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An experimental investigation of the multipath propagation of ultrawideband (UWB) microwave chaotic radio pulses in a wireless channel has been carried out. Based on the results of measurements, conditions of receiving chaotic radio pulses upon passage via a multipath channel are established for various signal delay times.
Vacuum birefringence produces a differential phase between orthogonally polarized components of a weak electromagnetic probe in the presence of a strong electromagnetic field. Despite representing a hallmark prediction of quantum electrodynamics, vacuum birefringence remains untested in pure light configurations due to the extremely large electromagnetic fields required for a detectable phase difference. Here, we exploit the programmable focal velocity and extended focal range of a flying focus laser pulse to substantially lower the laser power required for detection of vacuum birefringence. In the proposed scheme, a linearly polarized x-ray probe pulse counterpropagates with respect to a flying focus pulse, whose focus moves at the speed of light in the same direction as the x-ray probe. The peak intensity of the flying focus pulse overlaps the probe over millimeter-scale distances and induces a polarization ellipticity on the order of 10 − 10 , which lies within the detection sensitivity of existing x-ray polarimeters. Published by the American Physical Society 2024
Motivated by the striking dependence of the valence electronic structure of transition metal surfaces on their crystallographic orientation, and by emerging experiments on laser-assisted extended ultraviolet (XUV) photoemission from solid surfaces, we calculate photoemission spectra from Cu(100) and Cu(111) surfaces as a function of the photoelectron final kinetic energy and the delay between the ionizing attosecond XUV pulse train and assisting infrared (IR) laser pulse. Our numerical simulations predict distinct differences in delay-dependent photoelectron energy distributions and photoemission time delays for Cu(100) and Cu(111) surfaces. Furthermore, these differences can be scrutinized experimentally with existing technology in a suggested in situ comparative RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) configuration by placing the two surfaces on a sliding platform while keeping all optical components and pathlengths fixed. Our calculations also show that the inclusion of the Fresnel-reflected incident IR pulse at the metal-vacuum interface modifies photoelectron spectra and photoemission time delays in a characteristic way that reveals the degree of spatial location of the initial electronic states.
The occurrence of radiofrequency (RF) breakdown limits operational electromagnetic gradients in accelerator structures. Experimental evidence often suggests that breakdown events are associated with temperature and dark current spikes on the surface of RF devices. In the past decade, there has been increased interest in unveiling the mechanism behind breakdown initiation in metal copper and copper alloys; however, efforts regarding a breakdown phenomenon in photocathode-relevant semiconductors have been more limited. In this work, we explore field-emission-assisted heating via Nottingham and Joule processes, as a possible candidate for breakdown initiation. For this, field emission from an intrinsic Cs2Te ultrathin film coated on a copper substrate was modeled within the Stratton–Baskin–Lvov–Fursey formalism, describing the processes and effects in the bulk and on the surface of a photocathode exposed to high RF electromagnetic fields. It is shown that a field-emission characteristic deviates significantly from the classical Fowler–Nordheim (FN) theory, whereby predicting that dark current is orders of magnitude lower than the one expected by FN law. Conventional pulsed heating was also found to impose negligible heating to the photocathode. Both conclusions suggest that a Cs2Te photocathode coated on a metal substrate would be insensitive to catastrophic thermal-material runaway breakdown, unlike what is observed for metal surfaces. Finally, a few unconventional breakdown candidate scenarios are identified and discussed, including thermoelastic deformation and avalanche breakdown.
The multiple colliding laser pulse concept formulated by Bulanov et al. ( Phys. Rev. Lett ., vol. 104, 2010 b , 220404) is beneficial for achieving an extremely high amplitude of coherent electromagnetic field. Since the topology of electric and magnetic fields of multiple colliding laser pulses oscillating in time is far from trivial and the radiation friction effects are significant in the high field limit, the dynamics of charged particles interacting with the multiple colliding laser pulses demonstrates remarkable features corresponding to random walk trajectories, limit circles, attractors, regular patterns and Lévy flights. Lastly, under extremely high intensity conditions the nonlinear dissipation mechanism stabilizes the particle motion resulting in the charged particle trajectory being located within narrow regions and in the occurrence of a new class of regular patterns made by the particle ensembles.
Apart from maximizing the strength of optical electromagnetic fields achievable at high-intensity laser facilities, the collision of several phase-matched laser pulses has been identified theoretically as a trigger of and way to study various phenomena. These range from the basic processes of strong-field quantum electrodynamics to the extraordinary dynamics of the generated electron-positron plasmas. This has paved the way for several experimental proposals aimed at both fundamental studies of matter at extreme conditions and the creation of particle and radiation sources. Because of the unprecedented capabilities of such sources, they have the potential to open up new opportunities for experimental studies in nuclear and quark-gluon physics. We perform here a systematic analysis of different regimes and opportunities achievable with the concept of multiple colliding laser pulses, for both current and upcoming laser facilities. Here, we reveal that several distinct regimes could be within reach of multi-petawatt laser facilities.
The dynamics that take place within just tens to hundreds of femtoseconds following the absorption of light by a molecule can play a critical role in how the absorbed energy is directed, allowing it to be used for a specific function or dissipated harmlessly. The form of chemical change that occurs rapidly in these molecules is called a “nonadiabatic electronic transition.” Such transitions are known to mediate energy flow in natural biological systems such as the ultraviolet photoprotection mechanism of DNA and the first step of the human vision response. Understanding how these mechanisms work precisely may help scientists achieve controlled manipulation of solar energy or optical control of a wide range of energy management functions in artificial systems. Experimental methods, however, have not yet allowed a precisely resolved and complete measurement of nonadiabatic electronic transitions. This constitutes a major obstacle to progress in the field. For progress to occur that would inform a wide body of research aiming to efficiently harness the energy of light for practical purposes, it is especially important to benchmark computational models of the molecules undergoing these rapid changes with experimental measurements, in order to learn which models are accurate. With Dept. of Energy funding, we have made strong progress towards establishing a new optical method for experimentally detecting the full nonadiabatic electronic transition. This requires having coordinated pulses of light covering the visible through the mid-infrared range of the electromagnetic spectrum that last only ten femtoseconds. We have developed a new, relatively simple approach for generating such pulses of laser light, and have incorporated them into a time-resolved spectrometer for measuring rapid changes in molecules. These tools can provide the greater precision and new types of data that are needed to benchmark computational models of molecular change and thus to make progress in the field. Our tools were tested on graphene, an excellent solid-state sample for verifying the capabilities and limitations of our instrumentation. The investment made in these tools by the Dept. of Energy Office of Science will allow new fundamental scientific understanding of energy dynamics in molecules in future studies.
This work presents a new multiscale method for coupling the 3D Maxwell's equations to the 1D telegrapher's equations. While Maxwell's equations are appropriate for modeling complex electromagnetics in arbitrary-geometry domains, simulation cost for many applications (e.g. pulsed power) can be dramatically reduced by representing less complex transmission line regions of the domain with a 1D model. By assuming a transverse electromagnetic (TEM) ansatz for the solution in a transmission line region, we reduce the Maxwell's equations to the telegrapher's equations. Here, we propose a self-consistent finite element formulation of the fully coupled system that uses boundary integrals to couple between the 3D and 1D domains and supports arbitrary unstructured 3D meshes. Additionally, by using a Lagrange multiplier to enforce continuity at the coupling interface, we allow for an absorbing boundary condition to also be applied to non-TEM modes on this boundary. We demonstrate that this feature reduces non-physical reflection and ringing of non-TEM modes off of the coupling boundary. By employing implicit time integration, we ensure a stable coupling, and we introduce an efficient method for solving the resulting linear systems. We demonstrate the accuracy of the new method on two verification problems, a transient O-wave in a rectilinear prism and a steady-state problem in a coaxial geometry, and show the efficiency and weak scalability of our implementation on a cold test of the Z-machine MITL and post-hole convolute.
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Nonlocal potential models have been used in place of the Coulomb potential in the Schrödinger equation as an efficient means of exploring high-field laser-atom interaction in previous works. Although these models have found use in modeling phenomena including photoionization and ejected electron momentum spectra, they are known to break electromagnetic gauge invariance. This paper examines if there is a preferred gauge for the linear field response and photoionization characteristics of nonlocal atomic binding potentials in the length and velocity gauges. Overall, it is found that the length gauge is preferable for a wide range of parameters.
We have conducted 0D, 1D, 2D, and 3D simulations of an idealized coaxial impedance-matched Marx generator (IMG) []. The 0D calculations were conducted with a four-element circuit model; the 1D, 2D, and 3D calculations were conducted with highly resolved, fully electromagnetic representations. The IMG consists of 30 stages distributed axially and connected electrically in series. Each stage is powered by two bricks separated by 180° and connected electrically in parallel. Each brick comprises two opposite-polarity capacitors in series with a single switch. The bricks drive an internal impedance-matched coaxial transmission line terminated by a resistive load. The simulations neglect effects due to the switch-triggering circuit, the capacitor-charging circuit, external conducting boundaries, and reactive components of the load. We find dimensionality does not significantly affect the electrical power delivered by the IMG to its load: peak load powers estimated by the 0D, 1D, 2D, and 3D simulations agree to within 1%. The 3D calculations demonstrate that electromagnetic power radiated by the bricks, and axial gaps between stages, reduces the peak load power by less than ∼ 1 % . Each simulation assumes the load impedance is 34% above that at which the load power is maximized. Operating an IMG with such an overmatched load offers several advantages while decreasing the peak load power by only 2%. The 0D, 1D, 2D, and 3D models outlined herein could be adapted to assess computationally competing IMG designs, and conduct a variety of numerical IMG experiments, an IMG is constructed. Published by the American Physical Society 2024
The purpose of this data set is to provide a means of characterizing the bedrock variability both within a single borehole location and across the East River Watershed. The East River is part of the Watershed Function Scientific Focus Area (WFSFA) located in the Upper Colorado River Basin, United States, and all boreholes are located within Mancos shale bedrock. The data set contains geophysical borehole logging data acquired in October 2018 in boreholes ER-GUM1 (East River- Gothic Upper Montane Borehole #1) and ER-GLS1 (East River- Gothic Lower Subalpine Borehole #1), and acquired in October 2019 in boreholes ER-PLM7 (East River- Pumphouse Lower Montane Borehole #7) and ER-PLM8 (East River- Pumphouse Lower Montane Borehole #8). It contains depth, natural gamma ray emission, spectral gamma ray emission(Th, K, U), magnetic susceptibility, fluid temperature and electrical conductivity, electromagnetic (EM) induction derived rock electrical resistivity, heat pulse and spinner flow measurements to estimate groundwater flow, and Nuclear Magnetic Resonance (NMR) derived water content and hydraulic conductivity. Data for each borehole are provided as comma delimited text files. For each borehole accurate location information is provided (based on RTK GPS (Real Time Kinematic Global Positioning System) surveying). Borehole logging data were acquired using Mount Sopris borehole tools, and Vista Clara Javelin for NMR data.
A thermionic RF gun is a compact and efficient source of electrons used in many practical applications. RadiaBeam Systems and the Advanced Photon Source at Argonne National Laboratory collaborate in developing of a reliable and robust thermionic RF gun for synchrotron light sources which would offer substantial improvements over existing thermionic RF guns and allow stable operation with up to 1A of beam peak current at a 100 Hz pulse repetition rate and a 1.5 μs RF pulse length. In this paper, we discuss the electromagnetic and engineering design of the cavity and report the progress towards high power tests of the cathode assembly of the new gun.
The existence of dark matter (DM) is supported by various macroscopic observations, but its microscopic nature remains elusive. The Galactic Center GeV gamma-ray excess (GCE) has been a leading candidate signal for particle dark matter annihilation. However, an unresolved population of millisecond pulsars (MSPs) in the bulge provides the alternative explanation for the excess. Identifying these MSPs in electromagnetic bands is difficult due to source confusion, pulse broadening, and extinction. Gravitational waves (GWs) provide a complementary probe: a steadily rotating, non-axisymmetric MSP emits a nearly monochromatic GW signal in the sensitive band of ground-based detectors, with amplitude set by its ellipticity. In this work, we systematically investigate the GW emission from the MSP population proposed to explain the GCE and its detectability with current and future detectors. We consider three major scenarios for the origin of ellipticity and model the population properties of these MSPs. We also consider both isolated MSPs and MSPs in binary systems, as well as Doppler effects in the detection. We find that while the signal is below the reach of current interferometers, next-generation detectors such as the Einstein Telescope (ET) and Cosmic Explorer (CE) can detect a fraction of those MSPs, offering a novel test of the MSP interpretation of the GCE. Future directed searches toward the Galactic Center with continued improvements in sensitivities will either uncover this long-sought MSP population or place stringent limits on their ellipticities and abundance, with important implications for both the astrophysical and dark-matter interpretations of the GCE.
We describe a direct magneto-optical approach to measuring the magnetic field driven by a narrow pulse width (<10 ns), 20 kA electrical current flow in the transmission line of a high energy pulsed power accelerator. The magnetic field and electrical current are among the most important operating parameters in a pulsed power accelerator and are critical to understanding the properties of the radiation output. However, accurately measuring these fields and electrical currents using conventional pulsed power diagnostics is difficult due to the strength of ionizing radiation and electromagnetic interference. Our approach uses a fiber coupled laser beam with a rare earth element sensing crystal sensor that is highly resistant to electromagnetic interference and does not require external calibration. Here, we focus on device theory, operating parameters, results from an experiment on a high energy pulsed power accelerator, and comparison to a conventional electrical current shunt sensor.
Exact four-photon resonance of collinear planar laser pulses is known to be prohibited by the classical dispersion law of electromagnetic waves in plasma. We show here that the renormalization produced by an arbitrarily small relativistic electron nonlinearity removes this prohibition. The laser frequency shifts in collinear resonant four-photon scattering increase with laser intensities. For laser pulses of frequencies much greater than the electron plasma frequency, the shifts can also be much greater than the plasma frequency and even nearly double the input laser frequency at still small relativistic electron nonlinearities. Furthermore, this may enable broad range tunable lasers of very high frequencies and powers. Since the four-photon scattering does not rely on the Langmuir wave, which is very sensitive to plasma homogeneity, such lasers would also be able to operate at much larger plasma inhomogeneities than lasers based on stimulated Raman scattering in plasma.
An ultra-low field pre-pulse Magnetic Resonance Imaging (PMRI) system for a head includes RF coils defining a bore for head access, a pre-pulse coil outside the RF coils, and a coil assembly including a main magnetic field coil and gradient coils outside the pre-pulse coil. The PMRI system includes a first cylindrical shield concentric with the RF coils and made from conductive materials. The first cylindrical shield partially encloses the RF coils and inside the pre-pulse coil for shielding the RF coils from environmental electromagnetic disturbances.
We report a numerical analysis of the stochastic acceleration of electrons, stipulated by a random change in the phase of the force acting on the electron. The main source of randomness is the random spatial distribution of electromagnetic fields in the focal region of multimode laser radiation. A typical frequency of the random phase change corresponding to the maximum impact of the effect under consideration lies in the range of (0.25–0.5)ν (ν is the radiation frequency of a neodymium laser). A wave packet model convenient for calculations taking into account the radiative transitions of the neodymium ion is proposed. The dependence of the average energy of relativistic electrons on the flux density in the range of 10{sup 15}–10{sup 18} W cm{sup -2} is calculated. The time dependence of the average electron energy during the laser pulse in the form of approximating formulas is constructed. The typical time for the development of stochastic heating of electrons is determined. It is found that the stochastic acceleration process weakly depends on the laser pulse duration, when the latter exceeds several hundred periods of the electromagnetic wave. (interaction of laser radiation with matter. laser plasma)