Date: Wed, 18 Feb 2004 11:52:58 -0500 (EST)
From: Marcus Hohlmann <hohlmann@fit.edu>
To: Tommaso Dorigo <tommaso.dorigo@pd.infn.it>
Cc: kephart@fnal.gov, wagner@fnal.gov, aseet@fnal.gov, binkley@fnal.gov,
     ambrose@fnal.gov, burkett@fnal.gov, hays@fnal.gov, roser@fnal.gov,
     allspach@fnal.gov, lannon@fnal.gov, matac@fnal.gov, fabio.sauli@cern.ch,
     jjv@slac.stanford.edu, niebuhr@mail.desy.de, lockyer@fnal.gov,
     luciano@fnal.gov
Subject: Re: Aging in Atlas MDT tubes: SiO accumulation: is this what we
    see ?

Hi Tommaso,

a similar report on ATLAS MDT's was made in 2001 at the DESY aging
workshop by Michael Kollefrath (U. Freiburg). They used the slightly
different gas mixture Ar/CH4/N2/CO2 94:3:2:1 which had very good drift
proprties. However, in an extensive MDT aging test they found massive
aging. Their claim is that the problem is not due to Si contamination, but
simply due to the presence of hydrocarbons (CH4) in the gas. Switching to
Ar/CO2 got rid of their problem. Unfortunately, they didn't write their
talk up for the proceedings, but the transparencies and video are on the
aging workshop web page, if anyone is interested.

I have the suspicion that the CDF problem might simply be related to
using hydrocarbons (C2H6) in the gas mixture. There are many recent
reports that gas mixture with hydrocarbon gases just don't work in
"high-rate" detectors and CDF certainly seems to be moving into that
high-rate category in Run 2.

Yours,

Marcus Hohlmann

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Marcus Hohlmann, Assist. Prof.                   email: hohlmann@fit.edu
Dept. of Physics & Space Science                 phone: +1 (321) 674-7275
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On Wed, 18 Feb 2004, Tommaso Dorigo wrote:

> Hi all,
>
> it appears that Atlas had a problem with silicon-oxide
> growths on drift tube wires of the Atlas MDT.
>
> I have no idea whether this is what we are experiencing - just
> a shot in the dark. But take a look at the attached document
> (unfortunately in Italian), part. on page 31, where photographs
> are shown of wires as a function of Z.
>
> The slide says:
>                   Aging problems
>
> - at TDR time: ternary mix AR(91%), N2(4%), CH4(5%). Seen aging problems.
> - Mixture now Ar - CO2 93/7
> - in 2002 found loss of gain due to growths on wires, Si and O
> - Effect only present when recircling
> - dependence on Z of length and density of growth
> - no anode or cathode deposition
> - probable cause: silicon presence (Si-O-Ch-X)
> - the molecule breaks next to anode and chains SI-O are created which
>   stick to anode.
>
> Cheers,
> Tommaso
>
> -----------------------------------------------------------------------------
> Dr. Tommaso Dorigo - Padova University
> E-mail: dorigo@pd.infn.it - URL http://home.fnal.gov/~dorigo/my.html
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