Fuel particle and impurity influxes have been investigated for ADITYA-U tokamak plasma operated with toroidal belt limiter using PMT based spectroscopic diagnostic system installed on machine. The influxes of hydrogen and impurity ions are estimated using various lines of sight (LoS) terminating on the graphite limiter and stainless steel wall to understand their contributions in recycled particle and impurities into the main plasma. It is found that the influxes of neutral hydrogen and oxygen are around 4 times higher in case of LoS terminating on the limiter than the wall while carbon influxes from the both LoSs are comparable. The comparable integrated particle influxes from both LoSs indicate the important role of the wall in the recycling and presence of the impurities in the plasma. The particle confinement time (τ p ) and recycling coefficient (R) are also estimated to quantify those from the estimated particle influxes. The τ p values vary between 8 to 25 ms when plasma electron density is in the range of 2.0 -3.2 × 10 19 m −3 . Analysis of recycling coefficient, R suggests that the Plasma Facing Component (PFC) acts as the particle sink at the beginning of the plasma operational campaign. The R values tend to become more than one as the campaign progresses suggesting that the PFC acting as the particle source.
A capacitive coupled radio frequency (RF) plasma system has been developed for producing tungsten coated graphite tiles using plasma assisted chemical vapor deposition (PACVD) technique. To characterize the deposition chamber for optimal plasma parameters, small amount of air is released into the hydrogen plasma purposefully to measure its gas temperature using spectral bands of nitrogen molecule. Optical emission spectra in the wavelength range 350 to 900 nm have been recorded with a miniature spectrometer. Molecular spectral bands of N 2 (B 3 g -A 3 + u ) have been observed and identified as three bands from the nitrogen 1PS (Δν = 2, 3 & 4). These bands are simulated using MATLAB code developed in-house by considering Boltzmann distribution of particles in the vibrational states. The experimental spectra have been modelled with the simulated spectrum through the best-fit technique by iterating the latter one with different temperature values. Boltzmann plot method is also utilized to evaluate plasma gas temperature using identified vibrational bands. The estimated temperature using spectral modelling method matches fairly well with Boltzmann plot method. The estimated vibrational temperatures are in the range of ∼7000 -8000 K, an order higher than the room temperature ∼300 K.
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