ABSTRACT
IAEA-F4-TM-42581
IAEA Technical Meeting on Atomic, Molecular and Plasma Material Interaction Data for
Fusion Science and Technology
Excited State Temperature of Atomic Helium in MAP-II Steady-state
Linear Divertor Simulator*
S. Kadoa
a
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, 611-0011 Japan
E-mail address of main author: kado[at]iae.kyoto-u.ac.jp
Measuring the ion and/or neutral temperatures in divertor/edge plasmas or divertor-simulating
low-temperature plasmas based on the passive optical emission spectroscopy is a challenging issue. In
this regime, low-principal quantum number (n) states exhibit only the Doppler broadening, while the
high-n states can exhibit both the Doppler and Stark broadenings if the electron density is relatively
high.
Doppler-Stark spectrometry [1] for helium plasmas was applied to the MAP-II (material and
plasma) steady-state linear divertor simulator at the University of Tokyo [2]. We have masured the
line profile of several atomic helium spectra (He I), in which the contribution balance of Gaussian
(Doppler component) and Lorentzian (Stark component) is different. In particular the transitions of
21S -31P (501.567 nm), 21S -71P (335.455 nm), and 23P -73D (370.500 nm) were found to be useful in
detecting the behavior of the excited state temperature [1].
We have pointed out that the 1P states population is dominantly contributed from the ground state
– reflecting the atomic temperature, due to the resonant transition and the radiation trapping processes.
On the other hand, high-n 3D states are dependent on the population flow between the states –
reflecting the ion temperature for the recombining plasma while the heated excited level above
Griem's boundary for the ionizing plasmas. This fact results in the thermal disequilibrium between the
states[3]. These senarios were suppoted by the evaluation based on the collisional-radiative model for
He I for which the electron temeprature and density were measured using a laser Thomson scattering
[4] and/or a electrostatic probe.
In the detached plasma for helium discharge where the volumetric recombination dominates, the
temperature of the electrons, ions and atoms became close to each other (~ 700 K), suggesting the
achievement of the thermal equilibrium around the gas temperature. In the ionizing plasmas, on the
other hand, the temperature of the excited states of the atomic helium was reveled to be dependent on
the states. This disequilibrium feature became more apparent as the electron density ne increases (1300
K ~ 20000 K for ne ~ 1013 cm-3).
References: [1] S. Kado Y. Iida, S. Kajita et.al., J. Plasma Fusion Res. 81, 810(2005). [2] S. Kado, K.
Suzuki, Y. Iida, and A. Muraki, J. Nucl. Matter. 415, S1174–S1177 (2011). [3] S. Kado, presented
at the PSI conference 2014 (Kanazawa, Japan) ; K. Suzuki, master thesis dissertation, the Univ.
Tokyo (2010)[in Japanese]. [4] F. Scotti and S. Kado, J. Nucl. Matter. J. Nucl. Matter. 390-391,
303-306 (2009).
*
The data presented in this contribution were obtaind when the author belonged to the University of Tokyo
(~2013). MAP-II device has recently been moved to Tsukuba University.
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