22P097-P
Design of IR thermography for divertor in ITER
ITERダイバータ用IRサーモグラフィーの設計
Masaki Takeuchi, Tatsuo Sugie, Hiroaki Ogawa and Yoshinori Kusama
竹内正樹, 杉江達夫，小川宏明，草間義紀
Japan Atomic Energy Agency
801-1, Mukouyama, 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

The conceptual design and physical investigations of the IR thermography for divertor in
ITER have started. For the temperature measurements of the divertor plates, this diagnostic
has a two color (wave length λ = 3, 5 μm) system and a spectroscopic system which has themeasurement performance with 30 wavelength points in 1-5 μm and 100 spatial points for eachwave length. From equatorial port, it observes the nearest inner divertor plate and 9.9 m away
outer divertor plate. In this study, a fundamental system is introduced and physical investigations
such as the effect of diffraction due to the size of the optical aperture and the emission intensityfrom divertor plates has been performed.
1. Background and Objective
The IR thermography for divertor [1] is one ofthe diagnostics which Japan is charge ofdevelopment. In this study, the conceptual design
and physical investigations of the IR
thermography have been performed to meet therequirement for ITER.
The objective of this diagnostics is ameasurement of the profiles of surface
temperature and thermal power load on the innerand outer divertor plates and a part of (30 %)baffles. A spectroscopic measurement in an IR
range of the emission light from the divertor
plates and baffles are performed. For advanced
control and physics studies, the IR thermography
for divetor has a role of the measurement withhigher time and spatial resolution than those ofother temperature diagnostics such as VIS/IR
cameras and thermocouples.
2. Specifications and system of IR thermography
for divertor
Table 1 shows the measurement requirements ofthe profiles of temperature and power load on
divertor plates. The
surfacetemperature
measurement is required in a wide range of
200-3600 °C with different time resolution (2 ms,0.02 ms), and precisive spatial resolution (3 mm).
The power load on divertor plates is calculated
from the surface temperature, side temperature ofdivertor plates measured by thermocouples,
temperatureof
coolingsystem,
thermalconductivity and so on.
For an achievement of the requirements, two
independent optical systems will be builded up.

One is a two color (wave length λ = 3, 5 μm)
system. This system has 2 detectors and thetemperature is derived from the ratio of each
emission light. The other one is a spectroscopic
system. This system is constituted of a spectrometerand a detector, which has the measurement
performance with 30 wavelength points in 1-5 μm
and 100 spatial points for each wave length.
Figure 1 shows the field of view of the IR
thermography for divertor. The optical system will
be installed in a port plug at an equatorial port. Boththe nearest inner divertor plate and a 9.9 m away
outer divertor plate are observed. In these regions, it
is possible to observe the divertor plate from thebottom to the top. The emission light is transmitted
from the front-end optics to the spectrometer andthe detector thorough the relay optics. A molybdenn
first mirror is used and there are some opticallabyrinths for neutron shielding. Two vacuum
windows made of sapphire are used. The sapphire
has a preferable transmission rate in 1-5 μm and arobust characteristic against the radiation byneutrons (~1019-1020 n / cm2).
Table 1. The measurement requirements of the profilesof temperature and power load on divertor plates.

the temperature under 1000 °C unlike other tworatios. Therefore, this ratio will be used in the 2color temperature measurement.

3. Effect of diffraction due to the aperture of theoptical system
It is generally known that a circle-like diffraction
pattern arises in the case of observation with acircle aperture. The following equation gives thelimit of resolution of optics for the Fraunhofer
diffraction.
Δy = 1.22 Lλ / dwhere, Δy is a spatial resolution on the observationarea, L is a distance from the aperture to observed
area and d is a diameter of the aperture. To meet thespatial resolution (3 mm), the aperture diameters ofd > 20 mm, d > 10 mm are needed for themeasurements of outer divertor and inner divertor,respectively.

2aperture diameter: d=60 mm, observed area: s=9 mm
10Ph [Photons / s]Fig.1. The field of view of the measurement area of theIR thrmography for divertor.

5. Other physical investigations and issues
The observed divertor plates and baffles have
3-dimensional structure and lean to the field ofview. Therefore, smaller spatial resolution of < 3mm is required. Furthermore, the spatial resolutionof the temperature derived from the observed
emissions is expected to be worse than 3 mm
because of the nonlinearity between temperatureand emission light. If the size of the optical apertureis larger, the spatial resolution becomes better inprinciple. It is also important to consider the focal
depth of lens in optical system for realize a precise
spatial resolution. The optimum optical system andthe detector are being investigated now. For a
degradation of optics and a deposition of impurities
and erosion of divertor plates which change theemissivity, a calibration system and shutter isneeded. The effect of neutron flux should beconsidered in selecting the optical material.

141010121010

λ=0.95-1.05 μm
λ=2.7-3.3 μm
λ=4.5-5.5 μm

81010106(a)44Ph(1 μm) / Ph(3 μm)
Ph(1 μm) / Ph(5 μm)
Ph(3 μm) / Ph(5 μm)3.5

Ratio of photons

4. Evaluation of the emission intensity from thedivertor plate
The emission intensity is calculated by Planck’s
equation for the blackbody emission. Figure 2
shows temperature dependence of the emission
intensity which enters into the aperture from theinner divertor plate in λ = 1, 3, 5 μm with 10 %band width and the ratio of the emission. In thiscase, the observed area on divertor plate is 9 mm2
and the aperture diameter is 60 mm, which hasenough emission intensity and good spatial
resolution Δy < 0.54 mm in λ = 1-5 μm. It has atendency for emission intensity to decrease astemperature decreases. Though the emission
intensity decays (~10-2-10-3) by the reflection andtransmission of mirrors and lenses, it will beenough to measure by a detector. An estimatedbremsstrahlung light may affect only under low
temperature (~250 °C). This is one of the issues ofthe measurement. In the case of the ratio of photonsof Ph (λ = 3 μm) / Ph (λ = 5 μm), it can measure1632.521.51(b)0.5001000

200030004000T [℃]
Fig.2. (a) Temperature dependence of the emission
intensity which enters into the aperture from the innerdivertor plate in λ = 1, 3, 5 mm with 10 % band widthand (b) the ratios of the emission.
Reference[1] A.J.H. Donne et al., Nucl. Fusion 47 (2007)
S337-S384.
Disclaimer: The views and opinions expressed herein do
not necessarily reflect those of the ITER organization.