[Sneap] alternatives to SF6

[Larry Lamm]

Larry,
 Chris is correct below when he mentions that we no longer use CO2 in 
our tank gas mix. We are running with about 10% SF6, the rest being 
nitrogen, with a tank pressure of about 180 psig. Our experiences, so 
far, have been very good, and we are able to operate at 10 MV or above 
with regularity.

Larry
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>
> Larry, As Nathan has said, adding a small percentage of SF6 to the normal
> 80/20 Nitrogen/CO2 blend that HVEC machines use, greatly improves
> performance.  If I am not mistaken, Notre Dame doesn't even use CO2 any
> more, just Nitrogen and SF6 to achieve 10+ MV on their FN.  The major
> obstacle that I see in your case is that you tank is probably not rated for
> the ~200 psi that we operate these blends at.  I am not sure if you will
> be able to operate Nitrogen/SF6 at only 80 psi and get stable performance.
> Has anyone with a Pelletron tried this?  Greg, has NEC ever done any tests
> along these lines??
>     In my files I find a paper by Phil Ashbaugh et al from Chalk River in
> 1965 where they compared pure SF6 to the Nitrogen/CO2 blend and found that
> the relative dielectric strength of SF6 to Nitrogen/CO2 in an EN was roughly
> 3:1 with the SF6 at 60 psi and the blend at 250 psi.
>     I also find a letter from a technical specialist at Allied Chemical
> dated 1979 to someone discussing using a blend of Nitrogen and SF6 in some
> electrical bus system.  I will attach that letter and a data table attached
> to it which gives breakdown voltages for various mixtures of these two gases
> at different pressures.  Hopefully this will be helpful.
> - Chris
>   
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-- 
Larry Lamm, Research Professor
Nuclear Structure Laboratory,
     Institute for Structure and Nuclear Astrophysics
University of Notre Dame
Lab: 574-631-7716
Office/Voice Mail: 574-631-7792
Fax: 574-631-5952
Email: llamm at nd.edu