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Author(s):
A. Fujisawa, S. Kubo, H. Iguchi, H. Idei, T. Minami, H. Sanuki, K. Itoh, S. Okamura, K. Matsuoka, K. Tanaka, S. Lee, M. Kojima, T.P. Crowley, Y. Hamada, M. Iwase, H. Nagasaki, H. Suzuki, N. Inoue, R. Akiyama, M. Osakabe, S. Morita, C. Takahashi, S. Muto, A. Ejiri, K. Ida, S. Nishimura, K. Narihara, I. Yamada, K. Toi, S. Ohdachi, T. Ozaki, A. Komori,
K. Nishimura, S. Hidekuma, K. Ohkubo, D.A. Rasmussen, J.B. Wilgen, M. Murakami, T. Watari and M. Fujiwara
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Title:
An Experimental Study of Plasma Confinement and Heating Efficiency through the Potential Profile Measurements with a Heavy Ion Beam Probe in the Compact Helical System
Date of publication:
Sep. 1996
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Key words:
potential profile, loss cone diagram, transition, momentum transport barrier, high power ECH, high electron temperature, MHD bursts, potential profile oscillation
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Abstract:
In the Compact Helical System (CHS), electrostatic potential profiles in steady states and transient phases of various plasmas have been measured with a 200keV heavy ion beam probe (HIBP). Potential profiles in steady states of the ECH and NBI plasmas show electron and ion root characteristics, respectively. Recent extension of the ECH system, in terms of power and controllability of focus point and polarization direction, produces a plasma with high central electron temperature of 2keV in 500kW ECH (53.2GHz) fundamental heating in 1.7T operation. A 300kW ECH heated plasma using second harmonic resonance at 0.9T has a positive profile with phi(0)=400V, which exhibits a unique characteristic suggesting an internal momentum transport barrier at rho=0.4. When the NBI is applied on this plasma, positive potential around the core region is kept for more than 10ms which is longer than the energy confinement time of a few ms, although the potential around the edge turns to be negative in about 5ms. During this phase, a dynamical behavior of potential, or transition phenomenon in a few hundred mu s, is also discovered around the core. A loss cone evaluation based on the measured potential profiles gives an insight of high energy particle behaviors for both positive and negative potential profiles. A periodic change in the potential profile and internal potential fluctuation were detected in MHD bursts phenomena observed in low density NBI plasmas.
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