Studies of high-δ (baffled) and low-δ (open) pumped divertor operation on DIII-D

We report new experimental results with the Radiative Divertor Project-outer baCe (RDP-OB) and cryopump in both upper single-null (USN) and double-null (DN) ELMing H-mode discharges. The baCed divertor reduced the core ionization (2‐2.5·), in reasonable agreement with predictions from UEDGE/DEGAS modeling (3.75·). The upper cryopump achieved density control of ne/ngw 0.22 (line density/Greenwald density) with Zeff 2 in high-d plasmas. The measured exhaust is comparable to the lower pump, except at lower core electron densities (ne < 5 · 10 19 m ˇ3 ). EAcient impurity exhaust was obtained with deuterium SOL flow. Preliminary experiments with DN operation has shown that the particle exhaust to the upper pump depends on the up/down magnetic balance. Preliminary experiments indicate that the DN exhaust is roughly 40‐50% of the USN exhaust at ne 4 · 10 19 m ˇ3 . ” 1999 Elsevier Science B.V. All rights reserved.