Evolution of the Electron Distribution Function in the Presence of Inverse Bremsstrahlung Heating and Collisional Ionization

Milder, A. L.; Le, Hai; Sherlock, M.; Franke, P.; Katz, J.; Ivancic, S. T.; Shaw, Jessica; Palastro, J. P.; Hansen, A. M.; Begishev, I. A.; Rozmus, W.; Froula, D. H.

doi:10.1103/physrevlett.124.025001

Cited by 20 publications

(10 citation statements)

References 18 publications

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“…Finally, the scattered power is convolved with a point-spread-function that describes the blurring into nearby pixels due to the internal structure of the diagnostic. Recent developments in Thomson-scattering analysis have allowed a better understanding of plasmas by loosening the assumptions on the shape of these velocity distribution functions [24,25]. These more complex models have additional free parameters further complicating and slowing the analysis.…”

Section: Thomson Scattering Theorymentioning

confidence: 99%

“…The traditional model based diagnostic algorithm, figure 1(a), is a generalization for many techniques that reflect the algorithm used in some previous work [24,25]. However, there are no standard analysis tools for Thomson scattering.…”

Section: Assessing the Performance Of The Algorithmmentioning

confidence: 99%

“…Once the laser turns off at 1000 ps the temperature and density drop as the plasma cools and expands. By defining the electron velocity distribution function as a super-Gaussian (exp[−(x/x 0 ) m ]) in 3D and projecting it on the measured ⃗ k, the super-Gaussian order can be extracted from the data as well [24] figure 6(c). This similarly showed an evolution of heating to a super-Gaussian order of 3.2 followed by cooling back to a super-Gaussian order of 2 once the heating laser is turned off.…”

Section: Assessing the Performance Of The Algorithmmentioning

confidence: 99%

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Qualitative and quantitative enhancement of parameter estimation for model-based diagnostics using automatic differentiation with an application to inertial fusion

Milder,

Joglekar,

Rozmus

et al. 2024

Mach. Learn.: Sci. Technol.

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Parameter estimation using observables is a fundamental concept in the experimental sciences. Mathematical models that represent the physical processes can enable reconstructions of the experimental observables and greatly assist in parameter estimation by turning it into an optimization problem which can be solved by gradient-free or gradient-based methods. In this work, the recent rise in flexible frameworks for developing differentiable scientific computing programs is leveraged in order to dramatically accelerate data analysis of a common experimental diagnostic relevant to laser–plasma and inertial fusion experiments, Thomson scattering. A differentiable Thomson-scattering data analysis tool is developed that uses reverse-mode automatic differentiation (AD) to calculate gradients. By switching from finite differencing to reverse-mode AD, three distinct outcomes are achieved. First, gradient descent is accelerated dramatically to the extent that it enables near real-time usage in laser–plasma experiments. Second, qualitatively novel quantities which require O ( 10 3 ) parameters can now be included in the analysis of data which enables unprecedented measurements of small-scale laser–plasma phenomena. Third, uncertainty estimation approaches that leverage the value of the Hessian become accurate and efficient because reverse-mode AD can be used for calculating the Hessian.

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Section: Thomson Scattering Theorymentioning

confidence: 99%

Section: Assessing the Performance Of The Algorithmmentioning

confidence: 99%

Section: Assessing the Performance Of The Algorithmmentioning

confidence: 99%

See 1 more Smart Citation

Qualitative and quantitative enhancement of parameter estimation for model-based diagnostics using automatic differentiation with an application to inertial fusion

Milder,

Joglekar,

Rozmus

et al. 2024

Mach. Learn.: Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…The sensitivity to ion temperature is evident in the shape of the peaks in the IAW feature; when comparing the calculated spectrum for the ion temperatures prior to the CBET interaction (t ∼ 0 ns) a significant difference is observed, demonstrating the sensitivity of the IAW spectrum to the changes in the ion temperature. The time-resolved Thomson-scattering spectra were calculated numerically using the standard multi-species collisionless spectral density function, which accounted for non-Maxwellian electron distribution functions [25,26]. ).…”

Section: Thomson Scatteringmentioning

confidence: 99%

Cross-beam energy transfer saturation: ion heating and pump depletion

Hansen¹,

Nguyen²,

Turnbull³

et al. 2022

Plasma Phys. Control. Fusion

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Cross-beam energy transfer (CBET) was measured in two regimes where the energy transfer saturation mechanism was determined by the plasma and laser beam conditions. Linear kinetic CBET theory agreed well with the measured energy transfer in all experiment conﬁgurations and at all probe beam intensities when accounting for pump depletion and the plasma conditions measured using Thomson-scattering. Simultaneous CBET and Thomson-scattering measurements enabled uncertainties in the plasma conditions to be isolated from CBET theory, which allowed the saturation mechanisms to be identiﬁed. In the perpendicular-beam conﬁguration the saturation mode was through ion heating, which resulted from ion trapping in the driven waves and subsequent ion-ion collisional heating. In the co-propagating beam conﬁguration there was minimal ion heating and the saturation mode was through pump depletion.

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“…With this motivation, LLE has developed an advanced optical Thomson scattering system that enables measurement of the EDF over four orders of magnitude [38]. The diagnostic employs an innovative optical collection system that comprises a primary and secondary aspheric mirror that enables scattered light to be collected over 120° with 1° of resolution.…”

Section: Laser–plasma Interaction Researchmentioning

confidence: 99%

Direct-drive laser fusion: status, plans and future

Campbell

Sangster

Goncharov

et al. 2020

Phil. Trans. R. Soc. A.

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Laser-direct drive (LDD), along with laser indirect (X-ray) drive (LID) and magnetic drive with pulsed power, is one of the three viable inertial confinement fusion approaches to achieving fusion ignition and gain in the laboratory. The LDD programme is primarily being executed at both the Omega Laser Facility at the Laboratory for Laser Energetics and at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. LDD research at Omega includes cryogenic implosions, fundamental physics including material properties, hydrodynamics and laser–plasma interaction physics. LDD research on the NIF is focused on energy coupling and laser–plasma interactions physics at ignition-scale plasmas. Limited implosions on the NIF in the ‘polar-drive’ configuration, where the irradiation geometry is configured for LID, are also a feature of LDD research. The ability to conduct research over a large range of energy, power and scale size using both Omega and the NIF is a major positive aspect of LDD research that reduces the risk in scaling from OMEGA to megajoule-class lasers. The paper will summarize the present status of LDD research and plans for the future with the goal of ultimately achieving a burning plasma in the laboratory. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

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Evolution of the Electron Distribution Function in the Presence of Inverse Bremsstrahlung Heating and Collisional Ionization

Cited by 20 publications

References 18 publications

Qualitative and quantitative enhancement of parameter estimation for model-based diagnostics using automatic differentiation with an application to inertial fusion

Qualitative and quantitative enhancement of parameter estimation for model-based diagnostics using automatic differentiation with an application to inertial fusion

Cross-beam energy transfer saturation: ion heating and pump depletion

Direct-drive laser fusion: status, plans and future

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