Spectroscopic measurement of impurity ion behavior in the GAMMA10 tandem mirror

Behavior of impurity ions has been investigated using visible spectroscopy in the GAMMA10 tandem mirror. A 40 channel visible spectrometer system has been developed for measurements of the ion temperature and ion flow velocity. The spectrometer consists of a 100 cm monochromator, a 40 channel optical fiber array and an image intensifier tube coupled with a charge coupled device TV camera. The spectra from low ionization states of oxygen and carbon are measured in ion cyclotron range of frequency heated plasmas. High ion temperatures (3-10 keV) of O⁴⁺ are observed in the anchor region, where the minimum B mirror field is produced by baseball coils. The O⁴⁺ ion is heated by the fourth harmonic frequency of O⁴⁺, which is most likely due to the cyclotron higher harmonic damping.