Scaling studies of the high mode pedestal
- General Atomics, San Diego, California92186-9784 (United States)
The structure and scaling of the H-mode (high mode) pedestal are examined for discharges in the DIII-D tokamak [{ital Plasma Physics and Controlled Fusion Research} (International Atomic Energy Agency, Vienna, 1986), p. 159]. For typical conditions, the pedestal values of the ion and electron temperatures T{sub i} and T{sub e} are comparable. Measurements of main ion and C{sup 6+} profiles indicate that the ion pressure gradient in the barrier is 50{percent}{endash}100{percent} of the electron pressure gradient for deuterium plasmas. The magnitude of the pressure gradient in the barrier often exceeds the predictions of infinite-n ballooning mode theory by a factor of 2. Moreover, via the bootstrap current, the finite pressure gradient acts to entirely remove ballooning stability limits for typical discharges. For a large dataset, the width of the pressure barrier {delta} is best described by the dimensionless scaling {delta}/R{proportional_to}({beta}{sub pol}{sup ped}){sup 0.4} where ({beta}{sub pol}{sup ped}) is the pedestal value of poloidal beta and R is the major radius. Scalings based on the poloidal ion gyroradius or the edge density gradient do not adequately describe overall trends in the data set and the propagation of the pressure barrier observed between edge-localized modes. The width of the T{sub i} barrier is quite variable and is not a good measure of the width of the pressure barrier. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 627775
- Report Number(s):
- CONF-971103-; ISSN 1070-664X; TRN: 98:006127
- Journal Information:
- Physics of Plasmas, Vol. 5, Issue 5; Conference: 39. annual meeting of the Division of Plasma Physics of the American Physical Society, Pittsburgh, PA (United States), 17-21 Nov 1997; Other Information: PBD: May 1998
- Country of Publication:
- United States
- Language:
- English
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