Helical Flux Compression Generators Research Articles

Design Improvements in Multi-sectional HFCG using Time-varying Skin Depth

Two-dimensional (2D) modelling procedure uses a filamentary-mesh approach and the dynamic matrix concept which are used in Helical Flux Compression Generator (HFCG) design. Although 2D modelling offer results which have been verified experimentally, yet none of the existing 2D-codes include the effect on skin depth that are caused from the high variation of current in very short duration of time. In most published codes, the formula that is used, provides simply a steady-state approximation of the skin depth. The influence of skin depth is represented approximately by using a static expression where frequency is assumed constant. This paper describes a new tactic by using a dynamic time-varying expression for skin depth, which is implemented for use with an existing 2D model. It is shown that effect of high change in current on skin effect is significant than those predicted by the constant skin depth formula.

An Algorithm for Designing of Cascaded Helical Flux Compression Generator

Cascaded helical flux compression generators (Cascaded-HFCG) are widely used to produce powerful current pulses in many industries, while there is no specific method to design these generators in any books or articles. In this paper, firstly some mechanical and electrical criteria are described, and then an algorithm is proposed based on these criteria. A computer code is written using MATLAB based on the proposed algorithm and some programs are prepared in COMSOL to calculate electrical parameters of the generators which can be used in the design procedure. The validity of the proposed algorithm is verified by simulation.

Development of compact explosively driven ferromagnetic seed source for helical magnetic flux compression generator

A compact explosively driven ferromagnetic generator (FMG) is developed for seed power source of helical magnetic flux compression generator (HMFCG). The mechanism of FMG is studied by establishing a magnetoelectric conversion model. Analytical calculations and numerical simulations are conducted on the magnetostatic field of open-circuit magnet in FMG. The calculation method for the magnet’s cross-sectional magnetic flux is obtained. The pulse sources made of different materials and equipped with different initiation modes are experimentally explored. Besides, the dynamic coupling experiments of FMG and HMFCG are carried out. The results show that, N35 single-ended and double-ended initiating FMGs have an energy conversion efficiency ηt not less than 14.6% and 24.4%, respectively; FMG has an output pulse current not less than 4kA and an energy of about 3J on 320nH inductive load; HMFCG experiences energy gains of about 2-3 times. FMG and HMFCG can be coupled to form a full-blast electrical driving pulse source.

Damage growth and recollection in aluminum under axisymmetric convergence using a helical flux compression generator

Damage initiation and evolution, failure, and recollection processes under axisymmetric convergence were studied in the Russian-Damage experimental series, a joint effort between the Los Alamos National Laboratory and the All-Russian Institute of Experimental Physics. A helical explosive magnetic generator was used to drive a cylindrical liner shell to produce shock wave loading of a concentric cylindrical target shell. Shock wave amplitude was controlled by the liner-to-target spacing and by the magnetic field amplitude. Variation of the current pulse duration produced either a single impact, to study damage initiation through failure, or a double impact, to study failure with recollection. Both full and partial recollection of the main crack was obtained. By fielding high-precision diagnostics to measure the dynamic drive conditions and material response and by employing post-shot metallographic analysis, this project produced well-characterized experimental data across a range of damage and recollection levels for the chosen material, aluminum. We present selected experimental results to illustrate the methodology and utility of this experimental technique.

Mathematical simulation of helical flux compression generator physics

Helical flux compression generators (HFCG) are used as sources of powerful peak currents and magnetic field strengths. We propose a numerical method of the HFCG resistance calculation, based on nonlinear magnetic diffusion. The method has been implemented with a two-dimensional HFCG model and demonstrated good agreement with experiments both at small and high conductor heating.

Calculation of Turn Skipping Losses in Helical Flux Compression Generators

In helical flux compression generators, the ohmic and intrinsic flux losses limit severely the performance of them. One of the sources of intrinsic flux losses is the turn skipping flux loss. This paper first introduces an accurate criterion for the prevention of the turn skipping phenomenon in these generators. Then, a novel method is presented to calculate the flux loss due to this phenomenon. In addition, an equivalent resistance is introduced to consider the effect of turn skipping flux loss on the generator performance. The calculation results show that, as soon as the turn skipping occurs, about 30% of a turn flux is lost and this value is increased rapidly with eccentricity increasing. Therefore, it is necessary to prevent this phenomenon as far as possible. The calculated output current of the simulated generator also shows that the maximum current when considering the turn skipping loss is about 15% of the maximum current in the case of ignoring it. Based on the authors' knowledge, quantification of the turn skipping flux losses has not been presented previously in the open literature.

An explosively driven high-power microwave pulsed power system

The increased popularity of high power microwave systems and the various sources to drive them is the motivation behind the work to be presented. A stand-alone, self-contained explosively driven high power microwave pulsed power system has been designed, built, and tested at Texas Tech University's Center for Pulsed Power and Power Electronics. The system integrates four different sub-units that are composed of a battery driven prime power source utilizing capacitive energy storage, a dual stage helical flux compression generator as the main energy amplification device, an integrated power conditioning system with inductive energy storage including a fast opening electro-explosive switch, and a triode reflex geometry virtual cathode oscillator as the microwave radiating source. This system has displayed a measured electrical source power level of over 5 GW and peak radiated microwaves of about 200 MW. It is contained within a 15 cm diameter housing and measures 2 m in length, giving a housing volume of slightly less than 39 l. The system and its sub-components have been extensively studied, both as integrated and individual units, to further expand on components behavior and operation physics. This report will serve as a detailed design overview of each of the four subcomponents and provide detailed analysis of the overall system performance and benchmarks.

螺线管型爆磁压缩发生器快速计算模型

螺线管型爆磁压缩发生器快速计算模型

螺旋型爆磁压缩脉冲发生器电阻及磁通损失的数值计算

螺旋型爆磁压缩脉冲发生器电阻及磁通损失的数值计算

含铝炸药爆轰产物导电式爆磁压缩发生器

含铝炸药爆轰产物导电式爆磁压缩发生器

Calculation of time-varying equivalent inductance and resistance of helical flux compression generators using the 2D filamentary method and dynamic matrix concept in the frequency domain

In this paper we present an approach to calculate the time-varying equivalent inductance and resistance of helical flux compression generators accurately. This approach is based on the 2D filamentary method and uses the dynamic matrix concept. By using this method, it is possible to consider both the effects of the armature presence and frequency on the inductance and resistance of the HFCGs. The latter effect has not been discussed in previous open literature. The validation of the presented method has been verified by measurement results.

A Compact Design for High Voltage Direct Current Circuit Breaker

The absence of current-zero points in the direct current (DC) waveform of high voltage DC (HVDC) circuit breakers makes the interruption process more severe than the case of conventional AC networks with sinusoidal currents. In this way, in the current HVDC networks, a parallel precharged capacitor is inserted to inject the reverse current into the interruption chamber of the vacuum circuit breaker and create the artificial current-zero points. In this paper, a novel method for reverse current injection has been proposed. In this method, two separate helical flux compression generators (HFCGs) have been applied to generate the reverse current and an intense axial magnetic field (AMF), respectively. Numerical simulation of high-current vacuum arc (VA) in the presence of very strong AMF has been presented. For this purpose, the magnetohydrodynamic equations describing the behavior of the VA are coupled to a simple circuit analysis and the previously developed multiphysics model of HFCG. The results indicate that the explosively driven current injection set can make current-zero points properly in a typical HVDC network and lead to successful interruption of fault current. This method needs much less volume and cost in comparison to the parallel precharged capacitor sets.

Fast-charging compact seed source for magnetic flux compression generators

Flux compression generators (FCGs) are some of the most attractive sources of single-use compact pulsed power available today due to their high energy density output and mobility. Driving FCGs requires some seed energy, which is typically provided by applying a high seed current, usually in the kiloampere range for midsized helical FCGs. This initial current is supplied by a high-current seed source that is capable of driving an inductive load. High-current seed sources have typically been comprised of discharging large capacitors using spark gaps and overvoltage triggering mechanisms to provide the prime power for FCGs. This paper will discuss a recent design of a self-contained (battery powered with full charge time less than 40 s), single-use compact seed source (CSS) using solid-state components for the switching scheme. The CSS developed is a system (0.005 m(3) volume and weighing 3.9 kg) capable of delivering over 360 J ( approximately 12 kA) into a 5.20 muH load with a trigger energy of microjoules at the TTL triggering level. The newly designed solid-state switching scheme of the CSS incorporates off-the-shelf high-voltage semiconductor components that minimize system cost and size as necessary for a single-use application. A detailed evaluation of the CSS is presented primarily focusing on the switching mechanics and experimental characterization of the solid-state components used in the system.

Utilization of a Nonexplosive Test Bed for Flux-Compression-Generator Electroexplosive Opening Switches

Helical flux compression generators (HFCGs) of a 50-mm form factor have been shown to produce output energies on the order of ten times the seeded value and a typical deposited energy of 3 kJ into a 3-muH inductor. One way to drive a high-power microwave source with an HFCG is by power conditioning, such as an inductive energy storage system (IESS). The output performance of the IESS is contingent upon the opening switch scheme, usually an electroexplosive fuse. Our previous work involving fuse parameter characterization has established a baseline for potential fuse performance. In order to optimize the electroexplosive wire fuse, we have constructed a nonexplosive test bed which simulates the HFCG output with high accuracy. We have designed and implemented a capacitor-based magnetic switching scheme to generate the near-exponential rise of the HFCG. The use of the nonexplosive HFCG test bed will allow the verification of scalability of the fuse parameter model and also allow testing of exotic fuse materials. The nonexplosive test bed has provided a more efficient method for electroexplosive switch development and has allowed us to expand the study of opening switches. We will also discuss the a priori calculated baseline fuse design and compare the experimental results of the gold-wire-material with the silver-wire-material baseline design. With the results presented, an accurate PSpice model applicable to our 45-kA HFCG systems will be available.

Improved Output Current Rise Time From Modified Helical Flux Compression Generators

Flux compression generators (FCGs) are widely used to generate extremely high power pulses. When a peak current from a seed source is flowing through the generator circuit, the chemical energy of high explosives is used to increase the amplitude of the output current pulse applied to the load. During the transfer of explosive energy to the output electrical pulse, the critical issue is achieving a change in the inductance in a fast and controlled way. There have been many significant experiments on different kinds of FCGs, and almost all of the theoretical models used to describe generator behavior are based on empirical equations. In this paper, simultaneous detonic, electromagnetic, and circuit simulations are used to study the characteristics of helical FCGs. For this purpose, the magnetic field diffusion and losses due to the induced currents in metallic components are considered in more detail. Based on the results of these theoretical considerations, new modifications for the FCG are proposed. It will be shown that the proposed modified FCG geometries yield output current rise times that are about 60% of those achieved with conventional helical FCGs generating the same current pulse amplitudes.

Small Helical Magnetic Flux-Compression Generators: Experiments and Analysis

In order to gain experience in explosive pulsed power and to provide experimental data for modeling, a small high-explosive-driven helical magnetic flux-compression generator (FCG) was designed at the Swedish Defence Research Agency (FOI). The generator, of which three have been built, has an overall length of 300 mm and a diameter of 70 mm. It could serve as the energy source in a pulse-forming network to generate high power pulses for various loads. This paper presents the design of, and tests with, this helical FCG. The generator had an initial inductance of 23 muH and was operated into a load of 0.2 muH. The generator is charged with 0.27 kg of high explosives (PBXN-5). Various types of diagnostics were used to monitor the operation of the generator, including current probes, optical fibers, and piezo gauges. With seed currents of 5.7 and 11.2 kA, final currents of 269 and 436 kA were obtained, corresponding to current amplification factors of 47 and 39. The peak of the current was reached about 30 mus after the time of crowbar. The two generators showed only small losses in terms of 2pi-clocking. Using signals from optical fibers, the deflection angle of the armature could be determined to be 10 deg in good agreement with hydrodynamic simulations of the detonation process and the detonation velocity to be 8.7 km/s in agreement with tabulated value.

Modeling of a Small Helical Magnetic Flux-Compression Generator

In order to gain experience in explosive pulsed power and to provide experimental data as the basis for computer modeling, a small high-explosive-driven helical magnetic flux-compression generator (FCG) was designed at the Swedish Defence Research Agency. The generator, of which three have been built, has an overall length of 300 mm and a diameter of 70 mm. It could serve as the energy source in a pulse-forming network to generate high-power pulses for various loads. This paper presents a simulation model of this helical FCG. The model, which was implemented in Matlab-Simulink, uses analytical expressions for the generator inductance. The model of resistive losses takes into account the heating of the conductors and the diffusion of the magnetic field into the conductors. The simulation results are compared with experimental data from two experiments with identical generators but with different seed currents, influencing the resistive losses. The model is used to analyze the performance of the generator.

Design and implementation of a flux compression generator nonexplosive test bed for electroexplosive fuses

Helical flux compression generators (HFCGs) of a 50mm form factor have been shown to produce output energies on the order of ten times the seeded value and a typical deposited energy of 3kJ into a 3μH inductor. By utilizing an electroexplosive fuse, a large dI∕dt into a coupled load is possible. Our previous work with a nonoptimized fuse has produced ∼100kV into a 15Ω load, which leads into a regime relevant for high power microwave systems. It is expected that ∼300kV can be achieved with the present two-stage HFCG driving an inductive storage system with electroexploding fuse. In order to optimize the electroexplosive wire fuse, we have constructed a nonexplosive test bed which simulates the HFCG output with high accuracy. We have designed and implemented a capacitor based, magnetic switching scheme to generate the near exponential rise of the HFCG. The varying inductance approach utilizes four stages of inductance change and is based upon a piecewise linear regression model of the HFCG wave form. The nonexplosive test bed will provide a more efficient method of component testing and has demonstrated positive initial fuse results. By utilizing the nonexplosive test bed, we hope to reduce the physical size of the inductive energy storage system and fuse substantially.

Initial transient process in a simple helical flux compression generator

An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current density in the stator, is developed by means of a diffusion equation. A relationship between frequency of the conducting current, root of the characteristic function of Bessel equation and decay time in the armature is given. The skin depth in the helical stator is calculated and is compared with the approximate one which is widely used in the calculation of magnetic diffusion. Our analytical results are helpful to understanding the mechanism of the loss of magnetic flux in both the armature and stator and to suggesting an optimal design for improving performance of the helical flux compression generator.

Pulsed high magnetic field sensor using polymethyl methacrylate

We propose and demonstrate the use of polymethyl methacrylate (PMMA) for sensing elements based on the Faraday effect for the measurement of a pulsed high magnetic field generated by helical magnetic flux compression generators (HMCGs). The magneto-optic properties of sensing elements made with PMMA are investigated. The inherent linear birefringence is substantially suppressed by carefully annealing PMMA blocks. The Verdet constant of V = 3.251 rad T−1 m−1 and the normalized temperature dependence of VL (the product of the Verdet constant and the length of the sensing element) of −2.04 × 10−4 °C−1 are measured in the annealed PMMA material. The pulsed high magnetic field of up to ∼27 kG is measured by the sensors made from annealed PMMA and the results are compared with those measured by inductive probes. They are in good agreement within ±1.5%. As an application, the annealed PMMA sensor is used in the measurement of a pulsed magnetic field generated by explosive-driven HMCGs.