Recovering non-Maxwellian particle velocity distribution functions from collective Thomson-scattered spectra

• Published in: AIP advances Vol. 13; no. 11; pp. 115328 - 115328-14
• Main Authors: Foo, B. C., Schaeffer, D. B., Heuer, P. V.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.11.2023; American Institute of Physics (AIP); AIP Publishing LLC
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Algorithms; Conditional probability; Distribution functions; non-Maxwellian distribution functions; numerical methods; Parameters; Plasma; Spectra; Thomson scattering; Velocity distribution
• ISSN: 2158-3226; 2158-3226
• DOI: 10.1063/5.0169393

Collective optical Thomson scattering (TS) is a diagnostic commonly used to characterize plasma parameters. These parameters are typically extracted by a fitting algorithm that minimizes the difference between a measured scattered spectrum and an analytic spectrum calculated from the velocity distribution function (VDF) of the plasma. However, most existing TS analysis algorithms assume that the VDFs are Maxwellian, and applying an algorithm that makes this assumption does not accurately extract the plasma parameters of a non-Maxwellian plasma due to the effect of non-Maxwellian deviations on the TS spectra. We present new open-source numerical tools for forward modeling analytic spectra from arbitrary VDFs and show that these tools are able to more accurately extract plasma parameters from synthetic TS spectra generated by non-Maxwellian VDFs compared to standard TS algorithms. Estimated posterior probability distributions of fits to synthetic spectra for a variety of example non-Maxwellian VDFs are used to determine uncertainties in the extracted plasma parameters and show that correlations between parameters can significantly affect the accuracy of fits in plasmas with non-Maxwellian VDFs.