Equilibrium calculation of Tohoku University heliac

Numerical analysis of equilibrium states in the heliac configuration is performed by using VMEC code. In the heliac configuration, it is possible to produce flux surfaces with the magnetic well under vacuum condition. Mercier instability is stabilized in a wide region of the plasma column in the deep well configuration. On the other hand, the local stability is limited only around a magnetic axis in the hill configuration. In the Mercier criterion, the well term has favorable effect on the local stability, while the geodesic curvature has negative effect. (author)