Ion temperature in the Reversatron II RFP

Abstract

A seven-channel, f14 polychrometer with UV quartz optics has been constructed for ion temperature measurements on the Reversatron II RFP (R/a=50 cm/8 cm). The spectrometer has a focal length of 1.1 m and utilizes an 1800-line/mm grating. The spectrum is spread over a linear array of photomultiplier tubes by a 2-mm-diameter quartz cylinder lens. Resolution is below 0.1 AA, and channel separation is 0.4 AA. Initial measurements have been made in 25-kA helium discharges with no conducting shell surrounding the resistive vacuum chamber. The He I line at 3888 AA, which is predominantly from the plasma edge, indicates T/sub i/ approximately=8 eV. The He II line at 4685 AA, which is less weighted by the edge, indicates T/sub i/ approximately=17 eV. A search is being made for impurity lines that are indicative of the central region of the discharge. Similar measurements will be made with other boundary conditions.<>