Vacuum Window Research Articles

Spectral in situ ellipsometer for thin layer measurements in thermonuclear fusion applications.

Ellipsometry is widely used to characterize the thickness and optical parameters of thin films deposited, for example, in industrial processes. It is based on the measurement of polarization change upon reflection of, for example, visible light at a material sample. Commercially available devices are designed for stationary applications and often rely on precise geometric adjustment of the optical setup to maximize the measurement precision. In this work, a simplified spectral ellipsometer is proposed and tested with the aim of flexible implementation in space-limited applications in thermonuclear fusion research: on the one hand, as a hand-held device for large thickness scans of coatings deposited on first-wall components inside the vacuum vessel of fusion experiments and, on the other hand, for in situ monitoring of plasma deposited coatings on diagnostic vacuum windows, reducing their transmission in the optical spectral range, which hampers spectroscopic diagnostics in long-pulse plasma experiments. The simplicity of the hardware setup is partially compensated by complex Bayesian inference of the coating parameters, which incorporates all uncertainties of the measurement and the model and provides a quantitative assessment of the final uncertainties of inferred coating parameters. The Bayesian inference based on synthetic observations is also used to optimize the diagnostic design, identifying the limiting parameters and quantifying their impact on final accuracy. For real-time analysis of layer thickness on first-wall components in fusion devices measured with the hand-held device, a neural network based analysis has been implemented, and promising test results are presented.

Investigation on the overall performance of hydrogel-based thermochromic windows with various structures

Thermochromic (TC) windows have attracted extensive attention due to their potential for improving building performance through the variation of optical properties in response to temperature. However, past studies on TC windows at the building scale primarily focused on optimizing and evaluating the properties of TC materials, with little attention paid to the varying window structures frequently encountered in engineering applications. In this study, the building performance of hydrogel-based TC windows was investigated from the structural perspective. A comprehensive simulation framework was developed, integrating overall performance simulations of energy consumption and indoor comfort. Using a self-fabricated hydrogel TC glass and an office building as the case study, the impact of the optical properties of the substrate glass on single, double, vacuum, and ventilation TC windows was analyzed. The results indicated that the optimal extinction coefficients for the studied windows range from 55 to 105 m−1 for visible irradiation and from 155 to 255 m−1 for near-infrared irradiation. Subsequently, the overall performance improvements of these types of TC windows relative to corresponding static versions were calculated. It was found that the impacts of TC glass on these four windows varied significantly. The electricity usage was reduced by 33 ∼ 53 %, and the thermal comfort and visual comfort were enhanced by –22 ∼ 20 % and 72 ∼ 100 %, respectively. This study reveals in detail how the TC window structure affects various aspects of building performance, aiming to inspire and guide the consideration of window structure in the practical applications of TC glass.

Investigation and Fabrication of a Low Loss and Wideband Single Crystal Diamond Vacuum Window for W-Band Traveling Wave Tube

Investigation and Fabrication of a Low Loss and Wideband Single Crystal Diamond Vacuum Window for W-Band Traveling Wave Tube

Developing a robust sensor for infrared imaging bolometers.

A new type of large area sensor for infrared imaging bolometers has been developed. It replaces the thin and fragile free-standing metal foils, which typically have been used, with a multi-layer coated sapphire (or diamond) substrate. Sapphire is transparent to mid-infrared wavelengths, is robust against transients, and can be thick enough to even be the vacuum window. The primary radiation absorber is still a thin deposited metal layer, but now it is partially insulated from the supporting sapphire substrate by a black (carbon-based) layer, which also acts as a blackbody remitter. Test results indicate 6× more noise equivalent power density (estimated NEPD = 23 W/m2 at 5ms camera exposure time, foil temperature decay time 60ms) for a 2μm gold-coated sapphire disk compared to estimated NEP = 4 W/m2 at 1.8ms exposure time, with foil decay time 420ms, for a nominal 2.5μm thick platinum-free-standing foil.

Realization of a gas puff imaging system on the Wendelstein 7-X stellarator.

A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the "Gas-Puff Imaging" (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system's plasma-facing components. The system features a pair of "converging-diverging" nozzles for partially collimating the gas puffed locally ≈135mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera. The DEGAS 2 neutral code was used to simulate the Hα (656nm) and HeI (587nm) line emission expected from well-characterized gas-puffs of H2 and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal-to-noise ratios (>100 at 2 Mframes/s) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the two-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge and scrape-off layer and in and around the magnetic islands outside the LCFS that make up the island divertor configuration employed on W7-X.

PHYSICAL AND MATHEMATICAL MODELING OF UNSTEADY COUPLED HEAT AND MASS TRANSFER IN CVD-DIAMOND WINDOWS OF THE SIBERIAN CIRCULAR PHOTON SOURCE

The results of physical and mathematical modelling in the ANSYS software package of three-dimensional unsteady coupled heat and mass transfer in the previously developed diamond vacuum window (DVW) of the workstation of the Siberian Circular Photon Source under construction are presented. Previous simulations have convincingly shown: the possibility of using a mini-channel cooling system to implement reliable and proper temperature management of this optical device, the advantage of a mini-channel cooling system over a one channel system in terms of fulfilling the optical requirements for DVW and its design. Here are detailed calculations of unsteady three-dimensional flow in the mini-channels of the cooling system, which will prevent possible dramatic destruction of the workstation due to local overheating of the CVD-diamond foil and its recrystallization.

Cryogenic focus measurement system for a wide-field infrared space telescope

We describe a technique for measuring focus errors in a cryogenic, wide-field, near-infrared space telescope. The measurements are made with a collimator looking through a large vacuum window, with a reflective cold filter to reduce the background thermal infrared loading on the detectors and optics. The vacuum window and cold filter introduce a wavefront error that we characterize using an autocollimating microscope. For the 200 mm diameter aperture f/3 space telescope SPHEREx, we achieve a focus position measurement with a ∼15µm systematic and a ∼5µm statistical error.

Materials adopted for particle beam windows in relevant experimental facilities

A beam vacuum window is a thin interface of separation between a volume under vacuum and a volume at a higher pressure traversed by particle beams. Their application is not only limited to particle accelerators, where they are typically installed inside the beamline to separate vacuum sectors, but also extends to other fields of nuclear research and to high-power hadron beam applications, such as spallation neutron sources and accelerator-driven systems. The main issue concerning the beam window technology resides intrinsically in the dual role of these components: the thickness of the window is supposed to be as thin as possible to allow the passage of the particles through matter with minimal interaction but, at the same time, enough resistant to maintain the required differential pressure between the two environments. Published by the American Physical Society 2024

PENERAPAN KESELAMATAN DAN KESEHATAN KERJA (K3) DI BAGIAN PENYIMPANAN REKAM MEDIS RUMAH SAKIT UMUM DAERAH X BANDUNG

Occupational safety and health can support the performance of officers during work, especially in medical record filing. Improperly implemented occupational safety and health causes work accidents. The purpose of occupational health and safety is to prevent, reduce, protect and even eliminate the risk of work accidents. Therefore, it is necessary to conduct research on occupational safety and health in Medical Record Filing. This study aims to reveal the implementation of occupational safety and health in Medical Record filing section in Hospital X. This research method uses a qualitative approach with a descriptive method. Interview and observation were used as data collection techniques. The subjects in this study were 8 medical record filing officers and 1 medical record filing room at Hospital X. The result showed that filing staff did not use personal protective equipment completely, the air temperature of filing room did not meet the threshold value, there were still disease vectors, the medical record filing room was dusty, there was no ventilation, and staff had work-related health problems such as dry cough and itching. Researchers suggest the efforts in socializing the importance of occupational safety and health (K3), adding personal protective equipment, adding air conditioners, buying vacuum cleaners, adding ventilation, windows or doors, maintaining cleanliness and completely applying K3 principles.

Design of compact high resolution imaging system for cold atom experiments

In cold atom experiments, high resolution imaging systems have been used to extract <i>in-situ</i> density information when studying quantum gases, which is one of the hot topics in this field. Such a system is usually called “quantum-gas microscope”. In order to achieve a long working distance and large magnification, high resolution imaging of cold atoms through a vacuum window usually requires a long distance between the atoms and the camera. However, due to space limitation caused by a large number of nearby optical elements, it may be difficult to realize a long imaging system, which is a common case in cold atom experiments. Herein we present an imaging system that can achieve a short distance between the atoms and the image plane with diffraction-limited 1 μm resolution and 50 magnification. The telephoto lens design is adopted to reduce the back focal length and enhance the pointing stability of the imaging lens. The system is optimized at an operating wavelength of 767 nm and corrects aberrations induced by a 5-mm-thick silica vacuum window. At a working distance of 32 mm, a diffraction-limited field of view of 408 μm is obtained. The simulation result shows that by changing the air space between lenses, our design operates across a wide range of window thicknesses (0–15 mm), which makes it robust enough to be used in typical laboratories. This compact imaging system is made from commercial on-shelf <i>Φ</i>2 in (1 in = 2.54 cm) singlets and consists of two components: a microscope objective with a numerical aperture of 0.47 and a telephoto objective with a long effective focal length of 1826 mm. Both are infinitely corrected, allowing the distance between them to be adjusted to insert optical elements for irradiating atoms with laser beams of different wavelengths without affecting the imaging resolution. Taking the manufacturing and assembling tolerances into consideration, the Monte Carlo analyses show that more than 95% of the random samples are diffraction-limited within the field of view. This high success rate ensures that these two objectives can be achieved easily in the experiment. Combined with its performance with other wavelengths (470–1064 nm), this imaging system can be used for imaging different atom species, such as sodium, lithium, and cesium.

Evaluation of low-loss alumina material for high-power RF windows

Conventional RF vacuum windows are made of metalized ceramics, hermetically brazed to a pillbox cavity. High-power windows, operating in ultra-high frequency (UHF) band, require the fabrication of ceramic disks with diameters on the order of 9”. Furthermore, a Titanium Nitride (TiN) multipactor suppression coating must be applied to the ceramic surfaces. The large size and complex internal geometry of these windows create challenges in validating the coating in the fully fabricated assembly. This study evaluates a novel low-loss alumina AO479U, provided by Kyocera, and a reactive sputtering process suitable to deposit a 10-20 nm thick TiN coating on a large diameter window. The paper will report the changes in the TiN coating through chemical cleaning and vacuum braze processes using stylus profilometry, optical microscopy, Scanning Electron Microscopy (SEM), and Rutherford Backscattering Spectroscopy (RBS).

Vacuum Window for IBA C18 Twin Cyclotron’s Beamline

Vacuum Window for IBA C18 Twin Cyclotron’s Beamline

Active correction of window Faraday effects for ITER laser diagnostics

Measurement of the change in polarization of a laser beam traversing a magnetized plasma is a standard diagnostic technique for extracting key plasma parameters, including density and current profile. Depending on the polarization orientation of the incident laser beam relative to theplasma magnetic field, the polarization change is denoted as either Faraday rotation or Cotton-Mouton effect. On ITER three laser diagnostics will make use of this effect to make their measurements. Unfortunately, this effect is also evident when the laser beam passes through the vacuum window. The large magnetic field and finite verdet constant of the window material mean that on ITER this effect — in particular faraday rotation — is non-negligible, and needs to be disentangled from the desired measurement parameter. The Toroidal Interferometer-Polarimeter (TIP) and Density Interferometer-Polarimeter (DIP), in particular, are affected. Both diagnostics use lasers in the 5–10 μm range, and will use zinc-selenide (ZnSe) as the vacuum window material. In order to compensate for the unwanted window distortion a sensor is being developed to monitor the magnetic field perpendicular to the window and activelycorrectfor the faraday rotation in real time. The sensor consists of an inductive coil closely fitted just in front of the window disc. It comprises several turns of fine wire in center-tap configuration. Both the raw voltage signal, as well as the integrated signal, will be monitored to estimate the magnetic field through the window disk. The system is designed to measure fields up to B <1 T with an accuracy of 0.01 T, at frequencies of D.C. to 1 kHz. The backend electronics will leverage off similar technology developed for other ITER magnetics systems. Using the real-time magnetic field information, in conjunction with published and/or measured data on the verdet constant of the ZnSe window material, in-house developed software will estimate the faraday rotation induced by passing through the window.An initial prototype of the sensor has been fabricated and results from preliminary characterization trials of the system are presented. Detailed testing is planned for the future using the DIP system prototype currently under development.

Energy assessment of advanced and switchable windows for less energy-hungry buildings in the UK

Globally, greenhouse gas emissions from the operational phase of buildings are significantly contributing towards climate change. Global and national efforts, through the Sustainable Development Goals and the UK's 2050 targets, aim to reduce these emissions with net zero energy buildings (NZEBs). A building's glazing plays a significant role in overall building energy consumption due to their traditionally ‘leaky’ nature. This study utilises experimental data from test cells and the International Glazing Database to evaluate the performance of advanced and smart/switchable windows on an existing low energy building (LEB) situated in north Wales, UK, as a step towards making the modelled building a NZEB. A number of glazing constructions were considered in this work; advanced window – vacuum, aerogel, vacuum-aerogel and smart window – PDLC, PDLC-aerogel and PDLC-vacuum, in their fixed and switching states. Results revealed that PDLC-vacuum offered the greatest reduction in building energy, yielding a theoretical U-value of 0.810–0.831 W/m2K and a G-value of 0.257–0.455. Despite its successes, it was notably susceptible to window orientation and window-to-wall ratio. Vacuum and aerogel glazing both offered similar energy savings, with the latter prone to overheating, stressing cooling loads. These advanced windows offered differing daylighting potential with vacuum able to meet 78% of useful daylight illuminance compared to aerogel's 60%. Given the prioritisation trilemma between heating, lighting and cooling needs of a building, PDLC-vacuum presents the best step towards a NZEB. As such, further efforts should concentrate on the development of a PDLC-vacuum window, maintaining smart window functionality and achieving low U-value for cold climates.

Optical measurements of the silicon vacuum window with anti-reflective sub-wavelength structure for ASTE Band 10.

For millimeter and submillimeter-wave astronomy, it is highly desirable to have vacuum windows within the receiver cryostat that exhibit low reflection, low loss, and a wide bandpass. The use of antireflective (AR) sub-wavelength structures (SWSs) on substrates has expanded the possibilities for creating new vacuum windows. Recently, a novel method of fabricating AR SWS on a silicon-on-insulator wafer has been proposed, and a vacuum window with a two-layer AR SWS has been developed for use with the Atacama Submillimeter Telescope Experiment Band 10 receiver. To thoroughly assess the characteristics of the silicon window sample, we conducted transmittance measurements using terahertz time-domain spectroscopy, and noise and beam measurements using an Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 receiver. We found that the silicon window sample exhibits characteristics comparable to the quartz window of the ALMA Band 10 receiver. The result strongly encourages applications of AR silicon windows in receivers with wider bandwidths.

DNA irradiating system with 35-keV electron beam

This work aims to design the experimental system for investigating the effect of low energy electron irradiation on DNA by means of particle tracking and mechanical strength simulations. The electron beam produced with a DC accelerator having uniform kinetic energy of 35keV and the current of 10nA is used as a source of primary electrons. Two situations of DNA irradiation, in vacuo and in ambient, are studied. For both cases, the main objective is to choose appropriate materials to serve as the windows for the in vacuo sample cell and the vacuum window for ambient electron beam extraction. Silicon nitride with varied thickness has been proposed to be used as the electron exposing window for the sample cell and has been examined in Geant4 particle tracking simulation and SolidWorks mechanical strength test while titanium (Ti), beryllium (Be), and high-density polyethylene (HDPE) are considered to be used as the vacuum window and the properties are studied with the same method. The optimal materials are used to construct the system where electron beam is irradiated on a DNA sample. The interaction of electrons with the DNA and its damages is performed with the Geant4-DNA simulation. Based on our limiting conditions, it is found that the DNA double strand breaks can only be observed when the DNA sample is irradiated inside the vacuum part of the accelerator unit.

Detailed Monte-Carlo characterization of a Faraday cup for proton therapy.

Experiments with ultra-high dose rates in proton therapy are of increasing interest for potential treatment benefits. The Faraday Cup (FC) is an important detector for the dosimetry of such ultra-high dose rate beams. So far, there is no consensus on the optimal design of a FC, or on the influence of beam properties and magnetic fields on shielding of the FC from secondary charged particles. To perform detailed Monte Carlo simulations of a Faraday cup to identify and quantify all the charge contributions from primary protons and secondary particles that modify the efficiency of the FC response as a function of a magnetic field employed to improve the detector's reading. In this paper, a Monte Carlo (MC) approach was used to investigate the Paul Scherrer Institute (PSI) FC and quantify contributions of charged particles to its signal for beam energies of 70, 150, and 228 MeV and magnetic fields between 0 and 25 mT. Finally, we compared our MC simulations to measurements of the response of the PSI FC. For maximum magnetic fields, the efficiency (signal of the FC normalized to charged delivered by protons) of the PSI FC varied between 99.97% and 100.22% for the lowest and highest beam energy. We have shown that this beam energy-dependence is mainly caused by contributions of secondary charged particles, which cannot be fully suppressed by the magnetic field. Additionally, it has been demonstrated that these contributions persist, making the FC efficiency beam energy dependent for fields up to 250 mT, posing inevitable limits on the accuracy of FC measurements if not corrected. In particular, we have identified a so far unreported loss of electrons via the outer surfaces of the absorber block and show the energy distributions of secondary electrons ejected from the vacuum window (VW) (up to several hundred keV), together with electrons ejected from the absorber block (up to several MeV). Even though, in general, simulations and measurements were well in agreement, the limitation of the current MC calculations to produce secondary electrons below 990eV posed a limit in the efficiency simulations in the absence of a magnetic field as compared to the experimental data. TOPAS-based MC simulations allowed to identify various and previously unreported contributions to the FC signal, which are likely to be present in other FC designs. Estimating the beam energy dependence of the PSI FC for additional beam energies could allow for the implementation of an energy-dependent correction factor to the signal. Dose estimates, based on accurate measurements of the number of delivered protons, provided a valid instrument to challenge the dose determined by reference ionization chambers, not only at ultra-high dose rates but also at conventional dose rates.

Matter radius of the doubly-magic ^{56}Ni measured in a storage ring

The matter radius of the doubly magic ^{56}Ni was extracted from a measurement of the differential cross section by employing, for the first time, elastic proton scattering in inverse kinematics with a radioactive beam at E_{kin}=390.2 MeV/nucleon circulating in a storage ring and passing an internal hydrogen gas-jet target with a revolution frequency of around 2 MHz. The novel experimental scheme is based on UHV-compatible Si detectors operated as active vacuum windows, which were implemented in the ESR storage ring at GSI. A matter radius <r_{m}^{2}>^{1/2}=3.74^{+0.03}_{-0.06} fm was extracted for the doubly-magic self-conjugate nucleus ^{56}Ni.

Radiation effects in optical coatings for ITER diagnostics

The aim is to provide an assessment of radiation damage in coated films on refractive substrates that could be used as relevant information to protect the field lenses in optical diagnostics for ITER. Radiation-resistant optical materials with transparent properties should transfer light from plasma to detectors through the interspace until the port cell area where they are located (more than 10 m from the vacuum window). These optical coatings and substrates should have resilience enough to withstand neutron and gamma irradiation without significant degradation of their transmittance.Coated sapphire (Al2O3 windows), YAG with Broad Band Anti-Reflective (BBAR) and substrates of BaF2/CaF2 protected with anti-humidity coating (Parylene-C) were extensively tested. After testing, transmission measurements and analysis of optical surfaces yield significant discoveries. All substrates showed good refractive performance under gamma radiation. On the contrary, Parylene-C did not resist temperatures above 100 degrees Celsius as expected, according to manufacturing specifications. In addition, it was observed that with an energy dose of 332 kGy of gamma rays and a significantly lower temperature of 50 degrees Celsius, the Parylene-C protection is also damaged. Coated sapphire had the best overall performance with respect to the neutron irradiation tests. Nevertheless, the decrease in transmission observed in the YAG and BaF2 coated samples is not significant for the expected cumulative neutron dose that these samples will receive at their location within the diagnostic.This information was considered for the selection of the best candidates as refractive lenses and optical coatings for the Preliminary Design Review (PDR) of ex-vessel components that will integrate the Wide-Angle Viewing System (WAVS) for ITER Equatorial Port 12.

MISTRAL campaign in support of W7-X long pulse operation

Following two initial campaigns [1], Stellarator Wendelstein 7-X (W7-X) has now completed the construction phase by installation of active cooling of all plasma facing components. The machine is presently commissioned for the next campaign (OP2) aiming at 1 GJ per pulse, e.g. 100 s at 10 MW, eventually aiming at 18 GJ, e.g. 1800 s at 10 MW. The key heating system is the Electron Cyclotron Resonance Heating (ECRH) system, consisting of 10 gyrotrons with power per gyrotron ranging from 0.6 MW up to 1.0 MW at 140 GHz. A phased upgrade of the installation is in progress with the addition of 2 gyrotrons and the development of 1.5 MW and 2.0 MW gyrotrons, such that at the end of the upgrade 4 gyrotrons will be available in each power class of 1.0, 1.5 and 2.0 MW [2]. The increased ECRH power, combined with O2 and X3 heating schemes at high densities, will lead to increased microwave stray radiation. This is non-absorbed microwave power that diffuses inside the vessel and is incident on all in-vessel components including vacuum windows and attached diagnostic systems. A fraction of the stray radiation is absorbed by resistive or dielectric losses of these components, leading to thermal loads that scale with stray radiation levels and pulse length. At W7-X a high power microwave stray radiation launch facility ’MISTRAL’ is available that is used to qualify invessel components for use at specified microwave surface power densities [Wm−2]. This paper reports on MISTRAL campaigns in 2020 2021 for testing of stray radiation loads during OP2 in W7-X, as well as on an EUROfusion program assessing stray radiation loads on ITER components. A dedicated, absolutely calibrated, caloric load was developed for the campaign to obtain measurement of stray radiation power levels as well as to conveniently expose samples. Amongst other we report on shielding concepts using metal enclosures combined with microwave absorbing coatings and dielectric heating of vacuum windows.