Electron Vortex Research Articles

Electron vortex beams for chirality probing at the nanoscale

Electron vortex beams for chirality probing at the nanoscale

The Electric Field and Its Impact on the Pitch Angle of Trapped Electrons in a Sub-ion-scale Magnetic Hole

Sub-ion-scale magnetic holes (MHs) are ubiquitous structures in plasmas across a wide range of environments. Despite previous observational and modeling efforts, the three-dimensional (3D) electric field in MHs has yet to be adequately resolved. In this study, utilizing high-resolution measurements of an MH (∼0.08ρ i × 0.14ρ i ) from the Magnetospheric Multiscale mission in Earth’s turbulent magnetosheath, we report this 3D electric field and unveil its roles and generation mechanism. A model is established to quantify the impacts of E ∥ on increasing the loss cone of trapped electrons. The electric field is attributed to electron convection and pressure gradient terms of generalized Ohm’s law. The MH, primarily coupling to the electron, is accompanied by electron jets. These electron jets can be interpreted as different segments of an electron vortex. These electron jets combined with nonideal electric fields not only lead to strong energy conversion ( j · ( E + v e × B ) ∼ 40 nW m−3) from the electromagnetic field to electrons but also enable energy conversion between different electron motion directions. Our study significantly clarifies the physical image of kinetic-scale MHs.

Controlling the initial separation distance between two electron plasma vortices in a Malmberg–Penning trap

This paper presents a novel method to continuously control the initial separation distance d between two plasma vortices of electrons. In this method, the two electron columns are initially confined individually in two coaxial Malmberg–Penning traps with different axial lengths. They rotate around the trap axis at different rotation frequencies due to the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{E}\ imes \\varvec{B}$$\\end{document} drift. Their different rotation rates cause periodic changes in their relative azimuthal positions. The initial conditions are established when the two columns are stretched along magnetic field lines of a unified Malmberg–Penning trap. This method precisely provides a simple and continuous adjustment of the initial d and facilitates efficient investigation of the interaction of the two plasma electron vortices.

Generation of ultrarelativistic vortex leptons with large orbital angular momenta

We put forward a novel method for generating ultrarelativistic vortex positrons and electrons with intrinsic orbital angular momenta (OAM) through nonlinear Breit-Wheeler (NBW) scattering of vortex γ photons. A complete angular momentum-resolved scattering theory has been formulated, introducing angular momenta of laser photons and vortex particles into the conventional NBW scattering framework. We find that vortex positron (electron) can be produced when the outgoing electron (positron) is generated along the collision axis. By unveiling the angular momentum transfer mechanism, we clarify that the OAM of the γ photon and the large angular momenta due to multiple laser photons are entirely transferred to the generated vortex leptons. Furthermore, the cone opening angle and superposition state of the vortex γ photon can be determined via the angular distribution of created pairs in NBW processes. Published by the American Physical Society 2024

Probing Topological Thermal Flux in Equilibrium Using Electron Beams.

Near nonreciprocal media at finite temperature, fluctuating near fields exhibit imbalanced thermal populations in opposite directions, generating equilibrium topological thermal fluxes that circulate the media. While the existence of these fluxes remains unconfirmed, we propose exploiting their interaction with free electron beams for detection. We establish a general framework to quantify thermal flux at any location near an object of arbitrary shape. This reveals unexplored properties of thermal flux spectra depending on their orientation. Further, we connect the electron scattering rate to the equilibrium thermal flux. As a specific example, electrons encountering a planar surface's perpendicular thermal flux preferentially scatter transversely. This measurable scattering distribution, i.e., via angle-resolved electron microscopy, allows us to recover the thermal flux spectrum. Additionally, electron interactions with equilibrium thermal fluxes surrounding local structures offer a novel approach to generating electron vortex beams.

Generation of vortex electrons in tunneling ionization of polyatomic molecules: Exact results in the zero-range potential model

Generation of vortex electrons in tunneling ionization of polyatomic molecules: Exact results in the zero-range potential model

Generation of Quantum Vortex Electrons with Intense Laser Pulses.

Accelerating a free electron to high-energy forms the basis for studying particle and nuclear physics. Here it is shown that the wave function of such an energetic electron can be further manipulated with the femtosecond intense lasers. During the scattering between a high-energy electron and a circularly polarized laser pulse, a regime is found where the enormous spin angular momenta of laser photons can be efficiently transferred to the electron orbital angular momentum (OAM). The wave function of the scattered electron is twisted from its initial plane-wave state to the quantum vortex state. Nonlinear quantum electrodynamics (QED) theory suggests that the GeV-level electrons acquire average intrinsic OAM beyond at laser intensities of 1020Wcm-2 with linear scaling. These electrons emit γ-photons with two-peak spectrum, which sets them apart from the ordinary electrons. The findings demonstrate a proficient method for generating relativistic leptons with the vortex wave functions based on existing laser technology, thereby fostering a novel source for particle and nuclear physics.

Electron vortices in the amplitude of the atomic ionization by a few-cycle circularly polarized laser pulse

Electron vortices in the amplitude of the atomic ionization by a few-cycle circularly polarized laser pulse

MMS Observations of Electron Vorticity in the Earth’s Magnetosheath

The Earth’s magnetosheath serves as a natural laboratory to study the transition of highly turbulent fluctuations. The fundamental information about plasma turbulences can be examined observationally with the help of electron vorticity measurements. This study presents the first statistics of the electron vorticity field in the magnetosheath by utilizing 4 yr data from NASA’s Magnetospheric Multiscale mission. In this study, the magnetosheath vorticity has a dominant perpendicular anisotropy. The vorticity field in the subsolar region is much stronger than that of magnetosheath flanks. Clear dusk-favored asymmetry for large vorticity is identified in the subsolar region. We examine that the electron flow vorticity in the turbulent magnetosheath is well anticorrelated with the electron density. The vorticity is of great importance in energy dissipation and electron heating in the magnetosheath flanks. This study can improve the current understanding of electron vorticity due to its ubiquitous role in space plasma turbulences.

Helicity of magnetic fields associated with non-relativistic electron vortex beams

The helicities of the magnetic fields associated with non-relativistic electron vortex beams are considered for radially extended Bessel modes. Investigating the helicity density of this system lies in realizing the unique electric and magnetic properties of electron vortex beams that influence their interactions with matter. We have evaluated the vector potential components needed for the derivation of the magnetic helicity density and found that this has a non-zero distribution. This is attributed entirely to the cylindrically symmetric density flux of the electron beam, which scales with the winding number ℓ . It is also related to the magnetic moments of the electron oriented along the z-direction, giving rise to the z-component of the magnetic field. We obtain different helicity distributions for different signs of winding number ±ℓ , which confirms the chiral character of the magnetic fields associated with the electron vortex beam. The physical consequences of taking the spin current density into consideration are also examined. This allows a comparison to be made between the evaluated total current helicities, one with and one without including the spin-polarization.

Angular momentum modulation of vortex Cherenkov radiation in optical waveguides.

Vortex free-electron radiation has attracted considerable interest because of its promising potential for applications in communication, high-density radiation sources, and particle detection. Here, we reveal angular momentum modulation of vortex Cherenkov radiation using subwavelength silicon waveguides. The topological charge of vortex radiation field can be controlled by the position parameters of two electron beams based on the rotational symmetry. Besides, the spin angular momentum is accompanied by the excited orbital angular momentum due to the spin-orbit interaction of light. In particular, the periodic evolution of spin and orbital angular momenta are demonstrated by breaking the symmetry of the waveguide. Our results provide a novel mechanism for flexibly regulating vortex electron radiation and exploring electro-optical interaction.

MMS Observations of Oscillating Energy Conversion and Electron Vorticity in an Electron‐Scale Layer Within a Southward Magnetopause Reconnection Exhaust

AbstractThe MMS satellites traversed a ∼6 di‐wide and ∼500 km/s southward reconnection exhaust at the dayside magnetopause on 6 December 2015 and ∼29 di from the associated X‐line region. A narrow ∼0.26–0.34 di layer of enhanced ±3.5 nW/m3 oscillating energy conversion perpendicular to the magnetic field resides in this exhaust. It contained two regions of diverging in‐plane electric fields in general agreement with two clockwise electron flow vortices and a proposed increase of the electron vorticity ∇ × Ve. The layer developed sunward of a unipolar Hall magnetic field for a duskward BM/BL ∼ 0.9 guide field. Each electron flow vortex supported a local ∆BM ∼ 10 nT strengthening of this Hall field. The presence of this electron‐scale layer in a southward exhaust for a duskward guide field is consistent with a two‐dimensional simulation of a similar structure that evolved from an X‐line into a northward exhaust for a similar strength dawnward guide field.

The Helicity of Magnetic Fields Associated with Relativistic Electron Vortex Beams

The Helicity of Magnetic Fields Associated with Relativistic Electron Vortex Beams

Nonstationary Laguerre–Gaussian states in a Magnetic Field

Abstract The Landau states of electrons with orbital angular momentum in magnetic fields are important in the quantum theories of metals and of synchrotron radiation at storage rings, in relativistic astrophysics of neutron stars, and in many other areas. In realistic scenarios, electrons are often born inside the field or injected from a field-free region, requiring nonstationary quantum states to account for boundary or initial conditions. This study presents nonstationary Laguerre–Gaussian (NSLG) states in a longitudinal magnetic field, characterizing vortex electrons after their transfer from vacuum to the field. Comparisons with Landau states and calculations of observables such as mean energy and root-mean-square (r.m.s.) radius show that the r.m.s. radius of the electron packet in the NSLG state oscillates in time around a significantly larger value than that of the Landau state. This quantum effect of oscillations is due to boundary conditions and can potentially be observed in various problems, particularly when using magnetic lenses of electron microscopes and linear accelerators. Analogies are drawn between a quantum wave packet and a classical beam of many particles in phase space, including the calculation of mean emittance of the NSLG state as a measure of its quantum nature.

Polarized vortex Smith-Purcell radiation with cascaded metasurfaces.

We introduce the concept of polarized vortex Smith-Purcell radiation by the interaction of an electron beam and cascaded metasurfaces. The spin and orbital angular momenta of Smith-Purcell radiation are determined by the cascaded metasurface that consists of a grating and a phase gradient metasurface. The grating converts the electron beam radiation into the desired polarized light, while the phase gradient metasurface generates the vortex light. Furthermore, the vortex Smith-Purcell radiation with linear and circular polarizations can be achieved by the various cascaded metasurfaces. In particular, the conversion of chirality in the Smith-Purcell radiation carrying circular polarization is accompanied by the alteration of positive and negative topological charges. This work paves the way for generating polarized vortex electron radiation and is beneficial to promote the development of free-electron-driven devices.

Transmission of vortex electrons through a solenoid

Transmission of vortex electrons through a solenoid

Single-shot fast cinematic imaging during merging process of multiple electron filaments in electrostatic potential well.

For the first time, details of the spatial and temporal acceptable evolution of the merging process of co-rotating electron vortices in a potential well are successfully captured using a "single-shot method" with a high temporal resolution of 10 µs. Four-electron filaments are trapped inside the Beam eXperiment-Upgrade linear trap [H. Himura, Nucl. Instrum. Methods Phys. Res. A 811, 100 (2016)] with a uniform axial magnetic field and co-axial multi-ring electrodes. Images of non-emitting electron filaments are captured using a high-speed camera with up to 1 000 000fps, a microchannel plate, a fast-decay phosphor screen of which fluorescence duration is 0.15 µs, and a super fine metallic mesh with an open area ratio of 89%. Images captured every 10 µs clearly show the growth of multiple short-wave instabilities in the wing trailing electron vortices. The experimental methods and measurement techniques presented in this paper can contribute to revealing exactly how small vortices evolve into a large structure or turbulence in a potential well through complex processes.

Reconstruction of Electron Vortex in Space Plasmas

Space plasmas are turbulent and maintain different types of critical points or flow nulls. Electron vortex, as one type of flow null structure, is crucial in the energy cascade in turbulent plasmas. However, due to the limited time resolution of the spacecraft observations, one can never analyze the three-dimensional properties of the electron vortex. In the present study, with the advancement of the FOTE-V method and the unprecedented high-resolution measurements from four Magnetospheric Multiscale spacecraft, we successfully identify the electron vortex and then reconstruct its three-dimensional topology of the surrounding electron flow field. The results of the reconstruction show that the configuration of the electron vortex is elliptical. Comparison between the observation and reconstruction scales of the vortex indicates the reliable reconstruction of the flow velocity. Our study sheds light on the understanding of the topology and property of the electron vortex and its relationship with kinetic-scale magnetic holes.

Effects of Electron Vortices on the Magnetic Structures in the Terrestrial Magnetosheath

AbstractElectron vortices are usually embedded within different magnetic structures in space plasmas. The effects, including the nonideal electric field, energy dissipation and magnetic field, of electron vortices on these magnetic structures are still unclear. Utilizing the unprecedented high‐resolution data from the Magnetospheric Multiscale mission in the terrestrial magnetosheath, we statistically investigate these effects on magnetic structures. Both nonideal electric fields and energy dissipation have no obvious correlations with the scales of electron vortices. However, compared to the scales, stronger correlations are found between the vorticities of electron vortices and nonideal electric fields, and energy dissipation, respectively. Most of electron vortices have positive contributions to magnetic fields of magnetic structures, such as strengthening the decrease (or increase) of Bt for current sheets and magnetic holes (or flux ropes and magnetic peaks). Our results reveal that the electron vortices play an important role in the evolution of magnetic structures.

Magnetic Hump Associated with Electron Vortex at Dipolarization Front

As the plasma boundary between two distinct plasma populations, dipolarization fronts (DFs) host abundant kinetic-scale substructures that change their normal directions and thus cause their deformation. However, studies on such deformation caused by an electron vortex have been lacking. Here, we present novel observations of a subion-scale magnetic hump (MHu) associated with an oblique electron vortex at a DF through strengthening three components of the magnetic field. A radial electric field in the MHu, showing bipolar variation, is also associated with the electron vortex as it is mainly ascribed to the electron convection term. There is apparent energy conversion ( J→·E→ ∼−0.3 nw m−3) from the particles to the electromagnetic field in the MHu’s leading part, which is accompanied by inflow and outflow of electromagnetic energy (nonzero ∇·S→ ). The other regions of the DF host opposite energy conversion ( J→·E→ > 0). Broadband parallel electrostatic waves are also observed in the MHu. Our study provides insights into the kinetic-scale processes at DFs.