Plasma radiation losses in the electrostatic limit

Abstract

Steady state ion drift configurations are usually treated as time-independent problems, hence radiation losses are usually ignored. This assumption is not strictly true when the number of charge carriers is small and their acceleration is big. According to Larmor formula , accelerating charges radiate. In spite of that, even if single charges accelerate, in the continuum DC limit, there is no radiation. This challenge is encountered in any plasma application based on a steady state ion drift, because ions accelerate under the influence of the electric field. Even if we assume the model of an average speed, defined by the average gas mobility multiplied by the electric field, the velocity changes because the electric field is not constant in magnitude or direction. One remarks that in any curvilinear DC electric current path, charge carriers are accelerated, raising the question of when are radiation losses significant. This issue is best analyzed in a canonical configuration of charges in circular motion. One single charge simply radiates power according to Larmor formula. When distributing the charge over the circle, the destructive interference between the field contributions of the different charges reduces the radiated power so that it goes to 0 in the continuum DC limit.

Keywords:

• radiation
• electrostatics
• accelerating charges

PACS:

• 52.30.-q
• 41.20.-q