Anomalous attenuation at low temperatures in a high intensity helium beam source

  • Hedgeland H
  • Jardine A
  • Allison W
 et al. 
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High-intensity supersonic helium beam sources are a critical component
in modern thermal energy

helium atom scattering apparatuses. In common with sources developed
elsewhere, we have

observed beam attenuation at low temperature as the helium flow through
the nozzle is increased.

A detailed analysis of the measurements demonstrates that direct backscattering
in the

nozzle-skimmer region is likely to be the major attenuation source.
A numerical model, which

describes the principle sources of scattering in the region between
source and skimmer, is shown to

provide a good description of the experimental data for a range of
flow conditions and for stagnation

temperatures between 37 and 300 K. The model includes partial accommodation
of atoms scattered

from surfaces of the skimmer and chamber, together with a realistic
scattering potential. We use the

model to predict the effect of various geometric alterations, aimed
at improving the ultimate beam


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  • H Hedgeland

  • A P Jardine

  • W Allison

  • J Ellis

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