Snowflake Divertor Simulation for EAST Experiment

Abstract

It is a challenge to handle the power and particle exhaust in fusion reactor. Several methods have been proposed to reduce the plasma-wall interaction by optimizing magnetic field topology at the divertor region. One of them is the so-called snowflake divertor (SFD) configuration [1], which is characterized by a second order null, i.e. the first derivatives of the poloidal magnetic field also vanish at the X-point where the poloidal magnetic field is zero. SFD experiment is one of the major tasks for the next Experimental Advanced Superconducting Tokamak (EAST) campaign in this year. Unlike DIII-D and NSTX which have realized SFD configuration, EAST does not have divertor coils which could be used to shape local flux distribution at divertor region. There are only 12 independent poloidal field (PF) coils to form SFD configuration in EAST, which is much less than TCV. These two factors restrict the flexibility of SFD equilibrium The SFD static equilibriums of EAST is investigated by FIXFREE [2] and EFIT [3] codes. The Tokamak Simulation Code (TSC) [4], a numerical model of the axisymmetric tokamak plasma and the associated control systems, has been benchmarked by several EAST ohmic discharges [5]. This code is used for EAST SFD scenario design. By TSC simulation, the plasma transition from normal divertor to SFD configuration is presented, and PF coils current waves are decided for EAST future experiments.