Development of Integrated SOL/Divertor Code and Simulation Study in JAEA

An integrated SOL/divertor code is being developed by the JAEA (Japan Atomic Energy Agency) for interpretation and prediction studies of the behavior of plasmas, neutrals, and impurities in the SOL/divertor region. A code system consists of the 2D fluid code for plasma (SOLDOR), the neutral Monte-Carlo code (NEUT2D), the impurity Monte-Carlo code (IMPMC), and the particle simulation code (PARASOL). The physical processes of neutrals and impurities are studied using the Monte Carlo (MC) code to accomplish highly accurate simulations. The so-called divertor code, SOLDOR/NEUT2D, has the following features: 1) a high-resolution oscillation-free scheme for solving fluid equations, 2) neutral transport calculation under the condition of fine meshes, 3) successful reduction of MC noise, and 4) optimization of the massive parallel computer. As a result, our code can obtain a steady state solution within 3 ˜ 4 hours even in the first run of a series of simulations, allowing the performance of an effective parameter survey. The simulation reproduces the X-point MARFE (multifaceted asymmetric radiation from edge) in the JT-60U. It is found that the chemically sputtered carbon at the dome causes radiation peaking near the X-point. The performance of divertor pumping in the JT-60U is evaluated based on particle balances. In regard to the divertor design of the next tokamak of JT-60U, the simulation indicates the dependencies of pumping effciency on the divertor geometry and operational conditions. The effciency is determined by the balance between the incident and back-flow fluxes into and from the exhaust chamber.