Breakdown Phase Research Articles

Optimizing energy storage performance of lead zirconate-based antiferroelectric ceramics by a phase modulation strategy

Dielectric energy storage has gained considerable significance owing to the high energy requirements of human society. Lead zirconate-based (PZ) antiferroelectric materials have received much attention due to their fast discharge rate, high power density, and low cost. Nevertheless, their low energy storage density seriously limits their practical applications. To overcome this limitation, the phase modulation strategy via chemical modification was adopted to optimize the breakdown strength and phase switching field. Specifically, the antiferroelectric ceramics of (Pb0.97−xGd0.02Srx)(Zr0.87Sn0.12Ti0.01)O3 were prepared by the tape-casting method. An apparent multistage phase transition behavior revealed for x ≥ 0.05 is rarely discussed in reported Sr2+ modified PZ system. This is attributed to the coexistence of the main orthorhombic phase and the tetragonal phase. Although the transition near the lower field reduces the energy storage slightly, the disruption of the long-range order stabilizes the antiferroelectricity of the orthorhombic phase, hence elevating its transition field. In addition, the tetragonal phase with lower polarization suppresses the electrostrain thus improving the breakdown strength. Consequently, an ultrahigh recoverable energy storage density of 14.5 J/cm3 with a high energy efficiency of 81 % is achieved at a high electric field of 717 kV/cm for (Pb0.92Gd0.02Sr0.05)(Zr0.87Sn0.12Ti0.01)O3. Moreover, the fatigue resistance of this composition is excellent within 26,000 fatigue cycles. Besides, it exhibits a high discharge energy density of 9.4 J/cm3 and a great power density of 387 MW/cm3. These results confirm that the energy storage properties of PZ-based antiferroelectric materials can be effectively optimized via a phase modulation strategy.

Ignition process of the plasma scalpel in normal saline: Numerical simulation and comparison to experiment

In this paper, the ignition process of the plasma scalpel is characterized by means of numerical simulation, shadowgraphy, and voltage–current measurements. The ignition process involves two phases: the pre-breakdown phase and the breakdown phase. Our study shows that in the pre-breakdown phase, the vapor layer is first generated around the corners of the active electrode and then gradually extends to cover the entire active electrode. Once the active electrode is fully covered by the vapor layer, the electric field reaches a maximum of 7.3 × 106 V m−1, which can cause discharge in the vapor layer. At this moment, the thickness of the vapor layer is approximately 100 μm. In the breakdown phase, the maximum electron density reaches 1018–1019 m−3. The plasma dissipates about 60% of the total power which is up to 125 W, thus enabling efficient cutting. In addition, we simulate the discharge characteristics of cutting various biological tissues. The results show that under the same voltage level, the higher the conductivity of biological tissues, the greater the discharge current. The biological tissues act as ballast resistors in equivalent circuits.

Experimental evaluation of the influence of the diffuser inlet to nozzle exit cross sectional area ratio on pressure oscillation in a high-altitude test facility

The ratio of diffuser inlet to nozzle exit area (Ad/Ae) is one of the most important parameters in designing and evaluating the performance of a high-altitude test facility (HATF). Typically, at motor pressures near start or operating pressure of the diffuser, the vacuum chamber pressure oscillates at a high Ad/Ae, which may be dangerous for the HATF. In the present study, the effect of the Ad/Ae on the starting and breakdown performance of a second throat exhaust diffuser (STED) has been investigated experimentally using a HATF supplied by high-pressure cold air apparatus. Upon examining the overall performance of the diffuser, it is observed that with an increase in Ad/Ae, the oblique sealing shock wave at the diffuser inlet undergoes significant changes in location and strength. This leads to a further reduction of the flow total pressure and a stronger separation of the flow along the diffuser. Consequently, flow instability arises during starting or breakdown phases near the STED starting or operating pressure. By frequency analysis, it is observed that as Ad/Ae increases, the number of oscillatory modes of the vacuum chamber pressure increases and the dominant frequency of the oscillations in these transient situations becomes larger. Additionally, there is a significant decrease in nozzle pressure related to the onset of pressure oscillations. Furthermore, with an increase in Ad/Ae from 1.27 to 7.81, the minimum starting pressure and breakdown pressure of STED increase by 20.33% and 28.47%, respectively. Also, the hysteresis range in performance of STED vanishes at high Ad/Ae values.

Inter-tissue differences in oxidative stress susceptibility reveal a less stable endothelial barrier in the brain than in the retina

Oxidative stress can impair the endothelial barrier and thereby enable autoantibody migration in Neuromyelitis optica spectrum disorder (NMOSD). Tissue-specific vulnerability to autoantibody-mediated damage could be explained by a differential, tissue-dependent endothelial susceptibility to oxidative stress. In this study, we aim to investigate the barrier integrity and complement profiles of brain and retinal endothelial cells under oxygen-induced oxidative stress to address the question of whether the pathomechanism of NMOSD preferentially affects the brain or the retina.Primary human brain microvascular endothelial cells (HBMEC) and primary human retinal endothelial cells (HREC) were cultivated at different cell densities (2.5*104 to 2*105 cells/cm2) for real-time cell analysis. Both cell types were exposed to 100, 500 and 2500 μM H2O2. Immunostaining (CD31, VE-cadherin, ZO-1) and Western blot, as well as complement protein secretion using multiplex ELISA were performed.HBMEC and HREC cell growth phases were cell type-specific. While HBMEC cell growth could be categorized into an initial peak, proliferation phase, plateau phase, and barrier breakdown phase, HREC showed no proliferation phase, but entered the plateau phase immediately after an initial peak. The plateau phase was 7 h shorter in HREC. Both cell types displayed a short-term, dose-dependent adaptive response to H2O2. Remarkably, at 100 μM H2O2, the transcellular resistance of HBMEC exceeded that of untreated cells. 500 μM H2O2 exerted a more disruptive effect on the HBMEC transcellular resistance than on HREC. Both cell types secreted complement factors H (FH) and I (FI), with FH secretion remaining stable after 2 h, but FI secretion decreasing at higher H2O2 concentrations.The observed differences in resistance to oxidative stress between primary brain and retinal endothelial cells may have implications for further studies of NMOSD and other autoimmune diseases affecting the eye and brain. These findings may open novel perspectives for the understanding and treatment of such diseases.

Interface engineering of polymer composite films for high-temperature capacitive energy storage

Polymer film capacitors encounter challenges in harsh conditions of high temperatures and electric fields because of large conduction loss and degraded breakdown strength (Eb). Herein, an interface engineering strategy is proposed to fluorinate the interfaces between the polyetherimide (PEI) matrix and wide bandgap boron nitride nanosheets (BNNSs) fillers. The composite films exhibit high-performance capacitive energy storage with a remarkable energy density of 5.73 J/cm3 and an ultrahigh efficiency of 91.22 % in conditions of 575 kV/mm and 150 °C. By adopting interfacial fluorination, the band structure of BNNSs is tailored to achieve a type II band alignment with PEI, promoting the dual trapping for both electrons and holes. It highly suppresses leakage current and reduces conduction loss. Typically, introducing fillers can compromise the properties of interfacial layers, creating weak points that trigger breakdown. Conversely, fluorinated interfaces exhibit an increased Young’s modulus and a reduced dielectric constant. According to the electromechanical breakdown theory, the interfacial Eb is increased. The breakdown phase propagation along the interfaces is thereby impeded, ultimately resulting in a further increase in overall Eb, reaching up to 589 kV/mm at 150 °C. Fluorinated interface engineering addresses interfacial challenges posed by fillers, enabling high-temperature energy storage capability in PEI-based capacitors.

Phase field model for electric-thermal coupled discharge breakdown of polyimide nanocomposites under high frequency electrical stress

In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of Polyimide (PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.

A novel lead‐free relaxor with endotaxial nanostructures for capacitive energy storage

AbstractDielectric capacitors with a fast charging/discharging rate, high power density, and long‐term stability are essential components in modern electrical devices. However, miniaturizing and integrating capacitors face a persistent challenge in improving their energy density (Wrec) to satisfy the specifications of advanced electronic systems and applications. In this work, leveraging phase‐field simulations, we judiciously designed a novel lead‐free relaxor ferroelectric material for enhanced energy storage performance, featuring flexible distributed weakly polar endotaxial nanostructures (ENs) embedded within a strongly polar fluctuation matrix. The matrix contributes to substantially enhanced polarization under an external electric field, and the randomly dispersed ENs effectively optimize breakdown phase proportion and provide a strong restoring force, which are advantageous in bolstering breakdown strength and minimizing hysteresis. Remarkably, this relaxor ferroelectric system incorporating ENs achieves an exceptionally high Wrec value of 10.3 J/cm3, accompanied by a large energy storage efficiency (η) of 85.4%. This work introduces a promising avenue for designing new relaxor materials capable of capacitive energy storage with exceptional performance characteristics.

Fluorinated interface engineering targeting high-performance multifunctional composites of BN/aramid nanofibers

Aramid nanofibers (ANFs)-based composites have attracted considerable interest in electronic and electrical engineering due to their exceptional thermal stability, high strength, and superior insulating properties. However, the performance of ANFs-based composites is severely confined by interfacial issues. Accordingly, a novel strategy of fluorinated interface engineering is proposed herein, by which the fillers are grafted by the fluorine-containing functional groups. The introduction of interfacial fluorination yields a dense and compact composite structure which stems from the improved compatibility at the matrix-filler interfaces. The tensile strength and thermal conductivity are increased by 30% and 50%, respectively. Additionally, the band structure variation is observed in the fluorinated BNNs, where the electron trap states are formed at the interface. With the deepened deep trap depth and increased density, the breakdown strength is enhanced by 50%. The breakdown phase field simulations also indicate the high discharge energy consumption by the fluorination effect.

Study of Ohmic breakdown and burnthrough phase of ADITYA tokamak

In the ADITYA tokamak, the plasma discharge is initiated through filament pre-ionization assisted breakdown, using the conventional inductively driven electric field. Following the breakdown of the neutral gas, the discharge is sustained by a successful burnthrough phase. The nature of the breakdown and burnthrough phase is studied by varying the parameters influencing it, such as the toroidal electric field, operating pressure, and lithium wall conditioning. The plasma initiation failures in the breakdown and burnthrough phase are identified, and optimized conditions of operating parameters are derived. The value of the Lloyd parameter Eϕ×BT/Bz in the ADITYA for plasma breakdown is found to be in the range of 1200–2100 V/m, which is consistent with other conventional tokamaks. The applied Ohmic input power must overcome the power losses due to fuel ionization and fuel and impurity radiation to achieve the complete burnthrough. The power requirement for the burnthrough phase is obtained experimentally and compared with the estimated values. The required Ohmic input power is found to be ∼60 kW for the successful burnthrough. Furthermore, it has been observed that the vessel wall coating with lithium reduces the impurities influx in the burnthrough phase and, thus, reduces the Ohmic input power consumption.

Breakdown and quasi-DC phase of a nanosecond discharge: Comparison of optical emission spectroscopy measurements with numerical simulations

A nanosecond atmospheric pressure plasma jet operated in pure nitrogen is studied by spatially and temporally resolved optical emission spectroscopy complementing the companion paper (Kuhfeld et al 2023 Plasma Sources Sci. Technol. 32 084001), where the discharge is investigated by means of Particle-in-Cell/Monte Carlo collisions (PIC/MCC) simulations and fluid models. Two temporal phases of the evolution of the discharge are identified: a fast breakdown and a quasi-DC phase. It is shown that during the breakdown phase several ionization waves develop, while after the breakdown the discharge has a structure similar to DC glow discharges, in agreement with the modeling predictions. The results of the measurements of the spatial-temporal dynamics of the light emission are compared with the distribution of densities of the and states reconstructed from the PIC/MCC simulations. A good agreement is demonstrated.

Parametric thermal-hydraulic analysis of the DEMO PF coils designed by CEA during the breakdown phase

EU-DEMO - the European DEMOnstration Fusion Power Plant, is being designed as an intermediate stage between the ITER experimental reactor and the future fusion power plant. The fully superconducting magnet system of the DEMO tokamak includes six Poloidal Field (PF) coils. Two different concepts of the DEMO PF winding packs are being developed by the EPFL-SPC (Switzerland) and CEA IRFM (France) teams. The current cycle of the PF coils consists of the following phases: Premagnetization (10 s), Plasma Current Ramp-Up (PCRU, 80 s), plasma burn (7200 s) and dwell (600 s). The PCRU phase starts with the fast breakdown (0.8 s), during which the operating current and magnetic field change very rapidly causing significant heat generation due to AC losses. Thus, the breakdown is potentially the most critical phase of normal operation of PF conductors regarding the temperature margin. This study was focused on the thermal-hydraulic analysis of the PF coils designed by CEA during breakdown. According to the CEA design, based on the 2018 DEMO reference, the PF coils are double-pancake wound with square NbTi Cable-in-Conduit Conductors with a central cooling channel. Operation of conductors designed for each PF coil was simulated with the THEA code by Cryosoft. Since the detailed reference current breakdown scenario for the PF coils is not available yet, the analysis was performed parametrically. We took into account the external or internal magnetic field profile along each PF conductor as well as heat generation due to the AC hysteresis losses and coupling losses (for the trial values of the parameter nτ = 100, 200 and 300 ms). The study was aimed at the estimation of the minimum temperature margin in each PF conductor during the breakdown and verification if it fulfills the performance criterion min(ΔTmarg) ≥ 1.5 K. The results of analysis should help in further improvements and optimization of the PF winding packs design.

Delayed phase switching field and improved capacitive energy storage in Ca2+-modified (Pb,La)(Zr,Sn)O3 antiferroelectric ceramics

Antiferroelectric ceramics have captured great attention on capacitive energy storage because of their giant power density and fast discharge speed, which is highly desirable for high- and pulsed-power devices. Nevertheless, the conflict between breakdown electric field and phase switching field of antiferroelectric ceramics blocks to achieve the optimum energy storage capability. In present letter, Ca2+-modified (Pb0.97La0.02)(Zr0.6Sn0.4)O3 ceramics achieved improved breakdown electric field, delayed phase switching field and multiple phase transition under high electric field simultaneously, giving rise to an ultrahigh recoverable energy density of 10.04 J/cm3 and a high energy storage efficiency of 83.95%. Furthermore, the ceramics also displayed excellent thermal reliability as temperature increased to 150 °C, and superior discharge behavior, characterized by Wdis of 5.17 J/cm3 and t0.9 of 5.18 μs. This work not only demonstrates the promising applications of PbZrO3-based antiferroelectric ceramics in energy storage capacitors, but also supplies an effective route to explore high-performance antiferroelectric materials.

Early dynamics of laser-induced plasma and cavitation bubble in water

The knowledge of early laser-induced plasma and cavitation bubble dynamics are of great importance for a better understanding of underwater laser-induced breakdown spectroscopy. In this work, we investigated the temporal evolution of the plasma and bubble at an early stage before 2 μs, by using fast imaging and shadowgraph techniques. It showed that the initial plasma forms at the laser focal point and then grows up toward the incident laser. As time evolves, the plasma expands simultaneously forward and backward to its peripheral region and a sub-plasma structure can be observed at low laser energies. The plasma has a good pulse-to-pulse repeatability during the laser pulse, while soon after the laser pulse (from 20 to 50 ns), it undergoes a severe pulse-to-pulse fluctuation with an inhomogeneous emission distribution. At longer times, the plasma becomes much stable again. To clarify the interrelationship between the bubble dynamics and the plasma characteristics, shadowgraph images of the bubble were shown and compared with the plasma images. It showed that the morphology of the bubble and its evolution have a good consistency with the morphology of plasma. The bubble radius as a function of time can be well expressed by the equation R=at0.4, and a is a constant related to the laser energy. By inspecting the evolution curve of the bubble wall and the bubble pressure calculated based on the Gilmore model, a transition phase from 20 to 50 ns can be identified between the moving breakdown phase and the thermal expansion phase. In this transition phase, both the bubble expansion speed and the bubble pressure drop drastically that may account for the severe plasma fluctuations as observed in this period. These results of early bubble dynamics provide insights into the critical role of bubble-plasma interaction on the characterization of laser-induced plasma in water.

Giant energy storage of flexible composites by embedding superparaelectric single-crystal membranes

Flexible organic-based composites embedding nanosheet-like inorganics with high energy storage density (U) are imperatively demanded for applications in portable electronics and sensors. However, the breakdown phases can easily bypass the discontinuous nanosheets, leading to the failure of conduction barriers. Here, continuous flexible Sm-doped BiFeO3-BaTiO3 (Sm-BFBT) membranes with superparaelectric characteristics were synthetized via etching a water-soluble Sr3Al2O6 buffer layer. With the single-crystal Sm-BFBT membranes embedded into poly(vinylidene fluoride), a giant U of 46.4 J/cm3 at 770 MV/m is achieved in the sandwich-structured composites, attributed to a formation of depolarized field induced by interfacial ions. Meanwhile, the composites exhibit a stable U of ∼20 J/cm3 at 550 MV/m during bending process, owing to the excellent flexibility of Sm-BFBT membranes originating from nanodomain switching. The proposed composites containing flexible 2D inorganic membranes offer unprecedented structural insights into the integration of high energy storage and stability of bending, and suggest potential uses in flexible energy storage devices.

Formation mechanisms of striations in a filamentary dielectric barrier discharge in atmospheric-pressure argon

Formation mechanisms of striations along the discharge channel of a single-filament dielectric barrier discharge (DBD) in argon at atmospheric pressure are investigated by means of a time-dependent, spatially two-dimensional fluid-Poisson model. The model is applied to a one-sided DBD arrangement with a 1.5 mm gap using a sinusoidal high voltage at the powered metal electrode. The discharge conditions are chosen to mimic experimental conditions for which striations have been observed. It is found that the striations form in both half-periods during the transient glow phase, which follows the streamer breakdown phase. The modelling results show that the distinct striated structures feature local spatial maxima and minima in charged and excited particle densities, which are more pronounced during the positive polarity. Their formation is explained by a repetitive stepwise ionisation of metastable argon atoms and ionisation of excimers, causing a disturbance of the spatial distribution of charge carriers along the discharge channel. The results emphasise the importance of excited states and stepwise ionisation processes on the formation of repetitive ionisation waves, eventually leading to striations along the discharge channel.

Quantum breakdown model: From many-body localization to chaos with scars

We propose a quantum model of fermions simulating the electrical breakdown process of dielectrics. The model consists of $M$ sites with $N$ fermion modes per site, and has a conserved charge $Q$. It has an on-site chemical potential $\mu$ with disorder $W$, and an interaction of strength $J$ restricting each fermion to excite two more fermions when moving forward by one site. We show the $N=3$ model with disorder $W=0$ show a Hilbert space fragmentation and is exactly solvable except for very few Krylov subspaces. The analytical solution shows that the $N=3$ model exhibits many-body localization (MBL) as $M\rightarrow\infty$, which is stable against $W>0$ as our exact diagonalization (ED) shows. At $N>3$, our ED suggests a MBL to quantum chaos crossover at small $W$ as $M/N$ decreases across $1$, and persistent MBL at large $W$. At $W=0$, an exactly solvable many-body scar flat band exists in many charge $Q$ sectors, which has a nonzero measure in the thermodynamic limit. We further calculate the time evolution of a fermion added to the particle vacuum, which shows a breakdown (dielectric) phase when $\mu/J<1/2$ ($\mu/J>1/2$) if $W\ll J$, and no breakdown if $W\gg J$.

Характеристики матричного катода из карбида кремния в предпробойных и пробойных условиях

This study assesses promising field electron sources based on silicon carbide monolithic field emission array (FEA). FEA is fabricated on single-crystal wafers of silicon carbide (0001C) 6H-SiC of n-type conductivity using the technology of two-stage reactive ion etching in SF6/O2/Ar atmosphere. To implement conditions close to breakdown, an experimental setup based on high-voltage narrow pulses generating device GKVI-300 was used. A series of nanosecond voltage pulses with amplitudes from 120 to 250 kV was generated. To study the characteristics of the FEA in the pre-breakdown state, the beam of field emitted electrons was separated from the ion torch or cathode plasma, formed in the following breakdown phases, by placing a 50-μm-thick titanium foil under zero potential into the interelectrode gap. Current-voltage characteristics of peak-currents vs. peak-voltages passing through the foil are close to rectilinear in the Fowler-Nordheim coordinates. The current-voltage characteristics plotted for each of the pulses along increasing and decreasing branches show a discrepancy (hysteresis). After the experiments, the silicon carbide cathode FEA was studied in a scanning electron microscope.

Characteristics of a silicon carbide field emission array under pre-breakdown conditions

This study assesses promising field electron sources based on silicon carbide monolithic field emission array (FEA). FEA is fabricated on single-crystal wafers of silicon carbide (0001C) 6H-SiC of n-type conductivity using the technology of two-stage reactive ion etching in SF6/O2/Ar atmosphere. To implement conditions close to breakdown, an experimental setup based on high-voltage narrow pulses generating device GKVI-300 was used. A series of nanosecond voltage pulses with amplitudes from 120 to 250 kV was generated. To study the characteristics of the FEA in the pre-breakdown state, the beam of field emitted electrons was separated from the ion torch or cathode plasma, formed in the following breakdown phases, by placing a 50-μm-thick titanium foil under zero potential into the interelectrode gap. Current-voltage characteristics of peak-currents vs. peak-voltages passing through the foil are close to rectilinear in the Fowler-Nordheim coordinates. The current-voltage characteristics plotted for each of the pulses along increasing and decreasing branches show a discrepancy (hysteresis). After the experiments, the silicon carbide cathode FEA was studied in a scanning electron microscope. Keywords: field electron emission, field emitter array, silicon carbide, pre-breakdown, high-voltage narrow pulses.

Refinement of the EC stray radiation estimates for ITER

The ITER ECRH&amp;CD system is composed by 24 gyrotrons at 170 GHz that will deliver 20 MW at the plasma. Up to 6.7 MW will be injected in the empty vacuum vessel at the beginning of each plasma discharge to provide the gas breakdown. In that phase and when the plasma absorption is non ideal, a certain level of EC non-absorbed power, usually addressed as stray radiation, will be present. The EC stray radiation interaction with ITER first wall and diagnostics has been described in preliminary works. A more refined assessment is here described, following update of the diffuse stray radiation model and update of the launchers optics parameters. The optical design of the EC equatorial launcher has been entirely redesigned to optimize the power deposition and minimize interaction with the launcher structures. The updated parameters for the 24 launched beams are now available and have been used to estimate the interaction of the beams to be used for the breakdown phase with the tokamak structures. The preliminary stray radiation model described every opening of the tokamak as a “black” hole, that is a perfect power sink. Refining this crude description, using for the openings a “grey” hole model, provide a better agreement with benchmarks from other alternative models. Examples of stray radiation estimates performed for various ITER structures, systems and diagnostics are discussed.

A Novel Digital Forensic Framework for Data Breach Investigation

Data breaches are becoming an increasingly prevalent and global concern due to their massive impact. One of the primary challenges in investigating data breach incidents is the unavailability of a specific framework that acknowledges the characteristics of a data breach incident and provides clear steps on how the investigative framework can comprehensively answer what, who, when, where, why, and how (5WH) questions. This paper aims to develop a novel digital forensic investigation framework that can overcome these data breach investigation challenges. The proposed framework utilizes the data breach breakdown phases to analyze data breach incidents according to their characteristics. The main contribution of our work is a novel digital forensic framework for data breach investigation that enhances the 5WH analysis depth by utilizing evidence classification and artifact visualization based on data breach breakdown phases. Furthermore, we design the framework components to provide comprehensive analysis results that make it easier for investigators to summarize the answers to the 5WH questions. To validate the framework, we apply it to a case study of enterprise-level data breach incidents. Based on the case study analysis, the proposed investigation framework successfully provides all the answers to the 5WH questions. This comprehensive answering ability is the study’s fundamental strength compared to other digital forensic investigation frameworks.