Varian StarCell Ion Pump l Problem

[Esin Soy]

Hi,

We have been using Varian StarCell Ion Pump for our UHV system. When we tried to turn HV on after bake out, we weren't able to observe any voltage generation on the controller and pump pressure was around 10-2 (on the contrary system pressure reading from the ion gauge shows -9). Pump can be turned on but HV cannot. 

Controller and cable is working but whenever they are connected to the pump there is a short circuit and no voltage generation. There was no unusual resistance between the pump body and the HV feedthrough or ground, besides pump body and HV feedthrough seems to be perfectly connected. In order to reduce or eliminate field emission leakage,we attempted to apply an over-voltage (hi-potting) by Tesla coil but the problem still persists. Does anyone know if that can be fixable without taking the pump out! Anyone had such a experience? Any suggestion would be appreciated.

Thank you

Esin

[Brandon McClimon]

Hi Esin,

We've had this issue, unfortunately we did have to take the pump out.  For us, the pump is below our TSP and deposition chamber so tiny metal flakes fall into it over time and eventually there is a short.  It's actually pretty easy to do with a couple people and a lab jack; it's pretty light once you take out the magnets.  Once you get it out, take everything apart inside and clean with alcohol.  Put it back together and check resistances.  Reattach and you're done.  Probably 2.5 hours with two people start to finish.

Brandon

[Petra Reinke]

Esin,

it is rather likely that you will have to take the pump out. If you do this, remove the magnets beforehand, which will greatly facilitate getting the pump out. You should take care to mark the orientation of the magnets. Before you take the pump apart you might talk to the vendor of your instrument to make sure you do not loose any warranty. 

We have taken the ion pumps off repeatedly, if you handle them with care and take notes of connections within the pump it is entirely possible. We usually check the pump visually before disconneting anything on the inside, and then vacuum the inside (yes, with the same vacuum cleaner you would use at home.... with a home made appendage to allow access to more narrow crevices). If it still shows a lot of little flakes coming out afterwards, we usually take it apart, clean, reassemble. 

Also, apart from an internal shortcircuit, it is not likely but possible that your magnets are demagnetized. In addition, it is possible that the HV is disconnected on the inside of the plug. 

good luck, Petra

On Tue, Jan 22, 2013 at 2:40 PM, Esin Soy <esi...@gmail.com> wrote:

--
Petra Reinke

Assoc. Professor

Department of Materials Science and Engineering

University of Virginia

phone: 434 924 7203

email: pr...@virginia.edu petra....@gmail.com

http://www.virginia.edu/ms/faculty/reinke.html

[Lipton-Duffin, Josh]

Hallo Esin,

When you say below that the "controller and cable are working", how have you checked this? Have you measured the HV at the back of the controller? Have you attempted to "switch on" the controller with the cable attached but not the pump to see if the HV does indeed rise? An ohmmeter across the cable ground and pin may not pick up a short, even a large finite resistance can cause you problems.

We have been plagued by this problem frequently, due to flakes of titanium falling off the TSP into the pump body. In our case we were able to measure a finite resistance between the HV pin and the grounding shell on the pump. A hi-pot may procedure may not work in this case, because your tesla coil may not be able to generate enough current to blow up the Ti flake causing the short. Instead we have applied a lower voltage/higher current ramp which evaporates the offending material via resistive heating.

You might also have luck if you GENTLY tap the edges of the pump with a rubber mallet, to see if this dislodges the short.

If this doesn't work, then I agree with the others that it's time for a clean-out. We used a shop vac followed by careful wipe-down with isopropanol.


Josh Lipton-Duffin
Research Associate/Associé de Recherche
Université du Québec, INRS-ÉMT
1650 Boul. Lionel Boulet
Varennes, QC CANADA J3X 1S2
Tel: +1 514 228 6910
Fax: +1 450 929 8102

[Esin Soy]

Hi Brandon,

Thank you very much for the advice and courage. It seems we need to take the pump out as you said.

Cheers

Esin

[Esin Soy]

Hi Petra,

Thank you very much for the awesome suggestions. We have never thought about the demagnetization but it seems ion pump is needed to be cleaned indeed. Remembering the marking of orientation will save us a huge time.

Cheers

Esin

email: pr...@virginia.edu petra.rei...@gmail.com

http://www.virginia.edu/ms/faculty/reinke.html

[Esin Soy]

Hello Josh,

we have attempted to switch on the controller with the cable attached but not the pump and saw the HV does rise.You are right, hi-pot didnt work well as much as we expected, it seems we need to take the pump out and clean. On the other hand\ can you please explain how did you applied resistive heating? Did you pump has a heating option on it is own?

Thank you very much for your valuable suggestions

Cheers

Esin