Shaking of Particle Beams to Remove Neutralizing Ions

Positive ions produced through ionization of the residual gas by the electron beam in an accelerator or storage ring can be trapped in the potential well of the beam and produce focusing forces on the beam that can shift the betatron frequency onto a resonance or stimulate other beam-dynamics effects. At low beam intensity the ions can be removed by means of the electric field imposed by clearing electrodes; however, at high intensity clearing electrodes can become ineffective when the local field of the beam is greater than that imposed by the electrodes or even harmful because of electromagnetic interaction between the beam and the electrode system. The ions can be removed also by letting them coast to the walls in the interval during an empty gap in the beam, but the length of the necessary gap in many cases is impractical. In this paper a new method, called "beam shaking", is proposed for removing the neutralizing ions by inducing increasingly larger amplitudes of ion oscillation about the beam until they are driven to the walls.