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Other experimental considerations

Several other experimental considerations concerning the construction of a jet source ion beam, are summarised below:

An increase in ion beam current and cooling could be obtained if the nozzle pressure was increased to pressures greater than 3 bar. The diffusion pump in the source region showed no signs of stalling when operating with Helium at 3 bar, (the backing line pressure was 0.05 torr, well below the maximum allowed value of 0.5 torr). However, any effect of higher pressures on the pinhole surface needs to be considered, although little damage to the nozzle was observed during the experiments documented in the previous sections.

An alternative method for increasing the beam current would be increasing the high voltage applied to the source region. However, this probably involves a re-design of the nozzle/gas line assembly, to prevent electrical breakdown, which inevitably occurs above 2.5 kV. Finally, water (see Bieske et al. [119]) or liquid nitrogen (see Carrington et al. [115]) cooling of the nozzle may yield further reduction in the beam temperature with only minor modifications to the existing apparatus.


next up previous contents
Next: Conclusions Up: Estimation of temperature Previous: Shielding the source   Contents
Tim Gibbon
1999-09-06