Magnetic field error analysis on TPX superconducting magnet misalignment

The Tokamak Physics Experiment (TPX) requires that certain magnetic field errors, in terms of Fourier components, be in the order of 10/sup -4/ of the field at the major radius. We have studied the field errors introduced from rigid coil displacements for both the toroidal field (TF) and poloidal field (PP) magnets. Fourier decomposition of the field errors was performed on a plasma surface with a D-shaped cross-section. For TF coils, field errors were calculated for all six degrees of freedom in displacements, and for PF coils, three degrees of freedom were considered. Superposition and linearity were verified for small displacements. To obtain the field errors of a whole TF magnet, a statistical approach with Monte-Carlo simulations was taken to combine the field errors from all 16 individual TF coils with each in six degrees of freedom. The simulation results suggested a new approach for allocating the field errors to different subsystems. The results also helped us to identify the major and minor contributors in field errors during the design and manufacturing stages for controlling the tolerances in parts and assembly.