Daniel Noll

JACoW : Space-Charge Compensation in the Transition Area Between LEBT and RFQ

The transition from a space-charge compensated beam in the LEBT to an uncompensated beam in the RFQ will influence the beam parameters. In order to investigate the impact of the electric fields on the space charge compensation, an insulated cone is used as a repeller electrode in front of the RFQ. Depending on the time dependent potential of the RFQ rods respectively to the beam potential, the compensation electrons may be prevented from moving into the RF field which oozes out of the RFQ entrance. The simulation studies are performed with the particle-in-cell code bender [1]. The simulations may substantiate measurements at the CW-operated RFQ in Frankfurt University [2] as well as at the foreseen MYRRHA LEBT-RFQ interface. [3]. In this contribution, a study on a LEBT-RFQ interface is shown.

Beam transport and space charge compensation strategies (invited)

The transport of intense ion beams is affected by the collective behavior of this kind of multi-particle and multi-species system. The space charge expressed by the generalized perveance dominates the dynamical process of thermalisation, which leads to emittance growth. To prevent changes of intrinsic beam properties and to reduce the intensity dependent focusing forces, space charge compensation seems to be an adequate solution. In the case of positively charged ion beams, electrons produced by residual gas ionization and secondary electrons provide the space charge compensation. The influence of the compensation particles on the beam transport and the local degree of space charge compensation is given by different beam properties as well as the ion beam optics. Especially for highly charged ion beams, space charge compensation in combination with poor vacuum conditions leads to recombination processes and therefore increased beam losses. Strategies for providing a compensation-electron reservoir at very low residual gas pressures will be discussed.