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Author(s):
J. Xu, K. Toi, H. Kuramoto, A. Nishizawa, J. Fujita, A. Ejiri, K. Narihara, T. Seki, H. Sakakita, K. Kawahata, K. Ida, K. Adachi, R. Akiyama, Y. Hamada, S. Hirokura, Y. Kawasumi, M. Kojima, I. Nomura, S. Ohdachi, K.N. Sato
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Title:
Measurement of Internal Magnetic Field with Motional Stark Polarimetry in Current Ramp-Up Experiments of JIPP T-IIU
Date of publication:
June 1996
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Key words:
Tokamak, Motional Stark Effect Polarimetry, Internal Poloidal Magnetic Field, Sawtooth, Partial Reconnection
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Abstract:
Multichannel polarization measurements of the Balmer alpha line of beam emission are performed using a 15-channel four-polarizer optical system on the JIPP T-IIU tokamak. The pitch angle of the internal magnetic field is obtained using a newly developed method where only sigma-components of the motional stark spectrum are analyzed to avoid difficulty due to the pi-component asymmetry caused by appreciable beam divergence. Radial profiles of intemal poloidal magnetic field and safety factor are successfully obtained in a current ramp-up discharge. The safety factor at the magnetic axis q(0) is about 1.7 just before the current ramp-up and gradually decreases close to unity during the current ramping phase till the appearance of sawtooth oscillations. In the sawtoothing phase, q(0) is further decreased to be obviously below unity, i.e., 0.7-0.8, which suggests that no complete reconnection of the poloidal magnetic flux takes place at the sawtooth crash.
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