The ESRF's Extremely Brilliant Source - a 4th Generation Light Source

International audienceAfter 20 years of operation, the ESRF has embarked upon an extremely challenging project - the Extremely Brilliant Source (ESRF - EBS) . The goal of this project is to construct a 4th generation light source storage ring inside the existing 844m long tunnel. The EBS will increase the brilliance and coherence by a factor of 100 with respect to the present ESRF storage ring. A major challenge is to keep the present ring operating 24x7 while designing and pre-constructing all the elements of the new ring. This is the first time a 4th generation light source will be constructing inside an existing tunnel. This paper concentrates on the control system aspects. The control system is 100% TANGO based. The paper will list the main challenges of the new storage ring like the Hot Swap Powersupply, the new timing system, how reliable operation was maintained while modernizing the injector control system and preparing the new storage ring control system, the new historical database, and how extensive use was made of software simulators achieve this