22P120-P
Progress in Design Study of ITER Poloidal Polarimeter
ITERポロイダル偏光計測装置の設計検討の進展
Kawano Yasunori1, Imazawa Ryota1, Ono Takehiro1, Ishikawa Masao1,Hayashi Toshimitsu1, Sato Kazuyoshi1, Kusama Yoshinori1,Ebisawa Katsuyuki2, Wakabayashi Kuniaki2, Katsumata Takahito2
1
河野康則 , 今澤良太1, 小野武博1, 石川正男1, 林 利光1, 佐藤和義1, 草間義紀1,海老澤克之2, 若林邦朗2, 勝又孝仁2
1

Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki 311-0193, Japan,K&K Engineering, LLC, 2-21-11 Komachi, Kamakura, Kanagawa 248-0006, Japan1
日本原子力研究開発機構 〒311-0193 茨城県那珂市向山801-1
2
合同会社K&Kエンジニアリング 〒248-0006 神奈川県鎌倉市小町2-21-11

2

The recent design progress of ITER poloidal polarimeter is presented.
As the basis of the design, threeguidelines are created.
According to these guidelines, a mirror module and a shutter in equatorial port
plug have been designed.
Candidate polarimetry methods for the primary roles and an approach forback-up / supplementary roles have been indicated along with the guidelines.

1. Introduction
In the ITER project, primary roles of the poloidal
polarimeter are current profile measurement(equivalently safety factor (q) profile measurement)
at core region of ITER plasmas [1].
In order tofulfill these roles, polarimetry to detect the Faraday
effect of far-infrared (FIR) laser beams (wavelength
λ~118 µm) is employed [2].
FIR laser beams arelaunched into the plasma from the equatorial port
and the upper port.
Since Japan will procure the poloidal polarimeter,
we have conducted the design study for it [3-5].
In this paper, guidelines for the design of thepoloidal polarimeter and recent progress in its
design study are presented.
2. Design Guidelines for Poloidal Polarimeter
Table 1 summarizes the measurement
requirements and diagnostics roles with respect tothe poloidal polarimeter [6,7]. As shown in Table
1, the poloidal polarimeter is expected to measure
not only the current profile but also otherparameters, e.g., line averaged electron density,
high frequency instabilities, etc.
The real-time
plasma control using the data from the poloidal
polarimeter is also anticipated.
Accordingly, thedata provided by the poloidal polarimeter shall bereliable and accurate enough in both physics andcontrol aspects for various kind of parameters.
Together with considering the significant
displacement and deformation of components of thepoloidal polarimeter under harsh nuclear andradiation environment in ITER, design guidelines

for the poloidal polarimeter have been created asfollowings.
(1) Mechanically simple, rigid and stablestructure is preferred for components which
are installed in vacuum.
(2) Polarimetry methods which are insensitive todisplacement and deformation of components
are preferred.
(3) Back-up and Supplementary roles areimplemented by dedicated sub-systems of thepoloidal polarimeter when it is necessary.
Table 1 Measurement requirements and roles withrespect to the poloidal polarimeter<Measurement Roles>
MP: Machine Protection, BC: Basic Control, AC: Advanced Control,
PHY: Physics Understanding<Diagnostics Roles>
P (Primary): diagnostic is well suited to the measurement
B (Backup): diagnostic provides similar data to primary, but has some
limitations
S (Supplementary): diagnostic validates or calibrates themeasurement, but is not complete in itself

3. Mirror Modules in Equatorial Port PlugFigure 1 shows the side view of the arrangementof plasma facing 1st and 2nd mirrors in the equatorial
port plug.
According to the design guideline (1),the mirror module in the equatorial port plug has
been designed as shown in Fig. 2.
There are two
specific design features oriented for the mirror
module, i.e., i) mirrors are fabricated by direct
machining and polishing of mirror block surfaces toeliminate number of components and ii) threeblocks are rigidly bolted each other to be a
mono-block as the mirror module.
By this design,high mechanical stability is expected.

Figure 1 Mirror arrangement in equatorial
port plug (side view)

4. Shutter in Equatorial Port Plug
An optical shutter system is used to protect 1stand 2nd mirrors against unnecessary impurity
deposition and surface sputtering during wallcleaning and plasma operation.
However, theshutter is one of the most challenging items todevelop since it needs reliable moving components
with water-cooling channels.
After theinvestigation of various shutter concepts, present
shutter design employs a water cooled shutter panel
connected to a spring coil by utilizing of the coolingwater tube itself, and the shutter is driven by areciprocating rod from outside the vacuum.
This
design provides a relatively simple configuration of
the shutter.
5. Methods of polarimetry
According to the guideline (2), polarimetry
methods which use interferometric signals are notpreferable.
Here, two candidates are picked up,i.e., 1) polarimetry by use of photo elastic
modulators and 2) polarimetry by use of rotating
polarizers or/and wave plates.
While the former
method needs R&D to demonstrate its feasibility at
λ~118 µm, the latter method is rather conventionaland simple method.
The latter method will beinvestigated as the future work.
6. Back-up and Supplementary roles
Candidate polarimetry methods mentioned in theprevious section would have limitation for back-up
and supplementary roles for electron density
measurement, especially in accuracy and temporal
resolution.
According to the guideline (3), we
consider that interferometer sub-system is effective
for the back-up and supplementary roles tocomplement the polarimetery for the primary roles.
References[1] A.E. Costley et al., Proc. 22nd IAEA Fusion Energy
Conference, Geneva, IT/P6-21 (2008)[2] A.J.H. Donn´e et al., Nuclear Fusion, 47 (2007) S337
[3] T. Yamaguchi et al., Plas. Phys. and Contr. Fusion,50 (2008) 045004[4] R. Imazawa et al, Rev. Sci. Instrum. 82 (2011)023116[5] R. Imazawa et al, Proc. 38th EPS Conf. Plasma Phys.,
Strasbourg (2011) P2.057, and to appear in Nucl. Fusion[6] Project requirements (Internal Document of ITEROrganization)[7] Diagnostics System Requirement Document (InternalDocument of ITER Organization)

Figure 2

Mirror module in equatorial port plug

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