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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 ($\rm I_p$) and discharge duration are 1MA and 100ms, respectively. TPE-RX is being operated in the medium $\rm I_p$ region ( $\rm I_p < 500kA$) 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 ($\rm R_pI_p$) as low as 12 V is obtained at low $\rm I_p$ ($\sim$ 150kA), but it increases with $\rm I_p$ and becomes 22V at $\rm I_p \sim 450kA$. However, it is shown that $\rm R_pI_p$ is gradually decreasing as the discharge cleaning has been continued. Further decrease of $\rm R_pI_p$ will be expected under the improved wall condition. In almost of all discharges, especially with large $\rm I_p$ ($>$ 250kA) the wall and phase locking of the MHD fluctuations is observed. However, several discharges without this mode locking are found in low $\rm I_p$ and low filling pressure cases. Measurements of electron density ( $\langle n_e \rangle$) by $\rm CO_2$ laser interferometer, electron temperature ($\rm T_e$) by soft x-ray pulse height analysis and ion temperature ($\rm T_i$) by CV Doppler broadening have been started. Measured values are $\rm\langle n_e \rangle \simeq 5\times 10^{18}m^{-3}$, $\rm T_e \sim 1000-1200eV$ and $\rm T_i \sim 130\pm 50eV$ for the discharge with $\rm I_p \sim 270kA$ and reversal/pinch parameters $\sim$ -0.1/1.6, although it is possible that this high $\rm T_e$ may correspond to high energy part and low $\rm T_i$ 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 $\rm I_p$ is found in the Doppler shift measurement of CV line.

   

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