Hexapole magnet system for thermal energy He3 atom manipulation

Abstract

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 He3 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 He3 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.

Anomalous attenuation at low temperatures in high-intensity helium beam sources

“…6,7 The beam source utilizes a nearly free jet expansion, operating in the low-pressure "diffusion-pumped" regime, 2 using a nozzle assembly with a 20 m aperture. 19,26 The beam is deposited into a small measurement chamber with a welldefined vacuum pumping speed. The centerline of the expansion is skimmed off using a 0.5 mm type 2 Beam Dynamics skimmer 8 before being passed through several differential pumping stages to reduce the background pressure around the beam.…”

Probing the short range spin dependent interactions by polarized $$^{3}$$ 3 He atom beams

“…In order to further improve the sensitivity of detecting the spin dependent short range interactions, we propose an experiment using nuclear spin polarized 3 He atom beams. Though in principle other spin-1/2 species as 129 Xe might also work, the polarized 3 He beam technique is more convenient, since it has been well developed and applied to the study of the surface dynamics in condensed matter physics for many years [18,19]. Reference [20] is a very nice review for the recent developments of the so-called polarized 3 He spin-echo technique.…”

“…The speed of the beam can be controlled by adjusting the nozzle temperature. Then the beam is polarized by a beam polarizer which is made of hexapole magnets [19]. High intensity (1.5 × 10 14 atoms/s reported in Ref.…”

A magnetically focused molecular beam source for deposition of spin-polarised molecular surface layers

“…The propagating beam goes through a 500 µm skimmer (2) and two further di↵erential pumping stages before entering the chamber which houses the focusing hexapole magnet (3). The hexapole magnet is built from 9 hexapole magnet elements following the basic design introduced by Jardine et al [23]. The magnetic field leads to a Zeeman splitting of the quantized energy levels, which depends on the projection of the spin along the quantization axis, I z .…”