Notable Findings From Recent Core-Edge Studies of High Power AT Plasmas on DIII-D

Recent experiments on DIII-D have focused on specific issues pertaining to high power, high performance hybrid plasmas, as characterized by $\beta_N$ = 3-4, H$_{98}$ = 1.3-1.7, P$_{IN}$ $\leq$ 20 MW, and q$_{95}$ $\cong$ 4.5-6.5. For these near-double null configurations, divertor peak heat flux (q$_P$) $\propto$ I$_P^{0.9}$ P$_{IN}^{0.9}$ at constant B$_T$. Carbon accumulation in the core rose significantly as P$_{IN}$ was increased, particularly when counter-beams were used; prompt beam particle losses by counter-beam injection to the outer midplane walls was 10-20\%. Nearly doubling the poloidal flux expansion at the divertor target resulted in only a fraction of the expected reduction in q$_P$. However, inhibiting particle escape from the divertor by baffling the SOL side of the target reduced q$_P$ by 30-40\%. The puff-and-pump radiating divertor was less effective in reducing q$_P$ while maintaining density control at highest P$_{IN}$ and $\beta_N$ than it was at lower P$_{IN}$ and $\beta_N$. Other features of high power AT operation will also be presented.