[Sneap] Turbo pumps and cesium

[Powell E. Barber]

Hi Klaus,

We've had some fun with Cs and Turbo's here at FSU on our polarized 
lithium source.  One of the turbos sits very near the charge exchange 
cell.

We use the Alcatel TMP 5400 which is field repairable.  We've had pretty
good success by keeping everything under vacuum or venting with inert
gas.  When maintenance is due, we vent and immediately remove and
disassemble the pump, rinsing everthing in DI water to remove any Cs/Li
from it.  The trick seems to be keeping moisture out until you can rinse
it.  Wet air (we're in Florida after all) along with the Cs/Li will
quickly corrode the aluminum pump parts.  The corrosion tends to be in
the lower stages of the turbo when it occurs.  We've had to replace
stator rings before, and I've even had to file the rotor once to remove
oxide buildup.  Fortunately, the low run speed of these pumps makes them
a bit tolerant of this sort of thing.

It's crude, but it works.  I suppose if one were starting over, a 
corrosive pump model might be employed to obviate these sorts of 
issues.

cheers,

Powell


On Tue, 23 Jan 2007, Klaus Bahner wrote:

> The SNEAP 2005 Meeting was held at Brookhaven National Laboratory.  Please visit the meeting Homepage at: https://www.bnl.gov/sneap2005/default.asp
> 
> The ATF-SNEAP 2006 web site is now available:
> http://www.ansto.gov.au/nugeo/conference/private/ATF_SNEAP.htm
> 
> ++++++++++++++++++++++++++++++++++++
> Dear Sneapers,
> 
> The vacuum in many (most?) sputter sources is maintained by turbopumps,
> quite often large ones, i.e. a significant investment. Since we are in the
> process of installing such a system, I wonder whether you take any
> precautions in order to limit the possible negative effect of the cesium
> vapour on the turbo and corresponding backing pump?
> Of course under normal conditions the amount of pumped cesium is only in the
> order of milligrams per hour, which still may accumulate to larger amounts
> after a long time - or in case of a malfunction, a runaway cesium reservoir
> may generate even higher loads . All turbo impellers, I have seen so far,
> are made from aluminum, which is easily attacked by cesium, at least once it
> is vented.
> The pump vendors I asked, claim that they have no or not enough experience
> with this kind of setup, in order to give any recommendations, followed by
> the statement that their pumps are not suitable for this application and any
> use of their pumps under these conditions is at our own risk, which is
> neither unexpected nor unreasonable. 
> Hence I would appreciate your input on this subject. Do you just ignore the
> problem (Does it pose a problem at all??) or do you try to avoid
> condensation of the cesium, either by heating the turbo or mechanical
> "baffles" in the vacuum chamber.
> 
> Thanks in advance
> Klaus Bahner
> 
> --------------------------------------------
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> University of Aarhus
> Ny Munkegade, Byg. 520
> DK - 8000 Aarhus C
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==========================================================
Powell E. Barber,  Sr. Engineer     850.644.6477 voice
Department of Nuclear Services      850.644.9848 fax
Nuclear Research Bldg RM 116
Mail Stop 4470
Florida State University
Tallahassee  FL  32306-4470

barber at nucmar.physics.fsu.edu
http://nucalf.physics.fsu.edu/~barber
==========================================================