The use of powerful hydrogen cluster jet targets in storage ring experimentsled to the need of precise data on the mean cluster velocity as function of thestagnation temperature and pressure for the determination of the volume densityof the target beams. For this purpose a large data set of hydrogen clustervelocity distributions and mean velocities was measured at a high densityhydrogen cluster jet target using a trumpet shaped nozzle. The measurementshave been performed at pressures above and below the critical pressure and fora broad range of temperatures relevant for target operation, e.g., at storagering experiments. The used experimental method is described which allows forthe velocity measurement of single clusters using a time-of-flight technique.Since this method is rather time-consuming and these measurements are typicallyinterfering negatively with storage ring experiments, a method for a precisecalculation of these mean velocities was needed. For this, the determined meancluster velocities are compared with model calculations based on an isentropicone-dimensional van der Waals gas. Based on the obtained data and the presentednumerical calculations, a new method has been developed which allows to predictthe mean cluster velocities with an accuracy of about 5%. For this two cut-offparameters defining positions inside the nozzle are introduced, which can bedetermined for a given nozzle by only two velocity measurements.
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