Measuring Ion Temperature from Thomson-Scattered Spectra of Non-Maxwellian Velocity Distributions in Magnetized Collisionless Shocks

Collisionless shocks are common features of many astrophysical systems and have been recently studied in scaled laboratory experiments by driving a laser-ablated piston plasma into a magnetized ambient plasma [1]. Diagnosing the electron and ion velocity distribution functions (VDFs) is crucial to understanding these systems, but the VDFs in collisionless shocks include multiple distinct ion and electron populations, making them highly non-Maxwellian. A key method for measuring these VDFs is Thomson scattering, but current Thomson analysis techniques usually assume the plasma is Maxwellian, which is a poor assumption in the case of collisionless shocks. Thus, we present a software pipeline for analyzing Thomson-scattered spectra of non-Maxwellian plasmas that inverts measured spectra to VDFs using a differential evolution fitting algorithm and a forward model for arbitrary VDFs. This pipeline is used to extract time-resolved ion heating across magnetized collisionless shocks in order to test theories of shock heating. The pipeline used in this analysis will build on and eventually be added to the open source PlasmaPy project.

[1] Schaeffer, et al., PRL 122, 245001 (2019).