Small cryostem for operation of Visible Light Photon Counters (VLPC)

We have designed, constructed, and operated a small cryostem which supports the operation of 32 channels of Visible Light Photon Counters (HISTE-IV VLPCs). The VLPCs are situated within a small enclosure which can be lowered into a 36-100 liter dewar. The enthalpy of the boil-off helium keeps the VLPCs cold, and allows the system to be operated with stability for many days within the desired temperature range of 6-7.5 K. The cryostem is instrumented with clear fiber waveguides which transport the light from an optical connector situated at the top of the cryostem and outside of the dewar to the photosensors at cryogenic temperatures within the dewar. Electrical signals from the VLPCs are amplified at room temperature using QPA02 preamplifiers. Details of design and performance are reviewed.