Developing on DIII-D a QH-mode edge solution for Q$=$10 in ITER.

Experiments on DIII-D are advancing toward a demonstration of access to and control of Q(uiescent)H-mode at normalized performance equivalent to Q$=$10 in plasmas with ITER shape and collisionality, and low NBI torque throughout the pulse length. Earlier experiments had shown that ELMs return at NBI torque magnitude below \textasciitilde 3.5 Nm, which is above the expected level of normalized torque input in ITER. Recent experiments have been able to extend QH-mode operation to lower torque \textasciitilde 2 Nm and higher energy confinement by increasing the plasma-wall gap at the outboard mid-plane, and by reducing the input energy of the beam-injected ions. Two hypotheses are being tested: (a) the outer gap affects the scrape-off layer flows and thus the rotation gradient at the edge of the plasma, known to affect QH-mode access; (b) fast ion losses bombarding the wall may release impurities that affect the edge collisionality and stability making QH-mode operation more difficult.