INTERNAL TRANSPORT BARRIERS IN OPTIMIZED SHEAR PLASMAS IN JET

Experiments using high-power heating during the current nmp-up phase o f the discharge have obtained the highest D-D neutron rates in JET; S- n = 5.6 x 10(16) neutrons s(-1) with n(e0), approximate to 6 x 10(19) m(-3), T-e0 approximate to 12 keV and T-i0 approximate to 26 keV. The best discharges (I-p = 3.3 MA and B-t = 3.4 tesla) have peaked pressur e profiles with a transport barrier located at tau/a = 0.55. The press ure peaking is limited by MHD modes and requires active input power co ntrol to achieve the best performance. Deuterium neutral beam injectio n into a tritium-rich target plasma has established internal transport barriers at power levels close to the lowest threshold for pure deute rium plasmas.