[RASMB] Elevated temperature operation with a turbomoledcular pump.

[Walter Stafford]

Dear RASMB-ers

	I have been testing a turbomolecular pump as a replacement 
for the standard diffusion pump on the XL-I. I am writing to report 
the results of that experiment.

On my machine, with the standard diffusion pump installed, I have not 
been able to run above about 23 degrees without having serious 
fogging of the interference condensing lens after about 15 minutes, 
making it impossible to take data.

About a month ago, with the help of the Beckman Serviceman and folks 
from the Axiden Division of Alcatel Vacuum Technology 
{http://www.adixen-usa.com/}, we installed an ATP80 TMP in place of 
the diffusion pump. Other than a flange that had to be machined to 
mate the TMP to the diffusion pump flange, it was a direct 
replacement. The original rough pump was used to back up the TMP.  
see: 
{http://www.adixen.com/all/dyn/products/products.php?id_prod=20&lg=us}

So far the results have been quite remarkable. After the first test 
of running for 4 days at 40 degrees, the optics were clean. The 
chamber was actually cleaner after the run than before. The TMP 
seemed to have removed all the residual oil that we were unable to 
remove after replacing the diffusion pump. It pumps down to 3-5 
micons in less than 5 minutes and ultimately to about 1-2 microns. 
The fringe patterns seem to be more stable (not sure exactly why, but 
I was informed that the regular diffusion pump heater normally cycles 
on and off; the flexing associated with that may explain it).

We use it routinely now for all runs and couldn't be happier with it.

Several labs have expressed an interest in installing one on their machines.

However, Beckman will not support the pump or provide one as standard 
equipment unless there is sufficient interest. A proper, Murphy-proof 
installation would require a firmware change and field service 
support to allow it to be included under the service contract and 
warranty.

I would like to take a survey of those who might be interested, so 
that we can convey that expression of interest to Beckman.

If you have an interest and think that running at higher than 20 
degrees or higher precision might be useful to you, please respond to 
this email by replying to the RASMB. I'll collect the responses and 
comments and forward them to the folks at Beckman.

It has opened new vistas for our research.

Thanks
Walter
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Walter F. Stafford III, Ph.D.
Analytical Ultracentrifugation Research Laboratory
Senior Scientist
Boston Biomedical Research Institute
64 Grove Street
Watertown, MA  02472-2829

main:(617) 926-8040
tel: (617) 658-7808
fax: (617) 972-1753

mailto:stafford at bbri.org

http://www.bbri.org/faculty/stafford/Stafford.html
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