Hi....
We have been working in a ultra-high vacuum (UHV) set up which is consisted of rotary, turbo, ion and titanium sublimation pump. As a first step, to achieve the UHV from low vacuum (LV) condition, we start ‘bake out’ process with the help rotary and turbo pump.
We perform such ‘bake out’ process routinely once in a couple of month without exploring the chamber to atmosphere.
Thereafter, after successful baking and achieving high vacuum (< 1.0 × 10-7 Torr), we switch on the ion pump. But sadly as we start to provide high voltage (~ 7.0 kV) bias among cathode and anode, it shows ‘short circuit error’.
Hence, we are unable to use ion pump to achieve better vacuum.
What is the probable reason for such response of ion pump?
How it could be solved?
With regards,
Anjan
Hello,
We have used ion pump in the past and didn't get such error. I don't know much about this situation, but you may check whether it is giving the same error in low bias voltage. If it is working fine with low voltage to medium high voltage then you can check at what voltage it is giving problem. You can check the documents for troubleshooting the ion pump. Maybe the following document will help
https://www.duniway.com/images/_pg/Ion-Pump-op-troubleshoot.pdf
Regards
Ashif Reza
Hi Anjan,
A high voltage short in an ion pump can be due to a Ti flake dropped into the ion pump from the Ti sublimation pump. If you are lucky you can resolve this without opening the system. Such flakes can often be burned by running a relatively high current at a low voltage between the anode and cathode of the pump. I have successfully done this with an external power supply, limiting the current to 5A and slowly increasing the voltage to about 60V. You can use the high voltage cable of the ion pump for this. During the "burning" procedure there are several short current spikes and slight increases in the system pressure. Try starting the pump with the normal power supply after that. The error can accrue again but you can repeat the procedure above several times. This should get your ion pump back to operating conditions without breaking the vacuum. Next time you do open the system, you should however, remove any Ti flakes near the Ti sublimation pump and possible flakes inside or near the ion pump. Here I recommend a clean hose attached to a vacuum cleaner.
Hope this helps and greetings to Tel Aviv from Hamburg,
Jonas
Dear Ashif,
Thank you very much for your reply.
We have tried to start the operation of ion pump at chamber pressure ~ 1.0 × 10-7 Torr . At this pressure level, we require to provide large bias ~ 7.0 KV for better ionization of gas molecules in the chamber. As the pressure is reduced, we can apply less bias ~ 3.0-5.0 KV.
The short circuit problem arises as soon as we switch on the ion pump.
We will look into the problem in more detail.
With regards...
Anjan
Dear Jonas,
Thank you very much for your reply.
We are also suspecting the presence of metal flake between the cathode and anode. We would follow your suggestion to recover from this problem without opening the chamber.
In extreme condition, we have to open the chamber and trace the possible presence of flakes.
With regards,
Anjan
Hi Anjan,
As explained by Jonas, the short circuit in ion pumps occur due to the Ti flakes which drops during baking. So be sure to remove all the deposited Ti flakes when you open the system next time, as these can be a constant source of short whenever you bake the system.
Dear Pramita Di,
Thank you very much for your valuable reply.
We are also guessing the presence of metal flakes among the cathode and anode is the probable reason. We will thoroughly check this part.
With regards,
Anjan
Hi Anjan,
Besides of metal flakes short-circuit in ion pump could be caused by (a) whiskers grown on Ti electrodes due to prolonged operation with too high voltage under UHV, and (b) conductive deposition on internal dielectric mounts and the feedthrough because of internal arcing. Whiskers can be blown off by 60V 5+A hot-potting, as was already suggested. In-UHV part of a eedthrough can be cleaned and re-assembled (if pump design allows it without welding). If you unable to remove the short by hot-potting then as a last resort you can try disassembling the ion pump, remove magnets, gently (!) tap on its walls with handle of a screwdriver or a piece of wood, use compressed air to blow out anything that would come out of it (outside wearing respirator or in a fume hood, don't breath the dust and don't get it on your clothes!) and try again. If nothing helps - the pump would have to be rebuilt.
To get some familiarity with troubleshooting ion pump issues I suggest you to read "Maintanance" section of this manua:l https://www.duniway.com/images/_pg/manual-duniway-ion-pumps.pdf as techniques described applicable to IGPs from all manufacturers.
Best of luck!
Dear Valery,
Thank you very much for your excellent reply. We will follow your suggestions.
With regards,
Anjan
If the procedures given above dont work, it might be possible that the isolator of the HV feedthtough or the isolators inside are covered by some deposits e.g. hydrocarbons converted to graphitic layers. These are only removable by disassembling the pump. for the standoff isolators you can use a solution of dichromate in hydrosulfuric acid and a very sophisticated rinse in pure water. The feedthrough may be cleaned by an abrasive household cleaner and again very sophisticated rinsing in water. Good luck
Dust particulates are more than likely to cause such error. Cleaning inner surface may solve the "error". My view incline similar with Jonas Warmuth.
The ion pump consists of two parts - the pump itself and the controller. Failure of the controller is unlikely. From the experience of my laboratory, the problem is in the pump itself. And, most likely, purely mechanical. For example, - a short circuit with a fallen nut ...After that I had to overhaul the pump.
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