Analysis of Magnetic Field Errors From Coil Displacement for the Material Plasma Exposure Experiment

The magnet system for the Material Plasma Exposure eXperiment (MPEX) provides the necessary field profile to enable RF source and heating along the length to meet the desired key performance parameters (KPPs) at the target area. The magnet system consists of six superconducting magnets and one room-temperature magnet. While each magnet has been designed with mechanical supports to maintain magnetic field alignment due to electromagnetic mechanical loading and cyclic operating modes, the positions of coil windings could drift or shift over each magnet subsystem. The magnetic field requirements for the plasma are that at any on-axis location over the length of the plasma volume, the off-axis axial field shall not vary more than 1% relative to the on-axis field, and the radial field component shall be less than 1% of the on-axis field. Because the diameter of the coils is much larger than the diameter of the plasma, the off-axis axial field requirement is not an issue; however, if the coils are shifted or tilted, the radial field component can exceed the allowable limit. Given that the specific amount of drift varies significantly depending on the global magnetic field strength and complexity of the magnet winding geometry, two analyses were carried out. This paper covers the amount of shift or tilt that the coil windings within each magnet subsystem can tolerate while still meeting the design requirements with respect to magnetic field. The allowable shift of each subsystem varies from 2.6 mm to 29.1 mm, and the tilt varies from 1.7 mm to 32.8 mm.