Drift kinetic effects and local current drive induced modification of magnetic shear on sawtooth activity in EU DEMO

Abstract

The sawtooth activity is investigated for an EU DEMO reference plasma, including kinetic effects from both thermal particles and fusion-born alphas. Kinetic effects are studied in conjunction with modification of the magnetic shear near the q= 1 surface (q is the safety factor) due to local current drive. Kinetic stabilization on the internal kink mode is found by both the non-perturbative MHD-kinetic hybrid code MARS-K (Liu et al 2008 Phys. Plasmas 15 112503) and the perturbative semi-analytic Porcelli model. The latter predicts full stabilization of the mode, when the local magnetic shear s 1 at the q= 1 surface is less than 1 (e.g. s 1 ∼ 0.6 as is the case for the target EU DEMO plasma without local current drive). By increasing the local magnetic shear with local current drive up to s 1 ∼ 2.8, one of the Porcelli sawtooth crash criteria can be satisfied, by accessing the ion-kinetic regime. Direct MARS-K non-perturbative eigenvalue computations, on the other hand, predict less kinetic stabilization of the internal kink and more robust triggering of the sawtooth crash in EU DEMO. The general trend of the predicted results remains similar though, between the MARS-K model and the Porcelli model.