Author: Mitchell, R.
Paper Title Page
Manufacture of a 7.5 M Long Cryogen-Free Magnet System for Neutron Decay Studies  
  • R. Mitchell, J. Good
    Cryogenic Ltd, Acton, London, United Kingdom
  The design of a large purpose built cryogen-free magnet is reviewed. The system has been manufactured for the Fundamental Neutron Physics Beamline at the Spallation Neutron Source in Oak Ridge, Tennessee. The magnet system will house a custom spectrometer and be used to measure a, the electron-neutrino correlation parameter, and b, the Fierz interference term in neutron beta decay. The cryostat is cylindrical, 7.5m along its axis and 1.43 m in diameter. It houses a complex set of niobium-titanium superconducting windings which provide a varying magnetic field profile along a 320mm diameter gold-plated UHV bore. The bore tube extends along the full length of the cryostat and has orthogonal ports connected to the neutron beamline. A vacuum of <3.10-10 mbar is achieved. The stray field generated by the magnet windings is compensated by a series of negatively wound co-axial windings which have approximately twice the diameter of the internal positive windings. The cryostat system will be housed in a passive steel shield to further compensate the stray field. No liquid cryogens are used for normal operation of the system.  
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