Electromagnetic Acceleration Research Articles

Modular electromagnetic railgun accelerator for high velocity impact studies.

A modular electromagnetic railgun accelerator facility named "RAFTAR" (i.e., Railgun Accelerator Facility for Technology and Research) has been commissioned and its performance has been characterized for high velocity impact testing on materials in a single-shot mode. In the first tests, RAFTAR demonstrated an acceleration of more than 1000m/s for an 8g solid aluminum-7075 armature projectile. The current fed was 220kA, having a muzzle time of about 1.75ms. It is a single pulse breech-fed rectangular bore (14 × 13mm2) railgun, and its 1.15m long barrel assembly consists of two parallel copper bars with an inter-gap of 13mm that are encased within 50mm thick high strength reinforced fiberglass sheets (Garolite G10-FR4) and bolted from both the sides. RAFTAR is powered by two capacitor bank modules that have a maximum stored energy of 160 kJ each (containing eight 178 μF/15kV capacitors), two high power ignitron switches, and a pulse shaping inductor. To obtain consistent acceleration of the armature inside the barrel, reversal of driving current is prevented, and its pulse duration is stretched by tactical integration of the crowbar switch and bitter coil inductor in the circuit. Armature projectile velocity measurement in-bore and outside in free space was performed by the time-of-flight technique using indigenously made miniature B-dot sensors and a novel shorting-foil arrangement, respectively. The time resolved measurement of the in-bore armature evidenced a velocity-skin-effect in the high acceleration phase. There is good agreement between the experimentally measured and theoretically predicted efficiency, confirming the optimal choice of operating parameters. The conclusion summarizes important experimental findings and analyzes the underlying causes that limit the performance of railguns.

Fokker–Planck Simulation of Fast-Ion Kinetics in Z-Pinch Implosion Taking into Account Electromagnetic Acceleration

Fokker–Planck Simulation of Fast-Ion Kinetics in Z-Pinch Implosion Taking into Account Electromagnetic Acceleration

Characteristics of plasma in a novel laser-assisted pulsed plasma thruster

A novel laser-assisted pulsed plasma thruster (LA-PPT) is proposed as an electric propulsion thruster, which separates laser ablation and electromagnetic acceleration. It aims for a higher specific impulse than that achieved with conventional LA-PPTs. Owing to the short-time discharge and the novel configuration, the physical mechanism of the discharge is unclear. Time and spatial-resolved optical emission spectroscopy was applied to investigate the variation in the plasma properties in the thruster discharge channel. The plasma species, electron temperature, and electron density were obtained and discussed. Our investigation revealed that there were H α , H β , H γ , H ε atoms, C I, C II, C III, C IV, Cl I, Cl II particles, and a small amount of CH, C3, C2, H2 neutral molecular groups in the plasma. The electron temperature of the discharge channel of the thruster was within 0.6–4.9 eV, and the electron density was within (1.1–3.0) 1018 cm−3, which shows that the optical emission spectroscopy method is to measure the electron excitation temperature and electron density in heavy particles. But the Langmuir probe method is to measure the temperature and density of free electrons. The use of laser instead of spark plug as the ignition mode significantly changed the plasma distribution in the discharge channel. Unlike the conventional PPT, which has high electron density near the thruster surface, LA-PPT showed relatively large electron density at the thruster outlet, which increased the thruster specific impulse. In addition, the change in the ignition mode enabled the electron density in the LA-PPT discharge channel to be higher than that in the conventional PPT. This proves that the ignition mode with laser replacing the spark plug effectively optimised the PPT performance.

Spectroscopic plasma plume study of a non-volatile liquid-fed pulsed plasma thruster

The development of small satellites weighing as little as 1 kg has accelerated along with the miniaturization of technology. However, there is still a lack of efficient micropropulsion systems at these scales. A possible solution is the pulsed plasma thruster, which has an inherently simple structure that is conducive towards miniaturization. As these thrusters were primarily developed in an era of larger satellites, there are systematic considerations that need to be taken into account. One of these is the propellant, where the conventional solid polytetrafluoroethylene (PTFE) propellant can be replaced with a non-volatile liquid perfluoropolyether (PFPE), enabling liquid-feeding approaches for propellant feeding. The physics behind the operation of a non-volatile liquid-fed pulsed plasma thruster still remains relatively unknown compared with the well-studied solid-fed archetype. We focus here on the use of emission spectroscopy to better understand the spatial distribution and temporal behavior of plasma components within a pulsed plasma thruster using non-volatile liquid PFPE. This is directly compared with solid PTFE to give us an understanding of the similarities and differences between the two propellant types. The overall results suggest that liquid PFPE may be a useful propellant in scenarios with a high thrust-to-power requirement and lower emphasis on electromagnetic acceleration. One such use-case is in coaxial or capillary discharge miniaturized pulsed plasma thrusters, where a significant portion of thrust is obtained from thermodynamic gas expansion rather than electromagnetic acceleration.

The fully-kinetic investigations on the ion acceleration mechanisms in an electron-driven magnetic nozzle

A fully kinetic particle-in-cell study is conducted to investigate the ion acceleration mechanisms in an electron-driven magnetic nozzle. All five powers contributing to the axial kinetic energy of ions are derived and evaluated under different magnetic field strength and inlet density profiles. Among them, the electrothermal and electromagnetic acceleration contributes over 98% of the total accelerating power. The dominating acceleration mechanism is found to be the electrothermal acceleration, covering two thirds of the axial accelerating power in the electron-driven magnetic nozzle. The electromagnetic mechanism is found to originate from four sources, among which the major accelerating and decelerating one are the diamagnetic acceleration driven by radial gradient of electron pressure and the E × B mechanism due to the inward ion detachment. The power induced by the viscous-stress of electrons contributes 14%–23% of the decelerating power, indicating the non-negligible influence of finite electron Larmor radius effect on the ion acceleration. Results indicates that the net effect of electromagnetic mechanism can even be decelerating when the magnetic field is too high with a uniform inlet. Finally, the conversion efficiency from the inlet thermal energy to the ion axial kinetic energy is derived and evaluated, which can reach as high as 65.0% under 0.25 T with a Gaussian-profile inlet. Raising the magnetic field to 0.75 T or a uniform inlet will decrease the conversion efficiency.

Optical Accelerometers for Detecting Low-Frequency Micro-Vibrations

Optical accelerometers are high-precision inertial sensors that use optical measurement technology to achieve high-precision and electromagnetic interference-resistant acceleration measurements. With the intensive research and development of optical accelerometers in recent years, their applications in inertial navigation, structural health monitoring, precision vibration isolation systems, wind turbine fault monitoring, earthquake monitoring, and other low-frequency vibration detection have flourished. Optical accelerometers have various schemes; however, their characteristics vary considerably due to different optical modulation schemes. This study aims to address the lack of systematic evaluation of currently available low-frequency optical accelerometers. Optical accelerometers can be classified into four categories in accordance with their optical modulation schemes: optical path-, optical intensity-, optical phase-, and optical wave-length-modulated accelerometers. The typical performance, advantages and disadvantages, and possible application scenarios of various optical accelerometers are summarized. This study also presents the current status and trends of low-frequency optical accelerometers in consideration of the growing demand for high-precision, low-frequency acceleration measurements.

Structural Performance Optimization Design of Continuously Accelerating Electromagnetic Weft Insertion System

This paper addresses the problem of low electromagnetic weft insertion acceleration performance of extra-large width automatic looms. Based on single-stage electromagnetic weft insertion and multi-stage intermittent electromagnetic weft insertion, a sectional combined continuous acceleration electromagnetic weft insertion design plan is proposed. First, a new type of weft gripper for electromagnetic weft insertion is designed on the basis of the traditional projectile, and a segmented combined structure optimization design is carried out on the 90 mm single-stage coil. Next, the electromagnetic weft insertion movement model is established to analyze the force and movement speed of the gripper during the movement. The amount of work done by the electromagnetic force of the combined coil determines the exit speed of the weft gripper. Finally, in order to find the best parameters of the combined coil structure to meet the requirements of the launch speed, the steady state and transient performance of the segmented combined continuous acceleration coil are analyzed using Maxwell simulation software. The launch performance of the combined coil with different axial lengths of 45 mm, 30 mm, and 15 mm is compared. The results show that the entire acceleration process is more stable and efficient when the combined coil length is 30 mm, the inner diameter is 18 mm, and the number of turns is 600.

Effects of carbon, graphite, and graphene as propellant dopants in a laser-electric hybrid acceleration system

With the combination of laser ablation and electromagnetic acceleration, the laser–electric hybrid thruster is now perceived as an advanced propulsion system to support the precise maneuvering of microsatellites. To improve the performance of a laser–electric hybrid acceleration thruster, we used carbon, graphite, and graphene as dopants to modify the polymeric propellant fed into it. The impulse bit, consumed mass, discharge success rate, specific impulse, momentum coupling coefficient, and efficiency were measured and analyzed. Results showed that these three dopants led to higher values of impulse bit, specific impulse, discharge success rate, efficiency, and momentum coupling coefficient. The samples doped with carbon and graphene yielded better performances than those doped with graphite. Furthermore, the propellant sample made of 5% graphene and 95% polytetrafluoroethylene yielded the highest impulse bit of 394.7 μN·s, largest specific impulse of 1012.05 s, highest momentum coupling coefficient of 16.21 N/MW, and maximal efficiency of 8.21%. Furthermore, we compared the performances of the doped samples at different filling ratios and different operations. It was found that 5% was the optimal doping ratio for the dopants of carbon and graphene, and a higher discharge width could effectively improve the performances of the carbon-doped and graphene-doped samples.

Speed control of a magnetic accelerator using adaptive control techniques

Advanced control algorithms are of great interest in control engineering, they make it possible to guarantee the correct operation of complex systems and improve their performance under adverse operating conditions, thanks to negative output feedback. In this work, two adaptive control algorithms are shown: controllers based on Gain Scheduling and Direct Self-Tuning Regulators, using them to control the velocity of an electromagnetic accelerator and comparing their results with those obtained by a classic PID regulator when the system is operated under adverse operating conditions (setpoint changes, load changes and noise resistance). lt shows how this type of regulators can exceed the performance of classical control algorithms, making them a very attractive alternative for digital systems based on microcontrollers, whose high processing capacity allows them to be easily implemented in a wide variety of processes, including nonlinear dynamical systems.

A predictive model for macro-performances applied to laser-assisted pulsed plasma thrusters

The laser-assisted pulsed plasma thruster is considered a promising propulsion system to support the tasks of microsatellites because of its high specific impulse and low volume. Different from the traditional pulsed plasma thruster, laser-assisted pulsed plasma thruster uses the laser to replace the spark plug for ignition, which can avoid ignition failure and remove the side effect of carbon deposition. Both the thrust efficiency and impulse bit are expected to increase after the plasma flow produced by laser ablation is further ionized and accelerated. Since there are a few macro-performance prediction models in laser-assisted pulsed plasma thrusters, this paper develops a model based on the laser ablation model and electromagnetic acceleration model to capture macro-performances of laser-assisted pulsed plasma thrusters. In this model, the initial velocity and mass of plasma flow can be obtained from the ablation model, and the acceleration model is utilized to describe the electromagnetic acceleration process of plasma flow. With this combined model, the discharge current, voltage, impulse bit, specific impulse, and thrust efficiency can be estimated. The deviation between the predicted results and experimental results was less than 10%, verifying the correctness of the developed model. The effects of different parameters on the performance are further investigated with this model.

Research on electromagnetic orbital accelerator

This paper describes the design process of the electromagnetic track accelerator system from both hardware and software aspects. It adopts three-level track acceleration and three groups of capacitors to store energy, and adds ZVS boost module to realize continuous acceleration of the electromagnetic track. The system works reliably.

Balistik Mühimmat Menzillerinin Hızlandırıcı Fırlatıcı Konsepti Kullanılarak Uzatılmasının Analizi

In this study, the feasibility of a new launcher concept that provides range extension for outdated ballistic munitions by speeding up them before their ignition is examined in detail. To analyze the efficiency of the new concept, multi-variable and single-variable optimization processes are conducted using the Multi-Objective Genetic Algorithm Method in the ModeFrontier environment. Launch angle, ejection velocity of the munition from the launcher, and ignition delay of the rocket motor after the ejection process are determined as design variables. An in-house MATLAB script is prepared and validated to perform numerical solutions of the munition’s two-dimensional trajectory. As a result of the optimization processes, graphical results are prepared to examine the effects of each design variable on munition’s range and to make a comparison between the flight trajectories of the munitions which are launched from classical and accelerator launchers. It is concluded that usage of the accelerator launcher concept provides approximately 20% range extension for the generic munition examined in this research when compared to the classical launcher. Since this new concept can easily be adapted to different types of outdated ballistic munitions and the cost of the accelerator launcher development process will probably less than the cost required to develop new munitions, it will be reasonable to develop accelerator launchers such as electromagnetic accelerators or catapult launchers in near future.

Electrostatic–magnetic hybrid ion acceleration for high-thrust-density operation

To achieve high-thrust-density operation, we propose electrostatic–magnetic hybrid ion acceleration in which the empirical thrust density limit of the electrostatic acceleration is surpassed without violent plasma oscillation by combing the collisional momentum transfer mechanism, which is the ion acceleration mechanism of the electromagnetic acceleration. To achieve hybrid ion acceleration, we experimentally obtained two design criteria: one near anode propellant injection and another at the on-axis hollow cathode location. The thrust characteristics of three thrusters composed of a slowly diverging magnetic field between an on-axis hollow cathode and a coaxially set ring anode were examined. By injecting xenon propellant along the anode inner surface, the electron impact ionization process was enhanced, and generated ions are electrostatically accelerated through the radial-inward potential gradient perpendicular to the axial magnetic lines of force. The hybrid ion acceleration characteristics were obtained only if these two criteria were satisfied and the obtained thrust was consistent with the thrust formula derived for steady-state, quasi-neutral plasma flows. In addition to the criteria, strengthening the magnetic field and enhancing the propellant mass flux were effective for improving thrust density without deteriorating thrust efficiency. Among the experimental conditions in this study, the maximum thrust density was 70 N/m2 with an anode specific impulse of 1200 s, which cannot be achieved in a purely electrostatic thruster with thrust density 6.3 times than that of a typical Hall thruster.

Comparative study of plume characteristics of polymeric propellants filled with different oxides for laser-electric hybrid thruster

Laser-electric hybrid thrusters have attracted increasing attention as a new concept for space propulsion systems because of their low weight, high propulsion performance, and controllable thrust. When the thruster works, the laser-ablation plasma induced by the laser irradiation of a solid target is additionally accelerated by electrical means in the discharge chamber, generating thrust. Therefore, a stable and continuous ablation plume is required to ensure the subsequent electromagnetic acceleration process. This study compared and analyzed the plume characteristics of polymeric propellants doped with different oxides under the same operating conditions. The plume images were examined using an ultrahigh-speed camera, and the plume length, expanding velocity, plume area, and normalized intensity distribution were collected from the plume images based on the image processing method. The results illustrated that the CuO dopant contributed to the rapid, stable, and massive formation of the ablation plume, and VO2 could make the plume have a certain distance from the ablation surface, and then reduce the particle reflux deposition effect to a certain extent. It was also found that the samples doped with CuO, NiO, and Fe2O3 generated a micro cluster with a duration of about 0.5 ms at the beginning of ablation, while the sample doped with VO2 did not generate such a cluster. There were two regions of high-intensity light in the plumes of the samples doped with CuO and VO2. Furthermore, the plume areas of the samples doped with NiO, VO2, and Fe2O3 experienced a quiescence of approximately 2 ms before rapid growth, while that of CuO continued to increase steadily.

The ablation characteristics of laser-assisted pulsed plasma thruster with metal propellant

In this study, a laser-assisted pulsed plasma thruster (LA-PPT) with a novel configuration is proposed as an electric propulsion thruster which separates laser ablation and electromagnetic acceleration. Owing to the unique structure of the thruster, metals can also be used as propellants, and a higher specific impulse is expected. The ablation quality, morphology, and plume distribution of various metals (aluminium alloy, red copper, and carbon steel) with different laser energies were studied experimentally. The ablation morphology and plume distribution of red copper were more uniform, as compared to those of other metals, and the ablation quality was higher, indicating its greater suitability for LA-PPT. The plume generated by nanosecond laser ablation of aluminium alloy expanded faster, which indicated that the response time of the thruster with aluminium alloy as the propellant was shorter. In addition, when the background pressure was 0.005 Pa, an obvious plume splitting phenomenon was observed in the ablation plume of the pulsed laser irradiating aluminium alloy, which may significantly reduce the utilisation rate of the propellant.

Winding vibration analysis of unbalanced transformer based on electromagnetic-mechanical coupling

Aiming at the problem of winding vibration of the transformer under unbalanced operation, the changes in winding current, internal magnetic leakage, and winding vibration characteristics in the three-phase Δ / Y transformer under different operating modes are studied through the electromagnetic-mechanical coupling. To simulate the internal electromagnetic environment of transformer during unbalanced operation state, a three-dimensional finite element simulation model is constructed. Then a dynamic model experiment platform was built to measure winding current and vibration acceleration of transformer under different conditions. The results of simulation and experiment show that the unbalanced phase differs from the normal phase in electromagnetic force and vibration acceleration by about two times, in a 20% unbalanced degree, which seriously endangers the stability of internal structure in transformer. The correctness of this model is verified by the comparison of simulation and experiment. It summarizes the variation law of electric field, magnetic field, and mechanical field of the transformer, and provides a feasible method for the extraction and identification of abnormal characteristics of unbalanced winding operation.

Spatial characteristics of rotating magnetic field (RMF) plasma acceleration method in open magnetic field configuration under partial RMF penetration

In typical electrodeless radio frequency plasma thrusters, application of a rotating magnetic field (RMF) is expected to drive an azimuthal electron current via the non-linear Hall-term effect, resulting in an additional electromagnetic acceleration effect in the presence of a diverging magnetic field. Large increases in ion Mach number and electron density were found, comparing cases with and without the RMF, under a partial RMF penetration into a plasma. Spatial characteristics of the RMF acceleration were investigated to clarify the causes of these increments: 2D profiles of plasma parameters and time-varying RMF components were measured. Partial penetration of the RMF into plasma with a phase retardation was found, but the RMF azimuthal current was driven. Large diamagnetic current derived from the large density gradient also increased by the RMF application. Synergistic acceleration effect derived from the driven RMF current and the density gradient results in the plasma acceleration effect even under the partial penetration.

The Application of a CMR-B-Scalar Sensor for the Investigation of the Electromagnetic Acceleration of Type II Superconductors.

In this paper, we investigated the behavior of a type II superconducting armature when accelerated by a pulsed magnetic field generated by a single-stage pancake coil. While conducting this investigation, we performed a numerical finite element simulation and an experimental study of the magnetic field dynamics at the edge of the pancake coil when the payload was a superconducting disc made from YBa2Cu3O7−x, cooled down to 77 K. The magnetic field measurements were performed using a CMR-B-scalar sensor, which was able to measure the absolute magnitude of the magnetic field and was specifically manufactured in order to increase the sensor’s sensitivity up to 500 mT. It was obtained that type II superconducting armatures can outperform normal metals when the launch conditions are tailored to their electromagnetic properties.

Influence of operating parameters on discharge mode of parallel-rail accelerator

Electromagnetic plasma accelerators which can generate hypervelocity and high density plasma jets have been widely used in the fields of nuclear physics and astrophysics. In this paper, an experimental platform of parallel-rail accelerator electromagnetically driven plasma is established, and the discharge modes under different discharge currents and gas injection conditions are studied through using magnetic probes, a spectrometer and an ICCD. A fast gas valve is used to inject argon into the rail electrode area. The time delay between the fast valve discharge and the parallel-rail accelerator discharge is fixed to be 450 μs. The waveform of power supply of the parallel-rail accelerator is a sinusoidal wave. The total capacitance is 120 μF, the total inductance is about 400 nH, and the maximum current is 170 kA. The fast valve current waveform is a double exponential waveform with a maximum current of 2.5 kA. When the discharge current is 40 kA, a current sheet with a certain thickness is generated, and the current sheet moves through different detection positions along the rail electrode at a certain velocity. Therefore, the working mode of the parallel-rail accelerator is the snowplow mode. As the discharge current increases, the trailing edge of the current channel is fixed during the current rising phase, and starts to move to the end of the rail during the current falling phase. A diffuse distributed current channel is formed, and the parallel-rail accelerator operates in a deflagration mode. As the gas injection mass increases, the current channel front velocity decreases to form a more concentrated distributed current channel, and the discharge mode turns into the snowplow mode. The stationary current channel in the deflagration mode is maintained mainly by ablating the electrode. The operating parameters mainly affect the rail voltage, which in turn affects the discharge mode of the parallel-rail accelerator. The rail voltage increases when the discharge current or the current rate of change increases. If the rail gap behind the current channel cannot withstand the high rail voltage under large discharge current or large current rate of change, the breakdown occurs, which results in the deflagration mode discharge.

Energy Conversions Associated With Magnetic Reconnection

AbstractWe present theoretical and computational analyses of energy conversions in a magnetized collisionless plasma. We first revisit the theoretical approach to energy conversion analysis and discuss the expected correlations between the different conversion terms. We then present results from a Hybrid‐Vlasov simulation of a turbulent plasma, focusing on the immediate vicinity of a reconnection site. Energy transfers are examined locally and correlations between them are discussed in detail. We show a good anticorrelation between pressure‐driven and electromagnetic acceleration terms. A similar but weaker anticorrelation is found between the heat flux and thermodynamic work acting on internal energies. It is the departure from these anticorrelations that drives the effective changes in the species’ kinetic and internal energies. We also show that overall energy gain or loss is statistically related to the local scale of the system, with higher conversion rates occurring mostly at the smallest local plasma scales. To summarize, we can say that the energization and de‐energization of a plasma is the result of the complex interplay between multiple electromagnetic and thermodynamic effects, which are best taken into account via such a point‐by‐point analysis of the system.