Density Control and Limit(s) in MST

The MST RFP is fueled by gas puffing and pellet injection. Densities (n$_{e})$ approaching and exceeding the Greenwald limit (n$_{G})$ have been achieved. In some discharges, the plasma terminates early when n$_{e}$ exceeds n$_{G}$. In others, n$_{e}$ exceeds n$_{G}$ without premature termination. While not yet approaching n$_{G}$, we have increased n$_{e}$ by 70{\%} in improved confinement PPCD plasmas with pellet injection. Sawtooth suppression is observed in high density standard plasmas fueled by pellets and/or gas puffing. Measurements with a multichord far infrared interferometer/polarimeter show that pellet injection peaks the density profile, raising the central density to 5 x 10$^{13}$ cm$^{-3}$, while flattening the current profile. Presently, the density achievable with gas puffing is limited by the throughput ($\sim $10 Torr*L/s per valve) of MST's puff valve system. A limited number of valves are being modified for higher throughput ($\sim $300 Torr*L/s per valve) to achieve higher densities. Work supported by U.S.D.O.E..