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Alfvén eigenmodes (AEs) driven by energetic electrons were investigated via hybrid simulations of an MHD fluid interacting with energetic electrons. The investigation focused on AEs with the toroidal number n = 4. Both energetic electrons with centrally peaked beta profile and off-axis peaked profile are considered. For the centrally peaked energetic electron beta profile case, a toroidal Alfvén eigenmode (TAE) propagating in the electron diamagnetic drift direction is found. The mode is mainly driven by deeply trapped energetic electrons. It is also found that a few passing energetic electrons spatially localized around rational surfaces can resonate with the mode. For the off-axis peaked energetic electron beta profile case, an AE propagating in the ion diamagnetic drift direction is found when a $q\mathrm{-profile}$ with weak magnetic shear is adopted. The destabilized mode is an elliptical-Alfvén-eigenmode-type (EAE-type) mode which has a spatial profile peaking at the rational surface and a frequency close to the second Alfvén frequency gap. It is found that passing energetic electrons and barely trapped energetic electrons are responsible for this EAE-type mode destabilization. The saturation levels are compared for a TAE with the same linear growth rate among energetic electron driven mode and energetic ion driven mode with isotropic and anisotropic velocity space distributions. The saturation level of TAE driven by trapped energetic electrons is comparable to that driven by energetic electrons with isotropic velocity space distribution where the contribution of trapped particles is dominant. It is found that the trapped energetic ion driven TAE has a larger saturation level than the passing energetic ion driven TAE, which indicates the difference in particle trapping by the TAE between trapped and passing energetic ions., source:Jialei Wang et al 2020 Nucl. Fusion 60 112012, source:https://doi.org/10.1088/1741-4326/ab6c79, identifier:0000-0002-8678-8075

The flapping states of a flexible fiber fully coupled to a three-dimensional turbulent flow are investigated via state-of-the-art numerical methods. Two distinct flapping regimes are predicted by the phenomenological theory recently proposed by Rosti et al. (Phys. Rev. Lett. 121:044501, 2018) the under-damped regime, where the elasticity strongly affects the fiber dynamics, and the over-damped regime, where the elastic effects are strongly inhibited. In both cases we can identify a critical value of the bending rigidity of the fiber by a resonance condition, which further provides a distinction between different flapping behaviors, especially in the under-damped case. We validate the theory by means of direct numerical simulations and find that, both for the over-damped regime and for the under-damped one, fibers are effectively slaved to the turbulent fluctuations and can therefore be used as a proxy to measure various two-point statistics of turbulence. Finally, we show that this holds true also in the case of a passive fiber, without any feedback force on the fluid., QC 20191105

0000-0002-8678-8075, Alfvén eigenmodes (AEs) driven by energetic electrons were investigated via hybrid simulations of an MHD fluid interacting with energetic electrons. The investigation focused on AEs with the toroidal number n = 4. Both energetic electrons with centrally peaked beta profile and off-axis peaked profile are considered. For the centrally peaked energetic electron beta profile case, a toroidal Alfvén eigenmode (TAE) propagating in the electron diamagnetic drift direction is found. The mode is mainly driven by deeply trapped energetic electrons. It is also found that a few passing energetic electrons spatially localized around rational surfaces can resonate with the mode. For the off-axis peaked energetic electron beta profile case, an AE propagating in the ion diamagnetic drift direction is found when a $q\mathrm{-profile}$ with weak magnetic shear is adopted. The destabilized mode is an elliptical-Alfvén-eigenmode-type (EAE-type) mode which has a spatial profile peaking at the rational surface and a frequency close to the second Alfvén frequency gap. It is found that passing energetic electrons and barely trapped energetic electrons are responsible for this EAE-type mode destabilization. The saturation levels are compared for a TAE with the same linear growth rate among energetic electron driven mode and energetic ion driven mode with isotropic and anisotropic velocity space distributions. The saturation level of TAE driven by trapped energetic electrons is comparable to that driven by energetic electrons with isotropic velocity space distribution where the contribution of trapped particles is dominant. It is found that the trapped energetic ion driven TAE has a larger saturation level than the passing energetic ion driven TAE, which indicates the difference in particle trapping by the TAE between trapped and passing energetic ions.

We analyze the twin beam radiation generated by parametric down-conversion in a hexagonally-poled photonic crystal representing an interesting monolithic source of path-entangled photonic states. We highlight a super-resonance condition associated with a four-mode entanglement state., QC 20210520

As an energy-preserving variant of laser hybrid welding, laser-assisted arc welding uses laser powers of less than 1 kW. Recent studies have shown that the electrical conductivity of a TIG welding arc changes within the arc in case of a resonant interaction between laser radiation and argon atoms. This paper presents investigations on how to control the position of the arc root on the workpiece by means of the resonant interaction. Furthermore, the influence on the welding result is demonstrated. The welding tests were carried out on a cooled copper plate and steel samples with resonant and non-resonant laser radiation. Moreover, an analysis of the weld seam is presented.

In recent years, the infrared and microwave properties of opal matrices have been intensively studied [1]. It is thought that the opal matrices containing nanoparticles of magnetic materials in the intersphere voids may form a most promising class of materials used in centimeter- and millimeter-wave devices [2, 3]. Nickel-zinc, cobalt-zinc, and other ferrites seem to be proper materials for the filling owing to a lucky combination of such properties as high resistivity, low dielectric loss, high Curie temperature, and chemical stability. Application of microwave methods seems to be effective since these methods enables to estimate the dynamical and relaxation parameters of materials. Microwave properties of opal matrices containing the nanoparticles of different ferrite-spinels in the inter-sphere voids are discussed in this work. Microwave properties are measured at frequencies of millimeter waveband. Variations of a microwave signal passed through the magnetic nanocomposite occur mainly due to variations of the surface impedance under magnetic resonance condition and due to absorption of the wave. At higher frequencies the antiresonance is possible in fields lower than the resonance field. The antiresonance manifests itself as a maximum of transmission and/or reflection coefficients. © 2013 IEEE., Scientific Council of the National Academy;of Sciences of Ukraine on Radio-Physics and;Microwave Electronics

Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical (QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell s equations. This allows to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation allows to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime it is often necessary to account simultaneously for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is here highlighted in a study of the optical power limiting with platinum-organic molecular compounds. © 2007 Materials Research Society., References: McKay, T.J., Bolger, J.A., Staromlynska, J., Davy, J.R., (1998) J. Chem. Phys, 118, p. 5537; Parker, C.A., (1968) Photoluminescence of solutions, , Elsevier; Cooper, T.M., McLean, D.C., Rogers, J.E., (2001) Chem. Phys. Lett, 349, p. 31; Norman, P., Cronstrand, P., Ericsson, J., (2002) Chem. Phys, 285, p. 207; Rogers, J.E., Cooper, T.M., Fleitz, P.A., Glass, D.J., McLean, D.G., (2002) J. Phys. Chem. A, 106, p. 10108; J. E. Rogers, K. A. Nguyen, D. C. Hufnagle, D. C. McLean, W. Su, K. M. Gossett, A. R. Burke, S. A. Vinogradov, R. Pachter, and P. A. Fleitz, J. Phys. Chern. A 107, 11331 (2003)Rogers, J.E., Slagle, J.E., McLean, D.G., Sutherland, R.L., Sankaran, B., Kannan, R., Tan, L.-S., Fleitz, P.A., (2004) J. Phys. Chem. A, 108, p. 5514; Baev, A., Gel mukhaniov, F., Macak, P., Ågreni, H., Luo, Y., (2002) J. Chem. Phys, 117, p. 6214; Baev, A., Gel mukhaniov, F., Kimberg, V., arid, H., Ågren, (2003) J. Phys. B: At. Mol. Opt. Phys, 36, p. 3761; Jackson, J.D., (1999) Classical Electrodynamics, , Wiley, New York, 3rd ed; Boyd, R.W., (1992) Nonlinear Optics, , Academic Press, Inc, San Diego; Gel mukhanov, F., Baev, A., Macak, P., Luo, Y., Ågren, H., (2002) J. Opt. Soc. Am. B, 19, p. 937; Becke, A.D., (1993) J. Chem. Phys, 98, p. 5648; Bergner, A., Dolg, M., Kuchle, W., Stoll, H., Preuss, H., (1993) Mol. Phys, 80, p. 1431; Andrae, D., Haussermann, U., Dolg, M., Stoll, H., Preuss, H., (1990) Theor. Chim. Acta, 77, p. 123; Hehre, W.J., Ditche̊ld, R., Pople, J.A., (1972) J. Chem. Phys, 56, p. 2257; Yanai, T., Tew, D.P., Handy, N.C., (2004) Chem. Phys. Lett, 393, p. 51; M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery Jr., R. E. Stratmann, J. C. Burant, et al. Gaussian 98 (1998), Gaussian Inc., Pittsburgh PA, 1998. See http://www.gaussian.comhttp://www.kjemi.uio.no/software/dalton/dalton.html, DALTON, a molecular electronic structure program, Release 2.0 2005, seePeach, M.J.G., Helgaker, T

The quasilinear diffusion coefficient deviates significantly from the lowest order Larmor radius scaling D proportional to nu(2n)(perpendicular to). This is not only caused by the finite Larmor radius effects, but also by the inhomogeneous electric field polarisation and the changes of the guiding centre orbits. The regions with strong interaction and the boundaries for resonant interaction are identified. At these boundaries the quasi linear diffusion coefficient becomes discontinuous. Anew Monte Carlo scheme has been developed to treat problems with discontinuous diffusion coefficients., QC 20111014

A new class of resonant exchange of power among three co-propagating modes in dielectric optical waveguides exhibiting Kerr-like nonlinearity is reported. Unlike the coupling of modes travelling in different, spatially separated channels as in the directional coupler (Jensen, IEEE J. Quantum Electron. QE-18 (1982) 1580; Chen, Snyder and Mitchell, Electron. Lett. 26 (1990) 77; Schmidt-Hattenberger, Trutschel and Lederer, Optics Lett. 16 (1991) 294) this paper points out the possibility of obtaining an efficient coupling of modes travelling in one single channel. The key point here is the imposition of a geometrical resonance between modes, to improve the coupling process. Due to this resonance condition, which is related with the wavelength through the propagation constants, the power exchange process is very sensitive to the wavelength., Peer Reviewed

A plasma electron accelerator based on the gyromagnetic autoresonance effect is described. Elec-trons of the initially cold internal-injection plasma (a classical ECR discharge) are accelerated in the mag-netic field of a magnetic mirror trap under a one-stage effect of the resonant microwave field and an addi-tional pulsed magnetic field. The synchronism in maintaining the resonance conditions is ensured by a smooth increase in the pulsed magnetic field in the course of a microwave pulse. At the moderate values of the input microwave power (up to 2.5 kW) and the steady-state and pulsed magnetic fields (each up to 1 kG), it is possible to obtain stable relativistic plasma bunches, in which the energy of the electron components is a few hundred keV. The measured X-ray bremsstrahlung spectra have features characteristic of the energy dis-tribution of photons, and the high-energy tails are recorded in the region of 600-800 keV. The dependences of the bremsstrahlung characteristics on the experimental conditions-the value of the steady-state magnetic field and the amplitude of the pulsed magnetic field-are investigated. The experimental data are in good agreement in the quantitative sense with the results of the computer simulation and with the earlier studies. © Pleiades Publishing, Ltd., 2012.

The future safety of the U.S. Navy warship depends on the development of a directed energy self-defense system to keep pace with the ever-improving technology of anti-ship missiles. Two candidates are reviewed. The free electron laser (FEL) has the most advantages, but a chemical laser proposed by TRW is ready for installation on existing ships. Initial testing of issues related to directed energy use at sea can be conducted with the chemical laser. When the technology of the FEL matures, it can replace the chemical laser to provide the best possible defense in the shortest period of time. Continuous tunability is a key advantage of the FEL over the conventional laser. But since the output wavelength is dependent on electron energy. It is subject to random fluctuations originating from the beam source. At the Stanford University Superconducting (SCA) Free Electron Laser (FEL) Facility, the effects are minimized through negative feedback by changing the input electron energy proportional to the observed wavelength drift. The process is simulated by modifying a short pulse FEL numerical program to allow the resonant wavelength to vary over many passes. The physical effects behind optical wavelength control are explained. A theory for the preferential nature of the FEL to follow the resonant wavelength from longer to shorter wavelengths is presented. Finally, the response of the FEL to a rapidly changing resonant wavelength is displayed as a transfer function for the system., http://archive.org/details/aoryforopticalwa1094539857, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.