The ECOMA particle detector
We introduce the concept of a new rocket-borne detector for the measurement of nanometer-scale meteoric dust particles. This particle detector is a combination of a Faraday-cup and a Xenon-flashlamp for the photo-ionization of meteor dust particles.
Design of the detector
The design of the Faraday cup comprises a collector electrode (held at the payload potential by a negative feedback loop of the electrometer) for the measurement of particles of either positive or negative charge and two grids (biased at ±3-6 V relative to payload potential) to shield the collector electrode against electrons and ions. This classical design of a Faraday Cup is combined with a Xenon-flashlamp (in the center of the Cup) which emits UV-photons for the active photo-ionization of particles.
The sensitive electrometer has two channels with corresponding sampling rates of 1 and 100 kHz. The flash lamp is operated at a repetition rate of 20 Hz. The detection scheme sketched below.
The duration of the current which is artificially produced by the photo-ionization induced by the flash light is shorter than 50 microseconds. In order to resolve this short pulse, we record the first 48 samples after the flash at a rate of 100 kHz (see middle panel in sketch above). These measurements yield information about the total particle number density.
In the 1 kHz channel we obtain 48 samples between two subsequent flashes (see lower panel in sketch above) where only the first sample (next to the flash) is influenced by the photo-current due to the flash lamp. Hence, the electrometer measures the natural net charge (either negative or positive) of the particles, if there is any. Hence, the measurements by this channel yield information about the number density of charged fraction of the meteor smoke particles.