Explore the vast range of titles available.

The possibilities to accelerate vortex electrons with orbital angular momentum (OAM) to relativistic energies and to produce vortex ions, protons, and other charged particles crucially depend on whether the OAM is conserved during the acceleration and on how phase space of the wave packet evolves. We show that both the OAM and a mean emittance of the packet, the latter obeying the Schrödinger uncertainty relation, are conserved in axially symmetric fields of electric and magnetic lenses, typical for accelerators and electron microscopes, as well as in Penning traps. Moreover, a linear approximation of weakly inhomogeneous fields works much better for single packets than for classical beams. We analyze quantum dynamics of the packet’s rms radius ⟨ ρ 2 ⟩, relate this dynamics to a generalized form of the van Cittert–Zernike theorem, applicable at arbitrary distances from a source and for non-Gaussian packets, and adapt the Courant–Snyder formalism to describe the evolution of the packet’s phase space. The vortex beams can therefore be accelerated, focused, steered, trapped, and even stored in azimuthally symmetric fields and traps, somewhat analogously to the classical angular-momentum-dominated beams. We also give a quantum version of the Busch theorem, which states how one can produce vortex electrons with a magnetized cathode during either field- or photoemission, as well as vortex ions and protons by using a magnetized stripping foil employed to change a charge state of ions. Spatial coherence of the packets plays a crucial role in these applications and we provide the necessary estimates for particles of different masses.

Various physical processes in association with magnetic reconnection occur over multiple scales from the microscopic to macroscopic scale lengths. This paper reviews multi-scale and cross-scale aspects of magnetic reconnection revealed in the near-Earth space beyond the general global-scale features and magnetospheric circulation organized by the Dungey Cycle. Significant and novel advancements recently reported, in particular, since the launch of the Magnetospheric Multi-scale mission (MMS), are highlighted being categorized into different locations with different magnetic topologies. These potentially paradigm-shifting findings include shock and foreshock transient driven reconnection, magnetosheath turbulent reconnection, flow shear driven reconnection, multiple X-line structures generated in the dayside/flankside/nightside magnetospheric current sheets, development and evolution of reconnection-driven structures such as flux transfer events, flux ropes, and dipolarization fronts, and their interactions with ambient plasmas. The paper emphasizes key aspects of kinetic processes leading to multi-scale structures and bringing large-scale impacts of magnetic reconnection as discovered in the geospace environment. These key features can be relevant and applicable to understanding other heliospheric and astrophysical systems.

A method of using intense Laguerre-Gaussian (LG) laser pulse is proposed to generate ultrarelativistic (multi-GeV) electron beams with controllable helical structures based on a hybrid electron acceleration regime in underdense plasmas, where both the longitudinal charge-separation electric field and transverse laser electric field play the role of accelerating the electrons. By directly interacting with the LG laser pulse, the topological structure of the accelerated electron beam is manipulated and it is spatially separated into multi-slice helical bunches. These results are clearly demonstrated by our three-dimensional particle-in-cell simulations and explained by a theoretical model based on electron phase-space dynamics. This novel regime offers a new degree of freedom for manipulating ultrashort and ultrarelativistic electrons, and it provides an efficient way for generating high-energy high-angular-momentum helical electron beams, which may find applications in wide-ranging areas.

We propose a method for sorting electrons by orbital angular momentum (OAM). Several methods now exist to prepare electron wavefunctions in OAM states, but no technique has been developed for efficient, parallel measurement of pure and mixed electron OAM states. The proposed technique draws inspiration from the recent demonstration of the sorting of OAM through modal transformation. We show that the same transformation can be performed on electrons with electrostatic optical elements. Specifically, we show that a charged needle and an array of electrodes perform the transformation and phase correction necessary to sort OAM states. This device may enable the analysis of the spatial mode distribution of inelastically scattered electrons.

Two types of filamentary currents (FCs) were observed inside a magnetic flux rope at the magnetopause by the Magnetospheric Multiscale mission. The first FC is identified as an electron vortex, while the other is a reconnecting current sheet. Stochastic electric fields were generated within the FCs, resulting in electron acceleration up to a few keV, similar to recent simulations of electron acceleration inside vortex, which is a second‐order Fermi acceleration. Furthermore, two FCs propagated at different speeds, causing compression in the region between them. Energetic electrons up to 200 keV were detected in the compressed region and displayed a double power‐law spectrum. Observations suggest that the electrons were mainly accelerated by betatron mechanism in the compressed region. The formation, evolution, and interaction of FCs provide a novel mechanism for electron acceleration. These results clearly show the significance of electron‐scale dynamics within flux rope. Plain Language Summary Magnetic reconnection is a fundamental plasma process by which magnetic energy is converted into the kinetic energy of charged particles. Understanding the acceleration mechanisms for the energetic electrons during magnetic reconnection is a long‐standing question in the study of space and astrophysical plasmas. Using Magnetospheric Multiscale observations at Earth's magnetopause, we present in situ evidence of electron acceleration up to 200 keV between two consecutive filamentary currents (FCs) inside a magnetic flux rope. Two FCs propagate at different speeds, with the second moving faster, thus causing a compressed region between them. These results provide an important new way for electron acceleration in magnetic reconnection. Key Points Two types of filamentary currents (FCs) were observed near the center of a magnetic flux rope Stochastic electric fields were generated inside two FCs and accelerated electrons Electrons were accelerated up to 200 keV in the compressed region between two currents by the betatron mechanism

Electron diffraction gratings can be used to imprint well-defined phase structure onto an electron beam. For example, diffraction gratings have been used to prepare electron beams with unique phase dislocations, such as electron vortex beams, which hold promise for the development of new imaging and spectroscopy techniques for the study of materials. However, beam intensity loss associated with absorption, scattering, and diffraction by a binary transmission grating drastically reduces the current in the beam, and thus the possible detected signal strength it may generate. Here we describe electron-transparent phase gratings that efficiently diffract transmitted electrons. These phase gratings produce electron beams with the high current necessary to generate detectable signal upon interaction with a material. The phase grating design detailed here allows for fabrication of much more complex grating structures with extremely fine features. The diffracted beams produced by these gratings are widely separated and carry the designed phase structure with high fidelity. In this work, we outline a fabrication method for high-efficiency electron diffraction gratings and present measurements of the performance of a set of simple prototypical gratings in a transmission electron microscope. We present a model for electron diffraction gratings that can be used to optimize the performance of diffractive electron optics. We also present several new holograms that utilize manipulation of phase to produce new types of highly efficient electron beams.

The coherent control of electron beams and ultrafast electron wave packet dynamics have attracted significant attention in electron microscopy as well as in atomic physics. In order to unify the conceptual pictures developed in both fields, we demonstrate the generation and manipulation of tailored electron orbital angular momentum (OAM) superposition states either by employing customized holographic diffraction masks in a transmission electron microscope or by atomic multiphoton ionization utilizing pulse-shaper generated carrier-envelope phase stable bichromatic ultrashort laser pulses. Both techniques follow similar physical mechanisms based on Fourier synthesis of quantum mechanical superposition states allowing the preparation of a broad set of electron states with uncommon symmetries. We describe both approaches in a unified picture based on an advanced spatial and spectral double slit and point out important analogies. In addition, we analyze the topological charge and discuss the control mechanisms of the free-electron OAM superposition states. Their generation and manipulation by phase tailoring in transmission electron microscopy and atomic multiphoton ionization is illustrated on a 7-fold rotationally symmetric electron density distribution.

Magnetic holes at the ion-to-electron kinetic scale (KSMHs) are one of the extremely small intermittent structures generated in turbulent magnetized plasmas. In recent years, the explorations of KSMHs have made substantial strides, driven by the ultra-high-precision observational data gathered from the Magnetospheric Multiscale (MMS) mission. This review paper summarizes the up-to-date characteristics of the KSMHs observed in Earth’s turbulent magnetosheath, as well as their potential impacts on space plasma. This review starts by introducing the fundamental properties of the KSMHs, including observational features, particle behaviors, scales, geometries, and distributions in terrestrial space. Researchers have discovered that KSMHs display a quasi-circular electron vortex-like structure attributed to electron diamagnetic drift. These electrons exhibit noticeable non-gyrotropy and undergo acceleration. The occurrence rate of KSMH in the Earth’s magnetosheath is significantly greater than in the solar wind and magnetotail, suggesting the turbulent magnetosheath is a primary source region. Additionally, KSMHs have also been generated in turbulence simulations and successfully reproduced by the kinetic equilibrium models. Furthermore, KSMHs have demonstrated their ability to accelerate electrons by a novel non-adiabatic electron acceleration mechanism, serve as an additional avenue for energy dissipation during magnetic reconnection, and generate diverse wave phenomena, including whistler waves, electrostatic solitary waves, and electron cyclotron waves in space plasma. These results highlight the magnetic hole’s impact such as wave-particle interaction, energy cascade/dissipation, and particle acceleration/heating in space plasma. We end this paper by summarizing these discoveries, discussing the generation mechanism, similar structures, and observations in the Earth’s magnetotail and solar wind, and presenting a future extension perspective in this active field.

The surprising message of Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)) was that photons could possess orbital angular momentum in free space, which subsequently launched advancements in optical manipulation, microscopy, quantum optics, communications, many more fields. It has recently been shown that this result also applies to quantum mechanical wave functions describing massive particles (matter waves). This article discusses how electron wave functions can be imprinted with quantized phase vortices in analogous ways to twisted light, demonstrating that charged particles with non-zero rest mass can possess orbital angular momentum in free space. With Allen et al. as a bridge, connections are made between this recent work in electron vortex wave functions and much earlier works, extending a 175 year old tradition in matter wave vortices. This article is part of the themed issue ‘Optical orbital angular momentum’.