MAGNETIC-FIELD ERROR ANALYSIS ON TPX SUPERCONDUCTING MAGNET MISALIGNMENT

The Tokamak Physics Experiment (TPX) requires that certain magnetic fi eld errors, in terms of Fourier components, be in the order of 10(-4) of the field at the major radius. We have studied the field errors int roduced from rigid coil displacements for both the toroidal field (TF) and poloidal field (PF) magnets. Fourier decomposition of the field e rrors was performed on a plasma surface with a D-shaped cross-section. For TF coils, field errors were calculated for all six degrees of fre edom in displacements, and for PF coils, three degrees of freedom were considered. Superposition and linearity were verified for small displ acements. To obtain the field errors of a whole TF magnet, a statistic al approach with Monte-Carlo simulations was taken to combine the fiel d errors from all 16 individual TF coils with each in six degrees of f reedom. 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 th e design and manufacturing stages for controlling the tolerances in pa rts and assembly.