Initial Vacuum Magnetic Field Mapping in the Compact Toroidal Hybrid

摘要

The Compact Toroidal Hybrid (CTH) is a low aspect ratio (R/a_(plasma) ≥ 3.5, R_0 = 0.75 m, a_(vessel) = 0.29 m, B ≤ 0.6 T) torsatron with a highly flexible vacuum magnetic field configuration designed for current-driven instability studies. Vacuum magnetic field mapping of the completed configuration is performed using a movable electron gun and phosphor-coated screen. These experiments compare the actual magnetic configuration with the design, verify the range of accessible magnetic configurations, and identify vacuum field errors. The main helical field is produced by a continuously-wound helical coil, and the vacuum rotational transform is varied with a set of toroidal field coils. Four independent poloidal field coil sets provide equilibrium control and shaping, and are also used for ohmic current drive.