7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Spectroscopy of highly charged ions with two complementaryelectron beam ion traps in TokyoNobuyuki Nakamura
Institute for Laser Science, The University of Electro-Communications
e-mail (speaker): n_nakamu@ils.uec.ac.jp
spectra using the two EBITs for identifying previously
unreported lines for a wide range of charge states [5-6].
For other studies that can not be introduced in thispresentation, please see our recent publications [7-8].
References[1] R. E. Marrs et al., Phys. Rev. Lett. 60 (1988) 1715.
[2] N. Nakamura et al., Phys. Scr. T73 (1997) 362.
[3] N. Nakamura et al., Rev. Sci. Instrum. 79 (2008)063104.
[4] N. Nakamura et al., Astrophys. J. 921 (2021) 115.
[5] Priti et al., Phys. Rev. A 102 (2020) 042818.
[6] Priti et al., Atoms 11 (2023) 57.
[7] N. Nakamura et al., Phys. Rev. Lett. 130 (2023)
113001.
[8] N. Kimura et al., Comm. Phys. 6 (2023) 8.

2
ratio

An electron beam ion trap (EBIT) [1] is a beneficial
device for studying the spectra of highly charged ions. It
consists of a Penning-like ion trap and aquasi-mono-energetic unidirectional electron beam
traveling through the trap. It can thus provide benchmark
spectra with a narrow charge state distribution under awell-defined plasma condition. It is thus helpful for
identifying previously unreported lines. At the Universityof Electro-Communications in Tokyo, we have beenusing two complementary EBITs, a high-energy device
called the Tokyo-EBIT [2] and a compact andlow-energy device called CoBIT [3], for studying highly
charged ions with a wide range of charge states. This talkpresents our recent studies performed with the two
EBITs relevant to astrophysical and fusion plasmas.
In the spectroscopic diagnostics of the solar corona,
the electron density, which is one of the most importantparameters, is generally diagnosed using intensity ratios
observed for density-sensitive line pairs. For proper
diagnostics, the sensitivity of the line pair intensity ratio
to the density should be described by a reliable
collisional radiative model evaluated by experimental
data obtained under well-defined conditions. Figure 1
shows the intensity ratio of density-sensitive line pairs inAr XIV, which is useful for the diagnostics of solar
corona active regions with a temperature higher than
3 MK [4]. The experimental results obtained using thetwo EBITs can be used to evaluate a collisional radiativemodel calculation shown by the solid lines. In thisexample, good agreement is obtained.
In the ITER fusion plasma, tungsten ions are
considered as the most unwanted impurity that causes
serious radiation loss. It is thus important to understandthe influx and charge evolution of tungsten ions in theplasma through spectroscopic diagnostics. Since thetemperature of the ITER plasma spans a wide range fromthe edge to the core regions, various spectroscopic dataof tungsten ions over a wide range of charge states are
required for proper diagnostics. We study tungsten

Ar XIV

1187.96
194.40257.37243.79CoBITTokyo−EBIT
08910

11−3

1213Log10(ne/cm )Figure 1. Electron density dependence of density
sensitive line intensity ratios in Ar XIV. The numbers
represent the wavelength of the lines in Angstrom. Theexperimental data from the Tokyo-EBIT and CoBIT areplotted in red and blue, respectively. The solid curve
represents the result of a CRM calculation.