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

TL;DR

This paper evaluates the power requirements and control schemes for sawtooth management in ITER using electron cyclotron current drive and ion cyclotron resonance heating, emphasizing the importance of active feedback and q=1 surface positioning.

Contribution

It proposes combined ECCD and ICRH control strategies for sawtooth suppression in ITER, highlighting the benefits of active feedback and q=1 surface control.

Findings

13MW ECCD can reduce sawtooth period below NTM trigger level

>10MW ICRH can supplement ECCD for longer natural sawtooth periods

Active feedback and q=1 surface control enhance control efficacy

Abstract

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