A Microwave Secondary Electron Multiplier

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Abstract
The construction and operation of a dynamic electron multiplier, of the type sometimes called a multipactor, is described. Briefly, the multipactor consists of two parallel secondary emissive plates having an alternating voltage across them. The magnitude of the voltage is adjusted so that the transit time across the gap for electrons starting with zero velocity from one of the plates when the field is passing through zero shall be just one‐half the period of the a.c. voltage. In this way, electrons and their secondary descendents can be made to bounce back and forth between the plates and multiplication takes place. The necessary phase relationships between the electrons and the field are discussed. The multipactor described here uses 10 cm microwave power to get the a.c. voltage. It has been used as a gamma‐ray detector in which case the cavity is ``broken down'' by the multiplication of a Compton electron ejected from the cavity wall by a gamma‐ray. This breakdown gives rise to a microwave pulse several millivolts high at a crystal rectifier. The efficiency of this process is about 1.5×10−5 count/gamma‐ray. The rise time of the pulse is calculated to be about 5×10−10 sec. and is measured to be less than 10−7 sec. The deadtime is presumed to be about 5 microseconds.

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