Author Topic: Cameca Gun Ion Pump Glitches  (Read 1579 times)

Probeman

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Cameca Gun Ion Pump Glitches
« on: February 21, 2017, 12:29:01 pm »
Hi all,
We've been having a recurring problem where the SX100 ion pump apparently "sparks" from a metal flake or whisker and the vacuum logic interprets this momentary increase in current (and possibly small increase in pressure) as a vacuum failure, and therefore turns off the ion pump and high voltage and displays the "Turn Gun Valve To Position 3" message, thereby killing the run.

I guess one solution would be to clean the ion pump elements by banging on them with a hammer(!) and using a vacuum cleaner to collect the debris as we've done in the past, but the problem eventually returns. So we're curious if this "sparking" isn't as bad as the vacuum system thinks it is and that perhaps we could add a time constant in the vacuum logic to reduce the sensitivity to these events and average over a longer period of time (say 10 or 20 seconds), so the vacuum logic doesn't shutdown things so quickly if it's just a momentary event lasting only a second or two.

Does anyone have any idea how long these "spark" events last in the ion pump?
john
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Probeman

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Re: Cameca Gun Ion Pump Glitches
« Reply #1 on: March 14, 2017, 04:54:00 pm »
Hi all,
We've been having a recurring problem where the SX100 ion pump apparently "sparks" from a metal flake or whisker and the vacuum logic interprets this momentary increase in current (and possibly small increase in pressure) as a vacuum failure, and therefore turns off the ion pump and high voltage and displays the "Turn Gun Valve To Position 3" message, thereby killing the run.

I guess one solution would be to clean the ion pump elements by banging on them with a hammer(!) and using a vacuum cleaner to collect the debris as we've done in the past, but the problem eventually returns. So we're curious if this "sparking" isn't as bad as the vacuum system thinks it is and that perhaps we could add a time constant in the vacuum logic to reduce the sensitivity to these events and average over a longer period of time (say 10 or 20 seconds), so the vacuum logic doesn't shutdown things so quickly if it's just a momentary event lasting only a second or two.

Does anyone have any idea how long these "spark" events last in the ion pump?
john

A bit more data...  we have eliminated the secondary gauge as a source of these "Turn Gun Valve To Position 3 " faults, so it appears the faults are from the ion pump in the gun.

Our ion pump elements are not more than 3 years old or so and our engineer says they look in good shape though there is some minor debris.  His examination of the Cameca schematics show that the current "suppression time" for ion pump faults has a time constant of around 1 second or so, but that the ion pump faults which are knocking our filament off  line can last as long as 5 seconds or so.  He is collecting more data to improve that observation.

In the mean time I'm curious if other Cameca instruments with tungsten filaments also see these ion pump faults...
john
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neko

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Re: Cameca Gun Ion Pump Glitches
« Reply #2 on: March 29, 2017, 12:46:09 pm »
We have a similar issue, but it's a leak somewhere below the gun valve. Goes out every day or two, unless the valve is in position 1 (was fine for about 6 days). Very frustrating, and I couldn't say how long the disruptions last, but sometimes it's not long enough to shut off the vacuum, even if I see a momentary reading in the -3Pa range. Always fun to restart a run in the AM. It's like watching paint dry, if paint sounded like a giant metal spider.

I wish I wasn't on XP, so I could remotely monitor the vacuum status and drive in to restart if it went out, that would save so much time!

Probeman

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Re: Cameca Gun Ion Pump Glitches
« Reply #3 on: March 29, 2017, 04:35:08 pm »
We have a similar issue, but it's a leak somewhere below the gun valve. Goes out every day or two, unless the valve is in position 1 (was fine for about 6 days). Very frustrating, and I couldn't say how long the disruptions last, but sometimes it's not long enough to shut off the vacuum, even if I see a momentary reading in the -3Pa range. Always fun to restart a run in the AM. It's like watching paint dry, if paint sounded like a giant metal spider.

I wish I wasn't on XP, so I could remotely monitor the vacuum status and drive in to restart if it went out, that would save so much time!

That is not a image I want to have in my head!

I should report that after our instrument engineer cleaned and scraped the ion pump elements we haven't had a single "Turn Gun Valve Position 3" problem yet and it's been about 3 weeks now!  He mentioned that there were quite a large accumulation of tiny metal flakes clustered on the pump elements where the magnetic field was concentrated.

Note on remote access for Win XP.  We use RealVNC for much of our remote access and it works great on all Windows and Mac platforms.
john
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shrikant

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Re: Cameca Gun Ion Pump Glitches
« Reply #4 on: October 06, 2017, 09:55:23 pm »
1. first thing is to clean the ion pump itself thoroughly. 2.check solid state relay  inside vacuum chassis or better replace it 3.Also good idea to check ion pump HV connector contact.

Probeman

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Re: Cameca Gun Ion Pump Glitches
« Reply #5 on: October 07, 2017, 09:31:27 am »
This is not a replacement for properly cleaning the ion pump elements, but as a temporary solution one can just give some a good solid taps with a screwdriver handle to the side of the ion pump housing, which seems to prevent such glitches for a while.  According to my instrument engineer, the theory is that small metal flakes and whiskers get broken off and fall to the bottom of the pump housing where they won't cause problems for a while.
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BenjaminWade

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Re: Cameca Gun Ion Pump Glitches
« Reply #6 on: October 08, 2017, 06:20:16 pm »
Hi all
Yes we had this problem occurring all the time on our SX51... the solution was to do exactly what you are doing. Bang the crap out of the outside housing of the elements with the handle of a screwdriver for a while. This seemed to stop the problem occurring for a good number of months, until it happened again.
We had in the past when it got bad removed the elements, vacuumed housing, and got the elements sand blasted and recoated, but the people who did that for us went out of business.

Cheers