Observation of cold, high-density plasma near the Doublet III limiter

Baker, D. R.; Snider, R. T.; Nagami, M.

doi:10.1088/0029-5515/22/6/008

Cited by 88 publications

(66 citation statements)

References 8 publications

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“…First reported on the Alcator C, ASDEX, Doublet III and FTU tokamaks, a MARFE is a toroidally symmetric, poloidally localized, strongly radiating region of high density and low temperature, typically seen on the high field side of a tokamak [62][63][64][65]34]. The original observations were on limited machines, [66] however similar phenomena have been observed on divertor experiments as well [67,46,47].…”

Section: Marfesmentioning

confidence: 94%

Density limits in toroidal plasmas

Greenwald

2002

Plasma Phys. Control. Fusion

467

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: Marfesmentioning

confidence: 94%

Density limits in toroidal plasmas

Greenwald

2002

Plasma Phys. Control. Fusion

467

477

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“…In limiter tokamaks, this ''wall'' MARFE normally leads to the density limit. [8][9][10][11] Recently, the wall MARFE was also observed in the divertor configuration in Joint European Torus ͑JET͒, where it occurs after the X-point MARFE and ultimately determines the maximum density in L-mode deuterium plasmas. 12 As demonstrated earlier, 7 unstable perturbations leading to the wall MARFE have their largest amplitude on the HFS.…”

Section: Introductionmentioning

confidence: 99%

The role of plasma–wall interactions in thermal instabilities at the tokamak edge

Tokar

Kelly

2003

Physics of Plasmas

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Plasma-wall interaction leads to the release of impurities and neutrals of the working gas, which contribute significantly to the energy losses from the plasma edge, and therefore, crucially affects the development of thermal instabilities in fusion devices. An analytical model for impurity radiation is proposed, which takes into account the erosion mechanisms of wall material and the motion of impurity particles across magnetic surfaces. The temperature dependence of radiation losses is found to be very different from that predicted by the coronal approximation often used in considering thermal instabilities. The consequences for the development of poloidally symmetric detachment and multi-faceted asymmetric radiation from the edge ͑MARFE͒ are analyzed. It is demonstrated that the MARFE threshold principally depends on the mechanism by which working gas neutrals are released from the wall and on the neutral's properties, e.g., their ionization rate.

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“…The poloidal location of the MARFE at the high-field edge and its radial extent reaching to closed flux surfaces has been seen as evidence for poloidally asymmetric transport of power across flux surfaces in the core plasma [1,4]. All of the above characteristics have led to the study of MARFEs both experimentally [1][2][3][5][6][7][8][9] and theoretically [10][11][12][13][14][15][16][17][18]. The modelling of the MARFE as an impurity radiation-condensation instability is fairly well accepted.…”

mentioning

confidence: 99%

Ultrahigh Densities and Volume Recombination inside the Separatrix of the Alcator C-Mod Tokamak

et al. 1998

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MARFEs are experimentally studied using spectroscopic techniques to determine their internal characteristics. We find the local density and temperature in the MARFE to be 2-3x10 21 m -3 and 0.7-1.0 eV respectively. The volume recombination rate is also large in the MARFE, 5-10x10 22 s -1 , similar in magnitude to the plasma source rate in the core. Because this plasma sink is located in confined regions of the plasma, the MARFE acts like a limiter; ions 'recycle' from the MARFE as neutrals. These characteristics have not been predicted by current models.

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Observation of cold, high-density plasma near the Doublet III limiter

Cited by 88 publications

References 8 publications

Density limits in toroidal plasmas

Density limits in toroidal plasmas

The role of plasma–wall interactions in thermal instabilities at the tokamak edge

Ultrahigh Densities and Volume Recombination inside the Separatrix of the Alcator C-Mod Tokamak

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