Date: Wed, 18 Feb 2004 11:52:58 -0500 (EST) From: Marcus Hohlmann To: Tommaso Dorigo 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 ------------------------------------------------------------------------- Marcus Hohlmann, Assist. Prof. email: hohlmann@fit.edu Dept. of Physics & Space Science phone: +1 (321) 674-7275 Crawford Science Building fax : +1 (321) 674-7482 Florida Institute of Technology web : www.fit.edu/~hohlmann 150 W. University Blvd. Melbourne, FL 32901 USA 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 > Office: B0 Trailers, #164-J - Phone (630)840-4374 - Fax (630)840-2968 > Address: Fermilab, M.S. #223, 60510 Batavia (IL) USA > In Italy: (39)0498277230 office - (39)041719351 home - (39)3497267845 cell. > -----------------------------------------------------------------------------