Requirements and Conceptual Superconducting Magnet Design for a 21 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometer
The National High Magnetic Field Laboratory (NHMFL) has identified as one of its next high-field persistent-magnet targets a 21 T superconducting magnet system to be used in a Fourier Transform Ion Cyclotron Resonance (FT-ICR) Mass Spectrometer. The required fundamental parameters of a 21 T central field and 110 mm warm bore diameter are similar to those already successfully demonstrated in the NHMFL's Ultra-Wide Bore 900 MHz Nuclear Magnetic Resonance magnet system. However, there are several ancillary requirements of the FT-ICR spectrometer that require technical attention such as fringe field restrictions requiring shielding, length of uniformity zone, magnitude of inhomogeneity, horizontal orientation of the magnet axis and a limitation on the length of the cryostat. This paper describes the overall system requirements, features and status of the superconducting magnet conceptual design proposed for meeting these requirements
Axial mechanical properties of epoxy impregnated superconducting solenoids at 4.2 K
The mechanical properties of superconducting solenoids along their longitudinal axes were characterized at 4.2 K through a series of tests on small epoxy impregnated coils. Three coil configurations were manufactured which consisted of two layers of either Nb/sub 3/Sn or NbTi. The Nb/sub 3/Sn conductor was insulated with E-Glass fiber braid insulation and the NbTi conductor was insulated with either polyester braid or Polyvinylformal (FORMVAR). Characteristics including the elastic modulus, allowable compressive stress, cyclic loading behavior, and, of primary interest, ultimate tensile strength were measured. Samples were compressed to 200 MPa and fatigued 100 cycles from -125 MPa to 25 MPa. The tensile strengths are shown to be dependent of the insulation material and range from 51.9 MPa to 62.8 MPa.
Cryostat Design for the “Bucket Test” of the NHMFL 900‐MHz NMR Magnet
The NHMFL 900‐MHz magnet is a 40‐MJ, 7‐t solenoid designed for NMR spectrometry in a 105‐mm warm bore. Prior to installation in its final cryostat, it was decided to test the magnet in an available “bucket” dewar to confirm proper operation of all components, requiring design and construction of a special cryostat for this purpose. The primary requirements for the cryostat were to use the existing bucket dewar (1.52‐m i.d. × 3.66‐m i.h.) and cool the magnet to near HeII temperatures as efficiently as possible. With the large and relatively short conduction path formed by the inner dewar wall and the 2 m3 vapor volume above the liquid capped by a 2 m2 surface at room temperature, the latter requirement was not an easy one to meet. In this paper we describe a cryostat design based on an internal, subatmospheric bath continuously fed by an external reservoir of normal liquid. The vapor stream evolved from the internal bath was used to intercept heat in various paths, e.g.: the incoming LHe stream, a system o...