Strong Beam Research Articles

Reconfigurable Photonic Lattices Based on Atomic Coherence

AbstractThe array of coupled optical waveguides, which is also viewed as a photonic lattice, can exhibit abundant photonic band structures depending on the desired spatial arrangements of involved waveguides. Studies of photonic lattices are usually performed in solid‐state materials, where the required periodic susceptibilities can be achieved by employing the femtosecond laser direct‐writing or optical induction method, and have spawned flourishing achievements in manipulating the behaviors of light. Recently, the concept of electromagnetically induced photonic lattice (EIPL) is proposed under the well‐known electromagnetically induced transparency (EIT) in coherently prepared multilevel alkali‐metal atomic systems, where the strong coupling beams producing EIT possess spatially periodic intensity profiles. The inherited instantaneous tunability of susceptibility from EIT‐modulated atomic coherence allows for the easy reconfigurability of EIPLs, which gives rise to exotic beam dynamics under such a readily controllable framework. This paper summarizes the historical overview and recent advances of the in situ and all‐optically reconfigurable EIPLs. The Introduction section provides the scheme and formation of the EIPL via atomic coherence. The following sections review the recently demonstrated dynamical properties of light in various 1D and 2D EIPLs and in compound EIPLs built by two coupling fields. The final section gives brief concluding remarks.

Formation and conversion of high-peak-power structured beams by an Nd:YVO4/Cr4+:YAG laser subject to tight-focusing off-axis pumping

A compact Nd:YVO4/Cr4+:YAG passively Q-switched laser in a near-hemispherical resonator is exploited to realize high-peak-power pulsed beams with high spatial degrees of freedom. Beneficial from the advantages of strong intracavity beam focusing as well as the point-like excitation condition for the proposed cavity design, various high-order structured pulses as coherent superpositions of multiple degenerate eigenmodes are stably generated under different off-axis pump schemes. Besides, by employing external-cavity astigmatic mode conversion (AMC), the oval-shaped and chessboard-like structured pulses under on-axis and 1D off-axis pumping are transformed into exotic modes with polygonal and figure-eight-shaped envelopes to further enrich the spatial complexity of the generated fields. With well-defined beam structures that are reconstructed using the analytical resonant wave functions of the resonator, the phase structures of AMC pulsed fields are numerically resolved to present a variety of singularity arrays. Experimental results reveal that the overall peak power of the on-axis and off-axis generated structured pulses respectively exceeds 600 W and 1 kW while maintaining good pulse train stability with peak-to-peak amplitude fluctuation to be less than 10% and 15%.

Research on column overdesign factor of reinforced concrete frame structures in the 2022 Ms 6.8 Luding earthquake

The strong column-weak beam failure mode of reinforced concrete (RC) frame structures is one of the most important targets of structural seismic design and is primarily realized by a reasonable column overdesign factor (COF). However, most RC frame structures in previous earthquakes were often subjected to strong beam-weak column failure modes. To address this issue, the RC frame with a strong column-weak beam failure mode and a typical strong beam-weak column RC frame in the 2022 Ms 6.8 Luding earthquake were intensively studied in this study. The differences between the two failure modes of the RC frame structure were comparatively analyzed at both the overall structure and member levels. A numerical simulation was conducted to obtain the structural response under actual ground motion. Finally, a probabilistic analysis method was adopted to process the COF data of the RC frame joints. The results indicate that the structural safety redundancy of the RC frame with the undesired failure mode cannot be fully utilized, whereas the RC frame with the strong column-weak beam failure mode allows more structural members to participate in the energy dissipation through a complex redistribution mechanism of internal forces. Damage to the infill wall further mitigates the degree of damage to the main structure and reduces the risk of soft-story failure. The COF of the actual RC frame structure shows a non-uniform distribution, and it is recommended that the COF be higher than 1.5 for the seismic design of the structure following the Chinese code.

Demonstration of shape analysis of neutron resonance transmission spectrum measured with a laser-driven neutron source

Laser-driven neutron sources (LDNSs) can generate strong short-pulse neutron beams, which are valuable for scientific studies and engineering applications. Neutron resonance transmission analysis (NRTA) is a nondestructive technique used for determining the areal density of each nuclide in a material sample using pulsed thermal and epithermal neutrons. Herein, we report the first successful NRTA performed using an LDNS driven by the Laser for Fast Ignition Experiment at the Institute of Laser Engineering, Osaka University. The key challenge was achieving a well-resolved resonance transmission spectrum for material analysis using an LDNS with a limited number of laser shots in the presence of strong background noise. We addressed this by employing a time-gated 6Li\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{6}{\ extrm{Li}}$$\\end{document}-glass scintillation neutron detector to measure the transmission spectra, reducing the impact of electromagnetic noise and neutron and gamma-ray flashes. Output waveforms were recorded for each laser shot and analyzed offline using a counting method. This approach yielded a spectrum with distinct resonances, which were attributed to 115In\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{115}\\,{\ extrm{In}}$$\\end{document} and 109Ag\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{109}{\ extrm{Ag}}$$\\end{document}, as confirmed through neutron transmission simulation. The spectrum was analyzed using the least-square nuclear-resonance fitting program, REFIT, demonstrating the possibility of using an LDNS for nondestructive areal-density material characterization.

First results of a newly-built hard-X-ray/soft-Gamma spectrometer imaging system: on the aspect of plasma disruptions

Abstract A new Hard X-ray and soft gamma-ray spectrometer imaging System (HXS) has been built for the 2-Dimensional measurements of plasma emitted photons on the Experimental Advanced Superconducting Tokamak (EAST). The system uses a 2-D Cadmium Zinc Telluride (CZT) detector and an integrated electronics, which is as a whole shielded by a tungsten box with a pinhole and is tangential to the toroidal field. Three classes of typical energy spectra have been summarized in differently experimental scenarios over the past campaigns. After performing tomography calculations, the local emissivity contours have been obtained in different energy ranges which obviously show the asymmetry on the plasma cross section. The spatial perturbation structure is similar to the magnetohydrodynamics (MHD) modes with low mode numbers. In particular, the runaway island found by an infrared camera [R. Jaspers et al, Phys. Rev. Lett. 72, 4093 (1994)] is also measured by the HXS. There exists a reversal population on the energy spectra in both slide-away and strong neutral beam injection (NBI) shots. It is consistently observed that the count rate is increased in the low energy range before the plasma disruptions. Calculations in phase space indicate that the accelerated momentum flux can be deflected back to the low energy region by the large pitch-angle scattering. In the post-disruption phase the plasma current is not replaced by runaway electrons due to tearing modes or transiently bursting instabilities. This paper constructs the basics for the proper use of HXS for Hard X-ray and Soft Gamma-ray measurements in future investigations of plasma disruptions.

Universal strategy study of applying passive metasurfaces to an intra-DC wireless-optical interconnection

Free-space optical (FSO) communication can reduce the routing complexity of data center networks (DCNs), not only ensuring high-capacity optical switching, but also owning similar flexibility to the wireless connectivity. Presently, mainstream wireless-optical switching units (WOSUs) have adopted serial beam control for unicasting. As a two-dimensional planar structure composed of meta-atoms with special electromagnetic properties arranged in a certain way, a passive metasurface (PMF) has strong parallel beam regulating capability. In this paper, we propose a wireless-optical intra-DC interconnection scheme based on PMFs. Through a real PMF chip, by adjusting the polarization of an incident beam, the power distribution between normal and abnormal reflected beams can be controlled. When both reflected beams are assigned with power, we obtain a pair of beams reflected in parallel, thus simultaneously communicating with two racks. In fact, we can perform 1-to-N (N≥2) multicast by using cascaded PMFs, and 1-to-N means that each source rack can communicate with N destination racks, i.e., a wide communication coverage range. However, the cascaded PMFs may result in huge chip costs and high accumulated power loss. In this paper, we only demonstrate the 1-to-2 communication ability of our PMFs, so the communication coverage may be still limited. Hence, by introducing electrostatic drive to control the PMF rotation, each source rack can achieve a wider communication coverage range than before. As a result, all racks within the coverage range have the ability to establish communication links with the source rack. To this end, we also design a neural network to mimic the PMF rotation, further improving the communication capability between racks. We then propose a DCN-topology reconfiguration algorithm supporting the coexistence of unicasting and multicasting, in order to make real-time decisions on the matching between FSO ports with minimized latency. Finally, we established a proof-of-concept prototype system to demonstrate the parallel beam control of our PMF. The test results show that the angle error is less than 0.1°, satisfying the accuracy requirements of WOSUs, and our PMF always has a good polarization response with the insertion loss of less than 2 dB under various azimuth angles or rotation planes.

Building Assessment Post Earthquake 21 November 2022 in Cianjur District

The earthquake that occurred in the Cianjur area, West Java on Monday 21 November 2022 at 13.21 WIB resulted in 635 fatalities and 56,000 houses that were damaged. The results of the assessment found that many houses and public facility buildings still did not meet the requirements for earthquake-resistant buildings, especially in the use of concrete materials, main reinforcement, stirrups in columns, beams, foundations and beam-column joint, and did not have a strong column-weak beam planning concept. This can be seen from the inability of the column to withstand/ carry the working load which causes the column to collapse and damage. Therefore, it is very necessary to pay attention to building planning in Disaster Prone Areas (DPA) in accordance with earthquake resistant building regulations SNI 1726:2019 and SNI 2847:2019

Shaping entangled photons through arbitrary scattering media using an advanced wave beacon

Entangled photons provide transformative new paths in the fields of communication, sensing, and computing. However, when entangled photons propagate through a complex medium, their correlations are scrambled. Using wavefront shaping to compensate for the scattering and retrieve the two-photon correlations is challenging due to the low signal-to-noise ratio of the two-photon signal. While previous works partly addressed this challenge by using feedback from a strong classical laser beam that co-propagates with the entangled photons, such methods frequently depend on assumptions about the complex medium, limiting the applicability of quantum wavefront shaping. In this work, we propose and demonstrate a new feedback mechanism that is inspired by Klyshko’s advanced wave picture: the classical laser beam is emitted in one of the detection modes, counter-propagates with one of the entangled photons, reflects at the crystal plane, and co-propagates with the other. The new Klyshko feedback allows compensation of scattering in arbitrary samples and even in situations where each photon propagates through a different scattering medium. Since the advanced wave picture applies whenever optical reciprocity is valid, such Klyshko optimization can be used across a wide range of configurations, offering a robust and alignment-free setup. We therefore believe this protocol will open the door for real-world applications of quantum wavefront shaping.

Effect of rotation on negative triangularity plasmas in DIII-D

Abstract At the DIII-D tokamak, plasmas with negative triangularity (NT) have been found to have similar energy confinement times as H-mode plasmas with positive triangularity. These NT plasmas also have a stable edge that inhibits H-mode, lacks dangerous edge transients, and has naturally low impurity confinement. For these reasons, NT plasmas have the potential to be a transformative reactor scenario. To determine the importance of strong co-current neutral beam torque for NT performance at DIII-D, scans of neutral beam torque at constant neutral beam power have been performed. These scans have shown that the energy confinement time for a basic, inductive NT scenario ( q 95 ≈ 2.8 ) decreases by 16% when torque is reduced to reactor levels. This reduction in confinement can be replicated with gyrofluid modeling that isolates the role of E × B shear in the change in transport. In a separate set of discharges with lower plasma current ( q 95 ≈ 4.2 ), no significant correlation between confinement time and rotation was found. Throughout this investigation, excellent MHD stability was observed, even with very low toroidal rotation. Further, low impurity confinement was found at multiple rotation levels. Throughout the campaign, rotation near the edge was counter-current, consistent with the measurement of counter-current intrinsic edge rotation, and these observations agree with NT results from the TCV tokamak.

Seismic flexural rehabilitation of RC coupling beams with FRP sheets: Evaluation of EBROG technique

Coupled shear walls (CSW) in reinforced concrete (RC) structures must be connected with stiff and strong coupling beams (CBs) to perform effectively during an earthquake. However, many RC buildings with CSW resisting systems have been designed and constructed with insufficient seismic requirements based on old codes and standards. During major earthquakes, these systems respond unsatisfactorily and may prematurely collapse. Strengthening of different RC members including CBs with fiber-reinforced polymer (FRP) sheets attached through externally-bonded reinforcement (EBR), though attractive, has always suffered from premature debonding of FRP from concrete substrate. The alternative externally-bonded reinforcement on grooves (EBROG) technique has been shown to overcome premature debonding when used instead of the EBR method. Therefore, this experimental study investigated the efficiency of rehabilitation with carbon FRP (CFRP) through the EBROG technique on the seismic behavior of flexural-deficient RC coupling beams. Furthermore, different patterns of flexural retrofit, as well as the effectiveness of FRP fans, have been studied to prevent undesirable debonding of CFRP strips. Four large-scale RC coupling beams have been identically constructed. The CB specimens were reinforced in such a way as to be flexural deficient, i.e., their loading capacities in shear were much more than that in bending. The CB specimens were then retrofitted with CFRP sheets in different patterns. The maximum peak loads of specimens CBF-1 L, CBF-1 L.F, and CBF-2 L.F increased by 37.0 %, 44.3 %, and 46.0 % over the control, respectively. Upon comparing the loading capacities of specimens CBF-1 L and CBF-1 L.F, it was found that FRP sheets installed through the EBROG method could delay premature debonding and utilize approximately 80 % of the CFRP's capacity. It was observed that using the EBROG technique and FRP fans at the termination point of FRP sheets, fully eliminated the debonding, and the full capacity of the CFRP sheets was utilized accompanied by their rupture, with improved ductility and increased load-carrying capacity of up to 46 %. It was also found that CFRP composites attached to concrete through the EBROG method significantly increased the strength, stiffness, ductility, and energy dissipation of CB specimens in terms of seismic rehabilitation.

Experimental study on seismic behavior of RCS joints with asymmetric friction connections and slabs

This paper introduces a new reinforced concrete column-steel beam (RCS) joint that employs asymmetric frictional connections (AFC) to improve energy dissipation and moment transfer, reducing stress concentrations within the joint’s core. Two RCS joint specimens with AFC and floor slabs were designed and tested under quasi-static loading to analyze the impact of bolt preload on seismic performance. The experimental results demonstrate that RCS joints with AFC and slabs exhibit favorable seismic behavior in terms of bearing capacity, energy dissipation, and stiffness degradation. Increasing bolt preload enhances the bearing capacity, stiffness, and energy dissipation capacity of the joints. The failure occurred at the steel beam splice connections, while only minor micro-cracks appeared in the reinforced concrete column when the joint's bearing capacity dropped below 80% of the peak load. Displacement at the column top was primarily influenced by steel beam and column deformation, with minimal contribution from joint core deformation. The use of AFC effectively reduced deformation in the joint core area, meeting seismic design code requirements for “strong columns-weak beams.”

ANALISIS KINERJA STRUKTUR PADA GEDUNG BERTINGKAT DENGAN ANALISIS PUSHOVER BERDASARKAN ATC-40

Indonesia is an area prone to earthquakes. Earthquakes can cause infrastructure damage and casualties. Efforts are needed to reduce the risk of earthquake hazards by strengthening earthquake-resistant infrastructure. The design procedures for earthquake-resistant buildings are carried out using a performance-based design approach. Building performance can be estimated through non-linear static pushover analysis. This research takes a case study in Jongke Market, Surakarta. This research aims to determine the capacity curve, performance level, and structure collapse mechanism. The method used is pushover analysis with the capacity spectrum. The result of this analysis is a capacity curve that processed to determine the level of structure performance referring to the drift ratio limitation table in the Applied Technology Council (ATC-40). Based on the results of this research, displacement that occurred in the x direction is 92 mm and in the y direction is 77 mm. Building displacement is good because the displacement that occurred is smaller than the displacement limit (control). The total maximum drift in the x direction is 0.007 and in the y direction is 0.006. The maximum inelastic total drift in the x direction is 0.005 and in the y direction is 0.004. Based on the drift ratio limitation table in the ATC-40 document, this building has an immediate occupancy performance level. Based on the plastic hinge mechanism formed, the existing structure also meets the ideal collapse concept (strong column-weak beam).

Experimental and numerical investigation of bolt-free preloaded connection for steel-framed modular buildings

This paper introduces an innovative bolt-free preloaded inter-module connection for steel-framed modular buildings, referred to as the ‘AJ’ connection. It provides the vertical connection between columns by engaging a preload induced by long steel rod bolts (SRB) and specially designed couplers. The preload is applied using a torque or impact wrench. Consequently, the connection simplifies the on-site assembly and disassembly processes of the modular building, thereby enhancing both construction speed and reusability of modules. In this study, the structural performance of the AJ connection was investigated experimentally and numerically. First, the coupler was tested under a uniaxial tensile load to check its strength. Then, preloading tests on assemblies of a coupler and a 3m long SRB were conducted to determine the torque-preload relationship. Subsequently, full-scale beam-to-column joints featuring the AJ connection were tested under monotonic loading to investigate its lateral-force resisting mechanism. Lastly, the seismic performance of the AJ connection was investigated using FE joint models calibrated against a combination of test results and geometric and material nonlinear analyses with imperfections (GMNIA). A comparative analysis with a welded connection was also conducted to evaluate the seismic performance of the AJ connection. The findings indicated that the AJ connection demonstrates seismic performance comparable to the welded connection, exhibiting Strong column-Weak beam behaviour for seismic moment-resisting frames. Additionally, it satisfies the ductility requirements for structures of ductility class DCM as specified by EN 1998–1.

FRBs from rapid spindown neutron stars

Abstract A fast radio burst (FRB) localized to a globular cluster (GC) challenges FRB models involving ordinary young magnetars. In this paper, we examine the rapid spindown millisecond neutron star (NS) scenario, which favours the dynamic environment in GCs. Fast spindown corresponds to a larger magnetic field than regular millisecond pulsars, which empirically favours giant pulse (GP) emission. The kinetic energy in millisecond NSs can readily exceed the magnetic energy in magnetars. The high inferred isotropic luminosity of most FRBs is challenging to explain in spin-down powered pulsars. A recent observation of a GP from the Crab pulsar, on the other hand, suggests highly Doppler-beamed emission, making the required energy orders of magnitude smaller than estimated with isotropic assumptions. Considering this strong beaming effect, GPs from a recycled pulsar with a modest magnetic field could explain the energetics and burst rates for a wide range of FRBs. The short life span accounts for a paucity of bright FRBs in the Milky Way neighbourhood. We point out that tidal disruption spin-up from a main sequence star can provide sufficient accretion rate to recycle a NS with mild magnetic field. It can also explain the observed source density and the spatial offset in the GC for FRB 20200120E. Frequency variation in the scattering tail for some of the brightest FRBs is expected in this scenario.

Charge transport mechanism and mechanical properties of rubidium cerium metaphosphate glasses

Cerium-doped glasses usually contain a mixture of Ce3+ and Ce4+ species, with the trivalent state being dominant. Quantitative determination of the redox ratio is complicated by the narrow energy gap between both states, leading to spectral overlap in optical absorption studies, and strong beam sensitivity in other techniques. However, it also indicates a way to induce electric conduction through electron hopping, with the additional benefit of visual transparency. Here, cerium phosphate glasses are reported in which the local optical basicity is varied through substitution of cerium by highly polarizable rubidium ions. This is done in order to control the Ce3+/ Ce4+ ratio. Electrical impedance spectroscopy is considered as an alternative means to assess the redox ratio by exploring the extent of polaron conduction. Complementary Raman and 31P MAS NMR spectroscopic studies provide structural insight on the process of mixed electronic and ionic charge transport. Meanwhile, a monotonic decrease in the elastic modulus and an abnormal change in Poisson's ratio when varying the composition corroborate structural interpretations.

Impact of Electron Precipitation on Brown Dwarf Atmospheres and the Missing Auroral H3+ Emission

Recent observations have demonstrated that very low-mass stars and brown dwarfs are capable of sustaining strong magnetic fields despite their cool and neutral atmospheres. These kilogauss field strengths are inferred based on strong, highly circularly polarized gigahertz radio emission, a consequence of the electron cyclotron maser instability. Crucially, these observations imply the existence of energetic nonthermal electron populations, associated with strong current systems, as are found in the auroral regions of the magnetized planets of the solar system. Intense auroral electron precipitation will lead to electron collisions with the H2 gas that should generate the ion H3+ . With this motivation, we targeted a sample of ultracool dwarfs, known to exhibit signatures associated with aurorae, in search of the K-band emission features of H3+ using the Keck telescopes on Maunakea. From our sample of nine objects, we found no clear indication of H3+ emission features in our low-to-medium-resolution spectra (R ∼ 3600). We also modeled the impact of an auroral electron beam on a brown dwarf atmosphere, determining the depth at which energetic beams deposit their energy and drive particle impact ionization. We find that the H3+ nondetections can be explained by electron beams of typical energies ≳2–10 keV, which penetrate deeply enough that any H3+ produced is chemically destroyed before radiating energy through its infrared transitions. Strong electron beams could further explain the lack of UV auroral detections and suggest that most or nearly all of the precipitating auroral energy must ultimately emerge as thermal emissions deep in brown dwarf atmospheres.

5G new radio multiuser precoding in geostationary satellite networks

SummaryThe multiuser precoding procedures standardized by the 3rd Generation Partnership Project (3GPP) for new radio (NR) represent a new opportunity to realize satellite precoding for capacity improvement, given the integration of non‐terrestrial networks in the 3GPP framework. This work analyses and numerically evaluates them for the geostationary satellite scenarios consolidated by the 3GPP. It shows that the preferred precoding matrix indicated by NR codebooks is not able to handle properly the inter‐beam interference and should only be used to estimate the propagation channel. To this aim, we propose the use of modified type II port selection codebooks reporting on the strongest beams, which correspond to the higher interferences. Since the obtention of high precoding gains requires the operation in rather high signal‐to‐noise regimes and the proper estimation of the interfering contributions from many beams, we propose to enlarge the maximum number of beams reported by each precoding matrix indicator (PMI) report, currently limited to four. As alternative, we also evaluate a sequential multi‐report framework considering the effects of channel‐state information aging and the user equipment (UE) processing times. It preserves the current limits on the number of reported beams but increases the system overhead signalling. The quantization of estimated coefficients is also analysed, not only from the overhead point of view but also to properly report weak interferers corresponding to distant beams, due to the increase in the number of reported beams. Moreover, we identify the minimum interference power a UE should be able to detect to achieve the theoretical large precoding gains.

Shaking table tests on inclined collapse mechanism of RC frame structures subjected to earthquakes

Inclined collapse of structures under strong earthquakes threatens the adjacent infrastructures. The collapse mode and collapse direction should be considered with caution to curb the secondary disaster in the urban area. However, current studies on the inclined collapse mechanism are predominantly limited to the qualitative and intuitive understanding. To fill this gap, this study presents an insight into the inclined collapse mechanism of the reinforced concrete (RC) frame structures with two typical features subjected to earthquakes, i.e., the structures with slab opening on one side of the first floor and the structures with disparate axial compression ratios of the first story columns on the opposite sides. First, shaking table tests were performed on two 1/10-scale three-story RC frame structure models undergoing inclined collapse. Then the multi-scale finite element models were established, validated against the test results and used for parametric studies. In the parametric studies, two coefficients were considered to describe the typical features of the RC frame structures, i.e., the strong column-weak beam ratio η and differential rate of the axial compression ratios λ. The test and numerical results found that the inclined collapse mechanism was attributed to the different distributions and discrepant resistance deterioration of the plastic hinges among the first story columns of the RC frame structures with the two features. This causes the inconsistent damage levels among the first story columns, the dominant direction of the lateral displacement, and the inclined collapse of the structures. Finally, the collapse mode and collapse direction can be controlled by appropriately adjusting the two coefficients η and λ for the structures with the typical features concerned in this study.

Strong–strong beam–beam simulations with lattices of circular e+e- colliders

Strong–strong beam–beam simulations for circular colliders are very time-consuming. Thus far, such simulations have predominantly utilized a linear transfer matrix to represent the full nonlinear lattice. Otherwise, when nonlinear lattices were included, beam–beam interactions were usually studied by using weak–strong or quasi-strong–strong numerical models. The next-generation circular colliders, including FCC-ee at CERN, CEPC in China, and the Super Tau-Charm Factories in China and Russia, will leverage the crab waist collision scheme with a large Piwinski angle. This scheme has already been employed in the two currently operational colliders, DAFNE and SuperKEKB. Accurate predictions of the performance of such colliders call for strong–strong beam–beam simulations, taking into account the interplay of the beam–beam interaction with lattice nonlinearities, impedances, and other collective effects. To answer this call, a novel code APES-T that allows integrating the direct strong–strong beam–beam simulations with element-by-element nonlinear tracking has been developed. To overcome the limitations in computing time, APES-T employs parallelization techniques. Specifically, the beam–beam module is parallelized using MPI programming, while the element-by-element tracking modules are parallelized using GPU programming. In this paper, we present the development of the APES-T code, its benchmark against the SAD code, and its application to the CEPC in investigating the interplay between beam–beam interaction, beamstrahlung, and lattices.

Simulations of dislocation contrast in dark-field X-ray microscopy.

Dark-field X-ray microscopy (DFXM) is a full-field imaging technique that non-destructively maps the structure and local strain inside deeply embedded crystalline elements in three dimensions. In DFXM, an objective lens is placed along the diffracted beam to generate a magnified projection image of the local diffracted volume. This work explores contrast methods and optimizes the DFXM setup specifically for the case of mapping dislocations. Forward projections of detector images are generated using two complementary simulation tools based on geometrical optics and wavefront propagation, respectively. Weak and strong beam contrast and the mapping of strain components are studied. The feasibility of observing dislocations in a wall is elucidated as a function of the distance between neighbouring dislocations and the spatial resolution. Dislocation studies should be feasible with energy band widths of 10-2, of relevance for fourth-generation synchrotron and X-ray free-electron laser sources.