Instructions for Preparing Manuscripts for the Proceedings of SPP-20

Characterization of divertor simulation plasma in GAMMA 10
K. Oki, M. Sakamoto, Y. Nakashima, Y. Akabane, Y. Nagatsuka, R. Nohara, M. Yoshikawa,
J. Kohagura, M. Yoshikawa, K. Hosoi, H. Takeda, K. Ichimura, M. Ichimura, and T. Imai
Plasma Research Center, University of Tsukuba
In the tandem mirror device GAMMA 10/PDX,
divertor simulation experiments have been
promoted using an end region [1, 2]. Recently, a
(D-module) has newly been installed at the end
region. A variety of experiments about divertor
physics and plasma-wall interaction (PWI) can be
carried out using the D-module, which consists of a
stainless-steel rectangular chamber (500×480 mm,
700 mm in length) with an inlet with diameter of
200 mm and two tungsten plates (350×300×0.2
mm) composing V-shape with their open-angle
from 15 to 80 degrees. A gas injection system is
prepared for radiation cooling and detachment
studies. At the back of the D-module, an exhaust
door for pumping is attached and its clearance is
The divertor simulation plasmas near the
V-shaped target plate are characterized by
measurement of electron temperature and density
using Langmuir probes and spectrometers in order
to study divertor physics and PWI. The Langmuir
probes are installed at 13 locations on the upper
target plate. Because effective ion temperature is as
high as 200 to 400 eV in the GAMMA 10/PDX end
region, finite ion temperature effect is taken into
account in estimation of electron density from the
ion saturation current [3]. He gas is also injected to
estimate the electron temperature and density from
the He I line intensity ratios using a
collisional-radiative model [4]. A viewing field of
the spectrometer for the He I lines is at 150 mm
away from the corner of the V-shaped target (on
Figure 1 shows dependence of electron
temperature and density measured using the
Langmuir probe on the open-angle of the V-shaped
target. These dependence is considered to be related
to PWI such as recycling. This figure also shows
the results without and with an additional ICRF.
With the additional ICRF, the electron temperature
decreases and the density increases. In the
mirror-confined core plasma (central region),
diamagnetism decreases by ~ 50 % and
line-averaged density increases by ~ 50 % due to
the additional ICRF. Therefore, the electron
temperature and density near the V-shaped target
change according to the core plasma parameters.
In this presentation, we will also show results
measured using the spectrometer, along with change
in the plasma parameters near the V-shaped target
by the gas injection for radiation cooling and so on.
Fig. 1. Electron temperature Te and density ne
measured using the Langmuir probe.
[1] Y. Nakashima, et al., Fusion Engineering and
Design 85 (2010) 956.
[2] Y. Nakashima, et al., Journal of Nuclear
Materials 415 (2011) S996.
[3] A. Tsushima and S. Kabaya, Journal of the
Physical Society of Japan 67 (1998) 2315.
[4] M. Goto, Journal of Quantitative Spectroscopy
& Radiative Transfer 76 (2003) 331.