Hannover 2013 – scientific programme

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MO: Fachverband Molekülphysik

MO 18: Experimental Techniques

MO 18.6: Talk

Wednesday, March 20, 2013, 15:15–15:30, F 102

Stationary Flow Conditions in Pulsed Supersonic Beams — •Wolfgang Christen and Bo-Gaun Chen — Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489 Berlin, http://clusterlab.de

One of the most relevant characteristics of pulsed supersonic jets is the duration of the steady hydrodynamic flow: Due to the complex collision dynamics at elevated densities current model calculations are based on the assumption of a quasi-continuous flow. Accordingly, a comparison of experimental results with theoretical models requires a sufficiently long opening of the valve. Too short opening times do not allow for the evolution of stationary beam properties and may lead to incorrect conclusions.

We present a comprehensive analysis of this key aspect, using a focused electron beam with a short on-time for tagging a localised portion of the expanding jet, permitting measurements with high spatio-temporal resolution. It also provides an invaluable diagnostic tool for characterising the evolution of beam properties within the very short particle bunches of fast acting valves. In particular, the study reveals that the true opening time of the valve may be strikingly longer than the control pulse applied to the valve driver. Although pulse durations as short as 10 µs are possible, much longer pulse durations are required for an optimised adiabatic cooling. Also, the in-depth analysis of arrival time distributions for different pulse durations of the valve allows for the identification of quasi-continuous flow conditions with respect to number density, translational temperature, and particle speed.