Back in the late 60's early 70's my dad worked as an aerospace physicist at
what was then AVCO Tulsa Division.
A big part of his work dealt with ion attitude sensors for vehicles. To do this
work he and his team fabricated ion guns from CRT electron guns. They had to do
the work in very high vacuum (I think it was 10e-13 or 10e-14 Torr). They used
oil diffusion pumps to get the vacuum low enough to use the ion pumps. Ion
pimps work by ionizing the few gas molecules in the chamber and accelerating
them into a target material so that they stick. If the pressure wasn't low
enough, the ion pumps wouldn't work. It took a couple of days to get the vacuum
to that point.
These were actually part of the vacuum chamber itself and were arrayed in a
ring a few inches below the glass bell jar. I remember that they got pretty
warm as they operated. But, I have no recollection of operating voltages or
currents.
Kim N5OP
"People that make music together cannot be enemies, at least as long as the
music lasts." -- Paul Hindemith
> On Jul 19, 2014, at 14:29, John Lyles <jtml@losalamos.com> 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
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|