Undulator scheme providing wide range magnetic field tuning

Various undulator schemes were investigated with the goal to find a scheme providing operative wide range K-strength variation without magnet gap changing. Computer simulations and experimental mock-ups were used. The best results were obtained with a novel scheme based on EM coils producing a strong longitudinal magnetic field and a periodical structure of steel poles supplied by additional permanent magnet arrays [A.A. Varfolomeev et al., Nucl. Instr. and Meth. A 318 (1992) 809]. This scheme is more compact, ensures less problems with cooling and gives the highest magnetic field strength for small lambda sub(w) values.