Abstract
An average minimum magnetic field with inner conductors for plasma confinement can be generated when current carrying helical conductors are placed in a uniform magnetic field. The helical currents are axially uni-directional and the axial field component produced by the currents is inverse to the uniform field near the axis. Inside the conductors, this axial component diminishes the uniform field, so that an average minimum field can be realized.
This magnetic field has both properties of multipole field and the Heliotron P field (multi-ring system+uniform field). When the pitch of the helical conductors is large compared with its radius, the properties of the multipolr field dominates, whereas the field with short pitch is like the Heliotron P field. The magnetic field is examined for linear configurations The helical currents are expressed by the Fourier expansion, and potentials U=-∫ dl/B and-∫ dl are computed by a digital computer. The ratio of the helical field on the axis to the uniform field is used as a parameter of the field configuration. It becomes evident that at appropriate values of the parameter closed magnetic surfaces appear near the axis and very deep potential wells are formed. The rotational transform is also very large.
