Eddy current analysis by incanet for a reversed field pinch device

Eddy current analysis for REPUTE-1, which is a Reversed Field Pinch (RFP) experimental device at the University of Tokyo, is presented. The error field problem is one of the most serious ones for plasma confinement in RFP. When the plasma current starts up, a large amount of eddy current flows in the plasma vessel. The plasma vessel consists of an inner vacuum vessel and an outer toroidal shell. The plasma vessel has many holes, for example, 108 holes in REPUTE-1, for vacuum pumping and plasma diagnosis. The flow pattern of the eddy current is badly distorted due to the existence of these holes. This distortion produces large ripples in the magnetic field generated by the eddy current in both the toroidal and poloidal directions; this is termed an error field. So far, the plasma confinement time has been measured as rather short compared to a design value in RFP experimental devices elsewhere because of the error field. In this analysis, we used the software tool named INCANET (IHI Induced Current Analysis Code by the Network Mesh Method). The toroidal and poloidal distributions of the error fields were numerically obtained by the three-dimensional eddy current analysis. When the total eddy current in the vacuum vessel is 30 kA, which corresponds to the typical RFP discharge of 200 kA plasma current, the radial component of the error field is 0.014–0.015 T at the edges of port holes, which is around 8% of the poloidal field generated by the plasma current itself.