24P026-P
H/He Partial Pressure Measurement by the Penning Gauge Spectroscopy
in the Divertor Region on LHD
LHD ダイバータ領域におけるペニング真空計分光による水素・ヘリウム分圧計測
Hisamichi Funaba, Masahiro Kobayashi, Suguru Masuzaki, Tomohiro Morisaki, Junichi Miyazawa,
Ryuichi Sakamoto, Mamoru Shoji, Masayuki Tokitani,
Hiroshi Yamada, Kazuo Kawahata, LHD Experiment Group
舟場久芳, 小林政弘, 増崎貴, 森崎友宏, 宮澤順一, 坂本隆一, 庄司主, 時谷政行,山田弘司, 川端一男, LHD 実験グループ
National Institute for Fusion Science322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan
核融合科学研究所 〒 509-5292 土岐市下石町 322-6
Two penning gauge spectroscopy systems are installed on the Large Helical Device (LHD) in order toevaluate the helium compression ratio at the divertor region with and without the bafﬂe structure. The
intensities of Hα and the line emission from He I in the penning gauge discharges are compared. The initial
calibration result shows that the partial pressure of helium at the divertor region with the bafﬂe structure ishigher than that at the position without the bafﬂe structure by almost one order.

1. Introduction
The compression ratio of helium at the divertor
region is important for the helium exhaust in a fusion reactor. On the Large Helical Device (LHD),
two of ten torus inboard side divertors have the bafﬂestructure [1]. In order to evaluate the helium compression ratio at the divertor region with and without
the bafﬂe structure, two penning gauge spectroscopy
systems are newly installed to the torus inner portsof LHD. The penning gauge spectroscopy can measure the partial pressures of neutral gases at each local position from the spectroscopic observation of thepenning discharge inside the gauge. This diagnostic
was developed at TEXTOR in order to distinguish thepartial pressures of deuterium and helium [2, 3]. It isalso used for the the helium exhaust study on JET [4].
The penning gauge spectroscopy is ﬁrst installedon LHD at 2004. Since it is located at the upper port,
it mainly measures the peripheral pressure of the vacuum vessel.
2. New penning gauge spectroscopy system
Two penning gauges are installed at the torus inner ports of LHD. One is located at the bafﬂe struc-tured divertor and the other is located at the divertor
region without the bafﬂe structure. The same type(Leybold PR36) of the gauge heads are used and thehigh voltage from the same power supply is used forthem. Although the penning gauge originally has permanent magnets of about 0.13 T in order to make themagnetic ﬁeld for the penning discharge, the permanent magnets are removed because the magnetic ﬁeld
strength at the torus inside is up to about 2 T whenthe magnetic ﬁeld strength at the magnetic axis, Bax ,is 2.75 T. It is possible to start penning discharge withthe magnetic ﬁeld of LHD. The dependence of signal
intensity on the magnetic ﬁeld strength is small at theregion of Bax ≥ 2 T.
The light in the penning gauges are transferred tothe visible spectrometer by optical ﬁbers. The signals from two different positions are simultaneously
detected by a CCD camera. As the wavelength range
is about 580 ∼ 730 nm, Hα and 4 lines of He I are observed in this range. For the helium partial pressure,the He I line of 667.8 nm is used. The time resolution is usually 200 ms for high density plasmas and500 ms for low density plasmas.

3. Experimental results
Figure 1 (g) ∼ (j) show an example of the comparison of the helium compression ratio between withand without the bafﬂe structure. This plasma washeated by the neutral beam injection (NBI) and theaveraged electron density was almost 6 × 1019 m−3(Fig. 1 (a, b)). The helium gas was injected by thesuper-sonic gas-puff (SSGP) at t = 3.8 s during thehydrogen gas was puffed (Fig. 1 (c, d)). Two signals of the ASDEX-type fast ion gauges are shown.
One is the signal at the divertor region without thebafﬂe structure (Fig. 1 (e)) and the other is the signal
at the bafﬂe structured divertor region (Fig. 1 (f)).
These signals are sum of the hydrogen and heliumpressures.
The signal intensity is derived by integrating in thewavelength range where the line signal appears. For
both of Hα and the He I (667.8 nm) line, the signal intensities of penning gauge spectroscopy at the bafﬂe
structured divertor is higher than those of the position
without the bafﬂe structure by about one order. Since
the signal intensity in Fig. 1 (h) is small, it should be
noted that the intensity below 20 is almost same as
the noise level. The calibration for deriving the pressure was made by ﬁlling hydrogen or helium gas andchanging their pressure in the vacuum vessel. Fromthe initial calibration results, the maximum helium
partial pressure values in Fig. 1 are 4.9 × 10−3 Pa for
Fig. 1 (h) and 5.2 × 10−2 Pa for Fig. 1 (j).
4. Summary
The penning gauge spectroscopy systems are installed at the divertor regions at the torus inner ports
with and without the bafﬂe structure. The initial calibration result shows that the partial pressure of helium at the divertor region with the bafﬂe structureis higher than that at the position without the bafﬂe
structure by almost one order.
Acknowledegment
The authors thank Dr. N. Noda, Prof. Y. Nakamura in NIFS and Dr. M. Lehnen in Forschungszentrum Jülich for their continuous support. This work
is supported by the TEXTOR collaboration,
NIFS10ULHH015 and NIFS10ULPP019.

References[1] S. Masuzaki, M. Kobayashi et al., Plasma and Fusion
Res. 6 (2011) 1202007.
[2] K.H. Finken, et al., Rev. Sci. Instrum. 63 (1992) 1.
[3] T. Denner, K.H. Finken, et al., Rev. Sci. Instrum. 67(1996) 3515.
[4] M. Lehnen, K.H. Finken, et al., Proc. 31st EPS
Conference on Plasma Phys., London, 2004, EGA
Vol.28G, P-1.138.

Fig. 1.

Temporal evolutions of some parameters andsignals in a plasma where helium gas was injected. (a)ECH and NBI heating pulses, (b) averaged electron density, (c) hydrogen gas-puff, (d) helium super-sonic gaspuff, (e) neutral pressure measured by the fast ion gauge atthe divertor region w/o bafﬂe structure, (f) neutral pressure
measured by the fast ion gauge at the divertor region with
bafﬂe structure, (g) Hα intensity in the penning gauge w/obafﬂe structured divertor, (h) He I (668nm) intensity in thepenning gauge w/o bafﬂe structured divertor, (i) Hα intensity in the penning gauge with bafﬂe structured divertor,and (j) He I (668nm) intensity in the penning gauge with
bafﬂe structured divertor.