Acoustic detection of electron impact in electron tubes

It has been found experimentally that when a pulsed electron beam strikes the surface of a solid body in a vacuum it produces elastic waves in the body. This process has been identified experimentally as a thermal effect of generally higher efficiency than would result from direct momentum transfer. This thermal effect permits detection of electron impact in pulsed evacuated devices such as microwave tubes by the use of simple elastic wave sensors outside the tubes. In pulsed electron tubes it is thus possible to detect and locate electron interception, the distribution of electron impact in a collector, and a number of other characteristics relating to electron flow.