Experiments with biased side electrodes in electron cyclotron resonance ion sources

TL;DR

This study investigates the use of biased side electrodes in electron cyclotron resonance ion sources to reduce radial plasma losses, demonstrating that electrostatic biasing can decrease ionic losses with varying effectiveness across different setups.

Contribution

It introduces and compares new electrode biasing techniques in ECRIS to mitigate plasma losses, expanding on previous experimental approaches.

Findings

Radial biasing reduces ionic losses in ECRIS.

Different electrode configurations show varying effectiveness.

Electrostatic biasing can improve ion source efficiency.

Abstract

The output of highly charged ions from an electron cyclotron resonance ion source (ECRIS) consists of ionic losses from a highly confined plasma. Therefore, an increase of the output of the ions of interest always is a compromise between an increase in the confinement and an increase of the losses.One route towards a solution consists of attacking the losses in directions (i.e., radial directions) that do not contribute to the required output. This was demonstrated in an experiment (using the Kei ECRIS at NIRS, Japan) where radial losses were electrostatically reduced by positively biasing one set of six side electrodes surrounding the plasma in side-ward directions attached (insulated) to the cylindrical wall of the plasma chamber. Recently new studies were performed in two laboratories using two essentially different ion sources. At the BioNano ECRIS (Toyo University, Japan) various sets of electrodes were used; each of the electrodes could be biased individually. At the Atomki ECRIS (Hungary), one movable, off-axis side electrode was applied in technically two versions. The measurements show indeed a decrease of ionic losses but different effectivities as compared to the biased disk.