2 wrote:
>>If the arc is extinguished quickly and not too much energy is dumped
>>into the tube, the tube can recover completely. There may not be much
>>visible evidence that the arc ever occurred (depending on the tube
>>construction). If the tube was hot, the getter can collect the gas
>>within a few seconds.
>
>** reference please
I got the old phys chem textbooks out of the attic and calculated that
the mean speed of a typical light gas atom originating at a temperature
of about 500C is of the order of 1000 m/s.
That means that the dwell time of a gas atom released into a typical
inter-electrode space (dimension ~1cm) is ~10 microseconds. That's
plenty of time to become involved in a gas arc, if there are enough
other atoms around.
Within the next second, that same atom rattling around inside a 3-500Z
of radius ~10cm could make anything up to several thousand collisions
with all the surfaces inside the tube. If it hits the glass, there is a
high probability that it will bounce off. But if it hits the getter,
there is a high probability that it will be trapped on the surface.
So within one second - time enough for several thousand attempts to trap
each atom - almost all the released atoms *will* have been trapped, and
the vacuum will have returned to normal.
This is totally consistent with John Lyles' observation of a "small blip
on the ion gauge" in pumped tubes whose pressure is being continuously
monitored.
Well, they did promise me that the kinetic theory of gases would come in
handy one day. They just didn't tell me it would take 35 years...
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
|