HIGH-CONCENTRATION MINORITY ION-CYCLOTRON RESONANCE HEATING IN JET

With a view to heating a 50/50 deuterium-tritium reactor plasma, ion cyclotron resonance heating (ICRH) at a power level of 10 MW has been demonstrated in JET for a minority hydrogen concentration as high as n(H)/n(He-3) less-than-or-equal-to 1. In high minority ICRH experiments using (H)-He-3 plasmas, improved bulk ion heating was observed when the minority ion tail temperature was lowered to a level below the critical energy, so that more than 50% of the tail power was transferred to the bulk ions. Further, T(i0) is-approximately-equal-to T(e0) is-approximately-equal-to 7 keV was obtained in limiter L-mode discharges (T(e0) and T(i0) are the central electron and ion temperatures, respectively). The global energy confinement was similar to that found in other ICRH L-mode discharges. It is shown that the observed tail temperature, fast ion energy and minority density are well understood in terms of minority ICRH physics and the Stix theory. Moreover, it is shown theoretically that when the wave is launched by an antenna in (0, pi) phasing from the low field side in large and hot reactor-like plasmas, strong single-pass damping can be maintained at concentrations of the minority species approaching that of the majority species. The occurrence of ion-ion hybrid mode conversion cut-off layers would be of no consequence, since most of the wave power is absorbed before it reaches this region.