抄録
A topological concept of the helicity prevailed mainly with the knottedness of magnetic lines of force is extended to the helicity with respect to current filaments and the one related to current vortex lines. In addition to these autohelicities, a crosshelicity produced by tangled two different kinds of closed filaments is defined and the mangetic energy is a typical example of it. Any autohelicity changes into the other autohelicity in time and a crosshelicity becomes another crosshelicity in a resistive plasma. The decay time of the current helicity is sensitive to the current profile in axially symmetrical toroidal systems. A variational principle using one autohelicity and one crosshelicity as constraints is applied to three different configurations. The material pressure integral of each equilibrium plasma is found to be a linear combination of an autohelicity and a crosshelicity.
