Hexapole magnet system for thermal energy 3He atom manipulation

We present design and construction details for a novel high field, small bore permanent hexapole magnet. The design is intended for focusing atomic beams of He-3 at thermal energies. The magnet uses an optimized polepiece design which includes vacuum gaps to enable its use with high intensity atomic and molecular beams. The 0.3 m long, 1 mm internal radius magnet achieves a polepiece tip field of 1.1 T using NdFeB permanent magnets and Permendur 49 polepieces. The polepiece shanks are designed to saturate so that the hexapole properties are determined predominantly by the shape of the polepiece tip. The performance of the hexapole assembly is demonstrated with an 8 meV He-3 beam in the beam source of the Cambridge spin echo spectrometer and the measured focused beam results show excellent agreement with theoretical predictions and negligible beam attenuation. (C) 2001 American Institute of Physics.