Operation at high performance in optimized shear plasmas in JET

Abstract

Heating during the early part of the current rise phase gives a low or\nnegative magnetic shear (= 0741-3335/40/6/020/img27(dq/dr)) in the\ncentre of JET plasmas. Under these conditions the confinement improves\nwith high additional heating power heating during the current ramp-up\nphase of the discharge. The reduction in the transport manifests itself\nas a peaking of the profiles with a large gradient region near\n0741-3335/40/6/020/img28 = 0.55. The best discharges have no transport\nbarrier at the edge of the plasma (L-mode). This allows central power\ndeposition by the neutral beams in JET. A control of the plasma\npressure, using feedback of the additional heating power in real-time,\nminimizes the impact of magnetohydrodynamic instabilities. As a result,\nthese discharges achieve the highest D-D neutron rates in JET;\n0741-3335/40/6/020/img29, with 0741-3335/40/6/020/img30,\n0741-3335/40/6/020/img31 and 0741-3335/40/6/020/img32.