Study of the equilibrium, stability and magnetic self-organization of line-tied toroidal plasma discharges

A set of electrodes are inserted into MRX (1) to generate line-tied toroidal plasmas which can be regarded as flux ropes. The 3-D structure of these plasmas is monitored by a fast framing camera and magnetic probes (2). Time resolved measurements of discharges with peak currents of 10--30 kA reveal that both stable and unstable flux ropes can be formed with their ends line-tied to the electrodes. It is found that the magnetic tension force of the toroidal field lines plays an important role in these equilibria. Using the $q$ value, which describes the rotational transform of field lines, the stability condition for external kink modes is found to be consistent with the Kruskal-Shafranov limit with modified line-tied boundary conditions. Additionally, internal relaxation events are observed even after the flux rope stabilizes against the external kink mode. The basic features of the self-organization events will also be discussed. (1) M. Yamada et al, Phys. Plasmas, v4,1936 (1997), (2) E. Oz et al: This conference.