Search

In this letter repulsion of phase-velocity dispersion curves of quasidipole eigenmodes of waveguides with non-circular cross section in non-axisymmetric anisotropic medium is studied by the semi-analytical finite element technique. Borehole waveguide is used as an example. The modeling helps in clarifying the nature of this phenomenon, which is accompanied by the rotation of the orientation of two quasidipole modes with frequency and by the exchange of their behavior at near-crossover point. The dispersion curves cross only in the presence of exact symmetry. Such a scenario is the alternative to the stress-induced anisotropy crossing of dispersion curves.

The computation of the spectrum of a waveguide with arbitrary anisotropy with spatial dependence is a challenging task due to the coupling between axial and azimuthal harmonics. This problem is tackled in cylindrical coordinates by extending a spectral method for the general case. By considering the matrix representation of the operator on the right-hand side of the governing equations, the latter are exactly reformulated as an infinite set of integro-differential equations. Essential part of this study is taking into account the coupling of different harmonics, which becomes evident from the kernels of these equations. Provided a waveguide is translationally invariant in the axial direction, the coupling of axial harmonics vanishes. A practical approximation and truncation procedure yields a generalized eigenvalue problem, which can be solved numerically to obtain the entire spectrum of the operator and to construct the dispersion curves for the eigenmodes. The spectral method is tested against the results from the measurements of dispersion curves for the monopole, dipole, and quadrupole normal modes of scaled boreholes in tilted transverse isotropy anisotropic rock sample. Besides, the comparison of dispersion curves calculated by the spectral method and those computed from the synthetic data is discussed.

The effect of a surface impedance load on the properties of axisymmetric quasi-Rayleigh waves propagating along the boundaries of a cylindrical cavity is investigated. By solving the problem by means of the impedance method, a dispersion equation for these waves is obtained. It is shown that the equation can be represented as the condition that the determinant of the sum of impedance matrices of the load and the medium is zero. Analysis of this equation allows one to investigate the effect of the surface load on the behavior of quasi-Rayleigh waves and on their critical frequencies. The conditions that should be met by the impedance load for quasi-Rayleigh waves to be absent near the cavity or for one or two such waves to exist are determined. The choice of the load is specified for the propagating quasi-Rayleigh wave to possess preset dispersion properties. The conclusions drawn on the basis of this study are illustrated by several examples of load models that can be implemented in practice.

A design is proposed and a resolving power is calculated for a detector that monitors the unauthorized transportation of high Z materials (nuclear materials with Z > 90) using the natural cosmic-ray muon flux. The identification of nuclear materials is based on the strong dependence of the multiple scattering angle on the matter charge upon traversing the matter by cosmic muons. It is proposed that chambers assembled from drift aluminum tubes similar to chambers used in the muon system of the ATLAS detector be used as the coordinate detector for the setup. The calculations show that the proposed variant of the setup makes it possible to detect the presence of nuclear materials with a weight of about 0.5–1 kg and higher in the inspected volume in a measurement time of several minutes.

Electron-cooling experiments have been carried out at the HIMAC-synchrotron in order to provide high-quality beams for medical and related research. For investigating the behavior of the free radicals, especially, the beam bunch was compressed by electron cooling with a triangle-wave RF-field. The dependences of the bunch length on the electron energy and the RF voltage were investigated under various intensities of Ar18+ beam. As a result, the bunch length was limited by around 20 ns due to the space-charge effect under an intensity of 1.33×106 ions/bunch and an RF amplitude of 340 V.

A new compact ion cooler ring (S-LSR) in Kyoto University has a circumference of 22.197 m and maximum magnetic rigidity of 1 T/m. One of the research subjects of S-LSR is a test bed to produce crystalline beams. Ring optics is designed to satisfy several required conditions for the beam ordering such as a small betatron phase advance and small magnetic error. We plan two cooling approaches. One is an electron beam cooling with 7 MeV proton beam from a linac. This target is 1-dimensional Coulomb strings. The beam-ordering simulation is carried out using the S-LSR parameters. The other is laser cooling with 35 keV Mg + beam from an ion source. The goal of the laser cooling experiment is to produce two-dimensional and three-dimensional crystals.