Stability and Confinement Optimisation in the Range q0 = 1-3 at JET

Steady-state operation of ITER at Q 5 is envisaged with a plasma current of 9MA, a large fraction of which must be provided by the bootstrap mechanism. In these conditions q95 will be 5 and the minimum value of q (qmin) is expected to be >1. Experiments have been performed on JET to vary the q-profile shape in this domain to investigate the effect on stability and confinement. The large ratio of resistive time (tR) to energy confinement time (tE) on JET (tR 4-8s and tR/tE 20-50 in these experiments at 1.1-1.6MA/1.6-2.3T) has allowed the study of a wide range of q-profile shapes without the need for fully non-inductive current drive. In these experiments two favourable domains have been identified: one with qmin in the range 1.0-1.5; and the other at qmin > 2.
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