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Title: Studies of H-Mode Plasmas Produced Directly by Pellet Injection in the DIII-D Tokamak

Abstract

A key issue for the physics of H-mode plasmas is to determine which plasma quantities are critical for the formation of the edge transport barrier. One approach is to directly perturb the edge plasma and observe the subsequent changes. In DIII-D, pellet injection has been used to directly change the edge plasma conditions and produce H-mode transitions. One hypothesis for the H-mode transition is that the attainment of a critical edge electron temperature is required for the transition [1-3]. This hypothesis is disproved in this paper. H-mode transitions were produced by injecting frozen deuterium pellets of diameter 2.7 mm from the inner wall of the DIII-D vessel into the high toroidal field side (HFS) and from the outer wall into the low field side (LFS) of the plasma. Both the HFS and LFS pellets produced significant increases in the edge electron density, which led to substantial reductions in the edge electron and ion temperatures. However, H-mode transitions were still produced with the lowered edge temperatures, implying that a critical edge temperature is not necessary for H-mode transitions. The pellet induced H-mode plasma exhibited clear pedestals in electron density and electron and ion temperatures at the plasma edge and persisted formore » the duration of the applied neutral beam power. The HFS pellet's penetration and deposition profiles were substantially deeper (up to {rho} {approx} 0.2) than that of the LFS pellet (up to {rho} {approx} 0.7). However, since both HFS and LFS pellets produced H-mode transitions, this implies that pellet penetration depth is not important the important factor is the large increase in the electron density right at the plasma edge produced by both types of pellets. The values of the edge plasma quantities at the H-mode transition were expressed in the parametric terms described in several theories and models of the H-mode transitions [4-6]. On comparison, the experimentally determined parameters at the H-mode transition were well below those required by several theoretical models. Finally, pellet injection reduced the neutral beam power required to produce the H-mode from 7.3 MW to 4.9 MW in plasmas which had the {del}B drift away from the X-point.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
General Atomics, San Diego, CA (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
766706
Report Number(s):
GA-A23420
TRN: US0109259
DOE Contract Number:  
AC03-99ER54463; AC05-00OR22725; FG03-86ER53225; FG03-96ER54373
Resource Type:
Conference
Resource Relation:
Conference: 27th European Physical Society Conference on Controlled Fusion and Plasma Physics, Budapest (HU), 06/12/2000--06/16/2000; Other Information: PBD: 1 Aug 2000
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DOUBLET-3 DEVICE; ELECTRON DENSITY; ELECTRON TEMPERATURE; ION TEMPERATURE; PELLET INJECTION; PENETRATION DEPTH; H-MODE PLASMA CONFINEMENT

Citation Formats

Gohil, P, Baylor, L R, Jernigan, T C, Burrell, K H, Carlstrom, T N, McKee, G R, and Rhodes, T L. Studies of H-Mode Plasmas Produced Directly by Pellet Injection in the DIII-D Tokamak. United States: N. p., 2000. Web.
Gohil, P, Baylor, L R, Jernigan, T C, Burrell, K H, Carlstrom, T N, McKee, G R, & Rhodes, T L. Studies of H-Mode Plasmas Produced Directly by Pellet Injection in the DIII-D Tokamak. United States.
Gohil, P, Baylor, L R, Jernigan, T C, Burrell, K H, Carlstrom, T N, McKee, G R, and Rhodes, T L. Tue . "Studies of H-Mode Plasmas Produced Directly by Pellet Injection in the DIII-D Tokamak". United States. https://www.osti.gov/servlets/purl/766706.
@article{osti_766706,
title = {Studies of H-Mode Plasmas Produced Directly by Pellet Injection in the DIII-D Tokamak},
author = {Gohil, P and Baylor, L R and Jernigan, T C and Burrell, K H and Carlstrom, T N and McKee, G R and Rhodes, T L},
abstractNote = {A key issue for the physics of H-mode plasmas is to determine which plasma quantities are critical for the formation of the edge transport barrier. One approach is to directly perturb the edge plasma and observe the subsequent changes. In DIII-D, pellet injection has been used to directly change the edge plasma conditions and produce H-mode transitions. One hypothesis for the H-mode transition is that the attainment of a critical edge electron temperature is required for the transition [1-3]. This hypothesis is disproved in this paper. H-mode transitions were produced by injecting frozen deuterium pellets of diameter 2.7 mm from the inner wall of the DIII-D vessel into the high toroidal field side (HFS) and from the outer wall into the low field side (LFS) of the plasma. Both the HFS and LFS pellets produced significant increases in the edge electron density, which led to substantial reductions in the edge electron and ion temperatures. However, H-mode transitions were still produced with the lowered edge temperatures, implying that a critical edge temperature is not necessary for H-mode transitions. The pellet induced H-mode plasma exhibited clear pedestals in electron density and electron and ion temperatures at the plasma edge and persisted for the duration of the applied neutral beam power. The HFS pellet's penetration and deposition profiles were substantially deeper (up to {rho} {approx} 0.2) than that of the LFS pellet (up to {rho} {approx} 0.7). However, since both HFS and LFS pellets produced H-mode transitions, this implies that pellet penetration depth is not important the important factor is the large increase in the electron density right at the plasma edge produced by both types of pellets. The values of the edge plasma quantities at the H-mode transition were expressed in the parametric terms described in several theories and models of the H-mode transitions [4-6]. On comparison, the experimentally determined parameters at the H-mode transition were well below those required by several theoretical models. Finally, pellet injection reduced the neutral beam power required to produce the H-mode from 7.3 MW to 4.9 MW in plasmas which had the {del}B drift away from the X-point.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2000},
month = {8}
}

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