Investigation of Parameters of the Ion Beam Formed in Crossed Electric and Magnetic Fields

The results of experimental investigations of the characteristics of the positive ion beam formed in an ionplasma system with discharge generation in crossed electric and magnetic fields are presented. The conditions for the discharge formation and the specific features of the developed configuration of the discharge unit are described. It is shown that such discharge systems are capable of forming broad lowenergy ion beams and can be used successfully in various fields of thinfilm technology.     

Investigation of Nonself-Maintained Discharge in Crossed Electric and Magnetic Fields with Closed Hall Current

A nonself-maintained discharge in crossed fields with a closed Hall current is experimentally investigated. Argon and xenon are used as the working medium. The discharge gap is characterized by a magnetic field uniform along the channel, by the absence of an insulating coating on the channel walls, and by the delivery of the working medium uniform over the channel section through the porous end diaphragm of the anode. Measurements of current distributions over the structural elements are performed. It is shown that, in the presence of a self-incandescent compensator cathode supporting a nonself-maintained discharge, an intense flux of accelerated ions is created with a high recovery factor of the working medium with about 30 eV spent for ion formation and the energy efficiency exceeding 0.5.     

Electric and Magnetic Fields Generated by SHS

Fast-moving reaction zones (combustion fronts) may generate transient electric potentials (up to 1.5 V) and weak magnetic fields (up to 20 nT) due to ionization processes and ion movement within and behind the reaction front. These time-varying electric and magnetic fields are most probably generated by an electric double layer within individual particles and a temporal excess of ion carriers within the sample. The shape and magnitude of the induced temporal signals depend on the reaction zone propagation mode, reaction mechanism, and reactant properties.     

Dynamic Remanent Vortices in Superfluid 3He-B

We investigate the decay of vortices in a rotating cylindrical sample of ³He-B, after rotation has been stopped. With decreasing temperature vortex annihilation slows down as the damping in vortex motion, the mutual friction dissipation α(T), decreases almost exponentially. Remanent vortices then survive for increasingly long periods, while they move towards annihilation in zero applied flow. After a waiting period Δt at zero flow, rotation is reapplied and the remnants evolve to rectilinear vortices. By counting these lines, we measure at temperatures above the transition to turbulence ∼0.6 T _c the number of remnants as a function of α(T) and Δt. At temperatures below the transition to turbulence T≲0.55 T _c, remnants expanding in applied flow become unstable and generate in a turbulent burst the equilibrium number of vortices. Here we measure the onset temperature T _on of turbulence as a function of Δt, applied flow velocity v=v _n−v _s, and length of sample L.     

Intensity Modulation Produced by Crossed Electric and Magnetic Field Electron Image Deflection Systems

It was found that intensity fringes were produced in a crossed electric and magnetic field electron image deflection system. The origin of these fringes is discussed.     

Boundary Effects in Superfluid Films

We have studied the superfluid density and the specific heat of the x − y model on latticesL×L×H withL≫H (i.e. on lattices representing a film geometry) using the Cluster Monte Carlo method. In theH-direction we applied staggered boundary conditions so that the order parameter on the top and bottom layers is zero, whereas periodic boundary conditions were applied in theL-directions. We find that the system exhibits a Kosterlitz-Thouless phase transition at theH-dependent temperatureT _c ^2D below the critical temperature T_gl of the bulk system. However, right at the critical temperature the ratio of the areal superfluid density to the critical temperature isH-dependent in the range of film thicknesses considered here. We do not find satisfactory finite-size scaling of the superfluid density with respect toH for the sizes ofH studied. However, our numerical results can be collapsed onto a single curve by introducing an effective thicknessH _eff=H+D (whereD is a constant) into the corresponding scaling relations. We argue that the effective thickness depends on the type of boundary conditions. Scaling of the specific heat does not require an effective thickness (within error bars) and we find good agreement between the scaling functionf ₁ calculated from our Monte Carlo results,f ₁ calculated by renormalization group methods, and the experimentally determined functionf ₁.     

Dynamics of Quantized Vortices in Superfluid Helium and Rotating Bose-Einstein Condensates

No Heading We study theoretically and numerically the dynamics of quantized vortices in superfluid helium and rotating Bose-Einstein condensates. After reviewing briefly the recent motivation, we discuss these topics with the emphasis on the research done by our group. One of the modern important problems is how superfluid turbulence relates to classical turbulence. First, we show that superfluid turbulence consisting of a vortex tangle has an energy spectrum consistent with the Kolmogorov law. Second, we discuss the vortex states that appear in a rotating channel with counterflow. In the field of atomic-gas Bose-Einstein condensation, the dramatic observations of quantized vortices were made for rotating condensates. By solving numerically the Gross-Pitaevskii equation, we found a whole story of the vortex lattice formation consistent with the observations.PACS numbers: 67.40.Vs, 47.32.Cc, 47.37.+q.     

Propagation of Quantized Vortices Driven by an Oscillating Sphere in Superfluid 4He

We performed numerical simulation of quantum turbulence at 0 K generated from remnant vortices attached to an oscillating sphere. The remnant vortices are extended by the sphere motion and form a tangle with emitting vortex loops. As time passes, the length of vortices in a computational volume becomes statistically steady. We investigate in the statistical steady state the distribution of the length of vortex loops and anisotropy of their propagation direction caused by the sphere oscillation. The propagation direction of the emitted vortex loops is anisotropic along the oscillation direction of the sphere. The obtained results are consistent with results obtained in the experimental study using vibrating wires in superfluid ⁴He.     

Observation of Optically Induced Spin Dephasing and Dynamics Under Combined Electric and Magnetic Fields in Semiconductor Quantum Wells

Journal of Superconductivity and Novel Magnetism - Magnetic field dependence of the electronic spin polarization (P), polarization decay and spin oscillation in gallium arsenide quantum wells is...     

Effect of Strong Magnetic Fields on Superfluid 3He in 98% Porosity Aerogel

No Heading We report our results of shear acoustic impedance measurements performed on superfluid ³He in 98% porosity silica aerogel. Experiments in high porosity aerogel provide unique opportunity to study the influence of disorder on a p-wave superfluid and compare the behavior with that of the well understood pure bulk. Our experiment is designed to detect acoustic signatures from both bulk liquid and liquid in aerogel. In the past, experiments on ³He in aerogel have been conducted in zero or low magnetic fields (< 1 tesla). We made measurements in magnetic fields as high as 15 tesla at 28.4 and 33.5 bars and observed a new phase in aerogel induced by magnetic fields splitting the superfluid transition into two.PACS numbers: 67.57Pq, 67.80Mg     

High Coercivity Sr-ferrite Magnetic Thin Films Induced by Various Underlayers

1. IntroductionRecelltly, permanellt magnetic films have beenwidely studied for the application in micro--electricalmechanical-system (MEMS). Rare earth magnet thinfilms, i.e. NdZFe14B or SmColl'ZI, are the mostpromising materials to be used to miniaturize the system due to their higher energy products. However,poor corrosion resistance against humidity limits theirapplication in some circumstances. The virtues ofhexagonal ferrite films derived from their anticorrosion capability against …     

Energy Spectrum of the Superfluid Velocity Made by Quantized Vortices in Two-Dimensional Quantum Turbulence

We discuss the configurations of vortices in two-dimensional quantum turbulence, studying energy spectrum of superfluid velocity and correlation functions with the distance between two vortices. We apply the above method to quantum turbulence described by Gross-Pitaevskii equation in Bose-Einstein condensates. We make two-dimensional quantum turbulence from many dark solitons through the dynamical instability. A dark soliton is unstable and decays into vortices in two- and three-dimensional systems. In our work, we propose a method of discriminating between the uncorrelated turbulence and the correlated turbulence. We decompose the energy spectrum into two terms, namely the self-energy spectrum E _self (k) made by individual vortices and the interactive energy spectrum E _int (k) made by interference of two vortices. The uncorrelated turbulence is defined as turbulence with E _int (k)?E _self (k), while the correlated turbulence is turbulence where E _int (k) is not much smaller than E _self (k). Our simulations show that in the decay of dark solitons, the vortices created consist of correlated pairs of opposite circulation vortices, leading to the correlated turbulence.     

The Dynamic Texture of Superfluid 3He-B at Very Low Temperatures and in High Magnetic Fields

No Heading We report experiments using a pair of crossed vibrating wire resonators (VWRs) in the B phase of superfluid ³He in the zero temperature ballistic limit and in magnetic fields up to the B to A phase transition field of 340 mT. The VWRs are sensitive mechanical probes of energy gaps, textures and turbulent flow. In high magnetic fields the energy gap is no longer isotropic but significantly distorted, and the damping measured by the VWRs increases. With the crossed pair, we find that we can reduce the damping measured by one VWR when we increase the drive on the other one. We suggest that the reduction arises from the orientation of the surrounding texture by superflow and the screening of quasiparticles by the creation of superfluid turbulence.PACS numbers: 67.57.Fg, 67.57.Hi.     

The Vortex Generation in Superfluid Helium and the Role of Neighbouring Vortices

The thermal activation or quantum tunneling is believed to be necessary for the vortex nucleated near a wall to escape from its vicinity, and for the vortex nucleated in the bulk to reach the critical size above which it can increase according to its own dynamics. This paper suggests the idea that there exists the possibility to understand these processes (without leaving the framework of hydrodynamics) as the result of the simultaneous presence of several vortices or the interaction between various sections of vortex lines.     

Collective Motion of Vortices Induced by A.C. Magnetic Field in the High Anisotropy BSCCO

The microwave dissipation induced by an ac magnetic field collinear to the dc magnetic field in the highly anisotropic BSCCO shows two signals. One, that occurs just below T _c in all superconductors, corresponds to changes in the microwave dissipation of the TAFF resistivity caused by a magnetic modulation. The other signal arises from a double frequency process, where the ac field prepares the vortex system to enable its interaction with the microwave. This signal whose response to the ac field is non-linear (NL) is studied in this work, mostly for the configuration where the dc and the ac magnetic field are parallel the a–b plane. We demonstrate that below B _dc=0.0025 T the ac field interacts with individual non-interacting vortices. Above B _dc=0.005 T, the ac induces simultaneously, collective motions of pinned vortices and Josephson unpinned vortices. The latter has a bell-shaped form and therefore can be identified as an oscillation mode induced by the magnetic microwave field. This oscillation mode is excited by the microwave magnetic field and therefore it differs from the Josephson plasma excitation mode or the vortex excitation mode where both are excited by the microwave electric field. Defects, high temperatures and high ac fields impedes the excitation of this mode. The results are discussed with respect to the vortex shaking effect and other experimental and theoretical results.     

Charged Tangles of Quantized Vortices in Superfluid 4He

We show that turbulence in superfluid ⁴He at low temperatures can be generated and probed by injected ions trapped on vortex cores. The results of our recent experiments, in which negative ions were injected during short and long periods, in different quantities, and into different applied electric fields, are outlined. Three very different mechanisms of vortex-assisted transport of trapped ions were observed: one is on isolated vortex rings while two others are associated with tangles of vortex lines. It seems there are two different types of vortex tangles that can be characterized by the velocity of ion motion through them: a drifting polarized tangle in a low-dissipation state that mainly advects trapped ions, and a more isotropic tangle in a highly-dissipative state, sustained by a continuous forcing by the ion current in an applied electric field, through which trapped ions move rapidly.