Embodiments of systems, devices, and methods relating to a beam system. An example beam system includes a charged particle source configured to generate a beam of charged particles, a pre-accelerator system configured to accelerate the beam, and an accelerator configured to accelerate the beam from the pre-accelerator system. The pre-accelerator system can cause the beam to converge as it is propagated from the source to an input aperture of the accelerator. The pre-accelerator system can further reduce or eliminate source disturbance or damage caused by backflow traveling from the accelerator toward the source.