Third International Symposium on Magnetic Suspension Technology

In order to examine the state of technology of all areas of magnetic suspension and to review recent developments in sensors, controls, superconducting magnet technology, and design/implementation practices, the Third International Symposium on Magnetic Suspension Technology was held at the Holiday Inn Capital Plaza in Tallahassee, Florida on 13-15 Dec. 1995. The symposium included 19 sessions in which a total of 55 papers were presented. The technical sessions covered the areas of bearings, superconductivity, vibration isolation, maglev, controls, space applications, general applications, bearing/actuator design, modeling, precision applications, electromagnetic launch and hypersonic maglev, applications of superconductivity, and sensors

준 이차원 보즈-아인슈타인 응집체에서 일어나는 열적 위상 요동

학위논문 (박사)-- 서울대학교 대학원 : 물리·천문학부(물리학전공), 2014. 2. 신용일.Quantum gases are well isolated, highly controllable, and defect-free systems which can simulate many body quantum phenomena that have been studied in condensed matter systems. To study two-dimensional superfluid, we have developed an experimental apparatus that can produce Bose-Einstein condensates (BEC) of Na-23 atoms. The apparatus can generate a pure condensate of 10^7 atoms in an optically plugged magnetic quadrupole trap within 17 s. The Berezinskii-Kosterlitz-Thouless (BKT) theory provides a general framework of the superfluid phase transition in two dimension, which does not involve spontaneous symmetry breaking and emergence of an order parameter below a critical temperature. Instead, it is the formation of vortex pairs with opposite circulations below the critical temperature that mediates the superfluid phase transition. Recently, it has been demonstrated that degenerate Bose gases confined in highly oblate harmonic potentials undergo the BKT phase transition. This thesis focuses on our experimental research on thermal phase fluctuations (i.e., long-wavelength phonons and vortex pairs) in the superfluid phase of trapped quasi-2D BECs. We have developed a quantitative probe to measure phase fluctuations in the 2D superfluid by free expansion, where the phase fluctuations in the sample were revealed as density modulations in the course of expansion. The power spectrum of the density fluctuations showed an oscillatory shape and the scaling behavior of the peak positions could be understood as a Talbot effect in matter waves. Employing this method, we demonstrated the thermal origin of phase fluctuations. We also investigated relaxation dynamics of nonequilibrium states of the quasi-2D system using the power spectrum. Thermally excited vortex pairs are the characteristic feature of the 2D superfluid. The quantized vortices are conventionally observed by a density-depleted core after expanding a trapped sample. The method, however, cannot be applied to the 2D sample because the density modulations after free expansion lower the vortex core visibility. We enhanced the core visibility by radial compression of the sample before the expansion so the phonon modes in the 2D sample were relaxed in a 3D environment. Measuring vortex distributions, we revealed the pairing feature by spatial correlations of the vortex positions. We also studied BKT-BEC crossover phenomena in a finite-size sample trapped in a quasi-2D harmonic potential by investigating the vortex profiles at various temperatures. Condensates of atoms have an internal spin structure so they can host various kinds of topological excitations. The two-dimensional Skyrmion is one of the topological spin textures in the anti-ferromagnetic spinor condensate and we imprinted the structure using the magnetic field sweep technique. The 2D Skyrmion spin texture has a finite Berry curvature because of the non-coplanar spin configuration. We studied a geometric Hall effect, with condensates trapped in a harmonic potential with the Skyrmion spin texture. Under a linear driving of the spin texture, we observed a condensate dipole motion resonantly developed into a circular motion, which demonstrates the existence of an effective Lorentz force.Abstract i List of Tables ix List of Figures x Chapter 1 Introduction 1.1 Bose-Einstein condensates of dilute gases . . . . . . . 4 1.2 Outline of the thesis . . . . . . . . . . . . . . . . . . . . . . . . 7 Chapter 2 Experimental setup 2.1 Laser system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2 Condensate machine . . . . . . . . . . . . . . . . . . . . . . 21 2.2.1 Oven chamber . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2.2 Zeeman slower . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.3 Main chamber . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2.4 Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.2.5 Imaging setup . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.2.6 Control system . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3 Magneto-optical trap . . . . . . . . . . . . . . . . . . . . . . . 34 2.3.1 Dark-MOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.3.2 Aligning the dark-MOT . . . . . . . . . . . . . . . . . . . . 36 Chapter 3 Evaporative cooling to Bose-Einstein condensates 3.1 Optically plugged magnetic quadrupole trap . . . . . . . 41 3.2 Bose-Einstein condensation. . . . . . . . . . . . . . . . . . 45 3.2.1 Radio frequency-induced evaporative cooling. . . . . 45 3.2.2 Producing Bose-Eisntein condensates . . . . . . . . . 52 3.3 Characterizing evaporation process . . . . . . . . . . . . 54 3.3.1 Rate equations for atom number and temperature . .54 3.3.2 Suppression of the non-adiabatic spin flip . . . . . . . 55 3.3.3 Numerical simulation of the evaporation process . . 57 Chapter 4 Phase fluctuations in a two-dimensional Bose gas 4.1 Phase transition in two dimensional Bose system. . . 64 4.1.1 Absence of Bose-Einstein condensation . . . . . . . . 64 4.1.2 Berezinskii-Kosteriltz-Thouless phase transition . . 66 4.1.3 Weakly interacting Bose gas in two dimension . . . .69 4.2 Qausi-two dimensional degenerate Bose gas . . . . . 72 4.2.1 Optical dipole trap . . . . . . . . . . . . . . . . . . . . . . . 72 4.2.2 Preparing degnerate Bose gas . . . . . . . . . . . . . . . 72 4.3 Probing thermal phase fluctuations by free expansion 77 4.3.1 Power spectrum of density fluctuations . . . . . . . . . 80 4.3.2 Thermal dependences of the phase fluctuations. . . 84 4.3.3 Non-equilibrium relaxation process. . . . . . . . . . . . 86 4.4 Observation of thermal vortex pairs in superfluid . . . . 88 4.4.1 Radial compression . . . . . . . . . . . . . . . . . . . . . . 89 4.4.2 Pair correlation. . . . . . . . . . . . . . . . . . . . . . . . . . 93 4.4.3 BKT-BEC crossover. . . . . . . . . . . . . . . . . . . . . . 95 4.4.4 Effects of the radial compression. . . . . . . . . . . . . 103 Chapter 5 Two-dimensional Skyrmion in a spinor condensate 5.1 Classification of topological excitations . . . . . . . . . 114 5.2 Polar phase vs ferromagnetic phase of spin-1 condensates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5.3 Spin texture imprinting by spin rotation . . . . . . . . . .122 5.3.1 Spin tilting by B-field rotation . . . . . . . . . . . . . . . 122 5.3.2 Skyrmion spin texture with a magnetic quadrupole field.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.3.3 Experimental results . . . . . . . . . . . . . . . . . . . . . 124 5.3.4 Characterization of the imprinting method . . . . . . 128 5.4 Topological Skyrmions. . . . . . . . . . . . . . . . . . . . . 131 5.4.1 Skyrmions in polar phase. . . . . . . . . . . . . . . . . . 131 5.4.2 Creation of highly charged Skyrmions . . . . . . . . . 133 5.4.3 Dynamical evolution of the Skyrmion . . . . . . . . . . 135 5.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Chapter 6 Geometric Hall effect with a Skyrmion spin texture 6.1 Gauge potential in a magnetic quadrupole field . . . . 151 6.2 Vortex ground state under the monopole gauge field 157 6.3 Geometric Hall effect in a spinor BEC . . . . . . . . . . .160 6.3.1 Sample preparation . . . . . . . . . . . . . . . . . . . . . 164 6.3.2 Emergence of Hall motion . . . . . . . . . . . . . . . . . 167 6.3.3 Quantized vortices in the circulating condensates. 171 Chapter 7 Conclusions Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Appendix C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Appendix D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Appendix E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 Appendix F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Appendix G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Appendix H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Appendix I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 Appendix J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 국문 초록 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 감사의 글 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203Docto

Fourth International Symposium on Magnetic Suspension Technology

In order to examine the state of technology of all areas of magnetic suspension and to review recent developments in sensors, controls, superconducting magnet technology, and design/implementation practices, the Fourth International Symposium on Magnetic Suspension Technology was held at The Nagaragawa Convention Center in Gifu, Japan, on October 30 - November 1, 1997. The symposium included 13 sessions in which a total of 35 papers were presented. The technical sessions covered the areas of maglev, controls, high critical temperature (T(sub c)) superconductivity, bearings, magnetic suspension and balance systems (MSBS), levitation, modeling, and applications. A list of attendees is included in the document

Investigation of diamagnetic bearings and electrical machine materials for flywheel energy storage applications

Recent trends in energy production have led to a renewed interest in improving grid level energy storage solutions. Flywheel energy storage is an attractive option for grid level storage, however, it suffers from high parasitic loss. This study investigates the extent to which passive diamagnetic bearings, a form of electromagnetic bearing, can help reduce this parasitic loss. Such bearings require three main components: a weight compensation mechanism (lifter-floater), a stabilizing mechanism and an electrical machine. This study makes use of a new radial modification of an existing linear multi-plattered diamagnetic bearing. Here a prototype is built and analytical expressions derived for each of the three main components. These expressions provide a method of estimating displacements, fields, forces, energy and stiffness in the radial diamagnetic bearing. The built prototype solution is found to lift a 30 [g] mass using six diamagnetic platters for stabilization (between ring magnets) with a disc lifter and spherical floater for weight compensation. The relationship between mass and number of platters was found to be linear, suggesting that, up to a point, increases in mass are likely possible and indicating that significant potential exists for these bearings where high stiffness is not needed – for instance in flywheel energy storage. The study examines methods of reducing bearing (parasitic) losses and demonstrates that losses occur in three main forms during idling: air-friction losses, electrical machine losses, stabilizing machine losses. Low speed (158 [rpm]) air-friction losses are found to be the dominant loss at 0.1 [W/m3]. The focus of this study, however, is on loss contributions resulting from the bearing’s electrical machine and stabilizing machine. Stabilizing machine losses are found to be very low at: 1 × 10−6 [W/m3] – this leaves electrical machine losses as the dominant loss. Such electrical machine losses are analysed and divided into eddy current loss and hysteresis loss. Two components of hysteresis loss are remanent field related cogging loss and remagetization loss. Eddy current losses in silicon steel laminations in an electrical machine are quite high, especially at high speeds, with losses in the order of 1 × 105 [W/m3]. Noting the further high cost of producing single unit quantities of custom lamination-based electrical machine prototypes, this high loss prompts a look at potentially lower cost ferrite materials for building these machines. A commercial sample of soft magnetite ferrite is shown to have equivalent eddy current losses of roughly 1 × 10−13 [W/m3]. The study notes that micro-structured magnetite has significant hysteresis loss. Such loss is in the order of 1 × 10−3 [W/m3] when referring to both remanence related cogging and remagnetization. This study, thus, extends its examination of loss to nano-structured magnetite. Magnetite nano-particles have shown superparamagnetic (no hysteresis) behaviour that promises the elimination of hysteresis losses. A co-precipitation route to the synthesis of these nano-particles is examined. A detailed examination involving a series of 31 experiments is shown to demonstrate only two pathways providing close-to-superparamagnetic behaviour. After characterization by Scanning Electron Microscope (SEM), X-Ray Diffractometer (XRD), Superconducting Quantum Interference Device (SQUID) and crude colorimetry, the lowest coercivity and remanence found in any given sample falls at −0.17 [Oe] (below error) and 0.00165 [emu/g] respectively. These critical points can be used to estimate hysteresis related power loss, however, to produce bulk ferrite a method of sintering or bonding synthesized powder is needed. A microwave sintering solution promises to preserve nano-structure when taking synthesized powders to bulk material. A set of proof-of-concept experiments provide the ground work for proposing a future microwave sintering approach to such bulk material production. The study uses critical points measured by way of SEM, XRD, SQUID characterization (e.g. remanence and coercivity) to implement a modified Jiles-Atherton model for hysteresis curve fitting. The critical points and curve fitting model allow estimation of power loss resulting from remanent related cogging and remagnetization effects in nano-structured magnetite. Such nano-structured magnetite is shown to exhibit hysteresis losses in the order of 1 × 10−4 [W/m3] from remagnetization and 1 × 10−7[W/m3] from remanence related cogging drag. These losses are lower than those of micro-structured samples, suggesting that nano-structured materials have a significant positive effect in reducing electrical machine losses for the proposed radial multi-plattered diamagnetic bearing solution. The lower parasitic loss in these bearings suggests excellent compatibility with flywheel energy storage applications

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 04)

For abstract, see N74-20609

Particle Physics Reference Library

This third open access volume of the handbook series deals with accelerator physics, design, technology and operations, as well as with beam optics, dynamics and diagnostics. A joint CERN-Springer initiative, the “Particle Physics Reference Library” provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A,B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open acces

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 05)

For abstract, see N75-13677

Interactions of spacecraft and other moving bodies with natural plasmas

Abstract compilation on spacecraft interactions with ionosphere, magnetosphere, and interplanetary plasm