Microsecond Pulse Duration Research Articles

The frequency spectrum and energy content in a pulse flux of terahertz radiation generated by a relativistic electron beam in a plasma column with different density distributions

This paper reports on the generation of a directed flux of electromagnetic radiation with an energy content of 10 J in the frequency range of 0.2—0.3 THz at a microsecond pulse duration in a beam-plasma system. The flux is generated when a relativistic electron beam (REB) pumps electron plasma waves in a magnetized plasma column. In the described experiments, this fundamentally new approach to generate terahertz radiation was carried out at the GOL-PET facility in the conditions of varying the beam current density and the plasma density in the appropriate ranges of 1—2 kA/cm2 and 1014—1015 cm−3. From the comparison of the flux energy spectrum measured experimentally in the frequency range 0.15—0.45 THz with the calculated one obtained using the previously proposed model of radiation generation in a beam–plasma system, it was shown that this process occurs through resonant pumping by REB of precisely the branch of upper-hybrid plasma waves. Mastering this new method to generate terahertz radiation opens the prospect of its use to obtain multi-megawatt radiation fluxes in the frequency range up to 1 terahertz and higher. For such a development approach the most promising beam for pumping plasma oscillations seems to be a kiloampere REB generated in a linear induction accelerator.

Structuring of the Surface of Thin Carbon Films During Activation by Microsecond Current Pulses

The influence of current activation by electric pulse breakdown on changes in surface morphology and emission characteristics of a field emission cathode made on the basis of carbon films obtained by deposition in a microwave gas discharge plasma was studied. Current activation of these films was carried out by applying voltage pulses of microsecond duration until an electrical breakdown occurred. It is shown that during activation, the morphology of the film surface in the breakdown region changes with the formation of a micro-sized emitting structure, which significantly improves the field emission characteristics of cathodes based on carbon films.

Optimizing ultrasound Doppler measurement precision: a comprehensive experimental approach

Experimental studies were conducted utilizing advanced equipment comprising a generator, tubing system, pump module, sonographer, and PC. The generator serves as the central component connected by tubes to the pump, forming a closed circuit. A tee in the tubing set prevents Doppler fluid leakage, with the fluid poured through a special funnel into the circuit post-connection. The Doppler fluid is evenly mixed by shaking its bottle to enhance signal strength. The entire system is sealed. The centrifugal pump generates continuous flows; different power modes were tested for 30 minutes each, with frequency shifts measured at angles α=15°, 30°, and 60°. Pump disconnection from the power supply prevents liquid entry during tubing connection. The pump module housing includes ventilation holes. A 3 by 8 cm Doppler prism, treated with ultrasonic gel, was connected to the tubing to capture data. A sonographer emitting signals at 2 MHz, with a gain range of 10 to 40 dB, was utilized for sound spectra analysis. High-mode operation, 4 microseconds pulse duration, and a 32 microseconds receiver gate were set. The ultrasound apparatus dimensions were 230 x 236 x 168 mm, with a power consumption of 27 VA. Data visualization was facilitated by an LED panel, with adjustable acoustic signal volume. A USB interface enabled connection to a PC for ease of use and data analysis. Special software facilitated graph generation depicting frequency vs. time dependence measurements. Frequency analysis yielded average (f-mean) and maximum (f-max) frequency values, with f-mean utilized to measure Doppler effect frequency shift. The presented data showcases various pump speeds and incidence angles, each yielding distinctive frequency characteristics.

Pulsed Field Ablation for the Treatment of Atrial Fibrillation: A Review and a Look into its Future

Pulsed field ablation (PFA) is a novel technology to treat atrial fibrillation (AF) utilizing electric fields to induce nonthermal irreversible electroporation of electrically active cardiac tissue to induce cardiac cell death. PFA offers improved safety benefits compared to traditional radiofrequency ablation (RFA) and cryoablation by specifically ablating only cardiac tissue. However, there are avenues for further optimization including neurological risk associated with microbubble formation and left atrial function post ablation. Various PFA devices with different electric pulse waveforms have been studied and tested in human trials, with the majority utilizing microsecond duration pulses. Shorter nanosecond duration pulses, or nanosecond PFA, is beginning to be studied for AF ablation. In this review we will delve into current waveforms used for PFA, areas for improvement, mechanisms behind nanosecond PFA, and its clinical impact for cardiac ablation.

Ferroelectric Ceramic Synthesis and Breakdown Characterization on Pulsed Condition Using High-Voltage Half-Sine Pulses of Microsecond Duration

Ferroelectric Ceramic Synthesis and Breakdown Characterization on Pulsed Condition Using High-Voltage Half-Sine Pulses of Microsecond Duration

A Laser with Intracavity Spectral Beam Combining with Continuous-Wave and Pulse-Periodic Pumping of Various Lasing Channels

The output spectral, temporal, and spatial parameters of a two-channel Yb-fiber laser operating in an incoherent intracavity spectral beam-combining mode were investigated. One of the laser channels operated in continuous pumping mode, and the second channel operated in pulse-periodic pumping mode with a pulse duration of microseconds. When the channels operated separately, continuous lasing at a wavelength of λ1 was observed in one channel, and pulsed lasing at a wavelength of λ2 was observed in the other. When both channels operated simultaneously, it was shown that during the pump pulse action, the laser switched operation to pulsed collective mode lasing at a wavelength of (λ1 + λ2)/2. Lasing at wavelengths λ1 and λ2 was not observed at this time.

Experimental study of stability and pollutant emissions of turbulent biogas flames under microsecond pulsed plasma

Biogas is a mixture of methane (50–80%.vol), carbon dioxide (20–45%.vol), and in smaller proportions of N2, O2, H2S, and NH3. For a high rate of CO2 in the biogas, the combustion can generate strong instabilities and the flame can be very lifted from the burner and even blown. To overcome these problems of instabilities and flame extinction, the use of a microsecond pulsed plasma is considered for this study. This study aims to characterize the effects of microsecond pulsed discharges on the stabilization and emission characteristics of non-premixed swirling biogas/air flames at different operating conditions of combustion (CO2 rate, power, and equivalence ratio) and plasma (pulse repetition frequency and input electrical voltage). The plasma is performed above a coaxial burner with a swirler of the oxidizer. It is generated by a DC-pulsed power generator with a high voltage (HV) pulse duration of a few microseconds. The burner consists of two concentric tubes and a central metal rod used as a cathode for the plasma. The outer tube contains a swirler and supplies the oxidant flow, and the inner tube delivers the fuel (methane, biogas) around the central metal rod. High voltage pulses are applied on two anode tungsten wires that are symmetrically arranged from either side of the cathode to obtain two plasma zones in the stabilization region of the flame. The burner is placed in a parallelepiped combustion chamber with a volume of 100x48x48 cm3. Mass flow rates of air and fuel are regulated by thermal mass flow controllers (Brooks SLA5851S). OH* chemiluminescence measurements are done to describe the structure and the flame stability throughout the lift-off heights (Hf) variation. Results showed that plasma generated by microsecond HV pulses can improve flame stability by decreasing its Hf especially at low fuel velocities. In this regard, the optical emission spectra (OES) were visualized. The results reveal that the pulsed plasma generates chemically active species such as excited N2*, CH*, OH* molecules, and H* atoms, leading to improved flame stability. Their intensities' dependence on the pulse repetition frequency, the sight position of the OES, the concentration of CO2 in the fuel, and the fuel velocities were investigated in detail. Furthermore, the NOx and CO emissions in the burned gas are investigated over a wide range of repetition pulse frequencies. It is seen that the microsecond pulsed plasma slightly increases the NOx emission and reduces CO concentration in the flue gases.

Thermo-Optical Measurements and Simulation in a Fibre-Optic Circuit Using an Extrinsic Fabry–Pérot Interferometer under Pulsed Laser Heating

Advantages of using an external Fabry–Pérot interferometer (EFPI) as a high-speed local temperature deformation sensor are demonstrated for the fibre-optic circuit combining a powerful laser beam for surface heating with a low-power probing radiation. The difference in the formation of the heating and probing radiation provides a simple basis for varying the gap between the fibre end and the surface in order to change the ratio between the heating and EFPI measuring areas. Using an example of modelling the laser heating by radiation from a standard single-mode fibre, we demonstrate the possibility of employing the EFPI to measure the temperature deformation of the surface on a quasi-isothermal area with the temperature close to the maximum at gap values of more than 100 μm. With the condition of preliminary calibration, the proposed scheme can be used to evaluate the heat treatment of the surface with the speed of the applied photodetector. The practical possibilities of the method are demonstrated on examples of heating some metal and semiconductor samples by laser pulses of microsecond duration.

Effects of pulsed gliding arc plasma on non-premixed CH4/CO2– air flame stability

Effects of carbon dioxide (CO2) addition and pulsed gliding arc (PGA) plasma on methane (CH4) flame stability and pollutant emissions are investigated in this paper. Two main parts are reported: the effects of CO2 addition to the fuel and the impact of PGA plasma on the characteristics of non-premixed CH4/CO2-air flames in a coaxial swirl burner. The burner consists of 2 concentric tubes, the central tube supplies the CH4 flow and the periphery one supplies the airflow. In the central tube, a metal rod is used as a cathode. To produce the PGA plasma, two other electrodes are symmetrically placed around the central one to obtain two PGA plasma zones in the stabilization area of flame. The combustor is a parallelepiped chamber, with a 0.48 m square cross section and 1 m height equipped with six windows on each side. This work primarily focuses on pollutant emissions (NOx and CO), flame structures, and stability. OH* chemiluminescence measurements are used to describe the structure and stability of the flame providing information on the flame lengths and lift-off heights. The lift-off heights and the flame lengths are determined as a function of the CO2 concentrations, ranging from 0% to 50% in the fuel, at a fixed swirl number and equivalence ratio. The results show that CO2 addition to the fuel changes significantly the flame shape and its behavior. The flame becomes more unstable at high CO2 percentages. CO2 addition dilutes reactants, reduces NOx production, and increases CO concentrations in the flue gases. To overcome the instabilities problems due to the addition of CO2, the PGA is used and investigated with different parameters of plasma and flame. PGA plasma is generated by a DC pulsed power generator with HV pulse duration of few microseconds. It is observed that the presence of PGA plasma decreases flame instabilities and reduces CO concentration in the flue gases.

On the mechanism of anomalous phenomena in current-carrying magnetized plasma

The explanation of the mechanisms of anomalous resistance and diffusion of plasma, as well as the generation of fast particles, is given from a unified position on the basis of experimental results obtained in plasma in a magnetically isolated diode of an electron accelerator with a microsecond pulse duration. It is shown that oscillations of the potential and current in plasma with current occur by charge separation and the formation of electric domains with a strong field. Electric domains are generated by means of runaway electrons resulting from the redistribution of the current density and its channelling in the current-carrying plasma. An increase in plasma resistance occurs due to a decrease in the number of electrons in the current-conducting state, since some of the plasma electrons pass into layers of excess negative charge of electric domains. The speed of movement of electrons in the composition of the electric domain is much lower than the velocity of electrons in the conducting state. The nucleation of domains is accompanied by microwave emission. Quasi-neutrals in whole electrical domains are injected into the region of the anode wall. The destruction of domains leads to the appearance of plasma channels between the anode and cathode plasma. The transverse electromagnetic waves generated during the nucleation of domains capture charged particles and inject them in a direction that is perpendicular to the insulating longitudinal magnetic field. Plasma turbulence occurs due to charge separation and the generation of electrical domains that create channels between the plasma and the chamber wall, as well as generating fluxes of fast particles.

High strain rate deformation of conductive materials with use of pulse magnetic fields

The study of metal deformation processes under extreme impacts is relevant due to the need to predict the behavior of materials in operational and critical modes using various deformation models. In this case, the key factor is to expand the range of experimentally determined/achievable parameters for their verification. The high energy density of the magnetic field and a reliable and simple technique for monitoring its parameters make it possible to use the magnetic pulse method of generating controlled pressure pulses of microsecond duration with an amplitude of ∼1 GPa. A classification of methods for high strain rate deformation of conductive materials by magnetic-pulse loading is carried out and features of magnetic-mechanical. An analysis of the experimental results showed the applicability of the magnetic-pulse method for studying plastic deformation processes with strain rates up to 104 1/s and more and the possibility to formulate requirements for the magnetic system and pulse current sources.

Experimental Investigation on Flow Characteristics and Ignition Performance of Plasma-Actuated Flame Holder

Improving the performance of flame holders has been a key focus of research on ramjet combustors. The plasma actuator has the potential to improve the ignition performance by manipulating the flow field of the flame holder. In this study, a plasma-actuated flame holder was designed. The aim of this study is to improve the performance of ramjet combustor by applying plasma discharge to the flame holder. The aerodynamic effects and ignition performance of the flame holder were investigated. The results demonstrated that the induced jet direction of the surface arc discharge was perpendicular to the actuator. The induced jet dissipated faster at lower pressures. The aerodynamic actuation intensity and jet area increased with the number of channels of surface arc discharges. Increasing discharge frequencies can increase the discharge times and jet height. The aerodynamic effects under a microsecond pulse duration were better than those under a nanosecond pulse duration. Actuators installed on the inside surface showed better performance than those installed outside. Under different total flow temperature conditions, the plasma-actuated flame holder significantly extended the ignition pressure limit and increased the combustion efficiency by 9.12% and 4.3% on average, respectively.

Electrochemical polishing of matrix stents of the 316LVM steel using microsecond pulses

With the development of minimally invasive treatment technology, coronary stents made of corrosion-resistant steel are in demand for restoring the patency of blood vessels. The effectiveness of coronary stenting depends on various factors, but the quality of the surface of the stents is a major factor. The higher the quality of the surface of the stent is, the less negative the effect on the circulatory system, arterial walls, and the higher the biocompatibility of the stent is. The complex shape, small cross-section, size, and low rigidity of coronary stents are the main reasons for the inability to ensure high surface quality using mechanical finishing methods. Therefore, electrochemical methods are used to polish stents. For electrochemical polishing (ECP) of stents, an electric mode based on direct current is traditionally used. The disadvantages of direct current ECP are excessive metal removal and the need to use electrolytes of complex compositions, often containing toxic components. As an alternative to the traditional ECP with the use of direct current, we have proposed a method of pulsed ECP using pulses of microsecond duration for polishing stents. The use of pulsed current allows one to achieve a significant increase in the efficiency of the SEC process, when, due to the localization of the anodic dissolution, the smoothing speed of the microroughness of the treated surface, referred to the total metal removal, increases significantly. The paper presents a comparative analysis of ECP modes using direct and pulse current to change the surface roughness, removal, radius of curvature of the edges, and corrosion resistance on the example of stents made of the 316LVM stainless steel. Based on the results of the studies, technological regimes of pulsed ECP were established that provide the highest quality polishing of the stent surface with a small metal removal with a slight rounding of the edges.

Mathematical modeling and study of thermoelastic behavior of a bimetallic layer with plane-parallel boundaries under the action of electromagnetic pulses

The dynamic problem of thermomechanics for a bimetallic layer with plane-parallel boundaries under the action of a homogeneous nonstationary electromagnetic field has been formulated. The thermal stress state, the bearing capacity, and the contact properties of the considered layer under the action of electromagnetic pulses of microsecond duration are numerically analyzed.

MoTe2-PVA as saturable absorber for passively Q-switched thulium-doped fluoride and erbium-doped fiber laser

Passively Q-switched fiber lasers in the S- and C-band region were demonstrated using molybdenum ditelluride (MoTe2) as the saturable absorber (SA). The MoTe2 was prepared using liquid phase exfoliation method, which was then embedded in the polyvinyl alcohol (PVA) polymer to form a MoTe2 thin film SA. By incorporating the MoTe2 SA in the thulium-doped fluoride fiber laser (TDFFL) and erbium-doped fiber laser (EDFL) cavities, stable Q-switched pulses were observed in the S-band and C-band region with microsecond pulse durations and tens of kilohertz repetition rate. The modulation depth and the saturation intensity of the MoTe2 SA were ∼ 38 % and ∼ 0.314 MWcm−2, respectively. The Q-switched operation can be tuned by employing a tunable bandpass filter (TBPF), covering the S-band and C-band region from 1453 nm to 1572 nm. Thus, the finding validates the feasibility of MoTe2 as a promising SA for a broadband optical applications.

Passively Q-switched semiconductor disk laser with microsecond pulse duration

A semiconductor disk laser was passively Q-switched by the use of a Cr4＋:YAG crystal and a semiconductor saturable absorb mirror, respectively, and stable Q-switched laser pulse trains with microsecond pulse duration were produced. The width and the repetition rate of the Q-switched pulses were 10 μs and 26.3 kHz when a Cr4＋:YAG crystal was inserted, while the pulse width and the repetition rate were 8 μs and 26.3 kHz when a semiconductor saturable absorb mirror was employed. Based on the time characteristics of the quantum structure in the active region of the semiconductor disk laser, and the time behaviors of the saturable absorbers, i.e., the Cr4＋:YAG crystal and the semiconductor saturable absorb mirror, the formatting mechanisms of the Q-switched pulses with width of microsecond magnitude were analyzed, and the related physical pictures of the passively Q-switched semiconductor disk laser were further disclosed.

A High-Efficiency Generator of High-Power High-Voltage Pulses of Microsecond Duration

A High-Efficiency Generator of High-Power High-Voltage Pulses of Microsecond Duration

Feasibility of lasing in the GaAs Reststrahlen band with HgTe multiple quantum well laser diodes

Operation of semiconductor lasers in the 20–50 µm wavelength range is hindered by strong non-radiative recombination in the interband laser diodes, and strong lattice absorption in GaAs-based quantum cascade structures. Here, we propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. Using a comprehensive model accounting for carrier drift and diffusion, electron and hole capture in quantum wells, Auger recombination, and heating effects, we show the feasibility of lasing at λ = 26, …, 30 µm at temperatures up to 90 K. The output power in the pulse can reach up to 8 mW for microsecond-duration pulses.

Space low earth orbit environment simulator for ground testing materials and devices

The design and operation of an experimental installation are described, used for simulating those factors that most greatly affect the properties of materials and microelectronic devices in conditions of the near Earth (Low Earth Orbit) environment. The simulator apparatus is in the form of a cylindrical metal vacuum chamber constructed and mounted to the electron accelerator facility of the Center for the Advancement of Natural Discoveries using Light Emission Synchrotron Research Institute (Armenia) which allows the production of accelerated electrons with the following parameters: ultra-short pulse duration (τ = 4·10−13 s), electron energy 3.5 MeV, pulse current intensity 60 A/cm2, pulse frequency 12 Hz. A comparison may be made with conventional electron accelerators, which employ micro-second pulse duration, and a far lower current intensity of 2∙10−3 A/cm2. Thus, the specific features of this installation enable the simulation of ultra-fast processes as occur in cosmic space or under other extreme conditions. Here, we present the initial results obtained, concerning the influence of high-density electron irradiation on the behavior of the electro-physical properties of silicon crystals. Peculiarities and differences are presented between the results obtained from silicon crystals irradiated by electrons with an energy of 3.5 MeV and a pulse duration of τ = 4·10−13 s, and those from silicon samples irradiated with 7.5 MeV or 50 MeV energy electrons, using conventional electron accelerators.

Аналитическая оценка магнитно-импульсного деформирования сплава TiNi

The magnetic pulse method is a method for creating controlled pressure pulses of microsecond duration. Although the method has been known since the 80s, it is usually used for revealing patterns of fracture processes of nonconductive materials. This method was practically not applied to shape memory alloys, with the exception of some works devoted to the three-point bending tests. We adapted the method for high-strain rate uniaxial tension of TiNi alloy specimens. The paper demonstrates the scheme of magnetic pulse method for uniaxial tension. Analytical assessments of the magnitude of the magnetic pressure created by magnetic-pulse drivers under the action of a current pulse, strain in the working part of the sample and the strain rate are carried out. For an analytical solution, the resistance of the material to external forces is proposed to be considered as a piecewise linear approximation to the stress-strain diagram. Analytical solution demonstrates qualitative and quantitative agreement with experiment, even for samples of TiNi alloy with a unique stress-strain diagram. It is a difficult task to estimate the strain rate at short loading pulses of 6 – 7 μs. However, in the first approximation, the results show that at the considered loading scheme, the strain rate reaches 6700 s−1 on average and in local areas it is estimated at 10 000 –12 000 s−1. Thus, having the parameters of the material and the parameters of the current pulse, it is possible to estimate the strain of the material with good accuracy and obtain an initial estimate of the strain rate.