Effects of ICRH on electrostatic fluctuations and particle transport in the boundary plasma of TEXTOR

Bora, D.; Ivanov, R.S.; Oost, G. Van; Samm, U.

doi:10.1088/0029-5515/31/12/010

Cited by 19 publications

(7 citation statements)

References 18 publications

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“…8 and 9) and increased antenna-plasma interactions. In this regard, it is interesting to recall that an increased DC radial flux was measured by SOL probes during ICRF heating in a different series of experiments on TEXTOR, presumably using screened antennas [24].…”

Section: Summary and Discussionmentioning

confidence: 99%

“…If rf convection is the dominant mechanism, the density depression is accompanied by an increased flux to the antenna (Figs 8 and 9) and increased antenna-edge plasma interactions. In this regard, it is interesting to recall that an increased DC radial flux was measured by SOL probes during ICRF heating in a different series of experiments on TEXTOR, presumably using screened antennas [27].…”

Section: Summary and Discussionmentioning

confidence: 99%

“…This potential is nearly constant along the equilibrium magnetic field but varies rapidly across it. The spatial variation of φ drives rapid E × B convection [12,20,23,24] which increases the flux of plasma to the antenna and thereby enhances the strength of the antenna-plasma interactions. The DC electric fields in the SOL and the convective fluxes have been measured with probes in several experiments (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of RF sheath interactions in TFTR

D’Ippolito¹,

Myra²,

Rogers³

et al. 1998

Nucl. Fusion

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New theoretical and experimental tools are applied to the analysis of ICRF antenna-edge plasma interactions in the Tokamak Fusion Test Reactor (TFTR) tokamak. A new numerical method for computing the three-dimensional rf sheath voltage distribution is used, and the quantitative predictions of rf sheath theory are compared with measurements of the edge density profile obtained by microwave reflectometry and with titanium impurity concentration data. It is shown that the local density depletion at the antenna is consistent with density pump-out by strong E × B convection into the Faraday screen. Modeling of the Faraday screen impurity influx shows that the calculated Ti impurity concentration based on this direct influx agrees with the measured concentration for π phasing. It is also shown that screening of impurity neutrals by ionization in the SOL is a large effect and increases with rf power. At high power over many shots, a fraction of the metal impurities migrates around the machine and is deposited on the limiters, providing a secondary source of titanium. The data shows that the central Ti concentration is strongly dependent on antenna phasing. Possible explanations for this phasing dependence are discussed.

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Section: Summary and Discussionmentioning

confidence: 99%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Analysis of RF sheath interactions in TFTR

D’Ippolito¹,

Myra²,

Rogers³

et al. 1998

Nucl. Fusion

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“…In fusion devices, such as tokamaks, turbulence is found to be responsible for a considerable part of the energy and particle losses in the boundary plasma. [6][7][8][9][10][11] Turbulent particle transport studies are routinely performed using multi-pin probe configurations [11][12][13] and the different pins are used for simultaneous measurements of fluctuating floating potential Ṽ F poloidal and radial electric fields Ẽ , Ẽ r , the local plasma density n, and its fluctuations ñ . The evaluation of turbulence-driven radial particle transport ⌫ r is possible by cross correlating the fluctuating quantities.…”

Section: Introductionmentioning

confidence: 99%

On the harmonic technique to measure electron temperature with high time resolution

Boedo¹,

Gray²,

Conn³

et al. 1999

Review of Scientific Instruments

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A detailed study of the harmonic technique, which exploits the generation of harmonics resulting from excitation of the nonlinearity of the single Langmuir probe characteristic, is presented. The technique is used to measure electron temperature and its fluctuations in tokamak plasmas and the technical issues relevant to extending the technique to high bandwidth ͑200 kHz͒ are discussed. The technique has been implemented in a fast reciprocating probe in the TEXTOR tokamak, gaining the ability to study denser and hotter plasmas than previously possible. A corrected analytical expression is derived for the harmonic currents. Measurement of the probe current by inductive pickup is introduced to improve electrical isolation and bandwidth. The temperature profiles in the boundary plasma of TEXTOR have been measured with high spatial ͑ϳ2 mm͒ and temporal ͑200 kHz͒ resolution and compared to those obtained with a double probe. The exact expansion of the probe characteristic in terms of Bessel functions is compared to a computationally efficient power series. Various aspects of the interpretation of the measurement are discussed such as the influence of plasma potential and density fluctuations. The technique is well suited to study fast phenomena such as transient plasma discharges or turbulence and turbulent transport in plasmas.

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“…[11,12,13,14] Recent theoretical work suggests the sheath can also interact directly with plasma filaments (blobs) and result in increased radial transport. [3,15] This mechanism could perhaps explain the observation from TEXTOR that the SOL density decay length was up to a factor of 4 longer for ICRF heated than neutral beam heated plasmas [16] and similar observations were made on JET. [17] A typical ICRF antenna consists of the current straps housed in an antenna box with a In tokamaks, Faraday screens have become standard plasma facing antenna components despite being an impurity source [5].…”

Section: Introductionmentioning

confidence: 79%

RF plasma edge interactions and their impact on ICRF antenna performance in Alcator C-Mod

Wukitch

Lipschultz

Marmar

et al. 2007

Journal of Nuclear Materials

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In Alcator C-Mod, we have investigated the compatibility of high power ion cyclotron range of frequencies antenna with high performance plasmas and all high-Z plasma facing components, to provide operational information for future devices such as ITER.Boronization appears to be critical achieving low radiated power plasmas and is eroded rapidly such that the best performance is lost when the integrated injected RF energy reaches ~50 MJ. Since Ohmic H-modes with similar integrated input energy show a significantly slower degradation, an RF erosion mechanism is playing a significant role. RF-enhanced sheaths on flux tubes connected from the antennas to the top of the outer divertor are the most likely erosion mechanism. Antenna operation without a Faraday screen was found to degrade antenna performance through increased impurity sources. ______________________________________________

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Effects of ICRH on electrostatic fluctuations and particle transport in the boundary plasma of TEXTOR

Cited by 19 publications

References 18 publications

Analysis of RF sheath interactions in TFTR

Analysis of RF sheath interactions in TFTR

On the harmonic technique to measure electron temperature with high time resolution

RF plasma edge interactions and their impact on ICRF antenna performance in Alcator C-Mod

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