Comparison of deuterium and hydrogen experiments in the Sustained Spheromak Physics Experiment

In this paper we report on the results of deuterium and hydrogen experiments in the Sustained Spheromak Physics Experiment (SSPX). We have compared ∼500 deuterium discharges with similar discharges in hydrogen. Typically, we produce H2 plasmas with peak toroidal currents in the range of 0.6 MA, electron temperatures (Te) of ∼200 eV and energy confinement times (τE) of ∼200 μs. The D2 fueled discharges show similar results to those with H2 fueling with no obvious differences in confinement time. Electron temperatures of ∼200 eV with similar electron densities were observed. Both the deuterium and hydrogen fueled discharges have a calculated thermal diffusivity below χe < 10 m2/s. However, the D2 fueled discharges had a factor of ∼5 increase in high-Z (titanium) impurity content suggesting an increase of physical sputtering. We find no significant mass scaling effects.