Observations of toroidal plasma rotation reversal in the Aditya-U tokamak

Abstract

An impurity ion toroidal rotation profile has been observed in the ohmic discharges of the Aditya-U tokamak from the Doppler-shifted passive charge exchange line emission of C5+ at 529 nm. The line has been monitored using a space-resolved visible spectroscopy diagnostic consisting of a 1 m multi-track spectrometer coupled with a charge coupled device (CCD) detector. In typical discharges with central chord-averaged electron density ≲2.5 × 1019 m−3, the maximum toroidal rotation velocity at the plasma core is found to be −20 km s−1 in the counter-current direction. Reversal of plasma toroidal rotation is observed for high electron density discharges with a central chord-averaged density of ~5 × 1019 m−3. During the rotation reversal, the direction of toroidal rotation changes to the co-current direction in the core. Interestingly, in the discharges with a central chord-averaged electron density of ≲2.5 × 1019 m−3, where neon gas is injected at the plasma current flat-top, the toroidal rotation reversal has been observed after the gas puff.