Intense Electromagnetic Pulses Research Articles

A LiNbO3 Linear Intense Electromagnetic Pulse (EMP) Sensor by Using Incident Lightwave Near Optical Axis

A LiNbO₃ Linear Intense Electromagnetic Pulse (EMP) Sensor by Using Incident Lightwave Near Optical Axis

Measurement of electromagnetic pulse in laser acceleration enhanced by near-critical density targets

High-power laser interactions with solid targets create an abundance of high-energy charged particles, resulting in the generation of intense electromagnetic pulses (EMPs), which are strongly pertinent to the target parameters. In this study, the characteristics of EMPs generated by relativistic femtosecond laser irradiation of double-layer targets composed of near-critical density carbon nanotube foams (CNFs) and an aluminum (Al) foil are investigated. The results demonstrate that the CNF double-layer targets accelerate proton energy by over 1.6 times compared to a single-layer Al plane target, thereby indirectly amplifying the EMP amplitude by over 3.6 times. The findings are beneficial to gaining insight into EMPs induced by femtosecond laser coupling with near-critical density targets and open a new avenue to achieve tunable EMPs by managing the material and structure of the target to optimize the coupling efficiency between the laser and solid targets.

Laser-driven electron emission and expansion for the generation and guidance of giant EMPs.

High-power laser interacting with matter generates intense electromagnetic pulses (EMPs), which are closely associated with laser and target parameters. In this study, EMPs induced by picosecond (ps) laser coupling with solid targets are recorded at the XG-III laser facility. Gold wire targets produce more intense EMPs with a maximum EMP value of 608 kV/m compared to some planar targets. EMP propagation in the normal direction is highly coincident with the expansion of detected hot electrons, which is verified by the particle-in-cell simulations. This work is expected to pave, to our knowledge, a new avenue for directional guidance of laser-driven EMPs.

Electromagnetic pulses produced by a picosecond laser interacting with solid targets

A high-power laser ablating solid targets induces giant electromagnetic pulses (EMPs), which are intimately pertinent to laser parameters, such as energy and pulse width. In this study, we reveal the features of EMPs generated from a picosecond (ps) laser irradiating solid targets at the SG-II picosecond petawatt (PSPW) laser facility. The laser energy and pulse, as well as target material and thickness, show determinative effects on the EMPs’ amplitude. More intense EMPs are detected behind targets compared to those at the other three positions, and the EMP amplitude decreases from 90.09 kV/m to 17.8 kV/m with the gold target thickness increasing from 10 μm to 20 μm, which is suppressed when the laser pulse width is enlarged. The results are expected to provide more insight into EMPs produced by ps lasers coupling with targets and lay the foundation for an effective EMP shielding design in high-power laser infrastructures.

Mitigation of electromagnetic pulses interfering with Thomson parabola ion spectrometers at XG-III laser facility.

The Thomson parabola ion spectrometer is vulnerable to intense electromagnetic pulses (EMPs) generated by a high-power laser interacting with solid targets. A metal shielding cage with a circular aperture of 1mm diameter is designed to mitigate EMPs induced by a picosecond laser irradiating a copper target in an experiment where additionally an 8-ns delayed nanosecond laser is incident into an aluminum target at the XG-III laser facility. The implementation of the shielding cage reduces the maximum EMP amplitude inside the cage to 5.2 kV/m, and the simulation results indicate that the cage effectively shields electromagnetic waves. However, the laser-accelerated relativistic electrons which escaped the target potential accumulate charge on the surface of the cage, which is responsible for the detected EMPs within the cage. To further alleviate EMPs, a lead wall and an absorbing material (ECCOSORB AN-94) were added before the cage, significantly blocking the propagation of electrons. These findings provide valuable insights into EMP generation in large-scale laser infrastructures and serve as a foundation for electromagnetic shielding design.

Measurement of high-power transient electromagnetic pulse field with integrated photonic electric-field sensor

To satisfy certain special requirements for high-power transient electromagnetic pulse (EMP) field measurements, such as high electric field intensity, broad bandwidth, fast rise time, and compact size, here is described an integrated electro-optic sensor. The frequency response in the range from 100 kHz to 12 GHz and the time-domain input/output characteristics of a sub-nanosecond EMP field with an intensity from 5 to 100 kV/m were experimentally characterized. The sensor was demonstrated to measure the time-domain waveform of the ultrawideband EMP field signals with a rise time of 0.35 ns and bandwidth of 1 GHz. In addition, the minimal detectable electric field strength was 16 mV/m/Hz1/2 in the frequency domain, and an intense sub-nanosecond electromagnetic pulse with a peak amplitude of 100 kV/m was observed in the time domain. The reported sensor is expected to be broadly used for intense EMP measurements.

Self-Guidance and Self-Focusing of Rippled Electromagnetic Radiation Pulse in High Density Magnetoactive Plasma


 Inside the plasma, when an intense rippled electromagnetic radiation pulse experiences self-focusing, one need to taking account of radial expansion in view of charge displacement due to ponderomotive force on electron and variation in the mass of oscillating electron under the influence of relativistic effect due to electromagnetic field. The extraordinary-mode (E-mode) propagation in a magnetoactive plasma, with stationary magnetic field, which is analogous to the wavering magnetic field of the electromagnetic radiation pulse, is the key feature for the self-guided propagation of rippling electromagnetic radiation pulse in magnetoactive plasma. If the condition for ultra-fast volume ionization is achieved, the radiation pulse itself can generate such a stationary magnetic field. It is demonstrated that external magnetic field affects the channels, causing them to bend. These effects cast new light on the phenomena of self-focusing of rippled electromagnetic radiation pulse. They raise the possibility of combining energy from several channels into one. It is found that the magnetic field strongly influences the plasma dynamic behavior and overall propagation of rippled electromagnetic radiation pulse.
 Keywords: Self-focusing, Self-guidance, Magnetized-plasma, Beam-propagation, Nonlinearity

Propagation of intense electromagnetic pulse with a small conical phase shift induced by Axicon optics.

The conical phase shift induced by the axicon generates a non-diffracting Bessel beam. In this paper, we examine the propagation property of an electromagnetic wave focused by a thin lens and axicon waveplate combination, which induces a small amount of conical phase shift less than one wavelength. A general expression describing the focused field distribution has been derived under the paraxial approximation. The conical phase shift breaks the axial symmetry of intensity and shows a focal spot-shaping capability by controlling the central intensity profile within a certain range near focus. The focal spot-shaping capability can be applied to form a concave or flattened intensity profile, which can be used to control the concavity of a double-sided relativistic flying mirror or to generate the spatially uniform and energetic laser-driven proton/ion beams for hadron therapy.

Massively parallel FDTD-FBMC simulations of nonlinear hole dynamics in silicon at cryogenic temperatures driven by intense EM THz pulses

THz spectroscopy with intense electromagnetic (EM) pulses offers unique avenues to study the charge carrier dynamics in semiconductors. Quantitative analysis of the experiment requires a detailed microscopic model that is based on the wave propagation within the sample and on the strongly nonparabolic dispersion relation of the valence bands. With a finite difference time domain (FDTD) solver for the EM wave in conjunction with a full band Monte Carlo (FBMC) model for the holes the generation of higher harmonics by the nonlinear hole response in the p-doped silicon sample can be simulated. Due to impurity freeze-out at the cryogenic temperature the hole density is low and the FDTD solver can be decoupled from the FBMC model by a perturbation approach. This enables the independent processing of a very large number of holes on a computer cluster with nearly 100% computational efficiency resulting in a very low level of stochastic noise, which is necessary to achieve a reasonable signal to noise ratio for the faint higher harmonics. The simulations show that at THz frequencies and cryogenic temperatures strong generation of higher harmonics is only possible, if the band structure is nonparabolic.

The protection design method of the engine control system under electromagnetic pulses.

This study assessed the survivability of an engine control system under intense electromagnetic pulses. It investigated the electromagnetic sensitivity of the system under the action of intense electromagnetic pulses. In this work, the evaluation focuses on the terminal circuit of the control system. It proposes a co-design method for electromagnetic pulse protection circuits on a printed circuit board. The electromagnetic interference mechanism and phenomena were analyzed through simulation and experiments. The electromagnetic susceptibility of the control system was tested using the bulk current injection test method, and the pulse coupling signal of the sensitive part was obtained. Subsequently, the terminal circuit was analyzed using a numerical calculation method. The pulse coupling signal was injected into the terminal circuit. Thus, we can determine why the control system exhibits sensitive phenomena. Then, a protection circuit of the terminal circuit was established. The design method's advantage is accurately locating the circuit's sensitive points and reducing the controller circuit's electromagnetic sensitivity by designing the circuit without drastically changing the original circuit. At the same time, the redundancy of protection circuit design can be effectively reduced.

Low Cost and Sustainable Test Methods to Study Vulnerabilities of Large-Scale Systems against EMP

Intense electromagnetic pulses are electromagnetic waves with sharp rise time, high field strength and short duration. They have attracted more and more attention in recent years because they can cause destructions or malfunctions of some key national core infrastructures, such as power grids, communication and financial networks, etc. Hence, it is important to harden these facilities to ensure that they can survive in the face of electromagnetic pulse attacks. A direct way to investigate the vulnerabilities of these facilities is placing them in the electromagnetic environments generated by EMP simulators. However, the scale of facilities under test are limited by the working volumes of simulators. With the increase in working volumes and field strength, the price and technical difficulty of simulators are increased. Therefore, low cost and sustainable test methods to investigate vulnerabilities of large-scale systems against EMP are proposed in this study. The study takes advantage of continuous wave immersion (CWI) test and pulse current injection (PCI) test methods, which are low cost and sustainable to predict the pulse responses and assess the nonlinear effect of large-scale facilities under EMP attacks. In a CWI test, the magnitude of the transfer function of large-scale systems or facilities can be measured, and the corresponding phase information of the transfer function can be reconstructed by minimum phase algorithm (MPA) if the systems meet the minimum phase condition. After acquiring the entire information of the transfer function, we can predict the responses of a system under threat-level EMP attacks. However, these responses are obtained under the assumption that the system does not have nonlinear effects. Because the CWI is a low-level test, it cannot simulate the threat-level EMP attacks. In the PCI test proposed here, a bulky pulse current is coupled into the system to stimulate enough current intensity, just as the system was attacked by threat-level EMPs. In this situation, the system would be destroyed, or any other nonlinear effect would occur in the system. After that, the problem is to determine the quantities of the injected current, and a few kinds of norms are introduced in this paper to define the quantities. The method proposed here innovatively takes the experimental results of CWI as reference inputs of PCI tests. In this paper, the accuracy of the response prediction is validated by means of simulations and experiments. Results show that as a low-level test method in the frequency domain, the CWI test method can not only analyze couplings of external electromagnetic energy from frequency domain but also predict responses of the facilities under high amplitude electromagnetic pulses. The nonlinear effect of large-scale facilities can be assessed by applying the PCI test method with the results from CWI prediction. Therefore, if infrastructures or facilities are too large to be tested under EMP simulators, an alternative approach is to carry out the CWI and PCI experiments.

High-order nonlinear terahertz probing of the two-band superconductor MgB2 : Third- and fifth-order harmonic generation

We report on high-order harmonic generation in the two-band superconductor ${\mathrm{MgB}}_{2}$ driven by intense terahertz electromagnetic pulses. Third- and fifth-order harmonics are resolved in time domain and investigated as a function of temperature and in applied magnetic fields crossing the superconducting phase boundary. The high-order harmonics in the superconducting phase reflects nonequilibrium dynamics of the superconducting order parameter in ${\mathrm{MgB}}_{2}$, which is probed via nonlinear coupling to the terahertz field. The observed temperature and field dependence of the nonlinear response allows to establish the superconducting phase diagram.

Intense Electromagnetic Pulses Generated From kJ-Laser Interacting With Hohlraum Targets

Irradiating hohlraum targets with high-power laser pulses is a promising approach to achieve inertial confinement fusion (ICF). Unfortunately, such interaction is accompanied by intense electromagnetic pulses (EMPs). The EMPs can interfere with various physical diagnostic signals and even cause a malfunction of some crucial equipment. In this study, EMPs generated due to kJ-laser coupling with hohlraum targets are recorded using B-dot probes inside the target chamber. The configuration of the hohlraum has a more remarkable effect on EMP amplitudes compared to laser energy. 0.6 mg/cc of He gas filling in the hohlraum and the presence of the capsule inside the hohlraum both dramatically reduce EMPs. Moreover, EMP frequencies corresponding to various hohlraums are basically below 1.75 GHz. Soft X-ray (0.1–4 keV) radiant flux is used to reveal the characteristics of EMPs. The conclusions are expected to enable us to better understand the relationship of EMPs with target configuration and laser energy.

Massively parallel FDTD full-band Monte Carlo simulations of electromagnetic THz pulses in p-doped silicon at cryogenic temperatures

In semiconductor samples with a low density of free charge carriers the current response to an intense electromagnetic pulse is weak and can be treated as a perturbation in the finite-difference-time-domain calculation of the electromagnetic field. Up to first order the electric field that drives the particles does not depend on their density and the particles can be simulated independently. This opens the door for massively parallel Monte Carlo simulations that can be processed efficiently on a computer cluster and a large number of particles can be simulated resulting in a very low noise level. By this full-band Monte Carlo finite-difference-time-domain approach the generation of higher harmonics in p-doped silicon at cryogenic temperatures is investigated. It is found that the higher harmonics are mostly due to the warped valence bands, which are discretized on adaptive unstructured tetrahedral grids in the k-space to avoid numerical artifacts.

Generation and regulation of electromagnetic pulses induced by hybrid laser pulses interacting with solid targets

In inertial confinement fusion, electromagnetic pulses (EMPs) can be produced during high-power laser interacting with solid targets, which are intimately related to laser intensity and laser energy. In this study, EMPs generated by hybrid laser pulses coupling with targets are recorded and analyzed. The results indicate that a single picosecond laser gives birth to the most intense EMPs, but they are remarkably suppressed when a nanosecond laser-shooting target is triggered before the picosecond and femtosecond laser. One possible hypothesis is proposed based on x-rays inducing pre-ablation that generates pre-plasma at the surfaces of the picosecond target and femtosecond target, leading to a sharp drop both in the energy and number of the emitting hot electrons and protons. The findings will deepen our understanding of the mechanism of EMPs’ generation and will also open a new avenue to regulate EMPs by hybrid laser pulses.

Parametric study of laser wakefield driven generation of intense sub-cycle pulses

Intense sub-cycle electromagnetic pulses allow one to drive nonlinear processes in matter with unprecedented levels of control. However, it remains challenging to scale such sources in the relativistic regime. Recently, a scheme that utilizes laser-driven wakes in plasmas to amplify and compress seed laser pulses to produce tunable, carrier-envelope-phase stable, relativistic sub-cycle pulses has been proposed. Here, we present parametric studies of this process using particle-in-cell simulations, showing its robustness over a wide range of experimentally accessible laser-plasma interaction parameters, spanning more than two orders of magnitude of background plasma density. The method is shown to work with different gas-jet profiles, including structured density profiles and is robust over a relatively wide range of driver laser intensities. Our study shows that sub-cycle pulses of up to 10mJ of energy can be produced.

Terahertz-field-induced second optical harmonic generation from Si(111) surface

We study, both experimentally and theoretically, the second-harmonic (SH) generation (SHG) of optical radiation assisted by intense terahertz electromagnetic pulses from the surface of high-resistivity Si(111). The study was performed within the framework of the analysis of the superposition of different SH sources, including the surface-dipole, bulk-quadruple, and electric-field-induced (EFI) bulk-dipole (arising from internal built-in and external terahertz fields) contributions. Azimuthal rotation anisotropy of SHG for an arbitrary mutual polarization of the terahertz, fundamental, and SH optical fields was calculated and experimentally verified. The strongest impact of the terahertz field on SHG was observed in the case where the polarizations of the terahertz and SH fields coincide. In these polarization configurations, the terahertz field added mainly an isotropic term to the SH azimuthal dependences. It has been demonstrated that the application of the terahertz field can be helpful for distinguishing the SHG mechanism. For the sample under study, the contribution to the SH energy from the built-in field-induced source was found to be >4 times greater than the contribution from the surface and quadrupole nonlinear sources. The dominance of the EFISHG allowed us to find the ratio between the components of a silicon third-order nonlinear tensor ${\ensuremath{\chi}}_{}^{(3)}(2\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},0)$: ${\ensuremath{\chi}}_{1122}={\ensuremath{\chi}}_{1212}\ensuremath{\approx}0.51{\ensuremath{\chi}}_{1111}$ and ${\ensuremath{\chi}}_{1212}\ensuremath{\approx}{\ensuremath{\chi}}_{1221}$ for the fundamental optical wavelength 790 nm.

Probing magnetic pulse welding of aluminium and steel sheets

Magnetic pulse welding is used to join overlapped thin sheets of dissimilar materials in solid state, which is not easy by fusion welding due to severe thermomechanical distortion and the formation of brittle intermetallic compounds. An intense electromagnetic pulse is employed that causes an impact between the overlapped parts leading to plastic deformation and rapid coalescence along the interface thereby posing a challenge to monitor the evolution of joint. An effort combining experimental investigation and numerical process modelling is presented here for a quantitative understanding of magnetic pulse welding of thin AA5754 and DC04 steel sheets with a flat linear coil of Cu-OFHC alloy. The numerical model couples an electromagnetic and a dynamic mechanical analysis to compute the transient electromagnetic pressure and the progressive impact between the parts and the plastic deformation that the parts experience for a given coil and sheet geometry and materials. The computed results of the impact velocity of the flyer on the target, the top and bottom part in the overlapped assembly, and the flyer–target contact length are examined against the corresponding experimentally measured results for several process conditions. The computed results are further used to elucidate the progressive nature of the evolution of the joint. Overall, the computational model has served as an important tool to uncover the underlying phenomena and identify suitable range of process conditions to produce a defect-free weld in magnetic pulse welding of sheets.

Research on calibration method of uniformity of radiation interference field of intense electromagnetic pulse

With the rapid development of electronic and electrical products, the working frequency of ite products is higher and higher, the influence frequency range of interference between electronic products is also expanding, the test frequency range of radiation anti-interference is improving, at the same time, more and more attention is paid to the requirements of radiation anti-interference test site. At present, the uniformity of radiation field is mainly realized by single point multiple test, which will inevitably lead to the measurement error due to the time-varying characteristics of the radiation signal itself; In addition, the test time is greatly increased and the test efficiency is low. In order to solve these problems, this paper designs a device which can realize multi-point test at one time and can automatically adjust the test area. The simulation shows that the device can meet the requirement of 9point uniformity test of radiation field in 500mm × 500mm ~ 1500mm × 1500mm area. On this basis, experiments are carried out in 1000mm × 1000mm test area for 1.35GHz and 2.88GHz. The experiments show that the test device can meet the requirement of 9point uniformity test and greatly improve the test efficiency and automation.

Distortion of Thomson Parabolic-Like Proton Patterns Due to Electromagnetic Interference

Intense electromagnetic pulses (EMPs) accompany the production of plasma when a high-intensity laser irradiates a solid target. The EMP occurs both during and long after the end of the laser pulse (up to hundreds of nanoseconds) within and outside the interaction chamber, and interferes with nearby electronics, which may lead to the disruption or malfunction of plasma diagnostic devices. This contribution reports a correlation between the frequency spectrum of the EMP and the distortion of Thomson parabola tracks of protons observed at the kJ-class PALS laser facility in Prague. EMP emission was recorded using a simple flat antenna. Ions accelerated from the front side of the target were simultaneously detected by a Thomson parabola ion spectrometer. The comparison of the two signals suggests that the EMP may be considered to be the source of parabolic track distortion.