3023/JN - Dilution Refrigerator and Magnet System

The Department of Physics and Astronomy at The University of Sheffield, with funding from the Science and Technology Facilities Council (STFC) requires a dilution refrigerator and magnet system for use in a search for hidden sector dark matter. The dilution refrigerator will be appropriate for cooling a two-component payload, consisting of (i) An electromagnetic resonator, such as a conducting-wall resonant cavity; and (ii) Ultra-low-noise readout electronics in as close proximity as possible to the resonator, allowing them to be coupled together. The space for the electromagnetic resonator should be threaded by a static magnetic field of nominal magnitude 8T, The ultra-low-noise readout electronics should be in a magnetic-field-free region, with magnetic field exclusion achieved via a combination of a field compensation coil and passive normal-conducting and superconducting shields mounted in the bore of the compensation coil. The operating base temperature of the refrigerator should be not more than 10mK at the mixing chamber plate, where the cooling power should be at least 12 microwatts at 20mK and at least 400 microwatts at 100mK. The experiment will run cold and at with the magnetic field threading the cavity for at least 6 months at a time without need to be warmed up. The refrigerator should utilize mechanical pre-cooling to a sufficiently low temperature for the dilution refrigerator to operate, so that the only liquid cryogens that are required are the helium3/helium4 mixture in the closed cycle dilution refrigerator unit and some liquid nitrogen that may be required for a cold trap in the gas handling unit. The system should incorporate its own reliable control system and software for ease of control, and this control system should also be remotely operable from the data acquisition system of the experiment, via an appropriate cable interface. A schedule of tests required to demonstrate function upon delivery of the apparatus are supplied in the technical specification.