Effect of RF heating on DC electric fields in the SOL of TEXTOR

Nieuwenhove, R. Van; Oost, G. Van; Vandenplas, P. E.; Moyer, R. A.; Gray, D.S.; Conn, R.W.

doi:10.1016/0920-3796(90)90085-k

Cited by 22 publications

(6 citation statements)

References 13 publications

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“…The steady E r smoothly connects the force-balanced E r and the RF sheath E r through the separatrix. The sign of the E r reverses near the separatrix, which is qualitatively consistent with the experimental measurements [24]. In the ohmic and ICRF heated discharges of TEXTOR, the radial profile of the DC radial electric field shows a structure that is similar to the solid line.…”

Section: The Physical Results In Shifted-circle Geometrysupporting

confidence: 88%

Calculation of the radial electric field with RF sheath boundary conditions in divertor geometry

Gui

Xia

et al. 2018

Nucl. Fusion

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The equilibrium electric field that results from an imposed DC bias potential, such as that driven by a radio frequency (RF) sheath, is calculated using a new minimal two-field model in the BOUT++ framework. Biasing, using an RF-modified sheath boundary condition, is applied to an axisymmetric limiter, and a thermal sheath boundary is applied to the divertor plates. The penetration of the bias potential into the plasma is studied with a minimal self-consistent model that includes the physics of vorticity (charge balance), ion polarization currents, force balance with , ion diamagnetic flow (ion pressure gradient) and parallel electron charge loss to the thermal and biased sheaths. It is found that a positive radial electric field forms in the scrape-off layer and it smoothly connects across the separatrix to the force-balanced radial electric field in the closed flux surface region. The results are in qualitative agreement with the experiments. Plasma convection related to the net flow in front of the limiter is also obtained from the calculation.

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Section: The Physical Results In Shifted-circle Geometrysupporting

confidence: 88%

Calculation of the radial electric field with RF sheath boundary conditions in divertor geometry

Gui

Xia

et al. 2018

Nucl. Fusion

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“…The main features of the poloidal and radial DC electric fields (Fig. l(a, b)) are consistent with those measured earlier on TEXTOR [14,16]. The measurements have been conducted both inside the LCFS and in the SOL.…”

Section: Resultssupporting

confidence: 87%

“…It is also possible to evaluate the poloidal rotational velocity of the plasma considering the radial DC electric field and the diamagnetic drift contribution estimated from the density and electron temperature profiles assuming Tj = T e [14,16]. However, this determination of the rotational velocity may be misleading because of uncontrolled sheath potential drops caused by secondary emission effects in the probes, although these effects are not strong in graphite [13].…”

Section: Experimental Set-up and Data Analysismentioning

confidence: 99%

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

et al. 1991

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Direct current (DC) driven and turbulence driven cross-field particle fluxes have been deduced from Langmuir probe measurements during discharges with ion cyclotron resonance heating (ICRH) in the TEXTOR tokamak. Spectral analysis of fluctuations of the floating potential at spatially separated probe pins has been used to determine the velocity associated with the poloidal rotation of the boundary plasma. Characteristics of the turbulence spectra of density and potential fluctuations at the edge during ICRH have been measured and compared with the corresponding spectra during standard ohmically heated discharges. It has been observed that both DC driven and turbulence driven fluxes increase significantly during ICRH. The measured high particle fluxes indicate motion in DC convective cells. The DC convective flux and the turbulence driven flux are partly counteracting.

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“…For megawatt power coupling, the rectified potential is generally large (~ kV) and has important consequences. In fusion experiments, rf sheaths cause a variety of deleterious interactions, such as impurity generation, 7 convective transport, [8][9][10] hot spots 11 , 12 and damage to the antenna and surrounding structures, and power dissipation, 13 caused by both the near-field 7 and far-field 14 waves. In many experiments, the heating efficiency with low-k || waves is poor, and sheath power dissipation is a likely candidate to explain this phenomenon.…”

Section: Introductionmentioning

confidence: 99%

A radio-frequency sheath boundary condition and its effect on slow wave propagation

2006

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Predictive modeling of radiofrequency wave propagation in high-power fusion experiments requires accounting for nonlinear losses of wave energy in the plasma edge and at the wall. An important mechanism of "anomalous" power losses is the acceleration of ions into the walls by rf sheath potentials. Previous work computed the "sheath power dissipation" non-self-consistently by post-processing fields obtained as the solution of models which did not retain sheaths. Here, a method is proposed for a self-consistent quantitative calculation of sheath losses by incorporating a sheath boundary condition (SBC) in antenna coupling and wave propagation codes. It obtains the self-consistent sheath potentials and spatial distribution of the time-averaged power loss in the solution for the linear rf fields. It can be applied for ion cyclotron and (in some cases) lower hybrid waves. The use of the SBC is illustrated by applying it to the problem of an electron plasma wave propagating in a waveguide. This model problem is relevant to understanding the low heating efficiency in direct ion-Bernstein wave launch.Implications for calculating sheath voltages driven by fast-wave antennas are also discussed.

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Effect of RF heating on DC electric fields in the SOL of TEXTOR

Cited by 22 publications

References 13 publications

Calculation of the radial electric field with RF sheath boundary conditions in divertor geometry

Calculation of the radial electric field with RF sheath boundary conditions in divertor geometry

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

A radio-frequency sheath boundary condition and its effect on slow wave propagation

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