Formation of convective cells during scrape-off layer biasing in the CASTOR tokamak

Abstract

We describe experiments with a biased electrode inserted into the scrape-off layer (SOL) of the CASTOR tokamak. The resulting radial and poloidal electric field and plasma density modification are measured by means of Langmuir probe arrays with high temporal and spatial resolutions. Poloidally and radially localized stationary structures of the electric field (convective cells) are identified and a related significant modification of the particle transport in the SOL is observed.

Control of test particle transport in a turbulent electrostatic model of the Scrape-Off-Layer

“…Several experiments [1,2] have been dedicated to the control of turbulence in magnetized plasmas. Although a modelling of some of the experiments has been achieved, there was to date no theoretical backing for such a procedure.…”

Local Effects of Biased Electrodes in the Divertor of NSTX

“…Therefore we can not assume a simple linear relationship between the LiI light level and the local electron density, and so use the LiI light only as a qualitative indication of where in space and time the electrodes were changing the local plasma. Figure 3 shows the way in which the electrode biasing was applied for [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] successive modulations cycles during the plasma current flat-top period for each shot in the database. Each modulation cycle consisted of 10 msec with the biasing on followed by 10 msec with the biasing off.…”

“…Evidence for convective cell formation induced by non-axisymmetric biased electrodes was previously obtained in JFT-2M [11], CASTOR [15], and MAST [18]. A prior experiment on NSTX also evaluated the effects of a pair of small biased electrodes inserted into the SOL just below the outer midplane limiter [19].…”

“…[6][7][8][9][10][11][12][13][14][15][16][17]. However, most of these aimed to create axisymmetric radial or poloidal electric fields in the plasma edge using electrodes or large-area wall biasing to control the edge plasma transport.…”

Properties of convective cells generated in magnetized toroidal plasmas

“…In CASTOR, an electrode was immersed in the SOL, leading to the formation of convective cells around the biased flux tube. 14 In NSTX, an array of four electrodes was installed in the SOL. 15 Experiments were performed in a wide range of regimes.…”