Transient Beam Loading Compensation in Low-energy Pulsed Linear Electron Accelerators

In pulsed traveling-wave high-intensity electron linacs large beam energy spreads are caused by the transient beam loading phenomenon. This energy spread is not only critical in high-energy accelerators, as the next generation of linear colliders, but it causes also problems in modern low-energy high-intensity linacs. Different compensation schemes were proposed recently for SLED driven structures in the framework of the Next Linear Collider project, but these schemes are too complicated for the compact low-energy linacs, that are widely used in scientific research, radiotherapy and industry. We propose a new method of transient beam loading compensation. This method is based on a step variation of the RF pulse amplitude during the filling time. A theoretical model is developed and a detailed study of beam loading compensation for different linac section types is performed, showing that very good energy spectra can be obtained, over a wide range of intensities and energies. The beam loading compensation scheme proposed here has been demonstrated to work very well in the 15 MeV Ghent University linear electron accelerator facility.