Toroidal field generation and magnetic-field relaxation in a Conical Theta Pinch generated configuration

Two different cone angles, 10 and 18 degree, were used to investigate the effect of the cone angle on the toroidal field generation and magnetic field structure evolution. The configuration was generated in the pinch and then translated into a 15 cm (diameter) x 70 cm (length) stainless steel flux conserver. The hydrogen fill gas was puffed from the small end of the cone resulting in a pressure of approximately 15 mT at the middle of the pinch. The peak line-averaged electron density of the plasmoid was 1-3 x 1015 cm-3 and its temperature was ∼5 eV. The magnetic field structure of the configuration was measured by four 3-dimensional internal magnetic probes. Within the range of the examined cone angle, θ ≤ 24 degree, the averaged toroidal field generation was measured to vary quadratically with the cone angle of the pinch (data for 24 degree and 1.7 degree were obtained from other experiments). Therefore, a spheromak-like configuration could be generated directly by a Conical Theta Pinch (e.g. 18 degree pinch) if the poloidal and the generated toroidal field had an appropriate distribution. The relaxation parameter, the ratio of the magnetic energy to magnetic helicity, time history indicates that the relaxation behaves like a turbulent relaxation process