Evaluation of ITER magnetic shear control possibilities using MICCD

Active sawtooth period control using minority ion cyclotron current drive, MICCD, has been proposed for ITER in order to avoid having neoclassical tearing modes triggered by long-period, large-amplitude, sawteeth. In this paper we evaluate the magnetic shear modification that is possible with the proposed ITER MICCD scheme, which uses a 3 He minority, and compare that to an alternative scheme which uses a H minority. MICCD drives two main current components; current carried by Doppler-resonant ions in passing orbits t hat have been heated to energies with lower bulk plasma collisionalities [1] and current carri ed by ions in broad trapped orbits [2]. The choice of minority is important primarily due to the difference in back current, i.e. the current carried by electrons dragged along by the minority ions and by the bulk plasma that flows opposite to the minority ions due to momentum conservati on. The relationship between the total driven current and the minority current is given by [3]: