Low Emittance Research Articles

Improving selectivity of thin film solar absorber by cobalt oxide grafted reduced graphene oxide

Reduced graphene oxide (rGO) modified cobalt oxide (Co3O4) nanocomposite (NC) thin films were prepared on aluminum substrates through dip-coating technique for solar selective absorber. The prepared rGO-Co3O4 NC thin films were characterized by X-ray diffraction, which revealed that the prepared samples have face centered cubic structure. Scanning electron microscopy showed that morphology of prepared thin films is comprised of spherical shaped grains with rough surface. Energy-dispersive X-ray spectra exhibited absence of impurities in the thin films. Raman spectra predicted spinel structure, combined vibrations of tetrahedral site and octahedral oxygen motions in the rGO-Co3O4 NC thin films. Optical properties were investigated by UV–Vis–NIR reflectance spectroscopy. The prepared thin films with a concentration of 1.0 wt% of rGO (1%-rGO-Co3O4) disclosed a highest solar absorptance (α = 89.95) and low thermal emittance (ε = 4.6) with a highest solar selectivity (ξ) of 19.55. These values indicated that the rGO-Co3O4 NC thin film samples can be ideal candidates as solar selective absorbers for solar thermal energy gadgets.

Observation of Monoenergetic Electrons from Two-Pulse Ionization Injection in Quasilinear Laser Wakefields

The generation of low emittance electron beams from laser-driven wakefields is crucial for the development of compact x-ray sources. Here, we show new results for the injection and acceleration of quasimonoenergetic electron beams in low amplitude wakefields experimentally and using simulations. This is achieved by using two laser pulses decoupling the wakefield generation from the electron trapping via ionization injection. The injection duration, which affects the beam charge and energy spread, is found to be tunable by adjusting the relative pulse delay. By changing the polarization of the injector pulse, reducing the ionization volume, the electron spectra of the accelerated electron bunches are improved.

Design of S-band photoinjector with high bunch charge and low emittance based on multi-objective genetic algorithm

Design of S-band photoinjector with high bunch charge and low emittance based on multi-objective genetic algorithm

Synthesis of Linear Black Gold Nanostructures Processable as Sunlight and Low-Energy Light Collecting Films for Photo-Thermoelectricity.

As one of the effort to cope with the energy crisis and carbon neutrality, utilization of low-grade energy generated indoors (e.g., light) is imperative because this saves building and house energy, which accounts for ≈40% of total energy consumption. Although photovoltaic devices could contribute to energy savings, it is also necessary to harvest heat from indoor lights to generate electricity because the light absorbed by materials is mostly transformed into heat. For daily life uses, materials should not only have high absorptance and low emittance but also be easily processed into various forms. To this end, this work synthesizes black aqueous suspensions containing winding and bent linear gold nanostructures with diameters of 3-5nm and length-to-diameter ratios of ≈4-10. Their optical and photo-thermal characteristicsareunderstood through experimental and theoretical investigations. Black gold nanostructures are conveniently processed into metal-dielectric films on metal, glass, and flexible substrates. The film on copper has an absorptance of 0.97 and an emittance of 0.08. Under simulated sunlight and indoor LED light illumination, the film has equivalent photo-thermal and photo-thermoelectric performances to a top-tier sunlight-collecting film. This work attempts to modify the film structure to generate more usable electricity from low-energy indoor light.

The application of encoder–decoder neural networks in high accuracy and efficiency slit-scan emittance measurements

A superconducting radio-frequency (SRF) photo injector is in operation at the electron linac for beams with high brilliance and low emittance (ELBE) radiation center and generates continuous wave (CW) electron beams with high average current and high brightness for user operation since 2018. The speed of emittance measurement at the SRF gun beamline can be increased by improving the slit-scan system, thus the measurement time for one phase space mapping can be shortened from about 15 min to 90 s. The convolution neural networks are applied to improve the efficiency and accuracy of beamlet images processing. In order to estimate the uncertainty in the calculation of normalized emittance, we analyze the main error contributions.

Bifacial Thermophotovoltaic Energy Conversion

Thermophotovoltaic (TPV) energy conversion efficiency has recently surpassed 30%. The key behind such high efficiency is the inclusion of a highly efficient mirror in the rear of the TPV cell that turns back to the thermal emitter the outband energy photons. Efficiencies over 50% could be theoretically attainable by approaching a mirror reflectance of 100%. However, the very few percent of outband absorption significantly deteriorate the conversion efficiency, especially at low emitter temperatures. Thus, current research focuses on developing advance mirror designs able to reach an extreme high outband reflectance over 95%. In this article I propose a bifacial TPV cell that enables very efficient photon recycling without using mirrors and that is less sensitive to outband optical losses. The key to this design is that the cell is introduced in a thermal emitter enclosure where it is irradiated from both sides. Then, outband photons transmit through the cell and are reabsorbed in the emitter. Therefore, the optical losses linked to the mirror/cell interface are eliminated, potentially enabling higher photon recycling efficiencies. This article presents a detailed balance simulation of an edge-cooled bifacial TPV cell to demonstrate that bifacial configuration enables higher conversion efficiencies and twice much as power density than monofacial designs, the latter being an advantage for moderate temperature and low-cost TPV power generation. Therefore, bifacial TPV cells are appealing for developing practical high-efficient and low-cost TPV devices for power generation in an extended range of heat source temperatures.

Designing Optical Coatings with Incorporated Thin Metal Films

In the world of nanomaterials and meta-materials, thin films are used which are an order of magnitude thinner than historically used in optical thin film coatings. A problem stems from the island structure that is seen as the film nucleates and grows until there is coalescence or percolation of the islands into a nearly continuous film. The application problem is that the indices of refraction, n and k, vary with thickness from zero thickness up to some thickness such as 30 or 40 nanometers for silver. This behavior will be different from material to material and deposition process to deposition process; it is hardly modeled by simple mathematical functions. It has been necessary to design with only fixed thicknesses and associated indices instead. This paper deals with a tool for the practical task of designing optical thin films in this realm of non-bulk behavior of indices of refraction; no new research is reported here. Historically, two applications are known to have encountered this problem because of their thin metal layers which are on the order of 10 nm thick: (1) architectural low emittance (Low-E) coatings on window glazing with thin silver layers, and (2) black mirrors which transmit nothing and reflect as little as possible over the visible spectrum with thin layers of chromium or related metals. The contribution reported here is a tool to remove this software limitation and model thin layers whose indices vary in thickness.

High-Quality Laser-Accelerated Ion Beams from Structured Targets

In this work, we reviewed our results on the prospect of increasing the quality of ion acceleration driven by high-intensity laser pulses using low-Z structured targets. It is shown that the radiation pressure acceleration mechanism dominates over target normal sheath acceleration for assumed laser target parameters when the laser intensity is high enough. The target thickness is optimized for this regime and double-layer structure is investigated. When a corrugation is fabricated on the interface of such a target, a relativistic instability with Rayleigh–Taylor and Richtmyer–Meshkov like features can be driven by the target interaction with a high intensity laser pulse. The proper development of this instability leads to the generation of a collimated quasi-monoenergetic ion beam with lower emittance, divergence, and energy spread compared to a single and double-layer target with planar interface. A steep-front laser pulse is used in our simulations to mitigate other type of instabilities arising at the target surface from the laser–target interaction. We discuss the use of a plasma shutter to generate the required pulse profile, which also locally increases intensity. The obtained shape improves the ion acceleration, including higher maximal energy and lower beam divergence, in our simulation of a high-Z target.

Field enhanced compact S-band gun employing a pin cathode

S-band RF-guns are highly developed for production of low emittance relativistic electron bunches, but need powerful klystrons for driving. Here, we present the design and first experimental tests of a compact S-band gun, which can accelerate electrons up to 180 keV powered by only 10 kW from a compact rack-mountable solid-state amplifier. A pin-cathode is used to enhance the RF electric field on the cathode up to 100 MV/m as in large-scale S-band guns. An electron bunch is generated through photoemission from a flat copper surface on the pin ex-cited by a UV laser pulse followed by a focussing solenoid producing a low emittance bunch with 0.1 mm mrad transverse emittance for up to 100 fC bunch charge. We are currently in the conditioning phase of the gun and first experiments show good agreement with simulations. The compact gun will serve three purposes: (i) it can be used directly for ultrafast electron diffraction; (ii) as an injector into a THz booster producing 0.3 MeV to 2 MeV electron bunches for ultrafast electron diffraction; (iii) The system in (ii) serves as an injector into a THz linear accelerator producing a 20 MeV beam for the AXSIS X-ray source project.

Dependence of CsK2Sb photocathode performance on the quality of graphene substrate film

A high-performance photocathode is required to advanced accelerators and electron microscopes. In particular, the CsK2Sb photocathode is of interest because it has features such as low emittance, excitability with visible light, and high quantum efficiency (QE). Generally, the CsK2Sb photocathode is produced by depositing a cathode element on a substrate, so that the cathode performance strongly depends on the surface condition of the substrate. We have found graphene as reusable substrate, which has the property of being chemically inactive. In this study, graphene film quality dependence of CsK2Sb photocathode performance was evaluated. Specifically, CsK2Sb photocathode was deposited using different quality graphene film substrates and their QE values and uniformity were compared. The quality of graphene films was analyzed using X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). We found that the graphene film can be cleaned by heating at 500 deg. The QE of the cathode on a good quality graphene film was higher and more uniform than that on a poor quality graphene film.

Status and powering test results of HTS undulator coils at 77 K for compact FEL designs

The production of low emittance positron beams for future linear and circular lepton colliders, like CLIC or FCC-ee, requires high-field damping wigglers. Just as compact free-electron lasers (FELs) require high-field but as well short-period undulators to emit high energetic, coherent photons. Using high-temperature superconductors (HTS) in the form of coated ReBCO tape superconductors allows higher magnetic field amplitudes at 4 K and larger operating margins as compared to low-temperature superconductors, like Nb-Ti.This contribution discusses the development work on superconducting vertical racetrack (VR) undulator coils, wound from coated ReBCO tape superconductors. The presented VR coils were modularly designed with a period length of 13 mm. Powering tests in liquid nitrogen of multiple vertical racetrack coils were performed at CERN. The results from the measurements are presented for three VR coils and compared with electromagnetic simulations.

Study of a possible silicon photomultiplier based readout of the large plastic scintillator neutron detector NeuLAND

The NeuLAND (New Large-Area Neutron Detector) plastic-scintillator-based time-of-flight detector for 0.1–1.6GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7m × 5 cm × 5 cm big plastic scintillator bars that are read out on each end by fast timing photomultipliers.Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a NeuLAND bar was instrumented on each end with a SiPM-based prototype of the same geometry as a 1” photomultiplier tube, including four 6 × 6mm2 SiPMs, amplifiers, high voltage supply, and microcontroller.Tests were carried out using the 35MeV electron beam from the superconducting Electron Linac for beams with high Brilliance and low Emittance (ELBE) with its picosecond-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1–60 electrons per bunch. Acqiris fast digitisers were used for data acquisition. In addition, off-beam tests using cosmic rays and the NeuLAND data acquisition scheme have been carried out.Typical time resolutions of σ≤ 120ps were found for ≥95% efficiency for minimum ionising particles, improving on previous work at ELBE and exceeding the NeuLAND timing goal of σ< 150ps. Over a range of 10–300MeV deposited energy in the NeuLAND bar, the gain was found to deviate by ≤10% (≤20%) from linearity for 35μm (75μm) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be lower than the expected cosmic-ray induced background in NeuLAND.

Anodization assisted preparation of diverse nanostructured copper oxide films for solar selective absorber

Copper oxide films with diverse morphologies are prepared on copper (Cu) substrate by anodization method. The concentration of aqueous NaOH solution used as electrolyte during the anodization process is found as crucial towards formation of different nanostructured films. The reaction temperature impact on chemical composition and morphology of films is also determined. X-ray diffraction patterns disclose that CuO and Cu2O are presented in films and the share between both could be altered by changing the NaOH concentration and applied potential. Scanning electron microscopy images unveiled formation of films with diverse morphologies comprised of nanorods, nanoflakes, nanoparticles, and nanoleaves. Raman spectra confirmed the presence of CuO mode and its significant peak intensity has indicated high crystallinity. The prepared films have displayed high solar absorptance (63.5%–77.3%), low thermal emittance (4.5%–5.5%), and better solar selectivity (>14). These results suggest that the anodization method can be employed as a potential technique to prepare facile and affordable solar selective absorbers.

High-entropy alloy nitride nanofilms via a co-sputtering method enable superior optical performance and thermal robustness

• HEN (ZrNbMo-Al-N) films are prepared through a reactive magnetron co-sputtering method. • A tri-layer SSA is fabricated based on HEN (ZrNbMo-Al-N) films. • The absorbers on Cu substrates show high absorptance (96.2%) and low emittance (6.6%). • The absorbers on SS Substrates exhibit superior thermal robustness at 400 °C. High-entropy ceramics are a new class of solar-thermal material with high configurational entropy, lattice distortion, and flexible component space. In this work, we report a tri-layer solar selective absorber based on high-entropy nitride (ZrNbMo-Al-N), which can be deposited on various substrates through reactive magnetron co-sputtering. The absorbers on Cu substrates exhibit a remarkable solar absorptivity of 96.2% and a suppressed thermal emissivity of 6.6%. Moreover, the absorbers on stainless steel (SS) substrates show superior thermal robustness. After annealing at 400 °C for 168 h in a vacuum condition, they retain a high absorptivity of 94.4% and a low thermal emissivity of 9.8%.

Design of Tender X-ray Absorption Spectroscopy Beamline in Taiwan Photon Source

A new tender X-ray absorption spectroscopy beamline for operating over the photon energy range from 1.7 keV to 11 keV is under construction at port 32 of the Taiwan Photon Source (TPS). The TPS 32A beamline uses two back-to-back water-cooled double crystal monochromators (DCMs), InSb(111) and Si(111), for achieving the wide energy tunability. The beamline design takes advantage of the low emittance of the TPS accelerator and a bending magnet (BM) to obtain a high-brightness focussed beam. In order to overcome the issue of poor thermal conductivity of InSb(111) crystals while facing high thermal load, we have implemented the following features : (i) we have controlled the flux and heat load by optimizing the source collection angle of 2 × 0.15 mrad2 (h × v), and (ii) we have installed water cooled double-bounce high harmonic rejection mirrors (HHRMs) with a variable incidence angle upstream of the DCM to reduce the heat load on the first InSb crystal. The DCM is followed by a 2:1 toroidal focusing mirror (TFM) which focuses the beam parallel to the floor of the experimental endstation. The simulated focus beam size is 0.9 × 0.9 mm2 (h × v, FWHM) using the InSb(111) DCM at 1.7 keV, and 0.2 × 0.45 mm2 (h × v, FWHM) using the Si(111) DCM at 4 keV, respectively. The photon flux is 1010 -1012 photons s−1 in the energy range of 1.7 to 11 keV at the sample stage after passing through the Be windows. The design parameters of photon flux and beam spot size will facilitate a tender X-ray source for carrying out high-quality X-ray absorption spectroscopy experiments.

Possibilities at the Polar beamline with APS-U

The Polar beamline will make use of the small emittance of the new APS-U storage ring and will offer extremely brilliant and coherent beam of variable polarization in the hard x-ray range. Tailored optics and experimental equipment will enable high spatial resolution dichroic spectroscopy, reflectivity and diffraction in combination with extreme pressures, low temperatures and high magnetic fields. Dichroic direct and ptychographic imaging of magnetic structures is being developed and will make use of the largely enhanced coherence of the low emittance source. We present an overview of the planned instrumentation and the upcoming new exciting possibilities.

GAUGING GREENHOUSE EMISSION THROUGH CBA, TRADE, FDI, AND POPULATION GROWTH

Introduction: Greenhouse gas emissions have a massive effect on the thinning of the earth's ozone layer, nowadays the industry is obligated to be as responsible for the process and output as possible in order to reduce carbon dioxide emissions (CO2). This study examines the implications of consumption-based accounting, trade, and foreign direct investment on greenhouse gas emissions from the least five emitters of different fuel types, according to the World Research Institute Indonesia, which are Japan, Brazil, Indonesia, Iran, and Canada from 2000 until 2020. Methods: The study employs a panel data regression using Random Effect Model-Hausman Test. Results: The findings show that foreign direct investment has a strong negative association with lowering greenhouse gas emissions. The greater the investment, the cleaner the air and atmosphere. Trade has a negative correlation with greenhouse gas emissions, this reflects increasing environmental consciousness among producers and/or increasing pressure for environmentally friendly operations from oversea. Since natural assets could convey their full economic potential on a sustainable ground. The population had a role in lowering carbon emissions as well. The results of the consumption-based emission regression show a significant positive relationship, which can clearly exacerbate climate change conditions. It is not astounding, given that CBA accounts for emissions throughout a product's or service's complete lifecycle. Conclusion and suggestion: This study advances the grasp of greenhouse gas emissions and the factors that influence others in the five lowest emitters. It is the first study towards using greenhouse gas emission data as the dependent variable, rather than consumption-based accounting data, which has been used in most previous studies.

Efficient Warming Textile Enhanced by a High-Entropy Spectrally Selective Nanofilm with High Solar Absorption.

Solar and radiative warming are smart approaches to maintaining the human body at a metabolically comfortable temperature in both indoor and outdoor scenarios. Nevertheless, existing warming textiles are ineffective in frigid climates because the solar absorption of selective absorbing coating is significantly reduced when coated on rough textile surface. Herein, for the first time, high-entropy nitrides based spectrally selective film (SSF) is introduced on common cotton through a one-step magnetron sputtering method. The well-designed refractive index gradient enables destructive interference effects, offering a roughness-insensitive high solar absorptance (92.8%) and low thermal emittance (39.2%). Impressively, the solar absorptance is 9.1% higher than the reported best-performing selective nanofilm-based textile. As a result, such a textile achieves a record-high photothermal conversion efficiency (82.2% under 0.6 suns, at 0°C). This textile yields a 3.5°C drop in the set-point of indoor air-conditioner temperature. Besides, in a winter morning with an air temperature of 7.5°C, it warms up the human skin by as large as 12°C under weak sunlight (350W m-2 ). More importantly, such a superior radiative warming performance is achieved by engineering the widely used cotton without compromising its breathability and durability, showing great potential for practical applications.

Effect of Rotational Speed on the Structural, Morphological, and Optical Properties of Biosynthesized Nickel Oxide Thin Films for Selective Solar Absorber Nanocoatings

This article presents a simple and low-cost green synthesized single-layer NiO selective solar absorber nanocoating prepared by spin coating on a Cu substrate at different rotational speeds (RS). The effects of substrate RS on the structural, morphological, chemical, and optical properties of the NiO nanocoatings were thoroughly investigated. The XRD results reveal the formation of pure diffraction peaks indexed to face-centered cubic NiO nanocoatings. SEM confirmed the uniform distribution of the NiO thin films with a nanosphere-like structure and the influence of RS variation on the formation of NiO nanostructures. EDS and XPS confirmed the presence of Ni and O in the green synthesized NiO coatings. AFM showed homogeneous nanopillar-like NiO thin films with the average surface roughness decreasing from 13.6 to 9.06 nm as the RS increased from 700 to 1300 RPM. Raman spectroscopy of the nanocoatings showed normal modes related to longitudinal optical and transverse optical phonons, and a combination of both, which implies the presence of a defect-rich or anti-ferromagnetically ordered NiO film responsible for the occurrence of more scattering peaks. UV–Vis–NIR and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the optical properties of the nanocoatings. The green synthesized NiO nanocoatings deposited at 700 RPM exhibited excellent solar absorptance (α) of 0.92 and low thermal emittance (ɛ) of 0.11. The optical properties of the selective materials obtained in the present work were correlated with the non-stoichiometric nature of the spin-coated sample, multiple reflections, and interference-induced light absorption on the green synthesized surface. These results suggest that the NiO thin films prepared through this simple and environmentally benign green synthesis method can be promising candidates for efficient solar selective absorbers.

Optical properties of bulk high-entropy diborides for solar energy applications

So far, the studies regarding the innovative High-Entropy Borides (HEBs), which belong to the more general class of Ultra-high temperature ceramics (UHTCs), have been entirely confined to their fabrication or characterization from the microstructural, mechanical and oxidation resistance viewpoints.In this work, the optical properties of two members of HEBs, i.e. (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 and (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, are evaluated for the first time to assess their possible utilization in the thermal solar energy field. The bulk samples (96.5 % and 97.4 % dense, respectively) are obtained as single-phase products by Spark Plasma Sintering (1950 °C/20 min/20 MPa) starting from powders previously synthesized by Self-propagating High-temperature Synthesis (SHS). The optical characterization, whose results are discussed by comparing HEBs to the individual borides, shows that they are characterized by intrinsic spectral selectivity and low thermal emittance, resulting therefore interesting for high-temperature solar absorbers applications.