Radial Electric Field Research Articles

Comment on: “Some aspects of the interaction of a magnetic quadrupole moment with an electric field in a rotating frame” [J. Math. Phys. 58, 102103 (2017)

We discuss results obtained recently for a quantum-mechanical model given by a neutral particle with a magnetic quadrupole moment in a radial electric field and a scalar potential proportional to the radial variable in cylindrical coordinates that also includes the noninertial effects of a rotating reference frame. We show that the conjectured allowed values of the cyclotron frequency are a mere artifact of the truncation of the power series used to solve the radial eigenvalue equation. Our analysis proves that the analytical expression for the eigenvalues is incorrect.

Enhancing plasma uniformity by employing non-uniform magnetic field modulation in capacitively coupled plasmas

A two-dimensional implicit electrostatic particle-in-cell model is applied for the simulation of non-uniformly magnetized capacitively coupled plasmas. In the absence of a magnetic field, the plasma density is concentrated at the center of the reactor, under the studied parameters. This leads to the formation of a radial density gradient and subsequently generates a radial electric field that causes the deflection of incident ions toward the bottom electrode. Minimizing ion deflection is imperative in order to prevent detrimental effects on plasma processing. In pursuit of this objective, a static magnetic field is applied to the capacitively coupled plasmas by installing direct current coils on the upper section of the reactor. This arrangement has been observed to considerably alter the radial distributions of plasma density and the incident angle of ion bombardment on the bottom electrode.

Effects of Magnetic Field Gradient on the Performance of a Magnetically Shielded Hall Thruster

The objective of this study is to investigate the effects of a magnetic field gradient on the performance of a magnetically shielded Hall thruster. The Particle-in-cell with Monte Carlo collision method (PIC-MCC) is used to simulate the discharge process of the thruster. The performance and plasma characteristics are obtained in conditions with different magnetic field gradients by numerical simulations. As the maximum of the gradient is increased from 1.2 to 3.33 T/m, the electron number density near the channel exit decreases, which leads to less ionization and a weaker radial electric field. As a result, the thrust and specific impulse are decreased, while the plume divergence angle is reduced.

Radial Electric Field Driven Collision-Induced Dissociation in a Miniature Continuous Atmospheric Pressure Interfaced Ion Trap Mass Spectrometer.

Miniature ion trap mass spectrometry with the unique ability of tandem-in-time analysis is extensively used in public security and environmental pollution detection. In this study, a novel radial electric field driven collision-induced dissociation (REFD-CID) is presented with high fragmentation efficiency for different species by adjusting the float DC, the initial kinetic energy of ions, and the pressure in a miniature continuous atmospheric pressure interfaced ion trap mass spectrometer (CAPI-ITMS). It is noteworthy that multiple fragment ions ([M+H-nC2H4]+, where n = 1, 2, 3) of triethyl phosphate were observed with a single injection of ions. The underlying mechanism of the REFD-CID revealed that the enhanced radial electric field by modulation of the float DC drove ions toward regions of intense RF field where broadband heating and dissociation of ions took place through theoretical simulations. Finally, the REFD-CID was utilized to improve the instrument performances. The existence of reagent ions led to a severe space charge effect as the ion injection duration of the CAPI-ITMS was extended to enhance the sensitivity of aniline. Through selective fragmentation of reagent ions, peak broadening and mass shift were eliminated, and meanwhile, a 28-fold improvement of aniline in a signal-to-noise ratio was achieved with the ion injection duration varying from 50 to 2500 ms. Moreover, isomeric illicit drugs (JWH-018 and acetylcodeine) were distinguished by generating multiple characteristic fragment ions, demonstrating potential applications in the identification of synthetic illicit drugs.

Robust stellarator optimization via flat mirror magnetic fields

Stellarator magnetic configurations need to be optimized in order to meet all the required properties of a fusion reactor. In this work, it is shown that a flat-mirror quasi-isodynamic (QI) configuration (i.e. a QI configuration with sufficiently small radial variation of the mirror term) can achieve small radial transport of energy and good confinement of bulk and fast ions even if it is not very close to perfect omnigeneity, and for a wide range of plasma scenarios, including low β and small radial electric field. This opens the door to constructing better stellarator reactors. On the one hand, they would be easier to design, as they would be robust against error fields. On the other hand, they would be easier to operate since, both during startup and steady-state operation, they would require less auxiliary power, and the heat loads on plasma-facing components caused by fast ion losses would be reduced to acceptable levels.

Relativistic superconductivity in 2D: An example

Recently, we formulated an effective scalar electrodynamics model of relativistic type-II superconductivity. We discussed possible electromagnetic behaviors of superconductivity along the lines of the nonrelativistic Ginzburg–Landau theory. This brief work considers a [Formula: see text]D condensate subjected not only to a homogeneous magnetic field but also to a static radial electric field (polar coordinates). The electric field is regarded to have two components: a central constant field and a Coulomb-like field with “charge” g, where g can take only evenly spaced real numbers. We provide the single-vortex supercurrent density together with its associated magnetic flux density for the ground state of the system. Feasible extensions of this example in [Formula: see text]D curvilinear geometries could explain some superconductivity phenomena which do not occur in planar [Formula: see text]D geometries.

Insight into What Is inside Swift Heavy Ion Latent Tracks in PET Film.

We present here a novel experimental study of changes after contact electrification in the optical transmission spectra of samples of both pristine and irradiated PET film treated with Kr+15 ions of energy of 1.75 MeV and a fluence of 3 × 1010 cm2. We used a non-standard electrification scheme for injecting electrons into the film by applying negative electrodes to both its surfaces and using the positively charged inner regions of the film itself as the positive electrode. Electrification led to a decrease in the intensity of the internal electric fields for both samples and a hypsochromic (blue) shift in their spectra. For the irradiated PET sample, electrification resulted in a Gaussian modulation of its optical properties in the photon energy range 2.3-3.6 eV. We associate this Gaussian modulation with the partial decay of non-covalent extended conjugated systems that were formed under the influence of the residual radial electric field of the SHI latent tracks. Our studies lead us to suggest the latent track in the PET film can be considered as a variband material in the radial direction. Consideration of our results along with other published experimental results leads us to conclude that these can all be consistently understood by taking into account both the swift and slow electrons produced by SHI irradiation, and that it appears that the core of a latent track is negatively charged, and the periphery is positively charged.

Analytical model and numerical simulation of relief well adjacent distance considering multi-layer media

Accurate measurement of adjacent well distance (AWD) is the key factor restricting the successful plugging of relief well (RW). Traditional ranging technology can't meet the accuracy requirements of AWD. Fortunately, magnetic ranging technology has shown great superiority in this respect. However, the magnetic ranging algorithm based on low-frequency injected current has always been a difficult problem. Therefore, based on the magnetic ranging principle of low frequency injection current, the propagation law of current in medium is revealed. Considering the effect of mud on current propagation, a multilayer medium model is established to improve the calculation accuracy of current intensity in adjacent casing. Through numerical simulation and experimental comparison, the validity of the analytical model is verified. Analysis results show that the intensity of injected current, the conductivity of medium and the distance between electrode and casing axis have a significant effect on the current of the casing. The radial electric field intensity fluctuates obviously on the interface of the medium. When the distance from the electrode to the casing axis is constant, the magnetic field strength of the measuring point is also affected by the distance from the electrode to the probe pipe and the relative inclination angle. According to the distance between the electrode and the axis of the casing, the optimal distance between the electrode and the probe tube can be obtained, so that the magnetic induction intensity of the measuring point is maximized. The results show that the multi-layer medium model is more suitable for the actual working conditions and the calculation error is minimal.

Snap-through instability in rotating dielectric elastomer tubes

Dielectric elastomers (DEs) have been widely used in soft robotics, high-performance actuators, and bioengineering. However, they may suffer from more failure modes than pure elastic elastomers when undergoing rotational motion. In this paper, we present a theoretical analysis of the finite deformation of rotating DE tubes, addressing the challenges associated with rotational motion in DEs. Our study focuses on the combined influence of a radial electric field and an axial pre-stretch. We numerically calculate three different materials, including neo-Hookean, Gent, and Ogden models, for rotating DE tubes and find that the snap-through instability caused by rotation occurs only in tubes with the Ogden model, resulting in dramatic deformation. Moreover, we study the effects of geometric dimensions and external loads and reveal the competition mechanism between the snap-through instability and electrical breakdown of DE tubes under external voltage. Significantly, our work presents practical thresholds that offer comprehensive guidance for designing and controlling of rotating DE tubes, preventing electrical breakdown during rapid deformation through the adjustment of external loads. This study provides novel insights and practical recommendations for the field of nonlinear deformation in rotating DE tubes.

Spontaneous formation of a transport barrier in helium plasma in a tokamak with circular configuration

We report on the first experimental observation of a spontaneously formed transport barrier in the tokamak with a circular configuration in helium plasmas. There was no external polarization of the plasma by electric field or other technique to form the barrier as it is typically used in tokamaks with circular plasma. In general, the transport barriers play an important role in plasma confinement especially in tokamaks with divertor configuration. In our experiments, we clearly observe distinct characteristics of a transport barrier, including a steep gradient of the electron temperature and an enhanced radial electric field along with the change in the plasma potential, floating potential, and electron temperature fluctuation. The electron temperature and the plasma potential are obtained by a combination of the ball-pen and Langmuir probe measurements with high temporal resolution on a shot-to-shot basis. This first experimental observation of the spontaneously formed transport barrier might bring new possibilities to obtain a fusion-relevant study of the edge plasma parameters and transport in helium plasmas even on small tokamaks.

Plasma sputtering of biased electrodes in an oblique magnetic field

The surface erosion of biased electrodes immersed in a radio frequency (RF) plasma was investigated in oblique magnetic fields ranging from 0.1 T to 3.5 T. The plasma potential and density in the vicinity of the biased electrode have been measured using an RF-compensated cylindrical Langmuir probe moved by a three-dimensional motorised arm in the ALINE facility at 0.1 T. The erosion profiles were determined for different gases (argon and helium), magnetic field strength and plasma volume for the same electrode surface area at an angle of 5∘ with the magnetic field in three different experimental geometries. The radial electric field (perpendicular to the magnetic field) in the plasma column has been deduced from plasma potential measurements. This radial field makes the ions converge to the core of the plasma column at grazing angles (30∘) and is reversed at larger angles. The ion flux on the sample increases with the magnetic field magnitude leading to a strong erosion inhomogeneity. At lower plasma volume, the erosion rate is sensitively enhanced. Local redeposition was identified using x-ray photoelectron spectroscopy on the surfaces exhibiting preferential deposition directions. Finally, the asymmetric erosion patterns obtained from a molybdenum layer etching are explained by the similar asymmetric density maps obtained with the probe and by the drift and the local sheath acceleration.

Particle-in-cell simulation of a cylindrical plasma mass separator based on Penning discharge with thermionic cathodes

This work is devoted to the modeling of a Penning discharge with a hot cathode, which is used to create a background plasma with a radial electric field in a plasma mass separator. We used a 2D3V electrostatic particle-in-cell plus Monte Carlo Collision (PIC/MCC) simulation model with a gyrokinetic approximation for magnetized electrons and a geometrical scaling scheme. The proposed model predicts the development of a rotating spoke structure, leading to fluctuations in the electric potential. The fluctuation amplitude and the averaged radial profile of the potential are in qualitative agreement with experiment. On the example of a model flow of silver and lead ions, we have shown that potential fluctuations can impair separation, leading to a partial overlap of ion deposition spots on a substrate. Each of the separated fractions contain about 11% impurities.

Algebraic and numerical studies on the roles of momentum conservation and self-adjointness in moment-based neoclassical particle fluxes

Algebraic and numerical studies on the roles of momentum conservation and self-adjointness in moment-based neoclassical particle fluxes

Excitation of radially propagating electrostatic shear Alfvén wave during the formation of ambipolar radial electric field in a stochastic magnetic field

A radially propagating electrostatic shear Alfvén wave (ωH mode) is found during the formation of ambipolar radial electric field in a magnetic stochastic layer through gyrokinetic simulation. It is found that the times scale of the ambipolar radial electric field formation is the damping time of the ωH mode. The frequency and damping rate of the ωH mode are theoretical derived, which are in good agreement with the simulation results.

Analysis of Flexoelectric Solids With a Cylindrical Cavity

Abstract Flexoelectricity, a remarkable size-dependent effect, means that strain gradients can give rise to electric polarization. This effect is particularly pronounced near defects within flexoelectric solids, where large strain gradients exist. A thorough understanding of the internal defects of flexoelectric devices and their surrounding multiphysics fields is crucial to comprehend their damage and failure mechanisms. Motivated by this, strain gradient elasticity theory is utilized to investigate the mechanical and electrical behaviors of flexoelectric solids with cylindrical cavities under biaxial tension. Closed-form solutions are obtained under the assumptions of plane strain and electrically impermeable defects. In particular, this study extends the Kirsch problem of classical elasticity theory to the theoretical framework of higher-order electroelasticity for the first time. Our research reveals that different length scale parameters of the strain gradient and bidirectional loading ratios significantly affect the hoop stress field, radial electric polarization field, and electric potential field near the inner cylindrical cavity of the flexoelectric solid. Furthermore, we validate our analytical solution by numerical verification using mixed finite elements. The congruence between the two methods confirms our analytical solution’s accuracy. The findings presented in this paper provide deeper insights into the internal defects of flexoelectric materials and can serve as a foundation for studying more complex defects in flexoelectric solids.

Turbulence spreading and its effects on the edge flows and turbulence during sawtooth cycles in the J-TEXT tokamak plasmas

Turbulence spreading and its effects on the edge flows and turbulence during sawtooth cycles in the J-TEXT tokamak plasmas are presented. These experiments were performed by Langmuir probe array and electron cyclotron emission. This study aims to understand the rapid transport phenomenon and the role of turbulence in driving flows. Beyond the mixing radius, the turbulence pulse moves faster than the sawtooth heat pulses. The results confirm the existence of turbulence spreading during sawtooth cycles. As the turbulence and heat pulses propagate to the edge, the edge turbulence, radial electric fields, pressures, and geodesic acoustic modes are all enhanced. Hysteresis relationships between the intensities of the turbulence and the radial electric fields are observed. The radial electric field lags behind the turbulence, and its intensity increases/decreases almost linearly with the increase/decrease in the turbulence intensity. The observation suggests that the edge flows are driven dominantly by turbulence during sawtooth cycles. The weakening/enhancement of the edge flows accompanies the increase/decrease in the ion collision rates during sawtooth cycles.

Shaping the edge radial electric field to create shearless transport barriers in tokamaks

Shaping the edge radial electric field to create shearless transport barriers in tokamaks

Poloidal impurity asymmetries, flow and neoclassical transport in pedestals in the plateau and banana regimes

Charge exchange recombination spectroscopy (CXRS) measures the radial electric field in the pedestal by measuring the impurity density, temperature and flow. Combined outboard and inboard CXRS measurements allow poloidal variations that arise due to the poloidal variation of the magnetic field to be determined. At present, impurity neoclassical pedestal models avoid the complications of treating finite poloidal gyroradius effects by assuming the impurity charge number is large compared with the main ion charge number. These models are extended slightly by retaining the impurity radial pressure gradient to demonstrate that no substantial effect occurs due to impurity diamagnetic effects. More importantly, the neoclassical model is significantly extended to obtain a more comprehensive treatment of the main ions in the plateau and banana regimes. A parallel impurity momentum equation is derived that is consistent with previous results in the banana regime and reduces to the proper large aspect ratio form required in the plateau regime. The implications for interpreting the CXRS measurements are discussed by writing all results in terms of the gradient drive and poloidal flow.

Focusing of Radially Polarized Electromagnetic Waves by a Parabolic Mirror

It is well-known that a strong longitudinal electric field and a small spot size are observed when radially polarized beams are tightly focused using a high numerical aperture parabolic mirror. The longitudinal electric field component can accelerate electrons along the propagation axis at high intensities in the focal region, which opens an application in particle acceleration. In this paper, we present a rigorous derivation of the electric field obtained when a radially polarized, monochromatic, flat-top beam is focused by a parabolic mirror. The formulae were deduced from the Stratton–Chu integral known from vector diffraction theory. We examined the influence of the focusing parameters on the distribution of both the longitudinal and radial electric field components. In the small numerical aperture and short wavelength regimes, excellent agreement was found with the results obtained from the Rayleigh–Sommerfeld formula. The calculation method can be adapted for various beam types and for electromagnetic pulses as well.

The phase-space structure of a nonlinear ion diffusion tensor in ion-temperature-gradient-driven turbulence

The phase-space structure of an ion diffusion tensor in ion temperature gradient (ITG)-driven turbulence is studied using the newly developed numerical code Numerical Diagnosis of Transport Matrix. The numerical results show that at both the linear and nonlinear stage, the diffusion tensor of ITG turbulence presents a typical ballooning structure in the poloidal direction and a magnetic drift resonance structure in velocity space. The D rr and D rK components of the diffusion tensor satisfy the Stokes–Einstein relation. It is found that the phase-space structure of the ion diffusion tensor at the linear stage is induced by the resonance between ions and ITG eigenmodes, while that at the nonlinear stage is induced by the resonance between ions and the daughter ballooning modes under the poloidal acceleration of nonlinear zonal radial electric fields.