A novel design for a high intensity micron-scale supersonic free-jet source is described. This design has been implemented in a scanning helium neutral atom microscope at Portland State University, but has not been otherwise investigated. It is proposed that removing the skimmer component of a free-jet source can, under correct operating conditions, allow a comparable intensity beam to be created at greatly reduced complexity. The dsmcFOAM OpenFOAM solver was used to model rarefied gas dynamics of skimmed and un-skimmed helium atom sources. This modeling suggests that gas-gas scattering and shock structures occur in un-skimmed sources but can be compensated for with small aperture diameters and high source flow rates. If the comparable operation of skimmed and un-skimmed sources can be demonstrated it will greatly reduce the cost and complexity of helium atom sources for neutral atom microscopy and other applications.
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