d_Atirdd 250 12/16116 3:06 PIA EFTA00286172 Spanking the Vacuum 251 are easier to accelerate to high energies. In 2976 a proton accelerator at the European Organization for Nuclear Research (CERN) in Geneva, the Super Proton Synchrotron (SPS), had just been commissioned as a conventional fixed-target accelerator operating with a proton beam