Radiation Damping Research Articles

Dipolar field effects in a solid-state NMR maser pumped by dynamic nuclear polarization.

We report the observations and the analysis of a pulsed solid state sustained maser generated by proton spins hyperpolarized by Dynamic Nuclear Polarization (DNP) at cryogenic temperatures. Similar unconventional behaviour was observed recently [Weber et al., Phys. Chem. Chem. Phys., 2019, 21, 21278-21286], with induction decays exhibiting multiple asymmetric maser pulses for short time (100 ms) and persistent for tens of second, when the spins are polarized negatively. We present new evidence of such DNP NMR masers, and shed light on previously observed but unexplained features of these masers through simulations of the non-linear spin dynamics using the Bloch-Maxwell-Provotrov (BMP) equations for radiation damping and DNP, and taking into account the (distant) dipolar field.

Oscillations in radiative damping of plasma resonances in a gated disk of a two-dimensional electron gas

We calculate the absorption spectra of a conductive disk in the presence of a metal gate. In our analysis, we use the conductivity described by the Drude model. We examine the frequency and line width of the absorption resonances associated with the excited plasma waves. They are estimated both numerically and analytically for the fundamental and axisymmetric plasma modes. The line width is determined by the collisional and radiative losses. In high mobility samples, the latter may dominate even when the resonant frequencies can be described by a standard quasistatic approximation, i.e., neglecting electromagnetic retardation. Placing a metal near the disk drastically affects the radiative broadening of the line width due to the interference of electromagnetic fields created by the disk and the metal charges. Bringing the disk in close proximity to the gate makes the total field almost vanish. In that case, the line width is defined solely by the collisional broadening. As the disk is moved away from the gate, the line width first shows a reduction since the plasmon transforms into plasmon-polariton, which is dressed with undamped electromagnetic field surrounding the disk. Then it increases and exhibits decaying oscillations, reaching the asymptotic value of the ungated disk.

Temperature-resilient anapole modes associated with TE polarization in semiconductor nanowires

Polarization-dependent scattering anisotropy of cylindrical nanowires has numerous potential applications in, for example, nanoantennas, photothermal therapy, thermophotovoltaics, catalysis, sensing, optical filters and switches. In all these applications, temperature-dependent material properties play an important role and often adversely impact performance depending on the dominance of either radiative or dissipative damping. Here, we employ numerical modeling based on Mie scattering theory to investigate and compare the temperature and polarization-dependent optical anisotropy of metallic (gold, Au) nanowires with indirect (silicon, Si) and direct (gallium arsenide, GaAs) bandgap semiconducting nanowires. Results indicate that plasmonic scattering resonances in semiconductors, within the absorption band, deteriorate with an increase in temperature whereas those occurring away from the absorption band strengthen as a result of the increase in phononic contribution. Indirect-bandgap thin ([Formula: see text]) Si nanowires present low absorption efficiencies for both the transverse electric (TE, [Formula: see text]) and magnetic (TM, [Formula: see text]) modes, and high scattering efficiencies for the TM mode at shorter wavelengths making them suitable as highly efficient scatterers. Temperature-resilient higher-order anapole modes with their characteristic high absorption and low scattering efficiencies are also observed in the semiconductor nanowires ([Formula: see text] nm) for the TE polarization. Herein, the GaAs nanowires present [Formula: see text] times greater absorption efficiencies compared to the Si nanowires making them especially suitable for temperature-resilient applications such as scanning near-field optical microscopy (SNOM), localized heating, non-invasive sensing or detection that require strong localization of energy in the near field.

Fully nonlinear numerical investigations on the dynamics of fluid resonance between multiple bodies in close proximity

Two-dimensional wave-induced fluid oscillations in two narrow gaps are numerically investigated in the time domain. The arbitrary-Lagrangian–Eulerian finite element model for free-surface flow problems is implemented based on the fully nonlinear potential flow theory. The aim of this study is to study the dynamic evolutions of gap resonance problems with focusing on both the initial transient and the final quasi-steady states, especially for the piston-mode oscillations of fluid bulk in multiple gaps that generally involve multiple response components and the nonlinear dynamic interactions between them. The transient and quasi-steady responses are examined through amplitude and phase analyses. The radiation damping and the time-dependent period-averaged phase adjustment are demonstrated to play significant roles in establishing the dynamic equilibrium process from the transient state to the quasi-steady state. The characteristics of the intrinsic synchronization modes of the quasi-steady oscillations allow us to derive the simplified formulas to predict the resonant and anti-resonant frequencies of the two-gaps system (two degrees-of-freedom) based on a simplified model of one degree-of-freedom. The predictive formulas provide useful insights into the dependence of resonant/anti-resonant frequencies on the relevant geometries of floating bodies. Significant nonlinear hardening stiffness behaviors of fluid responses between multiple bodies in close proximity are further demonstrated by different incident wave amplitudes. The effects of incident wave amplitudes on the amplitudes of responses and higher order harmonics are found to be highly dependent on the frequency bands. The contributions of the higher-order harmonics on the overall responses are explained utilizing the Fourier transformations analysis.

Estimate of largest velocities for Vlasov–Poisson plasma with radiation damping

In this article, we study the asymptotic behavior of classical solutions to three‐dimensional Vlasov–Poisson system with radiation damping arising in plasma physics. For smooth solutions with compact support in phase space, the growth estimate of the largest velocity of plasma particles is improved to . As a consequence, some better estimates of the charge density and electrostatic field are obtained.

A phase‐field model for quasi‐dynamic nucleation, growth, and propagation of rate‐and‐state faults

AbstractDespite its critical role in the study of earthquake processes, numerical simulation of the entire stages of fault rupture remains a formidable task. The main challenges in simulating a fault rupture process include the complex evolution of fault geometry, frictional contact, and off‐fault damage over a wide range of spatial and temporal scales. Here, we develop a phase‐field model for quasi‐dynamic fault nucleation, growth, and propagation, which features two standout advantages: (i) it does not require any sophisticated algorithms to represent fault geometry and its evolution; and (ii) it allows for modeling fault nucleation, propagation, and off‐fault damage processes with a single formulation. Built on a recently developed phase‐field framework for shear fractures with frictional contact, the proposed formulation incorporates rate‐ and state‐dependent friction, radiation damping, and their impacts on fault mechanics and off‐fault damage. We show that the numerical results of the phase‐field model are consistent with those obtained from well‐verified approaches that model the fault as a surface of discontinuity, without suffering from the mesh convergence issue in the existing continuous approaches to fault rupture (e.g., the stress glut method). Further, through numerical examples of fault propagation in various settings, we demonstrate that the phase‐field approach may open new opportunities for investigating complex earthquake processes that have remained overly challenging for the existing numerical methods.

Steady-state solutions of split beams in electron storage rings

Recently, a novel operation method for synchrotron light sources with transversely split beams has been explored to fulfill the rising demand for flexible and high-throughput X-ray sources required in such diverse fields as time-resolved X-ray spectroscopy, molecular chemistry in organic cells, high-resolution medical imaging, quantum materials science or sustainable energy research. Within that novel operation mode, additional stable regions are produced in the horizontal phase space by operating an electron storage ring on a resonance that is driven by the nonlinear sextupole or octupole magnets. In the longitudinal phase space, a similar split can be produced by introducing an oscillation of the synchrotron phase via a modulation of the phase of the radiofrequency resonator. Strong radiation damping in electron storage rings, however, has to be overcome before additional regions in phase space can become populated by particles and form stable islands. This damping mechanism changes the dynamics of the system and causes diffusion between the different islands in phase space, raising the question what kind of equilibrium state exists in the asymptotic temporal limit. In this paper, a finite-differences approximation in rotating action-angle coordinates is used to solve the Vlasov–Fokker–Planck equation and to study the obtained equilibrium states for the longitudinal as well as the transverse case. The number of solution vectors and the magnitude of the corresponding singular values of the matrix of the underlying finite-differences equation are used as abstract indicators to define the required parameter set that provides stable additional beamlets. As a consequence, the beamlets have a stability that is close to that of the main beam in terms of diffusion caused by the radiation damping and quantum excitation.

Non-hydrostatic modelling of the wave-induced response of moored floating structures in coastal waters

Predictions of the wave-induced response of floating structures that are moored in a harbour or coastal waters require an accurate description of the (nonlinear) evolution of waves over variable bottom topography, the interactions of the waves with the structure, and the dynamics of the mooring system. In this paper, we present a new advanced numerical model to simulate the wave-induced response of a floating structure that is moored in an arbitrary nearshore region. The model is based on the non-hydrostatic approach, and implemented in the open-source model SWASH, which provides an efficient numerical framework to simulate the nonlinear wave evolution over variable bottom topographies. The model is extended with a solution to the rigid body equations (governing the motions of the floating structure) that is tightly coupled to the hydrodynamic equations (governing the water motion). The model was validated for two test cases that consider different floating structures of increasing geometrical complexity: a cylindrical geometry that is representative of a wave-energy-converter, and a vessel with a more complex shaped hull. A range of wave conditions were considered, varying from monochromatic to short-crested sea states. Model predictions of the excitation forces, added mass, radiation damping, and the wave-induced response agreed well with benchmark solutions to the potential flow equations. Besides the response to the primary wave (sea-swell) components, the model was also able to capture the second-order difference-frequency forcing and response of the moored vessel. Importantly, the model captured the wave-induced response with a relatively coarse vertical resolution, allowing for applications at the scale of a realistic harbour or coastal region. The proposed model thereby provides a new tool to seamlessly simulate the nonlinear evolution of waves over complex bottom topography and the wave-induced response of a floating structure that is moored in coastal waters.

Stereographic projection to and from the Bloch sphere: Visualizing solutions of the Bloch equations and the Bloch–Riccati equation

Stereographic projection mapping is typically introduced to explain the point at infinity in the complex plane. After this brief exposure in the context of complex analysis, students rarely get an opportunity to fully appreciate stereographic projection mapping as an elegant and powerful technique on its own with many fruitful applications in the physical sciences. Here, using a classical description of nuclear magnetic resonance in the rotating frame, I show how stereographic projection mapping to and from the Bloch sphere can be used for visualizing solutions to Bloch's equation and the Bloch–Riccati equation, respectively. After developing the fundamentals of stereographic projection mapping using examples drawn from nuclear spin precession in the rotating frame, the method is then applied to visualizations of composite pulse excitation of a spin-1/2 system and to radiation damping in a system of isolated spins-1/2. In the case of the radiation-damped system, these visualizations provide particularly vivid illustrations of loxodromic Möbius transformation dynamics.

Effects of Parameters on Non-Linear Seismic Analysis of Fixed Offshore Platform

Fixed offshore structures in seismically active zones are likely to have deformations large enough to exceed the elastic limits of materials under strong ground motions. Therefore, investigation of nonlinear response of offshore structures under dynamic loadings is very interesting to structural engineers. Nonlinear behavior of structures is highly related with the soil properties and soil behavior. The main purpose of this study is to investigate and show the methodology for inelastic dynamic analyses of fixed-offshore structures under the 10,000-year earthquake loadings. The investigation in this study includes the effect of soil radiation damping, soil-pile gapping, and soil degradation on fixed offshore structures. Additionally, the effect of the direction of earthquake is included in this study. An offshore structure model ‘Platform A’ is modeled in CAPFOS. 10,000-year earthquake events are considered and for this purpose, two different earthquakes are used: Hector Mine Earthquake (1999) and Landers Earthquake (1992). These ground motion records are scaled to have a resulting earthquake that has a return period of 10,000-year. CAPFOS software is used to complete time-history analyses with these earthquakes. Results indicate that: (i) Considering the soil radiation damping negligible is not correct, because without the radiation damping, the total damping ratio is estimated as % 3, while including radiation damping raises the ratio to % 4.5, (ii) soil-pile gapping and soil radiation damping generate adverse effects on analyses outcome, and (iii) using high values of soil degradation factors is not always conservative.

Simultaneous measurements of unstable and stable Alfvén eigenmodes in JET

In this paper, we report the novel experimental observation of both unstable and stable toroidicity-induced Alfvén eigenmodes (TAEs) measured simultaneously in a JET tokamak plasma. The three-ion-heating scheme (D-DNBI-3He) is employed to accelerate deuterons to MeV energies, thereby destabilizing TAEs with toroidal mode numbers n = 3–5, each decreasing in mode amplitude. At the same time, the Alfvén eigenmode active diagnostic resonantly excites a stable n = 6 TAE with total normalized damping rate −γ/ω 0 ≈ 1%–4%. Hybrid kinetic-MHD modeling with codes NOVA-K and MEGA both find eigenmodes with similar frequencies, mode structures, and radial locations as in experiment. NOVA-K demonstrates good agreement with the n = 3, 4, and 6 TAEs, matching the damping rate of the n = 6 mode within uncertainties and identifying radiative damping as the dominant contribution. Improved agreement is found with MEGA for all modes: the unstable n = 3–5 and stable n = 2, 6 modes, with the latter two stabilized by higher intrinsic damping and lower fast ion drive, respectively. While some discrepancies remain to be resolved, this unique validation effort gives us confidence in TAE stability predictions for future fusion devices.

Silver mirror for enhancing the magnetic plasmon resonance and sensing performance in plasmonic metasurface

We report a novel method for enhancing magnetic plasmon resonances (MPRs) and sensing performance of metasurface consisting of a 1D Ag nanogroove array by using an opaque Ag mirror. The Ag mirror can block the transmission channel of light, so the radiative damping of MPRs excited in Ag nanogrooves is strongly reduced, and therefore the linewidth of MPRs is noticeably decreased. Because of ultra-narrow bandwidth and great magnetic field enhancement at MPRs, the metasurface shows very high sensitivity (S = 700 nm RIU−1, S* = 70 RIU−1) and figure of merit (FOM = 100, FOM* = 628), which holds great potential in the label-free biomedical sensing.

AlH lines in the blue spectrum of Proxima Centauri

ABSTRACT The recently computed ExoMol line lists for isotopologues of AlH are used to analyse the blue spectrum (4000–4500 Å) of Proxima Cen (M5.5 V). Comparison of the observed and computed spectra enables the identification of a large number of 27AlH lines of the A 1Π –X 1Σ+ band system: The spectral range covering 1-0, 0-0, and 1-1 bands are dominated by clearly resolved AlH lines. We reveal the diffuse nature of transitions close to the dissociation limit which appears in the form of increasingly wider (up to 5 Å) and shallower (up to the continuum confusion limit) AlH line profiles. The predicted wavelengths of AlH diffuse lines are systematically displaced. The effect of broadening by predissociation states on the line profiles is included by increasing the radiative damping rate by up to 5 orders of magnitude. We determine empirical values of damping rates for a number of the clean 0-0 Q-branch transitions by comparing the observed and synthetic stellar spectra. We find excellent agreement between our damping rates and lifetimes available in the literature. A comparison of 27Al1H ExoMol and REALH spectra shows that the observed spectrum is better described by the ExoMol line list. A search for 26Al1H lines in the Proxima Cen spectrum does not reveal any notable features; giving an upper limit of 27Al1H /26Al1H >100.

Flexible manipulation of plasmon dephasing time via the adjustable Fano asymmetric dimer

It is highly desirable to flexibly and actively manipulate the dephasing time of a plasmon in many potential applications; however, this remains a challenge. In this work, by using femtosecond time-resolved photoemission electron microscopy, we experimentally demonstrated that the Fano resonance mode in the asymmetric nanorod dimer can greatly extend the dephasing time of a femtosecond plasmon, whereas the non-Fano resonance results in a smaller dephasing time due to the large radiative damping, and flexible manipulation of the dephasing time can be realized by adjusting one of the nanorods in the Fano asymmetric dimer. Interestingly, it was found that plasmon resonance wavelengths both appeared red-shifted as the length of the upper or lower nanorods increased individually, but the dephasing time varied. Furthermore, it also indicated that the dephasing time can be prolonged with a smaller ascending rate by increasing the length of both the nanorods simultaneously while keeping the dimer asymmetry. Meanwhile, the roles of radiative and nonradiative damping in dephasing time are unveiled in the process of nanorod length variation. These results are well supported by numerical simulations and calculations.

Electron-Impact Ionization of the Tungsten Ions: W38+ − W45+

In this manuscript, we present our calculations of detailed electron-impact single ionization cross-sections for tungsten ions, spanning charge states W38+− W45+. The level-to-level distorted-wave method implemented in the flexible atomic code (FAC) was used for calculation. Comparison between the present level-to-level distorted wave treatment and previous configuration-averaged calculations has been performed for the W45+ ion, and we explore the possible reason for the difference observed between two calculations. We demonstrate the importance of radiative damping on the total electron-impact ionization cross-section for the W43+ ion. Present calculations provide missing cross-sections for W38+− W45+. The data obtained are expected to be useful for modeling plasmas for fusion applications, especially for the ITER community.

Quasibound states in a one-dimensional grating for electro-optic modulation

For modulation in free space using the linear electro-optic effect, a narrow-linewidth resonance is favorable when a minimal voltage is preferred to fully shift the resonance. Here a method is proposed to engineer the quasibound states in a slab waveguide consisting of electro-optic polymer and metal gratings, in order to achieve narrow-linewidth resonances for electro-optic modulation. This quasibound state features a strong out-of-plane electric field component located at the position of the metal strips constituting the grating, which also work as the interdigitated electrodes, and thus, the optical mode can interact with the electrostatic field efficiently. The radiation damping of the quasibound state can be controlled by changing the relative position of the neighboring metal strips, while the optical mode can maintain the same periodicity as the electrostatic field. This method also offers prospects for engineering narrow-linewidth resonances for other applications.

WAVE ENERGY CONVERTER SYSTEM ANALYSIS PERFORMANCE WITH PITCH MOTION IN VARIOUS DIMENSIONS AND DRAFT FOR APPLIED IN INDONESIA SEA

In Indonesia, national electricity consumption is expected continue to rise every year. One solution to meet the needs of electrical energy is to use clean energy that is sustainable to environment. Seeing Indonesia as an archipelagic country, One of renewable energy that could develop is ocean energy (Wave Energy Converter). Wave Energy Converter can be converted into electrical energy through a converter in the form of a floating structure. The structure will respond to the external force of the ocean waves into the pitching motion. The pitch movement will move a series of tools which are then channeled into a generator to produce electrical energy. The structure is said to be effective if it produces a large enough performance value. In this study the structure is modeled with various drafts and dimensions to obtain the most optimal hydrostatic parameter values. Furthermore, from this value, it is possible to estimate the amount of electrical energy that can be generated by adding a uniformed PTO damping value for each structure. From the results of the study, it was found that each structure with the same PTO damping value of 5×104kNm has a different performance value in each wave period. From the results of the analysis, it is found that the greater the value of mass and radiation damping, the greater the energy generation and performance of the structure. The structure that has the best performance is structure-6 with a Performance value of 72.12% at a wave period of 9 seconds which match with North Sumatera mean wave period.

Toroidal Alfvén eigenmode stability in JET internal transport barrier afterglow experiments

In this work, we use reduced and perturbative models to examine the stability of toroidal Alfvén eigenmodes (TAEs) during the internal transport barrier (ITB) afterglow in JET experiments designed for the observation of alpha driven TAEs. We demonstrate that in JET-like conditions, it is sufficient to use an incompressible cold plasma model for the TAE to reproduce the experimental adiabatic features such as frequency and position. When ion cyclotron resonant heating (ICRH) is used to destabilize TAEs, the core-localised modes that are predicted to be most strongly driven by minority ICRH fast ions correspond to the modes observed in the DD experiments, and conversely, modes that are predicted to not be driven are not observed. Linear damping rates due to a variety of mechanisms acting during the afterglow are calculated, with important contributions coming from the neutral beam and radiative damping. For DT equivalent extrapolations of discharges without ICRH heating, we find that for the majority of modes, alpha drive is not sufficient to overcome radiative damping.

Ultranarrow Linewidth Coupling Resonance in Flexible Plasmonic Nanopillar Array for Enhanced Biomolecule Detection

AbstractPlasmonic nanostructures, due to their extremely strong confinement and enhancement of optical field, have emerged as a potential tool in myriad applications, ranging from nano‐laser to surface‐enhanced Raman scattering (SERS) and biosensing. To break through the restriction of intrinsic losses and radiative damping in metal nanostructures resulting in broad plasmon resonance, a plasmonic nanostructure sensor employing hexagonal nanopillar array on flexible substrate to form the bilayer gold cap‐hole coupling structure is proposed and demonstrated. The sensor is fabricated by the combination of vacuum coating and template transfer, and experimentally exhibits an ultranarrow plasmon resonance coupling mode with a linewidth of 4.5 nm. Such a sharp linewidth resonance originates from the coupling of geometrical‐induced Wood's anomaly (WA) and Fabry–Perot (FP) modes. Benefiting from this ultranarrow resonance, a figure of merit (FOM) of 140.6 and spectroscopic detection noise down to 0.02 nm are demonstrated in the bulk refractive index (RI) sensing. Furthermore, the nanopillar array enables the detection of bovine serum albumin biomolecular with the detection limit of 0.27 µm. The plasmonic array device can be further investigated for more potential practical utility that are valuable and significant for label‐free biomolecular sensing with high sensitivity and high throughput.

Analytical study on the aerodynamic and hydrodynamic damping of the platform in an operating spar-type floating offshore wind turbine

Accurate evaluation of aerodynamic damping and hydrodynamic damping is critical to response prediction and vibration control of spar-type floating offshore wind turbines. This paper presents a comprehensive analytical study of these two damping sources with respect to platform motions. Aerodynamic damping is evaluated by a newly derived aerodynamic damping matrix based on linearisation of aerodynamic resultant forces at tower top. Both radiation and viscous drag effects are considered for hydrodynamic damping. The former is analytically expressed in the form of a radiation damping matrix, while the latter is derived based on Morison's equation and strip theory. A simplified model is established based on the analytical damping expressions and successfully verified against FAST and Aqwa. Under various operational conditions, the damping ratios for different degrees of freedom of the platform are estimated using complex modal analysis. It is found that the modal damping ratios arising from different sources can be very different for different vibration modes of the platform, and the tower flexibility is proved to have negligible impact on the platform damping. For a typical operational state, surge, sway, pitch and yaw motions are highly damped, with the roll motion intermediately damped and the heave motion nearly undamped.