High Voltage Pulse Research Articles

Experimental study of cavitation development in liquid in pulsed non-uniform electric field under the action of ponderomotive forces

In this paper, the Rayleigh scattering method is used to study the formation of cavitation in water in a pulsed inhomogeneous electric field when a nanosecond high voltage pulse is applied to a needlelike electrode. The observational results confirm the theoretical picture of cavitation development under the action of electrostrictive ponderomotive forces. The values of the negative pressure, the average size of the cavitation nanovoids, and their concentration were obtained from these measurements, which are in agreement with theoretical estimates.

Experimental Study on Underwater Cylindrical Acoustic Wave Generated by High-Voltage Pulse Excited Cable

Experimental Study on Underwater Cylindrical Acoustic Wave Generated by High-Voltage Pulse Excited Cable

Slice emittance measurements using a slit-grid system and a fast wall-current monitor.

The time evolution of beam properties in an electron bunch with the duration of a nanosecond was measured with a time resolution of several tens of picoseconds. A combination of horizontal and vertical slits cuts the beamlet from the original beam, with the current waveform of the beamlet measured using a fast wall-current monitor. The reconstruction of the waveform data obtained by scanning these two slits over the entire beam area provided the time evolution of the spatial profile. A similar measurement using two horizontal (vertical) slits separated by a certain distance also provides the time evolution of the phase-space profile. Using this method, the initial beam extracted from the CeB6 thermionic electron gun of the x-ray free-electron laser (XFEL) SACLA was evaluated. Although the slice emittance in the bunch was measured to be constant, the centroid of the spatial profile moved in the transverse direction by a few hundred micrometers in the 0.6ns flat-top region. This movement arises from the temporal variation in the rectangular high-voltage pulse of the beam chopper and can cause an increase in the projected emittance. These measurements are important for evaluating the conditions of the initial beam emitted from the cathode and processed downstream of the gun. Hence, the proposed diagnostic system will play an important role in developing an extremely low-emittance electron beam or an artificial electron beam with a multi-bunch or micro-bunch structure that enhances the brightness of the XFEL light.

A novel ADE system with tunable droplet size and ejection height

Acoustic droplet ejection (ADE) has been proven to move liquids in droplet form from a container to mid-air. However, the droplet sizes produced using the traditional ADE setups are proportional to their heights if the physical framework is unchanged. This limitation obstructs further employment of ADE technology since having the exact sizes of droplets at a specific location or different sizes at different locations is required for many applications. To overcome this limitation and enable more possible applications of ADE, this study proposed an innovative ADE configuration that could manipulate the size and height of the ADE droplets with only electrical signals. To achieve this, a low-voltage driving period and a pinhole structure were added to create a water mound before ejection. First, simulations were conducted to validate the proposed method and find the parameters of the novel ADE setup. After that, a driving circuit featuring a high-voltage pulser and a field-programmable gate array was built. However, a 3D spherical resin model was printed to focus the acoustic wave on the water surface, and a cover with a pinhole was added to create water mound. To observe the behavior of the droplets, a recording system and detection algorithm were developed to capture and identify the dimension/height of the droplets, respectively. Finally, the proposed ADE configuration successfully manipulated the droplet size at the same ejecting height under three driving voltages (65, 70, and 75 V) and pinhole diameters (3.7, 4, and 4.4 mm).

Electrical pruning of Pinus radiata epicormic growths

A novel method for pruning epicormic growths with high voltage energy pulses is presented. This method could be utilized in autonomous forest management, for example by a drone carrying an electrical pulse generator and applicator pruning device. In a laboratory setting, short duration, high voltage pulses of electricity were generated using a capacitor network and a current source. These pulses were applied to Pinus radiata needles and the relative tissue injury to the needles was assessed by estimating electrolyte leakage from the needles in deionised water using electrical conductivity (EC) measurements. EC was positively correlated with the electrical energy applied. This validated the theory that electrical stimuli can cause increased cell death in plant matter. The cell damage, based on electrolyte leakage, caused by stimulating a Pinus radiata needle with a single 1.5 J pulse of energy was 21 % of the maximum, where the maximum was found to result in an EC of 333 µS/cm per gramme of needle in a 45 ml solution. These results from testing on needles removed from the tree confirm the potential of electrical pruning of epicormic growths. Future testing on live in-situ needles will be implemented to determine the level at which cell death induced by the application of high voltage pulses is sufficient to prune epicormic growths, given that mechanical and biotic factors of needles removed from the tree may enhance the rate of cell death in harvested samples.

Abstract 4134: The abscopal effect of combination IRE with αPD-1 treatment against PDACs

Abstract Pancreatic ductal adenocarcinoma (PDAC) is associated with a high capacity of metastatic dissemination, which results in a dismal 5-year relative survival rate. Irreversible electroporation (IRE) represents an innovative intervention utilizing short high-voltage electric pulses to induce cell death through either permanent membrane lysis or disruption of cellular homeostasis. Previous studies from our lab have demonstrated that the combination of IRE and immune checkpoint blockade using anti-PD-1 antibody (αPD-1) enhances the infiltration of CD8+ cytotoxic T cells, significantly prolonging survival in an orthotopic murine PDAC model. However, the impact of IRE/αPD-1 on metastatic PDAC tumors, known as the abscopal effect, remains unclear. In this investigation, we bilaterally implanted C57BL/6J mice with subcutaneous KRAS* PDAC tumors, treating the right flank tumors with or without IRE, in conjunction with or without αPD-1 administered intraperitoneally. Tumor growth in both the treated (with or without IRE) and untreated (abscopal) left flank tumors was closely monitored until humane euthanasia or long-term survival. In a separate study, mice serum and tumor tissues were collection on the 5th day post-IRE/αPD-1 treatment. Luminex cytokine assays were conducted on the collected serum, and immunostaining was performed on tumor tissue. Results demonstrated significantly enhanced antitumor activity in both IRE-treated and untreated tumors on mice treated with combined IRE and αPD-1, leading to a marked extension of overall survival. Luminex cytokine assays revealed a substantial increase in crucial cytokines, including IL-2, IFN-gamma, IL-18, IL-19, and IL-3, known for their pivotal roles in fostering cytotoxic T lymphocyte development, promoting T cell differentiation into effector T cells, and facilitating the recruitment of effector CD8+ T cells to the tumor microenvironment. Moreover, immunofluorescence staining of tumor tissue illustrated a notable accumulation of CD169+ macrophages in IRE-treated tumors compared to untreated tumors. Tumors from the combined IRE with αPD-1 group exhibited increased CD8+ T cell accumulation compared to other groups. These data suggest IRE combined with PD-1 blockade promotes robust antitumor immune, leading to systemic antitumor activity and robust abscopal effect. Citation Format: Qizhen Cao, Nicholas A. Egan, Weiyi Peng, Chun Li. The abscopal effect of combination IRE with αPD-1 treatment against PDACs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4134.

Abstract 6640: Zap! Irreversible electroporation in pancreatic cancer cells induces proinflammatory cell death and improves progression free survival

Abstract Pancreatic cancer is the third leading cause of cancer-related death due to its late diagnosis, few treatment options, and extremely low survival rates due to its immunosuppressive microenvironment. Irreversible electroporation (IRE),is a tumor non-thermal ablation technique that applies high-voltage electrical pulses to permeabilize the cell membrane that is irreversible and leads to necrotic cell death. IRE has had strong success in clinical trials nevertheless, little is known about the effect of IRE beyond the initiation of cell death in the tumor tissue. We hypothesize that IRE can not only induce cell death by membrane disruption to facilitate a proinflammatory microenvironment but also causes death via cell cycle arrest. We utilized in-vitro, and immunocompetent in-vivo murine models to investigate changes to pancreatic cancer and the tumor microenvironment. Our findings show that treating the cells with an increasing voltage of IRE induces more cell death. We observed cell cycle arrest in the G1 phase which may have been caused by DNA damage. There was upregulation of DNA damage repair machinery in the treated samples. Our histopathology data suggests increased necrosis on the tumor treated with IRE, as also PCR array analysis showed more proinflammatory cell death caused by pyroptosis. Finally, we demonstrated a reduction in the tumor size and a better survival rate aftertreatment. Our data suggest that Irreversible electroporation has a promising future in inducing proinflammatory type of cell death in the tumor and benefits increased patient survival. More investigation is needed to define ideal parameters for the electrical pulses and device development for tumor ablation in larger animals like porcine models. Citation Format: Manali Powar, Khan Mohammad Imran, Irving C. Allen, Rafael V. Davalos, Zaid Salamah, Kenneth Aycock, Rebecca M. Brock, Sheryl Coutermarsh-Ott, Katie Orr. Zap! Irreversible electroporation in pancreatic cancer cells induces proinflammatory cell death and improves progression free survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6640.

Ultrafast Metal-Free Microsupercapacitor Arrays Directly Store Instantaneous High-Voltage Electricity from Mechanical Energy Harvesters.

Harvesting renewable mechanical energy is envisioned as a promising and sustainable way for power generation. Many recent mechanical energy harvesters are able to produce instantaneous (pulsed) electricity with a high peak voltage of over 100 V. However, directly storing such irregular high-voltage pulse electricity remains a great challenge. The use of extra power management components can boost storage efficiency but increase system complexity. Here utilizing the conducting polymer PEDOT:PSS, high-rate metal-free micro-supercapacitor (MSC) arrays are successfully fabricated for direct high-efficiency storage of high-voltage pulse electricity. Within an area of 2.4 × 3.4cm2 on various paper substrates, large-scale MSC arrays (comprising up to 100 cells) can be printed to deliver a working voltage window of 160V at an ultrahigh scan rate up to 30V s-1. The ultrahigh rate capability enables the MSC arrays to quickly capture and efficiently store the high-voltage (≈150V) pulse electricity produced by a droplet-based electricity generator at a high efficiency of 62%, significantly higher than that (<2%) of the batteries or capacitors demonstrated in the literature. Moreover, the compact and metal-free features make these MSC arrays excellent candidates for sustainable high-performance energy storage in self-charging power systems.

An 8 mm endoscopic histotripsy array with integrated high-resolution ultrasound imaging

An 8 mm diameter, image-guided, annular array histotripsy transducer was fabricated and characterized. The array was laser etched on a 5 MHz, 1–3 dice and fill, PZT-5H/epoxy composite with a 45 % volume fraction. Flexible PCBs were used to electrically connect to the array elements using wirebonds. The array was backed with a low acoustic impedance epoxy mixture. A 3.6 by 3.8 mm, 64-element, 30 MHz phased array imaging probe was positioned in the center hole, to co-align the imaging plane with the bubble cloud produced by the therapy array. A custom 16-channel high voltage pulse generator was used to test the annular array for focal lengths ranging from 3- to 8-mm. An aluminum lens-focussed transducer with a 7 mm focal length was fabricated using the same piezocomposite and backing material and tested along with the histotripsy array. Simulated results from COMSOL FEM models were compared to measured results for low voltage characterization of the array and lens-focussed transducer. The measured transmit sensitivity of the array ranged from 0.113 to 0.167 MPa/V, while the lens-focussed transducer was 0.192 MPa/V. Simulated values were 0.160 to 0.174 MPa/V and 0.169 MPa/V, respectively. The measured acoustic fields showed a significantly increased depth-of-field compared the lens-focussed transducer, while the beamwidths of the array focus were comparable to the lens. The measured cavitation voltage in water was between 254 V and 498 V depending on the focal length, and 336 V for the lens-focussed transducer. The array had a lower cavitation voltage than the lens-focussed transducer for a comparable operating depth. The histotripsy array was tested in a tissue phantom and an in vivo rat brain. It was used to produce an elongated lesion in the brain by electronically steering the focal length from 3- to 8-mm axially. Real time ultrasound imaging with a Doppler overlay was used to target the tissue and monitor ablation progress, and histology confirmed the targeted tissue was fully homogenized.

Review on Pulsed Electric Fields: A New Horizon in Food Processing Health Techniques

Pulsed electric fields (PEF) are a novel, non-thermal, promising, and energy-efficient method of food preservation that utilizes short electrical pulses for microbial inactivation by causing minimal impacts on the quality attributes of food. In the PEF method, high-voltage pulses are generated between two electrodes immersed in fluid or paste-like foods to sterilize them by passing electricity through the food. PEF technology is predominantly applied in processing dairy, eggs, meat, fish, and liquid foods like juices and milk to inhibit microbial growth. As a non-thermal food preservation technique, PEF effectively manages biological hazards. Current research extends beyond microbial inactivation, demonstrating PEF's capability to enhance juice extraction from plant materials and to improve the efficiency of food drying and dehydration processes. Moreover, this technique targets the cytoplasmic membrane to enhance the selective release of intracellular compounds without the adverse effects of heat on extract quality and characteristics. Its low-energy pretreatment process also facilitates high yields in extraction. In addition, this process can improve the antioxidant activity, immunomodulatory activity, and inhibitory activity of ACE and can degrade pesticide residue as well. While much research focuses on PEF's microbial reduction, fewer studies examine its effects on the quality and consumer acceptance of treated foods. However, recent studies are highlighting the potential of PEF technology in achieving higher yields and preserving the quality of nutrients in food products.

Review of High Voltage Pulsed Power Supplies and Power Electronics in Pulse Power Generation

Recently, pulse-shaped power supplies have become more popular. Pulsed power is versatile and useful as a supply method since it can take several shapes and has many pulse characteristics. The release of electrons, protons, and neutrons from an atom and the synthesis of molecules to generate ions or other molecules require a lot of immediate energy. Pulsed power is needed for decomposition, molecular fusion and material joining, radiation generation (e.g., electrons, lasers, radar), explosive processes for concrete recycling, wastewater and exhaust gas treatment, and material surface treatments. Industrial and environmental applications require pulsed power, which requires efficient and adaptive pulse modulators. Higher-quality repeating pulses are needed for plasma fusion and laser weapons. Marx Generators, Magnetic Pulse Compressors, Pulse Forming Networks, and Multistage Blumlein Lines have several uses. Pulse modulators use spark gap and hydrogen thyratron gas/magnetic switching technologies for their high voltage tolerance and low-rise times. These creatures are inefficient, unreliable, repetitious, and short-lived. These devices are heavy, bulky, and expensive. Solid-state switching technology can replace conventional devices, improving pulse supply. High-frequency switching repeats the pulsed power supply. These items are compact, efficient, affordable, reliable, and durable. Solid-state transistor applications may not meet switch voltage ratings and rise time constraints. Various power electronics configurations can produce solid-state high-voltage pulses.

Reactive species and mechanisms of perfluorooctanoic acid (PFOA) degradation in water by cold plasma: The role of HV waveform, reactor design, water matrix and plasma gas

The scope of this study was to optimize dielectric barrier discharge (DBD) plasma for the degradation of perfluorooctanoic acid (PFOA) in water by comparing several critical aspects such as pulsed-plasma waveform (nanosecond and microsecond high voltage (HV) pulses), reactor configuration (gas–liquid treatment and underwater plasma bubbles), water matrix and plasma gas. The physicochemical properties and species concentration of plasma-treated water, under the aforementioned conditions, were also determined and correlated with PFOA degradation. PFOA was more efficiently degraded by air–liquid DBD compared to DBD-based underwater air-plasma bubbles consistent with the surfactant nature of PFOA and the more intense plasma-liquid interaction and species formation prevailing during gas–liquid treatment compared to plasma bubbles treatment. After 30 min of gas–liquid DBD treatment, the degradation of PFOA in ultrapure water was >99.9, 98.8, 95.1 and 63% under air-, N2-, Ar- and O2-plasma respectively, whereas its degradation was almost equally effective in the whole range of its initial concentration (10 to 0.1 mg/L). Air was almost equally effective at degrading PFOA in ultrapure and tap water, while argon was much more effective at degrading PFOA in tap water (>99.9% after 20 min) possibly due to the prevailing alkaline conditions (pH ∼8.7) favoring its degradation. Faster PFOA degradation was achieved under HV micropulses compared to HV nanopulses. Nevertheless, in terms of energy requirements, HV nanopulses were superior to HV micropulses, with the lowest electrical energy per order achieved under nanopulsed-argon (∼23.6 kWh/m3). The results of this study could contribute important knowledge to the development of plasma-based treatment of PFOA-contaminated water.

Challenges in Measurement of Low-Value ESL and ESR of High-Performance PFN Capacitors for Klystron Modulator

In the high voltage line type pulse modulators, Pulse Forming Network (PFN) capacitors are one of the important components. These capacitors operate at peak kilo ampere current range and at repetition rate in the range of a few hundred hertz. The performance of these capacitors is critical w.r.t. overall system performance, and they are required to operate at high power density and low losses with high reliability. The Equivalent Series Inductance (ESL) and Equivalent Series Resistance (ESR) are two critical parameters that affect the performance of these capacitors. PFN modulator demands a capacitor of very low ESL and ESR for reliable operation and generation of high-voltage pulses. Higher ESR value adversely affects the performance of the capacitor by raising its temperature and thus deteriorating its life. ESL value does not directly affect life, but it affects the quality of high voltage pulse. In RRCAT, the PFN capacitors purchased from Indian manufacturers were showing high-temperature rise and failures. Therefore, new capacitors were designed to have lower ESL and ESR values. Measurement of ESL and ESR is important to evaluate the performance of the capacitors. The low value of these parameters makes their measurement a challenging task and requires special techniques. For low values of ESL and ESR (less than 100 mΩ) measurement, a differential measurement technique was used in which modification and different layouts were explored to improve the repetitive accuracy of the measurements. The differential ESR and ESL measurement techniques with more emphasis on the low-value ESR measurement will be discussed in the paper.

Comparative Study of Different High Voltage Switches Used in Pulsed High Voltage Application

High-voltage switches play a crucial role in pulsed power applications, where the efficient and reliable control of highvoltage pulses is required. This study aims to compare different types of high-voltage switches commonly used in pulsed power systems including electromechanical switches, vacuum switches, gas-filled switches, triggered spark gaps and solidstate switches. The comparison study focuses on key performance parameters such as voltage handling capability, current carrying capacity, turn-on time, and repetition rates are considered to provide a comprehensive study and analysis of the switch’s suitability for different pulsed power applications. Gas-filled switches such as spark gaps, thyratrons and ignitrons have been used in pulsed power systems due to their high voltage handling capability and low switching losses. However, they suffer from a limited lifetime and require maintenance and periodic replacement. Solid-state switches, i.e. Silicon-Controlled Rectifiers (SCRs), Insulated Gate Bipolar Transistors (IGBTs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) offer advantages in terms of longevity, reliability, and reduced maintenance. However, they have limitations in high-voltage applications and exhibit higher switching losses. The findings of this comparison study will assist researchers, engineers, and system designers in selecting the most appropriate high-voltage switch for pulsed power applications, considering the specific requirements and constraints of the system. This will ultimately contribute to the advancement and optimization of pulsed power technologies across a wide range of scientific, industrial, and strategic applications.

Extendable high gain low current/high pulse modified quadratic–SEPIC converter for water treatment applications

Substantial attention has been drawn over the past few years by high step-up dc-dc converters owing to their applications in a wide range. Apart from renewable energy applications, high voltage/ high pulse converters are efficiently used in water treatment applications. The converter suggested a combination of Quadratic and SEPIC converters with a diode-capacitor cell. This topology generates high-voltage repetitive pulses with a single semiconductor switch and reduced component count. The stress across the components is less than the high-gain converters reported in the literature. The topology has an extendable feature by increasing the number of diode-capacitor cells without affecting the stress. The superiority of the high pulse generating topology is validated with a similar converter in the literature. This paper discusses the nL5 simulator results for the proposed rated topology required for water treatment. A scaled-down 50 W prototype is tested for various input voltages to generate high voltage pulse, and the analytical study is validated.

Calculation and experimental determination of the speed of advancement of the plasma leader channel of a pulse spark discharge in atmospheric air

Goal. Calculation and experimental determination of middle speed vL of advancement of plasma leader channel of a pulse spark discharge in the long air interval of the double-electrode discharge system (DEDS) «tip-plane». Methodology. Bases of the theoretical electrical engineering and electrophysics, electrophysics bases of technique of ultra- and high-voltage and high pulse currents, bases of high-voltage pulse technique and measuring technique. Results. The close calculation and experimental method of determination of middle speed vL of advancement of plasma leader channel of an electric pulse spark discharge is offered in the long air interval of DEDS «tip-plane». This method is based on the offered calculation empiric formula for finding of the indicated speed vL and results of decoding of oscillograms of process of cut of in-use standard interconnect аperiodic pulse of over- and high-voltage of temporal shape of Tm/Тd≈200 μs/1990 μs of positive polarity at an electric hasp in indicated DEDS of long air intervals with their minimum length of lmin, numeral making 1,5 m (first case) and 3 m (second case). It is shown that middle speed vL of advancement in atmospheric air of front of plasma channel of positive leader of an electric pulse spark discharge in probed DEDS «tip-plane» for two considered applied cases at lmin=1,5 m of lmin=3 m numeral makes approximately vL≈(1±0,03)∙105 m/s. The found numeral value of this speed vL well coincides with the known experimental information for speed of advancement of vL≈105 m/s in atmospheric air of plasma channel of negative leader for a long storm spark discharge in DEDS «charged cloud-earth». It is set that for the standard interconnect аperiodic pulse of high- and ultra- voltage of temporal shape of Tm/Тd≈200 μs/1990 μs of positive polarity middle value of aggressive strength Ed of high pulse electric field in the air interval of probed DEDS «tip-plane» numeral makes minimum length of lmin=1,5 m near Ed1≈360,8 kV/m, and for his minimum length of lmin=3 m of − Ed2≈313,4 kV/m. Originality. The comfortable is developed in the use and reliable in practical realization technicians-and-engineers calculation and experimental method of research in the conditions of high-voltage electrophysics laboratory of difficult electro-discharge processes of development of leader hasp of long air intervals and determination of minimum electric durability of air insulation of electrical power engineering and electrophysics equipment on working voltage of classes of 330-1150 kV. Practical value. Application in area of industrial electrical power engineering and high-voltage pulse technique of the got numeral electrophysics results and offered calculation and experimental method of determination of middle speed vL of advancement in atmospheric air of plasma channel of leader of a long spark discharge will allow, from one side, to deepen our scientific knowledges about a long electric pulse spark discharge in an air dielectric, and, from other side, to develop high-voltage electrical power engineering and electrophysics devices with enhanceable reliability of their work both in normal operation and malfunctions.

Optimizing liberation of phosphate ore through high voltage pulse fragmentation

This study investigates the selective high voltage pulse (HVP) fragmentation and its role in enhancing the metallurgical performance in phosphate ore processing. We have adapted the use of HVP fragmentation to enable the complete comminution of the considered ore, without the need for additional grinding steps. The efficiency of the HVP process strongly depends upon two parameters – the discharge ratio and the electric field, which, combined, allow for an improved liberation. Furthermore, for the same feed, the high voltage pulse fragmentation provides a coarser product with fewer fines. This study also emphasizes an improved liberation of the target mineral, carbonate fluorapatite, in the 100–315 μm fraction, while concentrating gangue minerals in the <100 μm size fraction. These findings are supported by X-ray tomography, validating the principle of pre-weakening induced by high voltage pulses on phosphate ore and further confirming the significance of our research.

Design of a Pulse Transformer for X-band Klystron

Future linear accelerators require klystrons with higher radio frequency (RF) to drive higher gradient accelerating structure. An x-band accelerator structure was used to accelerate electrons at the Shanghai Soft X-ray Free Electron Laser Facility (SXFEL) in Shanghai Advanced Research Institute, Chinese Academy of Sciences (SARI-CAS). A pulse transformer is a crucial device in an RF system. This study presents a high-voltage pulse transformer used for a 50 MW x-band pulsed klystron in SXFEL. Typical specifications of the pulse transformer are peak pulse voltage 420 kV, peak pulse current 300 A, 50 Hz repetition rate and 1.5 μs flat-top pulse width. Design and optimization of pulse transformer are achieved by using equivalent circuit analytic methods and computational aided simulation. The relevant experiments show that this pulse transformer can meet the requirements of 50MW x-band klystron.

Study on fracture characteristics and mechanisms of red sandstone under high-voltage pulse discharge

To investigate the influences of geometrical size and discharge voltage of the pulse discharge equipment on the fracture characteristics and mechanisms of sandstone under high-voltage pulses, a series of experiments was conducted using a high-voltage pulse discharge device on sandstone circular disc specimens of sandstone with a thickness of 10 mm. These experiments covered a range of disc diameters ranging from 50 mm to 142 mm and discharge voltages from 15 kV to 40 kV. Through these experiments, the fracture characteristics of sandstone at both macroscopic and microscopic levels were investigated. In the experiments, a quantitative analysis of surface fracture was undertaken based on fracture density and fractal damage. Additionally, using the principle of energy equivalence, numerical simulation methods were used to study the damage evolution process in sandstone. The research results indicate that the formation and distribution of fractures in the sandstone specimens are significantly affected by geometrical size and discharge voltage. By analyzing the interaction between stress waves and fracture propagation, combined with indoor experimental results, the fracture mechanism was revealed. The high temperature and shock wave generated by the plasma channel leads to the crushing zone near the electrode, while the circumferential tensile component of the stress wave can result in radial fractures, and the reflected tensile wave leads to circumferential and radial fractures near the boundary.

Experimental and numerical study on the facture behavior of heated-granite subjected to high-voltage electric pulse

High-voltage electric pulse (HVEP) technology holds tremendous potential for addressing rock fragmentation challenges in deep resource extraction. This study investigated the fracture behavior of granite subjected to HVEP at elevated temperatures. HVEP discharge experiments with varying peak voltages were conducted on heated-granite flakes. Experimental results indicated that peak voltages exceeding 96 kV applied to granite flakes heated to 400 °C resulted in electrical breakdown and penetration fractures. Additional experiments involved heating granite flakes to different temperatures and applying HVEP at a constant 120 kV voltage. These experiments allowed for the observation and analysis of granite’s fracture behavior under various conditions. Scanning Electron Microscopy (SEM) was used to evaluate microstructural changes. Furthermore, Particle Flow Code (PFC) numerical simulation method was adopted to investigate the electrical fracture mechanism, treating it as a point explosion load to replicate granite’s electrical disintegration process. This study elaborated on the electrical fracture process, crack expansion modes in granite, and the influence of rock temperature on primary radial crack initiation, propagation, and the proportion of shear and tensile cracks. The investigation delved into the temperature’s role by focusing on the plasma channel formation as a critical time point. This study has the potential to contribute to a more comprehensive understanding of the factors influencing HVEP rock breaking.