“…Electron linacs are widely used in facilities of radiotherapy, nondestructive inspection, container inspection system at the Customs, industrial computed tomography (ICT), etc. For a low-energy linac during its normal run, the electron beam loss takes place in the accelerator tube, in the bending magnet, in the attachment of components [1] , in the electron transportation tubes [2,3] , etc. In common RF accelerators, among the total electrons emitted by the electron gun, only electrons whose phases are within a particular interval can be accelerated stably.…”