Electron Bernstein Wave Applications for Stellarators

Electron Bernstein Waves (EBW) provide a mechanism to heat electrons in over-dense plasma using microwave sources. The mode conversion between ordinary or extra-ordinary waves and EBW depends on density gradients in the plasma edge, the angle of incidence, and the polarization of the incoming waves. General considerations for the efficiency of mode conversion to EBW in stellarator geometries are discussed. For cold, dense edge-plasma conditions, Coulomb collisions can cause parasitic absorption in the initial propagation region of the EBW, but collisional damping should not be a problem for the sharp edge gradients and temperatures > or approx. 50 eV in the Quasi-Poloidal Stellarator (QPS). Scenarios for using fixed launch angles with polarization optimization to maximize transmission during the density evolution in QPS are possible