Flux Compression Generator Research Articles

Analysis of non-destructive current simulators of flux compression generators.

Development and evaluation of power conditioning systems and high power microwave components often used with flux compression generators (FCGs) requires repeated testing and characterization. In an effort to minimize the cost and time required for testing with explosive generators, non-destructive simulators of an FCG's output current have been developed. Flux compression generators and simulators of FCGs are unique pulsed power sources in that the current waveform exhibits a quasi-exponential increasing rate at which the current rises. Accurately reproducing the quasi-exponential current waveform of a FCG can be important in designing electroexplosive opening switches and other power conditioning components that are dependent on the integral of current action and the rate of energy dissipation. Three versions of FCG simulators have been developed that include an inductive network with decreasing impedance in time. A primary difference between these simulators is the voltage source driving them. It is shown that a capacitor-inductor-capacitor network driving a constant or decreasing inductive load can produce the desired high-order derivatives of the load current to replicate a quasi-exponential waveform. The operation of the FCG simulators is reviewed and described mathematically for the first time to aid in the design of new simulators. Experimental and calculated results of two recent simulators are reported with recommendations for future designs.

Research on Indirect Charging Radio Frequency Explosive Magnetic Flux Compression Generator

It is necessary to make full use of explosive energy and reduce the loss of unnecessary energy when we study high-powered radio frequency explosive magnetic flux compression generator . Therefore, this paper proposed that indirect charging was used in radio frequency explosive magnetic flux compression generator. Based on the equivalent circuit theory, we studied the interaction of two loops in the case of indirect charging. The numerical simulation results showed that we must choose appropriate circuit parameters of charging in order to guarantee the radio frequency explosive magnetic flux compression generator to run steadily.

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.

Theoretical analyses of current amplification in a new kind of plasma magnetic flux compression generator

The physics process in a new kind of plasma magnetic field compression generator (MFCG) without the preliminary magnetic field is studied with a zero-dimensional theoretical model. It is found that the plasma liner is accelerated in the conduction stage and is decelerated in the compression stage. The geometry parameters of MFCG effect the load current amplification significantly. The geometry parameters need to be chosen carefully to make the acceleration space and the deceleration space being suitable for the generator circuit and the injected plasma liner to obtain the optimal amplification factor. For the given driven circuit, the typical amplification factor of load current is greater than 2.

Magnetic Field Probe for Noninvasive Diagnostics of FCG Operation: Simulation and Experiment

2-D simulation of the flux compression generator (FCG) operation enables the calculation of the local magnetic field outside the FCG stator. The magnetic field strength at a certain point outside the FCG stator is shown to be dependent on the stator geometry, the electric current in the FCG circuit, and the snapshot of the armature position with respect to the observation point. The measurements made by the dedicated probe placed on the stator support shell confirm the simulation results. The distinguished points of the time-dependent magnetic field strength make it possible to place the magnetic field probe on the stator support shell for noninvasive diagnostics of the FCG operation.

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.

Fast modeling of flux trapping cascaded explosively driven magnetic flux compression generators

To predict the performance of flux trapping cascaded flux compression generators, a calculation model based on an equivalent circuit is investigated. The system circuit is analyzed according to its operation characteristics in different steps. Flux conservation coefficients are added to the driving terms of circuit differential equations to account for intrinsic flux losses. To calculate the currents in the circuit by solving the circuit equations, a simple zero-dimensional model is used to calculate the time-varying inductance and dc resistance of the generator. Then a fast computer code is programmed based on this calculation model. As an example, a two-staged flux trapping generator is simulated by using this computer code. Good agreements are achieved by comparing the simulation results with the measurements. Furthermore, it is obvious that this fast calculation model can be easily applied to predict performances of other flux trapping cascaded flux compression generators with complex structures such as conical stator or conical armature sections and so on for design purpose.

爆磁压缩发生器与高阻抗负载匹配调制电路

爆磁压缩发生器与高阻抗负载匹配调制电路

爆磁压缩发生器模拟装置的设计与仿真

爆磁压缩发生器模拟装置的设计与仿真

Influences of Capacitance Value Changing in Explosive Magnetic Frequency Generator

Radio frequencies explosive magnetic flux compression generator, which use capacitors as the load, is a kind of maneuverable device for generating and radiating electromagnetic pulse. From the equivalent circuit principle analysis on explosive magnetic frequency generator, the influence of capacitance variation discipline on operation current and oscillation frequency is analyzed based on the further analysis of the influence and comparison of inductance variation discipline on time and frequency characteristic of operation current. Then the center frequency of operation current under the circumstance of adopting different capacitance value when dynamic inductance linear changing has been calculated by software programming.

The investigation of a compact auto-connected wire-wrapped pulsed transformer

For the power conditioning circuit used to deliver power efficiently from flux compression generator (FCG) to the load with high impedance, an air-cored and wire-wrapped transformer convenient in coaxial connection to the other parts is investigated. To reduce the size and enhance the performance, an auto-connection is adopted. A fast and simple model is used to calculate the electrical parameters of the transformer. To evaluate the high voltage capability, the voltages across turns and the electric field distribution in the transformer are investigated. The calculated and the measured electrical parameters of the transformer show good agreements. And the safe operating voltage is predicted to exceed 500 kV. In the preliminary experiments, the transformer is tested in a power conditioning circuit with a capacitive power supply. It is demonstrated that the output voltage of the transformer reaches -342 kV under the input voltage of -81 kV.

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.

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.

Analytical Investigation of Radiation Characteristic for Radio Frequencies Magnetic Flux Compression Generator

Radio frequencies magnetic flux compression generator is capable of producing and radiating ultra high power electromagnetic pulse by compressing magnetic field. As a maneuverable device, radio frequencies magnetic flux compression generator design has been developed and tested, it has been found widespread use in many fields. The radio performance is one of the most important parameters for radio frequencies magnetic flux compression generator. In this paper, the output current and voltage is given based on equivalent circuit model. In a bid to deliberate the radiation characteristic particularly, ring armature is equivalent to loop antenna in the light of electrically small loop antenna theory. The output voltage is used to feed antenna. Through analysis, the values of radiation strengths around radio frequencies magnetic flux compression generator 10 meters 50 meters 100 meters away are given. On the basis of the above analysis and discussion, the radiation characteristic for RF MFCG could be comprehended precisely.

Detonating Cord for Flux Compression Generation using Electrical Detonator No. 33

The paper highlights the use of electrical detonators for magnetic flux compression generator applications which requires synchronisation of two events with precise time delay of tens of ms and jitter within a few ms. These requirements are generally achieved by exploding bridge wire type detonators which are difficult to develop and are not commercially available. A technique has been developed using commercially available electrical detonator no. 33 to synchronise between peak of seed current in stator coil and detonation of explosive charge in armature. In present experiments, electrical signal generated by self-shorting pin due to bursting of electrical detonator has been used to trigger the capacitor discharge and the detonating cord of known length has been used to incorporate predetermined delay to synchronise the events. It has been demonstrated that using electrical detonator and known length of detonating cord, the two events can be synchronised with predetermined delay between 31 and 251 ms with variation of ± 0.5ms. The technique developed is suitable for defence applications like generation of high power microwaves using explosive driven magnetic flux compression generators. Defence Science Journal, 2011, 61(1), pp.19-24 , DOI:http://dx.doi.org/10.14429/dsj.61.30

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

Miniature Explosively Driven High-Current Transverse-Shock-Wave Ferromagnetic Generators

Comprehensive studies of explosively driven ferromagnetic generators (FMGs) have been performed. It has been experimentally established that the initial magnetostatic energy stored in the magnetic element of the FMG (determined by the magnet's maximum energy product (BH)max and its volume), not the residual magnetic flux density Br, is the principal parameter that determines the output energy and the amplitude of the signals produced by the generator. Systematic studies were carried out with miniature high-current FMGs containing Nd2Fe14B high-energy hard ferromagnetic elements having a wide range of sizes. Utilization of transverse-shock demagnetization of Nd2Fe14B magnets (shock wave propagates across the magnetization vector \mmb M) instead of longitudinal-shock demagnetization dramatically changed the design of the FMGs and reduced the mass of the explosives used by two orders of magnitude in comparison with that used in longitudinal FMGs. Data for the initial magnetic flux and shock-induced magnetic flux change in Nd2 Fe14B magnets are presented. It was shown that FMGs with a volume of 25 cm3 are capable of producing pulsed currents with amplitudes of up to 4.4 kA and rise times of 23 μs in the seed coil of a magnetic flux compression generator.

Design Improvements to High-Explosive Pulsed-Power Isentropic-Compression Experiments

A series of 1-D isentropic-compression experiments (ICE) has been initiated using the high-explosive pulsed-power (HEPP) system. Accurate high-stress isentropic equation-of-state (EOS) data had been reported using the HEPP-ICE system. A number of important advantages of the system were demonstrated, including higher stresses, higher accuracy, and larger sample sizes than those of other methods. Several potential design improvements have since been identified and tested. The storage inductor was eliminated, and the experiment was performed before the output of the plate flux compression generator could short-circuit itself. This eliminated the loss of current that occurs when the generator plates bounce apart. A new design of explosively formed fuse opening switch was employed with a multipoint initiation system that reduced the explosive mass, significantly reduced the timing jitter by eliminating air gaps, and minimized flux losses. In addition, with this new switch, the resistance-versus-time profile may be adjusted by controlling the initiation times of its four quadrants. Anomalous results were obtained with the new switch. The results of using this switch in an EOS experiment on pure tantalum are reported.

Modeling and Simulation of Simple Flux-Trapping FCGs Utilizing PSpice Software

A novel modeling and simulation method for flux-trapping flux-compression generators (FT-FCGs) is presented, which utilizes PSpice circuit-simulation software to solve complex differential equations derived from circuit analysis. The primary motivation for the model development is the desire for a technique to rapidly design and prototype FT-FCGs for use as drivers in high-power microwave sources. The derivation of FT-FCG equations will be given, both in the ideal (lossless) and nonideal cases. For the nonideal case, three flux conservation coefficients are added to the equations to account for intrinsic flux loss in the circuit. Time-varying inductance curves are calculated using zero-dimensional models found in literature and adapted to fit this model. A simple FT-FCG design is used as an example to show the steps taken to complete a simulation. The same design was also fabricated and tested for comparison with predicted results from the model. A comparison of the waveforms acquired through simulation and experiment was found to result in good agreement for a given set of values for the flux conservation coefficients. A discussion of the derived equations, both lossless and nonideal, is given, as well as a discussion on the investigation of the impact of the three flux constants on the circuit. Analysis is offered on the results of this investigation, and conclusions are given on the effectiveness of this model to predict FT-FCG behavior.

Conductivity and Permittivity of Hydrogen Under Isentropic Magnetic Compression up to 3 Mbar

An experimental technique for isentropic compression of solid and liquid substances up to ultrahigh pressures is discussed. A pulsed ultrahigh magnetic field up to 1000 T is produced by an explosive flux-compression generator MC-1. A smooth shock-free pulse of pressure in a coaxial metal chamber of few cubic centimeters is obtained. A radio-frequency technique of conductivity and permittivity measurement is applied. The conductivity of solid hydrogen isentropically compressed with the initial temperature less that 14 K was estimated at about 1 (Ohm m)−1 under the pressure of 3 Mbar. A sharp rise of the relative permittivity as a precursor of a metal-insulator transition was observed.