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(EXP4/11) Divertor RFP Experiment on TPE-2M

K. Hayase, Y. Sato, S. Kiyama, M. Watanabe*, K. Sugisaki

Electrotechnical Laboratory, Tsukuba, Ibaraki, 305-8568 Japan
* Permanent Address: Faculty of Engineering, Iwate University, Morioka, Iwate, Japan

Abstract.  The divertor discharge of reversed field pinch (RFP) is being studied in TPE-2M. To understand the recycling process and the characteristic divertor plasma behaviors, the device was reconstructed so as to have an enough divertor space. In the new device the shell is installed in the vacuum vessel. The major and minor radii of the shell are 0.87 and 0.28 m respectively. Visible spectroscopic observation showed that both light and heavy impurity lines decreased, while D$ \alpha$ from the diverter plate region increased. This indicates that the divertor acts effectively in the new structural configuration. The newly found phenomenon in this vacuum vessel - shell structure is a large-amplitude axis oscillation of plasma column along with the divertor point direction, that is, the shell cut direction. It seems to be induced by the large shell cut angle or its structural form. This sort of large amplitude oscillation may enhance the flux loss in RFP. In the improved shell structure, in which the open angle of shell cut was reduced to a half (15 degrees) and the shape of shell inner surface was made quasi-circular, that oscillation is effectively suppressed. The loop voltage is relatively high in both cases, which seems due to the large - angle shell cut.

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IAEA 2001