Measurement of energy loss and energy diffusion of charged test particles in a field-free near equilibrium plasma

Abstract

The parallel energy loss and parallel energy diffusion of a nearly monoenergetic, well collimated, and tenuous test particle beam in a plasma has been measured. Parallel refers to the initial beam direction. Test particles of H1 +, H2 +, H3 +, and Ar+ at energies of 1, 2, and 3 keV were utilized. The parameter X ranged from 0.28 to 3.03, where X = (test particle speed)/(plasma electron thermal speed). The near equilibrium, field-free, and highly homogeneous plasma consisted of electrons and singly ionized Cs both at a temperature of 2100 °K and a density of 1×1011 cm−3. The energy loss data are compared both to classical theories with phenomenological cutoffs and to fully convergent theories. The best agreement is obtained with the work of Itikawa and Aono. The energy diffusion results are compared to the theory of Spitzer, and to the Spitzer theory with nondominant terms added. The agreement is satisfactory except for X≳1.5.