The effect of high-velocity dust particle impacts on microchannel plate (MCP) detectors

The detection efficiency and durability of a microchannel plate (MCP) detector to direct impacts of high-velocity dust particles is investigated experimentally. A new type of in situ time-of-flight cosmic dust analyzer instrument has been developed, where the ion detector is exposed to occasional impacts of cosmic dust particles. The dust accelerator facility operated at the University of Colorado is used to directly measure the effect of dust impacts on a commercial, off-the-shelf microchannel plate (MCP) detector. The MCP is exposed to approx. 480 dust particle impacts from wide size and velocity ranges of 0.05-1.6 mu m radii and 2-35 km/s, respectively. The dust impact events are registered with 96% efficiency. Of these, 57% of the output signals are single charge pulses, and 43% are more complex signals that suggest ion feedback mechanisms within the detector. For all dust detection events, the output charge pulse is significantly larger than those from the detection of single ions or photons. The gain of the MCP detector shows no apparent degradation after the bombardment. In the investigated size/velocity range, the dust particles do not pose a risk of damaging the MCP. Scanning electron microscope images show that the impact generated craters are small, on the order of the size of the impacting particles. The performed measurements and the extrapolation of the results to the worst case expected to occur for the duration of a spaceflight mission indicate that MCP detectors require protection from dust impacts in order to reduce the risk of detector damage for these types of dust analyzer instruments, and a mechanism for providing protection is described.