State transitions, hysteresis, and control parameters on DIII-D

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The theory of turbulence decorrelation by ExB velocity shear is the leading candidate to explain the changes in turbulence and transport that are seen at the plasma edge at the L to H transition. Based on this, a key question is: What are the conditions or control parameters needed to begin the formation of the E{sub r} shear layer and thus trigger the L to H transition? On the DIII-D tokamak, the authors are attacking this question both through direct tests of the various theories and by trying to gain insight into the fundamental physics by investigating the control parameters ... continued below

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5 p.

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Thomas, D. M.; Groebner, R. J.; Carlstrom, T. N.; Osborne, T. H. & Petrie, T. W. July 1998.

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  • General Atomic Company
    Publisher Info: General Atomics, San Diego, CA (United States)
    Place of Publication: San Diego, California

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Description

The theory of turbulence decorrelation by ExB velocity shear is the leading candidate to explain the changes in turbulence and transport that are seen at the plasma edge at the L to H transition. Based on this, a key question is: What are the conditions or control parameters needed to begin the formation of the E{sub r} shear layer and thus trigger the L to H transition? On the DIII-D tokamak, the authors are attacking this question both through direct tests of the various theories and by trying to gain insight into the fundamental physics by investigating the control parameters which have a major effect on the power threshold. In this paper the authors describe results of studies on oscillating discharges where the plasma transitions continuously between L and H states. By following the dynamics of the plasma state through the forward and back transitions, they can represent the evolution of various control parameter candidates as a trajectory in various parametric spaces. The shape of these control curves can illustrate the specific nonlinearities governing the L-H transition problem, and under the proper conditions may be interpreted in the context of various phase-transition based models. In particular, the hysteresis exhibited in the various curves may help to clarify causality (what are the critical parameters) and may serve as tests of the models, given sufficient experimental accuracy. At present they are looking at T{sub e}, E{sub r} and ballooning/diamagnetic parameters as possible control parameter candidates.

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5 p.

Notes

INIS; OSTI as DE98007257

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  • 25. European Physical Society conference on controlled fusion and plasma physics, Prague (Czech Republic), 29 Jun - 3 Jul 1998

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  • Other: DE98007257
  • Report No.: GA--A22907
  • Report No.: CONF-980678--
  • Grant Number: AC03-89ER51114;FG05-88ER53266
  • Office of Scientific & Technical Information Report Number: 638248
  • Archival Resource Key: ark:/67531/metadc695162

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  • July 1998

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  • Aug. 14, 2015, 8:43 a.m.

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  • April 18, 2016, 6:08 p.m.

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Thomas, D. M.; Groebner, R. J.; Carlstrom, T. N.; Osborne, T. H. & Petrie, T. W. State transitions, hysteresis, and control parameters on DIII-D, article, July 1998; San Diego, California. (digital.library.unt.edu/ark:/67531/metadc695162/: accessed October 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.