Impurity Behavior in High Performance ADITYA Tokamak Plasmas

Abstract

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_α, O¹⁺, and C²⁺ emissions normalized with electron density (n_e), and visible continuum normalized with n_e² 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.