Commissioning and First Operation of the Large Hadron Collider (LHC)

After some fifteen years of construction, the Large Hadron Collider (LHC) was commissioned at CERN, the European Organization for Nuclear Research in 2008. This high-energy particle accelerator of 26.7 km circumference – the largest scientific instrument ever built – brings into collision intense beams of protons and ions to probe the structure of matter and study the forces acting on its elementary components at the TeV scale, an order of magnitude higher than the previous stateof-the-art. To guide and focus its particle beams, the LHC uses several thousands high-field superconducting magnets operating in superfluid helium at 1.9 K. The project therefore constitutes a technological feat: all its components were developed, industrialized and series produced by industrial companies according to demanding specifications. Started as a CERN undertaking – by decision of the CERN Council and its twenty European member states – the project soon became global with special contributions from Canada, India, Japan, Russia and the United States of America. After recalling the technical stakes of the project, we present the main results from the construction and commissioning phases and from the first beam operation. We also summarize the detailed investigations conducted after the incident of 19 September 2008, to analyze its causes and draw conclusions for repair and consolidation. We finally report on the restart of the machine i n 2009 and on its first operation for physics.