Eddy current effect study on the JT-60 plasma equilibrium control

The A-φ method (A is the magnetic vector potential and φ is the scalar potential) was applied to eddy current analysis in the JT-60 tokamak fusion device. This analysis agrees with the coil excitation experiments much better than the filament-current-coil approximation. The accuracy of the A-φ method is estimated by comparing it with the analytical solution of magnetic field penetration into an infinitely long cylindrical conductor. A JT-60 plasma equilibrium-control-dynamics (ECD) model including eddy currents induced in the vacuum vessel is proposed for control system design and analysis. Considering the plasma-vessel interaction, the one-point plasma model and its equilibrium force balance are assumed. Comparison of the simulation and experimental data identifies the essential points for reproduction of the plasma ECD: (a) The magnetic field induced by the plasma motion is proportional to its velocity. (b) Magnetic field penetration is regarded as a response of a first-order differential equation. Application limits of the employed model are also identified: (a) Plasma volume effects are not accurately involved. (b) The influence of eddy current on shape evolution is not taken into consideration. (orig.)