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Özkan ŞAHİN Uludağ University Physics Department Bursa -TURKEY

CF4, measurements and calculations. Özkan ŞAHİN Uludağ University Physics Department Bursa -TURKEY. Available data. Single wire chamber r a = 25 µ m, r c = 0.9 cm Gas 1000 hPa pressure, 20 °C temperature Gain Order of 10 5 Error on gain < 10%. Calculation Method.

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Özkan ŞAHİN Uludağ University Physics Department Bursa -TURKEY

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  1. CF4, measurements and calculations Özkan ŞAHİNUludağ University Physics DepartmentBursa -TURKEY

  2. Available data 7th RD51 Collaboration Meeting , 13-15 April 2011, CERN Single wire chamber ra = 25 µm, rc = 0.9 cm Gas 1000 hPa pressure, 20 °C temperature Gain Order of 105 Error on gain < 10%

  3. Calculation Method • Effective Townsend coefficient (attachments included) calculated by Magboltz 9.0.1 version [S.F. Biagi, NIM A421 (1999) 234–240] Attachment Photon feedback • Unabsorbed fotons from Ar, • secondary avalanches, at high gain, • over exponential increases on semi -log gain plots • almostuncorrelated, free parameter. Ionisations: Ar 15.76 eV, CF4 15.90 eV Ar – CF4 is NOT a Penning mixture Dissociative excitation of CF4 at 12.56 eV 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA

  4. Fits I CF4 75% CF4 50% Calculation Experiment CF4 20% CF4 10% Photonfeedback 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA

  5. Fits I CF4 5% CF4 1% 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA • Why the calculations are bigger than the experimental data ??? • Attachments could have an effect but not at high fields • Should include the photon feedback terms !!! • Not possible to get an agreement if only take into account feedback !!! • Could gain scaling factors play the major role ??? • No, we have already tried !!! • Other explanations , ideas ???, welcome !!!

  6. Fits II CF4 75% CF4 50% • Dissociativeexcitation of CF4 CF4 20% CF4 10% • Dissociativeexcitation of CF4 • Feedbackparameter 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA

  7. Fits II CF4 5% CF4 1% 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA • Almost perfectly fine agreements by using Dissociative excitation of CF4 and Feedback parameter • No need to use gain scaling factors • But, too early to be sure about Dissociative excitation parameters (see the table on the next page) • Magboltz CF4 ionisation cross sections could probably be too high ??? • Should be checked !!!

  8. Dissociative excitation & Feedback parameters • Increasewith Argonconcentration • But,improbabletohave> -1 dissociativeexcitationparameter 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA

  9. Summary • Ionisation and dissociative excitation (may be attachment) cross sections of CF4 in Magboltz should be checked carefully • Ionisation checked 1 year ago, seem correct !!! • Seems no need to use gain scaling factors • But feedback parameters are essential to reproduce the experimental data (except Ar 25% - CF4 75% mixture) NEXT: • It will be possible to handle triple mixtures of CF4 with more confidence ( Ar – CO2 – CF4 ) • Understanding of CF4 may also be important for ALICE TPC gas mixtures (Ne 90% – CF4 10%) 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA

  10. Thanks & ??? 10th RD51 Collaboration Meeting , 30 September - 05 October 2012, Stony Brook, NY, USA

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