Investigation ofZ_effand impurity behaviour in lithium coating experiments with full metallic first wall in HT-7 tokamak

Abstract

The control of the impurity level in magnetically confined plasmas is a critical issue for future fusion devices. All the graphite tiles have been replaced by molybdenum tiles as limiter materials in the 2011 spring campaign in order to further reduce the recycling and hydrogen content of the plasma. A lithium coating technique has been applied as an important wall conditioning method to the HT-7 tokamak. The effective ion charge Z eff and impurity behavior with full metallic first walls of high-Z materials and lower hydrogen recycling have been investigated in a series of lithium coating experiments in this paper. Plasma performance and impurity behavior without wall coatings are studied in the early stage of the campaign. Comparison of Z eff with different plasma-facing components has been made. A typical lithium coating experiment has been analyzed in order to understand the effect of lithium coating. The evolution of main impurity line radiation, Z eff and the H/(H + D) ratio is analyzed in detail as lithium coating is repeated, indicating that lithium coating is a very effective tool to control impurity level and reduce hydrogen recycling. Furthermore, a boronization is conducted at the end of this campaign in order to make comparison with lithium coating. Experimental results show that lithium coating has much more advantages in edge recycling control, though it does not reduce impurity level as effectively as boronization.

Investigation of the behavior of effective charge of Aditya tokamak plasmas

“…This condition is most easily fulfilled in the visible region of the plasma radiation. Then, bremsstruhlang continuum radiation in the visible region is widely used to estimate Z eff of the tokamak plasma [2,[8][9][10][11][12] since this method can be used whatever may be the number of impurity species present in the plasma, and can be applied under different experimental conditions. Not only that, visible bremsstruhlang continuum measured using simple optics without coupling through vacuum transmission line with tokamak brings an added advantage than other wavelength region of plasma radiation spectrum.…”

Performance of the lithium metal infused trenches in the magnum PSI linear plasma simulator

“…Low core impurity concentrations [1], more stable plasmas [1,2], and improvements in energy confinement time [3] are merely some of these, however, fueling rates would probably need to be increased to maintain plasma density [4]. Literature shows that lithium causes a reduction in Zeff of the plasma [5,6]. NSTX has seen broadened plasma pressure profiles, leading to higher beta stability for high performance H-mode discharges when using lithium [7].…”

Simulation study of the influences of beryllium on the tokamak start-up process

“…Besides, the breakdown is also related to other parameters, such as stray magnetic field, and prefill pressure (Lloyd et al 1991). Chew's work presented a three-dimensional simulation of a hydrogen discharge to expand to the tokamak ohmic breakdown (Chew et al 2021) and compared different scatter models for electron-neural collisions.…”

“…Therefore, it has drawn much attention to the tokamak plasma discharge with the ITER-like wall, including simulation and experimental studies. Experiments in an HT-7 tokamak with full metallic first walls have shown that with lithium coating, the impurity level and hydrogen recycling have been decreased (Chen et al 2014). A more detailed analysis of beryllium poisoning can be found elsewhere (Wróblewska et al 2021).…”

“…Experiments in an HT-7 tokamak with full metallic first walls have shown that with lithium coating, the impurity level and hydrogen recycling have been decreased (Chen et al. 2014). A more detailed analysis of beryllium poisoning can be found elsewhere (Wróblewska et al.…”