Measurements of poloidal rotation velocity using charge exchange spectroscopy in a large helical device

Absolute measurements of poloidal rotation velocity with the accuracy up to 1 km/s (2 pm in wavelength) were done using charge exchange spectroscopy in a large helical device. Radial profiles of the absolute Doppler shift of charge exchange emission with a beam are obtained from spectra measured with four sets of optical fiber arrays that view downward and upward at the poloidal cross section with and without neutral beam injection. By arranging the optical fiber from four arrays close to each other at the entrance slit, the apparent Doppler shift due to aberrations of the spectrometer and due to interference of the cold component (the charge exchange between He-like oxygen and thermal neutrals 8 pm from the charge exchange emission with a beam) can be eliminated from the measurements. The measured poloidal rotation velocity is 1–3 km/s in the electron diamagnetic direction at half of the plasma minor radius.