Comparison of rotamak plasma discharges in cylindrical and spherical devices

Abstract

A new cylindrical chamber rotamak with one magnetic coil added in the midplane was constructed, and a series of experiments were performed at this device for comparison with the experiments previously conducted at a spherical chamber device. The experiments have been conducted in two regimes: the field-reversed configuration (FRC) and the spherical tokamak (ST) configuration when a steady toroidal magnetic field is added. The results from the new device further confirm that within a certain range of the equilibrium magnetic field Bv, the plasma current driven by a rotating magnetic field (RMF) grows linearly with Bv in both FRC and ST rotamak discharges. The ST configuration is more stable and allows one to achieve higher plasma current Ip with a proper choice of the toroidal field (TF); plasma current is found to reach its maximum at an optimum value of the applied TF. The measured plasma current, electron density and temperature in the cylindrical device are lower than those measured in the spherical device. The quadrupole structure of the self-generated toroidal magnetic field in the FRC regime is observed in both devices but with different magnitudes. In the cylindrical device, when a current is applied in the middle coil, plasma current can be enhanced up to 250% depending on the initial conditions.