The Design of a Reflection Electron Energy Loss Spectrometer Attachment for Low Voltage Scanning Electron Microscopy

This paper presents the design of a reflection electron energy spectrometer (REELS) attachment for low voltage scanning electron microscopy (LVSEM) applications. The design is made by carrying out a scattered electron trajectory ray paths simulation. The spectrometer attachment is small enough to fit on the specimen stage of an SEM, and aims to acquire nanoscale spatially resolved REELS information. It uses a retarding field electrostatic toroidal sector energy analyzer design, which is able to lower the kinetic energies of elastically backscattered electrons to pass energies of 10 eV or less. For the capture of 1 keV BSEs emitted in the polar angular range between 40 to 50°, direct ray-tracing simulations predict that the spectrometer attachment will have an energy resolution of around 0.4 eV at a pass energy of 10 eV, and 0.2 eV at a pass energy of 5 eV. This predicted performance will make it a suitable REELS attachment for SEMs that use field emission electron sources.

Fast and versatile polarization control of X-ray by segmented cross undulator at SPring-8

An X-ray is the well-known probe to examine structure of materials, including our own bodies. The X-ray beam, especially at the wavelength of nanometers, has also become significant to directly investigate electronic states of a sample. Such an X-ray is called a soft X-ray and polarization dependence of the light-matter interaction further unveils the microscopic properties, such as orbitals or spins of electrons. Generation of high brilliant beams of the polarized X-ray has linked to development of our experimental science, and it has been made by radiation from relativistic electrons at the synchrotron radiation facilities over the world. Recently, we constructed a new polarization-controlled X-ray source, the segmented cross undulator, at SPring-8, the largest synchrotron radiation facility in the world. The operation is based on interference of X-ray beams, which is sharply contrast to the conventional method of regulating electron trajectory by the mechanical control of magnets. The paradigm shift opened the measurement innovations and allowed us to design new experimental approaches to capture signals that have been hidden in materials. The present review describes the novel X-ray source with the principle of operation and the technical details of optimization. Examples of the frontier spectroscopies that use unique optical properties of the source are introduced, followed by the future prospects for next generation synchrotron radiation facilities.

Spontaneous and stimulated electron–photon interactions in nanoscale plasmonic near fields

The interplay between free electrons, light, and matter offers unique prospects for space, time, and energy resolved optical material characterization, structured light generation, and quantum information processing. Here, we study the nanoscale features of spontaneous and stimulated electron–photon interactions mediated by localized surface plasmon resonances at the tips of a gold nanostar using electron energy-loss spectroscopy (EELS), cathodoluminescence spectroscopy (CL), and photon-induced near-field electron microscopy (PINEM). Supported by numerical electromagnetic boundary-element method (BEM) calculations, we show that the different coupling mechanisms probed by EELS, CL, and PINEM feature the same spatial dependence on the electric field distribution of the tip modes. However, the electron–photon interaction strength is found to vary with the incident electron velocity, as determined by the spatial Fourier transform of the electric near-field component parallel to the electron trajectory. For the tightly confined plasmonic tip resonances, our calculations suggest an optimum coupling velocity at electron energies as low as a few keV. Our results are discussed in the context of more complex geometries supporting multiple modes with spatial and spectral overlap. We provide fundamental insights into spontaneous and stimulated electron-light-matter interactions with key implications for research on (quantum) coherent optical phenomena at the nanoscale.

Speed-up of simulation of magnetization process for large-scale HTS undulator of X-FEL based on power-law macro-model

The Pure-type HTS undulator is proposed to achieve a high-intensity magnetic field and small size undulator for a compact free-electron laser (FEL). A high precision simulation is required before making the real machine since the sizes and positions are difficult to adjust after the HTSs are magnetized in the cryostat. For this purpose, authors have been developed a numerical simulation code for the magnetization process of HTS undulator of X-FEL based on the power-law macro-model. In this paper, the previously developed simulation code can be speeded up by carefully optimizing the parameters of the power-law macro-model for the 3-HTS magnets model and a large-scale simulation can be performed in an acceptable time by using a multipole expansion for the Biot–Savart law. In addition, for practical applications, the influence of the fluctuation of the magnets thickness and critical current for the electron trajectory are evaluated by using the speed-up simulation code.

Attosecond streaking using a rescattered electron in an intense laser field

When an atom or molecule is exposed to a strong laser field, an electron can tunnel out from the parent ion and moves along a specific trajectory. This ultrafast electron motion is sensitive to a variation of the laser field. Thus, it can be used as a fast temporal gate for the temporal characterization of the laser field. Here, we demonstrate a new type of attosecond streaking wherein a rescattered electron trajectory is manipulated by an ultrashort laser pulse. The vector potential of the laser pulse is directly recorded in the photoelectron spectra of the rescattered electron. In contrast to high harmonic generation methods, our approach has no directional ambiguity in space, leading to complete in situ temporal characterization. In addition, it provides timing information on ionization and re-scattering events. Therefore, our approach can be a useful tool for the investigation of strong-field processes triggered by rescattering, such as non-sequential double ionization and laser-induced electron diffraction.

Simulation of discharge process of Hall thruster under the internal and external cathode conditions

Hall thruster has been used widely in orbit correction and station-keeping of geostationary satellites for the advantage of high specific impulse, long life, and high reliability. The cathode is an important part of Hall thruster, which can neutralize ion beam and provide electrons to the thruster for ionization. At present, the position of cathode can be divided into two kinds: internal cathode and external cathode. And the discharge parameters under the two different cathode positions is very different, such as the coupling voltage and the ion density. And this paper considers the mechanism of influence of the cathode position on the discharge process of Hall thruster, the discharge process of Hall thruster under internal and external cathode conditions was simulated by PIC-MCC simulation method. The simulation results show that the electron conduction near the thruster outlet is relatively strong under the internal cathode condition. The trajectory of electrons emitted from the cathode position under the two conditions is further simulated. The simulation results show that the electrons will be bound by the magnetic field and form a virtual cathode when they enter the simulation area. The lower coupling voltage under the internal cathode condition is explained by comparing the positions of virtual cathode. At the same time, some electrons emitted from the internal cathode position can quickly reach the main beam region. The ion density distribution is also compared. The ionization regions of Xe+, Xe2+ and Xe3+ ions are relatively outside under the internal cathode condition, and the peak densities of Xe2+ and Xe3+ ions are relatively low. Compared with the experimental results, it is shown that the electron trajectory in the plume region has a significant effect on the plume shape.

Electron acceleration of a surface wave propagating in wiggler-assisted plasma

In this paper, we study the electron acceleration by a surface plasma wave (SPW) propagating through two parallel metal sheets in the presence of wiggler magnetic field strength. The configuration of interest consists of a helical magnetostatic wiggler, an external magnetic field and two parallel metal half-spaces. Dispersion relation of SPW in the attendance of helical magnetostatic wiggler is recognized and observed as compared with that of without wiggler 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 SPW. Numerical results depict that with increasing of [Formula: see text]-parameter [Formula: see text] is the ratio of wiggler frequency to plasma frequency), minimum modes of SPW have an increasing trend and with increase of the wiggler frequency, the normalized frequencies decreased and a gap appeared between them. Furthermore, it is seen that with increase of the [Formula: see text]-parameter, the value of the kinetic energy as compared with the absence of the wiggler magnetic field increased. In fact, the electron energy gained is higher in the presence of a helical magnetostatic wiggler as compared with the absence of wiggler field. In addition, it is observed that due to effects of the wiggler field and SPW field, the electron traverses more distance in the propagation direction of the laser pulse.