Hello John,
On Saturday, July 19, 2014, you wrote:
> Ion Pumps are worthy of a wikipedia check. They are used in high vacuum
> systems, once the vacuum is established with a roughing pump such as a
> Roots blower style or mechanical chug-chug recipocating. They help
> maintain the vacuum absorbing small qtys of free molecules. However,
> they are mounted via a tabulation or tubing off the main vessel, so they
> have limitations. Big tubes might have a 2 liter/sec 'appendage' pump.
> They don't actually have any moving parts, using a voltage of 3000-7000
> volts DC through a current limited power supply. In particle
> accelerators, plasma sources, ion beam, or ion implantation sources,
> they might be much larger, like the size of a keg. These require power
> sources of 50 mA or so, while the little ones run off of 100 uA or less.
> In vacuum tube manufacture they are used along with another more modern
> devices called a cryo-pump. Like was said earlier, big tubes of over 100
> kW dissipation often have appendage ion pumps mounted underneath. You
> can tell the quality of the vacuum from the power supply current, and
> when the tube is heated in operation and outgasses, the spikes in
> current will indicate the event, can be used to even interlock the HV or
> bias so that the tube won't run with trashed vacuum. This helps prevent
> internal arcing from the outgassing from damaging the grids and cathode.
> 73
> John
> K5PRO
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Out of curiosity, what sort of vacuum levels do ceramic tubes, say a
3CX3000, have within them when new? Has there ever been any papers on
how the vacuum is created and the tube sealed? It's one of those
subjects I just accepted. "oh, it has a vacuum in it, or it should
have". I have never really seen anything showing HOW it's developed
and the tube sealed. Thanks, interesting stuff!
--
Best regards,
Chris mailto:chris@chriswilson.tv
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