Speaker
Description
A permanent-magnet-based, microwave-driven helium ion source for the production of 1 mA positive beam and 20 µA negative beam via charge exchange is under development. Electron-trajectory simulations have been carried out to investigate a discharge phenomenon observed in the extraction system. The simulations revealed the formation of a charge trap caused by the topology of the permanent-magnet field near the extraction region. The trap leads to the accumulation of secondary electrons generated by beam collisions with the background gas. As a consequence, the extraction system becomes susceptible to electrical discharges between electrodes, limiting achievable beam transport and focusing performance.
Simulations performed with the ion optics library IBSimu indicate that the discharge issue can be mitigated either by replacing the conventional puller-einzel extraction configuration with a diode extraction geometry or by increasing the distance between the electrodes and the magnetic-field minimum. This work presents the magnetic-field structure responsible for the trap formation and discusses the relevance of the phenomenon for permanent-magnet-based ion sources generally.
| Email address | rebekka.m.nagy@jyu.fi |
|---|---|
| Visitor's Visa | no |
| Classification | Numerical simulations of sources, beams, space-charge, ion-optics |