Free Electron Research Articles

Collection efficiencies of cylindrical and plane parallel ionization chambers: analytical and numerical results and implications for experimentally determined correction factors

Objectives. To derive a collection efficiency formula, fGauss , for cylindrical ionization chambers in pulsed radiation beams from a volume recombination model of Boag et al (1996 Phys. Med. Biol. 41 885–97) including free electrons. To validate fGauss and a parallel plate chamber formula fexp using an ion transport code and calculate changes in collection efficiencies caused by electric field charge screening at 0.1–100 mGy doses-per-pulse. And to determine collection efficiencies CE∞ predicted at infinite voltage in the absence of avalanche effects by fitting scaled formulae to efficiencies computed for 100–400 V chamber voltages and 10 and 100 mGy doses-per-pulse. Approach. Calculations were performed for an idealized parallel plate chamber with 2 mm electrode separation d , and for an idealized cylindrical chamber with 0.5 and 2.333 mm inner and electrode radii rin and rout . Main results. fGauss and fexp predict the same collection efficiencies for cylindrical and parallel plate chambers satisfying d2=(rout2−rin2)ln(rout/rin)/2 , an equivalence condition met by the chambers studied. Without charge screening, efficiencies computed using the code equalled fGauss and fexp . With screening, efficiencies changed by ⩽0.03%, ⩽1.1% and ⩽21.3% at 1, 10 and 100 mGy doses-per-pulse, and differed between the chambers by ⩽0.9% and ⩽19.6% at ⩽10 and 100 mGy dose-per-pulse. For fits of fexp and fGauss , CE∞ values were ⩽1.2% and ⩽17.6% from unity at 10 and 100 mGy per pulse respectively, closer than for other formulae tested. Significance. Allowing for screening, fGauss and fexp described computed collection efficiencies to within 0.03%, 1.1% and 21.3% at doses-per-pulse ⩽1, 10 and 100 mGy. Equivalence of the two chambers broke down at 100 mGy per pulse. Departures of CE∞ values from unity suggest that collection efficiencies determined experimentally by fitting fGauss or fexp to readings made at multiple voltages will be accurate to within 1.2% and 17.6% at 10 and 100 mGy per pulse respectively.

Cryogenic system of the high performance 1.3 GHz 9-cell superconducting radio frequency prototype cryomodule

High quality factor 1.3 GHz 9-cell superconducting radio frequency (SRF) cavity cryomodule is the core technology of the international advanced accelerator. China’s first high-quality factor 1.3 GHz 9-cell SRF cavity cryomodule was developed, assembled and tested at the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences for the Dalian Advanced Light Source (DALS) and Circular Electron Positron Collider (CEPC) R&D. The 9-cell cavities in the cryomodule achieved a high average intrinsic quality factor (Q0) of 3.8 × 1010 at 16 MV/m and 3.6 × 1010 at 21 MV/m in the horizontal test. With such high specifications, the SRF cavity system has corresponding requirements for the cryogenic system. Key criteria for stable and reliable operation include a dependable cryogenic refrigeration system and process design, good thermal insulation, pressure control, temperature uniformity, and quench protection, etc. IHEP has successfully completed cryogenic testing development of the first 1.3 GHz 9-cell SRF prototype cryomodule. The whole cooldown period was 74 h, and the automatic cooldown was completed. The successful development and implementation of the 1.3 GHz superconducting cryomodule cryogenic system will provide a stable and reliable test environment for advanced superconducting cavity cryogenic testing, which will be critical in promoting the further development of the Free Electron Laser (FEL) and CEPC projects.

Metallic Degenerately Doped Free-Electron-Confined Plasmonic Nanocrystal and Infrared Extinction Response

In this paper, synthetically scaled-up degenerately n-type doped indium tin oxide (Sn:In2O3) nanocrystals are described as highly transparent conductive materials possessing both optoelectronic and crystalline properties. With tin dopants serving as n-type semiconductor materials, they can generate free-electron carriers. These free electrons, vibrating in resonance with infrared radiation, induce strong localized surface plasmon resonance (LSPR), resulting in efficient infrared absorption. To commercialize products featuring Sn:In2O3 with localized surface plasmon resonance, a scaled-up synthetic process is essential. To reduce the cost of raw materials during synthesis, we aim to proceed with synthesis in a large reactor using industrial raw materials. Sn:In2O3 can be formulated into ink dispersed in solvents. Infrared-absorbing ink formulations can capitalize on their infrared absorption properties to render opaque in the infrared spectrum while remaining transparent in the visible light spectrum. The ink can serve as a security ink material visible only through infrared cameras and as a paint absorbing infrared light. We verified the transparency and infrared absorption properties of the ink produced in this study, demonstrating consistent characteristics in scaled-up synthesis. Due to potential applications requiring infrared absorption properties, it holds significant promise as a robust platform material in various fields.

Efficient removal of tetracycline antibiotic by nonthermal plasma-catalysis combination process

This study presents an innovative approach to plasma catalysis by employing nonthermal plasma type gliding arc with various iron oxides -Fe(II), Fe(III) and Ferrate Fe(VI)- for the removal of tetracycline antibiotic (TC). The experimental results demonstrated significant improvements in degradation rates, with plasma-Fe(VI) achieving complete degradation after 15 min of treatment and the plasma-Fe(II) achieving 97.28% removal after 30 min. The effect of TC initial concentration and catalyst dose was investigated, revealing that lower TC concentration favored the degradation and shortened treatment times with even a minimum amount of catalyst doses enhancing degradation results. Higher total organic carbon (TOC) removal was achieved in the combination systems (83.01%; 82.07%; and 42.82% for plasma/Fe(VI); plasma/Fe(II); and plasma /Fe(III) respectively) compared to plasma alone barely achieved 25.67% of mineralization. Additionally, the study examined the role of various radical scavengers-targeting <sup>•</sup>OH, superoxide, and free electrons- in the degradation process. TC intermediates were also identified, degradation pathways were proposed, and the intermediates toxicity was assessed. This research contributes to a deeper understanding of organic compounds treatment using nonthermal plasma, combination with the ferrate process or other catalysts.

MXene Supported Surface Plasmon Polaritons for Optical Microfiber Ammonia Sensing.

The properties of surface plasmons are notoriously dependent on the supporting materials system. However, new capabilities cannot be obtained until the technique of surface plasmon enabled by advanced two-dimensional materials is well understood. Herein, we present the experimental demonstration of surface plasmon polaritons (SPPs) supported by single-layered MXene flakes (Ti3C2Tx) coating on an optical microfiber and its application as an ammonia gas sensor. Enabled by its high controllability of chemical composition, unique atomistically thin layered structure, and metallic-level conductivity, MXene is capable of supporting not only plasmon resonances across a wide range of wavelengths but also a selective sensing mechanism through frequency modulation. Theoretical modeling and optics experiments reveal that, upon adsorbing ammonia molecules, the free electron motion at the interface between the SiO2 microfiber and the MXene coating is modulated (i.e., the modulation of the SPPs under applied light), thus inducing a variation in the evanescent field. Consequently, a wavelength shift is produced, effectively realizing a selective and highly sensitive ammonia sensor with a 100 ppm detection limit. The MXene supported SPPs open a promising path for the application of advanced optical techniques toward gas and chemical analysis.

Enhanced electrical insulation properties of 2-isopropenyl-2-oxazoline grafted polypropylene for high voltage direct current power cables

Polymers have been extensively used for high voltage direct current transmission systems as insulation power cables. Space charge accumulation consistently remains the primary factor contributing to the degradation of the electrical insulation properties of polymers. Grafting modification is a valid approach for suppressing the injection of space charges and free electrons by inducing deep traps. In this paper, the modified polypropylene grafted the group with low ionization energy is reported. The deep traps are revealed by the thermally stimulated depolarization current experiment and the band structure as well as the electrostatic potential by density functional theory simulation. The method with the innovative hybrid functional and basis set is adopted to establish the average local ionization distribution of the grafting group, thus confirming its strong electrophilicity. Furthermore, the modified polypropylene has been proved to obtain higher breakdown strength and operational stability by experiments. This work can provide insights for the design and selection of power cables with excellent electrical insulation properties.

Investigating structural property of human hair by using infrared free electron lasers

Intense infrared (IR) rays can heat matters and evaporate waters thermally. One of the possible applications will be hair dryer, although the irradiation effects of IR rays on the hair have not been fully explored. In this study, we first examined the interaction of IR rays at various wavelengths from 3.0 µm (near IR) to 90 µm (far IR) with the surface structure of human hair by using IR free electron lasers (FELs). IR-FEL is an accelerator-based pico-second pulse laser, and the feature is the wavelength-tunability with the high-photon density. When one thread of hair was irradiated by the FEL of 6–7 mJ energy at 60 µm, the cleavage occurred, and the morphological destruction was observed on scanning-electron microscopy images after the irradiations at 70 µm and 6.1 µm (amide I). Synchrotron-radiation infrared microspectroscopy showed that those FEL irradiations decreased a shoulder band at 1710 cm−1 that corresponds to carboxyl group in melanin or fatty acids and increased absorption intensity at 500–600 cm−1. On the contrary, the FEL at 90 µm little changed either the surface morphology or the infrared absorption spectra. Interestingly, near-IR FELs at 3.0–3.5 µm induced bending of a hair, and 2D mapping of protein secondary conformations revealed that β-sheet was more increased than the other conformations on the surface of the bending area even at low pulse energy (1–3 mJ). As a result, the structural damage of the hair was least at 90 µm, which implies an ideal wavelength for drying hair mildly.

Biochar, microbes, and biochar-microbe synergistic treatment of chlorinated hydrocarbons in groundwater: a review.

Dehalogenating bacteria are still deficient when targeted to deal with chlorinated hydrocarbons (CHCs) contamination: e.g., slow metabolic rates, limited substrate range, formation of toxic intermediates. To enhance its dechlorination capacity, biochar and its composites with appropriate surface activity and biocompatibility are selected for coupled dechlorination. Because of its special surface physical and chemical properties, it promotes biofilm formation by dehalogenating bacteria on its surface and improves the living environment for dehalogenating bacteria. Next, biochar and its composites provide active sites for the removal of CHCs through adsorption, activation and catalysis. These sites can be specific metal centers, functional groups or structural defects. Under microbial mediation, these sites can undergo activation and catalytic cycles, thereby increasing dechlorination efficiency. However, there is a lack of systematic understanding of the mechanisms of dechlorination in biogenic and abiogenic systems based on biochar. Therefore, this article comprehensively summarizes the recent research progress of biochar and its composites as a "Taiwan balm" for the degradation of CHCs in terms of adsorption, catalysis, improvement of microbial community structure and promotion of degradation and metabolism of CHCs. The removal efficiency, influencing factors and reaction mechanism of the degraded CHCs were also discussed. The following conclusions were drawn, in the pure biochar system, the CHCs are fixed to its surface by adsorption through chemical bonds on its surface; the biochar composite material relies on persistent free radicals and electron shuttle mechanisms to react with CHCs, disrupting their molecular structure and reducing them; biochar-coupled microorganisms reduce CHCs primarily by forming an "electron shuttle bridge" between biological and non-biological organisms. Finally, the experimental directions to be carried out in the future are suggested to explore the optimal solution to improve the treatment efficiency of CHCs in water.

High performance one-step grown half-moon shaped YBCO bulk superconductors

High-temperature superconducting (HTS) undulator exploiting the high trapped field of HTS bulk superconductors enables the design of extremely short-period insertion devices for synchrotron light sources and free electron lasers. In such a promising application the trapped field performance and the uniformity of the HTS bulk superconductors are essential. In this study, the half-moon shaped YBa2Cu3O7−δ (YBCO) single-grain superconductors have been directly grown by the top-seeded melted-growth method. Half-moon shaped samples directly grown from preforms with four different type of seed crystal arrangements were compared with that cut from larger cylindrical bulk superconductors in regarding to the trapped magnetic fields and correspondingly the distribution. We found that the arrangement of seed crystals greatly affects the melt-growth process and hence the homogeneity of the samples. The one-step grown half-moon shaped samples show higher trapped field (B trap), 0.542 T for a 24 mm and 0.785 T for a 32 mm diameter sample, and better uniformity of trapped field distribution compared to that obtained from machining with B trap of 0.427 T and 0.528 T. It was found that the growth sectors would be restricted when the seed crystal was placed at the edge of a preform, and the angle of the seed crystal, parallel or 45° to the long edge would influence the melt growth as well.

Singular dielectricnanolaser with atomic-scale field localization.

Compressing the optical field to the atomic scale opens up possibilities for directly observing individual molecules, offering innovative imaging and research tools for both physical and life sciences. However, the diffraction limit imposes a fundamental constraint on how much the optical field can be compressed, based on the achievable photon momentum1,2. In contrast to dielectric structures, plasmonics offer superior field confinement by coupling the light field with the oscillations of free electrons in metals3-6. Nevertheless, plasmonics suffer from inherent ohmic loss, leading to heat generation, increased power consumption and limitations on the coherence time of plasmonic devices7,8. Here we propose and demonstrate singular dielectric nanolasers showing a mode volume that breaks the optical diffraction limit. Derived from Maxwell's equations, we discover that the electric-field singularity sustained in a dielectric bowtie nanoantenna originates from divergence of momentum. The singular dielectric nanolaser is constructed by integrating a dielectric bowtie nanoantenna into the centre of a twisted lattice nanocavity. The synergistic integration surpasses the diffraction limit, enabling the singular dielectricnanolaser to achieve an ultrasmall mode volume of about 0.0005 λ3 (λ, free-space wavelength), along with an exceptionally small feature size at the 1-nanometre scale. To fabricate the required dielectric bowtie nanoantenna with a single-nanometre gap, we develop a two-step process involving etching and atomic deposition. Our research showcases the ability to achieve atomic-scale field localization in laser devices, paving the way for ultra-precise measurements, super-resolution imaging, ultra-efficient computing and communication, and the exploration of light-matter interactions within the realm of extreme optical field localization.

Structure Function Studies of Photosystem II Using X-Ray Free Electron Lasers.

The structure and mechanism of the water-oxidation chemistry that occurs in photosystem II have been subjects of great interest. The advent of X-ray free electron lasers allowed the determination of structures of the stable intermediate states and of steps in the transitions between these intermediate states, bringing a new perspective to this field. The room-temperature structures collected as the photosynthetic water oxidation reaction proceeds in real time have provided important novel insights into the structural changes and the mechanism of the water oxidation reaction. The time-resolved measurements have also given us a view of how this reaction-which involves multielectron, multiproton processes-is facilitated by the interaction of the ligands and the protein residues in the oxygen-evolving complex. These structures have also provided a picture of the dynamics occurring in the channels within photosystem II that are involved in the transport of the substrate water to the catalytic center and protons to the bulk.

Glycyrrhetinic acid interaction with solvated and free electrons studied by the CIDNP and dissociative electron attachment techniques.

Electron transfer plays a crucial role in living systems, including the generation of reactive oxygen species (ROS). Oxygen acts as the terminal electron acceptor in the respiratory chains of aerobic organisms as well as in some photoinduced processes followed by the formation of ROS. This is why the participation of exogenous antioxidants in electron transfer processes in living systems is of particular interest. In the present study, using chemically induced dynamic nuclear polarization (CIDNP) and dissociative electron attachment (DEA) techniques, we have elucidated the affinity of solvated and free electrons to glycyrrhetinic acid (GA)-the aglicon of glycyrrhizin (the main active component of Licorice root). CIDNP is a powerful instrument to study the mechanisms of electron transfer reactions in solution, but the DEA technique shows its effectiveness in gas phase processes. For CIDNP experiments, the photoionization of the dianion of 5-sulfosalicylic acid (HSSA2-) was used as a model reaction of solvated electron generation. DEA experiments testify that GA molecules are even better electron acceptors than molecular oxygen, at least under gas-phase conditions. In addition, the effect of the solvent on the energetics of the reactants is discussed.

Mixed Crystalline Covalent Heptazine Frameworks with Built-in Heterojunction Structures towards Efficient Photocatalytic Formic Acid Dehydrogenation.

Covalent heptazine frameworks (CHFs) are widely utilized in the recent years as potential photocatalysts. However, their limited conjugated structures, low crystallinity and small surface areas have restricted the practical photocatalysis performance. Along this line, we report herein the synthesis of a kind of mixed crystalline CHF (m-CHF-1) with built-in heterojunction structure, which can efficiently catalyze the formic acid dehydrogenation by visible light driven photocatalysis. The m-CHF-1 is synthesized from 2,5,8-triamino-heptazine and dicyanobenzene (DCB) in the molten salts, in which DCB plays as organic molten co-solvent to promote the rapid and ordered polymerization of 2,5,8-triamino-heptazine. The m-CHF-1 is formed by embedding phenyl-linked heptazine (CHF-Ph) units in the poly(heptazine imide) (PHI) network similar to doping. The CHF-Ph combined with PHI form an effective type II heterojunction structure, which promote the directional transfer of charge carriers. And the integration of CHF-Ph makes m-CHF-1 have smaller exciton binding energy than pure PHI, the charge carriers are more easily dissociated to form free electrons, resulting in higher utilization efficiency of the carriers. The largest hydrogen evolution rate reaches a value of 42.86 mmol h-1 g-1 with a high apparent quantum yield of 24.6 % at 420 nm, which surpasses the majority of other organic photocatalysts.

An analytical model to ascertain A.C. electrical conductivity of metal matrix composites

ABSTRACT With regard to an inherent understanding of electrical conductivity exhibited by monolithic metals and alloys system and metal matrix composite system under alternating current field, a long-standing unresolved issue, an analytical model is developed following classical free electron theory along with a typical conceptualisation of ‘effective relaxation time’ that combines conventional relaxation time (in view of collision of free electrons with lattice defects) and the time between successive cyclic reversals of electric field (the inverse of frequency). Two prime phenomena (electron scattering and polarisation at particle–matrix interface) are further conceived for metal matrix composite system containing particles. The developed model is found to closely follow (% deviation << 10) the available experimental result in the literature on A.C. electrical conductivity of 6063Al alloy and 6063Al–TiO2 composite systems. The model further ascertains certain system-specific parameters; such as, relaxation time under A.C. field, effective scattering factor and effective relaxation time aid from interface polarisation to specify the system behaviour under alternating current field. Accordingly, the model adequately explains the declining trend of A.C. electrical conductivity with increasing frequency in monolithic alloy system and an enhancement of A.C. electrical conductivity in metal matrix composite system in the presence of particles together with a non-declining trend even on increasing frequency.

Free electrons spin-dependent Kapitza–Dirac effect in two-dimensional triangular optical lattice

Abstract The free electron spin dynamics in Kapitza–Dirac (KD) effect had been studied theoretically in one-dimensional standing wave of EUV to X-ray laser with extremely high intensity, which is far beyond experimental realization. Here, we propose to achieve the free electron spin-dependent KD effect in two-dimensional triangular optical lattice with spatial inversion symmetry breaking, and the theoretical results reveal that laser with wavelength in visible or near-IR and five orders of magnitude decreased intensity could lead to obvious spin-dependent KD effect. This work provides the way to realize the free electron spin-dependent KD effect experimentally.

Structured electrons with chiral mass and charge.

Chirality is a phenomenon with widespread relevance in fundamental physics, material science, chemistry, optics, and spectroscopy. In this work, we show that a free electron can be converted by the field cycles of laser light into a right-handed or left-handed coil of mass and charge. In contrast to phase-vortex beams, our electrons maintained a flat de Broglie wave but obtained their chirality from the shape of their expectation value in space and time. Measurements of wave function densities by attosecond gating revealed the three-dimensional shape of coils and double coils with left-handed or right-handed pitch. Engineered elementary particles with such or related chiral geometries should be useful for applications in chiral sensing, free-electron quantum optics, particle physics or electron microscopy.

Wavelength scaling and multicolor operation of a plasma-driven attosecond x-ray source via harmonic generation

The generation of high-power coherent soft x-ray pulses of sub-100 as duration and 10 nm wavelength using beams from a GeV energy plasma wakefield accelerator has been recently investigated in Emma []. As a future upgrade to this concept, this contribution investigates scaling to shorter x-ray wavelengths by cascading undulators tuned to higher harmonics of the fundamental. We present two simulation studies for plasma-driven attosecond harmonic generation schemes with final photon wavelengths of 2 and 0.40 nm. We demonstrate in these schemes that using undulators with retuned fundamental frequencies can produce GW-scale pulses of sub-nm radiation with tens of attosecond-scale pulse lengths, an order of magnitude shorter than current state-of-the-art attosecond x-ray free electron lasers (XFELs). This multipulse multicolor operation will be broadly applicable to attosecond pump-probe experiments. Published by the American Physical Society 2024

Evolution of level population in Ar interacting with XFEL pulses: impact of resonant absorptions

Theoretical exploration of the population dynamics at fine-structure levels of Ar atoms interacting with ultrafast ultraintense x-ray free electron laser (XFEL) pulses is conducted. A time-dependent rate equation based on a detailed-level accounting approach is applied for tracking population levels, encompassing microscopic atomic processes such as photoexcitation, radiative decay, photoionization and Auger decay. A Monte Carlo algorithm is implemented to solve large-scale rate equations efficiently. The primary investigation centers on generating Ar17+ through resonant absorption by the second-harmonic radiation of the x-ray pulse. The calculated population ratios of Ar17+ to Ar16+ align well with the experimental measurements (LaForge et al 2021 Phys. Rev. Lett. 127 213202). In comparison to the transition energy of the strongest line, (1s2)0→(1s1/22p3/2)1 of Ar16+, there is a distinct ∼25 eV red shift in the peak ratio, which is attributed to the presence of intricate resonant channels in the lower ionization stages. The results demonstrate the sensitivity of the population ratio Ar17+/Ar16+ to the laser pulse parameters such as x-ray pulse duration, bandwidth and the contribution of second-harmonic radiation, indicating their potential as diagnostic tools in future experiments.

Empirical orthogonal function based modelling of ionosphere using Turkish GNSS network

The study investigates ionospheric total electron content (TEC) variation over Turkey from the five selected global navigation satellite system (GNSS) stations situated in diverse parts of Turkey. The geomagnetic indices are used and observed TEC are modeled with the technique known as Empirical orthogonal function (EOF). It is valuable to note that the correlation coefficient between observed GNSS TEC values and EOF TEC values varies from 0.8020 to 0.9394. The root means square error (RMSE) values between observed GNSS TEC values and EOF TEC lie between 3.1665 TECU to 4.4220 TECU. These results show that the EOF model performs quite well in the Turkish region and can present the model TEC variations perfectly. Finally, these GNSS observed and EOF-predicted TEC values along with geomagnetic indices are studied with the tropospheric wind speed. The results showed that both observed and modeled TEC have very low correlations with tropospheric wind speed and do not provide any significant value. Hence, we concluded that the ionospheric region is not affected by tropospheric wind speed. It happens because the tropospheric wind speed is a matter of the lower troposphere and its atmospheric pressure while the ionosphere is far from the earth and depends upon the number of free electrons.

Enhancement of gasochromic response to hydrogen of WO3 thin films by post-process modification and catalyst selection

The gasochromic properties of WO3 thin films deposited by electron beam evaporation were investigated, focusing on their structural, morphology and optical changes caused by heat treatment. Moreover, the influence of the thickness and type of catalyst on the gasochromic properties of WO3 was examined. X-ray diffraction measurements revealed that WO3 thin films annealed up to 473 K remained amorphous, whereas annealing at 673 K and above, initiated crystallization into a monoclinic structure. Gasochromic behaviour was observed in response to hydrogen exposure, with the most significant changes occurring in films annealed at 673 K with a thin adlayer of palladium catalyst. A gasochromic response of 1.84 was achieved for H2 concentration as low as 25 ppm. The process of gasochromic colouration was correlated with the changes of free charge carrier concentration calculated based on Drude free electron theory. XPS analysis confirms WO3 reduction under hydrogen exposure, validating proposed colouration mechanisms. These comprehensive findings offer insights into optimizing gasochromic thin films for various sensing applications.