posters 5th Asia-Pacific NMR Symposium 2013

Cryogen-free superconducting magnet design for NMR (#176)

Michael Mallett 1 , Donald Pooke 1 , Gianni Ferrante 2 , Salvatore Bubici 2
  1. HTS-110, Lower Hutt, New Zealand
  2. Stelar srl, Mede, Italy

For NMR applications, fields above 1.5 tesla are only practical with superconducting magnets. It has long been thought that the challenges of vibration, stability, and robustness made traditional superconducting magnets impractical for industrial NMR applications. We report the development and successful operation of cryogen-free High Temperature Superconducting (HTS) magnets for NMR operating at 4.7 T (200MHz) and 3 T (125MHz) that address these issues.

To overcome the burden of helium and nitrogen refills, cryogen-free magnets are attractive for materials research applications such as beamline magnets and hard disk drive materials research. The availability of high capacity HTS conductors has made  development of magnets  suitable for NMR application possible. NMR systems using self-shielded HTS-NMR magnets have now accumulated several years of successful operation in five different countries. In particular the 3T system for relaxometry, provides a vital tool in the development of new contrast agents for magnetic resonance imaging.  

Magnets were manufactured using BSSCO superconductors and exhibit homogeneity of 0.25 ppm before electric shimming for FT-NMR applications and 15 ppm for variable field relaxometry application. High capacity cryocoolers enable rigid coil supports to be used whilst maintaining operating temperatures at 15-30 K, where the wire performance can sustain the desired high fields.  HTS magnets do not operate in a persistent-current mode, special high stability power supplies are used to operate the magnet at any desired field strength.

These magnets will form the basis of a new class of NMR instrument for industrial environments, enabling innovative solutions that combine variable field relaxometry with FT-NMR. Future developments will include higher fields for both variable field relaxometry and FT-NMR.