Disruption mitigation on Alcator C-Mod using high-pressure gas injection: Experiments and modeling toward ITER

Abstract

High-pressure gas-jet injection disruption mitigation is investigated on Alcator C-Mod. The experimental results are encouraging for ITER. Gas-jets delivers reliable and substantial disruption mitigation of thermal loads and halo currents at the ITER field and pressure. The gas injection is compatible with a metallic wall. The gas-jets provide sufficient radiative energy dissipation on a timescale even faster than required for ITER. Runaway electrons are suppressed, however a better understanding of this suppression is still required for ITER. Present 0-D calculations of the gas delivery and global plasma response match important experimental data such as overall quench time and the current quench L/R time. Frictional dissipation may be important for gas delivery down the long tubes that will probably be required for ITER. However deep gas and/or impurity penetration is not required for mitigation, relieving technical requirements for the gas pressure in ITER. Initial studies with the non-ideal MHD simulation NIMROD show that radiation-induced MHD plays a critical role in thermal quench particle and energy dynamics. The application of a newly available version of NIMROD, with more complete atomic physics, shows promise in matching the experimental trends and could be an invaluable tool for increasing our confidence in designing efficient disruption mitigation for ITER.