Time resolved coherence imaging spectrometer on WEGA stellarator

Abstract

Imaging sensor technologies such as charge coupled devices and complementary metal-oxide-semiconductor have made remarkable progress in recent years. Fast imaging systems based on these new technologies are now being routinely employed for advanced fusion diagnostics. Since two-dimensional imaging considerably improves the investigation of three-dimensional structural physics, we have installed and operated the first high-speed two-dimensional coherence imaging camera system for the study of ion temperatures and flow velocities in the WEGA stellarator based on the Doppler broadening of 468.6 nm He II line emission. The coherence imaging camera was able to image the complete plasma poloidal cross-section over a toroidal region spanning 10°. The camera was used for basic plasma studies, including electron cyclotron resonance heating (ECRH) power step experiments. The ion temperature of helium plasmas in WEGA is found to be 1.5-2.0 eV at maximum (26 kW) ECRH power. The plasma rotates in the E × B direction with speeds between 500 and 1000 m s-1, increasing at higher ECRH power. It was confirmed that the flow direction reverses with the direction of the magnetic field. The observed ion temperatures and flows were cross checked against a multi-channel Echelle spectrometer and satisfactory agreement obtained.