“Detector walk” in position-sensitive detectors with biased microchannel plates

Abstract

The spatial resolution of high-accuracy microchannel plate (MCP) detectors has reached the values, where the so-called detector walk (or image blurring) 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 variation of the charge footprint position for events with different gains. Events with higher gains are shifted in the direction of the pore bias and the absolute value of this shift is directly proportional to the absolute value of the detector gain. Variation of the detector modal gain from 7.5×106 to 2.5×107 resulted in a ∼100 μm image offset for a 13°-biased MCP positioned at a distance of 8.5 mm from the anode with an accelerating rear field of 75 V/mm. We also extended our previous study of another type of detector walk associated with fluctuations of the accelerating rear field. Image displacements as functions of the rear accelerating field for both 13°- and 19°-biased MCPs were measured and compared with the results of computer simulation based on our charge cloud propagation model presented earlier. A good agreement between the experimental and simulated data verifies the validity of the model for different MCPs.