[Amps] Ion Pump

Roger (K8RI) k8ri at rogerhalstead.com
Sun Jul 20 22:02:04 EDT 2014

On 7/20/2014 8:07 PM, Hardy Landskov wrote:

This is well outside my realm of experience.  The claim of 1 X 10^-12 
would be extremely difficult to obtain.
https://en.wikipedia.org/wiki/Vacuum .  So far, I've not found a 
definitive answer to the actual vacuum required in normal production, 
power tubes tat are use at amateur power levels, or several times higher.


Roger (K8RI)

> Roger,
> As an EE myself now retired, have any experiments or production units 
> of vacuum tubes been done while the shuttle program was ongoing? Maybe 
> there is the vacuum of outer space that might be better than what's 
> achieveable on earth but you might collect particles floating by as 
> well from space junk that would negate the advantages. Just curious or 
> maybe it's classified....or maybe just impractible.
> 73 Hardy N7RT
> ----- Original Message ----- From: "Roger (K8RI)" 
> <k8ri at rogerhalstead.com>
> To: <amps at contesting.com>
> Sent: Sunday, July 20, 2014 3:33 PM
> Subject: Re: [Amps] Ion Pump
>> On 7/20/2014 3:12 PM, John Lyles wrote:
>>> Although this doesn't have much to do with the building of 
>>> amplifiers, it does shed insight into some of the complications of 
>>> making good tubes and how the technology there has impacted other 
>>> industries.
>>> General Electric was one of the first to recognize that vacuum tubes 
>>> (their Pliotrons and Kenotrons) required better vacuum than the 
>>> Audion's had that were made by DeForest companies. So naturally, a 
>>> lot of development came from GE and also benefited their Xray tubes.
>>> K8RI's experience (below) is helpful here. I am in RF engineering 
>>> and only observe vacuum experts doing their stuff from the 
>>> sidelines. We work hand in hand, of course, in not applying RF power 
>>> until vacuum is sufficient. I know of several instances at particle 
>>> accelerator laboratories where oil contamination from diffusion 
>>> pumps created a costly mess. I didn't think we have them for pumping 
>>> between 10^-1 and -6. The big roughing pumps are indeed rotary. We 
>>> use cryo pumps and ion pumps, maybe the cryos are for in-between? I 
>>> know they have to be regenerated regularly.
>> I should add that the chilled water or liquid N2 "cold traps" are 
>> also called "Back gassing traps" whose purpose is to prevent the 
>> gasses in the pumps from getting into the chambers on which they are 
>> pumping.  The liquid N2 traps also aid the pumping as they remove 
>> many molecules of gas. When you fill the N2 trap, the vacuum goes 
>> down almost immediately, but they are not filled until there is a 
>> vacuum on the pump or any moisture would freeze to the baffle and 
>> then slowly sublime, slowing pumping substantially.
>> The diffusion pump is a very simple device, but might take a bit of 
>> space to explain.
>> 73
>> Roger (K8RI)
>>> Our accelerator cavities need to be in the low 10^-7 Torr or we get 
>>> many discharges from the extreme RF voltages there. Electron 
>>> accelerators need much better vacuum. I believe that big tubes must 
>>> be better than -6 to minimize damaging flashovers during conditioning.
>>> 73
>>> John
>>> K5PRO
>>>> From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
>>>> Roughing pumps do not normally get anywhere near the vacuum needed to
>>>> start an Ion pump.   We used a roughing pump to get to 10^-1 Torr, 
>>>> then
>>>> a diffusion pump to make 10^-6, (-7.with a liquid N2 cold trap) At 
>>>> that
>>>> point we'd start the ion pump.  Once it was working, we'd valve off 
>>>> the
>>>> diffusion pump inlet as the ion pump would not work in parallel 
>>>> with the
>>>> diffusion pump. It would pull oil, or mercury fumes out of the 
>>>> diffusion
>>>> pump.
>>>> We used ion pumps on a mass spectrometer. It created a beam of ions
>>>> containing the material to be analyzed. This beam passed between two
>>>> curved and charged plates inside a powerful electromagnet. IIRC the
>>>> poles were about 10" in diameter with the magnet weighing around a 
>>>> ton.
>>>> However the last time I worked on that was "maybe in or around 1980.
>>>>    An ion pump is basically a big diode that collects ions on the
>>>> surface, or getter.  They have no exhaust.  Starting one at the 
>>>> typical
>>>> 10^-1 Torr of a roughing pump would quickly contaminate the ion pump.
>>>> Penning tubes will light up with plasma around 1 X 10^-1. The 
>>>> ionization
>>>> will go out around 1 X 10^-2.  The ion pump would need much better 
>>>> than
>>>> that to start.
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