Deuterium-tritium TFTR plasmas with high internal inductance

Deuterium-tritium plasmas with increased plasma internal inductance, li, have been produced in TFTR to investigate stability limits at high li, Ip, and B0, and to assess fusion power production in these plasmas. A novel technique of plasma initiation at low edge safety factor, qa, has allowed operation at Ip up to 2.3 MA and li up to 1.5. These plasmas exhibit larger sawtooth inversion radii than plasmas with lower li at the same Ip. The sawteeth are stabilized at sufficiently large injected neutral beam heating power, Pb, consistent with a model of ω*-stabilization. The stability limit due to disruption is consistent with a scaling of the maximum βN ≡ 108<βt>aB0/Ip being proportional to li. Increased energy confinement, attained by lithium conditioning of the limiter, has exceeded that of supershot plasmas at heating power levels above 30 MW. Fusion powers of up to 8.7 MW have been generated in these plasmas. At the maximum attempted Ip and B0, the plasmas are no longer limited by gross plasma instability, but rather by limiter power handling. Plasmas with reversed central shear and increased li due to increased edge magnetic shear have also been created. The stability limit for these plasmas also exhibits an increase in the maximum βN with increased li. (author). 21 refs, 6 figs