Comparison of radiating divertor behaviour in single-null and double-null plasmas in DIII-D

'Puff-and-pump' radiating divertor scenarios, applied to both upper single-null (SN) and double-null (DN) H-mode plasmas, result in a 30?60% increase in radiated power with little or no decrease in ?E. Argon was injected into the private flux region of the upper divertor, and plasma flow into the upper divertor was enhanced by a combination of deuterium gas puffing upstream of the divertor targets and particle pumping at the targets. For the same constant deuterium injection rate, argon penetrated the main plasma of SNs more rapidly and reached a higher steady-state concentration when the B ? ?B-ion drift direction was towards the divertor (V?B?) rather than away from the divertor (V?B?). We also found that the initial rate at which argon accumulated inside DN plasmas was more than twice that of comparable SN plasmas having the same B ? ?B-ion drift direction. In DNs, the radiated power was not shared equally between divertors during argon injection. Only when the B ? ?B ion drift direction was away from the divertor were both significant increases in divertor radiated power and an accumulation of argon in the divertor observed, based on spectroscopic measurements of Ar?II. Our data suggest that an unbalanced DN shape where the B ? ?B-ion drift is directed away from the dominant divertor may provide the best chance of successfully coupling a radiating divertor approach with a higher performance H-mode plasma.

[1]  S. Wolfe,et al.  A new look at density limits in tokamaks , 1988 .

[2]  L. Horton,et al.  Effect of divertor geometry on boundary and core plasma performance in ASDEX Upgrade and JET , 1999 .

[3]  T. Petrie,et al.  Impurity enrichment and radiative enhancement using induced SOL flow in DIII-D , 1999 .

[4]  D. A. Knoll,et al.  2-D Fluid Transport Simulations of Gaseous/Radiative Divertors , 1994 .

[5]  L. Horton,et al.  Helium and neon enrichment studies in the JET Mark IIAP and Mark IIGB divertors , 2002 .

[6]  D. N. Hill,et al.  Impurity enrichment studies with induced scrape-off layer flow on DIII-D , 1998 .

[7]  T. W. Petrie,et al.  Changes in Edge and Scrape-off Layer Plasma Behavior Due to Variation in Magnetic Balance , 2003 .

[8]  M. Wade,et al.  Direct measurement of divertor exhaust neon enrichment in DIII-D , 1997 .

[9]  R. C. Isler,et al.  Impurities in tokamaks , 1984 .

[10]  A. Chankin.  Classical drifts in the tokamak SOL and divertor: models and experiment , 1997 .

[11]  T. Petrie,et al.  The role of magnetic geometry on the poloidal distribution of ELM-induced peak particle flux at the divertor targets in DIII-D , 2003 .

[12]  T. Petrie,et al.  Variation of particle exhaust with changes in divertor magnetic balance , 2005 .

[13]  T. Petrie,et al.  Compatibility of the Radiating Divertor with High Performance Plasmas in DIII-D , 2007 .

[14]  T. S. Taylor,et al.  Physics of advanced tokamaks , 1997 .

[15]  J. Rice,et al.  Impurity compression and enrichment studies on Alcator C-Mod , 1999 .