1. Calor 2002, 25-29 march 2002Auguste Besson1 Argon purity measurement of the D0 calorimeter Auguste Besson (ISN - Grenoble) for the D0 collaboration 10 th International Conference on Calorimetry in High Energy Physics Calor 2002.

2. Calor 2002, 25-29 march 2002Auguste Besson2 Argon purity measurement of the calorimeter Argon Test Cell (A.T.C.) –measures the equivalent O 2 pollution with 2 radioactive sources  & . –general setup, cryostat, electronics Calibration –  Source –  Source Measurements and results Conclusion A. Besson, Y. Carcagno, G. Mondin, G. Sajot with help from Solveig ALBRAND, Germain BOSSON, Philippe MARTIN

3. Calor 2002, Auguste Besson3 The D0 calorimeter 1 Barrel + 2 End Caps1 Barrel + 2 End Caps Liquid ArgonLiquid Argon U (EM) / Cu-Stainless steel (Had.)U (EM) / Cu-Stainless steel (Had.) 5000 towers :5000 towers :  x  = 0.1 x 0.1 4 EM read out layers4 EM read out layers 4/5 Had read out layers4/5 Had read out layers  (EM) / E ~ 16% /  E  (EM) / E ~ 16% /  E  (Had) / E ~ 50% /  E  (Had) / E ~ 50% /  E Central Cal. South End Cap North End Cap

4. Calor 2002, 25-29 march 2002Auguste Besson4 Why do we have to monitor the Argon purity ? Shower : liquid argon ionization. Liquid Argon purity : Any electronegative molecule (O 2 ) absorbs electrons and decreases the signal. E=10kV/cm, gap=2mm (ATLAS LARG-NO-53) Need purity better than ~ 0.5 ppm Monitor precisely the pollution. Pollution (ppm) (collected signal) / (ideal signal) (collected signal) / (ideal signal)

5. Calor 2002, 25-29 march 2002Auguste Besson5 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 in an adjustable electric field E through a gap between electrodes : d = 2.15 mm. The collected charge depends on the pollution p and on the field E. Gap : d = 2.15 mm

6. Calor 2002, 25-29 march 2002Auguste Besson6 System used in Run I (1992-96) 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

7. Calor 2002, 25-29 march 2002Auguste Besson7 ATC General setup

8. Calor 2002, 25-29 march 2002Auguste Besson8 ATC operating condition Temperature (K) Pressure (bar absolute)

9. Calor 2002, 25-29 march 2002Auguste Besson9 Signal cables High Voltage sources LN2 exchange

10. Calor 2002, 25-29 march 2002Auguste Besson10 Alpha source measurements  particle : highly ionizing particle Energy deposited over ~ 20  m constant currant Ramping on the electric field E (~20 values) Collected charge = f (E,p) ~ 40 000 evts / value normalized signal : PedestalSignalPulser

11. Calor 2002, 25-29 march 2002Auguste Besson11 Alpha : principles of the measurement With absorption length Recombination Collected charge Absorption (a,b,c = constants) with Trapping constant  : = 0.142  0.014 cm 2.kV -1.ppm

12. Calor 2002, 25-29 march 2002Auguste Besson12 Alpha: absorption Theoritical expression of the absorption

13. Calor 2002, 25-29 march 2002Auguste Besson13 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

14. Calor 2002, 25-29 march 2002Auguste Besson14 Alpha : errors estimates Statistic errors : –Statistics and fit error ~  0.07 ppm Systematic errors : –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 –trapping constant  = 0.142  0.014 Other systematics : – electronics and non linearity of the preamp. – temperature effects, etc. Need a calibration.

15. Calor 2002, 25-29 march 2002Auguste Besson15 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

16. Calor 2002, 25-29 march 2002Auguste Besson16 Errors on the pollution : Volume of liquid Argon : 8-10 liters  5 % Volume of O 2 : 8.3  0.1 cm 3 Pressure of O 2 : 15  0.5 P.S.I. Calibration (2)  Source Measured / nominal E (kV/cm) Absorption Error on the nominal pollution ~ 10 %

17. Calor 2002, 25-29 march 2002, A.Besson Argon Sample Nominal Pollution Measured Pollution Cylinder 1 0.1  0.070.04  0.12 Cylinder 2 0.1  0.070.05  0.12 Cylinder 3 0.1  0.070.06  0.12 Cylinder 4 0.1  0.070.11  0.12 Cylinder 5 0.1  0.070.12  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)

18. Calor 2002, 25-29 march 2002Auguste Besson18 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) Nominal Pollution (ppm) Error measurement (ppm)

19. Calor 2002, 25-29 march 2002Auguste Besson19 Alpha : C.C. and calibration, example Measured / nominal C.C.

20. Calor 2002, 25-29 march 2002Auguste Besson20 Nominal Pollution (ppm) Trapping constant  measurement Trapping constant  : Trapping constant  :  Relates absorption length, field E and pollution p : main error for absolute measurements. Its value is not very well known : With our calibration :  = 0.141  0.011 cm 2.ppm/kV  parameter  = 0.142  0.014 cm 2.ppm/kV (Andrieux et al. NIM A 427, 568 -1999)  = 0.138  0.019 cm 2.ppm/kV average

21. Calor 2002, 25-29 march 2002Auguste Besson21 Characteristics –Complete spectrum. –Low ionizing particle the tracks cross the gap –Use a trigger gap in Coincidence to decrease the noise No theoritical formula : empirical fit Beta Source With a, b, c, d, g parameters of the fit.

22. Calor 2002, 25-29 march 2002Auguste Besson22 Beta: parameters vs pol. A et B given by the calibration.

23. Calor 2002, 25-29 march 2002Auguste Besson23 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 Pollution (ppm) Error measurement (ppm)

24. Calor 2002, 25-29 march 2002Auguste Besson24 Beta: example of C.C. measurement C.C.

25. Calor 2002, 25-29 march 2002Auguste Besson25 Beta: example of N.E.C. measurement N.E.C.

26. Calor 2002, 25-29 march 2002Auguste Besson26 Beta: example of S.E.C. measurement S.E.C.

27. Calor 2002, 25-29 march 2002Auguste 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 (ppm)

28. Calor 2002, 25-29 march 2002Auguste Besson28 Conclusion and outlook Errors on measurements :  Absolute measurements and 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 alpha internal cells of the calorimeter (Purity monitoring by Mainz Univ.) Trapping constant measurement “Experiments must be reproduceable, they should fail the same way each time.”

29. Calor 2002, 25-29 march 2002Auguste Besson29