The basic features of microwave propagation and electron-cyclotron damping in ELMO Bumpy Torus (EBT) devices are investigated to provide an understanding of the heating of the toroidal core plasma component. The characteristics of microwave propagation in EBT geometry, where there is strong variation of along field lines, are described and contrast is made with the electron-cyclotron heating (ECH) of tokamaks. Linear cyclotron damping calculations are presented for plasmas having parameters typical of EBT-I and parameters projected for EBT-II. It is shown that the extraordinary mode is completely absorbed near the fundamental cyclotron resonance when propagating from the high-magnetic-field side (mirror throat). For EBT-I parameters, heating by the ordinary mode at the fundamental cyclotron resonance and by both modes at the second-harmonic resonance is negligible. For projected EBT-II parameters, the ordinary mode is heavily damped at the fundamental and the extraordinary mode is heavily damped at the second harmonic. Since the right-hand cut-off prevents injected extraordinary-mode energy from propagating to the cyclotron resonance, a mechanism must exist outside of geometrical optics by which the extraordinary mode reaches resonance. It is argued that this mechanism is the conversion of ordinary-mode energy to extraordinary mode in the high-field region upon wall reflection.
Electron cyclotron wave propagation and absorption in the Compact Ignition Tokamak