Speaker
Description
Wall conditioning is an essential technique to control particle recycling on the wall surfaces and to realize stable discharges of fusion plasma. In recent large devices, superconducting coils are installed for high performance and long discharges, and Wall Conditioning with Electron Cyclotron resonance (ECWC) is planned as an inter-shot wall conditioning to avoid frequent de-energization of magnet system. ECWC plasma is produced by EC resonance and tends to localize, and therefore control of poloidal field is needed to extend the plasma toward the wall surface for conditioning.
An ECWC plasma usually has no conferment region and has strong plasma-neutral interactions. These physical conditions are similar to divertor plasma, and therefore a divertor plasma transport code EMC3-EIRENE was employed. This code can use a general mesh structure apart from magnetic flux surfaces. A simple cartesian-type mesh at a reference toroidal position was used, and the meshes at different toroidal positions were made by field-tracing in the range from -10 to 10 degrees, i.e., 1/18 of a torus with periodic condition. The first wall shape of JT-60SA of Operation Phase 1 was used, and two discharge conditions were chosen: discharge numbers E101164 with O1-mode EC and E101166 with X2-mode. The heating distributions were assumed to be vertically elongated profile at the resonance position near the inboard first wall for O1-mode and localized two-point regions at the resonance along the trace of the EC wave including a reflection for X2 mode. The heating power were chosen as 800 kW and 180 kW estimated from the experiment conditions, respectively.
Our first-in-kind modeling with the three-dimensional code has successfully generated EC plasma with the magnetic field and the first wall of the real device. The preliminary results showed a qualitative agreement with 2D image observations in experiments: 1) the radiation region with O1-mode tends to elongate vertically near the first wall corresponding to the heating region, 2) the radiation region with X2-mode tends to localize in a certain magnetic field configuration, and 3) a magnetic field configuration with a simple horizontal poloidal field component gives wide plasma covering almost all the device for O1-mode but no wide plasma for X2-mode. However, our results suggested that the radiation distribution significantly depends on electron temperature and density affected by a discharge condition, and therefore direct comparison with experiment results are needed to validate the results and will be addressed as future issues.