Acceptances and trajectory correction in the ELFE recirculating linear accelerator

Abstract Analytical studies of the beam transport in a recirculating linear accelerator are derived and compared to simulations made for the Electron Laboratory For Europe (ELFE) linac. In this project, the electron beam is accelerated by three passes in a long (1 km) linac, up to 15 GeV. To transport three simultaneous beams in the linac, two main questions arise: optimization of the acceptances, which decrease from pass to pass, and correction of the beam central trajectories. While the focusing inside the linac and the injection energy may be chosen to optimize the acceptances, the displacement of the beam central trajectory is mostly dependent on the correction scheme. The best correction scheme appears to be a simultaneous optimization of the three beam central trajectories. This method is similar to beam-based alignment techniques, which may be used either as an alternative or as a complementary solution. These methods appear to be very successful, and may be applied to any scheme involving one or several long recirculating linac(s).