An Efficient H⁻/ D⁻ Extraction in Neutral Beam Injection (NBI) Ion Sources

The negative ion source development has reached performances very close to those required by the ITER project; see for example the test facility ELISE results*. A main residual problem seems to be the great amount of co-extracted electrons in the top part of the source. The introduction of a magnetic filter to remove the electrons from the extraction zone of the source causes ExB particle drifts (or shifts) which move both ions and electrons towards the top (or bottom depending on the B direction); in the top part the electron concentration and extracted current increase and that limits the extracted ion amount. In this contribution, as a possible solution, the application of a Planar Ion Funnel (PIF) extraction electric field configuration** on the source exit is proposed. The electric field line shape of PIF configuration, not only should break the perpendicularity between the magnetic filter B and the extraction electric field E in such a way to prevents the ExB particle drifts, but also should give a more efficient field shape for the H-/D- extraction. Preliminary simulations of D- and e⁻ trajectories are presented to confirm the efficiency of the PIF system.
Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand