A Longterm Aging Study of the Honeycomb Drift Tubes of HERA-B Using a Circulated and Purified CF -Gas Mixture

Transcription

1 A Longterm Aging Study of the Honeycomb Drift Tubes of HERA-B Using a Circulated and Purified CF -Gas Mixture 4 M. Capeáns, K. Dehmelt, M. Hohlmann, B. Schmidt a c b b c a CERN (Geneva) b DESY (Hamburg) University of Mainz Klaus Dehmelt

2 Motivation for aging study: Recirculating gas-system with CF4 -gas mixture for the OTR Need to test purifiers Monitoring of pollutants Y Simulation of the OTR and its gas-system Longterm-behaviour of Honeycomb Drift Tubes for the OTR

3 Honeycomb Drift Tube (HDC) of the OTR Pocalon Foil Signal Wires Pocalon, 75m Coated with Cu & Au Endpiece G10-strips Signal wires, Au/W, 25m Single Layer Double Layer 5mm / 10mm

4 Gas: Ar / CF 4 / CO 2 Gas: Ar / CF 4 / CO 2 International Workshop on Counting Gas for the OTR Interaction rate: 40MHz needs Gas mixture: Ar:CF 4:CO 2 ( 65:30:5) due to Drift velocity: 140 m / ns (4-6kV/cm) Price of CF 4: ~50 / kg Gas volume of OTR: 3 ~ 22 m η Hit [%] % 65% / 35% / 0% 65% / 32% / 3% 65% / 30% / 5% 65% / 28% / 7% YRecirculating gas system U Hochspannung [kv] R.Pernack η Spur [%] % / 35% / 0% 65% / 32% / 3% 65% / 30% / 5% 65% / 28% / 7% U Hochspannung [kv] R.Pernack

5 Recirculating gas-system: Air (leaks) Plasma chemistry products? (Processes in avalanche,material outgassing,crack products) ACCUMULATION! Needs purification. The Purifiers for the OTR Y R3-11G Catalyst: Removal of oxygen 46% Cu (highly dispersive) 2Cu + O2 2CuO Regenerative Molsieve 3A: Removal of H2O (and other pollutants?) Inverse sieve

6 Experimental Setup for Aging Test Honeycomb test module: 16 drift tubes, each of 40cm X-ray source: length Cu-anode, running at 20kV Beam spot size ~ 12cm diameter Customized gas system: Operation in open-loop & closed loop Regulated chamber pressure (no bubbler) Monitoring main & trace gas components Removal of oxygen & water Electronic readout system: FADC, ADC, Currentmeter

7 HDC-test-modules: 2 x 16 channels, two coated pocalon foils Equipment Test Modules & DAQ Gas outlet Frontend-electronics Gas inlet DAQ

8 Equipment - Gas Supply PID-flow regulated, very clean gas system, chamber covered with Mylar-foil

9 Equipment Gas Monitoring Gas Chromatograph HP5890, Mass spectrometer + Electron Capture Detector with individual chromatography columns Commercial Commercial Quality of Counter gas Pollutants (if any) oxygen meter dewpoint sensor

10 Aging Test Procedures Examination of module functionality Irradiation of half circle area ( øy12cm) Readout of 3 wires (PH-spectra) Current monitoring Monitoring of T, p Monitoring of gas quality HERA-B OTR gas-conditions: Recirculation Gas purification Fresh gas ~ 2% / h Monitoring of PH-spectra

11 Aging test: Gas Gain Development I 1.) 2.) 3.) Break Relative raw gas gain development and current for all periods Break 1.) No Purification, open loop 2.) Molsieve, closed loop 3.) Molsieve + R3, closed loop

12 Aging test: Gas Gain Development II 1,4 1,3 1,2 1,1 1 Molsieve in loop Rel. Gas Gain 1,1 1 0,9 Rel. Gas Gain 0,9 0,8 Molsieve removed 0,8 0,7 SWPC --- Wire No ,7 SWPC 0,6 Jul/23/1999 Jul/25/1999 Jul/27/1999 Jul/29/1999 Jul/31/1999 Date Run without purification: a Correlation of HDC and SWPC 0,6 Aug/3 Aug/4 Aug/5 Aug/6 Aug/7 Aug/8 Date Not saturated molsieve changes gas-composition

13 Aging test: very high irradiation 1,4 1,3 1,2 1,1 1 0,9 0,8 0,7 0,6 Module201-Wire07 Corrected to amb. pressure & temp Time in hrs Irradiation performed with ~1A / cm closed loop without purification High irr. Low irr. Observation of dark pulses (khz) Observation of pollutants: CH2Cl2 C2H6F2Si Disappeared when switching to open loop Disappeared with purification (closed loop)

14 Aging test: Gas Gain Development III Corrected to p & T F1 G=G`x(( 1/P i )xp) i x( T i /T) i F2 ~2.3C / cm Accumulated ~0.2 A / cm Different periods of operation: w/o purification Molsieve R3-11

15 The open module Gas outlet colored G10-strip shows spark traces Irradiation area visible No wire was ruptured

16 Summary and conclusion Total accumulated charge ~2.3 C / cm within ~ 3000 hours within closed loop and purification Equivalent to more than three years of nominal HERA-B conditions in the hottest region No significant losses in gain observed Deviations in gain explainable due to ambient conditions REMARK: after continuing of irradiation chamber became unusable. Reason?? Under investigation.

17 direction of drift start International Workshop on Equipment Gas Chromatograph Basic idea: separation of gas components Agilent time

18 Equipment Gas Chromatograph Detectors Ar/CF /CO 4 2 Mass spectrometer: Quadrupole mass filter Identification of components H O 2 Library spectrum of CF 4 CO 2 CF 4 H O 2 Unknown species Electron Capture Detector (ECD): in detector volume Y I electronegative speciesy const IKconst