High Energy LHC Document prepared for the European HEP strategy update

The LHC will run to produce physics at the energy frontier of 13-14 TeV c.o.m. for protons for the next 20-25 years. The possibility of increasing the proton beam energy well beyond its nominal value of 7 TeV has been addressed in a study group in 2010 and then discussed in a workshop in October 2010. The reuse of the CERN infrastructure, the “ease” in producing luminosity with proton circular collider and the practical and technical experience gained with LHC, all are concurring reasons to explore this route. The High Energy LHC relies on the “natural” evolution of the LHC technologies. The High Luminosity LHC (HL-LHC) demands going 50% beyond the limit of magnetic field of LHC: therefore HL-LHC can be considered as the first milestone in the path toward the highest energy. The beam energy is set by the strength of superconducting magnets: assuming a dipole field in the range 16-20 T, the maximum attainable collision energy falls in the range of 26 to 33 TeV in the centre of mass. The driving technology is the superconductivity, and final performance and cost of HE-LHC are directly related to the progress of this technology. However, this machine will requires substantial advance in many other domains: from accelerator physics to collimation (with increased beam energy and energy density), from beam injection and beam dumping with a double rigidity to handling a synchrotron radiation level almost 20 times the LHC one, a real challenge for vacuum and cryogenics. However, the synchrotron radiation will also constitute a real advantage for HE-LHC design: for the first time a hadron collider will benefit of a short dumping time 1-2 hours instead of 13-25 h (longitudinal and transverse respectively) of the present LHC