Travelling Wave Tube

A traveling wave tube (TWT) is a high-tech vacuum tube. TWTs are used as high-power microwave amplifiers in:

Satellites (DirecTV, DirecPC, pagers, telephones, XMradio, etc.)
Military radar systems (missile guidance, aircraft / missile tracking, jamming systems)
Civilian radar systems
Civilian microwave radios (e.g. British "Marconi" system)

Some web-sites about TWTs:

http://www.twtas.com/about_hed.htm -- official vendor site, with product specs and photographs. [Broken link, but available via the WaybackMachine]
http://www.twtas.com/abouttwt.htm -- technical overview, with factory tour. [Broken link, but available via the WaybackMachine]
http://www.tmd.co.uk/microwave/pt6019.htm -- vendor photograph [original photograph at http://web.archive.org/web/20011224180113/http://www.tmd.co.uk/Graphics/evd1364.jpg]
http://ranier.oact.hq.nasa.gov/SCRS_Page/Historic/TWTA.html -- spacecraft
http://www.lucent.com/museum/1944trw.html -- inventors wearing suits [BrokenLink]
http://sdphca.ucsd.edu/TWT.html -- engineering drawing

Two excellent off-line texts on TWTs are:

Jim Hansen's TWT / TWTA Handbook, published in 1992 by what is now L-3 Electron Technologies (EDD). The handbook is written (and illustrated) for non-physicists, such as potential customers and new technicians fresh out of high school. Excerpts are on-line at http://www.twtas.com/abouttwt.htm. [Broken link, but available via the WaybackMachine]
Scott Gilmour. Principles of Traveling Wave Tubes. ISBN 0-89006-720-1 Written at the level of an upper-division college physics course. Prerequisite: Electromagnetism.

EDD also makes the Xenon Ion Propulsion System (XIPS). NASA used these IonThrusters to propel the Deep Space 1 probe. Boeing uses them to keep its new satellites in orbit. http://www.twtas.com/pictures/factorywalk/xips/xipspage.html [Broken link, but available via the WaybackMachine]

When I worked on Marconi microwave radios (late 60s, early 70s) I had to go to a special tech school (High Wycombe) to learn how that stuff worked as opposed to the Lenkurt klystrons I was used to. Bloody science fiction. Very cool stuff. Helical coil of thin wire running down the inside of a finger-sized glass (vaccuum) tube with a large metal head. Sleeved in a jacket of silicone grease. Tuned by rotating the tube along its axis for max gain.

I'd like to say I fully understood how it worked, but that's more hubris than I can muster just now. I could keep it alive and keep working levels and do the maintenance and repair on the racks, but actually grasping the electro-math that ran it was something else. Hats off to whoever figured out how to make a useful RF amplifier/modulator with it.

We pronounced it "twot" in our organization.

CategoryHardware