Preliminary investigation on the requirements of the first wall and limiter of HL-2M prior to its detailed design

Abstract

Some plasma facing components (PFCs) have to face extreme environments with high heat load as well as high particle flux during tokamak operations. Specifying the conditions of the PFCs of a tokamak during discharges is a critical issue prior to detailed design of a new device. Heat loads on different regions of PFCs are the most important parameters for PFCs and have to be provided as input into the engineering design. Particularly for the limiter, more investigations of heat loads are required since a number of accidents, including the one involving the JET limiter, have occurred due to underestimation of heat loads. In this paper, the factors affecting the heat loads of the first wall and the limiter of HL-2M are discussed. Several typical operation scenarios, including the first plasma, the start-up phase and flat-top phase of normal operations, and the key transient conditions, specifically disruptions and vertical displacement events, are analyzed for HL-2M, and the heat load specifications of different regions of PFCs are presented. Then the temperature rise and material erosion of PFCs are also evaluated. The results show that under the typical operation scenarios discussed in this paper, heat loads on the PFCs except the limiter are tolerable and temperature rise and material erosion are acceptable too. As for the limiter, the results reveal that the plasma current has to be lower than 0.5 MA if the plasma is operated in a limiter configuration. The investigation also implies that it is feasible to implement the first plasma without the first wall of graphite for the first plasma discussed in this analysis. However, the values obtained in this paper are based on a few simplifications, and further simulations are required involving ripple loss, start-up evolution, and the influence of ELMs on PFCs during further investigations.