Pulse Current Flows Research Articles

Short rise- and decay-time Z-pinch currents for soft x-ray laser excitation

The article addresses how to create inductance-free plasma and use it to excite soft x-ray lasers. The method employs a bifilar phenomenon in which one part of the pulsed current flows via the plasma column while the other part runs in the opposite direction via the closely placed external conductor. The electromagnetic fields formed by the plasma and return conductor are adjusted by lowering the distance between them to neutralize the magnetic field of the bifilar. Because the net transient magnetic field is drastically reduced, the plasma-conductor mutual inductance is near zero during current rise and decay. The inductance-free (L ∼ 2 nH) 35 cm-long Z pinches in a 3.1 mm-diameter argon-filled alumina capillary with current rise and decay times of 15 ns, dI/dt > 1012 A/s, and amplitudes up to 17 kA were predicted, realized, and verified to be suitable for pumping soft x-ray Ar+8 lasers. Without the bifilar phenomenon, the 35 cm Z pinches obey a 200 nH inductance that restricts the rise and decay durations of currents to 150 ns. The 35 cm Z pinches with 2 nH inductance generated 46.9 nm laser pulses with up to 4 μJ of energy and a beam divergence of 2 mrad at a low operating voltage of 35–45 kV, compared to 0.1–0.8 MV for similar lasers. The bifilar method could find applications in many research and technological fields, where the rise and decay times of discharge currents play a key role.

Analysis of heating of printed circuit board conductors on a metal base for spacecraft devices at pulsed current

The article presents the results of the analysis of heating of printed circuit conductors of printed circuit boards mounted on a metal base, on-board device of spacecraft when pulsed current flows through them. Thermal transient and impulse characteristics of a system consisting of a printed conductor and a printed circuit board are considered. The analysis of the dependence of the temperature rise rate of printed conductors and the duration of transient processes on the linear dimensions of the system elements is given. It is noted in the article that the time of transient processes most strongly depends on the thickness of the layer of insulating materials. All the results were obtained in the process of modeling transients in the ANSYS 2019 R1 Transient Thermal module. Practical recommendations on the consideration of thermal transients in printed conductors in the design of printed circuit boards are given.

Intrinsic Effect of Pulsed Current on the Recrystallization of Deformed AZ31 Alloy.

Two ensemble configurations were designed to investigate the intrinsic effect of a pulsed current on the recrystallization of rolled AZ31 alloy. The samples with a total reduction of about 60% were crystallized at 473K for 5 min when treated with the pulsed current. By forcing the pulsed current flow only through the graphite die, and the sample was heated by Joule effect, a microstructure with a grain size of ~5 μm was formed and the recrystallized fraction achieved 60% reduction. Moreover, a fully recrystallized microstructure with a grain size of ~9 μm was obtained when heated with Joule and athermal effects by forcing the pulsed current flow through the sample only. Based on the experimental results, the recrystallization behavior of deformed AZ31 under a pulsed current should be governed by the high Joule heating effect, which could generate transient high stress in the sample due to the nonsynchronous change in temperature and thermal expansion. The athermal effect of the pulsed current could enhance the dislocation mobility and thus accelerate coarsening of the recrystallization grains, but it should not be the key factor governing the recrystallization behavior of rolled AZ31B. This led to the p erroneous conclusion that the athermal effect of pulsed current played a crucial role in the recrystallization of deformed alloys.

Development of an x-ray detector by polycrystalline diamond and its application in Z-pinch x-ray detection.

Large-grain-sized polycrystalline diamond films are fabricated by electron assisted chemical vapor deposition. A pure SP3 carbon bond in the cubic lattice structure is confirmed by Raman spectrum analysis. The grain size is on the order of several hundreds of μm or larger. Interlaced-finger electrodes are imprinted onto a 6 × 6 mm2 × 500 µm film to fabricate the x-ray detector. The width of every finger is 25 µm, and the distance between nearby fingers is 25 μm. Strong x ray irradiates when a pulsed current flows through a double-layer nested tungsten wire array in the Z-pinch. This diamond detector now works as one of the main x-ray detectors for the Z-pinch device. The diamond detector is calibrated using a plastic scintillator. The comparison between the signal measured by these two methods confirms that the large-grain-sized polycrystalline diamond is a good candidate for the detection of nanosecond pulsed x ray.

Densification of pure magnesium by spark plasma sintering-discussion of sintering mechanism

In this study, high-quantity pure magnesium was prepared by SPS, and the sintering densification mechanism was discussed by using numerical simulation and simultaneous experiment. Results show that a layer of dense magnesium oxide was formed at the surface of Mg particles, and the oxide reduction can be observed owing to the effect of oxide film removal in SPS. The high energy pulsed current flows preferentially through particle contact surfaces, which provides the conditions for the generation of micro-arc between particles and the temperature at the particles contact point can be up to 1979 °C. With the low pressure at the initial sintering stage, local high temperature induced by micro-arc makes the melting (even evaporation) appearance. At the same sintering temperature of 570 °C, the obvious difference in bending strength also demonstrates the significance of spark discharge in SPS. The formation process of sintering neck demonstrates that sintering process is the reflection of melting (even evaporation), diffusion and plastic deformation. In order to realize tiny area and high-quality connection between powder particles, an innovative powder sintering technology using high-frequency pulse electric current (High frequency pulse current assisted sintering) is proposed based on the enlightenment of the skin, proximity and arc discharge effect of high-frequency pulse current. This technology is also instructive for other alloys and engineering materials.

A New Finite-Element Method to Deal With Motion Problem of Electromagnetic Rail Launcher

In dynamic launching processing of the electromagnetic rail launcher (ERL), the armature is sliding along the rail while the pulse current flows through the interface between the armature and rails. The distribution of physical fields at the interface of the rail and the armature is quite complex, and meanwhile they may be phenomena like abrasion, melt, erosion, and cutting, which are typical problems of rapid electrical contact sliding. For numerical analysis of ERL considering the movement of armature at the velocity of v, a new method has been introduced in this paper, which has used $v\cdot A = 0$ as a gauge condition by tree technique in Whitney elements. By this method, the interface condition of E has been satisfied while the continuity of the electric scalar potential $\varphi $ and the magnetic vector A across the interface of two conductor region has also been ensured. Finally, the 2-D and 3-D finite-element model has been built by the edge element method. The results of the model have been analyzed and compared with EMAP3D code’s, which have verified the described methods.

Analysis on heating performance and thermal forming of lightweight alloy using pulse current heating

Abstract Abstract: Pulse current getting through the lightweight alloy sheet could have thermal and non-thermal effects. AlLi alloy and Al MMCs materials were used to study on pulse current heating behaviors and thermal forming performance. The high-intensity pulse current flows through the sheet and generates the tremendous Joule heat. The sheet were heated to forming temperature in several second and arrived at steady state between energy input and losses. The thermal forming set-up using pulse current heating was design and the process parameters were confirmed. The results shows that the channel parts of AlLi alloy and Al MMCs materials were successfully formed and exhibited good shape retention, surface quality, and high geometry accuracy.

Local Structure and Electrochemical Performances of Garnet-like Solid Electrolyte Densified By Spark Plasma Sintering

Garnet-like lithium-ion conducting solid electrolytes attracts great interests for their potential application to all solid state batteries with lithium anode. One of drawbacks of this material is severer sintering condition (typically >1200°C and > 10 h). It has been demonstrated that spark plasma sintering (SPS) successfully accelerates the sintering of garnet-like solid electrolytes like other materials. On SPS, large pulse current flows across grain interfaces to cause high temperature locally and facilitate sintering. It is possible that such locally generated heat would cause inhomogeneity in the obtained specimen. In this paper, we prepared pellets of garnet-like Li6.5La3Zr1.5Ta0.5O12 (LLZT) and investigated the sintering mechanism by focusing on the inhomogeneity inside the pellets. In addition, the ionic conductivity as well as anti-short-circuit properties will be also demonstrated. LLZT powder was synthesized by solid state reactions using LiOH, La2O3, ZrO2 and Ta2O5. Except for Li, other starting materials were mixed with a stoichiometric ratio. Amount of Li source was by 10% higher than the stoichiometric ratio to compensate the loss of Li on the following calcination, which was conducted at 900°C for 10 h in air. Calcined powder was sintered using graphite dies by SPS with a sintering temperature of 900-1100°C, pressure of 12.5-50 MPa and time of 1-30 min under vacuum. Crystalline structure of LLZT powder and sintered pellets were confirmed by XRD. To confirm distribution of phases along depth, XRD profiles were repeatedly recorded after surface of the pellets was polished for certain thickness. On one side of pellets, which corresponds to anode of pulse current of SPS, La2Zr2O7 was observed. This impurity was confirmed only on the anode and disappeared with polishing the surface, suggesting inhomogeneous decomposition, possibly caused by electrolysis. Interestingly, on cathode, no impurity phase was confirmed by XRD. When the La2Zr2O7 is formed as a result of electrolysis, reduction should occur on cathode. The cathode product is possibly amorphous carbon reduced by Li2CO3 that had been produced on surface of LLZT particles by absorption of CO2. The Li2CO3 is supposed to play another role on SPS. When LLZT powder with smaller particle size was used for SPS, more La2Zr2O7 was produced, suggesting the resistance between electrodes were reduced by molten Li2CO3. In addition to the La2Zr2O7, asymmetric impurity formation was visually confirmed. On anode side, the pellets were white, while cathode sides looked dark grey to black. However, the XRD did not show any impurity phases, indicating the origin of the dark color was amorphous. By taking account of the electrolysis of LLZT on anodes to form La2Zr2O7, it is plausible that amorphous carbon was produced on cathodes due to the electrochemical reduction of CO3 2− of Li2CO3. These impurities were formed in the region within ca. 100-300 μm from the surface of pellets for both cathode and anode sides. Therefore, it is necessary to polish pellets for at least 300 μm for both sides before the pellets are used for electrochemical cells. When these impurities were removed, the obtained pellets exhibited very high density of 96% and high ionic conductivity of 7×10−4 S cm−1 at 298 K, which are attractive properties for all solid state batteries. DC polarization was applied to investigate the anti-short-circuit properties of the pellets using a symmetric cell of Li | LLZT | Li. Direct current density was progressively increased from ±20 μA cm−2. Each dc polarization was applied for 30 min. for one direction, and after repeating 5 cycles for both directions, next higher current density was applied. Although short-circuit was confirmed at 200 μA cm−2 (Figure), it was confirmed that the resistance gradually decreased, indicating the dendrite of Li was growing inside the LLZT even at low current density of 20 μA cm−2. The limit current density of 200 μA cm−2 was comparable to reported values on pellets prepared by conventional solid state sintering process. Figure 1

Design and Evaluation of the Driving Coil on Induction Coilgun

Driving coils in a multistage induction coilgun are stacked end to end forming a barrel. During launching, the pulsed current flows through the driving coil, and the electromagnetic force propels the projectile ahead. The driving coil endures not only the radial expansionary force because of the magnetic flux compression, but also the axial force due to the compressive force and counterforce of the projectile. In the process of coil design, both the mechanical strength and the electrical insulation must be considered. Due to the nonlinearity of insulation materials, the theoretical calculation cannot reflect the true state for the driving coil. The conventional static-state test method is analyzed and verified through experiments. The experimental results show that this method is ineffective for the multistage launching, because it neglects the axial counterforce and does not reflect the true state of launching. An improved method for evaluating the coil strength is proposed based on the analysis of the basic principle. The projectile is accelerated by the former stages, and the testing coil accelerates the projectile with an initial speed. Equipment for testing single coil is designed and installed in the muzzle of the existing multistage coilgun. The experimental results show that this method can test the coil's mechanical strength and electrical insulation more effectively than the conventional method. The dynamic-state method can be used to approximately evaluate the performance of different types of the coil. The structure of the driving coil can be improved through testing and evaluating, which provides experimental reference for the multistage induction coilgun design.

Pulsed regime of a spin-injection oscillator

A spin-injection oscillator in the pulsed regime is studied for the first time at different time parameters of current pulses using an opto-acoustic transducer in the absence of chopper. The reciprocity principle is violated when the direction of current in the pulse is reversed in the pulsed regime of the terahertz generation. The radiation signal of the spin-injection emitter is proportional to the number of charges that are injected by a current pulse and does not depend on the energy that is released in the presence of the pulsed current flow.

Bulging of 1420 Al-Li alloy based on Pulse Current

The pulse current auxiliary forming technology has been widely applied for the fabrication of complex sheet metal parts. However, the potential of high-density pulse current to generate high electromagnetic forces, which can be taken as drive forces in forming process, hasn’t been paid enough attention. Compared with the traditional gas bulging technology, bulging based on pulse current has two main advantages. One is that metal sheets can be formed directly by electromagnetic forces instead of the air pressure, and thus the airtightness of die is not an issue. The other is that the forming performance can be improved by the electro plastic effect induced by pulse currents during deformation. In this paper, to validate the effectiveness of this novel method, a special electromagnetic system for bulging of 1420 Al-Li Alloy has been designed and fabricated, in which a high-density pulse current flows through two parallel 1420 Al-Li Alloy sheets in opposite directions to generate repulsive forces for bulging. Finally, both the numerical and experimental studies are carried out to study the forming behaviour of sheets.

Effect of pulse current on thermal performance and deep drawing of SiCp/2024Al composite sheet

The effect of pulse current on heating performance and thermal deep drawing of SiCp/2024Al composite sheets was studied in this work. The high-intensity pulse current flows through the sheet and generates the tremendous Joule heat. The heating performance and temperature distribution were investigated to confirm process parameters. The temperature of specimen is up to around 673 K at a rate of 13.5 K/s under the current density of 21.7 A/mm2. The stainless steel inserts make temperature difference reduced by 73.3 %. Moreover, the workpiece was successfully deep drawn and exhibited good surface quality. The dimensional accuracy achieved within ±0.2 mm.

Observation of internal pulsed current flow through the ZnO specimen in the spark plasma sintering method

In spark plasma sintering (SPS), it is supposed that a part of the large pulsed sintering current flows into the specimen and affects the sintering behavior. To clarify the influence of the internal pulsed current that flows through the specimen during SPS, measurement of the electrical resistance of the specimen was conducted using Pt electrodes and the internal pulsed current was successfully observed using a magnetic probe during the sintering of ZnO and other materials. Two Pt electrodes were installed on the sides of a ZnO sample through a carbon die, and decrease of electrical resistance was observed with the progress of sintering. The internal current that flows through the specimen during SPS was several hundred ampere, and the ratio of the internal current to the total current was found to be dependent on the material and the progress of SPS process.

Analysis of Near Field Noise Voltage Caused by Pulse Current on Power Electronics Circuits

Recently, the design procedure of a power electronics circuit structure is discussed for high power density circuits or thin structure converters. Control circuits of the converter circuit may connect close to the power circuit. When the pulse current flows into the power circuit, it radiates the magnetic field and may generate near field noise voltage to the control circuit. Therefore, it is important for the power electronics circuits to evaluate the near field noise voltage by experiment. This paper shows the measurement results of the near field noise voltage and the electromagnetic force voltage of a small area loop antenna from the 15A, 100kHz buck chopper circuit. Moreover, this paper discusses that the noise voltage may affect the control circuits in the high power density circuits.

Mechanical design of a synchronous rotating machines with Gd-Ba-Cu-O HTS bulk pole-field magnets operated by a pulsed-field magnetization with armature copper coils

We studied a high-temperature superconducting (HTS) synchronous motor assembled with melt-textured Gd-Ba-Cu-O bulk pole-field magnets. The structure of a HTS motor is an axial gap type with neither brushes/slip rings nor iron core. The specific feature is that the rotor pole-field magnets of bulk are magnetized with pulsed current flow through vortex-type armature copper windings. The rotor pole bulks and armature coils are cooled down with liquid nitrogen. Cooling and magnetization of bulk pole field magnets are performed inside of the rotor. The trapped peak magnetic field of more than 0.5 T of the bulk magnets provided the motor performance of 3.1 kW with 720 rpm. In order to attain high output, single rotor plate with 8 bulks was substituted with a twinned rotor plates with 16 bulks together with triple layer armature units. We report on the test results and performance of the present twinned rotor-type HTS synchronous motor.

Quench time lag and its statistical characteristics of NbTi mechanical PCS measured with pulsed current

This paper describes quench time lag characteristics of NbTi mechanical PCS through which pulsed current flows. The quench of the mechanical PCS takes place when the switch current is slowly increased and exceeds a critical value I/sub T0/. On the other hand, quench of the PCS through which pulsed current flows does not occur at the moment of the instantaneous current exceeding I/sub T0/, but takes place after a time delay T/sub D/. The quench time lag T/sub D/ depends on rise time and peak value of the pulsed current I/sub p/. A theoretical model is proposed to show that T/sub D/ corresponds to time in which a superconducting connection bridge is heated up to a critical temperature mainly by flux flow loss. T/sub D/ sharply fluctuates when I/sub p/ is just over the static critical current I/sub T0/, but remarkably decreases when I/sub p/ is further increased. It is found that statistical characteristics of T/sub D/ are well fitted to the Weibull distribution function.

Method and apparatus for charging a secondary battery by supplying pulsed current as charging current

In a method for charging a secondary battery having a positive electrode, a negative electrode, and an electrolyte, a pulsed current is supplied to the secondary battery to make the pulsed current flow between the positive electrode and the negative electrode through the electrolyte to thereby charge the secondary battery. The pulsed current comprises positive pulse current which has a positive pulse amplitude corresponding to a first current density of 1µA/cm2 to 100 mA/cm2 in the positive electrode. However, it may have negative pulse current each following after each positive pulse and having a negative amplitude corresponding to a second current density not greater than a quarter of the first current density.

Transistor Form of Nuclear Particle Detector

A transistor form of nuclear particle detector has been fabricated using 20,000 ohm-cm p-type silicon. With such high resistivity silicon and a wafer 10 mils thick, a bias voltage of 30 to 40 volts extends the depletion layer almost completely through the wafer, leaving a thin p-region so that the whole wafer becomes a transistor. A particle entering the device through the collector depletion layer produces ionization in this layer which is quickly swept out. The charge separation is such that the emitter is forward biased and a transistor pulse current flows subsequent to the collector diode current. The current time characteristics of the device will be shown and the gain of the device will be considered both for light radiation and particle pulse signals. From a detailed consideration of the gain-bias characteristics the lifetime in the base of the transistor can be calculated. This will be compared to the response time of the unit. The detector surface has been shown to have sensitivity variations by comparing the gain of the device obtained with a small light beam at several points on the surface. Variations in sensitivity are indicated by the shape of the resolution curves. Signal to noise ratios obtained are comparable to those realized with good amplifiers and similar area diodes. This, combined with noise and gain data, indicates that the device is amplifying the signal and the collector junction noise current by the same factor. Typical gain figures are 200 to 300.