The second phase of cryo-mechanical integration of the SPIRou spectrograph is underway at IRAP/OMP (Toulouse, France), with cryostat cooling tests as part of the acceptance procedure.
Following assembly and alignment of the cryo-mechanics, the primary vacuum pump, turbo-molecular pump, cryogenic compressors and all gauges and sensors have been connected.
The first step was to establish the vacuum inside the cryostat down to 10-2 mbar. The turbo-molecular pump then resumed to reach a higher vacuum of 10-5 mbar. This stage, during which all the materials inside the cryostat exit naturally (rejecting dust and particles, in particular the multilayer insulation), takes a few days to reach a stable state.
Cooling can then begin, using compressors and helium coolers to lower the temperature inside the cryostat from room temperature (300 K) down to 80 K. A key parameter for the velocimetric accuracy of SPIRou is temperature stability to within 2 mK. This performance, already achieved during the integration phase in Victoria at the NRC-H laboratories, will be validated during this first cooling cycle.
These activities are led by Leslie Saddlemyer and Rob Messing, both from NRC-H (Victoria, Canada) and Nicolas Striebig from IRAP / OMP.