A1 Journal article (refereed)
Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma (2022)

Toivanen, V., Bhaskar, B. S., Koivisto, H., Maunoury, L., Tarvainen, O., & Thuillier, T. (2022). Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma. Physics of Plasmas, 29(1), Article 013501. https://doi.org/10.1063/5.0069638

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Publication details

All authors or editors: Toivanen, V.; Bhaskar, B. S.; Koivisto, H.; Maunoury, L.; Tarvainen, O.; Thuillier, T.

Journal or series: Physics of Plasmas

ISSN: 1070-664X

eISSN: 1089-7674

Publication year: 2022

Volume: 29

Issue number: 1

Article number: 013501

Publisher: American Institute of Physics

Publication country: United States

Publication language: English

DOI: https://doi.org/10.1063/5.0069638

Publication open access: Not open

Publication channel open access: Delayed open access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/79401

Abstract

Electron Cyclotron Resonance (ECR) ion source plasmas are prone to kinetic instabilities. The onset of the instabilities manifests as emission of microwaves, bursts of electrons expelled from the plasma volume, and the collapse of the extracted highly charged ion (HCI) currents. Consequently, the instabilities limit the HCI performance of ECR ion sources by limiting the parameter space available for ion source optimization. Previous studies have shown that the transition from stable to unstable plasma regime is strongly influenced by the magnetic field structure, especially the minimum field value inside the magnetic trap (Bmin). This work focuses to study the role of the magnetic confinement on the onset of the kinetic instabilities by probing the influence of the injection and extraction mirror field variation on the instability threshold. The experiments have been performed with a room-temperature 14.5 GHz ECR ion source with an axially movable middle coil that provides flexible control over the axial field profile and especially the Bmin, which was used to quantify the variation in the instability threshold. The experimental results show that variation of the extraction field Bext, which defines the weakest magnetic mirror, correlates systematically with the variation of the instability threshold; decreasing the Bext allows higher threshold Bmin. The result demonstrates the importance of electron confinement and losses on the plasma stability. The connection between the weakest mirror field and the onset of instabilities is discussed taking into account the variation of magnetic field gradient and resonance plasma volume.

Keywords: plasma physics; plasma (gases); particle accelerators; cyclotrons

Free keywords: plasma confinement; electron energy distribution functions; plasma heating; magnetic mirrors; cyclotron resonance; ions and properties; plasma instabilities; ion sources

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Ministry reporting: Yes

VIRTA submission year: 2022

JUFO rating: 1