Ion pump instability

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Ahmed Tahir
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Ion pump instability

Post by Ahmed Tahir »

Dear All,

I am writing this to share a vacuum instability issue in UHV setup. The system includes a SAES D 100-5 (5 l/s pumping capacity) ion getter pump that is showing periodic fluctuations where pressure rises from ~2.0e-07Pa to ~3.0e-06Pa, a difference of almost a decade. The attached image would be helpful to understand the issue.

Image

The periodic fluctuations are similar to the one observed in Argon instability. However, the ion pump was installed only three months ago and Ar instability associated with aging should not be a problem. Could it be a leak? As the system is achieving a nice base pressure, I am not inclined to open any part and expose it to atmosphere. Need kind help and suggestions to fix the issue.

Best Regards
Uzair
Ahmed Tahir
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Re: Ion pump instability

Post by Ahmed Tahir »

The image is available on the following link:

https://ibb.co/kyydrL7

Best Regards
Uzair
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Dennis P Brown
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Re: Ion pump instability

Post by Dennis P Brown »

I know someone that uses ion pumps and I could ask; however, I'm not clear - this decade fluctuation is occurring constantly for the unit under vacuum (I looked at the diagram and that's what it appears to me as)? Also, is it always occurring basically at the same time period (every 7 or so hours)? Can't see a leak being periodic - that would seem strange unless the system is purging automatically after a buildup.
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Sophie Yang
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Re: Ion pump instability

Post by Sophie Yang »

Judging from your picture, it is the problem of "argon instability" of the secondary ion pump. The appearance of argon instability is related to working time and working pressure. For example, if a two-stage ion pump works at - 6 Torr, argon instability will occur after several thousand hours. If a two-stage ion pump works at - 5torr, argon instability will occur in only a few hundred hours.
Since the gas released instantaneously in each cycle is argon, this phenomenon can be effectively observed by using the RGA.
If want to solve this problem, you can replace the three-stage ion pump, such as Agilent Starcell.
This problem may also occur because the argon partial pressure of the system is too high and the pumping speed of the ion pump you use is very small. I wonder if you used a turbo molecular pump with good pumping effect for argon before starting the ion pump? I think RGA will also tell us the answer to this question.
argon instability
argon instability
Ahmed Tahir
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Re: Ion pump instability

Post by Ahmed Tahir »

@Dennis P Brown
Many thanks for your comments. Your observation is correct. The fluctuations are very periodic (about every 7 hours). We did a Helium leak test but no leak was detected. The source of this periodic purging could be Ar instability as suggested by Sophie Yang. We request for suggestion to get rid of the issue without exposing the system to Air..
Ahmed Tahir
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Re: Ion pump instability

Post by Ahmed Tahir »

@Sophie Yang
Many thanks for your comments.
The periodic fluctuations do suggest "Ar instability " but I am confused that how a pump that was replaced just a few months ago could develop this problem. As per my understanding, an ion pump may develop this issue after being in operation for many years?
We baked the system at 150C for several hours with turbomolecular pumping before turning on the ion pump.
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Sophie Yang
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Re: Ion pump instability

Post by Sophie Yang »

There are three methods to solve the problem of ion pump argon instability:
1. Do not bake the ion pump when the ion pump is working. If the temperature rises, argon will be released.
2.Use two stage ion pump with slotted cathode.
3.Replace the three-stage ion pump, such as Agilent Starcell.
To prevent chamber exposed to the air, you can close the gate valve of the ion pump and remove the ion pump for replacement.
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Sophie Yang
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Re: Ion pump instability

Post by Sophie Yang »

The occurrence of argon instability is not only related to the working time, but also to the working pressure.
For example, do you ensure that the ion pump is started and operated at a pressure below - 6torr. If the working pressure is high, it will only take hundreds or thousands of hours, and argon instability will occur.
Besides, is the ion pump you use brand new? And whether there is a process gas source of argon in your system
John Futter
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Re: Ion pump instability

Post by John Futter »

QUzair
how about complying with this sites rules
Ie full real name not Quzair
Ahmed Tahir
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Re: Ion pump instability

Post by Ahmed Tahir »

@Sophie Yang

Many thanks for your suggestions.
The ion pump was brand new when we replaced it a few months ago. The ion pump is turned on only when we have reached a pressure below -07 torr. Unfortunately, we amy not be able to change the ion pump t this time so we need to find a solution with the current setup.
We baked the system last week for about 60 hrs with ion pump off and turbomolecular pump running. Then we turned on the ion pump after achieving a good roughing vacuum (-07 torr). We achieved a good base pressure of -09 torr on Monday 22 Aug. After that the pressure started to rise steadily until today when we got our first spike associated to the Ar instability.

Best
Ahmed Tahir
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