Vacuum Magnetic Flux Surface Measurements Made on the Compact Toroidal Hybrid

Abstract

Understanding the behavior of plasmas in magnetic confinement fusion devices typically requires accurate knowledge of the magnetic field structure. In stellarator-type confinement devices, the helical magnetic field is produced by currents in external coils. The field lines may be traced experimentally in the absence of plasma. Vacuum magnetic field mapping experiments were performed on the recently-constructed Compact Toroidal Hybrid (CTH) with a movable electron gun and phosphor-coated screen. These experiments verify the range of accessible magnetic configurations, compare the actual magnetic configuration with the design configuration, and identify vacuum field errors that lead to perturbations of the vacuum magnetic flux surfaces. The experimental field mapping results are compared to computer simulations based on accurate models of the magnet coils that produce the field. Modifications are made to the coil models to achieve better agreement between the simulations and the experimental results. This process resulted in a model of the CTH magnetic coils of that accurately describes the experimental field mapping results and can be used as the basis of a better model of the vacuum magnetic field of CTH in preparation for plasma studies.