Recent Experiments on Alternative Dipole Phasing with the JET A2 ICRF Antennas
Using the JET A2 ICRF antennas, experiments were carried out to assess the performance of three different dipole phasing configurations relevant for the operation of the ICRF antenna in ITER. Three similar discharges with dipole (0p0p), "symmetric dipole" (0pp0) and "super dipole" (00pp) phasings were compared. In the "super dipole" case, higher coupling was confirmed but lower heating efficiency and much stronger plasma wall interaction were observed, as corroborated, respectively, by the analysis of the diamagnetic energy response to the ICRF power steps and by the observation of a considerable temperature rise of the antenna limiters and septa in the 00pp case. These observations were found to be in line with simulations of the ICRF wave absorption and with High Frequency Structure Simulator (HFSS) modeling of the RF fields near the antenna.