Turbulent transport reduction by<i>E</i> <i>B</i>velocity shear during edge plasma biasing: recent experimental results

Oost, G. Van; mek, J. Ad; Antoni, V.; Balan, P.; Boedo, J.A.; Devynck, P.; uran, I.; Eliseev, L.G.; Gunn, J.; Hron, M.; Ioniţă, C.; Jachmich, S.; Kirnev, G.; Martines, E.; Melnikov, A. V.; Schrittwieser, R.; Silva, Carlos; ckel, J. St; Tendler, M.; Varandas, C.; Schoor, M. Van; Vershkov, V.A.; Weynants, R.

doi:10.1088/0741-3335/45/5/308

Cited by 136 publications

(35 citation statements)

References 52 publications

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“…Subsequently, many experiments have used external bias to study modification of the plasma turbulence and transport. [5][6][7][8] Recent experiments [8][9][10] in the upgraded Large Plasma Device 11 (LAPD) at the University of California, Los Angeles (UCLA) have studied the effect of the sheared flow on the edge turbulence and turbulent transport by biasing a section of the vacuum chamber wall. Linear and nonlinear simulations to model the plasma instabilities based on LAPD parameters are also developed.…”

Section: Introductionmentioning

confidence: 99%

Sheared-flow induced confinement transition in a linear magnetized plasma

et al. 2012

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A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875(1991]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (dn=n $ ed/=kT e $ 0:5) are observed at the plasma edge, accompanied by a large density gradient (L n ¼ jr ln nj À1 $ 2 cm) and shearing rate (c $ 300 kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (V bias ) on the obstacle and the axial magnetic field (B z ) strength. In cases with low V bias and large B z , improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E Â B drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller B z , large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m ¼ 1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.

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Section: Introductionmentioning

confidence: 99%

Sheared-flow induced confinement transition in a linear magnetized plasma

et al. 2012

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“…The predicted ion loss currents were in the range ≈15-150 Amps, which is comparable to the currents used to create H-modes in the electrode biasing experiments [6,7]. However, there are many limitations, uncertainties and omissions in the modeling, as described in the next section.…”

Section: Icrh Modelingmentioning

confidence: 64%

“…Edge electrode biasing experiments have certainly shown that an externally imposed radial current of ≈20-200 A can create an H-mode-like transport barrier [6,7], and a clear correlation has been shown between edge potential changes and the L-H transition [8]. Thus it would be useful if some non-intrusive means could be found to control ion loss to the wall and thereby control the H-mode transition.…”

Section: Introductionmentioning

confidence: 99%

Edge Minority Heating Experiment in Alcator C-Mod

Zweben¹,

Terry²,

Bonoli³

et al. 2005

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An attempt was made to control global plasma confinement in the Alcator C-Mod tokamak by applying ICRH heating power to the plasma edge in order to deliberately create a minority ion tail loss. In theory, an edge fast ion loss could modify the edge electric field and so stabilize the edge turbulence, which might then reduce the H-mode power threshold or improve the H-mode barrier. However, the experimental result was that edge minority heating resulted in no improvement in the edge plasma parameters or global stored energy, at least at power levels of P RF ≤ 5.5 MW. A preliminary analysis of these results is presented and some ideas for improvement are discussed.

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“…2 have been registered at a radial position of r p = 79 mm, the Katsumata tunnel is oriented upstream to the toroidal plasma current. During a part of the flat top phase of the discharge, an additional electrode, inserted radially at r E = 60 mm near the position of the last-closed flux surface (LCFS) was biased to a voltage of +100 V. A more detailed description of the biasing experiment on CASTOR can be found in [8]. Fig.…”

Section: Segm1 Segm2mentioning

confidence: 99%

Measurements of the Parallel and Perpendicular Ion Temperatures by Means of an Ion‐sensitive Segmented Tunnel Probe

Balan

Schrittwieser

Adámek

et al. 2004

Contrib. Plasma Phys.

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Localised ion temperature measurements can only be performed with special electric probes where the electron component of the current is kept off from the collector. In a strong magnetic field the effect can be utilised that the electron gyro-radius is much smaller than that of the ions. This method was developed by Katsumata and Okazaki (Japan J. Appl. Phys. 6, 123 (1967)). We have used a so-called tunnel probe (which consists of a conductive tunnel, terminated by an isolated back plate) by adding a diaphragm in front. Thereby the tunnel is prevented from incident electrons at any potential of both electrodes. By sweeping the potential across the tunnel, the perpendicular ion temperature can be inferred. By segmenting the tunnel axially in two parts also the parallel ion temperature can be determined. When the electrodes are biased to ion saturation, the ratio between the ion currents, which reach the first and the second segment, respectively, is a measure for the parallel ion temperature. The dependence of the ratio of the currents has to be determined by a PIC simulation.

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Turbulent transport reduction byE Bvelocity shear during edge plasma biasing: recent experimental results

Cited by 136 publications

References 52 publications

Sheared-flow induced confinement transition in a linear magnetized plasma

Sheared-flow induced confinement transition in a linear magnetized plasma

Edge Minority Heating Experiment in Alcator C-Mod

Measurements of the Parallel and Perpendicular Ion Temperatures by Means of an Ion‐sensitive Segmented Tunnel Probe

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