Atlas "Baby-Demo"

Evaporative CO2 has been selected as the main detector cooling technology for the Phase II upgrade of the LHC silicon detectors at CERN. In order to provide input to the ATLAS Pixel TDR about the minimum attainable cooling temperature by the end of 2017, ATLAS, with a contribution of CMS, has launched a dedicated detector cooling R&D study nick-named Baby-DEMO. The Baby-DEMO is the demonstration of a typical 2PACL CO2 cooling plant operating at the lowest temperature ever achieved. A real size ATLAS mock-up is used to hold realistic manifolding as its critical path might have strong impact on the cooling performance. Additionally, the "Baby-DEMO" program addresses the study of high power flexible vacuum insulated coaxial transfer lines and warm nose boiling enhancement as possible solutions for the Phase II upgrade. This paper describes the system design including CO2 plant, primary chiller and typical distribution. Challenges and solutions used to achieve the lowest possible evaporation temperatures are reported. The result of this study, even if at the preliminary stage, are of great interest for the design of the cooling systems that ATLAS and CMS will use in the Phase II era.