Plasma heating in stellarators at the fundamental ion cyclotron frequency

Abstract

The propagation and absorption of Alfvén waves at ω≈ωci is studied in a straight nonuniform helical plasma with elliptical cross section, placed in an inhomogeneous l=2 magnetic field created by helical windings. The model antenna with a spectrum of kz induces the m=+1 poloidal harmonic. In a uniform plasma in a uniform magnetic field the antenna excites the m=+1 fast wave fields. These fields are right-handed almost everywhere in the plasma and they are not absorbed by plasma ions. In the nonuniform helical l=2 magnetic field under certain conditions the antenna excites mostly the m=+1 fast wave and left-handed m=−1 slow wave fields. The coupling between these waves in the nonuniform magnetic field leads to the excitation of the left-handed wave field component near the plasma center and to the heating of plasma ions by this wave component. Collisionless absorption by plasma ions is assumed. The power deposition distribution in the plasma is examined for different plasma parameters. Results demonstrate that effective heating of the central part of the plasma at ω=ωci is possible for the low density plasmas in small scale devices. Because of the restrictions in the model, no firm conclusions can be made about the effectiveness of this method for high density plasmas in large scale devices.