Forward Beam Research Articles

Synchrotron Radiation Reflections in the CLIC Beam Delivery System

Synchrotron radiation (SR) reflction is an important issue for future linear colliders. High fluxes of SR might impact the performance of the detector, through irradiation of the forward luminosity and beam quality calorimeters or of the innermost layers of the vertex detector. The photon reflections depend on the beam pipe apertures' size, their shape, and materials used with various surface roughness. In this work, we present a study of SR including reflection for the 380GeV and 3 TeV beam parameters and optics of the Compact Linear Collider's Final Focus System. The simulations of the SR reections using the Synrad+ software are presented and the impact on the detector is discussed.

Synchrotron Radiation Reflections in the CLIC Beam Delivery System

Synchrotron radiation (SR) reflction is an important issue for future linear colliders. High fluxes of SR might impact the performance of the detector, through irradiation of the forward luminosity and beam quality calorimeters or of the innermost layers of the vertex detector. The photon reflections depend on the beam pipe apertures' size, their shape, and materials used with various surface roughness. In this work, we present a study of SR including reflection for the 380GeV and 3 TeV beam parameters and optics of the Compact Linear Collider's Final Focus System. The simulations of the SR reections using the Synrad+ software are presented and the impact on the detector is discussed.

Mechanism of stimulated Mie scattering: Light-induced redistribution of self-assembled nanospheres of two-photon absorbing chromophore.

We report the observation of backward stimulated Mie scattering (SMS) due to light-field induced spatial redistribution of self-assembled nanospheres of a two-photon resonant organic chromophore in water, pumped by ∼10-ns laser pulses of ∼816-nm wavelength. The pump-energy threshold for generating backward stimulated scattering in such a system is remarkably lower than that in pure water. The gain of backscattering originates from an induced Bragg grating that reflects partial energy from the pump beam into the backward Mie scattering beam. Based on the experimental fact that the time-delay of the SMS pulse onset depends on both the pump level and the viscosity of the solvent, a physical model of SMS generation is proposed. Our experimental results have shown that the major contribution to the formation of an induced Bragg grating is spatial redistribution of nanoparticles suspended in the liquid. These nanoparticles are driven by a force that is proportional to the intensity gradient of the standing-wave field resulting from interference between the forward pump beam and the backward Mie scattering beam. When the nanoparticle motion is frozen in a gel-like medium, no SMS is observed, which experimentally supports the validity of the proposed physical model.

Planar Beam Steerable Parasitic Array Antenna System Design Based on the Yagi-Uda Design Method

A planar beam steerable array antenna system is proposed with dual-control circuits for feeding and reactive loadings. Two orthogonally arranged planar dipoles are excited by SPDT switching circuits, while the forward and backward beam directions are controlled by the adjusted effective electric lengths of the parasitic dipole elements. The adjusted parasitic dipoles are designed to play the alternative roles of directors and reflectors based on the Yagi-Uda antenna theory. The proposed antenna system with four-way switchable beams has been implemented on a planar substrate and evaluated for orthogonal four-way beam steering performance with good agreement.

Computational prediction of plasma protein binding of cyclic peptides from small molecule experimental data using sparse modeling techniques

BackgroundCyclic peptide-based drug discovery is attracting increasing interest owing to its potential to avoid target protein depletion. In drug discovery, it is important to maintain the biostability of a drug within the proper range. Plasma protein binding (PPB) is the most important index of biostability, and developing a computational method to predict PPB of drug candidate compounds contributes to the acceleration of drug discovery research. PPB prediction of small molecule drug compounds using machine learning has been conducted thus far; however, no study has investigated cyclic peptides because experimental information of cyclic peptides is scarce.ResultsFirst, we adopted sparse modeling and small molecule information to construct a PPB prediction model for cyclic peptides. As cyclic peptide data are limited, applying multidimensional nonlinear models involves concerns regarding overfitting. However, models constructed by sparse modeling can avoid overfitting, offering high generalization performance and interpretability. More than 1000 PPB data of small molecules are available, and we used them to construct a prediction models with two enumeration methods: enumerating lasso solutions (ELS) and forward beam search (FBS). The accuracies of the prediction models constructed by ELS and FBS were equal to or better than those of conventional non-linear models (MAE = 0.167–0.174) on cross-validation of a small molecule compound dataset. Moreover, we showed that the prediction accuracies for cyclic peptides were close to those for small molecule compounds (MAE = 0.194–0.288). Such high accuracy could not be obtained by a simple method of learning from cyclic peptide data directly by lasso regression (MAE = 0.286–0.671) or ridge regression (MAE = 0.244–0.354).ConclusionIn this study, we proposed a machine learning techniques that uses low-dimensional sparse modeling to predict the PPB value of cyclic peptides computationally. The low-dimensional sparse model not only exhibits excellent generalization performance but also improves interpretation of the prediction model. This can provide common an noteworthy knowledge for future cyclic peptide drug discovery studies.

Experimental investigation of the detection and location of a target in layered media by using the TR-RTM mixed method

Targets in layered media can be detected and located using a time reversal (TR)-reversed-time migration (RTM) mixed method. In this study, this single emission-multiple receiving method is tested experimentally by using two types of layered media and three types of targets. The signal reflected at the interface and the signal scattered by the target are measured by each receiver to obtain the travel time for several transmitter-receiver pairs. Thereafter, the amplitude ratio between the two measured signals is compared with the theoretical amplitude. The RTM process involves the convolution of the forward acoustic beam from the source with the backward acoustic beam from the receiver which adds an appropriate delay determined on the measured travel time data. By using this approach, the acoustic field distribution can be obtained, and the position of the target can be determined. Moreover, the measured positions of the target are compared with the actual position to validate the accuracy of this technique.

Electroweak logarithms in inclusive cross sections

We develop the framework to perform all-orders resummation of electroweak logarithms of Q/M for inclusive scattering processes at energies Q much above the electroweak scale M. We calculate all ingredients needed at next-to-leading logarithmic (NLL) order and provide an explicit recipe to implement this for 2 → 2 processes. PDF evolution including electroweak corrections, which lead to Sudakov double logarithms, is computed. If only the invariant mass of the final state is measured, all electroweak logarithms can be resummed by the PDF evolution, at least to LL. However, simply identifying a lepton in the final state requires the corresponding fragmentation function and introduces angular dependence through the exchange of soft gauge bosons. Furthermore, we show the importance of polarization effects for gauge bosons, due to the chiral nature of SU(2) — even the gluon distribution in an unpolarized proton becomes polarized at high scales due to electroweak effects. We justify our approach with a factorization analysis, finding that the objects entering the factorization theorem do not need to be SU(2) × U(1) gauge singlets, even though we perform the factorization and resummation in the symmetric phase. We also discuss a range of extensions, including jets and how to calculate the EW logarithms when you are fully exclusive in the central (detector) region and fully inclusive in the forward (beam) regions.

Dual-Band Leaky-Wave Antenna Based on Dual- Mode Composite Microstrip Line for Microwave and Millimeter-Wave Applications

A dual-mode composite microstrip line (DMC-MSL) is reported in this paper for the purpose of designing dual-band antennas and devices with a large frequency ratio. The metallic strip of the conventional MSL is replaced with a substrate integrated waveguide (SIW) arranged into a thin dielectric laminate, which leads to that two modes operating in different frequency bands, i.e., the quasi-TEM mode and the TE10-like mode, can propagate along the transmission line structure simultaneously. The DMC-MSL with a dual-layered planar configuration combines the merits of the MSL and the SIW. In addition, by adjusting the permittivity of the dielectric laminate used for realizing the thin SIW, the frequency ratio of the two operating modes can be varied flexibly. Based on the DMC-MSL structure, a novel dual-band leaky-wave antenna is presented. Periodic parasitic microstrip patches and the transverse slot array etched on the SIW are introduced in order to generate the required spatial harmonics. A feed structure that can excite the two operating modes of the DMC-MSL separately is designed as well. The fabricated prototype verifies that backward and forward frequency-scanning radiation beams are achieved within the low-frequency band from 5.75 to 8.5 GHz and the high-frequency band from 35 to 41.5 GHz, respectively. The proposed DMS-MSL structure and the leaky-wave antenna offer a new mean to implement antennas and devices for microwave and millimeter-wave dual-band applications.

Design guidelines for single and dual wide band leaky periodic microstrip line antennas

Leaky wave antennas using periodic microstrip lines are natural choices for versatile beam scanning applications. In this work, a shorted stub and an open stub are simultaneously used in the same unit cell to generate resonant frequencies dependent on the stub dimensions. Placing one such resonant frequency at the second Bragg stop band, a single wideband response is obtained. Next, the stub lengths are tuned to obtain two resonant frequencies which are placed at the second and fourth Bragg stop bands, respectively to obtain a dual wideband response. Design guidelines are outlined for obtaining these wide bands and corresponding radiation regions. Two such geometries with single and dual-band nature are fabricated. The single wide-band antenna has a pass-band from 5.89 to 11.57 GHz with a beam scanning range of −56° to 33°. The dual-band antenna has two pass-bands radiating in the frequency range 5-6.5 GHz and 10.7-14.7 GHz. Beam scanning range in the first pass-band is −72° to −5°. The second pass-band, in part, demonstrates a dual-beam nature with the forward beam scanning from 28.9° to 54.5° and backward beam scanning from −54.5° to 14.76° as the frequency varies from 12 to 14.5 GHz.

Development of radiation-hard scintillators and wavelength-shifting fibers

Future circular and linear colliders as well as the Large Hadron Collider in the High-Luminosity era have been imposing unprecedented challenges on the radiation hardness of particle detectors that will be used for specific purposes e.g. forward calorimeters, beam and luminosity monitors. We perform research on the radiation-hard active media for such detectors, particularly calorimeters, in two distinct categories: quartz plates coated with thin, radiation-hard organic or inorganic compounds, and intrinsically radiation-hard scintillators. In parallel to the effort on identifying radiation-hard scintillator materials, we also perform R&D on radiation-hard wavelength shifting fibers in order to facilitate a complete active medium for detectors under harsh radiation conditions. Here we describe the recent advances in the developments of radiation-hard scintillators and wavelength shifting fibers. We will discuss recent and projected measurements and future directions in development of radiation-hard active media.

The influence of air-filled structures on wave propagation and beam formation of a pygmy sperm whale (Kogia breviceps) in horizontal and vertical planes.

The wave propagation, sound field, and transmission beam pattern of a pygmy sperm whale (Kogia breviceps) were investigated in both the horizontal and vertical planes. Results suggested that the signals obtained at both planes were similarly characterized with a high peak frequency and a relatively narrow bandwidth, close to the ones recorded from live animals. The sound beam measured outside the head in the vertical plane was narrower than that of the horizontal one. Cases with different combinations of air-filled structures in both planes were used to study the respective roles in controlling wave propagation and beam formation. The wave propagations and beam patterns in the horizontal and vertical planes elucidated the important reflection effect of the spermaceti and vocal chambers on sound waves, which was highly significant in forming intensive forward sound beams. The air-filled structures, the forehead soft tissues and skull structures formed wave guides in these two planes for emitted sounds to propagate forward.

Effects of scanning speed on the laser beam profile measurements by vibrating wire

For measuring laser beam profiles, a vibrating wire monitor (VWM) has been introduced. The measurements were carried out at different speeds of scan. Preliminary estimates were made for the calculation of the VWM response times with respect to the thermal losses along the wire, and radiative and convective losses. These estimates, however, do not determine the difference between the beam profile and the frequency response of the VWM for a given scan rate. To evaluate the reliability of the frequency response of the VWM, comparisons between forward and reverse beam scans at different speeds have been used. The results of these scans are used to correct the thermal inertia in the frequency response of the VWM.

Monitoring the KATRIN source properties within the beamline

The KArlsruhe TRItium Neutrino (KATRIN) experiment will measure the mass of the neutrino with a sensitivity of 0.2 eV (90 % CL). The Forward Beam Monitor (FBM) is a monitoring system which comprises of a complex mechanical setup capable of inserting a detector board into the KATRIN beamline at the end of the source and transport section. The detector board contains a Hall sensor, a temperature gauge, and two PIN diodes which can detect electrons from the source with a precision of 0.1 % in less than a minute within an electron flux density of 106 s−1mm−2.

The nonlinear behavior of whistler waves at the reconnecting dayside magnetopause as observed by the Magnetospheric Multiscale mission: A case study

AbstractWe show observations of whistler mode waves in both the low‐latitude boundary layer (LLBL) and on closed magnetospheric field lines during a crossing of the dayside reconnecting magnetopause by the Magnetospheric Multiscale (MMS) mission on 11 October 2015. The whistlers in the LLBL were on the electron edge of the magnetospheric separatrix and exhibited high propagation angles with respect to the background field, approaching 40°, with bursty and nonlinear parallel electric field signatures. The whistlers in the closed magnetosphere had Poynting flux that was more field aligned. Comparing the reduced electron distributions for each event, the magnetospheric whistlers appear to be consistent with anisotropy‐driven waves, while the distribution in the LLBL case includes anisotropic backward resonant electrons and a forward resonant beam at near half the electron‐Alfvén speed. Results are compared with the previously published observations by MMS on 19 September 2015 of LLBL whistler waves. The observations suggest that whistlers in the LLBL can be both beam and anisotropy driven, and the relative contribution of each might depend on the distance from the X line.

Single-neutron knockout from 20C and the structure of 19C

The low-lying unbound level structure of the halo nucleus 19C has been investigated using single-neutron knockout from 20C on a carbon target at 280 MeV/nucleon. The invariant mass spectrum, derived from the momenta of the forward going beam velocity 18C fragment and neutrons, was found to be dominated by a very narrow near threshold (Erel=0.036(1) MeV) peak. Two less strongly populated resonance-like features were also observed at Erel=0.84(4) and 2.31(3) MeV, both of which exhibit characteristics consistent with neutron p-shell hole states. Comparisons of the energies, measured cross sections and parallel momentum distributions to the results of shell-model and eikonal reaction calculations lead to spin-parity assignments of 5/21+ and 1/21− for the levels at Ex=0.62(9) and 2.89(10) MeV with Sn=0.58(9) MeV. Spectroscopic factors were also deduced and found to be in reasonable accord with shell-model calculations. The valence neutron configuration of the 20C ground state is thus seen to include, in addition to the known 1s1/22 component, a significant 0d5/22 contribution. The level scheme of 19C, including significantly the 1/21− cross-shell state, is well accounted for by the YSOX shell-model interaction developed from the monopole-based universal interaction.

Competition and Energy Transfer Between Forward and Backward Four-Wave Mixing via Atomic Coherence

Two four-wave mixing (FWM) processes with different directions and frequencies can coexist and interfere in a four-level inverted-Y-type atomic system, the generated FWM beams fall into two different electromagnetically induced transparency windows. We report Autler–Townes splitting and dressed suppression and enhancement of two generated FWM beams. In the case of matched slow FWM beams, two FWM processes compete and exchange their energies between them, the forward four-wave beam give its energy to the backward four-wave beam by interaction for long distance. Such studies of two FWM beams can have vital applications in studying the higher-order nonlinear optical processes, generating correlated photon pairs and quantum information processing.

Generating high-yield positrons and relativistic collisionless shocks by 10 PW laser

AbstractRelativistic collisionless shock charged particle acceleration is considered as a possible origin of high-energy cosmic rays. However, it is hard to explore the nature of relativistic collisionless shock due to its low occurring frequency and remote detecting distance. Recently, there are some works attempt to solve this problem by generating relativistic collisionless shock in laboratory conditions. In laboratory, the scheme of generation of relativistic collisionless shock is that two electron–positron pair plasmas knock each other. However, in laboratory, the appropriate pair plasmas have been not generated. The 10 PW laser pulse maybe generates the pair plasmas that satisfy the formation condition of relativistic collisionless shock due to its ultrahigh intensity and energy. In this paper, we study the positron production by ultraintense laser high Z target interaction using numerical simulations, which consider quantum electrodynamics effect. The simulation results show that the forward positron beam up to 1013/kJ can be generated by 10 PW laser pulse interacting with lead target. The estimation of relativistic collisionless shock formation shows that the positron yield satisfies formation condition and the positron divergence needs to be controlled. Our results indicate that the generation of relativistic collisionless shock by 10 PW laser facilities in laboratory is possible.

Exact time-periodic solutions and nonlinear polarization attraction

We find exact time-periodic solutions to the nonlinear equations that describe the polarization interaction of two intense counter-propagating beams in a randomly birefringent fiber, expressed in terms of the forward and backward beam Stokes vectors. The overlap function between the forward signal beam and the backward pump beam has an exact expression in terms of an elliptic integral and varies periodically along the fiber. For specific parameters, this overlap function takes the form of a soliton, with an almost constant value at all points on the fiber except for a pulse located at the soliton center. In the soliton configuration, the system displays polarization attraction for any beam intensities and arbitrary fiber lengths. We show how to solve the vector equations for the forward and backward beam Stokes vectors, using a shooting method to implement the endpoint boundary conditions, and plot the trajectories on the Poincare sphere.

Simulation research and theoretical study on measurement of atmospheric optical turbulence and wind profile using the correlation of gradient-tilt

In this article, a theoretical method based on the fluctuation of gradient tilt (G-tilt) of active light source is proposed to estimate the horizontal profiles of atmospheric optical turbulence (Cn2) and transverse wind. The G-tilt, related to the average phase gradient, is in the same direction as the average ray direction. And G-tilt angle is considered to be equal to the ratio between the centroid position offset and the focal length. In this method, a theoretical model based on lidar system is set up, in which forward scatter light beams at different distances are taken as beacons. These beacons are detected by a two-aperture telescope. And two light columns, from which we can obtain the information about G-tilt angle, are imaged by these beacons. In order to obtain the turbulence intensity and wind velocity from G-tilt angle with our theoretical model, the differential cross-correlation expressions of G-tilt angle and its derivative are derived in detail. These two expressions are based on the spatial cross-correlation function obtained from Rytov approximation and Taylor's frozen-flow hypothesis for Kolmogorov turbulence. Simultaneously, path weighting functions of Cn2 and wind velocity are derived, and the effects of path weighting functions on the calculation of our method are analyzed. Based on such an analysis, to realize the inversion of turbulence intensity and transverse wind, the matrix transformation algorithm is proposed. We ignore some minimal values of the path weighting functions in our algorithm so that the ill-conditioned matrix is avoided. Besides, numerical simulation is used for preliminarily validating this method. In our simulation, Cn2 varies randomly between 10-15 m-2/3 and 10-14 m-2/3 while wind velocity ranges from -5 m/s to 10 m/s. The sign of the wind velocity represents the direction of wind. According to the simulation results, the horizontal profiles of atmospheric optical turbulence and transverse wind calculated are consistent with their theoretical values no matter whether there exists Gaussian noise. When the ratio between the standard deviation of Gaussian noise we added and the original signal is 0.2, the maximum relative error of logarithmic Cn2 is 3.4%, and the correlation coefficient between the calculated results and theoretical values for Cn2 is 0.8. Besides, the maximum absolute error of wind velocity is 1.82 m/s, and the correlation coefficient between the calculated results and theoretical values for wind velocity is 0.9. Even if the horizontal profiles of atmospheric optical turbulence and transverse wind vary largely, the calculation results of our method remain stable. Therefore, a new idea is provided for measuring atmospheric turbulence and wind.

Polarization-dependent Zeeman spectroscopy in the two-photon ^3S_1/2−^4D_3/2,5/2 transition in Na vapor

By using the two-photon absorption technique, we have theoretically and experimentally investigated fine and hyperfine Zeeman structures of the 3S1/2−4D3/2,5/2 transition in a hot Na vapor in the presence of a magnetic field. Among 80 possible Zeeman lines, 10 lines were found to be forbidden, and the remaining 70 allowed lines were classified into four different manifolds: 3S1/2, F=2 to 4D5/2, F=2 to 4D3/2, F=1 to 4D5/2, and F=1 to 4D3/2. The Zeeman spectra of each manifold critically depended upon the polarization configurations of the forward and backward excitation laser beams. The peak position, the peak height, and the polarization dependence of each Zeeman component were fully analyzed and compared with the theoretical predictions, resulting in fair agreement between theory and experiment.