Distribution Of Deflection Angles Research Articles

Material budget imaging with multi-GeV electrons - calibration and applications for 2D material scanning

The technique of material budget imaging (MBI) uses multi-GeV electrons to directly measure the material budget ϵ = x/X 0 of a material with thickness x and its radiation length X 0. The beam particles are deflected by multiple Coulomb scattering and the deflection angle distribution is centered at zero with a width depending on the traversed material. Hence, a reconstruction of kink angles using individual electron trajectories measured in high resolution beam telescopes allows to estimate the material budget by applying appropiate models of multiple scattering theory, such as the Highland formula. Measurements at the DESY II testbeam were performed with various materials in terms of thickness and type for a calibration of the MBI technique. The material budget is an important quantity for the design of high-energy particle detectors. Therefore, the material budget of unknown materials can be experimentally measured as well as complex material distributions can be imaged in 2D.

The preferential orientation of magnetic switchbacks and its implications for solar magnetic flux transport

Context. Magnetic switchbacks in the solar wind are large deflections of the magnetic field vector, which often reverse their radial component, and are associated with a velocity spike consistent with their Alfvénic nature. The Parker Solar Probe (PSP) mission revealed them to be a dominant feature of the near-Sun solar wind. Where and how they are formed remains unclear and subject to discussion. Aims. We investigate the orientation of the magnetic field deflections in switchbacks to determine if they are characterized by a possible preferential orientation. Methods. We compute the deflection angles, ψ = [ϕ, θ]T, of the magnetic field relative to the theoretical Parker spiral direction for encounters 1 to 9 of the PSP mission. We first characterize the distribution of these deflection angles for quiet solar wind intervals and assess the precision of the Parker model as a function of distance from the Sun. We then assume that the solar wind is composed of two populations, the background quiet solar wind and the population of switchbacks, the latter of which is characterized by larger fluctuations. We model the total distribution of deflection angles we observe in the solar wind as a weighed sum of two distinct normal distributions, each corresponding to one of the populations. We fit the observed data with our model using a Monte Carlo Markov chain algorithm and retrieve the most probable mean vector and covariance matrix coefficients of the two Gaussian functions, as well as the population proportion. This method allows us to quantify the properties of both the quiet solar wind and the switchback populations without setting an arbitrary threshold on the magnetic field deflection angles. Results. We first confirm that the Parker spiral is a valid model for quiet solar wind intervals at PSP distances. We observe that the accuracy of the spiral direction in the ecliptic is a function of radial distance, in a manner that is consistent with PSP being near the solar wind acceleration region. We then find that the fitted switchback population presents a systematic bias in its deflections, with a mean vector consistently shifted toward lower values of ϕ (−5.52° on average) and θ (−2.15° on average) compared to the quiet solar wind population. This results holds for all encounters but encounter 6, and regardless of the magnetic field main polarity. This implies a marked preferential orientation of switchbacks in the clockwise direction in the ecliptic plane, and we discuss this result and its implications in the context of the existing switchback formation theories. Finally, we report the observation of a 12-hour patch of switchbacks that systematically deflect in the same direction, such that the magnetic field vector tip within the patch deflects and returns to the Parker spiral within a given plane.

Sperm motility in modulated microchannels

Sperm cells swim through the fluid by a periodic wave-like beating of their flagellum. At low Reynolds numbers and in confinement, the directed motion of sperm and other microswimmers is strongly influenced by steric and hydrodynamic wall interactions. We model sperm motility in mesoscale hydrodynamics simulations by imposing a planar traveling bending wave along the flagellum. Sperm are simulated swimming in curved, straight, shallow and zigzag-shaped microchannels. Changes in the sidewall modulations and the imposed beat pattern allow the identification of a strong dependence of the surface attraction on the beat-shape envelope of the sperm cell. For swimming in zigzag microchannels, the deflection-angle distribution at sharp corners is calculated and found to be in good agreement with recent microfluidic experiments. The simulations reveal a strong dependence of the deflection angle on the orientation of the beat plane with respect to the channel sidewall, and thus deepen the understanding of sperm navigation under strong confinement. Detachment of sperm, while swimming along curved walls, is dominated by the change of beat-plane orientation. Therefore, either the emergence of a nonplanar component of the flagellar beat with increasing wavelength or the strong confinement in shallow channels drastically increases wall attraction. Our simulation results reveal a consistent picture of passive sperm guidance that is dominated by the steric interactions of the beat pattern with the nearby surfaces.

Feasibility of track-based multiple scattering tomography

We present a tomographic technique making use of a gigaelectronvolt electron beam for the determination of the material budget distribution of centimeter-sized objects by means of simulations and measurements. In both cases, the trajectory of electrons traversing a sample under test is reconstructed using a pixel beam-telescope. The width of the deflection angle distribution of electrons undergoing multiple Coulomb scattering at the sample is estimated. Basing the sinogram on position-resolved estimators enables the reconstruction of the original sample using an inverse radon transform. We exemplify the feasibility of this tomographic technique via simulations of two structured cubes—made of aluminium and lead—and via an in-beam measured coaxial adapter. The simulations yield images with FWHM edge resolutions of (177 ± 13) μm and a contrast-to-noise ratio of 5.6 ± 0.2 (7.8 ± 0.3) for aluminium (lead) compared to air. The tomographic reconstruction of a coaxial adapter serves as experimental evidence of the technique and yields a contrast-to-noise ratio of 15.3 ± 1.0 and a FWHM edge resolution of (117 ± 4) μm.

A method to align a bent crystal for channeling experiments by using quasichanneling oscillations

A method to calculate both the bent crystal angle of alignment and radius of curvature by using only one distribution of deflection angles has been developed. The method is based on measuring of the angular position of recently predicted and observed quasichanneling oscillations in the deflection angle distribution and consequent fitting of both the radius and angular alignment by analytic formulae. In this paper this method is applied on the example of simulated angular distributions over a wide range of values of both radius and alignment for electrons. It is carried out through the example of (111) nonequidistant planes though this technique is general and could be applied to any kind of planes. In addition, the method application constraints are also discussed. It is shown by simulations that this method, being in fact a sort of beam diagnostics, allows one in a certain case to increase the crystal alignment accuracy as well as to control precisely the radius of curvature inside an accelerator tube without vacuum breaking. In addition, it speeds up the procedure of crystal alignment in channeling experiments, reducing beamtime consuming.

Planar channeling and quasichanneling oscillations in a bent crystal

Particles passing through a crystal under planar channeling experience transverse oscillations in their motion. As channeled particles approach the atomic planes of a crystal, they are likely to be dechanneled. This effect was used in ion-beam analysis with MeV energy. We studied this effect in a bent crystal for positive and negative particles within a wide range of energies in sight of application of such crystals at accelerators. We found the conditions for the appearance or not of channeling oscillations. Indeed a new kind of oscillations, strictly related to the motion of over-barrier particles, i.e. quasichanneling particles, has been predicted. Such oscillations, named planar quasichanneling oscillations, possess a different nature than channeling oscillations. Through computer simulation, we studied this effect and provided a theoretical interpretation for them. We show that channeling oscillations can be observed only for positive particles while quasichanneling oscillations can exist for particles with either sign. The conditions for experimental observation of channeling and quasichanneling oscillations at existing accelerators with available crystal has been found and optimized.

Characterizing Brittle Fracture by Modeling Crack Deflection Angles from the Microstructure

This study introduces a simple analytical model for fracture toughness to bridge the length scales from grain size to bulk thickness by assembling a virtual crack path from the angles recorded on an unfractured microstructure, which is a great challenge in fracture mechanics due to the high geometrical complexity. Good agreement is found between a crack deflection angle distribution measured from 5764 crack segments and the prediction by the model and the possible influence of residual stress is quasi quantitatively discussed. A total of 7.4% of the crack segments observed acted as crack bridges, while 7.3% was predicted by the model. A quantification of how high an angle needs to be to turn crack deflection into crack bridging is given. The ratio of fracture toughness from grain boundary to grain, G1c(gb)/G1c(g), was measured indirectly from all samples to be between 0.3 and 0.35.

Crack propagation in silicon nitride ceramics under various temperatures and grain boundary toughness

Crack deflection angles and fracture modes were investigated by elaborative observation of 5764 crack deflections, generated at 77K, 159K, 293K and 500K, in silicon nitride (Si3N4) ceramics. In addition, the effects of grain boundary toughness on crack propagation in Si3N4 ceramics were statistically analyzed based on a two-dimensional, polycrystalline model. The results demonstrated that temperature (77–500K) had little influence on crack advance, but the change of grain boundary toughness contributed a lot to the change of crack propagation. The distribution of deflection angles varied distinctly and the fraction of transgranular fracture increased when the grain boundary toughness increased.

Kinematics of hypervelocity stars in the triaxial halo of the Milky Way

Hypervelocity stars (HVSs) ejected by the massive black hole at the Galactic center have unique kinematic properties compared to other halo stars. Their trajectories will deviate from being exactly radial because of the asymmetry of the Milky Way potential produced by the flattened disk and the triaxial dark matter halo, causing a change of angular momentum that can be much larger than the initial small value at injection. We study the kinematics of HVSs and propose an estimator of dark halo triaxiality that is determined only by instantaneous position and velocity vectors of HVSs at large Galactocentric distances (r>~50kpc). We show that, in the case of a substantially triaxial halo, the distribution of deflection angles (the angle between the stellar position and velocity vector) for HVSs on bound orbits is spread uniformly over the range 10--180deg. Future astrometric and deep wide-field surveys should measure the positions and velocities of a significant number of HVSs, and provide useful constraints on the shape of the Galactic dark matter halo.

Dominant Directions of Epicenter Distribution of Regional Mining-induced Seismicity Series in Upper Silesian Coal Basin in Poland

The regional mining-induced seismicity of the Upper Silesian Coal Basin, Poland forms two major and two minor spatial clusters. The directional patterns of seismic series from the major clusters were studied with the use of the analysis of deflections. The seismic series is parameterized by the deflection angle of the straight line connecting epicenters of every two consecutive events, measured from NS direction. The trends of epicenter migration are characterized by modes of distribution of the deflection angle, estimated by the nonparametric kernel method. The distribution of deflection angles for the studied seismic series is not random. Altogether four trends of epicenter migration have been identified: two are connected with the subseries of events that belong to the same cluster and are related to the shape of the clusters, whereas the other two, linked to the subseries of events that alternate between the clusters, indicate that mutual positions of events in such series are not random. The results support recent hypotheses pertaining to low tectonic instability of this region.

Internal and translational atomic states in a laser-deflected beam

The authors study the effect of level degeneracy and of the polarisation of the driving field on the correlated evolution of the translational states and of the number of fluorescent photons for atoms in a monochromatic radiation field. The evolution equations are formally solved for the case of deflection of an atomic beam by a laser beam. They give explicit solutions for the distribution of deflection angles in several special cases.

Efficient transverse deflection of neutral atomic beams using spontaneous resonance-radiation pressure

We report the efficient transverse deflection of all atoms in a well-collimated sodium atomic beam by the spontaneous radiation pressure of a beam of resonance light which illuminates the atomic beam at right angles. Our results are obtained using two cw single-mode dye lasers to excite the two ground-state levels of sodium; this enables all atoms to interact with the light and it also eliminates optical pumping of the ground state. We obtained deflection angles greater than 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ rad which was ten times the divergence angle of the undeflected atomic beam; these deflections are due to the spontaneous scattering of more than 200 photons by each atom. The distribution of deflection angles is well described by a simple calculation. Fitting theory to experiment indicates that a fractional atomic excitation of 24 percent was obtained at an intensity of approximately 1 W/${\mathrm{cm}}^{2}$. When single-frequency light was used, only a fraction of the atoms were deflected, and the deflection angles were much smaller due to optical pumping.