Microtron injector for LEP

In the 15 to 100 GeV position electron Colliding Beam Machine (LEP) under study by the European Committee for Future Accelerators it is intended to use a 460 MeV accumulation ring (ACR) to collect a previously bunched beam of electrons or positrons before it is injected into a booster synchrotron. It is proposed to compress the longitudinal bunch length in the ACR by means of two r.f. systems that act on the beam one after the other like in the Positron Intensity Accumulator. Long beam pulses of 2 to 3 microsec can then be injected into ACR with multiturn injection. Compared to previous proposals the injected beam current can be reduced, and great savings in terms of peak microwave power can be achieved. Further economy and reliability in the LEP front-end machine can be gained by the use of an electron-positron racetrack microtron. The general concepts of such a microtron are indicated.