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Author(s):
Y. Hamada, A. Nishizawa, Y. Kawasumi, K. Narihara, K. Sato, T. Seki, K. Toi, H. Iguchi, A. Fujisawa, K. Adachi, A. Ejiri, S. Hidekuma, S. Hirokura, K. Ida, J. Koong, K. Kawahata, M. Kojima, R. Kumazawa, H. Kuramoto, R. Liang, H. Sakakita, M. Sasao, K. N. Sato, T. Tsuzuki, J. Xu, I. Yamada, T. Watari, I. Negi
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Title:
Measurement of Profiles of the Space Potential in JIPP T-IIU Tokamak Plasmas by Slow Poloidal and Fast Toroidal Sweeps of a Heavy Ion Beam
Date of publication:
Feb. 1994
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Key words:
HIBP, potential, tokamak, analyzer, beam
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Abstract:
By the use of simultaneous fast toroidal and slow poloidal sweeps of a heavy ion beam, plasma potential profiles in JIPP T-IIU tokamak are measured at the rate of 120 spatial profiles per second. A new method to eliminate the error due to the change of out-of-plane entrance angle caused by large plasma current, is successfully applied. One of the key factors is the very homogeneous characteristics of the energy analyzer along the wide slit length. A shaped electrode system, instead of guard rings with a resistor chain, successfully increases the homogeneity of an analyzer. The error due to the significant change of an in-plane entrance angle during a poloidal sweep is carefully minimized and calibrated by a secondary beam ionized by neutral gas introduced in a vacuum vessel. The depth of the measured potential at the plasma center reaches more than 1.5 keV in ohmic plasmas with the ion temperature of 600 eV. In some cases, a rather wide region of positive potential and a sharp decrease of the potential in the center of the plasma are observed.
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