Manchester Particle Physics Seminars, Colloquia and Meetings

Greg Hallewell: From the Speed of Sound to the Speed of Light: and beyond! Ultrasonic Multi-Gas Analysis: from Cherenkov Refractometry through fluorocarbon silicon tracker cooling to Xenon anaesthesia.

Friday, 15 May 2020 from to (Europe/London)
at Zoom
Please note, the seminar will be held via Zoom Connections will begin at 12:30 with the seminar beginning at 13:00.

Continuous optical measurement of refractive index in dynamically-changing gas mixtures is very demanding. Monitoring sound velocity is simpler and very reliable. Logging the speed of sound in the gas radiator of a Cerenkov detector is in itself a monitor of the speed of light, and with it the thresholds in GeV for detecting charged particle species  mu ±, pi ±, K ±, p ±. This ultrasonic ("sonar") technique was first used with fluorocarbons in the SLD CRID at the SLAC linear collider, and later in the DELPHI and COMPASS RICHs.

Saturated (C_nF_(2n+2)) fluorocarbons are used as non-conductive radiation-resistant coolants in LHC detectors. They are expensive and environmentally-degrading, so in ATLAS  a  leak detection system based on sound velocity is a vital part of the detector control system. Custom sonar gas analyzers continuously monitor  coolant leaks from the pixel, SCT and IBL detectors and also monitor (and eliminate) ingressed air from the roof-top condenser of 90-metre C3F8 thermosiphon recirculator which replaced a compressor system in September 2018. 

Our instruments transmit sound in opposite directions in a moving gas stream: the difference in transit time is proportional to the flow while the average is compared with concentration vs. sound velocity tables to simultaneously monitor the concentrations of the components. A precision of ~ 2.10-5 is continuously achieved in ATLAS monitoring C3F8 ingress into nitrogen. A custom large aperture sonar also measures mass flows of C3F8 vapour up to 1.2 kgs-1 ascending from the ATLAS pit to the thermosiphon condenser.

Advanced new ultrasonic algorithms allow analysis of mixtures with more than two gases; concentrations of a pair of gases of particular interest can be measured on top of a varying known baseline of other gases, whose thermodynamic data are in the on-line database accessed by the algorithm. This approach is particularly well suited to analysis of anaesthetic gas mixtures containing xenon and oxygen, along with known concentrations of water vapour,  CO2 etc. Funding for this R&D into acoustic monitoring and xenon recycling for xenon-based anaesthesia has been received.

The presentation will discuss the technology, use and performance of ultrasonic gas analysis in the various particle physics scenarios and in xenon-based anaesthesia.