Effect of Multiple Periodic Gas Puff on Neutral Temperature in ADITYA-U Tokamak

Full text: The fuel gas injection in measured quantity during the current flat-top region of ADITYA-U tokamak discharges has been observed to modify significantly the edge and scape-off-layer (SOL) plasma properties. The effect of these gas puffs on the neutral temperature and their penetration in the edge and SOL region has been studied by measuring the Hydrogen Balmer-α emission spectra at 656.28 nm from different lines-of-sight in the edge and SOL region in both high and low field regions of ADITYA-U. The neutral temperature is estimated from the Doppler broadening of the measured H spectrum by appropriately removing the contribution from the Zeeman splitting of the spectral lines. A computer simulation code has been developed in-house which generates synthetic chord-averaged H_α emission spectra at different radius of the plasma using the electron temperature, density and the magnetic field strength of that radial location measured with other diagnostics. The code includes all the broadening mechanisms such as Doppler, Zeeman, Stark or pressure broadening for simulating the H emission spectrum along with proper convolution of the instrumental width of the measuring system. Depending on the strength of the magnetic field, the code incorporates 7 Zeeman components in case of normal Zeeman splitting, whereas 48 components (18π and 30σ) are included in the case of Paschen-Back Zeeman splitting. The simulated spectra are used to obtain true values of neutral temperatures by iteratively fitting them to the measured spectrum from the edge and SOL region of ADITYA-U tokamak. Furthermore, the developed code has been used to isolate the cold, warm and hot (charge exchange) components of the hydrogen atoms from the measured H emission spectra from the edge region of ADITYA-U tokamak. (author)