Improved particle control for high integrated plasma performance in Japan Atomic Energy Research Institute Tokamak-60 Upgrade

Abstract

Pellet fueling and impurity transport have been investigated in high poloidal-beta (βp) and reversed shear (RS) plasmas. It is observed that pellet injection from the high-field side at the top is more effective for density increase in the neutral-beam-heated plasma compared with pellet injection from the low-field-side midplane. This observation is consistent with the radial displacement theoretically predicted based on the E×B drift model, where deeper deposition is suggested for the high-field-side pellet injection. Using the high-field-side top pellets, the accessible density region of the high βp plasmas is extended to 70% of the Greenwald density with a confinement enhancement factor over the ITER89P scaling of 1.94, a normalized beta of 2.2, and a bootstrap current fraction of 60%. The impurity diffusivity at the internal transport barrier is only higher by a factor of 2–4 than the neoclassical prediction in the RS plasma. In contrast, the impurity diffusivity is two orders of magnitude higher than the neoclassical prediction and smaller by a factor of 5 than the theoretical prediction based on turbulence model in the high βp plasma. The helium-exhaust capability is enhanced and Zeff is reduced by increasing divertor recycling in the RS plasma, although confinement degrades with increasing divertor recycling.