Tailoring magnetic energies to form dipole skyrmions and skyrmion lattices
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Montoya, S. A.↗
SEARCH · Engineering Papers
Results for “DIPOLE MAGNET”
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Prospects for searching axionlike particle dark matter with dipole, toroidal and wiggler magnets
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Magnetic Field Compensation by DC Degaussing, Magnetic Shielding, and AC Dipole Steering
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Neal, R.↗
Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1
The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-{beta} (local {beta} {approx} 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-{beta} confinement.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
The one-dimensional camelback potential in the parallel dipole line trap: Stability conditions and finite size effect
We recently demonstrated a magnetic parallel dipole line (PDL) system that serves as a unique diamagnetic trap with a fascinating one-dimensional camelback potential along its longitudinal axis. The system can be realized with a pair of transversely magnetized cylindrical magnets and a cylindrical graphite rod as the trapped object. In this paper, we present more detailed experimental and theoretical studies of the finite size effect of the rod and its impact on the stability and oscillation dynamics of the trap. We show that the camelback potential effect only occurs when the length of the PDL system is beyond certain critical length (L C ). The length of the trapped rod determines the “effective camelback potential” and is subject to maximum and minimum values for the trap to be stable. Both length and radius of the rod determine the damping dynamics or the quality factor of the oscillator. Finally, these characteristics are important for designing the PDL trap system for various sensing applications, for example, we demonstrated a PDL trap gas viscometer system through measurement of the oscillation damping time constant.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
THE LIGHT CURVE AND INTERNAL MAGNETIC FIELD OF THE MODE-SWITCHING PULSAR PSR B0943+10
A number of radio pulsars exhibit intriguing mode-switching behavior. Recent observations of PSR B0943+10 revealed correlated radio and X-ray mode switches, providing a new avenue for understanding this class of objects. The large X-ray pulse fraction observed during the radio-quiet phase (Q-mode) was previously interpreted as a result of changing obscuration of X-rays by dense magnetosphere plasma. We show that the large X-ray pulse fraction can be explained by including the beaming effect of a magnetic atmosphere, while remaining consistent with the dipole field geometry constrained by radio observations. We also explore a more extreme magnetic field configuration, where a magnetic dipole displaced from the center of the star produces two magnetic polar caps of different sizes and magnetic field strengths. These models are currently consistent with data in radio and X-rays and can be tested or constrained by future X-ray observations.
79 ASTRONOMY AND ASTROPHYSICS↗
The Interaction Region of PEP-II
The PEP-II e{sup +}e{sup -} collider turned off last year after a very successful 9 years of running. The accelerator achieved a peak luminosity of 12 x 10{sup 33} cm{sup -2} s{sup -1}, 4 times over the design of 3 x 10{sup 33} cm{sup -2} s{sup -1}. The peak beam currents were quite high; over 3 A for the positron beam and over 2 A for the electron beam. The beams were stored in separate storage rings. The PEP-II design called for a head-on collision at the interaction point (IP). This was possible because of the asymmetric beam energies (9 on 3.1 GeV) and was achieved using permanent magnet (PM) dipoles. I describe the actual interaction region (IR) layout including some of the design constraints that led to the final design and discuss operation issues related to the IR design.
43 PARTICLE ACCELERATORS↗
Coupled Transient Finite Element Simulation of Quench in Jefferson Lab's 11 GeV Super High Momentum Spectrometer Superconducting Magnets
This paper presents coupled transient thermal and electromagnetic finite element analysis of quench in the Q2, Q3, and dipole superconducting magnets using Vector Fields Quench code. Detailed temperature distribution within coils and aluminum force collars were computed at each time step. Both normal (quench with dump resistor) and worst-case (quench without dump resistor) scenarios were simulated to investigate the maximum temperatures. Two simulation methods were utilized, and their algorithms, implementation, advantages, and disadvantages are discussed. The first method simulated the coil using nonlinear transient thermal analysis directly linked with the transient circuit analysis. It was faster because only the coil was meshed and no eddy current was modeled. The second method simulated the whole magnet including the coil, the force collar, and the iron yoke. It coupled thermal analysis with transient electromagnetic field analysis which modeled electromagnetic fields including eddy currents within the force collar. Since eddy currents and temperature in the force collars were calculated in various configurations, segmentation of the force collars was optimized under the condition of fast discharge.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Dynamics of Coupled Magnetic Vortices in Trilayer Conducting Nanocylinder
Solving numerically the generalized Landau–Lifshitz equation, we have carried out the micromagnetic investigation of the dynamics of two dipole-coupled magnetic vortices in a trilayer nanocolumn under the action of the external magnetic field directed perpendicular to the sample plane and spin-polarized electric field. The possible existence of different regimes of vortex motion, depending on the polarized current, is demonstrated. The current dependence of the oscillation frequency for the case of stationary dynamics of coupled vortices with the same frequency has been established. The possibility of controlling the frequency of the stationary vortex motion and tuning the control current amplitude by the external magnetic field is shown. Using the analytical method for simplified description of the dynamics of coupled vortices, the current and magnetic-field dependences of the frequency have been obtained, which are qualitatively consistent with the numerical data.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
MAGNETIC FIELDS IN EARLY PROTOSTELLAR DISK FORMATION
We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian and Vishniac model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called “magnetic braking catastrophe.” In particular, we provide a detailed study of the dynamics of a 0.5 M{sub ⊙} protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, “reconnection diffusion,” removes the magnetic flux from the disk; the other involves the change of the magnetic field's topology, but does not change the absolute value of the magnetic flux through the disk. We demonstrate that for the first mechanism, turbulence causes a magnetic flux transport outward from the inner disk to the ambient medium, thus decreasing the coupling of the disk to the ambient material. A similar effect is achieved through the change of the magnetic field's topology from a split monopole configuration to a dipole configuration. We explore how both mechanisms prevent the catastrophic loss of disk angular momentum and compare both above turbulent reconnection mechanisms with alternative mechanisms from the literature.
79 ASTRONOMY AND ASTROPHYSICS↗
Phase transition studies of BiMnO{sub 3}: Mean field theory approximations
We studied the phase transition and magneto-electric coupling effect of BiMnO{sub 3} by employing mean field theory approximations. To capture the ferromagnetic and ferroelectric transitions of BiMnO{sub 3}, we construct an extended Ising model in a 2D square lattice, wherein, the magnetic (electric) interactions are described in terms of the direct interactions between the localized magnetic (electric dipole) moments of Mn ions with their nearest neighbors. To evaluate our model, we obtain magnetization, magnetic susceptibility and electric polarization using mean field approximation calculations. Our results reproduce both the ferromagnetic and the ferroelectric transitions, matching very well with the experimental reports. Furthermore, consistent with experimental observations, our mean field results suggest that there is indeed a coupling between the magnetic and electric ordering in BiMnO{sub 3}.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
The one and a half monopoles solution of the SU(2) Yang–Mills–Higgs field theory
Recently we have reported on the existence of finite energy SU(2) Yang–Mills–Higgs particle of one-half topological charge. In this paper, we show that this one-half monopole can co-exist with a ’t Hooft–Polyakov monopole. The magnetic charge of the one-half monopole is of opposite sign to the magnetic charge of the ’t Hooft–Polyakov monopole. However the net magnetic charge of the configuration is zero due to the presence of a semi-infinite Dirac string along the positive z-axis that carries the other half of the magnetic monopole charge. The solution possesses gauge potentials that are singular along the z-axis, elsewhere they are regular. The total energy is found to increase with the strength of the Higgs field self-coupling constant λ. However the dipole separation and the magnetic dipole moment decrease with λ. This solution is non-BPS even in the BPS limit when the Higgs self-coupling constant vanishes. -- Highlights: •This one-half monopole can co-exist with a ’t Hooft–Polyakov monopole. •The magnetic charge of the one-half monopole and one monopole is of opposite sign. •This solution is non-BPS. •The net magnetic charge of the configuration is zero. •This solution upon Cho decomposition is only singular along the negative z-axis.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Low-energy scattering of molecules and ions in a magnetic field
We describe calculations of elastic and inelastic scattering of neutral molecules and cold ions in a magnetic field. The molecule is assumed to have a magnetic and electric dipole moment. The external magnetic field splits the ground rovibrational energy levels of the molecule. The highest energy state within the ground rovibrational manifold increases in energy as the distance to the ion decreases leading to a repelling potential. At low energy, inelastic collisions are strongly suppressed due to the large distance of closest approach. Thus, a collision between a neutral molecule and a cold ion will lead to a decrease in the molecule’s kinetic energy with no change in internal energy. We present results for the specific case of OH molecules cooled by Be + , Mg + , or Ca + ions. Also, we perform molecular dynamics simulations of ions and molecules in a combined Paul trap and time-averaged orbiting potential trap. Furthermore, our results suggest that sympathetic cooling of neutral molecules by ions would be possible if cold ions and molecules could be simultaneously trapped.
74 ATOMIC AND MOLECULAR PHYSICS↗
Energy upgrade as regards quench performance
Since the cross section for W production increases rapidly with energy, we consider the possibility of increasing the collision energy of polarized protons at RHIC. The limits of present hardware are examined with a particular emphasis on the quench training performance of magnets. Ignoring the limits of the DX magnets, the short-sample currents for the main arc (8 cm) dipoles could allow an increase of more than 30%, however we estimate 400 to 500 training quenches for the just 8 cm dipoles to reach this level. We propose that a 10% increase in energy might be achieved with the present hardware configuration. Raising the beam energy to 275 GeV ({radical}s = 550 GeV) should increase the W production rate by almost 50% from the 250 GeV level for the same optics with identical {beta}*'s at the collision points.
43 PARTICLE ACCELERATORS↗
FEA Model and Mechanical Analysis of the Nb 3 Sn 15-T Dipole Demonstrator
Nb$_{3}$Sn magnets with a nominal operation field of ~15 T are being considered for the large hadron collider (LHC) energy upgrade high-energy large hadron collider (HE-LHC) and a post-LHC future circular collider. To demonstrate the feasibility of 15-T accelerator quality dipole magnets, the U.S. magnet development program is developing a single-aperture 15-T Nb$_{3}$Sn dipole demonstrator based on a 4-layer graded cos-theta coil with 60 mm aperture and cold iron yoke. The main design challenges for 15-T accelerator magnets include large Lorentz forces at this field level. To counteract them, an innovative mechanical structure based on a vertically split iron yoke, locked by large aluminum IC-clamps and supported by a thick stainless steel skin, has been developed at Fermilab. To study the performance of the structure, a parametric multiphysics finite element analysis (FEA) model has been set up. This paper describes the numerical model as well as the results of a sensitivity analysis of the effect of geometrical tolerances and assembly parameters.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Coulomb excitations for a short linear chain of metallic shells
A self-consistent-field theory is given for the electronic collective modes of a chain containing a finite number, N, of Coulomb-coupled spherical two-dimensional electron gases arranged with their centers along a straight line, for simulating electromagnetic response of a narrow-ribbon of metallic shells. The separation between nearest-neighbor shells is arbitrary and because of the quantization of the electron energy levels due to their confinement to the spherical surface, all angular momenta L of the Coulomb excitations, as well as their projections M on the quantization axis, are coupled. However, for incoming light with a given polarization, only one angular momentum quantum number is usually required. Therefore, the electromagnetic response of the narrow-ribbon of metallic shells is expected to be controlled externally by selecting different polarizations for incident light. We show that, when N = 3, the next-nearest-neighbor Coulomb coupling is larger than its value if they are located at opposite ends of a right-angle triangle forming the triad. Additionally, the frequencies of the plasma excitations are found to depend on the orientation of the line joining them with respect to the axis of quantization since the magnetic field generated from the induced oscillating electric dipole moment on one sphere can couple to the induced magnetic dipole moment on another. Although the transverse inter-shell electromagnetic coupling can be modeled by an effective dynamic medium, the longitudinal inter-shell Coulomb coupling, on the other hand, can still significantly modify the electromagnetic property of this effective medium between shells.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Exploring the Focusing Mechanism of the NuMI Horn Magnets
Neutrinos at the Main Injector (NuMI) is a project at Fermilab that provides an intense beam of neutrinos used by a number of experiments. NuMI creates a beam of pions that decay into neutrinos, muons, and other particles. Muons are registered by the muon monitors. Magnetic horns are the key elements of the NuMI beam line. This paper uses the muon beam profile observed at the muon monitors to study the NuMI horn focusing mechanism. It is found that the horn magnet generates dipole and quadrupole fields to focus pions. This suggests that the optics of the horn magnet are predominantly linear. Our study shows that the muon beam profile accurately detects the horn current within 0.05%.
43 PARTICLE ACCELERATORS↗
Generation of kinetic Alfven waves in the high-latitude near-Earth magnetotail: A global hybrid simulation
In this paper, effects of a fast flow in the tail plasma sheet on the generation of kinetic Alfven waves (KAWs) in the high-latitude of the near-Earth magnetotail are investigated by performing a two-dimensional (2-D) global-scale hybrid simulation, where the plasma flow is initialized by the E×B drift near the equatorial plane due to the existence of the dawn-dusk convection electric field. It is found that firstly, the plasma sheet becomes thinned and the dipolarization of magnetic field appears around (x,z)=(−10.5R{sub E},0.3R{sub E}), where R{sub E} is the radius of the Earth. Then, shear Alfven waves are excited in the plasma sheet, and the strong earthward flow is braked by the dipole-like magnetic field. These waves propagate along the magnetic field lines toward the polar regions later. Subsequently, KAWs with k{sub ⊥}≫k{sub ∥} are generated in the high-latitude magnetotail due to the existence of the non-uniformity of the magnetic field and density in the polar regions. The ratio of the electric field to the magnetic field in these waves is found to obey the relation (δE{sub z})/(δB{sub y} )∼ω/k{sub ∥} of KAWs. Our simulation provides a mechanism for the generation of the observed low-frequency shear Alfven waves in the plasma sheet and kinetic Alfven waves in the high-latitude near-Earth magnetotail, whose source is suggested to be the flow braking in the low-latitude plasma sheet.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗