The cryogenic MOS unit for LUCIFER

The LUCIFER MOS unit has been designed to exchange long-slit and multi-slit masks between two mask storage cabinets and the focal plane area. In combination with auxiliary cryostats, the MOS unit also permits the exchange of cold mask cabinets between LUCIFER and the auxiliary cryostats. Main functional components of the MOS unit are: a focal plane interface accepting the active mask, a mask handling unit transporting the masks between the focal plane mount and their storage locations, a stationary and an exchangeable cabinet holding 10 longslit and 23 multi-slit masks respectively, the translation drives for the exchangeable cabinet and the mask handling unit, and the mask locking unit securing the masks in their cabinets. For mask cabinet exchange, the LUCIFER cryostat as well as the auxiliary cryostats are equipped with 32 cm clear diameter gate valves. A test cryostat has been built to test all MOS unit functions at LN2 temperature. Most of the MOS unit components have been completed. System tests at ambient have started. First results are presented.