60 Years of Particle Accelerators

1. Accelerator Developments • Since 1954 43.9 mm 28 mm 60 Years of Particle Accelerators The CERN accelerator complex was built over 60 years by successive developments, each accelerator serving as injector for the following ones, each time more powerful. 1953 CERN … sur Arve In 1953 the Meyrin site did not exist and the PS (proton Synchrotron) division set itself up in 1953-1956 in the confines of the Institute of Physics, Quai Ansermet, on the shores of the Arve river in Geneva. Here is what a lab looked like then: Powerful computers did not exist then and to determine the shape of magnets one had to proceed by building mock-ups: In 1989 the large 27km tunnel is completed, under Swiss and French territories; particles know no borders! If LHC continues until 2035, this 600 MCHF infrastructure will have served the large e+e- collider LEP and the LHC for 50 years. While measuring the mass of the Z boson with a very precise method, physicists, among which the Swiss Albert Hofmann and JörgWenninger, with Alain Blondel (University of Geneva), realized that the effect of terrestrial tides had to be corrected. By changing the size and shape of the accelerator by a few hundred microns, the tides were modifying the energy of the beams! • This is a picture of members of the magnet group sitting on the first combinedfunctionmagnet unit. This photo wastaken at the Institute of Physics in Geneva. • 1st rank, left to right: R. Tinguely, C. Germain, G. Plass, D. Neet, B. de Raad, M. Cavallaro, K.H. Reich, G. Kuhn, J. Nilsson, C.A. Ramm, Paillard • 2d rank: L. Resegotti, M. Niklaus, C.J. Zilverschoon, R. Bertolotto, Marcellin, G. Brianti, P. Collet • Debout derrière : B. Kuiper • Today, all these people have retired, but the magnets are stillpulsing. The PS is at the heart of the CERN acceleratorcomplex. MZ=91.1872  0.0022 GeV Precision measurements from LEP will remain unique for many years. • EPFL LPAP contributions in development of superconducting magnets for the LHC and HL-LHC Project: • Experimental characterization of heat transfer in LHC Super Conducting coils operating in superfluid helium (He II)Fundamental investigation of He II heat transport laws in narrow channel • A Finite Element Model of the LHC Dipole Cold Mass with Hysteretic, Non-linear Behavior and Single Turn Description: Towards the Interpretation of Magnet Quenches AcceleratorTechnologycollaborations Field emission in the LEP Superconducting RF cavities CERN often turned to University to solve technological problems affecting accelerators. This was the case for the LEP accelerating cavities. In order to store electrons and positrons at the high energy required to hunt the Higgs boson, a high acceleration was needed at each turn of the machine, leading to a high power consumption. This required the use of superconducting cavities (left below). LHC Dipole Superconducting cable Dipole cross section FE model However, when reaching high fields these cavities started emitting electrons ejected from the metal of the cavities walls, this preventing good performance. The challenge was taken up by the group of Pr. Oystein Fischer at University of Geneva. A complex instrument ‘ESCALAB’ was built to study surfaces in various conditions. This marvel comprised, all under extreme vacuum, a Auger Spectrometer, a microprobe for field emission and an electronic microscope. (Right) Heat Transfer 4-5 times ! The inspection of surfaces revealed that impurities were the source of emissions. Analysis showed that a high temperature treatment reduced emissions drastically. This method was applied to the LEP2 cavities, and has been used since for several accelerators in the world.