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Argon purity measurement of the calorimeter

Argon purity measurement of the calorimeter. A. Besson, Y. Carcagno, G. Mondin, G. Sajot (ISN - Grenoble). Argon Test Cell (A.T.C.) measures the equivalent O 2 pollution with 2 radioactive s ources  & . general device, cryostat, electronics  Source Measurement and calibration

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Argon purity measurement of the calorimeter

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  1. Argon purity measurement of the calorimeter A. Besson, Y. Carcagno, G. Mondin, G. Sajot (ISN - Grenoble) • Argon Test Cell (A.T.C.) • measures the equivalent O2 pollution with 2 radioactive sources  & . • general device, cryostat, electronics •  Source • Measurement and calibration •  Source • Measurement and calibration • Conclusion Auguste Besson

  2. Why do we have to measure the Argon purity ? • Electromagnetic shower : • liquid argon ionization. • Liquid Argon purity : • Any electronegative molecule (O2 ) • absorbs electrons and decrease the signal. (collected signal) / (ideal signal) • Want purity better • than 0.5 ppm • Measure precisely the pollution. Pollution (ppm) E=10kV/cm, gap=2mm (ATLAS LARG-NO-53) Auguste Besson

  3. Principles: 2 radioactive sources  and  • ALPHA • 5.5 MeV, T = 430 ans • BETA • 3.5 MeV, T = 1 an, 40kBq • Sources electrodeposited on a stainless steel electrode. • Sources immerged in liquid Argon (@ ~ 85 K). • Ionisation, drift of the charges thanks to adjustable electric field E. • Gap between electrodes :d = 2.15 mm. • The collected charge depends on the pollution p and on the field E. Auguste Besson

  4. General setup Auguste Besson

  5. Auguste Besson

  6. Cryostat Auguste Besson

  7. ATC LN2 exchange Signal cables sources High Voltage Auguste Besson

  8. A.T.C. history • System used in Run I (1990-96) • LAr stocked in a dewar for 5 years in a dewar(~ 20 000 gallons) • Upgrade for Run II • New Beta source • New electronics (preAmplis, Pulsers, etc.) • Data acquisition soft in LabWindows/CVI • Added a O2 pollution system for calibration • complete check of the cryostat (leak detection, checks of valves, etc.) • Calibration of system(2000) • Dewar purity measurement • July 2000 and october 2000 (before filling the Calorimeter) • Calorimeter measurements : • December 2000 andDec. 2001 Auguste Besson

  9. Alpha source measurements •  particle : highly ionizing particle Energy deposited over ~ 20 m constant currant • Ramping on the electric field E (~20 points) • Collected charge = f (E,p) • ~ 40 000 evts / point • normalized signal : Pedestal Signal Pulser Auguste Besson

  10. Alpha : principles of the measurement • Collected charge • Recombination with (a,b,c = constants) • Absorption With radiation length Trapping constant : = 0.142 cm2.kV-1.ppm Auguste Besson

  11. Alpha: absorption Theoritical expression of the absorption Auguste Besson

  12. Alpha absorption: an example Fit of Abs(E,p) vs E. Argon from dewar. • Black : fit = 0.37 ppm • Blue : fit - 0.1 ppm • Red : fit + 0.1ppm Absorption E (kV/cm) Auguste Besson

  13. Alpha : errors estimates • Main sources of errors : • Statistics and fit error ~  0.07 ppm • High Voltage ~ 2 % • gap between electrodes : d = 2.15  0.05 mm • Error on parameters: a = 474  1.4 kV/cm b = 0.143  0.006 cm/kV c = 0.403  0.010 • Error on trapping constant  = 0.142  0.014 • Other systematics : • electronics and non linearity of the preamp. • temperature effects, etc. Example: for p = 0.5 ppm  p ~  0.17 ppm Need a calibration. Auguste Besson

  14. Alpha calibration • Recipe • Start from a high purity Argon sample < 0.1 ppm • Pollute with a well known amount of O2 (for instance 0.5 ppm) • mix well, wait for 1 or 2 hours • Measure Auguste Besson

  15.  Source Calibration (2) • Errors on the pollution : • Argon quantity : • 8-10 liters  5 % • Volume of O2 : • 8.3  0.1 cm3 • Pressure of O2 : • 15  0.5 P.S.I. • Error on the nominal pollution ~ 10 % Absorption Measured / nominal E (kV/cm) Auguste Besson

  16. Alpha : calibration results Nominal (ppm) Measured (ppm)

  17. Alpha : errors Error vs nominal pollution (ppm) Linear Fit gives the final errors. Auguste Besson

  18. Alpha : C.C. and calibration Measured / nominal Auguste Besson

  19. Beta Source • Installation : October 2000 • Complete spectrum. • Low ionizing particle • the tracks cross the gap • Use a trigger gap to decrease the noise • No theoritical formula:empirical fit With a, b, c, d, gparameters of the fit. Auguste Besson

  20. Beta: parameters vs pol. A et B given by the calibration. Auguste Besson

  21. Beta: errors Auguste Besson

  22. Beta: calibration and C.C. Measured / nominal Auguste Besson

  23. Beta: calibration and N.E.C. Measured / nominal Auguste Besson

  24. Beta: calibration and C.C. Auguste Besson

  25. Beta: calibration and N.E.C. Auguste Besson

  26. Beta: calibration and S.E.C. Auguste Besson

  27. Summary of measurements Measurements compatible and stable Auguste Besson

  28. Conclusion and outlook • Errors on measurements :  Absolute errors.  better than  0.15 ppm • We checked the stability of purity compared to last year measurements.  Purity OK for the 3 calorimeters < 0.5 ppm  No need to apply correction for calorimeter response  Give a calibration for the internal cells (Mainz Univ.) • http://isnwww.in2p3.fr/d0/purete/cryostat.html • DØ notes 3799 et 3827. Auguste Besson

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