Abstract
Research was originally carried out to evaluate plasma performance with a tungsten (W) divertor on EAST using the bundled charge state model by the coupled multi-fluid plasma and kinetic neutral code SOLPS-ITER. This work focuses on the comparisons of several bundled charge state models of W and the all W ion model in low and high recycling divertor operational regimes. It is found that bundled charge state models have a pronounced effect on the reduction of computational time and computer memory and provide an improved marked code speed by a factor of more than five. In the low recycling regime, compared to the full W charge state model, the differences in the plasma parameters at both divertor targets are within 15% for different bundling schemes. In the high recycling regime, no significant difference between bundled charge state models and the all charge state model is observed due to the very low W concentration (∼10−6). It, therefore, indicates that bundled charge state models of W can describe divertor parameters well to a considerable degree. Besides, the errors of tungsten concentration (CW) and the effective ion charge number (Zeff) at the outer mid-plane for bundled models are within 40% inside the separatrix. At the same time, highly resolved bundled models with more than 20 W fluids can describe the radiation power loss consistently within 50% as compared with the all charge state model, while it varies greatly from one aggressively bundled model to the other, especially for core radiation, which is strongly related to the bundling schemes for relatively high charge states.
Highlights
Divertors,[1] as key components, play an important role in modern tokamak devices and future fusion reactors
It is found that bundled charge state models can significantly speed up the simulation process and reduce the computational time by a factor of more than five for aggressively bundled models, which take up less computer memory
In the low recycling regime, compared to the full W charge state model, the differences in peak values of T e, ne, qdep, and Γdep at both divertor targets are within 9% by using more highly resolved bundling schemes with more than 20 W fluids, while the maximum error for aggressively bundled models is less than 12.5%
Summary
Divertors,[1] as key components, play an important role in modern tokamak devices and future fusion reactors. Control of the deposited power load and erosion at divertor targets to an acceptable level is one of the pivotal issues to be solved to meet the demand of plasmas with a high power and long pulse in advanced tokamak devices. The bundled charge state model has been developed for high Z impurities in SOLPS-ITER9 to speed up the simulation process. Bonnin and Coster have performed a test on several bundling schemes for the ASDEXupgrade device.[11] It shows that the simulation process is speeded up markedly by bundling, and the differences in net erosion and deposition of W are modest between bundled charge state models and full. Before using the W bundled charge state models to analyze experimental results, in this paper, we carry out detailed comparisons of the full W treatment on EAST by focusing on the effects of W bundling schemes on the plasma parameter profiles at divertor targets.
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