Decoupling the effects of plasma current, density and temperature on DIII-D H-mode energy confinement

Experiments that decoupled H-mode plasma current, density and temperature have been performed on the DIII-D tokamak by the application of divertor cryopumping. Deuterium ELMing H-mode steady state discharges were operated in the single null configuration with neutral beam heating. A power-law dependence of the ELMing thermal confinement was assumed with the result that the thermal energy confinement depends weakly on density and strongly on plasma current. A local power balance analysis generally found that the ion and electron diffusivity was unchanged with an approximate factor of two change in density at constant temperature. In contrast, both the electron and ion diffusivities increased with increasing temperature at constant density. These plasmas were simulated with the Rebut - Lallia - Watkins critical temperature gradient model. Our results indicate that the temperature dependence of the model does not fit the DIII-D data; the model was too optimistic at the highest power. However, the density dependence of the model agrees well with DIII-D data.