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In this work, a 1-D extended fluid model is built to investigate the effects of the electric waveform supplying a dielectric barrier microdischarge plasma. Three symmetric waveforms (sine, square, and triangle) are used in this study in addition to one asymmetric waveform (positive ramp). The results of numerical experiments show that the discharge activity is strongly affected by the applied voltage waveform, where the dielectric-barrier glow discharge (DBD) in case of the sine and triangle waveforms is more filamentary (with series of narrow current density peaks) when compared with the square waveforms. Although the discharge period of the sine and triangle waveforms is high, the rms value of its current is lower than that in the case of the square waveforms. [ABSTRACT FROM AUTHOR]

In laser acceleration dynamics of the electron, the approximate value of the longitudinal component of the electric field has been considered in all analytical and numerical calculations. In this article, an exact analytical expression for the longitudinal component of the electric field in a spindle-shaped laser-produced plasma channel formed by Bessel laser pulse propagation is derived. To this end, first, the dimensions of the channel are obtained by balancing the ponderomotive and electrostatic forces acting on the plasma channel, and then an analytical expression for the longitudinal electric field of the channel is calculated. Finally, substituting the exact fields in the electron equation of motion, the dynamics of the electron inside the channel and also the electron energy gain are studied. The result of the numerical analysis shows that the real longitudinal component of the electric field of the channel changes the electron energy gain significantly. We also found that the longitudinal electric field of laser does not always counteract the transverse component of the field so that the electron can gain or lose energy from both of them simultaneously. [ABSTRACT FROM AUTHOR]

Levitation of pollen particles has been demonstrated in a radio frequency (RF) plasma. Pollen particles from Japanese cypress are levitated to various heights from lower electrode, where they spontaneously form quasi ordered state. Levitating pollen particles are identified from divinylbenzene particles in real-time using the polarization imaging technique. [ABSTRACT FROM AUTHOR]

The intensity of the shockwave generated by the high-current pulse discharge in the liquid is mainly determined by the deposited energy during the accelerated expansion stage of the arc plasma channel. Under the same discharge condition, there is randomness in the shape of the arc channel. Generally, longer arc channels have larger impedance, which can obtain more energy and generate stronger shockwaves. In this article, a comprehensive test platform for high-current pulse discharge in liquid was established; the voltage, current, and far-field shockwaves were measured; and the development images of the arc channel were taken. Considering the influence of temperature, channel expansion, and radiant energy, a calculation method of electrohydraulic shockwaves based on the improved arc impedance model was established. The initial values and parameters of the model were selected by comparison with the test results to ensure their accuracy. The arc channel current, time-varying resistance, deposition energy, and far-field shockwaves were calculated and compared with the test results to verify the rationality of the model. The calculation of electrohydraulic shockwaves based on the improved arc impedance model can provide theoretical guidance for optimizing the industrial application of shockwaves. [ABSTRACT FROM AUTHOR]

In this article, a numerical model is presented, where the self-consistent spatial distribution of the plasma potential near isolated dust particles is calculated. The dust particles shape is ellipsoid of revolution. This article demonstrates large-scale studies of the characteristics of the “dust particle—ion cloud” system measured for the various parameters of dusty plasma. These parameters are the shape and size of dust particles, the strength of the external electrostatic field, and the ion mean free path. The approximations describing the system characteristics on the plasma parameters are presented. [ABSTRACT FROM AUTHOR]

In laser acceleration of ions by the radiation pressure acceleration (RPA) mechanism, the efficiency of energy and momentum transfer to ions increases if the shape of the laser pulse is suitably tailored. Numerical results are presented for the Gaussian, Lorentzian, and hyperbolic secant pulse shapes of the incident laser interacting with an ultrathin, ultra-dense plasma foil. The numerical results show that the energy and momentum imparted to the ions by the hyperbolic laser pulse are 1.17 and 1.11 times more compared to the Lorentzian shaped pulse of approximately the same intensity. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) and gas-insulated switchgear (GIS) has been recognized as a crucial factor for electric field distortion that results in the reduction of surface flashover voltage. This article reports on the gaseous ionization dependence of the charge accumulation pattern on a real-size epoxy insulator with multiarc surface profile by using various gas atmospheres. A coaxial electrode system was designed to investigate the charging behavior under dc voltages of −10, −20, and −30 kV. The insulator and electrodes were placed in a metal-enclosed test chamber, which was filled with 0.1 MPa air or 0.4 MPa SF6/N2 mixture to estimate the influence of the gas atmosphere on the charge accumulation behavior by a Kelvin-type probe. The accumulation mechanism and the electric field distortion induced by the charges were demonstrated based on numerical simulation. The results indicated that positive charges were accumulated in the shape of speckle on insulator surface in air, whereas both positive and negative charges were accumulated in SF6/N2 mixture and positive charge speckles appeared in SF6/N2 mixture only when the voltage raised up to −30 kV. It is considered that the charge accumulation behavior is determined by the competition result among the bulk, the gas and the surface conductions. As compared with the case in air, gaseous ionization in SF6/N2 mixture is more difficult to occur, which leads to the obvious difference in the charge accumulation pattern. [ABSTRACT FROM AUTHOR]

A sheet beam electron gun with high compression ratio and long transmission distance performance for W-band traveling-wave tube (TWT) is presented. A beam focusing electrode (BFE) with two pairs of unequal length outstretched structures is designed to provide equal positions of beam waist in both horizontal and vertical planes, which is beneficial to obtain large compression ratio and keep the beam cross section shape over a long distance. The operational voltage is set as 30 kV. The beam current is 0.505 A, and the corresponding cathode current density is about 5.59 A/cm2. The simulation results show that the electron gun can provide a stable sheet beam under a 0.85-T magnet field. The compression ratio of the obtained sheet beam can be over 35, and the sheet beam can be transported through a 126-mm beam tunnel without interception with a 0.6 fill factor. The parameter sensitivities of the gun are analyzed and discussed as well. [ABSTRACT FROM AUTHOR]

A model of a thermionic cathode in a planar diode in which the Poisson and Vlasov equations are solved in 3-D assuming an infinite magnetic field is presented. We explore how 2-D work function variations across the cathode surface may affect the transition between temperature-limited and space-charge-limited flow, commonly known as the “knee” of the Miram curve. We study a variety of work function distributions, both realistic and idealized, and demonstrate how emission from the lowest work function regions dominates the total anode current even when such regions make up a relatively small fraction of cathode area. Our model also illustrates the ability of cathodes to reach the full Child–Langmuir current despite the presence of a sizeable nonemitting region. We find that as the length scale of these work function variations decreases, the Miram knee grows sharper, indicating improved cathode performance. [ABSTRACT FROM AUTHOR]

This article presents a study of neutron emission on the PFZ-200 plasma focus at the Department of physics on FEE CTU in Prague, Czech Republic. In order to achieve the highest and most stable neutron yields, the deuterium working gas pressure and the anode shape were systematically varied. We observed the plasma time to the pinch and the discharge current by the Rogowski coil and neutron emission by the silver activation detector and scintillation time-of-flight detectors. The imploded plasma was visualized using a fast X-ray pinhole camera with a gated microchannel plate detector. The experiment presents the z-pinch discharges with the current maximum above 200 kA and the average neutron yields of ${3 \times 10^{8}}$ neutrons/shot. Measured pinch times were in the range from 1.65 to 1.85 $\mu \text{s}$. The hollow round anode configuration performed the most stable neutron yields with a deviation under 20%. [ABSTRACT FROM AUTHOR]

Terahertz communication is considered as a potential solution to alleviate the communication blackout. However, it is not clear how the shape parameters of the vehicle affect the propagation of terahertz communications in the plasma sheath. In this article, the influence of half-angle on the plasma flow and terahertz propagation characteristics around blunt cone vehicle was investigated using the numerical hypersonic hydrodynamic model and multilayer transmission model. The maximum electron number density in the plasma sheath near the antenna decreases with the decreasing half-angle. The thickness of the high-density section in the plasma sheath is almost unaffected by the half-angle. As a result, the terahertz wave attenuation decreases with the decreasing half-angle. The half-angle is reduced from 20° to 5°, and the attenuation of electromagnetic waves is reduced by about 25 dB. Therefore, reducing the half-angle of blunt cone vehicle can effectively reduce the attenuation of electromagnetic waves. Finally, the feasibility of lowering the half-angle to solve the blackout problem during the whole reentry process was discussed; the results show the operating frequency of terahertz wave that maintains normal communication when the half-angle is 1° is reduced by 0.1 THz compared with the half-angle of 9°. Based on the study, a new scheme combining the reduction of half-angle of blunt cone vehicle and terahertz communication was proposed in this article to mitigate the RF blackout. [ABSTRACT FROM AUTHOR]

Armature design plays a significant role in determining the performance of an induction coilgun. In this article, aluminum projectiles of 10.5-mm length and 21.7-mm outer diameter but of different shapes and thicknesses are fired from different initial positions inside the barrel having an outer diameter of 25 mm and a thickness of 1.5 mm with the coil wound over it. The coilgun is powered by charging a 504- $\mu \text{F}$ capacitor bank up to 800 V and discharging it through the coils of a three-stage induction coilgun. Experiments are also performed at different initial charging voltages of the capacitor bank. For each firing, muzzle velocity of the projectile and efficiency of the induction coilgun are studied. Positions and muzzle velocities of the projectiles are measured using infrared sensors. A maximum muzzle velocity of 23.86 m/s with a projectile of mass 2.8 g and a maximum efficiency of 0.76% with a projectile of mass 8.5 g have been achieved with the present hardware setup in the laboratory. Experimental results are analyzed using the transient solver of the commercial software, ANSOFT Maxwell. From the analyses presented in this article it is found that the projectile having the highest muzzle velocity has a thickness equal to the skin depth and has a uniform current density distribution along its thickness as well. This article concludes that projectile thickness being equal to the skin depth of the projectile results in significant increase in its muzzle velocity and reduction in its mass which is an important design consideration of the induction coilgun. Secondly, each projectile has an initial firing position which is the best to achieve the highest muzzle velocity i.e., the highest efficiency of the induction coilgun and this position depends on the dimension and shape of the projectile. [ABSTRACT FROM AUTHOR]

In this article, a novel approach for optimizing a practical 270° bent electron gun has been proposed by using JUPYTER NOTEBOOK, an open-source web application utilizing PYTHON script, aiding faster data processing and mathematical computations. For this purpose, a 3-D cost function has been formulated to optimize the position of the anode with respect to the filament which aims at maximizing the beam power density, maximizing beam parallelism or laminar flow and optimizing beam shape. CST Studio-Particle Tracking Module is used for gun design, magnetic field design, and for the study and analysis of generated electron beam trajectories by performing both electrostatic and electromagnetic 3-D gun simulations. Unlike the conventional 270° bent transverse electron guns using Helmholtz coils for generating uniform magnetic fields, here permanent magnets have been used for generating nonuniform magnetic fields making the overall system compact along with electromagnets and magnetic shunts for precise beam maneuvering. Magnetic fields are experimentally measured by using Gauss meter which match well with that of the simulated values. The electron gun was fabricated and trial experiments were conducted under high vacuum environment. Experimental validation was done by puncturing a stainless steel plate kept at 90° and 270° positions above the crucible and the results match well with the simulated results. [ABSTRACT FROM AUTHOR]

Currently, metal detectors are actively used in the detection of treasures, underground cavities, historical artifacts, lost manhole covers and land mines, as well as firearms and other weapons for public security purposes. Metal detectors are categorized into four groups, based on their operating principles. Beat-frequency oscillation and resonant frequency oscillation are the two early techniques used in metal detectors. Detectors based on the said principles are not preferred due to frequency stability issues. Induction balance (IB) and pulse induction (PI) detectors are more widely used. Recent studies in the literature are mostly focused on the improvement of detection depth, sensitivity, discrimination capability, and soil balancing characteristics of metal detectors. There are many variables affecting detection depth, including detector operating frequency; search coil size; minerals in the soil; and target size, shape, type, and orientation. Among the aforesaid variables, various studies exist in the literature on search coil size and shape. These studies were conducted in vacuum or in nonmetallic media such as sand, not covering parameters such as target size, shape, type, and orientation. A novel PI metal detector was developed in this article, for the purpose of determining the effects of changes in the aforesaid target-related parameters on detection depth in a medium consisting of soil with metallic properties. First, a 3-D mechanical scanner system and the detector’s microcontroller electronics were manufactured in order to ensure position-controlled and parallel-to-the-surface mobility for the detector’s search coil. Subsequently, a data collection module was designed to process the detector’s electronic output data at 24-bit resolution and send data to a computer, as well as a software program to assess and record the data received by the computer. Then, aluminum, brass, iron, and copper objects with known geometric properties were buried in a soil with 28.5% magnetic particle content and 4.1% natural humidity, and detector data collected at various positions of the search coil, with the help of the 2-D motion of the mechanical system to which it is connected, were transferred to the digital medium. Such field scans, conducted for each object at a height of 5 cm above surface, enabled detection of the ($x$ , $y$) position where the detector produced maximum output. The search coil was then fixed at such ($x$ , $y$) positions and the depth of the object to the soil surface was increased in increments of 1 cm along the $z$ -axis. The procedure was repeated until the detector produced zero output, and the data were recorded into the computer. The study discusses the effects of parameters such as object size, shape, and type on maximum detection height for the detector developed. [ABSTRACT FROM AUTHOR]

Steady-state interaction between stationary grains mediated by plasmas at ultracold superfluid helium temperatures is investigated using particle-in-cell (PIC) simulations with Monte-Carlo collisions. A wide-ranging parametric exploration of interdependence of the physical parameters and its consequence on overall grain–plasma dynamics for cryogenic dusty plasmas is presented. Charging of the grains and the density of trapped ions exhibit a remarkable dependence on the particle shape. Grain charging shares a direct relation with ion flow strength as well and manifests contrasting trends at flow strength $M_{\text {th}}\leq 5$ and $M_{\text {th}}\geq 5$. A comparison of an isolated grain electric field and potential with the two-grain–plasma system asserts that the field due to an isolated grain is precisely of the same order as the two grain field at subsonic flows. Binding-energy range is estimated to be 0.16–22 eV at $M_{\text {th}}$ = 0–15 and supports the possibility of molecule-like dust structure formation at ultracold temperatures. [ABSTRACT FROM AUTHOR]

Wendelstein 7-X (W7-X) was constructed from 2005 until 2015 at the Max-Planck-Institute for Plasma Physics, Greifswald, Germany. W7-X is one of the world’s largest stellarator; it is five-fold symmetric; has a superconducting magnet system; and weighs about 1000 tons. W7-X started its first operation in 2015 with up to 4.3-MW electron cyclotron resonance heating (ECRH) and a heating duration of up to 6 s, and injected energy per pulse up to 4 MJ. The injected energy per pulse increased up to 200 MJ, for example, for 100 s at 2 MW and also 30 s at 5 MW in the third operation campaign in 2019. The machine was upgraded twice since 2016 and a third upgrading phase is being carried out now. The main aim of upgradation is the increase of the plasma energy as well as the increase of the heating energy flow through the machine. That requires, among others, the installation of a high heat flux (HHF) divertor and the strengthening of the associated cooling system. This contribution provides a general overview of the construction of W7-X. It summarizes some engineering lessons learned in the construction phases and in the first operation campaigns (OP1.1, OP1.2a, and OP1.2b). Furthermore, this article explains the technology challenges as well as modifications due to the first experiences in commissioning and operation. Technical, organizational, and schedule aspects of the assembly are discussed as well. [ABSTRACT FROM AUTHOR]

We present a Bayesian spectral fitting method developed for spectroscopic data analysis, particularly (but not solely) in the context of fusion energy research. The presented techniques are particularly valuable to estimating moments and corresponding uncertainties whenever the spectra result from line-integrated measurements in nonuniform plasmas, for which the approximation of atomic line shapes being ideal Gaussians gives poor estimates. We decompose multiple, potentially overlapping spectral lines into a sum of Gauss–Hermite polynomials, whose properties allow efficient truncation and uncertainty quantification, often with only three free parameters per atomic emission line. Tests with both synthetic and experimental data demonstrate the effectiveness and robustness where more standard nonlinear fitting routines may experience difficulties. A parallelized version of our implementation is publicly released under an open source license. 1 https://github.com/Maplenormandy/bsfc [ABSTRACT FROM AUTHOR]

Electrode shape plays an important role in collecting efficiency of the arista electrode in electrostatic precipitation (ESP). Using hydrodynamic model coupled with Poisson’s equation and applying finite element method, the characteristics of Trichel pulse under hyperboloid electrode and hemispherical electrode were compared. The numerical model is established in dry air at atmospheric pressure, using a traditional needle-to-plane configuration, which is simplified from the model of arista electrode and a plate in ESP. Combined with the motion equation of dust particle, the motion characteristics of the dust particles at different positions in negative corona discharge with different electrode shapes are studied. Under the same average power, the anode of the hemispherical electrode collects more than twice as many dust particles as the hyperboloid electrode, and the number of dust particles attached to the cathode is a little less than that of the hyperboloid electrode, in the early stage of ESP. [ABSTRACT FROM AUTHOR]

The laser-induced fluorescence (LIF) diagnostic with highly saturated stimulation scheme was conducted to investigate the propulsion performance of a Hall thruster. A Gaussian inverse filter was employed to isolate the Doppler shift and broadening from a measured LIF spectrum by deconvolution. Besides the average velocity and temperature of the singly ionized Xe, parameters about the overall propulsion performance were also evaluated in this work, which indicates a relatively ideal working state with average ion efficiency for acceleration above 60%, comprehensive average velocity of 18 950 m/s, plume divergence angle of 37.26° and ionization degree of 83%. In addition, error analysis in the LIF measurement was conducted quantitatively and detailedly from different aspects, which is not included in previous research. Results show that the average velocity precision is rather high with a high-quality signal, typically with a relative error about 0.64% under the signal SNR 43.96 dB. Especially, the error by laser output fluctuation can be remarkably restrained by a highly saturated stimulation scheme in this article. [ABSTRACT FROM AUTHOR]

In this paper, a 25-kW bipolar pulsed-power supply for strategic mineral exploration has been described. A 500-V, 12.5-A unit module consisting of a highly efficient LCC resonant converter and a full-bridge-based bipolar pulse-switching unit is designed. The LCC resonant converter has a trapezoidal-shaped resonant current for reduced conduction loss. For achieving high power density, the leakage inductance of the transformer is used as resonant inductance without an external inductor. Moreover, the designed gate drive circuit based on the repetitive short pulse is proposed to operate the frequency range from dc to 8 kHz and reduce the size of the gate transformer. Four modules are connected in series and parallel in order to operate the power supply in either loop mode or grounded dipole mode. Depending on the load condition, the pulse power source capable of delivering the required high voltage and low current (2 kV, 12.5 A) or low voltage and high current (500 V, 50 A) is operated either in grounded dipole mode or loop mode, respectively. In order to satisfy the output voltage balancing of the four modules, the third wire is wound to compensate for the transformer of the LCC resonant converter. Finally, the design of the bipolar pulsed-power supply has been verified based on the experimental results of the field test. [ABSTRACT FROM AUTHOR]

A coaxial multilayered film-winded pulse-forming line (shortened as winded PFL) is a novel compact device to produce pulses with amplitude up to 100 kV and width longer than 10 ns, which was put forward by Su et al. [a coaxial multilayered film-winded PFL,laser, and particle beams, 36(1), 69–75(2017)]. A quasi-rectangular pulse with amplitude higher than 1 MV can be formed if several stages of this winded PFL are connected in series. However, the top of the output pulse of this PFL unit is not “flat”, with a “recess” about 10%. By analyzing the wave transmission process, it is found that this “recess” is due to a large local impedance in the series PFL unit. Two methods are put forward to decrease the local impedance of the series PFL unit in order to shape the output pulse. One is to fill a polymer insulator in the proper position in the series PFL unit; the other is to redesign the configuration of the outer conductor of the PFL unit. With the transient wave simulation method, it is found that the first method can reduce the recess to a level of 5.5%, and the second can reduce the recess to a level of 2.5%. In the end, the feasibility of the first method is verified by experiments. [ABSTRACT FROM AUTHOR]

Prestrike phenomenon in circuit breakers (CBs) can cause electromagnetic transients in power systems. Therefore, the investigation of this phenomenon has considerable importance. The scope of this paper is to investigate the effects and importance of arcing contact shape on the prestrike in SF6 gas CBs. In order to simulate the prestrike with high accuracy, a multi-physics model is developed precisely. In this model, equations of motion of the SF6 gas, the electric charge conservation equation, turbulent equations, heat transfer equation in fluids, and the governing equations of an electric circuit in which the CB works are considered simultaneously. The numerical study is performed on a 72.5-kV single pressure puffer type SF6 CB. Three different types of arcing contacts are investigated in this paper. Numerical results show that the arcing contact shapes have an important effect on the prestrike in gas type CBs. [ABSTRACT FROM AUTHOR]

The aim of the work is analysis of current–voltage characteristics (CVCs) of vacuum arc for the high-current pulse. The arc was ignited by the opening of the electrodes and was fed with half-sine current pulse of 10-ms duration. CuCr axial magnetic field (AMF) contacts were used. Investigations for each contact system were performed in the range of arc currents up to the levels of guaranteed failure when transient recovery voltage (TRV) applied. Oscillograms of current and arc voltage were compared with the results of high-speed video. We propose a method for compact presentation of video filming in the form of Xt-diagrams. It is shown that analysis of CVCs allows determining the ignition character and duration of arc development stage. Correlation between durations of arc development and magnetic field setting has been found. We have found out that the nature of the ignition does not affect the state of the developed arc in the investigated contact systems. We conclude that neither voltage oscillograms nor CVCs can determine the onset of evaporation from anode, and the very presence of evaporation from anode is observed also at currents that are significantly below failure ones and is not a failure criterion. [ABSTRACT FROM AUTHOR]

We present a theoretical study on the mode competition for the planar multiple-beam extended-interaction circuit. The circuit consists of a multigap resonant cavity which is also oversized in the transverse direction, leading to a complex mode distribution. We found that the mode competition is highly relevant to the synchronous characteristics between the multigap resonant cavity and the beams, which depends on the standing-wave field distribution along the interaction paths rather than the dispersion curves. It is demonstrated that the interaction electric field of higher order modes can be characterized by a pure shape factor with a set of complex coefficients. In this way, the interaction between the higher order transverse modes and the coplanar multiple beams can be modeled. As a result, a beam-loading model was developed, which is capable of predicting the stability for the modes in higher passbands. Numerical results are presented, benchmarked against the 3-D particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

Saturated absorption (SA) spectra of argon arcjet plasma with the effect of strong velocity-changing collisions were numerically investigated. The spectrum was numerically reproduced by simulating the change of the velocity distribution interacting with the pump laser using the rate equation system representing two electronic states in the argon atoms. The SA spectra were classified into five types, which are composed of the linear combination of the Gaussian function, Lorentzian function, and inverted pedestals. We drew the maps of the types of the SA spectrum by varying the collision-induced velocity redistribution rate in the two electronic states and the decay rate among them. The possibility of the determination of the collisional parameters from the experiments was also discussed. [ABSTRACT FROM AUTHOR]

Electrode ablation is a key factor that affects the life and performance of the direct current arc plasma generator, which is closely related to the near-electrode behavior of the arc. Compared with the constricted-type arc root, diffused-type arc root is more conducive to reduced thermal load, thereby improving the electrode life and the discharge stability. The attachment behavior of the arc root is related to the transport properties of the arc near the electrode wall and the aerodynamic and electromagnetic forces on the root of the arc. From this point of view, aerodynamical dispersion of the arc root using a converging–diverging nozzle was proposed, and the key factors that affect the dispersion were analyzed and verified. [ABSTRACT FROM AUTHOR]

A rotationally axisymmetric 2-D numerical simulation of a dc suspension plasma spray (SPS) torch with an axial injection system is performed to discuss the interaction between the plasma fluid and suspensions. A two-way coupling model is used for modeling the behavior of plasma fluid and suspensions with mutual interaction effects through momentum and energy transfer. To deeply understand the mutual interaction effects, the numerical simulation using a one-way coupling model, in which the influence of suspensions on the characteristics of plasma fluid is not taken into account, is also performed for comparison. A suspension feed rate is parametrically varied to discuss its influence on the characteristics of plasma fluid and suspensions. Numerical results show that the two-way interaction substantially impacts the velocities and temperatures of plasma fluid and suspensions, and the trajectories of suspensions in the dc SPS torch with an axial injection system. It is also shown from the numerical results that the increase in suspension feed rate results in decreasing the electric current density around the central axis of the plasma torch and expanding the region with electric current in the radial direction. [ABSTRACT FROM AUTHOR]

It is well known that the influence of nuclear force, e.g., nuclear elastic scattering (NES), appears in an ion scattering process when ion energy increases. NES caused by high-energy particles forms the non-Maxwellian component in the ion distribution function. The non-Maxwellian component is named knock-on tail. The knock-on tail gives various effects on fusion plasma. Therefore, it is important to conduct an experiment in order to understand the impact of the NES effects. The NES effects are affected by the “shape and size” of the knock-on tail and the “shape and size” of the knock-on tail depends on plasma conditions. Therefore, we newly propose the method to observe the correlation between the NES effects and the plasma conditions by using Doppler effects for the $\gamma$ -ray-generating reaction, i.e., 6Li(d, p)7Li nuclear reaction, in ITER-like deuterium plasma. We can capture the impact of the NES effect caused by the change in the plasma conditions, i.e., electron temperature, deuteron density, proton beam power, and proton beam energy by capturing the change in the $\gamma$ -ray spectrum. On the basis of the Boltzmann–Fokker–Planck model, we showed the validity of the method by simulation. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence diagnostic technique is applied here to probe xenon neutrals and single-charged ions in an ambipolar plasma source. A single tunable diode laser is employed for pumping both following transitions: $6s{~}^{\mathrm {2}} {[{1/2}]}_{\mathrm {1}}^{\mathrm {0}}$ – $6p{~}^{2} {[{3/2}]}_{\mathrm {1}}^{\mathrm {0}}$ (centered at 834.68 nm; air) and $5d{\mathrm {[{4}]}}_{\mathrm {7/2}}$ – $6p{\mathrm {[{3}]}}_{\mathrm {5/2}}$ (centered at 834.72 nm; air), for Xe I and Xe II detection, respectively. The corresponding decay states are $6s{\mathrm {[{3/2}]}}_{\mathrm {1}}^{\mathrm {0}}$ and $6s{\mathrm {[{2}]}}_{\mathrm {3/2}}$ leading to fluorescence signal at 473.415 and 541.915 nm, respectively. A detailed description of the experimental setup along with time-averaged fluorescence signals are presented, demonstrating the possible application of the above adjacent pumping wavelengths in xenon ambipolar plasmas for probing both ions and neutrals under various operating conditions. A comprehensible discussion to what extent the registered laser-induced fluorescence signals mirror velocity distribution functions is realized, following hyperfine splitting and isotopic shift analysis. [ABSTRACT FROM AUTHOR]

Barrel and pulsed power supply modules are two crucial parts of an electromagnetic launcher (EML), in terms of overall efficiency. One of the most important features of the barrel side is the armature geometry. In this paper, the shape of the armature of an EML with 10-MJ current pulse generator, 1000-kA peak current, and 4.5-ms excitation time is optimized by using independent variables to define the exact geometry of the armature. The main goal is to maximize the muzzle kinetic energy of the projectile with 300-g mass including pressure and contact current constraints. Finite-element method (FEM) is used to calculate the muzzle kinetic energy of the EML for different armature geometries. Genetic algorithm is used as the optimization method. Since the contact resistance between the armature and the rail affects the distribution of contact current density, contact resistance is also modeled in FEM. It is observed that armature shape optimization study increases the muzzle kinetic energy to 596 kJ and the muzzle velocity to 1993 m/s. [ABSTRACT FROM AUTHOR]

Charge transportation expressed as a Lissajous figure usually is a standard method for the analysis of discharge power and energy in surface dielectric barrier discharge (SDBD). In this paper, the charge transportation characteristics under different parameters of power supply and actuator configurations are investigated, and the mechanisms of two typical Lissajous figures are discussed theoretically. Experimental results show that when the plasma distribution is quasi-diffuse mode, the Lissajous figure is almond shape correspondingly, while the plasma distribution looks like separated-channel mode, the Lissajous figure presents a parallelogram shape. Based on an improved time-varying lumped-element circuit model, two equivalent circuits of SDBD under two plasma distributions are built, and the Lissajous figures are calculated theoretically. Calculations and analysis results indicate that the two kinds of Lissajous figures under different plasma distribution modes are due to the current pulse durations and equivalent dielectric capacitances caused by plasma distributions acting together. The protrusions of Lissajous figures are caused by the current narrow pulses in the characteristics of separated-channel mode, while Lissajous figures under quasi-diffuse mode have no protrusions. [ABSTRACT FROM AUTHOR]

Recent studies have found that the surface flashover strength of oil-impregnated insulation paper can be improved by the modification of nanoparticles. To reveal the working mechanism, this paper presents an experimental study on the effects of TiO2 nanoparticles on streamer propagation process at the surface of oil-based nanofluid-impregnated insulation paper under lightning impulse voltage. The results show that the surface flashover voltage of nanofluid-impregnated insulation paper is significantly increased by 34.6%. Streamer characteristics including shape and length at the surface of oil-impregnated insulation paper were investigated using the schlieren technique. It is indicated that streamer characteristics are dramatically changed by the addition of TiO2 nanoparticles. For nanofluid-impregnated insulation paper, streamers with more but much shorter branches tend to develop into adjacent nanofluid rather than clinging to the paper compared to that for pure oil-impregnated paper. The reason responsible for the shape dissimilarity lies in the change of electrical force due to the permittivity difference between oil and paper. Furthermore, more shallow traps introduced by nanoparticles contribute to the faster surface charge dissipation of nanofluid-impregnated paper, reducing the charge accumulation at the streamer head and suppressing the electric field distortion. Thus, it is hard for streamers to develop at the surface of nanofluid-impregnated paper, resulting in an increase of surface flashover strength. [ABSTRACT FROM AUTHOR]

An investigation was performed to measure the arc temperature and arc shape in a SF6 circuit breaker (CB) during large current interruption. Experiments were conducted with a 126-kV SF6 CB. To measure the arc shape and the spatial distribution of the arc temperature effectively, the nozzle was replaced with a transparent organic glass material made from a polytetrafluoroethylene material. The arc shape variation was captured by a high-speed camera, and optical filters were installed on the camera in the case of overexposure. The arc temperature measurement was performed by obtaining the spectral line intensities of Cu I 510.5, Cu I 515.3, and Cu I 521.8 nm through a spectrograph, and the temperature was calculated by the two-line method. Measurements were performed during the entire operating process. The variations in the arc temperature with operating time were obtained. The established method was effective for measuring variations in the arc shape and temperature throughout the entire operating process. [ABSTRACT FROM AUTHOR]

Thermal characteristics were studied for the cross section of plane, convex, and concave rails by channel cooling and surface/channel cooling at repetition rate: 10 and 20 shots/min, respectively. The simulations were all done for 10 sequential shots. During 10 shots time, the peak temperature in three type rails by two cooling approaches is much lower than melting point of rail. Peak temperature in concave rail by two cooling conditions is the highest at the same moment within 10 shots time under identical conditions. Maximal temperature in three type rails by two cooling methods, all increases exponentially with time. In light of obtaining lower peak temperature in rail, convex rail is better than plane and concave rail. In terms of avoiding ablation and gouging, surface/channel cooling is better than channel cooling. [ABSTRACT FROM AUTHOR]

Experimental advanced superconducting tokamak (EAST) device is a D-shaped full superconducting tokamak with actively water cooled plasma-facing components. Before this upgrade, three generations divertors, which are steel divertor, carbon divertor, and international thermonuclear experimental reactor-like upper divertor, have been applied, respectively. To achieve long-pulse and high- $\beta $ H-mode plasma, new plasma configurations and shapes have been modeled and optimized in 2016 on EAST. The new geometry of lower divertor heavily relies on numerical simulations of the plasma in EAST. The new divertor is designed to fit the high- $\beta $ H-mode plasma and endure the heat flux up to 10 MW/m2. To achieve this goal, the lower carbon divertor will be replaced in EAST, which is now in conceptual design phase. Compared to the outer target side, the inner target side is prone to plasma detachment. First, the geometry and physics of the divertor should be better designed with the advanced physical operation mode. Second, the divertor should be in advanced geometry and high efficient cooling structure. Third, considering balance the detachment between inner target side and outer target side. This paper mainly introduces the research progress of the fourth-generation tungsten divertor in EAST. [ABSTRACT FROM AUTHOR]

Currently, the fast evolution of cameras in recent years has made them promising tools for diagnostics of Tokamak. The solution presented in this paper consists of a prototype of high-speed visible image acquisition and processing system (HVIAPs) dedicated for experimental advanced superconducting tokamak shape and position control. Graphics processing unit (GPU) and field-programmable gate array (FPGA) are typically used as accelerators or co-processors in addition to a CPU. Such a heterogeneous computing system can combine the advantages of its individual components. The main imaging equipment components used for this system are four high-resolution fast cameras equipped with fiber interface. Image data from the cameras are received by the frame grabber card based on the FPGA and transmitted to the GPU via the peripheral component interconnect express interface. The software support for the system includes low-level drivers and application programming interface libraries for all components and the algorithm developed for image processing. The offline image process results are compared to equilibrium fitting code, which is a commonly used reconstruction method, with an average error of 1.5 cm. The total processing time for one frame is less than 0.3 ms. [ABSTRACT FROM AUTHOR]

A purely geometric approach has been investigated to reconstruct the Demonstration Fusion Power Reactor (DEMO) plasma boundary for control purposes. The whole plasma boundary is reconstructed by using a deformable template method based on B-splines. The final curve shape is achieved by minimizing the distance between a limited number of estimated and measured (at present provided by an equilibrium code) plasma boundary points along the reflectometer lines of sight. The resulting unconstrained optimization problem is solved by a simulated annealing algorithm. The method is complemented by including the available plasma and poloidal field coil current measurements to refine the boundary reconstruction in the X-point region. The robustness with respect to random measurement random errors and to a reduction in the number of measurements is discussed. The main equilibrium and shape geometric quantities (such as plasma cross-sectional area, plasma center position, elongation, and triangularity) were computed and compared to the corresponding quantities of a DEMO reference equilibrium. [ABSTRACT FROM AUTHOR]

International thermonuclear experimental reactor (ITER) diagnostic port plugs perform many functions including nuclear shielding and structural support of diagnostic system, while allowing for diagnostic access to the plasma. With design advancing, the in-port diagnostic components are integrated into the port plug structure, and the diagnostic shield modules (DSMs) are customized to accommodate various in-port diagnostic components. This paper summarizes results of transient electromagnetic analysis using Opera 3-D in support of recent design activities for ITER diagnostic upper port plug 14 (UPP14) and upper port plug 11 (UPP11). A complete distribution of disruption loads on each component in the two ports is presented. Impacts of different design features to the electromagnetic loads are discussed. [ABSTRACT FROM AUTHOR]

Melamine formaldehyde microspheres are widely used in dusty plasma experiments for their monodispersity, sphericity, low mass density, and well defined sizes. This paper summarizes problems that were encountered in numerous applications of these grains in different laboratory simulations. and the already published results are discussed in view of new experiments. The main results of this paper are connected with changes of the grain mass due to the decreased pressure and/or increased temperature and variations of the grain dimensions, its shape, and mass density under electron or ion bombardments. By contrast to the work function estimated from field emission properties, we have found the photoelectric work function (4.5 eV) being close to that expected. A sputtering of the grains using a 30-keV ion beam revealed their unexpected heterogeneity. [ABSTRACT FROM AUTHOR]

This paper reports the levitation of micro-organisms in the sheath of radio-frequency (RF) plasma. Based on simple force-balance calculations, the required electric field for the levitation of micro-organisms has been estimated. It is predicted that micro-organisms could levitate at the periphery of the sheath. Experimental results demonstrate the levitation of two species of bacillus micro-organisms Escherichia coli (E. coli) and Klebsiella pneumoniae in an RF plasma. The almost monodiverse Klebsiella pneumoniae levitating in the RF plasma formed an ordered state similar to a 2-D Coulomb crystal. Diverse E. coli particles demonstrate the tendency that the levitating height of micro-organisms decreases as the radius of particles increases. Levitating micro-organisms in plasmas can be referred as dusty plasmas. [ABSTRACT FROM AUTHOR]

In this paper, a method to reconstruct the diffraction field in a millimeter-wave substrate integrated waveguide ten-way power divider by shape optimization technology is proposed. The diffraction field is reconstructed by changing the location of the metallized via hole array, which can be regarded as a continuous cylindrical reflector. The receiving diffraction field is optimized to a quasi-plane wave to be received by a transition array to achieve good magnitude and phase balance as a power dividing circuit. The proposed power divider is operated at the center frequency of 33 GHz, and over the entire Ka-band 26.5-40 GHz the return loss is less than -21 dB. The simulated insertion loss is about -12.6 dB corresponding to 54.7% power combining efficiency considering the dielectric loss, conductor loss, and radiation loss. [ABSTRACT FROM AUTHOR]

A specially designed beam profile monitor (BPM) was produced to be assembled over a biased target plate, with the aim of studying the effect of an ion beam deceleration system on the beam fluence due to beam dispersion. The new BPM was developed with a shape as flat as possible, so it could be attached to a biased target plate without affecting the target geometry, using a slit scan method to produce an high-resolution beam profile. This system was designed and installed on the high current ion implanter at the Laboratório de Aceleradores e Tecnologias de Radiação, at the Campus Tecnológico e Nuclear, of Instituto Superior Técnico, in Lisbon. The system is capable of showing the ion beam profile for low-energy ion beams below 15 keV, using a beam deceleration system. [ABSTRACT FROM PUBLISHER]

In this paper, prebreakdown streamers in transformer oil and transformer oil-based TiO2 nanofluid were observed by the schlieren method under positive lightning impulse voltage. Streamers in the nanofluid have numerous branches with much shorter length, whereas in the pure oil, they exhibit only certain filaments with longer length. The discrepancy in positive streamer pattern of both oils is further investigated under a range of applied voltages. The complexity of streamer patterns was quantitatively described using the fractal analysis method. Results indicate that the fractal dimension of streamer patterns shows different changing tendencies in both oils, and it keeps higher value in the nanofluid than that in pure oil during the whole propagation process, well corresponding with streamer propagating structures. Moreover, a new parameter, the ratio of fractal dimension to propagation length (D/L), is introduced to classify the complex streamer patterns for the first time. Three propagation zones in both nanofluid and pure oil are clearly categorized by the value of D/L, providing a quantitative way to distinguish the streamer patterns. [ABSTRACT FROM PUBLISHER]

This paper explores the use of pulsed alternators driving a railgun with 32-MJ muzzle energy. A series of modular pulsed alternator power system (MPAPS) with the different number of modules is designed and analyzed based on the scaling laws. The system performances are simulated using MATLAB. Taking into account all system performances, especially the output current pulse-shape flexibility, the MPAPS composed of six alternators is selected. The six modules are divided into three pairs of matched contra-rotating pulsed alternators; each pair has the independent firing time. By optimizing the voltage and the firing time of each pair, a relatively flat-topped current pulse is produced. The average-to-peak acceleration ratio of railgun reaches 0.67. Therefore, this design of MPAPS is an option for a long-range railgun. [ABSTRACT FROM PUBLISHER]

Armature is very important for a synchronous induction coil launcher which can transform the electric energy to kinetic energy and push the load forward. The structure of the armature will influence the kinetic energy conversion efficiency directly. This paper analyzes the armature structure of a capacitor-driven synchronous induction coil launcher. Length and thickness of the armature are analyzed that how these parameters influence the maximum velocity and system efficiency of the launcher. Current filaments model is used to calculate the motion characteristics of a tubular linear induction motors, which is verified by an experiment and finite-element code. Genetic algorithm optimizer is used to calculate the best trigger times of the coils and the maximum velocity under the conditions of different length and thickness of the armature. It is shown that when the armature mass is fixed, length and thickness of the armature will greatly increase the velocity of the armature. The best length of the armature should be almost 2–2.5 times the length of the coil. The best thickness of the armature could be estimated by skin depth. [ABSTRACT FROM PUBLISHER]

In this paper, two kinds of abnormal rail-armature contact states are assumed and simulated, and the simulated B-dot probe waveforms are compared with the results from the experiments. Through theoretical analysis, simulations, and experiments, relations between the abnormal contact states and the output waveforms of the B-dot probe are investigated. Results show that with the help of the B-dot probe output waveforms, the transition position can be obtained and the intervals between the parallel circuit branches, which are created by the arcs arising from the abnormal contact states, can be primarily measured. [ABSTRACT FROM PUBLISHER]

Measuring the velocity and displacement of the armature and current for a rail gun is important. The common method uses B-dot probes to acquire the discrete time points when the armature passes by them. These points can be interpolated into a curve of the armature’s displacement. Actually, the common interpolation method has some disadvantages. Some probes may break down, and the interpolation method is regardless of the process between the discrete points. So it is difficult to get the armature’s position at any time and the exact velocity at any position. Aiming at these disadvantages, this paper presents an improved method, which based on both B-dot points and the main current waveform. A B-dot probe beside the rails easily gives this waveform. The shape of the current waveform helps us to fit the curve with enough physical information. The new method can give a more precise velocity of the armature at an arbitrary position between two B-dot probes’ positions. It is also practical outside of two B-dot probes’ positions too. And it still works when some B-dot probes fail. Moreover, the current waveform with the adjusted amplitude is also calculated out. The launching experimental results and currents measured by Rogowski coils show that the improved method is highly suited for the velocity and current measurement for a rail-gun system. [ABSTRACT FROM PUBLISHER]

New geometrical counterparts to the conventional Einzel lens, cubic, and the continuous body electrostatic (CBE) lenses are introduced and their performances are investigated in terms of different aberrations and input beam properties. Design curves for the continuous body electrostatic lens are presented. Relative sensitivity is proposed as a figure of merit, based on which the focusing characteristics of the two new lenses are compared with that of a conventional Einzel, and a quadrupole lenses of the same size, as well. Moreover, performance and characteristics of the lenses are compared in terms of their corresponding sensitivities to the applied voltage and the incidence beam nonidealities. Electric field distributions of the lenses are studied, and different aberrations are discussed. It is shown that considering chromatic nonparaxial beams, the CBE lens outperforms the conventional Einzel lens in terms of the sensitivity and the absolute value of the lens demagnification. [ABSTRACT FROM AUTHOR]

The feasibility of using plasmatized exhaust to reduce engine rear bistatic radar cross section (RCS) is studied. The possible range of plasma density inside a jet engine when alkaline additives are used in fuel is analyzed via the Saha equation, and the results show that there should be high density plasma. Next, the S-band rear bistatic RCS of a jet engine with or without the vector thrust nozzle is simulated using a finite-difference time-domain code. Then, the RCS when exhaust is plasmatized is simulated to make comparison. The results show that even with low density plasma, the effective shape of the vector thrust nozzle is changed, and the RCS is reduced. As the plasma density becomes higher, the reflection becomes stronger and the radar wave penetration into the plasmatized exhaust becomes less. The change in RCS is strongly related to the direction and shape of the jet exhaust, besides the plasma density. [ABSTRACT FROM PUBLISHER]

Nonlinear transmission lines (NLTLs) are nonlinear LC ladder networks that can act as a nonlinear and dispersive medium, thus allowing the generation of soliton bursts. Several papers have been published indicating that NLTLs offer a new option for pulse shaping and RF generation. In this paper, we investigated the response of an NLTL driven by three different pulse shapes: a rectangular, a half sine, and a triangular waveform. The performance of the NLTL was evaluated through time- and frequency-domain analysis of the RF signal sampled at the 29th section of a 30-section capacitive NLTL. The frequency of the generated RF signal is correlated with the shape of the input signal, whereby the output frequency can be adjusted by the amplitude-time characteristics of the pulse at the input of the capacitive NLTL. Higher frequency oscillations, around 30 MHz, were generated by the rectangular wave train due to its shorter rise time. The propagation of solitons along the NLTL is influenced by the input pulse rise time. Namely, the rectangular pulse showed smaller delay time as it had the shortest rise time (less than 10 ns). Maximum efficiency was obtained for the input pulsewidth of 150 ns under a duty cycle of 1/3 for the three pulse shapes (rectangular, half sine, and triangular), and this combination of parameters yielded the highest RF conversion efficiency of the NLTL. The capacitive NLTL showed a higher RF conversion efficiency (16.4%) when driven by the rectangular input signal. [ABSTRACT FROM AUTHOR]