Geometry effects on ion heating at ion cyclotron frequencies

Abstract

The interaction of ions with electromagnetic waves at frequencies on the order of the ion cyclotron frequency is studied without the assumption of geometrical optics. Instead, it is assumed that the time for an ion to travel one wavelength is large compared with the wave period. Such a scaling admits nontrivial effects of the plasma geometry and is particularly appropriate to the ELMO Bumpy Torus experiment. The relevant frequency range is from one to a moderate multiple of the ion cyclotron frequency. It is shown that the ion response may be represented by the usual cold ion conductivity and with appropriate jump conditions across the fundamental resonant surface. Nonresonant energy transfer is calculated and shown to exist under many circumstances, depending on the antenna and electron response. Expressions are given for the resonant energy absorption at the fundamental and second harmonic. At higher harmonics, the nonresonant energy transfer is large compared with the resonant absorption.