Analysis, Simulation and Design of Cryogenic Systems for ALMA Band 5 Prototype Cartridge

Paper in proceeding, 2009

The ALMA frontend is designed for ten separate receivers channels covering 30-960 GHz range; the receiver accommodates these receiver channels as pluggable, fully electrically autonomous cartridges. These cartridges share the same cryogenic cooler. ALMA Band 5 cartridge is a dual-polarization heterodyne receiver employing 2SB SIS mixers with IF band 4-8 GHz and covers the frequency 163-211 GHz. The prototype for the ALMA Band 5 cartridge development is carried out by Group for Advanced Receiver Development (GARD) in Gothenburg, Sweden with the aim to provide six Band 5 cartridges for ALMA Project. The first prototype cartridge is currently being assembled. ALMA Band 5 cartridge is the lowest frequency channel in the ALMA receiver that employs all cold optics and thus has the biggest rim of the mirrors amongst other ALMA bands placed on the 4K cartridge plate. The size of the optics and its supporting brackets puts severe constrains on the design of the receiver. Another important issue of the Band 5 cartridge design, as well as other ALMA cartridges, is a very tight thermal budget. In this report, we present analysis and simulation results for the thermal and mechanical design of the ALMA Band 5 cartridge that has been carried out using different FEM software packages such as CFDesign and ANSYS. We compare simulation results obtained with these software and the analytical calculations. For the mechanical design, the major focus was put on the cartridge and the optics support structure deformation with cooling.