Emittance Variation of a High-Current Relativistic Electron Beam in a Bend Magnet

The article presents the investigation results on the main angular divergence sources of a high-current relativistic electron beam when it passes through a real 12° bend magnet of the transport system in the linear induction accelerator (LIA), being developed by collaboration of Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia, and Russian Federal Nuclear Center—Zababakhin All-Russia Research Institute of Technical Physics (RFNC-VNIITF). The main results of the work are the calculated trajectories of the beam electrons, the shape of its cross section, as well as the change in the normalized emittance of the beam as it passes through the region of the bend magnet. It was shown that at typical beam parameters—electron energy of 20 MeV, beam current of 2 kA, and beam radius of 2 cm—the emittance of a high-current relativistic electron beam with uniform current and charge densities after the bend element is determined mostly by the magnet aberrations and much less by the beam self-fields. Optimization of the dipole magnet geometry made it possible to achieve a substantial decrease in the beam emittance with geometric expansion of the magnet in the median plane of the beam.