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

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 to the parameters of L‐2. Two heating schemes were considered: (1) low‐field launching of the ordinary wave at the fundamental resonance and (2) low‐field launching of the extraordinary wave at the second harmonic. Significant power absorption (up to 100%) of the extraordinary mode at the second harmonic resonance was obtained. A multipass absorption model was used to estimate the contribution to plasma heating of the power that remains after the first pass which 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.