Partially relaxed magnetohydrodynamic equilibria with bias-flux leakage obtained in a helicity-driven spheromak

In the flux amplification compact torus experiment, the bias flux penetrates the wall of the flux conserver because it has been switched on a suitably long time prior to the production of a seed spheromak. The magnetohydrodynamic equilibrium configurations with a non-constant lambda(= mu(0)j.B/\B\(2)) profile of a helicity-driven spheromak incorporating the situation of the bias-flux leakage out of the flux conserver are numerically determined by using the novel combination of the finite difference and the boundary element method. Here mu(0), j and B are the permeability of vacuum. the current density and the magnetic field, respectively. The results of computations show that the effects of the bias-flux leakage cause a slight rise of the entire safety factor q in the case of I-C/I-P = 0.4 (I-C and I-P denote the total current of coil and plasma, respectively) because of the decrease in poloidal field over all space. Then, they also give rise to a 22.0% decrease in the magnetic flux inside the separatrix.