Plane-wave Field Research Articles

Quantum radiation reaction spectrum of electrons in plane waves

In previous works we derived equations for the average momentum of high-energy electrons experiencing quantum radiation reaction in strong electromagnetic plane-wave background fields. In this paper we derive similar equations for the momentum spectrum. We formulate the equations in terms of the cumulative function and study the relation between the equations for the spectrum and the equations for the moments, analyze the structure of the low-energy expansions, and finally explain how our formulation is essentially in terms of a “Green’s function” which allows us to study the dynamics without choosing a specific initial wave packet (or particle-bunch distribution). Published by the American Physical Society 2024

Estimation of acoustical materials sound absorption coefficient under oblique incidence plane wave and diffuse field via Allard model inversion

A technique for estimating the sound absorption of materials under oblique incidence plane wave and diffuse field excitations is proposed. It requires a mobile loudspeaker and a pair of fixed microphones above a layer of absorbing material. Starting from sound pressure measurements made above the material surface for multiple source positions and by inverting Allard’s propagation model, the proposed method allows for the identification of two effective (or equivalent) parameters, namely, the complex effective density and the complex wave number. Obtaining these parameters makes it possible to estimate the sound absorption coefficient for a plane wave with any angle of incidence or under a diffuse acoustic field by summation over the angles. The results are compared to theoretical values calculated using the Johnson-Champoux-Allard model and to reference measurements obtained using an impedance tube, a small cabin, a large reverberant room, and a sound field synthesis method. One of the limitations of this method lies in the assumptions associated with the Allard model to describe the sound field above the material (assumed to be isotropic, homogeneous, of constant thickness, and to behave like an equivalent fluid). The main advantages are (1) that the sound absorption coefficient can be estimated under oblique incidence plane wave and diffuse acoustic field with values that are always in a physical range (between 0 and 1), and (2) that samples of the order of the square meter without specific preparation can be tested which reduces the constraints associated with impedance tube or reverberant room measurements.

On the area-averaged effective sound absorption coefficient of porous materials excited by a monopole

The area-averaged effective sound absorption coefficient (SAC) of a rigid-backed homogeneous porous material subjected to a monopole excitation is calculated as the absorbed-to-incident sound power ratio. Using Allard's model to describe the sound propagation above the porous material, an analytical model for this power-based SAC is proposed and proves to give a good approximation of the sound absorption performance under monopole excitation of sufficiently large areas of material. The impact of factors on the power-based SAC, such as monopole height, material radial dimension used to calculate the sound powers, and material properties is discussed. The power-based SAC frequency-dependent behavior is analyzed through sound intensity field assessments at the material surface and is compared to normal incident plane wave and diffuse field SACs. The sound absorption behavior of sound absorbers under monopole excitation exhibits notable distinctions and peculiar results compared to those observed under plane wave and diffuse fields, particularly at low frequencies and for sources close to the material.

Quantum ESPRESSO towards performance portability: GPU offload with OpenMP

In recent years, significant strides have been made to enable Quantum ESPRESSO (QE) to operate on heterogeneous HPC architectures, effectively harnessing the computational capabilities of GPUs. Initially, emphasis has been placed on NVIDIA-based hardware and software infrastructure. Nonetheless, the HPC landscape is multifaceted and intricate, prompting the project to prioritize achieving peak performance across various GPU models. To this end, efforts are being directed towards empowering QE to leverage AMD and Intel GPUs through OpenMP offload directives. In this paper, coding approach and benchmark tests of the OpenMP porting of Plane-Wave Self-Consistent Field (PWSCF) code is presented and discussed.

Fourier metasurface cloaking: unidirectional cloaking of electrically large cylinder under oblique incidence.

The existence of a non-electrically-small scatterer adjacent to the source can severely distort the radiation and lead to a poor electromagnetic compatibility. In this work, we use a conducting hollow cylinder to shield a cylindrical scatterer. The cylinder is shelled with a single dielectric layer enclosed by an electromagnetic metasurface. The relationship between the scattering field and the surface impedance is derived analytically. By optimizing the Fourier expansion coefficients of the surface impedance distribution along ϕ-dimension, the scattering cross-section can be effectively reduced. This unidirectional cloaking method is valid for both TM/TE and non-TM/TE incident field and is not limited to a plane-wave incident field. The accuracy and effectiveness of the method are verified by four cloaking scenarios in microwave regime. We demonstrate that with the surface impedance obtained by the proposed method, a metasurface is designed with physical subwavelength structures. We also show a cloaking scenario under a magnetic dipole radiation, which is closer to the case of a realistic antenna. This method can be further applied to cloaking tasks in terahertz and optical regimes.

Tuning the magnetic properties of doped ZnS using transition metal doping: A multi-scale computational approach

Transition metal (TM)-doped dilute magnetic semiconductors (DMS) have emerged as promising materials for spintronic applications such as spin-polarized transport and information storage. However, achieving robust room-temperature ferromagnetism in DMS remains a key challenge. This work undertakes a comprehensive investigation of the effects of Ti- and Cr-doping and (Ti,Cr)-codoping on the structural, electronic, and magnetic properties of wurtzite ZnS using first-principles pseudopotential plane-wave self-consistent field calculations and Monte Carlo simulations. The first-principles DFT calculations were performed using the spin-polarized GGA+U approach to account for strong electron–electron interactions. Structural relaxations revealed expanded lattice parameters and bond lengths for the doped systems compared to pure ZnS, attributed to the larger ionic radii of the dopants. Formation energy calculations confirmed the thermodynamic stability of doping. The band structure and density of states analysis demonstrated the half-metallic nature of the doped ZnS systems with 100% spin polarization induced by strong hybridization between the TM-3d and S-3p states. This mediates robust ferromagnetic coupling, with total magnetic moments around 4-8 μB/cell depending on dopant type and concentration. To complement the zero-temperature DFT results, temperature-dependent Monte Carlo simulations using the single-spin flip Heat Bath algorithm were implemented. The modeling of magnetization, susceptibility, specific heat, and hysteresis loops enabled extracting Curie temperatures up to 427.6 K for 12.5% Cr-doped ZnS. The synergistic combination of first-principles DFT and Monte Carlo computational techniques provides significant insights into tailoring the magnetic properties of TM-doped ZnS dilute magnetic semiconductors. The tunability of structural, electronic, and magnetic characteristics through control of dopant selection and concentration demonstrates the promising potential of transition metal-doped ZnS for spintronic devices operable at room-temperature.

Assessment of acoustical materials sound absorption coefficient under oblique incidence plane wave and diffuse field using a virtual source antenna

The measurement of the absorption coefficient of acoustic materials is usually performed in an impedance tube under normal incidence on a small sample, or in a reverberant room under diffuse field incidence on a large sample of material. Both methods are prone to well-documented experimental limitations and errors. The approach proposed here uses a virtual source antenna (a point source moved at successive positions) over a material sample typically 1 to 4 m2 in size, and a fixed microphone pair directly above the material surface. Several methods have been tested to reconstruct the absorption coefficient under oblique plane wave or diffuse field incidence. Among these, the inversion of the Allard propagation model over an absorbing plane, in order to extract the material properties (complex wavenumber and density) from measured microphone transfer functions, is presented here. Absorption coefficients are shown for various acoustic materials.

Computational study on structural, elastic, mechanical and optical properties of K2AgAs ternary semiconductor compound

In this study, the structural, electronic, elastic, mechanical, and optical properties of a new Zintl phase K2AgAs ternary semiconductor compound have been investigated by the first-principles method using the plane-wave self-consistence field method. A triangulation of different exchange-correlation functionals, including local density approximation-LDA-PZ, generalized gradient approximation (GGA)-Q2D, GGA-BLYP, GGA-Perdew–Burke–Ernzerhof (PBE), GGA-PBESol, and GGA-revPBE, have been utilized to predict the properties of the material. The computed structural properties predicted that the K2AgAs compound is thermodynamically stable, and the lattice parameters are consistent with the reported experimental values. The electronic properties show that the bandgap ranges between 0.6645 and 1.1915 eV, while the conduction and valence bands are formed mainly through the hybridization of the As-2p, Ag-2p and Ag-3d, As-2p states, respectively, with other states making minimal contribution. From the calculation of elastic properties, K2AgAs were predicted to be mechanically stable. Notably, K2AgAs has been predicted to absorb light within the ultraviolet-visible regime. Owing to their good thermodynamic and mechanical stability, wide coverage of absorption in the UV-Vis region of the solar spectrum, and narrow bandgaps, K2AgAs can be formed/synthesized and applied as the active photoactive material in solar cells and other photovoltaics.

On the status of channeling radiation and laser based radiation sources

A unified description of channeling radiation (CR) in oriented crystals (OC) and radiation in the field of an intense plane wave (laser radiation sources – LRS) is proposed in terms of two Lorentz-invariant parameters. The case of planar positron channeling (quasi-channeling) and linearly polarized laser wave is considered in detail up to TeV energies. The crucial difference between LRS and CR is that in the former case both invariants are independent, while in channeling they are linearly related to each other. This leads to a strong limitation on the range of possible values of these invariants in OC. On the other hand, OC make it possible to study QED processes in strong non-uniform external fields.

Tracking aftershock sequences using empirical matched field processing

SUMMARY Extensive aftershock sequences present a significant problem to seismological data centres attempting to produce near real-time comprehensive seismic event bulletins. An elevated number of events to process and poorer performance of automatic phase association algorithms can lead to large delays in processing and a greatly increased human workload. Global monitoring is often performed using seismic array stations at considerable distances from the events involved. Empirical matched field processing (EMFP) is a narrow-frequency band array signal processing technique that recognizes the inter-sensor phase and amplitude relations associated with wavefronts approaching a sensor array from a given direction. We demonstrate that EMFP, using a template obtained from the first P arrival from the main shock alone, can efficiently detect and identify P arrivals on that array from subsequent events in the aftershock zone with exceptionally few false alarms (signals from other sources). The empirical wavefield template encodes all the narrow-band phase and amplitude relations observed for the main shock signal. These relations are also often robust and repeatable characteristics of signals from nearby events. The EMFP detection statistic compares the phase and amplitude relations at a given time in the incoming data stream with those for the template and is sensitive to very short-duration signals with the required characteristics. Significant deviations from the plane wavefront model that typically degrade the performance of standard beamforming techniques can enhance signal characterization using EMFP. Waveform correlation techniques typically perform poorly for aftershocks from large earthquakes due to the distances between hypocentres and the wide range of event magnitudes and source mechanisms. EMFP on remote seismic arrays mitigates these difficulties; the narrow-band nature of the procedure makes arrival identification less sensitive to the signals’ temporal form and spectral content. The empirical steering vectors derived for the main shock P arrival can reduce the frequency dependency of the slowness vector estimates. This property helps us to automatically screen out arrivals from outside of the aftershock zone. Standard array processing pipelines could be enhanced by including both plane-wave and empirical matched field steering vectors. This would maintain present capability for the plane-wave steering vectors and provide increased sensitivity and resolution for those sources for which we have empirical calibrations.

Master formulas for photon amplitudes in a combined constant and plane-wave background field

The worldline formalism has previously been used for deriving compact master formulas for the QED N - photon amplitudes in vacuum, in a constant field and in a plane-wave field. Here we carry this program one step further by deriving master formulas for the scalar and spinor QED one-loop N-photon amplitudes in the background of the “parallel” special case of a combined constant and plane-wave field.

Coiled quarter wavelength resonators for low-frequency sound absorption under plane wave and diffuse acoustic field excitations

To reduce their space requirement, quarter wavelength resonators are coiled up into a spiral to have the shape of a flat cylinder. The practical implementation of these resonators is tested using 3D printing, laser cutting and machining. Numerical simulations and impedance tube measurements are first compared for a normally incident plane wave excitation. This step allows to evaluate the effect of the resonator’s inlet diameter, internal wall thickness, overall height as well as its constitutive material. A series of samples are then 3D printed following the identified optimal geometrical configuration. An array of resonators is tested alone and in combination with a glass wool layer under diffuse acoustic field excitation in a small reverberation chamber. The obtained results show that coiled quarter wavelength resonators can provide large sound absorption at their lowest resonance frequency and under both considered excitations, even if the largest external dimension of the resonators is only 1/18th of the targeted acoustic wavelength.

Analysis of the Terminal Response Characteristics of the Twisted Three-Wire Cable Excited by a Plane Wave Field

A twisted three-wire cable model with uniform twisting characteristics is proposed in this paper, and its terminal response under external electromagnetic wave irradiation is calculated using the TLM method based on Taylor model. The triple-stranded triple-helix structure is determined in the method and the parametric equations of the twisted wire bundle in the Cartesian coordinate system are provided. Then, the frequency domain equations for the voltage and current of the twisted three-wire cable under field-to-wire coupling are derived and extended to apply to scenarios with arbitrary polarization and irradiation in the incident direction based on the transmission-line theory. Finally, the response laws of the twisted three-wire wire with different cable lengths, termination loads, and pitches coupling under external electromagnetic wave irradiation are studied. A uniform twisted three-wire cable can suppress the increased induced current on the cable. In addition, the excellent characteristics of the twisted three-wire cable in terms of immunity to electromagnetic interference are also verified by comparing the frequency domain response with that of a parallel three-wire cable.

Study of structural, magnetic and electronic properties of a new off-stoichiometric series of full-Heusler alloy Co2Nb1+xZ1−x (Z = Sn, In, Ga): Ab initio approach

Using ab initio calculation, we investigate systematically the structural, electronic and magnetic properties of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50). Here, Plane-Wave self-consistent field (PWscf) program implemented in open-source Quantum Espresso software package within generalized gradient approximation (GGA) - Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation functional has been used. Equilibrium lattice parameters in cubic austenitic phase of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50) have been inquired. It has been found out that except Co2NbSn, all the compositions do not show martensitic structural transition. The microscopic origin for this has been associated with Jahn-Teller distortion of Co 3deg orbitals in close proximity of the Fermi level. The density of states for both tetragonal and 4 O orthorhombic structure in martensitic phase of Co2NbSn have been investigated. Moreover, from the density of states plots we have recognized the metallic character of Co2NbSn. However, Co2NbGa & Co2NbIn and all of the off-stoichiometric alloys have been anticipated to possess partial half-metallic character. Furthermore, we have examined the total magnetic moment and average atomic magnetic moments in off-stoichiometric Co2Nb1+xZ1−x in the cubic phase to understand the effect of Nb doping in stoichiometric compounds. Nb doping increases the total magnetic moment due to increased Nb-Co hybridization of d orbitals.

Resonance, Rayleigh flows, and thermal choking: Compressible coolant states in porous electromagnetic heat exchangers

Electromagnetic (EM) heat exchangers (HX) are systems that convert EM energy into heat or mechanical work. One potential design consists of a porous lossy ceramic material heated by EM waves with a compressible gas coolant. EM heating of ceramics is nonlinear, since the loss factor is temperature dependent. Designing such EM HXs requires an understanding of coupling between temperature, the electric field, and gas dynamics at the pore scale. To mimic this microscale phenomenon, a single channel with a high-speed gas coolant in perfect thermal contact with a thin solid ceramic layer is considered, with an applied plane-wave electric field propagating normal to the channel walls. From a thin-domain asymptotic analysis, the conservation laws reduce to a Rayleigh flow in the gas coupled with averaged thermal energy conservation equations at leading order. The model predicts that the kinetic energy of the gas increases up to 12.5 times the inlet value when thermal runaway occurs in the ceramic region for the cases considered, and thermal choking is possible when the coolant reaches the sonic state. Local maxima of efficiency occur on a discrete set of ceramic thicknesses that correspond to Fabry–Bragg resonances of the electric field.

Resummation of the α expansion for nonlinear pair production by an electron in a strong electromagnetic field

We show how to resum the Furry-picture $\ensuremath{\alpha}$ expansion in order to take quantum radiation reaction and spin transition into account in the nonlinear trident process in (pulsed) plane-wave background fields. The results are therefore nontrivial functions of both the background field strength, $eE$, and the coupling to the quantized photon field, $\ensuremath{\alpha}={e}^{2}/4\ensuremath{\pi}$. The effective expansion parameter, $T$, is $\ensuremath{\alpha}$ times $eE/m\ensuremath{\omega}\ensuremath{\gg}1$, which makes higher orders in $\ensuremath{\alpha}$ important. We show that they can change the sign of the spin-dependent part already at $T<1$, which will be experimentally accessible. We also present a new resummation method that essentially does to a convergent series what Borel-Pad\'e resummation does to an asymptotic series.

Performance analysis and enhancement of a PVDF-based P-P sound intensity probe

This study investigates the feasibility of a laminated polyvinylidene fluoride (PVDF) structure for realising a pressure–pressure (P-P) intensity probe, as well as the effects of various backing materials on the performance of the probe. The PVDF structure consists of two parallel PVDF films that serve roles as pressure sensors, and each of them is laminated between stiff plates. The sensitivity and directivity of these pressure sensors are examined numerically and experimentally. The physical properties and configuration of the PVDF sensing structure are optimised for the best sensing performance. For frequencies below 15 kHz, the averaged voltage outputs of the two PVDF films are proportional to the sound pressure of the incident plane sound wave. It has a flat frequency response and omni-directional directivity pattern. The difference between the outputs is proportional to the particle velocity of the incident sound, featured by a dipole directivity pattern and almost-linear dependence upon frequency. Such under-covered properties of the pressure- and velocity-generated voltages for the integrated sensing structure demonstrate its suitability for intensity estimation in the aforementioned frequency range. This study shows that the probe can determine the intensity of a plane wave field below an upper-frequency limit with pre-determined probe gains. The upper limit is determined by the finite-difference approximation error introduced by the pressure gradient method. Small errors exist in narrow frequency bands around resonances and are sensitive to the pressure-intensity index, which is the ratio of the mean square pressure to the sound intensity. These errors are caused by variations of probe gains due to the resonances and can be reduced by careful calibration around the resonance frequencies.

Nonlinear Compton scattering and nonlinear Breit-Wheeler pair production including the damping of particle states

In the presence of an electromagnetic background plane wave field, electron, positron, and photon states are not stable because electrons and positrons emit photons and photons decay into electron-positron pairs. This decay of the particle states leads to an exponential damping term in the probabilities of single nonlinear Compton scattering and nonlinear Breit-Wheeler pair production. In this paper, we investigate analytically and numerically the probabilities of nonlinear Compton scattering and nonlinear Breit-Wheeler pair production including the particle states' decay. For this, we first compute spin- and polarization-resolved expressions of the probabilities, provide some of their asymptotic behaviors, and show that the results of the total probabilities are independent of the spin and polarization bases. Then, we present several plots of the total and differential probabilities for different pulse lengths and for different spin and polarization quantum numbers. We observe that it is crucial to take into account the damping of the states in order for the probabilities to stay always below unity, and we show that the damping factors also scale with the intensity and pulse duration of the background field. In the case of nonlinear Compton scattering, we show numerically that the total probability behaves like a Poissonian distribution in the regime where the photon recoil is negligible. In all considered cases, the kinematic conditions are such that the final particles momenta transverse to the propagation direction of the plane wave are always much smaller than the particles longitudinal momenta and the main spread of the momentum distribution on the transverse plane is along the direction of the plane wave electric field.

Non-Uniform Gratings That Radiate Preselected Plane Waves

A generalized Poisson summation formula produces exact expressions for the locations and strengths of line currents that radiate preselected plane waves. The line currents can be in free space or placed above a perfectly conducting ground plane. Closed-form expressions are obtained for the line current locations and amplitudes when the plane-wave parameters have periodic amplitudes and propagation vectors. A corresponding wire-impedance solution is derived that employs thin-wire approximations and takes into account all multiple interactions between wires. Remarkably, this solution holds even when the required impedance values are nonperiodic. The plane-wave parameters within one period determine the period of the impedance values and, thus, determine how many different types of loaded wires are required. For general nonperiodic plane-wave parameters, the line-source locations and amplitudes can be determined from an FFT approach involving a complex-contour integral, and the corresponding wire impedances can be computed numerically. With these impedance solutions, the number of degrees of freedom for the planar grating has been increased significantly to allow for the creation of a wide range of plane-wave fields.

Quasiclassical representation of the Volkov propagator and the tadpole diagram in a plane wave

The solution of the Dirac equation in the presence of an arbitrary plane wave, corresponding to the so-called Volkov states, has provided an enormous insight in strong-field QED. In [Phys. Rev. A \textbf{103}, 076011 (2021)] a new "fully quasiclassical" representation of the Volkov states has been found, which is equivalent to the one known in the literature but which more transparently shows the quasiclassical nature of the quantum dynamics of an electron in a plane-wave field. Here, we derive the corresponding expression of the propagator by constructing it using the fully quasiclassical form of the Volkov states. The found expression allows one, together with the fully quasiclassical expression of the Volkov states, to compute probabilities in strong-field QED in an intense plane wave by manipulating only 2-by-2 rather than 4-by-4 Dirac matrices as in the usual approach. Moreover, apart from the exponential functions featuring the classical action of an electron in a plane wave, the fully quasiclassical Volkov propagator depends only on the electron kinetic four-momentum in the plane wave, which is a gauge-invariant quantity. Finally, we also compute the one-loop tadpole diagram in a plane wave starting from the Volkov propagator and we find that after renormalization it identically vanishes.