Effects of defects and surface roughness on the vortex penetration and vortex dynamics in superconductor-insulator-superconductor multilayer structures exposed to RF magnetic fields: numerical simulations within TDGL theory

2022 ◽  
Author(s):  
Qing-Yu Wang ◽  
Cun Xue ◽  
Chao Dong ◽  
You-He Zhou
Keyword(s):  
Magnetic Field ◽  
Surface Roughness ◽  
Magnetic Fields ◽  
Radio Frequency ◽  
Numerical Simulations ◽  
Vortex Dynamics ◽  
Multilayer Structures ◽  
Static Case ◽  
Actual Performance ◽  
Rf Magnetic Field

Abstract The vortex penetration and vortex dynamics are significantly important to superconducting devices, for example the superconducting cavities, since the vortex motions would create substantial dissipation. In experiments, different kinds of defects, as well as different degrees of surface roughness were observed. By considering these in superconductor-insulator-superconductor (SIS) structures, the vortex penetration and vortex dynamics are very complex due to the interactions with defects and the influence of surface roughness, especially for radio-frequency (RF) magnetic field, which are quite different from ideal defect-free SIS multilayer structures. In this paper, within Ginzburg-Landau theory, we perform numerical simulations to study the effects of nanoscale defects, surface roughness, and cracks in the coating layer on the vortex penetration and superheating field in Nb3Sn-I-Nb multilayer structures exposed to a quasi-static magnetic field. The validations of the numerical simulations are verified by good consistency with previous theoretical results in ideal defect-free SIS multilayer and single Nb structures. Furthermore, we explore the vortex dynamics and induced voltages in SIS multilayer structures exposed to RF magnetic fields for both ideal defect-free structures and real situations including surface roughness. Our numerical simulations indicate that, unlike the quasi-static case, the advantage of SIS multilayer structures over a single Nb structure depends on the degrees of surface roughness as well as the frequency and amplitude of the RF magnetic field. The results of this paper provide deep insight to evaluate the actual performance-limiting of next-generation superconducting radio-frequency (SRF) cavities with different proposed candidate materials, which are quite susceptible to nonideal surface.

RADIO-FREQUENCY EREAKDOWN CONTROLLED BY DRIFT OF ELECTRONS IN AN INHOMOGENEOUS MAGNETIC FIELD

1961 ◽  
Vol 39 (7) ◽  
pp. 983-992
Author(s):  
L. T. Shepherd ◽  
H. M. Skarsgard
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radio Frequency ◽  
Inhomogeneous Magnetic Field ◽  
Breakdown Field ◽  
Electron Theory ◽  
Loss Mechanism ◽  
Field Versus ◽  
Average Electron ◽  
The Magnetic Field

A study has been made of r-f. breakdown in which the controlling loss mechanism arises from the drift of electrons in an inhomogeneous magnetic field. The study was carried out using a toroidal system with parallel r-f. electric and steady magnetic fields. An approximate average-electron theory of drift-controlled breakdown is presented. Experimental measurements of breakdown r-f. electric field versus magnetic field were made at various pressures from 1.25 to 6.0 × 10−3 mm of Hg, using hydrogen and helium gases. A radio frequency of 8 Mc/sec was used. Magnetic fields up to 2000 gauss were employed. The r-f. breakdown field was found to vary as the inverse square root of the magnetic field as predicted by the theory.

Surface Roughness Optimization in End Milling of Stainless Steel AISI 304 with Uncoated WC-Co Insert Under Magnetic Field

2012 ◽  
Vol 576 ◽  
pp. 119-122 ◽  
Author(s):  
A.K.M. Nurul Amin ◽  
Syidatul Akma Sulaiman ◽  
Siti Noor Izzati Mohd Zainun ◽  
M.D. Arif
Keyword(s):  
Magnetic Field ◽  
Surface Roughness ◽  
Magnetic Fields ◽  
Permanent Magnets ◽  
End Milling ◽  
Desirability Function ◽  
Low Carbon Steel ◽  
Machining Process ◽  
Low Carbon ◽  
Novel Approach

Chatter phenomenon is a major issue as it greatly affects the topography of machined parts. Due to the inconsistent character of chatter, it is extremely difficult to predict resultant surface roughness in a machining process, such as end milling. Also, recent studies have shown that chatter can be suitably damped using magnetic fields. This paper, thus, focuses on a novel approach of minimizing surface roughness in end milling of Mild (Low Carbon) Steel using uncoated WC-Co inserts under magnetic field from permanent magnets. In this experiment, Response Surface Methodology (RSM) approach using DESIGN EXPERT 6.0 (DOE) software was used to design the experiments. The experiments were performed under two different cutting conditions. The first one was cutting under normal conditions, while the other was cutting under the application of magnetic fields from two permanent magnets positioned on opposite sides of the cutter. Surface roughness was measured using Mitutoyo SURFTEST SV-500 profilometer. The subsequent analysis showed that surface roughness was significantly reduced (by as much as 67.21%) when machining was done under the influence of magnetic field. The experimental results were then used to develop a second order empirical mathematical model equation for surface roughness and validated to 95% confidence level by using ANOVA. Finally, desirability function approach was used to optimize the surface roughness within the limiting values attainable in end milling.

scholarly journals The Effect of Small Scale Motion on an Essentially-Nonlinear Dynamo

2010 ◽  
Vol 6 (S271) ◽  
pp. 367-368
Author(s):  
Benjamin M. Byington ◽  
Nicholas H. Brummell ◽  
Steven M. Tobias
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Small Scale ◽  
Local Velocity ◽  
Dissipative Effects ◽  
Dynamo Mechanism ◽  
New Type ◽  
Scale Motion

AbstractA dynamo is a process by which fluid motions sustain magnetic fields against dissipative effects. Dynamos occur naturally in many astrophysical systems. Theoretically, we have a much more robust understanding of the generation and maintenance of magnetic fields at the scale of the fluid motions or smaller, than that of magnetic fields at scales much larger than the local velocity. Here, via numerical simulations, we examine one example of an “essentially nonlinear” dynamo mechanism that successfully maintains magnetic field at the largest available scale (the system scale) without cascade to the resistive scale. In particular, we examine whether this new type of dynamo at the system scale is still effective in the presence of other smaller-scale dynamics (turbulence).

Numerical simulations for ferromagnetic resonance of nano-size island structures probed by radio-frequency scanning tunneling microscopy

2021 ◽  
Author(s):  
Yudai Sato ◽  
Masahiro Haze ◽  
Hung Hsiang Yang ◽  
Kanta Asakawa ◽  
Susumu Takahashi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radio Frequency ◽  
Scanning Tunneling Microscopy ◽  
Ferromagnetic Resonance ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Frequency Scanning ◽  
Out Of Plane ◽  
Rf Magnetic Field ◽  
Nano Size

Abstract We numerically calculated ferromagnetic resonance (FMR) spectra taken on a single-domain nano-size ferromagnetic island structure in the configuration of radio-frequency scanning tunneling microscopy (RF-STM), where RF electromagnetic waves are introduced into the tunneling gap through the probe tip. In this scheme, near-field in-plane azimuthal RF magnetic field induces FMR of an out-of-plane magnetized island situated below the tip under the external out-of-plane magnetic field. The amount of the magnetization of the island is effectively reduced by the resonance and the reduction can be detected from the spin-polarized tunneling conductance. From the calculated spectra we found that the FMR signal becomes larger with a smaller tip-sample distance and a sharper tip. It is also revealed that the azimuthal RF magnetic field and therefore the FMR signal are enhanced when a tip is located near the edge of the island.

scholarly journals Dynamically dominant magnetic fields in the diffuse interstellar medium

2008 ◽  
Vol 4 (S259) ◽  
pp. 87-88 ◽  
Author(s):  
Andrew Fletcher ◽  
M. Korpi ◽  
A. Shukurov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Interstellar Medium ◽  
Numerical Simulations ◽  
Hydrodynamic Model ◽  
Mass Conservation ◽  
Unstable Flow ◽  
Gas Density ◽  
The Magnetic Field

AbstractObservations show that magnetic fields in the interstellar medium (ISM) often do not respond to increases in gas density as would be naively expected for a frozen-in field. This may suggest that the magnetic field in the diffuse gas becomes detached from dense clouds as they form. We have investigated this possibility using theoretical estimates, a simple magneto-hydrodynamic model of a flow without mass conservation and numerical simulations of a thermally unstable flow. Our results show that significant magnetic flux can be shed from dense clouds as they form in the diffuse ISM, leaving behind a magnetically dominated diffuse gas.

scholarly journals Numerical determination of the cutoff frequency in solar models

2020 ◽  
Vol 640 ◽  
pp. A4 ◽  
Author(s):  
T. Felipe ◽  
C. R. Sangeetha
Keyword(s):  
Magnetic Field ◽  
Wave Propagation ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Acoustic Waves ◽  
Cutoff Frequency ◽  
Quiet Sun ◽  
Radiative Losses ◽  
The Magnetic Field

Context. In stratified atmospheres, acoustic waves can only propagate if their frequency is higher than the cutoff value. The determination of the cutoff frequency is fundamental for several topics in solar physics, such as evaluating the contribution of the acoustic waves to the chromospheric heating or the application of seismic techniques. However, different theories provide different cutoff values. Aims. We developed an alternative method to derive the cutoff frequency in several standard solar models, including various quiet-Sun and umbral atmospheres. The effects of magnetic field and radiative losses on the cutoff are examined. Methods. We performed numerical simulations of wave propagation in the solar atmosphere using the code MANCHA. The cutoff frequency is determined from the inspection of phase-difference spectra computed between the velocity signal at two atmospheric heights. The process is performed by choosing pairs of heights across all the layers between the photosphere and the chromosphere to derive the vertical stratification of the cutoff in the solar models. Result. The cutoff frequency predicted by the theoretical calculations departs significantly from the measurements obtained from the numerical simulations. In quiet-Sun atmospheres, the cutoff shows a strong dependence on the magnetic field for adiabatic wave propagation. When radiative losses are taken into account, the cutoff frequency is greatly reduced and the variation of the cutoff with the strength of the magnetic field is lower. The effect of the radiative losses in the cutoff is necessary to understand recent quiet-Sun and sunspot observations. In the presence of inclined magnetic fields, our numerical calculations confirm that the cutoff frequency is reduced as a result of the reduced gravity experienced by waves that propagate along field lines. An additional reduction is also found in regions with significant changes in the temperature, which is due to the lower temperature gradient along the path of field-guided waves. Conclusions. Our results show solid evidence that the cutoff frequency in the solar atmosphere is stratified. The cutoff values are not correctly captured by theoretical estimates. In addition, most of the widely used analytical cutoff formulae neglect the effect of magnetic fields and radiative losses, whose role is critical for determining the evanescent or propagating nature of the waves.

scholarly journals THE QUANTUM HALL EFFECT IN GRAPHENE

2012 ◽  
Vol 26 (13) ◽  
pp. 1250084 ◽  
Author(s):  
PAOLO CEA
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Hall Effect ◽  
Quantum Hall Effect ◽  
Quantum Hall ◽  
Landau Levels ◽  
Dynamical Generation ◽  
Dirac Sea

We investigate the quantum Hall effect in graphene. We argue that in graphene in presence of an external magnetic field there is dynamical generation of mass by a rearrangement of the Dirac sea. We show that the mechanism breaks the lattice valley degeneracy only for the n = 0 Landau levels and leads to the new observed ν = ±1 quantum Hall plateaus. We suggest that our result can be tested by means of numerical simulations of planar Quantum Electro Dynamics with dynamical fermions in an external magnetic fields on the lattice.

scholarly journals Formation of Solar Prominences with Normal and Inverse Polarities

1993 ◽  
Vol 141 ◽  
pp. 138-142
Author(s):  
G. S. Choe ◽  
L. C. Lee
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Thermal Instability ◽  
Dynamic Evolution ◽  
Solar Prominence ◽  
Solar Prominences

AbstractNumerical simulations of solar prominence formation are presented employing photospheric horizontal motions as boundary conditions. Three different combinations of magnetic field configurations and footpoint motions are considered: (1) a bipolar arcade with a footpoint shear, (2) an arcade exposed to a shearing and converging motion, (3) two adjacent arcades undergoing a shearing and converging motion. In each case, it is found that the dynamic evolution of magnetic fields can force the plasma into a thermal instability leading to the formation of a prominence.

A New Magnetic Polishing Liquid (MPL) for Precision Surface Finishing

2006 ◽  
Vol 315-316 ◽  
pp. 671-675 ◽  
Author(s):  
J. Jiang ◽  
Yong Bo Wu ◽  
Xu Yue Wang ◽  
M. Kato
Keyword(s):  
Magnetic Field ◽  
Surface Roughness ◽  
Magnetic Fields ◽  
Experimental Result ◽  
Surface Finishing ◽  
Hydrodynamic Characteristics ◽  
Magnetic Clusters ◽  
Abrasive Particles ◽  
Magneto Rheological ◽  
The Magnetic Field

This paper presents a new magnetic polishing liquid (MPL) produced by mixing sub-micron or micron order abrasive particles into a magnetic compound fluid (MCF) and its fundamental performance in surface finishing. MCF is an intelligent fluid, which is developed by mixing a magnetic fluid (MF) and a Magneto-rheological fluid (MRF) into a solvent, and hence reacting upon magnetic fields. In the present work, seven kinds of kerosene-based MPLs were prepared. The hydrodynamic characteristics of MPLs such as the viscosities under different magnetic fields were investigated. The obtained result indicated that the viscosity increases with the growing of the magnetic field and that the type of MPL affects greatly the viscosity. This phenomenon was discussed by observing the magnetic clusters formed in MPL. It was observed that the magnetic clusters are distributed along the magnetic fluxes. An experimental result indicated that the surface roughness varies with polishing time and gets smallest at a certain value of magnetic field strength.

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