[Sneap] Turbo pumps and cesium

[Gianluca Quarta]

Dear all,

I confirm the experience of Karl, we are running a turbopump (Leybold
TW250) on our Cs sputtering ion source (HVEE846B) used for routine AMS 14C
measurements without any major problem other than normal maintenance.
It has worked smoothly for more than five years.
We also have a (chemical) turbo pump (Leybold 600C)intalled on our
"multipurpose" injector formed by a Cs sputter source (HVEE860C) and a
duoplasmatron source (HVEE358) which is usually operated with He and a Li
exchange canal (operated at 500°C). The pump is mounted just on the vacuum
chamber, perpendicular to the beam direction, about 50 cm from the ionizer
of the sputter source, above the exchange canal. Also in this case we did
not have major problems for more than four years. We just open regularly
the vacuum chamber to check the inside of the beam line, to clean the
electrode of the lenses and the canal itself but we never had to change
the pump.

Cheers,

Gianluca

-- 
Dr. Gianluca QUARTA
Assistant Professor
CEDAD, AMS Radiocarbon Dating Facility
Department of Engineering of Innovation
University of Salento, Italy
Via per Monteroni, 73100, Lecce
ITALY







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
>
> ++++++++++++++++++++++++++++++++++++
> Hello Klaus,
> We have run an Alcatel turbo and fore pump on our AMS Cs sputter source
> for over 10 years without major issues, other than regular maintenance
> on the fore pump. The pump was located ~0.5 m downstream from the
> ionizer at right angle to the beam line. In my opinion, the Cs vapor has
> little chance to make it all the way to the pump past plenty of cold
> surface and we never had to worry about the stators/rotors. It is
> different in the case Powell describes, where the pump sits near a
> charge exchange canal. We had a similar experience as the Floridians
> with our Mg charge exchange canal, actually trashing a turbo after a
> short time of operation.
> Cheers,
> Karl
>
> 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
>>
>> --------------------------------------------
>> AMS 14C Dating Laboratory
>> University of Aarhus
>> Ny Munkegade, Byg. 520
>> DK - 8000 Aarhus C
>> Phone: +45 8942 3736
>> Fax:   +45 8612 0740
>> --------------------------------------------
>>
>>
>> _______________________________________________
>> Sneap mailing list
>> Sneap at mail.tunl.duke.edu
>> http://mail.tunl.duke.edu/mailman/listinfo/sneap
>>
>>
>
> _______________________________________________
> Sneap mailing list
> Sneap at mail.tunl.duke.edu
> http://mail.tunl.duke.edu/mailman/listinfo/sneap
>