Cameca Gun Ion Pump Glitches

[Probeman]

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

[Probeman]

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

[neko]

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]

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

[shrikant]

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]

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.

[BenjaminWade]

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

[Probeman]

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

So the last time our engineer cleaned the ion pump elements we didn't see the "Turn Gun Valve Position 3" (ion pump glitch) message for about 6 months. But now it's returned with a vengeance.  Does any one have any suggestions on cleaning the ion pump filaments (which seem othewise in fine shape) to avoid these "glitches"?

[Probeman]

So can a leaky detector window be a problem on a Cameca (with a spectrometer separation window) even though the sample chamber vacuum is good?

[JonF]

Our SX100 almost definitely has a leaky window on SP5 and the ion pump tripping out seems to be associated with it. The vacuum in our WDS is pretty poor at the minute (or at least was last time I checked!), but the chamber vacuum is good (ours is a turbo pumped system). I also noticed some unusual behaviour on the bubbler of SP5.
Changing out the detector window was on the list of things to do before we all shut down, and it'll be at the top of the list when I get back (along with replace the blown filament).

[Probeman]

Our SX100 almost definitely has a leaky window on SP5 and the ion pump tripping out seems to be associated with it. The vacuum in our WDS is pretty poor at the minute (or at least was last time I checked!), but the chamber vacuum is good (ours is a turbo pumped system). I also noticed some unusual behaviour on the bubbler of SP5.
Changing out the detector window was on the list of things to do before we all shut down, and it'll be at the top of the list when I get back (along with replace the blown filament).

Breaking EPMA news: after a visual inspection our instrument engineer found a "pinhole" leak in one of our spectrometer/column separation windows, replaced it, pumped down, and our vacuum in the sample and gun have improved by an order of magnitude.

After 10 hours, so far so good.

[Probeman]

Our SX100 almost definitely has a leaky window on SP5 and the ion pump tripping out seems to be associated with it. The vacuum in our WDS is pretty poor at the minute (or at least was last time I checked!), but the chamber vacuum is good (ours is a turbo pumped system). I also noticed some unusual behaviour on the bubbler of SP5.
Changing out the detector window was on the list of things to do before we all shut down, and it'll be at the top of the list when I get back (along with replace the blown filament).

Breaking EPMA news: after a visual inspection our instrument engineer found a "pinhole" leak in one of our spectrometer/column separation windows, replaced it, pumped down, and our vacuum in the sample and gun have improved by an order of magnitude.

After 10 hours, so far so good.

Our gun and sample chamber vacuum hasn't been this good in years!   



If like Jon and I, you are seeing less than ideal vacuum readings in your Cameca and your ion pump keeps tripping, I think you ought to check your column separation windows for pin holes.

[Philipp Poeml]

We also had Ar migrating into the ion pump causing it to arc from time to time. Was discussed in the sx50-users list around March 2019.

[Probeman]

Somehow I missed that, but I can confirm that our ion pump is working great since we changed out the bad column separation window.

Here's a question: how does JEOL prevent "poisoning" of their ion pumps from P-10 argon if they don't have column separation windows? They must have very "tight" detector windows!

[JonF]

Update on ours: I found a bad detector window and having checked all the column separation windows, ended up replacing one thick film window that looked a bit blown (couldn't really see any holes though). Surprisingly, the thin film windows all looked pristine, so I'm not convinced any of the column windows were actually bad.

I stuck the detector window under a microscope and took a few pictures.





For scale, the window is approx 1 cm across the short dimension, the hole up to maybe 1 mm in length.

Typically, this window was from SP5 and was a pig to get out as we have the liquid nitrogen anti-contamination dewar fitted, severely reducing access.

Top tip: fill all the gaps in the table underneath with tin foil or blue roll! When the circlip holding the detector pops off, or when you drop it on refitting, it will fall in to the tin foil and not down in to the bottom of the instrument amongst the pipes and cabling. Saved my bacon, that did! 

I'm waiting a while for the vacuum to recover before I restart the ion pump, but fingers crossed this has sorted out the ion pump tripping out!