Positive Polarity Pulses Research Articles

The influence of asymmetrical bipolar pulses and interphase intervals on the bipolar cancellation phenomenon in the ovarian cancer cell line

The application of negative polarity electrical pulse (↓) following positive polarity pulses (↑) may induce bipolar cancellation (BPC), a unique physiological response believed to be specific to nanosecond electroporation (nsEP). The literature lacks analysis of bipolar electroporation (BP EP) involving asymmetrical sequences composed of nanosecond and microsecond pulses. Moreover, the impact of interphase interval on BPC caused by such asymmetrical pulse needs consideration. In this study, the authors utilized the ovarian clear carcinoma cell line (OvBH-1) model to investigate the BPC with asymmetrical sequences. Cells were exposed to pulses delivered in 10-pulse bursts but as uni- or bipolar, symmetrical, or asymmetrical sequences with a duration of 600 ns or 10 µs and electric field strength equal to 7.0 or 1.8 kV/cm, respectively. It was shown that the asymmetry of pulses influences BPC. The obtained results have also been investigated in the context of calcium electrochemotherapy. The reduction of cell membrane poration, and cell survival have been observed following Ca2+ electrochemotherapy. The effects of interphase delays (1 and 10 µs) on the BPC phenomenon were reported. Our findings show that the BPC phenomenon can be controlled using pulse asymmetry or delay between the positive and negative polarity of the pulse.

Electric charge build-up and dissipation at pulsed streamer corona by EFISH and probe measurements

This work examines the dynamics of volumetric electric charge deposited by a single pin electrode streamer corona in atmospheric air at ambient conditions. Recent studies show that, at pulse-periodic operation, electric charge remains in surrounding air after the first discharge. This residual charge significantly affects the electric field distribution and morphology of discharges at subsequent pulses. In this study, the residual electrical potential/field was measured during and after dissipation of a pulsed 80 kV streamer corona of alternating polarity. This was accomplished using electrostatic probes and the electric field induced second harmonic method (EFISH generation). The residual volumetric charge of a positive pulse polarity streamer corona occupies a zone of up to 80 mm from the electrode. The subsequent application of a negative polarity pulse leads to partial neutralization of the previous charge and the generation of a region with a high-amplitude electric field. The propagation of following positive polarity pulses is limited by the residual positive volumetric charge. The EFISH method reveals the magnitude of the electric field at discharge propagation and electrostatic probes inform the polarity. Intensified imaging acquisition was used to evaluate the spatial distribution and dynamics of corona discharge during the alternating polarity waveform.

Ionization wave propagation in a long capillary tube in the presence of a low-current glow discharge in low-pressure helium

The experimental results on the study of the positive ionization wave propagating along a long capillary tube are presented. The ionization wave was initiated by eigther high-voltage pulse of positive polarity applied over a long capillary tube with helium or high-voltage pulse applied over the same tube but in presence of low-current glow discharge. The spreading of this wave is accompanied by the surface charge deposition. The usage of the fine-sectioned outer electrode allows one to find out the features of the positive ionization wave in both cases (with or without low-current discharge).

Compact high-current pulse generator for laboratory studies of high energy density matter.

We present the design and parameters of a compact and mobile high-current pulse generator, which can be applied in the study of warm dense matter in university laboratories. The generator dimensions are 550 × 570 × 590mm3, the weight is ∼70kg, and it consists of four "bricks" connected in parallel. Each brick, made up of 2 × 40 nF, 100 kV low-inductance capacitors connected in parallel, has its own multi-gap and multichannel ball gas spark switch, triggered via a capacitively coupled triggering by a positive polarity pulse of ∼80 kV amplitude and ∼15ns rise time. At a charging voltage of ∼70 kV, the generator produces a ∼155 kA current pulse with a rise time of ∼220ns on a ∼15 nH inductive short-circuit load and a ∼90 kA amplitude current pulse in the underwater electrical explosion of a copper wire.

Computational Study of Discharge Process in Plasma Actuator for Enhanced Electrohydrodynamic Force Generation toward Low-Voltage Operation

Numerical simulations of discharge process in two types of actuator modules were conducted to obtain better understanding of the process of electrohydrodynamic (EHD) force generation toward the low-voltage operation. The charge accumulated on the dielectric surface can be absorbed by the additional downstream-side exposed electrode, which is a component of the adjacent actuator module in a multi-module plasma actuator, when positively-DC-biased negative polarity pulses are applied. The elimination of the surface charge results in EHD force enhancement. The enhanced EHD force is also obtained when a negatively-DC-biased positive polarity pulses are applied. The applied voltage affects the surface charge profile and EHD force enhancement by the downstream-side exposed electrode. Under our simulation condition, the positively-DC-biased negative pulses obtain larger enhancement of EHD force compared to that obtained by the negatively-DC-biased positive pulses.

Effect of Defibrillation on the Performance of an Implantable Vagus Nerve Stimulation System

Background Vagus Nerve Stimulation delivers Autonomic Regulation Therapy (ART) for heart failure (HF), and in a pilot study has been associated with improvement in heart rate, heart rate variability, left ventricular function, 6-minute walk distance, NYHA class, and quality of life. VNS is delivered using an implantable pulse generator (IPG) and a lead placed around the cervical vagus nerve. Because patients with HF may receive concomitant cardiac defibrillation therapy, testing was conducted to determine the effect of defibrillation (DF) upon the VNS system. Methods DF testing was conducted on three Model 103 IPGs, which have identical hardware to the VITARIA™ system used to deliver ART for HF. DF testing evaluated whether DF had any permanent effects on the VNS system, and that programmed software settings and data capture were recoverable through reprogramming. Testing was conducted according to the methodology specified in the international standard ISO 14708-1 for active implantable medical devices. All of the testing equipment was verified to be in proper working order with current calibration. Each IPG was connected to a defibrillation pulse generator (MegaPulse Defib) and subjected to a series of voltage spikes, monophasic pulses, and biphasic pulses. The pulse amplitude was 140 V, and was connected to the device through a 300 Ω resistor. For each application of energy, three positive-polarity pulses were delivered 20 seconds apart, followed by a 60-second pause, and three negative-polarity pulses 20 seconds apart (Figure). Results The specified series of high-energy pulses were successfully delivered to each of the three devices. All three IPGs passed the electrical tests, and interrogation confirmed that software and data were unchanged from the pre-programmed values. No shifts in parameters or failures were observed. Conclusions Implantable VNS systems equivalent to VITARIA were tested for immunity to defibrillation, and were found to be unaffected by a series of high-energy defibrillation pulses. These results suggest that this VNS system can be used safely and continue to function after patients have been defibrillated.

High-voltage 10 ns delayed paired or bipolar pulses for in vitro bioelectric experiments

Recent studies proved that classical bio-effects induced by nanosecond pulsed electric field (nsPEF) can be reduced by the delivery of a negative polarity pulse generated immediately after a positive polarity pulse. This phenomenon is known as “bipolar cancellation” and it was reported for a wide range of bipolar pulses with pulse duration from 2 ns to 900 ns. On the contrary, paired pulses, i.e., two identical pulses with the same polarity, increased traditional nsPEF outcomes. Herein, we propose a novel robust and flexible generator, based on the frozen-wave concept, able to produce a broad range of pulses with the duration of 10 ns and delay between 17 and 360 ns. Numerical simulations and experimental measurements were performed to fully characterize the proposed generator. YO-PROTM-1 uptake was investigated in the U87-MG human glioblastoma cell line as a marker of membrane permeabilization in response to 10 ns, 11.5MV/m nsPEF. Our results showed that bipolar cancellation occurred for delays of 0–30 ns and decreased as a function of the interphase interval. In addition, we observed that cellular response following the application of paired nsPEF was more than two-fold compared to the unipolar pulse response and was independent from the interphase interval.

Применение индукционных датчиков в исследованиях быстропротекающих процессов

When testing on a rocket track, one of the most difficult problems is the system for controlling and launching pyrotechnic devices at a given coordinate. The way of start-up and device for its implementation, is intended to provide actuation of pyrotechnic means during acceleration of the rocket trains on the rails rocket catapult track to hypersonic speeds with ejection test subject in free flight. The method is based on the principle of generating current pulses for triggering pyrotechnic devices of moving stages of a rocket train using induction sensors. The same principle makes it possible to implement a non-contact method for starting recording systems and a device for measuring the average speed of a thrown object in continuous media. The method is based on the principle of generating triggering signals (rectangular pulses of positive polarity) for starting the recording equipment with synchronization of the launch along the path in a given coordinate and measuring the speed of the object being thrown at the time of its passage through the measuring section. The methods of starting recording systems and the results obtained as a result of hydrodynamic and terradynamic experiments are presented.

Modeling of a Dielectric-Barrier Discharge-Based Cold Plasma Combustion Ignition System

We present a computational modeling study of plasma phenomena in a dielectric-barrier discharge (DBD) for automotive combustion ignition applications. The study was performed using a self-consistent, two-temperature plasma model with finite-rate plasma chemical kinetics for methane-air combustion mixture. The structure of a DBD discharge and the yield of active combustion enhancing radicals from the discharge is quantified for positive and negative pulsing, and a comparison is made with a single electrode corona discharge. The DBD plasma develops as a streamer discharge with individual streamers preferentially emerging from sharp features on the bare electrode of DBD which quickly propagates to the opposite dielectric surface where it is quenched. The dielectric barrier therefore self-limits the discharge resulting in a total radical yield that saturates in time. The corona on the other hand provides a radical yield that can continuously increase in time. The negative polarity pulsing of the DBD results in a more intense plasma with a higher radical yield compared to a positive polarity pulse. Simulations are also performed for a long 1-μs duration afterglow period once the active pulse is terminated. The active combustion enhancing radicals are found to remain relatively stable in density over this duration, indicating that ~100-kHz pulse repetition rates can sustain or even gradually increase the radical densities over long durations of transient time.

Recording Radiation in the Near-Ultraviolet Range to Determine the Initial Ignition Voltage of Surface Discharge in Air

The method of radiation recording in the near-ultraviolet range arising at the surface electric discharge. In the experiment, a double-electrode cell is used in the mode of a power supply by a single rectangular pulse of positive polarity. Using a photoelectric multiplier, a coincidence between the moment of appearance of the discharge current and moment of appearance of the radiation arising at it is specified, which is important for determination of the initial voltage of appearance of the discharge.

Burst and continuous high frequency irreversible electroporation protocols evaluated in a 3D tumor model

High frequency irreversible electroporation (H-FIRE) is an emerging cancer therapy which uses bursts of alternating polarity pulses to target and destroy the membranes of cells within a predictable volume. Typically, 2 µs pulses are rapidly repeated 24–50 times to create a 48–100 µs long energy burst. Bursts are repeated 100× at 1 Hz, resulting in an integrated energized time of 0.01 s per treatment. A 3D in vitro tumor model was used to investigate H-FIRE parameters in search of optimal energy timing protocols. Monopolar IRE treatments (100 × 100 µs positive polarity pulses) resulted in a lethal electric field threshold of 423 V cm−1. Baseline H-FIRE treatments (100 × 100 µs bursts of 2 µs pulses) resulted in a lethal threshold of 818 V cm−1. Increasing the number of H-FIRE bursts from 100× to 1000× reduced the lethal threshold to 535 V cm−1. An alternative diffuse H-FIRE protocol, which delivers 4 µs pulse cycles (one positive and one negative 2 µs pulse) continuously at 100 Hz, resulted in the lowest H-FIRE lethal threshold of 476 V cm−1. Finite element simulations using 5 kV pulses predict an IRE ablation volume of 3.9 cm3 (1.7 cm diameter) and a maximum H-FIRE ablation volume of 5.3 cm3 (2.4 cm diameter) when a clinical electrode and grounding pad configuration is used. Ablations as large as 15.7 cm3 (3.3 cm diameter) are predicted for H-FIRE treatments with 10 kV pulses. These results combine to demonstrate the importance of electrode geometry, pulse timing, and clinical delivery protocols for the creation of large clinically meaningful ablations.

Oblique Interaction of Dust-ion Acoustic Solitons with Superthermal Electrons in a Magnetized Plasma

The oblique interaction between two dust-ion acoustic (DIA) solitons travelling in the opposite direction, in a collisionless magnetized plasma composed of dynamic ions, static dust (positive/negative) charged particles and interialess kappa distributed electrons is investigated. By employing extended Poincare–Lighthill–Kuo (PLK) method, Korteweg–de Vries (KdV) equations are derived for the right and left moving low amplitude DIA solitons. Their trajectories and corresponding phase shifts before and after their interaction are also obtained. It is found that in negatively charged dusty plasma above the critical dust charged to ion density ratio the positive polarity pulse is formed, while below the critical dust charged density ratio the negative polarity pulse of DIA soliton exist. However it is found that only positive polarity pulse of DIA solitons exist for the positively charged dust particles case in a magnetized nonthermal plasma. The nonlinearity coefficient in the KdV equation vanishes for the ne...

Electric field measurements in nanosecond pulse discharges in air over liquid water surface

Electric field in nanosecond pulse discharges in ambient air is measured by picosecond four-wave mixing, with absolute calibration by a known electrostatic field. The measurements are done in two geometries, (a) the discharge between two parallel cylinder electrodes placed inside quartz tubes, and (b) the discharge between a razor edge electrode and distilled water surface. In the first case, breakdown field exceeds DC breakdown threshold by approximately a factor of four, 140 ± 10 kV cm−1. In the second case, electric field is measured for both positive and negative pulse polarities, with pulse durations of ∼10 ns and ∼100 ns, respectively. In the short duration, positive polarity pulse, breakdown occurs at 85 kV cm−1, after which the electric field decreases over several ns due to charge separation in the plasma, with no field reversal detected when the applied voltage is reduced. In a long duration, negative polarity pulse, breakdown occurs at a lower electric field, 30 kV cm−1, after which the field decays over several tens of ns and reverses direction when the applied voltage is reduced at the end of the pulse. For both pulse polarities, electric field after the pulse decays on a microsecond time scale, due to residual surface charge neutralization by transport of opposite polarity charges from the plasma. Measurements 1 mm away from the discharge center plane, ∼100 μm from the water surface, show that during the voltage rise, horizontal field component (Ex) lags in time behind the vertical component (Ey). After breakdown, Ey is reduced to near zero and reverses direction. Further away from the water surface (≈0.9 mm), Ex is much higher compared to Ey during the entire voltage pulse. The results provide insight into air plasma kinetics and charge transport processes near plasma-liquid interface, over a wide range of time scales.

On the physical nature of apokampic discharge

Experimental and theoretical investigations of a diffuse jet (streamer) of apokampic discharge are carried out for various values of air pressure. It is established experimentally that this regime of pulse-periodic discharge is formed stage by stage. At the first stage, in a microsecond discharge of a voltage pulse of positive polarity, a potential spark channel formed during the first pulses between two needle electrodes is transformed into a diffuse channel. At the second stage, a weakly glowing halo is formed near the discharge channel, and a bright offshoot arises near the bending point. Finally, at the third stage of discharge in the steadystate mode, for frequencies of a few to tens of kilohertz in each pulse, the offshoot becomes a source of plasma bullets (streamers) moving with a velocity of up to 200 km/s. As a result of simulation of a streamer in atmospheric pressure air under conditions corresponding to the experimental data, a propagation velocity of up to 400 km/s is obtained for the streamer. It is shown that the formation of a jet significantly depends on the air temperature.

Plasma action on helium flow in cold atmospheric pressure plasma jet experiments

In this work, helium flow modifications, visualized by schlieren imaging, induced by the plasma generated in a plasma jet have been studied in conditions used for biomedical treatments (jet being directed downwards with a low helium flow rate). It has been shown that the plasma action can shift up to few centimeters downstream the effects of buoyancy, which allows to the helium flow to reach a target below in conditions for which it is not the case when the plasma is off. This study reveals the critical role of large and long lifetime negative ions during repetitive operations in the kHz regime, inducing strong modifications in the gas propagation. The cumulative added streamwise momentum transferred to ambient air surrounding molecules resulting from a series of applied voltage pulses induces a gradual built up of a helium channel on tens of millisecond timescale. In some conditions, a remarkable stable cylindrical helium channel can be generated to the target with plasma supplied by negative polarity voltage pulses whereas a disturbed flow results from positive polarity operation. This has a direct effect on air penetration in the helium channel and then on the reactive species production over the target which is of great importance for biomedical applications. It has also been shown that with an appropriate combination of negative and positive polarity pulses, it is possible to benefit from both polarity features in order to optimize the plasma plume propagation and plasma delivery to a target.

Circuit simulation of electrical breakdown in air using Kind's equal-area criterion

The object of the research is the circuit simulation model of a streamer breakdown of a rod-rod air gap when exposed to positive voltage pulses. One of the most problematic places in this task is determination of the time interval of the streamer propagation. The lower bound of this interval corresponds to the beginning of the streamer propagation, and the upper bound corresponds to the time when the streamer reaches the opposite electrode. To create such model, it is not enough to take into account only the functional relationship between the breakdown voltage and the spacing between the electrodes.With the help of Kind's equal-area criterion in the circuit simulation programs it is possible to create the model of electrical breakdown of any air gap, including the rod-rod configuration.The article shows how to create the model of electrical breakdown of the air gap in the evaluation version of the Micro-Cap 11 circuit simulator. Using the model, the breakdown time of the air gap is determined when subjected to the lightning pulses of positive polarity with different amplitudes. Wherein, the moments of breakdown of the air gap both at the front and at the tail of the applied voltage pulse are measured. Simulation results are compared with experimental data. It is determined that the simulation relative error does not exceed 10%. As experimental data, the experimentally obtained expression for the volt-time characteristic of the rod-rod air gap subjected to the positive polarity voltage pulses is used.The proposed model allows to predict the volt-time characteristic of various air gaps in a virtual experiment. The model can be used in scientific work or in the educational process as an auxiliary tool for visual demonstration of the conditions for the electric breakdown in long air gaps.

Formation of dielectric silicon compounds by reactive magnetron sputtering

The paper is devoted to the study of reactive magnetron sputtering of the silicon target in the ambient of inert argon gas with reactive gas, nitrogen or oxygen. The magnetron was powered by two mid-frequency generators of a rectangular pulse of opposite polarity. The negative polarity pulse provides the sputtering of the target. The positive polarity pulse provides removal of accumulated charge from the surface of the target. This method does not require any special devices of resistances matching and provides continuous sputtering of the target.

SPM probe-assisted surface nanostructuring of boron-doped diamond

Surface modification of conductive boron-doped diamond has been conducted using the electrical field of the probe of a scanning probe microscope (SPM) at varying relative humidity (RH) of the ambient environment. It has been found that, under the action of positive polarity pulses applied to the sample via a grounded SPM probe, the sample material undergoes modification. The modification pattern depends on atmospheric RH: low (up to 32%) and high humidity values (above 35%) lead to the formation of cavities and protrusions, respectively. It has been found that the resulting protrusions exhibit temporary instability; that is, a protrusion is partially transformed into an array of nanoobjects. The mechanism of modification of boron-doped diamond–local anodic oxidation–has been discussed.

Generation and diagnostics of pulsed intense ion beams with an energy density of 10 J/cm².

The paper presents the results of a study on transportation and focusing of a pulsed ion beam at gigawatt power level, generated by a diode with explosive-emission cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: the first pulse is of negative polarity (500 ns, 100-150 kV), and this is followed by a second pulse of positive polarity (120 ns, 200-250 kV). To reduce the beam divergence, we modified the construction of the diode. The width of the anode was increased compared to that of the cathode. We studied different configurations of planar and focusing strip diodes. It was found that the divergence of the ion beam formed by a planar strip diode, after construction modification, does not exceed 3° (half-angle). Modification to the construction of a focusing diode made it possible to reduce the beam divergence from 8° to 4°-5°, as well as to increase the energy density at the focus up to 10-12 J/cm(2), and decrease the shot to shot variation in the energy density from 10%-15% to 5%-6%. When measuring the ion beam energy density above the ablation threshold of the target material (3.5-4 J/cm(2)), we used a metal mesh with 50% transparency to lower the energy density. The influence of the metal mesh on beam transport has been studied.

Intense ion beam generation in a diode with explosive emission cathode in self-magnetically insulated mode

This paper presents a review of experimental studies on pulsed intense ion beam generation in self-magnetically insulated diodes with an explosive emission cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: the first pulse is of negative polarity (300–500 ns, 100–150 kV), and this is followed by a second pulse of positive polarity (150 ns, 250–300 kV). The ion beam energy density is 0.5–5 J/cm2 depending on the diode geometry. We have developed a new spiral geometry of the diode. In a spiral diode it is possible to increase the efficiency from 5–9% (previously studied diodes) up to 20–25%. We conducted a study on shot-to-shot variation in the ion beam parameters. It was found that the standard deviation of the energy density does not exceed 11%, whilst the same variation for ion current density was 20–30%. Focusing properties of an ion beam have been significantly improved by using a metal shield on the grounded electrode. Use of the shield on the grounded electrode provides decrease in the beam divergence from 11° to 7.5–8°.