Electron-ion energy partition when a charged particle slows in a plasma: results

This paper concerns plasmas in which the electrons and ions may have different temperatures. This is a case that must be examined because nuclear fusion processes, such as those that appear in ICF capsules, have ions whose temperature runs away from the electron temperature. A fast charged particle traversing a plasma--such as the α particle created in deuterium-tritium fusion--loses its energy to both the electrons and the ions in the plasma. In this paper, we present and discuss the results for the energy partition, the fractions E(e)/E(0) and E(I)/E(0) of the initial energy E(0) of this projectile particle that are deposited into the electrons and ions when it has slowed to its minimum energy distribution. The calculations, performed in the following paper [Brown, Preston, and Singleton Jr., Phys. Rev. E 86, 016407 (2012)], use a well-defined Fokker-Planck equation for the phase-space distribution of the charged projectiles in a weakly to moderately coupled plasma. The Fokker-Planck equation holds to first subleading order in the dimensionless plasma coupling constant, which translates to computing to order n ln n (leading) and n (subleading) in the plasma density n. We present an examination of the energy partition for the general case, in which the temperatures of the ions and electrons in the background plasma are not equal. The energy partitions for a background plasma in thermal equilibrium have been previously computed, but the order n terms have not been calculated, only estimated. Our Fokker-Planck formulation provides an unambiguous, precise definition of the energy fractions.