3 - Microchannel plates

Summary

Introduction

MicroChannel plates (MCPs) are compact electron multipliers of high gain and military descent which, in their two decades as ‘declassified’ technology (Ruggieri, 1972), have been used in a wider range of particle and photon detection problems than perhaps any other detector type.

A typical MCP consists of ∼ 10⁷ close-packed channels of common diameter D, formed by the drawing, etching and firing in hydrogen of a lead glass matrix. At present, the most common values of D are 10 or 12.5 μm, although pore sizes as small as 2 μm have begun appearing in some manufacturer's literature. Each of the channels can be made to act as an independent, continuous-dynode photomultiplier. MicroChannel plates (or channel multiplier arrays or multichannel plates, as they are sometimes known) are therefore used, in X-ray astronomy as in many other fields, for distortionless imaging with very high spatial resolution.

The idea of replacing the discrete dynodes (gain stages) of a conventional photomultiplier (Knoll, 1979) with a continuous resistive surface dates from 1930 (Ruggieri, 1972). It was only in the early 1960s, however, that the first channel electron multipliers (CEMs), consisting of 0.1-1 mm diameter glass or ceramic tubes internally coated with semiconducting metallic oxide layers, were constructed in the USSR (Oshchepkov et al. 1960) and United States (Goodrich and Wiley, 1962). Somewhat later, parallel-plate electron multipliers (PPEMs) were developed with rectangular apertures more suited to the exit slits of certain types of spectrometer (Spindt and Shoulders, 1965; Nilsson et al. 1970).