Development of an operational scenario for a current hole plasma using TSC on Alcator C-MOD

A current hole develops when the q-profile is extremely deeply reversed and the toroidal current density becomes zero around the center of a tokamak plasma. In order to investigate the possibility of creating a current hole on Alcator C-mod, TSC and LSC (ray-tracing with 1D FP) simulations have been carried out. Using experience from the OH-less experiments on JT-60U[1] it is found that the plasma evolves towards a current hole configuration with a moderate LHCD power ($\sim$ 1MW) at a plasma current of 300kA, when a compound spectrum is employed. The plasma produced is nearly $100\%$ driven by LHCD in steady-state with a very small bootstrap current, providing a good test for our understanding of the current hole. These simulations are being used to formulate an experiment on Alcator C-mod. A possibility of increasing the bootstrap current by additional ICRF heating will also be discussed. [1] S. Shiraiwa, et al., Phys. Rev. Lett. 92, 035001 (2004)