
1) Microwave technology 2) Vacuum tube
Found on
https://www.crosswordclues.com/clue/gyrotron

A Gyrotron is a high powered linear beam vacuum tube which generates millimeter-wave electromagnetic waves by the cyclotron resonance of electrons in a strong magnetic field. Output frequencies range from about 20 to 250 GHz, covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from tens of kilowatts to...
Found on
http://en.wikipedia.org/wiki/Gyrotron

(from the article `electron tube`) One major type of fast-wave electron tube is the gyrotron ( figure). Sometimes called the cyclotron resonance maser, this device can generate ...
Found on
http://www.britannica.com/eb/a-z/g/86

oscillating tube used to generate high power millimetric waves in the 10 GHz - 100 GHz band
Found on
http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=815-07-32

<radiobiology> A device for producing microwave energy that utilises a strong axial magnetic field in a cavity resonator to produce azimuthal bunching of an electron beam. ... (09 Oct 1997) ...
Found on
http://www.encyclo.co.uk/local/20973
No exact match found.