LOCAL CURRENTS IN MAGNETIC-FLUX TUBES AND FLUX ROPES

A magnetic flux tube is a cylindrical region inside which there exists an axial magnetic field that is much larger than the field outside. M agnetic flux tubes exist in nature, for example, in the sun's photosph ere. We show here that magnetic flux tubes can exist as self-excited d ynamos within conducting fluids, in regions where the fluid velocity h as a negative radial velocity, in cylindrical coordinates. We find exp ressions for the local current density, the magnetic force density, th e gas pressure, the ohmic power dissipation, the stored magnetic energ y, the inductance, and the inherent time constant. A flux rope is a fl ux tube, plus an axial current and its azimuthal magnetic field. The a xial current cannot be generated locally, but it could be injected at one end; that will be the object of another paper.