Electron Bernstein Wave Core Deposition via O-X-B Double Mode Conversion in TCV

In the first results of electron Bernstein wave heating (EBWH) via O-X-B double mode conversion in a medium aspect ratio tokamak performed in TCV, the total power absorption efficiency was typically 60% and the deposition was made off-axis to avoid the central sawteeth perturbation that would prevent a clear detection of the deposition location. Central power deposition is however needed to maximize the global EBWH effects. Therefore, initial experiments have been started to optimize central deposition using an equatorial rather than poloidally oblique launch. A toroidal field scan provided promising central deposition results within a small database, in preparation for dedicated central high power deposition. The deposition location in presence of strong sawteeth could be determined from the slope break of soft X-ray traces at the EC power switch-ON times, in conditions where usual methods failed. Further analysis of these discharges will be presented. In particular, the difference between the experimental results and the non-relativistic calculations of deposition locations appears more significant than in the earlier off-axis deposition experiments, which provides a good opportunity for the simulation of relativistic ray propagation effects.