Interest in RGAs (possibly a candidate for an FAQ?)

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Dan Knapp
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Dan Knapp » Wed Aug 07, 2019 11:05 am

The original publication is:
An electrostatic autoresonant ion trap mass spectrometer
A. V. Ermakov, and B. J. Hinch
Review of Scientific Instruments 81, 013107 (2010); https://doi.org/10.1063/1.3276686
It includes the circuit diagrams.
The Kimball Physics eV parts are indeed quite expensive. An amateur with access to metalworking shop facilities could make the needed parts. There is no way around buying an electron multiplier, which would then be the most expensive component. Never buy a used multiplier on eBay; the reason it’s there is that it was replaced.

ian_krase
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by ian_krase » Wed Aug 07, 2019 7:30 pm

Can't you make your own discrete dynode electron multipliers? AFAIK all you need is beryllium copper -- or perhaps "silver-magnesium alloy".

Jerry Biehler
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Jerry Biehler » Thu Aug 08, 2019 5:38 am

Just use a faraday cup. You really don't need the extra sensitivity of a EM for most things. I suppose you could also take the guts out of a small PMT and use that too. Or salvage the MCP out of an old image intensifier tube.

A friend and I were looking at what it would take to rejuvenate a channeltron. It might not be too hard, they are one of the simpler designs out there.

But in the end just keep an eye out for a used RGA on ebay. I have picked all mine up for under $200 which is way cheaper than you could even think about building one for. Just keep and eye out for the gotchas. The old inficon quadrex units are still good and you dont have to worry about software.

Justin Fozzard
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Justin Fozzard » Thu Aug 08, 2019 9:10 am

Here is a link to get a free copy of the Ermakov and Hinch paper on Sci-Hub:

https://sci-hub.se/10.1063/1.3276686

Here is a link to locate Sci-Hub when it moves around:
https://whereisscihub.now.sh/

Or use this to go direct to the home page:
https://whereisscihub.now.sh/go

I often find useful papers on Sci-Hub and they can usually be downloaded without a paywall.

Dan Knapp
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Dan Knapp » Thu Aug 08, 2019 11:28 am

In regard to the EM discussion, I think an EM will be required for a home built ion trap RGA. I don’t think one could get enough ion current out of the trap to detect with just a Faraday cup.
There have been reports of rejuvenating continuous dynode multipliers (e.g. Channeltrons), but I was never successful in bringing one back to life. It would be interesting to hear if anyone else has been successful. I have a drawer full of dead ones.
Last edited by Dan Knapp on Fri Aug 09, 2019 1:37 am, edited 1 time in total.

Roberto Ferrari
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Roberto Ferrari » Thu Aug 08, 2019 4:46 pm

With regard to EM, my experience servicing mass spectrometers is as follows:
Washing them with isopropyl alcohol (IPA) and drying it with clean, dry N2 usually permits to extend lifetime.
Scrubbing with a cotton swab and extensive washing with IPA sometimes recovered a rebel one.
Manufacturers prevent about exposure in air but in my experience someones left by a whole year exposed to air worked fine when returned to work.

Dan Knapp
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Dan Knapp » Fri Aug 09, 2019 1:44 am

Roberto, are you referring to continuous dynode or discrete dynode multipliers. I have successfully rejuvenated discrete dynode (beryllium copper) multipliers by a variation of the method you describe, but not channeltrons. For discrete dynode multipliers, the process is essentially a cleaning. Indeed, years ago we routinely washed and baked the multiplier every time we opened a mass spec. We would install the multiplier hot and try to get it under vacuum before it cooled. The continuous dynode multipliers undergo a chemical change on the surface, and rejuvenation attempts to restore the original chemical composition of the surface. A continuous dynode multiplier that is simply surface contaminated can be successfully cleaned with solvent followed by baking, but one that has lost gain by surface chemistry change requires a chemical treatment to restore function. I’ve never been able to make the chemical rejuvenation work.

Jerry Biehler
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Jerry Biehler » Fri Aug 09, 2019 7:10 am

The preamp and amp circuits for the faraday cup designs are out there. I have the schematics for the quadrex RGAs, should be easy enough to copy. But I still would never want to build a RGA. I have other things I would rather be not doing. lol

Yeah, we were looking at possibly just recoating the channeltron. I found details on the coating but I cant remember what that is right now, id have to go look again.

Roberto Ferrari
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Re: Interest in RGAs (possibly a candidate for an FAQ?)

Post by Roberto Ferrari » Fri Aug 09, 2019 2:52 pm

Dan, I was talking of continuous EM.
My guess is that succesful intervent cleaned contaminated surfaces. May be partially but good enough to recover function.
Probably those that never recovered got chemical changes.
All in all, I recommend to give a try.

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