22P138-P
Progress in development of the edge Thomson scattering system in ITER
ITER 周辺トムソン散乱計測装置の開発の進展
Takaki Hatae, Eiichi Yatsuka, Toshimitsu Hayashi, Takehiro Ono and Yoshinori Kusama
波多江仰紀，谷塚英一，林利光，小野武博，草間義紀
Division of ITER Project, Fusion Research and Development Directorate, Japan Atomic Energy Agency
801-1, Mukoyama, Naka, Ibaraki 311-0193, Japan
日本原子力研究開発機構 〒311-0193 茨城県那珂市向山801-1
Design and development for the edge Thomson scattering system in ITER have been progressed. This paper presents two topics from the recent progress. For the first topic, the prototype YAG laser system has
been assembled, and optimization of laser optics and operation parameters has been conducted. For thesecond topic, initial mechanical design for collection optics and laser beam injection optics has been carried out. From the design, the technical issue which should be solved in the next stage is discussed.

1. Introduction
An edge Thomson scattering system in ITER is adiagnostic system which measures electron temperature (Te) and density (ne) at a periphery of theITER plasma. This system is required to measure Teand ne over a relatively narrow spatial area(r/a>0.85), but with a high spatial resolution (5 mmat the midplane). Two topics are reported from therecent progress in development of the system: (1)YAG laser system, (2) mechanical design for collection optics and laser beam injection optics.

Fig.1. Schematic of the edge Thomson scattering system in ITER

2. YAG laser system
A repetitively-pulsed YAG laser system having
output energy of 5 J and a repetition rate of 100 Hz
is necessary to meet the measurement requirements
for ITER. We have assembled a prototype YAGlaser system [1] with two beam lines, and eachbeam line has four laser amplifiers. In the originaldesign, the laser was designed that each beam line
had capabilities of 5 J and 50 Hz, and each beamline was alternatively fired to realize 100 Hz of therepetition rate. However, parasitic oscillation at thehigh power laser amplification restricted laser out-put energy. To suppress the parasitic oscillation, theoperation parameter has been changed, i.e., pumping energy is reduce to a half, but repetition rate isdoubled (100 Hz). Considering the heat load tolaser rods, it means that new operation parameter isequivalent to old operation parameter. As an initial
result, 2.6 J of output energy at 100 Hz has beenobtained from one beam line under this condition.
Achievement of target performance (5 J, 100 Hz) is
expected by operating two beam lines simultaneously.
3. Mechanical design for collection optics andlaser beam injection optics
Mechanical components for the collection optics
and the laser beam injection optics have been designed based on their optical design [2,3]. Namely,
mirror and lens holders, shutter and their driving
mechanism have been designed as shown in Fig.2.
Three mirrors for the collection optics and shutter
are grouped together in one unit, each components
can be individually adjusted from outside of vacuum vessel. A field lens in the port plug is also adjustable from outside.
As an example, a mechanical design for the firstmirror of collection optics is described. This component is installed near the plasma, and it is incomparatively severe environment. The mirror
holder has been designed with two rotation axes
and one linear motion axis as shown in Fig.3.
When substrate of mirror is used as copper, electromagnetic force due to the disruption has been
analyzed by the equivalent circuit method. The
electromagnetic force on the surface is calculated as
7.9! 104 N. In this case, the shear stress of a support
shaft is 250 MPa, the shear stress transgresses the(a)Water-coolingchannel(b)Fig.2. Collection optics in the port plug(c)Pitching
YawingSlide
Fig.3. External view of the first mirror.

tensile strength of stainless (240 MPa). When themolybdenum substrate is employed, the stress decreases to 1/9 of that in the case of copper substrate.
It is expected that the mechanical strength of themirror holder to the electromagnetic force is enoughin the case of the molybdenum substrate.
Thermal analysis has been carried out under following assumption as shown in Fig. 4.
• Nuclear heating: 2 MW/m3• Radiation heat from plasma: 0.05 MW/m2
In the case of copper and molybdenum substrates,
surface temperature is below 300 °C. However, deformation amounts on the mirror surface are 1 mm
and 1.8 mm, respectively. This deformation is a verylarge quantity considering as an optical system. Inorder to realize it as the optical system, the design
which makes smaller deformation is required.
4. Conclusion
Recent progress in development of the edge
Thomson scattering system is reported. Regarding
the YAG laser system, a prototype YAG laser system has been developed, and optimization of adjustment is carried out. The adjustment work entersin the final stage, we will achieve the target performance (5 J, 100 Hz) soon. As for the mechanicalFig.4. Results of thermal analysis in the case of copper
substrate. (a) cooling water channel, (b) temperature
profile, (c) deformation profile

design for collection optics and laser beam injection
optics, initial design has been conducted. From results, we found that there are some technical issues
considering electromagnetic force, cooling design
and adjustment of the optical system, especially forthe first mirror. Only one kind of simple water-cooling channel was tried in the cooling design.
Based on the result, the more effective cooling methods such as a fin structure in the water channel areunder examination to reduce the thermal deformation.
Acknowledgments
One of the authors (TH) is grateful to Dr. K.
Ebisawa and Mr. K. Wakabayashi for their valuable
discussions.
References[1] T. Hatae, et al.: J. Plasma Fusion Res. SERIES 9(2010) 253.
[2] E. Yatsuka, et al.: Rev. Sci. Instrum. 81 (2010)
10D541.
[3] E. Yatsuka, et al.: “Optical design for the edge
Thomson scattering system in ITER”, Proc. 27th
JSPF annual meeting, Hokkaido, 2010, 01P02.

The views and opinions expressed herein do notnecessarily reflect those of the ITER Organization.