High Pressure Supersonic Gas Jet Fueling on NSTX

A supersonic gas injector (SGI) has been developed for fueling and diagnostic applications on NSTX. The SGI is comprised of a small de Laval converging-diverging graphite nozzle, a commercial piezoelectric gas valve, and a diagnostic package, all mounted on a movable probe at a low field side midplane port location. The nozzle operated in a pulsed regime at room temperature, reservoir deuterium pressure up to 2500 Torr (50 PSIA), flow rate up to 65 Torr 1 /s (4.55e2f particles/s), and a measured Mach number of about 4. In initial experiments the SGI was used for fueling of ohmic and 2 -6 MW NBI-heated L-and H-mode plasmas. Reliable H-mode access was obtained with SGI fueling, with a fueling efficiency in the range 0.1 -0.3. Good progress was also made toward a controlled density SGI-fueled H-mode plasma scenario with the flow rate of the uncontrolled high field side (HFS) gas injector reduced by up to 20. These experiments motivated a number of SGI upgrades: 1) the maximum plenum pressure has been increased to 5000 Torr (100 PSIA), 2) the plenum pressure volume has been doubled, 3) the gas delivery system has been changed to allow for injection of various gases, 4) a multi-pulse capability has been implemented. As a result of the upgrades, the maximum flow rate increased to about 130 Torr 1 /s. Laboratory gas jet characterization tests indicated a Mach number of about 4 with H2 and I) , and 4-6 with He and N2. Plasma experiments demonstrated the high-pressure gas jet fueling compatibility with H-mode plasmas, high fueling efficiency (0.1 -0.3), and high SOL penetration.