A Concept for Measuring Electron Distribution Functions Using Collective Thomson Scattering

A.B. Langdon\footnote{A. B. Langdon, Phys. Rev. Lett. \textbf{44}, 575 (1980).} proposed that stable non-Maxwellian distribution functions are realized in coronal inertial confinement fusion plasmas via inverse bremsstrahlung heating. For ${Zv_{\mbox{osc}}^{2} } \mathord{\left/ {\vphantom {{Zv_{\mbox{osc}}^{2} } {v_{\mbox{th}}^{2} >1,}}} \right. \kern-\nulldelimiterspace} {v_{\mbox{th}}^{2} >1,}$ the inverse bremsstrahlung heating rate is sufficiently fast to compete with electron--electron collisions. This process preferentially heats the subthermal electrons leading to super-Gaussian distribution functions. A method to identify the super-Gaussian order of the distribution functions in these plasmas using collective Thomson scattering will be proposed. By measuring the collective Thomson spectra over a range of angles the density, temperature and super-Gaussian order can be determined. This is accomplished by fitting non-Maxwellian distribution data with a super-Gaussian model; in order to match the density and electron temperature to within 10{\%}, the super-Gaussian order must be varied. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.