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2. Experimental and Numerical Analysis of Faulty Operation of a Superconducting Solenoid Made of Tape with High Temperature Superconductor.
- Author
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Skiba, Blazej, Tomkow, Lukasz, Kulikov, Evgeniy, Drobin, Valeriy, and Malecha, Ziemowit
- Subjects
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NUMERICAL analysis , *SOLENOIDS , *HIGH temperature superconductors , *ADHESIVE tape , *MAGNETIC fields , *DENSITY currents , *CRITICAL currents , *LIQUID nitrogen - Abstract
Superconducting magnets allow obtaining high magnetic fields. The application of tapes with high temperature superconductors enables them to operate in liquid nitrogen, thus decreasing operational costs. However, ceramic structure of the tapes is prone to mechanical damages, which can decrease critical current density and lead to malfunction of the device. This work presents the results of the analysis of the operation of a faulty superconducting magnet. Preliminary design considerations and expected performance are calculated numerically. The experimental results show the degeneration of the structure of the tape. Possible causes of damage and available remedies are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
3. Numerical analysis on the characteristics of particle orbits in quasi-axisymmetric stellarator.
- Author
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Su, C. Y., Chen, S. Y., Liu, H. F., Mou, M. L., Guo, W. P., and Tang, C. J.
- Subjects
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PARTICLE analysis , *NUMERICAL analysis , *ORBITS (Astronomy) , *MAGNETIC fields - Abstract
Based on the magnetic field configuration of the Chinese First Quasi-axisymmetric Stellarator (CFQS) device, three types of orbits such as the passing orbit, blocked trapped orbit, and localized trapped orbit are simulated using the Boris algorithm. Also, the orbital topology, orbit transition, and loss characteristics of these particles under different initial conditions are studied in this paper. It is found that there exists a transition from blocked trapped orbits to localized trapped orbits due to small continuous helical ripples. This phenomenon is analyzed as follows: we define the angle between the particle drift velocity ( v → D ) and the radial direction ( ρ ^ ) as β. If the blocked-localized transition appears in the region where β > 9 0 ○ , the localized particles will return to the blocked particles and be constrained. However, if the blocked-localized transition happens in the region where β < 9 0 ○ , localized particles will drift out of the last closed flux surface and be lost. The simulation results show that the loss of localized particles in the CFQS is mainly located in some specific regions within the vicinity of the toroidal angle φ = 0 ○ , 18 0 ○ and the poloidal angle θ = 9 0 ○ . [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
4. Characterizing filamentary magnetic structures in counter-streaming plasmas by Fourier analysis of proton images.
- Author
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Levesque, Joseph, Kuranz, Carolyn, Handy, Timothy, Manuel, Mario, and Fiuza, Frederico
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MAGNETIC structure , *IMAGE analysis , *FOURIER analysis , *COLLISIONLESS plasmas , *ELECTROMAGNETIC fields , *MAGNETIC fields , *NUMERICAL analysis - Abstract
Proton imaging is a powerful tool for probing electromagnetic fields in a plasma, providing a path-integrated map of the field topology. However, in cases where the field structure is highly inhomogeneous, inferring spatial properties of the underlying field from proton images can be difficult. This problem is exemplified by recent experiments, which used proton imaging to probe the filamentary magnetic field structures produced by the Weibel instability in collisionless counterstreaming plasmas. In this paper, we perform analytical and numerical analyses of proton images of systems containing many magnetic filaments. We find that, in general, the features observed on proton images do not directly correspond to the spacing between magnetic filaments (the magnetic wavelength) as has previously been assumed and that they instead correspond to the filament size. We demonstrate this result by Fourier analysis of synthetic proton images for many randomized configurations of magnetic filaments. Our results help guide the interpretation of experimental proton images of filamentary magnetic structures in plasmas. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
5. Numerical Study on Distribution Law of Magnetic Field and Temperature Field around the Crack Induced by Eddy Currents.
- Author
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Min He, Wenpei Zheng, Laibin Zhang, and Fan Zhou
- Subjects
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ELECTRIC field strength , *MAGNETIC fields , *TEMPERATURE effect , *NUMERICAL analysis , *FRACTURE mechanics , *EDDY currents (Electric) - Abstract
Alternative current field measurement (ACFM) and eddy current thermography are both induced by eddy currents, and it is a commonality between them. The commonality has laid a good foundation for the combination of the two testing techniques. In this paper, a numerical study on distribution law of magnetic field and temperature field around the crack using eddy current excitation is carried out. The feasibility of the combination of ACFM and eddy current thermography is discussed as well. A specimen made of ferromagnetic material is tested by a U-shaped inducer, and a semielliptical crack is built on the specimen. The distribution law of magnetic field and temperature field is both studied using the same eddy current excitation. The relationship between the crack size and distribution of magnetic field and temperature field is identified by altering the length and depth of the crack. Through comparisons, the magnetic distribution law around the crack in this paper is consistent with that of ACFM, and the maximum temperature difference around the crack meets the inspection requirement of a thermal imager. These findings might make it possible to eventually combine ACFM and eddy current thermography. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
6. Benchmark of Numerical Tools Simulating Beam Propagation and Secondary Particles in ITER NBI.
- Author
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Sartori, E., Veltri, P., Dlougach, E., Hemsworth, R., Serianni, G., and Singh, M.
- Subjects
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NUMERICAL analysis , *PLASMA beam injection heating , *FEASIBILITY studies , *ION beams , *MAGNETIC fields - Abstract
Injection of high energy beams of neutral particles is a method for plasma heating in fusion devices. The ITER injector, and its prototype MITICA (Megavolt ITER Injector and Concept Advancement), are large extrapolations from existing devices: therefore numerical modeling is needed to set thermo-mechanical requirements for all beam-facing components. As the power and charge deposition originates from several sources (primary beam, co-accelerated electrons, and secondary production by beam-gas, beam-surface, and electron-surface interaction), the beam propagation along the beam line is simulated by comprehensive 3D models. This paper presents a comparative study between two codes: BTR has been used for several years in the design of the ITER HNB/DNB components; SAMANTHA code was independently developed and includes additional phenomena, such as secondary particles generated by collision of beam particles with the background gas. The code comparison is valuable in the perspective of the upcoming experimental operations, in order to prepare a reliable numerical support to the interpretation of experimental measurements in the beam test facilities. The power density map calculated on the Electrostatic Residual Ion Dump (ERID) is the chosen benchmark, as it depends on the electric and magnetic fields as well as on the evolution of the beam species via interaction with the gas. Finally the paper shows additional results provided by SAMANTHA, like the secondary electrons produced by volume processes accelerated by the ERID fringe-field towards the Cryopumps. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
7. Structural Optimization of the Halbach Array PM Rim Thrust Motor.
- Author
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Haichuan Cao and Weihu Chen
- Subjects
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COLLOID thrusters , *PROPULSION systems , *TORQUE , *MAGNETIC fields , *AIR gap flux - Abstract
The Rim-driven Thruster (RDT) integrates the thrust motor and the propeller, which can effectively reduce the space occupied by the propulsion system, improve the propulsion efficiency, and thus has important research value and broad market prospects. The Halbach Permanent Magnet Rim Thrust Motor (HPMRTM) can improve the torque density of the propulsion motor by utilizing the unilateral magnetic field of the Halbach array. In this paper, the numerical method is used to study the electromagnetic performance of the motor under different Halbach array parameters. The relationship between motor parameters such as air-gap flux density, electromagnetic torque and Halbach array parameters is obtained, and then the motor structure is optimized. By comparing with Common Permanent Magnet RTM, the advantages of HPMRTM are verified. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
8. Numerical research on a 4 MW 170 GHz coaxial gyrotron with a double electron beam.
- Author
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Hou, Shenyong, Yu, Shen, and Li, Hongfu
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GYROTRONS , *ELECTRON beams , *OHMIC resistance , *NUMERICAL analysis , *MAGNETIC fields - Abstract
In this paper, a coaxial gyrotron with a double electron beam is investigated on the ohmic loss, starting current, mode competition, and beam wave interaction. Its beam-wave interaction equation and dependence of the starting current on the static magnetic field and parameter K (the ratio of the current of an electron beam to the total current of a double electron beam) are given. On this basis, a 4 MW 170 GHz coaxial gyrotron with a double electron beam is studied. By the numerical calculation, the influence of K on the starting current is analyzed under a given static magnetic field and at different guiding center radii of the double electron beam. Studies show that the ability of the gyrotron to suppress the mode competition has a relation with the selection of the guiding center radii of the two electron beams. Then, the investigation of a time-dependent multi-mode competition of the gyrotron is performed, which shows that the gyrotron can stably operate in the T E 38 , 18 − mode. The results show that by considering the ohmic loss, the gyrotron can operate at 170.4 GHz with the output power of 4.04 MW and the beam-wave interaction efficiency of 35.47% when B = 6.82 T, U = 88 KV, I = 129 A, and K = 0.4. Each of the two electron beams in the gyrotron has different beam-wave interaction efficiencies. Compared to the coaxial gyrotron with one electron beam, the beam-wave interaction efficiency of each electron beam in the coaxial gyrotron with a double electron beam has a different increase. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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9. Analysis of the performance of permanent magnetic stepping motor with trapezoid stator tooth.
- Author
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Liu, C. P., Li, Y. C., Liu, K. H., Wu, K. T., and Yao, Y. D.
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STEPPING motors , *OPTICAL scanners , *NUMERICAL analysis , *MAGNETIC fields , *SIMULATION methods & models - Abstract
With the rapid development of automation techniques, the claw-poled stepping motors are widely used, especially in optical scanners. Most research on stepping motors has concentrated on electrical properties, but a few papers have reported on the performance in relation to the magnetic-field distribution. The purpose of this study is to analyze the effect of the shape of the stator tooth and to search for the optimal parameters using a magnetic-circuit simulation technique. Through numerical calculations, the optimal performance conditions can be obtained by varying the ratio between the two bases of the trapezoid teeth between 1/5 and 1/3, and varying the ratio between the heights of individual teeth in relation to the separation between the two yokes from 11/15 to 13/15. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
10. Large-scale and highly accurate magnetic field analysis of magnetic shield.
- Author
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Takahashi, Y., Wakao, S., and Kameari, A.
- Subjects
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MAGNETIC fields , *FINITE element method , *MAGNETIC properties , *NUMERICAL analysis , *MAGNETOSTATICS - Abstract
This paper describes a large-scale and highly accurate magnetostatic field analysis targeting a magnetic shield. The hybrid finite element–boundary element method and the magnetic moment method do not require mesh division for the free space and can easily treat the nonlinearity of magnetic property. Therefore, these methods are considered very effective for the analysis of a magnetic shield which has a high aspect ratio of the size scale to the thickness. However, large memory and computational time have been required due to the dense matrices generated by those integral-based formulations. To overcome the difficulties, we introduce the fast multipole method into the hybrid method and the magnetic moment method. Furthermore, to achieve more reduction of CPU time, we propose an effective preconditioning technique suitable for the hybrid method. Some numerical results that demonstrate the effectiveness of these approaches are also presented. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
11. The mechanism of propulsion of a model microswimmer in a viscoelastic fluid next to a solid boundary.
- Author
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Ives, Thomas R. and Morozov, Alexander
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VISCOELASTICITY , *PROPULSION systems , *MAGNETIC fields , *HEAT transfer , *NUMERICAL analysis - Abstract
In this paper, we study the swimming of a model organism, the so-called Taylor's swimming sheet, in a viscoelastic fluid close to a solid boundary. This situation comprises natural habitats of many swimming microorganisms, and while previous investigations have considered the effects of both swimming next to a boundary and swimming in a viscoelastic fluid, seldom have both effects been considered simultaneously.We re-visit the small wave amplitude result obtained by Elfring and Lauga ["Theory of locomotion through complex fluids," in Complex Fluids in Biological Systems, Biological and Medical Physics, Biomedical Engineering, edited by S. E. Spagnolie (Springer New York, New York, NY, 2015), pp. 283-317] and give a mechanistic explanation to the decoupling of the effects of viscoelasticity, which tend to slow the sheet, and the presence of the boundary, which tends to speed up the sheet. We also develop a numerical spectral method capable of finding the swimming speed of a waving sheet with an arbitrary amplitude and waveform. We use it to show that the decoupling mentioned earlier does not hold at finite wave amplitudes and that for some parameters the presence of a boundary can cause the viscoelastic effects to increase the swimming speed of microorganisms. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
12. MFL SIGNAL INVERSION USING THE FINITE ELEMENT NETWORK.
- Author
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Ramuhalli, Pradeep
- Subjects
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MAGNETIC flux , *MAGNETIC fields , *NUMERICAL analysis , *FINITE element method , *ARTIFICIAL neural networks , *MATERIALS testing , *NONDESTRUCTIVE testing - Abstract
Iterative algorithms that incorporate a numerical forward model have been typically used to solve the problem of flaw profile estimation from measured magnetic flux leakage (MFL) data. These approaches use the forward model to determine the measurement signal for a given defect profile, and obtain the desired profile by iteratively minimizing a cost function. The use of numerical models is computationally expensive, and alternative forward models are needed. This paper presents a finite element neural network (FEN) obtained by embedding a finite element model in a parallel neural network architecture that enables fast and accurate solution of the forward problem. Previous results have indicated that the FEN performance as a forward model is comparable to that of the conventional finite element method. In this paper, we investigate the applicability of the FEN to determining flaw profiles from MFL data in pipeline inspection and present results on synthetic MFL data. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
13. Numerical Analysis of the Temperature Field in A Magneto-Rheological Brake.
- Author
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Bosioc, A. I., Muntean, S., Susan-Resig, R. F., Borbáth, I., and Vékás, L.
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NUMERICAL analysis , *TEMPERATURE effect , *MAGNETORHEOLOGICAL fluids , *COMPUTER simulation , *MAGNETIC fields - Abstract
The paper focuses on numerical analysis of temperature field into a magneto-rheological break. The magnetorheological fluid is used for a brake operated at different speeds. The magneto-rheological brake application was developed due to the magnetic control and fast response. The two dimensional axi-symmetric computational domain corresponds to the experimental magneto-rheological break. The numerical simulations have been performed for seven speed values with zero magnetic field. Firstly, the temperature map for magneto-rheological break is computed. Secondly, the temperature value obtained on the outside casing wall is validated against experimental data. Next, the maximum temperature value was identified based on numerical simulation in a point located into the magnetorheological fluid. The numerical results will be used to improve the magneto-rheological break operation/design. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
14. Numerical Analysis of the Temperature Field in A Magneto-Rheological Brake.
- Author
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Bosioc, A. I., Muntean, S., Susan-Resiga, R. F., Borbáth, I., and Vékás, L.
- Subjects
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NUMERICAL analysis , *TEMPERATURE effect , *MAGNETORHEOLOGY , *COMPUTER simulation , *MAGNETIC fields - Abstract
The paper focuses on numerical analysis of temperature field into a magneto-rheological break. The magnetorheological fluid is used for a brake operated at different speeds. The magneto-rheological brake application was developed due to the magnetic control and fast response. The two dimensional axi-symmetric computational domain corresponds to the experimental magneto-rheological break. The numerical simulations have been performed for seven speed values with zero magnetic field. Firstly, the temperature map for magneto-rheological break is computed. Secondly, the temperature value obtained on the outside casing wall is validated against experimental data. Next, the maximum temperature value was identified based on numerical simulation in a point located into the magnetorheological fluid. The numerical results will be used to improve the magneto-rheological break operation/design. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
15. Numerical study of the formation process of ferrofluid droplets.
- Author
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Liu, Jing, Yap, Yit Fatt, and Nguyen, Nam-Trung
- Subjects
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NUMERICAL analysis , *MAGNETIC fluids , *DROPLETS , *MAGNETIC fields , *MATHEMATICAL models , *STRAINS & stresses (Mechanics) , *LIQUID-liquid interfaces , *EQUATIONS - Abstract
This paper numerically investigates the influence of a uniform magnetic field on the droplet formation process at a microfluidic flow focusing configuration. The mathematical model was formulated by considering the balance of forces such as interfacial tension, magnetic force, and viscous stress across the liquid/liquid interface. A linearly magnetizable fluid was assumed. The magnetic force acts as a body force where the magnetic permeability jumps across the interface. The governing equations were solved with finite volume method on a Cartesian fixed staggered grid. The evolution of the interface was captured by the particle level set method. The code was validated with the equilibrium steady state of a ferrofluid droplet exposed to a uniform magnetic field. The evolution of the droplet formation in a flow focusing configuration was discussed. The paper mainly analyzes the effects of magnetic Bond number and the susceptibility on the velocity field and the droplet size. The droplet size increased with increasing magnetic strength and susceptibility. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
16. Lower-hybrid drift and Buneman instabilities in current sheets with guide field.
- Author
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Yoon, P. H. and Lui, A. T. Y.
- Subjects
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DRIFT mobility , *PLASMA confinement , *DISPERSION relations , *ELECTROSTATICS , *DENSITY gradient centrifugation , *MAGNETIC fields , *NUMERICAL analysis , *PLASMA instabilities - Abstract
Lower-hybrid drift and Buneman instabilities operate in current sheets with or without the guide field. The lower-hybrid drift instability is a universal instability in that it operates for all parameters. In contrast, the excitation of Buneman instability requires sufficiently thin current sheet. That is, the relative electron-ion drift speed must exceed the threshold in order for Buneman instability to operate. Traditionally, the two instabilities were treated separately with different mathematical formalisms. In a recent paper, an improved electrostatic dispersion relation was derived that is valid for both unstable modes [P. H. Yoon and A. T. Y. Lui, Phys. Plasmas 15, 072101 (2008)]. However, the actual numerical analysis was restricted to a one-dimensional situation. The present paper generalizes the previous analysis and investigates the two-dimensional nature of both instabilities. It is found that the lower-hybrid drift instability is a flute mode satisfying k·B=0 and k·∇n=0, where k represents the wave number for the most unstable mode, B stands for the total local magnetic field, and ∇n is the density gradient. This finding is not totally unexpected. However, a somewhat surprising finding is that the Buneman instability is a field-aligned mode characterized by k×B=0 and k·∇n=0, rather than being a beam-aligned instability. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
17. High energy micro electron beam generation using chirped laser pulse in the presence of an axial magnetic field.
- Author
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Akou, H. and Hamedi, M.
- Subjects
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FORCE & energy , *ELECTRON beams , *LASER pulses , *MAGNETIC fields , *AXIAL flow , *GAUSSIAN processes , *NUMERICAL analysis - Abstract
In this paper, the generation of high-quality and high-energy micro electron beam in vacuum by a chirped Gaussian laser pulse in the presence of an axial magnetic field is numerically investigated. The features of energy and angular spectra, emittances, and position distribution of electron beam are compared in two cases, i.e., in the presence and absence of an external magnetic field. The electron beam is accelerated with higher energy and qualified in spatial distribution in the presence of the magnetic field. The presence of an axial magnetic field improves electron beam spatial quality as well as its gained energy through keeping the electron motion parallel to the direction of propagation for longer distances. It has been found that a 64 μm electron bunch with about MeV initial energy becomes a 20 μm electron beam with high energy of the order of GeV, after interacting with a laser pulse in the presence of an external magnetic field. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
18. Bounds imposed on the sheath velocity of a dense plasma focus by conservation laws and ionization stability condition.
- Author
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Auluck, S. K. H.
- Subjects
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DENSE plasma focus , *CONSERVATION laws (Physics) , *IONIZATION energy , *PHYSICS experiments , *MAGNETIC fields , *NUMERICAL analysis - Abstract
Experimental data compiled over five decades of dense plasma focus research are consistent with the snowplow model of sheath propagation, based on the hypothetical balance between magnetic pressure driving the plasma into neutral gas ahead and "wind pressure" resisting its motion. The resulting sheath velocity, or the numerically proportional "drive parameter," is known to be approximately constant for devices optimized for neutron production over 8 decades of capacitor bank energy. This paper shows that the validity of the snowplow hypothesis, with some correction, as well as the non-dependence of sheath velocity on device parameters, have their roots in local conservation laws for mass, momentum, and energy coupled with the ionization stability condition. Both upper and lower bounds on sheath velocity are shown to be related to material constants of the working gas and independent of the device geometry and capacitor bank impedance. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
19. A study on bifurcations and structure of phase space concerning intrinsic localized modes in a nonlinear magneto-mechanical lattice.
- Author
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Kimura, Masayuki, Matsushita, Yasuo, and Hikihara, Takashi
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BIFURCATION theory , *PHASE space , *STRUCTURAL dynamics , *MAGNETIC fields , *LATTICE field theory , *NUMERICAL analysis , *EXISTENCE theorems , *NONLINEAR optics - Abstract
A magneto-mechanical lattice proposed in this paper is one of the nonlinear lattices in which intrinsic localized mode(ILM) exists. A bifurcation diagram concerning ILMs is investigated with respect to the magnitude of nonlinear coupling force. In addition, the possibility of the existence of moving ILM is discussed based on the phase structure around an unstable ILM which is numerically examined by computing unstable manifolds of the unstable ILM. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
20. Energy band structures for electrons on the triangular lattice with uniform magnetic field.
- Author
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Szakács, Zs.
- Subjects
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ENERGY bands , *TRIANGULARIZATION (Mathematics) , *LATTICE theory , *MAGNETIC fields , *NUMERICAL analysis , *POWER spectra - Abstract
In the present paper the electron on the triangular lattice with uniform perpendicular magnetic field [1,2] is considered. The energy band structure is visualized using numerical computations. The energy bands as a function of the magnetic field display a Hofstadter butterfly [3,4] type diagram. The influence of the hopping parameters on the energy spectra is also taken into account. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
21. Fusion neutron generation computations in a stellarator-mirror hybrid with neutral beam injection.
- Author
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Moiseenko, V. E. and Ågren, O.
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NUCLEAR fusion , *STELLARATORS , *NEUTRAL beams , *PLASMA injection , *NUCLEAR reactors , *NUMERICAL analysis , *MAGNETIC fields - Abstract
In the paper [Moiseenko V.E., Noack K., Ågren O. 'Stellarator-mirror based fusion driven fission reactor' J Fusion Energy 29 (2010) 65.], a version of a fusion driven system (FDS), i.e. a sub-critical fast fission assembly with a fusion plasma neutron source, is proposed. The plasma part of the reactor is based on a stellarator with a small mirror part. Hot ions with high perpendicular energy are assumed to be trapped in the magnetic mirror part. The stellarator part which connects to the mirror part and provides confinement for the bulk (deuterium) plasma. In the magnetic well of the mirror part, fusion reactions occur from collisions between a of hot ion component (tritium) with cold background plasma ions. RF heating is one option to heat the tritium. A more conventional method to sustain the hot ions is neutral beam injection (NBI), which is here studied numerically for the above-mentioned hybrid scheme. For these studies, a new kinetic code, KNBIM, has been developed. The code takes into account Coulomb collisions between the hot ions and the background plasma. The geometry of the confining magnetic field is arbitrary for the code. It is accounted for via a numerical bounce averaging procedure. Along with the kinetic calculations the neutron generation intensity and its spatial distribution are computed. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
22. Magnetic field of a combined plasma trap.
- Author
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Kotenko, V. G., Moiseenko, V. E., and Ågren, O.
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PLASMA gases , *MAGNETIC fields , *RADIATION trapping , *STELLARATORS , *NUMERICAL analysis , *SIMULATION methods & models , *TOROIDAL magnetic circuits - Abstract
This paper presents numerical simulations performed on the structure of a magnetic field created by the magnetic system of a combined plasma trap. The magnetic system includes the stellarator-type magnetic system and one of the mirror-type. For the stellarator type magnetic system the numeric model contains a magnetic system of an l=2 torsatron with the coils of an additional toroidal magnetic field. The mirror-type magnetic system element is considered as being single current-carrying turn enveloping the region of existence of closed magnetic surfaces of the torsatron. The calculations indicate the existence of a vast area of the values of the additional magnetic field magnitude and magnetic field of the single turn where, in principle, the implementation of the closed magnetic surface configuration is quite feasible. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
23. Numerical Realization of a Shell Model for Impurity Spreading in Plasmas.
- Author
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Tokar, M. Z. and Koltunov, M.
- Subjects
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NUMERICAL analysis , *PLASMA devices , *MAGNETIC fields , *HEAT balance (Engineering) , *IONIZATION (Atomic physics) , *TRANSPORT equation - Abstract
In plasmas of fusion devices impurity particles are released as a consequence of wall erosion and are seeded deliberately for diverse purposes. Often they enter the plasma volume from small spots and spread away both along and perpendicular to the magnetic field. This process is described by continuity, motion and heat balance equations taking into account such physical processes as ionization by electrons, friction and heating in coulomb collisions with background ions, etc. In present paper we introduce a shell model where solutions of these equations, such as the densities of different impurity ions, are approximated by functions decaying exponentially from the source region due to the ionization into higher charged states. By integrating the original transport equations over several space regions, we get a set of ordinary differential equations describing the time evolution of the characteristic values for the impurity ion densities, fluxes, temperatures, and the dimensions along and across the magnetic field of the clouds where different states are predominantly localized. The equations obtained include time derivatives of complex non-linear combinations of the variables in question. Two numerical approaches to solve such equations are elaborated and compared by considering the spreading of lithium particles in deuterium plasma. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
24. Physics and engineering studies on the MITICA accelerator: comparison among possible design solutions.
- Author
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Agostinetti, P., Antoni, V., Cavenago, M., Chitarin, G., Pilan, N., Marcuzzi, D., Serianni, G., and Veltri, P.
- Subjects
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ION accelerators , *PHYSICS experiments , *NUMERICAL analysis , *DEUTERIUM ions , *PLASMA gases , *ENGINEERING design , *MAGNETIC fields - Abstract
Consorzio RFX in Padova is currently using a comprehensive set of numerical and analytical codes, for the physics and engineering design of the SPIDER (Source for Production of Ion of Deuterium Extracted from RF plasma) and MITICA (Megavolt ITER Injector Concept Advancement) experiments, planned to be built at Consorzio RFX. This paper presents a set of studies on different possible geometries for the MITICA accelerator, with the objective to compare different design concepts and choose the most suitable one (or ones) to be further developed and possibly adopted in the experiment. Different design solutions have been discussed and compared, taking into account their advantages and drawbacks by both the physics and engineering points of view. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
25. VALIDATION OF MAGNETIC FLUX LEAKAGE COMPUTATIONAL RESULTS AGAINST EXPERIMENTAL DATA.
- Author
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Etcheverry, J. I. and Sánchez, G. A.
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MAGNETIC flux , *ELECTRIC leakage , *NOTCH effect , *MACHINING , *NUMERICAL analysis , *PREDICTION models , *COMPUTER software , *MAGNETIC permeability , *MAGNETIC fields - Abstract
Results of detailed experimental measurements of the leaked magnetic field for two different steel plates with a machined notch presented in a companion paper are compared against the numerical predictions using commercial software COMSOL. The accuracy of the results is discussed in detail, as well as the ingredients that allow obtaining satisfactory computational results. Some interesting conclusions that derive from the numerical computations are also presented. For instance, the influence of the notch length on the amplitude of the recorded signal, the need to have a precise measurement of the magnetic permeability up to magnetic fields much higher than the magnetic field in the bulk of the material, etc. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
26. SIMULATION OF EDDY CURRENT INSPECTION INCLUDING MAGNETIC FIELD SENSOR SUCH AS A GIANT MAGNETO-RESISTANCE OVER PLANAR STRATIFIED MEDIA COMPONENTS WITH EMBEDDED FLAWS.
- Author
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Prémel, Denis, Decitre, J. M., and Pichenot, G.
- Subjects
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SIMULATION methods & models , *ELECTRIC currents , *MAGNETIC fields , *MAGNETORESISTANCE , *DETECTORS , *NUMERICAL analysis , *ELECTRIC coils , *COMPUTER software - Abstract
The ECT inspection of a conductive component consists in detecting the perturbation of the induced currents due to a flaw. Among new detectors, Giant Magneto-Resistance (GMR) or Giant Magnetic Impedance sensors, which are sensitive to the magnetic field above the surface of the component, have shown growing interest due to their high performances with respect to classical bobbin coils. In this communication, we present a numerical model based on the volume integral approach which allows computing the components of the perturbed magnetic field due to a given notch embedded in a planar stratified media. Though the inducer may be chosen arbitrary in a list of potential exciting coils, rectangular coils or current foils are very useful for generating a uniform current flow orientated perpendicularly to the length of the flaw. This paper presents firstly some numerical results considering two kinds of distinct numerical models, and then some experimental results will be presented for different kinds of practical applications. This numerical model results in new computation facilities which have been translated into new functionalities in the last version of the CIVA software. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
27. Turbulence, Energy Transfers and Reconnection in Compressible Coronal Heating Field-line Tangling Models.
- Author
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Dahlburg, R. B., Rappazzo, A. F., and Velli, M.
- Subjects
- *
TURBULENCE , *NUMERICAL analysis , *RUNGE-Kutta formulas , *MAGNETIC fields , *FINITE differences - Abstract
MHD turbulence has long been proposed as a mechanism for the heating of coronal loops in the framework of the Parker scenario for coronal heating. So far most of the studies have focused on its dynamical properties without considering its thermodynamical and radiative features, because of the very demanding computational requirements. In this paper we extend this previous research to the compressible regime, including an energy equation, by using HYPERION, a new parallelized, viscoresistive, three-dimensional compressible MHD code. HYPERION employs a Fourier collocation—finite difference spatial discretization, and uses a third-order Runge-Kutta temporal discretization. We show that the implementation of a thermal conduction parallel to the DC magnetic field induces a radiative emission concentrated at the boundaries, with properties similar to the chromosphere—transition region—corona system. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
28. Modeling of Crack Front Singularity in 3D Piezoelectromagnetic Media by Weakly Singular SGBEM.
- Author
-
Rungamornrat, Jaroon and Senjuntichai, Teerapong
- Subjects
- *
BOUNDARY element methods , *INTEGRAL equations , *ELECTROMAGNETISM , *NUMERICAL analysis , *MAGNETIC fields - Abstract
In this paper, a numerical technique for calculating the intensity factors (strength of singularity) for cracks in a three-dimensional, generally anisotropic, piezoelectromagnetic medium is presented. The technique is based upon a symmetric Galerkin boundary element method (SGBEM) with a weakly singular, weak-form integral equation for the generalized surface traction (including the surface force, the surface electric charge, and the surface magnetic induction) on the crack surface being employed as a key formulation. The crucial feature of the governing integral equation is that it contains only weakly singular kernels of the type o(1/r); as a consequence, this allows Co interpolations to be utilized in the numerical approximation and, in addition, reduces computational effort for the numerical integration of singular and nearly singular integrals. In the numerical treatment, special interpolations have been adopted in the local region near the crack front in order to accurately capture the behavior of fields near the singularity line (crack front). Another important aspect of these near front interpolations is that they contain information that can be used to directly extract the intensity factors along the crack front. Extensive numerical experiments have revealed that the technique developed yields highly accurate numerical solutions for the strength of singularity present at the singularity line. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
29. Electron Energy Distribution Function Measurements by Langmuir Probe in ITER like Negative Ion Sources.
- Author
-
Crowley, B., Homfray, D., Fantz, U., Boilson, D., and Hemsworth, R. S.
- Subjects
- *
LANGMUIR probes , *NUMERICAL analysis , *ANIONS , *ION sources , *MAGNETIC fields - Abstract
Determining d2I/dV2 from a traditional Langmuir probe trace using numerical techniques is inherently noisy and generally yields poor results. We have developed a Langmuir probe system based on a method first used in the 1950’s by Boyd and Twiddy. The system measures the 2nd derivative directly. This paper presents results from the driver and extraction regions of the KAMABOKO III ITER like negative ion source. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
30. Analysis of magnetic abrasive finishing with slotted magnetic pole.
- Author
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Jayswal, S. C., Jain, V. K., Dixit, P. M., Ghosh, S., Castro, J.C., and Lee, J.K.
- Subjects
- *
FINITE element method , *NUMERICAL analysis , *MAGNETIC pole , *ELECTROMAGNETISM , *NANOSTRUCTURED materials , *MAGNETIC fields - Abstract
Magnetic Abrasive Finishing (MAF) is relatively a new finishing process among the advanced finishing processes in which the workpiece is kept in the magnetic field created by two poles of an electromagnet. The working gap between the workpiece and the magnet is filled with magnetic abrasive particles. A flexible magnetic abrasive brush is formed, acting as a multipoint cutting tool, due to the effect of magnetic field in the working gap. This process is capable of producing the surface finish of nanometer range. Most of the researchers have been using the electromagnet having a slot in it to improve the performance of the process but hardly any information is available about its effect on the process performance. This paper deals with the effect of a slot made in the electromagnet on the forces and surface quality during MAF. An experimental set-up is designed and fabricated for the measurement of the magnetic field distribution in the working gap. The magnetic field is simulated using a finite element model of the process. The magnetic field is also measured experimentally to validate the theoretical results. It indicates a good agreement between the experimental results and simulated values. The finite element method is further used for the evaluation of the magnetic force and surface quality during MAF. To our surprise it is found that the force under the slot is negative, even then process performance is improved. MAF process removes a very small amount of material by indentation and rotation of the magnetic abrasive particles in the circular tracks. Due to rotation of the magnetic abrasive flexible brush, grooves are formed on the workpiece surface which decides the surface profile after MAF. Surface quality is determined on the basis of the surface profile achieved by equating the volume of groove produced. These results show an improvement in finishing rate while using a slotted pole surface. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
31. Numerical study of transition to supersonic flows in the edge plasma.
- Author
-
Goswami, Rajiv, Artaud, Jean-François, Imbeaux, Frédéric, and Kaw, Predhiman
- Subjects
- *
PHASE transitions , *SUPERSONIC flow , *PLASMA boundary layers , *TOKAMAKS , *NUMERICAL analysis , *MAGNETIC fields - Abstract
The plasma scrape-off layer (SOL) in a tokamak is characterized by ion flow down a long narrow flux tube terminating on a solid surface. The ion flow velocity along a magnetic field line can be equal to or greater than sonic at the entrance of a Debye sheath or upstream in the presheath. This paper presents a numerical study of the transition between subsonic and supersonics flows. A quasineutral one-dimensional (1D) fluid code has been used for modeling of plasma transport in the SOL along magnetic field lines, both in steady state and under transient conditions. The model uses coupled equations for continuity, momentum, and energy balance with ionization, radiation, charge exchange, and recombination processes. The recycled neutrals are described in the diffusion approximation. Standard Bohm sheath criterion is used as boundary conditions at the material surface. Three conditions conducive for the generation of supersonic flows in SOL plasmas have been explored. It is found that in steady state high (attached) and low (detached) divertor temperatures cases, the role of particle, momentum, and energy loss is critical. For attached case, the appearance of shock waves in the divertor region if the incoming plasma flow is supersonic and its effect on impurity retention is presented. In the third case, plasma expansion along the magnetic field can yield time-dependent supersonic solutions in the quasineutral rarefaction wave. Such situations can arise in the parallel transport of intermittent structures such as blobs and edge localized mode filaments along field lines. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
32. On the dynamics of non-spherical magnetic microbubbles.
- Author
-
Lind, Steven J.
- Subjects
- *
MICROBUBBLES , *SURFACE tension , *BOUNDARY element methods , *MAGNETIC fields , *NUMERICAL analysis , *DRUG delivery systems - Abstract
Magnetic microbubbles are a relatively recent development with the potential to greatly improve the efficacy of the minimally invasive drug-delivery procedure sonoporation. However, very little is known about the dynamics of magnetic microbubbles, in general. In this paper, a novel mathematical model and numerical method are developed to simulate the dynamics of non-spherical magnetic microbubbles in vitro. The ambient fluid is assumed to be inviscid and the flow irrotational, enabling a generalized Bernoulli equation to be derived that includes surface tension effects and the effect of the applied magnetic field. The governing equations are solved using the boundary element method in which both the bubble surface and the velocity potential are represented by cubic splines. Results show that magnetic microbubble dynamics are highly dependent on the magnetic susceptibility difference, ∆X, between the bubble and the ambient fluid, with the sign and magnitude of ∆X dictating the direction and velocity of any formed liquid jets. Importantly, it is shown that the magnetic field can provide an additional means of flow control to the experimental investigator: in the presence of surface tension, weak magnetic fields do not generate jets. However, increasing the magnitude of the magnetic field can instigate jet formation, and increase the maximum and time-averaged jet velocities. Experimentally relevant parameter values are also considered, and results suggest that a combined application of magnetic and ultrasound fields is required to generate the high-speed bubble collapse events most likely to maximise cell poration and drug delivery. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
33. A new approach for magnetic curves in 3D Riemannian manifolds.
- Author
-
Bozkurt, Zehra, Gök, Ismail, Yaylı, Yusuf, and Ekmekci, F. Nejat
- Subjects
- *
RIEMANNIAN manifolds , *MAGNETIC fields , *DIVERGENCE theorem , *DIMENSIONAL analysis , *MATHEMATICAL analysis , *NUMERICAL analysis - Abstract
A magnetic field is defined by the property that its divergence is zero in a threedimensional oriented Riemannian manifold. Each magnetic field generates amagnetic flow whose trajectories are curves called as magnetic curves. In this paper, we give a new variational approach to study the magnetic flow associated with the Killing magnetic field in a three-dimensional oriented Riemann manifold, (M³, g). And then, we investigate the trajectories of the magnetic fields called as N-magnetic and Bmagnetic curves. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
34. Dynamics of quasi-spherical Z-pinch implosions with mass redistribution and displacement modification.
- Author
-
Zhang, Yang, Ding, Ning, Li, Zheng-Hong, Sun, Shun-Kai, Xue, Chuang, Ning, Cheng, Xiao, De-Long, and Huang, Jun
- Subjects
- *
Z-pinch , *PLASMA dynamics , *ATOMIC mass , *MAGNETIC fields , *GAS flow , *KINETIC energy , *NUMERICAL analysis , *DEFORMATIONS (Mechanics) - Abstract
Implosions of (quasi-)spherical loads with mass redistribution and displacement modification are investigated numerically. Both methods can theoretically counterbalance the nonuniformity of magnetic pressure along the load surface and realize quasi-spherical Z-pinch implosions. Mass redistribution is feasible for spherical loads with large radius and weight, while the displacement modification is more suitable for light loads, such as those composed of wire arrays. Simulation results suggest that, for mass redistributed spherical loads, wall instabilities induced by polar mass flows will deform the imploding shell. For prolate spherical loads, in which the wall instability cannot develop, the kinetic energy distribution is disturbed at high latitude. These passive behaviors and their possible mitigation methods, such as reshaping the electrode, are investigated numerically in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
35. Finite-temperature corrections to the time-domain equations of motion for perpendicular propagation in nonuniform magnetized plasmas.
- Author
-
Tierens, W. and De Zutter, D.
- Subjects
- *
EQUATIONS of motion , *THEORY of wave motion , *TIME-domain analysis , *TEMPERATURE effect , *MAGNETIC fields , *DISCRETE systems , *NUMERICAL analysis - Abstract
In this paper we extend the new techniques of W. Tierens and D. D. Zutter, J. Comput. Phys. 231, 5144 (2012) to include finite Larmor radius effects up to second order in the Larmor radius. We limit ourselves to the case of propagation perpendicular to the background magnetic field Bvector 0. We show that our time-domain technique is able to produce the lowest-order Bernstein wave (a wave believed to be useful for heating fusion devices [H. P. Laqua, Plasma Phys. Controlled Fusion 49, R1 (2007)]). The discrete equations retain many of the favourable properties described in W. Tierens and D. D. Zutter, J. Comput. Phys. 231, 5144 (2012), i.e., unconditional stability and a straightforward relation between the second-order accurate continuous dispersion relation and the dispersion relation of the discretized problem. The theory is illustrated by a place-independent and a place-dependent temperature numerical example. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
36. Random walk of magnetic field lines in dynamical turbulence: A field line tracing method. II. Two-dimensional turbulence.
- Author
-
Guest, B. and Shalchi, A.
- Subjects
- *
TURBULENCE , *PLASMA astrophysics , *MAGNETIC fields , *RANDOM walks , *COMPUTER simulation , *NUMERICAL analysis , *MAGNETOSTATICS - Abstract
The wandering of magnetic field lines is an important topic in theoretical plasma physics and astrophysics. Previous analytical work, as well as computer simulations, is based on magnetostatic models to warrant mathematical and numerical tractability. Recently, we have studied the first time field line random walk in dynamical turbulence by using a field line tracing method. These calculations were performed for a slab model of the turbulence. It is the purpose of the present paper to use the latter method to compute the field line diffusion coefficient for dynamical two-dimensional turbulence. Two models for the dynamical correlation function are used, namely the damping model of dynamical turbulence and the nonlinear anisotropic dynamical turbulence model. It is shown that the largest scales of the turbulence and the choice of the dynamical turbulence model have a strong influence on the diffusivity of the field lines and the absolute value of the diffusion coefficient. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
37. Numerical study of an 8 mm third-harmonic peniotron with a gradual reversal of the magnetic field.
- Author
-
Wu, Xinhui, Li, Jiayin, Hu, Biao, Zhao, Xiaoyun, and Li, Tianming
- Subjects
- *
MAGNETIC fields , *HARMONIC analysis (Mathematics) , *NUMERICAL analysis , *DISTRIBUTION (Probability theory) , *PREDICTION models , *MICROWAVES , *ENERGY conversion , *ELECTRODES - Abstract
A novel large-orbit electron gun with a gradual reversal of the magnetic field for the 8 mm third-harmonic peniotron is numerically studied in this paper. In the permanent magnetic condition, an electron beam with axial velocity spread of 4.78%, guiding center deviation of 7.18%, and velocity ratio of 2.2 is generated in the gun, satisfying the special requirements of beam-wave interaction in the third-harmonic peniotron. Compared with the traditional three stage method, it is unnecessary here to generate a thin tubular electron beam before the reversal point and the mutational distribution of reversal magnetic field. In addition, the emission band can be placed in the area of axial magnetic field where its magnitude decreases gradually, which reduces the structure complexity and the difficulties in tube-making process greatly. Finally, the peniotron is predicted to yield an output power of 31.9 kW at 30 GHz, with its microwave conversion efficiency of up to 49.4%, which shows the perfect matching between its high frequency system and its electron-optical system. According to the numerical calculations, the device performance is very sensitive to the relative axial position between the magnetic system and the electrode system. If the magnetic system shifts 0.8 mm to the right, the device efficiency would decrease from 49.4% to 31.7%. This phenomenon provides meaningful information in the device hot-test. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
38. Ring-shaped velocity distribution functions in energy-dispersed structures formed at the boundaries of a proton stream injected into a transverse magnetic field: Test-kinetic results.
- Author
-
Voitcu, Gabriel and Echim, Marius M.
- Subjects
- *
SPECTRAL energy distribution , *DISTRIBUTION (Probability theory) , *PROTONS , *MAGNETIC fields , *ELECTRIC fields , *HARMONIC functions , *NUMERICAL analysis - Abstract
In this paper, we discuss the formation of ring-shaped and gyro-phase restricted velocity distribution functions (VDFs) at the edges of a cloud of protons injected into non-uniform distributions of the electromagnetic field. The velocity distribution function is reconstructed using the forward test-kinetic method. We consider two profiles of the electric field: (1) a non-uniform E-field obtained by solving the Laplace equation consistent with the conservation of the electric drift and (2) a constant and uniform E-field. In both cases, the magnetic field is similar to the solutions obtained for tangential discontinuities. The initial velocity distribution function is Liouville mapped along numerically integrated trajectories. The numerical results show the formation of an energy-dispersed structure due to the energy-dependent displacement of protons towards the edges of the cloud by the gradient-B drift. Another direct effect of the gradient-B drift is the formation of ring-shaped velocity distribution functions within the velocity-dispersed structure. Higher energy particles populate the edges of the proton beam, while smaller energies are located in the core. Non-gyrotropic velocity distribution functions form on the front-side and trailing edge of the cloud; this effect is due to remote sensing of energetic particles with guiding centers inside the beam. The kinetic features revealed by the test-kinetic solutions have features similar to in-situ velocity distribution functions observed by Cluster satellites in the magnetotail, close to the neutral sheet. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
39. Magnetic field gradient effects on Rayleigh-Taylor instability with continuous magnetic field and density profiles.
- Author
-
Yang, B. L., Wang, L. F., Ye, W. H., and Xue, C.
- Subjects
- *
MAGNETIC fields , *PERTURBATION theory , *THICKNESS measurement , *PHASE transitions , *DENSITY , *NUMERICAL analysis , *LINEAR statistical models - Abstract
In this paper, the effects of magnetic field gradient (i.e., the magnetic field transition layer effects) on the Rayleigh-Taylor instability (RTI) with continuous magnetic field and density profiles are investigated analytically. The transition layers of magnetic field and density with two different typical profiles are studied and the analytic expressions of the linear growth rate of the RTI are obtained. It is found that the magnetic field effects strongly reduce the linear growth rate of the RTI, especially when the perturbation wavelength is short. The linear growth rate of the RTI increases with the thickness of the magnetic field transition layer, especially for the case of small thickness of the magnetic field transition layer. When the magnetic field transition layer width is long enough, the linear growth rate of the RTI can be saturated. Thus when one increases the width of the magnetic field transition layer, the linear growth rate of the RTI increases only in a certain range, which depends on the magnetic field strength. The numerical results are compared with the analytic linear growth rates and they agree well with each other. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
40. The magnetic Rayleigh-Taylor instability for inviscid and viscous fluids.
- Author
-
Chambers, K. and Forbes, L. K.
- Subjects
- *
PLASMA instabilities , *INVISCID flow , *VISCOUS flow , *MAGNETIC fields , *ELECTRIC currents , *MAGNETIC permeability , *NUMERICAL analysis , *INTERFACES (Physical sciences) - Abstract
The Rayleigh-Taylor instability arises whenever two fluids with different densities are arranged such that the heavier fluid sits above the lighter fluid, with a sharp interface in between. The magnetic Rayleigh-Taylor instability has the further complication due to the presence of a magnetic field throughout both media. The two fluids in question may also have differing magnetic properties, such as the magnetic permeability. When the fluids in consideration are in fact plasmas comprised of charged particles, induced currents, magnetic fields, and Lorentz forces can all act in ways that will affect the stability of the system. Stable base flows exist for the 2D case, and small sinusoidal disturbances to the base flow will grow in the unstable scenario. The numerical method described in this paper calculates the growth of the interface in the nonlinear regime, since closed form solutions are obtained only in the linear approximation. Through the analysis of both the fluid and magnetic vorticities and streamfunctions, the simulated results can be explained from the principles of magnetohydrodynamics. A range of simulations is presented, looking at cases with different initial conditions, cases with strong and weak magnetic fields, and cases with magnetic fields oriented at different angles relative to the interface of the two fluids. It is shown in particular how different initial conditions give rise to outcomes that are very different in terms of the geometry of the interface between the two fluids, primarily the differences between a single mode disturbance and a multimode disturbance to the interface at time t = 0. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
41. Electrostatic beams from tailored plasmas in a Penning-Malmberg trap.
- Author
-
Weber, T. R., Danielson, J. R., and Surko, C. M.
- Subjects
- *
ELECTROSTATICS , *PLASMA gases , *MAGNETIC fields , *ELECTRON distribution , *POSITRON beams , *NUMERICAL analysis , *SIMULATION methods & models - Abstract
In recent work, a technique was developed to extract high quality beams from single-component plasmas confined in a Penning-Malmberg trap in a 4.8 T magnetic field. In this paper, a procedure is developed to extract these beams from the confining magnetic field and then focus them to create especially tailored electrostatic beams. Electron beams are extracted from the field in two stages: they are first transported to a region of reduced field (1 mT), and then taken to zero field with a nonadiabatic, fast extraction. Once in the field-free region, the beams are focused using an Einzel lens. Experimental results and numerical simulations are presented to illustrate the extraction and focusing process. Theoretical expressions are developed to describe the modifications to the relevant beam energy and spatial distributions. Where possible, analytic expressions are presented for the case relevant here of beams with Gaussian radial profiles. Beam emittance considerations are discussed as well as prospects for further development of these techniques. Application of these techniques to provide high-quality positron beams is also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
42. A method for finding three-dimensional magnetic skeletons.
- Author
-
Haynes, A. L. and Parnell, C. E.
- Subjects
- *
DIMENSIONAL analysis , *MAGNETIC fields , *PLASMA gases , *MAGNETOHYDRODYNAMICS , *PLASMA dynamics , *FIELD theory (Physics) , *NUMERICAL analysis - Abstract
Magnetic fields are an essential component of a plasma. In many astrophysical, solar, magnetospheric, and laboratory situations the magnetic field in the plasma can be very dynamic and form highly complex structures. One approach to unraveling these structures is to determine the magnetic skeleton of the field, a set of topological features that divide the magnetic field into topologically distinct domains. In general, the features of the magnetic skeleton are difficult to locate, in particular those given by numerical experiments. In this paper, we propose a new set of tools to find the skeleton of general magnetic fields including null points, spines, separatrix surfaces, and separators. This set of tools is found to be considerably better at finding the skeleton than the currently favored methods used in magnetohydrodynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
43. Magnetohydrodynamic waves in the presence of relative motion between two populations of a plasma system.
- Author
-
Kumar, Subhash and Singh, Harinder P.
- Subjects
- *
MAGNETOHYDRODYNAMIC waves , *MAGNETIC fields , *SPACE plasmas , *MAGNETOHYDRODYNAMICS , *DISPERSION relations , *STABILITY (Mechanics) , *NUMERICAL analysis - Abstract
The paper investigates the role of relative motion between the fluid components of a plasma model, which is simulated by concatenation of two anisotropic magnetohydrodynamic (MHD) fluids, on the propagation of low-frequency waves and instabilities. The gyrotropic pressure of both the MHD components is given by generalized polytropic laws that allow the system to reduce to a variety of states. The linearized analysis is carried out and dispersion relation is derived using the normal mode technique. The dispersion relation, which gives numerous earlier results as special cases, is discussed both analytically as well as numerically for parameters appropriate for the space plasma. It is found that the relative motion between the two components, besides modifying the condition for fire-hose instability, causes the concatenated system to exhibit different kinds of relative ordering of the magnitudes of phase speeds of the various MHD modes in the directions parallel and antiparallel to the magnetic field. The relative motion between the components also influences the phase relationship between density and magnetic field fluctuations for the various compressive modes in the background ambient plasma. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
44. Constraints on an empirical equation for asymmetry-induced transport.
- Author
-
Eggleston, D. L.
- Subjects
- *
PLASMA gases , *MAGNETIC fields , *PARTICLES (Nuclear physics) , *ELECTRON transport , *NUMERICAL analysis - Abstract
Previous work on asymmetry-induced transport in a modified Malmberg–Penning trap showed that the radial particle flux was empirically constrained to be of the form Γ(ε)=-(B0/B)1.33D(ε)[∇n0+f(ε)], where ε=ω-lωR, ωR(r)=vθ/r is the column rotation frequency, ω and l are the asymmetry frequency and azimuthal mode number, ∇n0 is the radial density gradient, B is the magnetic field, B0 is an empirical constant, and D(ε) and f(ε) are unknown functions. In this paper, it is shown that further constraints can be placed upon D(ε) and f(ε) by comparing data near the ε=0 points to a first order expansion of Γ(ε). It is shown that dD/dε(0)≠0, in contradiction to resonant particle theory, and that f(ε) can only be a fraction of the size predicted by that theory. Finally, it is shown that dD/dε(0) exhibits a power-law scaling with radius, magnetic field, and the bias of the center conductor of the trap. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
45. Size scaling effects on the particle density fluctuations in confined plasmas.
- Author
-
Vázquez, Federico and Márkus, Ferenc
- Subjects
- *
PLASMA gas research , *DIFFUSION , *MAGNETIC fields , *NONEQUILIBRIUM thermodynamics , *PARTICLES (Nuclear physics) , *NUMERICAL analysis , *MATHEMATICAL models - Abstract
In this paper, memory and nonlocal effects on fluctuating mass diffusion are addressed in the context of fusion plasmas. Nonlocal effects are included by considering a diffusivity coefficient depending on the size of the container in the transverse direction to the applied magnetic field. It is obtained by resorting to the general formulation of the extended version of irreversible thermodynamics in terms of the higher order dissipative fluxes. The developed model describes two different types of the particle density time correlation function. Both have been observed in tokamak and nontokamak devices. These two kinds of time correlation function characterize the wave and the diffusive transport mechanisms of particle density perturbations. A transition between them is found, which is controlled by the size of the container. A phase diagram in the {L,2π/k} space describes the relation between the dynamics of particle density fluctuations and the size L of the system together with the oscillating mode k of the correlation function. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
46. Numerical experiments on plasmoids entering a transverse magnetic field.
- Author
-
Gunell, H., Walker, J. J., Koepke, M. E., Hurtig, T., Brenning, N., and Nilsson, H.
- Subjects
- *
SPHEROMAKS , *MAGNETIC fields , *MAGNETOSPHERE , *NUMERICAL analysis , *SIMULATION methods & models - Abstract
Plasma from the Earth’s magnetosheath has previously been observed inside the magnetosphere. Inhomogeneities in the magnetosheath plasma, here called plasmoids, can impact the magnetopause and doing so set up a polarizing field that allows it to penetrate the magnetopause and enter the magnetosphere. A set of simulations of plasmoids with different dimensions is presented in this paper. For plasmoids that are longer than those previously published, waves propagating upstream from the barrier are found. It is also found that the penetration process causes the part of the plasmoid that is upstream of the barrier to rotate. The role of plasmoid width and cross sectional shape in penetration is studied, and for plasmoids that are less than half an ion gyroradius wide, the plasmoid is compressed to obtain a vertically oriented elliptical cross section, regardless of the initial shape. When the initial plasmoid width exceeds the ion gyroradius, the plasmoid still penetrates through a mechanism involving a potential that propagates upstream from the magnetic barrier. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
47. The role of plasma elongation on the linear damping of zonal flows.
- Author
-
Angelino, P., Garbet, X., Villard, L., Bottino, A., Jolliet, S., Ghendrih, Ph., Grandgirard, V., McMillan, B. F., Sarazin, Y., Dif-Pradalier, G., and Tran, T. M.
- Subjects
- *
TOKAMAKS , *FUSION reactors , *MAGNETIC fields , *TURBULENCE , *NUMERICAL analysis - Abstract
Drift wave turbulence is known to self-organize to form axisymmetric macroscopic flows. The basic mechanism for macroscopic flow generation is called inverse energy cascade. Essentially, it is an energy transfer from the short wavelengths to the long wavelengths in the turbulent spectrum due to nonlinear interactions. A class of macroscopic flows, the poloidally symmetric zonal flows, is widely recognized as a key constituent in nearly all cases and regimes of microturbulence, also because of the realization that zonal flows are a critical agent of self-regulation for turbulent transport. In tokamaks and other toroidal magnetic confinement systems, axisymmetric flows exist in two branches, a zero frequency branch and a finite frequency branch, named Geodesic Acoustic Modes (GAMs). The finite frequency is due to the geodesic curvature of the magnetic field. There is a growing body of evidence that suggests strong GAM activity in most devices. Theoretical investigation of the GAMs is still an open field of research. Part of the difficulty of modelling the GAMs stems from the requirement of running global codes. Another issue is that one cannot determine a simple one to one relation between turbulence stabilization and GAM activity. This paper focuses on the study of ion temperature gradient turbulence in realistic tokamak magnetohydrodynamic equilibria. Analytical and numerical analyses are applied to the study of geometrical effects on zonal flows oscillations. Results are shown on the effects of the plasma elongation on the GAM amplitude and frequency and on the zonal flow residual amplitude. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
48. Numerical calculation of the Hamada basis vectors for three-dimensional toroidal magnetic configurations.
- Author
-
Talmadge, J. N. and Gerhardt, S. P.
- Subjects
- *
NUMERICAL calculations , *NUMERICAL analysis , *FERROMAGNETIC materials , *MAGNETIC domain , *MAGNETIC fields , *FIELD theory (Physics) , *MAGNETICS - Abstract
The moment equation approach to neoclassical transport is used to calculate neoclassical particle and heat fluxes, impurity transport, the ambipolar electric field, and momentum damping rates. These equations are often written in Hamada coordinates which makes it easier to obtain analytic solutions. However, previous simplifying assumptions used to evaluate the basis vectors analytically are often invalid for advanced stellarator configurations. In this paper, a numerical method is presented by which the Hamada basis set can be determined for an arbitrary three dimensional toroidal confinement device by integrating along a magnetic field line. The method is applied to the magnetic configuration in the Helically Symmetric Experiment [F. S. B. Anderson, A. F. Almagri, D. T. Anderson, P. G. Matthews, J. N. Talmadge, and J. L. Shohet, Fusion Technol. 27, 273 (1995)] and compared to the large-aspect-ratio tokamak approximation to the basis set. The results indicate that the numerical technique is a more accurate method to specify the basis vectors, especially in a device with negligible toroidal curvature. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
49. Spin-up of a liquid metal flow driven by a rotating magnetic field in a finite cylinder: A numerical and an analytical study.
- Author
-
Nikrityuk, Petr A., Ungarish, Marius, Eckert, Kerstin, and Grundmann, Roger
- Subjects
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NUMERICAL analysis , *LIQUID metals , *CYLINDER (Shapes) , *MOTION , *MAGNETIC fields , *OSCILLATIONS - Abstract
This paper presents a combined numerical and analytical study of the impulsive axisymmetric spin-up from rest of an isothermal liquid metal in a closed cylinder. The motion of the liquid is caused by the action of a low-frequency, low-induction rotating magnetic field, whose magnetic Taylor number is in the range (0.01–0.9) Tacr 3D with Tacr 3D given by Grants and Gerbeth. The computations were performed for cylindrical containers of aspect ratios (diameter/ height) R equal to 0.5, 1, and 2. The numerical simulations are compared with the predictions of an analytical model, valid for small Ekman numbers E extending a former work by Ungarish. The first phase of the motion from rest is an initial adjustment: the inviscid fluid begins to rotate due to the externally forced azimuthal acceleration, and concomitantly a meridional velocity field is induced by the unbalanced centrifugal effects; this occurs during, approximately, the first revolution about the axis. Subsequently, the spin-up flow is dominated by an axially independent swirl in the core (which can be regarded as a geostrophic mode) and Bödewadt (Ekman) layers on the top-bottom boundaries. This is accompanied by inertial oscillations. Both the development of the swirl motion and the decay of the inertial mode occur on the spin-up time scale predicted by the asymptotic model. The investigation also points out the important role of the aspect-ratio parameter in the analysis of the magnetohydrodynamics-driven spin-up. The efficiency of the driving decays strongly for R>0.6 and becomes close to zero at R ≈3.3. The numerical results confirm the analytical inference that the thickness of the sidewall layer for the angular velocity adjustment is E¼ ∕ √R, and when this parameter is larger than 0.3 the sidewall influence gains dominance over the Ekman-layer effects. The frequency of the inertial oscillations increases with R. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
50. Modeling and analysis of a magnetically levitated synchronous permanent magnet planar motor.
- Author
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Kou, Baoquan, Zhang, Lu, Li, Liyi, and Zhang, Hailin
- Subjects
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FINITE element method , *MAGNETICS , *NUMERICAL analysis , *MAGNETIC fields , *ELECTROMAGNETIC fields - Abstract
In this paper, a new magnetically levitated synchronous permanent magnet planar motor (MLSPMPM) driven by composite-current is proposed, of which the mover is made of a copper coil array and the stator are magnets and magnetic conductor. The coil pitch τt and permanent magnet pole pitch τp satisfy the following relationship 3nτt = (3n ± 1)τp. Firstly, an analytical model of the planar motor is established, flux density distribution of the two-dimensional magnet array is obtained by solving the equations of the scalar magnetic potential. Secondly, the expressions of the electromagnetic forces induced by magnetic field and composite current are derived. To verify the analytical model and the electromagnetic forces, finite element method (FEM) is used for calculating the flux density and electromagnetic forces of the MLSPMPM. And the results from FEM are in good agreement with the results from the analytical equations. This indicates that the analytical model is reasonable. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
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