Evolution of 2D deuterium and impurity radiation profiles during transitions from attached to detached divertor operation in DIII-D

This paper presents the detailed evolution of conditions along both the inn er and outer divertor legs during the transition from attached ELMing II-mo de to partially detached divertor (PDD) operation in DIII-D. Visible emissi on profiles in a poloidal plane show that in ELMing H-mode prior to deuteri um gas injection, CIII emission peaks in the inner SOL near the X-point and deuterium emission (from ionization and recombination) peaks at the inner target plate near the inner strike point (SP). The spatial profil of the re combination and ionization zones, determined by forming images of the ratio of intensities from simultaneous images of D-alpha and D-gamma emission, s how that recombination dominates the inner leg emission near the target; io nization dominates in a polidally narrow zone upstream in the inner leg. Af ter deuterium injection, when the PDD transition begins, the profil of carb on visible emission show first an increase in the inner SOL near the X-poin t, followed by increases in emission in the lower regions of the outer leg. Deuterium emission at the transition onset decreases at the ISP and increa ses across the private flux region below the X-point. As the transition to PDD conditions proceeds the deuterium emission increases in the private flu x region; recombination dominates near the floor nd ionization higher near the X-point. Carbon emission appears along both divertor legs and at the X- point. In the final quasi-steady PDD state, the recombination emission in t he outer leg is near the separatrix and along the target plate; emission fr om collisional excitation dominates in the upper part of the outer leg just below the X-point, and carbon emission is localized at the X-point. These results suggest that transport of neutral deuterium between the inner and o uter divertor legs through the private flux region plays an important role in the initiation of outer leg detachment in DIII-D. (C) 1999 Elsevier Scie nce B.V. All rights reserved.