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The ITER Edge Thomson scattering (ETS) system provides electron temperature and density profile measurements in the ITER tokamak. In collection optics, the front-end metallic first and second mirrors are expected to experience contamination with beryllium, tungsten and construction materials. Plasma cleaning based on a low-pressure radiofrequency discharge is expected to sputter contaminants. In the plasma cleaning system, a water-cooled first mirror is combined with a powered electrode. Water cooling was realized as a notch filter for the driving frequency with the electrode grounded for a DC-voltage. To understand plasma cleaning effects, a new test model reproducing the ETS First and the Second mirror geometries in a vacuum chamber was developed. Ion energies and fluxes were measured for 40–50 MHz discharges in argon and helium at 1–10 Pa with and without the notch filter for various power transmission schemes. Powers in plasma were increased to 300–400 W to achieve ion fluxes suitable for cleaning. 40 MHz discharges were used for cleaning as being more stable. In helium at 5 Pa the ion flux of 1.3·1019 ions·m−2 s−1 and the ion energies of 120–140 eV were considered for cleaning. Sputtering rates of metal layers were measured at 4–5 nm h−1 for W/WO3 films. Sputtering rates were non-uniform over the electrode and were lower than 0.5 nm h−1 at the edges. At 40–50 MHz, two independent discharges could be ignited at the First and the Second mirrors in argon and helium, and were maintained with minimum interference. Redeposition rate on the walls was estimated as 1–1.5 nm h−1, mainly consisting of the chamber construction materials. Parasitic discharges were observed at powers above 200 W in plasma and influenced plasma stability at pressures 1–2 Pa. The results are important for a number of ITER optical diagnostics where plasma cleaning of front-end water-cooled diagnostic mirrors shall be used.

ITER計画において、５つの計測装置（マイクロフィッションチェンバー、周辺トムソン散乱計測装置、ポロイダル偏光計、ダイバータ不純物モニター、ダイバータIRサーモグラフィー）の設計活動を進めている。併せて設計を確実にするために、プロトタイプ製作、光学素子の放射線照射試験、振動試験等を行っている。また、仏国原子力規制の対象となる真空境界を形成する機器（真空導入端子）については、認証試験の準備を進めている。講演では、これらの計測装置の設計の進展と今後の計画について発表する。, プラズマ・核融合学会

ITER真空容器の真空ポートの一つである下部ポート内の機器には、中性子遮蔽と搭載する計測機器に給電する役割がある。核融合反応による中性子によって下部ポート内の機器は放射化されるため、保守作業時には遠隔操作で作業（遠隔保守作業）を行い、下部ポート内から取り出す必要がある。また、ITER真空容器内の機器に要求されている清浄度、厳しい熱環境に耐えうる機器でなければならない。本件では、軽量で低放出ガス量な中性子遮蔽体及び急激な温度勾配による熱応力を緩和する構造を設けた電気コネクタについて報告する。, 31st Symposium on Fusion Technology (SOFT2020)

Several key components of ITER – such as toroidal filed (TF) coils, conductor for center solenoid (CS) coils, components of neutral beam (NB) system, electron cyclotron heating system, divertor, detritiation system, blanket remote handling system, plasma diagnostic systems, and test blanket system – have been designed and manufactured by JADA (Japan Domestic Agency) for ITER project. The recent highlights of progress and achievements by JADA will be reported. JADA procures all TF coil structures (19 sets), and a TF coil structure comprises inboard and outboard structure. The 4th TF coil structure has already been delivered to EU. Regarding the inboard structure, 10 sets of manufacturing have been completed, and 9 sets of welding assembly processes are ongoing. Regarding the outboard structure, 8 sets of manufacturing have been completed, and 11 sets of welding assembly processes are ongoing. JADA assembles 9 TF coils, and an assembly process of the 1st and 2nd TF coil is carrying out. Regarding the 1st TF coil, case closure welding and gap-filling impregnation have been completed, and then its final machining has started. Regarding the 2nd TF coil, the case closure welding has been completed, and the gap-filling impregnation will be started soon. The Final Acceptance Test (FAT) of 1st and 2nd TF coils will be completed by the end of 2019 and March 2020, respectively. JADA has contributed to the construction of the NB test facility (NBTF) at Padua in Italy, which has the identical design to the ITER NB system. Components for high voltage (HV) power supply – such as HV bussing, 1 MV transmission line, DC generators, and the test power supply – were fabricated and were delivered to Padua. The first integration test between components procured by EU and Japan has been completed in July 2019. DC 1.2 MV for 1 hour was applied to the high voltage deck 1 (HVD1, EU) and to the 1 MV insulating transformer (JA) through the 1 MV transmission line (JA). In September 2019, all components from the terminal of JA component to the Beam Source Vessel (EU) were finally connected by installing HV busing as the 1MV feedthrough to beam source. The FAT will be started in 2020. JADA procures 8 gyrotrons for heating and current drive. The FATs have been passed for 1st and 2nd gyrotron. Achieved parameters on CW operation were output power 1MW for 300 s with 50% of efficiency, 95 % of repeatability. 5 kHz power modulation for 60 seconds is also achieved. Regarding 3rd and 4th gyrotron, manufacturing has been completed, and conditioning of the 3rd gyrotron has started. Manufacture of anode/body power supplies for 4 gyrotrons also have been completed. As stated above, procurement activities carried out by JADA make steady progress in accordance with agreed schedule., 12th Asia Plasma and Fusion Association Conference

本研究では、トムソン散乱によるITERの周辺部プラズマの電子温度及び密度計測に使用する光学素子のうち、レーザー入射用減反射コート付き合成石英基板（レーザー窓）、レーザー伝送用誘電体ミラー、集光光学系用減反射コート付きガラス基板（レンズ用素子）、ポラライザーについてガンマ線及び中性子照射試験を行った。 計測用レーザーとして使用するYAGレーザーの波長である1064 nmでは、透過率・反射率及びレーザー誘起損傷（LIDT）の劣化は起こっていないことが分かった。レーザー窓については、10 MGy照射した方がむしろ1064 nmでのLIDTが上昇した。減反射コート付き合成石英基板にガンマ線及び中性子を照射し、透過率の変化を測定した。ガンマ線照射により3%、中性子照射により2%程度の透過率低下が生じた。さらに、集光光学系の色収差補正用の耐放射線性レンズ材料3種類（ショット社製BK7G18、LF5G19、SF6G05）に中性子を照射した。これら3種類のレンズ材料は、10 MGy程度のガンマ線照射に対して透過率の劣化がほとんどないことが既に知られている。照射前後の透過率を測定した結果、SF6G05については、波長600 nm以上でほぼ透過率を維持していることが分かった。ポラライザーについては、市販のワイヤーグリッドポラライザーにガンマ線及び中性子を照射し、透過率及び消光比を測定した。その結果、ソーラボ社製WP25L-UBについてはガンマ線及び中性子照射後も性能を維持していることが分かった。 ITER周辺トムソン散乱計測用の光学素子に対して、ITERで想定されるガンマ線及び中性子を照射し、多くの素子で問題なく使用できる見通しを得た。, 第36回プラズマ・核融合学会年会

Numerous plasma-near mirrors of optical diagnostics in ITER require protection from erosion and deposition caused by impinging particles. This is achieved by 63 Diagnostic Shutters, which shall operate in vacuum under high thermal and neutron fluxes over 20 years without maintenance, ruling out standard engineering solutions. In fact, these conditions are unprecedented even on fusion devices. Hence,qualification R&D efforts are extensive, because if a shutter fails, so does the respective diagnostic.Shutter design tasks are widespread among Domestic Agencies and their suppliers, because every shutter is part of the diagnostic it shall protect when not in use. However, as these highly resembling systems have obvious synergy potential, a coordination strategy for all ITER shutters was implemented at IO. An extensive shutter experience collection including failure reports from 14 fusion devices was per-formed. These are summarized in the present work. For the first time, the state-of-the-art of shutters is thereby defined and assessed as to its applicability to ITER. Furthermore, design-driving environmental effects due to the specific operating conditions are recalled and evaluated. The findings of both assessments are put into context with the current designs of all ITER shutters. In a next step, these are reviewed with emphasis on synergies between different shutter systems. Finally, recommendations on necessary prototyping and generic components are given.

This paper reports the gamma-ray irradiation effects on optical coatings and polarizers to be used in the ITER edge Thomson scattering system (ETS). Outside a diagnostic port-plug, in the Interspace, a total dose of the order of 1 MGy is expected through 20 years of ITER operation. In this study, gamma-ray irradiation experiments were performed up to 10 MGy. A high peak power laser beam, i.e. a pulse energy of 5 J and a pulse duration of ~4 ns, is needed for a Thomson scattering measurement in ITER. Laser-induced damage threshold (LIDT) of anti-reflection (AR) and high-reflection (HR) coatings at the laser wavelengths after gamma-ray irradiation were investigated. Contrary to expectation, LIDT of AR coating is more likely higher for the irradiated samples at a wavelength of 1064 nm. Regarding HR coatings, LIDT was not noticeably degraded by gamma-ray irradiation. Regarding polarizers, no degradation of transmission and extinction ratio was observed at visible and near infrared wavelength ranges when a wire-grid polarizer substrate is made of fused silica. Since a signal of ETS is almost linearly polarized, a wire-grid polarizer enables to improve signal to noise ratio of electron temperature and density measurements by Thomson scattering in ITER., The 14th International Symposium on Fusion Nuclear Technology

A poloidal polarimeter system will be installed in ITER to identify the safety factor profile in the plasma core region by measuring polarization change of a probing laser beam passing through plasma. Far-infrared laser beam, injected in a plasma, is reflected by a corner-cube retro-reflector mounted on first wall panels and returns to a diagnostic room. Although the corner-cube retro-reflectors will be exposed to high neutron and radiation fluxes, they will be passively cooled by heat conduction to the first wall panels. The challenging of designing the corner-cube retro-reflector is (1) cooling capability and (2) difference of thermal expansion of different materials. The first wall panel is made of stainless steel, while the corner-cube retro-reflectors is made of tungsten because of high resistivity to plasma sputtering. A special adapter is necessary for tightly fixing tungsten retro-reflectors and strongly touching the stainless-steel wall (the first wall panel) for the sake of high thermal conduction. However, the coefficient of thermal expansion of tungsten and stainless steel is different by a factor of four. It is difficult to touch both the tungsten retro-reflectors and stainless-steel wall with high contact pressure. The authors developed new adapter design consisting of two parts. One part takes care of fixing the position of tungsten retro-reflectors and the other part takes care of good thermal conduction. Thermal and structural analysis results show that the new design can meet the design criteria of ductile damage, plastic damage and thermal creep. A prototype of the new design is under fabrication to demonstrate the manufacturability., 14th International Symposium on Fusion Nuclear Technology (ISFNT)

JADA (ITER Japan Domestic Agency) are developing to procure five diagnostic systems, microfission chamber (MFC), poloidal polarimeter (PoPola), Edge Thomson Scattering (ETS), divertor impurity monitor (DIM) and divertor infrared thermography (IRTh). The reliability in the ITER radiation conditions of relevant equipment to be installed in the vacuum vessel, in the interspaces (IS) between the vacuum boundary and the biological shield and in the port cells (PC) outside the biological shields should be evaluated. In this study, we have launched gamma-ray irradiation experiments in QST Takasaki Advanced Radiation Research Institute from 2018.

The ITER radiological environment will not allow operators to calibrate the optics near the vacuum vessel. An in-situ calibration of spectral transmission from the collection optics to the detector by analyzing two Thomson scattering spectra resulting from two laser beams having different wavelengths was investigated experimentally in the large helical device (LHD). We can measure electron temperature accurately and calibrate spectral transmission at the same time even when spectral transmission degrades during the experimental campaign.