Radial profiles of 2p-1s heliumlike oxygen lines measured from the compact helical system using a vacuum crystal spectrometer

The vacuum crystal spectrometer (Johann type; RAP crystal) has been designed and developed to measure soft x-ray lines in the vicinity of 20 Angstrom. A photodiode array and a two-stage multichannel plate were used as a detector. Radial profiles of heliumlike oxygen lines were successfully obtained from NBI plasmas in the compact helical system with a spectral resolution of 525 (=λ/Δλ). The radial profile in the intensity ratio of Y(3P1→1S0) to W(1P1→1S0) was also obtained. The intensity ratio among 2l-1l transitions of the heliumlike oxygen are calculated as a function of the electron temperature and the electron temperature profile was obtained from the ratio. The obtained electron temperature was compared with one from a Thomsom scattering measurement. As a result, the comparison showed a good agreement. copyright 1997 American Institute of Physics