance the progress toward a TeV linear accelerator using a single-stage system without guiding structures. The recently proposed NSF OPAL laser facility could be the transformative technology that enables this grand challenge in laser-plasma acceleration. We review the viable parameter space for DLWFA based on the scaling of its performance with laser and plasma parameters, and we compare that performance to traditional laser wakefield acceleration. These scalings indicate the necessity for ultrashort, high-energy laser architectures such as NSF OPAL to achieve groundbreaking electron energies using DLWFA. Initial results from MTW-OPAL, the platform for the 6-J DLWFA demonstration experiment, show a tight, round focal spot over a distance of 3.7 mm. New particle-in-cell simulations of that platform indicate that using hydrogen for DLWFA reduces the amount of laser light that is distorted due to refraction at ionization fronts. An experimental path, and the computational and technical design work along that path, from the current status of the field to a single-stage, 100-GeV electron beam via DLWFA on NSF OPAL is outlined. Progress along that path is presented. △ Less

Submitted 30 April, 2025; originally announced May 2025.

Comments: 20 pages, 11 figures. Submitted to Physics of Plasmas

X-ray free-electron lasing in a flying-focus undulator

Authors: D. Ramsey, B. Malaca, T. T. Simpson, M. Formanek, L. S. Mack, J. Vieira, D. H. Froula, J. P. Palastro

Abstract: Laser-driven free-electron lasers (LDFELs) replace magnetostatic undulators with the electromagnetic fields of a laser pulse. Because the undulator period is half the wavelength of the laser pulse, LDFELs can amplify x rays using lower electron energies and over shorter interaction lengths than a traditional free-electron laser. In LDFELs driven by conventional laser pulses, the undulator uniformi… ▽ More Laser-driven free-electron lasers (LDFELs) replace magnetostatic undulators with the electromagnetic fields of a laser pulse. Because the undulator period is half the wavelength of the laser pulse, LDFELs can amplify x rays using lower electron energies and over shorter interaction lengths than a traditional free-electron laser. In LDFELs driven by conventional laser pulses, the undulator uniformity required for high gain necessitates large laser-pulse energies. Here, we show that a flying-focus pulse provides the undulator uniformity required to reach high gain with a substantially lower energy than a conventional pulse. The flying-focus pulse features an intensity peak that travels in the opposite direction of its phase fronts. This enables an LDFEL configuration where an electron beam collides head-on with the phase fronts and experiences a near-constant undulator strength as it co-propagates with the intensity peak. Three-dimensional simulations of this configuration demonstrate the generation of megawatts of coherent x-ray radiation with 20 times less energy than a conventional laser pulse. △ Less

Submitted 6 March, 2025; v1 submitted 16 October, 2024; originally announced October 2024.

Dephasingless two-color terahertz generation

Authors: Tanner T. Simpson, Jeremy J. Pigeon, Kyle G. Miller, Dillon Ramsey, Dustin H. Froula, John P. Palastro

Abstract: A laser pulse composed of a fundamental and an appropriately phased second harmonic can drive a time-dependent current of photoionized electrons that generates broadband THz radiation. Over the propagation distances relevant to many experiments, dispersion causes the relative phase between the harmonics to evolve. This "dephasing" slows the accumulation of THz energy and results in a multi-cycle T… ▽ More A laser pulse composed of a fundamental and an appropriately phased second harmonic can drive a time-dependent current of photoionized electrons that generates broadband THz radiation. Over the propagation distances relevant to many experiments, dispersion causes the relative phase between the harmonics to evolve. This "dephasing" slows the accumulation of THz energy and results in a multi-cycle THz pulse with significant angular dispersion. Here, we introduce a novel optical configuration that compensates the relative phase evolution, allowing for the formation of a half-cycle THz pulse with almost no angular dispersion. The configuration uses the spherical aberration of an axilens to map a prescribed radial phase variation in the near field to a desired longitudinal phase variation in the far field. Simulations that combine this configuration with an ultrashort flying focus demonstrate the formation of a half-cycle THz pulse with a controlled emission angle and 1/4 the angular divergence of the multi-cycle pulse created by a conventional optical configuration. △ Less

Submitted 6 June, 2024; originally announced June 2024.

Laboratory realization of relativistic pair-plasma beams

Authors: C. D. Arrowsmith, P. Simon, P. Bilbao, A. F. A. Bott, S. Burger, H. Chen, F. D. Cruz, T. Davenne, I. Efthymiopoulos, D. H. Froula, A. M. Goillot, J. T. Gudmundsson, D. Haberberger, J. Halliday, T. Hodge, B. T. Huffman, S. Iaquinta, F. Miniati, B. Reville, S. Sarkar, A. A. Schekochihin, L. O. Silva, R. Simpson, V. Stergiou, R. M. G. M. Trines , et al. (4 additional authors not shown)

Abstract: Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black holes and neutron star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with such pair plasmas. Their behaviour is quite different from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components and their role in the dy… ▽ More Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black holes and neutron star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with such pair plasmas. Their behaviour is quite different from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components and their role in the dynamics of such compact objects is believed to be fundamental. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies which are rather limited. We present first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN's Super Proton Synchrotron (SPS) accelerator. The produced pair beams have a volume that fills multiple Debye spheres and are thus able to sustain collective plasma oscillations. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations. △ Less

Submitted 8 December, 2023; originally announced December 2023.

Comments: 14 pages, 8 figures

Space-time structured plasma waves

Authors: J. P. Palastro, K. G. Miller, R. K. Follett, D. Ramsey, K. Weichman, A. V. Arefiev, D. H. Froula

Abstract: Electrostatic waves play a critical role in nearly every branch of plasma physics from fusion to advanced accelerators, to astro, solar, and ionospheric physics. The properties of planar electrostatic waves are fully determined by the plasma conditions, such as density, temperature, ionization state, or details of the distribution functions. Here we demonstrate that electrostatic wavepackets struc… ▽ More Electrostatic waves play a critical role in nearly every branch of plasma physics from fusion to advanced accelerators, to astro, solar, and ionospheric physics. The properties of planar electrostatic waves are fully determined by the plasma conditions, such as density, temperature, ionization state, or details of the distribution functions. Here we demonstrate that electrostatic wavepackets structured with space-time correlations can have properties that are independent of the plasma conditions. For instance, an appropriately structured electrostatic wavepacket can travel at any group velocity, even backward with respect to its phase fronts, while maintaining a localized energy density. These linear, propagation-invariant wavepackets can be constructed with or without orbital angular momentum by superposing natural modes of the plasma and can be ponderomotively excited by space-time structured laser pulses like the flying focus. △ Less

Submitted 15 September, 2023; v1 submitted 12 September, 2023; originally announced September 2023.

Dephasingless laser wakefield acceleration in the bubble regime

Authors: Kyle G. Miller, Jacob R. Pierce, Manfred V. Ambat, Jessica L. Shaw, Kale Weichman, Warren B. Mori, Dustin H. Froula, John P. Palastro

Abstract: Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield.… ▽ More Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield. Here, we demonstrate that a single space-time structured laser pulse can be used for ionization injection and electron acceleration over many dephasing lengths in the bubble regime. Simulations of a dephasingless laser wakefield accelerator driven by a 6.2-J laser pulse show 25 pC of injected charge accelerated over 20 dephasing lengths (1.3 cm) to a maximum energy of 2.1 GeV. The space-time structured laser pulse features an ultrashort, programmable-trajectory focus. Accelerating the focus, reducing the focused spot-size variation, and mitigating unwanted self-focusing stabilize the electron acceleration, which improves beam quality and leads to projected energy gains of 125 GeV in a single, sub-meter stage driven by a 500-J pulse. △ Less

Submitted 25 August, 2023; originally announced August 2023.

Comments: 18 pages, 4 figures

Programmable and arbitrary-trajectory ultrafast flying focus pulses

Authors: M. V. Ambat, J. L. Shaw, J. J. Pigeon, K. G. Miller, T. T. Simpson, D. H. Froula, J. P. Palastro

Abstract: "Flying focus" techniques produce laser pulses with dynamic focal points that travels distances much greater than a Rayleigh length. The implementation of these techniques in laser-based applications requires the design of optical configurations that can both extend the focal range and structure the radial group delay. This article describes a method for designing optical configurations that produ… ▽ More "Flying focus" techniques produce laser pulses with dynamic focal points that travels distances much greater than a Rayleigh length. The implementation of these techniques in laser-based applications requires the design of optical configurations that can both extend the focal range and structure the radial group delay. This article describes a method for designing optical configurations that produce ultrashort flying focus pulses with arbitrary-trajectory focal points. The method is illustrated by several examples that employ an axiparabola for extending the focal range and either a reflective echelon or a deformable mirror-spatial light modulator pair for structuring the radial group delay. The latter configuration enables rapid exploration and optimization of flying foci, which could be ideal for experiments. △ Less

Submitted 11 July, 2023; originally announced July 2023.

Spatiotemporal control of two-color terahertz generation

Authors: Tanner T. Simpson, Jeremy J. Pigeon, Manfred Virgil Ambat, Kyle G. Miller, Dillon Ramsey, Kale Weichman, Dustin H. Froula, John P. Palastro

Abstract: A laser pulse composed of a fundamental and properly phased second harmonic exhibits an asymmetric electric field that can drive a time-dependent current of photoionized electrons. The current produces an ultrashort burst of terahertz (THz) radiation. When driven by a conventional laser pulse, the THz radiation is emitted into a cone with an angle determined by the dispersion of the medium. Here w… ▽ More A laser pulse composed of a fundamental and properly phased second harmonic exhibits an asymmetric electric field that can drive a time-dependent current of photoionized electrons. The current produces an ultrashort burst of terahertz (THz) radiation. When driven by a conventional laser pulse, the THz radiation is emitted into a cone with an angle determined by the dispersion of the medium. Here we demonstrate that the programmable-velocity intensity peak of a spatiotemporally structured, two-color laser pulse can be used to control the emission angle, focal spot, and spectrum of the THz radiation. Of particular interest for applications, a structured pulse with a subluminal intensity peak can drive highly focusable, on-axis THz radiation. △ Less

Submitted 2 June, 2023; originally announced June 2023.

Cross-beam energy transfer in conditions relevant to direct-drive implosions on OMEGA

Authors: K. L. Nguyen, L. Yin, B. J. Albright, D. H. Edgell, R. K. Follett, D. Turnbull, D. H. Froula, J. P. Palastro

Abstract: In cross-beam energy transfer (CBET), the interference of two laser beams ponderomotively drives an ion-acoustic wave that coherently scatters light from one beam into the other. This redirection of laser beam energy can severely inhibit the performance of direct-drive inertial confinement fusion (ICF) implosions. To assess the role of nonlinear and kinetic processes in direct-drive-relevant CBET,… ▽ More In cross-beam energy transfer (CBET), the interference of two laser beams ponderomotively drives an ion-acoustic wave that coherently scatters light from one beam into the other. This redirection of laser beam energy can severely inhibit the performance of direct-drive inertial confinement fusion (ICF) implosions. To assess the role of nonlinear and kinetic processes in direct-drive-relevant CBET, the energy transfer between two laser beams in the plasma conditions of an ICF implosion at the OMEGA laser facility was modeled using particle-in-cell simulations. For typical laser beam intensities, the simulations are in excellent agreement with linear kinetic theory, indicating that nonlinear processes do not play a role in direct-drive implosions. At higher intensities, CBET can be modified by pump depletion, backward stimulated Raman scattering, or ion trapping, depending on the plasma density. △ Less

Submitted 25 April, 2023; originally announced April 2023.

Exact solutions for the electromagnetic fields of a flying focus

Authors: D. Ramsey, A. Di Piazza, M. Formanek, P. Franke, D. H. Froula, B. Malaca, W. B. Mori, J. R. Pierce, T. T. Simpson, J. Vieira, M. Vranic, K. Weichman, J. P. Palastro

Abstract: The intensity peak of a "flying focus" travels at a programmable velocity over many Rayleigh ranges while maintaining a near-constant profile. Assessing the extent to which these features can enhance laser-based applications requires an accurate description of the electromagnetic fields. Here we present exact analytical solutions to Maxwell's equations for the electromagnetic fields of a constant-… ▽ More The intensity peak of a "flying focus" travels at a programmable velocity over many Rayleigh ranges while maintaining a near-constant profile. Assessing the extent to which these features can enhance laser-based applications requires an accurate description of the electromagnetic fields. Here we present exact analytical solutions to Maxwell's equations for the electromagnetic fields of a constant-velocity flying focus, generalized for arbitrary polarization and orbital angular momentum. The approach combines the complex source-point method, which transforms multipole solutions into beam-like solutions, with the Lorentz invariance of Maxwell's equations. Propagating the fields backward in space reveals the space-time profile that an optical assembly must produce to realize these fields in the laboratory. Comparisons with simpler paraxial solutions provide conditions for their reliable use when modeling a flying focus. △ Less

Submitted 3 November, 2022; v1 submitted 14 October, 2022; originally announced October 2022.

Ion and Electron Acoustic Bursts during Anti-Parallel Magnetic Reconnection Driven by Lasers

Authors: Shu Zhang, Abraham Chien, Lan Gao, Hantao Ji, Eric G. Blackman, Russ Follett, Dustin H. Froula, Joseph Katz, Chikang Li, Andrew Birkel, Richard Petrasso, John Moody, Hui Chen

Abstract: Magnetic reconnection converts magnetic energy into thermal and kinetic energy in plasma. Among numerous candidate mechanisms, ion acoustic instabilities driven by the relative drift between ions and electrons, or equivalently electric current, have been suggested to play a critical role in dissipating magnetic energy in collisionless plasmas. However, their existence and effectiveness during reco… ▽ More Magnetic reconnection converts magnetic energy into thermal and kinetic energy in plasma. Among numerous candidate mechanisms, ion acoustic instabilities driven by the relative drift between ions and electrons, or equivalently electric current, have been suggested to play a critical role in dissipating magnetic energy in collisionless plasmas. However, their existence and effectiveness during reconnection have not been well understood due to ion Landau damping and difficulties in resolving the Debye length scale in the laboratory. Here we report a sudden onset of ion acoustic bursts measured by collective Thomson scattering in the exhaust of anti-parallel magnetically driven reconnection using high-power lasers. The ion acoustic bursts are followed by electron acoustic bursts with electron heating and bulk acceleration. We reproduce these observations with 1D and 2D particle-in-cell simulations in which electron outflow jet drives ion-acoustic instabilities, forming double layers. These layers induce electron two-stream instabilities that generate electron acoustic bursts and energize electrons. Our results demonstrate the importance of ion and electron acoustic dynamics during reconnection when ion Landau damping is ineffective, a condition applicable to a range of astrophysical plasmas including near-Earth space, stellar flares, and black hole accretion engines. △ Less

Submitted 29 March, 2023; v1 submitted 26 September, 2022; originally announced September 2022.

Linear colliders based on laser-plasma accelerators

Authors: C. Benedetti, S. S. Bulanov, E. Esarey, C. G. R. Geddes, A. J. Gonsalves, A. Huebl, R. Lehe, K. Nakamura, C. B. Schroeder, D. Terzani, J. van Tilborg, M. Turner, J. -L. Vay, T. Zhou, F. Albert, J. Bromage, E. M. Campbell, D. H. Froula, J. P. Palastro, J. Zuegel, D. Bruhwiler, N. M. Cook, B. Cros, M. C. Downer, M. Fuchs , et al. (18 additional authors not shown)

Abstract: White paper to the Proceedings of the U.S. Particle Physics Community Planning Exercise (Snowmass 2021): Linear colliders based on laser-plasma accelerators White paper to the Proceedings of the U.S. Particle Physics Community Planning Exercise (Snowmass 2021): Linear colliders based on laser-plasma accelerators △ Less

Submitted 4 July, 2022; v1 submitted 15 March, 2022; originally announced March 2022.

Comments: Contribution to Snowmass 2021, Accelerator Frontier

Direct measurement of non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma

Authors: Abraham Chien, Lan Gao, Shu Zhang, Hantao Ji, Eric G. Blackman, William Daughton, Adam Stanier, Ari Le, Fan Guo, Russ Follett, Hui Chen, Gennady Fiksel, Gabriel Bleotu, Robert C. Cauble, Sophia N. Chen, Alice Fazzini, Kirk Flippo, Omar French, Dustin H. Froula, Julien Fuchs, Shinsuke Fujioka, Kenneth Hill, Sallee Klein, Carolyn Kuranz, Philip Nilson , et al. (2 additional authors not shown)

Abstract: Magnetic reconnection is a ubiquitous astrophysical process that rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy, and non-thermal energetic particles, including energetic electrons. Various reconnection acceleration mechanisms in different low-$β$ (plasma-to-magnetic pressure ratio) and collisionless environments have been proposed theoretically and stu… ▽ More Magnetic reconnection is a ubiquitous astrophysical process that rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy, and non-thermal energetic particles, including energetic electrons. Various reconnection acceleration mechanisms in different low-$β$ (plasma-to-magnetic pressure ratio) and collisionless environments have been proposed theoretically and studied numerically, including first- and second-order Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields, and direct acceleration by the reconnection electric field. However, none of them have been heretofore confirmed experimentally, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for \textit{in-situ} measurements and short mean free paths for \textit{ex-situ} measurements. Here we report the direct measurement of accelerated non-thermal electrons from low-$β$ magnetically driven reconnection in experiments using a laser-powered capacitor coil platform. We use kiloJoule lasers to drive parallel currents to reconnect MegaGauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations. Our results therefore validate one of the proposed acceleration mechanisms by reconnection, and establish a new approach to study reconnection particle acceleration with laboratory experiments in relevant regimes. △ Less

Submitted 24 January, 2022; originally announced January 2022.

Comments: 13 pages, 6 figures

Optical diagnostics of laser-produced plasmas

Authors: S. S. Harilal, M. C. Phillips, D. H. Froula, K. K. Anoop, R. C. Issac, F. N. Beg

Abstract: Laser-produced plasmas (LPPs) engulf exotic and complex conditions ranging in temperature, density, pressure, magnetic and electric fields, charge states, charged particle kinetics, and gas-phase reactions, based on the irradiation conditions, target geometries, and the background cover gas. The application potential of the LPP is so diverse that it generates considerable interest for both basic a… ▽ More Laser-produced plasmas (LPPs) engulf exotic and complex conditions ranging in temperature, density, pressure, magnetic and electric fields, charge states, charged particle kinetics, and gas-phase reactions, based on the irradiation conditions, target geometries, and the background cover gas. The application potential of the LPP is so diverse that it generates considerable interest for both basic and applied research areas. Although most of the traditional characterization techniques developed for other plasma sources can be used to characterize the LPPs, care must be taken to interpret the results because of their small size, transient nature, and inhomogeneities. The existence of the large spatiotemporal density and temperature gradients often necessitates non-uniform weighted averaging over distance and time. Among the various plasma characterization tools, optical-based diagnostic tools play a key role in the accurate measurements of LPP parameters. The optical toolbox contains optical probing methods (Thomson scattering, shadowgraphy, Schlieren, interferometry, velocimetry, and deflectometry), optical spectroscopy (emission, absorption, and fluorescence), and passive and active imaging. Each technique is useful for measuring a specific property, and its use is limited to a certain time span during the LPP evolution because of the sensitivity issues related to the selected measuring tool. Therefore, multiple diagnostic tools are essential for a comprehensive insight into the entire plasma behavior. In recent times, the improvements in performance in the lasers and detector systems expanded the capability of the aforementioned passive and active diagnostics tools. This review provides an overview of optical diagnostic tools frequently employed for the characterization of the LPPs and emphasizes techniques, associated assumptions, and challenges. △ Less

Submitted 15 August, 2022; v1 submitted 21 January, 2022; originally announced January 2022.

Comments: 44 pages, 31 figures

Report number: PNNL-SA-162786

Journal ref: Reviews of Modern Physics, 94(3), 035002 (2022)

Insensitivity of a turbulent laser-plasma dynamo to initial conditions

Authors: A. F. A. Bott, L. Chen, P. Tzeferacos, C. A. J. Palmer, A. R. Bell, R. Bingham, A. Birkel, D. H. Froula, J. Katz, M. W. Kunz, C. -K. Li, H-S. Park, R. Petrasso, J. S. Ross, B. Reville, D. Ryu, F. H. Séguin, T. G. White, A. A. Schekochihin, D. Q. Lamb, G. Gregori

Abstract: It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous, asymmetric, weakly magnetised laser-produced plasma jets can generate strong stochastic magnetic fields via the small-scale turbulent dynamo mechanism, provided the magnetic Reynolds number of the plasma is sufficiently large. In this paper, we compare such a plasma with one aris… ▽ More It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous, asymmetric, weakly magnetised laser-produced plasma jets can generate strong stochastic magnetic fields via the small-scale turbulent dynamo mechanism, provided the magnetic Reynolds number of the plasma is sufficiently large. In this paper, we compare such a plasma with one arising from two pre-magnetised plasma jets whose creation is identical save for the addition of a strong external magnetic field imposed by a pulsed magnetic field generator (`MIFEDS'). We investigate the differences between the two turbulent systems using a Thomson-scattering diagnostic, X-ray self-emission imaging and proton radiography. The Thomson-scattering spectra and X-ray images suggest that the presence of the external magnetic field has a limited effect on the plasma dynamics in the experiment. While the presence of the external magnetic field induces collimation of the flows in the colliding plasma jets and the initial strengths of the magnetic fields arising from the interaction between the colliding jets are significantly larger as a result of the external field, the energy and morphology of the stochastic magnetic fields post-amplification are indistinguishable. We conclude that, for turbulent laser-plasmas with super-critical magnetic Reynolds numbers, the dynamo-amplified magnetic fields are determined by the turbulent dynamics rather than the seed fields and modest changes in the initial flow dynamics of the plasma, a finding consistent with theoretical expectations and simulations of turbulent dynamos. △ Less

Submitted 5 January, 2022; originally announced January 2022.

Comments: 13 pages, 12 figures

Spatiotemporal control of laser intensity through cross-phase modulation

Authors: Tanner T. Simpson, Dillon Ramsey, Phil Franke, Kathleen Weichman, Manfred Virgil Ambat, David Turnbull, Dustin H. Froula, John P. Palastro

Abstract: Spatiotemporal pulse shaping provides control over the trajectory and range of an intensity peak. While this control can enhance laser-based applications, the optical configurations required for shaping the pulse can constrain the transverse or temporal profile, duration, or orbital angular momentum (OAM). Here we present a novel technique for spatiotemporal control that mitigates these constraint… ▽ More Spatiotemporal pulse shaping provides control over the trajectory and range of an intensity peak. While this control can enhance laser-based applications, the optical configurations required for shaping the pulse can constrain the transverse or temporal profile, duration, or orbital angular momentum (OAM). Here we present a novel technique for spatiotemporal control that mitigates these constraints by using a "stencil" pulse to spatiotemporally structure a second, primary pulse through cross-phase modulation (XPM) in a Kerr lens. The temporally shaped stencil pulse induces a time-dependent focusing phase within the primary pulse. This technique, the "flying focus X," allows the primary pulse to have any profile or OAM, expanding the flexibility of spatiotemporal pulse shaping for laser-based applications. As an example, simulations show that the flying focus X can deliver an arbitrary-velocity, variable-duration intensity peak with OAM over distances much longer than a Rayleigh range. △ Less

Submitted 17 November, 2021; v1 submitted 22 October, 2021; originally announced October 2021.

Nonlinear Thomson scattering with ponderomotive control

Authors: D. Ramsey, B. Malaca, A. Di Piazza, M. Formanek. P. Franke, D. H. Froula, M. Pardal, T. T. Simpson, J. Vieira, K. Weichman, J. P. Palastro

Abstract: In nonlinear Thomson scattering, a relativistic electron reflects and re-radiates the photons of a laser pulse, converting optical light to x rays or beyond. While this extreme frequency conversion offers a promising source for probing high-energy-density materials and driving uncharted regimes of nonlinear quantum electrodynamics, conventional nonlinear Thomson scattering has inherent tradeoffs i… ▽ More In nonlinear Thomson scattering, a relativistic electron reflects and re-radiates the photons of a laser pulse, converting optical light to x rays or beyond. While this extreme frequency conversion offers a promising source for probing high-energy-density materials and driving uncharted regimes of nonlinear quantum electrodynamics, conventional nonlinear Thomson scattering has inherent tradeoffs in its scaling with laser intensity. Here we discover that the ponderomotive control afforded by spatiotemporal pulse shaping enables novel regimes of nonlinear Thomson scattering that substantially enhance the scaling of the radiated power, emission angle, and frequency with laser intensity. By appropriately setting the velocity of the intensity peak, a spatiotemporally shaped pulse can increase the power radiated by orders of magnitude. The enhanced scaling with laser intensity allows for operation at significantly lower electron energies and can eliminate the need for a high-energy electron accelerator. △ Less

Submitted 9 August, 2021; originally announced August 2021.

Comments: 23 pages, 4 figures

Optical Shock-Enhanced Self-Photon Acceleration

Authors: Philip Franke, Dillon Ramsey, Tanner T. Simpson, Dustin H. Froula, John P. Palastro

Abstract: Photon accelerators can spectrally broaden laser pulses with high efficiency in moving electron density gradients. When driven by a conventional laser pulse, the group velocity walk-off experienced by the accelerated photons and deterioration of the gradient from diffraction and refraction limit the extent of spectral broadening. Here we show that a laser pulse with a shaped space-time and transve… ▽ More Photon accelerators can spectrally broaden laser pulses with high efficiency in moving electron density gradients. When driven by a conventional laser pulse, the group velocity walk-off experienced by the accelerated photons and deterioration of the gradient from diffraction and refraction limit the extent of spectral broadening. Here we show that a laser pulse with a shaped space-time and transverse intensity profile overcomes these limitations by creating a guiding density profile at a tunable velocity. Self-photon acceleration in this profile leads to dramatic spectral broadening and intensity steepening, forming an optical shock that further enhances the rate of spectral broadening. In this new regime, multi-octave spectra extending from $400 nm - 60 nm$ wavelengths, which support near-transform limited $< 400 as$ pulses, are generated over $<100 μ$m of interaction length. △ Less

Submitted 22 September, 2021; v1 submitted 20 July, 2021; originally announced July 2021.

Strong suppression of heat conduction in a laboratory replica of galaxy-cluster turbulent plasmas

Authors: J. Meinecke, P. Tzeferacos, J. S. Ross, A. F. A. Bott, S. Feister, H. -S. Park, A. R. Bell, R. Blandford, R. L. Berger, R. Bingham, A. Casner, L. E. Chen, J. Foster, D. H. Froula, C. Goyon, D. Kalantar, M. Koenig, B. Lahmann, C. -K. Li, Y. Lu, C. A. J. Palmer, R. Petrasso, H. Poole, B. Remington, B. Reville , et al. (10 additional authors not shown)

Abstract: Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a stochastically tangled magnetic field whose energy is close to equipartition with the energy of the turbulent motions \cite{zweibel1997, Vacca}. In the cluster cores, the temperatures remain anomalously high compared to what might be expected considering that the radiative cooling time is short relative to the Hubble time \… ▽ More Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a stochastically tangled magnetic field whose energy is close to equipartition with the energy of the turbulent motions \cite{zweibel1997, Vacca}. In the cluster cores, the temperatures remain anomalously high compared to what might be expected considering that the radiative cooling time is short relative to the Hubble time \cite{cowie1977,fabian1994}. While feedback from the central active galactic nuclei (AGN) \cite{fabian2012,birzan2012,churazov2000} is believed to provide most of the heating, there has been a long debate as to whether conduction of heat from the bulk to the core can help the core to reach the observed temperatures \cite{narayan2001,ruszkowski2002,kunz2011}, given the presence of tangled magnetic fields. Interestingly, evidence of very sharp temperature gradients in structures like cold fronts implies a high degree of suppression of thermal conduction \cite{markevitch2007}. To address the problem of thermal conduction in a magnetized and turbulent plasma, we have created a replica of such a system in a laser laboratory experiment. Our data show a reduction of local heat transport by two orders of magnitude or more, leading to strong temperature variations on small spatial scales, as is seen in cluster plasmas \cite{markevitch2003}. △ Less

Submitted 18 May, 2021; originally announced May 2021.

Journal ref: Sci. Adv. 8, eabj6799 (2022)

Cross-beam energy transfer saturation by ion trapping-induced detuning

Authors: K. L. Nguyen, L. Yin, B. J. Albright, A. M. Hansen, D. H. Froula, D. Turnbull, R. K. Follett, J. P. Palastro

Abstract: The performance of direct-drive inertial confinement fusion implosions relies critically on the coupling of laser energy to the target plasma. Cross-beam energy transfer (CBET), the resonant exchange of energy between intersecting laser beams mediated by ponderomotively driven ion-acoustic waves (IAW), inhibits this coupling by scattering light into unwanted directions. The variety of beam interse… ▽ More The performance of direct-drive inertial confinement fusion implosions relies critically on the coupling of laser energy to the target plasma. Cross-beam energy transfer (CBET), the resonant exchange of energy between intersecting laser beams mediated by ponderomotively driven ion-acoustic waves (IAW), inhibits this coupling by scattering light into unwanted directions. The variety of beam intersection angles and varying plasma conditions in an implosion results in IAWs with a range of phase velocities. Here we show that CBET saturates through a resonance detuning that depends on the IAW phase velocity and that results from trapping-induced modifications to the ion distribution functions. For smaller phase velocities, the modifications to the distribution functions can rapidly thermalize in the presence of mid-Z ions, leading to a blueshift in the resonant frequency. For larger phase velocities, the modifications can persist, leading to a redshift in the resonant frequency. Ultimately, these results may reveal pathways towards CBET mitigation and inform reduced models for radiation hydrodynamics codes to improve their predictive capability. △ Less

Submitted 15 April, 2021; originally announced April 2021.

Towards the Optimisation of Direct Laser Acceleration

Authors: A. E. Hussein, A. V. Arefiev, T. Batson, H. Chen, R. S. Craxton, A. S. Davies, D. H. Froula, Z. Gong, D. Haberberger, Y. Ma, P. M. Nilson, W. Theobald, T. Wang, K. Weichman, G. J. Williams, L. Willingale

Abstract: Experimental measurements using the OMEGA EP laser facility demonstrated direct laser acceleration (DLA) of electron beams to (505 $\pm$ 75) MeV with (140 $\pm$ 30)~nC of charge from a low-density plasma target using a 400 J, picosecond duration pulse. Similar trends of electron energy with target density are also observed in self-consistent two-dimensional particle-in-cell simulations. The intens… ▽ More Experimental measurements using the OMEGA EP laser facility demonstrated direct laser acceleration (DLA) of electron beams to (505 $\pm$ 75) MeV with (140 $\pm$ 30)~nC of charge from a low-density plasma target using a 400 J, picosecond duration pulse. Similar trends of electron energy with target density are also observed in self-consistent two-dimensional particle-in-cell simulations. The intensity of the laser pulse is sufficiently large that the electrons are rapidly expelled from along the laser pulse propagation axis to form a channel. The dominant acceleration mechanism is confirmed to be DLA and the effect of quasi-static channel fields on energetic electron dynamics is examined. A strong channel magnetic field, self-generated by the accelerated electrons, is found to play a comparable role to the transverse electric channel field in defining the boundary of electron motion. △ Less

Submitted 18 January, 2021; originally announced January 2021.

Comments: 21 pages, 7 figures

Generating ultra-dense pair beams using 400 GeV/c protons

Authors: C. D. Arrowsmith, N. Shukla, N. Charitonidis, R. Boni, H. Chen, T. Davenne, D. H. Froula, B. T. Huffman, Y. Kadi, B. Reville, S. Richardson, S. Sarkar, J. L. Shaw, L. O. Silva, R. M. G. M. Trines, R. Bingham, G. Gregori

Abstract: A previously unexplored experimental scheme is presented for generating low-divergence, ultra-dense, relativistic, electron-positron beams using 400 GeV/c protons available at facilities such as HiRadMat and AWAKE at CERN. Preliminary Monte-Carlo and Particle-in-cell simulations demonstrate the possibility of generating beams containing $10^{13}-10^{14}$ electron-positron pairs at sufficiently hig… ▽ More A previously unexplored experimental scheme is presented for generating low-divergence, ultra-dense, relativistic, electron-positron beams using 400 GeV/c protons available at facilities such as HiRadMat and AWAKE at CERN. Preliminary Monte-Carlo and Particle-in-cell simulations demonstrate the possibility of generating beams containing $10^{13}-10^{14}$ electron-positron pairs at sufficiently high densities to drive collisionless beam-plasma instabilities, which are expected to play an important role in magnetic field generation and the related radiation signatures of relativistic astrophysical phenomena. The pair beams are quasi-neutral, with size exceeding several skin-depths in all dimensions, allowing for the first time the examination of the effect of competition between transverse and longitudinal instability modes on the growth of magnetic fields. Furthermore, the presented scheme allows for the possibility of controlling the relative density of hadrons to electron-positron pairs in the beam, making it possible to explore the parameter spaces for different astrophysical environments. △ Less

Submitted 9 November, 2020; originally announced November 2020.

Journal ref: Phys. Rev. Research 3, 023103 (2021)

Nonlinear spatiotemporal control of laser intensity

Authors: Tanner T. Simpson, Dillon Ramsey, Philip Franke, Navid Vafaei-Najafabadi, David Turnbull, Dustin H. Froula, John P. Palastro

Abstract: Spatiotemporal control over the intensity of a laser pulse has the potential to enable or revolutionize a wide range of laser-based applications that currently suffer from the poor flexibility offered by conventional optics. Specifically, these optics limit the region of high intensity to the Rayleigh range and provide little to no control over the trajectory of the peak intensity. Here, we introd… ▽ More Spatiotemporal control over the intensity of a laser pulse has the potential to enable or revolutionize a wide range of laser-based applications that currently suffer from the poor flexibility offered by conventional optics. Specifically, these optics limit the region of high intensity to the Rayleigh range and provide little to no control over the trajectory of the peak intensity. Here, we introduce a nonlinear technique for spatiotemporal control, the "self-flying focus," that produces an arbitrary trajectory intensity peak that can be sustained for distances comparable to the focal length. The technique combines temporal pulse shaping and the inherent nonlinearity of a medium to customize the time and location at which each temporal slice within the pulse comes to its focus. As an example of its utility, simulations show that the self-flying focus can form a highly uniform, meter-scale plasma suitable for advanced plasma-based accelerators. △ Less

Submitted 3 December, 2020; v1 submitted 24 September, 2020; originally announced September 2020.

Major Scientific Challenges and Opportunities in Understanding Magnetic Reconnection and Related Explosive Phenomena in Solar and Heliospheric Plasmas

Authors: H. Ji, J. Karpen, A. Alt, S. Antiochos, S. Baalrud, S. Bale, P. M. Bellan, M. Begelman, A. Beresnyak, A. Bhattacharjee, E. G. Blackman, D. Brennan, M. Brown, J. Buechner, J. Burch, P. Cassak, B. Chen, L. -J. Chen, Y. Chen, A. Chien, L. Comisso, D. Craig, J. Dahlin, W. Daughton, E. DeLuca , et al. (83 additional authors not shown)

Abstract: Magnetic reconnection underlies many explosive phenomena in the heliosphere and in laboratory plasmas. The new research capabilities in theory/simulations, observations, and laboratory experiments provide the opportunity to solve the grand scientific challenges summarized in this whitepaper. Success will require enhanced and sustained investments from relevant funding agencies, increased interagen… ▽ More Magnetic reconnection underlies many explosive phenomena in the heliosphere and in laboratory plasmas. The new research capabilities in theory/simulations, observations, and laboratory experiments provide the opportunity to solve the grand scientific challenges summarized in this whitepaper. Success will require enhanced and sustained investments from relevant funding agencies, increased interagency/international partnerships, and close collaborations of the solar, heliospheric, and laboratory plasma communities. These investments will deliver transformative progress in understanding magnetic reconnection and related explosive phenomena including space weather events. △ Less

Submitted 16 September, 2020; originally announced September 2020.

Comments: 4 pages (including a title page), white paper submitted to Helio2050 workshop at https://www.hou.usra.edu/meetings/helio2050/. arXiv admin note: substantial text overlap with arXiv:2004.00079

Laser-plasma acceleration beyond wave breaking

Authors: J. P. Palastro, B. Malaca, J. Vieira, D. Ramsey, T. T. Simpson, P. Franke, J. L. Shaw, D. H. Froula

Abstract: Laser wakefield accelerators rely on the extremely high electric fields of nonlinear plasma waves to trap and accelerate electrons to relativistic energies over short distances. When driven strongly enough, plasma waves break, trapping a large population of the background electrons that support their motion. This limits the maximum electric field. Here we introduce a novel regime of plasma wave ex… ▽ More Laser wakefield accelerators rely on the extremely high electric fields of nonlinear plasma waves to trap and accelerate electrons to relativistic energies over short distances. When driven strongly enough, plasma waves break, trapping a large population of the background electrons that support their motion. This limits the maximum electric field. Here we introduce a novel regime of plasma wave excitation and wakefield acceleration that removes this limit, allowing for arbitrarily high electric fields. The regime, enabled by spatiotemporal shaping of laser pulses, exploits the property that nonlinear plasma waves with superluminal phase velocities cannot trap charged particles and are therefore immune to wave breaking. A laser wakefield accelerator operating in this regime provides energy tunability independent of the plasma density and can accommodate the large laser amplitudes delivered by modern and planned high-power, short pulse laser systems. △ Less

Submitted 20 August, 2020; originally announced August 2020.

Time-resolved fast turbulent dynamo in a laser plasma

Authors: A. F. A. Bott, P. Tzeferacos, L. Chen, C. A. J. Palmer, A. Rigby, A. Bell, R. Bingham, A. Birkel, C. Graziani, D. H. Froula, J. Katz, M. Koenig, M. W. Kunz, C. K. Li, J. Meinecke, F. Miniati, R. Petrasso, H. -S. Park, B. A. Remington, B. Reville, J. S. Ross, D. Ryu, D. Ryutov, F. Séguin, T. G. White , et al. (3 additional authors not shown)

Abstract: Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ($\mathrm{Pm} < 1$). However, the… ▽ More Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ($\mathrm{Pm} < 1$). However, the same framework proposes that the fluctuation dynamo should operate differently when $\mathrm{Pm} \gtrsim 1$, the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports a new experiment that creates a laboratory $\mathrm{Pm} \gtrsim 1$ plasma dynamo for the first time. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities and magnetic fields, which allows us to explore various stages of the fluctuation dynamo's operation. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude from its initial value and saturate dynamically. It is shown that the growth of these fields occurs exponentially at a rate that is much greater than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized MHD simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems. △ Less

Submitted 24 July, 2020; originally announced July 2020.

Comments: 12 pages, 9 figures

Vacuum acceleration of electrons in a dynamic laser pulse

Authors: Dillon Ramsey, Philip Franke, Tanner Simpson, Dustin Froula, John Palastro

Abstract: A planar laser pulse propagating in vacuum can exhibit an extremely large ponderomotive force. This force, however, cannot impart net energy to an electron: As the pulse overtakes the electron, the initial impulse from its rising edge is completely undone by an equal and opposite impulse from its trailing edge. Here we show that planar-like "flying focus" pulses can break this symmetry, imparting… ▽ More A planar laser pulse propagating in vacuum can exhibit an extremely large ponderomotive force. This force, however, cannot impart net energy to an electron: As the pulse overtakes the electron, the initial impulse from its rising edge is completely undone by an equal and opposite impulse from its trailing edge. Here we show that planar-like "flying focus" pulses can break this symmetry, imparting relativistic energies to electrons. The intensity peak of a flying focus-a moving focal point resulting from a chirped laser pulse focused by a chromatic lens-can travel at any subluminal velocity, forwards or backwards. As a result, an electron can gain enough momentum in the rising edge of the intensity peak to outrun and avoid the trailing edge. Accelerating the intensity peak can further boost the momentum gain. Theory and simulations demonstrate that these dynamic intensity peaks can backwards accelerate electrons to the MeV energies required for radiation and electron diffraction probes of high energy density materials. △ Less

Submitted 10 July, 2020; originally announced July 2020.

Journal ref: Phys. Rev. E 102, 043207 (2020)

Laser-driven Collisionless Shock Acceleration of Ions from Near-critical plasmas

Authors: S. Tochitsky, A. Pak, F. Fiuza, D. Haberberger, N. Lemos, A. Link, D. H. Froula, C. Joshi

Abstract: This paper overviews experimental and numerical results on acceleration of narrow energy spread ion beams by an electrostatic collisionless shockwave driven by 1 um (Omega EP) and 10 um (UCLA Neptune Laboratory) lasers in near critical density CH and He plasmas, respectively. Shock waves in CH targets produced high-energy 50 MeV protons (energy spread of <30%) and 314 MeV C6+ ions (energy spread o… ▽ More This paper overviews experimental and numerical results on acceleration of narrow energy spread ion beams by an electrostatic collisionless shockwave driven by 1 um (Omega EP) and 10 um (UCLA Neptune Laboratory) lasers in near critical density CH and He plasmas, respectively. Shock waves in CH targets produced high-energy 50 MeV protons (energy spread of <30%) and 314 MeV C6+ ions (energy spread of <10%). Observation of acceleration of both protons and carbon ions to similar velocities is consistent with reflection of particles off the moving potential of a shock front. For shocks driven by CO2 laser in a gas jet, 30 MeV peak in He ion spectrum was detected. Particle-in-cell simulations indicate that regardless of the target further control over its density profile is needed for optimization of accelerated ion beams in part of energy spread, yield and maximum kinetic energy. △ Less

Submitted 11 June, 2020; originally announced June 2020.

Comments: 16 pages, 7 figures

Journal ref: Will be published in Physics of Plasmas, 2020

Major Scientific Challenges and Opportunities in Understanding Magnetic Reconnection and Related Explosive Phenomena throughout the Universe

Authors: H. Ji, A. Alt, S. Antiochos, S. Baalrud, S. Bale, P. M. Bellan, M. Begelman, A. Beresnyak, E. G. Blackman, D. Brennan, M. Brown, J. Buechner, J. Burch, P. Cassak, L. -J. Chen, Y. Chen, A. Chien, D. Craig, J. Dahlin, W. Daughton, E. DeLuca, C. F. Dong, S. Dorfman, J. Drake, F. Ebrahimi , et al. (75 additional authors not shown)

Abstract: This white paper summarizes major scientific challenges and opportunities in understanding magnetic reconnection and related explosive phenomena as a fundamental plasma process. This white paper summarizes major scientific challenges and opportunities in understanding magnetic reconnection and related explosive phenomena as a fundamental plasma process. △ Less

Submitted 31 March, 2020; originally announced April 2020.

Comments: 6 pages, 1 figure, white paper submitted to both Plasma 2020 and Astro 2020 Decadal Surveys

Building high accuracy emulators for scientific simulations with deep neural architecture search

Authors: M. F. Kasim, D. Watson-Parris, L. Deaconu, S. Oliver, P. Hatfield, D. H. Froula, G. Gregori, M. Jarvis, S. Khatiwala, J. Korenaga, J. Topp-Mugglestone, E. Viezzer, S. M. Vinko

Abstract: Computer simulations are invaluable tools for scientific discovery. However, accurate simulations are often slow to execute, which limits their applicability to extensive parameter exploration, large-scale data analysis, and uncertainty quantification. A promising route to accelerate simulations by building fast emulators with machine learning requires large training datasets, which can be prohibi… ▽ More Computer simulations are invaluable tools for scientific discovery. However, accurate simulations are often slow to execute, which limits their applicability to extensive parameter exploration, large-scale data analysis, and uncertainty quantification. A promising route to accelerate simulations by building fast emulators with machine learning requires large training datasets, which can be prohibitively expensive to obtain with slow simulations. Here we present a method based on neural architecture search to build accurate emulators even with a limited number of training data. The method successfully accelerates simulations by up to 2 billion times in 10 scientific cases including astrophysics, climate science, biogeochemistry, high energy density physics, fusion energy, and seismology, using the same super-architecture, algorithm, and hyperparameters. Our approach also inherently provides emulator uncertainty estimation, adding further confidence in their use. We anticipate this work will accelerate research involving expensive simulations, allow more extensive parameters exploration, and enable new, previously unfeasible computational discovery. △ Less

Submitted 8 October, 2020; v1 submitted 17 January, 2020; originally announced January 2020.

Journal ref: Mach. Learn.: Sci. Technol. 3 (2022) 015013

Photon Acceleration in a Flying Focus

Authors: A. J. Howard, D. Turnbull, A. S. Davies, P. Franke, D. H. Froula, J. P. Palastro

Abstract: A high-intensity laser pulse propagating through a medium triggers an ionization front that can accelerate and frequency-upshift the photons of a second pulse. The maximum upshift is ultimately limited by the accelerated photons outpacing the ionization front or the ionizing pulse refracting from the plasma. Here we apply the flying focus--a moving focal point resulting from a chirped laser pulse… ▽ More A high-intensity laser pulse propagating through a medium triggers an ionization front that can accelerate and frequency-upshift the photons of a second pulse. The maximum upshift is ultimately limited by the accelerated photons outpacing the ionization front or the ionizing pulse refracting from the plasma. Here we apply the flying focus--a moving focal point resulting from a chirped laser pulse focused by a chromatic lens--to overcome these limitations. Theory and simulations demonstrate that the ionization front produced by a flying focus can frequency-upshift an ultrashort optical pulse to the extreme ultraviolet over a centimeter of propagation. An analytic model of the upshift predicts that this scheme could be scaled to a novel table-top source of spatially coherent x-rays. △ Less

Submitted 30 April, 2019; originally announced May 2019.

Comments: 7 pages, 4 figures, 1 table

Journal ref: Phys. Rev. Lett. 123, 124801 (2019)

Laser-Plasma Interactions Enabled by Emerging Technologies

Authors: J. P. Palastro, F. Albert, B. Albright, T. M. Antonsen Jr., A. Arefiev, J. Bates, R. Berger, J. Bromage, M. Campbell, T. Chapman, E. Chowdhury, A. Colaïtis, C. Dorrer, E. Esarey, F. Fiúza, N. Fisch, R. Follett, D. Froula, S. Glenzer, D. Gordon, D. Haberberger, B. M. Hegelich, T. Jones, D. Kaganovich, K. Krushelnick , et al. (29 additional authors not shown)

Abstract: An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems. An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems. △ Less

Submitted 30 April, 2019; originally announced April 2019.

Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 $μ$m lasers

Authors: A. Pak, S. Kerr, N. Lemos, A. Link, P. Patel, F. Albert, L. Divol, B. B. Pollock, D. Haberberger, D. Froula, M. Gauthier, S. H. Glenzer, A. Longman, L. Manzoor, R. Fedosejevs, S. Tochitsky, C. Joshi, F. Fiuza

Abstract: Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $μ$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy sp… ▽ More Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $μ$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratio are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and C$^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions. △ Less

Submitted 18 October, 2018; originally announced October 2018.

Comments: Accepted for publication in Physical Review Accelerators and Beams

Resonance absorption of a broadband laser pulse

Authors: J. P. Palastro, J. G. Shaw, R. K. Follett, A. Colaïtis, D. Turnbull, A. Maximov, V. Goncharov, D. H. Froula

Abstract: Broad bandwidth, infrared light sources have the potential to revolutionize inertial confinement fusion (ICF) by suppressing laser-plasma instabilities. There is, however, a tradeoff: The broad bandwidth precludes high efficiency conversion to the ultraviolet, where laser-plasma interactions are weaker. Operation in the infrared could intensify the role of resonance absorption, an effect long susp… ▽ More Broad bandwidth, infrared light sources have the potential to revolutionize inertial confinement fusion (ICF) by suppressing laser-plasma instabilities. There is, however, a tradeoff: The broad bandwidth precludes high efficiency conversion to the ultraviolet, where laser-plasma interactions are weaker. Operation in the infrared could intensify the role of resonance absorption, an effect long suspected to be the shortcoming of early ICF experiments. Here we present simulations exploring the effect of bandwidth on resonance absorption. In the linear regime, bandwidth has little effect on resonance absorption; in the nonlinear regime, bandwidth suppresses enhanced absorption resulting from the electromagnetic decay instability. These findings evince that regardless of bandwidth, an ICF implosion will confront at least linear levels of resonance absorption. △ Less

Submitted 28 September, 2018; originally announced October 2018.

Transport of high-energy charged particles through spatially-intermittent turbulent magnetic fields

Authors: L. E. Chen, A. F. A. Bott, P. Tzeferacos, A. Rigby, A. Bell, R. Bingham, C. Graziani, J. Katz, M. Koenig, C. K. Li, R. Petrasso, H. -S. Park, J. S. Ross, D. Ryu, T. G. White, B. Reville, J. Matthews, J. Meinecke, F. Miniati, E. G. Zweibel, S. Sarkar, A. A. Schekochihin, D. Q. Lamb, D. H. Froula, G. Gregori

Abstract: Identifying the sources of the highest energy cosmic rays requires understanding how they are deflected by the stochastic, spatially intermittent intergalactic magnetic field. Here we report measurements of energetic charged-particle propagation through a laser-produced magnetized plasma with these properties. We characterize the diffusive transport of the particles experimentally. The results sho… ▽ More Identifying the sources of the highest energy cosmic rays requires understanding how they are deflected by the stochastic, spatially intermittent intergalactic magnetic field. Here we report measurements of energetic charged-particle propagation through a laser-produced magnetized plasma with these properties. We characterize the diffusive transport of the particles experimentally. The results show that the transport is diffusive and that, for the regime of interest for the highest-energy cosmic rays, the diffusion coefficient is unaffected by the spatial intermittency of the magnetic field. △ Less

Submitted 30 March, 2020; v1 submitted 13 August, 2018; originally announced August 2018.

Comments: Updated Author and Reviewer Information, 23 pages 17 figures

Journal ref: Astrophys. J. 892:114, 2020

Numerical Simulation of magnetized jet creation using a hollow ring of laser beams

Authors: Y. Lu, P. Tzeferacos, E. Liang, R. K. Follett, L. Gao, A. Birkel, D. H. Froula, W. Fu, H. Ji, D. Lamb, C. K. Li, H. Sio, R. Petrasso, M. Wei

Abstract: Three dimensional FLASH magneto-hydrodynamics(MHD) modeling is carried out to interpret the OMEGA laser experiments of strongly magnetized, highly collimated jets driven by a ring of 20 OMEGA beams. The predicted optical Thomson scattering spectra and proton images are in good agreement with a subset of the experimental data. Magnetic fields generated via the Biermann battery term are amplified at… ▽ More Three dimensional FLASH magneto-hydrodynamics(MHD) modeling is carried out to interpret the OMEGA laser experiments of strongly magnetized, highly collimated jets driven by a ring of 20 OMEGA beams. The predicted optical Thomson scattering spectra and proton images are in good agreement with a subset of the experimental data. Magnetic fields generated via the Biermann battery term are amplified at the boundary between the core and the surrounding of the jet. The simulation predicts multiple axially aligned magnetic flux ropes with alternating poloidal component. Future applications of the hollow ring configuration in laboratory astrophysics are discussed. △ Less

Submitted 18 November, 2018; v1 submitted 19 June, 2018; originally announced June 2018.

Ionization waves of arbitrary velocity driven by a flying focus

Authors: J. P. Palastro, D. Turnbull, S. -W. Bahk, R. K. Follett, J. L. Shaw, D. Haberberger, J. Bromage, D. H. Froula

Abstract: A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or "flying," focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. We present analytical… ▽ More A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or "flying," focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. We present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionization wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high harmonic generation, and THz generation. △ Less

Submitted 20 December, 2017; originally announced December 2017.

Journal ref: Phys. Rev. A 97, 033835 (2018)

Laboratory evidence of dynamo amplification of magnetic fields in a turbulent plasma

Authors: P. Tzeferacos, A. Rigby, A. Bott, A. R. Bell, R. Bingham, A. Casner, F. Cattaneo, E. M. Churazov, J. Emig, F. Fiuza, C. B. Forest, J. Foster, C. Graziani, J. Katz, M. Koenig, C. -K. Li, J. Meinecke, R. Petrasso, H. -S. Park, B. A. Remington, J. S. Ross, D. Ryu, D. Ryutov, T. G. White, B. Reville , et al. (5 additional authors not shown)

Abstract: Magnetic fields are ubiquitous in the Universe. Extragalactic disks, halos and clusters have consistently been shown, via diffuse radio-synchrotron emission and Faraday rotation measurements, to exhibit magnetic field strengths ranging from a few nG to tens of $μ$G. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are… ▽ More Magnetic fields are ubiquitous in the Universe. Extragalactic disks, halos and clusters have consistently been shown, via diffuse radio-synchrotron emission and Faraday rotation measurements, to exhibit magnetic field strengths ranging from a few nG to tens of $μ$G. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of the luminous matter. The standard theoretical model for the origin of these strong magnetic fields is through the amplification of tiny seed fields via turbulent dynamo to the level consistent with current observations. Here we demonstrate, using laser-produced colliding plasma flows, that turbulence is indeed capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. These results support the notion that turbulent dynamo is a viable mechanism responsible for the observed present-day magnetization of the Universe. △ Less

Submitted 9 February, 2017; originally announced February 2017.

Comments: Submitted for publication, 5 pages 4 figures with supplementary information (25 pages 9 figures)

Numerical modeling of laser-driven experiments aiming to demonstrate magnetic field amplification via turbulent dynamo

Authors: P. Tzeferacos, A. Rigby, A. Bott, A. R. Bell, R. Bingham, A. Casner, F. Cattaneo, E. M. Churazov, J. Emig, N. Flocke, F. Fiuza, C. B. Forest, J. Foster, C. Graziani, J. Katz, M. Koenig, C. -K. Li, J. Meinecke, R. Petrasso, H. -S. Park, B. A. Remington, J. S. Ross, D. Ryu, D. Ryutov, K. Weide , et al. (7 additional authors not shown)

Abstract: The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model behind cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo to the values observed. We have conceived experiments that aim to demonstrate and… ▽ More The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model behind cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo to the values observed. We have conceived experiments that aim to demonstrate and study the turbulent dynamo mechanism in the laboratory. Here we describe the design of these experiments through simulation campaigns using FLASH, a highly capable radiation magnetohydrodynamics code that we have developed, and large-scale three-dimensional simulations on the Mira supercomputer at Argonne National Laboratory. The simulation results indicate that the experimental platform may be capable of reaching a turbulent plasma state and study dynamo amplification. We validate and compare our numerical results with a small subset of experimental data using synthetic diagnostics. △ Less

Submitted 9 February, 2017; originally announced February 2017.

Comments: Accepted for publication on Physics of Plasmas, 15 pages 12 figures

Essential criteria for efficient pulse amplification via Raman and Brillouin scattering

Authors: R. M. G. M. Trines, E. P. Alves, E. Webb, J. Vieira, F. Fiuza, R. A. Fonseca, L. O. Silva, J. Sadler, N. Ratan, L. Ceurvorst, M. F. Kasim, M. Tabak, D. Froula, D. Haberberger, P. A. Norreys, R. A. Cairns, R. Bingham

Abstract: Raman and Brillouin amplification are two schemes for amplifying and compressing short laser pulses in plasma. Analytical models have already been derived for both schemes, but the full consequences of these models are little known or used. Here, we present new criteria that govern the evolution of the attractor solution for the seed pulse in Raman and Brillouin amplification, and show how the ini… ▽ More Raman and Brillouin amplification are two schemes for amplifying and compressing short laser pulses in plasma. Analytical models have already been derived for both schemes, but the full consequences of these models are little known or used. Here, we present new criteria that govern the evolution of the attractor solution for the seed pulse in Raman and Brillouin amplification, and show how the initial laser pulses need to be shaped to control the properties of the final amplified seed and improve the amplification efficiency. △ Less

Submitted 14 November, 2016; originally announced November 2016.

Comments: 14 pages, 4 figures, submitted to Physical Review Letters in July 2016

Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows

Authors: C. M. Huntington, F. Fiuza, J. S. Ross, A. B. Zylstra, R. P. Drake, D. H. Froula, G. Gregori, N. L. Kugland, C. C. Kuranz, M. C. Levy, C. K. Li, J. Meinecke, T. Morita, R. Petrasso, C. Plechaty, B. A. Remington, D. D. Ryutov, Y. Sakawa, A. Spitkovsky, H. Takabe, H. -S. Park

Abstract: Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of sufficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilitie… ▽ More Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of sufficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilities in experiments has been challenging. Using a proton probe to directly image electromagnetic fields, we present evidence of Weibel-generated magnetic fields that grow in opposing, initially unmagnetized plasma flows from laser-driven laboratory experiments. Three-dimensional particle-in-cell simulations reveal that the instability efficiently extracts energy from the plasma flows, and that the self-generated magnetic energy reaches a few percent of the total energy in the system. This result demonstrates an experimental platform suitable for the investigation of a wide range of astrophysical phenomena, including collisionless shock formation in supernova remnants, large-scale magnetic field amplification, and the radiation signature from gamma-ray bursts. △ Less

Submitted 19 March, 2015; v1 submitted 12 October, 2013; originally announced October 2013.

Journal ref: Nat Phys. 11(2), 173-176, 2015