22P137-P
Progress of Impurity Influx Monitor (divertor) for ITER
ITERダイバータ不純物モニターの開発の進展
Hiroaki Ogawa, Atsushi Iwamae, Tatsuo Sugie, Masaki Takeuchi and Yoshinori Kusama
小川宏明，岩前 敦，杉江達夫，竹内正樹，草間義紀
Japan Atomic Energy Agency
801-1, Mukoyama,Naka, 310-0193, Japan
日本原子力研究開発機構 〒310-0193 那珂市向山８０１－１
The impurity influx monitor (divertor) is one of the diagnostic system developed by Japan. In order toincrease the detected signals, new optical design work has been carried out by using achromatic lenses. Asa result, the detected signal was expected 10 times larger. The impact of the in-vessel wall refection to theoptical diagnostic in ITER is an important issue. We measured the By-directional Reflection Distribution
Function (BRDF) on the Tungsten block used in the divertor dome and baffle, and simulated by using theray-tracing code and a model of the Tungsten block surface. Simulated result was qualitatively agreed withthe measured one.

1. Introduction
Main objective of the Impurity Influx Monitor(divertor) for ITER is to measure the position of
the ionization front, the density profiles, andinfluxes of impurities and hydrogen isotopes (H,D and T) in the divetor region in order to control
the divertor plasma. In order to realize
measurements, four optical systems are installedon the four positions, that is, on the upper port,
the equatorial port, the divertor port and thedivertor cassette.
In this paper, we present the new optical designusing the achromatic lenses to increase thedetected signal and to restrict the increase sizes of
the components. The result of By-directional
Reflection
Distribution
Function(BRDF)
measurement of the tungsten block used on theITER divertor baffle and dome, which are thefundamental data for the estimation of the effectof the wall reflection is also presented.
2. New Optical Design
In order to measure weak spectra, it isnecessary to increase detected signals. All theoptics are installed a narrow space in the port
plug, the divertor port, the divertor cassette, andthe port cell. Sizes of optical components arerestricted.
The detected signals have been estimated byusing the B2-EIRENE code and Collisionalradiative model [1]. The result indicated that it wasnecessary for the measurement of the weak line
such as HeI generated by the fusion reaction toincrease the detected signals up 10 times larger thanthe present design. If we design the optical system
by using mirror only, the size of the collection

optics became very large and there was no space toinstall the optical fiber array to transfer thereceiving light to the spectrometers.

Fig. 1 Top view of the new equatorial port optics. Two
achromatic lenses are installed outside the vacuum
vessel.

(a)

(b)

50 mm

Fig.2 Spot diagrams and images of optical fiber (0.2 mmdia.) at divertor region. (a) light starts from the edge ofthe fiber array (b) light starts from the center of the fiber
arrayThen, the achromatic lenses have been used forreduction of the size of the collection optics andinstallation of the optical fiber array as shown inFig.1. The achromatic lenses are made of silica

(SiO2) and high purity calcium fluoride (CaF2). The
degradation of transmittance of CaF2 was small
after -ray irradiation up to 30 kGy but the effect of
the neutron irradiation has been not known now. As
a result of optical design code analysis, thenumerical apparatus (NA) for the optical fiber side
was increased up to 0.12 from 0.03. As a result, thedetected signal increases ore than 10 times larger
and weak line such as HeI generated by the fusion
reaction is expected to be measured.
The spot diagram and the image of optical fiber(0.2 mm dia.) on the divertor are also calculated byusing the optical design code. The size of theoptical fiber array is 2 mmW x 18 mmH. The lightstarted from center of the optical fiber bundle andthe corner of the optical fiber is shown in Fig. 2These results indicate that the image of the opticalfiber (0.2 mm dia.) on the divertor region is lessthan the required value of 50 mm.
3. Effect of the Wall Reflection
In the ITER optical measurement system, theeffect of the wall reflection on the measurement
is an important issue. Because the first wall of thevacuum vessel is covered by Beryllium and thedivertor dome and baffles are made of Tungsten.
The surface reflection from the W surface seems
to have a large influence on the impurity influx
Monitor. In order to assess the effect, themeasurement of BRDF of materials is necessary.
We measured BRDF of the tungsten (W) surface.
The W-surface milled by the fraise was measured
by using the laser microscope. The measured
engraved lines were linear shape and themaximum depth was 2.8 m. The space between
the engraved lines was 1 to 100 m.
In the case the light incidented perpendicular to
the engraved lines, reflected light traced linear in
the incidence plane. On the other hand in the casethe light incidented parallel to the engraved lines,
the reflected line traced an arc shape as shown inFig. 3.

lines, peak at the reflected light was that thereflected angle equal to the incident angle case.
The significant difference was not observed
between two wavelengths. In the case of the lightincidents parallel to engraved lines, the reflected
light was an arc shape. The radii of the arc andprofiles of reflected light were decreased withincreasing the incident angle
By using the measured W-surface model, wehave been carried out for both the light incidents
parallel and perpendicular to the surface. Figure 4
shows models and obtained images. The obtained
image was qualitatively agrees with that ofmeasured one.

Fig. 4 Ray-trace analysis of the reflection of theW-surface.
4. Smmary
In order to increase detected signals, new opticaldesign have been carried out by using achromaticlenses made of silica and the calcium fluoride as aresults detected signal expected 10 times larger andthe size of collection optics is almost same asprevious design. And the BRDF of W-surface wasmeasured. To evaluate the effect of the surface
reflection on the optical measurement in ITER,
simulation using the LightTools code will be
carried out in the future.
References[1] A. Iwamae, T. Sugie, H. Ogawa and Y. Kusaama:
Plasma and Fusion Res. Vol. 4 49 (2009).

W-Block

W-Block

Fig.3 Image of the reflected light (a) light incident
perpendicular to engraved lines (b) light incident
parallel to the engraved lines

We measured BRFD of both case by using the 2laser diode ( = 652 nm and 473 nm). In the caseof the light incidents perpendicular to engraved

The view and options express herein do notnecessarily reflect those of ITER Organization