Modeling of the Hα Emission from ADITYA Tokamak Plasmas

Abstract

The spatial profile of Hα spectrum is regularly measured using a high-resolution multi-track spectrometer in ADITYA tokamak to study the neutral particle behavior. The Monte Carlo neutral particle transport code DEGAS2 is used to model the experimental Hα spectral emissions. Through the modeling of the spectral line profile of Hα, it is found that the neutral hydrogen, which is produced from molecular hydrogen and molecular hydrogen ion dissociation processes contributes 56% to the total Hα emission, and the atoms which are produced from charge-exchange process have 30% contribution. Furthermore, the experimentally measured spatial profile of chord integrated brightness was modeled for the two plasma discharges having relatively high and low density to understand the neutral particle penetration. The presence of neutrals inside the core region of the ADITYA tokamak is mainly due to the charge-exchange process. Furthermore, it is observed that neutral particle penetration is lower in higher density discharge.

Physics studies of ADITYA & ADITYA-U tokamak plasmas using spectroscopic diagnostics

“…The emissivity radial profile was having peak around ρ (=r/a) of 0.8 and decreases around 10 times at ρ = 0.47 [45]. This profile has been employed to study the neutral dynamic [46,47] and details of contribution from various atomic and molecular processes in the H α emission are estimated by modelling it using DEGAS2 [48], neutral transport code. It requires the machine geometry, electron density and temperature, particle source and various atomic and molecular processes, for example ionization, dissociation, recombination, and charge exchange etc, happening inside the plasma.…”