<title>Charge cloud asymmetry in detectors with biased MCPs</title>

Abstract

The spatial resolution of current MCP based detector devices (<10micrometers ) has reached the point when such phenomena as charge cloud asymmetry becomes important for the ultimate detector performance. We present a systematic study of the MCP charge cloud spatial distribution at the plane of the readout element. Our new readout - cross strip (XS) anode combined with a set of preamplifiers for each anode finger - allowed us to measure directly the distribution of electrons at the anode. The measurements of the charge cloud profile were done with a high accuracy owing to the extremely high spatial resolution of the XS anode - about 5 micrometers FWHM. The asymmetry of the charge cloud related to MCP channel bias was observed directly in these measurements. Our charge cloud propagation model was used to simulate the observed charge cloud asymmetry. Results of our calculations were compared with the experimental data, and a good agreement between those proves the validity of the model, which can be used for simulation of the charge cloud distribution in a wide range of detector operating parameters.