Improved Confinement in Highly Powered Advanced Tokamak Scenarios on DIII-D

DIII-D has recently demonstrated improved energy confinement by injecting neutral gas into high performance Advanced Tokamak (AT) plasmas during high power operation. Representative parameters are: q$_{95}$ = 6, $P_{IN}$ up to 15 MW, $H_{98}$ = 1.4–1.8, and $\beta_N$ = 2.8–4.2. Unlike in lower and moderate powered AT plasmas, $\tau_E$ and $\beta_N$ increased (and $\nu_{ELM}$ decreased) as density was increased by deuterium gas puffing. We discuss how the interplay between pedestal density and temperature with fueling can lead to higher ballooning stability and a peeling/kink current limit that increasers as the pressure gradient increases. Comparison of neon, nitrogen, and argon as “seed” impurities in high $P_{IN}$ ATs in terms of their effects on core dilution, $\tau_E$, and heat flux ($q_{\bot}$) reduction favors argon. In general, the puff-and-pump radiating divertor was not as effective in reducing $q_{\bot}$ while maintaining density control at highest $P_{IN}$ than it was at lower $P_{IN}$.