Aspects of the use of saturated fluorocarbon fluids in high energy physics

The excellent dielectric properties of saturated (CnF(2n+2)) fluorocarbons have allowed their use in direct immersion liquid cooling of electronics, including the Cray series of supercomputers, and as heat transfer media in vapour phase soldering and burn-in testing of electronics. Their high UV optical transparency, non-flammability and non-toxicity have led to their use as liquid and gas radiator media for Cherenkov detectors: such fluids have been used as liquid and gaseous radiators in numerous particle physics and astroparticle physics experiments.The systems used to circulate and purify fluorocarbon Cherenkov radiator fluids often rely on thermodynamic cycles similar to those of the refrigerants recently developed to replace chlorofluorocarbons. Since such new refrigerants are designed to disintegrate under UV exposure in the upper atmosphere, they are correspondingly not radiation-resistant, and cannot be used for direct cooling of particle detectors in demanding radiation environments, such as at the CERN Large Hadron Collider. However the pure saturated fluorocarbon molecules are extremely radiation resistant due to the presence of only single C-F bonds. Their use as evaporative refrigerants was pioneered at CPPM for the ATLAS pixel detector and has been chosen for the cooling of all the silicon detectors in the experiment, and also for cooling the semiconductor vertex detectors of the ALICE and TOTEM experiments at LHC. These fluids are also used as liquid phase cooling fluids in ATLAS and CMS. The evaporative mode exploits the latent heat or enthalpy of vaporization, allowing the circulation of a lower coolant mass than in a monophase cooling system of the same refrigerative capacity. Coupled with the lower fluorocarbon viscosity - compared with aqueous antifreeze-based coolants - this permits the use of narrower delivery tubing to the detectors, resulting in a smaller '%X0'contribution to the detector material budget. Ultrasonic techniques for the vapour phase analysis of fluorocarbon Cherenkov radiators were developed as an alternative to UV refractometry for the SLD Cherenkov Ring Imaging Detector at the Stanford Linear Accelerator Center during the 1980s. Subsequently the technique has been used in many other Ring Imaging Cherenkov Detectors and also in the petro-chemical industry and for MOCVD (metal organic chemical vapour deposition) manufacture of semiconductors. The technique has also been demonstrated to have possible application in the vapour phase analysis of gas mixtures used in clinical anesthesia. Such vapour phase analysis techniques are again under evaluation for the possible cooling of the upgraded ATLAS silicon tracker. The work of the author related to various applications of these versatile fluorocarbon fluids is discussed in this memoire.