-
Ultrafast Nonthermal Lattice Destabilization and Suppression of Polar Optical Scattering in Electronically Excited $α$-SiO$_2$ from First-Principles and Deep Neural Network Potential Modeling
Authors:
Iyyappa Rajan Panneerselvam,
Mark Yeung,
Charlotte Palmer,
Brendan Dromey,
Lorenzo Stella
Abstract:
We present a multiscale first-principles-to-machine-learning approach to investigate ultrafast lattice dynamics in electronically excited $α$-SiO$_2$. Ab initio molecular dynamics (AIMD) based on electronic-temperature-dependent density functional theory (DFT) are used to train electronic-temperature-dependent deep neural network potentials (DNNPs). The use of DNNPs enables atomistic modeling at n…
▽ More
We present a multiscale first-principles-to-machine-learning approach to investigate ultrafast lattice dynamics in electronically excited $α$-SiO$_2$. Ab initio molecular dynamics (AIMD) based on electronic-temperature-dependent density functional theory (DFT) are used to train electronic-temperature-dependent deep neural network potentials (DNNPs). The use of DNNPs enables atomistic modeling at near-DFT accuracy of large $α$-SiO$_2$ cells with thousands of atoms. In particular, DNNPs allowed us to obtain accurate phonon band structures and molecular dynamics (MD) of $α$-SiO$_2$ excited by a sudden increase in electronic temperature. With increasing electronic temperature, $T_e$, pronounced lattice destabilization of $α$-SiO$_2$ is found, as evidenced by violations of elastic stability criteria, substantial volumetric expansion, a sharp reduction of the bulk modulus, and progressive weakening of Si-O bonding due to antibonding-state occupation. From the electronic and phonon band structures, we estimated the Frohlich coupling constant, which decreases as $T_e$ increases, suggesting a crossover to a nonpolar phase of $α$-SiO$_2$ at elevated electronic temperature. This is corroborated by the Bader charge analysis. We also suggest that polar optical phonon scattering should be strongly suppressed at $T_e > 2$ eV. From large-cell DNNP-MD simulations, we show that a well-defined thermal equilibrium, as defined by the Maxwell-Boltzmann distribution, is not achieved over the first few hundred femtoseconds. This behavior explains the non-monotonic equilibration of the kinetic temperature after a sudden rise of $T_e$. After $T_e$ is raised to 2.6 eV, Si and O atoms first equilibrate separately at two different temperatures, suggesting an atomic fluid phase, in agreement with recent experimental and theoretical findings.
△ Less
Submitted 30 July, 2026;
originally announced July 2026.
-
Design of experiments characterising heat conduction in magnetised, weakly collisional plasma
Authors:
T. A. Vincent,
P. Ariyathilaka,
L. Creaser,
C. Danson,
D. Lamb,
J. Meinecke,
C. A. J. Palmer,
S. Pitt,
H. Poole,
C. Spindloe,
P. Thomas,
E. Tubman,
L. Wilson,
W. J. Garbett,
G. Gregori,
P. Tzeferacos,
T. Hodge,
A. F. A. Bott
Abstract:
Heat conduction in weakly collisional, magnetised plasma is challenging to model accurately due to multifaceted physics governing heat-carrying electrons, including microinstabilities that scatter electrons and modify heat transport. Capturing these effects requires multidimensional kinetic theory simulations, which are computationally expensive. Experimental constraints overcome this issue, resul…
▽ More
Heat conduction in weakly collisional, magnetised plasma is challenging to model accurately due to multifaceted physics governing heat-carrying electrons, including microinstabilities that scatter electrons and modify heat transport. Capturing these effects requires multidimensional kinetic theory simulations, which are computationally expensive. Experimental constraints overcome this issue, resulting in improved understanding of thermal transport in systems such as the intra-cluster medium of galaxy clusters, and the hot-spot in inertial confinement fusion. In this paper, we present a new experimental platform that produces a weakly collisional high-\b{eta} plasma expected to be susceptible to the whistler heat-flux instability. This platform, to be fielded on the Orion laser, enables characterisation of whistler-regulated thermal conductivity. The platform design is assessed using radiation-magnetohydrodynamics simulations with the code FLASH. Simulations using three thermal conduction models predict conductivity suppression by over an order of magnitude relative to the Spitzer value at whistler saturation, demonstrating the efficacy of the platform.
△ Less
Submitted 10 February, 2026;
originally announced February 2026.
-
Compressed Sensing Methods for Memory Reduction in Monte Carlo Simulations
Authors:
Ethan Lame,
Camille Palmer,
Todd Palmer,
Ilham Variansyah
Abstract:
Monte Carlo simulations of neutronic systems are computationally intensive and demand significant memory resources for high-fidelity modeling. Compressed sensing enables accurate reconstruction of signals from significantly fewer samples than traditional methods. The specific implementation of compressed sensing investigated here involves the use of overlapping cells to collect tallies. Increasing…
▽ More
Monte Carlo simulations of neutronic systems are computationally intensive and demand significant memory resources for high-fidelity modeling. Compressed sensing enables accurate reconstruction of signals from significantly fewer samples than traditional methods. The specific implementation of compressed sensing investigated here involves the use of overlapping cells to collect tallies. Increasing the number of samples improves the reconstruction accuracy, although the marginal gains diminish with more samples. Reconstruction quality is strongly influenced by the sparsity parameter used in basis pursuit denoising. Across the three test cases considered, memory reductions of up to 81.25% (96.25%) are demonstrated for 2D (3D) reconstructions, with select scenarios achieving reconstruction errors within 1 standard deviation of the corresponding high-fidelity reference results.
△ Less
Submitted 7 February, 2026;
originally announced February 2026.
-
Interplay of Variance Reduction and Population Control in Monte Carlo Neutron Transport
Authors:
Jordan Northrop,
Ilham Variansyah,
Todd Palmer,
Camille Palmer
Abstract:
Monte Carlo methods are widely used for neutron transport simulations at least partly because of the accuracy they bring to the modeling of these problems. However, the computational burden associated with the slow convergence rate of Monte Carlo poses a significant challenge to running large-scale simulations. The continued improvement in high-performance computing capabilities has put exascale t…
▽ More
Monte Carlo methods are widely used for neutron transport simulations at least partly because of the accuracy they bring to the modeling of these problems. However, the computational burden associated with the slow convergence rate of Monte Carlo poses a significant challenge to running large-scale simulations. The continued improvement in high-performance computing capabilities has put exascale time-dependent Monte Carlo neutron transport simulations within reach. Variance reduction techniques have become an essential component to the efficiency of steady-state simulations, and population control techniques are an integral part of time-dependent simulations, but combining them can create algorithmic conflicts. This study investigates the performance of steady-state variance reduction techniques when extended to time-dependent problems and examines how variance reduction and population control techniques combine to impact the effectiveness of time-dependent simulations. Simulations were conducted using various combinations of these techniques across multiple test problems to assess their performance. While this study does not examine all possible variance reduction and population control combinations, the findings emphasize the importance of carefully selecting algorithms to simulate large-scale time-dependent problems effectively. Notably, using weight windows with weight-based combing for population control can significantly hinder simulation performance, whereas pairing weight windows with uniform combing can provide the efficiencies necessary for successfully computing the results of massive problems. Further performance gains were observed when steady-state weight windows were replaced with time-dependent versions.
△ Less
Submitted 26 September, 2025;
originally announced September 2025.
-
A Momentum-Resolved X-ray Thomson Scattering Benchmark of Electronic-Response Models in Warm Dense Aluminium
Authors:
Dmitrii S. Bespalov,
Ulf Zastrau,
Zhandos A. Moldabekov,
Thomas Gawne,
Tobias Dornheim,
Moyassar Meshhal,
Alexis Amouretti,
Michal Andrzejewski,
Karen Appel,
Carsten Baehtz,
Erik Brambrink,
Khachiwan Buakor,
Carolina Camarda,
David Chin,
Gilbert Collins,
Céline Crépeisson,
Adrien Descamps,
Jon Eggert,
Luke Fletcher,
Alessandro Forte,
Gianluca Gregori,
Marion Harmand,
Oliver S. Humphries,
Hauke Höppner,
Jonas Kuhlke
, et al. (36 additional authors not shown)
Abstract:
The robust diagnosis of conditions generated in warm dense matter (WDM) experiments remains a persistent challenge. Here we describe the measurement of shock-compressed aluminium at 50 GPa with angle-resolved femtosecond x-ray Thomson scattering (XRTS) over a wide range of scattering wavevectors at the European XFEL. The measured plasmon dispersion and line shape show that the de facto standard ap…
▽ More
The robust diagnosis of conditions generated in warm dense matter (WDM) experiments remains a persistent challenge. Here we describe the measurement of shock-compressed aluminium at 50 GPa with angle-resolved femtosecond x-ray Thomson scattering (XRTS) over a wide range of scattering wavevectors at the European XFEL. The measured plasmon dispersion and line shape show that the de facto standard approach for analysing XRTS spectra, based on uniform-electron-gas models, systematically overestimates the resonance energy by up to 8 eV. We present an ab initio approach that agrees within the experimental uncertainty and demonstrates that accounting for shock-induced disorder is critical for interpreting shock-compressed systems, providing evidence that ab initio treatments are required for reliable XRTS inference in warm dense aluminium.
△ Less
Submitted 6 May, 2026; v1 submitted 12 September, 2025;
originally announced September 2025.
-
Measurement of ion acceleration and diffusion in a laser-driven magnetized plasma
Authors:
J. T. Y. Chu,
J. W. D. Halliday,
C. Heaton,
K. Moczulski,
A. Blazevic,
D. Schumacher,
M. Metternich,
H. Nazary,
C. D. Arrowsmith,
A. R. Bell,
K. A. Beyer,
A. F. A. Bott,
T. Campbell,
E. Hansen,
D. Q. Lamb,
F. Miniati,
P. Neumayer,
C. A. J. Palmer,
B. Reville,
A. Reyes,
S. Sarkar,
A. Scopatz,
C. Spindloe,
C. B. Stuart,
H. Wen
, et al. (3 additional authors not shown)
Abstract:
Here we present results from an experiment performed at the GSI Helmholtz Centre for Heavy Ion Research. A mono-energetic beam of chromium ions with initial energies of $\sim 450$ MeV was fired through a magnetized interaction region formed by the collision of two counter-propagating laser-ablated plasma jets. While laser interferometry revealed the absence of strong fluid-scale turbulence, accele…
▽ More
Here we present results from an experiment performed at the GSI Helmholtz Centre for Heavy Ion Research. A mono-energetic beam of chromium ions with initial energies of $\sim 450$ MeV was fired through a magnetized interaction region formed by the collision of two counter-propagating laser-ablated plasma jets. While laser interferometry revealed the absence of strong fluid-scale turbulence, acceleration and diffusion of the beam ions was driven by wave-particle interactions. A possible mechanism is particle acceleration by electrostatic, short scale length kinetic turbulence, such as the lower-hybrid drift instability.
△ Less
Submitted 28 February, 2026; v1 submitted 9 September, 2025;
originally announced September 2025.
-
Characterization and automated optimization of laser-driven proton beams from converging liquid sheet jet targets
Authors:
G. D. Glenn,
F. Treffert,
H. Ahmed,
S. Astbury,
M. Borghesi,
N. Bourgeois,
C. B. Curry,
S. J. D. Dann,
S. DiIorio,
N. P. Dover,
T. Dzelzainis,
O. Ettlinger,
M. Gauthier,
L. Giuffrida,
R. J. Gray,
J. S. Green,
G. S. Hicks,
C. Hyland,
V. Istokskaia,
M. King,
B. Loughran,
D. Margarone,
O. McCusker,
P. McKenna,
Z. Najmudin
, et al. (9 additional authors not shown)
Abstract:
Compact, stable, and versatile laser-driven ion sources hold great promise for applications ranging from medicine to materials science and fundamental physics. While single-shot sources have demonstrated favorable beam properties, including the peak fluxes necessary for several applications, high repetition rate operation will be necessary to generate and sustain the high average flux needed for m…
▽ More
Compact, stable, and versatile laser-driven ion sources hold great promise for applications ranging from medicine to materials science and fundamental physics. While single-shot sources have demonstrated favorable beam properties, including the peak fluxes necessary for several applications, high repetition rate operation will be necessary to generate and sustain the high average flux needed for many of the most exciting applications of laser-driven ion sources. Further, to navigate through the high-dimensional space of laser and target parameters towards experimental optima, it is essential to develop ion acceleration platforms compatible with machine learning learning techniques and capable of autonomous real-time optimization. Here we present a multi-Hz ion acceleration platform employing a liquid sheet jet target. We characterize the laser-plasma interaction and the laser-driven proton beam across a variety of key parameters governing the interaction using an extensive suite of online diagnostics. We also demonstrate real-time, closed-loop optimization of the ion beam maximum energy by tuning the laser wavefront using a Bayesian optimization scheme. This approach increased the maximum proton energy by 11% compared to a manually-optimized wavefront by enhancing the energy concentration within the laser focal spot, demonstrating the potential for closed-loop optimization schemes to tune future ion accelerators for robust high repetition rate operation.
△ Less
Submitted 8 August, 2025;
originally announced August 2025.
-
The CMS Barrel Timing Layer: test beam confirmation of module timing performance
Authors:
F. Addesa,
P. Akrap,
A. Albert,
B. Allmond,
T. Anderson,
J. Babbar,
D. Baranyai,
P. Barria,
C. Basile,
A. Benaglia,
A. Benato,
M. Benettoni,
M. Besancon,
N. Bez,
S. Bhattacharya,
R. Bianco,
D. Blend,
A. Boletti,
A. Bornheim,
R. Bugalho,
A. Bulla,
B. Cardwell,
R. Carlin,
M. Casarsa,
F. Cetorelli
, et al. (105 additional authors not shown)
Abstract:
First of its kind, the barrel section of the MIP Timing Detector is a large area timing detector based on LYSO:Ce crystals and SiPMs which are required to operate in an unprecedentedly harsh radiation environment (up to an integrated fluence of $2\times10^{14}$ 1 MeV $n_{eq}/cm^2$). It is designed as a key element of the upgrade of the existing CMS detector to provide a time resolution for minimum…
▽ More
First of its kind, the barrel section of the MIP Timing Detector is a large area timing detector based on LYSO:Ce crystals and SiPMs which are required to operate in an unprecedentedly harsh radiation environment (up to an integrated fluence of $2\times10^{14}$ 1 MeV $n_{eq}/cm^2$). It is designed as a key element of the upgrade of the existing CMS detector to provide a time resolution for minimum ionizing particles in the range between 30-60 ps throughout the entire operation at the High Luminosity LHC. A thorough optimization of its components has led to the final detector module layout which exploits 25 $\rm μm$ cell size SiPMs and 3.75 mm thick crystals. This design achieved the target performance in a series of test beam campaigns. In this paper we present test beam results which demonstrate the desired performance of detector modules in terms of radiation tolerance, time resolution and response uniformity.
△ Less
Submitted 15 April, 2025;
originally announced April 2025.
-
On the resolution of dual readout calorimeters
Authors:
S. Eno,
L. Wu,
M. Y. Aamir,
S. V. Chekanov,
S. Nabili,
C. Palmer
Abstract:
Dual readout calorimeters allow state-of-the-art resolutions for hadronic energy measurements. Their various incarnations are leading candidates for the calorimeter systems for future colliders. In this paper, we present a simple formula for the resolution of a dual readout calorimeter, which we verify with a toy simulation and with full simulation results. This formula can help those new to dual…
▽ More
Dual readout calorimeters allow state-of-the-art resolutions for hadronic energy measurements. Their various incarnations are leading candidates for the calorimeter systems for future colliders. In this paper, we present a simple formula for the resolution of a dual readout calorimeter, which we verify with a toy simulation and with full simulation results. This formula can help those new to dual readout calorimetry understand its strengths and limitations. The paper also highlights that the dual readout correction works not just to compensate for binding energy loss, but also for energies escaping the calorimeter or clustering algorithm. Formulae are also presented for approximate resolutions and energy scales in terms of different sources of response.
△ Less
Submitted 29 January, 2025; v1 submitted 25 January, 2025;
originally announced January 2025.
-
Optimization of LYSO crystals and SiPM parameters for the CMS MIP timing detector
Authors:
F. Addesa,
T. Anderson,
P. Barria,
C. Basile,
A. Benaglia,
R. Bertoni,
A. Bethani,
R. Bianco,
A. Bornheim,
G. Boldrini,
A. Boletti,
A. Bulla,
M. Campana,
B. Cardwell,
P. Carniti,
F. Cetorelli,
F. De Guio,
K. De Leo,
F. De Riggi,
J. Dervan,
E. Fernandez,
A. Gaile,
M. Gallinaro,
A. Ghezzi,
C. Gotti
, et al. (46 additional authors not shown)
Abstract:
For the High-Luminosity (HL-LHC) phase, the upgrade of the Compact Muon Solenoid (CMS) experiment at CERN will include a novel MIP Timing Detector (MTD). The central part of MTD, the barrel timing layer (BTL), is designed to provide a measurement of the time of arrival of charged particles with a precision of 30 ps at the beginning of HL-LHC, progressively degrading to 60 ps while operating in an…
▽ More
For the High-Luminosity (HL-LHC) phase, the upgrade of the Compact Muon Solenoid (CMS) experiment at CERN will include a novel MIP Timing Detector (MTD). The central part of MTD, the barrel timing layer (BTL), is designed to provide a measurement of the time of arrival of charged particles with a precision of 30 ps at the beginning of HL-LHC, progressively degrading to 60 ps while operating in an extremely harsh radiation environment for over a decade. In this paper we present a comparative analysis of the time resolution of BTL module prototypes made of LYSO:Ce crystal bars read out by silicon photo-multipliers (SiPMs). The timing performance measured in beam test campaigns is presented for prototypes with different construction and operation parameters, such as different SiPM cell sizes (15, 20, 25 and 30 $\rm μm$), SiPM manufacturers and crystal bar thicknesses. The evolution of time resolution as a function of the irradiation level has been studied using non-irradiated SiPMs as well as SiPMs exposed up to $2\times 10^{14}~n_{eq}/cm^2$ fluence. The key parameters defining the module time resolution such as SiPM characteristics (gain, photon detection efficiency, radiation induced dark count rate) and crystal properties (light output and dimensions) are discussed. These results have informed the final choice of the MTD barrel sensor configuration and offer a unique starting point for the design of future large-area scintillator-based timing detectors in either low or high radiation environments.
△ Less
Submitted 11 October, 2024;
originally announced October 2024.
-
Noninvasive cavity-based charge diagnostic for plasma accelerators
Authors:
Simon Bohlen,
Olena Kononenko,
Jan-Patrick Schwinkendorf,
Florian Grüner,
Dirk Lipka,
Martin Meisel,
Charlotte Palmer,
Theresa Staufer,
Kristjan Põder,
Jens Osterhoff
Abstract:
The charge contained in an electron bunch is one of the most important parameters in accelerator physics. Several techniques to measure the electron bunch charge exist. However, many conventional charge diagnostics face serious drawbacks when applied to plasma accelerators. For example, integrating current transformers (ICTs or toroids) have been shown to be sensitive to the electromagnetic pulses…
▽ More
The charge contained in an electron bunch is one of the most important parameters in accelerator physics. Several techniques to measure the electron bunch charge exist. However, many conventional charge diagnostics face serious drawbacks when applied to plasma accelerators. For example, integrating current transformers (ICTs or toroids) have been shown to be sensitive to the electromagnetic pulses (EMP) originating from the plasma, whereas scintillating screens are sensitive to background radiation such as betatron radiation or bremsstrahlung and only allow for a destructive measurement of the bunch charge. We show measurements with a noninvasive, cavity-based charge diagnostic (the DaMon), which demonstrate its high sensitivity, high dynamic range and resistance towards EMP. The measurements are compared to both an ICT and an absolutely calibrated scintillating screen.
△ Less
Submitted 11 March, 2024;
originally announced March 2024.
-
Rotational spectroscopic characterisation of the [D2,C,S] system: an update from the laboratory and theory
Authors:
Natalia Inostroza-Pino,
Valerio Lattanzi,
C. Zachary Palmer,
Ryan C. Fortenberry,
Diego Mardones,
Paola Caselli,
Oko E. Godwin,
Timothy J. Lee
Abstract:
The synergy between high-resolution rotational spectroscopy and quantum-chemical calculations is essential for exploring future detection of molecules, especially when spectroscopy parameters are not available yet. By using highly correlated ab initio quartic force fields (QFFs) from explicitly correlated coupled cluster theory, a complete set of rotational constants and centrifugal distortion con…
▽ More
The synergy between high-resolution rotational spectroscopy and quantum-chemical calculations is essential for exploring future detection of molecules, especially when spectroscopy parameters are not available yet. By using highly correlated ab initio quartic force fields (QFFs) from explicitly correlated coupled cluster theory, a complete set of rotational constants and centrifugal distortion constants for D$_2$CS and cis/trans-DCSD isomers have been produced. Comparing our new ab initio results for D$_2$CS with new rotational spectroscopy laboratory data for the same species, the accuracy of the computed B and C rotational constants is within 0.1% while the A constant is only slightly higher. Additionally, quantum chemical vibrational frequencies are also provided, and these spectral reference data and new experimental rotational lines will provide additional references for potential observation of these deuterated sulfur species with either ground-based radio telescopes or space-based infrared observatories.
△ Less
Submitted 15 November, 2023;
originally announced November 2023.
-
Geant4 simulations of sampling and homogeneous hadronic calorimeters with dual readout for future colliders
Authors:
S. V. Chekanov,
S. Eno,
S. Magill,
C. Palmer,
L. Wu
Abstract:
Hadronic calorimeters with dual readout measure both scintillation and Cherenkov lights produced in their active media. They offer improvements in energy resolution and, therefore, have become increasingly interesting due to the need for precision jet measurements at Higgs factories. This paper presents Geant4 simulations of single-particle responses in sampling and homogeneous calorimeters, and d…
▽ More
Hadronic calorimeters with dual readout measure both scintillation and Cherenkov lights produced in their active media. They offer improvements in energy resolution and, therefore, have become increasingly interesting due to the need for precision jet measurements at Higgs factories. This paper presents Geant4 simulations of single-particle responses in sampling and homogeneous calorimeters, and demonstrates the effect of inclusion of Cherenkov light in the reconstruction of energies. The simulations are performed with a single-photon precision.
△ Less
Submitted 6 November, 2023;
originally announced November 2023.
-
Effects of oxygen on the optical properties of phenyl-based scintillators during irradiation and recovery
Authors:
C. Papageorgakis,
M. Y. Aamir,
A. Belloni,
T. K. Edberg,
S. C. Eno,
B. Kronheim,
C. Palmer
Abstract:
Plastic scintillators are a versatile and inexpensive option for particle detection, which is why the largest particle physics experiments, CMS and ATLAS, use them extensively in their calorimeters. One of their challenging aspects, however, is their relatively low radiation hardness, which might be inadequate for very high luminosity future projects like the FCC-hh. In this study, results on the…
▽ More
Plastic scintillators are a versatile and inexpensive option for particle detection, which is why the largest particle physics experiments, CMS and ATLAS, use them extensively in their calorimeters. One of their challenging aspects, however, is their relatively low radiation hardness, which might be inadequate for very high luminosity future projects like the FCC-hh. In this study, results on the effects of ionizing radiation on the optical properties of plastic scintillator samples are presented. The samples are made from two different matrix materials, polystyrene and polyvinyltoluene, and have been irradiated at dose rates ranging from $2.2\,$Gy/h up to $3.4\,$kGy/h at room temperature. An internal boundary that separates two regions of different indices of refraction is visible in the samples depending on the dose rate, and it is compatible with the expected oxygen penetration depth during irradiation. The dose rate dependence of the oxygen penetration depth for the two matrix materials suggests that the oxygen penetration coefficient differs for PS and PVT. The values of the refractive index for the internal regions are elevated compared to those of the outer regions, which are compatible with the indices of unirradiated samples.
△ Less
Submitted 8 December, 2023; v1 submitted 23 October, 2023;
originally announced October 2023.
-
Reduction of light output of plastic scintillator tiles during irradiation at cold temperatures and in low-oxygen environments
Authors:
B. Kronheim,
A. Belloni,
T. K. Edberg,
S. C. Eno,
C. Howe,
C. Palmer,
C. Papageorgakis,
M. Paranjpe,
S. Sriram
Abstract:
The advent of the silicon photomultiplier has allowed the development of highly segmented calorimeters using plastic scintillator as the active media, with photodetectors embedded in the calorimeter, in dimples in the plastic. To reduce the photodetector's dark current and radiation damage, the high granularity calorimeter designed for the high luminosity upgrade of the CMS detector at CERN's Larg…
▽ More
The advent of the silicon photomultiplier has allowed the development of highly segmented calorimeters using plastic scintillator as the active media, with photodetectors embedded in the calorimeter, in dimples in the plastic. To reduce the photodetector's dark current and radiation damage, the high granularity calorimeter designed for the high luminosity upgrade of the CMS detector at CERN's Large Hadron Collider will be operated at a temperature of about -30$^\circ$C. Due to flammability considerations, a low oxygen environment is being considered. However, the radiation damage to the plastic scintillator during irradiation in this operating environment needs to be considered. In this paper, we present measurements of the relative decrease of light output during irradiation of small plastic scintillator tiles read out by silicon photomultipliers. The irradiations were performed using a $^{60}\mathrm{Co}$ source both to produce the tiles' light and as a source of ionizing irradiation at dose rates of 0.3, 1.3, and $1.6\,$Gy/hr, temperatures of -30, -15, -5, and 0$^\circ$C, and with several different oxygen concentrations in the surrounding atmosphere. The effect of the material used to wrap the tile was also studied. Substantial temporary damage, which annealed when the sample was warmed, was seen during the low-temperature irradiations, regardless of the oxygen concentration and wrapping material. The relative light loss was largest with 3M$^{\tiny \textrm{TM}}$ Enhanced Specular Reflector Film wrapping and smallest with no wrapping, although due to the substantially higher light yield with wrapping, the final light output is largest with wrapping. The light loss was less at warmer temperatures. Damage with $3\%$ oxygen was similar to that in standard atmosphere. Evidence of a plateau in the radical density was seen for the 0$^\circ$C data.
△ Less
Submitted 3 August, 2023;
originally announced August 2023.
-
Control Systems and Data Management for High-Power Laser Facilities
Authors:
Scott Feister,
Kevin Cassou,
Stephen Dann,
Andreas Döpp,
Philippe Gauron,
Anthony J. Gonsalves,
Archis Joglekar,
Victoria Marshall,
Olivier Neveu,
Hans-Peter Schlenvoigt,
Matthew J. V. Streeter,
Charlotte A. J. Palmer
Abstract:
The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than was possible using the prior generation. Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology. A distributed networked control system can enable laboratory-wide automation and feedback control loops. T…
▽ More
The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than was possible using the prior generation. Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology. A distributed networked control system can enable laboratory-wide automation and feedback control loops. These higher-repetition-rate experiments will create enormous quantities of data. A consistent approach to managing data can increase data accessibility, reduce repetitive data-software development, and mitigate poorly organized metadata. An opportunity arises to share knowledge of improvements to control and data infrastructure currently being undertaken. We compare platforms and approaches to state-of-the-art control systems and data management at high-power laser facilities, and we illustrate these topics with case studies from our community.
△ Less
Submitted 2 June, 2023;
originally announced June 2023.
-
Automated control and optimisation of laser driven ion acceleration
Authors:
B. Loughran,
M. J. V. Streeter,
H. Ahmed,
S. Astbury,
M. Balcazar,
M. Borghesi,
N. Bourgeois,
C. B. Curry,
S. J. D. Dann,
S. DiIorio,
N. P. Dover,
T. Dzelzanis,
O. C. Ettlinger,
M. Gauthier,
L. Giuffrida,
G. D. Glenn,
S. H. Glenzer,
J. S. Green,
R. J. Gray,
G. S. Hicks,
C. Hyland,
V. Istokskaia,
M. King,
D. Margarone,
O. McCusker
, et al. (10 additional authors not shown)
Abstract:
The interaction of relativistically intense lasers with opaque targets represents a highly non-linear, multi-dimensional parameter space. This limits the utility of sequential 1D scanning of experimental parameters for the optimisation of secondary radiation, although to-date this has been the accepted methodology due to low data acquisition rates. High repetition-rate (HRR) lasers augmented by ma…
▽ More
The interaction of relativistically intense lasers with opaque targets represents a highly non-linear, multi-dimensional parameter space. This limits the utility of sequential 1D scanning of experimental parameters for the optimisation of secondary radiation, although to-date this has been the accepted methodology due to low data acquisition rates. High repetition-rate (HRR) lasers augmented by machine learning present a valuable opportunity for efficient source optimisation. Here, an automated, HRR-compatible system produced high fidelity parameter scans, revealing the influence of laser intensity on target pre-heating and proton generation. A closed-loop Bayesian optimisation of maximum proton energy, through control of the laser wavefront and target position, produced proton beams with equivalent maximum energy to manually-optimized laser pulses but using only 60% of the laser energy. This demonstration of automated optimisation of laser-driven proton beams is a crucial step towards deeper physical insight and the construction of future radiation sources.
△ Less
Submitted 1 March, 2023;
originally announced March 2023.
-
Performance of the CMS High Granularity Calorimeter prototype to charged pion beams of 20$-$300 GeV/c
Authors:
B. Acar,
G. Adamov,
C. Adloff,
S. Afanasiev,
N. Akchurin,
B. Akgün,
M. Alhusseini,
J. Alison,
J. P. Figueiredo de sa Sousa de Almeida,
P. G. Dias de Almeida,
A. Alpana,
M. Alyari,
I. Andreev,
U. Aras,
P. Aspell,
I. O. Atakisi,
O. Bach,
A. Baden,
G. Bakas,
A. Bakshi,
S. Banerjee,
P. DeBarbaro,
P. Bargassa,
D. Barney,
F. Beaudette
, et al. (435 additional authors not shown)
Abstract:
The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing med…
▽ More
The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly readout by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data.
△ Less
Submitted 27 May, 2023; v1 submitted 9 November, 2022;
originally announced November 2022.
-
Miniaturized Modules for Space Based Optical Communication
Authors:
J. Edmunds,
L. Henwood-Moroney,
N. Hammond,
E. Prowse,
K. Hall,
L. Szemendera,
N. Davoudzadeh,
P. Holland,
K. Simpson,
C. Palmer,
L. Stampoulidis,
P. Kean,
M. Welch,
E. Kehayas
Abstract:
We present recent progress in developing miniaturized optical receiver amplifiers for space communications.
We present recent progress in developing miniaturized optical receiver amplifiers for space communications.
△ Less
Submitted 4 October, 2022;
originally announced October 2022.
-
Dose rate effects in radiation-induced changes to phenyl-based polymeric scintillators
Authors:
Christos Papageorgakis,
Mohamad Al-Sheikhly,
Alberto Belloni,
Timothy K. Edberg,
Sarah C. Eno,
Yongbin Feng,
Geng-Yuan Jeng,
Abraham Kahn,
Yihui Lai,
Tyler McDonnell,
Christopher Palmer,
Ruhi Perez-Gokhale,
Francesca Ricci-Tam,
Yao Yao,
Zishuo Yang
Abstract:
Results on the effects of ionizing radiation on the signal produced by plastic scintillating rods manufactured by Eljen Technology company are presented for various matrix materials, dopant concentrations, fluors (EJ-200 and EJ-260), anti-oxidant concentrations, scintillator thickness, doses, and dose rates. The light output before and after irradiation is measured using an alpha source and a phot…
▽ More
Results on the effects of ionizing radiation on the signal produced by plastic scintillating rods manufactured by Eljen Technology company are presented for various matrix materials, dopant concentrations, fluors (EJ-200 and EJ-260), anti-oxidant concentrations, scintillator thickness, doses, and dose rates. The light output before and after irradiation is measured using an alpha source and a photomultiplier tube, and the light transmission by a spectrophotometer. Assuming an exponential decrease in the light output with dose, the change in light output is quantified using the exponential dose constant $D$. The $D$ values are similar for primary and secondary doping concentrations of 1 and 2 times, and for antioxidant concentrations of 0, 1, and 2 times, the default manufacturer's concentration. The $D$ value depends approximately linearly on the logarithm of the dose rate for dose rates between 2.2 Gy/hr and 70 Gy/hr for all materials. For EJ-200 polyvinyltoluene-based (PVT) scintillator, the dose constant is approximately linear in the logarithm of the dose rate up to 3400 Gy/hr, while for polystyrene-based (PS) scintillator or for both materials with EJ-260 fluors, it remains constant or decreases (depending on doping concentration) above about 100 Gy/hr. The results from rods of varying thickness and from the different fluors suggest damage to the initial light output is a larger effect than color center formation for scintillator thickness $\leq1$ cm. For the blue scintillator (EJ-200), the transmission measurements indicate damage to the fluors. We also find that while PVT is more resistant to radiation damage than PS at dose rates higher than about 100 Gy/hr for EJ-200 fluors, they show similar damage at lower dose rates and for EJ-260 fluors.
△ Less
Submitted 8 August, 2023; v1 submitted 29 March, 2022;
originally announced March 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.
-
The data-driven future of high energy density physics
Authors:
Peter W. Hatfield,
Jim A. Gaffney,
Gemma J. Anderson,
Suzanne Ali,
Luca Antonelli,
Suzan Başeğmez du Pree,
Jonathan Citrin,
Marta Fajardo,
Patrick Knapp,
Brendan Kettle,
Bogdan Kustowski,
Michael J. MacDonald,
Derek Mariscal,
Madison E. Martin,
Taisuke Nagayama,
Charlotte A. J. Palmer,
J. Luc Peterson,
Steven Rose,
J J Ruby,
Carl Shneider,
Matt J. V. Streeter,
Will Trickey,
Ben Williams
Abstract:
The study of plasma physics under conditions of extreme temperatures, densities and electromagnetic field strengths is significant for our understanding of astrophysics, nuclear fusion and fundamental physics. These extreme physical systems are strongly non-linear and very difficult to understand theoretically or optimize experimentally. Here, we argue that machine learning models and data-driven…
▽ More
The study of plasma physics under conditions of extreme temperatures, densities and electromagnetic field strengths is significant for our understanding of astrophysics, nuclear fusion and fundamental physics. These extreme physical systems are strongly non-linear and very difficult to understand theoretically or optimize experimentally. Here, we argue that machine learning models and data-driven methods are in the process of reshaping our exploration of these extreme systems that have hitherto proven far too non-linear for human researchers. From a fundamental perspective, our understanding can be helped by the way in which machine learning models can rapidly discover complex interactions in large data sets. From a practical point of view, the newest generation of extreme physics facilities can perform experiments multiple times a second (as opposed to ~daily), moving away from human-based control towards automatic control based on real-time interpretation of diagnostic data and updates of the physics model. To make the most of these emerging opportunities, we advance proposals for the community in terms of research design, training, best practices, and support for synthetic diagnostics and data analysis.
△ Less
Submitted 22 November, 2021;
originally announced November 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.
-
Spectrally peaked proton beams shock accelerated from an optically shaped overdense gas jet by a near-infrared laser
Authors:
George S. Hicks,
Oliver C. Ettlinger,
Marco Borghesi,
David C. Carroll,
Robert J. Clarke,
Emma-Jane Ditter,
Timothy P. Frazer,
Ross J. Gray,
Aodhan McIlvenny,
Paul McKenna,
Charlotte A. J. Palmer,
Louise Willingale,
Zulfikar Najmudin
Abstract:
We report on the generation of impurity-free proton beams from an overdense gas jet driven by a near-infrared laser ($λ_L=1.053$ $\mathrmμ m$). The gas profile was shaped prior to the interaction using a controlled prepulse. Without this optical shaping, a 30$\pm$4 nCsr$^{-1}$ thermal spectrum was detected transversely to the laser propagation direction with a high energy 8.27$\pm$7 MeV, narrow en…
▽ More
We report on the generation of impurity-free proton beams from an overdense gas jet driven by a near-infrared laser ($λ_L=1.053$ $\mathrmμ m$). The gas profile was shaped prior to the interaction using a controlled prepulse. Without this optical shaping, a 30$\pm$4 nCsr$^{-1}$ thermal spectrum was detected transversely to the laser propagation direction with a high energy 8.27$\pm$7 MeV, narrow energy spread (6$\pm$2 %) bunch containing 45$\pm$7 pCsr$^{-1}$. In contrast, with optical shaping the radial component was not detected and instead forward going protons were detected with energy 1.32$\pm$2 MeV, 12.9$\pm$3 % energy spread, and charge 400$\pm$30 pCsr$^{-1}$. Both the forward going and radial narrow energy spread features are indicative of collisionless shock acceleration of the protons.
△ Less
Submitted 28 April, 2021;
originally announced April 2021.
-
Time-resolved fast turbulent dynamo in a laser plasma
Authors:
A. F. A. Bott,
P. Tzeferacos,
L. Chen,
C. A. J. Palmer,
A. Rigby,
A. Bell,
R. Bingham,
A. Birkel,
C. Graziani,
D. H. Froula,
J. Katz,
M. Koenig,
M. W. Kunz,
C. K. Li,
J. Meinecke,
F. Miniati,
R. Petrasso,
H. -S. Park,
B. A. Remington,
B. Reville,
J. S. Ross,
D. Ryu,
D. Ryutov,
F. Séguin,
T. G. White
, et al. (3 additional authors not shown)
Abstract:
Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ($\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.
-
A tunable plasma-based energy dechirper
Authors:
R. D'Arcy,
S. Wesch,
A. Aschikhin,
S. Bohlen,
C. Behrens,
M. J. Garland,
L. Goldberg,
P. Gonzalez,
A. Knetsch,
V. Libov,
A. Martinez de la Ossa,
M. Meisel,
T. J. Mehrling,
P. Niknejadi,
K. Poder,
J. -H. Roeckemann,
L. Schaper,
B. Schmidt,
S. Schroeder,
C. Palmer,
J. -P. Schwinkendorf,
B. Sheeran,
M. J. V. Streeter,
G. Tauscher,
V. Wacker
, et al. (1 additional authors not shown)
Abstract:
A tunable plasma-based energy dechirper has been developed at FLASHForward to remove the correlated energy spread of a 681~MeV electron bunch. Through the interaction of the bunch with wakefields excited in plasma the projected energy spread was reduced from a FWHM of 1.31$\%$ to 0.33$\%$ without reducing the stability of the incoming beam. The experimental results for variable plasma density are…
▽ More
A tunable plasma-based energy dechirper has been developed at FLASHForward to remove the correlated energy spread of a 681~MeV electron bunch. Through the interaction of the bunch with wakefields excited in plasma the projected energy spread was reduced from a FWHM of 1.31$\%$ to 0.33$\%$ without reducing the stability of the incoming beam. The experimental results for variable plasma density are in good agreement with analytic predictions and three-dimensional simulations. The proof-of-principle dechirping strength of $1.8$~GeV/mm/m significantly exceeds those demonstrated for competing state-of-the-art techniques and may be key to future plasma wakefield-based free-electron lasers and high energy physics facilities, where large intrinsic chirps need to be removed.
△ Less
Submitted 4 January, 2019; v1 submitted 15 October, 2018;
originally announced October 2018.
-
Observation of Laser Power Amplification in a Self-Injecting Laser Wakefield Accelerator
Authors:
M. J. V. Streeter,
S. Kneip,
M. S. Bloom,
R. A. Bendoyro,
O. Chekhlov,
A. E. Dangor,
A. Döpp,
C. J. Hooker,
J. Holloway,
J. Jiang,
N. C. Lopes,
H. Nakamura,
P. A. Norreys,
C. A. J. Palmer,
P. P. Rajeev,
J. Schreiber,
D. R. Symes,
M. Wing,
S. P. D. Mangles,
Z. Najmudin
Abstract:
We report on the depletion and power amplification of the driving laser pulse in a strongly-driven laser wakefield accelerator. Simultaneous measurement of the transmitted pulse energy and temporal shape indicate an increase in peak power from $187 \pm 11$ TW to a maximum of $318 \pm 12$ TW after 13 mm of propagation in plasma density of $0.9 \times 10^{18}$ cm$^{-3}$. The power amplification is c…
▽ More
We report on the depletion and power amplification of the driving laser pulse in a strongly-driven laser wakefield accelerator. Simultaneous measurement of the transmitted pulse energy and temporal shape indicate an increase in peak power from $187 \pm 11$ TW to a maximum of $318 \pm 12$ TW after 13 mm of propagation in plasma density of $0.9 \times 10^{18}$ cm$^{-3}$. The power amplification is correlated with the injection and acceleration of electrons in the nonlinear wakefield. This process is modeled by including localized redshift and subsequent group delay dispersion at the laser pulse front.
△ Less
Submitted 21 June, 2018; v1 submitted 15 October, 2017;
originally announced October 2017.
-
The FLASHForward Facility at DESY
Authors:
A. Aschikhin,
C. Behrens,
S. Bohlen,
J. Dale,
N. Delbos,
L. di Lucchio,
E. Elsen,
J. -H. Erbe,
M. Felber,
B. Foster,
L. Goldberg,
J. Grebenyuk,
J. -N. Gruse,
B. Hidding,
Zhanghu Hu,
S. Karstensen,
A. Knetsch,
O. Kononenko,
V. Libov,
K. Ludwig,
A. R. Maier,
A. Martinez de la Ossa,
T. Mehrling,
C. A. J. Palmer,
F. Pannek
, et al. (13 additional authors not shown)
Abstract:
The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of quality sufficient to be used in a free-electron laser. The plasma wave will be driven by high-current density electron beams from the FLASH linear accelerator and will explore both external and internal…
▽ More
The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of quality sufficient to be used in a free-electron laser. The plasma wave will be driven by high-current density electron beams from the FLASH linear accelerator and will explore both external and internal witness-beam injection techniques. The plasma is created by ionising a gas in a gas cell with a multi-TW laser system, which can also be used to provide optical diagnostics of the plasma and electron beams due to the <30 fs synchronisation between the laser and the driving electron beam. The operation parameters of the experiment are discussed, as well as the scientific program.
△ Less
Submitted 18 August, 2015; v1 submitted 13 August, 2015;
originally announced August 2015.
-
Buffered spectrally-peaked proton beams in the relativistic-transparency regime
Authors:
N. P. Dover,
M. J. V. Streeter,
C. A. J. Palmer,
H. Ahmed,
B. Albertazzi,
M. Borghesi,
D. C. Carroll,
J. Fuchs,
R. Heathcote,
P. Hilz,
K. F. Kakolee,
S. Kar,
R. Kodama,
A. Kon,
D. A. MacLellan,
P. McKenna,
S. R. Nagel,
M. Nakatsutsumi,
D. Neely,
M. M. Notley,
R. Prasad,
G. Scott,
M. Tampo,
M. Zepf,
J. Schreiber
, et al. (1 additional authors not shown)
Abstract:
Spectrally-peaked proton beams ($E_{p}\approx 8$ MeV, $ΔE\approx 4$ MeV) have been observed from the interaction of an intense laser ($> 10^{19 }$ Wcm$^{-2}$) with ultrathin CH foils, as measured by spectrally-resolved full beam profiles. These beams are reproducibly generated for foil thicknesses (5-100 nm), and exhibit narrowing divergence with decreasing target thickness down to…
▽ More
Spectrally-peaked proton beams ($E_{p}\approx 8$ MeV, $ΔE\approx 4$ MeV) have been observed from the interaction of an intense laser ($> 10^{19 }$ Wcm$^{-2}$) with ultrathin CH foils, as measured by spectrally-resolved full beam profiles. These beams are reproducibly generated for foil thicknesses (5-100 nm), and exhibit narrowing divergence with decreasing target thickness down to $\approx 8^\circ$ for 5 nm. Simulations demonstrate that the narrow energy spread feature is a result of buffered acceleration of protons. Due to their higher charge-to-mass ratio, the protons outrun a carbon plasma driven in the relativistic transparency regime.
△ Less
Submitted 13 June, 2014;
originally announced June 2014.
-
Two-state thermodynamics of the ST2 model for supercooled water
Authors:
Vincent Holten,
Jeremy C. Palmer,
Peter H. Poole,
Pablo G. Debenedetti,
Mikhail A. Anisimov
Abstract:
Thermodynamic properties of the ST2 model for supercooled liquid water exhibit anomalies similar to those observed in real water. A possible explanation of these anomalies is the existence of a metastable, liquid-liquid transition terminated by a critical point. This phenomenon, whose possible existence in real water is the subject of much current experimental work, has been unambiguously demonstr…
▽ More
Thermodynamic properties of the ST2 model for supercooled liquid water exhibit anomalies similar to those observed in real water. A possible explanation of these anomalies is the existence of a metastable, liquid-liquid transition terminated by a critical point. This phenomenon, whose possible existence in real water is the subject of much current experimental work, has been unambiguously demonstrated for this particular model by most recent simulations. In this work, we reproduce the anomalies of two versions of the ST2 model with an equation of state describing water as a non-ideal "mixture" of two different types of local molecular order. We show that the liquid-liquid transition in the ST2 water is energy-driven. This is in contrast to another popular model, mW, in which non-ideality in mixing of two alternative local molecular orders is entropy-driven, and is not sufficiently strong to induce a liquid-liquid transition.
△ Less
Submitted 17 February, 2014; v1 submitted 17 December, 2013;
originally announced December 2013.
-
Optical probing of shocks driven into overdense plasmas by laser hole-boring
Authors:
N. P. Dover,
C. A. J. Palmer,
M. Babzien,
A. R. Bell,
A. E. Dangor,
T. Horbury,
M. Ispiriyan,
M. N. Polyanskiy,
J. Schreiber,
S. Schwartz,
P. Shkolnikov,
V. Yakimenko,
I. Pogorelsky,
Z. Najmudin
Abstract:
Observations of the interaction of an intense λ0 \approx 10 μm laser pulse with near-critical overdense plasmas (ne = 1.8 - 3 nc) are presented. For the first time, transverse optical probing is used to show a recession of the front surface caused by radiation pressure driven hole-boring by the laser pulse with an initial velocity > 10^6 ms-1, and the resulting collisionless shocks. The collisionl…
▽ More
Observations of the interaction of an intense λ0 \approx 10 μm laser pulse with near-critical overdense plasmas (ne = 1.8 - 3 nc) are presented. For the first time, transverse optical probing is used to show a recession of the front surface caused by radiation pressure driven hole-boring by the laser pulse with an initial velocity > 10^6 ms-1, and the resulting collisionless shocks. The collisionless shock propagates through the plasma, dissipates into an ion-acoustic solitary wave, and eventually becomes collisional as it slows further. These conclusions are supported by PIC simulations which show that the initial evolution is dominated by collisionless mechanisms.
△ Less
Submitted 22 May, 2012; v1 submitted 21 May, 2012;
originally announced May 2012.
-
Non-invasive characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation
Authors:
S. Kneip,
C. McGuffey,
J. L. Martins,
M. S. Bloom,
V. Chvykov,
F. Dollar,
R. Fonseca,
S. Jolly,
G. Kalintchenko,
K. Krushelnick,
A. Maksimchuk,
S. P. D. Mangles,
Z. Najmudin,
C. A. J. Palmer,
K. Ta Phuoc,
W. Schumaker,
L. O. Silva,
J. Vieira,
V. Yanovsky,
A. G. R. Thomas
Abstract:
We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by $v_{\perp}/v_{\parallel}$, the measured longitudinal spectrum $γ_\parallel$ and the transverse electron bunch size in the bubble $r_{\perp}$. The latter is obtained via th…
▽ More
We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by $v_{\perp}/v_{\parallel}$, the measured longitudinal spectrum $γ_\parallel$ and the transverse electron bunch size in the bubble $r_{\perp}$. The latter is obtained via the measurement of the source size of the x-rays emitted by the accelerating electron bunch in the bubble. We measure a \textit{normalised} RMS beam transverse emittance $<0.5$ $π$ mm$\:$mrad as an upper limit for a spatially gaussian, spectrally quasi-monoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.
△ Less
Submitted 27 May, 2011;
originally announced May 2011.
-
X-ray phase contrast imaging of biological specimens with tabletop synchrotron radiation
Authors:
S. Kneip,
C. McGuffey,
F. Dollar,
M. S. Bloom,
V. Chvykov,
G. Kalintchenko,
K. Krushelnick,
A. Maksimchuk,
S. P. D. Mangles,
T. Matsuoka,
Z. Najmudin,
C. A. J. Palmer,
J. Schreiber,
W. Schumaker,
A. G. R. Thomas,
V. Yanovsky
Abstract:
Since their discovery in 1896, x-rays have had a profound impact on science, medicine and technology. Here we show that the x-rays from a novel tabletop source of bright coherent synchrotron radiation can be applied to phase contrast imaging of biological specimens, yielding superior image quality and avoiding the need for scarce or expensive conventional sources.
Since their discovery in 1896, x-rays have had a profound impact on science, medicine and technology. Here we show that the x-rays from a novel tabletop source of bright coherent synchrotron radiation can be applied to phase contrast imaging of biological specimens, yielding superior image quality and avoiding the need for scarce or expensive conventional sources.
△ Less
Submitted 12 May, 2011;
originally announced May 2011.
-
Complete temporal characterisation of asymmetric pulse compression in a laser wakefield
Authors:
J. Schreiber,
C. Bellei,
S. P. D. Mangles,
C. Kamperidis,
S. Kneip,
S. R. Nagel,
C. A. J. Palmer,
P. P. Rajeev,
Z. Najmudin
Abstract:
We present complete experimental characterisation of the temporal shape of an intense ultrashort 200-TW laser pulse driving a laser wakefield. The phase of the pulse was uniquely measured using (second order) frequency resolved optical gating (FROG). The pulses are asymmetrically compressed, and exhibit a positive chirp consistent with the expected asymmetric self-phase modulation due to photon ac…
▽ More
We present complete experimental characterisation of the temporal shape of an intense ultrashort 200-TW laser pulse driving a laser wakefield. The phase of the pulse was uniquely measured using (second order) frequency resolved optical gating (FROG). The pulses are asymmetrically compressed, and exhibit a positive chirp consistent with the expected asymmetric self-phase modulation due to photon acceleration/deceleration in a relativistic plasma wave. The measured pulse duration decreases linearly with increasing length and density of the plasma, in quantitative agreement with the intensity dependent group velocity variation in the plasma wave.
△ Less
Submitted 18 October, 2010;
originally announced October 2010.
-
Monoenergetic proton beams accelerated by a radiation pressure driven shock
Authors:
C. A. J. Palmer,
N. P. Dover,
I. Pogorelsky,
M. Babzien,
G. I. Dudnikova,
M. Ispiriyan,
M. N. Polyanskiy,
J. Schreiber,
P. Shkolnikov,
V. Yakimenko,
Z. Najmudin
Abstract:
High energy ion beams (> MeV) generated by intense laser pulses promise to be viable alternatives to conventional ion beam sources due to their unique properties such as high charge, low emittance, compactness and ease of beam delivery. Typically the acceleration is due to the rapid expansion of a laser heated solid foil, but this usually leads to ion beams with large energy spread. Until now, con…
▽ More
High energy ion beams (> MeV) generated by intense laser pulses promise to be viable alternatives to conventional ion beam sources due to their unique properties such as high charge, low emittance, compactness and ease of beam delivery. Typically the acceleration is due to the rapid expansion of a laser heated solid foil, but this usually leads to ion beams with large energy spread. Until now, control of the energy spread has only been achieved at the expense of reduced charge and increased complexity. Radiation pressure acceleration (RPA) provides an alternative route to producing laser-driven monoenergetic ion beams. In this paper, we show the interaction of an intense infrared laser with a gaseous hydrogen target can produce proton spectra of small energy spread (~ 4%), and low background. The scaling of proton energy with the ratio of intensity over density (I/n) indicates that the acceleration is due to the shock generated by radiation-pressure driven hole-boring of the critical surface. These are the first high contrast mononenergetic beams that have been theorised from RPA, and makes them highly desirable for numerous ion beam applications.
△ Less
Submitted 18 June, 2010; v1 submitted 16 June, 2010;
originally announced June 2010.
-
Micron-scale Fast Electron Filamentation and Recirculation determined from Rear Side Optical Emission in High Intensity Laser-Solid Interactions
Authors:
C. Bellei,
S. R. Nagel,
S. Kar,
A. Henig,
S. Kneip,
C. Palmer,
A. Sävert,
L. Willingale,
D. Carroll,
B. Dromey,
J. S. Green,
K. Markey,
P. Simpson,
R. J. Clarke,
H. Lowe,
D. Neely,
C. Spindloe,
M. Tolley,
M. Kaluza,
S. P. D. Mangles,
P. McKenna,
P. A. Norreys,
J. Schreiber,
M. Zepf,
J. R. Davies
, et al. (2 additional authors not shown)
Abstract:
The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation. A halo that surrounds the main region of emission is also polarized, and is attribute…
▽ More
The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation. A halo that surrounds the main region of emission is also polarized, and is attributed to the effect of electron recirculation. The variation of the amplitude of the transition radiation with respect to observation angle provides evidence for the presence of {$μ$m-size} filaments.
△ Less
Submitted 25 February, 2010;
originally announced February 2010.
-
A Bright Spatially-Coherent Compact X-ray Synchrotron Source
Authors:
S. Kneip,
C. McGuffey,
J. L. Martins,
S. F. Martins,
C. Bellei,
V. Chvykov,
F. Dollar,
R. Fonseca,
C. Huntington,
G. Kalintchenko,
A. Maksimchuk,
S. P. D. Mangles,
T. Matsuoka,
S. R. Nagel,
C. Palmer,
J. Schreiber,
K. Ta Phuoc,
A. G. R. Thomas,
V. Yanovsky,
L. O. Silva,
K. Krushelnick,
Z. Najmudin
Abstract:
Each successive generation of x-ray machines has opened up new frontiers in science, such as the first radiographs and the determination of the structure of DNA. State-of-the-art x-ray sources can now produce coherent high brightness keV x-rays and promise a new revolution in imaging complex systems on nanometre and femtosecond scales. Despite the demand, only a few dedicated synchrotron facilit…
▽ More
Each successive generation of x-ray machines has opened up new frontiers in science, such as the first radiographs and the determination of the structure of DNA. State-of-the-art x-ray sources can now produce coherent high brightness keV x-rays and promise a new revolution in imaging complex systems on nanometre and femtosecond scales. Despite the demand, only a few dedicated synchrotron facilities exist worldwide, partially due the size and cost of conventional (accelerator) technology. Here we demonstrate the use of a recently developed compact laser-plasma accelerator to produce a well-collimated, spatially-coherent, intrinsically ultrafast source of hard x-rays. This method reduces the size of the synchrotron source from the tens of metres to centimetre scale, accelerating and wiggling a high electron charge simultaneously. This leads to a narrow-energy spread electron beam and x-ray source that is >1000 times brighter than previously reported plasma wiggler and thus has the potential to facilitate a myriad of uses across the whole spectrum of light-source applications.
△ Less
Submitted 9 December, 2009;
originally announced December 2009.