(EX/P1-16) Compatibility of the Radiating Divertor With High Performance Plasmas in DIII-D

T.W. Petrie1), M.R. Wade1), N.H. Brooks1), M.E. Fenstermacher2), M. Groth2), A.W. Hyatt1), R.C. Isler3), C.J. Lasnier2), A.W. Leonard1), M.A. Mahdavi1), G.D. Porter2), M.J. Schaffer1), J.G. Watkins4), W.P. West1), DIII–D Team
1) General Atomics, San Diego, California, United States of America
2) Lawrence Livermore National Laboratory, Livermore, California, United States of America
3) Oak Ridge Institute of Science Education, Oak Ridge, Tennessee, United States of America
4) Sandia National Laboratories, Albuquerque, New Mexico, United States of America

Abstract.  We report on recent DIII-D experiments that successfully applied a radiating divertor scenario to high performance ``hybrid” plasmas [T.C. Luce, et al., Nucl. Fusion 43 (2003) 321]. In the puff-and-pump approach [M.J. Schaffer, et al., Nucl. Mater. 241-243 (1997) 585] used here, argon was injected near the outer divertor target, plasma flows into both the inner and outer divertors were enhanced by a combination of particle pumping near both divertor targets and deuterium gas puffing upstream of the divertor targets, and a ``dome” structure in the private flux region isolated the inner divertor from the outer divertor. Good hybrid conditions were maintained (e.g. energy confinement time normalized to ITER89p 2 and normalized plasma β≅2.4), and the argon accumulation in the main plasma was modest. The peak heat flux at the outer divertor target was reduced by a factor of ≅2.5, while the peak heat flux at the inner target fell by only 20%. This was largely due to a much higher argon concentration near the outer divertor target than near the inner target (7 times). Exhaust enrichment (ER) as high as 64 were obtained, and ER was insensitive to the argon injection rate. (ER is defined as the ratio of the neutral argon pressure in the baffle plenum to the atomic-equivalent pressure of deuterium in the baffle plenum, divided by the ratio of argon density to electron density in the main plasma.) The asymmetry in the argon distribution and the favorable enrichment values arose largely from the closed and partitioned divertor geometry and from the frictional forces due to the enhanced divertor flow, which impeded the escape of argon from the outer divertor. Although the argon density profiles were more peaked than the electron profiles at high argon injection rates, the emissivity profiles in the main plasma remained ``hollow”. Our results suggest that independent control of both the radiating properties at the inner and outer divertor targets can be controlled independently. UEDGE [T.D. Rognlien, et al., Plasma Phys. 34 (1994) 362] and MIST [R.A. Hulse, Nucl. Technol. Fusion 3 (1983) 259] modelings are used to assess the argon behavior in the divertor and main plasmas.
* Work supported by US DOE under DE-FC02-04ER54698, W-7405-ENG-48, DE-AC04-94AL85000.

Full paper available (PDF)