Reduction of heat load of LCGT cryostat

An unexpected large heat load was observed in a cooling test of the cryostat for a prototype cryogenic interferometric gravitational wave detector. By conducting additional studies involving an experiment and a simulation, we found that the large heat load was caused by conduction of thermal radiation in a thermal radiation shield pipe, which was inserted in the beam duct to reduce solid angle from 300K to 4K. To achieve the design of LCGT cryogenic system, the heat load had to be reduced below a few percent. By introducing metal baffles in the shield pipe, this requirement was fulfilled.