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(EXP2/10) Investigation of Density Limit Processes in DIII-D

   
R. Maingi , L. R. Baylor , T. Jernigan , M. Murakami , M. R. Wade 
Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.
 
M. A. Mahdavi , T. W. Petrie , A. W. Hyatt , R. J. La Haye , A. W. Leonard , R. T. Snider , R. D. Stambaugh , D. M. Thomas , W. P. West 
 
General Atomics, P.O. Box 85608, San Diego, California 92186-9784, U.S.A.  
J. W. Cuthbertson , D. G. Whyte 
University of California, San Diego, California, U.S.A.
 
D. N. Hill , C. J. Lasnier 
Lawrence Livermore National Laboratory, Livermore, California, U.S.A.
 
J. G. Watkins 
Sandia National Laboratories, Albuquerque, New Mexico, U.S.A.

Abstract
A series of experiments has been conducted in DIII-D  to investigate density-limiting processes. We have studied divertor detachment  and MARFEs  on closed field lines and find semi-quantitative agreement with theoretical calculations of onset conditions. We have shown that the critical density for MARFE onset at low edge temperature scales as $I_p/a^2$ , i.e. similar to Greenwald scaling. We have also shown that the scaling of the critical separatrix density with heating power at partial detachment onset agrees with Borass' model. Both of these processes yield high edge density limits for reactors such as ITER . By using divertor pumping and pellet fueling we have avoided these and other processes and accessed densities $> 1.5\times$ Greenwald limit  scaling with H-mode  confinement, demonstrating that the Greenwald limit is not a fundamental limit on the core density.

   

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