Apparatus and method for super-cooled operation of a cryostat with low quantities of coolant

Abstract

A cryostat arrangement ( 1 ′) having a vacuum container ( 2 ) and an object ( 4 ) to be cooled, which is arranged inside the vacuum container. A neck tube ( 8 ) leads to the object, and a cooling arm ( 10 ) of a cold head ( 11 ), around which a closed cavity ( 9 ) is formed, is arranged in the neck tube, which is sealed off fluid-tight in relation to the object and is filled with cryogenic fluid in normal operation. A thermal coupling element ( 15 ) couples the cryogenic fluid in the cavity to the object. A pump device ( 14 ), to which the cavity is connected via a valve ( 13 ) and with which the cavity is pumped out if the cold head fails. A monitoring unit ( 17 ) monitors the cooling function of the cold head, and activates the pump device to pump out the cavity if the cooling function of the cold head drops.

What is claimed is: 
     
         1 . A cryostat arrangement, comprising:
 a vacuum container containing an object to be cooled, wherein the vacuum container has a neck tube which leads to the object, a cooling arm of a cold head at least partially arranged in the neck tube, a closed cavity which is sealed off fluid-tight with respect to the object and is formed around the cooling arm and at least partially filled with a cryogenic fluid in normal operation, and a thermal coupling element configured to thermally couple the cryogenic fluid in the cavity with the object,   a pump device, to which the cavity is connected via an activatable valve and configured to pump the cavity out in the event of a drop in cooling function of the cold head, and   a monitoring unit configured to monitor the cooling function of the cold head, and to activate the pump device in response to a drop in the cooling function of the cold head such that the cavity is pumped out.   
     
     
         2 . The cryostat arrangement according to  claim 1 , wherein the object to be cooled comprises a superconducting magnetic coil system or a cryogen container. 
     
     
         3 . The cryostat arrangement as claimed in  claim 1 , further comprising a pressure sensor connected to the cavity and configured to output an output signal to the monitoring unit, wherein the monitoring unit is configured to activate the pump device to pump out the cavity as soon as the output signal of the pressure sensor exceeds a predefined first threshold value P max . 
     
     
         4 . The cryostat arrangement according to  claim 3 , wherein the pressure sensor is arranged in the cavity, and wherein 100 mbar≤P max ≤500 mbar. 
     
     
         5 . The cryostat arrangement as claimed in  claim 3 , wherein the pump device, following activation when exceeding the first threshold value P max , pumps out the cavity only until the output signal of the pressure sensor falls below a predefined second threshold value P min . 
     
     
         6 . The cryostat arrangement as claimed in  claim 5 , wherein 75 mbar≤P min ≤300 mbar. 
     
     
         7 . The cryostat arrangement as claimed in  claim 1 , wherein the activatable valve is configured as a regulating valve. 
     
     
         8 . The cryostat arrangement as claimed in  claim 7 , wherein the pump device is configured to operate at constant speed and/or constant pumping capacity. 
     
     
         9 . The cryostat arrangement as claimed in  claim 1 , wherein the pump device is configured to operate with variable speed and/or variable pumping capacity. 
     
     
         10 . The cryostat arrangement as claimed in  claim 9 , wherein the variable speed and/or the variable pumping capacity regulates pressure in the cavity. 
     
     
         11 . The cryostat arrangement as claimed in  claim 9 , wherein the activatable valve is configured as an ON/OFF valve. 
     
     
         12 . The cryostat arrangement as claimed in  claim 1 , wherein the pump device comprises an electrically operated suction pump buffered by an autonomous power source. 
     
     
         13 . The cryostat arrangement as claimed in  claim 12 , wherein the electrically operated suction pump is buffered with a battery. 
     
     
         14 . The cryostat arrangement as claimed in  claim 1 , wherein the pump device comprises a cryopump. 
     
     
         15 . The cryostat arrangement as claimed in  claim 14 , wherein the cryopump is integrated into the cryostat arrangement and comprises pumping cold surfaces that are thermally coupled to the object. 
     
     
         16 . The cryostat arrangement as claimed in  claim 15 , further comprising a connecting line that extends completely inside the vacuum container from the cavity to the pumping cold surfaces. 
     
     
         17 . The cryostat arrangement as claimed in  claim 1 , further comprising a supply line connected to the cavity and configured to refill the cavity with cryogenic fluid after the cooling function of the cavity is put back in the normal operation. 
     
     
         18 . A method for operating a cryostat arrangement comprising a vacuum container, an object to be cooled, and a thermal coupling element, wherein the object is arranged inside the vacuum container, wherein the vacuum container has a neck tube which leads to the object, wherein a cooling arm of a cold head is at least partially arranged in the neck tube, wherein a closed cavity, which is sealed off fluid-tight with respect to the object, is formed around the cooling arm, wherein the cavity is at least partially filled with a cryogenic fluid in normal operation, and wherein the thermal coupling element is configured to thermally couple the cryogenic fluid in the cavity with the object,
 comprising pumping the cavity out via a pump device such that the pressure in the cavity does not exceed a predefined first threshold value P max .   
     
     
         19 . The method as claimed in  claim 18 , wherein the cavity is pumped out via the pump device such that the pressure in the cavity does not fall below a predefined second threshold value P min <P max . 
     
     
         20 . The method as claimed in  claim 18 , further comprising using helium as a cryogenic fluid, and operating the pump device such that in the normal operation, the pressure in the cavity is between 100 mbar and 500 mbar. 
     
     
         21 . The method as claimed in  claim 20 , wherein the pressure in the cavity is between 200 mbar and 300 mbar. 
     
     
         22 . The method as claimed in  claim 18  for operating a cryostat arrangement, wherein the pump device is connected to the cavity via an activatable valve, and wherein a monitoring unit monitors the cooling function of the cold head and/or the pressure in the cavity, further comprising activating the pump device via the monitoring unit if the cooling function of the cold head drops and/or if the pressure in the cavity exceeds the predefined first threshold value P max  such that the cavity is pumped out to a pressure below the threshold value P max .