High power ICRF heating on the divertor tokamak ASDEX

Steinmetz, K.; Fußmann, G.; Gruber, O.; Niedermeyer, H.; Müller, E.; Ryter, F.; Wagner, F.; Wesner, F.; Braun, F.; Hofmeister, F.; Noterdaeme, J.‐M.; Puri, S.; Söll, M.; Wedler, H.; Bartiromo, R.; Becker, G.; Bosch, H.‐S.; Brocken, H.; Eberhagen, A.; Gehre, O.; Gernhardt, J.; Gierke, G. von; Giuliana, A.; Glock, E.; Haas, G.; Janeschitz, G.; Karger, F.; Keilhacker, M.; Kislyakov, A.; Klüber, O.; Kornherr, M.; Kotzé, P. B.; Lenoci, M.; Lisitano, G.; Mayer, H. M.; McCormick, K.; Meisel, D.; Mertens, V.; Mürmann, H.; Poschenrieder, W.; Rapp, H.; Roth, J.; Schneider, F.; Siller, G.; Smeulders, P.; Söldner, F. X.; Steuer, K.-H.; Vlases, G.; Zasche, D.; Speth, E.; Vollmer, O.

doi:10.1088/0741-3335/28/1a/020

Cited by 17 publications

(21 citation statements)

References 2 publications

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“…Tests with a movable steel plate indicated that metal erosion in the scrape-off layer was due to sputtering by ions, perhaps involving a postulated suprathermal component. Before the carbonization, the TEXTOR edge plasma and scrape-off layer were strongly perturbed by the ICRF pulse, and impurity problems limited the RF pulse to 200 kW for 100 ms. A similar success in using wall carbonization to overcome enhanced impurity levels during ICRF heating was also recently reported at the diverted tokamak ASDEX (2.3 MW, 1 s ICRF) [7].…”

Section: Discussionsupporting

confidence: 66%

“…As discussed below, early ICRF experiments on tokamaks were often plagued by large metallic impurity influxes which severely limited the amount of RF power delivered to the plasma and the temperature increases obtained. Although in several recent experiments [2][3][4][5][6][7] this problem has been studied and, to some extent, overcome, there is no clear consensus as to the principal source of metal impurities or the dominant mechanism for their release. Impurity generation during ICRF heating involves the complex interactions between the scrape-off layer plasma, the RF fields, and the materials exposed to the scrape-off layer [8], namely the limiter, the walls and the ICRF antenna structure, which must be near the plasma to ensure good coupling.…”

Section: Introductionmentioning

confidence: 99%

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Impurity generation during ICRF heating experiments on Alcator C

et al. 1986

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Observations of impurity behavior are presented from ICRF heating experiments at 180 MHz performed over a variety of conditions on the Alcator C tokamak, using graphite limiters and stainless steel antenna Faraday shields. Spectroscopic observations revealed significant increases in metal impurity concentrations during the RF pulse, with iron levels increasing by as much as a factor of 12 at the highest RF powers (-350-400 kW). Analysis of the inferred iron source rates shows an approximately linear dependence on RF power up to 400 kW. with no clear dependence on resonance conditions or bulk plasma parameters.However, a sharp increase in the temperature in the limiter shadow region was observed during the ICRF pulse, which was well correlated with the iron influx rate. It is concluded from this and other evidence that physical sputtering of the Faraday shield due to an elevated sheath potential is the primary source of metal impurities during ICRF heating on Alcator C. The same process, occurring at the graphite limiter, is believed to be the dominant source of carbon and oxygen. Calculated sputtering yields obtained from an edge erosion code demonstrate the plausibility of this model.

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Section: Discussionsupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Impurity generation during ICRF heating experiments on Alcator C

et al. 1986

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“…Measurements were performed during ICRF heating of an Ohmic plasma or of a plasma preheated by NI(H°-*H + ,D + ,Eo=40keV,P N i=0.8-3.5MW)inthe double null divertor mode of the ASDEX tokamak [11,12]. The ICRF heating schemes were hydrogen minority heating (D(H), 33.5 MHz, n H /n e * 5%) and hydrogen second harmonic heating (2 COQH, 67 MHz) in pure hydrogen plasmas or hydrogen-deuterium mixtures (n H /(n H + n D ) = 25-100%).…”

Section: Resultsmentioning

confidence: 99%

Parametric decay in the edge plasma of ASDEX during fast wave heating in the ion cyclotron frequency range

et al. 1988

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Two types of parametric decay instabilities were observed in the scrape-off layer of ASDEX during hydrogen second harmonic heating, in a single as well as in a two ion species plasma. The first type was identified as decay into an ion Bernstein wave and an ion cyclotron quasi-mode, and the second as decay into an ion Bernstein wave and a low frequency electron quasi-mode. The parametric decay processes are due to the high electric fields near the fast wave antennas. Theoretical growth rate calculations predict a threshold for the electric fields near the antennas. In the relevant experiments the electric fields, estimated from a full-wave code, indeed exceeded the thresholds. These parametric decay processes, as well as the harmonics of the generator frequency also seen in the scrape-off layer, provide a mechanism that might contribute to the observed direct energy deposition in the edge plasma and to ICRF induced impurity production.

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“…Second harmonic heating in a one-component plasma has been investigated experimentally on PLT, JFT-2M and ASDEX [27][28][29], with the aim of studying the absorption of the magnetosonic wave near the second harmonic of the ion species. It was shown that the net ICR effect was to produce an anisotropic ion tail in the direction perpendicular to the magnetic field.…”

Section: Appendix Slow Wave Absorption At the Impurity Ion Second Har...mentioning

confidence: 99%

Influence of partially stripped impurity ions on the cyclotron absorption of the fast magnetosonic wave in TFR plasmas

1986

Nucl. Fusion

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Injection of vanadium ions by the laser blowoff technique has permitted the impurity content in TFR plasmas to be modified purposely before ion cyclotron resonance (ICR) heating experiments in the mode conversion regime. The initial rate of increase in the central deuteron temperature T D (0) has thus been enhanced. By solving the wave propagation equation in the WKB approximation, it has been possible to account for the enhanced dT D (0)/dt value by wave energy deposition on resonating V 21+ ions, provided a fraction (of the order of 10%) of these ions has been accelerated to the tens of keV range. Previous experimental ICR heating results, in conditions such that the proton cyclotron layer is outside the limiter radius, can be explained by similar resonance processes on intrinsic metal impurity ions.

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High power ICRF heating on the divertor tokamak ASDEX

Cited by 17 publications

References 2 publications

Impurity generation during ICRF heating experiments on Alcator C

Impurity generation during ICRF heating experiments on Alcator C

Parametric decay in the edge plasma of ASDEX during fast wave heating in the ion cyclotron frequency range

Influence of partially stripped impurity ions on the cyclotron absorption of the fast magnetosonic wave in TFR plasmas

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