"Detector walk" in position-sensitive detectors with biased microchannel plates

The spatial resolution of high-accuracy microchannel plate (MCP) detectors has reached the values, where the so-called detector walk (or image blurrin g) may start to limit any further improvements. Image blurring with gain is studied in detail for detectors incorporating angular-biased MCPs. It was found that the presence of the pore bias at the output MCP results in a var iation of the charge footprint position for events with different gains. Ev ents with higher gains are shifted in the direction of the pore bias and th e absolute value of this shift is directly proportional to the absolute val ue of the detector gain. Variation of the detector modal gain from 7.5 x 10 (6) to 2.5 x 10(7) resulted in a similar to 100 mu m image offset for a 13 degrees-biased MCP positioned at a distance of 8.5 mm from the anode with a n accelerating rear field of 75 V/mm. We also extended our previous study o f another type of detector walk associated with fluctuations of the acceler ating rear field. Image displacements as functions of the rear accelerating field for both 13 degrees- and 19 degrees-biased MCPs were measured and co mpared with the results of computer simulation based on our charge cloud pr opagation model presented earlier. A good agreement between the experimenta l and simulated data verifies the validity of the model for different MCPs. (C) 2000 American Institute of Physics. [S0034-6748(00)00311-7].