L–H transition studies on DIII-D to determine H-mode access for operational scenarios in ITER

A comprehensive set of L–H transition experiments has been performed on DIII-D to determine the requirements for access to H-mode plasmas in ITER's first (non-nuclear) operational phase with H and He plasmas and the second (activated) operational phase with D plasmas. The H-mode power threshold, P TH , was evaluated for different operational configurations and auxiliary heating methods for the different main ion species. Helium plasmas have significantly higher P TH than deuterium plasmas at low densities for all heating schemes, but similar P TH as deuterium plasmas at high densities except for H-neutral beam injection-heated discharges, which are still higher. Changes in P TH are observed when helium concentration levels in deuterium plasmas exceed 40%. There is a strong dependence of P TH on the magnetic geometry in the vicinity of the divertor. The trend of decreasing P TH with decreasing X-point height is observed for all of the main ion species irrespective of the heating method, which appears to indicate that there is a common physics process behind this effect for all of the ion species. Helium and deuterium plasmas exhibit a significant increase in P TH for strong resonant magnetic perturbations. The application of a local magnetic ripple of 3% from test blanket module mock-up coils did not change P TH in deuterium plasmas.