Plasma and Fusion Research

Volume 19, 1301028 (2024)

Letters

First Attempt at Photoionized Plasma Production with VUV Radiation in Synchrotron Light Source UVSOR-III
Masahiro KOBAYASHI1), Shinji YOSHIMURA1), Hiroshi IWAYAMA2), Naonori KONDO2), Jun-ichi TAKAHASHI3), Hiroshi OTA2), Masahiro KATOH2,4), Kensei KOBAYASHI3) and Hiroaki NAKAMURA1)
1)
National Institute for Fusion Science, Toki 509-5292, Japan
2)
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3)
Yokohama National University, Yokohama 240-8501, Japan
4)
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
(Received 6 April 2024 / Accepted 1 July 2024 / Published 10 September 2024)

Abstract

Photoinduced processes such as photoionization and photoexcitation in the vacuum ultra violet (VUV) energy range are considered important for the divertor region in nuclear fusion reactors and in interstellar space because the cross sections (photoionization, photoexcitation) of these processes in relevant species (hydrogen, helium, neon, argon, and biomolecules) become large in that energy range. Herein, a photoionization experiment was conducted for the first time in the synchrotron light source UVSOR-III with VUV photon energies. The synchrotron light source has the advantage of capability to change photon energy continuously over a wide range and high beam repetition rates. These features allow the simulation of the divertor region and interstellar radiation field to systematically investigate photoinduced processes. Using argon as the sample gas, plasma production was evidenced by the detection of electron current in Langmuir probe measurements. Although an accurate evaluation of the plasma parameters was challenging because of the large scatter of probe data, the possible ranges of plasma parameters are discussed based on a 0D model of photoionization plasmas [R.M. van der Horst et al., J. Phys. D: Appl. Phys. 48, 285203 (2015)] and a newly proposed 1D model in the steady state. Analysis result indicates that plasma density is in the range of 1010 - 1011 m-3. Additionally, the further development of experiments is discussed for realizing higher plasma densities and for studying photoinduced processes in the divertor region in nuclear fusion reactors and interstellar plasma in terms of the chemical evolution of biomolecules.

Keywords

photoionization, synchrotron light source, plasma, divertor, nuclear fusion, astrobiology

DOI: 10.1585/pfr.19.1301028

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