Local scrape-off layer control using biased electrodes in NSTX

Zweben, S. J.; Maqueda, R. J.; Roquemore, A. L.; Bush, C. E.; Kaita, R.; Marsala, R.; Raitses, Yevgeny; Cohen, R. H.; Ryutov, D. D.

doi:10.1088/0741-3335/51/10/105012

Cited by 24 publications

(26 citation statements)

References 34 publications

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“…We also assume that the He neutral density is not fluctuating on the space-time scale of the turbulence, although there could be some shadowing effect due to the turbulence itself [45]. On the other hand, there is good evidence that the GPI turbulence signals in the SOL correlate well with Langmuir probe turbulence signals when measured on the same field line, for example in C-Mod [19] and NSTX [53], and TPE-RX [54].…”

Section: G Limitations and Uncertaintiesmentioning

confidence: 99%

Comparison of edge turbulence imaging at two different poloidal locations in the scrape-off layer of Alcator C-Mod

et al. 2013

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This paper describes 2-D imaging measurements of plasma turbulence made in the scrape-off layer of the Alcator C-Mod tokamak simultaneously at two different poloidal locations, one near the outer midplane and the other near the divertor X-point region. These images were made with radial and poloidal resolution using two gas puff imaging (GPI) diagnostics, which were not directly connected along a B field line. The turbulence correlation structure has a significantly different tilt angle with respect to the local flux surfaces for the midplane and X-regions, and a slightly different ellipticity and size. The time-averaged turbulence velocities can be different in the midplane and Xregions, even within the same flux surface in the same shot, and in most cases the fluctuations in poloidal velocity in these two regions were not correlated. These structures are partially consistent with a magnetic flux tube mapping model, and the velocities are compared with various poloidal flow models.2

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Section: G Limitations and Uncertaintiesmentioning

confidence: 99%

Comparison of edge turbulence imaging at two different poloidal locations in the scrape-off layer of Alcator C-Mod

et al. 2013

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“…Time-independent biasing is used in plasma experiments for different purposes, namely for the measure of the ion and electron temperatures with electrostatic probes, 2,3 in plasma thrusters for space propulsion, 4 to study the effect of shear flow on turbulence, [6][7][8][9] for the study of dust particles, 5 and for the control of turbulence in magnetic fusion devices. [10][11][12] A bias may induce local perturbations of the plasma potential. Electric fields are then produced and can give rise to plasma currents, which may close at the sheath.…”

Section: Introductionmentioning

confidence: 99%

Potential of a plasma bound between two biased walls

et al. 2012

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An analytical study is presented for an one-dimensional, steady-state plasma bound between two perfectly absorbing walls that are biased with respect to each other. Starting from a description of the plasma sheaths formed at both walls, an expression relating the bulk plasma potential to the wall currents is derived, showing that the plasma potential undergoes an abrupt transition when currents cross a critical value. This result is confirmed by numerical simulations performed with a particle-in-cell code.

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“…15 In the MAST experiments, on the contrary, this factor was % 1. 13 This was expected, however, as the ratio of grounded to biased surfaces was at most equal to 3 (taking into account grounded ribs of both the upper and the lower divertors).…”

Section: A 1d Versus 2dmentioning

confidence: 86%

“…14 In NSTX, an array of four electrodes was installed in the SOL. 15 Experiments were performed in a wide range of regimes. Strong local effects on the SOL profiles were measured and clear evidence of convective cell formation could be inferred.…”

Section: Introductionmentioning

confidence: 99%

Properties of convective cells generated in magnetized toroidal plasmas

et al. 2012

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Parallel resistivity and ohmic heating of laboratory dipole plasmas Phys. Plasmas 19, 082509 (2012) Influence of charging process and size distribution of dust grain on the electric conductivity of dusty plasma Phys. Plasmas 19, 083703 (2012) Stationary electron velocity distribution function in crossed electric and magnetic fields with collisions Phys. Plasmas 19, 083503 (2012) Measurements of parallel electron velocity distributions using whistler wave absorption Rev. Sci. Instrum. 83, 083503 (2012) Additional information on Phys. Plasmas Convective cells for turbulence control, generated by means of biased electrodes, are investigated in the simple magnetized toroidal plasmas of TORPEX. A two-dimensional array of 24 electrodes is installed on a metal limiter to test different biasing schemes. This allows influencing significantly both radial and vertical blob velocities. It is shown that these changes agree quantitatively with the flows deduced from the time averaged potential perturbations induced by the biasing. Detailed measurements along and across the magnetic field provide a rather clear picture of the effect of biasing on time averaged profiles. The biased electrodes produce perturbations of the plasma potential and density profiles that are fairly uniform along the magnetic field. Background flows influence the location where potential variations are induced. The magnitude of the achievable potential variations in the plasma is strongly limited by cross-field currents and saturates at large bias voltages once the electrodes draw electron saturation current. A quantitative discussion on the origin of cross-field currents is presented, considering contributions related with diamagnetic drifts, ion inertia, collisions with neutrals, and viscosity.

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Local scrape-off layer control using biased electrodes in NSTX

Cited by 24 publications

References 34 publications

Comparison of edge turbulence imaging at two different poloidal locations in the scrape-off layer of Alcator C-Mod

Comparison of edge turbulence imaging at two different poloidal locations in the scrape-off layer of Alcator C-Mod

Potential of a plasma bound between two biased walls

Properties of convective cells generated in magnetized toroidal plasmas

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