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The metallic first mirrors (FMs) of ITER optical diagnostics will face erosion caused by particles from the fusion plasma, as well as redeposition of materials originating from the first wall. Both processes can degrade their reflectivity over time. In vacuo plasma cleaning is planned to restore their optical properties. Several mirror materials were tested for the FM application. Currently, mirrors based on nanocrystalline rhodium (Rh) coatings or single crystal molybdenum (Mo) are considered as the mainstream approach. However, previous research indicates that repetitive cleaning of nanocrystalline mirrors can cause surface patterning, which negatively impacts their optical performance. Additionally, FMs are vulnerable to in-vessel coolant leaks, which could severely degrade their optical properties. Literature shows that exposing Rh mirrors to steam results in the formation of a thin layer of Rh oxide and the development of voids in the top 1 µ m of the coating. Despite this, plasma cleaning has been shown to restore the pristine reflectivity of the mirrors. This paper discusses the potential of utilizing platinum (Pt) as an FM material. Pt and Rh were subjected to cyclic plasma cleaning and steam ingress tests, after which their morphology and optical properties were measured and analyzed using XPS, SEM, FIB and spectrophotometry. Additionally, the neutron-induced transmutation of Pt and Rh was assessed with respect to ITER and DEMO irradiation scenarios.

The deposition/erosion on optical diagnostic components—mirrors—is a critical issue in reactor class devices with long-pulsed high fluence plasma operation. The paper presents results of the three-dimensional Monte–Carlo code ERO2.0 for two diagnostic aperture and first mirror geometries to be deployed in ITER, along with a separate simulation study that aims to replicate results from an experimental first-mirror study carried out on JET. Promisingly, very little plasma and impurity deposition on mirrors for the anticipated plasma durations is found in the ERO2.0 modelling taking into account the current ITER Research Plan and a material mix with beryllium first wall and a tungsten divertor. The post-mortem analysis of mirrors exposed during the experiment and the initial benchmarking efforts on the JET mirror experiment are also broadly consistent, increasing the confidence in predictions for ITER.

• A full-scale mock-up of the SiC first mirror mount assembly for the ITER divertor VUV spectrometer was designed and manufactured to validate its performance under realistic operating conditions. The mock-up incorporates all the critical components of the actual assembly, including the mirror holder main body, side-cover plate, spring plate assemblies, and alignment fixing plate. • The design features a double-mount structure with positioned spring plate assemblies to accommodate thermal expansion and resist vibrational loads. The spring plate assemblies are made of non-magnetic and vacuum-compatible materials to ensure compatibility with the ITER environment. • Comprehensive vibration tests were performed on the full-scale mock-up. The tests included resonance search, sine dwell, and random vibration tests, with a specific focus on simulating the conditions during vertical displacement events (VDEs) of varying severity. • The SiC mirror mount assembly successfully withstood the rigorous vibration test campaign without damage or performance degradation, validating the design for the demanding ITER environment. The results demonstrate the effectiveness of the double-mount structure and spring plate assembly design in ensuring the mirror's stability and alignment during ITER operation. The divertor vacuum ultraviolet (VUV) spectrometer is a diagnostic system in the ITER tokamak, monitoring impurity content and behavior in the divertor region. The first mirror of the spectrometer, made of silicon carbide (SiC), is exposed to harsh environmental conditions, including high temperatures and significant inertial loads from electromagnetic disruption events. To ensure its reliable performance, we have designed and tested a robust mirror holder assembly. This paper introduces a novel design of the first mirror holder assembly for the ITER divertor VUV spectrometer and presents the results from comprehensive vibration tests conducted on a full-scale mock-up. The design features a double-holder structure with spring plate assemblies to accommodate thermal expansion and resist vibrational loads. The mock-up underwent a series of resonance search, sine dwell, and random vibration tests, replicating the expected loads during vertical displacement events in ITER. The mirror holder assembly and the dummy mirror successfully withstood the vibration tests without damage, validating the design for the ITER environment. The results demonstrate the robustness and reliability of the mirror holder assembly, ensuring the accurate and reliable operation of the divertor VUV spectrometer in ITER. [ABSTRACT FROM AUTHOR]

In ITER, several first mirrors (FMs) are expected to be DC-grounded with the water cooling lines being implemented as a quarter wavelength (λ /4) RF-filter. DC-grounding of the FMs can significantly increase the plasma potential V p, which could trigger an increased wall sputtering and associated re-deposition on the FMs during plasma cleaning. To understand the scope of this impact, helium discharges were excited with DC-grounded FMs in an ITER-sized mock-up of a first mirror unit (FMU) using wall materials with different sputtering energy thresholds (E th). Additionally, a part of the FM was electrically isolated from the RF to study its impact on the erosion/re-deposition properties on the surface. The E th of the wall materials, as well as its native oxide layers, had a significant influence on the re-deposition observed on the FMs. With high E th where walls were unsputtered, both the DC-grounded and electrically isolated parts of the FM were free of deposits. However, with low E th where the walls were sputtered, there was a net wall re-deposition on the DC-grounded parts of the FM, while electrically isolated parts were still relatively clean. Further, to study the impact of floating wall components, Cu walls in the FMU were isolated from the ground. Here the walls developed a floating potential V f and the ion energy at the walls was lowered to e (V p âˆ' V f). The floating walls, in this case, were relatively unsputtered and the FMs experienced a net cleaning with total reflectivity of the mirror preserved at pristine mirror levels. This work shows that electrically isolating the FM as well as the wall surface minimizes wall re-deposition in presence of λ /4 filter and therefore are promising techniques for effective FM cleaning in ITER. [ABSTRACT FROM AUTHOR]

Mirrors for light transmittance will be used in more than 30 optical and laser diagnostics installed in the ITER tokamak reactor. Their reliable performance depends largely on the degradation rate of the first mirror directly facing the plasma. The fluxes of neutral atoms, mostly D, T, and Be, from the plasma are the most dangerous for the first mirror. The interaction with the high-energy atoms can lead to sputtering of the mirror surface; redeposition of beryllium sputtered from the walls of the vacuum chamber can lead to the formation of a film on the mirror. This paper gives a conservative estimate of the degradation rate of in-vessel mirrors in the equatorial channels of the H-alpha and Visible Spectroscopy diagnostics. Calculations were performed for stationary ITER operation using the Zemax OpticStudio program. The results show that the working area of the first mirror will be sputtered at a rate of no more than 100 nm/year, which is an acceptable erosion load for mirrors made of single-crystal molybdenum. Beryllium film formation is expected only at the edges of the mirror (outside the working area). Possible contamination of the working part of the mirror as a result of accidents or plasma events can be eliminated using the mirror cleaning system installed into the first mirror unit. For the other in-vessel mirrors, the estimate predicts no significant degradation owing to their location at a long distance from the plasma. [ABSTRACT FROM AUTHOR]

The first mirrors of optical diagnostics in ITER are exposed to high radiation and fluxes of particles which escape the plasma, in the order of 1020 m−2s−1. At the position of the mirror, the flux may still reach about 1018 m−2s−1. First mirrors are thus the most vulnerable in-vessel optical components, being subject to erosion, esp. by fast charge-exchange neutrals, or to deposition of impurities at flux rates which can reach 0.05 nm/s. The material selected for the reflecting surface must combine a high optical reflectivity in a wide spectral range and a sufficient resistance to physical sputtering during normal operation and during mirror cleaning discharges, if any is installed. Rhodium (103 Rh) was identified early as a possible or even promising candidate. It combines several attractive properties, for instance a mass which leads in most cases to low sputtering yields together with an optical reflectance (R Rh ≈ 75 %) which is much higher than of some other options. R Rh is insensitive to large temperature changes. Rhodium is fairly inert and its low oxidation is an appreciable advantage in case of steam ingress events. The core-plasma CXRS diagnostic in ITER (UPP 3) have now turned to Rh as a baseline. The aim is to procure monocrystalline rhodium (SC-Rh) to mitigate the increase of the diffuse reflection with the damage due to physical sputtering. [ABSTRACT FROM AUTHOR]

One of the important aspects of the service life of the first and second optical mirrors (FM and SM) in ITER UWAVS diagnostics is to understand the influence of plasma cleaning on materials re-deposition and optical surface quality after multiple cleaning cycles. The capacitively coupled RF 30–60 MHz system is a candidate for the UWAVS mirror cleaning. It generates ion fluxes of tens of electron-volts, sputtering contaminants as well as construction materials. In the present report, we discuss materials re-deposition after cleaning with 30–60 MHz discharges inside the prototype of the front-end vacuum compartment. Typical ion energies were below 100 eV at the RF electrode and 20–30 eV at the grounded wall. Materials sputtered from the FM were deposited at various locations and on the SM. The deposition rates were estimated as 0.05 nm/hour or lower. The experiments showed advantages of Molybdenum as a plasma facing construction material due to lower sputtering. Traces of Fluorine were found, which may indicate cable damage at higher powers. The single-crystal Mo-mirror mock-up was etched at 0.5–1 nm/hr. rate. The mirror reflectivity showed satisfactory results after 60 h of exposure, with 50–60 nm removed. The overall effect on the reflectivity considering full service time is yet to be investigated. [ABSTRACT FROM AUTHOR]

• Conservative estimation of DT and Be neutral fluxes on the first mirrors of H-alpha and Visible spectroscopy in stationary modes of ITER was done. • Zemax software was used for calculation of attenuation factors in real geometry of equatorial port-plugs. • Optical area of the first mirror will remain clean being occupied by erosion-dominated zone. • Contamination of the first mirror edges will not affect the diagnostics performance. • In-situ mirror cleaning system will be used in case of eventual contamination of the optical area. The first mirrors of all optical diagnostics in ITER will be exposed to the fluxes of neutrals, mainly D, T and Be. This can lead to formation of erosion and deposition zones on the mirror surface. In this work, the fluxes of neutral D, T and Be on the first mirror of H-alpha diagnostics in the equatorial ports were analyzed with Zemax OpticStudio software. Only stationary modes of ITER were considered. The geometry of viewing cutouts in diagnostic shielding modules (DSM) and the model of the first mirror units (FMU) were taken from the ENOVIA database. It is shown that the net erosion is dominating in major part of the first mirror zone with erosion rate ≈100 nm/year. The net deposition zone is located on the edges of the mirror, where deposition rate reaches up to 900 nm/year. Being made of single crystal molybdenum, the mirrors will keep their optical properties under erosion over the whole ITER lifetime. The contaminated edges are not important for the light collection and imaging of the SOL emission in the areas of interest at the ITER first wall within the selected field-of-view. The DC plasma discharge mirror cleaning system will be used to recover FM performance in case of eventual contamination. [ABSTRACT FROM AUTHOR]

• We studied the erosion (and deposition) effect on the SiC mirror sample caused by high-energy neutral particles for the expected environmental condition of the field mirror of ITER divertor VUV spectrometer. • By ZEMAX software with a simplified entrance duct model, the flux of neutral particles reaching the first mirror (the field mirror) was calculated based on the particle flux in the first wall. The total depth of erosion on the first mirror of ITER divertor VUV spectrometer was calculated to be around 9 nm using the input particle flux from SOLPS-ITER code. • The erosion resistance test was performed on the SiC mirror sample using the laboratory-scale plasma device to assess the mirror surface damage by erosion from the charge exchange neutral particles of ITER. • In the experiment, the SiC mirror sample was exposed to H + and D + plasmas upto the total erosion depth of 650 nm, and this value is larger than the expected total erosion depth in the first mirror. The surface roughness change of Δ ∼ 0.7 nm was measured, and this mirror degradation is within the allowable level considering the expected initial mirror roughness of the first mirror ∼ 1 nm. A series of tests have been performed to validate the resistance of the Silicon Carbide (SiC) mirror as the first mirror material of ITER VUV spectrometers to all ITER environmental conditions. In the present paper, we focused on the erosion (and deposition) of the SiC mirror sample caused by high-energy neutral particles. The flux of neutral particles reaching the first mirror was calculated using the ZEMAX software with a simplified entrance duct model. In the calculation, the particle flux reaching the first wall is necessary and the previously reported values derived from the SOLPS calculations were used. Based on this estimated particle flux, the erosion resistance tests were performed to check the erosion effect due to the high-energy neutral particles on the first mirror of ITER divertor VUV spectrometer. In the experiment, erosion was induced by exposing the SiC mirror sample to hydrogen and deuterium plasmas (and ions). The target fluence of incident ions in experiment is based on the estimation of the flux of neutral particles in ITER. The surface shape, composition, erosion depth, and surface roughness were measured to check the damage of the mirror surface after erosion test. Based on simulations and erosion resistance tests, it was concluded that the SiC mirror can be used as the first mirror of ITER divertor VUV spectrometer. [ABSTRACT FROM AUTHOR]

Abstract First metallic mirrors used in optical diagnostics such as the Upper Wide Angle Viewing System (UWAVS) in ITER may undergo contamination with beryllium and tungsten. Contamination levels of 10 nm can significantly degrade mirror performance. A UWAVS first mirror cleaning system prototype uses radio-frequency (RF) gas discharge to remove contaminants. Although tungsten is not expected to be a main contaminant, removing it with ion sputtering may become challenging due to the high atomic mass. Cleaning tests were focused on 10–20 nm tungsten layers removal from various substrates using a tailored RF circuit in He and Ne. W-coatings were also produced on an existing single-crystal (SC) Mo-mirror 105 mm diameter. He and Ne were chosen for many tests due to their effectiveness and suitability for ITER operations. Sputtering conditions were determined through ion energy measurements. Ion energies of 100–150 eV and currents of 0.5–0.8 A/m2 were found to be optimum for 30–40 MHz RF discharges. The cleaning rate in He was 0.3–0.5 nm/hour for W-deposits. Etching rate of 1 nm/hour was observed for the Mo-mirror. No surface roughness degradation was determined with SEM and optical interferometry after mirror material was removed. Overall exposure time of the SC Mo-mirror was 100 h. [ABSTRACT FROM AUTHOR]

In ITER, first mirrors for the Upper Wide Angle Viewing System (UWAVS) are expected to experience contamination with beryllium and tungsten. Contamination levels of 10 nm can degrade mirror performance. In the UWAVS, a first mirror cleaning system will use radio-frequency (RF) gas discharge. A mockup in representative geometry was developed. The tests focused on power delivery, hardware survivability, cleaning uniformity, and removal of contaminants. Using RF discharges without introducing surface damage was confirmed. Sputtering was investigated for 10–20 nm thick Al-coatings used as proxies for Be due to health and safety issues. Helium was chosen for many tests due to its effectiveness and suitability for ITER operations. The most effective cleaning was obtained in Helium at 5 Pa, 36–43 MHz, and 50–150 W. The sputtering conditions were determined through ion energy measurements. Ion energies of 100–150 eV and currents of 0.5–0.8 A/m 2 were found to be optimum. The measured cleaning rate in He for Al- and Al-oxide was 1.5–3 nm/hour. Aluminum was used as a proxy material for Be. The setup was operated for 500 h. No significant chamber contamination was identified. [ABSTRACT FROM AUTHOR]

The first mirrors of ITER diagnostic systems are the most vulnerable ones since they are directed to the plasma and are subjected to erosion and intensive impurity deposition. To keep their optical performance and maintainability, single crystalline molybdenum and rhodium have been considered as mirror materials, subject to intensive investigations including R&Ds and mirror cleaning studies. The paper presents specific design and structural issues of the first mirror of 300 mm in the size considered for the ITER core charge exchange recombination spectroscopy (cCXRS). Such a large mirror can be assumed as a generic one for solid middle (size) mirrors (up to 100 mm in diameter) and for composed large mirrors (diameter >150 mm) that are potentially made of an assembly of smaller pieces. The main design aspects like the first mirror material, the cooling capability of passively and actively cooled mirrors and the mechanical behavior of rhodium and molybdenum mirrors composed of single crystals pieces (i.e. plates and tiles) have been addressed and studied. The mirror design is supported by extensive structural and multi-field analysis. [ABSTRACT FROM AUTHOR]

The surface morphology of optical sputter-resistant nanocrystal molybdenum coatings formed by magnetron sputtering is investigated. The coatings deposited onto polished polycrystalline molybdenum mirrors have defects of two types: large crystalline inclusions protruding above the coating surface and areas with sharp boundaries corresponding to those of grains on the polycrystalline substrate surface. Preliminary treatment of the substrate surface by sputtering with the simultaneous deposition of substrate material removed defects of both types. A theoretical model of coating formation explaining the mechanism of improvement in its structural uniformity during surface preparation by the proposed method is presented. [ABSTRACT FROM AUTHOR]

First mirrors (FMs) used in optical diagnostics in ITER are confronted with a serious threat of the re-deposition of impurities eroded from plasma facing components. The radio frequency plasma cleaning method was applied to remove deposits on stainless steel (SS) and polycrystalline molybdenum (Mo) FMs for recovering their high reflectivity. After cleaning process, the amorphous carbon film deposited on SS FM was successfully removed. The total reflectivity was recovered up to 95% and the diffuse reflectivity was lower than 5%. The roughness of the cleaned SS mirror was almost not changed compared with the initial value. For Mo mirror, the total reflectivity was restored to 85% in the visible wavelength, while the diffuse reflectivity was increased to 17% due to higher roughness. The XPS analysis on Mo mirror surface showed that Mo carbide was formed at the interface between the substrate and film, which made a contribution to the difference of cleaning results from SS mirror. [ABSTRACT FROM AUTHOR]

First mirrors are essential plasma-facing components (PFCs) for fusion devices. Erosion and redeposition on first mirrors are of interest, since they cause degradation of signal intensity. In order to trace deposition/erosion characteristics of amorphous hydrogenated carbon (a-C:H) films on first mirrors, two manipulators attached at midplane and divertor regions of KSTAR vacuum vessel are utilized. A net deposition rate of 0.3–0.5 nm/s during a discharge and an erosion rates of 0.1 nm/s during He ion cyclotron wall conditioning (ICWC) are obtained. Property of redeposited layers are different depending on the location, varying from soft polymer-like to hard diamond-like a-C:H layers. For the deposition and erosion of metal layers, a plan for a dedicated experimental session has been set at KSTAR. [ABSTRACT FROM AUTHOR]

The Equatorial Visible/Infra-Red Wide Angle Viewing System (WAVS) is one of the ITER key diagnostics owing to its role in machine investment protection through the monitoring of Plasma Facing Components (PFCs) by Infra-Red thermography and visible imaging. Foreseen to be installed in 4 equatorial port plugs to maximize the coverage of divertor, first wall, heating antennas and upper strike zone, the WAVS will likely be composed of 15 lines of sight and 15 optical systems transferring the light along several meters from the PFCs through the port plug and interspace up to detectors located in the port cell. After a conceptual design phase led by ITER Organization, the design is being further developed through a Framework Partnership Agreement signed between the European Domestic Agency, Fusion for Energy, and a consortium gathering CEA, CIEMAT (with INTA as third party) and Bertin Technologies company. The next design step is the System Level Design (SLD) which will enable to consolidate the WAVS specifications as well as the performance realistically achievable (taking into account ITER and project constraints). The SLD has been preceded by a preparatory phase aiming at clarifying the WAVS functions and identifying critical prototyping. The outcomes of this preparatory phase are reported in this paper. First a review by the consortium of the WAVS measurement specifications is presented, for the purpose of a clearer separation of measurement parameters mandatory for machine protection (with stringent requirements) from those relevant for machine control and physics studies. Secondly the main features of the diagnostic are summarized, including a description of its current design, a preliminary analysis of its interfaces and a high level functional analysis. Finally the status of the R&D which may be necessary to validate the diagnostic design is presented. On the one hand, this R&D could consist in testing materials and coatings of optical components to characterize their behavior under the harsh environment of ITER. On the other hand R&D activities could concern prototyping and testing of subsystems of the diagnostic which have been identified as critical, such as the first mirrors and their associated devices (shutter and cleaning system) and the differential movement compensation system. [ABSTRACT FROM AUTHOR]

At first a detailed fast shutter design was finalized for the ITER core charge exchange recombination spectroscopy (CXRS) diagnostic. The shutter has approximately 70 kg of mass and a length of 2.1 m. It operates in fractions of a second (0.7 s) protecting critical optical components against degradation and providing means of calibration for the optical system. The shutter structure is driven by a bidirectional frictionless helium actuator, with forces and axial strokes of 3.4 kN and 2 mm respectively. The shutter structure consists of: (a) two blades made of CuCrZr and stainless steel, calibration surfaces (currently Al 2 O 3 ) on the top and on the bottom a protective TZM (Mo–0.5Ti–0.08Zr) screens, (b) two arms interconnected that form one cooling circuit including the blades, (c) a bumper system to limit the arms movement, and (d) a support. A description of these components and their functions are given in this paper, followed by some issues, and their corresponding solutions or ongoing investigations, encountered during the design work. Detailed manufacturing drawings have been developed as the deliverable final product of this design stage, and are used in the prototyping phase which includes testing, numerical benchmarking, and validation of the shutter concept. [ABSTRACT FROM AUTHOR]

The ITER core charge exchange recombination spectroscopy diagnostics (cCXRS) occupies the vacuum vessel upper port #3 and includes, in its generic version, the following in-vessel components: an optical mirror system, a shutter, the diagnostic first wall and the neutron shielding block. The most vulnerable diagnostic mirror is obviously the first one (M1) directly observing the plasma. The M1 reference option is made of a single crystalline molybdenum (ScMo). The paper indicates major aspects influencing the first mirror design and identifies the most reasonable and reliable concept for cCXRS M1 at present. The applicability of the option presented is determined by many reasons, and especially, by the ITER generic upper port plug and its customization flexibility. The largest dimension of the mirror polished face is ∼300 mm. Such large ScMo workpieces are currently not available on the market. The mirror should be designed as an assembly of several ScMo pieces joined together. The M1 design is supported by multifield thermal, electromagnetic and structural analyses. The performed study confirms the feasibility of the proposed solutions. At the same time, the paper indicates numerous technological issues of the M1 unit to be solved in future. [ABSTRACT FROM AUTHOR]

The effect of deuterium ion beam irradiation on the reflectivity of mirror-like pulsed laser deposited (PLD) thin film of rhodium is reported. The deposition parameters; target-substrate distance and background helium gas pressure were optimized to obtain the good quality rhodium films, of higher thickness, oriented preferentially in (1 1 1) plane. The rhodium thin films deposited at optimum PLD parameters were exposed to 10, 20, and 30 keV deuterium ion beam. The changes in surface morphology and UV–Visible–FIR reflectivity of mirror-like rhodium thin films, as a function of energy of deuterium ion beam, after exposure are reported. [ABSTRACT FROM AUTHOR]

Abstract: For the ITER core charge exchange recombination spectroscopy (CXRS) upper port plug #3 (UPP) diagnostics, a fast shutter is necessary for the first optical mirrors. The shutter concept for the reference CXRS layout has been well developed and studied focusing on the structure dynamic behavior. This paper presents two shutter concepts for the new baseline layout. Concept-1 is similar to the reference concept, including the helium actuator attached to the diagnostic shielding module (DSM) in the primary vacuum. Concept-2 considers the actuator outside the primary vacuum. It is attached to the back side of the UPP and connected to the shutting mechanism with a push–pull rod. Assembly and disassembly, actuator location, and actuation type are key issues for concept assessment. For a feasibility study, two different leak cases for the shutter concepts have also been analyzed. Concept-1 requires a specialized actuator design compatible with the in-vessel conditions. The actuator size is limited by the lack of available space in the DSM. This option needs complex procedures to access the actuator for maintenance. Concept-2 allows the use of standard pneumatic/hydraulic actuators and other industrial components. Space allocation is needed inside the UPP to accommodate the push–pull rod system. Concept-2 allows independent maintenance procedures for the actuator(s) and the shutting mechanism. It was generally concluded that both options are suitable for the new baseline layout, and are to be studied in detail. [Copyright &y& Elsevier]

Abstract: The ITER core charge exchange recombination spectroscopy (core CXRS) is a diagnostic system designed to collect the light emitted from interaction of the Diagnostic Neutral Beam (DNB) with the core plasma and guides it via a mirror labyrinth through the Upper Port Plug toward a fiber bundle, which then transmits the light to a set of spectrometers for spectral analysis. The first mirror (M1), being the most important part of the optical system which defines workability of the entire CXRS, works in direct view of the plasma. The latter strongly impacts the mirror causing its surface erosion and deposition with degradation of the optical capability. The fast shutter (FS) is supposed to play the main role in reducing the time of the first mirror exposition to the plasma. The performed work is focused on the detailed thermal and hydraulic analyses of the main components of the M1 protecting device (blades, arms and actuator) and its cooling and pneumatic systems. The performed analysis confirms, in general, the workability of the helium-operated shutter and verifies the pneumatic actuation concept proposed for the M1 protecting device. [Copyright &y& Elsevier]

Mirror like Molybdenum thin films on SS substrate in vacuum (10−3 Pa) and in Helium environment has been achieved by Pulsed Laser Deposition (PLD) Technique. The PLD thin films of Molybdenum have been characterized by using X-ray Diffraction (XRD) pattern, Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Energy Dispersive X-ray (EDX). The specular reflectivity was recorded with Fourier Transform Infra-Red spectrometer and UV-Visible spectrometer. The optical quality of the thin films was tested via interferometric technique. At the optimum deposition parameters, the crystal orientation was in Mo(110) phase. The FIR-UV-Visible reflectivity of the mirror was found to be closed to that of the polished bulk Molybdenum and Stainless Substrate (SS) substrate. [ABSTRACT FROM AUTHOR]

Abstract: Metallic mirrors are foreseen to play a crucial role for all optical diagnostics in ITER. Therefore, the development of reliable techniques for the production of mirrors which are able to maintain their optical properties in the harsh ITER environment is highly important. By applying magnetron sputtering and evaporation techniques, rhodium and molybdenum films have been prepared for tokamak tests. The films were characterised in terms of chemical composition, surface roughness, crystallite structure, reflectivity and adhesion. No impurities were detected on the surface after deposition. The effects of deposition parameters and substrate temperature on the resulting crystallite structure, surface roughness and hence on the reflectivity, were investigated. The films are found to exhibit nanometric crystallites with a dense columnar structure. Open boundaries between the crystallite columns, which are sometimes present after evaporation, are found to reduce the reflectivity as compared to rhodium or molybdenum references. [Copyright &y& Elsevier]

Abstract: The paper presents component concepts developed for the ITER core charge exchange recombination spectroscopy (cCXRS). They are based on the cCXRS layout of 2009, named as reference design option. It includes an outer shell, carrying a blanket shield module and a shielding cassette. The cassette, attached to the outer shell, carries secondary mirrors and a retractable tube. The tube holds a first mirror (M1) and a shutter. Development priority is given to the M1, M1 holder, shutter, calibration system and retractable tube. These units are the most critical from reliability point of view. The developed design approaches could be likely used as generic or prototype solutions for a cCXRS diagnostic port plug in future. Before prototyping critical components as the M1 holder and shutter, the final cCXRS conceptual design has to meet forthcoming changes in the ITER diagnostic upper port plug (UPP) and blanket system. The integrated first wall—diagnostic shield modules, first wall recession, blanket shaping and generic UPP layout have considerable impact on the layout of the cCXRS and its components. The paper presents a preliminary solution for integration of the customized reference cCXRS into expected ITER blanket and UPP layouts. [Copyright &y& Elsevier]

Abstract: A systematic numerical study of the deposition of Be and C atoms on the ITER main chamber first mirrors and their erosion due to fast D(T) atoms has been carried out. The calculations are based on Monte-Carlo neutral transport modelling (with the EIRENE code) on a simulated steady-state plasma background. A generic reduced model of cylindrical and conical diagnostic ducts is considered. The results indicate that the sputtering of the mirrors can be made acceptably small if they are installed in sufficiently long ducts. At the same time the deposition of impurities can be a serious issue even for mirrors protected in long channels. However, the calculations of deposition are not very reliable at the current stage and a need to seriously improve them is indicated. [Copyright &y& Elsevier]

Abstract: Fast degradation of in-vessel optics is one of the most serious problems for all optical diagnostics in ITER. To provide the resistance to mechanical and thermal stresses along with a high stability of optical characteristics under deposition-dominated conditions we suggest using high-reflective metallic (Ag or Al) film mirrors coated on silicon substrate and protected with thin oxide film in the divertor Thomson Scattering (TS) diagnostics. The mirrors coated with Al2O3 and ZrO2 films were tested under irradiation by deuterium ions. The experimental results on the oxide films sputtering are discussed in the context of their applicability for the first mirror protection in ITER. [Copyright &y& Elsevier]

Abstract: The first mirror (M1) as an important part of the CXRS diagnostic system is responsible for acquisition and transportation of the optical signal of required quality from the ITER plasma to detectors. At the same time, the M1 is the most vulnerable component of this system working in drastic and severe conditions caused by its location in the direct view of the plasma. To minimize impurities deposition and guarantee the required lifetime for M1 its temperature shall be maintained within the operational range of 350±50°C. The computation of M1 of the reference CXRS design demonstrates that, firstly, helium is the best candidate among the analyzed gases (He, N2, Ar) to be used as a coolant to maintain the M1 temperature in the required operational range of 350±50°C giving the highest heat transfer coefficient and the lowest hydraulic losses at moderate flow rates (v gas =40–60m/s) and, secondly, optimization of the cooling channels configuration together with an increase in the gas velocity and/or with heat transfer intensifiers makes it possible to provide the required M1 temperature conditions. [Copyright &y& Elsevier]

This paper describes the preliminary engineering investigation of the optical labyrinth and the first and second mirror mounts of the ITER core LIDAR diagnostics. The optical labyrinth is in a very sensitive location being close and open to the plasma. Therefore, it has been examined carefully to be able to provide different solutions satisfying the needs of the diagnostics. The present conceptual design considered the covering of the light path, the integration of the labyrinth into the port plug, as well as the shape, color, and material of the labyrinth inner surface. It was absolutely necessary, since the undesirable phenomena of scattered light and sputtered particles reaching the mirroring surface must be handled. Nevertheless, cooling/baking has also been considered, and appropriate solutions have been presented. Regarding the mirror mounts, concepts have been created. It has been identified that the mirrors must be conditioned at a certain temperature; therefore, cooling/baking options were developed. The cooling/baking and, particularly, the neutron absorption functions were detected to be essential for the extension tubes. The development basically focused on the different installation methods of the neutron-shielding plates, which also allow the tubes to be kept in the required temperature range. The result of the development was that a water-steel mixture varied through the length of the extension tubes could provide the maximum neutron shielding. This solution could satisfy the very strict six-orders-of-magnitude neutron absorption required to maintain the postoperation safety. The conceptual engineering design has been supported by the preliminary thermal analysis of the mirror extension tubes. [ABSTRACT FROM AUTHOR]

Abstract: A plug for the ITER core charge exchange recombination spectroscopy (core CXRS) is located in the upper port 3. It transfers the light emitted by interaction of plasma ions with the diagnostic neutral beam (DNB). The plug consists of a main shell, a shielding cassette and a retractable tube. The tube carries the first mirror (M1) with a shutter and allows multiple replacements of M1. A large uncertainty in the M1 lifetime has initiated a new design option with M1 located as far as possible from the first wall. A fast shutter has been proposed to enhance M1 protection. It operates consistently with a pulsed DNB and uses elastic bearings. Three-point attachment scheme of blanket shield modules (BSMs) has been suggested. It is capable to react electromagnetic loads caused by eddy- and halo-currents for any BSM option with a good design margin. The concern has been raised with regards to the forces caused by halo current and applied to the entire plug. Possible solutions are either to shunt and support the plug to the port in the frontal part, or re-attach all BSM in this belt from the plugs to the vacuum vessel. [Copyright &y& Elsevier]

• Modeling includes RF electrical circuit for ETS First Mirror plasma cleaning. • Compact vacuum notch-filter structure is considered for several frequencies. • Matching with a passive vacuum pre-matcher suits low plasma impedances. • Plasma impedance is measured in a representative geometry in helium and argon plasma. • Generator power of 1 kW may be needed to produce sufficient ion flux in cleaning plasma. The ITER Edge Thomson scattering system provides measurements of the electron temperature and density profiles at the periphery plasma of the ITER tokamak for physics studies and advanced plasma control. The front-end of the system contains a relatively large 23 cm × 25.8 cm metal first mirror (FM). Radio-frequency plasma is considered to remove contaminants from the FM. The new design approach for the power transmission circuit for plasma cleaning includes a pre-matching element next to the FM and a notch-filter. The FM is water-cooled and the water cooling pipe length is tuned as a notch filter for the driving frequency. The power dissipation in the circuit elements was analyzed in a series of simulations at frequencies 30, 40 and 50 MHz. New plasma impedance values used for the model were measured in argon and helium plasma at 1–10 Pa in a special mock-up of the front-end optics compartment. The results define inductance, capacitance and geometry of pre-matching elements and help to predict the performance of the plasma cleaning circuit. [ABSTRACT FROM AUTHOR]

Abstract: Glass and copper mirrors were exposed inside the HL-2A vacuum chamber. Arc discharge mark has been found on the glass mirror. The optical transmission character of test mirrors has been measured. The main components of the deposited materials on the first mirror are carbon and iron analyzed by AES. The Monte-Carlo method has been used to simulate the defending effect of the shield for test mirror. After a 2 years tokamak experiment, one can find that the reflectivity of copper mirror decline slower than that of glass mirror. The first mirror is polluted easier during glow discharge and wall processing than omhic discharge. Using buffer and shutter can play down the pollution, especially during the glow discharge and wall processing. [Copyright &y& Elsevier]

• It is shown that the M1 design based on the use of a thin single-crystal rhodium (ScRh) plate and a special WCu composite is feasible and robust. A rhodium nanocrystalline coating (NcRh) is kept as an optional solution. • The mirror is equipped with an adjustment of 3 DOFs (two rotations and translation) keeping a possibility to recover the initial mirror position without an additional readjustment. • A compatibility with in-situ repetitive cleaning is provided with implementation of the required insulation and gaps. Design option of the RF feeding line connector is presented. • Successful connection between ScRh/WCu samples is achieved. The high quality of the diffusion bonding is confirmed with FIB and metallography examinations, and by mechanical test resulting in the average shear strength of 233.3 MPa. The ITER core charge exchange recombination spectroscopy, which contains five in-port optical mirrors, is intended to transfer the visible light emitted by interaction of the plasma with the diagnostic neutral beam to the corresponding spectrometers. The first mirror (M1) is a key and the most vulnerable component of the diagnostics. In order to provide the required mirror lifetime, maintainability and structural integrity, M1 is composed of special materials, i.e. it is made of a thin 1 mm single-crystal rhodium (ScRh) plate diffusion bonded to a specially matched tungsten-copper substrate. A rhodium nanocrystalline coating (NcRh) can be an option. The paper presents the evolution of the M1 design developed for the optical layout of 2018. M1 is adjustable and cleanable with about 100÷500 procedures of 60 MHz plasma discharge. The mirror design is supported by multifield thermal, electromagnetic and structural analyses and uses experimental data of R&Ds made by Forschungszentrum Juelich, Germany. The study confirms the working capacity of the developed mirror solution. [ABSTRACT FROM AUTHOR]

• Modeling includes RF electrical circuit for 55.E6.VSRS first mirror plasma cleaning. • 4 parallel mineral-insulated vacuum RF cables reduce line impedance. • Matching with a passive L-C pre-matcher suits low plasma impedances. • Matching requires several times less power with a pre-matcher. • Models calculate pre-matcher dimensions for 20, 40 and 50 MHz. • Output power of 150–200 W produces 50 W in cleaning plasma. • Active matcher in the RF power circuit can move to the diagnostic room. The Visible Spectroscopy Reference System (55.E6.VSRS) is going to be one of the first optical diagnostic systems in the ITER tokamak chamber, for which plasma cleaning system of front-end optics has to be implemented. In order to extract light out of the fusion plasma towards diagnostic sensor systems, a set of optics forming a labyrinth will be employed. The VSRS front-end contains a 100 mm diameter first mirror (FM) that is expected to experience contamination with beryllium and tungsten degrading its performance. To maintain or restore the FM optical performance, a high-frequency-discharge-based plasma cleaning system will be implemented. The high-frequency power transmission circuit will contain four parallel mineral insulated radio-frequency (RF) cables, pre-matching elements, signal splitters and a number of interfaces. The circuit ends with the FM, where plasma is ignited in front of it. The FM is combined with the RF power electrode. The whole RF signal transmission circuit is modelled based on realistic characteristics of RF components such as cables and feedthroughs, their dimensions and ITER operational requirements. The goal is to understand the RF power budget, power distributions and losses in the components critical for the design. First simulation results confirm that the presence of a passive L-C pre-matching element next to the FM is critical for acceptable power consumption in the circuit. The results are also useful for other ITER optical diagnostics where RF plasma cleaning of the FM is foreseen and where similar power transmission circuits may be used. [ABSTRACT FROM AUTHOR]

• First mirror cleaning using 60 MHz very high frequency was optimized. • The pre-matching element is reducing the power consumption. • Cleaning homogeneity on a curved and large size mirror was measured. • End-of-Cleaning Indicator using Optical Emission Spectroscopy was demonstrated. For the fusion reactor ITER, a mandatory monitor of the fusion device and plasma will be performed with optical diagnostic systems. For the metallic first mirrors, the recovery of the reflectivity losses due to dust deposition is proposed to be carried out for 14 different optical diagnostic systems by the plasma cleaning technique. In this work, we studied the influence of the electrode area on the electrode potential as a function of the applied power with a 60 MHz radio very high frequency source. Unshielded copper disks with different diameters were constructed to study the impact of the electrode area in the range of 90 cm2 to 1200 cm2, which corresponds to an Edge Thomson Scattering area ratio of 0.15 to 2. It was observed that the absolute value of the resulting bias decreased from 280 V to 15 V with the increase of the area for a given RF power. Moreover, the power consumption was reduced by 43 % using a pre-matching element close to the vacuum feedthrough. The cleaning homogeneity on a curved and a large size mirror was studied, and the difference between the center and edge maximum/minimum was around 20 % and 40 % for the curved and large size mirror, respectively. For ITER, it is required to have an End-of-Cleaning Indicator (ECI), which shows when the cleaning process would be stopped. In this work, we studied the feasibility of Optical Emission Spectroscopy (OES) as a real-time control tool for the RF cleaning process. With 13.56 or 60 MHz, it was possible to use OES as ECI by following the molybdenum (Mo), rhodium (Rh), and aluminum (Al) emission lines. The decrease of Al I line and increase of the Mo I and Rh I line were recorded as a function of the cleaning time. [ABSTRACT FROM AUTHOR]

The Visible Spectroscopy Reference System (VSRS.55.E6) is going to be one of the first optical diagnostics in the ITER tokamak chamber. For the VSRS diagnostic system, the 100 mm diameter first mirror (FM) located at the front end of the optical system is expected to experience contamination primarily with beryllium and tungsten. Small levels of contamination (on the order of 10 nm) can significantly degrade the optical performance of the mirror. In the VSRS design, a plasma FM cleaning system will be implemented to maintain or restore optical performance. An RF discharge operating in a 30–60 MHz frequency range in an inert gas such as Helium, Argon, or Neon is a candidate technology for the VSRS FM cleaning. In the present report, we analyze the composition of the high-frequency electrical circuit with a plasma load. Characteristics of critical components including the generator, matching unit, cables outside and inside the vacuum vessel, air-to-vacuum interfaces and the electrode are considered. The effect of the plasma cleaning is discussed based on the numbers of ion fluxes and energies obtained in the similar research program. The proposed analysis may be useful for other diagnostic systems using RF plasma for cleaning and connected to long RF-feed and water cooling lines. • RF discharge in inert gas is planned for first mirror cleaning in ITER diagnostics. • Vacuum line transmitting RF signal can be damaged due to power dissipation. • Mineral insulated and rigid coax RF elements are planned to prevent line damage. • Variable frequency generator can be used for RF circuit tuning. • High-frequency RF plasma can reduce sputtering of mirror and wall components. [ABSTRACT FROM AUTHOR]