Power requirements for electron cyclotron current drive and ion cyclotron resonance heating for sawtooth control in ITER

摘要

13MW of electron cyclotron current drive (ECCD) power deposited inside the q= 1 surface is likely to reduce the sawtooth period in ITER baseline scenariobelow the level empirically predicted to trigger neo-classical tearing modes(NTMs). However, since the ECCD control scheme is solely predicated uponchanging the local magnetic shear, it is prudent to plan to use a complementaryscheme which directly decreases the potential energy of the kink mode in orderto reduce the sawtooth period. In the event that the natural sawtooth period islonger than expected, due to enhanced alpha particle stabilisation forinstance, this ancillary sawtooth control can be provided from > 10MW of ioncyclotron resonance heating (ICRH) power with a resonance just inside the q = 1surface. Both ECCD and ICRH control schemes would benefit greatly from activefeedback of the deposition with respect to the rational surface. If the q = 1surface can be maintained closer to the magnetic axis, the efficacy of ECCD andICRH schemes significantly increases, the negative effect on the fusion gain isreduced, and off-axis negative-ion neutral beam injection (NNBI) can also beconsidered for sawtooth control. Consequently, schemes to reduce the q = 1radius are highly desirable, such as early heating to delay the currentpenetration and, of course, active sawtooth destabilisation to mediate smallfrequent sawteeth and retain a small q = 1 radius.