What's this component? Was a national secret in the 1940s.

The OP here. I'll explain what it is later if no one cares to guess.

If you're interested in electronics, you probably know its name and purpose, as I did. But it happens to be a little difficult to "extract". I had been meaning to get my hands on one of these for ages. Finally got one!

What's so intriguing to me is that the internal geometry is what makes it function, and was (as I understand it) the genius involved in making the first working version.

It's a magnetron. It what makes our microwave ovens work.

OP here again. That's what it is.

There are some good pictures of a cutaway of a magnetron here:

http://en.wikipedia.org/wiki/Cavity_magnetron

It's kind of amazing that you can create microwaves with nothing more than a high voltage, a magnet, and a cavity with precisely the right shape.

It's a magnetron of course. AFAIK the "warming" effect of microwaves was discovered by accidentally melt chocolate.

Could a home microwave's magnetron be converted into an antenna? what possible use could it have?, are they good for data transmission? the microwave antennas I mean, not the ovens.. It could be cool to have a dyi super high power wifi of some kind!