Higher Fusion Power Gain with Current and Pressure Profile Control in Strongly Shaped DIII-D Tokamak Plasmas

Fusion power has been increased by a factor of 3 in DIII-D by tailoring the pressure profile to avoid the kink instability in $H$-mode plasmas. The resulting plasmas are found to have neoclassical ion confinement. This reduction in transport losses in beam-heated plasmas with negative central shear is correlated with a dramatic reduction in density fluctuations. Improved magnetohydrodynamic stability is achieved by controlling the plasma pressure profile width. In deuterium plasmas the highest gain $Q$ (the ratio of fusion power to input power), was 0.0015, corresponding to an equivalent $Q$ of 0.32 in a deuterium-tritium plasma.