Variable-Period Undulators - A Potential Source for Storage Ring, ERL and FEL Applications

A unique capability to vary the length of magnetic period in an undulator can be achieved with a geometry based on staggered arrays of permeable poles placed in a magnetic solenoid. The new classes of solenoid-derived undulators, which do not use permanent magnets, have the potential to provide wide tunability of the first and third energy harmonics by varying the length of the magnetic period and solenoid field, and deliver only small powers at undesired harmonics. The magnetic and spectral properties of such 'variable-period undulator' operating on the proposed PETRA III storage ring are presented to demonstrate the superior performance of such a device in comparison to conventional permanent-magnet hybrid undulators. They have the potential to be useful as synchrotron radiation sources at both currently operating and future low-emittance storage rings, energy-recovery linacs (ERLs), and free-electron lasers (FELs)