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Direct plasma potential measurements by a novel probe
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SYSNO ASEP 0103225 Document Type C - Proceedings Paper (int. conf.) R&D Document Type Conference Paper Title Direct plasma potential measurements by a novel probe Title Přímé měření potenciálu plazmatu pomocí nové sondy Author(s) Adámek, Jiří (UFP-V) RID, ORCID
Stöckel, Jan (UFP-V) RID
Hron, Martin (UFP-V) RID, ORCID
Ryszawy, Jiří (UFP-V)
Tichý, M. (CZ)
Schrittwieser, R. (AT)
Ionita, C. (AT)
Balan, P. (AT)
Martines, E. (IT)
Van Oost, G. (BE)Source Title Proceedings of the 31th EPS Conference on Controlled Fusion and Plasma Physics. - London, 2004 Pages s. 514-515 Number of pages 2 s. Publication form CD-ROM - CD-ROM Action EPS Conference on Controlled Fusion and Plasma Physics /31./ Event date 28.06.2004-02.07.2004 VEvent location London Country GB - United Kingdom Event type WRD Language eng - English Country GB - United Kingdom Keywords tokamak, probe Subject RIV BL - Plasma and Gas Discharge Physics R&D Projects GA202/03/0786 GA ČR - Czech Science Foundation (CSF) CEZ AV0Z2043910 - UFP-V Annotation For the determination of the plasma potential in tokamaks emissive probes and heavy ion beam probes have been used, but these diagnostics are still not used as a routine technique. In practice the floating potential Vfl is usually measured by Langmuir probes. The plasma potential Fpl is then derived from the simple formula of the Langmuir probe theory (without magnetic field): Vfl = Fpl - Te ln(Ri), where Te is the electron temperature in eV. The quantity Ri represents the ratio of the electron and ion saturation currents: Ri = . The theoretical value of ln(Ri) in hydrogen plasma is about 2.5. The basic idea of the direct plasma potential measurements is to adjust Ri equal to one. If this can be achieved, the floating potential of the probe is equal to the plasma potential. This contribution presents the design as well as the first experimental results of a novel probe, by which the value of Ri can be modified. The probe head, shown in the figure, consists of a conically shaped collector, which is shielded by an isolating tube of boron nitride. The collector is moveable inside the tube and is either completely shielded or partially exposed to the plasma. In the ideal case, when the collector is hidden inside the tube, as shown in the figure, only ions with sufficiently large Larmor radii reach the collector surface. In this case the collecting area for electrons is negligible. When the collector is shifted towards to the plasma the electron current increases. Experiments at the CASTOR tokamak (R = 40 cm, a = 8.5 cm, BT = 1.3 T, IP @ 10 kA) have verified that Ri can indeed be adjusted close to one, when the position of the collector is chosen properly. The floating potential of the probe also varies with the position of the collector. Therefore, such a configuration can be used for a direct determination of the plasma potential in a tokamak environment as an alternative for the emissive probe. Workplace Institute of Plasma Physics Contact Vladimíra Kebza, kebza@ipp.cas.cz, Tel.: 266 052 975 Year of Publishing 2005
Number of the records: 1