Plasma density behavior in the Hefei tokamak-7

Gao, Xiang; Jie, Yinxian; Yang, Yu; Xia, Chengyi; Wei, M. S.; Zhang, S. Y.; Cheng, Y. F.; Hu, Liqun; Mao, Jiangyu; Tong, X. D.; Wan, Baonian; Guang-li, Kuang; Li, J. G.; Zhao, Yanping; Luo, Junhua; Qiu, Ning; Yang, Kun; Li, G.; Xie, Jinbo; Wan, Y. X.

doi:10.1063/1.874144

Cited by 29 publications

(15 citation statements)

References 15 publications

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“…While the impurity content, as measured by Z EFF , usually drops with density [52], overall radiation, which scales as n e n Z , usually increases. Improvements in wall conditioning which leads to lower levels of impurities have also allowed operation at higher densities [22,[6][7][8][9][10][11][12][13][14][15] at least up to a point. It is notable however, that experiments where Z EFF is reduced below 2-2.5 don't see a further increase in the limit [3,53].…”

Section: General Observationsmentioning

confidence: 99%

“…The first is to find operational scenarios which maximize the density, particularly the central density, and second, to investigate the physics which underlies the limit. Techniques for wall conditioning [6][7][8][9][10][11][12][13][14][15] have been developed which enable operation at higher densities. Methods such as central fueling or edge pumping which can lead to peaked density profiles have allowed operation at higher average and peak density as described below in sections 2.2.3 and 2.2.6.…”

Section: Motivationmentioning

confidence: 99%

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Density limits in toroidal plasmas

Greenwald

2002

Plasma Phys. Control. Fusion

458

477

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In addition to the operational limits imposed by MHD stability on plasma current and pressure, an independent limit on plasma density is observed in confined toroidal plasmas. This review attempts to summarize recent work on the phenomenology and physics of the density limit. Perhaps the most surprising result is that all of the toroidal confinement devices considered operate in similar ranges of (suitably normalized) densities. The empirical scalings derived independently for tokamaks and reversed field pinches (RFP) are essentially identical, while stellarators appear to operate at somewhat higher densities with a different scaling. Dedicated density limit experiments have not been carried out for spheromaks and field-reversed configurations (FRC), however "optimized" discharges in these devices are also well characterized by the same empirical law. In tokamaks, where the most extensive studies have been conducted, there is strong evidence linking the limit to physics near the plasma boundary thus it is possible to extend the operational range for line-averaged density by operating with peaked density profiles. Additional particles in the plasma core apparently have no effect on density limit physics. While there is no widely accepted, first principles model for the density limit, research in this area has focussed on mechanisms which lead to strong edge cooling. Theoretical work has concentrated on the consequences of increased impurity radiation which may dominate power balance at high densities and low temperatures. These theories are not entirely satisfactory as they require assumptions about edge transport and make predictions for power and impurity scaling that may not be consistent with experimental results. A separate thread of research looks for the cause in collisionality enhanced turbulent transport. While there is experimental and theoretical support for this approach, understanding of the underlying mechanisms is only at a rudimentary stage and no predictive capability is yet available..

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Section: General Observationsmentioning

confidence: 99%

Section: Motivationmentioning

confidence: 99%

Density limits in toroidal plasmas

Greenwald

2002

Plasma Phys. Control. Fusion

458

477

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“…The HT-7 is a superconducting device [4], which was rebuilt from the original Russian T-7 tokamak in 1994. It has a major radius R = 1.22 m and a minor radius a = 0.27 m in the circular cross-section.…”

Section: Experimental Set-upmentioning

confidence: 99%

“…DIII-D was operated successfully with an all-graphite wall, dramatically reducing metal impurity accumulations without increasing the influx of low-Z impurities. The Hefei tokamak-7 (HT-7) is a superconducting tokamak [4] with the limiter configuration designed to operate with a high power and a long duration discharge. The last closed flux surface was defined by the main poloidal limiter in 1999, which receives the highest heat loads and largest flux of high-energy particle bombardment from the plasma.…”

Section: Introductionmentioning

confidence: 99%

Study of the operational region with new graphite limiters in the Hefei tokamak-7

Asif

team²

2006

Plasma Devices and Operations

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A new set of actively cooled toroidal double-ring graphite limiters has been developed in the Hefei tokamak-7 for long pulse operation. The extension of the operational region and the density behaviour with graphite limiters have been studied in this paper. An extended high-density region at high plasma currents and low q a was obtained. The density profile with graphite limiters was studied in order to compare the results with those of the previous molybdenum limiters.

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“…The graphite-based first wall components have been designed and tested to sustain particle and heat exhausts under steady-state conditions in Tore Supra. HT-7 is a superconducting tokamak [1] with the limiter configuration designed to operate with high power and long duration discharge. In past operations with the Mo limiter, due to energetic particles bombardment and overheating problem, the plasma discharge was usually terminated by the very strong hard X-ray radiation, hot spot and high-Z impurities.…”

Section: Introductionmentioning

confidence: 99%