VERY HIGH CONFINEMENT DISCHARGES IN DIII-D AFTER BORONIZATION

A regime of very high confinement (VH mode) has recently been observed in DIII-D with global energy confinement times up to a factor of 3.5 above the ITER89-P L-mode scaling [Nucl. Fusion 30, 1999 (1990)] and 1.5 to 2 times greater than the DIII-D/JET edge-localized-mode-free H-mode scaling relation [Nucl. Fusion 31, 73 (1991)]. These discharges were obtained after boronization in DIII-D and are characterized by low radiated power and Z(eff), increasing confinement time during the VH phase of the discharge and low Ohmic target density. The low radiated power and Z(eff) are a consequence of the boronization. During the VH phase these discharges exhibit an inward shift in the region of highest electric field shear and a large calculated edge bootstrap current. The outer region (rho greater than or similar to 0.85) is calculated to be in the second stable regime to ideal ballooning modes.