Numerical study on effect of external magnetic field, current profile, arc current and arc column radius on helical instabilities of arcs

This model differs from previous works in that the electrical conductivity (and the current profile) is approximated in a more realistic way (parabolic instead of flat profile). The magnetohydrodynamic equations in an electrostatic approximation serve as the starting point of the theory. The effects of the external axial magnetic field, current profile, arc current and arc column radius on the helical instabilities of arcs were numerically studied. Numerical results show that the short wavelength perturbation can be stabilized by positive direction magnetic field, whereas the long wavelength perturbation can be stabilized by reverse magnetic field when the current profile is the uniform distribution. In the short wavelength perturbation case, the effect of positive direction magnetic field on the arc stability is very small when the current profile has a parabolic distribution. However, its stabilizing effect is enhanced for the long wavelength perturbation. The intermediate and long wavelength perturbation can also be stabilized by reverse magnetic field. The low current is beneficial for stabilizing arcs.