Magnetic structure for circular ion accelerator

Abstract

A magnet structure for use in a circular ion accelerator, such as e.g. a synchrocyclotron comprises a cold-mass structure including superconducting magnetic coils ( 20, 25 ), at least one dry cryocooler unit ( 10, 11, 12, 13 ) coupled with the cold-mass structure for cooling the latter and a magnetic yoke structure ( 30 ) with a return yoke ( 35 ) configured radially around said coils ( 20, 25 ). The return yoke ( 35 ) comprises an opening in which said dry cryocooler unit ( 10, 11, 12, 13 ) is received so as to be in thermal contact with said cold-mass structure.

The invention claimed is:  
     
       1. A magnet structure for use in a circular ion accelerator comprising:
 a cold-mass structure including superconducting magnetic coils; 
 at least one dry cryocooler unit coupled with the cold-mass structure and configured to cool the cold-mass structure; and 
 a magnetic yoke structure including a return yoke configured radially around the superconducting magnetic coils; 
 wherein the return yoke comprises an opening in which the at least one dry cryocooler unit is received so as to be in thermal contact with the cold-mass structure. 
 
     
     
       2. A magnet structure for use in a circular ion accelerator comprising:
 a cold-mass structure including superconducting magnetic coils; 
 at least one dry cryocooler unit coupled with the cold-mass structure and configured to cool the cold-mass structure; and 
 a magnetic yoke structure including a return yoke configured radially around the superconducting magnetic coils, 
 wherein the return yoke comprises an opening in which the at least one dry cryocooler unit is received so as to be in thermal contact with the cold-mass structure, the at least one dry cryocooler unit being received in the opening in a position essentially perpendicular to a central axis of the superconducting magnetic coils. 
 
     
     
       3. A magnet structure for use in a circular ion accelerator comprising:
 a cold-mass structure including superconducting magnetic coils; 
 a plurality of dry cryocooler units coupled with the cold-mass structure and configured to cool the cold-mass structure; and 
 a magnetic yoke structure including a return yoke configured radially around the superconducting magnetic coils, 
 wherein the return yoke comprises an opening in which the at least two dry cryocooler units are received so as to be in thermal contact with the cold-mass structure, the at least two dry cryocooler units being superimposed at a same radial position. 
 
     
     
       4. The magnet structure according to  claim 1 , comprising two openings spaced by an angle of 180°in the return yoke, wherein at least one cryocooler unit is received in each of the two openings. 
     
     
       5. The magnet structure according to  claim 4 , wherein two cryocooler units are superimposed in each of the two openings. 
     
     
       6. The magnet structure according to  claim 1 , wherein the cold-mass structure includes a bobbin associated with the superconducting magnetic coils, and the at least one dry cryocooler unit is in thermal contact with the bobbin. 
     
     
       7. The magnet structure according to  claim 6 , wherein the superconducting magnetic coils includes a current lead that is in thermal contact with the at least one dry cryocooler unit, so that the at least one dry cryocooler unit simultaneously cools the bobbin and the current lead. 
     
     
       8. The magnet structure according to  claim 6 , wherein the at least one dry cryocooler unit comprises a terminal cooling stage member that is in thermal contact with an outward wing of the bobbin, and the outward wing is in contact with a radial outer part of the magnetic coils. 
     
     
       9. The magnet structure according to  claim 1 , wherein the magnet structure has a central axis and a median plane perpendicular to the central axis, and the opening in which the at least one dry cryocooler unit is received is symmetric with regard to the median plane. 
     
     
       10. The magnet structure according  claim 1 , comprising a cryostat enclosing the cold-mass structure and forming a vacuum chamber for keeping the cold-mass structure under vacuum, the vacuum chamber comprising a radial vacuum chamber extension, and the at least one dry cryocooler unit including at least one cooling stage housed in the vacuum chamber extension, and a head part with a connector protruding out of the radial vacuum chamber extension. 
     
     
       11. The magnet structure according to  claim 10 , further comprising tie rods configured to support the cold-mass structure, each of the tie rods being positioned partly within a hollow tube, which extends the vacuum chamber for passing through the magnetic yoke structure. 
     
     
       12. The magnet structure according to  claim 11 , wherein at least one of the hollow tubes is coupled to a vacuum pump configured to create a vacuum in the cryostat. 
     
     
       13. The magnet structure according to  claim 1 , wherein:
 the cold mass structure includes at least two superconducting magnetic coils comprising a material being superconducting below a nominal temperature, the at least two superconducting magnetic coils being configured for having a common central axis; and a bobbin configured to support the at least two superconducting magnetic coils; and 
 the magnet structure further includes: 
 a cryostat enclosing the cold-mass structure and forming a vacuum chamber for keeping the cold-mass structure under vacuum, wherein the magnetic yoke structure surrounds the cryostat. 
 
     
     
       14. A synchrocyclotron comprising a magnet structure according to  claim 1 . 
     
     
       15. The magnet structure according to  claim 1 , wherein the at least one dry cryocooler is received in the opening such that the at least one cryocooler is essentially in a horizontal position.