Evaluation of a novel parabolic plasma electrode advantage in a triode extraction system of a helicon ion source: simulation and experiment

Abstract

Abstract An industrial type of Amirkabir helicon ion source (AHIS-II) equipped with a novel triode extraction system has been designed and developed at the Helicon Plasma Laboratory of Amirkabir University of Technology for material-processing applications. An experimental study was conducted to investigate the effects of two new types of plasma electrodes on ion beam characteristics. In particular, the Khoshhal electrode as a new improved plasma electrode and the optimized Pierce plasma electrode were both compared in inductively coupled plasma in the m = +1, −1 helicon plasma modes of operation. In this work, the AHIS-II device, with its ability to work continuously, was able to extract a ∼1 mA argon ion beam using a triode extraction system equipped with a Khoshhal plasma electrode at a 20 kV extraction voltage in the m = +1 helicon mode of operation. As part of this work, the R parameter, the ratio of the voltage applied to the plasma and acceleration electrodes in triode extraction systems was introduced, and its effects on ion beam characteristics including beam emittance, diameter, and current were studied. In this study, beam optical characteristics including beam emittance, diameter, current, and profile were calculated and measured by the IBSimu ion optical code. The analysis of the argon ion beam highlights that the ion beam characteristics can be affected not only by the plasma electrode geometry design, R parameter, and extraction voltage associated with the extraction process, but also by the plasma source’s operational parameters, such as the RF power delivered to the half-helix antenna and the gas flow rate.