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Two series of conical wire holders were designed that can generate different values of positive (with outward direction) and negative (with inward direction) radial electric fields on wire surfaces in negative polarity wire electrical explosion (WEE) in vacuum. The influences of positive and negative radial electric fields on the evolution and axial inhomogeneity of the WEE were studied with the conical–planar electrodes. The results suggest that the radial electric field does have significant influence on the axial inhomogeneity in WEE. The positive radial electric field can increase the energy deposition, while the negative radial electric field can decrease the energy deposition, which then leads to different energy deposition structures. This study provides some help for better understanding of the axial inhomogeneity in the process of WEE; another potential use of the observed effect is to cause different sections of wire to explode at different times, which may introduce a possible approach for adjusting axial inhomogeneity of WEE through electric field regulation. [ABSTRACT FROM AUTHOR]

We carry out several numerical simulations to illustrate how the radial electric field (Er) impacts the edge magnetohydrodynamic (MHD) instabilities. The analyses reveal that Er-shear (Er′, here the prime denotes the derivative with respect to the radial direction) tends to stabilize the kink/Peeling–Ballooning modes by dephasing the perturbed radial velocity (ṽr) and displacement (ξ̃r). However, Er-curvature (Er″) tends to destabilize the kink/peeling modes by inducing a phase lock between ṽr and ξ̃r. More specifically, the ratio between them could be measured to quantify their relative competition strength. Consequently, the shape of Er is crucial to the shape of linear growth rate spectrum γ(n) (here n is the toroidal mode number), which further determines the nonlinear dynamics. On the one hand, relatively larger Er-curvature causes narrower γ(n), leading to larger nonlinear energy loss fraction. On the other hand, relatively larger Er-shear has the opposite effect.

We draw attention to an interesting possibility in the design and operation of stellarator fusion reactors, which has hitherto been considered unrealistic under burning-plasma conditions. Thanks to recent advances in stellarator optimisation theory, it appears possible to create a positive (outward-pointing) radial electric field in the plasma core by carefully tailoring the geometry of the magnetic field. This electric field is likely to expel highly charged impurities from the centre of the plasma through neoclassical transport and thus eliminate, or at least mitigate, a long-standing problem in stellarator physics. Further out, the electric field is expected to suddenly change sign from positive to negative, thus creating a region of strongly sheared flow, which could locally suppress turbulent transport and enhance overall energy confinement. [ABSTRACT FROM AUTHOR]

The radial electric field plays an important role in plasma confinement in tokamaks and can be generated through neutral beam injection. In this study, we propose a model for calculating the radial electric field resulting from tangential local neutral beamlet injection, aiming to externally control and improve plasma confinement. The Neutral beamlet ion and Energetic particles Orbit mover and Electric field solver code has been developed to analyze this issue, and its simulation results have been validated against results from other codes as well as measurements from correlation reflectometers. The charge separation is primarily caused by the redistribution and loss of beam ions due to magnetic gradient and curvature drift as well as collision effects, and it is maintained through continuous beamlet injection. The electric field is calculated using Poisson’s equation, taking into account both classical and neoclassical polarization effects. The results demonstrate that despite the high losses and low heating efficiency associated with localized beamlets, they are capable of generating a significant radial electric field characterized by a steep gradient. This presents opportunities for external control of the electric field, potentially enhancing plasma confinement.

The fast ions and electrons generated by neutral beam injection (NBI) can induce charge separation, resulting in radial electric fields. Employing beamlet injection of small cross-section may effectively generate radial electric field, and adjusting beamlet parameters allows active control over their distribution. A new NBI injection geometry system has been developed in the NEOE code to explore the potential for vertical beamlets injection in future fusion reactor scenarios. Both high-field side and low-field side beamlet vertical injections can establish radial electric fields. In scenarios dominated by collision effects, the direction of the radial electric field is influenced by the toroidal angle of the beamlet. Adjusting the poloidal angle can alter the location of the electric field shear. Injecting particles into the trapped region using broader banana orbits can establish electric fields within the plasma core. Alternatively, injecting particles into the passing region can yield higher electric fields. Under future reactor conditions, conservative estimates of the electric field shear may even surpass critical velocities, potentially contributing to instability suppression.

We study the nonlinear deformation of a soft dielectric tube subjected to an external electric field induced by two outer fixed electrodes. The tube follows an electro-elastic, ideal dielectric, neo-Hookean free energy and is longitudinally either constrained or free; in general, it deforms by shrinking and finding an equilibrium configuration closer to the inner electrode. The non-homogeneous system of governing equations is solved numerically with details given for each type of boundary conditions. The notion of contraction limit is introduced and emergence of electromechanical instability for both problems is noted with the relevant modes studied at some relevant points of the stretch–voltage actuation curve. [ABSTRACT FROM AUTHOR]

Gyrokinetic simulation of the toroidal rotation of plasma with a stochastic magnetic field perturbation is carried out. The simulation results suggest that the stochastic magnetic perturbation drives the plasma to toroidally rotate through the ambipolar radial electric field E r established on the timescale of electron transit time. It is found that this spontaneous flow driven on the timescale less than an ion–ion collision time is the parallel return flow of the E r × B drift. The ion–ion collisional effect further changes the parallel return flow to the toroidal rigid-body flow after a few ion–ion collision times. This simulation result is consistent with the toroidal rigid-body rotation observed in tokamak experiments with a stochastic layer induced by the externally applied resonant magnetic perturbation. [ABSTRACT FROM AUTHOR]

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.

Measurement of the internal magnetic field is crucial for determining the equilibrium, stability, and current density of a plasma in a tokamak. A motional Stark Effect (MSE) diagnostic was developed to provide a measurement of the internal magnetic field in tokamaks by analyzing the emission from the interaction of the plasma particle with an injected neutral beam. The Stark effect causes the shifting and splitting of deuterium spectral lines due to the Lorentz electric field. However, it is difficult to accurately measure the internal magnetic field components since the radial electric field inherently formed inside the plasma is mixed with the Lorentz field. Under the circumstances in the Korea Superconducting Tokamak Advanced Research (KSTAR) device, one possible approach is to derive a radial electric field by measuring and comparing the polarization angles from the full and half-energy components of the neutral beam. To utilize the polychromatic MSE diagnostics in KSTAR, the half-energy component wavelength bands according to various magnetic field and beam energy combinations have been calculated, and the filter combinations required for those measurements have been selected. The Stokes-filter model used to evaluate the effect of multiple-ion-source neutral beam injection on the MSE measurements has been extended to infer the sensitivity of this approach to take the non-ideal bandpass filter effects into account. [ABSTRACT FROM AUTHOR]

The radial electric field in the Wendelstein 7-X stellarator is computed by means of self-consistent, global, neoclassical simulations using the gyrokinetic particle-in-cell code EUTERPE. The simulation results are compared with local predictions obtained from a transport code using locally computed neoclassical transport coefficients. The analysis focuses on ion-electron-root transitions and investigates their dependence on collisionality, normalised ion gyroradius, and the electron-ion temperature ratio. Several of the results cannot be reproduced using conventional, local neoclassical transport theory. An approximate criterion for root transitions is derived, which results in an analytical scaling law that is useful for understanding how the position of the transition layer varies with plasma parameters.

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. [ABSTRACT FROM AUTHOR]

This paper presents a relativistic mechanism that can create a non-uniformity of a radial electric field on the low side and the high toroidal magnetic field side of tokamak plasmas. This mechanism is associated with the significant current velocity of electrons in the plasma for many experimental modes of tokamak operation. It is important that electric fields arise without the separation of charges in the plasma. The traditional approach to determining radial electric fields in tokamak plasmas gives a uniform radial electric field on magnetic surfaces inside the plasma, while there are no radial electric fields outside the plasma. The presented mechanism leads to the appearance of an electric field outside the plasma with a current, and a non-uniformity of the radial electric field on magnetic surfaces appears inside the plasma. The proposed mechanism can explain the experimentally measured non-uniformity of C+6 carbon ion toroidal rotation velocities in the Tore-Supra tokamak plasma. [ABSTRACT FROM AUTHOR]

The steady Von Kármán flow and heat transfer of an incompressible electrically conducting fluid, in which Hall impact exists, are studied over an infinite radially shrinking rotating disk in presence of a magnetic field in the present paper as follows, (i) Navier-Stokes equations, Maxwell equation and energy equation have been modified in the presence of the Hall impact, applied the uniform magnetic field, and applied the radial electric field, (ii) Numerical solutions of the partial differential equations which govern the modified Navier-Stokes equations, Maxwell equation and energy equation are obtained by using the Chebyshev collocation technique for different values of the Hall parameters, magnetic interaction, radial electric parameters, Eckert and rotation numbers, (iii) The accuracy of the method is verified by comparing with the results in the literature, (iv) The influences of these parameters in these equations system are depicted graphically and analyzed.

Currently, the lateral electric field excited resonators are used for the creation of various sensors. We have recently proposed a new type of acoustic resonator called radial electric field excited disk acoustic resonator. The advantage of this type of resonator is its high sensitivity to mechanical and electrical boundary conditions on its free surface. This makes it possible to determine both the acoustic and electrical properties of a thin layer of material deposited on the free end of the resonator. In this work, we used a radial electric field excited disk acoustic resonator of Russian-made barium plumbum zirconate titanate (BPZT) piezoceramics. With the help of this resonator, the material constants for the piezoceramic sample were refined, and their temperature dependencies were determined. Then, this resonator was used to determine the elastic modulus, viscosity, and conductivity of the chitosan acetate film in air and ammonia vapors of various concentrations. It was shown that the chitosan acetate film under the influence of ammonia vapor significantly changes its mechanical properties and increases its electrical conductivity thousands of times, and then completely restores its properties.

Based on a heuristic model of the scrape-off-layer (SOL) plasma dynamics, a new type of limit-cycle-oscillation (LCO) is shown to be possible in the SOL region. The key trigger process is the positive feedback amplification of the SOL radial electric field through the SOL turbulence suppression and temperature profile steepening. This SOL-LCO can make the edge plasma inside the separatrix also have an oscillation motion, taking the features qualitatively similar to those observed in the recent ASDEX Upgrade experiment (Cavedon et al 2017 Nucl. Fusion 57 014002). With the above positive feedback process much more feasible when the ion magnetic curvature drift direction is toward the X -point, the present model also provides an explanation of why the LCO is mostly observed in such a favorable magnetic configuration.

The formation of the equilibrium radial electric field (Er) has been studied experimentally at ASDEX Upgrade (AUG) in L-modes of "favorable" (ion ∇ B -drift toward primary X-point) and "unfavorable" (ion ∇ B -drift away from primary X-point) drift configurations, in view of its impact on H-mode access, which changes with drift configurations. Edge electron and ion kinetic profiles and impurity velocity and mean-field Er profiles across the separatrix are investigated, employing new and improved measurement techniques. The experimental results are compared to local neoclassical theory as well as to a simple 1D scrape-off layer (SOL) model. It is found that in L-modes of matched heating power and plasma density, the upstream SOL Er and the main ion pressure gradient in the plasma edge are the same for either drift configurations, whereas the Er well in the confined plasma is shallower in unfavorable compared to the favorable drift configuration. The contributions of toroidal and poloidal main ion flows to Er, which are inferred from local neoclassical theory and the experiment, cannot account for these observed differences. Furthermore, it is found that in the L-mode, the intrinsic toroidal edge rotation decreases with increasing collisionality and it is co-current in the banana-plateau regime for all different drift configurations at AUG. This gives rise to a possible interaction of parallel Pfirsch–Schlüter flows in the SOL with the confined plasma. Thus, the different H-mode power threshold for the two drift configurations cannot be explained in the same way at AUG as suggested by LaBombard et al. [Phys. Plasmas 12, 056111 (2005)] for Alcator C-Mod. Finally, comparisons of Er profiles in favorable and unfavorable drift configurations at the respective confinement transitions show that also the Er gradients are all different, which indirectly indicates a different type or strength of the characteristic edge turbulence in the two drift configurations. [ABSTRACT FROM AUTHOR]

Global gyrokinetic particle simulations show that the radial electric field (Er) shear can suppress the kinetic ballooning mode (KBM) in a toroidal plasma. The linear KBM growth rate reaches a maximum when the toroidal rotation induced by the ion diamagnetic shear is canceled by the E × B flow shear. High toroidal-mode-number (high-n) KBMs are more sensitive to the Er shear than low-n KBMs. Nonlinear simulations find that both the Er shear and a self-generated zonal flow can reduce the nonlinear KBM saturation level with smaller particle and ion heat transport. Meanwhile, the zonal flow can weaken the suppressing effects of the Er shear on KBM nonlinear saturation amplitude. The radial correlation length of the turbulence is reduced by the Er shear and the zonal flow. [ABSTRACT FROM AUTHOR]

Sheared flows are known to reduce turbulent transport by decreasing the correlation length and/or intensity of turbulent structures. The transport barrier that takes place at the edge during improved regimes such as H mode, corresponds to the establishment of a large shear of the radial electric field. In this context, the radial shape of the radial electric field or more exactly of the perpendicular E Ă— B velocity appears as a key element in accessing improved confinement regimes. In this paper, we present the radial profile of the perpendicular velocity measured using Doppler back-scattering system at the edge of the plasma, dominated by the E Ă— B velocity, during the first campaigns of the WEST tokamak. It is found that the radial velocity profile is clearly more sheared in lower single null configuration (with the B Ă— ∇ B magnetic drift pointing toward the active X -point) than in upper single null configuration for ohmic and low current plasmas (B = 3.7 T and q 95 = 4.7), consistently with the expectation comparing respectively ‘favourable’ versus ‘unfavourable’ configuration. Interestingly, this tendency is sensitive to the plasma current and to the amount of additional heating power leading to plasma conditions in which the E Ă— B velocity exhibits a deeper well in USN configuration. For example, while the velocity profile exhibits a clear and deep well just inside the separatrix concomitant with the formation of a density pedestal during Lâ€"H transitions observed in LSN configuration, deeper E r wells are observed in USN configuration during similar transitions with less pronounced density pedestal. [ABSTRACT FROM AUTHOR]