Mirror Unit Research Articles

Cleaning of two mirrors in the first mirror unit using radiofrequency capacitively coupled plasma

First mirror (FM) cleaning, using radio frequency (RF) plasma, has been proposed to recover FM reflectivity in nuclear fusion reactors such as the International Thermonuclear Experimental Reactor (ITER). To investigate the influence of simultaneous cleaning of two mirrors on mirror cleaning efficiency and uniformity, experiments involving single-mirror cleaning and dual-mirror cleaning were conducted using RF capacitively coupled plasma in the laboratory. For the test and simultaneous cleaning of two mirrors, the FM and second mirror (SM), both measuring 110 mm × 80 mm, were placed inside the first mirror unit (FMU). They were composed of 16 mirror samples, each with a dimension of 27.5 mm × 20 mm. These mirror samples consist of a titanium–zirconium–molybdenum alloy substrate, a 500 nm Mo intermediate layer and a 30 nm Al2O3 surface coating as a proxy for Be impurities. The cleaning of a single first mirror (SFM) and the simultaneous cleaning of the FM and SM (DFM and DSM) lasted for 9 h using Ar plasma at a pressure of 1 Pa. The total reflectivity of mirror samples on the DSM did not fully recover and varied with location, with a self-bias of −140 V. With a self-bias of −300 V, the total reflectivity of mirror samples on the SFM and DFM was fully recovered. The energy dispersive spectrometer results demonstrated that the Al2O3 coating had been completely removed from these mirror samples. However, the mass loss of each mirror sample on the SFM and DFM before and after cleaning varied depending on its location, with higher mass loss observed for mirror samples located in the corners and lower loss for those in the center. Compared with SM cleaning, the simultaneous cleaning of two mirrors reduced the difference between the highest and lowest mass loss. Furthermore, this mass loss for the mirror samples of the DFM facing the DSM was increased. This indicated that mirror samples cleaned face to face in the FMU simultaneously could influence each other, highlighting the need for special attention in future studies.

Optical performance of a solar dish concentrator formed by the same size mirror located on parabolic frame

Solar dish concentrator with low cost and meeting the flux distribution is always pursued for the efficient utilization of concentrated solar energy. This paper investigates the optical performance of a solar dish concentrator formed by using a number of identical square mirror units arranged on a parabolic surface frame. The manufacturing of the mirror surface of this concentrator requires only one kind of mold, which has the significant advantage of low-cost manufacturing. Three common types of mirror units including the parabolic mirror (focal length fm), spherical mirror (radius Rm) and plane mirror are considered. The influence of key geometric parameters including the mirror width d (250–750 mm) and dimensionless parameters such as f1/D, fm/f1 and Rm/f1 (f1 is the focal length of parabolic frame) on its optical performance indexes such as the focused spot size (i.e., intercept width w), average local concentrator ratio (LCR), peak LCR and flux uniformity is analyzed using ray-tracing method, and the correctness of optical model and concentrator optical function is verified by outdoor concentrating experiments. The results show that the concentrator composed of parabolic or spherical mirrors can easily obtain a small circular focusing spot with high LCR and the intercept width can be easily controlled within 200 mm, the peak LCR can reach 34457 (average LCR is 12898), and average LCR reaches 14794 (peak LCR is 29497) at the smallest spot with w = 38.4 mm, which can be a low-cost alternative to parabolic dish concentrator. The concentrator with plane mirrors are easier to obtain square focusing spots with excellent flux uniformity, w can be controlled from 180 to 380 mm and uniform LCR is between 100 and 1400, which is very suitable for concentrating photovoltaic field.

Progress and challenges of the ECH transmission line design for DTT

The design of the Transmission Line (TL) as a part of the Electron Cyclotron Heating (ECH) system for Divertor Tokamak Test facility (DTT) is approaching the conceptual design maturity. With an ECH system of 16 MW installed for the first phase and with a total of 32 gyrotrons (170 GHz, ≥ 1 MW, 100 s) the TL design is undertaking the challenge of an evacuated Multi-Beam TL (MBTL) concept to deliver the large number of beam lines from the gyrotron hall to the torus hall buildings. The system is organized in 4 clusters, each of them including 8 beamlines. The routing consists of single-beam TL section used to connect the gyrotron output to a beam-combiner mirror unit for each cluster, a common MBTL running in a suspended corridor reaching the Tokamak building and a beam-splitter mirror unit to connect to the ex-vessel optics and launchers sections located in the equatorial and upper ports of one sector, for a total of 4 DTT sectors. The TL mirrors will be actively water cooled to cope with the heat load in long pulses due to the high power incident radiation, with the possibility to include advanced concepts for the cooling design compatible with additive manufacturing technology. The characteristics of the system and its components are presented, showing both the progress of the adopted solutions and the current design. Since the main challenge of this TL is to maintain the overall losses below 15%, in this paper we present the expected ohmic and spillover losses, including beam coupling simulations evaluating losses given by high order Transverse Electro-Magnetic modes (i.e. aberrations). We describe how the effects have been estimated with electromagnetic simulations and how losses could be mitigated, since TL efficiency could significantly drop due to the presence of non-idealities, like the deformations of mirrors surface ascribed to the microwaves heat loads and possible misalignments and aberrations effects occurring along the line.

Multi-staged ERO2.0 simulation of material erosion and deposition in recessed ITER mirror assemblies

In reactor class devices, with long pulse, high fluence plasma operation and with diagnostic systems that cannot easily be maintained, a critical issue is the deposition/erosion of wall materials and its impact on key optical diagnostic components — mirrors. A workflow for recessed volume simulation was developed for the three-dimensional Monte-Carlo code ERO2.0 (Romazanov, 2020), consisting of multiple simulation stages starting from first wall erosion to more focussed volumes around the key components. This complex workflow has been found to be mandatory to have meaningful statistics of interaction processes on the mirror because the physical fluxes of particles into recessed volumes are extremely low compared to first wall fluxes, leading to unsatisfying statistics in the case of standard Monte-Carlo simulations. The workflow is introduced with the example of a diagnostic mirror assembly in equatorial port 12 behind panels 14 and 15 in the diagnostic first wall in ITER, assuming a beryllium first wall of the main vessel, a stainless steel mirror unit and two molybdenum mirrors embedded in a port plug for neutron shielding. The simulation case corresponds to an H-mode burning plasma case from SOLPS modelling, for which the incoming flux distributions of deuterium neutrals into the recessed volume were simulated by the neutrals transport code EIRENE.

In-vessel final design of the ITER Wide Angle Viewing System in equatorial port 12

The ITER Wide Angle Viewing System (WAVS) is a major diagnostic for machine protection, plasma control and physics analysis. It will measure the surface temperature of the plasma facing components by infrared thermography and will image the plasma emission in the visible range. The global system is composed of 15 lines of sight located in four equatorial ports, covering more than 80% of the tokamak internal surface.This article focuses on the In-Vessel components of the three lines of sight of the diagnostic in equatorial port 12, which have to be installed for the “first plasma” of ITER.The main components of the system are the First Mirror Unit (FMU) and the Hot Dog-Leg (HDL). The FMU contains two mirrors and all associated equipment allowing their support, protection, cleaning and monitoring. It is a critical component since it has to sustain severe constraints (harsh nuclear environment, plasma proximity, complex interfaces) while it has to achieve challenging optical performances. All elements of the FMU are actively cooled. Furthermore, a pneumatic shutter to avoid direct contamination of the mirrors during first wall conditioning phases can close the FMU. The HDL is composed of two mirrors generating a labyrinth avoiding the direct neutron streaming and transmitting the optical beam toward the windows and the Ex-Vessel components of the WAVS.The main design aspects of the FMU and HDL are presented in this paper. These In-Vessel components have been presented to their Final Design Review (FDR) in July 2022 and their design is mature enough to outline the main features to comply with all the challenging requirements of the ITER machine.

All-optical multi-level amplitude regenerator in a polarization-effect optimized nonlinear-optical loop mirror (PE-NOLM) configuration.

We propose a modified configuration of the nonlinear-optical loop mirror (NOLM) unit by introducing the polarization-effect optimization (PE) into a nonlinear Sagnac interferometer through a polarization-maintaining optical coupler, enabling significant extension of the regeneration region (RR) of the all-optical multi-level amplitude regenerator. We carry out the thoughtful investigations on this PE-NOLM subsystem, and reveal the collaboration mechanism between the Kerr nonlinearity and the PE effect in only one unit. Moreover, the proof-of-concept experiment and its theoretical discussion of multiple-level operation have been performed, observing the 188% enhancement on the RR extending and the consequent 4.5 dB signal-to-noise ratio (SNR) improvement for a 4-level pulse amplitude modulated (PAM4) signal compared to the conventional NOLM scheme.

Порівняння 3D-моделей об’єктів, побудованих за матеріалами наземного лазерного сканування

The purpose of the work was to assess the accuracy and functionality of the 3D model obtained as a result of the 3D scanning and post-processing. The article discusses 3D modeling methods and their characteristics. The procedure for working with a 3D scanner is studied and its principle of operation is given. Scan data was post-processed to create 3D models of varying accuracy. The equipment used for the scanning is a FARO Focus Laser S150 terrestrial laser scanner. SCENE was used for post-processing. The object for scanning with a ground laser scanner was six identical logs of wood. The functionality and accuracy of the models are determined. Three-dimensional scanning of the research objects was carried out from six stations to obtain a full-fledged point cloud. At each station, the device was installed in the working position on the horizontal level using the inclinometer readings. Scanning was performed after selecting the appropriate shooting mode. It was taken into account that during scanning, no object can touch the mirror unit, because during operation, the scanner rotates clockwise by 180 degrees. Scanning in this study was carried out in color, so the scanner rotated 360 degrees. Based on ground laser scanning data, 3D models of cut tree trunks of the same size were built. All models are built with different accuracy for comparison and determination of the optimal one in terms of reliability and load. The obtained research results, as well as the technique itself, can be used in forestry by forestry and various structures related to wood analysis. Also, if we consider only our industry, the research data can be useful for the cadastre of park territories, etc. In the course of the conducted research, 3D models with different accuracies and memory volumes were obtained, which can be used to solve the relevant tasks. The functionality of using models consists in choosing the number of polygons that will affect the amount of memory. It should be noted that the functionality of the models lies in the convenience of their use on any device, compared to point clouds, which are demanding on the hardware component of a computer. The accuracy of the models is high in all cases. This makes it possible to use them to solve many problems, taking into account the needs. So, we can conclude that the use of models is relevant due to high accuracy and functionality.

Wireless Piezoelectric Motor Drive

Nanopositioners with embedded piezoelectric motors are used in a variety of industries, from microscopy to laser processing or measurement systems. A concrete example would be fine-tuning of multiple mirror or lens units in a system. After fine adjustment of a mirror or lens, its position is expected to be maintained when the system is not energized. Features such as small size, direct drive, and maintaining position with high rigidity at power off make inertia-type piezoelectric motors suitable for such “set and go”-type applications. However, wiring with dedicated control electronics for each positioner can increase system complexity. In this study, a wireless driving method for piezoelectric inertia-type motors is introduced for the first time, to the best of our knowledge. In our approach, sawtooth signals for driving a two-phase piezoelectric inertia motor are converted into two complementary pulse-width-modulated (PWM) signals at 1.0 MHz and amplified by class-D amplifier topology, in which GaN transistors are implemented. The amplified complementary PWM signals are applied to a transmitter coil. A receiver coil, which forms an LC network with the capacitances of the piezoelectric multilayer actuators, picks up the driving signals. The filtered voltage waveform by the receiver coil is converted into a modified sawtooth signal, which can operate the piezoelectric inertia-type motor wirelessly. Initial measurements revealed that even a single driving pulse can be transmitted to the receiver coil and precise movements of the slider can be obtained. Mean step sizes for single pulse drive are 140 nm in one direction and 125 nm in the reverse direction.

Development of the Multi-Beam Transmission Line for DTT ECRH system

The DTT tokamak, whose construction is starting in Frascati (Italy), will be equipped with an ECRH system of 16 MW for the first operation phase and with a total of 32 gyrotrons (170 GHz, ≥ 1 MW, 100 s), organized in 4 clusters of 8 units each in the final design stage. To transmit this large number of power beams from the gyrotron hall to the torus hall building a Quasi-Optical (QO) approach has been chosen by a multi-beam transmission line (MBTL) similar to the one installed at W7-X Stellarator. This compact solution, mainly composed of mirrors in “square arrangement” shared by 8 different beams, minimizes the mode conversion losses. The single-beam QOTL is used to connect each gyrotron MOU output to a beam-combiner mirror unit and, after the MBTL, from a beam-splitter mirror unit to the exvessel and launchers sections located in the equatorial and upper ports of 4 DTT sectors. A novelty introduced is that the mirrors of the TLs are embodied in a vacuum enclosure, using metal gaskets, to avoid atmospheric absorption losses and microwave leaks. The TL, designed for up to 1.5 MW per single power beam, will have a total optical path length between 84 m and 138 m from the gyrotrons to the launchers. The main straight section will travel along an elevated corridor ~10 m above the ground level. The development of the optical design reflects the constraints due to existing buildings and expected neutron flux during plasma operation. In addition, the power throughput of at least 90% should be achieved.

Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

The first mirror (FM) cleaning operations in ITER are expected to be executed in the presence of a T magnetic field. In the RF plasma cleaning configuration, this would have a significant influence on the plasma properties, ion energy, angle of incidence as well as flux spatial distribution. To this end, RF discharges were excited in an ITER-sized mock-up of a first mirror unit (FMU) consisting of a powered first mirror M1 and a grounded second mirror M2 placed in a homogeneous 3 T magnetic field. The plasma discharge was confined in a beam extending in the direction of the magnetic field, consequently wetting a limited portion of the FMU walls. In the DC-decoupled scheme (without λ/4 filter), this considerably influenced the self-bias voltage V DC that develops on M1. Changing the angle α between M1 normal and magnetic field, modified the plasma wetted wall area A g and the resulting V DC varied by over two orders of magnitude. Plasma exposure experiments were also done in the DC-coupled scheme (with λ/4 filter), wherein the angle and wetted surface determined the area of wall sputtered. Increasing α led to an increase in the sputtered wall area A g, and consequently the wall deposition on grounded M2. However, in all the cases M1 was entirely clean with the exception of edge deposits in some. In contrast, both M1 and M2 are coated with wall deposits in the absence of a magnetic field and a similar plasma exposure. The results show that plasma cleaning with λ/4 filter in a 3 T magnetic field at ITER could potentially prevent the parasitic wall deposition on FMs. The results also highlight the importance of FM orientation in the magnetic field and the wetted area in the plasma cleaning in both the DC-coupled and decoupled schemes within the ITER diagnostic systems.

Dual-function flexible metasurface for absorption and polarization conversion and its application for radar cross section reduction

In this paper, a flexible metasurface with dual functions of absorption and polarization conversion is proposed and applied for radar cross section (RCS) reduction. The metasurface unit adopts a metallic-backed structure, and its width and thickness are approximately 0.62 and 0.24 times the free-space wavelength at the center working frequency, respectively. Different from the traditional metasurface, the resonators with low-frequency absorption and high-frequency polarization conversion are horizontally combined to achieve dual-function integration without the use of tunable elements. The structure adopts a flexible substrate, which is also suitable for conformal conditions. From 3.74 to 14.84 GHz, the metasurface has good impedance matching characteristics. The metasurface performs effective absorption and polarization conversion in the frequency bands of 3.78–6.34 GHz and 7.90–14.80 GHz, respectively. The absorption is mainly achieved through the ohmic loss of the lumped resistance, while the polarization conversion is performed through the electromagnetic resonance of the metallic structure. Then, the sample prototype is fabricated for demonstration, and the measurement result is well consistent with the simulation one. Furthermore, the checkerboard-arrangement array of the metasurface and its mirror unit can efficiently reduce the RCS over 7 dB in the range of 3.52–15.28 GHz. As expected, the proposed flexible metasurface can not only be used as an absorber/polarization converter but also be combined to realize broadband RCS reduction, which is of great significance for multi-function and conformal stealth applications.

Re-deposition of ITER-grade Be on plasma gun facility QSPA-Be: Characterization & plasma cleaning

Studies of contaminants obtained by spraying ITER-grade Be on a quasi-stationary plasma gun facility QSPA-Be are presented. Contaminating films, consisting mainly of Be and O in approximately equal proportions, were deposited on substrates of quartz, sapphire, single crystalline silicon (SC-Si) and NaCl crystal. Characterization of the deposits was performed using SEM, XPS, EBS, AFM, SE, TEM&SAED and micro-interferometry showing polycrystalline BeO films similar as found in JET-ILW. Films on SC-Si and NaCl were used to characterize their composition and morphology. The cleaning rates in the 81.36 MHz RF discharges in He or D2 at 2 Pa were measured on the SC-Si target. The measured etching rate of the deposited films was several times higher than the rate calculated from the theoretical value of beryllium oxide sputtering yield. Test cleaning of these contaminants was carried out in a capacitively coupled RF discharge (CCRF) from the surface of sapphire and quartz plates, which were considered as a mock-ups of the protective window of the first mirror unit (FMU) designed for ITER divertor Thomson scattering diagnostic system (DTS).

Study of wall re-deposition on DC-grounded ITER-relevant mirrors with RF plasma in a first mirror unit

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 − 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.

A new design of launcher mirror for EAST electron cyclotron resonance heating system

Significant progress has been achieved on EAST tokamak with the electron cyclotron resonance heating (ECRH), but the maintenance current EC launcher is very complicated after each campaign period. In order to reduce the maintenance frequency and cut down the maintenance cost, a new launcher mirror unit was developed based on adjusting the water cooling pipe lines layout and designing the detachable mirror. It improves the bending conditions and extends the life of the metal hoses effectively. Meanwhile, in situ replacement of the mirror reflector inside the device could be realized with the new design. The new launcher mirror employs a type of dot-matrix water cooling channel structure. It is demonstrated that the cooling design satisfies ECRH operating requirement with lower mass flow by fluid-thermal-solid coupling analysis.

Tunable high resolution spectrometer for H-alpha and visible spectroscopy in ITER

A tunable-band high resolution spectrometer (HRS) was designed to study the fine structure of H-alpha and impurity lines in order to separate the divertor stray light (DSL) and the scrape-off layer (SOL) emission required for H-alpha and visible spectroscopy diagnostics in ITER. The spectral resolution not worse than ~0.01 nm is needed to resolve similar Zeeman lines in the SOL and DSL components shifted with a small offset due to some difference of the magnetic field in the divertor and at the ITER first walls. HRS optical design is based on the pseudo-autocollimation scheme with a pair of coplanar holographic gratings and spatially separated back-reflected optical beam. This scheme provides independence of a dispersion versus the wavelength in the whole spectral range, together with acceptable F-number up to f/4.5 of the input/output lenses. Grating and back-reflection mirror units are mount to the motorized rotational platforms with remote control realized in LabView software.The HRS prototype was manufactured and tested to verify the design characteristics. The main parameters: spectral range, inverse linear dispersion, spectral resolution and contrast were measured at 65˚ and 75˚ light incidence angles to the gratings. The inverse linear dispersions are 0.206 nm/mm and 0.13 nm/mm respectively, with 0.01 nm spectral resolution at 65˚ angle measured by scientific-grade PCO edge 4.2 CMOS camera. Close-wavelength contrast of 1:6•10−6 was measured at δλ = 2.5 nm spectral distance from the He-Ne laser line. The total spectral range is 400..700 nm with a tunable sub-band of 1.3÷2.7 nm spectral width defined by the position of holographic gratings.

Comparison of evaluated nuclear data for neutron irradiation damage calculation in fusion spectra

The present work analyzes the neutron irradiation damage in fusion applications with different evaluated nuclear data. Comparing with fission reactions, higher quality nuclear data (including the differential cross sections) are required for fusion irradiation damage calculations. Taking the neutron irradiation damage of iron as an example, a 11% difference between JEFF-3.3 and ENDF/B-VIII.0 is found in a First Mirror Unit (FMU) located in the ITER diagnostic first wall, while the differences are within 4% in fission reactors. The deviation of neutron irradiation damage among different nuclear data is much more important for tungsten isotopes. The total damage rates of natural tungsten computed with JEFF-3.1.1, JEFF-3.3, JENDL-4.0, and TENDL-2019 are respectively 55%, 56%, 66%, and 44% larger than the value calculated with ENDF/B-VIII.0 (= FENDL-3.1d in the fast energy region) in an ITER FMU (and 56%, 60%, 69%, and 47% larger in the tungsten divertor). The differences are reduced to smaller than 20% if the recoil energy-angular distributions of the (n,2n) reaction in ENDF/B-VIII.0 are removed. It is noteworthy that the irradiation damage of tungsten is largely underestimated if the atomistic simulation results and the six nuclear data libraries (including FENDL-3.1d) analyzed in the present work are applied.

Measurement of density profile and fluctuations using a multi-channel terahertz solid-state interferometer system on Keda Torus eXperiment (KTX).

A five-chord interferometer based on terahertz solid state sources has been successfully installed on the Keda Torus eXperiment (KTX), a reversed field pinch machine. The optical design has been carefully optimized for the uniform distribution of beam light to fully use the limited power source (∼2 mW). By setting the telescopic mirror unit, the beam waist is located in the center of the vacuum vessel and its diameter is in the range of the Rayleigh length. The beam width across the plasma area is improved to ∼20mm to minimize crosstalk and beam energy loss. After careful beam alignment, the phase noise for each channel can reach 0.004π. The radial profiles of electron density on the KTX are inverted, and density fluctuation associated with instabilities is shown based on the forward-scattering signals.

Electromagnetic analysis of ITER equatorial Wide Angle Viewing System (WAVS) in-vessel components

In the framework of ITER diagnostics, the visible and infrared equatorial Wide Angle Viewing System (WAVS, referenced as 55.G1.C0 in ITER Plant Breakdown Structure) plays a key role. Indeed, this system is devoted to monitor the surface temperature of the plasma facing components by infrared thermography and to image the edge plasma emission in the visible range. As a consequence, it is mandatory to verify that WAVS components are able to withstand all the foreseen loads and load combinations. This paper is dedicated to present the methods and results of electromagnetic (EM) and Transient Structural (TS) analyses for determining the loads due to Eddy Currents and the associated stresses and displacements in the in-vessel components of WAVS at its Preliminary Design Review (PDR) stage.Specifically, the analysed WAVS in-vessel components comprise First Mirror Units, shutters and Hot Dog Legs of the EPP#12 (Equatorial Port Plug). The selected EM loads derive from the IO-assumed worst EM scenario for EPP#12 (specifically a plasma exponential major disruption).Given the variation maps of the global magnetic field in the regions of interest during the transient, the EM loads have been estimated using a local 3D EM model of the WAVS components by means of the ANSYS Electromagnetics Suite v.19.2, employing the tool ANSYS Maxwell. Successively, the obtained results have been used as inputs to the corresponding TS analyses (carried out using ANSYS Workbench v.19.2). Therefore, the related outcomes can be combined with the set of all other structural studies (i.e. thermal and seismic analyses) to assess the overall mechanical behaviour of the components under study for the WAVS PDR level. Moreover, the results obtained have shown how EM loads are often design driving loads for the WAVS components.

Estimation of the Degradation Rate of the In-Vessel Mirrors for the H-Alpha and Visible Spectroscopy Diagnostics in ITER

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.

Day-Ahead Energy Management for Pelagic Island Microgrid Groups Considering Non-Integer-Hour Energy Transmission

Pelagic islanded microgrid groups (PIMGGs) can be developed into resource islands and load islands with the electric vessel achieving the interisland energy transmission. For such multi-microgrid structure, the interisland energy transmission time affected by environmental factors is likely to be non-integer hour (such as 23min), resulting in mismatching with the standard day-ahead scheduling step (1h). However, rounding the transit time may bring about large errors in optimization results, while using an elaborate scheduling step to approach the transit time will result in heavy computing burden due to numerous variables. To address the above problems, this paper proposes a novel day-ahead energy management system (EMS). Firstly, analyzing the impact of environmental factors including wind, ocean current, and wave, a centralized energy management framework considering the non-integer-hour energy transmission is designed. Furthermore, an optimal EMS operation model based on the 1-hour scheduling step is proposed. It eliminates the errors from rounding by coordinating the original and mirror unit commitments. Additionally, the optimization model is converted into a mixed-integer linearization programming (MILP) problem using a two-stage method including preprocessing and linearizing stage. Simulation studies on Taiping Island, Honma Island and Bolan Reef indicate the proposed EMS is effective and beneficial for PIMGGs.