Fields analysis of helical wiggler

The general solution of scalar magnetic potential at any interior point of a cylindrical helix wiggler was attained and the expression of magnetic field on axis was also given by solving Lapace's equation. The magnetic field distributions of several kinds of helical wiggler were derived from combination and superposition of the magnetic field, such as right-handed bifilar helix wiggler, lefthanded fifilar helix wiggler,crossed double helix wiggler, autoguide field wiggler, multiwound wiggler and asymmetric wound wiggler and so on．