SOLPS modelling of detachment in lower single-null divertor for China Fusion Engineering Testing Reactor

China Fusion Engineering Testing Reactor (CFETR) is proposed as a good complement to ITER for demonstration of fusion energy. The main goals of CFETR are fusion power 50∼200 MW, duty cycle time 0.3∼0.5 and a tritium breeding ratio ≥1.2. CFETR is based on both physics and some technologies of ITER. Therefore, lower single-null (LSN) divertor (also called ITER-like divertor) is a basic choice for CFETR. The heat power from core plasma into scrapped-off layer (SOL) is estimated as 100 MW, which implies that the divertor must have enough ability to reduce the heat power via radiation before it lands on divertor targets. Therefore, the heat load onto divertor targets will not exceed the engineering limit of 10 MW/m². In the physical design of ITER divertor, a partly detached operating is preferred to provide enough radiation ability and to avoid undesirable influence on core plasma. It is also curial to find an appropriate operation region for CFETR divertor. In this work, to predict the operation status of CFETR divertor, the Scrapped-off Layer Plasma Simulation (SOLPS) code is used for numerical simulation. SOLPS is a coupled code constituted by multi-fluid plasma simulation code B2.5 and Monte Carlo neutral simulation code EIRENE. Based on the preliminarily designed magnetic configuration and divertor geometry of the LSN divertor for CFETR, a density scan are performed via a increase of D₂ gas puffing rates in the range of 0.0∼5.0 × 10²³ s^-1 for SOLPS simulations. Along with the increase of gas puffing rate, it can be seen that a gradually change of the operation status, which is from low-recycling regime to high-recycling regime and finally to detachment. C impurity concentration is lower than 4% in the plasma core region, which shows strong impurity screening of the divertor. (author)