The effects of race-track and DRAKON configurations on MHD equilibria and stabilities in toroidal devices

Based on a three-dimensional (3-D) code which instead of treating the full magnetohydrodynamic (MHD) equations directly, the effects of race-track and DRAKON (a Russian acronym for long equilibrium configuration) configurations on MHD equilibria and stabilities in toroidal devices are studied numerically. The equilibria are calculated by applying the method of steepest descent to the variational principle for the plasma and vacuum potential energy, stabilities can be answered by examining the asymptotic behavior of solutions for large artificial time. Numerical results show that as the ratio of length to width (that is, elongated ratio) of the race-track increases the degree of distortion of magnetic surfaces increases until the nested system breaks down, and loses its equilibrium. For DRAKON configurations, it is found that the distortion of magnetic surfaces becomes more severe with an increasing ratio of length to width and finally the nested system breaks down and the equilibria disappear eventually.