Effects of Toroidal Forces in Current Loops Embedded in a Background Plasma.

A study is made of dynamical properties of a three-dimensional semi-toroidal current loop embedded in a high-temperature stratified background plasma. The model loop carries a toroidal current density J sub t and poloidal current density J sub p, producing the magnetic field components B sub p and B sub t, respectively. Starting with a non-forces-free current loop in stable MHD equilibrium described by ic J x B - div p O where the major radial forces as well as the minor radial forces are explicitly balanced, the dynamical properties resulting from major radial pertubations are investigated. The condition for instability is given in terms of a circuit parameter epsilon which is a measure the flux associated with the overall current distribution. The current loop and is due to the toroidal geometry of the pressure gradient and drag force due to the ambient gas. For the equilibrium loops studied, the motion is found to be subsonic. Time evolution of the loops and the magnetic energy converted via drag heating are presented. Results are also presented for loops with relatively strong current and magnetic fields which are not in equilibrium initially. It is found that for sufficiently large current, a current loop can be driven supersonically through the background gas, accompanied by shocks and rapid shock heating of the ambient gas. The wide range of dynamical behavior exhibited by current loops, and the pros and cons of the model are discussed in the context of current loops in the solar corona.