Decreasing Electron Energy Research Articles

The Influence of Humidity on Electron Transport Parameters and Insulation Performance of Air

The environmental conditions affect the external insulation performance of power equipment. In order to study the physical characteristics of air discharge, the microscopic process of electron–molecule collision in the air based on the Boltzmann equation has been studied in this paper. The influence of humidity on the air gap insulation performance was also analyzed. The calculation results show that with the temperature 300 K and the pressure 1.0 atm, the electron energy distribution function and electron transport parameters varied with the air relative humidity. As the air relative humidity is increased by each 30%, the average electron energy decreases by about 0.2 eV, the reduced electron mobility decreases by about 0.25 × 1023 [1/(V·m·s)], the reduced electron diffusion coefficient decreases by about 0.2 × 1024 [1/(m s)], and the effective ionization coefficient decreases by about 4 × 10−24 m2. As the air relative humidity increases from 0% to 60%, the critical breakdown electric field increases by 1.22 kV/cm.

Record high extraction efficiency of free electron laser oscillator

The highest extraction efficiency (9.4%) of a free electron laser (FEL) oscillator has been achieved at the midinfrared FEL facility of Kyoto University. Because of the interaction between the electron beam and FEL electromagnetic field, a maximum electron energy decrease of 16% was observed. The measured energy decrease was consistent with the measured FEL spectrum. An FEL micropulse energy of ∼100 μJ with the expected few-cycle pulse duration at a wavelength of 11 μm was observed. This result is an important milestone for the high-extraction-efficiency FEL oscillator and will contribute to the strong-field physics of atoms and molecules.

Nonlinear Interactions between Free Electrons and Nanographenes.

Free electrons act as a source of highly confined, spectrally broad optical fields that are widely used to map photonic modes with nanometer/millielectronvolt space/energy resolution through currently available electron energy-loss and cathodoluminescence spectroscopies. These techniques are understood as probes of the linear optical response, while nonlinear dynamics has escaped observation with similar degree of spatial detail, despite the strong enhancement of the electron evanescent field with decreasing electron energy. Here, we show that the field accompanying low-energy electrons can trigger anharmonic response in strongly nonlinear materials. Specifically, through realistic quantum-mechanical simulations, we find that the interaction between ≲100 eV electrons and plasmons in graphene nanostructures gives rise to substantial optical nonlinearities that are discernible as saturation and spectral shifts in the plasmonic features revealed in the cathodoluminescence emission and electron energy-loss spectra. Our results support the use of low-energy electron-beam spectroscopies for the exploration of nonlinear optical processes in nanostructures.

A Numerical Investigation on the Reactive Species Generation and Its Correlation With Electron Energy in Atmospheric-Pressure Helium/Humid Air Plasma Jets

In this work, the reactive species generation and its correlation with electron energy in atmospheric-pressure helium/humid air plasma jets have been numerically investigated based on a needle-plane electrode geometry by using a 2-D fluid model. With the increase in the voltage amplitude, the averaged electron energy increases, the respective averaged densities of OH, O(1D), and O− increase, while the averaged H2O2 density decreases. Therefore, between the species generation and electron energy, there is a negative correlation for H2O2 and a positive correlation for OH, O(1D), and O−. In addition, as the humid air concentration increases, the averaged electron energy decreases, but the respective averaged densities of OH, O(1D), O−, and H2O2 increase. Consequently, there is a negative correlation between these species generations and electron energy. Finally, this work shows that a proper high humid air concentration in the plasma jets applied for biomedicine may allow expected electron energy and also generate abundant reactive species.

Pathways in the molecular fragmentation for the C2H5OH/He electrical discharge

ABSTRACTThis study focuses on the glow discharge generated with a gases mixture of Ethanol (C2H5OH) and Helium (He), at different concentrations maintained at a total pressure of 2.0 Torr. We used optical emission spectroscopy (OES) to analyze the discharge mixture at different concentrations of Helium. Single Langmuir probe data was used to determine the Electron Energy Distribution Function (EEDF). For the total C2H5OH/He mixture plasma concentrations, the EEDF has a Maxwellian distribution function. A decrease in He concentration results in significant changes in the EEDF, this behavior is related to the increase in the C2H5OH percentage must increase the energy loses of the electrons in the inelastic collision with C2H5OH producing a significant change in the EEDF, therefore, the EEDF pattern results in an increase of electron–molecule reaction rates. The rise in electron temperature for increasing Helium percentage is explained by the decreasing electron energy loss in the inelastic collisions with C2H5OH molecule. It observes a decrease of electron density ne as a function of the Helium percentage, which can be related to the ratio between ionization cross sections of Helium and C2H6O molecule. The active species are generated in the electron-molecule processes, which are associated with electron impact dissociation of C2H5OH and Helium electronic impact excitation in the gas phase. The emission optical spectra (OES) show changes in the intensity of the most important peaks of the plasma mixture, which indicates the dependence in the formation of the plasma as a function of the percentage of the gases. The changes in the intensities of the same observed species are due to different processes of excitation and ionization energies of the system, in addition to the increase of He metastable states He I. Hydrogen is the main product obtained from the decomposition of C2H5OH.

Pitch Angle Scattering of Energetic Electrons by BBFs

AbstractField line curvature scattering by the magnetic field structure associated with bursty bulk flows (BBFs) has been studied, using simulated output fields from the Lyon‐Fedder‐Mobarry global magnetohydrodynamic code for specified solar wind input. There are weak magnetic field strength (B) regions adjacent to BBFs observed in the simulations. We show that these regions can cause strong scattering where the first adiabatic invariant changes by several factors within one equatorial crossing of energetic electrons of a few kiloelectron volts when the BBFs are beyond 10RE geocentric in the tail. Scattering by BBFs decreases as they move toward the Earth or when the electron energy decreases. For radiation belt electrons near or inside geosynchronous orbit we demonstrate that the fields associated with BBFs can cause weak scattering where the fractional change of the first invariant (μ0) within one equatorial crossing is small, but the change due to several crossings can accumulate. For the weak scattering case we developed a method of calculating the pitch angle diffusion coefficient Dαα. Dαα for radiation belt electrons for one particular BBF were calculated as a function of initial energy, equatorial pitch angle, and radial location. These Dαα values were compared to calculated Dαα for a dipole field with no electric field. We further compared Dαα values with that of stretched magnetic fields calculated by Artemyev et al. (2013, https://doi.org/10.5194/angeo-31-1485-2013) at r≈7RE. Results show that scattering by BBFs can be comparable to the most highly stretched magnetic field they studied.

Monte Carlo calculation of the backscattering coefficient of thin films of low on high atomic number materials and the reverse as a function of the incident electron energy and film thickness

In this study a CASINO Monte Carlo model has been used to investigate the behavior of the backscattering coefficient (η) for C-layer deposited on Au-substrate as well as for Au-layer deposited on C-substrate as a function of top-layer thickness and primary electron energy (0.5–10 keV). As the top-layer thickness increases and primary electron energy decreases, η-values became more affected by the material of the top layer. It depends on the maximum primary electron range compared with the thickness of the deposited top layer. The backscattering coefficient of a thin C-layer deposited on Au-substrate sharply increases toward Au values as the primary electron energy increases following the C bulk values. However, in the case of a thin Au-layer deposited on C-substrate, the backscattering coefficient starts with a value of that of a pure Au and increases to reach its maximum value and then starts decreasing toward the values of the C-substrate. The minimum and the maximum on the results are shifted toward the high energies as the top-layer thickness increases. The energy distribution of the backscattered electrons emerged from a thin 5 nm C-layer deposited on Au-substrate as well as from a thin 5 nm Au-layer deposited on C-substrate has been investigated as a function of primary electron energy. The results show the dependence of the backscattered electron energy distribution as well as the η-values on the differential scattering cross section.

Electron acceleration by a circularly polarized electromagnetic wave publishing in plasma with a periodic magnetic field and an axial guide magnetic field

In this paper, we study the electron acceleration by a circularly polarized electromagnetic wave propagating through plasma in the presence of a periodic and an axial guide magnetic field. A numerical calculation in MATLAB software was developed by employing the fourth-order Runge–Kutta method for studying the electron energy and electron trajectory in plasma medium. The equations governing the electron momentum and energy which describe electron acceleration by a circularly polarized laser pulse have been obtained. It is shown that by choosing an appropriate wiggler field frequency at short distances, the electron retains an adequate amount of energy. In addition, it is found that due to the simultaneous existence of the wiggler field and field of laser pulse and their combined effects, the electron in the direction of the laser pulse propagating, turns around and subsequently, the electron transverse momentum increases and as a result the electron escapes from the laser pulse near the laser pulse peak. Furthermore, it is seen that by increasing the laser intensity, the electron energy decreases and by decreasing to an appropriate value while employing a wiggler magnetic field, a higher peak of energy is gained.

The discharge characteristics in nitrogen helicon plasma

Discharge characteristics of helicon plasma in nitrogen and argon-nitrogen mixtures were investigated experimentally by using a Langmuir probe, a B-dot probe, and an optical emission spectrum. Helicon wave discharge is confirmed by the changes of electron density and electromagnetic signal amplitude with the increasing RF power, which shows three discharge stages in nitrogen, corresponding to E-mode, H-mode, and W-mode discharges in helicon plasma, respectively. Discharge images in the radial cross section at different discharge modes through an intensified charge coupled device (ICCD) show a rapid increase in luminous intensity along with the RF power. When the nitrogen discharge is in the W-mode, the images show that the strongest luminance locates near the plasma boundary and no blue core appears in the axial center of tube, which is always observed in argon W-mode discharge. The “big blue” or blue core is a special character in helicon plasma, but it has not been observed in nitrogen helicon plasma. In nitrogen-argon mixtures, a weak blue core is observed in ICCD images since the nitrogen content is increased. The electric field turns to the periphery in the distribution of the radial field and the electron temperature decreases with the increasing nitrogen content, especially when the blue core disappears. The different behaviors of the electron impact and the energy consumption in nitrogen helicon plasma are suggested to be responsible for the decrease in electron energy and the change in the electric field distribution.

Band Jahn Teller Like Distortion In TiPd Shape Memory Alloy On Addition Of Magnetic Impurity Co

In this paper, we have reported the electronic structure and magnetic properties of TiPd alloyed with two different concentrations of magnetic impurity Co in the framework of density functional theory using the full potential linearized augmented plane wave method. The prominent high temperature shape memory alloy (HTSMA) - TiPd, undergoes martensitic transformation from the parent B2 (cubic) phase to the product B19 (orthorhombic) phase. Among the two configurations [Ti(Pd,Co) and (Ti,Co)Pd] considered, Co is found to prefer Ti sublattice more than the Pd sublattice from the formation energy calculations for both B2 and B19 phases. The addition of Co induced magnetic behaviour in the compounds investigated. The densities of states (total, site and angular momentum decomposed) are studied in detail. Band Jahn Teller (BJT) effects are used to understand structural instability in solids. In BJT, the peak in the vicinity of Fermi level, in the spin down channel of the high symmetry phase splits or broadens on deformation. A band Jahn Teller like broadening is observed in the density of states curve of Ti25Pd50Co25. This broadening is accompanied by a decrease in electronic energy and number of states at Fermi level. BJT effect is an accompanying feature of martensitic transformation.

SU‐F‐T‐86: Electron Dosimetric Effects of Bolus and Lens Shielding in Treating Superficial Eye Lesions

Purpose:Electron therapy for the treatment of ocular lymphomas requires the lens to be shielded to prevent secondary cataracts. This work evaluates the dosimetry under a suspended eyeshield with and without bolus for low energy electron fields.Methods:Film (GafChromic EBT3) dosimetry and relative output factors were measured for 6, 8, and 10 MeV electron energies. A customized 5 cm diameter circle electron orbital cutout was constructed for a 6×6 cm applicator with a lens shield, 1 cm diameter Cerrobend cylinder with 2.2 cm length, suspended from an XV film covering the open field. Relative output factors were measured using a Scanditronix electron diode in a solid water phantom. Depth dose profiles were collected for bolus thicknesses of 0, 3, and 5 mm in solid water at a source to surface distance (SSD) of 100 cm. These measurements were repeated in a Rando phantom.Results:At 5 mm, the approximate distance of the lens from the surface of the cornea, the estimated dose in solid water under the suspended lens shield was reduced to 16%, 14%, and 13% of the unblocked dose at the same depth, for electron energies of 6, 8, and 10 MeV, respectively. Applying bolus increased estimated doses under the block to 22% for 3‐mm and 32% for 5‐mm thicknesses for a 6 MeV incident electron beam. This effect is reduced for higher energies where the corresponding values were 15.5% and 18% for 3‐mm and 5‐mm for an 8 MeV electron beam.Conclusion:The application of bolus to treat superficial eye lesions of the conjunctiva increases lens dose at a depth of 5‐mm under the shielding block with decreasing electron energy. Careful selection of electron energy is needed to account for electron scatter under the lens shield with the application of bolus in order to prevent cataracts.

Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause

AbstractBased on high‐resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field‐aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field‐aligned potentials).

Femtosecond cooling of hot electrons in CdSe quantum-well platelets.

Semiconductor quantum wells are ubiquitous in high-performance optoelectronic devices such as solar cells and lasers. Understanding and controlling of the (hot) carrier dynamics is essential to optimize their performance. Here, we study hot electron cooling in colloidal CdSe quantum-well nanoplatelets using ultrafast two-photon photoemission spectroscopy at low excitation intensities, resulting typically in 1-5 hot electrons per platelet. We observe initial electron cooling in the femtosecond time domain that slows down with decreasing electron energy and is finished within 2 ps. The cooling is considerably faster at cryogenic temperatures than at room temperature, and at least for the systems that we studied, independent of the thickness of the platelets (here 3-5 CdSe units) and the presence of a CdS shell. The cooling rates that we observe are orders of magnitude faster than reported for similar CdSe platelets under strong excitation. Our results are understood by a classic cooling mechanism with emission of longitudinal optical phonons without a significant influence of the surface.

Resonance raman spectra of linear polymer molecule

The present paper summarizes the characteristics of resonance Raman spectra of the linear polymer molecule, and its relations with the molecular structure, including: electronic spectra(ultraviolet-visible absorption spectrum), Raman spectra characteristics and its relations with external field; Modulation relation between the electron energy gap and CC atom vibration; Several experimental results were obtained: The UV-visible absorption spectra are red-shifted with decreasing temperature, increasing solvent density and reducing solution concentration, and because the linear polymer molecule has high structured order, decreasing pi electron energy gap; extended pi electronic delocalization, large effective conjugation length, large intensity of the Raman activity, Ramrnan spectrum are red-shifted, with large scattering cross section. "Am plitude modes" are the ideal theory models to study the linear polymer molecule.

A Microscopic Study of Before-Arc Process in Metal Vapor Plasma's Proximal Cathode Region. Part II the Influence of Macroscopic Parameters on the Proximal Cathode Region

The moment of vacuum breaker contacts opening to arc creating process is an unbalanced gaseous breakdown process. This before-arc process is the foundation of studying arc process. The mechanism of the metal vapor arc is different from other gas medium and contains complex electrode process. The proximal cathode region is the important area for vacuum arc forming and it is affected by many factors. The influences of the different electrode separations, different secondary emission coefficient on electronic density, electronic temperature and electric potential, were analysed in this paper. The simulation results show that the change of electrode separations barely impacts the thickness of sheath and the decrease of electrode separations will lead to the decrease of electronic energy near the cathode sheath. The increase of secondary electron emission will increase charged particles energy, which is the important condition of forming cathode sheath.

Simulation of hollow cathode discharge by combining the fluid model with a transport model for metastable Ar atoms

The characteristics of rectangular hollow cathode discharge are studied based on a fluid model combined with a transport model for metastable Ar atoms in argon. The distribution of potential, density of electrons and ions, and the density of metastable atoms are calculated at a pressure of 10 Torr. The peak density of electron and ion is 4.7×1012 cm-3, and the peak density of metastable atoms is 2.1×1013 cm-3. Results obtained in terms of fluid-metastable hybrid model are compared with that in terms of the fluid model, which show that the electron produced by stepwise ionization is one of the important source of new electrons, and the metastable atoms have an obvious effect on the hollow cathode discharge. Compared with the results calculated in terms of fluid model, the density of electrons obtained in terms of hybrid model increases, and the depth of cathode sheath and the averaged electron energy decrease.

Sci-Sat AM: Brachy - 02: Extracting Wair from the 1976 electron beam measurements of domen and lamperti.

The average energy expended by an energetic electron to create an ion pair in air, Wair is an important quantity in radiation dosimetry. The data obtained by Domen and Lamperti using electron beams in the energy range from 15 to 50 MeV can be used to extract a value for Wair if the electron stopping powers of graphite and air are assumed to be known. We use Monte Carlo techniques to reanalyze these data and obtain a new estimate for the value of Wair Using the EGSnrc Monte Carlo and its associated user codes, as well as the best availabl-e stopping power data for graphite, we calculate the perturbation effects due to the calorimeter and ionization chamber and the effect of extrapolating from scattered to plane-parallel beams. Without further adjustments, the extracted values of Wair show a significant trend as the mean electron energy decreases. We show that part of this trend can be attributed to an incorrect value of the density assigned to the graphite absorbers and part to the likelihood that the nominal energy assigned to the low-energy electron beams is not correct. Using all the data, we obtain a value for Wair of 33.84 eV per ion pair with a relative standard uncertainty of 0.4 %. This result serves to complement values obtained using 60 Co γ-rays, for which the value of the mean excitation of graphite contributes significantly to the uncertainty.

Valence-band-ordering of a strain-free bulk ZnO single crystal identified by four-wave-mixing spectroscopy technique

Spectroscopic and temporal four-wave-mixing (FWM) measurements are carried out on a strain-free bulk ZnO single crystal, in order to clarify the valence-band-ordering. Under the collinearly polarized lights with the electric-field component parallel to the c-axis, which can excite dipole-allowed Γ1-excitons, the FWM signal appears only in the energies corresponding to the B-exciton. Under the cross-linear polarization configuration exciting both Γ5- and Γ1-excitons, the FWM signal arising from the two-photon-coherence is absent in the energies corresponding to A-exciton. Both the results indicate that Γ1-exciton state belongs exclusively to B-exciton, meaning that the valence-band ordering is Γ9-Γ7-Γ7 in order of decreasing electron energy for the present strain-free ZnO single crystal.

UV and IR auroral emission model for the outer planets: Jupiter and Saturn comparison

Planetary aurora display the dynamic behavior of the plasma gas surrounding a planet. The outer planetary aurora are most often observed in the ultraviolet (UV) and the infrared (IR) wavelengths. How the emissions in these different wavelengths are connected with the background physical conditions are not yet well understood. Here we investigate the sensitivity of UV and IR emissions to the incident precipitating auroral electrons and the background atmospheric temperature, and compare the results obtained for Jupiter and Saturn. We develop a model which estimates UV and IR emission rates accounting for UV absorption by hydrocarbons, ion chemistry, and H 3 + non-LTE effects. Parameterization equations are applied to estimate the ionization and excitation profiles in the H 2 atmosphere caused by auroral electron precipitation. The dependences of UV and IR emissions on electron flux are found to be similar at Jupiter and Saturn. However, the dependences of the emissions on electron energy are different at the two planets, especially for low energy (<10 keV) electrons; the UV and IR emissions both decrease with decreasing electron energy, but this effect in the IR is less at Saturn than at Jupiter. The temperature sensitivity of the IR emission is also greater at Saturn than at Jupiter. These dependences are interpreted as results of non-LTE effects on the atmospheric temperature and density profiles. The different dependences of the UV and IR emissions on temperature and electron energy at Saturn may explain the different appearance of polar emissions observed at UV and IR wavelengths, and the differences from those observed at Jupiter. These results lead to the prediction that the differences between the IR and UV aurora at Saturn may be more significant than those at Jupiter. We consider in particular the occurrence of bright polar infrared emissions at Saturn and quantitatively estimate the conditions for such IR-only emissions to appear.

Laser induced C(60) cage opening studied by semiclassical dynamics simulation.

Laser induced opening of the C60 cage is studied by a semiclassical electron-radiation-ion dynamics technique. The simulation results indicate that the C60 cage is abruptly opened immediately after laser excitation. The opening of the C60 cage induces a quick increase in kinetic energy and a sharp decrease in electronic energy, suggesting that the breaking of the C60 cage efficiently heats up the cluster and enhances the thermal fragmentation of C60 fullerene.