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From: Rene Tschaggelar on 13 Apr 2010 09:04
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.
From: Tim Williams on 13 Apr 2010 10:35
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.
http://www.google.com/#q=0.5*electron+mass*(30cm%2F40ns)^2%2Felectron+charge

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Rene Tschaggelar" <none(a)none.net> wrote in message
news:rZZwn.112711$sx5.105125(a)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.


From: Rene Tschaggelar on 13 Apr 2010 10:44
Our TWT has an anode voltage of -14kV and a
current in the range of 60mA.
And yes, the signal propagation of the
electron beam matches the signal velocity
on the helix.
I was puzzled that there are 1400 wavelengths
stored in the helix, while I expected much less.

Rene

Tim Williams wrote:
> 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.
> http://www.google.com/#q=0.5*electron+mass*(30cm%2F40ns)^2%2Felectron+charge
>
> Tim
>
From: Phil Hobbs on 13 Apr 2010 10:57
On 4/13/2010 9:04 AM, Rene Tschaggelar wrote:
> 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.

Wow. The beam velocity is about c*sqrt(2*16keV/511keV) or 7.5e7 m/s, so
for a 30 cm tube, the transit time should be just about exactly 4 ns.
Are you sure you didn't drop a decimal place somewhere?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: John Larkin on 13 Apr 2010 11:11
On Tue, 13 Apr 2010 15:04:05 +0200, Rene Tschaggelar <none(a)none.net>
wrote:

>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.

Seems a lot. How did you measure the delay?

John

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