LN2 continuous flow cryostats: a compact vibration free cooling system for single to multiple detector systems

Abstract

In comparison to mechanical cryo-coolers, liquid nitrogen cooling has the double advantage to be free of vibration and to remain not affected by power failure. The paper reports about a very compact cryostat using a continuous circulation of liquid nitrogen which is provided from an external storage tank. Since years, this cryostat is intensively used on the ESO VLT to cool either optical or Infra Red detectors. After an introduction presenting the principle, the paper reports the performance of the cryostat recorded over many years of utilization. We also present a few additional developments which allow the use of the cryostat for more exotic applications such that Nasmyth rotating instruments or extremely stable radial velocity spectrograph. With the construction of MUSE, a new era has started for this cryostat. The large multi IFU instrument requires 24 cryostats. The last chapter of the paper describes this futurist system which is close to completion.