Impact of non-Maxwellian electron velocity distribution functions on inferred plasma parameters in collective Thomson scattering

Milder, A. L.; Ivancic, S. T.; Palastro, J. P.; Froula, Dustin

doi:10.1063/1.5085664

Cited by 19 publications

(10 citation statements)

References 28 publications

(14 reference statements)

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“…Note that both the ion feature degeneracy with respect to electron temperature and super-Gaussian exponent, as well as the ability for electron features to break that degeneracy, were previously predicted [21]. These errors in density and temperature that would result from measuring only the electron or the ion feature, along with a Maxwellian assumption, have significant ramifications for previous Thomson scattering experiments [21,22].…”

Section: E28290j1mentioning

confidence: 82%

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Impact of the Langdon effect on crossed-beam energy transfer

et al. 2019

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The prediction that laser plasma heating distorts the electron distribution function away from Maxwellian and towards a super-Gaussian distribution dates back four decades [1]. In conditions relevant to inertial confinement fusion, however, no direct evidence of this so-called "Langdon effect" has previously been observed. Here, measurements of the spatially and temporally resolved Thomson scattering spectrum indicate the presence of super-Gaussian electron distribution functions that are consistent with existing theory [2]. In such plasmas, ion acoustic wave frequencies increase monotonically with the super-Gaussian exponent [3]. Our results show that the measured power transfer between crossed laser beams mediated by ion acoustic waves requires a model that accounts for the non-Maxwellian electron distribution function, whereas the standard Maxwellian calculations overpredict power transfer over a wide region of parameter space. Including this effect is expected to improve the predictive capability of crossed-beam energy transfer modeling at the National Ignition Facility and may restore a larger operable design space for inertial confinement fusion experiments. This is also expected to motivate further inquiry in other areas impacted by non-Maxwellian electron distribution functions, such as laser ministration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and

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Section: E28290j1mentioning

confidence: 82%

“…As is evident in Fig. 3(b Thomson scattering analysis [21,22], other laser-plasma instability growth rates [3], the design of high-fluence plasma beam combiners [17], x-ray spectroscopy analysis [2, 27], magnetohydrodynamics [28], and other plasma diagnostics [29].…”

Section: E28290j1mentioning

confidence: 99%

Impact of the Langdon effect on crossed-beam energy transfer

et al. 2019

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“…Non-Maxwellian distributions are also relevant for a number of experimental measurements that are sensitive to the shape of the distribution. [3,27] We also simulated a nonlocal thermal transport problem in a uniform plasma taking into account detailed atomic kinetics. The overall picture of nonlocal heat flow remains unchanged, but the propagation of thermal wave depends strongly on atomic kinetics.…”

Section: Discussionmentioning

confidence: 99%

“…In addition to modifying the absorption rates, non-Maxwellian electron distributions can also impact how various plasma parameters are inferred from measurements. [3,27] The results in this section indicate that atomic kinetics need to be included in the model to capture the correct distribution.…”

Section: Inverse Bremsstrahlung Heatingmentioning

confidence: 99%

Influence of atomic kinetics on inverse bremsstrahlung heating and nonlocal thermal transport

Sherlock

Scott

2019

Phys. Rev. E

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This paper describes a computational model that self-consistently combines physics of kinetic electrons and atomic processes in a single framework. The formulation consists of a kinetic Vlasov-Boltzmann-Fokker-Planck equation for free electrons and a non-Maxwellian collisional-radiative model for atomic state populations. We utilize this model to examine the influence of atomic kinetics on inverse bremsstrahlung (IB) heating and nonlocal thermal transport. We show that atomic kinetics affects non-linear IB absorption rates by further modifying the electron distribution in addition to laser heating. We also show that accurate modeling of nonlocal heat flow requires a self-consistent treatment of atomic kinetics, because the effective thermal conductivity strongly depends on the ionization balance of the plasma.

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“…[1] Raman scattering, an inelastic scattering process associated with the transition in a molecule's rotational or vibrational state, provides molecular number densities and the rotational/vibrational temperatures. Thomson scattering from free electrons allows measuring electron temperature and density and the electron energy distribution function [2], fundamental properties that define the composition of plasma [3].…”

Section: Introductionmentioning

confidence: 99%

High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters

Bak¹,

Betancourt²,

Rekhy³

et al. 2022

Preprint

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Laser light scattering systems with volume Bragg grating (VBG) filters, which act as a spectral/angular filter, have often been used as a point measurement technique with spatial resolution as low as a few hundred µm defined by the beam waist. In this work, we demonstrate how VBG filters can be leveraged for spatially resolved measurements with several µm resolution perpendicular to the laser propagation axis over a few mm along the beam propagation axis. The rejection ring, as determined by the angular acceptance criteria of the filter, is derived analytically, and the use of the ring for 1D laser line rejection is explained. For the example cases presented, having a focused probe beam waist with a diameter of ∼ 150 µm, the rejection ring can provide up to several mm length along the beam propagation axis for a 1D measurement, which is also tunable. Additionally, methods to further extend the measurable region are proposed and demonstrated; using a collimation lens with a different focal length or using multiple VBG filters. The latter case can minimize the scattering signal loss, without the trade-off of the solid angle. Such use of multiple VBGs is to extend the measurable region along the beam axis, which differs from the commonly known application of multiple filters to improve the suppression of elastic interferences. 1D rotational Raman and Thomson scattering measurements are carried out on pulsed and DC discharges to verify this method. The system features compactness, simple implementation, high throughput, and flexibility to accommodate various experimental conditions.

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Impact of non-Maxwellian electron velocity distribution functions on inferred plasma parameters in collective Thomson scattering

Cited by 19 publications

References 28 publications

Impact of the Langdon effect on crossed-beam energy transfer

Impact of the Langdon effect on crossed-beam energy transfer

Influence of atomic kinetics on inverse bremsstrahlung heating and nonlocal thermal transport

High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters

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