Emittance Variation Research Articles

Flexible polyaniline/carbon quantum dots films for enhanced electrochromic performance

Polyaniline (PANI) conducting polymers exhibit potential electrochromic properties. However, the electrochromic response of PANI films in the infrared (IR) ranges is restricted by their dense structure. Herein, the polyaniline/carbon quantum dots (PANI/CQDs) films were synthesized with sulfuric acid (SA) and CQDs as the dopants. The tetrahedral structures of SA contribute to the formation of highly oriented lamellar PANI. The synergistic effect between CQDs and PANI promotes the loose and porous surface morphology, thereby improving the electrochromic performance of PANI film. The PANI/CQDs porous film for the polymerization charge of 0.5C (PANI/CQDs-5) shows the optimal electrochromic properties and IR modulation capacity, achieving an optical contrast (ΔT) values of 53 % at 850 nm, and with the emittance variation (Δε) values of 0.41, 0.46 and 0.42 in 3–5 μm, 8–14 μm, and 2.5–25 μm, respectively. Furthermore, the switching time of the PANI/CQDs-5 films for coloration and blanching are 2.5 s and 3.6 s, respectively, with over 95 % retention after 100 cycles. Theoretical calculations verified that PANI/CQDs composite films displayed outstanding electron and ion transfer kinetics, facilitating superior electrochromic properties.

Theoretical investigation of VO2 smart window with large-scale dynamic infrared emittance adjustment for adaptive thermal management

Thermochromic windows based on vanadium dioxide (VO2) are widely used in architectural windows due to its reversible phase change process. However, traditional VO2 windows only manage solar radiative transmittance and their emittance variation trend in the mid-infrared contradicts realistic requirements, which seriously hinders the further development of thermochromic windows. To address this issue, a VO2 full-spectrum smart window based on theoretical calculations is proposed for adaptive adjustment of solar spectral transmittance and thermal emittance. We cleverly utilize a thin Ag layer to construct a Fabry-Perot (FP) resonant cavity with the VO2 layer to achieve forward modulation of the emittance in the atmospheric window. Notably, the smart window has 83.8 % emittance modulated ability, which enables effective control of radiative cooling and has greatly exceeded the reported performance of the smart windows while maintaining 72.8 % high visible transparency. Energy consumption analysis indicates that the smart window has high energy-saving potential worldwide, achieving over 60 MJ/m2 energy-saving effect. This simple and easy-to-manufacture smart window expands the research scope of windows and broadens application prospects in thermal management, infrared camouflage, and building energy conservation.

Unprecedented Spatial Manipulation and Transformation of Dynamic Thermal Radiation Based on Vanadium Dioxide.

Reconfigurable infrared (IR) materials have widespread applications in thermal management and smart IR concealment. Although various reconfigurable IR materials can be customized by positive or negative differential VO2-based resonators, their insightful mechanism remains unknown. Here, we comprehensively investigate the fundamental design rule of reconfigurable thermal radiation between positive and negative differential thermal radiation properties for the first time. Importantly, the skin depth of VO2 film in the metal state is investigated to clarify the transformation from positive to negative differential thermal radiation properties, and the critical thickness is further derived, providing important guidance in designing the reconfigurable thermal radiation regulator. Furthermore, the reconfigurable multistate thermal images had been presented into one plate. The resulting emittance variation (△ε8-14μm) of the VO2-based resonator can change from 0.61 to -0.53, which consummates the ability for diverse demands such as infrared concealment, thermal illusion, and thermal management. This work constitutes a promising and universal route toward designing whole smart devices and may create new scientific and technological opportunities for platforms that can benefit from reconfigurable electromagnetic manipulation.

Emittance and energy spread compensation in future synchrotron light sources

This paper shows a result of the effect on the beam emittance and energy spread induced by active insertion device (ID) in future synchrotron light sources. The online ID magnetic gap data of Shanghai Synchrotron Radiation Facility (SSRF) was sampled to evaluate the emittance variation in an 864mRing with the beam emittance of 26 pm⋅rad. A new compensation method using two compensation wigglers was developed to simultaneously improve both the beam emittance and energy spread stability, resulting in improved brightness stability during operation.

Investigation of thermal control in phase-changing ABO3 perovskites via first-principles predictions: general mechanism of emittance.

Phase-change thermal control has recently seen increased interest due to its significant potential for use in smart windows, building insulation, and optoelectronic devices in spacecraft. Tunable variation in infrared emittance can be achieved by thermally controlling the phase transitions of materials at different temperatures. A high emittance in the mid-infrared region is usually caused by resonant phonon vibrational modes. However, the fundamental mechanism of emittance variation during the phase-change process remains elusive. In this work, the electronic bandgaps, phononic structures, optical-spectrum properties, and formation energies of 76 kinds of phase-changing ABO3 perovskites were predicted based on first-principles calculations in the mid-infrared region. The variation in emittance between two phases of a single material was found to have an exponential correlation with the bandgap difference (R2 ∼ 0.92). Furthermore, a strong linear correlation (R2 ∼ 0.92) was found between the emittance variation and the formation-energy difference, and the emittance variation was also strongly correlated with the volume-distortion rate (R2 ∼ 0.90). Finally, it was concluded that a large lattice vibrational energy, a high formation energy, and a small cell volume are conducive to high emittance. This work provides a strong dataset for training machine-learning models, and it paves the way for further use of this novel methodology to seek efficient phase-change materials for thermal control.

Low Solar Absorptance, High Emittance Performance Thermochromic VO2-Based Smart Radiator Device.

Thermochromic vanadium dioxide (VO2)-based smart radiator devices (SRDs) display emittance variation with changes in temperature, making them very promising for energy-efficient thermal control of spacecrafts in general, and nanosatellites in particular. However, the high solar absorptance of the VO2-based SRDs remains too high for their intended application. Based on an approach combining optical simulation and experimental work, I demonstrate that an additional top stack layer alternating between high and low refractive indices made of a-Si(25 nm)/SiO2(67 nm) reduces the solar absorptance of a VO2-based SRD by 35% (from 0.43 to 0.28) while keeping the emittance performance of the SRD within the requirements for the intended application (low-temperature emittance εL = 0.35, high-temperature emittance εH = 0.81 and emittance tuneability with temperature Δε = 0.46). I also discuss factors to consider while designing additional top stack layers alternating between high and low refractive indices to further decrease the SRD's solar absorptance without affecting its emittance performance.

Suppression of emittance variation in extremely low emittance light source storage rings

A passive method based on an optimized quasiachromatic condition effectively suppresses emittance variation during the independent tuning of insertion devices (IDs), which is one of the major obstacles for conducting precise experiments in extremely low emittance light source storage rings. This method, simple and easy to apply to any light source storage ring, reduces the emittance variation to potentially less than 1% by carefully optimizing dispersion leakage at the straight sections where the IDs are installed according to an actual condition of the ID independent tuning.

Variable infrared emittance mechanisms of electrochromic film based on poly(aniline) under various doping concentrations of camphorsulfonic acid

Poly (aniline) (PANI) is considered an ideal material for the modulation of infrared (IR) radiation due to its excellent electrochromic properties. However, the camphorsulfonic acid doping mechanism which results in emittance modulation is not clearly understood. With the goal of enhancing the IR emittance variation (Δε), a PANI film was synthesized by a chemical oxidation and spraying method, and the doping mechanism of CSA concentration effect on Δε was studied by combining Raman spectra, X-ray photoelectron spectra and density functional theory calculations. The results demonstrate that with increasing camphorsulfonic acid concentration, the effect of the doping concentration on the emittance of PANI/Au films can be divided into two stages: (1) the change in the emittance is mainly caused by the shortening of optical penetration depth either under the state of dopant free (non-doped) or a low CSA doping concentration; (2) the change in emittance is mainly caused by the increase in reflectivity of the PANI layer under the increased doping. Due to the joint action of the two factors, the emittance of the PANI film first increases and then decreases with increasing concentration of CSA, and the maximum Δε (0.45) is realized at 1 M. This paper clarifies the mechanism of PANI films with different CSA dopant concentrations and could provide a way to increase the emittance modulation range by adjusting the concentration of the dopants.

Emittance Variation of a High-Current Relativistic Electron Beam in a Bend Magnet

The article presents the investigation results on the main angular divergence sources of a high-current relativistic electron beam when it passes through a real 12° bend magnet of the transport system in the linear induction accelerator (LIA), being developed by collaboration of Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia, and Russian Federal Nuclear Center—Zababakhin All-Russia Research Institute of Technical Physics (RFNC-VNIITF). The main results of the work are the calculated trajectories of the beam electrons, the shape of its cross section, as well as the change in the normalized emittance of the beam as it passes through the region of the bend magnet. It was shown that at typical beam parameters—electron energy of 20 MeV, beam current of 2 kA, and beam radius of 2 cm—the emittance of a high-current relativistic electron beam with uniform current and charge densities after the bend element is determined mostly by the magnet aberrations and much less by the beam self-fields. Optimization of the dipole magnet geometry made it possible to achieve a substantial decrease in the beam emittance with geometric expansion of the magnet in the median plane of the beam.

Effect of ionic liquid electrolytes on the electrochemical stability and optical tunability of polyaniline-based infrared variable emittance devices

In this study, ionic liquids (ILs) are used instead of conventional volatile aqueous or organic electrolytes to fabricate durable polyaniline (PANI)-based infrared variable emittance devices (IR-VEDs). It is of significance to find that different IL electrolyte systems have a great effect on the electrochemical stability and IR tunability of the PANI films. The present PANI films exhibit much better electrochemical stability when cycling in ILs having tetrafluoroborate and bis(trifluoromethylsulfonyl)imide anions than cycling in ILs with dicyanamide and tricyanomethanide anions. Furthermore, compared with pure IL electrolytes, the addition of high-mobility cations (Li+) into ILs can significantly enhance the IR tunability of PANI films. The IR-VED based on a preferable ionogel electrolyte membrane exhibits a high emittance variation (Δԑ) of 0.42 in 2.5–25 µm region, and fast switching times of 14.6 s/17.0 s. More importantly, the device still maintains a high Δԑ value of 0.35 after 500 electrochemical cycles, demonstrating promising applications in the dynamic IR regulation field.

Thermal Emittance of $$\hbox {La}_{0.7}\hbox {Ca}_{0.3-x}\hbox {K}_x\hbox {MnO}_3$$ La 0.7 Ca 0.3 - x K x MnO 3 Coatings on Aluminum Substrate

A novel thermal control coating was presented based on the thermochromism of manganite. The pigment of K-doped manganite nanoparticles was dispersed into polymer matrix to prepare the coating with curing below 200 $$^{\circ }$$ C. The nanoparticles size mainly distributes around 100–200 nm, and it shows a comparable stoichiometric ratio. The phase transition of the nanoparticles was observed from ferromagnetic metallic to paramagnetic insulator state. With increasing K doping level, the phase transition temperature increases, achieving controllable adjustment. Coating surface with and without pore defect was obtained by different polymer matrix. A sharp emittance variation was observed with increasing temperature in K-doped coating. The variation magnitude of emittance is up to 0.46, which is attractive to space thermal control. It is suggested that the pigment content of 50 wt% is sufficient to realize a large emittance variation.

Variable emittance behavior of smart radiative coating

Smart radiative coating on yttria stabilized zirconia (YSZ) substrate was prepared by the sol-gel LaSrxMnO3 (x = 0.125, 0.175 and 0.2) nanoparticles and the binder composed of terpineol and ethyl cellulose. The crystallized structure, grain size, chemical compositions, magnetization and the surface morphology were characterized. The thermal radiative properties of coating in the infrared range was evaluated from infrared reflectance spectra at various temperatures. A single perovskite structure is detected in sol-gel nanoparticles with size 200 nm. Magnetization measurement reveals that room temperature phase transition samples can be obtained by appropriate Sr substitution. The influence of surface conditions and sintering temperature on the emittance of coating was observed. For rough coatings with root-mean-square roughness 640 nm (x = 0.125) and 800 nm (x = 0.175) , its emittance increment is 0.24 and 0.26 in in the temperature range of 173–373 K. Increasing sintering temperature to 1673 K, coating emittance variation improves to 0.3 and 0.302 respectively. After mechanical polishing treatment, the emittance increment of coatings are enhanced to 0.31 and 0.3, respectively. The results suggested that the emittance variation can be enhanced by reducing surface roughness and increasing sintering temperature of coating.

Rf-induced beam dynamics in rf guns and accelerating cavities

In this paper, a detailed discussion of the rf-related beam dynamics in rf guns and accelerating cavities is presented. Other rf-gun-related aspects such as space charge and cathode physics are not treated. An effective start phase is introduced in order to yield a better description for the synchronous phase, the energy gain, and the bunch compression factor in gun cavities. Energy spread and longitudinal emittance are treated in a form applicable to guns as well as to accelerating cavities. Discussions on the transverse emittance include the chromatic emittance variation at high emission phases and effects of field asymmetries and combined solenoid-cavity sections.

Optimization of Thermal Emittance Tuneability of La (Sr, Ca)MnO<sub>3</sub> Thin-Film Materials in 173-373 K

For the purpose of maximizing the thermal emittance variation of La (Sr, Ca) MnO3 thin films in the temperature range 173-373 K, thin film optical mechanism and mathematical optimization method were used to determine the thin film structure, including substrate type, thin film chemical composition and the optimized film thickness. The optimization results indicate the variation amplitude of La (Sr, Ca) film infrared emittance reaches to 0.62, which is 35% more than that of ceramic type smart radiation materials. The designed thin film structure can be used to enhance the thermal control efficiency of spacecraft greatly.

Thermoelastic analysis of a bearing-cage weld seam

This manuscript discusses the implementation of a thermo-elastic setup and analysis, to monitor and record the stress levels at the weld-seam of a bearing-cage, under different loadings. The setup includes a high speed, ultra sensitive infrared focal plane array and in-house developed pre and post-processing codes. The pre-processing neutralizes the emittance variation with the cage geometry using new mapping scheme, while the post-processor creates spatial neighbourhoods to average the stress signal and reduce the detector and the environment noise; also the algorithm checks for the adiabatic conditions through the synchronicity between the load cyclic frequency and that of the temperature differentials. The thermo-elastic investigation is done at different loadings from 20 - 140 Lbf at a frequency of 10 Hz, in two modes: a calibration mode with the weld-seam located at 9 o'clock position and a detailed mode with the weld-seam at 6 o'clock location. A Finite Element FE simulation is used to adjust the thermo-elastic constant using the calibration trials (weld at 9 o'clock). The detailed trials (weld at 6 o'clock) are then compared with the FE simulation, showing good agreement in predicting the stress values and maps. The proposed hardware and software map the stresses 3 dimensionally for the weld region with a 25 MPa resolution, in real-time and is found to resolve stress changes for each 20 Lbf loading.

Performance simulation and design of the magnetic bunch compressor for the infrared free-electron laser at the Pohang light source test linac

A chicane bunch compressor was designed for the infrared free-electron laser project at the Pohang Light Source test linac. The bunch compressor has triplet quadrupoles before and after the chicane to obtain a transversely uncorrelated beam at the center of the bunch compressor. In this paper, we describe the design considerations of the chicane that provides a compression from 3 ps rms to 250 fs rms a beam energy of 100 MeV . Simulations provide predictions of emittance variation with the chicane parameters and the linac RF phase in the precompressor. The simulations also indicate that the normalized emittance in the designed bunch compressor increases from 5 mm mrad to about 5.5 mm mrad.

Conducting Polymer (CP) infrared electrochromics in spacecraft thermal control and military applications

The implementation of advanced CP-based far-IR electrochromics in an actual spacecraft (NASA's ST5 mission to be launched 2003) and defense(IR-homingmissile countermeasure)application is described. For spacecraft thermal control, the modification of fundamental CP properties and innovative device design required to pass the rigors of space (e.g. 10 -7 Torr, +/- 90 °C, high radiation, p/e and atomic-O fluxes, ESD/EMP) while meeting the minimum performance(Emittance variation of 0.42) are described. Space qualification test results presented show the surprising versatility of CPs. For the military application, detailed data, in the form of IR camera pictures, are presented. These encompass a variety of environments (e.g. foliage, sand, water, sky, snow) and modes (e.g. total darkness, heat from behind, front, cooling from behind) These show excellent IR camouflage performance under all conditions.

Large, Switchable Electrochromism in the Visible Through Far-Infrared in Conducting Polymer Devices

Advanced materials with large and dynamic variation in thermal properties, sought for urgent defense and space applications, have heretofore been elusive. Conducting polymers (CPs) have shown some intrinsic variation of mid- to far-infrared (IR) signature in this respect, but the practical utilization of this has remained elusive. We report herein the first significant IR electrochromism in any material, to our knowledge, in the 0.4 through 45 μm region. This is seen in practical CP devices in the form of thin (<0.5 mm), flexible, entirely solid-state, variable area (1 cm2 to 1 m2) flat panels. Typical properties include: very high reflectance variation; switching times <2 s; cyclabilities of 105 cycles; emittance variation from 0.32 to 0.79; solar absorptance variation from 0.39 to 0.79; operating temperatures of –35 to +85 °C; durability against γ-radiation to 7.6 Mrad, vacuum to 10–6 torr, and simulated solar wind (e.g., 6.5 × 1016 e/cm2 @ 10 keV).

Design and performance simulations of the bunch compressor for the Advanced Photon Source Low-Energy Undulator Test Line free-electron laser

A magnetic bunch compressor was designed and commissioned to provide higher peak current for the Advanced Photon Source's Low-Energy Undulator Test Line free-electron laser [S. V. Milton et al., Phys. Rev. Lett. 85, 988 (2000)]. Of great concern is limiting emittance growth due to coherent synchrotron radiation. Tolerances must also be carefully evaluated to find stable operating conditions and ensure that the system can meet operational goals. Automated matching and tolerance simulations allowed consideration of numerous configurations, pinpointing those with reduced error sensitivity. Simulations indicate significant emittance growth up to 600 A peak current, for which the normalized emittance will increase from 5 to about $8.5\ensuremath{\mu}\mathrm{m}$. The simulations also provide predictions of emittance variation with chicane parameters and precompressor linac phase, which we hope to verify experimentally.

Performance of SRRC 1.3 GeV electron booster synchrotron

The characteristics and the performance of SRRC 1.3 GeV electron booster synchrotron are described in this report. Operation parameters, such as synchrotron tune, betatron tune, momentum compaction factor, betatron function, chromaticity etc. were measured at injection energy, 50 MeV, DC mode; and compared with calculated results at a tune of v x = 4.40, v y = 2.43. The tune drift and the bunch length variation of accelerated beam have been studied. The energy spread and the beam emittance variation during ramping were derived. The diagnostics instrumentation used in this experiment was described. Comparison between experimental results and theoretical expectations is presented.