Diagnostics for the Biased Electrode Experiment on NSTX
Authors: A.L. Roquemore, S.J. Zweben, C.E. Bush, R. Kaita, R. J. Marsalsa, and R.J. Maqueda
Abstract:
A linear array of four small biased electrodes was installed in NSTX in an attempt to control the width of the scrape-off layer (SOL) by creating a strong local poloidal electric field. The set of electrodes were separated poloidally by a 1 cm gap between electrodes and were located slightly below the midplane of NSTX, 1 cm behind the RF antenna and oriented so that each electrode is facing approximately normal to the magnetic field. Each electrode can be independently biased to ±100 volts. Present power supplies limit the current on two electrodes to 30 amps the other two to 10 amps each. The effect of local biasing was measured with a set of Langmuir probes placed between the electrodes and another set extending radially outward from the electrodes, and also by the gas puff imaging diagnostic (GPI) located 1 m away along the magnetic field lines intersecting the electrodes. Two fast cameras were also aimed directly at the electrode array. The hardware and controls of the biasing experiment will be presented and the initial effects on local plasma parameters will be discussed.
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Published in : Part of the Proceedings of the 17th TopicalConference on High-Temperature Plasma Diagnostics, Albuquerque, NewMexico, May 2008.
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Download PPPL-4392 (pdf 547KB 15pp)
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