Comparison of Predicted and Measured Electromagnetic Data for Alcator C-MOD

Alcator C-MOD is the latest in a line of high field, compact tokamaks built and operated by the Plasma Fusion Center at MIT. From the electromagnetic standpoint the machine is characterized by toroidal field (TF) coils with sliding joints, a poloidal field (PF) coil set that is inside the bore of the TF coils, and very thick-sectioned, toroidally continuous, vacuum vessel and metal structures. The tokamak is cooled to liquid nitrogen temperatures and pulsed. At the toroidal field of 9 T, the maximum temperature in the TF rises to approximately room temperature. The pulsed nature of the current together with this wide temperature range requires a solution of the coupled electromagnetic and thermal diffusion problems. In addition, eddy currents induced in the thick electrically conducting structures perturb the spatial and temporal distribution of the poloidal magnetic field in the vacuum chamber, especially for the plasma breakdown and initiation phase and during fast plasma position control. The transient electromagnetic field problem associated with these regimes must be taken into account in the design and analysis of the tokamak. The results of analyses of the electromagnetic behavior of Alcator C-MOD will be compared with measured data.