Superconducting magnet system with pulse tube cooler

Abstract

A superconducting magnet system with an operating temperature T 1 <3K which is disposed in a first helium tank ( 4 ) of a cryostat ( 1 ), wherein a second helium tank ( 2 ) is provided which is connected to the first helium tank ( 4 ) and contains liquid helium at an operating temperature T 2 >3K, wherein a cooling means is provided in the first helium tank ( 4 ) which generates an operating temperature T 1 <3K in that first helium tank ( 4 ) is characterized in that the cooling means is the cold end ( 19 ) of a pulse tube cooler ( 11 ) whose warm end ( 10 ) is disposed outside of the cryostat ( 1 ). The inventive magnet system minimizes the helium consumption thereby providing continuous measuring operation.

1 . A magnet system having a superconducting magnet disposed in a cryostat, the system comprising: 
 a first helium tank disposed in the cryostat, the superconducting magnet being disposed in said first helium tank, said first helium tank containing liquid helium at an operating temperature T 1 <3K;    a second helium tank disposed in the cryostat above and in liquid helium communication with said first helium tank, said second helium tank containing liquid helium at an operating temperature T 2 >3K; and    a pulse tube cooler, said pulse tube cooler having a cold end disposed in said first helium tank to generate said operating temperature T 1 <3K, said pulse tube cooler having a warm end disposed outside of the cryostat, below said first helium tank.    
   
   
       2 . The magnet system of  claim 1 , wherein the magnet system is structured and dimensioned for magnetic resonance measurements.  
   
   
       3 . The magnet system of  claim 1 , wherein said pulse tube cooler has several stages.  
   
   
       4 . The magnet system of  claim 1 , wherein said pulse tube cooler has two stages.  
   
   
       5 . The magnet system of  claim 3 , wherein a stage of said pulse tube cooler upstream of said cold end is thermally conductingly connected to a radiation shield disposed in the cryostat.  
   
   
       6 . The magnet system of  claim 5 , wherein said radiation surrounds said first and said second helium tanks to replace a liquid nitrogen tank in the cryostat.  
   
   
       7 . The magnet system of  claim 1 , further comprising a thermal barrier disposed in the cryostat between said first and said second helium tanks, said thermal barrier having a residual conductivity to further cool helium in said second helium tank and minimize consumption of liquid helium therein.  
   
   
       8 . The magnet system of  claim 1 , wherein said second helium tank has a heater to adjust a pressure in said second helium tank through heating.  
   
   
       9 . The magnet system of  claim 1 , wherein said pulse tube cooler contains a regenerator material substance having a phase transition.  
   
   
       10 . The magnet system of  claim 9 , wherein said phase transition is a magnetic phase transition.  
   
   
       11 . The magnet system of  claim 10 , wherein said the regenerator material is magnetically shielded in the cryostat.  
   
   
       12 . The magnet system of  claim 1 , wherein said pulse tube cooler contains helium as a regenerator material.  
   
   
       13 . The magnet system of  claim 1 , wherein a section of said pulse tube cooler which contains a regenerator is disposed at a location in the cryostat having a minimum magnetic field during operation.  
   
   
       14 . The magnet system of  claim 1 , wherein the cryostat and said pulse tube cooler are designed and dimensioned such that helium must not be refilled into the cryostat during operation of the magnet system.  
   
   
       15 . The magnet system of  claim 1 , wherein the magnet system comprises a main field magnet coil and an active shielding coil which is disposed coaxially with respect to and radially outside of said main field magnet coil, wherein a common axis of said main field and said active shielding coils is vertical and said cold end of said pulse tube cooler is disposed between said main field magnet coil and said shielding coil.  
   
   
       16 . The magnet system of  claim 1 , wherein said cryostat has a valve for filling-in helium, said valve being connected to at least one of said first and said second helium tanks.