Propagation of lower hybrid resonance cones in tokamaks

Abstract

The trajectory of the lower hybrid resonance cone surface is calculated for propagation in the helical magnetic field of a tokamak. The surface is found to be a deformed cone, having symmetry axis following the magnetic field helicity. By superimposing cone fields excited by adjacent, poloidally separated point sources, the field excited by a source of finite poloidal extend is deduced. For sources having large poloidal extent, the superimposed cones destructively interfere everywhere except in a small region of constructive reinforcement which is located towards the plasma center; sources having small poloidal extent excite an individual resonance cone, which extends from near the plasma center all the way to the wall. Numerical calculations are presented for Verasator, Alcator-A and -C, JFT-2, and PLT tokamak parameters.