The point of a TWT over regular tubes is changing the paradigm on how electrons do work, so that should be due to propagation of the electron beam itself.
As I recall, TWTs work by shooting an electron beam (= constant velocity) down a helix, where, due to spooky action and black magic, the beam turns into bunches and somehow does work on the electromagnetic field. The result, gain. The delay should be essentially the propagation of the beam. Maybe with a velocity factor for the helix, or somewhat shorter for the feedpoints being somewhere along it, etc.
Whatever the case, I'm guessing your anode voltage is close to 160V.
formatting link
*electron+mass*(30cm%2F40ns)^2%2Felectron+charge
Tim
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"Rene Tschaggelar" wrote in message
news:rZZwn.112711$sx5.105125@newsfe16.iad...
> Since we were having a long delay in a system I
> came to measure the delay of a traveling wave tube
> (TWT) amplifier. The delay is in the order of 40ns,
> which at 34.6GHz correspond to about 1380 wavelengths
> or 13m of free space. The tube is in the order
> of 30cm long.
> I was aware it has two helix inside but considered
> them to be 10 turn or so.