Impurity Behavior in High Performance ADITYA Tokamak Plasmas

Impurity behavior has been studied for the high performance Ohmically heated ADITYA tokamak plasmas operated with higher toroidal magnetic field and multiple gas puffs. The neutral hydrogen and impurity emissions in the visible range were monitored by photo multiplier tube (PMT) based system in which interference filter used for wavelength selection. The VUV spectral line emissions from impurities, such as C4+, O5+ and Fe14+, were also recorded by a VUV survey spectrometer operated in the 10 - 180 nm. It has been found that H-alpha, O1+, and C2+ emissions normalized with electron density (n(e)), and visible continuum normalized with n(e)(2) show a gradual decrease with increase in density indicating lower impurity concentration in these discharges. The VUV emission also shows the similar trend with increasing n(e). Indeed, the impurity transport study using iron emissions confirms that the iron concentration reduces with increasing n(e). This is also corroborated by the observed reduction in plasma effective charge, Z(eff) and radiation power loss with the increase in n(e). These results clearly indicate that the improved confinement for ADITYA plasma are correlated with reduction of impurities concentration in those discharges. (C) 2022 The Japan Society of Plasma Science and Nuclear Fusion Research