Investigation of shock formed in the flow of plasma into a magnetic funnel

Abstract

Thomson scattered laser light from plasma has been used to determine the time resolved electron density and temperature of the shock formed in the axial injection of plasma into a dipole magnetic field. These measurements were obtained in a region upstream from the throat of the magnetic funnel for low-β hydrogen, deuterium, and helium plasmas accelerated by a conical pinch tube. The observed increase in electron temperature cannot be explained by compression since the temperature peak occurred prior to the maximum density. A hybrid shock involving a collisionless transfer of longitudinal to transverse ion energy due to the magnetic field gradient and electron heating due to Coulomb collisions with ions is consistent with the observed electron temperature and density time history. The thermalization of cold electrons and hot ions is shown to be sufficiently fast to provide the observed increase in entropy across the shock front.