Magnet Module

The Magnet Module is being assembled at Caltech.
  • The heart of the magnet module consists of two primary coils: one to produce the primary holding field (B0 ~ 30 milliGauss) and one to producing the oscillating “spin dressing” field (fd ~ 1 kiloHertz, Bd ~ 0.4 Gauss). There are also shim coils to tune the fields to get to the required uniformity and apply intentional gradients for systematic studies.
  • The magnet module is surrounded by a closed cylinder of superconducting lead to provide a final layer of protection against unwanted magnetic field variations. In addition to providing shielding, the cylinder endcaps act as magnetic mirrors, effectively lengthening the cylinder and greatly reducing fringe fields.
  • A cryogenic ferromagnetic layer acts as a flux return and improves field uniformity, mitigating the effect of errors in wire placement and reducing field distortions caused by the lead shield.
  • A copper eddy-current shield layer prevents heating of the cryogenic ferromagnetic layer during operation of the spin dressing coil.
  • A magnetic cloak layer wrapped on the outside of the superconductor layer reduces distortions of the MSE Coil field caused by the lead shield.
  • The entire package is built using a fiberglass space frame designed to provide the requisite position tolerance (<0.5mm over its 2.5m diameter) while respecting the non-metallic requirement inside the spin dressing copper shield and using the minimal material to keep cooling requirements manageable.
  • Assembly of one of the magnet’s horizontal hoops.
  • The magnet coils and shielding layers must be kept cold (well below the 7.2K superconducting transition of lead). So they are mounted inside the Outer Vacuum Chamber (OVC) to prevent warming through conduction, and inside two nested layers of thermal radiation shielding.