Measurements of beat-wave-accelerated electrons in a toroidal plasma.

Abstract

Electrons are accelerated by large amplitude electron plasma waves driven by counterpropagating microwaves with a difference frequency approximately equal to the electron plasma frequency. Energetic electrons are observed only when the phase velocity of the wave is in the range 3${\mathit{v}}_{\mathit{e}}$${\mathit{v}}_{\mathrm{ph}}$7${\mathit{v}}_{\mathit{e}}$ (${\mathit{v}}_{\mathrm{ph}}$ was varied 2${\mathit{v}}_{\mathit{e}}$${\mathit{v}}_{\mathrm{ph}}$10${\mathit{v}}_{\mathit{e}}$), where ${\mathit{v}}_{\mathit{e}}$ is the electron thermal velocity, (${\mathit{kT}}_{\mathit{e}}$/${\mathit{m}}_{\mathit{e}}$${)}^{1/2}$. As the phase velocity increases, fewer electrons are accelerated to higher velocities. The measured current contained in these accelerated electrons has the power dependence predicted by theory, but the magnitude is lower than predicted [B. I. Cohen et al., Nucl. Fusion 28, 1519 (1988)].