Ray tracing and absorption of electron cyclotron waves in the L-2 stellarator

Abstract

The absorption of electron cyclotron waves in L-2 stellarator plasmas has been investigated by adapting the RAYS geometrical optics code developed at Oak Ridge National Laboratory for the parameters of L-2. Two heating schemes were considered: (1) launching of the ordinary wave from the low magnetic field side at the fundamental resonance and (2) launching of the extraordinary wave from the low magnetic field side at the second harmonic resonance of the electron cyclotron gyrofrequency. Significant power absorption (up to 100%) of the extraordinary mode at the second harmonic resonance was obtained. For the plasma parameters of L-2, the single-pass absorption of the extraordinary wave was twice that of the ordinary wave. A multipass absorption model was used to estimate the contribution to plasma heating of the power that remains after the first pass and is subsequently reflected from the vessel walls. Finally, results obtained with the RAYS code and with a code developed at the Institute of Automation and Electrometry were compared and found to be in good agreement.