Fitting electron spectrum from AMS-02 by pulsar electrons

In this work, we aim to explain the latest data of cosmic-ray electrons from AMS-02 by an electron background model and pulsar electrons. We consider an electron background model which includes primary and secondary electrons. We assume that pulsars are major sources of the electron excess. Since electrons easily lose their energy through the interstellar radiation field and the magnetic field via inverse Compton scattering and synchrotron radiation, respectively, they propagate in a short length. We adopt nearby pulsar data in the distance of 1 kpc from the Australia Telescope National Facility (ATNF) pulsar catalogue. By using a Green’s function of an electron propagation model, we then fit pulsar parameters (i.e. the spectral index, the fraction of the total spin-down energy and the cutoff energy) for several cases of a single pulsar. With a combination of the electron background model, several cases of pulsar spectrum are able to explain the electron excess.

Model of electric charge distribution in the trap of a close-contact TENG system

Electron propagation in a trapped state between an insulator and a metal during very close contact in a triboelectric nanogenerator (TENG) system was considered in this study. A single energy level (E0) was assumed for the trap and wave function inside the trap, which is related to the ground state energy. The phase of the waveform in the metal (neglecting the rebound effect at the wall) was assumed very small (δ′ ≪ 1) because of the large size of the metal. The contact distance between the trap and metal is very small, which allows us to ignore the vacuum potential. Based on our results, the probability of finding an electron inside the trap as a function of time was found to be in oscillation (i.e., back-and-forth propagation of the electron between the trap and metal leads to an equilibrium state). These results can be used to understand the quantum mechanisms of continuous contact, particularly in sliding-mode TENG systems.

Effect of rear surface fields on hot, refluxing and escaping electron populations via numerical simulations

After a population of laser-driven hot electrons traverses a limited thickness solid target, these electrons will encounter the rear surface, creating TV/m fields that heavily influence the subsequent hot-electron propagation. Electrons that fail to overcome the electrostatic potential reflux back into the target. Those electrons that do overcome the field will escape the target. Here, using the particle-in-cell (PIC) code EPOCH and particle tracking of a large population of macro-particles, we investigate the refluxing and escaping electron populations, as well as the magnitude, spatial and temporal evolution of the rear surface electrostatic fields. The temperature of both the escaping and refluxing electrons is reduced by 30%–50% when compared to the initial hot-electron temperature as a function of intensity between $10^{19}$ and $10^{21}~~\text{W}/\text{cm}^{2}$ . Using particle tracking we conclude that the highest energy internal hot electrons are guaranteed to escape up to a threshold energy, below which only a small fraction are able to escape the target. We also examine the temporal characteristic of energy changes of the refluxing and escaping electrons and show that the majority of the energy change is as a result of the temporally evolving electric field that forms on the rear surface.

Development of mini-undulators for a table-top free-electron laser

The development of laser wakefield accelerators (LWFA) over the past several years has led to an interest in very compact sources of X-ray radiation – such as “table-top” free electron lasers. However, the use of conventional undulators using permanent magnets also implies system sizes which are large. In this work, we assess the possibilities for the use of novel mini-undulators in conjunction with a LWFA so that the dimensions of the undulator become comparable with the acceleration distances for LWFA experiments (i.e., centimeters). The use of a prototype undulator using laser machining of permanent magnets for this application is described and the emission characteristics and limitations of such a system are determined. Preliminary electron propagation and X-ray emission measurements are taken with a LWFA electron beam at the University of Michigan.

Tunable fractional Fourier transform implementation of electronic wave functions in atomically thin materials

A tunable fractional Fourier transform of the quantum wave function of electrons satisfying either the Schrödinger or the Dirac equation can be implemented in an atomically thin material by a parabolic potential distribution applied on a direction transverse to that of electron propagation. The difference between the propagation lengths necessary to obtain a fractional Fourier transform of a given order in these two cases could be seen as a manifestation of the Berry phase. The Fourier transform of the electron wave function is a particular case of the fractional Fourier transform. If the input and output wave functions are discretized, this configuration implements in one step the discrete fractional Fourier transform, in particular the discrete Fourier transform, and thus can act as a coprocessor in integrated logic circuits.