Magnetic Flux Compression Research Articles

Space experiments using superconducting magnet technology

We report on a fast-track experiment on the International Space Station (ISS) with the Earth’s magnetic field, which has been recognized as a major task for a better understanding of our planet. For this purpose, YBCO bulk superconductors have been prepared, transported and stored on board the ISS. The properties of single grain superconducting bulk will be investigated before and after the ISS experiments. In parallel, the magnetic interaction between BEarth and our YBCO bulk was investigated. An external 3D Helmholtz coil cancels unwanted electromagnetic fields down to 5 μT. Highly sensitive flux-gate sensors monitored the magnetic configuration as the ceramic plate was cooled to cryogenic temperatures. Shielding and field concentration effects of the Earth’s magnetic field were observed and discussed. Thermally induced magnetic flux compression for future long-duration space missions was successfully tested, enabling future spacecraft shielding and braking functions.

Role of magnetic pressure forces in fluctuation dynamo saturation

ABSTRACT Using magnetohydrodynamic simulations of fluctuation dynamos in turbulent flows with rms Mach numbers $\mathcal {M}_{\rm rms}= 0.2, 1.1$, and 3, we show that magnetic pressure forces play a crucial role in dynamo saturation in supersonic flows. First, as expected when pressure forces oppose compression, an increase in anticorrelation between density and magnetic field strengths obtains even in subsonic flows with the anticorrelation arising from the intense but rarer magnetic structures. In supersonic flows, due to stronger compressive motions density and magnetic field strength continue to maintain a positive correlation. However, the degree of positive correlation decreases as the dynamo saturates. Secondly, we find that the unit vectors of ∇ρ and ∇B2 are preferentially antiparallel to each other in subsonic flows. This is indicative of magnetic pressure opposing compression. This antiparallel alignment persists in transonic and supersonic flows at dynamo saturation. However, compressive motions also lead to the emergence of a parallel alignment in these flows. Finally, we consider the work done against the components of the Lorentz force and the different sources of magnetic energy growth and dissipation. We show that while in subsonic flows, suppression of field line stretching is dominant in saturating the dynamo, the picture is different in supersonic flows. Both field line stretching and compression initially amplifies the field. However, growing magnetic pressure opposes further compression of magnetic flux which tends to reduce the compressive motions. Simultaneously, field line stretching also reduces. But, suppression of compressive amplification dominates the saturation of the dynamo.

압축구조 개선을 통한 분로리액터의 소음 저감에 관한 연구

Recently, with the development of the city center around the substation, complaints about noise are increasing. Shunt reactors are a major source of noise in substations. To reduce the noise of the shunt reactor, research on the magnetic circuit and structural design for optimizing the compression distribution are important. In this paper, the magnetic flux distribution and compression distribution of the magnetic element were calculated using a finite element analysis program, and the reduction effect was analyzed by measuring the noise. Introducing a study that improved the distribution of magnetic flux by applying a magnetic flux control panel to the vibration caused by the magnetomotive force generated from the magnetic element, and reduced noise by changing the shape of the compression structure.

Study on electrical conductivity of detonation products of aluminized explosives

Using the thermodynamic equilibrium constant method and JWL-Miller equation of state, based on the calculation of the thermodynamic parameters such as the composition, pressure, and explosion temperature of the detonation products of aluminized explosives in the Magnetocumulative generator, the Saha ionization equation, and gas conductivity calculation model are used to write Matlab code to calculate the electron density and conductivity of the detonation products of the magnetic flux compression generator. The temporal and spatial variation law of electron density and conductivity is revealed. The simulation shows that the thickness of the maximum conductivity layer in the detonation process is about 1 mm and moves at a uniform speed following the CJ surface. The maximum conductivity of HMX/Al (70/30) is 1.88e5 Ω−1·m−1, with an error of 6%, and the maximum conductivity of RA1 (HMX / DNAN / Al) is 2.7e4 Ω−1·m−1

Development of a transient complex impedance measurement device used in quasi-isentropic compression experiments.

A complex impedance measurement device with a short response time and high noise immunity is presented in this paper. The device based on a radio-frequency reflectometer was specially developed for electro-physical property investigations of materials in quasi-isentropic compression experiments. The maximum operating frequency of the device is up to 600MHz for reducing intense low-frequency noises. Meanwhile, an off-line signal processing code was developed to improve the response time of the device to less than 10ns. Using the device, the complex impedance and electrical conductivity of water compressed by an explosive-driven magnetic flux compression generator were measured, and an abrupt change in the complex impedance of water caused by a liquid-solid transition was directly observed under intense electromagnetic interference.

Effect of laser preheat in magnetized liner inertial fusion at OMEGA

Integrated magnetized liner inertial fusion (MagLIF) experiments on the OMEGA laser system are modeled to investigate the effects of laser preheat on implosion performance. In both simulations and experiments, preheating the fuel with a laser enhances the neutron yield, with the maximum yield occurring at an optimal preheat laser energy. Increasing the preheat energy past the optimal value reduces the neutron yield. In simulations, the rate of the drop in neutron yield depends on the inclusion of the Nernst effect. The Nernst effect advects the magnetic field away from the center of the fuel region during the preheat stage of MagLIF on OMEGA and weakens magnetic-flux compression. If the Nernst effect is not included, the simulated drop in yield past the optimal preheat laser energy is more gradual as opposed to the sharper drop seen in experiments. Simulations are able to model trend in measured ion temperatures seen in experiments. A mix model is used to show that including mix from the wall in the simulated fuel region further degrades the yield and lowers the optimal preheat laser energy. Simulations with mix predict that increasing the initial axial magnetic field may still enhance yield performance in integrated implosions.

Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets

This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realizable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10 kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally driven or current-driven transport is dominating.

New Evidence of Interaction Between Grain and Boundaries Subsystems in Granular High-Temperature Superconductors

Granular high-temperature superconductors (HTSs) exhibit magnetotransport properties, including the clockwise magnetoresistance hysteresis. The hysteresis is explained by the concept of an effective field in the subsystem of grain boundaries, where the observed dissipation occurs. The effective field in the intergrain medium is determined by a superposition of the external field H and the field induced by the magnetic response of HTS grains. The magnetic flux compression in the intergrain medium provides an increase of the effective field. The magnetoresistance hysteresis of polycrystalline YBa2Cu3O7-δ has a bright feature: In a fairly wide external field range, the hysteresis width ΔH(H) is found to be almost linear, ΔH ≈ H. This behavior is considered to be universal over the entire temperature range corresponding to the superconducting state (the investigations have been carried out at temperatures of 77 K and 4.2 K). The analysis of the magnetoresistive and magnetic properties has shown that the upper boundary of the field range of the ΔH ≈ H regime is consistent with the field of complete penetration into HTS grains. This is indicative of the strong interrelation between the magnetotransport and magnetic properties of granular HTSs.

Magneto-induced Mullins effect of anisotropic MREs under compression mode

The filled elastomer materials exhibit obvious stress-softening phenomenon after initial stretching, which is called the Mullins effect. Since magnetorheological elastomers tend to work under a magnetic field, it will show a different magneto-induced Mullins effect of traditional materials. Therefore, in this paper, the effects of anisotropy, magnetic flux density, pre-strain and compression times on the magneto-induced Mullins effect were studied by rheometer. The results demonstrated that, under a fixed magnetic flux density, when the arrangement of magnetic particles is perpendicular to the magnetic field, the residual strain energy of the material is the smallest. This indicates that the magneto-induced Mullins effect is the weakest and the stability of the material is the best. Meanwhile, when the compression pre-strain is constant, the materials will show an obvious stress-hardening phenomenon under magnetic field. When the arrangement of magnetic particles is 30° to the magnetic field, the force between the particles is the smallest. This indicates that the magneto-induced Mullins effect is the weakest and the performance stability is the best. At the same time, this paper attempts to establish the corresponding model of the magneto-induced Mullins effect from the perspective of strain energy. The error between the fitting and the experimental results is less than 3%, which shows that the model can well explain the phenomena obtained in the experiment.

Универсальность поведения гистерезиса магнитосопротивления и его температурной эволюции для гранулярных высокотемпературных сверхпроводников Y-Ba-Cu-O

The work is devoted to the establishment of regularities in the behavior of the magnetoresistance hysteresis R(H) of granular high-temperature superconductors (HTS) of the yttrium system. We carried out a comparative study of the magnetotransport properties of granular HTSC samples, which have (i) approximately the same magnetic properties and temperatures of the onset of the superconducting transition (90.5–93.5 K, which characterizes HTS grains) and (ii) different values of the transport critical current JC (which characterizes the intergrain boundaries). Despite the significant scatter in the JC values (more than an order of magnitude) of the three samples studied, a universal behavior of the magnetoresistance hysteresis was found, apparently inherent in all granular Y-Ba-Cu-O. The R(H) hysteresis is very wide, and in a sufficiently large interval of the external field, the dependence of the hysteresis width of the magnetoresistance H on the field Hdec (external field H = Hdec for a decreasing hysteresis branch) is close to a linear function: H ≈ Hdec. This behavior is observed for the entire temperature range of realization of the superconducting state (the studies were carried out at temperatures of 77–88 K and 4.2 K). The explanation of the obtained result is based on the concept of consideration the effective field in the intergrain boundaries. This effective field is the superposition of the external field and the field induced by the magnetic moments of the grains. The field induced by the grains, in turn, is significantly enhanced in the region of intergrain boundaries due to the effect of the magnetic flux compression (the length of the intergrain boundaries is several orders of magnitude smaller than the size of the HTS grains). The above is confirmed from the analysis of the R(H) hysteresis for a composite HTS sample based on Y-Ba-Cu-O and CuO, in which the length of the intergranular boundaries is purposefully increased, as a result, the effect of the flux compression is less pronounced, and the hysteresis R(H) narrows.

Evolution characteristic of axial magnetic field and Nernst effect in magnetized liner inertial fusion

Axial magnetic field is one of the main parameters of magnetized liner inertial fusion (MagLIF), which is greatly different from other traditional inertial confinement fusion configurations. The introduce of axial magnetic field dramatically increases energy deposit efficiency of alpha particles, when initial <i>B</i><i><sub>z</sub></i> increases from 0 to 30 T, the ratio of deposited alpha energy rises from 7% to 53%. In the MagLIF process, the evolvement of magnetic flux in fuel can be roughly divided into three main stages: undisturbed, oscillation, and equilibrium. The distributions and evolution characteristic of axial magnetic field are both determined by the liner conductivity, fuel conductivity, and the fluid dynamics. The pressure imbalance between fuel and liner, caused by laser injection, is the source of fluid oscillation, which is an intrinsic disadvantage of laser preheating method. This fluid oscillation does not lead the magnetic flux to decrease monotonically in the fuel during implosion process, but oscillate repeatedly, even increase in a short time. Nernst effect plays a negative role in MagLIF process. As initial axial magnetic field decreases from 30 to 20 to 10 T, the Nernst effect causes magnetic flux loss to increase from 28% to 44% to 73% correspondingly, and the deposited alpha energy ratio drops from 44% to 27% to 4% respectively. So the initial magnetic field is supposed to be moderately high. The radial distribution of temperature in fuel should be as uniform as possible after preheating, which is helpful in reducing the influence of Nernst effect. Compared with Nernst effect, the end loss effect is much responsible for rapid drawdown of fusion yield. A large number of physical images are acquired and summarized through this work, which are helpful in understanding the process of magnetic flux compression and diffusion in MagLIF process. The simulation can act as a powerful tool and the simulation results can serve as a useful guidance for the future experimental designs.

Механизмы, определяющие гистерезис магнитосопротивления гранулярного ВТСП в присутствии парамагнитного вклада, на примере HoBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=-

The hysteretic magnetoresistance of granular high-temperature superconductor (HTSC) HoBa2Cu3O7-δ is investigated. Superconductors of the YBCO family with magnetic rare earth elements (Nd, Ho, Er, Sm, Yb, Dy) in place of yttrium are characterized by a significant paramagnetic contribution to the total magnetization. Impact of this paramagnetic contribution on the magnetotransport properties is analyzed using the concept of an effective field in an intergranular medium. Lines of magnetic induction from paramagnetic moments do not concentrate in intergranular boundaries, and, thus, have an insignificant effect on magnetotransport properties of granular HTSC. At the same time, there are strong concentration of magnetic flux in the intergranular boundaries due to Meissner currents and Abrikosov vortices. This magnetic flux compression determines the magnetotransport properties of granular HTSCs, including YBCO with magnetic rare earth elements.

Model of the Behavior of a Granular HTS in an External Magnetic Field: Temperature Evolution of the Magnetoresistance Hysteresis

A model for describing the magnetoresistance behavior in a granular high-temperature superconductor (HTS) that has been developed in the last decade explains a fairly extraordinary form of the hysteretic R(H) dependences at T = const and their hysteretic features, including the local maximum, the negative magnetoresistance region, and the local minimum. In the framework of this model, the effective field Beff in the intergrain medium has been considered, which represents a superposition of the external field and the field induced by the magnetic moments of HTS grains. This field can be written in the form Beff(H) = H + 4παM(H), where M(H) is the experimental field dependence of the magnetization and α is the parameter of crowding of the magnetic induction lines in the intergrain medium. Therefore, the magnetoresistance is a function of not simply an external field, but also the “internal” effective field R(H) = f(Beff(H)). The magnetoresistance of the granular YBa2Cu3O7 – δ HTS has been investigated in a wide temperature range. The experimental hysteretic R(H) dependences obtained in the high -temperature range (77–90 K) are well explained using the developed model and the parameter α is 20–25. However, at a temperature of 4.2 K, no local extrema are observed, although the expression for Beff(H) predicts them and the parameter α somewhat increases (~30–35) at this temperature. An additional factor that must be taken into account in this model can be the redistribution of the microscopic current trajectories, which also affects the dissipation in the intergrain medium. At low temperatures under the strong magnetic flux compression (α ~ 30–35), the microscopic trajectories of the current Im can change and tunneling through the neighboring grain is preferred, but the angle between Im and Beff will be noticeably smaller than 90°, although the external (and effective) field direction is perpendicular to the macroscopic current direction.

Estimation of the electromagnetic screens efficiency for the compensation of slot leakage fluxes in the pulsed electromechanical generator

Purpose. There are considered in the paper the four possible configurations of electromagnetic screens for compensation of the flux leakage of slots in the electromechanical pulse generator with a compression of magnetic flux. It is underlined the expediency of slot leakage inductance reduction as the method for increasing of coefficient of magnetic energy amplification in the process of flux compression. Methodology. Efficiency of each configuration of screens has been evaluated on the reduction of slot leakage inductance magnitude. To realize it the problem of pulsed field distribution in the teeth zone of generator has been solved by the finite elements method with application of professional version of software program QuickField v.6.1. Originality. There was manufactured the physical model of teeth zone in which the active conductor of slots was divided on 9 parallel sections along the height of slot. Results. With current supply from the source of alternating current at frequency 400 Hz that was measured a current distribution between the sections of active conductor both at the absence of electromagnetic screens and at their presence. Practical value. It is shown, that screening of slot leakage flux provides the more uniform distribution of current along the sections of active conductor with a corresponding reduction of slot leakage inductance..

One-dimensional integrated simulations of magnetized liner inertial fusion

Magnetized liner inertial fusion (MagLIF) integrates the advantages of traditional magnetic confinement fusion with those of inertial confinement fusion, and thus has promising potentials because theoretically it can dramatically lower the difficulties in realizing the controlled fusion. For the systematic simulating of MagLIF, we build up an integrated one-dimensional (1D) model to describe the complex process, which includes the terms of magnetization, laser preheating, liner implosion, fusion reaction, end loss effect, and magnetic flux compression. According to this model we develop an integrated 1D code–MIST (magnetic implosion simulation tools) , and specifically we propose a simplified model to describe the end loss effect based on the flow bursting theory, so the code is able to consider two-dimensional effects within 1D calculations. We also present a specific expression of magnetic diffusion equation where the Nernst effect term is taken into consideration, which is very important if there exists a temperature gradient perpendicular to magnetic field lines. Such conditions are fully satisfied in the MagLIF process. We use experimental data of aluminum liner implosions to verify the magneto-hydrodynamic module of our code, those shots (0607 & 0523) are performed on FP-1 facility (2 MA, 7.2 μs), and results show good agreement with the calculated velocity of inner flyer or target surface and other measurements. Comparison with code LASNEX and HYDRA (used by Sandia Laboratory) is also made to assess the fusion module, and the results show that our calculations are physically self-consistent and roughly coincide with the results from LASNEX and HYDRA, a key difference appears at fuel temperature, and the factors that might cause this difference are discussed. With this integrated model and 1D code, our work would provide a powerful tool for the future experimental research of MagLIF.

Модель поведения гранулярного ВТСП во внешнем магнитном поле: температурная эволюция гистерезиса магнитосопротивления

Abstract A model for describing the magnetoresistance behavior in a granular high-temperature superconductor (HTS) that has been developed in the last decade explains a fairly extraordinary form of the hysteretic R ( H ) dependences at T = const and their hysteretic features, including the local maximum, the negative magnetoresistance region, and the local minimum. In the framework of this model, the effective field B _eff in the intergrain medium has been considered, which represents a superposition of the external field and the field induced by the magnetic moments of HTS grains. This field can be written in the form B _eff( H ) = H + 4πα M ( H ), where M ( H ) is the experimental field dependence of the magnetization and α is the parameter of crowding of the magnetic induction lines in the intergrain medium. Therefore, the magnetoresistance is a function of not simply an external field, but also the “internal” effective field R ( H ) = f ( B _eff( H )). The magnetoresistance of the granular YBa_2Cu_3O_7 – δ HTS has been investigated in a wide temperature range. The experimental hysteretic R ( H ) dependences obtained in the high -temperature range (77–90 K) are well explained using the developed model and the parameter α is 20–25. However, at a temperature of 4.2 K, no local extrema are observed, although the expression for B _eff( H ) predicts them and the parameter α somewhat increases (~30–35) at this temperature. An additional factor that must be taken into account in this model can be the redistribution of the microscopic current trajectories, which also affects the dissipation in the intergrain medium. At low temperatures under the strong magnetic flux compression (α ~ 30–35), the microscopic trajectories of the current I _ m can change and tunneling through the neighboring grain is preferred, but the angle between I _ m and B _eff will be noticeably smaller than 90°, although the external (and effective) field direction is perpendicular to the macroscopic current direction.

Laser-driven magneto-inertial fusion with magnetized cylindrical target

Laser-driven magneto-inertial fusion assumed plasma and magnetic flux compression by quasisymmetric laser-driven implosion of magnetized target. We develop a 1D radiation magnetohydrodynamic code and a formulation for the one-fluid two-temperature equations for simulating compressible non-equilibrium magnetized target plasma. Laser system with pulse radiation with 10 ns duration is considered for numerical experiments. A numerical study of a scheme of magnetized laser-driven implosion in the external magnetic field is carried out.

Optimal Design and Testing of the Driving Coil on Induction Coilgun

The driving coil, as a key element of synchronous induction coilgun, 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 armature. Dielectric breakdown and mechanical structure damage occurs frequently. Meanwhile, the driving coil should have high energy conversion efficiency as a pusher to accelerate the armature. Therefore, it is important to choose the appropriate structure and parameters in order to achieve a high launching performance. In this paper, the factors that influence the system efficiency are analyzed first. Different structure designs of the driving coil with the same inductance are evaluated. The effect of different calibers on the system efficiency is analyzed. The simulation result shows that the structure of the driving coil should be chosen according to the practical launching requirement while the magnetic coupling should be increased. Second, the electromagnetic force applied on the coil is calculated and the stress is analyzed. The thickness and displacement of the containment are calculated on the condition of unyielding. In order to validate the accuracy of the theoretical analysis, an electromagnetic-mechanical coupling finite element model is built. Comparing two calculation results, the error is small. Therefore, the method can be used to guide the design of the driving coil. Finally, a driving coil is fabricated according to the calculation results and experimented through static and dynamic tests. The experimental results show that the driving coil performs well and have high conversion efficiency. It provides a theoretical and experimental basis for the future design of multistage induction coilgun.

A Compact Explosive-Driven Flux Compression Generator for Reproducibly Generating Multimegagauss Fields

Explosive-driven magnetic flux generator is one of the most efficient techniques for producing ultrahigh magnetic fields in a relatively large volume. To create a more reliable system suitable for extreme magnetic fields applications, a compact explosive-driven magnetic flux compression system with a small amount of explosive for generating multimegagauss fields was developed. In this paper, the design for reproducibly generating megagauss fields, and the experimental results of this generator are presented in detail. The experimental results show that peak fields in the range of 580–710 T can be reliably generated by the generator with about 3-kg Comp-B explosive.

Demagnetization Process Analysis and Numerical Simulation of Magnet with Shock Wave from Compact Explosively Driven Ferromagnetic Generator

For compact explosively driven ferromagnetic impulse source used in magnetic flux compression generators, the relations between the magnet’s demagnetization rate and the shock wave pressure are theoretically analyzed. A nonlinear finite element method is adopted to conduct numerical simulation on the magnet’s impact loading process. The propagation rules and pressure distributions of shock wave within hollow cylindrical NdFeB magnet caused by lateral impact of single-ended and double-ended initiating explosives are explored. The numerical simulation results show that, the pressures at both ends resulting from lateral impact of double-ended initiating explosives on hollow cylindrical magnet are low; double-ended initiating has faster demagnetization rate, swifter variation of flux and higher electromotive force of inductive output than single-ended initiating.