Pulsed Power System Research Articles

Phenomenological Studies for Optimizing Subsonic Underwater Discharges

Powerful subsonic underwater discharges are used as a tool in various industrial applications. The aim of this article is to find the essential design parameters required for a pulsed-power system to efficiently drive such discharges. Using different capacitor banks and electrode geometries, a large number of studies were conducted in an effort to better understand the phenomenology of the discharge. Without developing a numerical model for the underwater plasma discharge, the phenomenological studies clearly demonstrated that the maximum pressure that can be generated depends on the discharge current, the distance between the electrodes, and the characteristic time of the discharge. The results of this work will allow the design of efficient pulsed-power-driven strong pressure impulse systems.

Pulsed Power Applications for Protein Conformational Change and the Permeabilization of Agricultural Products.

Pulsed electric fields (PEFs), which are generated by pulsed power technologies, are being tested for their applicability in food processing through protein conformational change and the poration of cell membranes. In this article, enzyme activity change and the permeabilization of agricultural products using pulsed power technologies are reviewed as novel, nonthermal food processes. Compact pulsed power systems have been developed with repetitive operation and moderate output power for application in food processing. Firstly, the compact pulsed power systems for the enzyme activity change and permeabilization are outlined. Exposure to electric fields affects hydrogen bonds in the secondary and tertiary structures of proteins; as a result, the protein conformation is induced to be changed. The conformational change induces an activity change in enzymes such as α-amylase and peroxidase. Secondly, the conformational change in proteins and the induced protein functional change are reviewed. The permeabilization of agricultural products is caused through the poration of cell membranes by applying PEFs produced by pulsed discharges. The permeabilization of cell membranes can be used for the extraction of nutrients and health-promoting agents such as polyphenols and vitamins. The electrical poration can also be used as a pre-treatment for food drying and blanching processes. Finally, the permeabilization of cell membranes and its applications in food processing are reviewed.

(Invited) Multi-Channel AlGaN/GaN Power Rectifiers: Breakthrough Performance up to 10 kV

High-voltage power rectifiers are widely used in renewable energy processing, electric grids, industrial motor drives, pulse power systems, among other applications. Today’s high-voltage rectifier market is dominated by bipolar Si diodes up to 6.5 kV, which suffer from slow reverse recovery. Wide-bandgap SiC unipolar diodes have been pre-commercialized up to 10 kV, which allows for a much higher switching speed. Recently, we have developed a new generation of high-voltage rectifiers based on the multi-channel AlGaN/GaN platform, which highlight a series of novel device designs incorporating the stacked two-dimensional electron gas (2DEG) channels, p-n junctions, and 3-D fin structures. With these innovations, the performances of our unipolar 1.2-10 kV multi-channel AlGaN/GaN Schottky rectifiers well exceed the Si and SiC 1-D limit, at the same time possessing a lower cost as compared to SiC counterparts. This paper reviews our efforts in the design, fabrication and characterization of these GaN devices. Our results show the tremendous promise of GaN for medium-voltage and high-voltage power electronics applications.

Investigation of an improved low-impedance meander pulse forming line based on glass ceramics

The meander pulse forming line (PFL) is a kind of prospective solid dielectric device for compact, reliable pulsed power systems. In this paper, the electrode structure of a PFL based on glass ceramics was designed with a Ω-shaped structure, which can improve the voltage strength of the PFL and increase the output pulse width. The electric field distribution and output waveform were obtained numerically. Experimental results illustrate that the improved PFL, with dimensions of 260 × 140 × 7 mm3, when used as a simple PFL could generate a well-shaped quasi-square pulse, with the output pulse duration of 85 ns, which is in agreement with the simulation within 14%. Under the conditions of 30 kV charging voltage, 50 Hz repetition frequency, and 4 Ω matching impedance, the lifetime of the solid dielectric PFL based on glass ceramics could be more than 1 × 106. Experiments show reasonable agreement with numerical analysis.

Achieving high energy storage performance and ultrafast discharge speed in SrTiO3-based ceramics via a synergistic effect of chemical modification and defect chemistry

Environmentally friendly energy storage materials with high energy storage performance and excellent stability for applications in pulse power systems are urgently needed. SrTiO3-based ceramics have a relatively high dielectric constant and a high breakdown strength (BDS). However, a low polarization strength in this system often yields a low energy storage density. In this paper, high energy storage performance of SrTiO3-based ceramics with the composition of (Sr1-x-y-φNayBix□φ)TiO3 (abbreviated as zSNBT, where x = 0.2 + 0.3z, y = 0.5z, φ = 0.1–0.1z, and z = 0.8–0.1; □ represents Sr vacancies) was achieved using a synergistic effect of chemical modification and defect chemistry. With the decrease of z, the ferroelectric macro-domain of zSNBT ceramics vanishes due to the original effect of paraelectric SrTiO3, significantly improving the BDS and energy storage performance. When z = 0.2, the material exhibited a single cubic phase structure with a nearly hysteresis-free P-E loop. The maximum BDS reached 390 kV/cm, and under such electric field, a large recoverable energy storage density (Wrec) of 3.94 J/cm3 and ultrahigh energy efficiency (η) of 94.71% were achieved simultaneously. Meanwhile, the 0.2SNBT ceramic showed good thermal stability and satisfying cycling stability in the temperature range of 20–160 °C. In addition, the 0.3SNBT ceramic demonstrated outstanding thermal stability with an ultrafast discharge speed (t0.9 ≤ 26 ns) in the temperature range of 20–180 °C. Furthermore, a simulation model containing grains and grain boundaries was established to explain the enhanced BDS and the energy storage performance. Fine and uniform grains with many grain boundaries significantly hindered the propagation of breakdown cracks, yielding a higher BDS value. These results indicate that zSNBT ceramics are promising environmentally friendly materials for pulse power capacitor applications.

(Bi0.5Na0.5)TiO3-based relaxor ferroelectrics with medium permittivity featuring enhanced energy-storage density and excellent thermal stability

High energy density, efficiency and thermal stability of energy-storage properties are extremely pivotal for the application of dielectric ceramics in advanced pulsed power systems. In this work, we utilize a composition-driven strategy to induce polar nanoregions, refine grain size and adjust permittivity of (1-x)Bi0.5(Na0.9Li0.1)0.5TiO3-xSr(Al0.5Nb0.25Ta0.25)O3 ceramics. As a result, an extraordinary Wrec of 6.43 J/cm3 and high η of 88% are simultaneously obtained in the x = 0.16 composition. Meanwhile, the x = 0.16 sample also shows good frequency stability (5–100 Hz), cycle stability (105 cycles) and superior thermal stability (-55 ~ 225 ℃). The enhanced breakdown strength is analyzed by Weibull distribution and mainly attributed to the decreased average grain size. The typical relaxor behavior is reflected by the broadened and diffused Raman spectra as well as the dispersive and temperature-stable dielectric curves. The existence of dynamic polar nanoregions as confirmed by piezoresponse force microscopy measurements enables the nearly hysteresis-free polarization–electric field response and the related frequency and cycle stability. The mitigated polarization saturation is related to the field-insensitive moderate permittivity and will be conducive to the energy-storage properties at elevated electric field. In addition, the temperature-dependent Raman spectra and the slightly fluctuated ΔP (Pm - Pr) value over the whole temperature range reflect the temperature-stable energy-storage properties. Hence, the current work may provide some novel perspectives for designing dielectric ceramics with enhanced energy-storage properties.

High breakdown strength and enhanced energy storage performance of niobate-based glass-ceramics via glass phase structure optimization

The dielectric capacitors with excellent energy storage characteristics, high power density and temperature stability are strongly desired in modern pulse power system and electronic industry. Thus, BKNAS-xPbO glass-ceramics were designed and prepared. Free oxygen in the glass phase which weakens the glass network structure can be adsorbed by trace Pb2+, thus improving the breakdown strength (BDS) of BKNAS glass-ceramics. Extremely high BDS (~2089 kV/cm) and excellent energy storage density (~17.62 J/cm3) were achieved in 0.6 mol% PbO doped BKNAS glass-ceramics. Moreover, the permittivity variance of BKNAS-0.6PbO glass-ceramics was less than 4.39% in the ultrawide temperature range (−80–300 °C), suggesting excellent temperature stability. The single layer capacitor made by BKNAS-0.6PbO glass-ceramics also exhibited excellent charge-discharge performance, in which the underdamped discharge power density reached 133.69 MW/cm3 as well as the overdamped discharge power density reached 146.89 MW/cm3 with ultrashort discharge time (<18 ns). The above results show that BKNAS-0.6PbO glass-ceramics possesses great potentiality for pulse capacitors owning to excellent energy storage property, temperature stability and charge-discharge performance.

Characterization of Flash X-Ray Source From a Marx-Based Pulse Power System

The source characterization of a Flash X-ray (FXR) device is essential in defining its utility for dynamic radiography. A Marx generator [550 kV, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\Omega $ </tex-math></inline-formula> , and 45 ns full-width half-maxima (FWHM)] based FXR source operating in the voltage range 200–550 kV has been characterized. The FXR electron beam diode has a cylindrical geometry with stainless steel (SS) knife-edge cathode and tapered tip Tungsten rod as anode. The FXR source is connected to the Marx generator-based pulsed power system using a flexible high-voltage cable feed through. The hard X-ray spectrum was measured using a differential absorption spectrometer (DAS). The FWHM of the spot size of FXR source was measured using a pinhole camera and was estimated to lie between 1.83 and 2.31 mm. The on-axis dose measured at 1 m matches well with the calculated dose <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D \alpha V^{2.2}I\Delta t$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> is the applied voltage and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> is the current, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta t$ </tex-math></inline-formula> the time duration.

Interposed pulsed power system for fast separation of radioactive beams

This paper presents the novel design of an interposed pulsed power system, developed to drive a fast-switching magnet with a large multi-mH load inductance, and high field amplitude (> 1 T). This modulator can produce variable flat-top pulses from 1 to 30 ms with rise and fall times of less than 0.5 ms at a variable duty cycle of 3–91% into a heavily inductive load. The system employs a novel over-voltage topology to overcome the inherent inductance and achieve the fast rise and fall times, switching to a precision DC supply to efficiently maintain the flattop without requiring many-kV voltage. We present a power source design consideration, including the results of computer modeling as well as the first experimental results of a modulator scaled test model will also be presented.

Enhanced thermal and frequency stability and decent fatigue endurance in lead-free NaNbO3-based ceramics with high energy storage density and efficiency

Lead-free ceramic capacitors have the application prospect in the dielectric pulse power system due to the advantages of large dielectric constant, lower dielectric loss and good temperature stability. Nevertheless, most reported dielectric ceramics have limitation of realizing large energy storage density (Wrec) and high energy storage efficiency (η) simultaneously due to the low breakdown electric field (Eb), low maximum polarization and large remanent polarization (Pr). These issues above can be settled by raising the bulk resistivity of dielectric ceramics and optimizing domain structure. Therefore, we designed a new system by doping (Bi0.5Na0.5)0.7Sr0.3TiO3 into 0.9NaNbO3-0.1Bi(Ni0.5Zr0.5)O3 ceramics, which simultaneously obtained a higher bulk resistivity by decreasing the grain size and achieved a smaller Pr by optimizing domain structure, thus the better Eb of 530 kV/cm and Wrec of 6.43 J/cm3 were achieved, η was improved from 34% to 82%. Besides, the 0.4BNST ceramics show excellent temperature, frequency and fatigue stability under the conditions of 20–180 °C, 1–100 Hz and 104 cycles, respectively. Meanwhile, superior power density (PD = 107 MW/cm3), large current density (CD = 1070 A/cm2) and discharge speed (1.025 μs) were achieved in 0.4BNST ceramic. Finally, the charge-discharge performance displayed good temperature stability in the temperature range of 30 °C–180 °C. The above results indicated that the ceramics have potential practical value in the field of energy storage capacitor.

Crystallization behavior, ultrahigh power density and high actual discharge energy density of lead-free borate glass-ceramics containing TiO2

This work presents SrO-BaO-Nb2O5-B2O3-P2O5-K2O-TiO2 glass-ceramics prepared by controlled crystallization method. The uniformly dense microstructure with fine grains can be achieved by introducing TiO2. The structural changes were confirmed by the results of SEM and TEM. The 0.5 mol% TiO2 added glass heated at 750 °C for 2 h demonstrates excellent comprehensive properties of εr= 110, BDS = 1408 kV/cm, high energy storage efficiency (η) of 92% and energy storage density of 9.65 J/cm3. The as-prepared glass-ceramic exhibits ultrahigh power density (86.21 MW/cm3), actual discharge energy density (1.00 J/cm3) and excellent temperature stability. These findings qualify this environment-friendly glass-ceramics as one potential candidate for energy storage applications, especially in high power and pulsed power system field.

Effective improved energy storage performances of Na0.5Bi0.5TiO3-based relaxor ferroelectrics ceramics by A/B-sites co-doping

Environmental-friendly relaxation ferroelectrics are anticipated as an excellent comprehensive energy storage performance materials due to their near-zero remnant polarization and slim hysteresis loop. Here, the relaxor ferroelectrics (1-x)Na0.5Bi0.5TiO3-x(Sr0.7La0.2)(Ti0.8Sn0.2)O3 ((1-x)NBT-xSLTS) ceramics with outstanding energy storage performances are synthesized by solid-state reaction. The dielectric properties exhibit obvious frequency dispersion characteristics, and the diffusion coefficient (γ) increases from 1.62 to 1.75 with the doping of SLTS. Also, a large polarization difference (∆P = 20.08 μC/cm2) and a high breakdown strength (Eb = 280 kV/cm) are also achieved simultaneously. As a result, a high recoverable energy density Wrec (~ 2.52 J/cm3), together with a satisfactory efficiency η (~ 89.3%), are attained in 0.55NBT-0.45SLTS ceramic. Additionally, the corresponding samples also show satisfactory stability over the wide temperature range of 20–140 °C, with the variables of Wrec and η are less than 7% and 2%, respectively. More importantly, this ceramic has an ultrashort discharge time τ0.9 (53 ns) and a high current density J (721.86 A/cm2). All these results reveal that 0.55NBT-0.45SLTS ceramic is an ideal lead-free next-generation candidate material for pulsed power systems.

Multiphase Engineered BNT-Based Ceramics with Simultaneous High Polarization and Superior Breakdown Strength for Energy Storage Applications.

Dielectric ceramics are crucial for high-temperature, pulse-power energy storage applications. However, the mutual restriction between the polarization and breakdown strength has been a significant challenge. Here, multiphase engineering controlled by the two-step sintering heating rate is adopted to simultaneously obtain a high polarization and breakdown strength in 0.8(0.95Bi0.5Na0.5TiO3-0.05SrZrO3)-0.2NaNbO3 (BNTSZNN) ceramic systems. The coexistence of tetragonal (T) and rhombohedral (R) phases benefits the temperature stability of BNTSZNN ceramics. Increasing the heating rate during sintering reduces the diffusion of SrZrO3 and NaNbO3 into Bi0.5Na0.5TiO3, which results in a high proportion of the R phase and a finer grain size. The overall polarization is enhanced by increasing the proportion of the high-polarization R phase, which is demonstrated using a first-principles method. Meanwhile, the finer grain size enhances the breakdown strength. Following this design philosophy, an ultrahigh Wdis of 5.55 J/cm3 and η above 85% is achieved in BNTSZNN ceramics as prepared with a fast heating rate of 60 °C/min given a simultaneously high polarization of 43 μC/cm2 and high breakdown strength of 350 kV/cm. Variations in the discharge energy density from room temperature to 160 °C are less than 10%. Additionally, such BNTSZNN ceramics exhibit an ultrafast discharge speed with τ0.9 at approximately 60 ns, which shows great potential in pulse-power system applications.

Realizing High Comprehensive Energy Storage and Ultrahigh Hardness in Lead-Free Ceramics.

Due to the presence of pores and low density, a high recoverable energy density (Wrec) value is usually obtained at the cost of energy storage efficiency (η) in lead-free potassium sodium niobate [(K, Na)NbO3, KNN] based ceramics, which also affects the hardness of ceramics, finally limiting the further development of practical applications. A high Wrec (∼3.60 J/cm3 ) and a high η (∼74.2%) are obtained in 0.975K0.5Na0.5NbO3-0.025LaBiO3 (0.975KNN-0.025LB) ceramics simultaneously under a high dielectric breakdown strength (DBS) of 340 kV/cm, together with a fast discharge rate (t0.9 ∼ 46 ns) and high power density (PD ∼ 49.4 MW/cm3). Further analysis of the intrinsic electronic structure is carried out via the first-principles calculation based on the density functional theory (DFT). An ultrahigh hardness (H) of 6.63 GPa can be accordingly obtained. This work combines excellent energy storage properties and ultrahigh hardness, which provides significant guidelines for applications in pulsed-power systems.

Relaxor ferroelectric Bi0.5Na0.5TiO3–Sr0.7Nd0.2TiO3 ceramics with high energy storage density and excellent stability under a low electric field

Bi0·.5Na0·.5TiO3 (BNT)-based lead-free dielectric materials have attracted extensive research in environment-friendly ferroelectrics due to their high dielectric constant and negligible remanent polarisation. In accordance with previous reports, although BNT-based ceramics obtain large recoverable energy storage density (Wrec > 3 J/cm3), they are commonly accompanied with high dielectric breakdown strength (Eb ≥ 200 kV/cm), which is unfavourable to the practical application of dielectric capacitors. In this study, novel (1-x)Bi0·5Na0·5TiO3-xSr0.7Nd0.2TiO3 (BNT-xSNT) materials were designed and fabricated. The introduction of Sr0.7Nd0.2TiO3 decreases the grain size and induces the polar nano regions. An outstanding recoverable energy storage density (Wrec = 3.09 J/cm3) with medium efficiency (η = 77%) is obtained at 182 kV/cm for 0.7BNT–0.3SNT ceramics. Good temperature stability (25–160 °C) and excellent frequency stability (5–200 Hz) are realised at 100 kV/cm. This research provides a promising energy storage ceramic material for pulsed power system applications and serves as reference for the integration and miniaturisation of electronic devices.

Simulations of hydrogen outgassing from a carbon fiber electrode

Outgassing remains a pertinent issue in high-power systems as it can lead to effects such as breakdown, surface flashover, and pulse shortening and is typically the first stage of deleterious plasma formation. In this context, experimental reports suggest that carbon fibers (CFs) may likely be a superior cathode material for low outgassing. Here, model-based assessments of outgassing from CFs are performed based on molecular dynamics simulations. Carbon fibers were generated based on interconnection of an array of graphene sheets resembling ladder-like structures. Our results of temperature-dependent diffusion coefficients for hydrogen in CFs are shown to exhibit Arrhenius behavior and have values smaller than copper by factors of 15.5 and 86.8 at 400 K and 1000 K, respectively. This points to even stronger improvements for operation at high temperatures, with the asymptotic diffusion constant ratio predicted to be ∼187. With reduced outgassing, higher temperature operation, and durability, our results support CF cathodes as an excellent choice for cathode material in high-power microwave and pulsed power systems.

Breakdown strength and energy density enhancement in polymer-ceramic nanocomposites: Role of particle size distribution

Polymer-ceramic nanocomposites play a very promising role for energy-storage in high power electronics and advanced pulsed power systems, due to their extremely fast charge-discharge capability. The low energy density is the key factor hindering their application, for which large endeavors have been made in the modulation of the fraction, morphology, size, and dispersion of the particle fillers but small in that of the size distribution, which is critical for energy-storage performance. We first investigated the role of this based on simulated nanocomposites with controlled lognormal distributions via a generation algorithm devised in this work. Dielectric response, breakdown behavior and energy-storage performance were explored for distributions with different standard deviations (SD) and mean values (MV), which were solved with the energy equivalence basis and a phase-field dielectric breakdown model. With the decrease of SD and MV, the effective permittivity declines slightly with enhanced permittivity change, which was related with the enhanced local electric field with intensified fluctuation and should be originated from the major contribution of the polymer matrix from the local energy perspective; whereas improved nominal breakdown strength was achieved owing to the weakened local maximum electric field, which leads to distinctly increased nominal energy density despite the slight decline of the permittivity. Keeping the fillers within a narrow disperse outperforms employing super fine particles. This work demonstrates that enhancement in breakdown strength and energy density can be attained via particle size distribution modulation, paving a new way for the further improvement of the energy-storage performance of polymer-ceramic nanocomposites.

A durable microsecond solid-state pulsed power system.

An all-solid-state microsecond pulsed power system has been tested in this paper. It can produce larger than 50 kV and microsecond-range pulses continuously for more than 9 × 104 shots into a resistive load at a repetition rate of 10 pps. The whole device has accumulatively operated more than 15 000 pulses at 100Hz and 3 × 105 pulses at 10Hz. This all-solid-state pulsed power system consists of a repetitive power supply, a four-stage Marx generator, a pulse forming network, and a resistive load. The repetitive power supply of the pulsed power system is calculated and analyzed first, followed by the introduction of the Marx generator and the three-section anti-resonance network. A polymer box of sodium chloride solution is applied as a resistive load with an impedance of 200 Ω. Repetitive experiments showed that this system is able to operate stably at 100Hz repetition rate without failure.

Prediction and experimental verification of erosion resistance of gas switch electrode materials

The gas spark switch is the most used key device in pulsed power systems. As a difficult problem affecting the performance of the gas spark switch, electrode erosion has always been of wide concern and has been studied by scholars. In order to reduce electrode erosion, the erosion resistance of the electrode materials is particularly critical. At present, researchers at home and abroad mainly perform a large number of experiments to compare the erosion resistance of different electrode materials, which require a lot of time and are expensive. Based on the theoretical derivation of the erosion heat conduction process and the analysis of the molten pool movement process, a theoretical prediction model of erosion resistance of electrode materials is established in this paper. The prediction results of this model are consistent with the experimental results of most researchers in the past. In order to further verify the accuracy of this model, this paper selected six electrode materials [stainless steel, brass, RHEAs (Refractory High Entropy Alloys), 90WCu alloy, 70WCu alloy, and 50WCu alloy] tested for 10 000 times under the experimental conditions of a peak current of 30 kA, a single discharge charge transfer of 78 mC, and 2 bars dry air. The final experimental results show that the six electrode materials ranked from weak to strong in erosion resistance: brass, stainless steel, 50WCu, 70WCu, RHEAs, and 90WCu, which is consistent with the prediction results of the model.

Automated signal classification in the C-2W fusion experiment.

In TAE Technologies' current experimental fusion device, C-2W (also called "Norman"), record breaking, advanced beam-driven field-reversed configuration plasmas are produced and sustained in steady state utilizing variable-energy neutral beams, expander divertors, end-bias electrodes, and an active plasma control system. With a rapid shot-pace and an extensive number of data channels, the amount of data generated necessitates automated signal processing. To this end, a machine learning algorithm consisting of a multi-layered neural network as well as other data processing software has been designed for signal feature identification, allowing for accurate and fast signal classification, anomalous condition detection, and providing for signal pre-processing. With a small set of training data, the neural network can be "bootstrapped" to provide a robust classification system while minimizing human oversight. An example using data from the theta pinch plasma formation pulsed power system is presented. With an overall accuracy of ∼97%-having classified more than 5 × 106 pulsed power signals-the classification scheme is more than sufficient to fine-tune machine set points. However, this technique can be used for near-real-time preprocessing of any plasma physics signal and has wide ranging application in fusion experiments for the varied data produced by plasma diagnostics.