We have a sputtering system equipped with quartz thickness measurement which the quartz is using a cooling circulate using water (normal pressure without pump). Any time I use a turbo pump to vacuum the chamber the pressure goes around 5*10^-4 Tor while running the cooling circulate is change the vacuum pressure to 3*10^-3 Tor, immediately. If i shut down the cooling circulate the pressure get back to 5*10^-4 in no time.
Why such thing happen? Any idea how can I solve it?
Thanks
Masoud
Sounds like you got a small leakage in your cooling circuit and some of the water is evaporating into your chamber.
If you turn of the cooling the evaporation will either stop entirely or the rest of the water will cool down due to fast evaporation until you get an ice film that cloggs your leakage.
Shouldn't the pressure be better than 5E-4 with the Turbo. If it does freeze and clogg the gap you might see an oscillatory behavior (freeze, thaw, freeze). To confirm it you might isolate the cooling (block it at one of the inlet/exit) and with a small pump (membrane might do) the other and see if the 5E-4 gets better.
Yep - David has a very good point how you can check if it's freezing.
@David - that also depends on the rotary speed of the pump, which might be adjustable. For some experiments we wanted higher base pressures and limited the rotation speed of the pump down to the lowest rot. frequency (and, of course, possible degassing from the wall and how airtight your machine is ;))
yes will work didn't realize they still made it. Not a good idea if its UHV and something has to be repaired/welded. And if its a part that moves a lot will have a shorter life time. But works has been known to save a beamtime (not mine I add).
They used an isopropanol or acetone diluted torrseal mixture which was sucked through the cooling line of an UHV manipulator and sealed very quickly lasted about two experiments worth. But please take care if it can be avoided, for a number of reasons, it should: e.g blocked cooling line and a difficult to repair cooling line.
Thanks everyone, I try my best to find the leak in my cooling system, unfortunately I still can not find it. I let the turbo work on 12000rpm and it reduced the pressure to 1E-4 Torr. When I open the cooling circuit it change to 5E-4. If i open the valve slowly it will stabilized on 5E-4 but if I do it fast it goes on the range of E-3. Any idea how can i find the place of leak in the cooling part?
thanks
can you take the cooling circuit out of the vacuum chamber?
If so, just check if you see any droplets forming when you run it seperately.
sounds as though its a big leak Masoud. Maybe taking it out and having a closer look is the best idea also you can test it separately with a Helium leak seeker. Also pumping down without it (blanking the other flanges off) should give you a better idea of what your base pressure is.
Given a water leak, the TMP will not pump the chamber very well. TMPs are notoriously bad at pumping water vapor. To confirm the leak before ripping and tearing, one could blow out the water and hook up He to the coolant line and a Leak detector to the chamber.
Finally we solve it by considering the leak in cooling circuit and found it. One of the joiners had very weird problem. Hopefully we can change it and it is OK now. Thanks I use all advises to find it. Thanks every one. Thanks Johannes and Thanks David for your time and consideration.
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