Compact adiabatic demagnetization refrigeration stage with integral gas-gap heat switch

Abstract

An adiabatic demagnetization refrigeration stage includes a salt pill, a magnet surrounding the salt pill, and a gas-gap heat switch interposed between the salt pill and the magnet. A method of operating an adiabatic demagnetization refrigeration stage includes using a magnet surrounding a salt pill to apply an increasing magnetic field to the salt pill, producing a gas to activate a gas gap heat switch interposed between the magnet and the salt pill to provide a path for heat flow from the salt pill through the magnet to a heat sink, and decreasing the magnetic field applied to the salt pill while adsorbing the gas to de-activate the gas gap heat switch to cool the salt pill to a lower temperature and cool an object attached to a cold tip extending from the salt pill.

1 . An adiabatic demagnetization refrigeration stage comprising:
 a salt pill;   a magnet surrounding the salt pill; and   a gas-gap heat switch interposed between the salt pill and the magnet.   
     
     
         2 . The refrigeration stage of  claim 1 , wherein the salt pill comprises a paramagnetic material refrigerant in a helium atmosphere enclosed in a copper container. 
     
     
         3 . The refrigeration stage of  claim 1 , comprising a port in fluid communication with both the gas gap heat switch and a gas source for providing a gas and charge pressure to the gas gap heat switch. 
     
     
         4 . The refrigeration stage of  claim 1 , comprising a passive gas gap heat switch. 
     
     
         5 . The refrigeration stage of  claim 4 , comprising a getter thermally coupled to the salt pill and in fluid communication with the gas-gap heat switch. 
     
     
         6 . The refrigeration stage of  claim 1 , comprising an active gas gap heat switch. 
     
     
         7 . The refrigeration stage of  claim 6 , comprising a getter in fluid communication with the gas-gap heat switch and having an independent temperature control. 
     
     
         8 . The refrigeration stage of  claim 1 , wherein the gas gap heat switch comprises an outer surface of the salt pill substantially concentric with an inner surface of the magnet and a gas confined there between. 
     
     
         9 . The refrigeration stage of  claim 1 , wherein the gas gap heat switch comprises radially extending fins of an outer surface of the salt pill interleaved with radially extending fins of an inner surface of the magnet and a gas confined there between. 
     
     
         10 . The refrigeration stage of  claim 1 , comprising a structure supporting the salt pill within the surrounding magnet. 
     
     
         11 . The refrigeration stage of  claim 10 , wherein the structure comprises a standoff positioned around a bellows attached to a first end of the salt pill to constrain axial and lateral motion. 
     
     
         12 . The refrigeration stage of  claim 10 , further comprising a hub circumscribing a second end of the salt pill and a plurality of stays connecting the hub and a concentric cylindrical sleeve. 
     
     
         13 . A method of operating an adiabatic demagnetization refrigeration stage comprising:
 using a magnet surrounding a salt pill to apply an increasing magnetic field to the salt pill;   producing a gas to activate a gas gap heat switch interposed between the magnet and the salt pill to provide a path for heat flow from the salt pill through the magnet to a heat sink; and   decreasing the magnetic field applied to the salt pill while adsorbing the gas to de-activate the gas gap heat switch to cool the salt pill to a lower temperature and cool an object attached to a cold tip extending from the salt pill.   
     
     
         14 . The method of  claim 13 , comprising regulating the magnetic field to maintain the salt pill at the lower temperature. 
     
     
         15 . The method of  claim 13 , comprising providing the gas and a charge pressure to the gas gap heat switch using a port in fluid communication with both the gap and a gas source. 
     
     
         16 . The method of  claim 13 , comprising producing the gas using a getter thermally coupled to the salt pill and in fluid communication with the gas-gap heat switch. 
     
     
         17 . The method of  claim 13 , comprising producing the gas using a getter in fluid communication with the gas-gap heat switch and having an independent temperature control. 
     
     
         18 . The method of  claim 13 , comprising providing an increased surface area for heat transfer through the gas gap heat switch by interleaving radially extending fins of an outer surface of the salt pill with radially extending fins of an inner surface of the magnet. 
     
     
         19 . The method of  claim 13 , comprising supporting the salt pill within the surrounding magnet using a standoff positioned around a bellows attached to a first end of the salt pill to constrain axial and lateral motion. 
     
     
         20 . The method of  claim 13 , comprising supporting the salt pill within the surrounding magnet using a hub circumscribing a second end of the salt pill and a plurality of stays connecting the hub and a concentric cylindrical sleeve.