Confinement heating and stability in the ELMO bumpy torus (EBT)

High power ECH (utilizing a 28-GHz gyrotron at power levels up to 200 kW, cw) and fast-wave ICH (in the frequency range 15-30 MHz at power levels up to 20 kW, cw) experiments on EBT-Scale (EBT-S) have yielded Te approximately 1.1 keV, n approximately 1-2*1018 m-3, and tau E approximately 6 ms. The ring and core loss rates scale as predicted by the neoclassical theory, and the plasma parameters have the predicted values for the densities, temperatures, and confinement times reachable in this small plasma radius (10 cm) device at low field (1.0 T). In addition, the following observations were made: (1) the stable operating window is larger at high power levels, (2) a substantial increase in energetic ion tails (Ti>100 eV) and a doubling of the ring electron stored energy (beta) were seen at the highest ICH power levels, and (3) a significant increase in core density and stabilization of hot electron modes was possible with gas puffing.

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