Showing 1–12 of 12 results for author: Betti, R

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)

Hot Spot Evolution Measured by High-Resolution X-Ray Spectroscopy at the National Ignition Facility

Authors: Lan Gao, B. F. Kraus, K. W. Hill, M. B. Schneider, A. Christopherson, B. Bachmann, M. Bitter, P. Efthimion, N. Pablant, R. Betti, C. Thomas, D. Thorn, A. G. MacPhee, S. Khan, R. Kauffman, D. Liedahl, H. Chen, D. Bradley, J. Kilkenny, B. Lahmann, E. Stambulchik, Y. Maron

Abstract: Evolution of the hot spot plasma conditions was measured using high-resolution x-ray spectroscopy at the National Ignition Facility (NIF). The capsules were filled with DD gas with trace levels of Kr, and had either a high-density-carbon (HDC) ablator or a tungsten (W)-doped HDC ablator. Time-resolved measurement of the Kr He$β$ spectra, absolutely calibrated by a simultaneous time-integrated meas… ▽ More Evolution of the hot spot plasma conditions was measured using high-resolution x-ray spectroscopy at the National Ignition Facility (NIF). The capsules were filled with DD gas with trace levels of Kr, and had either a high-density-carbon (HDC) ablator or a tungsten (W)-doped HDC ablator. Time-resolved measurement of the Kr He$β$ spectra, absolutely calibrated by a simultaneous time-integrated measurement, allows inference of the electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. By matching the calculated hot spot emission using a collisional-radiative code to experimental observations, the hot spot size and areal density are determined. These advanced spectroscopy techniques further reveal the effect of W dopant in the ablator on the hot spot parameters for their improved implosion performance. △ Less

Submitted 6 July, 2026; originally announced July 2026.

Journal ref: Phys. Rev. Lett. 128, 185002 (2022)

A Hybrid Scheme to Achieve Highest Implosion Performance on the OMEGA Laser

Authors: P. S. Farmakis, L. Ceurvorst, V. Gopalaswamy, D. Cao, K. S. Anderson, A. Lees, D. Patel, R. Betti

Abstract: Merging direct and indirect-drive has long been viewed as an optimal hybrid laser-fusion scheme that combines the uniformity of x rays with the efficiency of direct illumination. We present the first integrated 2D simulations of hybrid shock drive (HSD) targets for the OMEGA laser. The HSD scheme [L. Ceurvorst et al., Phys. Rev. E 101 063207 (2020)] uses x rays from a thin Au-coated x-ray converte… ▽ More Merging direct and indirect-drive has long been viewed as an optimal hybrid laser-fusion scheme that combines the uniformity of x rays with the efficiency of direct illumination. We present the first integrated 2D simulations of hybrid shock drive (HSD) targets for the OMEGA laser. The HSD scheme [L. Ceurvorst et al., Phys. Rev. E 101 063207 (2020)] uses x rays from a thin Au-coated x-ray converter outer shell to drive the initial shock into a standard direct-drive capsule. Direct illumination is used to implode the target after the first shock. The design effectively suppresses laser-imprint seeding of hydrodynamic instabilities, maintaining shell integrity during the implosion. This scheme will enable fielding low-adiabat, high-convergence implosions on OMEGA with expected performance greatly exceeding those of current designs. HSD targets are projected to significantly enhance fusion yields, potentially increasing the record Lawson parameter by $\sim$85\% on OMEGA while effectively eliminating the requirement for laser smoothing. These results position HSD as a robust platform for high-performance implosions, paving the way for advanced high-gain inertial fusion energy targets. △ Less

Submitted 13 May, 2026; originally announced May 2026.

Comments: 16 pages, 4 figures, 2 tables, submitted to Physical Review Letters; author-prepared manuscript

Human-in-the-Loop Meta Bayesian Optimization for Fusion Energy and Scientific Applications

Authors: Ricardo Luna Gutierrez, Sahand Ghorbanpour, Ejaz Rahman, Varchas Gopalaswamy, Riccardo Betti, Vineet Gundecha, Aarne Lees, Soumyendu Sarkar

Abstract: Inertial Confinement Fusion (ICF) holds transformative promise for sustainable, near-limitless clean energy, yet remains constrained by prohibitively high costs and limited experimental opportunities. This paper presents Human-in-the-Loop Meta Bayesian Optimization (HL-MBO), a framework that integrates expert knowledge with few-shot, uncertainty-aware machine learning to accelerate discovery in da… ▽ More Inertial Confinement Fusion (ICF) holds transformative promise for sustainable, near-limitless clean energy, yet remains constrained by prohibitively high costs and limited experimental opportunities. This paper presents Human-in-the-Loop Meta Bayesian Optimization (HL-MBO), a framework that integrates expert knowledge with few-shot, uncertainty-aware machine learning to accelerate discovery in data-scarce, high-stakes scientific domains. HL-MBO introduces a meta-learned surrogate model with an expert-informed acquisition function to recommend candidate experiments. To foster trust and enable informed decisions, HL-MBO also provides interpretable explanations of its suggestions. We show HL-MBO outperforms current BO methods on ICF energy yield optimization, as well as benchmarks in molecular optimization and critical temperature maximization for superconducting materials. △ Less

Submitted 30 April, 2026; originally announced May 2026.

Comments: Accepted at IJCAI 2026 (35th International Joint Conference on Artificial Intelligence)

Effects of External Magnetic Fields on the Multi-mode Rayleigh-Taylor Instability

Authors: Xin Bian, Riccardo Betti, Dongxiao Zhao, Hussein Aluie

Abstract: The magneto-Rayleigh-Taylor instability (mRTI) is a key process in inertial confinement fusion and is thought to be widespread in the interstellar medium, where it can concentrate plasma into discrete structures. We present resistive MHD simulations of the nonlinear evolution of multi-mode mRTI in both two and three dimensions, examining the effects of uniform external magnetic fields oriented eit… ▽ More The magneto-Rayleigh-Taylor instability (mRTI) is a key process in inertial confinement fusion and is thought to be widespread in the interstellar medium, where it can concentrate plasma into discrete structures. We present resistive MHD simulations of the nonlinear evolution of multi-mode mRTI in both two and three dimensions, examining the effects of uniform external magnetic fields oriented either parallel or perpendicular to the initial interface. In both 2-D and 3-D, weak parallel fields enhance mixing-zone growth, whereas stronger fields suppress it. For perpendicular fields, growth is initially inhibited but becomes enhanced at later times. These behaviors arise from magnetic tension, which modifies flow anisotropy, buoyancy, drag, and vortex dynamics. The interplay of these mechanisms governs the distinct ways in which magnetic fields influence mRTI evolution. △ Less

Submitted 23 December, 2025; originally announced December 2025.

Generation of Strong Fields with Subcritical Density Plasmas to Study the Phase Transitions of Magnetized Warm Dense Matter

Authors: Irem Nesli Erez, Jonathan R. Davies, Jonathan L. Peebles, Riccardo Betti, Pierre-A. Gourdain

Abstract: Warm dense matter (WDM) is a regime where Fermi degenerate electrons play an important role in the macroscopic properties of a material. Recent experiments have brought us closer to understanding unmagnetized processes in WDM, but magnetized WDM remains unexplored because kilotesla magnetic fields are required. Although there are examples of field compression generating such fields by imploding pr… ▽ More Warm dense matter (WDM) is a regime where Fermi degenerate electrons play an important role in the macroscopic properties of a material. Recent experiments have brought us closer to understanding unmagnetized processes in WDM, but magnetized WDM remains unexplored because kilotesla magnetic fields are required. Although there are examples of field compression generating such fields by imploding pre-magnetized targets, these existing methods give no independent control over the parameters of the magnetized plasma and result in limited laser access for sample creation and diagnosis. In this paper, numerical simulations show that kilotesla magnetic fields can be obtained by shining laser beams onto the inner surface of a cylindrical target, rather than on the outer surface. This approach relies on field compression by a low density high-temperature plasma, rather than a high-density, low-temperature plasma, used in the more conventional approach. With this novel configuration, the region of peak magnetic field is mostly free of plasma, hence other beams can reach a sample placed in the region of the peak field to form WDM and diagnose it. △ Less

Submitted 13 February, 2025; v1 submitted 1 November, 2023; originally announced November 2023.

Experiments conducted in the burning plasma regime with inertial fusion implosions

Authors: J. S. Ross, J. E. Ralph, A. B. Zylstra, A. L. Kritcher, H. F. Robey, C. V. Young, O. A. Hurricane, D. A. Callahan, K. L. Baker, D. T. Casey, T. Doeppner, L. Divol, M. Hohenberger, S. Le Pape, A. Pak, P. K. Patel, R. Tommasini, S. J. Ali, P. A. Amendt, L. J. Atherton, B. Bachmann, D. Bailey, L. R. Benedetti, L. Berzak Hopkins, R. Betti , et al. (127 additional authors not shown)

Abstract: An experimental program is currently underway at the National Ignition Facility (NIF) to compress deuterium and tritium (DT) fuel to densities and temperatures sufficient to achieve fusion and energy gain. The primary approach being investigated is indirect drive inertial confinement fusion (ICF), where a high-Z radiation cavity (a hohlraum) is heated by lasers, converting the incident energy into… ▽ More An experimental program is currently underway at the National Ignition Facility (NIF) to compress deuterium and tritium (DT) fuel to densities and temperatures sufficient to achieve fusion and energy gain. The primary approach being investigated is indirect drive inertial confinement fusion (ICF), where a high-Z radiation cavity (a hohlraum) is heated by lasers, converting the incident energy into x-ray radiation which in turn drives the DT fuel filled capsule causing it to implode. Previous experiments reported DT fuel gain exceeding unity [O.A. Hurricane et al., Nature 506, 343 (2014)] and then exceeding the kinetic energy of the imploding fuel [S. Le Pape et al., Phys. Rev. Lett. 120, 245003 (2018)]. We report on recent experiments that have achieved record fusion neutron yields on NIF, greater than 100 kJ with momentary fusion powers exceeding 1PW, and have for the first time entered the burning plasma regime where fusion alpha-heating of the fuel exceeds the energy delivered to the fuel via compression. This was accomplished by increasing the size of the high-density carbon (HDC) capsule, increasing energy coupling, while controlling symmetry and implosion design parameters. Two tactics were successful in controlling the radiation flux symmetry and therefore the implosion symmetry: transferring energy between laser cones via plasma waves, and changing the shape of the hohlraum. In conducting these experiments, we controlled for known sources of degradation. Herein we show how these experiments were performed to produce record performance, and demonstrate the data fidelity leading us to conclude that these shots have entered the burning plasma regime. △ Less

Submitted 8 November, 2021; originally announced November 2021.

Scale interactions and anisotropy in Rayleigh-Taylor turbulence

Authors: Dongxiao Zhao, Riccardo Betti, Hussein Aluie

Abstract: We study energy scale-transfer in Rayleigh-Taylor (RT) flows by coarse-graining in physical space without Fourier transforms, allowing scale analysis along vertical direction. Two processes are responsible for kinetic energy flux across scales: baropycnal work $Λ$, due to large-scale pressure gradients acting on small-scales of density and velocity, and deformation work $Π$, due to multi-scale vel… ▽ More We study energy scale-transfer in Rayleigh-Taylor (RT) flows by coarse-graining in physical space without Fourier transforms, allowing scale analysis along vertical direction. Two processes are responsible for kinetic energy flux across scales: baropycnal work $Λ$, due to large-scale pressure gradients acting on small-scales of density and velocity, and deformation work $Π$, due to multi-scale velocity. Our coarse-graining analysis shows how these fluxes exhibit self-similar evolution that is quadratic-in-time, similar to RT mixing layer. We find that $Λ$ is a conduit for potential energy, transferring energy non-locally from the largest scales to smaller scales in the inertial range where $Π$ takes over. In 3D, $Π$ continues a persistent cascade to smaller scales, whereas in 2D $Π$ re-channels the energy back to larger scales despite the lack of vorticity conservation in 2D variable density flows. This gives rise to a positive feedback loop in 2D-RT (absent in 3D) in which mixing layer growth and the associated potential energy release are enhanced relative to 3D, explaining the oft-observed larger $α$ values in 2D simulations. Despite higher bulk kinetic energy levels in 2D, small inertial scales are weaker than in 3D. Moreover, the net upscale cascade in 2D tends to isotropize the large-scale flow, in stark contrast to 3D. Our findings indicate the absence of net upscale energy transfer in 3D-RT as is often claimed; growth of large-scale bubbles and spikes is not due to "mergers" but solely due to baropycnal work $Λ$. △ Less

Submitted 23 November, 2021; v1 submitted 7 June, 2020; originally announced June 2020.

Pump-Depletion Dynamics and Saturation of Stimulated Brillouin Scattering in Shock Ignition Relevant Experiments

Authors: S. Zhang, J. Li, C. M. Krauland, F. N. Beg, S. Muller, W. Theobald, J. Palastro, T. Filkins, D. Turnbull, D. Haberberger, C. Ren, R. Betti, C. Stoeckl, E. M. Campbell, J. Trela, D. Batani, R. Scott, M. S. Wei

Abstract: As an alternative inertial confinement fusion scheme with predicted high energy gain and more robust designs, shock ignition requires a strong converging shock driven by a shaped pulse with a high-intensity spike at the end to ignite a pre-compressed fusion capsule. Understanding nonlinear laser-plasma instabilities in shock ignition conditions is crucial to assess and improve the laser-shock ener… ▽ More As an alternative inertial confinement fusion scheme with predicted high energy gain and more robust designs, shock ignition requires a strong converging shock driven by a shaped pulse with a high-intensity spike at the end to ignite a pre-compressed fusion capsule. Understanding nonlinear laser-plasma instabilities in shock ignition conditions is crucial to assess and improve the laser-shock energy coupling. Recent experiments conducted on the OMEGA-EP laser facility have for the first time demonstrated that such instabilities can $\sim$100\% deplete the first 0.5 ns of the high-intensity laser pump. Analysis of the observed laser-generated blast wave suggests that this pump-depletion starts at 0.01--0.02 critical density and progresses to 0.1--0.2 critical density. This pump-depletion is also confirmed by the time-resolved stimulated Raman backscattering spectra. The dynamics of the pump-depletion can be explained by the breaking of ion-acoustic waves in stimulated Brillouin scattering. Such strong pump-depletion would inhibit the collisional laser energy absorption but may benefit the generation of hot electrons with moderate temperatures for electron shock ignition [Shang et al. Phys. Rev. Lett. 119 195001 (2017)]. △ Less

Submitted 30 August, 2019; originally announced September 2019.

Journal ref: Phys. Rev. E 103, 063208 (2021)

Analysis of trends in experimental observables and reconstruction of the implosion dynamics for direct-drive cryogenic targets on OMEGA

Authors: A. Bose, R. Betti, D. Mangino, K. M. Woo, D. Patel, A. R. Christopherson, V. Gopalaswamy, O. M. Mannion, S. P. Regan, V. N. Goncharov, D. H. Edgell, C. J. Forrest, J. A. Frenje, M. Gatu Johnson, V. Yu Glebov, I. V. Igumenshchev, J. P. Knauer, F. J. Marshall, P. B. Radha, R. Shah, C. Stoeckl, W. Theobald, T. C. Sangster, D. Shvarts, E. M. Campbell

Abstract: This paper describes a technique for identifying trends in performance degradation for inertial confinement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA that achieved inferred hot-spot pressures ~56+/-7 Gbar [S… ▽ More This paper describes a technique for identifying trends in performance degradation for inertial confinement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA that achieved inferred hot-spot pressures ~56+/-7 Gbar [S. Regan et al., Phys. Rev. Lett. 117, 025001 (2016)]. All the experimental observables pertaining to the core could be reconstructed simultaneously with the same combination of low and mid modes. This suggests that in addition to low modes, that can cause a degradation of the stagnation pressure, mid modes are present that reduce the size of the neuron and x-ray producing volume. The systematic analysis shows that asymmetries can cause an overestimation of the total areal density in these implosions. It is also found that an improvement in implosion symmetry resulting from correction of either the systematic mid or low modes would result in an increase of the hot-spot pressure from 56 Gbar to ~80 Gbar and could produce a burning plasma when the implosion core is extrapolated to an equivalent 1.9 MJ symmetric direct illumination [A. Bose et al., Phys. Rev. E 94, 011201(R) (2016)]. △ Less

Submitted 27 March, 2018; originally announced March 2018.