Breakdown Phenomena Research Articles

Prebreakdown and Breakdown Phenomena in HFO Gas Under Impulse Voltage—Part II: Quasi-Uniform Field

Breakdown phenomena in the HFO1234ze(E) gas are studied under impulse voltage in moderately divergent field, with field enhancement factor η < 10. The first breakdown voltage recorded in new HFO with clean electrodes is higher than in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . However, the degradation of HFO by discharges induces the formation of soot deposited on electrodes, which strongly facilitates the inception of subsequent pre-breakdown leaders: both inception field and statistical delay to inception are reduced. As a consequence, the breakdown voltage of HFO with polluted electrodes drops, and becomes lower than in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> in identical conditions. This deleterious effect is not recorded in negative polarity.

Prebreakdown and Breakdown Phenomena in HFO Gas Under Impulse Voltage—Part I: Divergent Field

Pre-breakdown and breakdown phenomena in HFO1234ze(E) gas are studied with a wide range of electrode geometries, characterized by a field enhancement factor η ranging from 1.7 (quasi uniform field) to 90 (very divergent field). As in SF6, breakdown in HFO results from the inception and propagation of leaders. Depending on the field geometry, the measured breakdown voltage represents either the voltage required for leader complete propagation (in divergent field, η > 10), or for inception (in quasi-uniform field, η < 10). This paper mostly concerns results obtained with divergent fields. Leader propagation in HFO is barely influenced by pressure, and the minimum voltage required for propagation to breakdown is slightly lower compared to SF6, explaining that lower breakdown voltages are recorded with HFO in divergent field. In such conditions, breakdown voltage is mainly determined by the gap distance. HFO degradation, evidenced by the formation of black soot after breakdown, has no influence on leader propagation, and hence on breakdown properties in divergent fields.

The investigation of lateral/heading characteristics and the influence of jet control at high attack angle

When the aircraft does high maneuvers at a high attack angle, the rapid transition of flight state induces a series of complex flow phenomena such as flow separation and vortex breakdown, leading to a series of uncommanded motions such as self-excited roll oscillation, which brings great danger to the flight of the aircraft. Therefore, it is important to investigate the mechanism of this phenomenon and suppress it. In this paper, the numerical method is based on Lattice Boltzmann Method (LBM) and Large Eddy Simulation (LES) for the SACCON standard flying-wing layout aircraft model. The accuracy of the numerical method is validated by comparing the simulation results of aerodynamic loads at different attack angles with the experimental results. Then the phenomena of the vortex breakdown and shedding at different roll angles and sideslip angles at high attack angles are analyzed, and the relationship between the jet flow coefficient and the control moment is obtained by adding the jet flow to the fuselage. Finally, the rolling motion of the aircraft is simulated in the dynamic simulation. The simulation results show that the model generates self-excited roll oscillations around a nonzero mean angle at high attack angles. The dynamic numerical simulation based on the LBM method can be an effective complementary tool for the study of the dynamic characteristics of the aircraft with a high attack angle.

The development status and future of the field effect transistor

FET is short for Field Effect Transistor (FET). There are two main types: Junction FET-JFET and metal-oxideSemiconductor FETs (MOS-FETs). Conduction by the majority of carriers, also known as a monopolar transistor. Itis part of voltage controlling semiconductor device. With the advantages of high input resistance (107 ~ 1015 Ω), lownoise, low power consumption, extensive dynamic range, easy integration, no secondary breakdown phenomenon, andwide safe working area, it has become a strong competitor of bipolar transistors and power transistors

Concept of consciousness transfer: creative and scientific research

The article analyzes the use of the consciousness transfer concept in the literature, cinema and science. Both techno-pessimism and techno-optimism are shown to be associated with the consciousness transfer idea. The main reasons for the desire of characters intention to use the consciousness transfer technology, which is also termed as breakdown phenomenon, are demonstrated through the example of the LitRPG subgenre and science fiction films. It is typical for novels and screen novels to demonstrate both positive and negative consequences of the consciousness transfer, but the attitude towards the possibility itself is predominantly positive. Unlike many science fiction theories, which are far from becoming reality, several major scientific projects are already working on the concept of the mind transfer. However, existing projects are far from implementing the consciousness transfer technology and are more often involved in solving particular problems associated with individual brain diseases, or exploring the social and humanitarian consequences of developing the virtual reality generally and the human presence in it particularly. It is concluded that for the modern literature and cinema, the concept of consciousness transfer has turned into a myth about the consciousness transfer, generated by the dream of the human mind omnipotence, combined with a pessimistic idea about the human morality and the human society unity. Furthermore, this myth also reflects a substantial part of the human life being already inside the digital reality.

Magnetic skyrmion Walker breakdown in cylindrical nanotubes

As topological spin textures, magnetic skyrmions in chiral magnets show a universal current-velocity relation when driven by spin transfer torques. In general, the skyrmions in chiral magnets do not exhibit Walker breakdown---a phenomenon that domain walls' motion modes will change from steady to precessional motion when the driving forces are sufficiently large. In this work, we studied the dynamics of magnetic skyrmions in cylindrical nanotubes numerically and analytically. The skyrmion performs a helical motion in the nanotube without external fields. However, we show that the skyrmion exhibits the Walker breakdown phenomenon when an external field is applied to the nanotube perpendicularly. A steady skyrmion motion is observed in the low current regime, while the skyrmion moves forward and back when the current is larger than a critical density. Our findings reveal a new way to tune the skyrmion dynamics beyond planar geometries.

기체 형상이 로터-기체 상호작용 소음에 미치는 영향에 관한 전산해석

Urban Air Mobility(UAM) or Advanced Air Mobility(AAM) has emerged as a next-generation transportation system based on electric-powered vertical takeoff and landing aircraft. Distributed Electric Propulsion(DEP) system is applied to most UAM aircraft, which inevitably accompanies an increase in the number of rotors or propellers, thus leading to a strong interaction between the rotor and the airframe. This study conducted a computational investigation of the effects of rotor-airframe interaction on aerodynamic performance and noise generation depending on the airframe shapes. Aerodynamic analysis was performed using Lattice Boltzmann Method(LBM) simulation, and the noise level was predicted using the Ffowcs Williams-Hawkings(FW-H) acoustic analogy with permeable boundary condition. Two different types of airframe geometry were considered: cylinder and conical airframes. The thrust coefficient of rotor blades with the conical airframe is higher than that of rotor blades with the cylinder airframe. Tip vortex breakdown phenomenon and transition into turbulent wake state were captured in both airframes. Moreover, it was observed that high-intensity noise was radiated over the broad surface of the airframe for the conical airframe case. The comparison of overall sound pressure level(OASPL) on the hemisphere showed the strong interaction between the rotors and conical airframe causes a considerable increase in the noise level, compared to the isolated rotor and rotor-cylinder airframe.

Breakdown voltages in thrust bearings: Behavior and Measurement

This paper investigates breakdown characteristics in the bearings of variable speed electric drive trains. The analyses reveal that breakdown phenomena previously known from high-voltage technology appear to also occur in the bearing contact, though at significantly lower voltages. By loading the bearing with AC voltage of different frequencies at various mechanical load points, five states, which range from partial discharge through arc discharge to a completely conductive channel, emerge. Consistent with the concept that the magnitude of the breakdown voltage depends on the lubricant film height, the contact force, and the frequency of the AC voltage, a thicker lubricant film results in a higher breakdown voltage, analogously to a capacitor with a larger plate spacing, which requires a higher potential difference to be punctured. Furthermore, the sinusoidal frequency of the AC load correlates with the breakdown voltage. The breakdown tends to occur earlier at low frequencies, which is illustrated by the fact that at low frequencies, capacitive behaviour can only be observed at higher speeds, i.e., at a larger lubrication gap, while no voltage can be built up over the bearing at lower speeds. An increase of the contact force for the same lubricant film height lowers the breakdown voltages. The reduction of the breakdown voltage by the contact force may result from an increase of the relative permittivity of the lubricant with higher pressure and likewise of the contact area; the increased area may also increase the number of surface-roughness peaks where an increase in the electric field occurs.

Role of shape anisotropy on thermal gradient-driven domain wall dynamics in magnetic nanowires

In this paper, we investigate the magnetic-domain wall (DW) dynamics in uniaxial/biaxial-nanowires under a thermal gradient (TG). The findings reveal that the DW propagates toward the hotter region in both nanowires. In uniaxial nanowire, the DW propagates accompanying a rotation of the DW-plane. In biaxial nanowire, the DW propagates in the hotter region, and the so-called Walker breakdown phenomenon is observed. The main physics of such DW dynamics is the magnonic angular momentum transfer to the DW. The hard (shape) anisotropy exists in biaxial-nanowire, which contributes an additional torque; hence DW speed is larger than that in uniaxial-nanowire. But the rotational speed is lower initially as hard anisotropy suppresses the DW-rotation. After certain TG, DW-plane overcomes the hard anisotropy and so the rotational speed increases slightly. With lower damping, the DW velocity is smaller and DW velocity increases with damping which is a contrary to usual desire. The reason is predicted as the formation of the standing spin-waves (by superposing the spin waves and its reflection from the boundary) which do not carry any net energy to DW. However, for larger damping, DW velocity decreases with damping since the magnon-propagation length decreases. Therefore, the above findings might be useful to realize the spintronics (i.e. racetrack-memory) devices.

Stability of breakdown phenomenon in N2, SF6, and their mixture under impulse voltages

In the self-breakdown experiment, it is demonstrated that the breakdown stability of 15% SF6/N2 was higher than that of pure SF6 and N2 in the non-uniform field under negative impulse voltages. In this paper, the stable breakdown phenomenon of the gas mixture is studied at the nanosecond scale. The corona process and streamer process of these three gases are investigated by using a high-speed framing camera. The stabilized corona and the abnormal streamer phenomena observed in the gas mixture discharge have a relation to the stable breakdown phenomenon. The stabilized corona is supposed to be the main reason that obstructs the development of negative steamer and stabilizes the supply of photons to the anode. Furthermore, the captured images of the streamer process in the gas mixture show that there is a negative ion sheath between the electrodes. The sheath keeps the corona stabilized near the cathode tip. In addition, photons emitted by the stabilized corona can ionize neutral particles near the anode. The generated photoelectrons and positive ions accumulate near the anode surface. The positive streamer occurs once the accumulation number reaches a certain value. In addition, the photon emission intensity and stability also have an influence on the stability of the positive streamer.

외부 전자기장에 의한 저잡음 증폭기의 고장 현상 분석

외부 전자기장에 의한 저잡음 증폭기의 고장 현상 분석

Time- and Position-Dependent Breakdown Volume Calculations to Explain Experimentally Observed Femtosecond Laser-Induced Plasma Properties

Focusing of femtosecond laser pulses in gases can produce different gas breakdown phenomena depending on the focusing conditions: from simple optical breakdown like laser “sparks” to a nonlinear optical breakdown like filamentation. The dynamics of such plasmas after the pulse exposure is dependent on the energy deposited by the laser in the breakdown volume. Using a time- and position-dependent breakdown model, we estimate the breakdown volume and show that the energy deposited by the laser in this breakdown volume determines the characteristics of laser-induced plasma in the post-pulse exposure regime. Experimentally we find that for different focal lengths there exists a threshold value of the energy density beyond which a transition from an ellipsoidal shape to a spherical shape can be observed, followed by a toroidal expansion of the produced plasma. When electron density and electron temperature are expressed as a function of the energy density, deviations from the parabolic dependence on irradiance are observed. They imply additional ionization by multiphoton ionization in the plasma volume that occurs when the peak power of the laser pulse is above the critical power for self-focusing in air. The relevance of this experimental and theoretical study is to prevent undesired self-focusing conditions during material processing, a step toward well-controlled laser-plasma etching without laser ablation.

Polyaniline Hybrids with Biological Tissue, and Biological Polymers as Physiological—Electroactive Materials

A sprout/polyaniline was synthesized via the chemical oxidative polymerization of aniline in the presence of natural sprout, based on a concept of cyborg plant composite. The composite consisted of both polyaniline and plants. The chemical structure was confirmed by infrared absorption spectroscopy measurements. Optical microscopy observation revealed that polyaniline was deposited into the micro-tissue of the sprout to form the conductive polymer bio-composite. Micro-optical fiber functions for the composite were visually confirmed. Furthermore, the sprout/polyaniline based organic diode exhibited an avalanche breakdown phenomenon. Next, a fucoidan/polyaniline composite as a physiological active material/conducting polymer composite was prepared. This composite showed good film-forming ability, electrochromism, and a micro-porous surface. This paper reports the preparation of conducting polymer composites with a combination of bio-tissue and bio-substance for the creation of bio-based electrically active organized architecture.

Electrical Characterization of Plasma-Assisted Electron Beam Source With Sub-mm Sheet Aperture

In this article, the electrical characterization of a plasma-assisted electron beam source with a sub-mm sheet aperture has been performed. The developed sheet electron beam source comprises a hollow cathode cavity, two floating anodes, and one ground potential anode with a sheet aperture of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times0.3$ </tex-math></inline-formula> mm. The source has been characterized under varying applied gap potential range, i.e., 10–30 kV in self-breakdown operating mode. The breakdown parameters and resultant beam parameters, such as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} - {I}$ </tex-math></inline-formula> characteristics, electron beam current density, duration to reach the conductive phase, and the energy transformation efficiency of the developed source, have been analyzed. The successive breakdown phenomenon has also been presented in the profile of the developed electron beam source.

A Study of the Velocity Field During Mitigation of Vortex Breakdown in Model Francis Turbine at High Load

Abstract Off-design operation leads to the development of flow instabilities like vortex breakdown phenomenon which manifests as an enlarged vortex core in the draft tube at high load operating conditions. These flow instabilities are known to potentially have detrimental effects on turbine performance necessitating investigations on their formative and mitigation mechanisms. This work clarifies the evolving velocity maps characterizing vortex breakdown seen in a model Francis turbine draft tube during the transition from high load to best efficiency point. Velocity measurements have been performed inside a draft tube cone using a 2D particle image velocimetry system. Results show a wake-like velocity profile characterizing the vortex core in the draft tube cone at high load condition. The vortex core is a centrally located flow feature embodying a quasi-stagnant flow with recirculation regions. Surrounding the core, an axial outflow is seen with shear layers arising at the interface of core and outflow due to a substantial velocity gradient. Mitigation of this vortex core through a load rejection operation was further investigated. It is seen that as the flowrate approaches the best efficiency point, the shear layers between the outflow and central stagnation region break. The breakup leads to an axially dominated and streamlined flow. This is enabled by the reduction of the swirl until no central flow separation at the stagnation point occurs. The flow at the best efficiency point is thus devoid of the vortex core due to the absence of flow stagnation, the primary instability causing the core development.

High-Power Test of Two Prototype X-Band Accelerating Structures Based on SwissFEL Fabrication Technology

This article presents the design, construction, and high-power test of two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -band radio frequency (RF) accelerating structures built as part of a collaboration between CERN and the Paul Scherrer Institute (PSI) for the compact linear collider (CLIC) study. The structures are a modified “tuning-free” variant of an existing CERN design and were assembled using Swiss free electron laser (SwissFEL) production methods. The purpose of the study is two-fold. The first objective is to validate the RF properties and high-power performance of the tuning-free, vacuum brazed PSI technology. The second objective is to study the structures’ high-gradient behavior to provide insight into the breakdown and conditioning phenomena as they apply to high-field devices in general. Low-power RF measurements showed that the structure field profiles were close to the design values, and both structures were conditioned to accelerating gradients in excess of 100 MV/m in CERN’s high-gradient test facility. Measurements performed during the second structure test suggest that the breakdown rate (BDR) scales strongly with the accelerating gradient, with the best fit being a power law relation with an exponent of 31.14. In both cases, the test results indicate that stable, high-gradient operation is possible with tuning-free, vacuum brazed structures of this kind.

Numerical simulation of gas breakdown characteristics in porous dielectric and theoretical analysis based on the capillary network model

Gas discharge in heterogeneous porous dielectric (PD) is becoming a reliable and popular low-temperature plasma technique in surface modification and plasma catalysis. However, the exact breakdown characteristics in the PD are not well studied due to experimental and diagnostic limitations. In this paper, a fluid model is then used to simulate the gas breakdown characteristics in real PD. It is found that the breakdown will selectively occur in PDs. The spatial distribution of PD determines regions of local breakdown. Variations in pressure result in the rearrangement of breakdown probability in each region of PD so that breakdown regions will change. In order to explain the selective breakdown phenomenon, based on the assumption that a PD can be simplified into a network consisting of multiple tortuous capillaries, we developed a theoretical model of the breakdown in a capillary network. Three geometrical factors, i.e. capillary tortuosity, capillary radius, and line porosity, are taken into the model to account for the effect of electric field distortion and electron loss on the dielectric walls in the presence of PD. The calculated results explain the selective breakdown phenomenon occurring in the numerical simulation. This paper simulates the breakdown in a real PD and provides a quantitative theoretical model to analyze the geometrical effect of PD on the breakdown. This paper will also provide insights into the design of optimal parameters for porous dielectric discharge in surface modification and plasma catalysis.

Experimental and numerical studies of the effects of the contraction ratios on the swirling flow characteristics of the model combustor outlet in lean gas turbines

Large Eddy Simulation (LES) is utilized in this work to study isothermal turbulent swirling flow characteristics for a lean partially premixed gas turbine model combustor. The goal is to investigate the influence of contraction ratio (CR) variation on the vortex breakdown phenomena features and the turbulence structure in these combustors. Particle image velocimetry (2D-PIV) measurements were carried out on a single-case model combustor using (air-air) phase to perform the mean flow behavior and the validation process under atmospheric conditions with CR equal to 0 (largest diameter, Dinlet = Doutlet), the equivalence ratio (φ) of 0.3, swirl number of (Sn) = 0.66 and Reynolds number of (Re) = 42,000. While five test cases with various CRs were applied in LES under the same conditions using (air-CH4) phase to predict the vortical structure and the precession vortex core (PVC). The CRs ranged as follows: 0, 50 %, 60 %, 70 % and 80 % (smallest diameter). Experimental and LES results show that there was a reasonable agreement between the PIV and LES results with maximum deviations of 2.8 % and 4.65 % for the normalized mean axial and radial velocities, respectively. As the CR was increased, the pressure drop and the mean axial velocity increased linearly at the contraction part. In addition, the downstream stagnation point and the size of the central toroidal recirculation zone (CTRZ) stabilized when CR = 60 %, 70 %, and 80 %. The swirl level was further enhanced by 40 % when CR = 60 % and 80 %. The presence of CR successfully suppressed the pressure and axial velocity fluctuations generated in the shear layer zones by 35 %. LES data was analyzed by Fast Fourier Transformation (FFT) and Proper Orthogonal Decomposition (POD) to investigate the PVC dynamics. The FFT showed four dominant frequencies as a result of the appearance of the PVC and vortex breakdown oscillation. The frequency of PVC (fpvc) decreased linearly with an increase in the CR where the fpvc was 20.8 Hz when CR = 0 and became 12.5 Hz at CR = 80 %. In contrast, the other frequencies were still constant even with increased CR at 187 Hz, 562 Hz, and 979 Hz. The POD analysis showed the first mode was more energetic and had 40 % of the total pressure fluctuations.

Prediction of Partial Discharge Inception Voltage for Electric Vehicle Motor Insulation Using Deep Learning

Monitoring the health of electric motor insulation by measuring the early breakdown phenomenon such as Partial discharge (PD) is required for the safer operation of electric vehicles (EVs). The prediction of partial discharge inception voltage (PDIV) is of great significance to evaluate the condition of motor insulation. This paper presents a method to predict the PDIV of electric motor magnetic wires winding. The data is driven by constructing a single point discharge model of turn-to-turn insulation of two magnetic wires. The model is simulated by varying the input parameters of magnetic wire configuration such as diameter, insulation thickness, winding temperature and insulation permittivity to calculate the PDIV based on Townsend discharge theory. The calculated PDIVs are used to train the convolution neural network (CNN)and extract the nonlinear relationship between characteristic variables and PDIV to test it for large data sets of magnetic wire. The predicted value is compared with the measured value, which proves the superiority and accuracy of the method in this paper. Based on the calculation results of the mean impact value algorithm, a method to improve the PDIV of the turn-to-turn insulation is given.

Cell-to-Cell Adhesion and Electrical Parameters of Murine Embryo Membranes After Cryopreservation by Vitrification

In this work, we have studied the impact of various stages of cryopreservation by vitrification in ethylene glycolsucrose medium on plasma membranes adhesive properties of 8-cell murine embryos and their specific electrical conductivity. Embryos were divided into the following experimental groups: the control, group 1 (incubation in vitrification medium) and group 2 (complete cycle of cryopreservation). The embryo exposure to vitrification medium did not affect their ability to cell-to-cell adhesion. After a complete cycle of cryopreservation, no embryo adhesion was observed. Electrical conductivity of embryo membranes was determined using the pulsed conductometry. After incubation in vitrification medium, their resistance to electric pulse was shown to decrease, that was manifested in the phenomenon of irreversible electric breakdown. The average values of electrical conductivity varied within the following ranges: ((12.1 ± 1.5)...(55.5 ± 2.6)), ((28.7 ± 5.7)...(44.± 8.9)), ((31.0 ± 9.3)...(87.9 ± 26.1)) μS/cm in the control, groups 1 and 2, respectively. These findings may be explained by appearance of first structural disorders in lipid bilayer of embryo membranes even at the stage of their incubation in vitrification medium. The lack of adhesive properties of blastomeres after vitrification-warming testified to a damage to the membrane adhesion proteins.