Image translational shifts in microchannel plate detectors due to the presence of MCP channel bias

A detailed study of possible image displacements in MCP detectors due to the presence of MCP pore bias is presented. We show that fluctuations of the rear accelerating field, characteristic to some MCP detector configurations, result in translational shifts of the entire image, which degrade the detector spatial resolution. It was experimentally observed that a 10% increase in the rear voltage of 400 V for a detector with 13°-biased MCPs and 8.5 mm MCP-to-anode distance results in a 32 μm shift of the image in the direction opposite to the pore bias. Increasing the voltage to 800 V induced a 200 μm image displacement. No displacement was observed for a detector with a 0°-biased output MCP. We also present a model for calculation of the charge footprint centroid in MCP detectors based on the output distribution function of the charge cloud. The results of our computer simulation of the image displacements prove to be in a very good agreement with the experimental data, thus providing the basis for extending our data to many different detector configurations.