Intense Electron Research Articles

Vertical characterization on global ionospheric variations during the magnetic storm in September 2017 with hierarchical subtraction method

This study investigates the global ionospheric responses at different altitudes during the geomagnetic storm in September 2017 by using the observations from IGS GIMs and GRACE, TerraSAR-X, COSMIC, Metop LEO satellite missions. According to different satellite heights, a hierarchical subtraction method is proposed to characterize the disturbance of total electron content (TEC) at the vertical regions of below 340 km , 340 ∼ 520 km , 520 ∼ 800 km and above 800 km , respectively. The integrated TEC from IRI-Plas2017 are applied to verify the feasibility and rationality of the proposed method and the electron density (Ne) profiles from the ionosonde and radio occultation (RO) measurements are used to explore the variations of Ne in different height regions. The resulting TEC disturbances ( Δ TEC) on a global scale show that: 1) There was significant increase on Ne peak in F2 region during the magnetic storm, due to the strong recombination in the lower ionosphere while more intense electron ionization in the upper ionosphere; 2) During the main phase, TEC enhancement had a tendency to drift westward, which may correlate with the twice Dst minimums. 3) The east–west and north–south hemispheric asymmetry of Δ TEC exist simultaneously in this magnetic storm. However, the former is mainly attributed to ionospheric plasma bubbles, while the latter might be the seasonal thermospheric effects or the energetic particle emissions.

Stacked Electron Diffusion Regions and Electron Kelvin–Helmholtz Vortices within the Ion Diffusion Region of Collisionless Magnetic Reconnection

Abstract The structure of the electron diffusion region (EDR) is essential for determining how fast the magnetic energy converts to plasma energy during magnetic reconnection. Conventional knowledge of the diffusion region assumes that the EDR is a single layer embedded within the ion diffusion region (IDR). This paper reports the first observation of two EDRs that stack in parallel within an IDR by the Magnetospheric Multiscale mission. The oblique tearing modes can result in these stacked EDRs. Intense electron flow shear in the vicinity of two EDRs induced electron Kelvin–Helmholtz vortices, which subsequently generated kinetic-scale magnetic peak and holes, which may effectively trap electrons. Our analyses show that both the oblique tearing instability and electron Kelvin–Helmholtz instability are important in three-dimensional reconnection since they can control the electron dynamics and structure of the diffusion region through cross-scale coupling.

Color centers in K–Na–Cl crystals induced by pulsed intense relativistic electron beam at 77 K

In order to reproduce the irradiation environment of Europa, NaCl-0-2mol%KCl crystals were grown and irradiated with pulsed intense relativistic electron beams at RT and 77 K in the optical absorbance spectra. The peak wavelength of the F-center was shortened by decreasing the measurement temperature and the KCl content. This phenomenon can be explained by the changes of the lattice constant and utilized to determine temperature and KCl content in the sea of Europa.

Multiple electron beam generation with different energies and comparable currents from a single cathode potential for high power traveling wave tubes (TWTs)

We present a technique for generating multiple electron beams with different energies and comparable currents from a single cathode stalk at a single potential using nested magnetically insulated coaxial diodes (MICDs). The application is for a multi-stream traveling wave tube. Particle-in-cell simulations are performed for an experimental parameter-based geometry where two thin-walled intense relativistic electron beams immersed in a strong uniform magnetic field propagate through a cylindrical vacuum channel. The analytically derived results are obtained by extending Fedosov’s solution for generating a hollow electron beam from an MICD on a cathode stalk in an infinite magnetic field. Two electron beams are generated and accelerated downstream assuming zero initial kinetic energy of the electrons from the cathodes. Results show both electron beam currents ranging from 66 to 2.8 kA with an energy difference ranging from 6% to 27% depending on voltages applied from 100 to 600 kV and the geometry of the two MICDs. An optimal geometry is a crucial factor in achieving the maximum energy difference between the electron beams for comparable currents. The analytical and numerical simulation results show good agreement. We are currently in the process of planning experiments using the electron beam accelerator (SINUS-6 at UNM) to validate the analytical and simulation results.

Large-scale and low-cost synthesis of porous carbon on the surface of commercial chlorinated polymers under the action of an intense electron beam of microsecond duration

The formation of a layer of porous carbon on the surface of low-cost commercial chlorinated polyvinyl chloride (CPVC) with the addition of ferrocene under the action of an intense electron beam of microsecond duration was investigated. The polymer was irradiated using a pulsed fore-vacuum plasma source of a large-diameter electron beam (cross-sectional area ∼100 cm2), which allows minimizes polymer charging during irradiation. The methods of scanning and transmission electron microscopy, EDX spectroscopy, Raman and X-ray photoelectron spectroscopy were used to study the carbon layers. We found that the carbon layer consists mainly of thin (∼10 nm) sheets of amorphous carbon containing curved graphene layers up to 4 nm in length. According to the XPS data analysis, the relative fraction of graphitized carbon (sp2-hybridized carbon) reaches 80% in the surface layer with a thickness of up to 3 nm. Possible mechanisms for the formation of a porous carbon layer on the CPVC surface were discussed. The porous carbon layer has a specific capacitance of 14 mF/cm2 at a scan rate of 5 mV/s. In many applications, it can be an alternative to the laser-induced graphene formed on the surface of expensive high-temperature polyimide.

Электронно-пучковая обработка поверхности металлических материалов, изготовленных аддитивным способом

A method for finishing the surface of metal materials manufactured by additive technologies with an intense pulsed electron beam, which can be an alternative to traditional processing methods is presented. The optimal irradiation modes for VT6 titanium alloy specimens produced by metal powder fusion and 308LSi stainless steel specimens produced by electron beam welding are determined. It is shown that the presented processing method leads to a visual decrease in porosity and a multiple decrease in the surface layer roughness (by 20 times (Ra)) of VT6 titanium alloy manufactured by an additive method. The surface roughness of 308LSi stainless steel specimens fabricated by electron beam welding decreases to 2.1 times in the longitudinal direction, to 5.2 times in the transverse relative to the surfacing plane. It is shown that the elemental composition, strength and tribological properties of the specimens do not change during irradiation in optimal modes. Tensile testing of irradiated specimens revealed an increase in tensile strength by 12%, ductility by 10% (VT6) and anisotropy of mechanical properties depending on the direction of tension relative to the surfacing plane (308LSi).

The resolution-vs.-accuracy dilemma in machine learning modeling of electronic excitation spectra

We present electronic ground and excited state properties of a new chemical space dataset, and suggest a strategy for efficient machine learning modeling of electronic spectral intensities.

Stable transmission of low energy electrons in glass tube with outer surface grounded conductively shielding

<sec>The electron microbeam is useful for modifying certain fragments of biomolecule. It is successful to apply the guiding effect to making the microbeam of positively charged particles by using single glass capillary. However, the mechanism for the electron transport through insulating capillaries is unclear. Meanwhile, previous researches show that there are oscillations of the transmission intensity of electrons with time in the glass capillaries with outer serface having no grounded conductive shielding, So, the application of glass capillary to making the microbeam of electrons is limited.</sec><sec>In this paper, the transmission of 1.5 and 0.9 keV electrons through the glass capillary without/with the grounded conductive-coated outer surface are investigated, respectively. This study aims to understand the mechanism for low energy electron transport in the glass capillaries, and find the conditions for the steady transport of the electrons. Two-dimensional angular distribution of the transported electrons and its time evolution are measured. It is found that the intensity of the transported electrons with the incident energy through the glass capillaries for the glass capillaries without and with the grounded conductive-coated outer surface show the typical geometrical transmission characteristics. The time evolution of the 1.5- keV electron transport presents an extremely complex variation for the glass capillary without the grounded conductive-coated outer surface. The intensity first falls, then rises and finally oscillates around a certain mean value. Correspondingly, the angular distribution center experiences moving towards positive-negative-settlement. In comparison, the charge-up process of the 0.9 keV electron transport through the glass capillary with the grounded conductive-coated outer surface shows a relatively simple behavior. At first, the intensity declines rapidly with time. Then, it slowly rises till a certain value and stays steady subsequently. The angular distribution of transported electrons follows the intensity distribution in general, but with some delay. It quickly moves to negative direction then comes back to positive direction. Finally, it regresses extremely slowly and ends up around the tilt angle. To better understand the physics behind the observed phenomena, the simulation for the interaction of the electrons with SiO<sub>2</sub> material is performed to obtain the possible deposited charge distribution by the CASINO code. Based on the analysis of the experimental results and the simulated charge deposition, the conditions for stabilizing the electron transport through glass capillary arepresented.</sec>

Linear electron accelerator for energy 8-50 MeV with injection from an electron source based on cluster plasma systems

For many years, one of the key problems of modern accelerator physics has been an increase of the rate of the energy gain in RF linear electron accelerators. The physical limits of the accelerating field intensity for metallic accelerating structures have been practically reached; therefore, new acceleration schemes are being considered, primarily acceleration in plasma and wakefield acceleration. The second aim is the generation of ultrashort (100 fs and less) electron bunches, for which RF photoguns are traditionally used. In this case, for RF photoguns, a serious problem that limits the intensity of electrons in a bunch is the influence of the own space charge during emission and acceleration in the near-cathode region, where the beam is weakly relativistic and the influence of the space charge on its dynamics plays the determinative role. The possibility of using a plasma cathode source as an injector for RF accelerator will considered. In the future, this may make it possible to bypass the limitations inherent in RF photoguns (sufficient influence of the space charge on the beam dynamics in the near-cathode region) and acceleration in the laser-plasma channel (low electron capture coefficient in the acceleration mode, wide energy spectrum - 10% or more at energies of tens and hundreds of megaelectrons). It is proposed to develop a combined accelerator in which a bunch generated in a laser-plasma channel is injected into a traditional metal structure. It is supposed that could be possible to generate a short (from 0.1 to 1.0 ps) electron bunches with an energy of several hundred kiloelectrons, which will make it possible to consider such source as an alternative to the photocathode. Next, the beam must be captured in the acceleration mode in a normally conducting section and accelerated to an energy of 50 MeV with the possibility of energy tuning. The features of such accelerator, the features of the electron bunch capturing in the acceleration mode, and the possible values of the energy spectrum in such a system will considered.

Effect of strong intersite Coulomb interaction on the topological properties of a superconducting nanowire

For superconducting nanowire with the pairing of extended s-type symmetry, Rashba spin-orbit interaction in a magnetic field, the influence of strong intersite charge correlations on single-particle Majorana excitations is analyzed. This problem is investigated on the basis of the density matrix renormalization group numerical method. It is shown that with an increase in the repulsion intensity of electrons located at the neighboring sites, two subbands emerge in the lower Hubbard band of the open system. Based on calculations of the Majorana polarization and degeneracy of the entanglement spectrum, it was found that a topologically nontrivial phase with one edge state survives at the edge of each of the subbands where the concentration of electrons or holes is minimal. Keywords: superconducting nanowires, Majorana zero modes, strong electron correlations.

Effect of strong intersite Coulomb interaction on the topological properties of a superconducting nanowire

For superconducting nanowire with the pairing of extended s-type symmetry, Rashba spin-orbit interaction in a magnetic field, the influence of strong intersite charge correlations on single-particle Majorana excitations is analyzed. This problem is investigated on the basis of the density matrix renormalization group numerical method. It is shown that with an increase in the repulsion intensity of electrons located at the neighboring sites, two subbands emerge in the lower Hubbard band of the open system. Based on calculations of the Majorana polarization and degeneracy of the entanglement spectrum, it was found that a topologically nontrivial phase with one edge state survives at the edge of each of the subbands where the concentration of electrons or holes is minimal. Keywords: superconducting nanowires, Majorana zero modes, strong electron correlations.

Calibration methods for charge integrating detectors

Since the introduction of the extremely intense X-ray free electron lasers, the need for low noise, high dynamic range and potentially fast charge integrating detectors has increased significantly. Among all the problems that research and development groups have to face in the development of such detectors, their calibration represents one of the most challenging and the collaboration between the detector development and user groups is of fundamental importance. The main challenge is to develop a calibration suite that is capable to test the detector over a wide dynamic range, with a high granularity and a very high linearity, together with a certain radiation tolerance and the possibility to well define the timings and the synchronization with the detector. Practical considerations have also to be made like the possibility to calibrate the detector in a reasonable time, the availability of the calibration source at the experimental place and so on. Such a calibration test suite is often not represented by a single source but by several sources that can cover different parts of the dynamic range and that need to be cross calibrated to have a final calibration curve. In this respect an essential part of the calibration is also to develop a mathematical model that allows calibrating the entire dynamic range, taking into account features that are calibration source and/or detector specific. The aim of this contribution is to compare the calibration for the AGIPD detector using several calibration sources such as internal current source, backside pulsing, IR pulsed laser, LED light and mono-energetic protons. The mathematical procedure used to calibrate the different sources will be discussed in great detail showing how to take into account a few shortcomings (like pixel coupling) that are common for many charge integrating detectors. This work has been carried out in the frame of the AGIPD project for the European X-ray Free Electron Laser.

Role of Second Harmonic in the Optimization of Microwave Conversion Efficiency From an Intense Relativistic Electron Beam

In this article, the effect of second harmonic (SH) on the microwave conversion efficiency in a klystron-like relativistic backward wave oscillator (RBWO) is investigated by the nonlinear theory, particle-in-cell (PIC) simulations, and experiments. The nonlinear theory of beam-wave interaction is developed with both the fundamental frequency and SH taken into account. The calculation results show that the optimized conversion efficiency is increased from 50% to 73% as the SH is included. The PIC simulations reveal that with the introduction of a dual-premodulation (DPM) cavity to increase the SH current and then the fundamental current modulation coefficient in a klystron-like RBWO, the conversion efficiency can be enhanced from 59% to 72%. In the klystron-like RBWO experiments, a significant efficiency increase from 58% for the device without the DPM cavity to 66% with the DPM cavity has been realized. As the electron beam power is 4 GW, the out powers of the fundamental frequency and SH are measured to be 2.6 GW and 100 MW, respectively. This provides helpful guidance to further increase the microwave conversion efficiency in high-power microwave sources driven by intense relativistic electron beams.

Experimental Study and Mathematical Modeling of the Processes Occurring in ZrN Coating/Silumin Substrate Systems under Pulsed Electron Beam Irradiation

This paper presents a study of a combined modification of silumin, which included deposition of a ZrN coating on a silumin substrate and subsequent treatment of the coating/substrate system with a submillisecond pulsed electron beam. The local temperature on the samples in the electron-beam-affected zone and the thickness of the melt zone were measured experimentally and calculated using a theoretical model. The Stefan problem was solved numerically for the fast heating of bare and ZrN-coated silumin under intense electron beam irradiation. Time variations of the temperature field, the position of the crystallization front, and the speed of the front movement have been calculated. It was found that when the coating thickness was increased from 0.5 to 2 μm, the surface temperature of the samples increased from 760 to 1070 °C, the rise rate of the surface temperature increased from 6 × 107 to 9 × 107 K/s, and the melt depth was no more than 57 μm. The speed of the melt front during the pulse was 3 × 105 µm/s. Good agreement was observed between the experimental and theoretical values of the temperature characteristics and melt zone thickness.

Kinetic Plasma Turbulence Generated in a 3D Current Sheet With Magnetic Islands

In this article we aim to investigate the kinetic turbulence in a reconnecting current sheet (RCS) with X- and O-nullpoints and to explore its link to the features of accelerated particles. We carry out simulations of magnetic reconnection in a thin current sheet with 3D magnetic field topology affected by tearing instability until the formation of two large magnetic islands using particle-in-cell (PIC) approach. The model utilizes a strong guiding field that leads to the separation of the particles of opposite charges, the generation of a strong polarization electric field across the RCS, and suppression of kink instability in the “out-of-plane” direction. The accelerated particles of the same charge entering an RCS from the opposite edges are shown accelerated to different energies forming the “bump-in-tail” velocity distributions that, in turn, can generate plasma turbulence in different locations. The turbulence-generated waves produced by either electron or proton beams can be identified from the energy spectra of electromagnetic field fluctuations in the phase and frequency domains. From the phase space analysis we gather that the kinetic turbulence may be generated by accelerated particle beams, which are later found to evolve into a phase-space hole indicating the beam breakage. This happens at some distance from the particle entrance into an RCS, e.g. about 7di (ion inertial depth) for the electron beam and 12di for the proton beam. In a wavenumber space the spectral index of the power spectrum of the turbulent magnetic field near the ion inertial length is found to be −2.7 that is consistent with other estimations. The collective turbulence power spectra are consistent with the high-frequency fluctuations of perpendicular electric field, or upper hybrid waves, to occur in a vicinity of X-nullpoints, where the Langmuir (LW) can be generated by accelerated electrons with high growth rates, while further from X-nullponts or on the edges of magnetic islands, where electrons become ejected and start moving across the magnetic field lines, Bernstein waves can be generated. The frequency spectra of high- and low-frequency waves are explored in the kinetic turbulence in the parallel and perpendicular directions to the local magnetic field, showing noticeable lower hybrid turbulence occurring between the electron’s gyro- and plasma frequencies seen also in the wavelet spectra. Fluctuation of the perpendicular electric field component of turbulence can be consistent with the oblique whistler waves generated on the ambient density fluctuations by intense electron beams. This study brings attention to a key role of particle acceleration in generation kinetic turbulence inside current sheets.

Stability and lifetime study of carbon nanotubes as cold electron field emitters for electron cooling in the CERN extra low energy antiproton ring

Electron cooling is a fundamental process to guarantee the beam quality in low energy antimatter facilities. In extra low energy antiproton, the electron cooler reduces the emittance blowup of the antiproton beam and thus delivers a focused and bright beam to the experiments at the unprecedentedly low kinetic energy of 100 keV. In order to achieve a cold beam at this low energy, the electron gun of the cooler must emit a monoenergetic and relatively intense electron beam. An optimization of the extra low energy antiproton electron cooler gun involving a cold cathode is studied, with the aim of investigating the feasibility of using carbon nanotubes (CNTs) as cold electron field emitters. CNTs are considered among the most promising field emitting material. However, stability data for emission operation over hundreds of hours, as well as lifetime and conditioning process studies to ensure optimal performance, are still incomplete or missing, especially if the purpose is to use them in operation in a machine such as extra low energy antiproton. This manuscript reports experiments that characterize these properties and ascertain whether CNTs are reliable enough to be used as cold electron field emitters for many hundreds of hours.

Multi-cycle of AISI 5135 steel modification by irradiation of the “film (Si (0.2 μm) + Nb (0.2 μm))/(AISI 5135 steel) substrate” system with an intense pulsed electron beam

Steel AISI 5135 surface layer modification carried out by high-cycle high-speed melting of the “film (Si + Nb)/(steel AISI 5135) substrate” system with an intense pulsed electron beam with an impact area of several square centimeters, have been implemented in a single vacuum cycle on the “COMPLEX” setup. The regime of the system “film (Si (0.2 μm) + Nb (0.2 μm))/(steel AISI 5135) substrate” irradiation with an intense pulsed electron beam (20 J/cm2, 200 μs, 3 pulses, 3 cycles) which makes it possible to form a surface layer with high thermal stability have been revealed. This layer is characterized by high hardness, more than 3 times higher than the hardness of AISI 5135 steel in the original (ferrite-pearlite structure) and wear resistance, more than 90 times higher than the wear resistance of the initial AISI 5135 steel. It is shown that the high strength and tribological properties of steel are due to the formation of the hardening phase particles (niobium silicide of Nb5Si3 composition).

Structure and mechanical properties of stainless-steel specimens, made by additive method, after pulsed electron beam treatment

The article presents a method for finishing the surface of metal products made by sequential electron-beam surfacing, which consists in modifying the surface with an intense low-energy electron beam of submillisecond duration. On the example of 308LSi stainless steel, the results of such processing are demonstrated, the optimal modes of exposure are determined. It is shown that as a result of pulsed electron-beam processing, a homogeneous polycrystalline structure without cracks is formed on the surface with unchanged, relative to the initial material, elemental composition, strength (microhardness) and tribological (wear rate) properties. In this case, the surface roughness is reduced to 2.1 times in the longitudinal direction relative to the surfacing plane, to 5.2 times in the transverse direction. Tensile tests of specimens showed anisotropy of mechanical properties depending on the direction of tension relative to the surfacing plane, which decreases after surface pulse electron-beam processing.

Structure and properties of high-chromium steel irradiated with a pulsed electron beam and nitrided in a low-pressure gas discharge plasma

Ion-plasma saturation of the surface of machine parts and mechanisms with gas elements (nitrogen, oxygen, carbon) is currently one of the most effective and widely used methods of surface hardening of metal products for various purposes in the industry of developed countries. The aim of this research is to develop a complex method for modifying the surface layer of AISI 310 steel, combining irradiation with an intense pulsed electron beam and subsequent nitriding in the plasma of a low-pressure gas discharge. As a result of the studies performed, the optimal parameters of modification were revealed, which make it possible to increase the hardness of the surface layer of steel by more than 11 times, relative to the hardness of the initial material, and 8 times, relative to the hardness of steel irradiated with a pulsed electron beam. In this case, the wear resistance of the steel exceeds the wear resistance of the original and irradiated material by more than 100 times. It has been established that the high strength and tribological properties of the modified steel are due to the formation of a two-phase (iron nitride and chromium nitride) layered nanoscale structure in the surface layer.

Efficiency Enhancement of a High Power Radial-Line Relativistic Klystron Amplifier Driven by Disk Intense Electron Beam

The power conversion efficiency of relativistic klystron amplifiers (RKAs) is severely limited by the strong space-charge repulsion force caused by the intense electron beam. A radial-line RKA (RL-RKA) driven by the disk beam may provide great potentials to alleviate this issue due to its radially propagating characteristic of the electron beam. However, such potential advantage of high efficiency has not been fully exploited in previous research due to the insufficient beam modulation and relatively low beam-wave coupling strength. In this article, an initial RL-RKA is improved significantly by utilizing a three-stage cascaded bunching link, a four-gap output cavity, and a lengthened drift tube. The three-stage cascaded bunching link plays a role in increasing the fundamental harmonic current and decreasing the velocity spread of the electron beam simultaneously. The four-gap output cavity is designed to improve the coupling impedance and strengthen the beam-wave power conversion. Moreover, a drift tube is lengthened suitably to boost the fundamental harmonic current further. Eventually, the power conversion efficiency of the RL-RKA is enhanced up to 67% by these measures, which indicates a significant advance over the initial state of 38%.