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Results for “ELECTROMAGNETIC PULSES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Femtosecond photocurrents at the FeRh/Pt interface

Femtosecond laser excitations of FeRh/Pt bilayers launch an ultrafast pulse of electric photocurrents in the Pt-layer and subsequently result in the emission of electromagnetic radiation in the THz spectral range. Analysis of the THz emission as a function of the polarization of the femtosecond laser pulse, external magnetic field, sample temperature, and sample orientation shows that the photocurrent can emerge due to vertical spin pumping and photo-induced inverse spin–orbit torque at the FeRh/Pt interface. Additionally, the vertical spin pumping from FeRh into Pt does not depend on the polarization of light and originates from ultrafast laser-induced demagnetization of the ferromagnetic phase of FeRh. The photo-induced inverse spin–orbit torque at the FeRh/Pt interface can be described in terms of a helicity-dependent effect of circularly polarized light on the magnetization of the ferromagnetic FeRh and the subsequent generation of a photocurrent.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Benchmarking semiclassical approaches to strong-field QED: Nonlinear Compton scattering in intense laser pulses

The recoil associated with photon emission is key to the dynamics of ultrarelativistic electrons in strong electromagnetic fields, as found in high-intensity laser-matter interactions and astrophysical environments such as neutron star magnetospheres. When the energy of the photon becomes comparable to that of the electron, it is necessary to use quantum electrodynamics (QED) to describe the dynamics accurately. However, computing the appropriate scattering matrix element from strong-field QED is not generally possible due to multiparticle effects and the complex structure of the electromagnetic fields. Therefore, these interactions are treated semiclassically, coupling probabilistic emission events to classical electrodynamics using rates calculated in the locally constant field approximation. Here, we provide comprehensive benchmarking of this approach against the exact QED calculation for nonlinear Compton scattering of electrons in an intense laser pulse. We find agreement at the percentage level between the photon spectra, as well as between the models' predictions of absorption from the background field, for normalized amplitudes a0 > 5. We discuss possible routes towards improved numerical methods and the implications of our results for the study of QED cascades.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Simulation of Conduction Cooled SRF Cavity

SRF cavities are used heavily in high energy physics research, and simplifying operation of SRF cavities could enable their use in many fields of industry. Liquid helium coolant systems are a notable complexity of operating SRF cavities, and replacing liquid helium with cryocooler conduction cooling is an important research and development interest. As part of this effort, a system consisting of a 650 MHz single cell cavity, a commercial grade pulse tube refrigerator, and an aluminum thermal link was simulated through finite element analysis. The electromagnetic fields inside the cavity, heat flow through the system, and temperature distribution of the thermal link and cavity were calculated. Based on the simulations, the pulse tube refrigerator is capable of supplying adequate cooling power to a cavity with \ce{Nb3Sn} coating operating with an accelerating gradient between 6 and 12 MV/m. The maximum simulated temperature of the cavity was below 7 K, and the oscilla tions in temperature introduced by the pulse tube refrigerator were shown to dampen in amplitude before reaching the cavity surface.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

DQ Admittance Model Extraction for IBRs via Gaussian Pulse Excitation

While $dq$ admittance models have shown to be very useful for stability analysis, extracting admittance models of inverter-based resources (IBRs) from the electromagnetic transient (EMT) simulation environment using frequency scans takes time. In this letter, a new perturbation method based on Gaussian pulses in combination with the system identification algorithms shows great promise for parametric $dq$ admittance model extraction. We present the $dq$ admittance model extracting method for a type-4 wind turbine. Challenges in implementing Gaussian pulse excitation are also pointed out. In conclusion, the extracted $dq$ admittance model via the new method shows to have a high matching degree with the measurements obtained from frequency scans.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam

The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today’s lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration ( ϵ > 500 MeV ) with an intense laser pulse (a 0 > 10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy ϵ crit > 30 MeV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

High-power tunable laser driven THz generation in corrugated plasma waveguides

The excitation of Terahertz (THz) radiation by the interaction of an ultrashort laser pulse with the modes of a miniature corrugated plasma waveguide is considered. Here, the axially corrugated waveguide supports the electromagnetic modes with appropriate polarization and subluminal phase velocities that can be phase matched to the ponderomotive potential associated with the laser pulse, making significant THz generation possible. This process is studied via full format Particle-in-Cell simulations that, for the first time, model the nonlinear dynamics of the plasma and the self-consistent evolution of the laser pulse in the case where the laser pulse energy is entirely depleted. It is found that the generated THz is characterized by lateral emission from the channel, with a spectrum that may be narrow or broad depending on the laser intensity. A range of realistic laser pulse and plasma parameters is considered with the goal of maximizing the conversion efficiency of optical energy to THz radiation. As an example, a fixed drive pulse (0.55 J) with a spot size of 15 μm and a duration of 15 fs produces a THz radiation of 37.8 mJ of in a 1.5 cm corrugated plasma waveguide with an on axis average density of 1.4 × 10 18 cm –3 .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Femtosecond pulse self-shortening in Kerr media: role of modulational instability in the spectrum formation

The mechanism of femtosecond pulse self-shortening in thin optical materials with Kerr nonlinearity is investigated. The experimentally observed spectral-angular distribution of the radiation intensity on the exit surface of a 1-mm-thick fused silica sample is compared with the results of numerical simulation based on solving the nonlinear Schrödinger equation for an electromagnetic wave with a transverse perturbation on the axis. Qualitative agreement between the calculated and experimental results confirms the hypothesis about the transient regime of multiple filamentation as a mechanism of femtosecond pulse self-shortening. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Simulation of Conduction Cooled SRF Cavity

SRF cavities are used heavily in high energy physics research, but the operational complexities of SRF cavities prevent their widespread use in industry. One notable complexity of operating an SRF cavity is liquid helium coolant, and replacing liquid helium with cryocooler conduction cooling is an important research and development interest. As part of this effort, a system consisting of a 650 MHz single cell cavity, a commercial grade pulse tube refrigerator, and a thermal conduction link was simulated through finite element analysis. The electromagnetic fields inside the cavity, heat flow through the system, and temperature distribution of the thermal link and cavity were calculated. Based on the simulation, we found that a 2 W @ 4.2 K pulse tube refrigerator is capable of cooling a single cell Nb 3 Sn coated cavity operating at up to 12 MV/m accelerating gradient. The maximum simulated temperature of the cavity was below 7 K, and the thermal conduction link was shown to significantly attenuate the cryocooler thermal oscillations at the location of the cavity

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Nonlocal, diamagnetic electromagnetic effects in magnetically insulated transmission lines

We identify the time-dependent physics responsible for the critical reduction of current losses in magnetically insulated transmission lines (MITLs) due to uninsulated space charge-limited currents of electrons emitted by field stress. A drive current of sufficiently short pulse length introduces a strong enough time dependence that steady-state results alone become inadequate for the complete understanding of current losses. The time-dependent physics can be described as a nonlocal, diamagnetic electromagnetic response of space charge limited currents. As the pulse length is increased or equivalently, the MITL length reduced, these time-dependent effects diminish and current losses converge to those predicted by the well-known Child–Langmuir law in the external (vacuum) fields. We present a simple one-dimensional (1D) model that encapsulates the essence of this physics. We find excellent agreement with 2D particle-in-cell simulations for two MITL geometries, Cartesian parallel plate and azimuthally symmetric straight coaxial. Based on the 1D model, we explore various scaling dependencies of MITL losses with relevant parameters, e.g., peak current, pulse length, geometrical dimensions, etc. We propose an improved physics model of magnetic insulation in the form of a Hull curve, which could also help improve predictions of current losses by common circuit element codes, such as BERTHA. Finally, we describe how to calculate the temperature rise due to electron impact within the 1D model.

Computer simulation↗
DOE OSTI2019

Current drive by high intensity, pulsed, electron cyclotron wave packets

The nonlinear interaction of electrons with a high intensity, spatially localized, Gaussian, electromagnetic wave packet, or beam, in the electron cyclotron range of frequencies is described by the relativistic Lorentz equation. There are two distinct sets of electrons that result from wave-particle interactions. One set of electrons is reflected by the ponderomotive force due to the spatial variation of the wave packet. The second set of electrons are energetic enough to traverse across the wave packet. Both sets of electrons can exchange energy and momentum with the wave packet. The trapping of electrons in plane waves, which are constituents of the Gaussian beam, leads to dynamics that is distinctly different from quasilinear modeling of wave-particle interactions. This paper illustrates the changes that occur in the electron motion as a result of the nonlinear interaction. The dynamical differences between electrons interacting with a wave packet composed of ordinary electromagnetic waves and electrons interacting with a wave packet composed of extraordinary waves are exemplified.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Electro-optical measurement of intense electric field on a high energy pulsed power accelerator

We describe a direct electro-optical approach to measuring a strong 118 MV/m narrow pulse width (~ 33 ns) electric field in the magnetically insulated transmission line (MITL) of a pulsed power accelerator. To date, this is the highest direct external electric field measured electro-optically in a pulsed power accelerator, and it is between two to three orders of magnitude higher than values reported in comparable high energy scientific experiments. The MITL electric field is one of the most important operating parameters in an accelerator and is critical to understanding the properties of the radiation output. However, accurately measuring these high fields using conventional pulsed power diagnostics is difficult due to the strength of interfering particles and fields. Our approach uses a free-space laser beam with a dielectric crystal sensor that is highly immune to electromagnetic interference and does not require an external calibration. Here we focus on device theory, operating parameters, laboratory and pulsed power accelerator experiments as well as challenges that were overcome in the measurement environment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Energy density in a collapsing electromagnetic wave

The relationship between the energy and the width of the spectrum of a collapsing electromagnetic wave and the maximum energy density at the focal point has been found. The solution method can be used to simulate the propagation of ultrashort pulses without using the slowly varying amplitude approximation. (isotope laser emission)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Direct visualization of electromagnetic wave dynamics by laser-free ultrafast electron microscopy

Integrating femtosecond lasers with electron microscopies has enabled direct imaging of transient structures and morphologies of materials in real time and space. Here, we report the development of a laser-free ultrafast electron microscopy (UEM) offering the same capability but without requiring femtosecond lasers and intricate instrumental modifications. We create picosecond electron pulses for probing dynamic events by chopping a continuous beam with a radio frequency (RF)–driven pulser with the pulse repetition rate tunable from 100 MHz to 12 GHz. As a first application, we studied gigahertz electromagnetic wave propagation dynamics in an interdigitated comb structure. We reveal, on nanometer space and picosecond time scales, the transient oscillating electromagnetic field around the tines of the combs with time-resolved polarization, amplitude, and local field enhancement. This study demonstrates the feasibility of laser-free UEM in real-space visualization of dynamics for many research fields, especially the electrodynamics in devices associated with information processing technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Effect of finite ion mass on relativistic self-induced transparency of plasma layers with a sharp boundary

We consider the effect of ion mobility on the threshold of relativistic self-induced transparency under irradiation of thin plasma layers by circularly polarised laser radiation. An analytical model of the motion of ions during the removal of electrons from the layer surface by the ponderomotive force of laser radiation is constructed. The model is used to analyse the motion of probe electrons in the resulting electromagnetic field. It is shown that the higher the ion mobility and the longer the laser pulse, the more stable the plasma layer to longitudinal perturbations of a finite value and the higher the threshold of self-induced transparency. These conclusions are verified by one-dimensional numerical simulation of a complete system of kinetic equations for plasma and Maxwell’s equations. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Direct measurements of anode/cathode gap plasma in cylindrically imploding loads on the Z machine

By deploying a photon Doppler velocimetry based plasma diagnostic, we have directly observed low density plasma in the load anode/cathode gap of cylindrically converging pulsed power targets. The arrival of this plasma is temporally correlated with gross current loss and subtle power flow differences between the anode and the cathode. The density is in the range where Hall terms in the electromagnetic equations are relevant, but this physics is lacking in the magnetohydrodynamics codes commonly used to design, analyze, and optimize pulsed power experiments. Here, the present work presents evidence of the importance of physics beyond traditional resistive magnetohydrodynamics for the design of pulsed power targets and drivers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Unitary quantum lattice simulations for Maxwell equations in vacuum and in dielectric media

Utilizing the similarity between the spinor representation of the Dirac and the Maxwell equations that has been recognized since the early days of relativistic quantum mechanics, a quantum lattice algorithm (QLA) representation of unitary collision-stream operators of Maxwell's equations is derived for both homogeneous and inhomogeneous media. A second-order accurate 4-spinor scheme is developed and tested successfully for two-dimensional (2-D) propagation of a Gaussian pulse in a uniform medium whereas for normal (1-D) incidence of an electromagnetic Gaussian wave packet onto a dielectric interface requires 8-component spinors because of the coupling between the two electromagnetic polarizations. In particular, the well-known phase change, field amplitudes and profile widths are recovered by the QLA asymptotic profiles without the imposition of electromagnetic boundary conditions at the interface. The QLA simulations yield the time-dependent electromagnetic fields as the wave packet enters and straddles the dielectric boundary. QLA involves unitary interleaved non-commuting collision and streaming operators that can be coded onto a quantum computer: the non-commutation being the very reason why one perturbatively recovers the Maxwell equations.

Physics↗
DOE OSTI2018

Electron Trapping from Interactions between Laser-Driven Relativistic Plasma Waves

Interactions of large-amplitude relativistic plasma waves were investigated experimentally by propagating two synchronized ultraintense femtosecond laser pulses in plasma at oblique crossing angles to each other. The electrostatic and electromagnetic fields of the colliding waves acted to preaccelerate and trap electrons via previously predicted, but untested injection mechanisms of ponderomotive drift and wake-wake interference. High-quality energetic electron beams were produced, also revealing valuable new information about plasma-wave dynamics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Mechanism of single-pulse ablative generation of laser-induced periodic surface structures

One of the remarkable capabilities of ultrashort polarized laser pulses is the generation of laser-induced periodic surface structures (LIPSS). The origin of this phenomenon is largely attributed to the interference of the incident laser wave and surface electromagnetic wave that creates a periodic absorption pattern. Although, commonly, LIPSS are produced by repetitive irradiation of the same area by multiple laser pulses in the regime of surface melting and resolidification, recent reports demonstrate the formation of LIPSS in the single-pulse irradiation regime at laser fluences well above the ablation threshold. In this paper, we report results of a large-scale molecular dynamics simulation aimed at providing insights into the mechanisms of single-pulse ablative LIPSS formation. The simulation performed for a Cr target reveals an interplay of material removal and redistribution in the course of spatially modulated ablation, leading to the transient formation of an elongated liquid wall extending up to ~600 nm above the surface of the target at the locations of the minima of the laser energy deposition. The upper part of the liquid wall disintegrates into droplets while the base of the wall solidifies on the time scale of ~2 ns, producing a ~100-nm-tall frozen surface feature extending above the level of the initial surface of the target. The properties of the surface region of the target are modified by the presence of high densities of dislocations and vacancies generated due to the rapid and highly nonequilibrium nature of the melting and resolidification processes. The insights into the LIPSS formation mechanisms may help in designing approaches for increasing the processing speed and improving the quality of the laser-patterned periodic surface structures.

Materials Science↗