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SUMMARY:Ultrasonic gas mixture analysis for Cherenkov Refractometry and co
 olant leak hunting in silicon trackers. - Greg Hallewell\, CNRS Marseille
DTSTART:20150414T140000Z
DTEND:20150414T150000Z
UID:TALK58209@talks.cam.ac.uk
CONTACT:Nick Barlow
DESCRIPTION:In a binary gas mixture at known temperature and pressure the 
 sound velocity is a unique function of the molar\nconcentrations of the t
 wo components.The technique is particularly sensitive to variations in  t
 race concentraton\nof a heavy vapour additive in a light carrier. Sound pu
 lse transmission in opposite  directions relative to the gas\nflow allows
  simultaneous flowmetry and mixture analysis  in the same instrument.\n\n
 Since the 1980's Ring Imaging Cherenkov (RICH) detectors have used fluoroc
 arbon gas radiators\, due to their high UV\ntransparency and tunable rang
 e of refractive index near atmospheric pressure. In the SLD barrel CRID a
 t the SLAC\nlinear collider C5F12 (perfluoropentane: mw 288) was mixed wit
 h 20% nitrogen. Continuous  real-time sound velocity\nmonitors ("sonars")
  at different heights in the radiator vessel monitored stratification  du
 ring fill and recovery\nof the fluorocarbon component\, without the need f
 or gas extraction to a refractometer. During long-term running the\nsonar
 s allowed correction of the mixture to stabilize the B=1 Cherenkov angle t
 o better  than +/- 0.2 mrad rms. The\ntechnique has since been used - les
 s extensively - in other RICH detectors.\n\nThe ATLAS silicon tracker uses
  C3F8 and CO2 evaporative cooling. Leaks of both these fluids  into the N
 2-purged\nenvelopes of the tracker are detectable by sonar instruments: C3
 F8 leak  concentrations less than 5.10^-5 being\nroutinely detectable in 
 the pixel and SCT envelopes. \n\nThe compressor-driven C3F8 evaporative s
 ystem is being replaced by a thermosiphon recirculator. \nTwo sonars are 
 installed in the system: one monitors air ingress into the condenser while
  the other will montior\nthe combined 0.4 m^3/s^-1 C3F8 return flow from t
 he tracker. \n\nAll the sonar instruments have custom electronics cummuni
 cating via Modbus TCP/IP with a Dell  Poweredge R610 SCADA\ncomputer runn
 ing WINCC. The sonar system is being integrated into the ATLAS detector c
 ontrol system and alarm\nhandler. \n\nWe have also demonstrated that the 
 barrel SCT can operate 9C colder with a blend of 75%C3F8/25% C2F6\, giving
  better\ntolerance to radiation damage under increased LHC luminosity. So
 nar instruments monitor C2F6/C3F8 blend stability\nto 0.3%. The sonar flo
 wmeter in the thermosiphon would perform this analysis should C2F6/C3F8\nb
 lends be used in the future.\n\nThese instruments are well adapted to many
  other applications where simultaneous flowmetery and analysis are\ndesire
 d\, including hydrcarbon/air mixtures\, gas mixtures for MOCVD semiconduc
 tor manufacture\, diving and clinical\nanaesthesia.\n
LOCATION:Rutherford Seminar Room B
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