Temperature characterisation of the CLOUD chamber at CERN

Wednesday, 17 December 2014
António Miguel Dias1, Joao Almeida1, Jasper Kirkby2, Serge Mathot1, Antti Onnela1, Alex Vogel1 and Sebastian Ehrhart1, (1)CERN European Organization for Nuclear Research, Geneva, Switzerland, (2)Goethe-University of Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany
Temperature stability, uniformity and absolute scale inside the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN are important for experiments on aerosol particle nucleation and ice/liquid cloud formation. In order to measure the air temperature, a comprehensive set of arrays ("strings") of platinum resistance thermometers, thermocouples and optical sensors have been installed inside the 26 m3 chamber. The thermal sensors must meet several challenging design requirements: ultra-clean materials, 0.01 K measurement sensitivity, high absolute precision (<0.1 K), 200 K - 373 K range, ability to operate in high electric fields (20 kV/m), and fast response in air (~1 s) in order to measure rapid changes of temperature during ice/liquid cloud formation in the chamber by adiabatic pressure reductions. This presentation will focus on the design of the thermometer strings and the thermal performance of the chamber during the CLOUD8 and CLOUD9 campaigns, 2013-2014, together with the planned upgrades of the CLOUD thermal system.