1. M.W. Fan, M.W. Poole and R.P. Walker, Some aspects of the design of plane periodic permanent magnets for use in undulators and free electron lasers, DL/SCI/TM30A.
2. K. Wille, DESY-Report 81-047 and private communication.
3. Design of focussing and guide structures for charged particle beams using REPM;Halbach,1981