High Mode Number Research Articles

Numerical study on the peeling–ballooning modes with electron cyclotron wave injection

The influence of electron cyclotron wave (ECW) injection with different deposition positions and injection powers on the evolution of peeling–ballooning (P–B) modes is studied with the BOUT++ code, in which the energy deposition and current drive of the ECW are calculated using a ray tracing code. It is shown that the changes in the profiles of plasma pressure, current density, and resistivity induced by ECW injection can significantly influence the linear property and the nonlinear evolution of P–B modes. For the linear simulation, the ECW deposited at the top of the pedestal makes the high toroidal mode number (n) P–B modes more unstable; however, it stabilizes the medium-n to high-n P–B modes when the ECW is deposited at the middle of the pedestal, and the ECW deposited at the bottom of the pedestal decreases the growth rate of P–B modes with medium-n. Further investigation shows that the injected ECW influences the characteristic of linear P–B modes by changing the diamagnetic effect, magnetic shear, pressure gradient, current density, resistivity, and so on. It is known from the nonlinear simulation that the energy loss caused by the edge localized mode (ELM) with ECW injection deposited at the top of the pedestal is nearly the same as that in the case without ECW injection, while the ECW deposited at the middle and bottom of the pedestal is helpful to decrease ELM energy loss. According to the analyses of the time evolution of the P–B mode toroidal spectrum, the physical mechanism of the decrease in ELM energy loss in the simulation is that ECW injection suppresses the most unstable toroidal harmonic of the P–B mode. On the other hand, the influence of ECW injection on P–B modes becomes more obvious when the power of the injected ECW increases. Moreover, the influence of current driven by the ECW on P–B modes is studied separately in this paper, which plays a different role from the bootstrap current.

Monolithic highly multi-mode XLMA-fiber resonator for high power operation.

Highly multi-mode fiber resonators can be an excellent solution to achieve high output power with homogeneous beam profiles, while nonlinear effects are suppressed due to the high number of modes and high mode-field areas. While highly reflective fiber-Bragg-gratings (HR-FBGs) are a well-developed technology in single-mode fibers, in multi-mode fibers HR-FBGs are under investigation to enable monolithic resonators. Here, we present a monolithic multi-mode fiber resonator in a > 50 µm core diameter XLMA-fiber. We achieve a slope efficiency of up to 50%, stable wavelength operation at 1074 nm and homogeneous beam profiles using an HR-FBG with app. 70% reflectivity.

Prospects for H-mode inhibition in negative triangularity tokamak reactor plasmas

Instability to high toroidal mode number (n) ballooning modes has been proposed as the primary gradient-limiting mechanism for tokamak equilibria with negative triangularity (NT) (δ) shaping, preventing access to strong H-mode regimes when δ is sufficiently negative. To understand how this mechanism extrapolates to reactor conditions, we model the infinite-n ballooning stability as a function of internal profiles and equilibrium shape using a combination of the CHEASE and BALOO codes. While the critical δ required for avoiding 2nd stability to high-n modes is observed to depend in a complicated way on various shaping parameters, including the equilibrium inverse aspect ratio, elongation and squareness, equilibria with NT are robustly prohibited from accessing the 2nd stability region, offering the prediction that NT reactors should maintain L-mode-like operation. In order to access high-n 2nd stability, the local shear over the entire bad curvature region must be sufficiently negative to overcome curvature destabilization on the low field side. Scalings of the ballooning-limited pedestal height are provided as a function of plasma parameters to aid future scenario design.

Study on divertor heat flux under n = 3 and n = 4 resonant magnetic perturbations using infrared thermography diagnostic in EAST

Resonant magnetic perturbations (RMPs) with high toroidal mode number n are considered for controlling edge-localized modes (ELMs) and divertor heat flux in future ITER H-mode operations. In this paper, characteristics of divertor heat flux under high-n RMPs (n = 3 and 4) in H-mode plasma are investigated using newly upgraded infrared thermography diagnostic in EAST. Additional splitting strike point (SSP) accompanying with ELM suppression is observed under both RMPs with n = 3 and n = 4, the SSP in heat flux profile agrees qualitatively with the modeled magnetic footprint. Although RMPs suppress ELMs, they increase the stationary heat flux during ELM suppression. The dependence of heat flux on during ELM suppression is preliminarily investigated, and further splitting in the original strike point is observed at during ELM suppression. In terms of ELM pulses, the presence of RMPs shows little influence on transient heat flux distribution.

Eddy Vertical Structure and Variability: Deepglider Observations in the North Atlantic

Abstract Hundreds of full-depth temperature and salinity profiles collected by Deepglider autonomous underwater vehicles (AUVs) in the North Atlantic reveal robust signals in eddy isopycnal vertical displacement and horizontal current throughout the entire water column. In separate glider missions southeast of Bermuda, subsurface-intensified cold, fresh coherent vortices were observed with velocities exceeding 20 cm s−1 at depths greater than 1000 m. With vertical resolution on the order of 20 m or less, these full-depth glider slant profiles newly permit estimation of scaled vertical wavenumber spectra from the barotropic through the 40th baroclinic mode. Geostrophic turbulence theory predictions of spectral slopes associated with the forward enstrophy cascade and proportional to inverse wavenumber cubed generally agree with glider-derived quasi-universal spectra of potential and kinetic energy found at a variety of locations distinguished by a wide range of mean surface eddy kinetic energy. Water-column average spectral estimates merge at high vertical mode number to established descriptions of internal wave spectra. Among glider mission sites, geographic and seasonal variability implicate bottom drag as a mechanism for dissipation, but also the need for more persistent sampling of the deep ocean. Significance Statement Relative to upper-ocean measurements of temperature, salinity, and velocity, deep ocean measurements (below 2000 m) are fewer in number and more difficult to collect. Deep measurements are needed, however, to explore the nature of deep ocean circulation contributing to the global redistribution of heat and to determine how upper-ocean behavior impacts or drives deep motions. Understanding of geographic and temporal variability in vertical structures of currents and eddies enables improved description of energy pathways in the ocean driven by turbulent interactions. In this study, we use newly developed autonomous underwater vehicles, capable of diving to the seafloor and back on a near daily basis, to collect high-resolution full ocean depth measurements at various locations in the North Atlantic. These measurements reveal connections between surface and deep motions, and importantly show their time evolution. Results of analyzing these vertical structures reveal the deep ocean to regularly “feel” events in the upper ocean and permit new comparisons to deep motions in climate models.

High‐Fidelity Analysis of ULF Wave Mode Structure Following Interplanetary Shock Compression of the Dayside Magnetopause Using MMS Multi‐Point Observations

AbstractDuring the 9 March 2018 event with two consecutive interplanetary shocks compressing the dayside magnetosphere, the azimuthal mode structure and frequency spectrum of ultra low frequency magnetic pulsations are resolved using a cross‐spectral analysis based on high‐fidelity multi‐probe Magnetospheric Multiscale Mission (MMS) magnetometer data. The results based on the MMS 4 and MMS 3 pair of measurements show that shock arrival leads to low mode () magnetic fluctuations in the Pc4‐5 regimes, and smaller spatial scale fluctuations implied by the dominant high mode numbers are observed after both shock signatures hit and passed the magnetosphere. Detailed evolution of the mode structure is also shown for the first shock to reveal the development of high mode structure from a bump‐on‐tail distribution at to a dominant peak at in about 10 min. In addition, an interesting change of sign in from negative to positive is observed as MMS crosses ∼11 MLT pre‐noon, which is consistent with the picture of wave generation by dayside magnetopause compression and then anti‐sunward propagation. For both shocks, the contribution of higher frequency waves (Pc‐4 range compared with Pc‐5) to the total wave power is found to be negligible before and after the shock impact, but it becomes more significant during the shock impact.

The stability of expanding reactive shocks in a van der Waals fluid

Despite the extensive literature accumulated since the pioneering works of D'yakov and Kontorovich in the 1950s, the stability of steady shocks is still an open question when realistic boundary conditions are accounted. The consideration of a supporting mechanism, which is indeed a necessary condition for shock steadiness, modifies the perturbation shock dynamics in the unstable range. The Noh problem is a suitable example to form steady expanding shocks. This configuration is of great interest to the high-energy-density-physics community because of its direct application to inertial confinement fusion and astrophysics, for which the stagnation of a supersonically converging material via an accretion shock front is ubiquitous. In this work, we extend the generalized Noh problem, both base-flow solution and linear stability analysis, to conditions where endothermic or exothermic transformations undergo across the shock. Within the spontaneous acoustic emission conditions found for a van der Waals gas [J. W. Bates and D. C. Montgomery, “The D'yakov-Kontorovich instability of shock waves in real gases,” Phys. Rev. Lett. 84, 1180 (2000)], we find that cylindrical and spherical expanding shocks become literally unstable for sufficiently high mode numbers. Counterintuitively, the effect of exothermicity or endothermicity across the shock is found to be stabilizing or destabilizing, respectively.

Electronic and phononic origins of BaSO4 as an ultra-efficient radiative cooling paint pigment

Radiative cooling has recently revived because of its significant potential for saving energy and combating climate change. Several ultra-efficient particle-matrix cooling nanocomposites such as BaSO4-acrylic paints have been demonstrated via trial-and-error approaches, but the atomistic characteristics of their pigments remain elusive. In this work, we use first-principles calculations to predict the full-spectrum optical constants of BaSO4, and successfully explain the ultra-high reflectance in the solar spectrum (0.28–2.5 μm) and simultaneously high normal emittance in the sky window (8–13 μm) observed in previous experiments. Efficient radiative cooling pigments require high refractive index n and low extinction coefficient κ in the solar spectrum. However, our results show that they cannot be tuned independently, but are both tied to the electronic band gap. Eliminating κ would require a high band gap, which would yield low n, creating a dilemma to address for radiative cooling. By systematic comparison, we show that BaSO4 outperforms the commonly used α-quartz (α-SiO2), and we identify two pertinent characters of BaSO4: i) Although the band gap of BaSO4 is high enough to eliminate solar absorption, it is also moderate enough to enable reasonably high refractive index for strong scattering, and ii) BaSO4 has complex crystal structure and appropriate bond strength that yield a high number of infrared-active zone-center optical phonon modes in the Reststrahlen bands, and these modes show strong four-phonon scattering which is a previously unknown mechanism that contributes to the high emissivity in the sky window. Our first-principles approach and physical insights pave the way for further search of efficient radiative cooling materials.

Physical design of a new set of high poloidal mode number coils in the EAST tokamak

An external resonant magnetic perturbation (RMP) field, which is an effective method to mitigate or suppress the edge localized mode (ELM), has been planned to be applied on the ELM control issue in ITER. A new set of magnetic perturbation coils, named as high m coils, has been developed for the EAST tokamak. The magnetic perturbation field of the high m coils is localized in the midplane of the low field side, with the spectral characteristic of high m and wide n, where m and n are the poloidal and toroidal mode numbers, respectively. The high m coils generate a strong localized perturbation field. Edge magnetic topology under the application of high m coils should have either a small or no stochastic region. With the combination of the high m coils and the current RMP coils in the EAST, flexible working scenarios of the magnetic perturbation field are available, which is beneficial for ELM control exploration on EAST. Numerical simulations have been carried out to characterize the high m coil system, including the magnetic spectrum and magnetic topology, which shows a great flexibility of magnetic perturbation variation as a tool to investigate the interaction between ELM and external magnetic perturbation.

Large Amplitude Axisymmetric Free Vibration of a Closed Two-Dimensional Spherical Pressure Vessel with a Constrained Volume

The nonlinear axisymmetric vibrational modes of a closed two-dimensional spherical pressure vessel with a constrained volume are presented using the fundamental forms of surfaces. The strain energy of the spherical pressure vessel is derived as a quadratic function of the initial Eulerian, added, and total Lagrangian strains. Two-dimensional bilinear elements described in spherical polar coordinates with the symmetric boundary condition along both sides of the meridian line are used for investigating the nonlinear axisymmetric mode shapes of a spherical pressure vessel. Numerical results were obtained by a nonlinear finite element approach and verified in the case of an empty spherical shell for both lower and upper branches. This study showed that the spherical pressure vessel gave a higher nonlinear axisymmetric natural frequency than the empty spherical shell. The elastic modulus has a large effect on the nonlinear axisymmetric frequencies of both the lower and upper branches for the spherical pressure vessel. Changing the thickness and initial internal pressure significantly affects only the lower branch of the spherical pressure vessel at high mode numbers. The results also indicate that the ratios of the nonlinear natural frequencies of the lower to upper branches decrease when the vibrational modes increase.

Forced vibration analysis of multi-degree-of-freedom nonlinear systems with the extended Galerkin method

In this study, the dynamic response behavior of a generalized nonlinear dynamic system is investigated using a newly proposed extended Galerkin method. The algebraic equations of vibration amplitudes are obtained through an integration of the weighted functions. The new method is equivalent to the harmonic balance method but with a much simpler calculation procedure and a higher efficiency. This is the first time to use the method for the analysis of nonlinear systems with high number of modes, manifesting that the method is applicable to forced vibrations of nonlinear behavior. The method is further validated by the numerical Runge-Kutta method.

Electro-magnetic vibration behavior of smart curved micro-/nanoshells

This paper investigates dynamic results of a small-scale-dependent panel subjected to a combination of mechanical, electrical, and magnetic loads using the shear defamation theory. Modified couple stress theory (MCST) is used for accounting small-scale effects in small sizes. Governing equations of motion are derived based on Hamilton’s principle in the cylindrical coordinate system. The micro panel is composed of an elastic core integrated with two piezoelectric/piezomagnetic layers at top and bottom. Microlength scale parameter is included in the couple stress tensor and symmetric curvature tensor to capture size dependency. The analytical solution is applied for the solution of the motion equations. The extended parametric results are provided to show natural frequencies in terms of main significant input parameters such as initial electric/magnetic loads, span angle, length to thickness, radius to thickness, and length to radius ratio. Furthermore, the effect of higher mode numbers along the axial and circumferential directions is studied on the responses. The numerical results indicate that the natural frequencies are increased with an increase in initial magnetic potential and a decrease in initial electric potential.

Stability of expanding accretion shocks for an arbitrary equation of state

We present a theoretical stability analysis for an expanding accretion shock that does not involve a rarefaction wave behind it. The dispersion equation that determines the eigenvalues of the problem and the explicit formulae for the corresponding eigenfunction profiles are presented for an arbitrary equation of state and finite-strength shocks. For spherically and cylindrically expanding steady shock waves, we demonstrate the possibility of instability in a literal sense, a power-law growth of shock-front perturbations with time, in the range of$h_c< h<1+2 {\mathcal {M}}_2$, where$h$is the D'yakov-Kontorovich parameter,$h_c$is its critical value corresponding to the onset of the instability and${\mathcal {M}}_2$is the downstream Mach number. Shock divergence is a stabilizing factor and, therefore, instability is found for high angular mode numbers. As the parameter$h$increases from$h_c$to$1+2 {\mathcal {M}}_2$, the instability power index grows from zero to infinity. This result contrasts with the classic theory applicable to planar isolated shocks, which predicts spontaneous acoustic emission associated with constant-amplitude oscillations of the perturbed shock in the range$h_c< h<1+2 {\mathcal {M}}_2$. Examples are given for three different equations of state: ideal gas, van der Waals gas and three-terms constitutive equation for simple metals.

Integrated ELM and divertor power flux control using RMPs with low input torque in EAST in support of the ITER research plan

Experiments have been carried out at the EAST tokamak to study ITER-relevant scenario integration issues, related to edge localized mode (ELM) control in H-mode plasmas by the application of three-dimensional (3D) resonant magnetic perturbations (RMPs), which have a large impact on the execution of the ITER research plan. The EAST experiments have successfully demonstrated ELM suppression at normalized torque inputs similar to ITER. The application of RMP fields with high toroidal mode number (n = 4) reduces the impact of ELM control on energy and particle confinement compared to those use lower n (n = 1, 2) RMPs. Injection of successive pellets is found to be effective in increasing the plasma density in ELM-suppressed H-modes and reducing the divertor power without triggering large ELMs at EAST. Access to high recycling and radiative divertor conditions while maintaining ELM suppression has been demonstrated in EAST by the use of gas fuelling and neon impurity seeding. Both approaches have been found to be effective in reducing power fluxes to the divertor strike points in near-separatrix lobes for both n = 2 and n = 4 RMPs. However, reduction of power fluxes in off-separatrix lobes is only effective for n = 4 RMP application, which is consistent with magnetic topology modelling (including plasma response) results showing a shallow penetration into the confined plasma region of field lines connected to these lobes compared to n = 2. The EAST results support the use of high n 3D fields for ELM suppression in ITER high Q DT scenarios since they provide optimum integration features regarding energy and particle confinement, pellet fuelling, radiative divertor operation while eliminating ELM transient power loads and being compatible with low torque input.

A neural network for prediction of high intensity resonance modes in magnetic multilayers

The use of magnetic materials as building blocks for frequency applications makes it possible to fabricate micrometer and nanometer high frequency devices. Moreover, devices with multiple high intensity modes for multiband devices can be designed by using magnetic multilayers. However, as the number of layers increases the multilayer becomes more complex, making it very difficult to find optimal configurations due to a big number of possible configurations. Fortunately, over the past decade a surge in the applicability and accessibility of machine learning algorithms and neural networks has been observed, which allow to analyse big quantities of data in search of complex patterns not always evident to humans. In this work, a theoretical model is used to generate approximately 10 × 106 data points, which in turn are used to train a neural network to calculate the number of high intensity resonance modes of three ferromagnetically coupled magnetic layers with an accuracy of over 99.8%. The neural network is then used to identify a configuration of the multilayer which provides the maximum number of high-intensity modes, and comparisons with the theoretical model are presented. Finally, the correlations between parameter were calculated over 600 million of data points, and clear guidelines for obtention of two high intensity resonance modes were identified. These results provide a simple way to find a configuration of the trilayer that have a high number of high intensity modes, thus greatly simplifying the design process of magnetic multi-band frequency devices.

Antiresonant driven systems for particle manipulation.

We report on the onset of antiresonant behavior of mass transport systems driven by time-dependent forces. Antiresonances arise from the coupling of a sufficiently high number of space-time modes of the force. The presence of forces having a wide space-time spectrum, a necessary condition for the formation of an antiresonance, is typical of confined systems with uneven and deformable walls that induce entropic forces dependent on space and time. We have analyzed, in particular, the case of polymer chains confined in a flexible channel and shown how they can be sorted and trapped. The presence of resonance-antiresonance pairs found can be exploited to design protocols able to engineer optimal transport processes and to manipulate the dynamics of nano-objects.

Inspecting the Mechanism of Fragment Hits Binding on SARS-CoV-2 Mpro by Using Supervised Molecular Dynamics (SuMD) Simulations.

Computational approaches supporting the early characterization of fragment molecular recognition mechanism represent a valuable complement to more expansive and low‐throughput experimental techniques. In this retrospective study, we have investigated the geometric accuracy with which high‐throughput supervised molecular dynamics simulations (HT‐SuMD) can anticipate the experimental bound state for a set of 23 fragments targeting the SARS‐CoV‐2 main protease. Despite the encouraging results herein reported, in line with those previously described for other MD‐based posing approaches, a high number of incorrect binding modes still complicate HT‐SuMD routine application. To overcome this limitation, fragment pose stability has been investigated and integrated as part of our in‐silico pipeline, allowing us to prioritize only the more reliable predictions.

Tunable mode control through myriad-mode fibers.

Multimode fibers are attractive for imaging, communication, computation, and energy delivery. Unfortunately, intermodal and polarization coupling precludes direct control of the delivered mode composition. We present a technique to tailor the mode composition at the output of a multimode fiber with thousands of modes, which we refer to as myriad-mode fiber, using its experimentally measured transmission matrix. While precise mode control has been demonstrated in typical multimode fibers with up to 210 modes, the method proposed here is particularly useful for high mode number fibers, such as when the number of modes is comparable to the number of modes of the wavefront shaping spatial light modulator. To illustrate the technique, we select different subsets of modes to create focal spots at the output of a fiber with 7140 modes. Importantly, we define efficiency and fidelity metrics to evaluate the mode control and demonstrate the relationship between efficiency, fidelity, and the spatial location of the spots across the distal fiber cross-section.

Oscillation properties of water droplets on a superhydrophobic surface and their correlations with droplet volume

In-depth understanding is limited to the oscillation properties of a droplet on a superhydrophobic surface, which are closely related to the contact line movement, droplet volume, and substrate amplitude, to name only a few factors. In the present work, we investigate the characteristics of droplet resonance amplitude, mode range, and resonance frequency, as well as their correlations with droplet volume (from 20 to 500 μL). In particular, the theoretical resonance frequency is mainly concerned and addressed. To this end, a model based on general hydrophobic surfaces proposed by Noblin et al. is employed, with its applicability to superhydrophobic surfaces examined. We propose a concept “virtual stationary point” for analyzing the errors from this model, with which we modify the model through using the correction coefficients. The main results are concluded as follows. 1) Under resonance, the change rate in droplet height rises with the increase of droplet volume and reduces with the increase of oscillation mode number. 2) Each number of oscillation mode corresponds to a frequency range, and the ends of adjacent mode ranges are connected to each other. These frequency ranges decrease with the increase of droplet volume. 3) Resonance frequency, <i>f</i>, decreases with the increase of droplet volume, <i>V</i>, and they are related approximated by <i>f</i> -<i>V</i><sup>–0.4</sup> under high mode numbers, which is different from <i>f</i> -<i>V</i><sup>–0.5</sup> as found on general hydrophobic surfaces. 4) Direct application of Noblin model to a superhydrophobic surface results in nonnegligible errors, because geometric characteristics in this case are different from those on a general hydrophobic surface, which leads to inaccuracy in counting the number of surface wave segments. In contrast, results from modified Noblin model accord well with experimental results.

Non-polynomial framework for stress and strain response of the FG-GPLRC disk using three-dimensional refined higher-order theory

This article presents a non-polynomial framework for bending responses of functionally graded-graphene nanoplatelets composite reinforced (FG-GPLRC) disk based upon three-dimensional refined higher-order shear deformation theory (3D-RHOSDT) for various sets of boundary conditions. By employing Hamilton’s principle, the structure's governing equations are derived and solved with the aid of the differential quadrature method (DQM). The rule of the mixture and modified Halpin–Tsai model are engaged to provide the effective material constant of the composite layers. Afterward, a parametric study is done to present the effects of weight fraction of GPLs, three kinds of FG patterns, shape mode, three kinds of boundary conditions, and different patterns of applied load on bending characteristics of the FG-GPLRC disk. The results show that in the outer and inner layers of the GPLRC disk, the structure with GPL-X and GPL-O patterns has the highest and lowest value of the shear stress, while in the middle layer, the mentioned relation between GPL patterns and shear stress changes to reverse. Another consequence is that the GPLRC disk has the best bending and static behavior against the sinusoidal pattern of applied load, and the structure shows weaker behavior against the uniform pattern. It is also observed that as the radius ratio increases, the buckled nodes are concentrated along the circumferential direction, and the mentioned issue is more considerable at the higher mode numbers.