Proposed Rapid Cooldown Technique for Pulse Tube Cryocoolers
Ray Radebaugh, Agnes O¿Gallagher, Michael A. Lewis, Peter E. Bradley
Some cryocooler applications, such as those for military operations dealing with high temperature superconducting (HTS) magnets, motors, or generators, require faster cooldown times than what can normally be provided with a cryocooler designed to accommodate a relatively small steady-state heat load. The current approach to achieve fast cooldown is to use a cryocooler oversized for steady-state operation. This paper proposes a new method applicable only to pulse tube cryocoolers that may decrease cooldown times a factor of two or three when cooling to temperatures in the range of 50 K to 80 K from room temperature without increasing the size of the cryocooler. Such temperatures are appropriate for HTS magnets, generators, or motors. The proposed method makes use of the resonance phenomena that occurs with an appropriately sized combination of inertance tube and reservoir volume. With a small reservoir, an LC resonance effect can occur at typical operating frequencies, with C being the compliance (volume) of the reservoir and inertance tube and L being the inertance of the inertance tube. At or near resonance the input acoustic impedance to the inertance tube is low, which allows for a high acoustic power flow at the pulse tube cold end for a given pressure amplitude. When the reservoir volume is increased to its normal size, the impedance increases to the value optimized for steady-state operation. A simple ball valve can then be used to change the reservoir volume and to switch from the fast cooldown mode to the steady-state mode. The higher acoustic power flow can be accommodated by the pulse tube and regenerator when they are at or near room temperature. In most cases the higher acoustic power in the fast cooldown mode does not require additional input power to the pressure oscillator because the load impedance is a closer match to that of the oscillator compared to that of the normal load during cooldown.
, O¿Gallagher, A.
, Lewis, M.
and Bradley, P.
Proposed Rapid Cooldown Technique for Pulse Tube Cryocoolers, Cryocoolers 14, Annapolis, MD, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50411
(Accessed June 2, 2023)