Cryostat configuration with cryocooler and gas gap heat transfer device

Abstract

A cryostat configuration for keeping liquid helium comprises an outer jacket ( 1 ) surrounding a helium container ( 2 ) connected at at least two suspension tubes ( 3 ) to the outer jacket ( 1 ), and with a neck tube ( 4 ) whose upper warm end ( 5 ) is connected to the outer jacket ( 1 ) and whose lower cold end ( 6 ) is connected to the helium container ( 2 ) and into which a multi-stage cold head of a cryocooler ( 7 ) is installed, wherein the outer jacket ( 1 ), the helium container ( 2 ), the suspension tubes ( 3 ) and the neck tube ( 4 ) delimit an evacuated space, and the helium container ( 2 ) is surrounded by at least one radiation shield ( 8 ) which is connected in a heat-conducting fashion to the suspension tubes ( 3 ) and also to a contact surface ( 9 ) on the neck tube ( 4 ) of the helium container ( 2 ). The cryostat configuration is characterized by a gas gap ( 13 ) between one or more cold stages of the cold head ( 7 ) and one or more contact surfaces ( 9 ) in the neck tube ( 4 ) which are each connected in a heat-conducting manner to a radiation shield ( 8 ) via a fixed, rigid or flexible thermal bridge ( 12 ), heat being transferred through the gas gap ( 13 ) from the respective radiation shield ( 8 ) to the corresponding cold stage of the cold head ( 7 ). A cryostat configuration of this type ensures that no vibrations of the cold head ( 7 ) stages pass detectably into the cryostat configuration, wherein the quality of the thermal connection between the cold head ( 7 ) and the radiation shield(s) ( 8 ) is nevertheless sufficient.

1 . A cryostat configuration for keeping liquid helium, the cryostat configuration comprising: 
 an outer jacket;    a helium container disposed within said outer jacket;    a least two suspension tubes connected between said helium container and said outer jacket;    a neck tube having an upper, warm end connected to said outer jacket and a lower, cold end connected to said helium container;    a cryocooler, said cryocooler having a multi-stage cold head extending into said neck tube, wherein said outer jacket, said helium container, said suspension tubes, and said neck tube delimit an evacuated space, wherein at least one cold stage of said cold head and at least one contact surface of said neck tube define a gas gap;    at least one radiation shield surrounding said helium container; and    a thermal bridging means for fixed, rigid or flexible heat-conducting connection between said at least one radiation shield and at least one suspension tube as well as between said at least one radiation shield and said at least one contact surface of said neck tube, wherein heat is transferred through said gas gap from said at least one radiation shield into said at least one cold stage.    
   
   
       2 . The cryostat configuration of  claim 1 , wherein said cryocooler is a pulse tube cooler.  
   
   
       3 . The cryostat configuration of  claim 1 , wherein helium is liquefied at a temperature of 4.2 K or less at a coldest cold stage of said cryocooler cold head.  
   
   
       4 . The cryostat configuration of  claim 1 , wherein tubes of said cold head of said cryocooler, above a first cold stage and/or in a region of further cold stages, are surrounded with thermal insulation.  
   
   
       5 . The cryostat configuration of  claim 1 , wherein a width of said gas gap can be freely adjusted.  
   
   
       6 . The cryostat configuration of  claim 1 , further comprising means for increasing areas of opposing heat transferring surfaces delimiting said gas gap.  
   
   
       7 . The cryostat configuration of  claim 6 , wherein said area increasing means comprises fins.  
   
   
       8 . The cryostat configuration of  claim 1 , wherein a colder, heat-transferring surface which is rigidly connected to a cold stage of said cryocooler cold head is disposed above a warmer, heat-transferring contact surface.  
   
   
       9 . The cryostat configuration of  claim 8 , wherein a width of said gas gap can be increased until a natural convection flow occurs therein.  
   
   
       10 . The cryostat configuration of  claim 1 , wherein a gas-flow through said gas gap is externally driven to improve heat transfer.  
   
   
       11 . The cryostat configuration of  claim 1 , wherein at least said one of said radiation shields includes a container holding liquid nitrogen, wherein said nitrogen is at least partially reliquefied after evaporation due to thermal connection between said radiation shield and said cold head of said cryocooler.  
   
   
       12 . The cryostat configuration of  claim 11 , further comprising a first heater disposed in or in contact with a nitrogen container.  
   
   
       13 . The cryostat configuration of  claim 12 , wherein said first heater is an electric heater.  
   
   
       14 . The cryostat configuration of  claim 1 , further comprising a second heater disposed in or in contact with said helium container.  
   
   
       15 . The cryostat configuration of  claim 14 , wherein said second heater is an electric heater.  
   
   
       16 . The cryostat configuration of  claim 1 , wherein the cryostat configuration is structured to hold a superconducting magnet.  
   
   
       17 . The cryostat configuration of  claim 16 , wherein the superconducting magnet is part of an apparatus for magnetic resonance for magnetic resonance imaging (MRI) or for nuclear magnetic resonance spectroscopy (NMR).