[Sneap] thermomechanical leak

[Walter Augustyniak]

Shon,
    I, too, found the part of the HVEC document (as did Chris) dealing with 
the installation of their standard TM leak.
What I found interesting is that their procedure called for opening the 
fully charged bottle into the manifold into the
ion source BEFORE the trapped gas in the capillary between the TM leak and 
the bottle, was first evacuated.
    We, at Bell Labs and Vanderbilt have always run the TM leak hot, with 
the bottle closed off, to get that one atmosphere
of air out of the line. We believe this is especially important with He 
gases, since it doesn't take long for the trapped air
in the Cu line to enter the gas bottle and contaminate the pure He. It may 
be less than 1 %, but still a factor in He+ yield.
    The down side of our procedure, is that if the fully charged gas bottle 
is opened to a hot TM leak, even if it is
electrically shut off, what had frequently happened was that this excess 
pressure would lead to a "plastic" flow
of the componenets inside the TM leak, and consequently, the Leak would not 
"close". We cured this by afterwards
simply cooling the TM structure with an air blast until it was at room temp. 
Then the gas bottle was opened. We have not
had a failure since instituting this procedure.
    I also found it interesting what Bob Krause diagnosed, possible failures 
as a result of running the leak at high temps
with no pressure behind them. We obviously left ourselves wide open by doing 
this pumpout of "the trapped atmosphere".
We always try to keep that run time to less than 20 min. but terminating the 
run as soon as we observe the vacuum falling rapidly.
    As far as not runing the leak when there is little or no pressure left 
in he bottle, it has often been the case where we have
"run out of  gas" during normal operations, and of course, we don't give in 
until we are sure that are problem is "no gas".
I believe the secret is to not spend any more time at the "hot" setting on a 
depleted bottle, than is necessary to assess the situation.

    Cheers,

        Walt Augustyniak
            Vanderbilt Univ

----- Original Message ----- 
From: "Shon B Gilliam" <sgilliam at physics.unc.edu>
To: <sneap at tunl.duke.edu>
Sent: Wednesday, November 29, 2006 11:44 AM
Subject: [Sneap] thermomechanical leak


> 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
>
> ++++++++++++++++++++++++++++++++++++
> We use the HVEC style thermomechanical leaks in our AN-2500 accelerator. 
> Does anyone know the maximum rating for the input gas pressure? I want to 
> know how high I can go with my gas bottle pressure before running into 
> leak control problems. Thanks.
>
> ============================
> Shon B. Gilliam
> Dept. of Physics & Astronomy
> UNC-Chapel Hill
> ============================
>
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