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(EX4/4) Reversed Field Pinch Experiment on a New Large Machine, TPE-RX

Y. Hirano, T. Shimada, Y. Yagi, S. Sekine, H. Sakakita, H. Koguchi, T. Osakabe, K. Hayase, Y. Sato, Y. Maejima and I. Hirota

Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba-shi, Ibaraki, Japan 305

Abstract.  Reversed field pinch (RFP) experiment on a new large machine, TPE-RX has been started from March 1998. Major and minor radii of TPE-RX are 1.7175m and 0.45m, and the maximum designed plasma current ( I_p) and discharge duration are 1MA and 100ms, respectively. TPE-RX is being operated in the medium I_p region ( I_p < 500kA) with discharge duration about 80ms and RFP discharges with good reproducibility are routinely obtained, where the precise compensation of error field at poloidal gap of thick shell is indispensable. In a series of initial phase of experiment, following results are obtained. Non-inductive part of toroidal loop voltage ( R_pI_p) as low as 12 V is obtained at low I_p ($\sim$ 150kA), but it increases with I_p and becomes 22V at I_p $\sim$ 450kA. However, it is shown that R_pI_p is gradually decreasing as the discharge cleaning has been continued. Further decrease of R_pI_p will be expected under the improved wall condition. In almost of all discharges, especially with large I_p (> 250kA) the wall and phase locking of the MHD fluctuations is observed. However, several discharges without this mode locking are found in low I_p and low filling pressure cases. Measurements of electron density ( $\langle$n_e$\rangle$) by CO₂ laser interferometer, electron temperature ( T_e) by soft x-ray pulse height analysis and ion temperature ( T_i) by CV Doppler broadening have been started. Measured values are $\langle$n_e$\rangle$ $\simeq$ 5×10¹⁸m^{- 3}, T_e $\sim$ 1000 - 1200eV and T_i $\sim$ 130±50eV for the discharge with I_p $\sim$ 270kA and reversal/pinch parameters $\sim$ -0.1/1.6, although it is possible that this high T_e may correspond to high energy part and low T_i may correspond to the value near the edge since the radiation profile of CV line is very hollow. An interesting dependence of plasma rotation on I_p is found in the Doppler shift measurement of CV line.

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