Electron velocity distribution functions driven by inverse bremsstrahlung heating are measured to be non-Maxwellian using a novel angularly resolved Thomson-scattering instrument and the corresponding reduction of electrons at slow velocities results in a $\sim 40\%$ measured reduction in inverse bremsstrahlung absorption. The distribution functions are measured to be super-Gaussian in the bulk ($v/v_{th}<3$) and Maxwellian in the tail ($v/v_{th}>3$) when the laser heating rate dominates over the electron-electron thermalization rate. Simulations with the particle code quartz show the shape of the tail is dictated by the uniformity of the laser heating.

• Received 2 November 2020
• Revised 15 February 2021
• Accepted 21 May 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.015001