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Andy,

I have used an ion pump on our noble gas mass spectrometer for the past 5
years. I sometimes have problemss with small field emission currents within
the pump as a result of flaking and discharging edges within the pump grid.
The effects of these field emission are generally seen as an increase in
pressure which fluctautes even thought there is no leak within the pumping
system itself. I remedy this by increasing the voltage to the pump which
serves to burn off the edges etc. After this the pump works fine. Check your
manual and see what they say regarding Field Emission Currents and how to
rectify this.

Tom
> ----------
> From:         Graeme Burton[SMTP:[log in to unmask]]
> Reply To:     Stable Isotope Geochemistry
> Sent:         Friday, November 12, 1999 8:28 AM
> To:   [log in to unmask]
> Subject:      Re: Ion Pump Problems
>
> Andy,
>
> We have cleaned out the ion pumps on our VG354.  We removed the
> titanium(?)
> mesh, small hands are useful!  WE didn't bother removing teh magnets.  I
> think we used isopropyl alcohol or acetone.  It took a lot of flushing and
> light rubbing with lab tissues to remove all of the particles.  We did
> this
> after discovering that light tapping on the ion pump caused dramatic drops
> in the vacuum.  Presumably loose particles were being liberated?
>
> What about the IG filaments?
>
>
> Graeme
>
>
> At 09:51 12/11/99 +0000, you wrote:
> >Dear List Members -
> >
> >I'm looking for advice on Ion pumps.
> >
> >The source ion pump our VG354 thermal ionisation mass spec appears to
> have
> >partially stopped working, leaving the vacuum just below 10-6 mBar. I've
> >baked out the system with no improvement. The pump controller is common
> to
> >a smaller ion pump on the analyser bench which appears to be working
> >correctly so I suspect the actual pump itself. There are also worrying
> >flickers on the meter of the power supply if we monitor the current being
> >drawn by the pump.
> >
> >Does anyone know if the pump can be dismantled and cleaned ?
> >Any advice on dealing with this type of problem would be gratefully
> >received !
> >
> >Thanks
> >Andy Midwood
> >
> >
> >
> >___________________________________________________
> >Dr Andy Midwood,
> >Analytical Group,
> >Macaulay Land Use Research Institute,
> >Craigiebuckler,
> >ABERDEEN,
> >AB15 8QH,
> >UK
> >Tel: +44 (0) 1224 318611
> >Fax: +44 (0) 1224 311556
> >Email: [log in to unmask]
> >http://www.mluri.sari.ac.uk
> >
> >
>