An example particle accelerator may include the following: a voltage source to sweep a radio frequency (RF) voltage in a cavity to accelerate particles from a plasma column, where the cavity has a magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity, and where the magnetic field has flux that bows at edges of the cavity; a regenerator to provide a magnetic field bump within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, particles output to an extraction point, where the regenerator is located at a radius in the cavity relative to the plasma column; and ferromagnetic arrangements located in the cavity proximate to the radius, where each ferromagnetic arrangement provides a magnetic field bump, and where ferromagnetic arrangements adjacent to the regenerator are separated from the regenerator by a space.