Improvement of Coupled Core-Edge Modelling Package for Analysis of Double Null and Snowflake Divertor Configurations

Abstract

A coupled core-edge modelling package including a mesh generator, VEGA, and a plasma transport solver, C2, is improved for analysis of the general Double Null (DN) and snowflake divertor configurations in a tokamak. Among the DN configuration, the Disconnected Double Null (DDN) configuration is commonly formed from the Connected Double Null (CDN) configuration because of the difficulty of yielding the same value at both X points. For the purpose of reducing heat loads to the divertor target, the snowflake divertor configuration is suggested recently. The mesh generator VEGA is upgraded to VEGA2.0 in order to generate a grid of these magnetic configurations. To achieve this goal, VEGA is reconstructed in C++ program language and modified to deal with the twisted grid and the first points finding algorithm. VEGA2.0 is benchmarked with VEGA for a reference connected double null (CDN) of KSTAR plasmas and evaluated with the grid quality factors. It shows that VEGA2.0 provides a better grid with respect to the low radial flux deviation in the boundary region of the computational domain. Also, the grid for the DDN and the snowflake divertor configurations in both KSTAR and VEST are successfully generated. A bridge code is developed for coupling VEGA2.0 to C2. In this code, the created grid matrix in VEGA2.0 is separated with respect to the separatrix line drawn from the X points and reallocated for the C2-preferred input format. This bridge code also adds one-dimensional data to obtain the magnetic surface averaged current profile and the diffusivity of heat and momentum. As a result, a coupled core-edge modelling package is prepared for analysis of both DDN and snowflake divertor configurations. The results of a coupled plasma transport simulation with the DDN configuration are presented.