Re: TC in a vacuum ... Re: TC vs Electron Gun

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Well.. more just for testing general breakdown over surfaces and the like
for antennas.. We also do multipactor testing, etc. (as you say, it's a big
issue, particularly as Solid State Power Amps are getting up there in power,
and folks want to build cavity filters and diplexers that have fairly high
Q).  For the moment, there's more interest in breakdowns around the Paschen
minimum (which oddly, happens to be what the atmosphere on Mars is like).
Yes folks, I'm going to get to run a semi-TC in a simulated Martian
atmosphere (assuming my little project gets funded (hope!)).

Multipactoring these days is mostly handled by analysis (you don't want to
find out it has the problem after you build it), and just verified
afterwards in the vacuum chamber.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, August 04, 2002 7:18 PM
Subject: Re: TC in a vacuum ... Re: TC vs Electron Gun


> Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>
>
> Tesla list wrote:
> >
> > Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
> >
> > Actually, we do something like running a TC in a vacuum when we run RF
> > breakdown tests in a large (the largest?) clear bell jar at JPL.
Granted, I
> > don't recall anyone running tests at 100 kHz, but at 400 MHz, you bet.
>
> Are you talking about looking for multipactor discharge?  If so, that's
> an old subject for me and I had a NASA contract to investigate
> "Multipactor Discharge in Space Electronics Systems" way back in the mid
> 1960's. I got bitten with that in building a  400 MHz bandpass filter
> for a 10 watt transmitter we built for the Grumman OAO, which I guess
> most people have forgotten about. Turned out that the coaxial resonators
> I built had perfect dimensions for resonance at the voltages at which it
> operated. About the same time JPL had a problem with multipactor in the
> transmitters for Ranger and a kid at JPL named Richard Woo apparently
> made a career studying the subject.
>
> This is just a little off the subject of TC's, but in the course of the
> study I found out that people had been having big troubles with
> multipactor for many years, from 50 MHz in a big Harvard linear
> accelerator to windows in TWT's, etc.  I talked to a lot of those guys
> and they had about the same story - it had been a total surprise to them
> and they had to go to incredible troubles to get rid of it.  Turns out
> that one-sided multipactor is also possible.
>
> As for the TC in space, the spacings for multipactor resonance would at
> 100 KYz would be of the order of 7.5 meters, and it is possible that
> multipactor might be experienced, although the normal operating voltage
> of a TC would probably be above the maximum allowable for multipactor.
> Of course, in the time when the secondary voltage was building up
> resonance might occur, in which case the voltage probably wouldn't go
> any higher and something would melt.
>
> Ed
>
>
>