Development of a cryogenic APPLE CPMUE15 at BESSY II

Building on the innovative design of the In-Vacuum APPLE IVUE32, a design for a 15mm period cryogenic elliptical undulator (CPMUE15) is proposed. The undulator is to be developed under the ATHENA collaboration. Initially designed to provide a radiator for the SINBAD facility at DESY, a comparison is made for a design to provide an Afterburner device for FLASH1.