Threshold Field Strength Research Articles

Dephasing of Strong-Field-Driven Excitonic Autler-Townes Doublets Revealed by Time- and Spectrum-Resolved Quantum-Path Interferometry.

Understanding dephasing mechanisms of strong-field-driven excitons in condensed matter is essential for their applications in quantum-state manipulation and ultrafast optical modulations. However, experimental access to exciton dephasing under strong-field conditions is challenging. In this study, using time- and spectrum-resolved quantum-path interferometry, we investigate the dephasing mechanisms of terahertz-driven excitonic Autler-Townes doublets in MoS_{2}. Our results reveal a dramatic increase in the dephasing rate beyond a threshold field strength, indicating exciton dissociation as the primary dephasing mechanism. Furthermore, we demonstrate nonperturbative high-order sideband generation in a regime where the driving fields are insufficient to dissociate excitons.

A Study on the Field Emission Characteristics of High-Quality Wrinkled Multilayer Graphene Cathodes.

Field emission (FE) necessitates cathode materials with low work function and high thermal and electrical conductivity and stability. To meet these requirements, we developed FE cathodes based on high-quality wrinkled multilayer graphene (MLG) prepared using the bubble-assisted chemical vapor deposition (B-CVD) method and investigated their emission characteristics. The result showed that MLG cathodes prepared using the spin-coating method exhibited a high field emission current density (~7.9 mA/cm2), indicating the excellent intrinsic emission performance of the MLG. However, the weak adhesion between the MLG and the substrate led to the poor stability of the cathode. Screen printing was employed to prepare the cathode to improve stability, and the influence of a silver buffer layer was explored on the cathode's performance. The results demonstrated that these cathodes exhibited better emission stability, and the silver buffer layer further enhanced the comprehensive field emission performance. The optimized cathode possesses low turn-on field strength (~1.5 V/μm), low threshold field strength (~2.65 V/μm), high current density (~10.5 mA/cm2), and good emission uniformity. Moreover, the cathode also exhibits excellent emission stability, with a current fluctuation of only 6.28% during a 4-h test at 1530 V.

Carbon nanotubes and hexagonal boron nitride nanosheets co‐filled ethylene propylene diene monomer composites: Improved electrical property for cable accessory applications

AbstractRubber‐based composites based on ethylene propylene diene monomer (EPDM) with excellent non‐linear electrical conductivity are preferred to serve as reinforced insulation in cable accessories, which can self‐adaptively regulate electric field distribution and avoid electric field concentration due to the non‐linear conductivity. The conductive carbon nanotubes (CNT) are filled into EPDM to improve the non‐linear conductivity, while the insulating hexagonal boron nitride nanosheets (h‐BN) are used to reconcile the electric breakdown strength. The results show that with the increase of CNT loading content, the non‐linear conductivity of CNT/h‐BN/EPDM composites becomes more prominent, accompanying the decrease of threshold field strength and increase of non‐linear coefficient. However, the electric breakdown strength of CNT/h‐BN/EPDM composites seriously deteriorates due to the increase of CNT content and temperature. By incorporating 10 wt.% h‐BN into the composites, the reduction percentage of breakdown strength can be significantly lowered, which is 19.95% of neat EPDM and 13.74% of CNT/h‐BN/EPDM composites at 70°C, respectively. The COMSOL Multiphysics simulation results demonstrate that using the CNT/h‐BN/EPDM composite as the reinforced insulation can eliminate the electric field concentration of the cable accessory as well as enable the cable accessory with good lightning shock resistance.

Pulsed Electric Field Inactivation of Microorganism Using Chambers With Different Electrode Topologies

The effects of electrode topology on pulsed electric field (PEF) inactivation of microorganisms was investigated in the present study. Three PEF treatment chambers with different electrode topologies, which were parallel-plane, coaxial, and co-field respectively, were designed and built. PEF inactivation of yeast Saccharomyces cerevisiae suspension was conducted using these chambers with different electric field strength and a number of impulses. The performance of PEF inactivation was assessed by comparison of the population density of treated and untreated yeast samples. The results showed that the sterilization rate, as a function of the specific energy density, followed the same tendency regardless of the electrode topology, electric field strength, or the number of impulses. This strong correlation suggested that the specific energy density (energy per unit mass) could play a dominant role in the PEF inactivation of microorganisms once the threshold field strength was reached.

Effect of Shear Action on Structural and Electrical Insulation Properties of Polypropylene

Polypropylene undergoes permanent alterations during the processing and manufacture of cables due to shear effects, which in turn affect all of its qualities. There are currently few research papers on the modulation of material structure and many performance parameters by the shear stress field. In this study, we examined the impact of various shear levels on the structural, mechanical, and electrical properties of polypropylene, as well as their relationships. The results indicated that shear strength decreased the material’s viscosity and oxidation resistance. As shear duration increased, crystallinity began to diminish. In the meantime, the crystallinity improved as the shear temperature rose. The thermal elongations of the sheared samples were all about 5%. Short-term shearing boosted the material’s toughness, but as the degree of shear continued to increase, the material’s toughness and rigidity steadily decreased. The storage modulus of the material decreased with increasing shear, the loss peak initially increased and subsequently decreased, the peak position shifted from low to high temperature, and the loss factor was relatively small. In samples sheared for brief periods, an accumulation of space charge and an increase in its nonlinear threshold field strength were observed. With increasing shear time, the material’s space charge accumulation was repressed, the current density initially grew and then reduced, and the nonlinear threshold field strength initially fell and then increased. Under shearing, the electrical strength of the material increased by approximately 2%. In addition, the presence of an antioxidant improved all of the aforementioned features.

Insulation Properties and Interfacial Quantum Chemical Analysis of Cross-Linked Polyethylene Under Different Degassing Time for HVDC Cable Factory Joint Applications

Degassing treatment is critical to remove cross-linking by-products in cross-linked polyethylene (XLPE) cable factory joints and prevent early insulation deterioration. In this article, 500-kV high-voltage direct-current (HVDC) cable factory joint samples were prepared, and the physicochemical and temperature-dependent electrical properties of the samples under different degassing times were investigated. The results show that prolonged degassing treatment increases the crystallinity and reduces the tensile properties of the XLPE samples. The samples without degassing have visible micropores near the interface, and these micropores can be eliminated after a longer degassing time. In addition, degassing treatment can reduce the current density, increase the threshold field strength, and enhance the breakdown strength of the samples. A significant negative charge accumulation appears at the interface of the sample without degassing, which dramatically distorts the electric field. Long-term degassing treatment can improve this phenomenon, and the accumulated charge at the interface at elevated temperatures is significantly reduced. Furthermore, a model of the molecular chain microstructure at the interface before and after degassing is proposed. The molecular chain’s energy band structure and electron cloud distribution at the interface are analyzed based on quantum chemical calculation. It is found that cable makers can improve the insulation properties of cable factory joints by appropriately extending the degassing time to avoid interface deterioration.

Polarization characteristics of polymer dispersed liquid crystal films and their effects on electro-optical properties

The electro-optical properties of polymer dispersed liquid crystal film vary with liquid crystal content and externally applied electric field, but the analysis of the film morphology cannot directly reflect the mechanism of electro-optical properties. Therefore, the polymer dispersed liquid crystal film prepared by blending liquid crystal material E7 and photopolymer NOA65 is used. Herein, the dielectric polarization regulated electro-optical properties and their related mechanisms under different liquid crystal content and electric fields are revealed. The results show that in a frequency range of 10<sup>–1</sup>–10<sup>6</sup> Hz, the film exhibits three relaxation processes respectively at low frequency, medium frequency and high frequency, which are generated by thermionic polarization, interfacial polarization and orientation polarization. According to the Arrhenius equation, the activation energy values of such polarization processes are calculated. It is found that with the increase of liquid crystal content, the activation energy of orientation polarization decreases from 0.88 eV to 0.83 eV, leading the threshold field strength and the saturation field strength of the diversion of liquid crystal molecule to decrease. Thermionic polarization under DC electric field forms an internal electric field, which causes the threshold field strength and saturation field strength to increase greatly, as compared with the scenarios under AC electric field. Such a thermionic polarization also leads the polarization relaxation time to increase, resulting in the extension of response time. This study is of guiding significance in further analyzing and improving the electro-optical properties of polymer dispersed liquid crystal films.

Nonlinear dielectric properties of polyimide in high AC electric field

The nonlinear dielectric properties of polyimide (PI) films, excited by high-intensity, AC electric fields, have been measured. This work highlights that nonlinear DC conduction is a component of the AC conductivity and dielectric loss response when surpassing a certain threshold field strength. An additional Poole–Frenkel polarization, induced by high-intensity, high-frequency fields, also contributes to the nonlinearity. This increases the dielectric losses through a charge de-trapping process, the so-called “jacking-up” effect. A novel expression that captures the large signal behavior of the complex permittivity is introduced using the Cole–Cole format. Finally, it is shown that the dielectric properties and power dissipation density in PI films remain fully linear and frequency-independent up to an AC electric field of EPF ∼100 Vrms/μm and more conservatively below a threshold field of EX ∼ 45 V/μm (i.e., end of the ohmic region). Consequently, polyimide-based insulated electronic devices that are designed to continuously operate below this threshold field (including both uniform and fringe fields) will remain immune to a frequency-dependent electrical aging. Their lifetime should not be affected in any way.

Nonlinear Surface Conductivity Characteristics of Epoxy Resin-Based Micro-Nano Structured Composites

Nonlinear composite materials serve to homogenize electric fields and can effectively improve the local concentration of the electric field in power systems. In order to study the nonlinear surface conductivity properties of micro-nano epoxy composites, two types of epoxy micro-nano composite specimens were prepared in the laboratory using the co-blending method. The surface conductivity of the composites was tested under different conditions using a high-voltage DC surface conductivity test system. The results show that the surface conductivity of micro-nano structured composites increases and then decreases with the rise of nanofiller doping concentration. The nonlinear coefficient was 1.781 at 4 wt% of doped nanostructured SiC, which was the most significant nonlinear coefficient compared to other doping contents. For the same doping concentration, the micro-nano structured composites doped with nanostructured SiC have more significant surface conductivity at the same test temperature with a nonlinear coefficient of 1.635. As the temperature increases, the surface conductivity of the micro-nano structured composite increases significantly, and the threshold field strength moves towards the high electric field. Along with the increase in temperature, the nonlinear coefficients of micro-nano composites after doping with nanostructured SiC showed a gradually decreasing trend. The temperature has little effect on the nonlinear coefficients of the micro-nano structured composites after doping with O-MMT.

Assembly of alumina particles in aqueous suspensions induced by high‐frequency AC electric field

AbstractThe role of high‐frequency alternating current (AC) electric field in the assembly of alumina particles in aqueous media was investigated. Field–particle interactions were in situ investigated for coarse and fine powder particles in very dilute suspensions. For both coarse and fine particles, AC field‐induced assembly led to the formation of chains of particles within a minute, which were aligned in the field direction. However, a much finer network of particle chains evolved in fine particle suspensions. Threshold field strength for chain formation was also lower for fine particles (28 V/mm) than for coarse particles (50 V/mm), suggesting stronger interactions for finer particles. Chain length increased with both field strength and field duration. Chain formation was attributed to mutual dielectrophoretic (DEP) interaction forces. Increase in DEP forces with field strength resulted in enhanced interactions. For finer particles, decreasing interparticle distance might have favored stronger interactions. Suspension microstructure was disrupted as soon as the field was removed. However, higher field duration was associated with an improved pattern stability and retention following the field removal. Finally, particle motion was studied in deliberately applied spatially nonuniform AC field, which revealed different mechanisms of chain formation for coarse (negative‐DEP) and fine (positive‐DEP) particles.

On the mechanisms of lightning initiation and positive leader intergrowth

A model of a leader breakdown in air was developed, in which the channel is formed by heating the streamer trace in the leader corona. To determine the initial conditions, the model of a streamer breakdown was proposed. The minimal field intensity required to support the streamer breakdown was determined. The dependence of the leader's speed on the cloud potential was obtained. The lightnings are initiated by relativistic avalanches, the formation threshold field strength of which is below the threshold of the streamer discharge. By comparing the thresholds of relativistic and streamer breakdowns the heights for realization of the proposed initiation mechanism are specified.

Backreaction of Schwinger pair creation in massive QED2

Particle-antiparticle pairs can be produced by background electric fields via the Schwinger mechanism provided they are unconfined. If, as in QED in (3+1)-d these particles are massive, the particle production rate is exponentially suppressed below a threshold field strength. Above this threshold, the energy for pair creation must come from the electric field itself which ought to eventually relax to the threshold strength. Calculating this relaxation in a self-consistent manner, however, is difficult. Chu and Vachaspati addressed this problem in the context of capacitor discharge in massless QED2 [1] by utilizing bosonization in two-dimensions. When the bare fermions are massless, the dual bosonized theory is free and capacitor discharge can be analyzed exactly [1], however, special care is required in its interpretation given that the theory exhibits confinement. In this paper we reinterpret the findings of [1], where the capacitors Schwinger-discharge via electrically neutral dipolar meson-production, and generalize this to the case where the fermions have bare masses. Crucially, we note that when the initial charge of the capacitor is large compared to the charge of the fermions, Q » e, the classical equation of motion for the bosonized model accurately characterizes the dynamics of discharge. For massless QED2, we find that the discharge is suppressed below a critical plate separation that is commensurate with the length scale associated with the meson dipole moment. For massive QED2, we find in addition, a mass threshold familiar from (3+1)-d, and show the electric field relaxes to a final steady state with a magnitude proportional to the initial charge. We discuss the wider implications of our findings and identify challenges in extending this treatment to higher dimensions.

Effect of Thermal Aging on Threshold Field Strength and Relative Permittivity of Cross-Linked Polyethylene with Different Cross-Linking Agent Contents

Effect of Thermal Aging on Threshold Field Strength and Relative Permittivity of Cross-Linked Polyethylene with Different Cross-Linking Agent Contents

Density scaling of error field penetration in radio-frequency-dominant heating plasmas in the EAST tokamak

The density scaling of n = 1 error field penetration is investigated under radio-frequency (RF)-dominant heated L-mode discharges in the EAST tokamak. It is found that the density scaling of the threshold field strength for error field penetration in lower-hybrid current drive (LHCD) plasmas is about , where b r represents the error field amplitude. The results show a weaker density dependence compared to that observed in the previous ohmic heated discharges (Wang et al 2018 Nucl. Fusion 58 056024). For a better understanding of the density scaling, it is compared with field penetration theories, and it is found that it lies in the Waelbroeck regime. The observed scaling is consistent with that evaluated with the magnetohydrodynamic (MHD) theory on error field penetration, for which all the physical parameters are determined experimentally. Due to the density dependence of LHCD heating efficiency, the stronger negative correlation between density and temperature results in a weaker density scaling in these LHCD plasmas. Using realistic parameters under LHCD and ohmic heating as input, respectively, the numerical results based on a reduced MHD model reproduce well the scaling from the error field penetration theory and the observations. Besides, the density scaling in various tokamak operational regimes is also numerically investigated. This provides an excellent validation of MHD theory on error field penetration in the RF-dominant heated L-mode discharges.

Deciphering the Deep Origin of Active Regions via Analysis of Magnetograms

Abstract In this work, we derive magnetic toroids from surface magnetograms by employing a novel optimization method, based on the trust region reflective algorithm. The toroids obtained in this way are combinations of Fourier modes (amplitudes and phases) with low longitudinal wavenumbers. The optimization also estimates the latitudinal width of the toroids. We validate the method using synthetic data, generated as random numbers along a specified toroid. We compute the shapes and latitudinal widths of the toroids via magnetograms, generally requiring several m's to minimize residuals. A threshold field strength is chosen to include all active regions in the magnetograms for toroid derivation, while avoiding non-contributing weaker fields. Higher thresholds yield narrower toroids, with an m = 1 dominant pattern. We determine the spatiotemporal evolution of toroids by optimally weighting the amplitudes and phases of each Fourier mode for a sequence of five Carrington Rotations (CRs) to achieve the best amplitude and phases for the middle CR in the sequence. Taking more than five causes “smearing” or degradation of the toroid structure. While this method applies no matter the depth at which the toroids actually reside inside the Sun, by comparing their global shape and width with analogous patterns derived from magnetohydrodynamic (MHD) tachocline shallow water model simulations, we infer that their origin is at/near the convection zone base. By analyzing the “Halloween” storms as an example, we describe features of toroids that may have caused the series of space weather events in 2003 October–November. Calculations of toroids for several sunspot cycles will enable us to find similarities/differences in toroids for different major space weather events.

Advances in Novel Low-Macroscopic Field Emission Electrode Design Based on Fullerene-Doped Porous Silicon

Perspective low-macroscopic field (LMF) emission prototype cathodes based on fullerene C60—doped porous silicon were realized via a two-stage technique comprising the electrochemical etching process of a monocrystalline silicon wafer and functionalization of the acquired porous silicon (PS) matrix with silver-doped fullerene-based carbon structures. The resulting LMF cathode prototypes were studied with SEM and EDS techniques. The formation of an amorphous silver-doped C60-based layer consisting of nanosized aggregates on the matrix surface was established. The emission characteristics of the prototypes were analyzed, crucial parameters including threshold field strength values, emission current density, and effective potential barrier height for electrons were considered. A novel LMF emission model is suggested. It was established that the emitter prototypes realized during this study are on par with or superior to modern and promising field cathodes.

Stability of skyrmion formation and its abnormal dynamic modes in magnetic nanotubes

We studied the stability of skyrmion formation and its abnormal dynamic motions in magnetic nanotubes with perpendicular magnetic anisotropy with respect to the tube surface. Unlike planar geometry, skyrmions, which are formed in an elliptical shape, are stabilized, to a greater or lesser degree, by the curved geometry, depending on the sign of the Dzyaloshinskii-Moriya Interaction (DMI) constant. The positive and negative signs of the DMI constant play a crucial role in the formation of skyrmions on the curved surface. These effects become stronger as the diameter of the tube decreases, quantitatively evidencing that the curvature-induced DM-like interaction also contributes to the stability of skyrmion formation. The dynamic modes of the skyrmion in the tubes are found to be as follows: two in-plane gyration modes in the counterclockwise (CCW) and clockwise (CW) rotation senses, and one out-of-plane breathing mode. On the other hand, in contrast to the planar geometry, the initial CCW gyration motion turns out to be a linear translational motion in the circumferential direction of the tube for cases where the strength of axial AC magnetic fields is greater than a threshold field strength. The direction of the translational motions is determined by the skyrmion helicity governed by the sign of the interfacial DMI constant. This work provides further physical insight into the static and dynamic properties of skyrmions formed in curved-geometry systems and also suggests its potential application to information processing devices.

Investigation of electrical properties of ZnO@Ag/EPDM composites

In this study, Ag conductive nanoparticles were successfully grown on ZnO semi-conductive nanosheets (abbreviated as ZnO@Ag) by combined sol–gel and liquid-phase chemical reduction methods. Both ZnO and ZnO@Ag are chosen as inorganic fillers, respectively, and EPDM is used as the matrix. The microstructures and electrical performances of the EPDM-based composites with different content of fillers have been systematically investigated. The results show that no nonlinear conductivity can be observed in pristine ethylene-propylene rubber (EPDM); however, obvious nonlinear conductivity appears in ZnO/EPDM composites with 10 wt. % ZnO. Especially, after introducing 10 wt. % ZnO@Ag into EPDM, the nonlinear conductive characteristics become much more remarkable compared with 10 wt. % ZnO/EPDM. As the content of ZnO@Ag and measured temperature increase, the threshold field strength that corresponds to nonlinear conductivity decreases gradually. Besides, the increase in conductivity accompanies a decrease in breakdown field strength. Compared to pristine EPDM (breakdown strength of 133.6 kV/mm), the breakdown field strength of 30 wt. % ZnO@Ag/EPDM reduces to 75.86 kV/mm at 30 °C and 51.36 kV/mm at 70 °C. In addition, both the dielectric constant and dielectric loss gradually increase with the increase in ZnO@Ag filling content due to the semi-conductive/conductive characteristics of fillers. As a consequence, this study provides an effective way to induce nonlinear conductivity for EPDM, and ZnO@Ag/EPDM composites may be used to homogenize the electric field and improve the performances of cable accessories.

Abstract 472: What electric field strength is necessary for maximum tumor-treating fields efficacy

Abstract Why Is 4 V/cm Electric Field Strength Necessary for Maximum Tumor-Treating Fields Efficacy? INTRODUCTION: Tumor Treating Fields (TTFields) extend overall survival in glioblastoma patients. Threshold field strength for TTFields is typically cited as 2V/cm. Yet plots of cell death vs. field strength in vitro indicate a power law relationship asymptotic to 4 V/cm for 100% efficacy. The mechanisms of action (MoA) of TTFields underlying this relationship are currently under investigation. TTFields are suspected of disrupting critical mitotic processes performed by large polar cellular molecules such as microtubules (MT). METHODS: Using the power law relationship for the energy (intensity, I) carried by an electric field and its amplitude (Eq. 1), we calculated energy vs. TTFields amplitude. (1) RESULTS: We suggest Eq. 1 is a likely source of the relationship between TTFields' amplitude and cell death proportion that has been demonstrated empirically. Further, Table 1 shows energy transmitted per unit MT surface area per TTFields cycle, specifically, the energy per MT dimer band around an MT helix per TTFields period of 5 µs. TTFields Field Strength (V/cm)Radiant Flux Density (W/nm2)Energy/(Cycle-Area) (J/nm2)Energy/MT Dimer/Cycle (J)Energy/MT Dimer Band/Cycle (J)113.3 × 10−186.63 × 10−234.01 × 10−224.17 × 10−20253.1 × 10−1826.6 × 10−231.60 × 10−211.67 × 10−193119 × 10−1859.7 × 10−233.61 × 10−213.75 × 10−194212 × 10−18106 × 10−236.42 × 10−216.67 × 10−195332 × 10−18166 × 10−231.00 × 10−201.04 × 10−186478 × 10−18239 × 10−231.44 × 10−201.50 × 10−18 A metric for disruption of cellular processes is 1-2 orders of magnitude greater than the thermal background energy in the cell, kT = 4.3 × 10−21 J. Table 1 shows that the energy absorbed by a MT dimer is insufficient to disrupt cellular processes at 2 V/cm, while due to energy increasing with square of field strength, at 5 V/cm it may be disruptive. For an entire dimer band around the MT helix, 2 V/cm appears to be sufficient, while 4 V/cm seems amply strong to disrupt MT function, in accordance with in vitro experiments. CONCLUSION: Assuming the power law of energy vs. electric field strength and the resulting energy absorbed by microtubule components, we found a correlation between typical TTFields' amplitudes and estimated disruption thresholds of MT function. TTFields MoA. 4 V/cm, not 2V/cm, should be the target field strength to realize the full efficacy of TTFields. Citation Format: Kristen W. Carlson, Jack A. Tuszynski, Socrates Dokos, Nirmal Paudel, Zeev Bomzon. What electric field strength is necessary for maximum tumor-treating fields efficacy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 472.

Achieving Remarkable Amplification of Energy-Storage Density in Two-Step Sintered NaNbO3-SrTiO3 Antiferroelectric Capacitors through Dual Adjustment of Local Heterogeneity and Grain Scale.

Antiferroelectric (AFE) materials exhibit outstanding advantages against linear or ferroelectric (FE) dielectrics in high-performance energy-storage capacitors. However, their energy-storage performances are usually restricted by both extremely large hysteresis and insufficiently high driving field of the AFE-FE phase transition, which has been a longstanding issue to be overcome in the community. In this work, we report a two-step sintered 0.83NaNbO3-0.17SrTiO3 (NN-ST) lead-free relaxor AFE R-phase ceramic with high relative density of ≥95% and large spans of average grain sizes from 1.2 to 8.2 μm, strikingly achieving a giant amplification of recoverable energy-storage density (Wrec) by 176%. Analyses of permittivity-temperature curves, Raman spectrum and microstructure demonstrate that remarkably enhanced Wrec values should be ascribed to the dual adjustment of local heterogeneity (nanoscale) and grain scale (microscale), resulting in the enhanced threshold field strength for dielectric breakdown and the increased critical electric fields for the AFE-FE phase transition. A high Wrec ≈ 1.60 J/cm3, a fast discharging rate t0.9 ≈ 520 ns, large current density ∼788 A/cm2, and large power density ∼55 MW/cm3 are achieved at room temperature in the NN-ST ceramic sample with an average grain size of ∼1.2 μm. These results suggest that the multiscale structure regulation should be an efficient way for achieving enhanced energy-storage properties in NN-ST relaxor AFE ceramics through a two-step sintering technique.