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February 2002, D0 meetingAuguste Besson1 Argon purity measurement of the calorimeter Argon Test Cell (A.T.C.) –measures the equivalent O 2 pollution with 2 radioactive sources & . –general device, cryostat, electronics Source –Measurement and calibration Source –Measurement and calibration Conclusion A. Besson, Y. Carcagno, G. Mondin, G. Sajot (ISN - Grenoble)
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February 2002, D0 meetingAuguste Besson2 Why do we have to measure the Argon purity ? Electromagnetic shower : liquid argon ionization. Liquid Argon purity : Any electronegative molecule (O 2 ) absorbs electrons and decrease the signal. E=10kV/cm, gap=2mm (ATLAS LARG-NO-53) Want purity better than 0.5 ppm Measure precisely the pollution. Pollution (ppm) (collected signal) / (ideal signal) (collected signal) / (ideal signal)
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February 2002, D0 meetingAuguste Besson3 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.
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February 2002, D0 meetingAuguste Besson4 General setup
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February 2002, D0 meetingAuguste Besson5
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February 2002, D0 meetingAuguste Besson6 Cryostat
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February 2002, D0 meetingAuguste Besson7 ATC Signal cables High Voltage sources LN2 exchange
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February 2002, D0 meetingAuguste Besson8 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 O 2 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 and Dec. 2001 A.T.C. history
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February 2002, D0 meetingAuguste Besson9 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 : PedestalSignalPulser
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February 2002, D0 meetingAuguste Besson10 Alpha : principles of the measurement With radiation length Recombination Collected charge Absorption (a,b,c = constants) with Trapping constant : = 0.142 cm 2.kV -1.ppm
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February 2002, D0 meetingAuguste Besson11 Alpha: absorption Theoritical expression of the absorption
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February 2002, D0 meetingAuguste Besson12 Alpha absorption: an example E (kV/cm) Absorption Fit of Abs(E,p) vs E. Argon from dewar. –Black : fit = 0.37 ppm –Blue : fit - 0.1 ppm –Red : fit + 0.1ppm
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February 2002, D0 meetingAuguste Besson13 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. Need a calibration. Example: for p = 0.5 ppm p ~ 0.17 ppm
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February 2002, D0 meetingAuguste Besson14 Recipe –Start from a high purity Argon sample < 0.1 ppm –Pollute with a well known amount of O 2 (for instance 0.5 ppm) –mix well, wait for 1 or 2 hours –Measure Alpha calibration
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February 2002, D0 meetingAuguste Besson15 Errors on the pollution : Argon quantity : 8-10 liters 5 % Volume of O 2 : 8.3 0.1 cm 3 Pressure of O 2 : 15 0.5 P.S.I. Error on the nominal pollution ~ 10 % Calibration (2) Source Measured / nominal E (kV/cm) Absorption
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February 2002, D0 meeting Argon Sample Nominal Pollution Measured Pollution Cylinder 1< 0.2 0.04 0.12 Cylinder 2< 0.2 0.05 0.12 Cylinder 3< 0.2 0.06 0.12 Cylinder 4< 0.2 0.11 0.12 Cylinder 5< 0.2 0.12 0.12 Polluted 0.40 0.110.43 0.12 Polluted 0.50 0.120.45 0.12 Polluted 0.52 0.120.49 0.12 Polluted 0.63 0.160.58 0.13 Polluted 0.69 0.150.77 0.13 Polluted 0.90 0.200.40 0.13 Polluted 0.97 0.141.01 0.14 Polluted 1.05 0.181.21 0.15 Polluted 1.30 0.251.34 0.16 Polluted 3.50 0.393.84 0.23 Polluted 4.00 0.444.04 0.30 Polluted 5.00 0.555.07 0.35 Alpha : calibration results Nominal (ppm) Measured (ppm)
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February 2002, D0 meetingAuguste Besson17 Alpha : errors measured pollutionError 0.2 ppm 0.12 0.3 ppm 0.12 0.5 ppm 0.12 1.0 ppm 0.14 2.0 ppm 0.18 3.0 ppm 0.23 5.0 ppm 0.35 Linear Fit gives the final errors. Error vs nominal pollution (ppm)
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February 2002, D0 meetingAuguste Besson18 Alpha : C.C. and calibration Measured / nominal
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February 2002, D0 meetingAuguste Besson19 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 Beta Source With a, b, c, d, g parameters of the fit.
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February 2002, D0 meetingAuguste Besson20 Beta: parameters vs pol. A et B given by the calibration.
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February 2002, D0 meetingAuguste Besson21 Beta: errors Measured pollution Error 0.1 ppm 0.09 0.2 ppm 0.10 0.3 ppm 0.10 0.5 ppm 0.12 0.8 ppm 0.15 1.0 ppm 0.17 1.2 ppm 0.19 1.5 ppm 0.22
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February 2002, D0 meetingAuguste Besson22 Beta: calibration and C.C. Measured / nominal
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February 2002, D0 meetingAuguste Besson23 Beta: calibration and N.E.C. Measured / nominal
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February 2002, D0 meetingAuguste Besson24 Beta: calibration and C.C.
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February 2002, D0 meetingAuguste Besson25 Beta: calibration and N.E.C.
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February 2002, D0 meetingAuguste Besson26 Beta: calibration and S.E.C.
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February 2002, D0 meetingAuguste Besson27 Summary of measurements Measurements compatible and stable SampleALPHABETADateDewar 0.34 0.15 - July 2000 Dewar 0.33 0.15 - Oct. 2000 C.C. 0.49 0.15 0.38 0.11 Dec. 2000 N.E.C. 0.16 0.15 0.21 0.10 Dec. 2000 C.C. 0.07 0.12 0.10 0.09 Dec. 2001 N.E.C. 0.11 0.12 0.09 0.09 Dec. 2001 S.E.C. 0.17 0.12 0.14 0.10 Dec. 2001
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February 2002, D0 meetingAuguste Besson28 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.
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