Spontaneous generation of toroidal magnetic field during spheromak formation in a conical Theta-pinch

Spheromaks have been generated in conical Theta-pinches in a similar manner to FRC generation in straight reversed-field Theta-pinches. The essential difference is that when a conical Theta-pinch coil is used, a toroidal component to the magnetic field spontaneously appears. The poloidal component is generated by quickly reversing the current in the coil after an initial bias field is embedded in the preionized plasma. The toroidal component is generated through a much more subtle physical process. Numerical calculations have shown that the Hall term can lead to the generation of toroidal magnetic fields during the formation of an FRC; however for a straight coil, symmetry demands equal and opposite fields at each end, so no net toroidal flux or helicity can be generated. A simple analysis shows that even for a conical coil, the Hall term by itself cannot generate significant toroidal magnetic flux or helicity. They will show that a combination of the Hall term with the plasma resistivity can result in toroidal fields of comparable magnitude to experimental observation