Ultra-precise particle velocities in pulsed supersonic beams

Analysis of the piezo- and pyroelectric response of PVDF foils as fast particle detectors in pulsed supersonic jets

We report the design and performance of a new, rugged, general-purpose particle detector consisting of a stretched foil of polyvinylidene difluoride. Several detectors have been built and evaluated for applications in pulsed supersonic jet experiments where, e.g., particle density shall be measured with high time resolution. The working principle is that a directed bunch of particles, moving in vacuum, collides with the sensitive detector area and generates an electric charge. This charge generation is due to both the piezo- and the pyroelectric effect and results in a very fast detector response. In our detailed analysis of the detected signal, the piezoelectric contribution is defined by the constitutive equations of piezoelectricity, which are used in combination with the concept of a driven damped circular membrane allowing to obtain an analytic solution. The pyroelectric contribution is described via the exchanged energy between the impinging particle pulse and the detector foil. Because both the piezo- and the pyroelectric effects can be exploited, additional information about the particle impact such as the coefficient of energy accommodation or the coefficient of restitution can be determined experimentally.

A low energy ion beam facility for mass spectrometer calibration: First results

The exploration of habitable environments around the gas giants in the Solar System is of major interest in upcoming planetary missions. Exactly this theme is addressed by the Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA), which will characterise Ganymede, Europa, and Callisto as planetary objects and potential habitats. The NIM, Neutral gas and Ion Mass spectrometer, is part of the PEP experiment and will be used to measure the chemical composition of the exospheres of the icy Jovian moons. We designed and developed a calibration facility (SATANS, Supersonic cATion and ANion Source), especially for use with the NIM instrument. In a first step, we established a low energy ion beam for positive ions in the range of 0.01-30 eV. Then we conducted beam velocity calibrations with a velocity uncertainty <5%, which provided exact settings and formulas for the cation beam velocity of different gas mixtures in the range of 1-15 km/s. In addition, first results are obtained by using the NIM prototype for direct ion beam measurements under realistic JUICE mission conditions, i.e., for velocities from 1 up to 7 km/s and even more.

Determination of hydrogen cluster velocities and comparison with numerical calculations

The use of powerful hydrogen cluster jet targets in storage ring experiments led to the need of precise data on the mean cluster velocity as function of the stagnation temperature and pressure for the determination of the volume density of the target beams. For this purpose a large data set of hydrogen cluster velocity distributions and mean velocities was measured at a high density hydrogen cluster jet target using a trumpet shaped nozzle. The measurements have been performed at pressures above and below the critical pressure and for a broad range of temperatures relevant for target operation, e.g., at storage ring experiments. The used experimental method is described which allows for the velocity measurement of single clusters using a time-of-flight technique. Since this method is rather time-consuming and these measurements are typically interfering negatively with storage ring experiments, a method for a precise calculation of these mean velocities was needed. For this, the determined mean cluster velocities are compared with model calculations based on an isentropic one-dimensional van der Waals gas. Based on the obtained data and the presented numerical calculations, a new method has been developed which allows to predict the mean cluster velocities with an accuracy of about 5%. For this two cut-off parameters defining positions inside the nozzle are introduced, which can be determined for a given nozzle by only two velocity measurements.