A Multi-MW Proton/Electron Linac at KEK

The main bottleneck' limiting the beam power in circular machines is caused by space charge effects that produce beam instabilities. To increase maximally the beam power of a proton driver’, it is proposed to build a facility consisting solely of a 2.5-GeV injector linac (PI) and a 20-GeV pulsed superconducting linac (SCL). Such a facility could be constructed using the existing KEK accelerator infrastructure. The PI, based on the European Spallation Source (ESS) linac, would serve both as an injector to the SCL and a source of proton beams that could be used to copiously produce, e.g., neutrons and muons. Protons accelerated by the SCL would be transferred through the KEK Tristan ring in order to create neutrino, kaon and muon beams for fixed-target experiments. At a later stage, a 70-GeV proton synchrotron could be installed inside the Tristan ring. The SCL, comprising 1.3-GHz ILC-type rf cavities, could also accelerate polarized or unpolarized electron beams. After acceleration, electrons could be used to produce polarized positrons, or may traverse an XFEL undulator.