ELM suppression in high-purity DIII-D helium plasmas

ELM suppression in He plasmas with D core concentrations of less than 20$\%$ have been obtained in ECR heated, ITER Similar Shaped plasmas with low pedestal toroidal rotation ($v_\phi<$10 km/s). Here, $n$=3 RMP fields are used to suppress large type-I ELMs at power levels marginally above the PL-H threshold ($P_{ECRH}$=2.9 MW). ELM suppression in He plasmas has also been obtained using balanced co- and counter-Ip injected D neutral beams, with P$_{NBI}$=1.7 MW which is near the P$_{L-H}$ threshold, resulting in $v_\phi\sim$ 0. The electron perpendicular rotation frequency during ELM suppression does not cross zero, assuming no uncertainty in the measurement, but remains slightly negative, with an average frequency of -5 krad/s, between 0.80 and 0.94 in normalized poloidal flux. This suggests that magnetic island screening is weak or nonexistent from the top of the H-mode pedestal inward to surfaces relatively deep in the core plasma.