A1 Journal article (refereed)
Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source (2020)

Tarvainen, O., Kronholm, R., Laitinen, M., Reponen, M., Julin, J., Toivanen, V., Napari, M., Marttinen, M., Faircloth, D., Koivisto, H., & Sajavaara, T. (2020). Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source. Journal of Applied Physics, 128(9), Article 094903. https://doi.org/10.1063/5.0020751

JYU authors or editors

Publication details

All authors or editors: Tarvainen, O.; Kronholm, R.; Laitinen, M.; Reponen, M.; Julin, J.; Toivanen, V.; Napari, M.; Marttinen, M.; Faircloth, D.; Koivisto, H.; et al.

Journal or series: Journal of Applied Physics

ISSN: 0021-8979

eISSN: 1089-7550

Publication year: 2020

Publication date: 07/09/2020

Volume: 128

Issue number: 9

Article number: 094903

Publisher: AIP Publishing

Publication country: United States

Publication language: English

DOI: https://doi.org/10.1063/5.0020751

Publication open access: Not open

Publication channel open access:

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/71672

Web address of parallel published publication (pre-print): https://arxiv.org/abs/2007.00521


The production of negative ions in cesium sputter ion sources is generally considered to be a pure surface process. It has been recently proposed that ion pair production could explain the higher-than-expected beam currents extracted from these ion sources, therefore opening the door for laser-assisted enhancement of the negative ion yield. We have tested this hypothesis by measuring the effect of various pulsed diode lasers on the O− beam current produced from Al2O3 cathode of a cesium sputter ion source. It is expected that the ion pair production of O− requires populating the 5d electronic states of neutral cesium, thus implying that the process should be provoked only with specific wavelengths. Our experimental results provide evidence for the existence of a wavelength-dependent photo-assisted effect but cast doubt on its alleged resonant nature as the prompt enhancement of beam current can be observed with laser wavelengths exceeding a threshold photon energy. The beam current transients observed during the laser pulses suggest that the magnitude and longevity of the beam current enhancement depends on the cesium balance on the cathode surface. We conclude that the photo-assisted negative ion production could be of practical importance as it can more than double the extracted beam current under certain operational settings of the ion source.

Keywords: particle accelerators; surface phenomena; ions; laser radiation

Free keywords: lasers; surface physics; electrostatic accelerators; pair production; ion sources

Contributing organizations

Ministry reporting: Yes

Reporting Year: 2020

JUFO rating: 1

Last updated on 2022-17-06 at 12:27