|
|
 |
|
The Cambridge Helium-3 Spin-Echo Spectrometer
The Cambridge instrument is designed to a enable the 3He spin-echo technique to be applied to a wide range of
surface dynamics experiments. It provides 3 order of magnitude improvement in resolution over existing
state of the art time-of-flight methods.
|
The photograph on the right shows the spectrometer, a full description of which is given in our Rev. Sci. Instrum. article (PDF here) [1].
Notable features include the polarisation of the helium beam, which is carried out using strong hexapole magnets,
which also focus the beam to improve intensity. Both the polariser hexapole [2,3] and the
analyser hexapole [4,5] use
carefully designed custom magnets to achieve maximum performance.
The spin-precession coils are based on the optimal field shape principle, and use a carefully designed
implementation achieved using detailed thermal and electromagnetic finite element simulations [5]. The 45 degree
geometry of the apparatus is designed to maximise the scattering performance and the range of surface experiments that
can be performed.
|
|
Figure 1: Photograph of the Cavendish spin-echo spectrometer (click for larger
version). The beam source is on the right, behind the helium-3 recycling system and control panel. The 3He beam
travels through the hexapole polariser and solenoid to the scattering chamber (top left). The scattered beam is
passed through the second solenoid and spin analyser, before finally reaching the detector (bottom
centre).
|
The following images and tables illustrate the layout and implementation of the Cambridge Spin-Echo instrument.
Figure 2: Top down schematic of the Cavendish spin-echo spectrometer (click for larger version)
| Parameter | Value |
|---|
| Total scattering angle | 44.4 degrees |
| 3He Angular Resolution | 0.1 degree |
| Nominal beam energy | 8 meV |
| Measured beam intensity | 1e14 atoms/second |
| Beam diameter at target | 2 mm |
| Energy resolution (spectrum reconstruction) | 2000 neV |
| Energy resolution (QE peak width) | 20 neV |
| Scattering chamber base pressure | 2e-10 mbar |
| Sample manipulator | 6 axis, titanium |
| Sample manipulator resolution | 0.003 degrees |
| Sample heating | Radiation / E-beam |
| Sample cooling | Liquid Nitrogen or Helium |
| Sample temperature range | 55 K - >1200 K |
References
- P. Fouquet, A.P. Jardine, S. Dworski, G. Alexandrowicz, W. Allison and J. Ellis, "Thermal energy 3He
spin-echo spectrometer for ultrahigh resolution surface dynamics measurements", Rev. Sci. Inst. 76, 053109
(2005).
- A. P. Jardine, P. Fouquet, J. Ellis and W. Allison, "Hexapole magnet system for thermal energy 3He manipulation",Rev. Sci. Inst. 72, 3834-3841 (2001).
- A. P. Jardine, "Quasi-elastic helium atom scattering: Interpretation and Instrumentation", PhD Thesis, University of Cambridge, November 2001.
- S. Dworski, G. Alexandrowicz, P. Fouquet, A. P. Jardine, W. Allison and J. Ellis, "Low aberration permanent hexapole magnet for atomic and molecular beam research", Rev. Sci. Inst. 75, 1963-1970 (2004).
- S. Dworski, "Atom Optical Methods for Surface Studies", PhD Thesis, University of Cambridge, October 2003
|
