Sawtooth control with modulated ICRH in JET-ILW H-mode plasmas

Abstract

Sawtooth pacing with modulated ion-cyclotron resonance heating (ICRH) has been demonstrated to be very efficient in JET-ILW L-mode plasmas (Lerche et al 2017 Nucl. Fusion 57 036027, Lennholm et al 2017 Fusion Eng. Des. 123 535-40), where the main heat source in the plasma centre is provided by the RF accelerated minority ions. In H-mode plasmas with substantial neutral beam injection power, this technique is more challenging since the fast beam particles have a stabilizing effect on the sawteeth, making it more difficult to trigger a sawtooth crash by removing the additional fast particle sources induced by ICRH inside the q = 1 surface. New results from JET-ILW experiments, showing that this technique can also be used in high power H-modes with considerable success will be presented, with focus on the sawtooth triggering efficiency at different pacing frequencies and plasma parameters, both during the flat-top phase of the discharges and during the H-mode exit and plasma termination.