A simple power deposition model for microwave heating in EBT-I

A simple model is presented for the production and absorption of ordinary- and extraordinary-mode energy in various regions of the ELMO Bumpy Torus plasma. The plasma is divided into two regions: (I) the low-magnetic-field side of the extraordinary-mode cutoff and (II) the high-field side of the cut-off. Energy balance equations are written for the sources (injection, mode conversion, and tunnelling) and sinks (mode conversion, absorption, and tunnelling) in each region, and simplified models are introduced to account for each of these processes. Since a typical ray makes several reflections from cavity wall surfaces before being absorbed, additional simplifying assumptions are made that the wave fields are an isotropic incoherent superposition of plane waves and that the energy density of each mode is uniform in a given region. – It is found that conversion between eigenmodes upon wall reflection and absorption of the extraordinary mode at the fundamental cyclotron resonance are the most rapid processes in EBT-I. The relative fractions of the injected power deposited in the various plasma components are typically 25% to the annulus, 22% to the core plasma, and 53% to the surface plasma. The partitioning of energy between the three plasma components is determined largely by geometric characteristics of the walls, the plasma, and the fundamental cyclotron resonant surface. The results are comparatively insensitive to other parameters of the model and in rough agreement with estimates of power deposition based on experimental data.