Magnetohydrodynamic equilibrium and stability of spheromak by boundary-fitted curvilinear coordinate system

The flux conserver actually used in spheromak experiments has an entrance hole and a duct to introduce a plasma into it. The effect of the hole keeps some magnetic surfaces from closing in the flux conserver. A method of closing all surfaces is to place an external coil near the entrance hole and apply an electric current Ic whose direction is opposite to the plasma current Ip. Equilibrium configurations of the spheromak plasma in the flux conserver with the external coil are determined by using the boundary-fitted curvilinear coordinate system. The stability of these configurations are investigated by using the Mercier criterion. The results of computations show the plasma confinement is poor if Ic/Ip ∼ 0, but it is considerably improved if Ic/Ip > approx 1/2 is satisfied. (author)