Triode Electron Gun of the LUE-200 Linear Accelerator,IREN Facility of the Laboratory of Neutron Physics,Joint Institute for Nuclear Research

Physics of Particles and Nuclei Letters - The electron injector (electron gun (EG)) is a triode system (cathode–control grid–anode with a second grid “wall”) with a grounded...     

Bose-Einstein condensates in strongly disordered traps

A Bose-Einstein condensate in an external potential consisting of a superposition of a harmonic and a random potential is considered theoretically. From a semiquantitative analysis we find the size, shape, and excitation energy as a function of the disorder strength. For positive scattering length and sufficiently strong disorder the condensate decays into fragments each of the size of the Larkin length L. This state is stable over a large range of particle numbers. The frequency of the breathing mode scales as 1/L(2). For negative scattering length a condensate of size L may exist as a metastable state. These findings are generalized to anisotropic traps.     

Electron fluid and quasiparticles in the quantum Hall effect

To explain fractional quantum Hall effect, it is necessary to take into account both the interaction between electrons and their interaction with impurities. We propose a simple model, where the Coulomb repulsion is replaced by a short range potential. For this model we are able to find many-body wave functions of the electron system interacting with impurities and calculate the Hall conductivityσ _xy. A simple physical picture, arising in the framework of this model, provides the understanding of a general reason for both fractional and integral quantum Hall effect. In the model, electrons forming a two-dimensional system, is supposed to occupy the first Landau level. The interaction of electrons is regarded as being small compared with the distance between the Landau levels. The radius of interaction is much less than the magnetic length. The following statements have been proved (Pokrovsky and Talapov 1985a,b; Trugman and Kivelson 1985). For the fillingν=1/m of the first Landau level the ground state is nondegenerate and has the wave functionΩ _w, proposed by Laughlin (1983). Forν, which is slightly less than 1/m the ground state is highly degenerate in the absence of impurities. It can be described as a system of noninteracting quasiholes as proposed by Laughlin (1983). These quasiholes float in the uniform incompressible fluid. Each quasihole has the charge |e|/m. The total number of quasiholes isq=S?mN, whereS is a number of states on the Landau level,N is the number of electrons. The impurities capture quasiholes. If the number of quasiholesq is less than the number of impuritiesN _i, then the ground state becomes nondegenerate. This fact permits us to calculateσ _xy (Pokrovsky and Talapov 1985b). Let there be a small electric fieldE in the system. In the absence of impurities the electron fluid is at rest in the frame of reference, moving with velocityν=cE/H. In this frame of reference the impurities move with the velocity ?v, carrying captured quasiholes. Therefore, the quasihole currents isj _q=(?ν)(| e|/m)q. Hence, in the initial frame of reference the total current isj=Nev+j _q=Sev/m. This means thatσ _xy=(1/m)e ²/2π?).     

Properties of ordered,continuously degenerate systems

Ordered continuously degenerate systems are shown to have some common properties associated with strong transverse fluctuations of the order parameter. Longitudinal fluctuations are related to the transverse ones in three-dimensional systems. The longitudinal susceptibility is infinitely large at zero external field and the longitudinal scattering is rather strong at low wavevectors.

Properties of two-dimensional degenerate systems depend on the dimensionality n of the order parameter. There is a phase transition at finite temperature T ₀ for n=2. At temperatures below T ₀ a ‘super-fluid density’ or ‘transverse rigidity’ arises. Probably no phase transition takes place for n≥3 since the effective temperature increases with the scale of fluctuations.

The role of singularities in phase transitions and a general topological classification of singularities is considered. Applications of the theory to magnets, liquid crystals, superfluids, superconductors and plasmas are demonstrated.     

Dark matter bodies in star and planet structures

The lowest frequency of the dipole f mode (surface gravity wave) of the Sun and some other stars is shown to be close to the orbital frequency of a trial body near the star surface, as well as the wave amplitude is shown to be resonantly increased to the values large enough to be observed. Therefore the Sun is considered to be a sensitive detector for hypothetical compact cosmic bodies made of dark matter particles. In this connection some possible characteristics of the dark matter bodies (DMB) are discussed, and DMB orbits in the Sun are calculated within a standard solar model in order to compare the wave amplitudes with data for the solar surface oscillations, and to estimate the masses and radii of the DMB. As well, some possible phenomena in star and planet structures are discussed with special attention on generation of flares of high X-ray classes, specific behavior of the Moon dust, formation of short-time vertical flows in deserts, oceans, and atmospheres on the Earth and other planets.     

Dielectric photonic crystal as medium with negative electric permittivity and magnetic permeability

We show that the two-dimensional photonic crystal (PC) made from a non-magnetic dielectric is a left-handed material in the sense defined by Veselago. Namely, it has negative values for both the electric permittivity ? and the magnetic permeability μ in some frequency range. This follows from a recently proven general theorem. The negative values of ? and μ are found by a numerical simulation. Using values |?| and |μ| for the medium surrounding the PC slab we simulate the Veselago lens, a unique optical device predicted by Veselago. An approximate analytical theory is proposed to calculate the values of ? and μ from the PC band structure. It gives the results that are close to those obtained by the numerical simulation. The theory explains how a non-zero magnetization arises in a non-magnetic PC.     

Hysteresis mediated by a domain wall motion

The position of an interface (domain wall) in a medium with random pinning defects is not determined unambiguously by the instantaneous value of the driving force, even on average. Employing the general theory of the interface motion in a random medium, we study this hysteresis, different possible shapes of the hysteresis loop, and the dynamical phase transitions between them. Several principal characteristics of the hysteresis, including the coercive force and the curves of dynamical phase transitions obey scaling laws and display a critical behavior in the vicinity of the mobility threshold. At finite temperature the threshold is smeared and a new range of thermally activated hysteresis appears. At a finite frequency of the driving force there exists a range of the non-adiabatic regime in which not only the position, but also the average velocity of the domain wall, displays hysteresis.     

Compact dark matter objects,asteroseismology, and gravitational waves radiated by sun

The solar surface oscillations observed by Crimean Astrophysical Observatory and Solar Helioseismic Observatory are considered to be excited by a small fraction of Dark Matter in form of Compact Dark Matter Objects (CDMO) in the solar structure. Gravitational Waves (GW) radiated by these CDMO are predicted to be the strongest at the Earth and are easily detectable by European Laser Interferometer Space Antenna or by Gravitational-Wave Observatory “Dulkyn” which can solve two the most challenging tasks in the modern physics: direct detection of GW and DM.     

One-Dimensional Dynamics of Jet Flows of Elastic Fluids

Flows of elasticoviscous liquids in free jets and in drawn filaments are investigated in the one-dimensional approximation. The interaction of the flows in the jet and the jet-forming die is taken into account. The structure of the transition zones, which ultimately degenerate into shock waves, is investigated. It is shown that depending on the type of instantaneous elastic response jet cross-section necking or swelling shocks may occur. The steady-state flow regimes are investigated numerically.