22P098-P
Development of beam emission spectroscopy system in Heliotron JTasuku Kagawa1, Shinji Kobayashi2, Shinichiro Kado3, Tetsutaro Oishi4, Yoko Nagae1,Shinsuke Ohshima5, Tohru Mizuuchi2, Kazunobu Nagasaki2, Hiroyuki Okada2, Takashi Minami2,
Satoshi Yamamoto2, Sadayoshi Murakami6, Hyunyong Lee1, Takayuki Minami1,Kiyofumi Mukai1, Linge Zang1, Shohei Arai1, Hiroto Watada1, Yoshinobu Wada1, Koji Mizuno1,Yuji Nakamura1, Kiyoshi Hanatani2, Shigeru Konoshima2, Fumimichi Sano2

1

Graduate School of Energy Science, Kyoto University Gokasho, Uji, Kyoto 611-0011,Japan
2
Institute of Advanced Energy, Kyoto UniversityGokasho, Uji, Kyoto 611-0011,Japan3
School of Engineering, The University of Tokyo Hongo 7-3-1, Bunkyo-ku,Tokyo 113-8656,Japan
4
Graduate School of Engineering,Nagoya University Hurocho,Tikusa-ku, Nagoya 464-8603,Japan
5
Pioneering Research Unit for Next Generation, Kyoto University Gokasho, Uji, Kyoto 611-0011,Japan
6
Graduate School of Engineering, Kyoto University
Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501,Japan

This paper reports the development of Beam Emission Spectroscopy (BES) for the density fluctuation
measurements in Heliotron J. To improve the performance of the previous BES system, we have installed
the optimized viewing chords which can observe the whole plasma region. The solid angle and theobservation volume of the objective optical system are also improved by 5 times and 2 times higher thanthat of the previous system. The signal-to-noise ratio of the beam emission intensity measured byavalanche photodiodes (APD) improved about 20 times higher than that of the previous system..

1. Introduction
To understand the characteristics of theanomalous transport is one of the important subjects
to improve plasma confinement. The anomaloustransport is thought to be induced by plasma
turbulence which emerges as plasma fluctuationsuch as density, temperture, potential and magnetic
fluctuations. Beam Emission Spectroscopy (BES) isa method to detect plasma density fluctuations.
When a Hydrogen neutral beam is injected into theplasma, the beam particles are excited by thecollisions with electrons or ions. A BES systemobserves Doppler-shifted Hα emission from thebeam particles (beam emission). The amount of theDoppler-shift of this emission is decided by thebeam velocity and the angle between sightlines andthe neutral beam. The intensity of the beamemission has a relation with the plasma density andits fluctuation.

I BE =()

A32
niσ i vbeam + ne σ e vbeam − ve hν∆V∆Ω / 4π (1)A31 + A32

Separating the beam emission from backgroundlight by spectroscopic method, the density
fluctuation can be evaluated at the point where thebeam and sightlines are crossed. In the previous
work to check the feasibility of the density
fluctuation measurement by BES for Heliotron J
plasmas [1], we found improvement in thesignal-noise-ratio (S/N) should be required. In thispaper, the improvements in the BES system and thepreliminary result of the BES measurement aredescribed.
2. Experimental Devices
Heliotron J is a plasma confinement device basedon a helical-axis heliotron configuration (R/a=1.2m/0.2 m) with an L/M=1/4 helical coil [2].

Two tangential neutral beam injection (NBI) lines
are installed in Heliotron J. The maximum
acceleration voltage and injection power of eachline are 30kV and 0.7 MW, respectively. One ofthese beam lines is used for BES measurement as adiagnostic beam. Each beam line has two ion
sources (upper and lower), of which vertical tilting
angle is ? 3.5?.
To investigate the possible sightlines with a good
spatial resolution for the Heliotron J configuration[1], model calculations were carried out based on
the beam trajectory analysis taking the beamabsorption process into account [3]. We have foundthe best ones by configuring the sightlines along themagnetic axis by using a newly designed viewingport. This system can observe the emission lightsfrom the region of 0.07<r/a<0.94 in a radial
direction of plasma. By using a 16 channel opticalfiber system, the high spatial resolution of Δr/a ?
±0.04 is realized. The emission light is transferred
to an interference filter, and the beam emission isseparated from the background light. The intensityof beam emission is measured with APD and
1 MHz ADC. Compared to the previous system, thesolid angle is increased from 1.2 10-5 sr to 5.7
10-5 sr and the observation volume is increased
from 28.9 cm3 to 60.2 cm3 by reconsideration of theoptical system. The transmittance of theinterference filter and the APD system are also
modified to improve the S/N ratio.

3. Results and discussions
The beam emission has been confirmed by amonochromator and a CCD camera. Figure 2 shows
the beam emission intensity and the transmittanceof the interference filter as a function of thewavelength. The full, half and one-third energy
components of the beam emission are separated
well from the background light by using theinterference filter. Because of the different injection
angles of the two ion sources, each component of
the beam emission shows multi peaks.
Figure 3 shows the time evolution of the beamemission intensity measured at r/a = 0.18, 0.45, 0.52,0.88. The BES intensity in the center of the plasma
is larger than that in the edge region.

Fig.3.Time evolution of beam emission intensity

The S/N ratio at r/a = 0.52 is about 30, which isabout 20 times higher than that of the previoussystem. To evaluate the radial structure of thedensity
fluctuation,
wewillapply
Fast-Fourier-Transform based spectrum analysis.

Fig.1. Sightlines of BES for Heliotron J

Fig.2. Filter transmittance and beam emission intensity
measured by monochromator and CCD camera system.

References[1]. S.Kobayashi. et al., Rev. Sci. Inst. 81 (2010)
10D726.
[2]. F.Sano, et al., Nucl. Fusion 45 (2005) 1557.
[3]. S.Murakami, et al., Trans. Fusion Tech. 27 (1995)
256.