Monday, July 8, 2013

1307.1587 (Alexander Täschner et al.)

Determination of hydrogen cluster velocities and comparison with
numerical calculations

Alexander Täschner, Esperanza Köhler, Hans-Werner Ortjohann, Alfons Khoukaz
An experimental method is presented which allows for the velocity measurement of single clusters using a time-of-flight technique. Based on this method a detection setup was build up and implemented at the high density hydrogen cluster jet target at the University of M\"{u}nster. The measured velocity distributions of hydrogen clusters produced in a de Laval type nozzle are presented for different nozzle temperatures and hydrogen input pressures. Furthermore the determined mean cluster velocities are compared with model calculations based on an isentropic one-dimensional van der Waals gas model. The obtained data can be described well by the inclusion of two free parameters representing a freeze-out position of the clusters inside the nozzle from the fluid beam. With the knowledge of these parameters the model calculations enable for precise predictions of the mean cluster velocities as function of the gas input parameters, which in turn can be used for the calculation of cluster beam thicknesses. Furthermore, the gained experimental and numerical results indicate different hydrogen cluster formation processes depending on the temperature and pressure before entering the nozzle.
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