Plasma-surface interactions in tokamaks

McCracken, G.M.; Stott, P.E.

doi:10.1088/0029-5515/19/7/004

Cited by 487 publications

(157 citation statements)

References 130 publications

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“…For example, ions may recombine or undergo charge-exchange collisions at the wall; they may adsorb to or be absorbed by the wall; and they may reflect or sputter impurities and wall material. 38 These processes have been studied for noble gases as well. For the case of argon, it is well-known that Ar readily forms monolayers on a number of surface materials, including graphite, 39 platinum, 40 rubidium, 41 potassium, 42 and cesium.…”

Section: Ion Recyclingmentioning

confidence: 99%

Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves

1998

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Large-amplitude drift wave fluctuations are observed to cause severe ion temperature oscillations in plasmas of the Caltech Encore tokamak ͓J. M. McChesney, P. M. Bellan, and R. A. Stern, Phys. Fluids B 3, 3370 ͑1991͔͒. Experimental investigations of the complete ion dynamical behavior in these waves are presented. The wave electric field excites stochastic ion orbits in the plane normal (Ќ) to B, resulting in rapid Ќ heating. Ion-ion collisions impart energy along ( ʈ ) B, relaxing the Ќ-ʈ temperature anisotropy. Hot ions with large orbit radii escape confinement, reaching the chamber wall and cooling the distribution. Cold ions from the plasma edge convect back into the plasma ͑i.e., recycle͒, causing further cooling and significantly replenishing the density depleted by orbit losses. The ion-ion collision period ii ϳT 3/2 /n fluctuates strongly with the drift wave phase, due to intense (Ϸ50%͒ fluctuations in n and T. Evidence for particle recycling is given by observations of bimodal ion velocity distributions near the plasma edge, indicating the presence of cold ions ͑0.4 eV͒ superposed atop the hot ͑4-8 eV͒ plasma background. These appear periodically, synchronous with the drift wave phase at which ion fluid flow from the wall toward the plasma center peaks. Evidence is presented that such a periodic heat/loss/recycle/cool process is expected in plasmas with strong stochastic heating.

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Section: Ion Recyclingmentioning

confidence: 99%

Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves

1998

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“…Table 1 summarizes typical operating parameters of the Alcator C tokamak device. Major experiments carried out on Alcator C include RF heating and current drivel 5 ' 1 6 , pellet injection' 7 18, impurity injection and transport analysis' 8 " 9 . The utilization of Bitter-type magnets enables Alcator C to operate at high field and high density.…”

Section: Manos and Mccrackens And Cohenmentioning

confidence: 99%

“…Those measurements can be used to predict material damage due to plasma-surface interaction processes such as evaporation and physical sputtering from surfaces within the vacuum vessel'' 7 . The evaluation of surface material integrity is important from the point of view of plasma purity and vessel lifetime.…”

Section: Introductionmentioning

confidence: 99%

Janus, a bidirectional, multifunctional plasma diagnostic

Wan

Yang

Lipschultz

et al. 1986

Review of Scientific Instruments

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Janus is a multiple function edge probe used to diagnose the Alcator C limiter shadow plasma whose components include two sets of identical diagnostics; each set facing a different direction. Included within each set of diagnostics are a retarding-field energy analyzer (RFEA), Langmuir probe, and calorimeter. Janus is constructed to make measurements both parallel and antiparallel to a magnetic field. It can withstand high heat fluxes and can be scanned perpendicular to the magnetic field in the limiter shadow. The RFEA can alternatively sample both the ion and electron parallel energy distribution functions during a tokamak discharge. From the Langmuir probe, one can infer electon temperature, density, and the plasma floating potential. The calorimeter independently detects the total parallel heat flux incident on an electrically floating plate. Together these three diagnostics enable detailed, localized edge plasma studies on Alcator C. This paper presents the design considerations for each of the diagnostics along with a brief summary of the analysis techniques. Some experimental results obtained using Janus will also be presented.

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“…The nonlinear relationship between T e (oc sheath potential), T,, and sputtering rate [16], imply a much greater increase in the sput The time behavior of the injected rf power correlates strongly with ion temperature and impurity brightness time histories. When, the rf power is constant, the edge ion temperature and the impurity source rate are constant.…”

Section: Effects Of the Icrf Fast Wave Injection Upon Impuritiesmentioning

confidence: 99%

The effect of ICRF on the Alcator C scrape-off layer plasma

Wan

Lipschultz

McDermott

et al. 1989

Journal of Nuclear Materials

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This paper presents a characterization of the Alcator C Scrape-Off Layer (SOL) plasma during ICRF hydrogen-minority fast wave heating experiments. The SOL plasma parameters were measured using a multifunctional probe, JANUS, which is capable of simultaneously measuring the ion and electron parameters both parallel and nntiparaUel with respect to the toroidal magnetic field. The probe data indicate, at low value of injected rf power, there is direct edge heating and density increases at radii greater than that of the antenna Faraday shield. Increasing the injected rf power spreads both the temperature and density increases throughout the edge region, flattening the radial profile:.. Varying the position of the resonance layer in the main plasma does not significantly change the effect of ICRF on the SOL parameters. Given this single spatial point characterization of the SOL. a crude estimate of power flow into and through the edge plasma indicate that ss20% of the ICRF power launched from the antenna is absorbed directly in the SOL plasma.Additional observation of the impurity source rates confirms the conclusions of an earlier paper, which attributed increasing central densities of high-Z impurities to the increase in physical sputtering rate at both the ICRF antenna's Faraday shield and the limiter surface.

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Plasma-surface interactions in tokamaks

Cited by 487 publications

References 130 publications

Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves

Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves

Janus, a bidirectional, multifunctional plasma diagnostic

The effect of ICRF on the Alcator C scrape-off layer plasma

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