Improvement of Plasma Performance with Lithium Wall Conditioning in Aditya Tokamak

Abstract

Lithiumization of the vacuum vessel wall of the Aditya tokamak using a lithium rod exposed to glow discharge cleaning plasma has been done to understand its effect on plasma performance. After the Li-coating, an increment of ∼100 eV in plasma electron temperature has been observed in most of the discharges compared to discharges without Li coating, and the shot reproducibility is considerably improved. Detailed studies of impurity behaviour and hydrogen recycling are made in the Li coated discharges by observing spectral lines of hydrogen, carbon, and oxygen in the visible region using optical fiber, an interference filter, and PMT based systems. A large reduction in O I signal (up to ∼ 40% to 50%) and a 20% to 30% decrease of Hα signal indicate significant reduction of wall recycling. Furthermore, VUV emissions from O V and Fe XV monitored by a grazing incidence monochromator also show the reduction. Lower Fe XV emission indicates the declined impurity penetration to the core plasma in the Li coated discharges. Significant increase of the particle and energy confinement times and the reduction of Z eff of the plasma certainly indicate the improved plasma parameters in the Aditya tokamak after lithium wall conditioning.

Investigation of Recycling and Impurities Influxes in ADITYA-U Tokamak Plasmas

“…This ratio of influxes can be considered as the indicative values of impurity concentration at the plasma edge. Then it can be stated that the concentration of carbon and oxygen impurities in ADITYA-U tokamak is almost similar to those found out in ADITYA tokamak through both spectroscopic estimation [27,28] and modelling ADITYA tokamak plasma by TSC code [29].…”

Investigation of neutral particle dynamics in Aditya tokamak plasma with DEGAS2 code

“…In this work, DEGAS2 code is used to study the neutral particle behavior in Aditya tokamak [19], which has a circular poloidal ring limiter at one particular toroidal location. Aditya tokamak is a mid-sized air-core tokamak with major (R) and minor (a) radii, 0.75 and 0.25 m, respectively.…”

Lanthanum Bromide (LaBr3(Ce)) based hard X-ray spectroscopic diagnostic for the study of runaway electrons at Aditya Tokamak

“…The ratios of τ RE and plasma energy confinement time, τ e , is shown as a function of plasma electron density, n e , in figure 7 and it becomes inversely proportional to n e . The details on the calculation of the τ e have been described in ref [34]. The ratio becomes lower than one for the densities higher than l.8 × 10 13 cm −3 .…”