Strong Pulsed Fields Research Articles

Superconducting memory and trapped magnetic flux in ternary lanthanum polyhydrides

Superconducting memory is a promising technology for data storage because of its speed, high energy efficiency, non-volatility, and compatibility with quantum computing devices. However, the need for cryogenic temperatures renders superconducting memory an extremely expensive and specialized device. Ternary lanthanum polyhydrides, due to their high critical temperatures of 240–250 K, represent a convenient platform for studying effects associated with superconductivity in disordered granular systems. In this work, we investigate trapped magnetic flux and memory effects in recently discovered lanthanum-neodymium (La,Nd)H10 and lanthanum-scandium (La,Sc)H12 superhydrides at a pressure of 175–196 GPa. We use a steady magnetic field of a few Tesla (T) and strong pulsed fields up to 68 T to create the trapped flux state in the compressed superhydrides. We find a clockwise hysteresis of magnetoresistance in cerium CeH9-10 and lanthanum-cerium (La,Ce)H10+x polyhydrides, a characteristic feature of granular superconductors. A study of the current-voltage characteristics and voltage-temperature curves of the samples with trapped magnetic flux indicates a significant memory effect in La-Sc polyhydrides already at 225–230 K.

Coherent excitation energy transfer processes in two-dimensional para-sexiphenyl molecular clusters

Excitation energy transfer is one of the most important factors affecting the applications of para-sexiphenyl devices. The study of exciton dynamics and exciton coherence effect of para-sexiphenyl clusters under external field excitation is important in order to improve the performance of molecular devices composed of para-sexiphenyl and its related derivatives. In this work, the two-dimensional disc-like para-sexiphenyl molecular cluster is used as the object of study. The molecular system is simplified into a two-level model based on its structural features and energy level distribution. Within the framework of density matrix theory, the exciton dynamics and exciton coherence behavior of disk-like para-hexaphene molecular clusters excited by different pulse fields are analyzed through using the mathematical mean value approximation of the operator. The results show that when long pulses are used to excite para-sexiphenyl clusters, the single exciton state characteristic appears and is insensitive to the change of excited external field strength. When the clusters are subjected to strong pulsed fields with short pulse widths, multiple excitons are excited simultaneously in the cluster, forming multiple exciton states, with the exciton energy levels shifting toward lower energy and new hybrid states appearing. In the optical response spectrum, there appear multiple resonance peaks. And as the pulse field is enhanced, the multi-exciton effect becomes apparent and the hybridization energy level increases. Under short pulse excitation, the excited states are distributed differently in different energy regions, but all of them show obvious symmetry. As the highest-energy exciton states of H-type clusters are preferentially excited, we analyze the exciton state population and the exciton coherence evolution with time in the high-energy exciton state. With the pulse field increases, Rabi oscillations appear and the exciton coherence effect increases. When the pulsed field reaches a certain field strength, the exciton oscillation cooperativity disappears in the first 100 fs, showing the non-local characteristic. The position of the wave trough of the exciton state population corresponds to the peak in the exciton coherence size. It indicates that when the pulse field is intense enough, a large number of molecules are in the exciton coherent state during the pulsed excitation, and transient out-of-domain phenomena occur.

All-optical pulse switching with a periodically driven dissipative quantum system.

All-optical switching used to switch the input optical signals without any electro-optical conversion plays a vital role in the next generation of optical information processing devices. Even all-optical switchings (AOSs) with continuous input signals have been widely studied, all-optical pulse switchings (AOPSs) whose input signals are pulse sequences have rarely been investigated because of the time-dependent Hamiltonian, especially for dissipative quantum systems. In this paper, we propose an AOPS scheme, where a strong pulsed field is used to switch another pulsed input signal. With the help of Floquet-Lindblad theory, we identify the control field that can effectively turn on/off the input signal whose amplitude envelope is a square-wave (SW) pulse train in a three-level dissipative system. By comparing the properties of the AOPSs controlled by a continuous-wave (CW) field and an SW control field, we find that the SW field is more suitable to be a practical tool for controlling the input SW signal. It is interesting to impress that the switching efficacy is robust against pulse errors. The proposed protocol is readily implemented in atomic gases or superconducting circuits and corresponds to AOPSs or all-microwave pulse switchings.

Maintaining Constant Pulse-Duration in Highly Dispersive Media Using Nonlinear Potentials

A method is shown for preventing temporal broadening of ultrafast optical pulses in highly dispersive and fluctuating media for arbitrary signal-pulse profiles. Pulse pairs, consisting of a strong-field control-pulse and a weak-field signal-pulse, co-propagate, whereby the specific profile of the strong-field pulse precisely compensates for the dispersive phase in the weak pulse. A numerical example is presented in an optical system consisting of both resonant and gain dispersive effects. Here, we show signal-pulses that do not temporally broaden across a vast propagation distance, even in the presence of dispersion that fluctuates several orders of magnitude and in sign (for example, within a material resonance) across the pulse’s bandwidth. Another numerical example is presented in normal dispersion telecom fiber, where the length at which an ultrafast pulse does not have significant temporal broadening is extended by at least a factor of 10. Our approach can be used in the design of dispersion-less fiber links and navigating pulses in turbulent dispersive media. Furthermore, we illustrate the potential of using cross-phase modulation to compensate for dispersive effects on a signal-pulse and fill the gap in the current understanding of this nonlinear phenomenon.

A Test Method for Linear Frequency Modulated Strong Pulse Field Using Time-Frequency Combination

In order to measure the linear frequency modulated (LFM) strong pulse field generated by high-power radars, a test method using time-frequency combination is proposed. On the basis of deriving the expressions of LFM pulse signal power, a measurement and evaluation method in time domain is given. According to the principle of root mean square (RMS) detection, a measurement and evaluation method in frequency domain is put forward. Through the combination of the two, the parameters of the LFM pulse field can be obtained such as the peak field strength, average field strength, pulse width, pulse repetition period and spectrum distribution. If the resolution bandwidth for the spectrum analyzer is greater than the occupied bandwidth of the LFM pulse signal, the measured results in the time domain and frequency domain can be mutually verified. The experiments are carried out to verify the method. The results show that the measured deviations of the peak field strength and average field strength of the LFM pulse field are not more than 2 dB, which indicates the test method is effective and feasible. It can meet the measurement requirements of LFM strong pulse field even if modulation parameters are unknown.

General Regularities and Differences in the Behavior of the Dynamic Magnetization Switching of Ferrimagnetic (CoFe2O4) and Antiferromagnetic (NiO) Nanoparticles

In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe2O4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force HC at the dynamic magnetization switching is markedly higher than HC at quasi-static conditions. HC increases as the pulse duration τP decreases and the maximum applied field H0 increases. The dependence of HC on field variation rate dH/dt = H0/2τP is a unambiguous function for CoFe2O4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH/dt, and the value of applied field H0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.

High Field MicroMRI Velocimetric Measurement of Quantitative Local Flow Curves.

Performing rheo-microMRI velocimetry at a high magnetic field with strong pulsed field gradients has clear advantages in terms of (chemical) sensitivity and resolution in velocities, time, and space. To benefit from these advantages, some artifacts need to be minimized. Significant sources of such artifacts are chemical shift dispersion due to the high magnetic field, eddy currents caused by the pulsed magnetic field gradients, and possible mechanical instabilities in concentric cylinder (CC) rheo-cells. These, in particular, hamper quantitative assessment of spatially resolved velocity profiles needed to construct local flow curves (LFCs) in CC geometries with millimeter gap sizes. A major improvement was achieved by chemical shift selective suppression of signals that are spectroscopically different from the signal of interest. By also accounting for imperfections in pulsed field gradients, LFCs were obtained that were virtually free of artifacts. The approach to obtain quantitative LFCs in millimeter gap CC rheo-MRI cells was validated for Newtonian and simple yield stress fluids, which both showed quantitative agreement between local and global flow curves. No systematic effects of gap size and rotational velocity on the viscosity of a Newtonian fluid and yield stress of a complex fluid could be observed. The acquisition of LFCs during heterogeneous and transient flow of fat crystal dispersion demonstrated that local constitutive laws can be assessed by rheo-microMRI at a high magnetic field in a noninvasive, quantitative, and real-time manner.

Общие закономерности и различия в поведении динамического перемагничивания ферримагнитных (CoFe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=-) и антиферромагнитных (NiO) наночастиц

Abstract In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe_2O_4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force H _C at the dynamic magnetization switching is markedly higher than H _C at quasi-static conditions. H _C increases as the pulse duration τ_ P decreases and the maximum applied field H _0 increases. The dependence of H _C on field variation rate dH / dt = H _0/2τ_ P is a unambiguous function for CoFe_2O_4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH / dt , and the value of applied field H _0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.

Nuclear magnetic resonance studies of translational diffusion in thermotropic ionic liquid crystals

ABSTRACT The NMR methodologies employed for investigating translational diffusion in anisotropic fluids and the results of their applications to ionic liquid crystals are reviewed. Experiments on ionic liquid crystals are preferably performed using oriented samples and require magnetic field gradients in orthogonal directions. Diffusion experiments in anisotropic systems with broad NMR lines are performed using line narrowing techniques and by application of strong static or pulsed field gradients for efficient gradient encoding/decoding of the spatial locations of molecules. Self-diffusion studies on various thermotropic ion-conductive materials exhibiting smectic, cubic, and columnar phases have been reported. Diffusion rates and anisotropy characterise the translational dynamics of ions in nanostructures and reflect the molecular ordering and ion pairing/dissociation processes. Distinct diffusion behaviours were observed for cations and anions. The knowledge of molecular mobility in ionic liquid crystals is important for the understanding their dynamic properties and is, therefore, valuable for the development of anisotropic soft materials for ion transport.

Structure and Properties of Sm – Co – Fe – Cu – Zr Magnets for High-Temperature Applications

Sm – Co – Fe – Cu – Zr sintered high-temperature permanent magnets (HTPM) produced by the “POZ-Progress” Company are studied. The microstructure of the magnets is determined by scanning electron microscopy and x-ray diffraction analysis. The Curie temperature and the magnetic properties of the materials are described. The hysteresis loops of the magnets are measured in strong pulsed fields at room and elevated temperatures. The temperature dependence of the magnetic susceptibility is plotted using the method of compensated transformer in a variable magnetic field.

Microwave Photonic Detector for Measuring Pulsed Electric Field Strengths in the Sub-Nanosecond Region

We provide a validated approach for microwave photonics as a means of developing high-speed noise-immune devices for measurement of strong pulsed electromagnetic fields. We develop a microwave photonic detector for measuring pulsed electric field strengths with a maximum transient-response rise time of 100 psec.

EXTRANEOUS ELECTROMAGNETIC RADIATION IMPACT ON WAVEGUIDE CHARACTERISTICS OF A SEMICONDUCTOR SUPERLATTICE

The subject matter is the mechanisms of emergence of instabilities in natural oscillations of semiconductor supertattices caused by their interaction with charged particle flows of extraneous electromagnetic radiation. The aim is calculating ratios to determine a degree of deviation of operating characteristics of semiconductor components from the norm, depending on the parameters of extraneous pulsed electromagnetic radiation. The objective is to model how currents that are induced with extraneous EMR interact with electrostatic oscillations of a semiconductor supertattice, using an implementation of (Cherenkov) resonance interaction of moving charges with electromagnetic oscillations under conditions where the phase velocity of the wave and the velocity of the charged particle are the same. The methods used: analytical methods for solving Maxwell's equations and medium equations in a framework of hydrodynamic approach. The following results are obtained. We have studied semiconductor components of electronic equipment (supertattices) being exposed to strong pulsed electromagnetic fields. The study was focused on the nature of changes in the working capacity of the components. We show that the effect of pulsed electromagnetic radiation is accompanied by an emergence of currents in the conductive hardware elements and an emergence of internal fields within them. One kind of reversible failures of semiconductor hardware elements is determined, based on interaction of extraneous radiation induced currents with the intrinsic fields of the supertattices of the hardware components. Similar failures occur under conditions of Cerenkov radiation (when the current is parallel to the structure boundary). It is shown that such interaction leads to energy losses in the induced currents spent to excitation of natural oscillations of the supertattice, i.e. to emergence of an oscillation generation mode that is characterized with a change in the volt-ampere characteristics of the hardware. Conclusion. The results obtained in this work can be used to evaluate the efficiency of active radio electronic devices (amplifiers, generators and converters of electromagnetic oscillations in the millimeter and sub-millimeter ranges) being exposed to extraneous pulsed electromagnetic fields. The comparative analysis of quantitative evaluations of reversible failures of semiconductor devices in dependence on the spatial configuration of the acting field (induced current parallel to the structure boundary) allows solving problems in optimizing the degree of distortion of the performance characteristics of these devices.

Dynamic Test Method Based on Strong Electromagnetic Pulse for Electromagnetic Shielding Materials with Field-Induced Insulator-Conductor Phase Transition

In order to measure the pulse shielding performance of materials with the characteristic of field-induced insulator-conductor phase transition when materials are used for electromagnetic shielding, a dynamic test method was proposed based on a coaxial fixture. Experiment system was built by square pulse source, coaxial cable, coaxial fixture, attenuator, and oscilloscope and insulating components. S11 parameter of the test system was obtained, which suggested that the working frequency ranges from 300 KHz to 7.36 GHz. Insulating performance is good enough to avoid discharge between conductors when material samples is exposed in the strong electromagnetic pulse field up to 831 kV/m. This method is suitable for materials with annular shape, certain thickness and the characteristic of field-induced insulator-conductor phase transition to get their shielding performances of strong electromagnetic pulse.

Photo-induced superconductivity

Recent advances in laser technology have made it possible to generate of precisely shaped strong-field pulses at terahertz frequencies. These pulses are especially useful to selectively drive collective modes of solids, for example, to drive materials in a fashion similar to what done in the synthetic environment of optical lattices. One of the most interesting applications involves the creation of non-equilibrium phases with new emergent properties. Here, I discuss coherent control of the lattice to favour superconductivity at ‘ultra-high’ temperatures, sometimes far above the thermodynamic critical temperature Tc.

Numerical simulation and experimental study on electromagnetic crimping of aluminium terminal to copper wire strands

Crimping of terminals to wire strands is crucial in electrical power transmission system. It has been reported that, in electrical inter connections, 60% failure takes place in crimped junctions. Improving crimped connections can decrease the resistance to the current flow through terminals, reduced power loss, sparks, and over-heating in the joints etc. To overcome these problems occurring in conventional crimping process a novel technique for effective wire crimping has been proposed in this paper. A strong pulsed electromagnetic field was used in wire crimping of aluminum terminal with copper wire. Numerical simulations were carried out using LS-DYNA™ software in the electromagnetic module. Its results were utilized to design the coil and to find the optimum discharge voltage required for uniform deformation of terminals. Experiments were carried out at optimized discharge voltages obtained from the numerical simulation results to demonstrate the feasibility of electromagnetic wire crimping process. Effect of the threaded and plain profile of crimped terminals was investigated. Results like terminal deformation, cross-sectional analysis, contact resistance, pullout strength and hardness testing were carried out. This work will be helpful to the industries where wire crimped connections are used in large numbers.

The anomalous interaction of electrons in strong pulsed light fields

The force of effective interaction between two nonrelativistic electrons inside the strong pulsed laser field of two mutually perpendicular light waves is studied theoretically. The magnetic interaction of effective electron currents makes the main contribution to this force. The magnitude and direction of the electron currents depend on the intensity of the waves. The force of magnetic interaction of effective electron currents may exceed the Coulomb force at long distances. As a result, the effective force of an electron pair’s interaction in the laser fields can be attractive as well as repulsive. Thus, the effect of attraction allows increasing the confinement time of electrons in comparison with the corresponding value without any external fields. The anomalous effect of electron repulsion was predicted. This effect allows electrons (after interaction) to scatter over distances exceeding by an order of magnitude corresponding distances without external fields. The appearance of the effective force of attraction may be experimentally verified in the framework of modern research projects where sources of pulsed laser radiation are used (SLAC, FAIR, XFEL, ELI, XCELS).

Creating coherent hole wave packets with strong-field pulses

SynopsisA new approach is identified that can generate highly coherent hole wave packets with multi-cycle strong-field pulses and stands in contrast to the usual idea of making the ionizing pulse as short as possible. The effect is demonstrated in atomic xenon with a spin-orbit wave packet involving the 5p-13/2 and 5p-11/2 ionic states. Tuning the driving frequency to an even fraction of the hole oscillation frequency ensures the creation of highly coherent holes.

Interaction of identically charged particles in a pulsed field of two laser waves propagating in the one direction

We consider the effective interaction force of identically charged nonrelativistic particles (electrons and heavy nuclei) in a strong pulsed field of two co-propagating laser waves. It is shown that under certain conditions, the effective interaction force can become a force of attraction. Moreover, it is possible to significantly increase the duration of the effective force of attraction via the time shift of the pulse peak of the second wave relatively to the first one. The appearance of the effective force of attraction may be experimentally verified in the framework of modern research projects, which use sources of pulsed laser radiation (FAIR, XFEL, ELI).

Spin–orbit effects in atomic high-harmonic generation

Spin–orbit interactions lead to small energy gaps between the outermost p1/2 and p3/2 shells of noble gas atoms. Strong-field pulses tunnel-ionize an electron out of either shell resulting in spin–orbit-driven hole motion. These hole dynamics affect the high-harmonic generation (HHG) yield. However, the spectral shape as well as the angular distribution of the HHG emission is not influenced by spin–orbit coupling. We demonstrate the spin–orbit effect on atomic krypton by solving the multi-electron Schrödinger equation with the time-dependent configuration-interaction singles approach. We also provide pulse parameters where this effect can be identified in experiments through an enhancement in the HHG yield as the wavelength of the strong-field pulse increases.

Dynamic nuclear polarisation via the integrated solid effect I: theory

In the hyperpolarisation method known as dynamic nuclear polarisation (DNP), a small amount of unpaired electron spins is added to the sample containing the nuclear spins and the polarisation of these unpaired electron spins is transferred to the nuclear spins by means of a microwave field. Traditional DNP uses weak continuous wave (CW) microwave fields, so perturbation methods can be used to calculate the polarisation transfer. A much faster transfer of the electron spin polarisation is obtained with the integrated solid effect (ISE) which uses strong pulsed microwave fields. As in nuclear orientation via electron spin locking, the polarisation transfer is coherent, similar to the coherence transfer between nuclear spins. This paper presents a theoretical approach to calculate this polarisation transfer.ISE is successfully used for a fast polarisation transfer from short-lived photo-excited triplet states to the surrounding nuclear spins in molecular crystals. These triplet states are strongly aligned in the photo-excitation process and do not require the low temperatures and strong magnetic fields needed to polarise the electron spins in traditional DNP. In the following paper, the theory is applied to the system naphthalene-h8 doped with pentacene-d14 which provides the photo-excited triplet states, and compared with experimental results.