Axial Channeling Research Articles

Twisted-photons distribution emitted by relativistic electrons at axial channeling

Within the framework of quantum electrodynamics we have developed a theory for radiation of twisted photons by axially channeled electrons that allowed us for the first time to draw the angular distribution of twisted photons emitted by channeled electrons.

Dynamical chaos and level splitting under the channeling of the high energy positrons in [100] direction of the silicon crystal

The motion of charged particles in a crystal in the axial channeling regime can be both regular and chaotic. The chaos in quantum case manifests itself in the statistical properties of the energy levels set. These properties have been studied previously for the electrons channeling along [110] direction of the silicon crystal, in the case when the classical motion was completely chaotic, as well as for the ones channeling along [100] direction, when the classical motion can be both regular and chaotic for the same energy depending on the initial conditions. Here we study the positrons channeling in [100] direction. This case is of special interest due to the substantial tunneling probability between dynamically isolated regular motion domains in the phase space. The interaction of the energy levels via tunneling distinctly changes the level spacing statistics. All transverse motion energy levels as well as corresponding stationary wave functions are computed numerically for the 30 GeV positrons channeling in [100] direction of the silicon crystal. The values of the matrix elements for the tunnel transitions areextractedfrom these data. These results confirm the chaos assistance for the tunneling and the level splitting. These values will be used in the further researches of the quantum chaos manifestations in the channeling phenomenon.

Energy losses of highly charged Arq+ ions during grazing incidence on tungsten surfaces

In this study, we investigate the energy loss of highly charged ions interacting with various tungsten surfaces. The analysis primarily focuses on elucidating the impact of electron density distributions on energy loss of ions. Furthermore, we explore the correlation between surface azimuthal angles and energy loss under both uniform and inhomogeneous electron density distributions. Utilizing the classical over-the-barrier model (COBM), simulations involving trajectory calculations, energy loss, charge-exchange processes, and surface electron distributions, etc., were performed. Remarkably, the significant influence of axial channeling of surfaces on ion energy loss is observed. For the comparison of ion energy loss under uniform and inhomogeneous electron density distributions, the results reveal a more pronounced effect of electron density inhomogeneity on ion energy loss at higher energy-loss values. Additionally, the calculated energy-loss spectra of Ar16+ ions grazing on graphite surfaces show reasonable agreement with experimental data. These findings are crucial for understanding the surface structure of crystals.

Grazing incidence fast atom diffraction: general considerations, semiclassical perturbation theory and experimental implications.

Using semiclassical methods, an analytical approach to describe grazing incidence scattering of fast atoms (GIFAD) from surfaces is described. First, we consider a model with a surface corrugated in the scattering plane, which includes the surface normal and the incidence direction. The treatment uses a realistic, Morse potential, within a perturbation approach, and correctly reproduces the basic GIFAD phenomenology, whereby the scattering is directed primarily in the specular direction. Second, we treat the more general case of scattering from a surface corrugated in two-dimensions. Using time averaging along the direction of fast motion in the incidence direction, we derive a time dependent potential for the GIFAD scattering away from a low index direction. The results correctly describe the observation that diffraction is seen only when the scattering plane is aligned close to a low-index direction in the surface plane. For the case of helium scattering from LiF(001) we demonstrate that the resulting theoretical predictions agree well with experiment and show that the analysis provides new information on the scattering time and the length scale of the interaction. The analysis also gives insights into the validity of the axial surface channeling approximation (ASCA) and shows that within first order perturbation theory, along a low-index direction, the full 3-dimensional problem can be represented accurately by an equivalent 2-dimensional problem with a potential averaged along the third dimension. In contrast, away from low-index directions, the effective 2-dimensional potential in the projectile frame is time-dependent.

Study of spontaneous radiation during axial channeling of relativistic positrons in hexagonal crystals

In the study, using the Moliere, Firsov and Barrett approximations, the interaction potentials of positively charged particles channeled along the c-axes in hexagonal crystals such as Be, Mg, Sc, Ti, Co, Zn, Se, Y, Zr, Tc, Ru, Cd, Te, La are calculated at T = 300K. For the Co crystal, the Doyle – Turner approximation was additionally used. It is demonstrated that in these directions, sufficiently deep potential wells are formed. Using optimal approximation functions, energy levels and their corresponding wave functions are determined for channeled positrons with Lorentz-factors of 25, 50, 75. Using these data for positron beams with various angular dispersions, spontaneous radiation spectra are calculated for all the investigated hexagonal crystals.

On angular features of axial channeling radiation in crystals

Channeling of light relativistic particles in crystals is accompanied by intense radiation emission known as channeling radiation. Typically all calculations of channeling radiation aim in getting the total radiation intensity and its dependence on the parameters of particles and crystals. In the same time, since the discovery, the angular behaviours of channeling radiation have been studied just in a few works, in which only a polar dependence of the radiation intensity near the forward direction is estimated. However, simple analysis of the interaction potential predicts very specific features to be observed in the angular distributions of channeling radiation, especially at axial regime. In this work, for the first time, the expressions for angular and spectral distributions of electromagnetic radiation at axial channeling of relativistic charged particles in thin crystals are analytically refined within the QED theory. Obtained results allows predicting complex structures of radiation intensity and polarisation distributions. The results obtained might be of special interests for experimental studies.

The continuous pack-off technology: A novel water-control method and application to offshore horizontal wells of limestone reservoir

Water-control for horizontal wells is a worldwide problem, while it is even harder for limestone reservoir because of the developed fractures and caves.The formation water can be connected to the wellbore by fractures or caves directly or indirectly. Make the wells easily water flooded.Segmented water-control is the consensus of the current mainstream mechanical water-control technologies for horizontal wells, the segments confine the water break-through influence scope to the segment where the water break-through formed. In order to achieve that, all the potential water break-through fractures and caves connected to wellbore should be concentratedly divided into less segments, but that depends on the distribution of fractures and caves. Otherwise, the number and the sealing location of the packers are also relying on the engineering technology and the well status.Fracture/cave axial channeling inside the formation is another problem. The fractures and caves interwoven inside the formation. The formation water can easily flow around the packers by fractures/caves and cause the sealing failure of packers and invalid segment.Meanwhile the conventional mechanical water-control methods have no ability to limit the flow conductivity of fractures and caves. In the segments with fractures/caves developed, the producing degree of the matrix will be low.As a result, the application effect of conventional water-control methods in limestone reservoir horizontal wells is limited.To conquer the fracture/cave channeling and achieve the water-control effect at the meantime, the article proposed a novel mechanical water-control method which combined particle-filling with inflow control device screens. The particle-filling is not an absolute sealing, but a limitation of flow rate in the pack area. Calculations show that the flow conductivity of a 5 mm fracture will decreased to 0.1% of the original after particle-filling. The particles filled into the annulus between the screens and the borehole wall can limit the axial annulus flow enormously, replaces the traditional packer sealing. The particles filled into the fractures will reduce the flow conductivity sharply, and no need to concern about the channeling inside the fractures and caves interwoven. Inflow-control devices are utilized to control radius flow rate and balance the production profile near well. The novel water-control method obtained the outstanding application results especially in the limestone reservoir, with the function of deep production profile control combined with wellbore water control, has the advantage of both chemical water shut-off and mechanical water-control methods.Successful application in reef limestone reservoir demonstrates the excellent feasibility of this novel water-control method. The oil rate increased 3.9 times after application to well A4A in Liuhua oil field South China Sea. For well A3, the initial water-cut is only one third of the average value compared with wells drilled in recent years at the same layer.It is found that the production effect of oil wells is positively correlated with overfilling amount. For higher overfilling amount, filling process optimization is carried out, and micro-fracturing is formed by increasing filling rate to the target reservoir. The max filling rate of oil well reached 292% by the improvement of filling technology.

Study of the critical angle of channeling of active metal ions through thin aluminum films

The spatial distributions of ions (K+, Na+) passed through thin polycrystalline and single-crystalline Al films with the thickness from 180 to 600 Angstrem and critical channeling angles have been studied. The ion energies have been varied within the range E0=10-30 keV. It has been shown that an increase in the energy of the primary ion beam leads to a decrease in the width of the maxima of the angular distribution, which is associated with a decrease in the critical channeling angle psicr. It has been found that the value psicr does not exceed 4-50 for axial channeling and 9-100 for planar channeling Keywords: critical angle, passage of ions, angular distribution, channeling, spatial distribution.

MBN explorer atomistic simulations of 855 MeV electron propagation and radiation emission in oriented silicon bent crystal: theory versus experiment

The method of relativistic molecular dynamics is applied for accurate computational modeling and numerical analysis of the channelling phenomena for 855 MeV electrons in bent oriented silicon (111) crystal. Special attention is devoted to the transition from the axial channelling regime to the planar one in the course of the crystal rotation with respect to the incident beam. Distribution in the deflection angle of electrons and spectral distribution of the radiation emitted are analyzed in detail. The results of calculations are compared with the experimental data collected at the MAinzer MIctrotron facility.

Crystal rainbow channeling potential for 〈1 0 0〉 and 〈1 1 1〉 cubic crystallographic crystals

In this work we show a way how the crystal rainbow channeling effect can be applied for obtaining the interaction potential between 2 MeV protons and the cubic crystallographic crystals, in the cases of axial channeling of protons along (001) and (111) crystal directions. The procedure for construction of this potential has been based on our previous work in which the rainbow morphology was crucial for their determination. However, important improvements have been made. As a result, the two axial channeling directions can be treated using the same physical arguments leading to more consistent values of the fitting parameters in the ion-atom interaction potential.

Computational Study on Characteristic Radiation Originated from Channeled Relativistic Electrons in Single-Wall Carbon Nanotubes

I calculated the number of bound states n for channeled electrons through single wall carbon nanotubes (n,m) at different values of electrons energy by using (Wetzel, Kramer's, Brillouin approximation)(WKB) method. The calculations executed according to the continuum model approximation given by Lindhard for the case of an axial channeling in single crystals. The estimated results of the maximum number of bound states of the channeled electrons in a zigzag (n, 0), armchair (n,n) and chiral(n,m) nanotubes have been performed using the Moliere potential. In this work we determined the emitted photon energy due to n, (n-1) transitions between higher -quantum states as a function of the electron energy up to 500 MeV. Also the energy levels of electrons channeled in different types of single wall carbon nanotubes by using Moliere potential were defined. It has been showed that the emitted photon energy in the forward direction is the energy difference between the successive initial and final states of the channeled electron. The energy of the emitted channeling radiation has been calculated for incident electron at 50 MeV. We calculated the emitted channeling radiation for incident electrons at 10, 50 and500 MeV with frequency in X-ray range.

Изучение критического угла каналирования ионов активных металлов через тонкие пленки алюминия

The spatial distributions of ions (K+, Na+) passed through thin polycrystalline and single-crystalline Al films with the thickness from 180 to 600 Å and critical channeling angles have been studied. The ion energies have been varied within the range E0 = 10-30 keV. It has been shown that an increase in the energy of the primary ion beam leads to a decrease in the width of the maxima of the angular distribution, which is associated with a decrease in the critical channeling angle ψcr. It has been found that the value ψcr does not exceed 4-50 for axial channeling and 9-100 for planar channeling.

Radiation reaction near the classical limit in aligned crystals

An accelerated charged particle emits electromagnetic radiation. If the driving force is sufficiently strong, the radiated energy becomes comparable to the kinetic energy of the particle and the back-action of the emitted radiation (radiation reaction) significantly alters the dynamics of the particle. The Landau-Lifshitz (LL) equation has been proposed as the classical equation to describe the dynamics of a charged particle in a strong electromagnetic field when the effects of radiation reaction are taken into account. Hitherto, the experimental problem in validating the LL equation has been to achieve sufficiently strong fields for radiation reaction to be important without quantum effects being prominent. Notwithstanding, here we provide a quantitative experimental test of the LL equation by measuring the emission spectrum for a wide range of settings for 50 GeV positrons crossing aligned silicon single crystals near the $(110)$ planar channeling regime as well as 40 GeV and 80 GeV electrons traversing aligned diamond single crystals near the $\langle100\rangle$ axial channeling regime. The experimental spectra are in remarkable agreement with predictions based on the LL equation of motion with small quantum corrections for recoil and, in case of electrons, spin and reduced radiation emission, as well as with a more elaborate quantum mechanical model. Our experiment clearly shows the inadequacy of the Lorentz force as the sole agent of force on the particles in the classical limit, due to its absence of radiative energy loss in describing the dynamics of high-energy charged particles in strong electromagnetic fields like those in aligned single crystals.

On the influence of periodicity in the arrangement of crystalline atomic strings upon the spectral and spectral-angular distribution of high-energy positively charged particle radiation in crystal

Spectral and spectral-angular distribution of the radiated energy in case of positron motion in an oriented crystal and in case of positron motion in the field of randomly located atomic strings (random strings approximation) when the angle between particle momentum and crystal axes is less than the critical angle of axial channeling were calculated. Obtained results showed that the peak in the emission spectrum is related to the quasi-regular motion of the above-barrier positrons in planar channels.

Ion channelling effect and damage accumulation in yttria-stabilized zirconia implanted with Ag ions

Yttria stabilized zirconia (YSZ) is well known as a radiation-resistant material. In this study, we present results from 400 keV Ag+ implantations of the (1 0 0) YSZ single crystals to fluences ranging from 5 × 1015 to 5 × 1016 cm−2. The damage depth profiling and accumulation were probed using Rutherford backscattering spectrometry in the channelling mode (RBS-C), Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The axial channelling effect of 2 MeV He+ ions in the implanted YSZ was studied. RBS-C provides us with detailed information about the displaced atoms density depth profiles progressing into greater depths, especially in the case of higher fluence. TEM was utilized to characterize the microstructure evolution and damage accumulation in the buried layer after the implantation. At the highest fluence (5 × 1016 cm−2), Ag depth profile in the depth of 30–130 nm was identified in TEM bright and dark field images as well as in the electron diffraction patterns. Ag depth profiles are in agreement with depth profiles determined by RBS which show maximum Ag concentration in the depth of 94 nm. The reason for the decrease of the deformation identified by XRD in the vertical direction is the defect formation.

Structure of Regions of Regular Motion in the Phase Space of Channeled Electrons

The motion of electrons in the axial channeling mode in the [100] direction of a Si crystal can be regular and chaotic (depending on the initial conditions). The contribution of regions of regular and chaotic dynamics to the quasiclassical density of energy levels of the transverse motion of electrons is found in this paper. The obtained values are used as parameters of the Berry—Robnik distribution describing the level spacing statistics in the case of the coexistence of regions of regular and chaotic motion.

Regular and chaotic motion domains in the channeling electron's phase space and mean level density for its transverse motion energy

The motion of charged particles in a crystal in the axial channeling regime can be both regular and chaotic. The chaos in quantum case manifests itself in the statistical properties of the energy levels set. These properties have been studied previously for the electrons channeling along [110] direction of the silicon crystal, in the case when the classical motion was completely chaotic. The case of channeling along [100] direction is of special interest because the classical motion here can be both regular and chaotic for the same energy depending on the initial conditions. The semiclassical energy level density (as well as its part that corresponds to the regular motion domains in the phase space) is computed for the 10 GeV channeling electrons and positrons. It is demonstrated that the level spacing distribution for both electrons and positrons can be better described by Berry-Robnik distribution than by both Wigner (completely chaotic case) or Poisson (completely regular case) distributions.

Angular momentum of radiation from a charge in circular and spiral motion

We study theoretically the vortex radiation of a relativistic charged particle. General expressions for the spectral and angular distributions of angular momentum of radiation are derived for an arbitrary moving charge. Special attention is given to calculation of the angular momentum of synchrotron radiation. We obtain the spectrum and the angular distribution of angular momentum carried by synchrotron radiation. Similar expressions for the angular momentum of radiation of a charge moving on a spiral trajectory are derived by use of Lorentz transformations. It is shown that the main part of angular momentum in this case is emitted at a small angle to the vortex axis. Relativistic charged particles at spiral motion are effective source of the vortex photon beams at wave lengths ranging from radio waves to gamma rays. The obtained equations can be used for calculations of the angular momentum emitted by charged particles in the helical undulators and at axial channeling in solid crystal.

On formation of exotic particles at channeling of low energy antiprotons in LiH crystals

In this work we propose a new method to form both protonium exotic $$ \mathrm{p}\overline{\mathrm{p}} $$ and lithium antiproton $$ \overline{\mathrm{p}}{\mathrm{Li}}^{+} $$ atoms by capturing the hydrogen H− and lithium Li+ ions of the LiH crystal lattice at planar or axial channeling of low-energy antiproton beams. Within sudden-perturbation approximation the probability for protons as well as for ions to be bound into different quantum levels defined by the antiproton Coulomb potential are calculated. It is shown that the probability strongly depends on the parameters of channeled antiprotons revealing various extremes (resonances): the functions of capture probabilities for all excited quantum states of antiproton are characterized by three most intense peaks. Higher probability to form heavier particles, namely antiproton lithium $$ \overline{\mathrm{p}}{\mathrm{Li}}^{+} $$, have been demonstrated.

Computational study on interatomic potentials to dynamic effects in rainbow scattering under axial channeling at Al(0 0 1) surface

The interatomic potentials between projectiles and target atoms have a strong influence on the rainbow angles corresponding to pronounced peaks in the angular distributions of scattered projectiles with slight angle, attributed to rainbow scattering (RS), under axial surface channeling conditions. Schüller and Winter (SW) (2009) have measured the dependence of rainbow angles on normal energies to the target surface of projectile energy in RS of reactive N atomic projectile under <1 0 0> axial channeling conditions at a Al(0 0 1) metal surface with projectile energies of 10–70 keV. The SW’s data were analyzed by computer simulations using the ACOCT code based on the binary collision approximation with interatomic pair potentials. The agreement between the ACOCT results using the ZBL pair potential with only a repulsive part and the experimental ones was found in RS for projectile energy of 70 keV. The experimental results included the dynamic effects indicating that rainbow angles increase with decreasing projectile energies at low normal energies were roughly reproduced by the ACOCT simulations for the HF-like pair potentials with an attractive part depending on projectile energies.