Ionic liquid ion sources utilize electric fields to evaporate and accelerate ions and ion clusters to ∼1 keV energies. Ion clusters may dissociate after evaporation, which is not a well-characterized phenomenon and has relevant consequences in many applications. We measure the dissociation rate-constants of ion clusters for several ionic liquids. It is found that ion cluster dissociation occurs on timescales of the order of 1–5 μs and follows a constant-rate equation in the region outside the ion source. Using the measured rate-constants, we estimate the post-emission ion cluster temperatures. We also qualify the way the electric field enhances the rate-constants. Finally, our work supports the hypothesis that ion clusters with many degrees of freedom have lower dissociation rates.
The main emphasis of this paper is on the use of Retarding Potential Analyzers (RPAs) for measuring the electron and ion distribution functions, density, and temperature of space plasmas and the charging level of spacecraft surfaces interacting with the plasmas. Multiple grids of progressively negative potential are used to suppress the secondary electrons produced at the entrance of an RPA. We point out that it is impossible to achieve complete suppression. The secondary electrons collected by the receiver may produce a spurious lump in the distribution measured. Improved designs and space applications for spacecraft charging and ionic liquid ion beam diagnostics are discussed. Spacecraft charging will be very important for planetary explorations, whereas ionic liquid ion beams will be important for spacecraft propulsion in the future.
A description is given of apparatus with which the rate of decay of sound energy in a room may be measured. A loud speaker is used as a source of sound. When the sound has reached a steady state the loud speaker circuit is opened and at the same time a timer is started. When the sound energy has decayed to some definite value the timer is automatically stopped.
If made in a portable form this equipment may be used to study the acoustical properties of auditoriums.
Attention is called to the errors which may occur in these measurements.
Measurements are given showing absorption due to diaphragm action of materials.
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