Azimuthal Electric Field Research Articles

Relativistic Analogues of the Aharonov-Bohm Effect and the Landau Quantization with the Lorentz Symmetry Violation Determined by Azimuthal Electric Fields and a Fixed Vector Field

We analyse the behaviour of the Dirac field under the effects of the violation of the Lorentz symmetry determined by a fixed time-like vector background and azimuthal electric fields. We show, from the interaction of the Dirac particle with an azimuthal electric field (proportional to the inverse of the radial distance) and the fixed time-like vector field, that analogues of the Aharonov-Bohm effect can be obtained. Besides, from the interaction of the Dirac field with an azimuthal electric field (proportional to the radial distance) and the fixed time-like vector field, therefore, a relativistic analogue of the Landau quantization can be achieved.

Acceleration of Dusty Plasma Flow in Azimuthal Electric and Radial Magnetic Fields

In the framework of the model of cold hydrodynamics, acceleration of the flow of dusty plasma in azimuthal electric and radial magnetic fields has been studied. The obtained results show that there are conditions under which macroscopic particles are captured and accelerated by the plasma flow.

Ускорение потока пылевой плазмы в азимутальном электрическом и радиальном магнитном полях

In the framework of the model of cold hydrodynamics, the acceleration of the dusty plasma flow in azimuthal electric and radial magnetic fields is studied. The results show that there are conditions under which macroscopic particles are captured and accelerated by the plasma flow.

RF and Thermal Analysis of Beam Compression Unit for a $W$ -Band Gyrotron

A four-section beam compression unit (BCU) with copper and aluminum nitride–silicon carbide (AlN-SiC) annular disks was proposed for a $W$ -band gyrotron. Various dimensional parameters were calculated, based on which the BCU was modeled in a high-frequency structure simulator (HFSS), and the transmission characteristics were plotted for various sets of dimensional parameters. The dimensional parameters were optimized for achieving the attenuation of more than 60 dB over 85–105 GHz. It was further examined that the hollow electron beam radius over various sections of the BCU should not lead to beam–wave interaction, and if so, it should not propagate toward the interaction cavity. For this purpose, azimuthal electric field intensities in various azimuthally symmetric modes below the operating mode were plotted against the radial coordinate in various sections of the BCU and checked for the azimuthal electric field intensity values with the range of beam radius in the corresponding section. The electric field intensity maxima should be avoided within the range of beam radius in the corresponding section. Furthermore, the transient thermal analysis of the BCU was carried out considering temperature varying thermal conductivity in two proposed models: 1) with radially constant and 2) radially varying heat loads within AlN-SiC disks to predict the maximum temperature attained in the ceramic as 76.8 °C and 88.5 °C, respectively, taking 8-L/min flow rate of deionized water and ten heat load pulses.

A Global Magnetohydrodynamic Simulation Study of Ultra-low-frequency Wave Activity in the Inner Magnetosphere: Corotating Interaction Region + Alfvénic Fluctuations

Abstract Using global magnetohydrodynamic (MHD) simulations, we investigate the role played by a complex solar structure composed of a corotating interaction region (CIR) followed by solar wind Alfvénic fluctuations on the magnetosphere’s nightside, equatorial electric field oscillations in the ultra-low-frequency range. A series of numerical experiments are performed employing synthetic solar wind inputs resembling those of a real CIR+Alfvénic fluctuation event that reached Earth’s magnetosphere on 2003 April 20. The following is found: (i) Radial electric field component fluctuations are excited via magnetopause boundary motions driven either by solar wind density variations characteristic of CIRs or by solar wind Alfvénic fluctuations with a given oscillation period. (ii) Azimuthal electric field component fluctuations nearer to Earth, that is, at radial distances R less than about 5R E ( Earth radius), are apparently not related to either of the two types of sinusoidal solar wind Alfvénic fluctuations used in this study featuring monochromatic frequencies of 0.833 mHz (20-minute period) and 1.666 mHz (10-minute period). Instead, these innermost azimuthal component fluctuations show enhanced activity when inner magnetosphere convection increases as a result of a southward turning of the interplanetary magnetic field component B z . (iii) Lastly, outermost (R ≳ 7 R E) azimuthal electric field oscillations weakly respond to monochromatic solar wind Alfvénic fluctuations by showing power spectral density peaks at both driving frequencies, but only near the flanks of the magnetopause, thus suggesting that such oscillations are being excited also owing to magnetopause boundary motions driven by solar wind Alfvénic fluctuations.

Experimental study of the effect of propellant asymmetrical distribution on anode current in a Hall effect thruster

This paper experimentally evaluated the effect of the disruption of the symmetrical distribution of the propellant on the characteristics of the anode current. The change in the asymmetry degree of the propellant distribution is achieved by supplying gas with a dual-cavity gas distributor. The results show that as the asymmetry degree increases, the magnitude of the anode current changes monotonically from a slow growth to a rapid growth, while the peak-to-peak value of the anode current exhibits a non-monotonic behavior. A preliminary analysis shows that the asymmetrical distribution of the propellant causes a nonuniform plasma generation along the azimuthal direction and consequently the appearance of an azimuthal electric field. The effect of the azimuthal electric field on the electron azimuthal drift as well as the induction of the electron axial drift are key factors that account for the change of the anode current and its oscillation.

Plasma formation and cross-field electron transport induced by azimuthal neutral inhomogeneity in an anode layer Hall thruster

The fluctuation of the azimuthal electric field caused by the electron drift instability or the rotating spokes in the E×B plasma is known to enhance the electron cross field transport. The increased electron current, observed during the operation of a Hall thruster with a nonuniform propellant supply in azimuthal direction, also appears to be related to the azimuthal electric field. In this paper, we experimentally investigate how neutral inhomogeneity in azimuth affects the plasma structure formation, and how this self-organized structure influences the electron cross field transport. We observed an axial-azimuthally varying space potential structure, which results in an alleviated effective axial potential profile and induces the azimuthal electric field. From the distributions of the light emission intensity and plasma density, we show that the azimuthal profile of plasma is skewed in the direction of Ez×Br drift of the magnetized electrons and that the spatial scale of the structure matches the spatial scale of the input neutral variation. The plasma structure reveals that the axial electron drift transport from the induced azimuthal electric field is the most dominant factor due to its equivalent mobility 1/B, which is two orders of magnitude greater than the classical collisional mobility perpendicular to the magnetic field. This indicates that neutrals contribute to the electron cross field transport not only directly through the elastic collisions but also indirectly through their influence on the formation of the plasma structure, which enhances the cross field transport. Lastly, we show that the effective electron mobility rides on 1/16Br line when deviating from the classical mobility line and that the effective Hall parameter is greatly reduced where Eθ develops.

Accessing electromagnetic properties of matter with cylindrical vector beams

Cylindrical vector beam (CVB) is a structured lightwave characterized by its topologically nontrivial nature of the optical polarization. The unique electromagnetic field configuration of CVBs has been exploited to optical tweezers, laser accelerations, and so on. However, use of CVBs in research fields outside optics such as condensed matter physics has not progressed. In this paper, we propose potential applications of CVBs to those fields based on a general argument on their absorption by matter. We show that pulse azimuthal CVBs around terahertz or far-infrared frequencies can be a unique and powerful mean for time-resolved spectroscopy of magnetic properties of matter and claim that an azimuthal electric field of a pulse CVB would be a novel way of studying and controlling edge currents in topological materials. We also demonstrate how powerful CVBs will be as a tool for Floquet engineering of nonequilibrium states of matter.

Numerical studies of the ExB electron drift instability in Hall thrusters

The properties of the ExB drift mode in Hall thrusters were investigated through particle-based simulations. Two different two-dimensional models coupling the ExB drift azimuthal direction with the axial accelerating field and radial magnetic field directions, respectively, were implemented assuming Cartesian slab geometry. While the azimuthal-axial model is self-sustaining through the closure of the anode-cathode circuit, the radial-azimuthal one is equipped with an injection system that preserves the number of ions and with a secondary electron emission module for electron-wall interaction. Results identify the linear growth and nonlinear saturation mechanisms consisting of electron heating along azimuthal and radial directions and of ion wave trapping. The latter leads to the ion rotation along the azimuthal direction giving the ion distribution a long tail. The discrete band structure of ExB electron drift instability evolves by an inverse cascade process toward small wavenumbers characterized by broader resonances giving to the spectrum an ion-acoustic-like nature. The larger lobes are due to electron heating and to the presence of a radial component by a modified two-stream instability. Important correlations at macroscopic level between the azimuthal modulation of the azimuthal electric field and the axial modulation of the accelerating field are proof of the complexity of the electron transport in Hall thrusters.

A new method to suppress the Rayleigh–Taylor instability in a linear device

Rayleigh–Taylor instability (RTI) is a primary hurdle for many different fusion approaches, most of which rely on external pressure to stabilize the plasma by impeding plasma displacement. In this paper, we report a novel method that utilizes a rotating magnetic field (RMF) to drive an azimuthal electron current to reduce the charge separation caused by RTI. The fluctuation measured in the central cell of the mirror device, approximately half a device length away from the RMF, is identified as the m = 1 mode and is suppressed by the RMF in the plug cell. The azimuthal electric fields of the fluctuation are found to decrease to almost zero, and the radial confinement is improved by more than a factor of ten. The separation of the RMF region from the central cell makes this stabilization method unique because the RMF, which can complicate the local magnetic field lines, has little influence on the magnetic field configuration in the central cell. This study may shed light on the use of resonant magnetic perturbations in tokamaks as well as on stabilization methods for many other fusion experiments.Rayleigh–Taylor instability (RTI) is a primary hurdle for many different fusion approaches, most of which rely on external pressure to stabilize the plasma by impeding plasma displacement. In this paper, we report a novel method that utilizes a rotating magnetic field (RMF) to drive an azimuthal electron current to reduce the charge separation caused by RTI. The fluctuation measured in the central cell of the mirror device, approximately half a device length away from the RMF, is identified as the m = 1 mode and is suppressed by the RMF in the plug cell. The azimuthal electric fields of the fluctuation are found to decrease to almost zero, and the radial confinement is improved by more than a factor of ten. The separation of the RMF region from the central cell makes this stabilization method unique because the RMF, which can complicate the local magnetic field lines, has little influence on the magnetic field configuration in the central cell. This study may shed light on the use of resonant magnetic p...

Rotating spoke instabilities in a wall-less Hall thruster: simulations

The low-frequency rotating plasma instability (spoke) in the ISCT200 thruster operating in the wall-less configuration was simulated with a 3 dimensional PIC MCC code. In the simulations an m = 1 spoke rotating with a velocity of 6.5 km s−1 in the E × B direction was observed. The rotating electron density structure in the spoke is accompanied by a strongly depleted region of the neutral gas, which clearly shows that the spoke instability is of an ionization nature, similar to the axial breathing mode oscillations. In the simulation the electron cross-field transport through the spoke core was caused by diffusion in the high-frequency (4–10 MHz), short-scale (3 mm) electric field oscillations. These short-scale oscillations play a crucial role in the thruster discharge as over 70% of the electron current to the anode originates from the spoke core. The rest of the current originates from the spoke front where the electron cross-field transport toward the anode is due to the E × B drift in the spoke macroscopic azimuthal electric field.

On the induced azimuthal electric field in the current drive of an odd-parity rotating magnetic field

The azimuthal electric field Eθω, which is induced by the axial oscillating magnetic field Bzω of the odd-parity Rotating Magnetic Field (RMF) scheme, is experimentally found to play an important role in driving the toroidal plasma current. In the odd-parity RMF scheme, Eθω at the middle plane of the field reversed configuration can generate the so-called punctuated betatron-orbital electrons to drive the toroidal current in addition to the current driven by the transverse component of RMF Brω, whereas Brω is the only driving mechanism in the even-parity scheme. In this work, Eθω (or Bzω) and Brω are each studied to account for different current driving mechanisms. We report that Eθω accounts for the more efficient current driving in our experiments.

Gyrotron multistage depressed collector based on E × B drift concept using azimuthal electric field. II: Upgraded designs

Multistage Depressed Collectors (MDCs) are nontrivial for high-frequency gyrotrons. A basic conceptual design of an E×B MDC using azimuthal electric fields was proposed in Part I of this series. In the present work, several upgraded design proposals based on the basic one will be elaborated. These proposals will significantly reduce the back-stream of electrons, which was the main drawback of the basic design proposal. Another upgraded design proposal will shrink the length and maximal radius of the MDC to be only a fraction of its full-length version. A conceptual design of the final MDC proposal will be given at the end.

Hybrid-mode analysis of circular waveguide with chiral dielectric lining for dispersion characteristics for potential application in broadbanding a gyro-traveling-wave tube

ABSTRACTA circular waveguide with chiral dielectric lining was analyzed for hybrid mode dispersion relation. In chiral dielectric lining region, the different radial propagation constants, and in the central free-space region only one radial propagation constant for the left- and right- circularly polarized waves were considered. A method was presented to obtain the hybrid-mode dispersion relation of the proposed structure using the field matching technique. A numerical computer code was developed to solve the hybrid-mode dispersion relation and the solutions were plotted to explore the dispersion characteristics and shaping with the change of material and geometry parameters of the structure. Further, the azimuthal electric field intensity was plotted against radial coordinate to explore the position of field maxima for placing the gyrating electron beam for the potential application of the structure in a gyro-traveling-wave tube. Thus, out of the two modes studied, EH01 and HE01, the later found suitable for the operation of a gyro-traveling-wave tube.

Three-dimensional particle-in-cell model of Hall thruster: The discharge channel

There are still many missing elements to complete the physical picture at the basis of the Hall thruster functioning. The origin of the anomalous electron cross-field transport often ascribed to azimuthal electron E × B drift instability remains decoupled from self-consistent ion axial acceleration and radial boundary conditions, at the same time. This study represents the first attempt to correlate the different mechanisms contributing to the electron transport by means of a fully kinetic three-dimensional Particle-in-Cell model. A geometrical scaling scheme has been used to make the simulation possible. This scheme irremediably changes what are some salient characteristics of the discharge, such as the wall interaction and the axial component of the electric field. For this reason, a critical assessment of the effects of reducing dimensions has been addressed. The present paper deals with the physics of discharge channel. Results confirm the occurrence of E × B drift instability along the azimuthal direction. The modulation is almost standing wave: it moves back and forth travelling only a short distance before being axially convected away. In addition, the dielectric floating potential nature of the lateral walls gives to the azimuthal modulation an important radial component creating an oblique pattern in the radial-azimuthal plane. As a consequence, the azimuthal electric field presents a double alternating structure: two phase-opposing waves are present in the first and second half of the radial extension between the two lateral walls. Finally, the effect of secondary electron emission from walls is not sufficient to guarantee the right electron current to neutralize the ion beam, but rather it works as an auxiliary mechanism (together with ion heating and azimuthal rotation) to saturate the electron drift instability leading to smaller amplitude oscillations.

Ion velocity analysis of rotating structures in a magnetic linear plasma device

The MISTRAL device is designed to produce a linear magnetized plasma column. It has been used a few years ago to study a nonlinear low frequency instability exhibiting an azimuthal number m = 2. By changing the experimental configuration of MISTRAL, this work shows experimental results on an m = 1 rotating instability with strongly different behavior. The spatio-temporal evolution of the ion velocity distribution function given by a laser-induced fluorescence diagnostic is measured to infer the radial and azimuthal velocities, ion fluxes, and electric fields. The naive image of a plasma exhibiting a global rotation is again invalidated in this m = 1 mode but in a different way. Contrary to the m = 2 mode, the rotation frequency of the instability is lower than the ion cyclotron frequency and ions exhibit a complex behavior with a radial outward flux inside the unstable arm and azimuthal ion fluxes always directed toward the unstable arm. The azimuthal ion velocity is close to zero inside the ionization region, whereas the radial ion velocity grows linearly with radius. The radial electric field is oriented inward inside the unstable arm and outward outside. An axial velocity perturbation is also present, indicating that contrary to the m = 2 mode, the m = 1 mode is not a flute mode. These results cannot be easily interpreted with existing theories.

RF simulation and improvements of an ion source test facility at HUST

Huazhong University of Science and Technology is developing a small RF based ion source for testing key techniques of the negative ion source. Numerical simulations of the source are performed with a commercial high frequency finite element analysis (FEA) software. The Faraday screen (FS) is included in the 3D model to reproduce the realistic electromagnetic fields in the driver. The plasma is approximated as a homogeneous electrically conducting medium in the discharge zone. Physical images of the electromagnetic (EM) fields in the driver with/without FS or plasma are presented and compared: (1) The FS suppresses effectively the axial electric field in the discharge zone, therefore diminishes the capacitive coupling between the antenna and plasma. (2) The existence of plasma intensifies the induced azimuthal electric field in the discharge zone and further enhances the inductive coupling between the antenna and plasma. The equivalent antenna impedances loaded with plasma are evaluated by this FEA method as well as an analytical method based on the ICP transformer model. The results are used to design the matching network, which employs a transformer-insulated Γ-type topology. Two strategies of matching by adjusting capacitors and operating frequency are investigated and proved both feasible. To improve the RF coupling between the antenna and plasma, an optimized concept design of the RF driver which employs the ferromagnetic enhancement technique is presented and the simulation results prove its feasibility.

Plasma Thruster Using Momentum Exchange in Crossed Magnetic Fields

We examine the creation and design of a plasma thruster based on the converting of radial and circumferential momentum of the plasma flow into the axial direction. The acceleration effect is formed by the azimuthal electric field which comes about as a variation of an external, axial magnetic flux. Simultaneously, the azimuthal electron and ion flows interact with the radial magnetic field via the Lorentz force. Owing to this process, the transformation of azimuthal momentum transfers into axial momentum. As a result, the electron and ion flows are accelerated in one axial direction. Estimations specifying the admissible range of parameters of this device and the plasma flow are derived.

Gyrotron multistage depressed collector based on E × B drift concept using azimuthal electric field. I. Basic design

Multistage Depressed Collectors (MDCs) are widely used in vacuum tubes to regain energy from the depleted electron beam. However, the design of an MDC for gyrotrons, especially for those deployed in fusion experiments and future power plants, is not trivial. Since gyrotrons require relatively high magnetic fields, their hollow annular electron beam is magnetically confined in the collector. In such a moderate magnetic field, the MDC concept based on E × B drift is very promising. Several concrete design approaches based on the E × B concept have been proposed. This paper presents a realizable design of a two-stage depressed collector based on the E × B concept. A collector efficiency of 77% is achievable, which will be able to increase the total gyrotron efficiency from currently 50% to more than 60%. Secondary electrons reduce the efficiency only by 1%. Moreover, the collector efficiency is resilient to the change of beam current (i.e., space charge repulsion) and beam misalignment as well as magnetic field perturbations. Therefore, compared to other E × B conceptual designs, this design approach is promising and fairly feasible.

The role of instability-enhanced friction on ‘anomalous’ electron and ion transport in Hall-effect thrusters

Using a self-consistent 2D particle-in-cell (PIC) simulation, we investigate the electron transport in Hall-effect thrusters. The PIC simulation is explicit in time and models the axial and azimuthal directions of a thruster without using any artificial parametric or geometric scaling factors. The applied discharge voltage and external magnetic field causes electrons to drift in the azimuthal direction, and this drives an instability in the plasma that produces large amplitude oscillations in both the plasma density and azimuthal electric field. A Fourier transform in time and space shows that the oscillations follow a dispersion relation similiar to that for an ion acoustic instability (in agreement with a recent kinetic theory). Correlated with the presence of this instability is an enhanced electron cross-field transport; even in the absence of electron-wall collisions and secondary electron emission. The amplitude of plasma density oscillations (but not electric field oscillations) is found to decrease significantly in a region just downstream of the thruster exit (before then increasing again), and reaches levels similar to those measured experimentally with collective light scattering techniques. By taking relevant velocity moments of the electron distribution function in the PIC simulations, we reconstruct each term in the electron momentum conservation equation and demonstrate that ‘anomalous’ electron transport can be explained entirely due to an instability-enhanced friction force between electrons and ions. This friction force acts as an additional momentum loss allowing electrons to cross the magnetic field, and as an accelerating force causing ions to rotate azimuthally in the same direction as the electrons. Clear evidence of ion-wave trapping in the instability electric field is observed.