Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, October 30
Exhibit Hall B,
Current and flux amplification in a coaxial helicity-injected spheromak are determined by a balance between transport of current (measured by j/B) from the plasma edge to the plasma core and losses to resistivity inside the separatrix. We model current drive in the approximations of nearly-closed flux surfaces and hyper-resistive (HR) transport in Ohm’s law using several approximate and/or ad hoc HR coefficients. Current on open fieldlines and transfer of helicity due to the n=1 kinking of the current column are parameterized. Flux and current amplification are limited if the boundary between edge plasma and closed surfaces is fixed, so the separatrix is determined by the free-boundary model in the Corsica code. Results are compared with SSPX results to evaluate the reality of the model and to estimate coefficients. The model is used for a preliminary optimization of the coaxial electrode geometry for possible upgrades.