electron gun

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An electrode, especially in a cathode-ray tube, that produces a beam of accelerated electrons.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics Any device that produces a stream of electrons, especially a narrow stream that is focused onto a phosphor screen.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the electrode that is the source of electrons in a cathode-ray tube or electron microscope; consists of a cathode that emits a stream of electrons and the electrostatic or electromagnetic apparatus that focuses it