Experiments With a 6-Valve Array for Massive Gas Injection for Disruption Mitigation in DIII-D

A 6-valve array was installed on the DIII-D to test massive gas injection for suppression of runaway electrons during disruptions. Previous experiments were limited by the peak flow rate from a single valve. Initial experiments show somewhat improved electron assimilation before the core thermal quench (TQ). Peak core mixing efficiencies of impurities injected into the vacuum vessel through the TQ are $\sim $10{\%}-40{\%}. Tests using up to 5 valves were done in H$_{2}$, He, and 98{\%} H$_{2}$-2{\%} Ar. These experiments injected as much gas before the TQ as previously obtained during the entire TQ/I$_{p}$ decay. They also showed the importance of maintaining the gas flow during the I$_{p}$ decay to maintain the density. Densities of up to 2x10$^{21}$ m$^{-3}$ were obtained ($\sim $10{\%} of the Rosenbluth density for runaway suppression), but it was still increasing with added valves.