Heating Optimization Studies at JET in Support of ITER
Experiments have been performed at JET in view of optimizing the heating systems for ITER. To optimize coupling of ICRH in ITER with foreseen large antenna-plasma distances, gas puffing in the SOL has been successfully applied. Up to 8MW of ICRF power has been coupled in this way to ELMy H-Mode plasmas. The D fundamental ICRH heating scheme was further explored in combined ICRH and deuterium NBI heated deuterium discharges in JET. A concentration of fast deuterons less than 10% is able to absorb up to half of the ICRH power, rendering the fundamental D heating scheme much more viable for ITER. A possible caveat is that due to the large Doppler shift of 1MeV beam ions in ITER, absorption of ICRH waves could also occur in scenarios where the cold resonance layer is outside of the plasma. Anomalous behaviour of the beam ions has been observed at high densities (close to the Greenwald limit). The effects cannot be explained by the MHD effects or sawteeth, and an anomalous diffusion coefficient has to be assumed for passing fast particles with pitch angles v|| /v > 0.7. This result has possible implications for beam heating on ITER.