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24. Tunnel probes for measurements of the electron and ion temperature in fusion plasmas

Author

Gunn, J, Schrittwieser, R, Balan, P, Ionita, C, Stockel, J, Adamek, J, Duran, I, Hron, M, Panek, R, Barina, O, Hrach, R, Vicher, M, Van Oost, G, Van Rompuy, T, Martines, E, Gunn JP, Schrittwieser R, Balan P, Ionita C, Stockel J, Adamek J, Duran I, Hron M, Panek R, Barina O, Hrach R, Vicher M, Van Oost G, Van Rompuy T, Martines E, Gunn, J, Schrittwieser, R, Balan, P, Ionita, C, Stockel, J, Adamek, J, Duran, I, Hron, M, Panek, R, Barina, O, Hrach, R, Vicher, M, Van Oost, G, Van Rompuy, T, Martines, E, Gunn JP, Schrittwieser R, Balan P, Ionita C, Stockel J, Adamek J, Duran I, Hron M, Panek R, Barina O, Hrach R, Vicher M, Van Oost G, Van Rompuy T, and Martines E

Abstract

We have developed tunnel probes for localized measurements of the electron and ion temperature in the edge plasma region of smaller tokamaks and stellarators. A normal tunnel probe for Te measurements consists of a metallic tunnel of 5 mm diameter and 5 mm length, with the axis parallel to the magnetic field. One side is open, the other side is closed by a metallic backplate, isolated from the tunnel. If both electrodes are biased negatively, ions flow into the office, and their current is distributed between the tunnel and the backplate. The ratio of the two ion currents is a function of T e. With an additional diaphragm in front of the orifice, the probe becomes ion sensitive, since the electrons are prevented from the tunnel because of their smaller gyroradius, but ions can still reach it. In this way, the perpendicular ion temperature can be derived. By segmenting the tunnel axially into two parts, also an approximate measure for the parallel ion temperature can be found.

Published
2004

25. Measurements of the parallel and perpendicular ion temperatures by means of an ion-sensitive segmented tunnel probe

Author

Balan, P, Schrittwieser, R, Adamek, J, Barina, O, De Beule, P, Duran, I, Gunn, J, Hrach, R, Hron, M, Lonita, C, Martines, E, Panek, R, Stockel, J, Van Den Berge, G, Van Oost, G, Van Rompuy, T, Vicher, M, Balan P, Schrittwieser R, Adamek J, Barina O, De Beule P, Duran I, Gunn JP, Hrach R, Hron M, Lonita C, Martines E, Panek R, Stockel J, Van Den Berge G, Van Oost G, Van Rompuy T, Vicher M, Balan, P, Schrittwieser, R, Adamek, J, Barina, O, De Beule, P, Duran, I, Gunn, J, Hrach, R, Hron, M, Lonita, C, Martines, E, Panek, R, Stockel, J, Van Den Berge, G, Van Oost, G, Van Rompuy, T, Vicher, M, Balan P, Schrittwieser R, Adamek J, Barina O, De Beule P, Duran I, Gunn JP, Hrach R, Hron M, Lonita C, Martines E, Panek R, Stockel J, Van Den Berge G, Van Oost G, Van Rompuy T, and Vicher M

Abstract

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.

Published
2004

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