Minimising Interference in Low-Pressure Supersonic Beam Sources

TL;DR

This paper introduces a simple analytical model for low-pressure supersonic beam sources that predicts interference effects, validated by experiments, and offers design recommendations to minimize interference especially at cryogenic temperatures.

Contribution

The paper presents a parameter-free analytical theory for low-pressure supersonic beam sources that simplifies previous complex models and guides interference minimization.

Findings

Skimmer interference is negligible compared to background gas attenuation at room temperature.

The model matches experimental data without free parameters.

Design recommendations are provided for cryogenic beam sources.

Abstract

Free-jet atomic, cluster and molecular sources are typically used to produce beams of low-energy, neutral particles and find application in a wide array of technologies, from neutral atom microscopes to instruments for surface processing. We present a simple analytical theory that is applicable to many of these sources, when (i) the nozzle-skimmer distance is such that free molecular flow is achieved and (ii) there is negligible interference within the skimmer itself. The utility of the model is demonstrated by comparing experimental data with calculations performed using the theory. In particular, we show that skimmer interference is negligible compared to attenuation by 'background' gas for room-temperature beams. Our treatment does not depend on any free parameters and obviates the complexity of previous theories. As a result, we are able to devise a number of design recommendations to minimize interference in sources operating with cryogenic-temperature beams.