Compact electron linac with a beam circulation

A linear accelerator with electrons passing through the accelerating system twice is described. The accelerator is equipped with the accelerating system 2.5 m long. The system of the beam return from the output of the accelerating system to the input forms ''a ring'' with the accelerating system in the vertical plane thus making the whole accelerator a fairly compact unit. Electrons are injected from the electron gun arranged at an angle of 90 deg to the axis of the accelerating system. During the repeated injection the electron flow passes through a pair of beam-bending magnets, which extract electrons onto the axis of the accelerating system along with the beam-bending magnet of the injection system. These three magnets form an achromatic system, in which the phase length of electron bunches with a momentum spread of +-5x10-2 increases by more than 1 deg. To adjust length of the beam return and electron injection in case of repeated acceleration in the optimum phase one arm of the return line from the injector side has been made flexible with the help of bellows. The isochronous beam return system comprises four similar magnets and two similar quadrupole lenses. Particle dynamics has been calculated at 3-7.5 MW input power and 0-0.3 A current