T. Kanki et al., PARTIALLY RELAXED MAGNETOHYDRODYNAMIC EQUILIBRIA WITH BIAS-FLUX LEAKAGE OBTAINED IN A HELICITY-DRIVEN SPHEROMAK, Journal of the Physical Society of Japan, 67(1), 1998, pp. 140-146
In the flux amplification compact torus experiment, the bias flux pene
trates 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 lam
bda(= mu(0)j.B/\B\(2)) profile of a helicity-driven spheromak incorpor
ating the situation of the bias-flux leakage out of the flux conserver
are numerically determined by using the novel combination of the fini
te difference and the boundary element method. Here mu(0), j and B are
the permeability of vacuum. the current density and the magnetic fiel
d, 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 o
f coil and plasma, respectively) because of the decrease in poloidal f
ield over all space. Then, they also give rise to a 22.0% decrease in
the magnetic flux inside the separatrix.