We present a survey of 1D kinetic particle-in-cell simulations of quasi-parallel non-relativistic shocks to identify the environments favorable for electron acceleration. We explore an unprecedented range of shock speeds $v_{rm sh}approx 0.067-0.267,c$, Alfv'{e}n Mach numbers $mathcal{M}_{rm A} = 5-40$, sonic Mach numbers $mathcal{M}_{rm s} = 5-160$, as well as the proton-to-electron mass ratios $m_{rm i}/m_{rm e}=16-1836$. We find that high Alfv'{e}n Mach number shocks can channel a large fraction of their kinetic energy into nonthermal particles, self-sustaining magnetic turbulence and acceleration to larger and larger energies. The fraction of injected particles is $lesssim 0.5%$ for electrons and $approx 1%$ for protons, and the corresponding energy efficiencies are $lesssim 2%$ and $approx 10%$, respectively. The extent of the nonthermal tail is sensitive to the Alfv'{e}n Mach number; when $mathcal{M}_{rm A}lesssim 10$, the nonthermal electron distribution exhibits minimal growth beyond the average momentum of the downstream thermal protons, independently of the proton-to-electron mass ratio. Acceleration is slow for shocks with low sonic Mach numbers, yet nonthermal electrons still achieve momenta exceeding the downstream thermal proton momentum when the shock Alfv'{e}n Mach number is large enough. We provide simulation-based parametrizations of the transition from thermal to nonthermal distribution in the downstream (found at a momentum around $p_{rm i,e}/m_{rm i}v_{rm sh} approx 3sqrt{m_{rm i,e}/m_{rm i}}$), as well as the ratio of nonthermal electron to proton number density. The results are applicable to many different environments and are important for modeling shock-powered nonthermal radiation.
{"title":"Electron Acceleration at Quasi-parallel Non-relativistic Shocks: A 1D Kinetic Survey","authors":"Siddhartha Gupta, Damiano Caprioli, Anatoly Spitkovsky","doi":"arxiv-2408.16071","DOIUrl":"https://doi.org/arxiv-2408.16071","url":null,"abstract":"We present a survey of 1D kinetic particle-in-cell simulations of\u0000quasi-parallel non-relativistic shocks to identify the environments favorable\u0000for electron acceleration. We explore an unprecedented range of shock speeds\u0000$v_{rm sh}approx 0.067-0.267,c$, Alfv'{e}n Mach numbers $mathcal{M}_{rm\u0000A} = 5-40$, sonic Mach numbers $mathcal{M}_{rm s} = 5-160$, as well as the\u0000proton-to-electron mass ratios $m_{rm i}/m_{rm e}=16-1836$. We find that high\u0000Alfv'{e}n Mach number shocks can channel a large fraction of their kinetic\u0000energy into nonthermal particles, self-sustaining magnetic turbulence and\u0000acceleration to larger and larger energies. The fraction of injected particles\u0000is $lesssim 0.5%$ for electrons and $approx 1%$ for protons, and the\u0000corresponding energy efficiencies are $lesssim 2%$ and $approx 10%$,\u0000respectively. The extent of the nonthermal tail is sensitive to the Alfv'{e}n\u0000Mach number; when $mathcal{M}_{rm A}lesssim 10$, the nonthermal electron\u0000distribution exhibits minimal growth beyond the average momentum of the\u0000downstream thermal protons, independently of the proton-to-electron mass ratio.\u0000Acceleration is slow for shocks with low sonic Mach numbers, yet nonthermal\u0000electrons still achieve momenta exceeding the downstream thermal proton\u0000momentum when the shock Alfv'{e}n Mach number is large enough. We provide\u0000simulation-based parametrizations of the transition from thermal to nonthermal\u0000distribution in the downstream (found at a momentum around $p_{rm i,e}/m_{rm\u0000i}v_{rm sh} approx 3sqrt{m_{rm i,e}/m_{rm i}}$), as well as the ratio of\u0000nonthermal electron to proton number density. The results are applicable to\u0000many different environments and are important for modeling shock-powered\u0000nonthermal radiation.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195853","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
David C. Speirs, Juan Ruiz-Ruiz, Maurizio Giacomin, Valerian H. Hall-Chen, Alan D. R. Phelps, Roddy Vann, Peter G. Huggard, Hui Wang, Anthony Field, Kevin Ronald
Plasma turbulence on disparate spatial and temporal scales plays a key role in defining the level of confinement achievable in tokamaks, with the development of reduced numerical models for cross-scale turbulence effects informed by experimental measurements an essential step. MAST-U is a well-equipped facility having instruments to measure ion and electron scale turbulence at the plasma edge. However, measurement of core electron scale turbulence is challenging, especially in H mode. Using a novel synthetic diagnostic approach, we present simulated measurement specifications of a proposed mm-wave based collective scattering instrument optimised for measuring both normal and binormal electron scale turbulence in the core and edge of MAST-U. A powerful modelling framework has been developed that combines beam-tracing techniques with gyrokinetic simulations to predict the sensitivity, localisation and spectral range of measurement. For the reconstructed MAST 022769 shot, a maximum measurable normalised bi-normal wavenumber of $k_{perp} rho_{e} sim 0.6$ was predicted in the core and $k_{perp} rho_{e} sim 0.79$ near the pedestal, with localisation lengths $L_{FWHM}$ ranging from $sim$ 0.4 m in the core at $k_{perp} rho_{e} sim 0.1$ to ~0.08m at $k_{perp} rho_{e} sim 0.45$. Synthetic diagnostic analysis for the 022769 shot using CGYRO gyrokinetic simulation spectra reveal that ETG turbulence wavenumbers of peak spectral intensity comfortably fall within the measurable range of the instrument from the core to the pedestal. The proposed diagnostic opens up opportunities to study new regimes of turbulence and confinement in association with upcoming non-inductive, microwave based current drive experiments on MAST-U and can provide insight into cross-scale turbulence effects, while having suitability to operate during burning plasma scenarios on future reactors such as STEP.
{"title":"Simulation and analysis of a high-k electron scale turbulence diagnostic for MAST-U","authors":"David C. Speirs, Juan Ruiz-Ruiz, Maurizio Giacomin, Valerian H. Hall-Chen, Alan D. R. Phelps, Roddy Vann, Peter G. Huggard, Hui Wang, Anthony Field, Kevin Ronald","doi":"arxiv-2408.15807","DOIUrl":"https://doi.org/arxiv-2408.15807","url":null,"abstract":"Plasma turbulence on disparate spatial and temporal scales plays a key role\u0000in defining the level of confinement achievable in tokamaks, with the\u0000development of reduced numerical models for cross-scale turbulence effects\u0000informed by experimental measurements an essential step. MAST-U is a\u0000well-equipped facility having instruments to measure ion and electron scale\u0000turbulence at the plasma edge. However, measurement of core electron scale\u0000turbulence is challenging, especially in H mode. Using a novel synthetic\u0000diagnostic approach, we present simulated measurement specifications of a\u0000proposed mm-wave based collective scattering instrument optimised for measuring\u0000both normal and binormal electron scale turbulence in the core and edge of\u0000MAST-U. A powerful modelling framework has been developed that combines\u0000beam-tracing techniques with gyrokinetic simulations to predict the\u0000sensitivity, localisation and spectral range of measurement. For the\u0000reconstructed MAST 022769 shot, a maximum measurable normalised bi-normal\u0000wavenumber of $k_{perp} rho_{e} sim 0.6$ was predicted in the core and\u0000$k_{perp} rho_{e} sim 0.79$ near the pedestal, with localisation lengths\u0000$L_{FWHM}$ ranging from $sim$ 0.4 m in the core at $k_{perp} rho_{e} sim\u00000.1$ to ~0.08m at $k_{perp} rho_{e} sim 0.45$. Synthetic diagnostic analysis\u0000for the 022769 shot using CGYRO gyrokinetic simulation spectra reveal that ETG\u0000turbulence wavenumbers of peak spectral intensity comfortably fall within the\u0000measurable range of the instrument from the core to the pedestal. The proposed\u0000diagnostic opens up opportunities to study new regimes of turbulence and\u0000confinement in association with upcoming non-inductive, microwave based current\u0000drive experiments on MAST-U and can provide insight into cross-scale turbulence\u0000effects, while having suitability to operate during burning plasma scenarios on\u0000future reactors such as STEP.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"185 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Kane, P. Drobniak, S. Kazamias, V. Kubytskyi, M. Lenivenko, B. Lucas, J. Serhal, K. Cassou, A. Beck, A. Specka, F. Massimo
The optimisation of the plasma target design for high quality beam laser-driven plasma injector electron source relies on numerical parametric studies using Particle in Cell (PIC) codes. The common input parameters to explore are laser characteristics and plasma density profiles extracted from computational fluid dynamic studies compatible with experimental measurements of target plasma density profiles. We demonstrate the construction of surrogate models using machine learning technique for a laser-plasma injector (LPI) electron source based on more than 12000 simulations of a laser wakefield acceleration performed for sparsely spaced input parameters [1]. Surrogate models are very interesting for LPI design and optimisation because they are much faster than PIC simulations. We develop and compare the performance of three surrogate models, namely, Gaussian processes (GP), multilayer perceptron (MLP), and decision trees (DT). We then use the best surrogate model to quickly find optimal working points to get a selected electron beam energy, charge and energy spread using different methods, namely random search, Bayesian optimisation and multi-objective Bayesian optimisation
{"title":"Surrogate Models studies for laser-plasma accelerator electron source design through numerical optimisation","authors":"G. Kane, P. Drobniak, S. Kazamias, V. Kubytskyi, M. Lenivenko, B. Lucas, J. Serhal, K. Cassou, A. Beck, A. Specka, F. Massimo","doi":"arxiv-2408.15845","DOIUrl":"https://doi.org/arxiv-2408.15845","url":null,"abstract":"The optimisation of the plasma target design for high quality beam\u0000laser-driven plasma injector electron source relies on numerical parametric\u0000studies using Particle in Cell (PIC) codes. The common input parameters to\u0000explore are laser characteristics and plasma density profiles extracted from\u0000computational fluid dynamic studies compatible with experimental measurements\u0000of target plasma density profiles. We demonstrate the construction of surrogate\u0000models using machine learning technique for a laser-plasma injector (LPI)\u0000electron source based on more than 12000 simulations of a laser wakefield\u0000acceleration performed for sparsely spaced input parameters [1]. Surrogate\u0000models are very interesting for LPI design and optimisation because they are\u0000much faster than PIC simulations. We develop and compare the performance of\u0000three surrogate models, namely, Gaussian processes (GP), multilayer perceptron\u0000(MLP), and decision trees (DT). We then use the best surrogate model to quickly\u0000find optimal working points to get a selected electron beam energy, charge and\u0000energy spread using different methods, namely random search, Bayesian\u0000optimisation and multi-objective Bayesian optimisation","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Marcinkevicius, E. Andersson Sunden, G. Ericsson, A. Hjalmarsson
The use of Thin-foil Proton Recoil (TPR) spectrometers for application in neutron spectroscopy is of high relevance for future fusion devices such as ITER, where neutron spectroscopy will play a crucial role in fuel content monitoring. Existing research based on simulations of the performance of TPR spectrometers at ITER has demonstrated positive results. However, experimental validation of the simulations would greatly benefit the reliability of conclusions. In this study, we designed and constructed a prototype TPR neutron spectrometer and employed a DT neutron generator as a neutron source to perform measurements. We compared the experimental results with the simulation results using the Geant4 model of the experiment. The simulation and experimental results match within silicon detector intrinsic energy resolution. This approach ensures the experimental validation of the Geant4 based simulations of the TPR spectrometer. The experimental results demonstrated the feasibility of utilizing nuclear reactions measured in silicon detectors, specifically $^{28}$Si(n,d) and $^{28}$Si(n,$alpha$), for energy calibration purposes. A comparison of the experiment and the simulation shows that the mean peak energy and full width at half maximum are within 150 keV. The calculated detector efficiency underestimates the experimentally determined efficiency up to 33%. Discrepancies in the measured energy spectrum indicate the need for a more refined model and experiment control. Overall, the successful validation of the developed Geant4 simulation model against the experimentally measured energy spectra increases confidence in the applicability of such simulation results in other devices. The demonstrated energy calibration highlights new possibilities for neutron spectrometer monitoring during operation at ITER.
{"title":"Validation of Thin-foil proton recoil neutron spectrometer prototype for application in high yield DT fusion devices","authors":"B. Marcinkevicius, E. Andersson Sunden, G. Ericsson, A. Hjalmarsson","doi":"arxiv-2408.16093","DOIUrl":"https://doi.org/arxiv-2408.16093","url":null,"abstract":"The use of Thin-foil Proton Recoil (TPR) spectrometers for application in\u0000neutron spectroscopy is of high relevance for future fusion devices such as\u0000ITER, where neutron spectroscopy will play a crucial role in fuel content\u0000monitoring. Existing research based on simulations of the performance of TPR\u0000spectrometers at ITER has demonstrated positive results. However, experimental\u0000validation of the simulations would greatly benefit the reliability of\u0000conclusions. In this study, we designed and constructed a prototype TPR neutron\u0000spectrometer and employed a DT neutron generator as a neutron source to perform\u0000measurements. We compared the experimental results with the simulation results\u0000using the Geant4 model of the experiment. The simulation and experimental\u0000results match within silicon detector intrinsic energy resolution. This\u0000approach ensures the experimental validation of the Geant4 based simulations of\u0000the TPR spectrometer. The experimental results demonstrated the feasibility of\u0000utilizing nuclear reactions measured in silicon detectors, specifically\u0000$^{28}$Si(n,d) and $^{28}$Si(n,$alpha$), for energy calibration purposes. A\u0000comparison of the experiment and the simulation shows that the mean peak energy\u0000and full width at half maximum are within 150 keV. The calculated detector\u0000efficiency underestimates the experimentally determined efficiency up to 33%.\u0000Discrepancies in the measured energy spectrum indicate the need for a more\u0000refined model and experiment control. Overall, the successful validation of the\u0000developed Geant4 simulation model against the experimentally measured energy\u0000spectra increases confidence in the applicability of such simulation results in\u0000other devices. The demonstrated energy calibration highlights new possibilities\u0000for neutron spectrometer monitoring during operation at ITER.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. A. Ryan, P. E. Tsai, A. R. Johansen, A. Youmans, D. P. Higginson, J. M. Mitrani, C. S. Adams, D. A. Sutherland, B. Levitt, U. Shumlak
Previous measurements of neutron energy using fast plastic scintillators while operating the Fusion Z Pinch Experiment (FuZE) constrained the energy of any yield-producing deuteron beams to less than $4.65 keV$. FuZE has since been operated at increasingly higher input power, resulting in increased plasma current and larger fusion neutron yields. A detailed experimental study of the neutron energy isotropy in these regimes applies more stringent limits to possible contributions from beam-target fusion. The FuZE device operated at $-25~kV$ charge voltage has resulted in average plasma currents of $370~kA$ and D-D fusion neutron yields of $4times10^7$ neutrons per discharge. Measurements of the neutron energy isotropy under these operating conditions demonstrates the energy of deuteron beams is less than $7.4 pm 5.6^mathrm{(stat)} pm 3.7^mathrm{(syst)}~keV$. Characterization of the detector response has reduced the number of free parameters in the fit of the neutron energy distribution, improving the confidence in the forward-fit method. Gamma backgrounds have been measured and the impact of these contributions on the isotropy results have been studied. Additionally, a time dependent measurement of the isotropy has been resolved for the first time, indicating increases to possible deuteron beam energies at late times. This suggests the possible growth of $m$=0 instabilities at the end of the main radiation event but confirms that the majority of the neutron production exhibits isotropy consistent with thermonuclear origin.
{"title":"Time-resolved measurement of neutron energy isotropy in a sheared-flow-stabilized Z pinch","authors":"R. A. Ryan, P. E. Tsai, A. R. Johansen, A. Youmans, D. P. Higginson, J. M. Mitrani, C. S. Adams, D. A. Sutherland, B. Levitt, U. Shumlak","doi":"arxiv-2408.05171","DOIUrl":"https://doi.org/arxiv-2408.05171","url":null,"abstract":"Previous measurements of neutron energy using fast plastic scintillators\u0000while operating the Fusion Z Pinch Experiment (FuZE) constrained the energy of\u0000any yield-producing deuteron beams to less than $4.65 keV$. FuZE has since been\u0000operated at increasingly higher input power, resulting in increased plasma\u0000current and larger fusion neutron yields. A detailed experimental study of the\u0000neutron energy isotropy in these regimes applies more stringent limits to\u0000possible contributions from beam-target fusion. The FuZE device operated at\u0000$-25~kV$ charge voltage has resulted in average plasma currents of $370~kA$ and\u0000D-D fusion neutron yields of $4times10^7$ neutrons per discharge. Measurements\u0000of the neutron energy isotropy under these operating conditions demonstrates\u0000the energy of deuteron beams is less than $7.4 pm 5.6^mathrm{(stat)} pm\u00003.7^mathrm{(syst)}~keV$. Characterization of the detector response has reduced\u0000the number of free parameters in the fit of the neutron energy distribution,\u0000improving the confidence in the forward-fit method. Gamma backgrounds have been\u0000measured and the impact of these contributions on the isotropy results have\u0000been studied. Additionally, a time dependent measurement of the isotropy has\u0000been resolved for the first time, indicating increases to possible deuteron\u0000beam energies at late times. This suggests the possible growth of $m$=0\u0000instabilities at the end of the main radiation event but confirms that the\u0000majority of the neutron production exhibits isotropy consistent with\u0000thermonuclear origin.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"6 1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141941534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. Yu. Bychenkov, A. V. Brantov, M. G. Lobok, A. S. Kuratov
Femtosecond laser pulse propagation in a relativistic self-trapping regime (RST) in a near-critical density plasma makes it possible to maximize the total charge of the accelerating electrons and laser-to-electrons conversion rate, that can be used to provide a large amount of the THz range coherent transition radiation. The three-dimensional particle-in-cell simulations demonstrate how such transition radiation generates when electrons escape into vacuum either from the low-density target itself, or after passing through a thin foil located at the target end. Advantage of the RST regime for generation of THz pulses is clearly demonstrated as compared to laser irradiation of such a standard target as a foil with preplasma on its front side. Simulation performed has shown that for the optimized laser-target matching a 2-J femtosecond laser pulse is able to produce quasi-unipolar Thz pulses with energy exceeding 100 mJ.
{"title":"Laser-triggered THz emission from near critical density targets","authors":"V. Yu. Bychenkov, A. V. Brantov, M. G. Lobok, A. S. Kuratov","doi":"arxiv-2408.04892","DOIUrl":"https://doi.org/arxiv-2408.04892","url":null,"abstract":"Femtosecond laser pulse propagation in a relativistic self-trapping regime\u0000(RST) in a near-critical density plasma makes it possible to maximize the total\u0000charge of the accelerating electrons and laser-to-electrons conversion rate,\u0000that can be used to provide a large amount of the THz range coherent transition\u0000radiation. The three-dimensional particle-in-cell simulations demonstrate how\u0000such transition radiation generates when electrons escape into vacuum either\u0000from the low-density target itself, or after passing through a thin foil\u0000located at the target end. Advantage of the RST regime for generation of THz\u0000pulses is clearly demonstrated as compared to laser irradiation of such a\u0000standard target as a foil with preplasma on its front side. Simulation\u0000performed has shown that for the optimized laser-target matching a 2-J\u0000femtosecond laser pulse is able to produce quasi-unipolar Thz pulses with\u0000energy exceeding 100 mJ.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141941529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. W. C. Dharma-wardanaNRC Canada, Dennis D. Klug, Hannah Poole, G. Gregori
Recent cutting-edge experiments have provided $in,situ$ structure characterization and measurements of the pressure ($P$), density ($bar{rho}$) and temperature ($T$) of shock compressed silicon in the 100 GPa range of pressures and up to $sim$10,000K. We present first-principles calculations in this $P,T,bar{rho}$ regime to reveal a plethora of novel liquid-liquid phase transitions (LPTs), making the interpretation of these experiments very challenging. The short-ranged ionic structure of the fluid is preserved under collective adjustments of many distant atoms when subject to compression and heating, with surprisingly little change in electrical and thermal conductivities $sigma$ and $kappa$. We match the experimental X-Ray Thompson scattering and X-ray diffraction data theoretically, and provide pressure isotherms, ionization data and compressibilities that support the above picture of liquid silicon as a highly complex LPT-driven ``glassy'' metallic liquid. These novel results are relevant to materials research, studies of planetary interiors, high-energy-density physics, and in laser-fusion studies.
最近的前沿实验提供了冲击压缩硅在100 GPa压力范围内的原位$结构表征和压力（$P$）、密度（$bar{rho}$）及温度（$T$）测量，最高可达$sim$10,000K。我们介绍了在这种$P,T,bar{rho}$制度下的第一原理计算，揭示了大量新颖的液-液相转变（LPT），使得对这些实验的解释非常具有挑战性。当受到压缩和加热时，流体的短程离子结构在许多遥远原子的集体调整下得以保留，而电导率和热导率（$sigma$和$kappa$）的变化之小令人惊讶。我们从理论上匹配了实验中的 X 射线汤普森散射和 X 射线衍射数据，并提供了压力等温线、电离数据和压缩率，支持上述液态硅作为高度复杂的 LPT 驱动的 "玻璃状 "金属液体的图景。
{"title":"Ionic structure, Liquid-liquid phase transitions, X-Ray diffraction, and X-Ray Thomson scattering in shock compressed liquid Silicon in the 100-200 GPa regime","authors":"M. W. C. Dharma-wardanaNRC Canada, Dennis D. Klug, Hannah Poole, G. Gregori","doi":"arxiv-2408.04173","DOIUrl":"https://doi.org/arxiv-2408.04173","url":null,"abstract":"Recent cutting-edge experiments have provided $in,situ$ structure\u0000characterization and measurements of the pressure ($P$), density ($bar{rho}$)\u0000and temperature ($T$) of shock compressed silicon in the 100 GPa range of\u0000pressures and up to $sim$10,000K. We present first-principles calculations in\u0000this $P,T,bar{rho}$ regime to reveal a plethora of novel liquid-liquid phase\u0000transitions (LPTs), making the interpretation of these experiments very\u0000challenging. The short-ranged ionic structure of the fluid is preserved under\u0000collective adjustments of many distant atoms when subject to compression and\u0000heating, with surprisingly little change in electrical and thermal\u0000conductivities $sigma$ and $kappa$. We match the experimental X-Ray Thompson\u0000scattering and X-ray diffraction data theoretically, and provide pressure\u0000isotherms, ionization data and compressibilities that support the above picture\u0000of liquid silicon as a highly complex LPT-driven ``glassy'' metallic liquid.\u0000These novel results are relevant to materials research, studies of planetary\u0000interiors, high-energy-density physics, and in laser-fusion studies.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"78 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141941535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Magnetic fields are an energetically important component of star-formation galaxies, but it is often difficult to measure their properties from observations. One of the complexities stems from the fact that the magnetic fields, especially in spiral galaxies, have a two-scale nature: a large-scale field, coherent over ${rm kpc}$ scales and a small-scale, random field with a scale of $lesssim$ $100~{rm pc}$. Moreover, it is known that the strength of small- and large-scale fields are comparable and this makes it even harder to find their imprints in radio polarisation observations such as the Faraday rotation measure, ${rm RM}$, which is the integral over the path length of the product of the thermal electron density and the parallel component of the magnetic field to the line of sight. Here, we propose and demonstrate the use of second-order structure functions of ${rm RM}$ computed with multiple higher-order stencils as a powerful analysis to separate the small- and large-scale magnetic field components. In particular, we provide new methods and calibrations to compute the scale and the strength of the large-scale magnetic field in the presence of small-scale magnetic fluctuations. We then apply the method to find the scale of large-scale magnetic fields in the nearby galaxies M51 and NGC 6946, using archival data and further discuss the need for computing the ${rm RM}$ structure functions with higher-order stencils. With multiple modern radio polarisation observatories and eventually the Square Kilometre Array, ${rm RM}$ observations will significantly improve in quantity and quality, and the higher-order stencil structure function techniques developed here can be used to extract information about multiscale magnetic fields in galaxies.
{"title":"Structure functions with higher-order stencils as a probe to separate small- and large-scale magnetic fields","authors":"Amit Seta, Christoph Federrath","doi":"arxiv-2408.04156","DOIUrl":"https://doi.org/arxiv-2408.04156","url":null,"abstract":"Magnetic fields are an energetically important component of star-formation\u0000galaxies, but it is often difficult to measure their properties from\u0000observations. One of the complexities stems from the fact that the magnetic\u0000fields, especially in spiral galaxies, have a two-scale nature: a large-scale\u0000field, coherent over ${rm kpc}$ scales and a small-scale, random field with a\u0000scale of $lesssim$ $100~{rm pc}$. Moreover, it is known that the strength of\u0000small- and large-scale fields are comparable and this makes it even harder to\u0000find their imprints in radio polarisation observations such as the Faraday\u0000rotation measure, ${rm RM}$, which is the integral over the path length of the\u0000product of the thermal electron density and the parallel component of the\u0000magnetic field to the line of sight. Here, we propose and demonstrate the use\u0000of second-order structure functions of ${rm RM}$ computed with multiple\u0000higher-order stencils as a powerful analysis to separate the small- and\u0000large-scale magnetic field components. In particular, we provide new methods\u0000and calibrations to compute the scale and the strength of the large-scale\u0000magnetic field in the presence of small-scale magnetic fluctuations. We then\u0000apply the method to find the scale of large-scale magnetic fields in the nearby\u0000galaxies M51 and NGC 6946, using archival data and further discuss the need for\u0000computing the ${rm RM}$ structure functions with higher-order stencils. With\u0000multiple modern radio polarisation observatories and eventually the Square\u0000Kilometre Array, ${rm RM}$ observations will significantly improve in quantity\u0000and quality, and the higher-order stencil structure function techniques\u0000developed here can be used to extract information about multiscale magnetic\u0000fields in galaxies.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141941536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jada Walters, Kristopher G. Klein, Emily Lichko, James Juno, Jason M. TenBarge
Instabilities driven by pressure anisotropy play a critical role in modulating the energy transfer in space and astrophysical plasmas. For the first time, we simulate the evolution and saturation of the parallel proton firehose instability using a multi-fluid model without adding artificial viscosity. These simulations are performed using a 10-moment, multi-fluid model with local and gradient relaxation heat-flux closures in high-$beta$ proton-electron plasmas. When these higher-order moments are included and pressure anisotropy is permitted to develop in all species, we find that the electrons have a significant impact on the saturation of the parallel proton firehose instability, modulating the proton pressure anisotropy as the instability saturates. Even for lower $beta$s more relevant to heliospheric plasmas, we observe a pronounced electron energization in simulations using the gradient relaxation closure. Our results indicate that resolving the electron pressure anisotropy is important to correctly describe the behavior of multi-species plasma systems.
{"title":"Electron Influence on the Parallel Proton Firehose Instability in 10-Moment, Multi-Fluid Simulations","authors":"Jada Walters, Kristopher G. Klein, Emily Lichko, James Juno, Jason M. TenBarge","doi":"arxiv-2408.04788","DOIUrl":"https://doi.org/arxiv-2408.04788","url":null,"abstract":"Instabilities driven by pressure anisotropy play a critical role in\u0000modulating the energy transfer in space and astrophysical plasmas. For the\u0000first time, we simulate the evolution and saturation of the parallel proton\u0000firehose instability using a multi-fluid model without adding artificial\u0000viscosity. These simulations are performed using a 10-moment, multi-fluid model\u0000with local and gradient relaxation heat-flux closures in high-$beta$\u0000proton-electron plasmas. When these higher-order moments are included and\u0000pressure anisotropy is permitted to develop in all species, we find that the\u0000electrons have a significant impact on the saturation of the parallel proton\u0000firehose instability, modulating the proton pressure anisotropy as the\u0000instability saturates. Even for lower $beta$s more relevant to heliospheric\u0000plasmas, we observe a pronounced electron energization in simulations using the\u0000gradient relaxation closure. Our results indicate that resolving the electron\u0000pressure anisotropy is important to correctly describe the behavior of\u0000multi-species plasma systems.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"99 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141941530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Petru-Vlad Toma, Andrei Cristian Opinca, Virgil Baran, Madalina Boca
We present a study of the scattering of a monochromatic helical laser beam, described by a Laguerre-Gauss solution of the Maxwell equations, on an electron sheet, initially at rest in the focal plane of the laser; the interaction is described in the framework of a local plane wave approximation. We calculate the scattered electromagnetic field observed in an arbitrary point at a large distance from the laser focal spot, by adding coherently the contributions of each electron in the electron sheet. Due to the interference effects, the radiation is emitted only into the forward direction, within a narrow cone, and it has a spatial structure that we analyze theoretically and numerically. For circularly polarized incident fields, the structure is also helical, with a helical index which depends on the helical index of the incident radiation and the harmonic order. These structures can be observed experimentally, as each harmonic order is emitted with a different frequency, and within cones of different opening angles. Our findings are in agreement with experimental results in the literature which demonstrate the generation of OAM carrying photons by radiation scattering on electrons.
{"title":"Coherent nonlinear Thomson scattering of Laguerre-Gauss beams on an electron sheet","authors":"Petru-Vlad Toma, Andrei Cristian Opinca, Virgil Baran, Madalina Boca","doi":"arxiv-2408.04412","DOIUrl":"https://doi.org/arxiv-2408.04412","url":null,"abstract":"We present a study of the scattering of a monochromatic helical laser beam,\u0000described by a Laguerre-Gauss solution of the Maxwell equations, on an electron\u0000sheet, initially at rest in the focal plane of the laser; the interaction is\u0000described in the framework of a local plane wave approximation. We calculate\u0000the scattered electromagnetic field observed in an arbitrary point at a large\u0000distance from the laser focal spot, by adding coherently the contributions of\u0000each electron in the electron sheet. Due to the interference effects, the\u0000radiation is emitted only into the forward direction, within a narrow cone, and\u0000it has a spatial structure that we analyze theoretically and numerically. For\u0000circularly polarized incident fields, the structure is also helical, with a\u0000helical index which depends on the helical index of the incident radiation and\u0000the harmonic order. These structures can be observed experimentally, as each\u0000harmonic order is emitted with a different frequency, and within cones of\u0000different opening angles. Our findings are in agreement with experimental\u0000results in the literature which demonstrate the generation of OAM carrying\u0000photons by radiation scattering on electrons.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"134 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141941533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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