Cryogenic Undulator for a Table Top FEL

A laser plasma accelerator is under development at the Max‐Planck‐Institut fur Quantenoptik in Garching. This accelerator will be part of an X‐ray table top FEL in the future. The FEL radiation will be produced with a small period in‐vacuum undulator. The coercivity of the magnetic material has to be sufficiently high in order to avoid demagnetization due to electron losses. The best performance can be achieved with a cryogenic permanent magnet undulator design. (Nd0.2Pr0.8)2Fe14B magnets are suited for low temperatures since they do not suffer from a spin reorientation. A new (Nd0.2Pr0.8)2Fe14B material has been characterized at various temperatures and the results are presented. Based on this material a 20 period prototype with a period length of 9 mm and a magnetic gap of 2.5 mm is currently under construction.