[Table of Contents]

Plasma and Fusion Research

Volume 2, S1093 (2007)

Regular Articles


Probing of Toroidal Electron Plasmas Confined on Helical Magnetic Surfaces
Y. YAMAMOTO, H. HIMURA, A. SANPEI, S. MASAMUNE, M. ISOBE1), S. OKAMURA1) and K. MATSUOKA1)
Kyoto Institute of technology, Department of Electronics, Matsugasaki, Kyoto 606-8585,Japan
1)
National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
(Received 4 December 2006 / Accepted 8 April 2007 / Published 20 November 2007)

Abstract

With a skillful probing system, both large negative space potential φs and low electron current Ip of helical nonneutral plasmas have been measured. For the φs measurement, a differential circuit with a high-voltage probe is employed. In order to prevent the signal from delaying due to the large output impedance of the high-voltage probe, an operational amplifier is used to reduce the output impedance to ideally zero. For the Ip measurement, an instrumentation amplifier is employed to precisely cancel the common-mode noise. In addition, to alleviate the thermal noise due to the large feedback resistance in the circuit, a trick of T-network resistance is utilized instead of the single large resistance. Furthermore, to cancel the significant ground loop current, the reference potential of the circuit is grounded across a small resistance (100Ω).


Keywords

helical nonneutral plasma, magnetic surface confinement, high-impedance emissive probe, large negative space potential, electrostatic probing system

DOI: 10.1585/pfr.2.S1093


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This paper may be cited as follows:

Y. YAMAMOTO, H. HIMURA, A. SANPEI, S. MASAMUNE, M. ISOBE, S. OKAMURA and K. MATSUOKA, Plasma Fusion Res. 2, S1093 (2007).