Using Collective Thomson Scattering to Characterize Velocity Distribution Functions of non-Maxwellian Plasmas

Electron and ion velocity distribution functions (VDFs) are important for understanding the dynamics occurring within nonlinear plasmas such as those of magnetized collisionless shocks. These VDFs can be measured in the laboratory with Thomson scattering diagnostics, but due to their non-Maxwellian nature, can be difficult to interpret with existing analysis tools which assume a Maxwellian plasma. We present an open-source software that can be used to fit Thomson spectra to arbitrary VDF models using a modular numerical scheme, which has been tested with synthetic Thomson-scattered spectra for robustness and error, using existing PlasmaPy code that handles strictly Maxwellian VDFs as a benchmark. Using an MCMC sampler, we were able to estimate the error and fit confidence for extracted plasma parameters. We find that when applied to commonly seen non-Maxwellian VDFs such as kappa distributions or supergaussians, the Maxwellian algorithm fails to accurately extract plasma parameters such as the density and equivalent temperature, while the new algorithm results in more accurate extracted plasma parameters and fitted VDFs if the correct VDF model is chosen.