[Amps] Ion Pump
cw_de_n5op at sbcglobal.net
Sat Jul 19 18:38:22 EDT 2014
I should add that my recollections are *quite* old -- I may be off about
how deep the vacuum was as it may not have been that deep.
On 7/19/2014 4:52 PM, Kim Elmore wrote:
> 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 at 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.
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Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
/"In theory there is no difference between theory and practice. But, in
practice, there is." //-- Attributed to many people; it's so true that
it doesn't matter who said it./
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