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Description
The neutral atoms in the plasma edge of nuclear fusion devices are typically modeled using a kinetic approach and more specifically the Monte Carlo (MC) code EIRENE [1]. Although EIRENE has been proved very reliable and effective, there are some drawbacks such as the statistical noise introduced by the MC techniques and the computational cost, which is significantly increased in high collisional regimes. Therefore, alternative approaches have been proposed including either the employment of more advanced kinetic stochastic codes (DSMC) [2] or of deterministic neutral fluid models [3] with considerable success. Always, the objective is the computationally robust and efficient coupling with the plasma edge model.
In the present work, instead of adopting a stochastic approach, an in-house deterministic solver, based on solid theoretical principles, utilizing a novel marching discrete velocity algorithm on unstructured grids [4] is developed and implemented to model the neutral particles in tokamak exhaust systems. The Boltzmann equation is accordingly replaced by suitable kinetic model equations, which are numerically solved, in a deterministic manner, by discretizing the particle velocity space via the method and the physical space via typical finite difference or volume schemes.
The bulk quantities are obtained by the moments of the particle distribution functions, while depending on the operating scenarios, various boundary conditions and coupling strategies with the plasma code may be applied. The validity of the proposed model is thoroughly assessed by modeling the neutral gas flow in a 2D-cut of the JET sub-divertor area and performing a systematic comparison with corresponding results in [2], where the DSMC method is introduced. Complimentary comparisons with the in-house gas distribution network code ARIADNE [5], which is also used to simulate the JET sub-divertor area are performed. The main advantages of the proposed approach compared to other available ones, include the detailed description of the flow at mesoscale without statistical noise with small computational effort.
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 - EUROfusion).
References:
[1] D. Reiter et al, Fusion Sci. Technol., 47, 172-186 (2005).
[2] S. Varoutis et al, Fusion Eng. Des., 121, 13-21 (2017).
[3] Wim Van Uytven et al, Nucl. Fusion, 62, 086023 (2022).
[4] G. Tatsios, Advanced deterministic and stochastic kinetic modeling of gaseous microscale transport phenomena, Volos, Greece: Ph.D. Dissertation, University of Thessaly, 2019.
[5] N.Vasileiadis et al, Fusion Eng. Des., 103, pp. 125-135 (2016).
