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(EX/C3-2) Core and Edge Aspects of Quiescent Double Barrier Operation on DIII-D, with Relevance to Critical ITB Physics Issues

E.J. Doyle¹⁾, T.A. Casper²⁾, K.H. Burrell³⁾, C.M. Greenfield³⁾, W.P. West³⁾, R.V. Budny⁴⁾, J.C. DeBoo³⁾, A.M. Garofalo⁵⁾, P. Gohil³⁾, R.J. Groebner³⁾, A.W. Hyatt³⁾, G.L. Jackson³⁾, T.C. Jernigan⁶⁾, J.E. Kinsey⁷⁾, L.L. Lao³⁾, C.J. Lasnier²⁾, J.-N. Leboeuf⁸⁾, T.C. Luce³⁾, M.A. Makowski²⁾, G.R. McKee⁹⁾, R.A. Moyer¹⁰⁾, M. Murakami⁶⁾, T.H. Osborne³⁾, W.A. Peebles¹⁾, C.C. Petty³⁾, M. Porkolab¹¹⁾, G.D. Porter²⁾, T.L. Rhodes¹⁾, J.C. Rost¹¹⁾, D.L. Rudakov¹⁰⁾, G.M. Staebler³⁾, E.J. Strait³⁾, M.R. Wade⁶⁾, G. Wang¹⁾, J.G. Watkins¹²⁾, L. Zeng^1)
 
1) University of California, Los Angeles, Los Angeles, USA
²⁾ Lawrence Livermore National Laboratory, Livermore, California, USA
³⁾ General Atomics, San Diego, California, USA
⁴⁾ Princeton Plasma Physics Laboratory, Princeton, New Jersey, USa
⁵⁾ Columbia University, New York, New York, USA
⁶⁾ Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
⁷⁾ Lehigh University, Bethlehem, Pennsylvania, USA
⁸⁾ Physics Department, University of California, Los Angeles, Los Angeles, California, USA
⁹⁾ University of Wisconsin, Madison, Madison, Wisconsin, USA
¹⁰⁾ University of California, San Diego, La Jolla, California, USA
¹¹⁾ Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
¹²⁾ Sandia National Laboratories, Albuquerque, New Mexico

Abstract.  This paper reports on the progress in the areas of internal transport barrier (ITB), Quiescent H-mode (QH-mode) and Quiescent Double Barrier (QDB) research on DIII-D. The QDB regime combines core transport barriers with an ELM-free, quiescent H-mode edge, resulting in sustained high performance operation ( $\beta_{N}^{}$H₈₉ product of 7 for 10 confinement times). These QDB discharges are of interest as: (a) They provide a convincing demonstration of quasi-steady-state ITB operation for >3.5 s, or $\sim$ 25 confinement times, limited only by NBI pulse length. (b) The QH-mode edge demonstrates that sustained, high-quality ELM-free H-mode operation is possible with density and radiated power control and (c) QDB discharges allow us to investigate critical ITB physics issues such as sustainment, impurity accumulation, theory-based understanding and current drive capability. *Work supported by U.S. DOE under Grants DE-FG03-01ER54615, DE-FG02-89ER53297, DE-FG02-92ER54141, DE-FG03-96ER54373, DE-FG03-95ER54294, DE-FG02-90ER54084, DE-FG03-86ER53225, and Contracts DE-AC03-99ER54463, DE-AC05-00OR22725, W-7405-ENG-48, DE-AC04-94AL85000.

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