Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence
Energy Technology Data Exchange (ETDEWEB)
Bodo, G.; Rossi, P. [INAF/Osservatorio Astrofisico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese (Italy); Cattaneo, F. [Department of Astronomy and Astrophysics, The University of Chicago, 5640 S. Ellis Avenue, Chicago IL 60637 (United States); Mignone, A., E-mail: bodo@oato.inaf.it [Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino (Italy)
2017-07-10
We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by magneto-rotational turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge—the winding gauge—that provides a natural interpretation in terms of the average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and the helicity flux for several realizations of dynamo action. We find in these cases that the system as a whole does not break reflectional symmetry and that the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.
Current drive by neutral beams, rotating magnetic fields and helicity injection in compact toroids
International Nuclear Information System (INIS)
Farengo, R.; Arista, N.R.; Lifschitz, A.F.; Clemente, R.A.
2003-01-01
The use of neutral beams (NB) for current drive and heating in spheromaks, the relaxed states of flux core spheromaks (FCS) sustained by helicity injection and the effect of ion dynamics on rotating magnetic field (RMF) current drive in spherical tokamaks (ST) are studied. (author)
International Nuclear Information System (INIS)
Bellandi, Jose; Guzzo, Marcelo M.; Hollanda, Pedro C. de
1997-01-01
Assuming that neutrino magnetic moment is not null, we study the evolution of neutrinos submitted to rotating magnetic fields, and the way the evolution can convert 'left' helicity neutrinos (actives) into 'right' neutrinos (sterile). We use the fact that the 'right' neutrinos do not interact with the detectors to obtain information on the neutrino magnetic field magnitude. For solving the neutrino evolution equation, the expansion method was combined with steady phase approximation used for the expansion integrals solution. The possibility of 'left' conversion into 'right' neutrinos has been calculated as function of the evolution matrix parameters (neutrino magnetic moment, electron density of the medium, the magnetic field magnitude and phase, etc). We made an attempt to obtain fitting of the parameter conditions in order to occur resonances in the neutrino transition probability, and therefore to obtain information on the limits for neutrino magnetic moments from the controlled beam helicity
The Use of Faraday Rotation Sign Maps as a Diagnostic for Helical Jet Magnetic Fields
International Nuclear Information System (INIS)
Reichstein, Andrea; Gabuzda, Denise
2012-01-01
We present maps of the sign of the Faraday Rotation measure obtained from multi-frequency radio observations made with the Very Long Baseline Array (VLBA). The Active Galactic Nuclei (AGN) considered have B-field structures with a central 'spine' of B-field orthogonal to the jet and/or a longitudinal B-field near one or both edges of the jet. This structure can plausibly be interpreted as being caused by a helical/toroidal jet magnetic field. Faraday Rotation is a rotation of the plane of polarization that occurs when the polarized radiation passes through a magnetized plasma. The sign of the RM is determined by the direction of the line-of-sight B-field in the region causing the Faraday Rotation, and an ordered toroidal or helical magnetic field associated with an AGN jet will thus produce a distinctive bilateral distribution of the RMs across the jet. We present and discuss RM-sign maps and their possible interpretation regarding the magnetic field geometries for several sources.
Numerical Study of Flow Motion and Patterns Driven by a Rotating Permanent Helical Magnetic Field
Yang, Wenzhi; Wang, Xiaodong; Wang, Bo; Baltaretu, Florin; Etay, Jacqueline; Fautrelle, Yves
2016-10-01
Liquid metal magnetohydrodynamic flow driven by a rotating permanent helical magnetic field in a cylindrical container is numerically studied. A three-dimensional numerical simulation provides insight into the visualization of the physical fields, including the magnetic field, the Lorentz force density, and the flow structures, especially the flow patterns in the meridional plane. Because the screen parameter is sufficiently small, the model is decoupled into electromagnetic and hydrodynamic components. Two flow patterns in the meridional plane, i.e., the global flow and the secondary flow, are discovered and the impact of several system parameters on their transition is investigated. Finally, a verifying model is used for comparison with the previous experiment.
Directory of Open Access Journals (Sweden)
Jongyul Kim
2017-05-01
Full Text Available We propose a position control method for a helical magnetic robot (HMR that uses the rotating frequency of the external rotating magnetic field (ERMF to minimize the position fluctuation of the HMR caused by pulsatile flow in human blood vessels. We prototyped the HMR and conducted several experiments in pseudo blood vessel environments with a peristaltic pump. We experimentally obtained the relation between the flow rate and the rotating frequency of the ERMF required to make the HMR stationary in a given pulsatile flow. Then we approximated the pulsatile flow by Fourier series and applied the required ERMF rotating frequency to the HMR in real time. Our proposed position control method drastically reduced the position fluctuation of the HMR under pulsatile flow.
Current drive by neutral beams, rotating magnetic fields and helicity injection in compact toroids
International Nuclear Information System (INIS)
Farengo, R.
2002-01-01
A Monte-Carlo code is used to study neutral beam current drive in Spheromaks. The exact particle trajectories are followed in the self-consistent equilibria calculated including the beam current. Reducing Z(eff) does not increase the current drive efficiency because the reduction of the stopping cross section is compensated by an increase in the electron canceling current. Significant changes in the safety factor profile can be produced with relatively low beam currents. Minimum dissipation states of a flux core spheromak sustained by helicity injection are presented. Helicity balance is used as a constraint and the resistivity is considered to be non-uniform. Two types of relaxed states are found; one has a central core of open flux surrounded by a toroidal region of closed flux surfaces and the other has the open flux wrapped around the closed flux surfaces. Non-uniform resistivity effects can be very important due to the changes they produce in the safety factor profile. A hybrid, fluid electrons particle ions, code is employed to study ion dynamics in FRCs sustained by rotating magnetic fields. (author)
Dynamic Chiral Magnetic Effect and Faraday Rotation in Macroscopically Disordered Helical Metals.
Ma, J; Pesin, D A
2017-03-10
We develop an effective medium theory for electromagnetic wave propagation through gapless nonuniform systems with a dynamic chiral magnetic effect. The theory allows us to calculate macroscopic-disorder-induced corrections to the values of optical, as well as chiral magnetic conductivities. In particular, we show that spatial fluctuations of the optical conductivity induce corrections to the effective value of the chiral magnetic conductivity. The absolute value of the effect varies strongly depending on the system parameters, but yields the leading frequency dependence of the polarization rotation and circular dichroism signals. Experimentally, these corrections can be observed as features in the Faraday rotation angle near frequencies that correspond to the bulk plasmon resonances of a material. Such features are not expected to be present in single-crystal samples.
Rotation influence on the plasma helical instability
International Nuclear Information System (INIS)
Gutkin, T.I.; Tsypin, V.S.; Boleslavskaya, G.I.
1980-01-01
The influence of the rotation on helical instability of a plasma with the fixed boundaries (HIFB) is investigated taking into account the compressibility. A case of infinitely long cylinder with distributed current is considered. Cases when a rotating plasma is confined by current magnetic field are analytically considered. It is shown that in the case of the fixed boundary taking into account the compressibility in the HIFB increment increases and the picture of the rotation influence on HIFB considerably changes. Besides, it is shown that in the case of high plasma pressures HIFB can stabilize as a result of the rotation
Helical spin rotators and snakes for RHIC
International Nuclear Information System (INIS)
Ptitsin, V.I.; Shatunov, Yu.M.; Peggs, S.
1995-01-01
The RHIC collider, now under construction at BNL, will have the possibility of polarized proton-proton collisions up to a beam energy of 250 Gev. Polarized proton beams of such high energy can be only obtained with the use of siberian snakes, a special kind of spin rotator that rotates the particle spin by 180 degree around an axis lying in the horizontal plane. Siberian snakes help to preserve the beam polarization while numerous spin depolarizing resonances are crossed, during acceleration. In order to collide longitudinally polarized beams, it is also planned to install spin rotators around two interaction regions. This paper discusses snake and spin rotator designs based on sequences of four helical magnets. The schemes that were chosen to be applied at RHIC are presented
SUPERCONDUCTING HELICAL SNAKE MAGNETS: CONSTRUCTION AND MEASUREMENTS
International Nuclear Information System (INIS)
Mackay, W.W.; Anerella, M.; Courant, E.
1999-01-01
In order to collide polarized protons, the RHIC project will have two snakes in each ring and four rotators around each of two interaction regions. Two snakes on opposite sides of each ring can minimize depolarization during acceleration by keeping the spin tune at a half. Since the spin direction is normally along the vertical direction in a flat ring, spin rotators must be used around an interaction point to have longitudinal polarization in a collider experiment. Each snake or rotator will be composed of four helical dipoles to provide the required rotation of spin with minimal transverse orbit excursions in a compact length of 10m. The basic helical dipole is a superconducting magnet producing a transverse dipole field which is twisted about the magnet axis through 360 o in a length of 2.4 m. The design and construction of the magnets is described in this paper
Energy Technology Data Exchange (ETDEWEB)
Li, Xing; Morgan, Huw; Leonard, Drew; Jeska, Lauren, E-mail: xxl@aber.ac.uk [Sefydliad Mathemateg a Ffiseg, Prifysgol Aberystwyth, Ceredigion, Cymru SY23 3BZ (United Kingdom)
2012-06-20
During 2011 September 24, as observed by the Atmospheric Imaging Assembly instrument of the Solar Dynamic Observatory and ground-based H{alpha} telescopes, a prominence and associated cavity appeared above the southwest limb. On 2011 September 25 8:00 UT, material flows upward from the prominence core along a narrow loop-like structure, accompanied by a rise ({>=}50,000 km) of the prominence core and the loop. As the loop fades by 10:00, small blobs and streaks of varying brightness rotate around the top part of the prominence and cavity, mimicking a cyclone. The most intense and coherent rotation lasts for over three hours, with emission in both hot ({approx}1 MK) and cold (hydrogen and helium) lines. We suggest that the cyclonic appearance and overall evolution of the structure can be interpreted in terms of the expansion of helical structures into the cavity, and the movement of plasma along helical structures which appears as a rotation when viewed along the helix axis. The coordinated movement of material between prominence and cavity suggests that they are structurally linked. Complexity is great due to the combined effect of these actions and the line-of-sight integration through the structure which contains tangled fields.
Theoretical aspects of magnetic helicity
International Nuclear Information System (INIS)
Hammer, J.H.
1985-01-01
The magnetic helicity, usually defined as K=integralA.Bdv, where A is the vector potential and B the magnetic field, measures the topological linkage of magnetic fluxes. Helicity manifests itself in the twistedness and knottedness of flux tubes. Its significance is that it is an ideal MHD invariant. While the helicity formalism has proven very useful in understanding reversed field pinch and spheromak behavior, some problems exist in applying the method consistently for complex (e.g., toroidal) conductor geometries or in situations where magnetic flux penetrates conducting walls. Recent work has attempted to generalize K to allow for all possible geometries
Magnetic Helical Micro- and Nanorobots: Toward Their Biomedical Applications
Directory of Open Access Journals (Sweden)
Famin Qiu
2015-03-01
Full Text Available Magnetic helical micro- and nanorobots can perform 3D navigation in various liquids with a sub-micrometer precision under low-strength rotating magnetic fields (<10 mT. Since magnetic fields with low strengths are harmless to cells and tissues, magnetic helical micro/nanorobots are promising tools for biomedical applications, such as minimally invasive surgery, cell manipulation and analysis, and targeted therapy. This review provides general information on magnetic helical micro/nanorobots, including their fabrication, motion control, and further functionalization for biomedical applications.
Superconducting Helical Snake Magnet for the AGS
Willen, Erich; Escallier, John; Ganetis, George; Ghosh, Arup; Gupta, Ramesh C; Harrison, Michael; Jain, Animesh K; Luccio, Alfredo U; MacKay, William W; Marone, Andrew; Muratore, Joseph F; Okamura, Masahiro; Plate, Stephen R; Roser, Thomas; Tsoupas, Nicholaos; Wanderer, Peter
2005-01-01
A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This "partial Snake" magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that t...
Parameterization and measurements of helical magnetic fields
International Nuclear Information System (INIS)
Fischer, W.; Okamura, M.
1997-01-01
Magnetic fields with helical symmetry can be parameterized using multipole coefficients (a n , b n ). We present a parameterization that gives the familiar multipole coefficients (a n , b n ) for straight magnets when the helical wavelength tends to infinity. To measure helical fields all methods used for straight magnets can be employed. We show how to convert the results of those measurements to obtain the desired helical multipole coefficients (a n , b n )
Magnetic helicity and active filament configuration
Romano, P.; Zuccarello, F.; Poedts, S.; Soenen, A.; Zuccarello, F. P.
2009-11-01
Context: The role of magnetic helicity in active filament formation and destabilization is still under debate. Aims: Although active filaments usually show a sigmoid shape and a twisted configuration before and during their eruption, it is unclear which mechanism leads to these topologies. In order to provide an observational contribution to clarify these issues, we describe a filament evolution whose characteristics seem to be directly linked to the magnetic helicity transport in corona. Methods: We applied different methods to determine the helicity sign and the chirality of the filament magnetic field. We also computed the magnetic helicity transport rate at the filament footpoints. Results: All the observational signatures provided information on the positive helicity and sinistral chirality of the flux rope containing the filament material: its forward S shape, the orientation of its barbs, the bright and dark threads at 195 Å. Moreover, the magnetic helicity transport rate at the filament footpoints showed a clear accumulation of positive helicity. Conclusions: The study of this event showed a correspondence between several signatures of the sinistral chirality of the filament and several evidences of the positive magnetic helicity of the filament magnetic field. We also found that the magnetic helicity transported along the filament footpoints showed an increase just before the change of the filament shape observed in Hα images. We argued that the photospheric regions where the filament was rooted might be the preferential ways where the magnetic helicity was injected along the filament itself and where the conditions to trigger the eruption were yielded.
Godbillon Vey Helicity and Magnetic Helicity in Magnetohydrodynamics
Webb, G. M.; Hu, Q.; Anco, S.; Zank, G. P.
2017-12-01
The Godbillon-Vey invariant arises in homology theory, and algebraic topology, where conditions for a layered family of 2D surfaces forms a 3D manifold were elucidated. The magnetic Godbillon-Vey helicity invariant in magnetohydrodynamics (MHD) is a helicity invariant that occurs for flows, in which the magnetic helicity density hm= A\\cdotB=0 where A is the magnetic vector potential and B is the magnetic induction. Our purpose is to elucidate the evolution of the magnetic Godbillon-Vey field η =A×B/|A|2 and the Godbillon-Vey helicity hgv}= η \\cdot∇ × η in general MHD flows in which the magnetic helicity hm≠q 0. It is shown that hm acts as a source term in the Godbillon-Vey helicity transport equation, in which hm is coupled to hgv via the shear tensor of the background flow. The transport equation for hgv depends on the electric field potential ψ , which is related to the gauge for A, which takes its simplest form for the advected A gauge in which ψ =A\\cdot u where u is the fluid velocity.
Energy Technology Data Exchange (ETDEWEB)
Nishimura, Seiya, E-mail: n-seiya@kobe-kosen.ac.jp [Kobe City College of Technology, Kobe, Hyogo 651-2194 (Japan)
2015-02-15
Magnetic islands are externally produced by resonant magnetic perturbations (RMPs) in toroidal plasmas. Spontaneous annihilation of RMP-induced magnetic islands called self-healing has been observed in helical systems. A possible mechanism of the self-healing is shielding of RMP penetration by helical ripple-induced neoclassical flows, which give rise to neoclassical viscous torques. In this study, effective helical ripple rates in multi-helicity helical systems are revisited, and a multi-helicity effect on the self-healing is investigated, based on a theoretical model of rotating magnetic islands. It is confirmed that effective helical ripple rates are sensitive to magnetic axis positions. It is newly found that self-healing thresholds also strongly depend on magnetic axis positions, which is due to dependence of neoclassical viscous torques on effective helical ripple rates.
Magnetic islands created by resonant helical windings
International Nuclear Information System (INIS)
Fernandes, A.S.; Heller, M.V.; Caldas, I.L.
1986-01-01
The triggering of disruptive instabilities by resonant helical windings in large aspect-ratio tokamaks is associated to destruction of magnetic surfaces. The Chirikov condition is applied to estimate analytically the helical winding current thresholds for ergodization of the magnetic field lines. (Autor) [pt
Helical modes generate antimagnetic rotational spectra in nuclei
Malik, Sham S.
2018-03-01
A systematic analysis of the antimagnetic rotation band using r -helicity formalism is carried out for the first time. The observed octupole correlation in a nucleus is likely to play a role in establishing the antimagnetic spectrum. Such octupole correlations are explained within the helical orbits. In a rotating field, two identical fermions (generally protons) with paired spins generate these helical orbits in such a way that its positive (i.e., up) spin along the axis of quantization refers to one helicity (right-handedness) while negative (down) spin along the same quantization-axis decides another helicity (left-handedness). Since the helicity remains invariant under rotation, therefore, the quantum state of a fermion is represented by definite angular momentum and helicity. These helicity represented states support a pear-shaped structure of a rotating system having z axis as the symmetry axis. A combined operation of parity, time-reversal, and signature symmetries ensures an absence of one of the signature partner band from the observed antimagnetic spectrum. This formalism has also been tested for the recently observed negative parity Δ I =2 antimagnetic spectrum in odd-A 101Pd nucleus and explains nicely its energy spectrum as well as the B (E 2 ) values. Further, this formalism is found to be fully consistent with twin-shears mechanism popularly known for such type of rotational bands. It also provides significant clue for extending these experiments in various mass regions spread over the nuclear chart.
Park, Kiwan
2017-12-01
In our conventional understanding, large-scale magnetic fields are thought to originate from an inverse cascade in the presence of magnetic helicity, differential rotation or a magneto-rotational instability. However, as recent simulations have given strong indications that an inverse cascade (transfer) may occur even in the absence of magnetic helicity, the physical origin of this inverse cascade is still not fully understood. We here present two simulations of freely decaying helical and non-helical magnetohydrodynamic (MHD) turbulence. We verified the inverse transfer of helical and non-helical magnetic fields in both cases, but we found the underlying physical principles to be fundamentally different. In the former case, the helical magnetic component leads to an inverse cascade of magnetic energy. We derived a semi-analytic formula for the evolution of large-scale magnetic field using α coefficient and compared it with the simulation data. But in the latter case, the α effect, including other conventional dynamo theories, is not suitable to describe the inverse transfer of non-helical magnetic energy. To obtain a better understanding of the physics at work here, we introduced a 'field structure model' based on the magnetic induction equation in the presence of inhomogeneities. This model illustrates how the curl of the electromotive force leads to the build up of a large-scale magnetic field without the requirement of magnetic helicity. And we applied a quasi-normal approximation to the inverse transfer of magnetic energy.
On the helicity of open magnetic fields
International Nuclear Information System (INIS)
Prior, C.; Yeates, A. R.
2014-01-01
We reconsider the topological interpretation of magnetic helicity for magnetic fields in open domains, and relate this to the relative helicity. Specifically, our domains stretch between two parallel planes, and each of these ends may be magnetically open. It is demonstrated that, while the magnetic helicity is gauge-dependent, its value in any gauge may be physically interpreted as the average winding number among all pairs of field lines with respect to some orthonormal frame field. In fact, the choice of gauge is equivalent to the choice of reference field in the relative helicity, meaning that the magnetic helicity is no less physically meaningful. We prove that a particular gauge always measures the winding with respect to a fixed frame, and propose that this is normally the best choice. For periodic fields, this choice is equivalent to measuring relative helicity with respect to a potential reference field. However, for aperiodic fields, we show that the potential field can be twisted. We prove by construction that there always exists a possible untwisted reference field.
Diffusion in a tokamak with helical magnetic cells
International Nuclear Information System (INIS)
Wakatani, Masahiro
1975-05-01
In a tokamak with helical magnetic cells produced by a resonant helical magnetic field, diffusion in the collisional regime is studied. The diffusion coefficient is greatly enhanced near the resonant surface even for a weak helical magnetic field. A theoretical model for disruptive instabilities based on the enhanced transport due to helical magnetic cells is discussed. This may explain experiments of the tokamak with resonant helical fields qualitatively. (author)
Helicity--vorticity turbulent pumping of magnetic fields in the solar dynamo
Pipin, V. V.
2012-01-01
The interaction of helical convective motions and differential rotation in the solar convection zone results in turbulent drift of a large-scale magnetic field. We discuss the pumping mechanism and its impact on the solar dynamo.
New formulae for magnetic relative helicity and field line helicity
Aly, Jean-Jacques
2018-01-01
We consider a magnetic field {B} occupying the simply connected domain D and having all its field lines tied to the boundary S of D. We assume here that {B} has a simple topology, i.e., the mapping {M} from positive to negative polarity areas of S associating to each other the two footpoints of any magnetic line, is continuous. We first present new formulae for the helicity H of {B} relative to a reference field {{B}}r having the same normal component {B}n on S, and for its field line helicity h relative to a reference vector potential {{C}}r of {{B}}r. These formulae make immediately apparent the well known invariance of these quantities under all the ideal MHD deformations that preserve the positions of the footpoints on S. They express indeed h and H either in terms of {M} and {B}n, or in terms of the values on S of a pair of Euler potentials of {B}. We next show that, for a specific choice of {{C}}r, the field line helicity h of {B} fully characterizes the magnetic mapping {M} and then the topology of the lines. Finally, we give a formula that describes the rate of change of h in a situation where the plasma moves on the perfectly conducting boundary S without changing {B}n and/or non-ideal processes, described by an unspecified term {N} in Ohm’s law, are at work in some parts of D.
A rotating helical sealing joint capable of partially melting
International Nuclear Information System (INIS)
Martin, Jean; Ollier, J.-L.; Petit, Paul.
1973-01-01
A coagulated rotating helical joint providing gas and liquid tightness along a rotating shaft, comprising: a metal sleeve connected to the wall through which passes the rotating sleeve, an intermediate sleeve made of a fusible material, inert with respect to the fluid to be sealingly retained, and finally the rotating shaft provided with an engraved helical thread in register with the intermediate sleeve. Means are provided for regulating the intermediate sleeve temperature so that a thin melted film is formed on said intermediate sleeve when in contact with the rotating threaded shaft. This can be applied in the nuclear industry, including cases when the intermediate sleeve is constituted by the fluid itself, then in the solid state [fr
Helical magnetized wiggler for synchrotron radiation laser
International Nuclear Information System (INIS)
Wang Mei; Park, S.Y.; Hirshfield, J.L.
1999-01-01
A helical magnetized iron wiggler has been built for a novel infrared synchrotron radiation laser (SRL) experiment. The wiggler consists of four periods of helical iron structure immersed in a solenoid field. This wiggler is to impart transverse velocity to a prebunched 6 MeV electron beam, and thus to obtain a desired high orbit pitch ratio for the SRL. Field tapering at beam entrance is considered and tested on a similar wiggler. Analytic and simulated characteristics of wigglers of this type are discussed and the performance of the fabricated wigglers is demonstrated experimentally. A 4.7 kG peak field was measured for a 6.4 mm air gap and a 5.4 cm wiggler period at a 20 kG solenoid field. The measured helical fields compare favorably with the analytical solution. This type of helical iron wigglers has the potential to be scaled to small periods with strong field amplitude
Helical magnetized wiggler for synchrotron radiation laser
Wang Mei; Hirshfield, J L
1999-01-01
A helical magnetized iron wiggler has been built for a novel infrared synchrotron radiation laser (SRL) experiment. The wiggler consists of four periods of helical iron structure immersed in a solenoid field. This wiggler is to impart transverse velocity to a prebunched 6 MeV electron beam, and thus to obtain a desired high orbit pitch ratio for the SRL. Field tapering at beam entrance is considered and tested on a similar wiggler. Analytic and simulated characteristics of wigglers of this type are discussed and the performance of the fabricated wigglers is demonstrated experimentally. A 4.7 kG peak field was measured for a 6.4 mm air gap and a 5.4 cm wiggler period at a 20 kG solenoid field. The measured helical fields compare favorably with the analytical solution. This type of helical iron wigglers has the potential to be scaled to small periods with strong field amplitude.
FITTING HELICAL SNAKE AND ROTATOR FIELD STRENGTH MEASUREMENTS IN RHIC
International Nuclear Information System (INIS)
RANJBAR, V.; LUCCIO, A.U.; MACKAY, W.W.; TSOUPAS, N.
2001-01-01
We examined recent multi-pole measurements for the helical snakes and rotators in RHIC to generate a full field map. Since multi-pole measurements yield real field values for B, field components we developed a unique technique to evaluate the full fields using a traditional finite element analysis software [1]. From these measurements we employed SNIG [2] to generate orbit and Spin plots. From orbit values we generated a transfer matrix for the first snake
Hybrid helical magnetic microrobots obtained by 3D template-assisted electrodeposition.
Zeeshan, Muhammad A; Grisch, Roman; Pellicer, Eva; Sivaraman, Kartik M; Peyer, Kathrin E; Sort, Jordi; Özkale, Berna; Sakar, Mahmut S; Nelson, Bradley J; Pané, Salvador
2014-04-09
Hybrid helical magnetic microrobots are achieved by sequential electrodeposition of a CoNi alloy and PPy inside a photoresist template patterned by 3D laser lithography. A controlled actuation of the microrobots by a rotating magnetic field is demonstrated in a fluidic environment. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Determining How Magnetic Helicity Injection Really Works
International Nuclear Information System (INIS)
Paul M Bellan
2001-01-01
OAK-B135 The goal of the Caltech program is to determine how helicity injection works by investigating the actual dynamics and topological evolution associated with magnetic relaxation. A new coaxial helicity injection source has been constructed and brought into operation. The key feature of this source is that it has maximum geometric simplicity. Besides being important for fusion research, this work also has astrophysical implications. Photos obtained using high-speed cameras show a clear sequence of events in the formation process. In particular, they show initial merging/reconnection processes, jet-like expansion, kinking, and separation of the plasma from the source. Various diagnostics have been developed, including laser induced fluorescence and soft x-ray detection using high speed diodes. Gas valves have been improved and a patent disclosure relating to puffed gas valves has been filed. Presentations on this work have been given in the form of invited talks at several university physics departments that were previously unfamiliar with laboratory plasma experiments
Magnetic helicity balance in the Sustained Spheromak Plasma Experiment
International Nuclear Information System (INIS)
Stallard, B.W.; Hooper, E.B.; Woodruff, S.; Bulmer, R.H.; Hill, D.N.; McLean, H.S.; Wood, R.D.
2003-01-01
The magnetic helicity balance between the helicity input injected by a magnetized coaxial gun, the rate-of-change in plasma helicity content, and helicity dissipation in electrode sheaths and Ohmic losses have been examined in the Sustained Spheromak Plasma Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)]. Helicity is treated as a flux function in the mean-field approximation, allowing separation of helicity drive and losses between closed and open field volumes. For nearly sustained spheromak plasmas with low fluctuations, helicity balance analysis implies a decreasing transport of helicity from the gun input into the spheromak core at higher spheromak electron temperature. Long pulse discharges with continuously increasing helicity and larger fluctuations show higher helicity coupling from the edge to the spheromak core. The magnitude of the sheath voltage drop, inferred from cathode heating and a current threshold dependence of the gun voltage, shows that sheath losses are important and reduce the helicity injection efficiency in SSPX
Scale Dependence of Magnetic Helicity in the Solar Wind
Brandenburg, Axel; Subramanian, Kandaswamy; Balogh, Andre; Goldstein, Melvyn L.
2011-01-01
We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k approximately equal to 2AU(sup -1) (or frequency nu approximately equal to 2 microHz) at distances below 2.8AU and at k approximately equal to 30AU(sup -1) (or nu approximately equal to 25 microHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10(sup 45) Mx(sup 2) cycle(sup -1) at large scales and to a three times lower value at smaller scales.
Global-Scale Consequences of Magnetic-Helicity Injection and Condensation on the Sun
Mackay, Duncan H.; DeVore, C. Richard; Antiochos, Spiro K.
2013-01-01
In the recent paper of Antiochos, a new concept for the injection of magnetic helicity into the solar corona by small-scale convective motions and its condensation onto polarity inversion lines (PILs) has been developed. We investigate this concept through global simulations of the Sun's photospheric and coronal magnetic fields and compare the results with the hemispheric pattern of solar filaments. Assuming that the vorticity of the cells is predominately counter-clockwise/clockwise in the northern/southern hemisphere, the convective motions inject negative/positive helicity into each hemisphere. The simulations show that: (i) On a north-south orientated PIL, both differential rotation and convective motions inject the same sign of helicity which matches that required to reproduce the hemispheric pattern of filaments. (ii) On a high latitude east-west orientated polar crown or sub-polar crown PIL, the vorticity of the cells has to be approximately 2-3 times greater than the local differential rotation gradient in order to overcome the incorrect sign of helicity injection from differential rotation. (iii) In the declining phase of the cycle, as a bipole interacts with the polar field, in some cases helicity condensation can reverse the effect of differential rotation along the East-West lead arm, but not in all cases. The results show that this newly developed concept of magnetic helicity injection and condensation is a viable method to explain the hemispheric pattern of filaments in conjunction with the mechanisms used in Yeates et al. (2008). Future observational studies should focus on determining the vorticity component within convective motions to determine, both its magnitude and latitudinal variation relative to the differential rotation gradient on the Sun.
Energy and helicity of magnetic torus knots and braids
Oberti, Chiara; Ricca, Renzo L.
2018-02-01
By considering steady magnetic fields in the shape of torus knots and unknots in ideal magnetohydrodynamics, we compute some fundamental geometric and physical properties to provide estimates for magnetic energy and helicity. By making use of an appropriate parametrization, we show that knots with dominant toroidal coils that are a good model for solar coronal loops have negligible total torsion contribution to magnetic helicity while writhing number provides a good proxy. Hence, by the algebraic definition of writhe based on crossing numbers, we show that the estimated values of writhe based on image analysis provide reliable information for the exact values of helicity. We also show that magnetic energy is linearly related to helicity, and the effect of the confinement of magnetic field can be expressed in terms of geometric information. These results can find useful application in solar and plasma physics, where braided structures are often present.
Helical Siberian snakes using dipole magnets
International Nuclear Information System (INIS)
Wienands, U.
1990-09-01
A family of multi-twist transverse-field spin rotators using discrete bending magnets is described that can be used as Siberian snakes. By varying the number of twists, snakes with quite small excursions can be constructed at only a small penalty in the overall field integral. Examples for a 1/4-twist snake and a 3-twist snake are presented, the first suitable for a very high energy machine and the second for use in the proposed TRIUMF Kaon Factory. (Author) (3 refs.)
International Nuclear Information System (INIS)
Fuchs, G.; Steffen, B.; Blenski, T.; Grosman, A.; Samain, A.
1985-05-01
The influence on the structure of the magnetic field of a tokamak produced by small helical currents flowing near the plasma in TORE SUPRA was investigated numerically by drawing Poincare plots. The current in the helical conductors, the pitch of the windings, the rotational transform and the plasma pressure have been varied. The topology of the magnetic field line structure is discussed in some detail and simple examples are given for illustration. (orig.)
MAGNETIC HELICITY FLUX IN THE PRESENCE OF SHEAR
International Nuclear Information System (INIS)
Hubbard, Alexander; Brandenburg, Axel
2011-01-01
Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac and Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.
Magnetic Helicity Flux in the Presence of Shear
Hubbard, Alexander; Brandenburg, Axel
2011-01-01
Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac & Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.
SIGNATURES OF RELATIVISTIC HELICAL MOTION IN THE ROTATION MEASURES OF ACTIVE GALACTIC NUCLEUS JETS
Energy Technology Data Exchange (ETDEWEB)
Broderick, Avery E [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Loeb, Abraham [Institute for Theory and Computation, Harvard University, Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2009-10-01
Polarization has proven to be an invaluable tool for probing magnetic fields in relativistic jets. Maps of the intrinsic polarization vectors have provided the best evidence to date for uniform, toroidally dominated magnetic fields within jets. More recently, maps of the rotation measure (RM) in jets have for the first time probed the field geometry of the cool, moderately relativistic surrounding material. In most cases, clear signatures of the toroidal magnetic field are detected, corresponding to gradients in RM profiles transverse to the jet. However, in many objects, these profiles also display marked asymmetries that are difficult to explain in simple helical jet models. Furthermore, in some cases, the RM profiles are strongly frequency and/or time dependent. Here we show that these features may be naturally accounted for by including relativistic helical motion in the jet model. In particular, we are able to reproduce bent RM profiles observed in a variety of jets, frequency-dependent RM profile morphologies, and even the time dependence of the RM profiles of knots in 3C 273. Finally, we predict that some sources may show reversals in their RM profiles at sufficiently high frequencies, depending upon the ratio of the components of jet sheath velocity transverse and parallel to the jet. Thus, multi-frequency RM maps promise a novel way in which to probe the velocity structure of relativistic outflows.
Magnetic configuration dependence of the shafranov shift in the Large Helical Device
Energy Technology Data Exchange (ETDEWEB)
Kobuchi, T; Ida, K; Yamada, H; Yokoyama, M; Watanabe, K Y; Sakakibara, S; Yoshinuma, M [National Institute for Fusion Science, 322-6 Oroshi-Cho, Toki-City, 509-5292 (Japan)
2006-06-15
The dependence of the Shafranov shift on magnetic field configuration, toroidicity and central rotational transform {iota}(0) in neutral beam heated plasma has been experimentally investigated in the Large Helical Device. The toroidicity of the plasma is controlled by the quadrupole field, while the central {iota}(0) is controlled by changing the distance of the current centre of the helical coil to the plasma. It is experimentally confirmed that both the lower toroidicity and the higher {iota}(0) contribute to the reduction of the Shafranov shift as predicted by the three-dimensional equilibrium code, VMEC.
Hamiltonian theory of vacuum helical torus lines of magnetic force
International Nuclear Information System (INIS)
Gnudi, Giovanni; Hatori, Tadatsugu
1994-01-01
For making plasma into equilibrium state, the lines of magnetic force must have magnetic surfaces. However in a helical system, space is divided into the region having magnetic surface structure and the region that does not have it. Accordingly, it is an important basic research for the plasma confinement in a helical system to examine where is the boundary of both regions and how is the large area structure of the lines of magnetic force in the boundary region. The lines of magnetic force can be treated as a Hamilton mechanics system, and it has been proved that the Hamiltonian for the lines of magnetic force can be expressed by a set of canonical variables and the function of time. In this research, the Hamiltonian that describes the lines of magnetic force of helical system torus coordination in vacuum was successfully determined concretely. Next, the development of new linear symplectic integration method was carried out. The important supports for the theory of determining Hamiltonian are Lie transformation and paraxial expansion. The procedure is explained. In Appendix, Lie transformation, Hamiltonian for the lines of magnetic force, magnetic potential, Taylor expansion of the potential, cylindrical limit approximation, helical toroidal potential and integrable model are described. (K.I.)
Differential rotation in magnetic stars
International Nuclear Information System (INIS)
Moss, D.
1981-01-01
The possibility that large-scale magnetic fields in stars are the product of a contemporary dynamo situated in the convective stellar core, rather than being a fossil from an earlier stage in the history of the star, is investigated. It is demonstrated that then the envelope will almost inevitably be in a state of differential rotation. Some simple models are constructed to illustrate the magnitude of the effects on the structure of the envelope and magnetic field. It is found that, for models which are relatively rapidly rotating, a modest differential rotation at the surface of the core may increase considerably the ratio of internal to surface field, but only give rise to a small surface differential rotation. (author)
Surface-Chemistry-Mediated Control of Individual Magnetic Helical Microswimmers in a Swarm.
Wang, Xiaopu; Hu, Chengzhi; Schurz, Lukas; De Marco, Carmela; Chen, Xiangzhong; Pané, Salvador; Nelson, Bradley J
2018-05-31
Magnetic helical microswimmers, also known as artificial bacterial flagella (ABFs), perform 3D navigation in various liquids under low-strength rotating magnetic fields by converting rotational motion to translational motion. ABFs have been widely studied as carriers for targeted delivery and release of drugs and cells. For in vivo/ in vitro therapeutic applications, control over individual groups of swimmers within a swarm is necessary for several biomedical applications such as drug delivery or small-scale surgery. In this work, we present the selective control of individual swimmers in a swarm of geometrically and magnetically identical ABFs by modifying their surface chemistry. We confirm experimentally and analytically that the forward/rotational velocity ratio of ABFs is independent of their surface coatings when the swimmers are operated below their step-out frequency (the frequency requiring the entire available magnetic torque to maintain synchronous rotation). We also show that ABFs with hydrophobic surfaces exhibit larger step-out frequencies and higher maximum forward velocities compared to their hydrophilic counterparts. Thus, selective control of a group of swimmers within a swarm of ABFs can be achieved by operating the selected ABFs at a frequency that is below their step-out frequencies but higher than the step-out frequencies of unselected ABFs. The feasibility of this method is investigated in water and in biologically relevant solutions. Selective control is also demonstrated inside a Y-shaped microfluidic channel. Our results present a systematic approach for realizing selective control within a swarm of magnetic helical microswimmers.
Chirality of Intermediate Filaments and Magnetic Helicity of Active Regions
Lim, Eun-Kyung; Chae, J.
2009-05-01
Filaments that form either between or around active regions (ARs) are called intermediate filaments. Even though there have been many theoretical studies, the origin of the chirality of filaments is still unknown. We investigated how intermediate filaments are related to their associated ARs, especially from the point of view of magnetic helicity and the orientation of polarity inversion lines (PILs). The chirality of filaments has been determined based on the orientations of barbs observed in the full-disk Hα images taken at Big Bear Solar Observatory during the rising phase of solar cycle 23. The sign of magnetic helicity of ARs has been determined using S/inverse-S shaped sigmoids from Yohkoh SXT images. As a result, we have found a good correlation between the chirality of filaments and the magnetic helicity sign of ARs. Among 45 filaments, 42 filaments have shown the same sign as helicity sign of nearby ARs. It has been also confirmed that the role of both the orientation and the relative direction of PILs to ARs in determining the chirality of filaments is not significant, against a theoretical prediction. These results suggest that the chirality of intermediate filaments may originate from magnetic helicity of their associated ARs.
Reduced bispectrum seeded by helical primordial magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Hortúa, Héctor Javier [Universidad Nacional de Colombia-Bogotá, Facultad de Ciencias, Departamento de Física, Carrera 30 Calle 45-03, C.P. 111321 Bogotá (Colombia); Castañeda, Leonardo, E-mail: hjhortuao@unal.edu.co, E-mail: lcastanedac@unal.edu.co [Grupo de Gravitación y Cosmología, Observatorio Astronómico Nacional, Universidad Nacional de Colombia, cra 45 No 26-85, Edificio Uriel Gutierréz, Bogotá, D.C. (Colombia)
2017-06-01
In this paper, we investigate the effects of helical primordial magnetic fields (PMFs) on the cosmic microwave background (CMB) reduced bispectrum. We derive the full three-point statistics of helical magnetic fields and numerically calculate the even contribution in the collinear configuration. We then numerically compute the CMB reduced bispectrum induced by passive and compensated PMF modes on large angular scales. There is a negative signal on the bispectrum due to the helical terms of the fields and we also observe that the biggest contribution to the bispectrum comes from the non-zero IR cut-off for causal fields, unlike the two-point correlation case. For negative spectral indices, the reduced bispectrum is enhanced by the passive modes. This gives a lower value of the upper limit for the mean amplitude of the magnetic field on a given characteristic scale. However, high values of IR cut-off in the bispectrum, and the helical terms of the magnetic field relaxes this bound. This demonstrates the importance of the IR cut-off and helicity in the study of the nature of PMFs from CMB observations.
Neoclassical current and plasma rotation in helical systems
International Nuclear Information System (INIS)
Nakajima, N.; Okamoto, M.
1991-01-01
In order to clarify geometrical effects of the magnetic field on the neoclassical theory in general toroidal systems, the neoclassical parallel particle flow, heat flux, current and plasma rotation of a multispecies plasma are examined using the moment approach on the basis of the original papers under the assumptions of no fluctuations, no external sources and losses except for a fast ion beam and an external inductive electric field, steady state, and |u a | Ta where u a and v Ta are the macro and thermal velocity of species a, respectively. Hence, we might have a point of view of unifying understanding the neoclassical theory in general toroidal systems. Three collisionality regimes, i.e., the 1/ν (in non-axisymmetric toroidal systems) or banana (in axisymmetric toroidal systems), plateau, and Pfirsch-Schlueter collisionality regimes are examined separately. (author) 8 refs
Gating-by-rotation: a solution to the problem of intratreatment motion in helical tomotherapy
International Nuclear Information System (INIS)
Kapatoes, J.M.; Olivera, G.H.; Schloesser, E.A.; Pearson, D.W.; Balog, J.P.; Ruchala, K.J.; Schmidt, R.; Reckwerdt, P.J.; Mehta, M.P.; Mackie, T.R.
2001-01-01
Purpose: To assess the feasibility of addressing intratreatment motion issues in helical tomotherapy by gating the treatments by rotation. Intratreatment motion is a problem common to all IMRT techniques. Traditional methods of gating in conformal radiotherapy and some forms of IMRT are not applicable to helical tomotherapy due to the continuous rotation of the gantry. An alternative method is presented. Materials and Methods: Rotation-gating in helical tomotherapy is the process in which one rotation of treatment is immediately followed by a rotation of non-treatment. This on-off strategy is repeated for the full treatment volume. During the treatment rotations, the patient is required to hold their breath while the intensity-modulated fan beam deposits dose. For the non-treatment rotations, the patient is allowed to breathe freely as all leaves of the MLC will be closed, the accelerator disabled, or both. The couch indexes normally for treatment rotations and holds the patient stationary during non-treatment rotations. An investigation was conducted to assess the feasibility of rotation-gating. Film was placed between two hemispheres of a water phantom and a continuous helical delivery was carried out with all leaves opened. The film was replaced and another treatment was performed employing rotation-gating. The two films were compared to assess the process. The films were irradiated to dose levels within the linear region of the film response curve (maximum film dose ∼35 cGy). Films were also acquired with all leaves closed to quantify leakage dose through the collimation systems. Results: Central profiles for the inferior-superior direction (parallel to the direction of translation) for both films are displayed in Figure 1. The profiles agree very well, illustrating that a rotation-gated treatment closely mimics a continuous helical delivery. The only significant discrepancy lay in the tails of the profiles: a higher film dose is seen for the rotation
Energy Technology Data Exchange (ETDEWEB)
Ocker, Stella Koch [Department of Physics, Oberlin College, Oberlin, OH 44074 (United States); Petrie, Gordon, E-mail: socker@oberlin.edu, E-mail: gpetrie@nso.edu [National Solar Observatory, Boulder, CO 80303 (United States)
2016-12-01
The hemispheric preference for negative/positive helicity to occur in the northern/southern solar hemisphere provides clues to the causes of twisted, flaring magnetic fields. Previous studies on the hemisphere rule may have been affected by seeing from atmospheric turbulence. Using Hinode /SOT-SP data spanning 2006–2013, we studied the effects of two spatial smoothing tests that imitate atmospheric seeing: noise reduction by ignoring pixel values weaker than the estimated noise threshold, and Gaussian spatial smoothing. We studied in detail the effects of atmospheric seeing on the helicity distributions across various field strengths for active regions (ARs) NOAA 11158 and NOAA 11243, in addition to studying the average helicities of 179 ARs with and without smoothing. We found that, rather than changing trends in the helicity distributions, spatial smoothing modified existing trends by reducing random noise and by regressing outliers toward the mean, or removing them altogether. Furthermore, the average helicity parameter values of the 179 ARs did not conform to the hemisphere rule: independent of smoothing, the weak-vertical-field values tended to be negative in both hemispheres, and the strong-vertical-field values tended to be positive, especially in the south. We conclude that spatial smoothing does not significantly affect the overall statistics for space-based data, and thus seeing from atmospheric turbulence seems not to have significantly affected previous studies’ ground-based results on the hemisphere rule.
Energy Technology Data Exchange (ETDEWEB)
Guo, Y. [School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210023 (China); Pariat, E.; Moraitis, K. [LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, F-92190 Meudon (France); Valori, G. [University College London, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT (United Kingdom); Anfinogentov, S. [Institute of Solar-Terrestrial Physics SB RAS 664033, Irkutsk, P.O. box 291, Lermontov Street, 126a (Russian Federation); Chen, F. [Max-Plank-Institut für Sonnensystemforschung, D-37077 Göttingen (Germany); Georgoulis, M. K. [Research Center for Astronomy and Applied Mathematics of the Academy of Athens, 4 Soranou Efesiou Street, 11527 Athens (Greece); Liu, Y. [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Thalmann, J. K. [Institute of Physics, Univeristy of Graz, Universitätsplatz 5/II, A-8010 Graz (Austria); Yang, S., E-mail: guoyang@nju.edu.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
2017-05-01
We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twist multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.
A multi-modular helical magnetic millirobot navigating in curved tubular environments
Directory of Open Access Journals (Sweden)
Seungmun Jeon
2017-05-01
Full Text Available This paper proposes a novel multi-modular helical magnetic millirobot (MHMM able to navigate in curved tubular environments. The proposed MHMM is basically composed of head, middle, and tail modules serially connected by a universal joint, and can employ more modules if necessary. The head module is a helical body with a magnetic rotary tip attached to the front end. Thus, once located in a curved tube filled with a fluid, the MHMM can effectively generate navigating or unclogging motions simply actuated by an external rotating magnetic field. This paper also examines the dynamic characteristics of the MHMM under various working conditions to manipulate the MHMM in a stable and safe manner. Then, it demonstrates various controlled motions of the MHMM in an in-vitro pulsatile flow environment to show the validity of the proposed structure and method.
Helical undulator based on partial redistribution of uniform magnetic field
Balal, N.; Bandurkin, I. V.; Bratman, V. L.; Fedotov, A. E.
2017-12-01
A new type of helical undulator based on redistribution of magnetic field of a solenoid by ferromagnetic helix has been proposed and studied both in theory and experiment. Such undulators are very simple and efficient for promising sources of coherent spontaneous THz undulator radiation from dense electron bunches formed in laser-driven photo-injectors.
Helical undulator based on partial redistribution of uniform magnetic field
Directory of Open Access Journals (Sweden)
N. Balal
2017-12-01
Full Text Available A new type of helical undulator based on redistribution of magnetic field of a solenoid by ferromagnetic helix has been proposed and studied both in theory and experiment. Such undulators are very simple and efficient for promising sources of coherent spontaneous THz undulator radiation from dense electron bunches formed in laser-driven photo-injectors.
Compensating Faraday Depolarization by Magnetic Helicity in the Solar Corona
Energy Technology Data Exchange (ETDEWEB)
Brandenburg, Axel; Ashurova, Mohira B. [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303 (United States); Jabbari, Sarah, E-mail: brandenb@nordita.org [School of Mathematical Sciences and Monash Centre for Astrophysics, Monash University, Clayton, VIC 3800 (Australia)
2017-08-20
A turbulent dynamo in spherical geometry with an outer corona is simulated to study the sign of magnetic helicity in the outer parts. In agreement with earlier studies, the sign in the outer corona is found to be opposite to that inside the dynamo. Line-of-sight observations of polarized emission are synthesized to explore the feasibility of using the local reduction of Faraday depolarization to infer the sign of helicity of magnetic fields in the solar corona. This approach was previously identified as an observational diagnostic in the context of galactic magnetic fields. Based on our simulations, we show that this method can be successful in the solar context if sufficient statistics are gathered by using averages over ring segments in the corona separately for the regions north and south of the solar equator.
Wang, Bo; Wang, Xiaodong; Etay, Jacqueline; Na, Xianzhao; Zhang, Xinde; Fautrelle, Yves
2016-04-01
In this study, an Archimedean helical permanent magnetic field was constructed and its driving effects on liquid metal were examined. A magnetic stirrer was constructed using a series of arc-like magnets. The helical distribution of its magnetic field, which was confirmed via Gauss probe measurements and numerical simulations, can be considered a combination of rotating and traveling magnetic fields. The characteristics of the flow patterns, particularly the transitions between the meridian secondary flow (two vortices) and the global axial flow (one vortex), driven by this magnetic field were quantitatively measured using ultrasonic Doppler velocimetry. The transient and modulated flow behaviors will be presented in a companion article. The D/ H dimension ratio was used to characterize the transitions of these two flow patterns. The results demonstrated that the flow patterns depend on not only the intrinsic structure of the magnetic field, e.g., the helix lead angle, but also the performance parameters, e.g., the dimensional ratio of the liquid bulk. The notable opposing roles of these two flow patterns in the improvement of macrosegregations when imposing such magnetic fields near the solidifying front were qualitatively addressed.
Generation of uniform magnetic field using a spheroidal helical coil structure
International Nuclear Information System (INIS)
Öztürk, Yavuz; Aktaş, Bekir
2016-01-01
Uniformity of magnetic fields are of great importance especially in magnetic resonance studies, namely in magnetic resonance spectroscopy applications (NMR, FMR, ESR, EPR etc.) and magnetic resonance imaging applications (MRI, FMRI). Field uniformity is also required in some other applications such as eddy current probes, magnetometers, magnetic traps, particle counters etc. Here we proposed a coil winding regime, which follows the surface of a spheroid (an ellipsoid of rotation); in light of previous theoretical studies suggesting perfect uniformity for a constant ampere per turn in the axial direction thereof. We demonstrated our theoretical results from finite element calculations suggesting 0.15% of field uniformity for the proposed structure, which we called a Spheroidal Helical Coil. (paper)
International Nuclear Information System (INIS)
Yang Shangbin; Zhang Hongqi
2012-01-01
To investigate the characteristics of large-scale and long-term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking to estimate the magnetic helicity evolution over solar cycle 23 from 1996 to 2009 using 795 MDI magnetic synoptic charts. The main results are as follows: the hemispheric helicity rule still holds in general, i.e., the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large-scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large-scale magnetic helicity flux over the solar disk changes from a negative value at the beginning of solar cycle 23 to a positive value at the end of the cycle, while the net accumulated magnetic helicity is negative in the period between 1996 and 2009.
Energy Technology Data Exchange (ETDEWEB)
Yang Shangbin; Zhang Hongqi, E-mail: yangshb@nao.cas.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing (China)
2012-10-10
To investigate the characteristics of large-scale and long-term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking to estimate the magnetic helicity evolution over solar cycle 23 from 1996 to 2009 using 795 MDI magnetic synoptic charts. The main results are as follows: the hemispheric helicity rule still holds in general, i.e., the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large-scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large-scale magnetic helicity flux over the solar disk changes from a negative value at the beginning of solar cycle 23 to a positive value at the end of the cycle, while the net accumulated magnetic helicity is negative in the period between 1996 and 2009.
Influence of external 3D magnetic fields on helical equilibrium and plasma flow in RFX-mod
International Nuclear Information System (INIS)
Piovesan, P; Bonfiglio, D; Bonomo, F; Cappello, S; Carraro, L; Cavazzana, R; Gobbin, M; Marrelli, L; Martin, P; Martines, E; Momo, B; Piron, L; Puiatti, M E; Soppelsa, A; Valisa, M; Zanca, P; Zaniol, B
2011-01-01
A spontaneous transition to a helical equilibrium with an electron internal transport barrier is observed in RFX-mod as the plasma current is raised above 1 MA (Lorenzini R et al 2009 Nature Phys. 5 570). The helical magnetic equilibrium can be controlled with external three-dimensional (3D) magnetic fields applied by 192 active coils, providing proper helical boundary conditions either rotating or static. The persistence of the helical equilibrium is strongly increased in this way. A slight reduction in the energy confinement time of about 15% is observed, likely due to the increased plasma-wall interaction associated with the finite radial magnetic field imposed at the edge. A global helical flow develops in these states and is expected to play a role in the helical self-organization. In particular, its shear may contribute to the ITB formation and is observed to increase with the externally applied radial field. The possible origins of this flow, from nonlinear visco-resistive magnetohydrodynamic (MHD) and/or ambipolar electric fields, will be discussed.
International Nuclear Information System (INIS)
Woodruff, S.; Hill, D.N.; Stallard, B.W.; Bulmer, R.; Cohen, B.; Holcomb, C.T.; Hooper, E.B.; McLean, H.S.; Moller, J.; Wood, R.D.
2003-01-01
By operating a magnetized coaxial plasma gun continuously with just sufficient current to enable plasma ejection, large gun-voltage spikes (∼1 kV) are produced, giving the highest sustained voltage ∼500 V and highest sustained helicity injection rate observed in the Sustained Spheromak Physics Experiment. The spheromak magnetic field increases monotonically with time, exhibiting the lowest fluctuation levels observed during formation of any spheromak (B-tilde)/B≥2%). The results suggest an important mechanism for field generation by helicity injection, namely, the merging of helicity-carrying filaments
Woodruff, S; Hill, D N; Stallard, B W; Bulmer, R; Cohen, B; Holcomb, C T; Hooper, E B; McLean, H S; Moller, J; Wood, R D
2003-03-07
By operating a magnetized coaxial plasma gun continuously with just sufficient current to enable plasma ejection, large gun-voltage spikes (approximately 1 kV) are produced, giving the highest sustained voltage approximately 500 V and highest sustained helicity injection rate observed in the Sustained Spheromak Physics Experiment. The spheromak magnetic field increases monotonically with time, exhibiting the lowest fluctuation levels observed during formation of any spheromak (B/B>/=2%). The results suggest an important mechanism for field generation by helicity injection, namely, the merging of helicity-carrying filaments.
Energy Technology Data Exchange (ETDEWEB)
Linkmann, Moritz; Sahoo, Ganapati; Biferale, Luca [Department of Physics and INFN, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome (Italy); McKay, Mairi; Berera, Arjun [School of Physics and Astronomy, University of Edinburgh, Peter Guthrie Tait Road, EH9 3FD, Edinburgh (United Kingdom)
2017-02-10
We present a numerical and analytical study of incompressible homogeneous conducting fluids using a helical Fourier representation. We analytically study both small- and large-scale dynamo properties, as well as the inverse cascade of magnetic helicity, in the most general minimal subset of interacting velocity and magnetic fields on a closed Fourier triad. We mainly focus on the dependency of magnetic field growth as a function of the distribution of kinetic and magnetic helicities among the three interacting wavenumbers. By combining direct numerical simulations of the full magnetohydrodynamics equations with the helical Fourier decomposition, we numerically confirm that in the kinematic dynamo regime the system develops a large-scale magnetic helicity with opposite sign compared to the small-scale kinetic helicity, a sort of triad-by-triad α -effect in Fourier space. Concerning the small-scale perturbations, we predict theoretically and confirm numerically that the largest instability is achived for the magnetic component with the same helicity of the flow, in agreement with the Stretch–Twist–Fold mechanism. Vice versa, in the presence of Lorentz feedback on the velocity, we find that the inverse cascade of magnetic helicity is mostly local if magnetic and kinetic helicities have opposite signs, while it is more nonlocal and more intense if they have the same sign, as predicted by the analytical approach. Our analytical and numerical results further demonstrate the potential of the helical Fourier decomposition to elucidate the entangled dynamics of magnetic and kinetic helicities both in fully developed turbulence and in laminar flows.
Chiral charge erasure via thermal fluctuations of magnetic helicity
International Nuclear Information System (INIS)
Long, Andrew J.; Sabancilar, Eray
2016-01-01
We consider a relativistic plasma of fermions coupled to an Abelian gauge field and carrying a chiral charge asymmetry, which might arise in the early Universe through baryogenesis. It is known that on large length scales, λ≳1/(αμ_5), the chiral anomaly opens an instability toward the erasure of chiral charge and growth of magnetic helicity. Here the chemical potential μ_5 parametrizes the chiral asymmetry and α is the fine-structure constant. We study the process of chiral charge erasure through the thermal fluctuations of magnetic helicity and contrast with the well-studied phenomenon of Chern-Simons number diffusion. Through the fluctuation-dissipation theorem we estimate the amplitude and time scale of helicity fluctuations on the length scale λ, finding δ H∼λT and τ∼αλ"3T"2 for a relativistic plasma at temperature T. We argue that the presence of a chiral asymmetry allows the helicity to grow diffusively for a time t∼T"3/(α"5μ_5"4) until it reaches an equilibrium value H∼μ_5T"2/α, and the chiral asymmetry is partially erased. If the chiral asymmetry is small, μ_5< T/α, this avenue for chiral charge erasure is found to be slower than the chiral magnetic effect for which t∼T/(α"3μ_5"2). This mechanism for chiral charge erasure can be important for the hypercharge sector of the Standard Model as well as extensions including U(1) gauge interactions, such as asymmetric dark matter models.
Experiments on helical modes in magnetized thin foil-plasmas
Yager-Elorriaga, David
2017-10-01
This paper gives an in-depth experimental study of helical features on magnetized, ultrathin foil-plasmas driven by the 1-MA linear transformer driver at University of Michigan. Three types of cylindrical liner loads were designed to produce: (a) pure magneto-hydrodynamic (MHD) modes (defined as being void of the acceleration-driven magneto-Rayleigh-Taylor instability, MRT) using a non-imploding geometry, (b) pure kink modes using a non-imploding, kink-seeded geometry, and (c) MRT-MHD coupled modes in an unseeded, imploding geometry. For each configuration, we applied relatively small axial magnetic fields of Bz = 0.2-2.0 T (compared to peak azimuthal fields of 30-40 T). The resulting liner-plasmas and instabilities were imaged using 12-frame laser shadowgraphy and visible self-emission on a fast framing camera. The azimuthal mode number was carefully identified with a tracking algorithm of self-emission minima. Our experiments show that the helical structures are a manifestation of discrete eigenmodes. The pitch angle of the helix is simply m / kR , from implosion to explosion, where m, k, and R are the azimuthal mode number, axial wavenumber, and radius of the helical instability. Thus, the pitch angle increases (decreases) during implosion (explosion) as R becomes smaller (larger). We found that there are one, or at most two, discrete helical modes that arise for magnetized liners, with no apparent threshold on the applied Bz for the appearance of helical modes; increasing the axial magnetic field from zero to 0.5 T changes the relative weight between the m = 0 and m = 1 modes. Further increasing the applied axial magnetic fields yield higher m modes. Finally, the seeded kink instability overwhelms the intrinsic instability modes of the plasma. These results are corroborated with our analytic theory on the effects of radial acceleration on the classical sausage, kink, and higher m modes. Work supported by US DOE award DE-SC0012328, Sandia National Laboratories
Cylindrical Taylor states conserving total absolute magnetic helicity
Low, B. C.; Fang, F.
2014-09-01
The Taylor state of a three-dimensional (3D) magnetic field in an upright cylindrical domain V is derived from first principles as an extremum of the total magnetic energy subject to a conserved, total absolute helicity Habs. This new helicity [Low, Phys. Plasmas 18, 052901 (2011)] is distinct from the well known classical total helicity and relative total helicity in common use to describe wholly-contained and anchored fields, respectively. A given field B, tangential along the cylindrical side of V, may be represented as a unique linear superposition of two flux systems, an axially extended system along V and a strictly transverse system carrying information on field-circulation. This specialized Chandrasekhar-Kendall representation defines Habs and permits a neat formulation of the boundary-value problem (BVP) for the Taylor state as a constant-α force-free field, treating 3D wholly-contained and anchored fields on the same conceptual basis. In this formulation, the governing equation is a scalar integro-partial differential equation (PDE). A family of series solutions for an anchored field is presented as an illustration of this class of BVPs. Past treatments of the constant-α field in 3D cylindrical geometry are based on a scalar Helmholtz PDE as the governing equation, with issues of inconsistency in the published field solutions discussed over time in the journal literature. The constant-α force-free equation reduces to a scalar Helmholtz PDE only as special cases of the 3D integro-PDE derived here. In contrast, the constant-α force-free equation and the scalar Helmholtz PDE are absolutely equivalent in the spherical domain as discussed in Appendix. This theoretical study is motivated by the investigation of the Sun's corona but the results are also relevant to laboratory plasmas.
The evolution of helical cosmic magnetic fields as predicted by MHD closure theory
Energy Technology Data Exchange (ETDEWEB)
Saveliev, Andrey; Sigl, Guenter [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Jedamzik, Kartsen [Univ. Montpellier-2. (France). Laboratoire Univers et Particules de Montpellier
2013-04-15
We extend our recent derivation of the time evolution equations for the energy content of magnetic fields and turbulent motions for incompressible, homogeneous, and isotropic turbulence to include the case of non-vanishing helicity. These equations are subsequently numerically integrated in order to predict the present day primordial magnetic field strength and correlation length, depending on its initial helicity and magnetic energy density. We find that all prior analytic predictions for helical magnetic fields, such as the epoch when they become maximally helical and their subsequent growth of correlation length L {proportional_to} a{sup 1/3} and decrease of magnetic field strength B {proportional_to} a{sup -1/3} with scale factor a are well confirmed by the simulations. An initially fully helical primordial magnetic field is a factor 4 x 10{sup 4} stronger at the present epoch then its non-helical counterpart when generated during the electroweak epoch.
Magnetic properties of the Ce2Fe17-x Mn x helical magnets up to high magnetic fields
International Nuclear Information System (INIS)
Kuchin, A.G.; Mushnikov, N.V.; Bartashevich, M.I.; Prokhnenko, O.; Khrabrov, V.I.; Lapina, T.P.
2007-01-01
Magnetic properties of the Ce 2 Fe 17- x Mn x , x=0-2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5-1 are helical antiferromagnets and those with 1 B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce 2 Fe 17- x Mn x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce 2 Fe 17- x Mn x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce 2 Fe 17- x Mn x , x=0.5-2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated
New helical-shape magnetic pole design for Magnetic Lead Screw enabling structure simplification
DEFF Research Database (Denmark)
Lu, Kaiyuan; Xia, Yongming; Wu, Weimin
2015-01-01
Magnetic lead screw (MLS) is a new type of high performance linear actuator that is attractive for many potential applications. The main difficulty of the MLS technology lies in the manufacturing of its complicated helical-shape magnetic poles. Structure simplification is, therefore, quite...
Hydromagnetic rotational braking of magnetic stars
International Nuclear Information System (INIS)
Fleck, R.C. Jr.
1980-01-01
It is suggested that the magnetic Ap stars can be rotationally decelerated to long periods by the braking action of the associated magnetic field on time scales of order 10 7 --10 10 years depending on whether the star's dipole field is aligned perpendicular or parallel to the rotation axis. Rotation includes a toroidal magnetic field in the plasma surrounding a star, and the accompanying magnetic stresses produce a net torque acting to despin the star. These results indicate that it is not necessary to postulate mass loss or mass accretion for this purely hydromagnetic braking effect
Directory of Open Access Journals (Sweden)
Y. Narita
2009-10-01
Full Text Available We develop an estimator for the magnetic helicity density, a measure of the spiral geometry of magnetic field lines, in the wave number domain as a wave diagnostic tool based on multi-point measurements in space. The estimator is numerically tested with a synthetic data set and then applied to an observation of magnetic field fluctuations in the Earth foreshock region provided by the four-point measurements of the Cluster spacecraft. The energy and the magnetic helicity density are determined in the frequency and the wave number domain, which allows us to identify the wave properties in the plasma rest frame correcting for the Doppler shift. In the analyzed time interval, dominant wave components have parallel propagation to the mean magnetic field, away from the shock at about Alfvén speed and a left-hand spatial rotation sense of helicity with respect to the propagation direction, which means a right-hand temporal rotation sense of polarization. These wave properties are well explained by the right-hand resonant beam instability as the driving mechanism in the foreshock. Cluster observations allow therefore detailed comparisons with various theories of waves and instabilities.
Potential Magnetic Field around a Helical Flux-rope Current Structure in the Solar Corona
Petrie, G. J. D.
2007-01-01
We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex tha...
Helical patterns of magnetization and magnetic charge density in iron whiskers
Templeton, Terry L.; Hanham, Scott D.; Arrott, Anthony S.
2018-05-01
Studies with the (1 1 1) axis along the long axis of an iron whisker, 40 years ago, showed two phenomena that have remained unexplained: 1) In low fields, there are six peaks in the ac susceptibility, separated by 0.2 mT; 2) Bitter patterns showed striped domain patterns. Multipole columns of magnetic charge density distort to form helical patterns of the magnetization, accounting for the peaks in the susceptibility from the propagation of edge solitons along the intersections of the six sides of a (1 1 1) whisker. The stripes follow the helices. We report micromagnetic simulations in cylinders with various geometries for the cross-sections from rectangular, to hexagonal, to circular, with wide ranges of sizes and lengths, and different anisotropies, including (0 0 1) whiskers and the hypothetical case of no anisotropy. The helical patterns have been there in previous studies, but overlooked. The surface swirls and body helices are connected, but have their own individual behaviors. The magnetization patterns are more easily understood when viewed observing the scalar divergences of the magnetization as isosurfaces of magnetic charge density. The plus and minus charge densities form columns that interact with unlike charges attracting, but not annihilating as they are paid for by a decrease in exchange energy. Just as they start to form the helix, the columns are multipoles. If one could stretch the columns, the self-energy of the charges in a column would be diminished while making the attractive interactions of the unlike charges larger. The columns elongate by becoming helical. The visualization of 3-D magnetic charge distributions aids in the understanding of magnetization in soft magnetic materials.
What Helicity Can Tell Us about Solar Magnetic Fields Alexei A ...
Indian Academy of Sciences (India)
Concept of magnetic/current helicity was introduced to solar physics about 15 ... represented by a thin flux tube model with flux , one can show that magnetic helicity,. Hm = (2π). −1 2 ... For example, spiral pattern of filaments forming sunspot ...
International Nuclear Information System (INIS)
Nakamura, Kazutaka; Himura, Haruhiko; Masamune, Sadao; Sanpei, Akio; Isobe, Mitsutaka
2009-01-01
In order to investigate the formation process of helical nonneutral plasmas, we calculate the orbits of electron injected in the stochastic magnetic field when the closed helical magnetic surfaces is correspond with the equipotential surfaces. Contrary to the experimental observation, there are no electrons inward penetrating. (author)
Directory of Open Access Journals (Sweden)
Mikiji Miyata
2015-10-01
Full Text Available A multi-point approximation method clarifies supramolecular chirality of twofold rotational or helical assemblies as well as bundles of the one-dimensional (1D assemblies. While one-point approximation of materials claims no chirality generation of such assemblies, multi-point approximations do claim possible generation in the 1D assemblies of bars and plates. Such chirality derives from deformations toward three-axial directions around the helical axes. The chiral columns are bundled in chiral ways through symmetry operations. The preferable right- or left-handed columns are bundled together to yield chiral crystals with right- or left-handedness, respectively, indicating that twofold helix symmetry operations cause chiral crystals composed of achiral components via a three-stepwise and three-directional process.
International Nuclear Information System (INIS)
Shi, Zhongyuan; Dong, Tao
2014-01-01
Highlights: • Variation of total entropy generation is investigated parametrically. • Pareto solution sets for heat transfer and flow friction components are obtained. • Dominant irreversibility component and impact of key variables are discussed. - Abstract: Based on the second law of thermodynamics, an entropy generation investigation is carried out under given dimensionless parameters, i.e. heat exchanger duty, heat flux, with respect to heat transfer and frictional pressure drop in a rotating helical tube heat exchanger with laminar convective flow. The entropy generation from heat transfer across a finite temperature difference – Ψ h decreases with increasing Dean number which represents the impact of centrifugal force induced secondary flow in enhancing heat transfer. Another aspect of increasing Dean number is that intensified momentum transfer in the radial direction also raises the entropy generation from frictional pressure drop – Ψ f , the superposed effect of which yields a decreasing–increasing trend of the total entropy generation-Ψ, a local minimum located in between. The rotation of the helical tube in streamwise (co-rotation) or counter streamwise (counter-rotation) direction leads to a decrease in Ψ h and a increase in Ψ f which complicates the situation that whether or where the minimum of total entropy generation exists is dependent on whether Ψ is dominated by Ψ h or Ψ f or somewhere in between. No difference is discerned between pairs of cases with constant wall temperature and uniform wall heat flux but the same set of variables and parameters. A multi-objective optimization targeting Ψ h and Ψ f simultaneously is implemented using the non-dominated sorting genetic algorithm II (NSGA II). Five solution sets are selected and compared with the conventional optimization in regard of Ψ distinguishing the Ψ h -dominated region from the Ψ f -dominated region, the dimensionless variable η 1 is found to be the most suitable
Increasing the magnetic helicity content of a plasma by pulsing a magnetized source.
Woodruff, S; Stallard, B W; McLean, H S; Hooper, E B; Bulmer, R; Cohen, B I; Hill, D N; Holcomb, C T; Moller, J; Wood, R D
2004-11-12
By operating a magnetized coaxial gun in a pulsed mode it is possible to produce large voltage pulses of duration approximately 500 mus while reaching a few kV, giving a discrete input of helicity into a spheromak. In the sustained spheromak physics experiment (SSPX), it is observed that pulsing serves to nearly double the stored magnetic energy and double the temperature. We discuss these results by comparison with 3D MHD simulations of the same phenomenon.
TIME EVOLUTION OF CORONAL MAGNETIC HELICITY IN THE FLARING ACTIVE REGION NOAA 10930
International Nuclear Information System (INIS)
Park, Sung-Hong; Jing, Ju; Wang Haimin; Chae, Jongchul; Tan, Changyi
2010-01-01
To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3 x 10 43 Mx 2 just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2 x 10 43 Mx 2 , in the corona over ∼1.5 days but also by noticeable injections of positive helicity through the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.
EVOLUTION OF MAGNETIC HELICITY AND ENERGY SPECTRA OF SOLAR ACTIVE REGIONS
International Nuclear Information System (INIS)
Zhang, Hongqi; Brandenburg, Axel; Sokoloff, D. D.
2016-01-01
We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA 11158 and NOAA 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of the energy-carrying magnetic structures increases. The magnetic helicity of NOAA 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30–60 Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field
EVOLUTION OF MAGNETIC HELICITY AND ENERGY SPECTRA OF SOLAR ACTIVE REGIONS
Energy Technology Data Exchange (ETDEWEB)
Zhang, Hongqi [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Brandenburg, Axel [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Sokoloff, D. D., E-mail: hzhang@bao.ac.cn [Department of Physics, Moscow University, 119992 Moscow (Russian Federation)
2016-03-10
We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA 11158 and NOAA 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of the energy-carrying magnetic structures increases. The magnetic helicity of NOAA 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30–60 Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field.
Kleeorin, N.
2018-06-01
We discuss a mean-field theory of the generation of large-scale vorticity in a rotating density stratified developed turbulence with inhomogeneous kinetic helicity. We show that the large-scale non-uniform flow is produced due to either a combined action of a density stratified rotating turbulence and uniform kinetic helicity or a combined effect of a rotating incompressible turbulence and inhomogeneous kinetic helicity. These effects result in the formation of a large-scale shear, and in turn its interaction with the small-scale turbulence causes an excitation of the large-scale instability (known as a vorticity dynamo) due to a combined effect of the large-scale shear and Reynolds stress-induced generation of the mean vorticity. The latter is due to the effect of large-scale shear on the Reynolds stress. A fast rotation suppresses this large-scale instability.
PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS
International Nuclear Information System (INIS)
Park, Sung-hong; Wang Haimin; Chae, Jongchul
2010-01-01
The main objective of this study is to better understand how magnetic helicity injection in an active region (AR) is related to the occurrence and intensity of solar flares. We therefore investigate the magnetic helicity injection rate and unsigned magnetic flux, as a reference. In total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr averaged helicity injection rate and unsigned magnetic flux are compared with the flare index and the flare-productive probability in the next 24 hr following a measurement. In addition, we study the variation of helicity over a span of several days around the times of the 19 flares above M5.0 which occurred in selected strong flare-productive ARs. The major findings of this study are as follows: (1) for a sub-sample of 91 large ARs with unsigned magnetic fluxes in the range from (3-5) x 10 22 Mx, there is a difference in the magnetic helicity injection rate between flaring ARs and non-flaring ARs by a factor of 2; (2) the GOES C-flare-productive probability as a function of helicity injection displays a sharp boundary between flare-productive ARs and flare-quiet ones; (3) the history of helicity injection before all the 19 major flares displayed a common characteristic: a significant helicity accumulation of (3-45) x 10 42 Mx 2 during a phase of monotonically increasing helicity over 0.5-2 days. Our results support the notion that helicity injection is important in flares, but it is not effective to use it alone for the purpose of flare forecast. It is necessary to find a way to better characterize the time history of helicity injection as well as its spatial distribution inside ARs.
Local instabilities in magnetized rotational flows: A short-wavelength approach
Kirillov, Oleg N.; Stefani, Frank; Fukumoto, Yasuhide
2014-01-01
We perform a local stability analysis of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the cas...
Helical magnetic axis configuration combined with l = 1 and weak l = -1 torsatron fields
International Nuclear Information System (INIS)
Kikuchi, Hitoshi; Saito, Katsunori; Gesso, Hirokazu; Shiina, Shoichi
1989-01-01
The superposition of a relatively weak l = -1 torsatron field on a main l = 1 torsatron field leads to the improvement of the confinement properties due to the formation of a local magnetic well, which results from the local curvature of the helical magnetic axis with a larger excursion in the major radius direction. This l±1 helical magnetic axis system has a comparatively simple, compact coil structure. Here the vacuum configuration properties of l = ±1 system are described. (author)
Magnetic nanofluids and magnetic composite fluids in rotating seal systems
International Nuclear Information System (INIS)
Borbath, T; Borbath, I; Boros, T; Bica, D; Vekas, L; Potencz, I
2010-01-01
Recent results are presented concerning the development of magnetofluidic leakage-free rotating seals for vacuum and high pressure gases, evidencing significant advantages compared to mechanical seals. The micro-pilot scale production of various types of magnetizable sealing fluids is shortly reviewed, in particular the main steps of the chemical synthesis of magnetic nanofluids and magnetic composite fluids with light hydrocarbon, mineral oil and synthetic oil carrier liquids. The behavior of different types of magnetizable fluids in the rotating sealing systems is analyzed. Design concepts, some constructive details and testing procedures of magnetofluidic rotating seals are presented such as the testing equipment. The main characteristics of several magnetofluidic sealing systems and their applications will be presented: vacuum deposition systems and liquefied gas pumps applications, mechanical and magnetic nanofluid combined seals, gas valves up to 40 bar equipped by rotating seal with magnetic nanofluids and magnetic composite fluids.
International Nuclear Information System (INIS)
Makhnovskiy, D. P.; Panina, L. V.; Mapps, D. J.
2001-01-01
This article concerns the investigation of the magnetic behavior of the surface impedance tensor cflx var-sigma in CoSiB amorphous wires having a residual torsion stress and a helical anisotropy. The full tensor cflx var-sigma involving three different components is found by measuring the S 21 parameter at a required excitation with a Hewlett-Packard network/spectrum analyzer at MHz frequencies. In general, the impedance plots versus axial magnetic field H ex exhibit a hysteresis related to that for the case of static magnetization. The diagonal components of cflx var-sigma (longitudinal var-sigma zz and circular var-sigma v ar-phi v ar-phi) show a sharp peak in a narrow field interval where the domain walls form and contribute to the ac magnetization dynamics. This peak is not seen for the off-diagonal component var-sigma zv ar-phi (var-sigma v ar-phi z ) since the existence of the domain structure suppresses it. Applying a dc bias current results in a gradual transition to a nonhysteretic asymmetrical behavior with an enhanced sensitivity. The portions of the experimental plots associated with the rotational dynamic process are in qualitative agreement with the theory based on a single-domain model. [copyright] 2001 American Institute of Physics
Electromagnetic fields of rotating magnetized NUT stars
International Nuclear Information System (INIS)
Ahmedov, B.J.; Khugaev, A.V.; Ahmedov, B.J.
2004-01-01
Full text: Analytic general relativistic expressions for the electromagnetic fields external to a slowly-rotating magnetized NUT star with nonvanishing gravitomagnetic charge have been presented. Solutions for the electric and magnetic fields have been found after separating the Maxwell equations in the external background spacetime of a slowly rotating NUT star into angular and radial parts in the lowest order approximation. The star is considered isolated and in vacuum, with different models for stellar magnetic field: i) monopolar magnetic field and II) dipolar magnetic field aligned with the axis of rotation. We have shown that the general relativistic corrections due to the dragging of reference frames and gravitomagnetic charge are not present in the form of the magnetic fields but emerge only in the form of the electric fields. In particular, we have shown that the frame-dragging and gravitomagnetic charge provide an additional induced electric field which is analogous to the one introduced by the rotation of the star in the flat spacetime limit
Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven ...
Indian Academy of Sciences (India)
tribpo
Key words. Sun—dynamo, helicity, turbulent convection. Extended abstract. Recent numerical simulations lead to the result that turbulence is much more mag- netically driven than believed. ... positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicity which is negative ...
Permanent-magnet helical undulator for a millimeter-wave free electron laser
International Nuclear Information System (INIS)
Lee, Jongmin; Jeong, Young-Uk; Lee, Byung-Cheol; Kim, Sun-Kook; Cho, Sung-Oh
1995-01-01
Permanent-magnet helical undulator for a millimeter-wave free-electron laser was designed and constructed. The configuration of the undulator is based on bifilar-type permanent-magnet helical undulator and Halbach-type planar undulator. This new configuration shows enhanced magnetic field and low field error. Period, total length and peak magnetic-field amplitude of the undulator is 36 mm, 900 mm and 1.44 kG, respectively. Adiabatic tapering of the magnetic field in end sides of the undulator was achieved using stepped soft-iron tubes. (author)
Earl, James A.
1992-01-01
When charged particles spiral along a large constant magnetic field, their trajectories are scattered by any random field components that are superposed on the guiding field. If the random field configuration embodies helicity, the scattering is asymmetrical with respect to a plane perpendicular to the guiding field, for particles moving into the forward hemisphere are scattered at different rates from those moving into the backward hemisphere. This asymmetry gives rise to new terms in the transport equations that describe propagation of charged particles. Helicity has virtually no impact on qualitative features of the diffusive mode of propagation. However, characteristic velocities of the coherent modes that appear after a highly anisotropic injection exhibit an asymmetry related to helicity. Explicit formulas, which embody the effects of helicity, are given for the anisotropies, the coefficient diffusion, and the coherent velocities. Predictions derived from these expressions are in good agreement with Monte Carlo simulations of particle transport, but the simulations reveal certain phenomena whose explanation calls for further analytical work.
Modified small angle magnetization rotation method in multilayer magnetic microwires
International Nuclear Information System (INIS)
Torrejon, J.; Badini, G.; Pirota, K.; Vazquez, M.
2007-01-01
The small angle magnetization rotation (SAMR) technique is a widely used method to quantify magnetostriction in elongated ultrasoft magnetic materials. In the present work, we introduce significant optimization of the method, particularly simplification of the required equipment, profiting of the very peculiar characteristics of a recently introduced family of multilayer magnetic microwires consisting of a soft magnetic core, insulating intermediate layer and a hard magnetic outer layer. The introduced modified SAMR method is used not only to determine the saturation magnetostriction constant of the soft magnetic nucleus but also the magnetoelastic and magnetostatic coupling. This new method has a great potential in multifunctional sensor applications
THE EFFECT OF ELECTRON THERMAL PRESSURE ON THE OBSERVED MAGNETIC HELICITY IN THE SOLAR WIND
Energy Technology Data Exchange (ETDEWEB)
Markovskii, S. A.; Vasquez, Bernard J.; Smith, Charles W., E-mail: sergei.markovskii@unh.edu, E-mail: bernie.vasquez@unh.edu, E-mail: charles.smith@unh.edu [Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)
2016-12-20
Statistical analysis of magnetic helicity spectra in the solar wind at 1 au is carried out. A large database of the solar wind intervals assembled from Wind spacecraft magnetic and plasma data is used. The effect of the electron thermal pressure on the wavenumber position of the helicity signature, i.e., the peak of the spectrum, is studied. The position shows a statistically significant dependence on both the electron and proton pressures. However, the strongest dependence is seen when the two pressures are summed. These findings confirm that the generation of the magnetic helicity is associated with an increasing compressibility of the turbulent fluctuations at smaller kinetic scales. It is argued that instrumental artifacts do not contribute to the helicity signature.
Dipolar vortex structures in magnetized rotating plasma
International Nuclear Information System (INIS)
Liu Jixing
1990-01-01
Dipolar solitary vortices of both electrostatic and electromagnetic character in low-β, in homogeneous rotating plasma confined in a constant external magnetic field were systematically presented. The main stimulus to this investigation is the expectation to apply this coherent structure as a candidate constituent of plasma turbulance to understand the anomalous transport phenomena in confined plasma. The electrostatic vortices have similar structure and properties as the Rossby vortices in rotating fluids, the electromagnetic vortices obtained here have no analogy in hydrodynamics and hence are intrinsic to magnetized plasma. It is valuably remarked that the intrinsic electromagnetic vortices presented here have no discontinuity of perturbed magnetic field δB and parallel current j(parallel) on the border of vortex core. The existence region of the new type of vortex is found much narrower than the Rossby type one. (M.T.)
Magnetic helices as metastable states of finite XY ferromagnetic chains: An analytical study
Popov, Alexander P.; Pini, Maria Gloria
2018-04-01
We investigated a simple but non trivial model, consisting of a chain of N classical XY spins with nearest neighbor ferromagnetic interaction, where each of the two end-point spins is assumed to be exchange-coupled to a fully-pinned fictitious spin. In the mean field approximation, the system might be representative of a soft ferromagnetic film sandwiched between two magnetically hard layers. We show that, while the ground state is ferromagnetic and collinear, the system can attain non-collinear metastable states in the form of magnetic helices. The helical solutions and their stability were studied analytically in the absence of an external magnetic field. There are four possible classes of solutions. Only one class is metastable, and its helical states contain an integer number of turns. Among the remaining unstable classes, there is a class of helices which contain an integer number of turns. Therefore, an integer number of turns in a helical configuration is a necessary, but not a sufficient, condition for metastability. These results may be useful to devise future applications of metastable magnetic helices as energy-storing elements.
Using Magnetic Helicity Diagnostics to Determine the Nature of Solar Active-Region Formation
Georgoulis, Manolis K.
Employing a novel nonlinear force-free (NLFF) method that self-consistently infers instantaneous free magnetic-energy and relative magnetic-helicity budgets from single photospheric vector magnetograms, we recently constructed the magnetic energy-helicity (EH) diagram of solar active regions. The EH diagram implies dominant relative helicities of left-handed or right-handed chiralities for the great majority of active regions. The amplitude (budget) of these helicities scales monotonically with the free magnetic energy. This constructive, strongly preferential accumulation of a certain sense of magnetic helicity seems to disqualify recently proposed mechanisms relying on a largely random near-surface convection for the formation of the great majority of active regions. The existing qualitative formation mechanism for these regions remains the conventional Omega-loop emergence following a buoyant ascension from the bottom of the convection zone. However, exceptions to this rule include even eruptive active regions: NOAA AR 11283 is an obvious outlier to the EH diagram, involving significant free magnetic energy with a small relative magnetic helicity. Relying on a timeseries of vector magnetograms of this region, our methodology shows nearly canceling amounts of both senses of helicity and an overall course from a weakly left-handed to a weakly right-handed structure, in the course of which a major eruption occurs. For this and similarly behaving active regions the latest near-surface formation scenario might conceivably be employed successfully. Research partially supported by the EU Seventh Framework Programme under grant agreement No. PIRG07-GA-2010-268245 and by the European Union Social Fund (ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund.
Energy Technology Data Exchange (ETDEWEB)
Yang, Bo; Jiang, Yunchun; Yang, Jiayan; Hong, Junchao; Xu, Zhe, E-mail: boyang@ynao.ac.cn, E-mail: yjy@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences, P.O. Box 110, Kunming 650011 (China)
2015-04-20
We present the first observation of the formation and eruption of a small circular filament driven by a rotating network magnetic field (RNF) in the quiet Sun. In the negative footpoint region of an inverse J-shaped dextral filament, the RNF was formed by the convergence to supergranular junctions of several magnetic flux patches of the same polarity, and it then rotated counterclockwise (CCW) for approximately 11 hr and showed up as a CCW rotating EUV cyclone, during which time the filament gradually evolved into a circular filament that surrounded the cyclone. When the calculated convergence and vortex flows appeared around the RNF during its formation and rotation phases, the injected magnetic helicity calculation also showed negative helicity accumulation during the RNF rotation that was consistent with the dextral chirality of the filament. Finally, the RNF rotation stopped and the cyclone disappeared, and, probably due to an emerging bipole and its forced cancellation with the RNF, the closure filament underwent an eruption along its axis in the (clockwise) direction opposite to the rotation directions of the RNF and cyclone. These observations suggest that the RNFs might play an important role in the formation of nearby small-scale circular filaments as they transport and inject magnetic energy and helicity, and the formation of the EUV cyclones may be a further manifestation of the helicity injected into the corona by the rotation of the RNFs in the photosphere. In addition, the new emerging bipole observed before the filament eruption might be responsible for destabilizing the system and triggering the magnetic reconnection which proves useful for the filament eruption.
Radio emission from a helical electron beam-plasma system in a twisted magnetic field
International Nuclear Information System (INIS)
Krishan, V.
1982-01-01
The excitation of electromagnetic radiation near the harmonics of electron plasma frequency from a helical electron beam travelling parallel to a helical magnetic field through a stationary inhomogeneous plasma is studied. The motivation behind this study is to explain the observed characteristics of the type III solar radio bursts and thus to predict the nature of the plasma system responsible for the generation of these radio bursts. (author)
Note: On-chip multifunctional fluorescent-magnetic Janus helical microswimmers
Energy Technology Data Exchange (ETDEWEB)
Hwang, G., E-mail: gilgueng.hwang@lpn.cnrs.fr; Decanini, D.; Leroy, L.; Haghiri-Gosnet, A. M. [Laboratoire de Photonique et de Nanostructures, CNRS, Route de Nozay, Marcoussis 91460 (France)
2016-03-15
Microswimmers integrated into microfluidic devices that are capable of self-illumination through fluorescence could revolutionize many aspects of technology, especially for biological applications. Few illumination and propulsion techniques of helical microswimmers inside microfluidic channels have been demonstrated. This paper presents the fabrication, detachment, and magnetic propulsions of multifunctional fluorescent-magnetic helical microswimmers integrated inside microfluidics. The fabrication process is based on two-photon laser lithography to pattern 3-D nanostructures from fluorescent photoresist coupled with conventional microfabrication techniques for magnetic thin film deposition by shadowing. After direct integration inside a microfluidic device, injected gas bubble allows gentle detachment of the integrated helical microswimmers whose magnetic propulsion can then be directly applied inside the microfluidic channel using external electromagnetic coil setup. With their small scale, fluorescence, excellent resistance to liquid/gas surface tension, and robust propulsion capability inside the microfluidic channel, the microswimmers can be used as high-resolution and large-range mobile micromanipulators inside microfluidic channels.
Studies of energetic-ion-driven MHD instabilities in helical plasmas with low magnetic shear
International Nuclear Information System (INIS)
Yamamoto, S.; Ascasibar, E.; Jimenez-Gomez, R.
2012-11-01
We discuss the features of energetic-ion-driven MHD instabilities such as Alfvén eigenmodes (AEs) in three-dimensional magnetic configuration with low magnetic shear and low toroidal field period number (N p ) that are characteristic of advanced helical plasmas. Comparison of experimental and numerical studies in Heliotron J with those in TJ-II indicates that the most unstable AE is global AE (GAE) in low magnetic shear configuration in spite of the iota and the helicity-induced AE (HAE) is also the most unstable AE in the high iota configuration. (author)
Ergodization of magnetic surfaces due to finite beta effect in a helical system
International Nuclear Information System (INIS)
Hayashi, Takaya.
1989-04-01
Breaking of magnetic surfaces due to finite beta effect in a l=2 heliotron/torsatron configuration is studied by using a newly developed three dimensional equilibrium code. Breaking can be suppressed by a larger aspect ratio configuration, shaping of magnetic surface (inward shift or prolate shape), pitch modulation of helical coils, or pressure profile control. (author)
International Nuclear Information System (INIS)
Staton, Robert J.; Langen, Katja M.; Kupelian, Patrick A.; Meeks, Sanford L.
2009-01-01
In this study, two potential sources of IMRT delivery error have been identified for helical tomotherapy delivery using the HiART system (TomoTherapy, Inc., Madison, WI): Rotational output variation and target degradation. The HiArt system is known to have output variation, typically about ±2%, due to the absence of a dose servo system. On the HiArt system, x-ray target replacement is required approximately every 10-12 months due to target degradation. Near the end of target life, the target thins and causes a decrease in the beam energy and a softening of the beam profile at the lateral edges of the beam. The purpose of this study is to evaluate the dosimetric effects of rotational output variation and target degradation by modeling their effects and incorporating them into recalculated treatment plans for three clinical scenarios: Head and neck, partial breast, and prostate. Models were created to emulate both potential sources of error. For output variation, a model was created using a sine function to match the amplitude (±2%), frequency, and phase of the measured rotational output variation data. A second model with a hypothetical variation of ±7% was also created to represent the largest variation that could exist without violating the allowable dose window in the delivery system. A measured beam profile near the end of target life was used to create a modified beam profile model for the target degradation. These models were then incorporated into the treatment plan by modifying the leaf opening times in the delivery sinogram. A new beam model was also created to mimic the change in beam energy seen near the end of target life. The plans were then calculated using a research version of the PLANNED ADAPTIVE treatment planning software from TomoTherapy, Inc. Three plans were evaluated in this study: Head and neck, partial breast, and prostate. The D 50 of organs at risk, the D 95 for planning target volumes (PTVs), and the local dose difference were used to
Rotating magnetizations in electrical machines: Measurements and modeling
Directory of Open Access Journals (Sweden)
Andreas Thul
2018-05-01
Full Text Available This paper studies the magnetization process in electrical steel sheets for rotational magnetizations as they occur in the magnetic circuit of electrical machines. A four-pole rotational single sheet tester is used to generate the rotating magnetic flux inside the sample. A field-oriented control scheme is implemented to improve the control performance. The magnetization process of different non-oriented materials is analyzed and compared.
Rotating magnetizations in electrical machines: Measurements and modeling
Thul, Andreas; Steentjes, Simon; Schauerte, Benedikt; Klimczyk, Piotr; Denke, Patrick; Hameyer, Kay
2018-05-01
This paper studies the magnetization process in electrical steel sheets for rotational magnetizations as they occur in the magnetic circuit of electrical machines. A four-pole rotational single sheet tester is used to generate the rotating magnetic flux inside the sample. A field-oriented control scheme is implemented to improve the control performance. The magnetization process of different non-oriented materials is analyzed and compared.
Magnetic field structure near the plasma boundary in helical systems and divertor tokamaks
International Nuclear Information System (INIS)
Nagasaki, Kazunobu; Itoh, Kimitaka
1990-02-01
Magnetic field structure of the scrape off layer (SOL) region in both helical systems and divertor tokamaks is studied numerically by using model fields. The connection length of the field line to the wall is calculated. In helical systems, the connection length, L, has a logarithmic dependence on the distance from the outermost magnetic surface or that from the residual magnetic islands. The effect of axisymmetric fields on the field structure is also determined. In divertor tokamaks, the connection length also has logarithmic properties near the separatrix. Even when the perturbations, which resonate to rational surfaces near the plasma boundary, are added, logarithmic properties still remain. We compare the connection length of torsatron/helical-heliotron systems with that of divertor tokamaks. It is found that the former is shorter than the latter by one order magnitude with similar aspect ratio. (author)
A study on stability of rotating magnets
International Nuclear Information System (INIS)
Higuchi, N.; Kaiho, K.; Ishii, I.
1996-01-01
Superconducting power generators are being developed in Japan, as a part of a R and D program on energy technology, the New Sunshine Project. In this development, national laboratories are taking a role of fundamental studies to contribute to the R and D being carried out mainly by the manufacturers involved in a research association, Super-GM. Stabilities of magnets in a high gravitational field up to 2,000 G are discussed, based upon the experimental results of forced quench tests in a set of rotating magnets, in order to establish the stability design criterion of field windings of superconducting generators. Relations of propagation velocities, recovery currents, minimum quench energy and heat transfer characteristics are studied, a good agreement between the experimental results and a theory confirmed the improvement of magnet stability in a high gravitational field because of the enhanced heat transfer characteristics
Behavior of magnetic islands in 3D MHD equilibria of helical devices
International Nuclear Information System (INIS)
Hayashi, T.; Sato, T.; Nakajima, N.
1994-09-01
Magnetic island formation in three-dimensional finite-β equilibria in the H-1 Heliac is studied by using the HINT code. It is found that the size of a dangerous island should increase with β but that a destruction of the equilibrium at low β is avoided because the rotational transform evolves to exclude the rational surface concerned. At higher β there is evidence of near-resonant flux surface deformations which may lead to an equilibrium limit. A reconnected equilibrium at still higher β exhibits a double island structure which is similar to homoclinic phase portraits which have been observed after separatrix reconnection in Hamiltonian systems. Physical mechanism of the island formation in finite-β helical equilibria is investigated to confirm there are cases where the global effect of the Pfirsch-Schlueter currents is important. The earlier theory is extended to elucidate the occurence of the complete self-healing of island when the resistive interchange criterion satisfied. (author)
Ultrasensitive magnetometers based on rotational magnetic excitation
International Nuclear Information System (INIS)
Hristoforou, E.; Svec, P. Sr.
2014-01-01
Three new types of fluxgate magnetometers are presented in this paper, able to monitor the three components of the ambient field, all of them based on the principle of rotational excitation field. The first type is based on Yttrium- Iron Garnet (YIG) single crystal film, magnetized with rotational field on its plane, where the 2"n"d, 4"t"h and 6"t"h harmonics offer the three components of the ambient field with sensitivity better than 1 pT at 0.2 Hz, its size being 25 cm"3. The second type is based on permalloy film, where the rotational excitation field on its plane offers change of magnetoresistance with sensitivity better than 10 pT at 1 Hz, uncertainty of 1 ppm and size ∼ 8 cm"3. The third type, is based on amorphous film, where the rotation field mode offer sensitivity better than 100 pT at 1 Hz, uncertainty of 10 ppm and size ∼ 10 mm"3. (authors)
Dynamics of local isolated magnetic flux tubes in a fast-rotating stellar atmosphere
International Nuclear Information System (INIS)
Chou, W.; Tajima, C.T.; Shibata, K.
1998-01-01
Dynamics of magnetic flux tubes in the fast rotating stellar atmosphere is studied. We focus on the effects and signatures of the instability of the flux tube emergence influenced by the Coriolis force. We present the result from a linear stability analysis and discuss its possible signatures in the course of the evolution of G-type and M-type stars. We present a three dimensional magnetohydrodynamical simulation of local isolated magnetic flux tubes under a magnetic buoyancy instability in co-rotating Cartesian coordinates. We find that the combination of the buoyancy instability and the Coriolis effect gives rise to a mechanism, to twist the emerging magnetic flux tube into a helical structure. The tilt angle, east-west asymmetry and magnetic helicity of the Twisted flux tubes in the simulations are studied in detail. The linear and nonlinear analyses provide hints as to what kind of pattern of large spots in young M-type main-sequence stars might be observed. We find that young and old G-type stars may have different distributions of spots while M-type stars may always have low latitudes spots. The size of stellar spots may decrease when a star becomes older, due to the decreasing of magnetic field. A qualitative comparison with solar observations is also presented
Magnetic Energy and Helicity in Two Emerging Active Regions in the Sun
Liu, Y.; Schuck, P. W.
2012-01-01
The magnetic energy and relative magnetic helicity in two emerging solar active regions, AR 11072 and AR 11158,are studied. They are computed by integrating over time the energy and relative helicity fluxes across the photosphere. The fluxes consist of two components: one from photospheric tangential flows that shear and braid field lines (shear term), the other from normal flows that advect magnetic flux into the corona (emergence term). For these active regions: (1) relative magnetic helicity in the active-region corona is mainly contributed by the shear term,(2) helicity fluxes from the emergence and the shear terms have the same sign, (3) magnetic energy in the corona (including both potential energy and free energy) is mainly contributed by the emergence term, and(4) energy fluxes from the emergence term and the shear term evolved consistently in phase during the entire flux emergence course.We also examine the apparent tangential velocity derived by tracking field-line footpoints using a simple tracking method. It is found that this velocity is more consistent with tangential plasma velocity than with the flux transport velocity, which agrees with the conclusion by Schuck.
Heisenberg Model in a Rotating Magnetic Field
Institute of Scientific and Technical Information of China (English)
LIN Qiong-Gui
2005-01-01
We study the Heisenberg model under the influence of a rotating magnetic field. By using a time-dependent unitary transformation, the time evolution operator for the Schrodinger equation is obtained, which involves no chronological product. The spin vectors (mean values of the spin operators) are obtained as explicit functions of time in the most general case. A series of cyclic solutions are presented. The nonadiabatic geometric phases of these cyclic solutions are calculated, and are expressed in terms of the solid angle subtended by the closed trace of the total spin vector, as well as in terms of those of the individual spins.
Moraitis, Kostas; Archontis, Vasilis; Tziotziou, Konstantinos; Georgoulis, Manolis K.
We calculate the instantaneous free magnetic energy and relative magnetic helicity of solar active regions using two independent approaches: a) a non-linear force-free (NLFF) method that requires only a single photospheric vector magnetogram, and b) well known semi-analytical formulas that require the full three-dimensional (3D) magnetic field structure. The 3D field is obtained either from MHD simulations, or from observed magnetograms via respective NLFF field extrapolations. We find qualitative agreement between the two methods and, quantitatively, a discrepancy not exceeding a factor of 4. The comparison of the two methods reveals, as a byproduct, two independent tests for the quality of a given force-free field extrapolation. We find that not all extrapolations manage to achieve the force-free condition in a valid, divergence-free, magnetic configuration. This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund.
Electrical manipulation of dynamic magnetic impurity and spin texture of helical Dirac fermions
Wang, Rui-Qiang; Zhong, Min; Zheng, Shi-Han; Yang, Mou; Wang, Guang-Hui
2016-05-01
We have theoretically investigated the spin inelastic scattering of helical electrons off a high-spin nanomagnet absorbed on a topological surface. The nanomagnet is treated as a dynamic quantum spin and driven by the spin transfer torque effect. We proposed a mechanism to electrically manipulate the spin texture of helical Dirac fermions rather than by an external magnetic field. By tuning the bias voltage and the direction of impurity magnetization, we present rich patterns of spin texture, from which important fingerprints exclusively associated with the spin helical feature are obtained. Furthermore, it is found that the nonmagnetic potential can create the resonance state in the spin density with different physics as the previously reported resonance of charge density.
Bian, He-Dong; Yang, Xiao-E.; Yu, Qing; Chen, Zi-Lu; Liang, Hong; Yan, Shi-Ping; Liao, Dai-Zheng
2008-01-01
Two helical coordination polymeric copper(II) complexes bearing amino acid Schiff bases HL or HL', which are condensed from 2-hydroxy-1-naphthaldehyde with 2-aminobenzoic acid or L-valine, respectively, have been prepared and characterised by X-ray crystallography. In [CuL] n ( 1) the copper(II) atoms are bridged by syn- anti carboxylate groups giving infinite 1-D right-handed helical chains which are further connected by weak C-H⋯Cu interactions to build a 2-D network. While in [CuL'] n ( 2) the carboxylate group acts as a rare monatomic bridge to connect the adjacent copper(II) atoms leading to the formation of a left-handed helical chain. Magnetic susceptibility measurements indicate that 1 exhibits weak ferromagnetic interactions whereas an antiferromagnetic coupling is established for 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data.
Rasskazov, Andrey; Chertovskih, Roman; Zheligovsky, Vladislav
2018-04-01
We introduce six families of three-dimensional space-periodic steady solenoidal flows, whose kinetic helicity density is zero at any point. Four families are analytically defined. Flows in four families have zero helicity spectrum. Sample flows from five families are used to demonstrate numerically that neither zero kinetic helicity density nor zero helicity spectrum prohibit generation of large-scale magnetic field by the two most prominent dynamo mechanisms: the magnetic α -effect and negative eddy diffusivity. Our computations also attest that such flows often generate small-scale field for sufficiently small magnetic molecular diffusivity. These findings indicate that kinetic helicity and helicity spectrum are not the quantities controlling the dynamo properties of a flow regardless of whether scale separation is present or not.
Evidence for a rotating helical filament in L1641, part of the Orion cloud complex
International Nuclear Information System (INIS)
Uchida, Y.
1991-01-01
Interstellar cloud structures, typically 10-30 pc long and 3-5 pc wide, are often seen extending outwards from dense clouds that show marked enhancement of star formation within them. We have used the Nagoya 4-m radiotelescope to study one such 'streamer', L1641, a part of the giant molecular-cloud complex in Orion, lying south of the Kleinmann-Low (KL) nebula. Using the 110-GHz line of 13 Co (J=1-0), we have obtained intensity and velocity data, and find within the streamer a dense filament with a helical structure, spinning in the same sense as the gas in the Orion KL region. We propose a model for this structure in which the streamer, through the action of the interstellar magnetic field, acts as an angular-momentum drain on the Orion KL region, allowing it to collapse. In this model, the ∼30-pc-long streamer is essential to the formation of the cloud, as well as the formation of stars within the dense cloud. (author)
Mechanism of viscosity effect on magnetic island rotation
Energy Technology Data Exchange (ETDEWEB)
Mikhailovskii, A.B.; Konovalov, S.V. [Institute of Nuclear Fusion, Russian Research Centre ' Kurchatov Institute' , Kurchatov Sq., 1, Moscow (Russian Federation); Pustovitov, V.D. [National Inst. for Fusion Science, Toki, Gifu (Japan); Tsypin, V.S. [Institute of Physics, University of Sao Paulo, Rua do Matao, Travessa R, SP (Brazil)
2000-04-01
It is shown that plasma viscosity does not influence the magnetic island rotation directly. Nevertheless, it leads to nonstationarity of the plasma velocity. This nonstationarity is the reason of the viscosity effect on island rotation. (author)
Disorder effects on helical edge transport in graphene under a strong tilted magnetic field
Huang, Chunli; Cazalilla, Miguel A.
2015-10-01
In a recent experiment, Young et al. [Nature (London) 505, 528 (2014), 10.1038/nature12800] observed a metal to insulator transition as well as transport through helical edge states in monolayer graphene under a strong, tilted magnetic field. Under such conditions, the bulk is a magnetic insulator which can exhibit metallic conduction through helical edges. It was found that the two-terminal conductance of the helical channels deviates from the expected quantized value (=e2/h per edge, at zero temperature). Motivated by this observation, we study the effect of disorder on the conduction through the edge channels. We show that, unlike for helical edges of topological insulators in semiconducting quantum wells, a disorder Rashba spin-orbit coupling does not lead to backscattering, at least to leading order. Instead, we find that the lack of perfect antialignment of the electron spins in the helical channels to be the most likely cause for backscattering arising from scalar (i.e., spin-independent) impurities. The intrinsic spin-orbit coupling and other time-reversal symmetry-breaking and/or sublattice parity-breaking potentials also lead to (subleading) corrections to the channel conductance.
International Nuclear Information System (INIS)
Antoni, Bernard; Nazet, Christian.
1975-07-01
A generator of electrical energy in which magnetic field compression is achieved by a solid explosive is described. The magnetic flux losses have been calculated for generators of various configurations by the skin depth concept. Calculations take the Joule heating of conductors into account. In helical generators the magnetic flux losses are higher than those calculated by considering diffusion only. Additional losses approximately as important as diffusion losses have already been observed elsewhere on similar devices. Detailed calculations of the motion of the explosively driven inner conductor show that losses come from the jumps encountered by sliding contact moving along the helix. The jumps are caused by little geometrical defects and the consequence on losses is strongly dependent on current intensity. The jumps decrease when the pitch of helix increases. The jumps are detrimental to the efficient use of the explosive energy. With helical generators only 5% of the energy is transferred into magnetic energy [fr
Effect of magnetic axis shift on neoclassical transport in helical torus
International Nuclear Information System (INIS)
Sanuki, Heiji; Todoroki, Jiro
2004-01-01
Neoclassical transport for large helical device (LHD) configurations is studied by solving the bounce-averaged Fokker-Planck equation. Numerical code employed in the present paper (CHD1) is much faster and more efficient than existing transport codes. Effects of the magnetic axis shift on the mono-energetic transport coefficients are studied in detail for the LHD configurations, revealing that a strong inward shift of the magnetic axis can reduce remarkably the neoclassical ripple transport. (author)
Directory of Open Access Journals (Sweden)
N. Tsoupas
2013-04-01
Full Text Available The principle of using multiple partial helical magnets to preserve the polarization of the proton beam during its acceleration was applied successfully to the alternating gradient synchrotron (AGS which currently operates with two partial helical magnets. In this paper we further explore this idea by using four partial helical magnets placed symmetrically in the AGS ring. This provides many advantages over the present setup of the AGS, which uses two partial helical magnets. First, the symmetric placement of the four helical magnets and their relatively lower field of operation allows for better control of the AGS optics with reduced values of the beta functions especially near beam injection and allows both the vertical and horizontal tunes to be placed within the “spin tune gap,” therefore eliminating the horizontal and vertical intrinsic spin resonances of the AGS during the acceleration cycle. Second, it provides a wider spin tune gap. Third, the vertical spin direction during beam injection and extraction is closer to vertical. Although the spin tune gap, which is created with four partial helices, can also be created with a single or two partial helices, the high field strength of a single helical magnet which is required to generate such a spin tune gap makes the use of the single helical magnet impractical, and that of the two helical magnets rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare them with those from the present setup of the AGS that uses two partial helical magnets. Although in this paper we specifically discuss the effect of the four partial helices on the AGS, this method which can eliminate simultaneously the vertical and horizontal intrinsic spin resonances is a general method and can be applied to any medium energy synchrotron which operates in similar energy range like the AGS and provides the required space to
Conceptual design of the superconducting magnet system for the helical fusion reactor
International Nuclear Information System (INIS)
Yanagi, Nagato; Hamaguchi, Shinji; Takahata, Kazuya; Natsume, Kyohei
2013-01-01
Current status of conceptual design of superconducting magnet system and low temperature system for the helical fusion reactor are introduced. There are three kinds of candidates of superconducting magnets such as Cable-in-conduit (CIC), Low-Temperature Superconductor (LTS) and High-Temperature Superconductor (HTS). Their characteristic properties, coil designs and cooling systems are stated. The freezer and low temperature distribution system, bus line and current lead, and excitation power source for superconducting coil are reported. The various elements of superconducting magnet system of FFHR-d1, partial cross section of FFHR helical coil using CIC, conceptual diagram of helical coil winding method of FFHR using CIC, relation among mass flow of supercritical helium supplied into CIC conductor and temperature increasing and pressure loss, cross section structure of LTS indirect-cooling conductor at 100 kA, cross section of 100-kA HTS conductor, connection method of helical coil segment and YBCO conductor are illustrated. (S.Y.)
Magnet design with 100-kA HTS STARS conductors for the helical fusion reactor
Yanagi, N.; Terazaki, Y.; Ito, S.; Tamura, H.; Hamaguchi, S.; Mito, T.; Hashizume, H.; Sagara, A.
2016-12-01
The high-temperature superconducting (HTS) option is employed for the conceptual design of the LHD-type helical fusion reactor FFHR-d1. The 100-kA-class STARS (Stacked Tapes Assembled in Rigid Structure) conductor is used for the magnet system including the continuously wound helical coils. Protection of the magnet system in case of a quench is a crucial issue and the hot-spot temperature during an emergency discharge is estimated based on the zero-dimensional and one-dimensional analyses. The number of division of the coil winding package is examined to limit the voltage generation. For cooling the HTS magnet, helium gas flow is considered and its feasibility is examined by simple analysis as a first step.
Helical-axis stellarators with noninterlocking planar coils
International Nuclear Information System (INIS)
Reiman, A.; Boozer, A.
1983-08-01
The properties of helical axis stellarator fields generated by unlinked, planar coils are described. It is shown that such fields can have a magnetic well and large rotational transform, implying large equilibrium and stability beta limits
Helical-axis stellarators with noninterlocking planar coils
Energy Technology Data Exchange (ETDEWEB)
Reiman, A.; Boozer, A.
1983-08-01
The properties of helical axis stellarator fields generated by unlinked, planar coils are described. It is shown that such fields can have a magnetic well and large rotational transform, implying large equilibrium and stability beta limits.
NMR system and method having a permanent magnet providing a rotating magnetic field
Schlueter, Ross D [Berkeley, CA; Budinger, Thomas F [Berkeley, CA
2009-05-19
Disclosed herein are systems and methods for generating a rotating magnetic field. The rotating magnetic field can be used to obtain rotating-field NMR spectra, such as magic angle spinning spectra, without having to physically rotate the sample. This result allows magic angle spinning NMR to be conducted on biological samples such as live animals, including humans.
FARADAY ROTATION: EFFECT OF MAGNETIC FIELD REVERSALS
International Nuclear Information System (INIS)
Melrose, D. B.
2010-01-01
The standard formula for the rotation measure (RM), which determines the position angle, ψ = RMλ 2 , due to Faraday rotation, includes contributions only from the portions of the ray path where the natural modes of the plasma are circularly polarized. In small regions of the ray path where the projection of the magnetic field on the ray path reverses sign (called QT regions) the modes are nearly linearly polarized. The neglect of QT regions in estimating RM is not well justified at frequencies below a transition frequency where mode coupling changes from strong to weak. By integrating the polarization transfer equation across a QT region in the latter limit, I estimate the additional contribution Δψ needed to correct this omission. In contrast with a result proposed by Broderick and Blandford, Δψ is small and probably unobservable. I identify a new source of circular polarization, due to mode coupling in an asymmetric QT region. I also identify a new circular-polarization-dependent correction to the dispersion measure at low frequencies.
FARADAY ROTATION: EFFECT OF MAGNETIC FIELD REVERSALS
Energy Technology Data Exchange (ETDEWEB)
Melrose, D B [SIfA, School of Physics, University of Sydney, NSW 2006 (Australia)
2010-12-20
The standard formula for the rotation measure (RM), which determines the position angle, {psi} = RM{lambda}{sup 2}, due to Faraday rotation, includes contributions only from the portions of the ray path where the natural modes of the plasma are circularly polarized. In small regions of the ray path where the projection of the magnetic field on the ray path reverses sign (called QT regions) the modes are nearly linearly polarized. The neglect of QT regions in estimating RM is not well justified at frequencies below a transition frequency where mode coupling changes from strong to weak. By integrating the polarization transfer equation across a QT region in the latter limit, I estimate the additional contribution {Delta}{psi} needed to correct this omission. In contrast with a result proposed by Broderick and Blandford, {Delta}{psi} is small and probably unobservable. I identify a new source of circular polarization, due to mode coupling in an asymmetric QT region. I also identify a new circular-polarization-dependent correction to the dispersion measure at low frequencies.
International Nuclear Information System (INIS)
Wink, Nicole M; McNitt-Gray, Michael F; Solberg, Timothy D
2005-01-01
While respiration-correlated CT is gaining acceptance in clinical radiotherapy, the effect of scanning parameters on the image quality has yet to be addressed. The intent of this study was to characterize the effects of gantry rotation and table speed on various image quality characteristics in multi-slice, helical, retrospectively-gated CT images. Images of stationary and moving phantoms were obtained in helical mode on a 20-slice CT scanner. Motion was generated by a computer-controlled platform capable of moving simultaneously in two dimensions. Motion was monitored using a pressure gauge inserted inside an adjustable belt. Selected scans were retrospectively gated into ten phases based on the monitored motion. Gantry rotation speeds of 0.5 s and 1.0 s were evaluated with pitches ranging from 0.1 to 0.45. Several parameters, including calculated object volumes, trajectory (movement from peak to trough), deformation (actual volume divided by volume created with the maximum diameter of contoured object) and z-axis resolution, were used to characterize image quality. These studies indicate that for objects in the peak phase of a movement pattern that simulates breathing, retrospectively gated scans using fast gantry rotation speeds produce volume, trajectory, deformation and z-axis resolution results comparable with those of a stationary object
Magnetic Field Studies in BL Lacertae through Faraday Rotation and a Novel Astrometric Technique
Directory of Open Access Journals (Sweden)
Sol N. Molina
2017-12-01
Full Text Available It is thought that dynamically important helical magnetic fields twisted by the differential rotation of the black hole’s accretion disk or ergosphere play an important role in the launching, acceleration, and collimation of active galactic nuclei (AGN jets. We present multi-frequency astrometric and polarimetric Very Long Baseline Array (VLBA images at 15, 22, and 43 GHz, as well as Faraday rotation analyses of the jet in BL Lacertae as part of a sample of AGN jets aimed to probe the magnetic field structure at the innermost scales to test jet formation models. The novel astrometric technique applied allows us to obtain the absolute position at mm wavelengths without any external calibrator.
Helical Magnetic Fields in AGN Jets Y. J. Chen1,2,∗ , G.-Y. Zhao1,2 ...
Indian Academy of Sciences (India)
Abstract. We establish a simple model to describe the helical mag- netic fields in AGN jets projected on the sky plane and the line-of-sight. This kind of profile has been detected in the polarimetric VLBI observa- tion of many blazar objects, suggesting the existence of helical magnetic fields in these sources. Key words.
International Nuclear Information System (INIS)
Sun, Tao; Huang, Qiang; Shi, Qing; Wang, Huaping; Li, Pengyun; Fukuda, Toshio; Hu, Chengzhi; Nakajima, Masahiro
2016-01-01
Helical structures assembled using alginate microfibers have a promising spatial architecture mimicking in vivo vessels for culturing vascular cells. However, the helical structure can only be assembled at the macroscale, since a microassembly-based approach has not yet been developed. In this paper, we propose a magnetic-field-based micromanipulation method to fabricate a helical microstructure. By microfluidic spinning, alginate microfibers encapsulating magnetic nanoparticles are synthesized to enable the control of an electromagnetic needle (EMN). We developed a microrobotic system to actuate a micropipette to fix a free end of the microfiber, and then move the EMN to reel the microfiber around a micropillar. The motion of the EMN is guided using an upright microscope and a side-view camera. Because of the limitation of operation space, a spacer sleeve was designed to keep the tip of the EMN attracted to the microfiber, and simultaneously to keep the other part of the EMN isolated from the microfiber. To ensure the availability of the microfiber for continuously coiling, we enable the EMN tip to slide on the surface of the microfiber without changing the tensioning of the microfiber for positioning control. Furthermore, stable and repeatable micromanipulation was achieved to form multi-turn microfiber coils based on the motion planning of the EMN. Finally, we successfully fabricated a helical microstructure that can be applied in vascular tissue engineering in the future. (paper)
Rotational magnetization of anisotropic media: Lag angle, ellipticity and accommodation
International Nuclear Information System (INIS)
Kahler, G.R.; Della Torre, E.
2006-01-01
This paper discusses the change in the ellipticity of two-dimensional magnetization trajectories as the applied field rotates from the easy axis to the hard axis of a material. Furthermore, the impact that the reversible magnetization has on the ellipticity is discussed, including the relationship between the magnetization squareness and the reversible component of the magnetization
Energy Technology Data Exchange (ETDEWEB)
Beidler, C; Brakel, R; Burhenn, R; Dinklage, A; Erckmann, V; Feng, Y; Geiger, J; Hartmann, D; Hirsch, M; Jaenicke, R; Koenig, R; Laqua, H P; Maassberg, H; Wagner, F; Weller, A; Wobig, H [Max-Planck Institut fuer Plasmaphysik, EURATOM Association, Greifswald (Germany)
2012-09-15
Stellarators, conceived 1951 by Lyman Spitzer in Princeton, are toroidal devices that confine a plasma in a magnetic field which originates from currents in coils outside the plasma. A plasma current driven by external means, for example by an ohmic transformer, is not required for confinement. Supplying the desired poloidal field component by external coils leads to a helically structured plasma topology. Thus stellarators - or helical confinement devices - are fully three-dimensional in contrast to the toroidal (rotational) symmetry of tokamaks. As stellarators can be free of an inductive current, whose radial distribution depends on the plasma parameters, their equilibrium must not be established via the evolving plasma itself, but to a first order already given by the vacuum magnetic field. They do not need an active control (like positional feedback) and therefore cannot suffer from its failure. The outstanding conceptual advantage of stellarators is the potential of steady state plasma operation without current drive. As there is no need for current drive, the recirculating power is expected to be smaller than in equivalent tokamaks. The lack of a net current avoids current driven instabilities; specifically, no disruptions, no resistive wall modes and no conventional or neoclassical tearing modes appear. Second order pressure-driven currents (Pfirsch-Schlueter, bootstrap) exist but they can be modified and even minimized by the magnetic design. The magnetic configuration of helical devices naturally possesses a separatrix, which allows the implementation of a helically structured divertor for exhaust and impurity control. (author)
A simplified numerical analysis of helical instabilities of arcs in axial magnetic field
International Nuclear Information System (INIS)
Gong Ye; Lu Wenyan; Liu Jinyuan; Zheng Shu; Gong Jiquan
2002-01-01
The energy equations were simplified by the correct electrostatic ordering under electrostatic approximation. The effects of the external axial magnetic field, the current profiles and arc currents on the helical instabilities of arcs were studied by using numerical method. In the presence of the external magnetic field, numerical results show that when the current profile of an arc column is the uniform distribution, the short wavelength perturbation can be stabilized by positive direction magnetic field, whereas the long wavelength perturbation can be stabilized by reverse magnetic field. When the current profile of an arc column has a parabolic distribution, in the short wavelength perturbation case, the effect of positive direction magnetic field on the arc stability is very small. However, its stabilizing effect is enhanced for the long wavelength perturbation. The intermediate and long wavelength perturbations can also be stabilized by reverse magnetic field
Observation of disruptions in tokamak plasma under the influence of resonant helical magnetic fields
International Nuclear Information System (INIS)
Araujo, M.; Vannucci, A.; Caldas, I.
1996-01-01
Disruptive instabilities were investigated in the small tokamak TBR-1 during the application of resonant helical magnetic fields created by external helical windings. Indications were found that the main triggering mechanism of the disruptions was the rapid increase of the m=2/n=1 mode which, apparently after reaching a certain amplitude, interacts with other resistive modes: the internal 1/1 mode in the case of minor disruptions. After the coupling, the growth of the associated islands would create a chaotic field line distribution in the region between the corresponding rational magnetic surfaces which caused the gross particle transport and, finally, destroyed the confinement. In addition, investigations on higher Z eff discharges in which a mixture of helium and hydrogen was used resulted in much more unstable plasmas but apparently did not alter basic characteristics of the disruptions
Experimental determination of limit angle of helical anisotropy in amorphous magnetic microwires
International Nuclear Information System (INIS)
Chizhik, A.; Zhukov, A.; Blanco, J.M.; Gonzalez, J.; Gawronski, P.
2009-01-01
The influence of the torsion stress on the surface magnetic structure in Co-rich amorphous glass covered microwires has been investigated. The limit angle of the surface helical anisotropy induced by the torsion stress has been determined in agreement with the model which considers the torsion stress as a interference of two tensile stresses of opposite signs directed at 45 deg. and 135 deg. relative to the longitudinal axis of the wire
Evidence for Mixed Helicity in Erupting Filaments
Muglach, K.; Wang, Y.-M.; Kliem, B.
2009-09-01
Erupting filaments are sometimes observed to undergo a rotation about the vertical direction as they rise. This rotation of the filament axis is generally interpreted as a conversion of twist into writhe in a kink-unstable magnetic flux rope. Consistent with this interpretation, the rotation is usually found to be clockwise (as viewed from above) if the post-eruption arcade has right-handed helicity, but counterclockwise if it has left-handed helicity. Here, we describe two non-active-region filament events recorded with the Extreme-Ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory in which the sense of rotation appears to be opposite to that expected from the helicity of the post-event arcade. Based on these observations, we suggest that the rotation of the filament axis is, in general, determined by the net helicity of the erupting system, and that the axially aligned core of the filament can have the opposite helicity sign to the surrounding field. In most cases, the surrounding field provides the main contribution to the net helicity. In the events reported here, however, the helicity associated with the filament "barbs" is opposite in sign to and dominates that of the overlying arcade.
Bifurcation of plasma cylinder equilibrium into a stationary helical flow with magnetic islands
International Nuclear Information System (INIS)
Gubarev, V.F.; Dmitrenko, A.G.; Fesenko, A.I.
1985-01-01
Introduction of the low-hydrodynamic viscosity into the system of nonlinear MHD-equations enabled to use the bifurcation theory for the investigation into nonlinear phenomena connected with a tearing mode. The existance of a stable stationary helical flow with magnetic islands in the vicinity of a neutral curve is established. Fransfer from an axisymmetric equilibrium of a plasma cylinder to a helical one takes place only under soft conditions at both sides of the neutral curve. This result confirms the fact that the tearing mode, actually, is not an instability and may be con sidered only as a reason of formation of equilibrium with splitted magnetic surfaces. Really, changing the q 0 parameter (q 0 is the value proportional to a value of stability margin) at the plasma filament boundary a plasma equilibrium is attained corresponding to a stable branch of the bifurcation curve. In this case, a stable branch of the bifurcation curve corresponds to a helical stationary flow with magnetic islands in the instabwility region determined from the linear theory
Final Technical Report - ''Determining How Magnetic Helicity Injection Really Works''
International Nuclear Information System (INIS)
Paul M. Bellan
2005-01-01
This research program involved direct observation of the complicated plasma dynamics underlying spheromak formation. Spheromaks are self-organizing magnetically dominated plasma configurations which potentially offer a simple, low-cost means for confining the plasma in a controlled thermonuclear fusion reactor. The spheromak source used in these studies was a coaxial co-planar magnetized plasma gun which was specifically designed to have the simplest relevant geometry. The simplicity of the geometry facilitated understanding of the basic physics and minimized confusion that would otherwise have resulted from complexities due to the experimental geometry. The coaxial plasma gun was mounted on one end of a large vacuum tank that had excellent optical access so the spheromak formation process could be tracked in detail using ultra-high speed cameras. The main accomplishments of this research program were (1) obtaining experimental data characterizing the detailed physics underlying spheromak formation and the development of new theoretical models motivated by these observations, (2) determining the relationship between spheromak physics and astrophysical jets, (3) developing a new high-speed camera diagnostic for the SSPX spheromak at the Lawrence Livermore National Lab, and (4) training graduate students and postdoctoral fellows
Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy
International Nuclear Information System (INIS)
Buznikov, N.A.; Antonov, A.S.; Granovsky, A.B.; Kim, C.G.; Kim, C.O.; Li, X.P.; Yoon, S.S.
2006-01-01
The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau-Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material
Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy
Energy Technology Data Exchange (ETDEWEB)
Buznikov, N.A. [Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow 125412 (Russian Federation) and Research Center for Advanced Magnetic Materials, Chungnam National University, Daeduk Science Town, Daejeon 305-764 (Korea, Republic of)]. E-mail: n_buznikov@mail.ru; Antonov, A.S. [Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow 125412 (Russian Federation); Granovsky, A.B. [Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Kim, C.G. [Research Center for Advanced Magnetic Materials, Chungnam National University, Daeduk Science Town, Daejeon 305-764 (Korea, Republic of)]. E-mail: cgkim@cnu.ac.kr; Kim, C.O. [Research Center for Advanced Magnetic Materials, Chungnam National University, Daeduk Science Town, Daejeon 305-764 (Korea, Republic of); Li, X.P. [Department of Mechanical Engineering and Division of Bioengineering, National University of Singapore, Singapore 119260 (Singapore); Yoon, S.S. [Research Center for Advanced Magnetic Materials, Chungnam National University, Daeduk Science Town, Daejeon 305-764 (Korea, Republic of); Department of Physics, Andong National University, Andong 760-749 (Korea, Republic of)
2006-01-15
The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau-Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material.
Energy Technology Data Exchange (ETDEWEB)
Zapiór, Maciej; Martinez-Gómez, David, E-mail: zapior.maciek@gmail.com [Physics Department, University of the Balearic Islands, Cra. de Valldemossa, km 7.5. Palma (Illes Balears), E-07122 (Spain)
2016-02-01
Based on the data collected by the Vacuum Tower Telescope located in the Teide Observatory in the Canary Islands, we analyzed the three-dimensional (3D) motion of so-called knots in a solar prominence of 2014 June 9. Trajectories of seven knots were reconstructed, giving information of the 3D geometry of the magnetic field. Helical motion was detected. From the equipartition principle, we estimated the lower limit of the magnetic field in the prominence to ≈1–3 G and from the Ampère’s law the lower limit of the electric current to ≈1.2 × 10{sup 9} A.
Zapiór, Maciej; Martínez-Gómez, David
2016-02-01
Based on the data collected by the Vacuum Tower Telescope located in the Teide Observatory in the Canary Islands, we analyzed the three-dimensional (3D) motion of so-called knots in a solar prominence of 2014 June 9. Trajectories of seven knots were reconstructed, giving information of the 3D geometry of the magnetic field. Helical motion was detected. From the equipartition principle, we estimated the lower limit of the magnetic field in the prominence to ≈1-3 G and from the Ampère’s law the lower limit of the electric current to ≈1.2 × 109 A.
[Magnetic helicity and current drive in fusion devices]. Final technical report
International Nuclear Information System (INIS)
1998-01-01
The research program focused on two main themes: (i) magnetic helicity and (ii) current drive by low-frequency waves. At first these themes seemed unrelated, but as time progressed, they became interwoven, and ultimately closely connected. A sub-theme is that while the MHD model of a plasma stimulates many intriguing counter-intuitive ideas for creating and sustaining magnetic confinement configurations, usually the crux of these schemes involves some sort of breakdown of MHD, i.e., involves physics which transcends MHD
Energy Technology Data Exchange (ETDEWEB)
Sangeetha, C. R.; Rajaguru, S. P., E-mail: crsangeetha@iiap.res.in [Indian Institute of Astrophysics, Bangalore-34 (India)
2016-06-20
We derive horizontal fluid motions on the solar surface over large areas covering the quiet-Sun magnetic network from local correlation tracking of convective granules imaged in continuum intensity and Doppler velocity by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory . From these we calculate the horizontal divergence, the vertical component of vorticity, and the kinetic helicity of fluid motions. We study the correlations between fluid divergence and vorticity, and between vorticity (kinetic helicity) and the magnetic field. We find that the vorticity (kinetic helicity) around small-scale fields exhibits a hemispherical pattern (in sign) similar to that followed by the magnetic helicity of large-scale active regions (containing sunspots). We identify this pattern to be a result of the Coriolis force acting on supergranular-scale flows (both the outflows and inflows), consistent with earlier studies using local helioseismology. Furthermore, we show that the magnetic fields cause transfer of vorticity from supergranular inflow regions to outflow regions, and that they tend to suppress the vortical motions around them when magnetic flux densities exceed about 300 G (from HMI). We also show that such an action of the magnetic fields leads to marked changes in the correlations between fluid divergence and vorticity. These results are speculated to be of importance to local dynamo action (if present) and to the dynamical evolution of magnetic helicity at the small-scale.
Magnetic suspension of a rotating system. Application to inertial flywheels
International Nuclear Information System (INIS)
Lemarquand, Guy
1984-01-01
The various possible magnetic suspension configurations compatible with rotating mechanical systems are defined from studies of the characteristics of different types of magnetic bearings. The results obtained are used in the design and realization of a magnetic suspension for an inertial flywheel. (author) [fr
Superparamagnetic beads in rotating magnetic fields: microfluidic experiments
Den Toonder, J.M.J.; Bokdam, M.
2008-01-01
The effect of the Mason number, ratio of viscous and magnetic force, on suspended superparamagnetic micro sized beads was investigated experimentally. Microfluidic experiments were performed in a set-up that generates a rotating homogeneous magnetic field. In the presence of a magnetic field, the
Evolution of the magnetic helicity flux during the formation and eruption of flux ropes
Energy Technology Data Exchange (ETDEWEB)
Romano, P. [INAF—Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania (Italy); Zuccarello, F. P. [Centre for Mathematical Plasma-Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven (Belgium); Guglielmino, S. L.; Zuccarello, F., E-mail: paolo.romano@oact.inaf.it [Dipartimento di Fisica e Astronomia—Sezione Astrofisica, Università di Catania, Via S. Sofia 78, I-95123 Catania (Italy)
2014-10-20
We describe the evolution and the magnetic helicity flux for two active regions (ARs) since their appearance on the solar disk: NOAA 11318 and NOAA 11675. Both ARs hosted the formation and destabilization of magnetic flux ropes. In the former AR, the formation of the flux rope culminated in a flare of C2.3 GOES class and a coronal mass ejection (CME) observed by Large Angle and Spectrometric Coronagraph Experiment. In the latter AR, the region hosting the flux rope was involved in several flares, but only a partial eruption with signatures of a minor plasma outflow was observed. We found a different behavior in the accumulation of the magnetic helicity flux in the corona, depending on the magnetic configuration and on the location of the flux ropes in the ARs. Our results suggest that the complexity and strength of the photospheric magnetic field is only a partial indicator of the real likelihood of an AR producing the eruption of a flux rope and a subsequent CME.
Divertor Heat Flux Reduction by Resonant Magnetic Perturbations in the LHD-Type Helical DEMO Reactor
Energy Technology Data Exchange (ETDEWEB)
Yanagi, N.; Sagara, A.; Goto, T.; Masuzaki, S.; Miyazawa, J., E-mail: yanagi@lhd.nifs.ac.jp [National Institute for Fusion Science, Toki (Japan)
2012-09-15
Full text: The conceptual design studies of the LHD-type helical fusion DEMO reactor, FFHR-d1, are progressing steadfastly. The LHD-type heliotron magnetic configuration equipped with the built- in helical divertors has a potential to realize low divertor heat flux in spatial average. However, the toroidal asymmetry may give more than a couple of times higher peak heat flux at some locations, as has been experimentally observed in LHD and confirmed by magnetic field-line tracing. By providing radiation dispersion accompanied with a plasma detachment, the heat flux may decrease significantly though the compatibility with a good core plasma confinement is an important issue to be explored. Whereas the engineering difficulties for developing materials to be used under the neutron environment require even further decrease of the heat flux (even though the heliotron is a unique configuration that divertor plates be largely shielded from the direct irradiation of neutrons by breeder blankets). In this respect, we proposed, in the last IAEA FEC, a new strike point sweeping scheme using a set of auxiliary helical coils, termed helical divertor (HD) coils. The HD coils carrying a few percent of the current amplitude of the main helical coils sweep the divertor strike points without altering the core plasma. Though this scheme is effective in dispersing the heat flux in the poloidal direction, the toroidal asymmetry still remains. The AC operation may also give unforeseen engineering difficulties. We here propose that the peak heat flux be mitigated using RMP fields in steady-state. The magnetic field-lines are numerically traced in the vacuum configuration and their footprints coming to the divertor regions are counted. Their fraction plotted as a function of the toroidal angle indicates that the peak heat flux be mitigated to {approx} 20 MW per square meters at 3 GW fusion power generation without having radiation dispersion when an RMP field is applied. We note that the
Polarized Kink Waves in Magnetic Elements: Evidence for Chromospheric Helical Waves
Energy Technology Data Exchange (ETDEWEB)
Stangalini, M.; Giannattasio, F. [INAF-OAR National Institute for Astrophysics, Via Frascati 33, I-00078 Monte Porzio Catone (RM) (Italy); Erdélyi, R. [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH (United Kingdom); Jafarzadeh, S. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo (Norway); Consolini, G.; Ermolli, I. [INAF-IAPS National Institute for Astrophysics, Via del Fosso del Cavaliere, 100, I-00133 Rome (Italy); Criscuoli, S. [NSO, National Solar Observatory, Boulder, CO 80303 (United States); Guglielmino, S. L.; Zuccarello, F., E-mail: marco.stangalini@inaf.it [Department of Physics and Astronomy, University of Catania, Via S. Sofia 78, I-95125 Catania (Italy)
2017-05-01
In recent years, new high spatial resolution observations of the Sun's atmosphere have revealed the presence of a plethora of small-scale magnetic elements down to the resolution limit of the current cohort of solar telescopes (∼100–120 km on the solar photosphere). These small magnetic field concentrations, due to the granular buffeting, can support and guide several magnetohydrodynamic wave modes that would eventually contribute to the energy budget of the upper layers of the atmosphere. In this work, exploiting the high spatial and temporal resolution chromospheric data acquired with the Swedish 1 m Solar Telescope, and applying the empirical mode decomposition technique to the tracking of the solar magnetic features, we analyze the perturbations of the horizontal velocity vector of a set of chromospheric magnetic elements. We find observational evidence that suggests a phase relation between the two components of the velocity vector itself, resulting in its helical motion.
Cho, Jungyeon
2011-05-13
Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence.
International Nuclear Information System (INIS)
Cho, Jungyeon
2011-01-01
Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence.
Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity
International Nuclear Information System (INIS)
Charbonneau, James; Zhitnitsky, Ariel
2010-01-01
The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation
Nuclear resonance apparatus including means for rotating a magnetic field
International Nuclear Information System (INIS)
Sugimoto, H.
1983-01-01
A nuclear magnetic resonance apparatus including magnet apparatus for generating a homogeneous static magnetic field between its magnetic poles, shims of a magnetic substance mounted on the magnetic poles to apply a first gradient magnetic field intensity distribution in a direction orthogonal as to the direction of line of magnetic force of the static magnetic field, gradient magnetic field generating electromagnetic apparatus for generating a second gradient magnetic field having a gradient magnetic field intensity distribution in superimposition with the static magnetic field and for changing the magnetic field gradient of the first gradient magnetic field, an oscillator for generating an oscillating output having a frequency corresponding to the nuclear magnetic resonance condition of an atomic nucleus to be measured, a coil wound around a body to be examined for applying the output of said oscillator as electromagnetic waves upon the body, a receiver for detecting the nuclear magnetic resonance signals received by the coil, a gradient magnetic field controller making a magnetic field line equivalent to the combined gradient magnetic fields and for rotating the line along the section of the body to be examined by controlling said gradient magnetic field generating electromagnetic apparatus and devices for recording the nuclear magnetic resonance signals, for reconstructing the concentration distribution of the specific atomic nuclei in the section of the body, and a display unit for depicting the result of reconstruction
The magnetic field generated by a rotating charged polygon
International Nuclear Information System (INIS)
Wan, Songlin; Chen, Xiangyu; Teng, Baohua; Fu, Hao; Li, Yefeng; Wu, Minghe; Wu, Shaoyi; Balfour, E A
2014-01-01
The magnetic field along the symmetry axis of a regular polygon carrying a uniform electric charge on its edges is calculated systematically when the polygon is rotated about this axis of symmetry. A group of circular current-carrying coils arranged concentrically about the axis of the polygon has been designed to simulate the magnetic field characteristics of the rotating charged polygon. The magnetic field of the simulated coils is measured using the PASCO magnetic field sensor. The results show that the theoretical calculation agrees well with the experimental results. (paper)
Design study of a normal conducting helical snake for AGS
Takano, Junpei; Okamura, Masahiro; Roser, Thomas; MacKay, William W; Luccio, Alfredo U; Takano, Koji
2004-01-01
A new normal conducting snake magnet is being fabricated for the Alternate Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). In the Relativistic Heavy Ion Collider (RHIC) project, a superconducting type helical dipole magnets had been developed and it performed successfully in high-energy polarized proton acceleration. The new AGS helical snake has the same basic magnetic structure but is more complicated. To achieve no beam shift and no beam deflection in one magnetic device, helical pitches and rotating angles were carefully calculated. Compared to a superconducting magnet, a normal warm magnet must have a large cross- sectional area of conductors which make it difficult to design a magnet with large helical pitch. We developed a modified window frame structure to accommodate the large number of conductors. Its three dimensional magnetic field was simulated by using OPERA3D/TOSCA. 3 Refs.
International Nuclear Information System (INIS)
Tziotziou, Kostas; Georgoulis, Manolis K.; Liu Yang
2013-01-01
In previous works, we introduced a nonlinear force-free method that self-consistently calculates the instantaneous budgets of free magnetic energy and relative magnetic helicity in solar active regions (ARs). Calculation is expedient and practical, using only a single vector magnetogram per computation. We apply this method to a time series of 600 high-cadence vector magnetograms of the eruptive NOAA AR 11158 acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory over a five-day observing interval. Besides testing our method extensively, we use it to interpret the dynamical evolution in the AR, including eruptions. We find that the AR builds large budgets of both free magnetic energy and relative magnetic helicity, sufficient to power many more eruptions than the ones it gave within the interval of interest. For each of these major eruptions, we find eruption-related decreases and subsequent free-energy and helicity budgets that are consistent with the observed eruption (flare and coronal mass ejection (CME)) sizes. In addition, we find that (1) evolution in the AR is consistent with the recently proposed (free) energy-(relative) helicity diagram of solar ARs, (2) eruption-related decreases occur before the flare and the projected CME-launch times, suggesting that CME progenitors precede flares, and (3) self terms of free energy and relative helicity most likely originate from respective mutual terms, following a progressive mutual-to-self conversion pattern that most likely stems from magnetic reconnection. This results in the non-ideal formation of increasingly helical pre-eruption structures and instigates further research on the triggering of solar eruptions with magnetic helicity firmly placed in the eruption cadre
International Nuclear Information System (INIS)
Pierrard, J.; Bruneton, C.; Bystricky, J.; Cozzika, G.; Deregel, J.; Ducros, Y.; Gaidot, A.; Khantine-Langlois, F.; Lehar, F.; Lesquen, A. de; Merlo, J.P.; Miyashita, S.; Movchet, J.; Raoul, J.C.; Van Rossum, L.; Kanavets, V.P.
1975-01-01
The spin rotation parameter R in pp and π + p elastic scattering at 45GeV/c has been measured at the Serpukhov accelerator, for /t/ ranging from 0.2 to 0.5(GeV/c) 2 . The results are presented, together with previous R measurements at 3.8, 6, 16 and 40GeV/c, and are compared with the predictions of Regge pole models. The equality of the values for R in proton-proton and pion-proton scattering, within the experimental errors, is a test of factorization of the residues. An s-channel helicity amplitude analysis for pion-nucleon scattering at 40GeV/c is made using all available data. Significant results are obtained for the non flip amplitude in isoscalar exchange and for flip amplitudes on both isovector and isoscalar exchanges. The helicity flip in isoscalar exchange is non negligible. The energy dependence of this amplitude, at 6, 16 and 40GeV/c, is compared with predictions of Regge pole models [fr
Energy Technology Data Exchange (ETDEWEB)
Stepanov, G.V., E-mail: gstepanov@mail.ru [State Scientific Research Institute of Chemistry and Technology of Organoelement Compounds, 105118 Moscow (Russian Federation); Borin, D.Yu. [TU Dresden, Magnetofluiddynamics, Measuring and Automation Technology, Dresden 01062 (Germany); Storozhenko, P.A. [State Scientific Research Institute of Chemistry and Technology of Organoelement Compounds, 105118 Moscow (Russian Federation)
2017-06-01
We propose the results of research on the magnetic properties of magnetoactive elastomers containing particles of a hard magnetic filler. According to our understanding, the mechanism of re-magnetizing of the composite is based on two competing processes, being the re-magnetizing of the magnetic filler and mechanical rotation of particles inside of the polymer matrix.
Possible relation between pulsar rotation and evolution of magnetic inclination
Tian, Jun
2018-05-01
The pulsar timing is observed to be different from predicted by a simple magnetic dipole radiation. We choose eight pulsars whose braking index was reliably determined. Assuming the smaller values of braking index are dominated by the secular evolution of the magnetic inclination, we calculate the increasing rate of the magnetic inclination for each pulsar. We find a possible relation between the rotation frequency of each pulsar and the inferred evolution of the magnetic inclination. Due to the model-dependent fit of the magnetic inclination and other effects, more observational indicators for the change rate of magnetic inclination are needed to test the relation.
Jeon, S. M.; Jang, G. H.; Choi, H. C.; Park, S. H.; Park, J. O.
2012-04-01
Different magnetic navigation systems (MNSs) have been investigated for the wireless manipulation of microrobots in human blood vessels. Here we propose a MNS and methodology for generation of both the precise helical and translational motions of a microrobot to improve its maneuverability in complex human blood vessel. We then present experiments demonstrating the helical and translational motions of a spiral-type microrobot to verify the proposed MNS.
A helical magnetic limiter for boundary layer control in large tokamaks
International Nuclear Information System (INIS)
Feneberg, W.; Wolf, G.H.
1981-01-01
In a tokamak configuration, superposition of the magnetic field of resonant helical windings which surround the toroidal plasma current outside the first wall destroys the magnetic surfaces in the boundary layer (ergodization). A transport model is analysed, where convective flow of the plasma from the boundary layer to the first wall permits elevated particle densities in the boundary layer and leads to very high particle and energy transport. The convective flow is driven by the pressure gradient along the field lines which intersect the toroidal wall at an oblique small angle epsilon. The required thickness Δ of the boundary layer is around 10 15 n -1 .cm -2 . As a result, the plasma temperature there can be reduced towards the threshold of critical plasma-wall-interaction processes, the plasma core can be shielded against impurities from the wall and, at the same time, a very short life-time of all particles in the boundary layer can be achieved (use of pumpholes and/or scrape-off-limiters for removing ash). Thus, this model also improves the concepts of edge radiation cooling. An estimate is given of the parameters of INTOR using only a weak helical perturbation field which conserves the magnetic surfaces in the plasma core: one can reach wall temperatures Tsub(w) between 20 and 30 eV in the presence of wall densities nsub(w) approaching 10 14 cm -3 . (author)
International Nuclear Information System (INIS)
Weber, Norbert; Galindo, Vladimir; Stefani, Frank; Weier, Tom
2015-01-01
The Tayler instability is a kink-type, current driven instability that plays an important role in plasma physics but might also be relevant in liquid metal applications with high electrical currents. In the framework of the Tayler–Spruit dynamo model of stellar magnetic field generation (Spruit 2002 Astron. Astrophys. 381 923–32), the question of spontaneous helical (chiral) symmetry breaking during the saturation of the Tayler instability has received considerable interest (Zahn et al 2007 Astron. Astrophys. 474 145–54; Gellert et al 2011 Mon. Not. R. Astron. Soc. 414 2696–701; Bonanno et al 2012 Phys. Rev. E 86 016313). Focusing on fluids with low magnetic Prandtl numbers, for which the quasistatic approximation can be applied, we utilize an integro-differential equation approach (Weber et al 2013 New J. Phys.15 043034) in order to investigate the saturation mechanism of the Tayler instability. Both the exponential growth phase and the saturated phase are analysed in terms of the action of the α and β effects of mean-field magnetohydrodynamics. In the exponential growth phase we always find a spontaneous chiral symmetry breaking which, however, disappears in the saturated phase. For higher degrees of supercriticality, we observe helicity oscillations in the saturated regime. For Lundquist numbers in the order of one we also obtain chiral symmetry breaking of the saturated magnetic field. (paper)
Rotating magnetic field current drive-theory and experiment
International Nuclear Information System (INIS)
Donnelly, I.J.
1989-01-01
Rotating magnetic fields have been used to drive plasma current and establish a range of compact torus configurations, named rotamaks. The current drive mechanism involves a ponderomotive force acting on the electron fluid. Recent extensions of the theory indicate that this method is most suitable for driving currents in directions perpendicular to the steady magnetic fields
International Nuclear Information System (INIS)
Stoschus, H.; Schmitz, O.; Frerichs, H.; Reiser, D.; Unterberg, B.; Lehnen, M.; Reiter, D.; Samm, U.; Jakubowski, M.W.
2012-01-01
Rotating resonant magnetic perturbation (RMP) fields impose a characteristic modulation to the edge electron density n e (r, t) and temperature T e (r, t) fields, which depends on the relative rotation f rel between external RMP field and plasma fluid. The n e (r, t) and T e (r, t) fields measured in the edge (r/a = 0.9–1.05) of TEXTOR L-mode plasmas are in close correlation with the local magnetic vacuum topology for low relative rotation f rel = −0.2 kHz. In comparison with the 3D neutral and plasma transport code EMC3-Eirene, this provides substantial experimental evidence that for low relative rotation level and high resonant field amplitudes (normalized radial field strength B r 4/1 /B t =2×10 -3 ), a stochastic edge with a remnant island chain dominated by diffusive transport exists. Radially outside a helical scrape-off layer, the so-called laminar zone embedded into a stochastic domain is found to exist. In contrast for high relative rotation of f rel = 1.8 kHz, the measured modulation of n e is shifted by π/2 toroidally with respect to the modelled vacuum topology. A pronounced flattening in T e (r) and a reduction in n e (r) is measured at the resonant flux surface and represents a clear signature for a magnetic island, which is phase shifted with respect to the vacuum island position. A correlated shift of the laminar zone radially outwards at the very plasma edge is observed suggesting that the actual near-field structure at the perturbation source is determined by the plasma response as well. (paper)
Achieved capability of the superconducting magnet system for the large helical device
International Nuclear Information System (INIS)
Satow, T.; Imagawa, S.; Yanagi, N.
2001-01-01
The Large Helical Device (LHD) is a plasma physics experimental device with a magnetic stored energy of 960 MJ, consisting of two sc (superconducting) helical coils and six sc poloidal coils. The trial operation and the first plasma discharge of the eight-year Phase I project for LHD were finished on 31 March 1998 as initially planned. The second experimental campaign was conducted by additional heating using two NBI devices. The third campaign started in June 1999 and was finished in January 2000. Many plasma heating tests up to a plasma field of 2.90 T were carried out. Major test results on the sc magnet system for LHD are as follows: (1) The LHD cryogenic system succeeded in 13,400-hour operation and proved its high reliability. (2) A central field of 2.91 T at a radius of 3.60 m was achieved at an H-I current of 11.08 kA, H-M current of 11.83 kA and an H-O current of 12.02 kA. (3) All six poloidal coils were excited stably. (4) Nine flexible sc bus-lines with a total length of 497 m were operated stably and safe. (author)
The Pressure and Magnetic Flux Density Analysis of Helical-Type DC Electromagnetic Pump
International Nuclear Information System (INIS)
Lee, Geun Hyeong; Kim, Hee Reyoung
2016-01-01
The developed pressure was made by only electromagnetic force eliminating probability of impurities contact, therefore the high reactivity materials such as alkali were best match to electromagnetic pump. The heavy ion accelerator facility by Rare Isotope Science Project (RISP) in Korea is trying to construct accelerator using liquid lithium for high efficiency of acceleration by decreasing charge state. The helical-type DC electromagnetic pump was employed to make a charge stripper that decrease charge state of heavy ion. The specification of electromagnetic pump was developed pressure of 15 bar with flowrate of 6 cc/s in the condition of 200℃. The pressure of DC electromagnetic pump was analyzed in the aspects of current and number of duct turns. The developed pressure was almost proportional to input current because relatively low flowrate made negligible of the electromotive force and hydraulic pressure drop. The pressure and magnetic flux density of helical-type DC electromagnetic pump were analyzed. The pressure was proportion to input current and number of duct turns, and magnetic flux density was higher when ferromagnet was applied at electromagnetic pump. It seems that number of duct turns could be increase and ferromagnet could be applied in order to increase pressure of DC electromagnetic pump with constant input current
International Nuclear Information System (INIS)
Nishimura, Shin
2009-01-01
Effects of the perturbed magnetic field with low toroidal mode numbers (n) are considered. One cause of this type of perturbation, which has recently been studied in tokamaks, is MHD-activities. In helical/stellarator, this low-n perturbation is sometimes artificially added for island diverters. In viewpoint of the neoclassical viscosities, these perturbed magnetic fields affect on both of bounce center drifts of toroidally trapped and ripple-trapped particles. However, in usual neoclassical analyses in helical/stellarator devices assuming periodic magnetic field strength, these effects had not been studied. For future studies in helical/stellarator devices, a method to use bounce-averaged drift kinetic equation for the toroidally trapped particles is proposed. (author)
Intermittent transport in edge plasma with a 3-D magnetic geometry in the Large Helical Device
International Nuclear Information System (INIS)
Tanaka, H.; Masuzaki, S.; Ohno, N.; Morisaki, T.; Tsuji, Y.
2013-01-01
Blobby plasma transport is a universally observed phenomenon in magnetic confinement devices, and it is considered to be closely related to edge plasma physics. We have investigated such an intermittent event observed inside the divertor region of the Large Helical Device by using a fast-scanning Langmuir probe with two electrodes. Ion saturation current fluctuations showed negative spikes in the divertor leg and positive spikes in the private region. Further, the time delay between the two fluctuations followed a unique trajectory in the positive-skewness region. We found common as well as different fluctuation characteristics between the LHD and tokamaks. We discuss the analysis results in relation to the blob-generation and propagation behaviors in the three-dimensional magnetic geometry around the divertor leg. In addition, we quantitatively estimated the blob propagation velocity and size based on a theoretical assumption
Helically linked mirror arrangement
International Nuclear Information System (INIS)
Ranjan, P.
1986-08-01
A scheme is described for helical linking of mirror sections, which endeavors to combine the better features of toroidal and mirror devices by eliminating the longitudinal loss of mirror machines, having moderately high average β and steady state operation. This scheme is aimed at a device, with closed magnetic surfaces having rotational transform for equilibrium, one or more axisymmetric straight sections for reduced radial loss, a simple geometrical axis for the links and an overall positive magnetic well depth for stability. We start by describing several other attempts at linking of mirror sections, made both in the past and the present. Then a description of our helically linked mirror scheme is given. This example has three identical straight sections connected by three sections having helical geometric axes. A theoretical analysis of the magnetic field and single-particle orbits in them leads to the conclusion that most of the passing particles would be confined in the device and they would have orbits independent of pitch angle under certain conditions. Numerical results are presented, which agree well with the theoretical results as far as passing particle orbits are concerned
International Nuclear Information System (INIS)
Stoschus, Henning
2011-01-01
Small three-dimensional (3D) magnetic perturbations can be used as a tool to control the edge plasma parameters in magnetically confined plasmas in high confinement mode (''H-mode'') to suppress edge instabilities inherent to this regime, the Edge Localized Modes (ELMs). In this work, the impact of rotating 3D resonant magnetic perturbation (RMP) fields on the edge plasma structure characterized by electron density and temperature fields is investigated. We study a low confinement (L-mode) edge plasma (r/a>0.9) with high resistivity (edge electron collisionality ν * e >4) at the TEXTOR tokamak. The plasma structure in the plasma edge is measured by a set of high resolution diagnostics: a fast CCD camera (Δt=20 μs) is set up in order to visualize the plasma structure in terms of electron density variations. A supersonic helium beam diagnostic is established as standard diagnostic at TEXTOR to measure electron density n e and temperature T e with high spatial (Δr=2 mm) and temporal resolution (Δt=20 μs). The measured plasma structure is compared to modeling results from the fluid plasma and kinetic neutral transport code EMC3-EIRENE. A sequence of five new observations is discussed: (1) Imaging of electron density variations in the plasma edge shows that a fast rotating RMP field imposes an edge plasma structure, which rotates with the external RMP rotation frequency of vertical stroke ν RMP vertical stroke =1 kHz. (2) Measurements of the electron density and temperature provide strong experimental evidence that in the far edge a rotating 3D scrape-off layer (SOL) exists with helical exhaust channels to the plasma wall components. (3) Radially inward, the plasma structure at the next rational flux surface is found to depend on the relative rotation between external RMP field and intrinsic plasma rotation. For low relative rotation the plasma structure is dominated by a particle and energy loss along open magnetic field lines to the wall components. For high
Energy Technology Data Exchange (ETDEWEB)
Stoschus, Henning
2011-10-13
Small three-dimensional (3D) magnetic perturbations can be used as a tool to control the edge plasma parameters in magnetically confined plasmas in high confinement mode (''H-mode'') to suppress edge instabilities inherent to this regime, the Edge Localized Modes (ELMs). In this work, the impact of rotating 3D resonant magnetic perturbation (RMP) fields on the edge plasma structure characterized by electron density and temperature fields is investigated. We study a low confinement (L-mode) edge plasma (r/a>0.9) with high resistivity (edge electron collisionality {nu}{sup *}{sub e}>4) at the TEXTOR tokamak. The plasma structure in the plasma edge is measured by a set of high resolution diagnostics: a fast CCD camera ({delta}t=20 {mu}s) is set up in order to visualize the plasma structure in terms of electron density variations. A supersonic helium beam diagnostic is established as standard diagnostic at TEXTOR to measure electron density n{sub e} and temperature T{sub e} with high spatial ({delta}r=2 mm) and temporal resolution ({delta}t=20 {mu}s). The measured plasma structure is compared to modeling results from the fluid plasma and kinetic neutral transport code EMC3-EIRENE. A sequence of five new observations is discussed: (1) Imaging of electron density variations in the plasma edge shows that a fast rotating RMP field imposes an edge plasma structure, which rotates with the external RMP rotation frequency of vertical stroke {nu}{sub RMP} vertical stroke =1 kHz. (2) Measurements of the electron density and temperature provide strong experimental evidence that in the far edge a rotating 3D scrape-off layer (SOL) exists with helical exhaust channels to the plasma wall components. (3) Radially inward, the plasma structure at the next rational flux surface is found to depend on the relative rotation between external RMP field and intrinsic plasma rotation. For low relative rotation the plasma structure is dominated by a particle and energy loss
Microscopic observation of magnetic bacteria in the magnetic field of a rotating permanent magnet.
Smid, Pieter; Shcherbakov, Valeriy; Petersen, Nikolai
2015-09-01
Magnetotactic bacteria are ubiquitous and can be found in both freshwater and marine environments. Due to intracellular chains of magnetic single domain particles, they behave like swimming compass needles. In external magnetic fields like the Earth's magnetic field, a torque is acting on the chain. This will cause the bacterium to be rotated and aligned with the external field. The swimming direction of magnetotactic bacteria can be controlled with external magnetic fields, which makes it convenient to study them under a light microscope. Usually, a special set of coils arranged around a light microscope is used to control the swimming magnetotactic bacteria. Here, we present a simple mechanical system with a permanent magnet, which produces a rotating magnetic field of nearly constant amplitude in the focal plane of a light microscope. The device is placed beside the light microscope and easily adaptable to almost any microscope and thus convenient for field experiments. To describe the trajectories qualitatively, a theoretical model of the trajectories is presented. This device can be used to control the swimming direction of magnetotactic bacteria and also for studying their magnetic and hydrodynamic properties.
A novel rotating experimental platform in a superconducting magnet.
Chen, Da; Cao, Hui-Ling; Ye, Ya-Jing; Dong, Chen; Liu, Yong-Ming; Shang, Peng; Yin, Da-Chuan
2016-08-01
This paper introduces a novel platform designed to be used in a strong static magnetic field (in a superconducting magnet). The platform is a sample holder that rotates in the strong magnetic field. Any samples placed in the platform will rotate due to the rotation of the sample holder. With this platform, a number of experiments such as material processing, culture of biological systems, chemical reactions, or other processes can be carried out. In this report, we present some preliminary experiments (protein crystallization, cell culture, and seed germination) conducted using this platform. The experimental results showed that the platform can affect the processes, indicating that it provides a novel environment that has not been investigated before and that the effects of such an environment on many different physical, chemical, or biological processes can be potentially useful for applications in many fields.
Rotation of dust plasma crystals in an axial magnetic field
International Nuclear Information System (INIS)
Cheung, F.; Prior, N.; Mitchell, L.
2000-01-01
Full text: Micron-sized melamine formaldehyde particles were introduced into argon plasma. As a result, the particles were negatively charged due to collision with the electrons within the plasma. With the right conditions, these particles formed a stable macroscopic crystal lattice, known as dust plasma crystal. In our experiment we conduct at Flinders University, we apply an external axial magnetic field to various configurations of dust plasma crystal. These configurations include small crystal lattices consisting of one to several particles, and large crystal lattices with many hundreds of particles. The magnetic field strength ranged from 0-32G and was uniform over the extent of the crystal. The crystals were observed to be rotating collectively in the left-handed direction under the influence of the axial magnetic field. In the case of the large crystals, the angular velocity was about 2 complete rotations per minute and was proportional to the applied magnetic field. The angular velocity changes only slightly depending on the plasma conditions. Neither radial variance in the angular velocity nor shear velocity in the vertical direction was observed in the crystal's rotational motion. In the case of the small crystals, we managed to rotate 2-6 particles (whether they are planar, 2 layers or tetrahedral). We discovered that the ease and the uniformity of the rotation of the different crystals increase as its rotational symmetry increases. Also an increase in the magnetic field strength will correspond to an increase in the angular velocity. Crystals in the shape of an annulus were also tested for theoretical reasons. The poster presentation will contain the experimental procedures, a detailed analysis and an explanation for such dust plasma crystal rotational motion
Power and momentum relations in rotating magnetic field current drive
Energy Technology Data Exchange (ETDEWEB)
Hugrass, W N [Flinders Univ. of South Australia, Bedford Park. School of Physical Sciences
1984-01-01
The use of rotating magnetic fields (RMF) to drive steady currents in plasmas involves a transfer of energy and angular momentum from the radio frequency source feeding the rotating field coils to the plasma. The power-torque relationships in RMF systems are discussed and the analogy between RMF current drive and the polyphase induction motor is explained. The general relationship between the energy and angular momentum transfer is utilized to calculate the efficiency of the RMF plasma current drive. It is found that relatively high efficiencies can be achieved in RMF current drive because of the low phase velocity and small slip between the rotating field and the electron fluid.
International Nuclear Information System (INIS)
Misguich, J.H.
2004-04-01
As a first step toward a nonlinear renormalized description of turbulence phenomena in magnetized plasmas, the lowest order quasi-linear description is presented here from a unified point of view for collisionless as well as for collisional plasmas in a constant magnetic field. The quasi-linear approximation is applied to a general kinetic equation obtained previously from the Klimontovich exact equation, by means of a generalised Dupree-Weinstock method. The so-obtained quasi-linear description of electromagnetic turbulence in a magnetoplasma is applied to three separate physical cases: -) weak electrostatic turbulence, -) purely magnetic field fluctuations (the classical quasi-linear results are obtained for cosmic ray diffusion in the 'slab model' of magnetostatic turbulence in the solar wind), and -) collisional kinetic equations of magnetized plasmas. This mathematical technique has allowed us to derive basic kinetic equations for turbulent plasmas and collisional plasmas, respectively in the quasi-linear and Landau approximation. In presence of a magnetic field we have shown that the systematic use of rotation matrices describing the helical particle motion allows for a much more compact derivation than usually performed. Moreover, from the formal analogy between turbulent and collisional plasmas, the results derived here in detail for the turbulent plasmas, can be immediately translated to obtain explicit results for the Landau kinetic equation
Energy Technology Data Exchange (ETDEWEB)
Misguich, J.H
2004-04-01
As a first step toward a nonlinear renormalized description of turbulence phenomena in magnetized plasmas, the lowest order quasi-linear description is presented here from a unified point of view for collisionless as well as for collisional plasmas in a constant magnetic field. The quasi-linear approximation is applied to a general kinetic equation obtained previously from the Klimontovich exact equation, by means of a generalised Dupree-Weinstock method. The so-obtained quasi-linear description of electromagnetic turbulence in a magnetoplasma is applied to three separate physical cases: -) weak electrostatic turbulence, -) purely magnetic field fluctuations (the classical quasi-linear results are obtained for cosmic ray diffusion in the 'slab model' of magnetostatic turbulence in the solar wind), and -) collisional kinetic equations of magnetized plasmas. This mathematical technique has allowed us to derive basic kinetic equations for turbulent plasmas and collisional plasmas, respectively in the quasi-linear and Landau approximation. In presence of a magnetic field we have shown that the systematic use of rotation matrices describing the helical particle motion allows for a much more compact derivation than usually performed. Moreover, from the formal analogy between turbulent and collisional plasmas, the results derived here in detail for the turbulent plasmas, can be immediately translated to obtain explicit results for the Landau kinetic equation.
Instabilities responsible for magnetic turbulence in laboratory rotating plasma
International Nuclear Information System (INIS)
Mikhailovskii, A.B.; Lominadze, J.G.; Churikov, A.P.; Erokhin, N.N.; Pustovitov, V.D.; Konovalov, S.V.
2008-01-01
Instabilities responsible for magnetic turbulence in laboratory rotating plasma are investigated. It is shown that the plasma compressibility gives a new driving mechanism in addition to the known Velikhov effect due to the negative rotation frequency gradient. This new mechanism is related to the perpendicular plasma pressure gradient, while the density gradient gives an additional drive depending also on the pressure gradient. It is shown that these new effects can manifest themselves even in the absence of the equilibrium magnetic field, which corresponds to nonmagnetic instabilities
Oscillating magnetic islands in a rotating plasma
International Nuclear Information System (INIS)
Persson, M.; Bondeson, A.
1990-01-01
The nonlinear evolution of tearing modes in the presence of sheared mass flow is studied as an initial value problem. It is shown that under certain conditions, when the mode is driven unstable primarily by the mass flow, the nonlinear evolution leads to a dynamic state in which the size and shape of the magnetic islands is oscillatory. 15 refs., 11 figs
International Nuclear Information System (INIS)
Mallick, Sougata; Mallik, Srijani; Bedanta, Subhankar
2015-01-01
Microdimensional triangular magnetic antidot lattice arrays were prepared by varying the speed of substrate rotation. The pre-deposition patterning has been performed using photolithography technique followed by a post-deposition lift-off. Surface morphology taken by atomic force microscopy depicted that the growth mechanism of the grains changes from chain like formation to island structures due to the substrate rotation. Study of magnetization reversal via magneto optic Kerr effect based microscopy revealed reduction of uniaxial anisotropy and increase in domain size with substrate rotation. The relaxation measured under constant magnetic field becomes faster with rotation of the substrate during deposition. The nature of relaxation for the non-rotating sample can be described by a double exponential decay. However, the relaxation for the sample with substrate rotation is well described either by a double exponential or a Fatuzzo-Labrune like single exponential decay, which increases in applied field
International Nuclear Information System (INIS)
Auffrau-Calvier, E.; Kersaint-Gilly, A. de; Desal, H.A.; Viarouge, M.P.; Havet, T.
1996-01-01
The aim of this work is to ascertain the role of the magnetic resonance angiography (MRA) and to compare it with the Doppler effect, the X-ray angiography and the new method of helical computerized tomography. Seventy one carotid bifurcations in 37 patients with suspected cerebral vascular events has been evaluated with the MRA and digitalized angiography, the reference method. The obtained data corroborate the good results proposed by other authors reporting in the literature and allow to propose this examination as a new means of investigating carotid bifurcations. Work with the helical computerized tomography appears to be promising too but there are few reported series. Therefore, there appears to be two interesting points: the reliability of distinguishing between very severe stenosis and occlusion, and the fine-tuned analysis of the plaque with detection of ulcerations. When a consistent approach is used to the evaluation of the carotid bifurcation, the Willis circle and the cerebral parenchyma, the MRA can complete the Doppler echo data and the preoperative arteriography can only be used in patients when the MRA and the Doppler echo results disagree. (authors)
International Nuclear Information System (INIS)
Zhmetko, D.N.; Zhmetko, S.D.
2009-01-01
The distribution of axes of easy magnetization close to a homogeneous distribution is revealed in each half-thickness of a ribbon after annealing it in a helical magnetic field. The transition from magnetic reversal of a ribbon by the displacement of two domain walls formed near a middle plane of a ribbon to magnetic reversal of a ribbon by displacement of two domain walls formed near to the main surfaces of a ribbon is found out during each half-period of a magnetic reversal.
Emergent rotational symmetries in disordered magnetic domain patterns.
Su, Run; Seu, Keoki A; Parks, Daniel; Kan, Jimmy J; Fullerton, Eric E; Roy, Sujoy; Kevan, Stephen D
2011-12-16
Uniaxial systems often form labyrinthine domains that exhibit short-range order but are macroscopically isotropic and would not be expected to exhibit precise symmetries. However, their underlying frustration results in a multitude of metastable configurations of comparable energy, and driving such a system externally might lead to pattern formation. We find that soft x-ray speckle diffraction patterns of the labyrinthine domains in CoPd/IrMn heterostructures reveal a diverse array of hidden rotational symmetries about the magnetization axis, thereby suggesting an unusual form of emergent order in an otherwise disordered system. These symmetries depend on applied magnetic field, magnetization history, and scattering wave vector. Maps of rotational symmetry exhibit intriguing structures that can be controlled by manipulating the applied magnetic field in concert with the exchange bias condition. © 2011 American Physical Society
Apparatus and method for materials processing utilizing a rotating magnetic field
Muralidharan, Govindarajan; Angelini, Joseph A.; Murphy, Bart L.; Wilgen, John B.
2017-04-11
An apparatus for materials processing utilizing a rotating magnetic field comprises a platform for supporting a specimen, and a plurality of magnets underlying the platform. The plurality of magnets are configured for rotation about an axis of rotation intersecting the platform. A heat source is disposed above the platform for heating the specimen during the rotation of the plurality of magnets. A method for materials processing utilizing a rotating magnetic field comprises providing a specimen on a platform overlying a plurality of magnets; rotating the plurality of magnets about an axis of rotation intersecting the platform, thereby applying a rotating magnetic field to the specimen; and, while rotating the plurality of magnets, heating the specimen to a desired temperature.
A harmonic expansion for the magnetic field of the helical solenoid
International Nuclear Information System (INIS)
Dewar, R.L.; Gardner, H.J.
1987-03-01
We discuss the boundary value problem for calculating the scalar magnetic potentials inside and outside of a helically symmetric solenoid. Under some circumstances the potentials can be expanded in infinite series of cylindrical harmonics. For a circular cross-section solenoid, we derive a Green's function integral representation of the series coefficients and calculate the radii of convergence of the series by a saddle point method. In some cases the cylinders of convergence can intersect the coil, so that there are physically accessible regions where the series fail to converge. Numerical evidence is presented to show that, even in some of these cases, the potentials can be accurately approximated by finite sums of cylindrical harmonics using boundary collocation
Gravitational convergence, shear deformation and rotation of magnetic forcelines
Giantsos, Vangelis; Tsagas, Christos G.
2017-11-01
We consider the 'kinematics' of space-like congruences and apply them to a family of self-gravitating magnetic forcelines. Our aim is to investigate the convergence and the possible focusing of these lines, as well as their rotation and shear deformation. In so doing, we introduce a covariant 1+2 splitting of the 3-D space, parallel and orthogonal to the direction of the field lines. The convergence, or not, of the latter is monitored by a specific version of the Raychaudhuri equation, obtained after propagating the spatial divergence of the unit magnetic vector along its own direction. The resulting expression shows that, although the convergence of the magnetic forcelines is affected by the gravitational pull of all the other sources, it is unaffected by the field's own gravity, irrespective of how strong the latter is. This rather counterintuitive result is entirely due to the magnetic tension, namely to the negative pressure the field exerts parallel to its lines of force. In particular, the magnetic tension always cancels out the field's energy-density input to the Raychaudhuri equation, leaving the latter free of any direct magnetic-energy contribution. Similarly, the rotation and the shear deformation of the aforementioned forcelines are also unaffected by the magnetic input to the total gravitational energy. In a sense, the magnetic lines do not seem to 'feel' their own gravitational field no matter how strong the latter may be.
Design Concepts for a Continuously Rotating Active Magnetic Regenerator
DEFF Research Database (Denmark)
Bahl, Christian Robert Haffenden; Engelbrecht, Kurt; Bjørk, Rasmus
2010-01-01
Design considerations for a prototype magnetic refrigeration device with a continuously rotating AMR are presented. Building the AMR from stacks of elongated plates of the perovskite oxide material La0.67Ca0.33-xSrxMn1.05O3, gives both a low pressure drop and allows grading of the Curie temperatu...
KIC 9451096: Magnetic Activity, Flares and Differential Rotation
Özdarcan, O.; Yoldaş, E.; Dal, H. A.
2018-04-01
We present a spectroscopic and photometric analysis of KIC 9451096. The combined spectroscopic and photometric modelling shows that the system is a detached eclipsing binary in a circular orbit and composed of F5V + K2V components. Subtracting the best-fitting light curve model from the whole long cadence data reveals additional low (mmag) amplitude light variations in time and occasional flares, suggesting a low, but still remarkable level of magnetic spot activity on the K2V component. Analyzing the rotational modulation of the light curve residuals enables us to estimate the differential rotation coefficient of the K2V component as k = 0.069 ± 0.008, which is 3 times weaker compared with the solar value of k = 0.19, assuming a solar type differential rotation. We find the stellar flare activity frequency for the K2V component as 0.000368411 h-1 indicating a low magnetic activity level.
New Limits on Extragalactic Magnetic Fields from Rotation Measures
Pshirkov, M. S.; Tinyakov, P. G.; Urban, F. R.
2016-05-01
We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalog to derive new, statistically robust, upper limits on the strength of extragalactic magnetic fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-α clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans' length coherence length to be below 1.7 nG at the 2 σ level, and fields coherent across the entire observable Universe below 0.65 nG. These limits do not depend on the particular origin of these cosmological fields.
Helical post stellarator. Part 1: Vacuum configuration
International Nuclear Information System (INIS)
Moroz, P.E.
1997-08-01
Results on a novel type of stellarator configuration, the Helical Post Stellarator (HPS), are presented. This configuration is different significantly from all previously known stellarators due to its unique geometrical characteristics and unique physical properties. Among those are: the magnetic field has only one toroidal period (M = 1), the plasma has an extremely low aspect ratio, A ∼ 1, and the variation of the magnetic field, B, along field lines features a helical ripple on the inside of the torus. Among the main advantages of a HPS for a fusion program are extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and improved particle transport characteristics
International Nuclear Information System (INIS)
Beković, Miloš; Trlep, Mladen; Jesenik, Marko; Hamler, Anton
2014-01-01
Magnetic fluids are distinct magnetic materials that have recently been the subject of extensive research precisely because of their unique properties. One of them is the heating effect when exposed to alternating magnetic fields, wherein the objective is to use this property in medicine as an alternative method for the treatment of tumors in the body. In this paper, we focus on two methods of magnetizing magnetic fluids, firstly using the alternating magnetic field (AMF), and secondly with the rotational magnetic field (RMF). The effects of the first are scientifically well-established, whilst the impact of RMF has not as yet been investigated as presented in this article. So far the effects of RMF have only been studied at low frequencies and high amplitudes, or vice versa. This article presents the results of heating at high frequencies and high magnetic field amplitudes, and the results compared with AMF. This paper presents the construction and implementation of a measuring system which is suitable both types of magnetic field. - Highlights: • Development of a new measurement system for the characterization of magnetic fluids. • System enables pulsed magnetic field, or a rotary magnetic field. • Analysis of the conditions to create a rotational magnetic field by means of a double power supply. • Good agreement between the analytical and numerical calculation of magnetic field and measurements. • Increase of the heating power when sample is exposed to rotating field compared to pulsating field
Magnetic force study for the helical afterburner for the European XFEL
Li, Peng; Wei, Tao; Li, Yuhui; Pflueger, Joachim
2017-05-01
At present the SASE3 undulator line at the European XFEL is using a planar undulator producing linear polarized soft Xray radiation only. In order to satisfy the demand for circular polarized radiation a helical undulator system, the so-called afterburner is in construction. It will be operated as a radiator using the pre-bunched beam of the SASE3 undulator system. Among several options for the magnetic structure the Apple-X geometry was chosen. This is a pure permanent magnet undulator using NdFeB material. Four magnet arrays are arranged symmetrically the beam axis. Polarization can be changed by adjusting the phase shift (PS) between the two orthogonal structures. The field strength can be adjusted either by gap adjustment or alternatively by the amplitude shift (AS) scheme. For an engineering design the maximum values of forces and torques on each of the components under worst case operational conditions are important. The superposition principle is used to reduce calculation time. It is found that the maximum forces Fx, Fy and Fz for a 2m long Apple-X undulator are 1.8*104N, 2.4*104N and 2.3*104N, respectively. More results are presented in this paper.
Cartagena-Sanchez, C. A.; Schaffner, D. A.; Johnson, H. K.; Fahim, L. E.
2017-10-01
A long-pulsed magnetic coaxial plasma gun is being implemented and characterized at the Bryn Mawr Plasma Laboratory (BMPL). A cold cathode discharged between the cylindrical electrodes generates and launches plasma into a 24cm diameter, 2m long chamber. Three separately pulsed magnetic coils are carefully positioned to generate radial magnetic field between the electrodes at the gun edge in order to provide stuffing field. Magnetic helicity is continuously injected into the flux-conserving vacuum chamber in a process akin to sustained slow-formation of spheromaks. The aim of this source, however, is to supply long pulses of turbulent magnetized plasma for measurement rather than for sustained spheromak production. The work shown here details the optimization of the magnetic field structure for this sustained helicity injection.
Electrodynamic Wireless Power Transmission to Rotating Magnet Receivers
International Nuclear Information System (INIS)
Garraud, A; Jimenez, J D; Garraud, N; Arnold, D P
2014-01-01
This paper presents an approach for electrodynamic wireless power transmission (EWPT) using a synchronously rotating magnet located in a 3.2 cm 3 receiver. We demonstrate wireless power transmission up to 99 mW (power density equal to 31 mW/cm 3 ) over a 5-cm distance and 5 mW over a 20-cm distance. The maximum operational frequency, and hence maximal output power, is constrained by the magnetic field amplitude. A quadratic relationship is found between the maximal output power and the magnetic field. We also demonstrate simultaneous, power transmission to multiple receivers positioned at different locations
Design concepts for a continuously rotating active magnetic regenerator
DEFF Research Database (Denmark)
Bahl, Christian Robert Haffenden; Engelbrecht, Kurt; Bjørk, Rasmus
2011-01-01
Design considerations for a prototype magnetic refrigeration device with a continuously rotating AMR are presented. Building the active magnetic regenerator (AMR) from stacks of elongated plates of the perovskite oxide material La0.67Ca0.33−xSrxMn1.05O3, gives both a low pressure drop and allows....... Focus is on maximising the magnetic field in the high field regions but also, importantly, minimising the flux in the low field regions. The design is iteratively optimised through 3D finite element magnetostatic modelling....
Towards age/rotation/magnetic activity relation with seismology
Directory of Open Access Journals (Sweden)
Mathur Savita
2015-01-01
Full Text Available The knowledge of stellar ages directly impacts the characterization of a planetary system as it puts strong constraints on the moment when the system was born. Unfortunately, the determination of precise stellar ages is a very difficult task. Different methods can be used to do so (based on isochrones or chemical element abundances but they usually provide large uncertainties. During its evolution a star goes through processes leading to loss of angular momentum but also changes in its magnetic activity. Building rotation, magnetic, age relations would be an asset to infer stellar ages model independently. Several attempts to build empirical relations between rotation and age (namely gyrochronology were made with a focus on cluster stars where the age determination is easier and for young stars on the main sequence. For field stars, we can now take advantage of high-precision photometric observations where we can perform asteroseismic analyses to improve the accuracy of stellar ages. Furthermore, the variability in the light curves allow us to put strong constraints on the stellar rotation and magnetic activity. By combining these precise measurements, we are on the way of understanding and improving relations between magnetic activity, rotation, and age, in particular at different stages of stellar evolution. I will review the status on gyrochronology relationships based on observations of young cluster stars. Then I will focus on solar-like stars and describe the inferences on stellar ages, rotation, and magnetism that can be provided by high-quality photometric observations such as the ones of the Kepler mission, in particular through asteroseismic analyses.
Faraday Rotation Measure Study of Cluster Magnetic Fields
Frankel, M. M.; Clarke, T. E.
2001-12-01
Magnetic fields are thought to play an important role in galaxy cluster evolution. To this end in this study, we looked at polarized radio sources viewed at small impact parameters to the cores of non-cooling flow clusters. By looking at non-cooling flow clusters we hoped to establish what magnetic fields of clusters look like in the absence of the compressed central magnetic fields of the cooling-flow cores. Clarke, Kronberg and Boehringer (2001) examined Faraday rotation measures of radio probes at relatively large impact parameters to the cores of galaxy clusters. The current study is an extension of the Clarke et al. analysis to probe the magnetic fields in the cores of galaxy clusters. We looked at the Faraday rotation of electromagnetic waves from background or imbedded radio galaxies, which were observed with the VLA in A&B arrays. Our results are consistent with previous findings and exhibit a trend towards higher rotation measures and in turn higher magnetic fields at small impact parameters to cluster cores. This research was made possible through funding from the National Science Foundation.
Rotating permanent magnet excitation for blood flow measurement.
Nair, Sarath S; Vinodkumar, V; Sreedevi, V; Nagesh, D S
2015-11-01
A compact, portable and improved blood flow measurement system for an extracorporeal circuit having a rotating permanent magnetic excitation scheme is described in this paper. The system consists of a set of permanent magnets rotating near blood or any conductive fluid to create high-intensity alternating magnetic field in it and inducing a sinusoidal varying voltage across the column of fluid. The induced voltage signal is acquired, conditioned and processed to determine its flow rate. Performance analysis shows that a sensitivity of more than 250 mV/lpm can be obtained, which is more than five times higher than conventional flow measurement systems. Choice of rotating permanent magnet instead of an electromagnetic core generates alternate magnetic field of smooth sinusoidal nature which in turn reduces switching and interference noises. These results in reduction in complex electronic circuitry required for processing the signal to a great extent and enable the flow measuring device to be much less costlier, portable and light weight. The signal remains steady even with changes in environmental conditions and has an accuracy of greater than 95%. This paper also describes the construction details of the prototype, the factors affecting sensitivity and detailed performance analysis at various operating conditions.
Engineered materials for all-optical helicity-dependent magnetic switching
Fullerton, Eric
2014-03-01
The possibilities of manipulating magnetization without applied magnetic fields have attracted growing attention over the last fifteen years. The low-power manipulation of magnetization, preferably at ultra-short time scales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. Here we explore the optical manipulation of the magnetization of engineered materials and devices using 100 fs optical pulses. We demonstrate that all optical - helicity dependent switching (AO-HDS) can be observed not only in selected rare-earth transition-metal (RE-TM) alloy films but also in a much broader variety of materials, including alloys, multilayers, heterostructures and RE-free Co-Ir-based synthetic ferrimagnets. The discovery of AO-HDS in RE-free TM-based synthetic ferrimagnets can enable breakthroughs for numerous applications since it exploits materials that are currently used in magnetic data storage, memories and logic technologies. In addition, this materials study of AO-HDS offers valuable insight into the underlying mechanisms involved. Indeed the common denominator of the diverse structures showing AO-HDS in this study is that two ferromagnetic sub-lattices exhibit magnetization compensation (and therefore angular momentum compensation) at temperatures near or above room temperature. We are highlighting that compensation plays a major role and that this compensation can be established at the atomic level as in alloys but also over a larger nanometers scale as in the multilayers or in heterostructures. We will also discuss the potential to extend AO-HDS to new classes of magnetic materials. This work was done in collaboration with S. Mangin, M. Gottwald, C-H. Lambert, D. Steil, V. Uhlíř, L. Pang, M. Hehn, S. Alebrand, M. Cinchetti, G. Malinowski, Y. Fainman, and M. Aeschlimann. Supported by the ANR-10-BLANC-1005 ``Friends,'' a grant from the Advanced Storage Technology Consortium, Partner University Fund
The Stability of Magnetized Rotating Plasmas with Superthermal Fields
DEFF Research Database (Denmark)
Pessah, Martin Elias; Psaltis, Dimitrios
2005-01-01
be taken fully into account. We demonstrate that the presence of a strong toroidal component in the magnetic field plays a non-trivial role. When strong fields are considered, the strength of the toroidal magnetic field not only modifies the growth rates of the unstable modes but also determines which...... modes are subject to instabilities. We find that, for rotating configurations with Keplerian laws, the magnetorotational instability is stabilized at low wavenumbers for toroidal Alfven speeds exceeding the geometric mean of the sound speed and the rotational speed. We discuss the significance of our......During the last decade it has become evident that the magnetorotational instability is at the heart of the enhanced angular momentum transport in weakly magnetized accretion disks around neutron stars and black holes. In this paper, we investigate the local linear stability of differentially...
Evidence for quantization of mechanical rotation of magnetic nanoparticles.
Tejada, J; Zysler, R D; Molins, E; Chudnovsky, E M
2010-01-15
We report evidence of the quantization of the rotational motion of solid particles containing thousands of atoms. A system of CoFe2O4 nanoparticles confined inside polymeric cavities has been studied. The particles have been characterized by the x-ray diffraction, transmission electron microscopy, plasma mass spectroscopy, ferromagnetic resonance (FMR), and magnetization measurements. Magnetic and FMR data confirm the presence of particles that are free to rotate inside the cavities. Equidistant, temperature-independent jumps in the dependence of the microwave absorption on the magnetic field have been detected. This observation is in accordance with the expectation that orbital motion splits the low-field absorption line into multiple lines.
International Nuclear Information System (INIS)
Park, Sung-Hong; Cho, Kyung-Suk; Bong, Su-Chan; Kumar, Pankaj; Kim, Yeon-Han; Park, Young-Deuk; Kusano, Kanya; Chae, Jongchul; Park, So-Young
2013-01-01
To better understand a preferred magnetic field configuration and its evolution during coronal mass ejection (CME) events, we investigated the spatial and temporal evolution of photospheric magnetic fields in the active region NOAA 9236 that produced eight flare-associated CMEs during the time period of 2000 November 23-26. The time variations of the total magnetic helicity injection rate and the total unsigned magnetic flux are determined and examined not only in the entire active region but also in some local regions such as the main sunspots and the CME-associated flaring regions using SOHO/MDI magnetogram data. As a result, we found that (1) in the sunspots, a large amount of positive (right-handed) magnetic helicity was injected during most of the examined time period, (2) in the flare region, there was a continuous injection of negative (left-handed) magnetic helicity during the entire period, accompanied by a large increase of the unsigned magnetic flux, and (3) the flaring regions were mainly composed of emerging bipoles of magnetic fragments in which magnetic field lines have substantially favorable conditions for making reconnection with large-scale, overlying, and oppositely directed magnetic field lines connecting the main sunspots. These observational findings can also be well explained by some MHD numerical simulations for CME initiation (e.g., reconnection-favored emerging flux models). We therefore conclude that reconnection-favored magnetic fields in the flaring emerging flux regions play a crucial role in producing the multiple flare-associated CMEs in NOAA 9236.
Broad-band linear polarization and magnetic intensification in rotating magnetic stars
International Nuclear Information System (INIS)
Degl'Innocenti, M.L.; Calamai, G.; Degl'Innocenti, E.L.; Patriarchi, P.
1981-01-01
Magnetic intensification is proposed as a mechanism to explain the general features of the variable broad-band linear polarization emerging from rotating magnetic stars. This mechanism is studied in detail, and some efforts are made to investigate the wide variety of polarization diagrams that can result from it. Theoretical results are compared with direct observations of the variable magnetic star 53 Cam to determine its geometric and magnetic configuration
Numerical studies of Siberian snakes and spin rotators for RHIC
International Nuclear Information System (INIS)
Luccio, A.
1995-01-01
For the program of polarized protons in RHIC, two Siberian snakes and four spin rotators per ring will be used. The Snakes will produce a complete spin flip. Spin Rotators, in pairs, will rotate the spin from the vertical direction to the horizontal plane at a given insertion, and back to the vertical after the insertion. Snakes, 180 degrees apart and with their axis of spin precession at 90 degrees to each other, are an effective means to avoid depolarization of the proton beam in traversing resonances. Classical snakes and rotators are made with magnetic solenoids or with a sequence of magnetic dipoles with fields alternately directed in the radial and vertical direction. Another possibility is to use helical magnets, essentially twisted dipoles, in which the field, transverse the axis of the magnet, continuously rotates as the particles proceed along it. After some comparative studies, the authors decided to adopt for RHIC an elegant solution with four helical magnets both for the snakes and the rotators proposed by Shatunov and Ptitsin. In order to simplify the construction of the magnets and to minimize cost, four identical super conducting helical modules will be used for each device. Snakes will be built with four right-handed helices. Spin rotators with two right-handed and two left-handed helices. The maximum field will be limited to 4 Tesla. While small bore helical undulators have been built for free electron lasers, large super conducting helical magnets have not been built yet. In spite of this difficulty, this choice is dictated by some distinctive advantages of helical over more conventional transverse snakes/rotators: (i) the devices are modular, they can be built with arrangements of identical modules, (ii) the maximum orbit excursion in the magnet is smaller, (iii) orbit excursion is independent from the separation between adjacent magnets, (iv) they allow an easier control of the spin rotation and the orientation of the spin precession axis
Shipley, G. A.; Awe, T. J.; Hutsel, B. T.; Slutz, S. A.; Lamppa, D. C.; Greenly, J. B.; Hutchinson, T. M.
2018-05-01
Auto-magnetizing (AutoMag) liners [Slutz et al., Phys. Plasmas 24, 012704 (2017)] are designed to generate up to 100 T of axial magnetic field in the fuel for Magnetized Liner Inertial Fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010)] without the need for external field coils. AutoMag liners (cylindrical tubes) are composed of discrete metallic helical conduction paths separated by electrically insulating material. Initially, helical current in the AutoMag liner produces internal axial magnetic field during a long (100 to 300 ns) current prepulse with an average current rise rate d I / d t = 5 k A / n s . After the cold fuel is magnetized, a rapidly rising current ( 200 k A / n s ) generates a calculated electric field of 64 M V / m between the helices. Such field is sufficient to force dielectric breakdown of the insulating material after which liner current is reoriented from helical to predominantly axial which ceases the AutoMag axial magnetic field production mechanism and the z-pinch liner implodes. Proof of concept experiments have been executed on the Mykonos linear transformer driver to measure the axial field produced by a variety of AutoMag liners and to evaluate what physical processes drive dielectric breakdown. A range of field strengths have been generated in various cm-scale liners in agreement with magnetic transient simulations including a measured field above 90 T at I = 350 kA. By varying the helical pitch angle, insulator material, and insulator geometry, favorable liner designs have been identified for which breakdown occurs under predictable and reproducible field conditions.
Rotating magnetic shallow water waves and instabilities in a sphere
Márquez-Artavia, X.; Jones, C. A.; Tobias, S. M.
2017-07-01
Waves in a thin layer on a rotating sphere are studied. The effect of a toroidal magnetic field is considered, using the shallow water ideal MHD equations. The work is motivated by suggestions that there is a stably stratified layer below the Earth's core mantle boundary, and the existence of stable layers in stellar tachoclines. With an azimuthal background field known as the Malkus field, ?, ? being the co-latitude, a non-diffusive instability is found with azimuthal wavenumber ?. A necessary condition for instability is that the Alfvén speed exceeds ? where ? is the rotation rate and ? the sphere radius. Magneto-inertial gravity waves propagating westward and eastward occur, and become equatorially trapped when the field is strong. Magneto-Kelvin waves propagate eastward at low field strength, but a new westward propagating Kelvin wave is found when the field is strong. Fast magnetic Rossby waves travel westward, whilst the slow magnetic Rossby waves generally travel eastward, except for some ? modes at large field strength. An exceptional very slow westward ? magnetic Rossby wave mode occurs at all field strengths. The current-driven instability occurs for ? when the slow and fast magnetic Rossby waves interact. With strong field the magnetic Rossby waves become trapped at the pole. An asymptotic analysis giving the wave speed and wave form in terms of elementary functions is possible both in polar trapped and equatorially trapped cases.
Nerve-muscle activation by rotating permanent magnet configurations.
Watterson, Peter A; Nicholson, Graham M
2016-04-01
The standard method of magnetic nerve activation using pulses of high current in coils has drawbacks of high cost, high electrical power (of order 1 kW), and limited repetition rate without liquid cooling. Here we report a new technique for nerve activation using high speed rotation of permanent magnet configurations, generating a sustained sinusoidal electric field using very low power (of order 10 W). A high ratio of the electric field gradient divided by frequency is shown to be the key indicator for nerve activation at high frequencies. Activation of the cane toad sciatic nerve and attached gastrocnemius muscle was observed at frequencies as low as 180 Hz for activation of the muscle directly and 230 Hz for curved nerves, but probably not in straight sections of nerve. These results, employing the first prototype device, suggest the opportunity for a new class of small low-cost magnetic nerve and/or muscle stimulators. Conventional pulsed current systems for magnetic neurostimulation are large and expensive and have limited repetition rate because of overheating. Here we report a new technique for nerve activation, namely high-speed rotation of a configuration of permanent magnets. Analytical solutions of the cable equation are derived for the oscillating electric field generated, which has amplitude proportional to the rotation speed. The prototype device built comprised a configuration of two cylindrical magnets with antiparallel magnetisations, made to rotate by interaction between the magnets' own magnetic field and three-phase currents in coils mounted on one side of the device. The electric field in a rectangular bath placed on top of the device was both numerically evaluated and measured. The ratio of the electric field gradient on frequency was approximately 1 V m(-2) Hz(-1) near the device. An exploratory series of physiological tests was conducted on the sciatic nerve and attached gastrocnemius muscle of the cane toad (Bufo marinus). Activation was
Ion heating due to rotation and collision in magnetized plasma
International Nuclear Information System (INIS)
Anderegg, F.; Stern, R.A.; Skiff, F.; Hammel, B.A.; Tran, M.Q.; Paris, P.J.; Kohler, P.
1986-01-01
The E x B rotation and associated collisional ion heating of noble-gas magnetized plasmas are investigated with high resolution by means of laser-induced fluorescence and electrical probes. Plasma rotation results from a radial potential gradient which can be controlled by biasing of the discharge electrodes. The time and space evolution of the potential, the rotation velocity v/sub t//sub h//sub e//sub t//sub a/, and the ion perpendicular temperature indicate that heating is due to the randomization of v/sub t//sub h//sub e//sub t//sub a/ by ion-neutral collisions, and leads to temperature increases as high as a factor of 50 over initial values
Helicity, Reconnection, and Dynamo Effects
International Nuclear Information System (INIS)
Ji, Hantao
1998-01-01
The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation
Nerve–muscle activation by rotating permanent magnet configurations
Nicholson, Graham M.
2016-01-01
Key points The standard method of magnetic nerve activation using pulses of high current in coils has drawbacks of high cost, high electrical power (of order 1 kW), and limited repetition rate without liquid cooling.Here we report a new technique for nerve activation using high speed rotation of permanent magnet configurations, generating a sustained sinusoidal electric field using very low power (of order 10 W).A high ratio of the electric field gradient divided by frequency is shown to be the key indicator for nerve activation at high frequencies.Activation of the cane toad sciatic nerve and attached gastrocnemius muscle was observed at frequencies as low as 180 Hz for activation of the muscle directly and 230 Hz for curved nerves, but probably not in straight sections of nerve.These results, employing the first prototype device, suggest the opportunity for a new class of small low‐cost magnetic nerve and/or muscle stimulators. Abstract Conventional pulsed current systems for magnetic neurostimulation are large and expensive and have limited repetition rate because of overheating. Here we report a new technique for nerve activation, namely high‐speed rotation of a configuration of permanent magnets. Analytical solutions of the cable equation are derived for the oscillating electric field generated, which has amplitude proportional to the rotation speed. The prototype device built comprised a configuration of two cylindrical magnets with antiparallel magnetisations, made to rotate by interaction between the magnets’ own magnetic field and three‐phase currents in coils mounted on one side of the device. The electric field in a rectangular bath placed on top of the device was both numerically evaluated and measured. The ratio of the electric field gradient on frequency was approximately 1 V m−2 Hz−1 near the device. An exploratory series of physiological tests was conducted on the sciatic nerve and attached gastrocnemius muscle of the cane toad
Yager-Elorriaga, D. A.; Lau, Y. Y.; Zhang, P.; Campbell, P. C.; Steiner, A. M.; Jordan, N. M.; McBride, R. D.; Gilgenbach, R. M.
2018-05-01
In this paper, we present experimental results on axially magnetized (Bz = 0.5 - 2.0 T), thin-foil (400 nm-thick) cylindrical liner-plasmas driven with ˜600 kA by the Michigan Accelerator for Inductive Z-Pinch Experiments, which is a linear transformer driver at the University of Michigan. We show that: (1) the applied axial magnetic field, irrespective of its direction (e.g., parallel or anti-parallel to the flow of current), reduces the instability amplitude for pure magnetohydrodynamic (MHD) modes [defined as modes devoid of the acceleration-driven magneto-Rayleigh-Taylor (MRT) instability]; (2) axially magnetized, imploding liners (where MHD modes couple to MRT) generate m = 1 or m = 2 helical modes that persist from the implosion to the subsequent explosion stage; (3) the merging of instability structures is a mechanism that enables the appearance of an exponential instability growth rate for a longer than expected time-period; and (4) an inverse cascade in both the axial and azimuthal wavenumbers, k and m, may be responsible for the final m = 2 helical structure observed in our experiments. These experiments are particularly relevant to the magnetized liner inertial fusion program pursued at Sandia National Laboratories, where helical instabilities have been observed.
Measurement of the torque on diluted ferrofluid samples in rotating magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Storozhenko, A.M. [Southwest State University, Kursk, 305040 (Russian Federation); Stannarius, R. [Otto von Guericke University Magdeburg, Magdeburg, 39016 Germany (Germany); Tantsyura, A.O.; Shabanova, I.A. [Southwest State University, Kursk, 305040 (Russian Federation)
2017-06-01
We study magnetic suspensions with different concentrations of ferromagnetic nanoparticles in a spherical container under the action of a rotating magnetic field. Experimental data on the concentration dependence of the rotational effect, viz. the torque exerted by the magnetic field, are presented. We explain the observed torque characteristics using a model that takes into account field-driven aggregation of the magnetic nanoparticles in stationary or slowly rotating fields. At sufficiently high rotation rates, the rotating magnetic field obviously destroys these aggregates, which results in a decreasing torque with increasing rotation frequency of the field. - Highlights: • The experimental study of the rotational effect in the magnetic fluids is presented. • The torque density non-monotonously depends on the magnetic field frequency. • Experimental data can be explained assuming aggregation of magnetic nanoparticles.
Measurement of the torque on diluted ferrofluid samples in rotating magnetic fields
International Nuclear Information System (INIS)
Storozhenko, A.M.; Stannarius, R.; Tantsyura, A.O.; Shabanova, I.A.
2017-01-01
We study magnetic suspensions with different concentrations of ferromagnetic nanoparticles in a spherical container under the action of a rotating magnetic field. Experimental data on the concentration dependence of the rotational effect, viz. the torque exerted by the magnetic field, are presented. We explain the observed torque characteristics using a model that takes into account field-driven aggregation of the magnetic nanoparticles in stationary or slowly rotating fields. At sufficiently high rotation rates, the rotating magnetic field obviously destroys these aggregates, which results in a decreasing torque with increasing rotation frequency of the field. - Highlights: • The experimental study of the rotational effect in the magnetic fluids is presented. • The torque density non-monotonously depends on the magnetic field frequency. • Experimental data can be explained assuming aggregation of magnetic nanoparticles.
International Nuclear Information System (INIS)
Yoshimura, H.; Wang, Z.; Wu, F.
1984-01-01
Differential rotation dependence of the selection mechanism for magnetic parity of solar and stellar cycles is studied by assuming various differential rotation profiles inn the dynamo equation. The parity selection depends on propagation direction of oscillating magnetic fields in the form of dynamo waves which propagate along isorotation surfaces. When there is any radial gradient in the differential rotation, dynamo waves propagate either equatorward or poleward. In the former case, field systems of the two hemispheres approach each other and collide at the equator. Then, odd parity is selected. In the latter case, field systems of the two hemispheres recede from each other and do not collide at the equator, an even parity is selected. Thus the equatorial migration of wings of the butterfly iagram of the solar cycle and its odd parity are intrinsically related. In the case of purely latitudibnal differential rotation, dynamo waves propagate purely radially and growth rates of odd and even modes are nearly the same even when dynamo strength is weak when the parity selection mechanism should work most efficiently. In this case, anisotropy of turbulent diffusivity is a decisive factor to separate odd and even modes. Unlike in the case of radial-gradient-dominated differential rotation in which any difference between diffusivities for poloidal and toroidal fields enhancess the parity selection without changing the parity, the parity selection in the case of latitudinal-gradient-dominated differential rotation depends on the difference of diffusivities for poloidal and toroidal fields. When diffusivity for poloidal fields iss larger than that for toroidal fields, odd parity is selected; and when diffusivity for toroidal fields is larger, even parity is selected
Matsumoto, Tadafumi; Sekiguchi, Jun'ichi; Asai, Tomohiko
In the formation of magnetized plasmoid by a magnetized coaxial plasma gun (MCPG), the magnetic helicity content of the generated plasmoid is one of the critical parameters. Typically, the bias coil to generate a poloidal flux is mounted either on the outer electrode or inside the inner electrode. However, most of the flux generated in the conventional method spreads even radially outside of the formation region. Thus, only a fraction of the total magnetic flux is actually exploited for helicity generation in the plasmoid. In the proposed system, the plasma gun incorporates a copper shell mounted on the outer electrode. By changing the rise time of the discharge bias coil current and the geometrical structure of the shell, the magnetic field structure and its time evolution can be controlled. The effect of the copper shell has been numerically simulated for the actual gun structure, and experimentally confirmed. This may increase the magnetic helicity content results, through increased poloidal magnetic field.
Cheng, Yu; Muroski, Megan E; Petit, Dorothée C M C; Mansell, Rhodri; Vemulkar, Tarun; Morshed, Ramin A; Han, Yu; Balyasnikova, Irina V; Horbinski, Craig M; Huang, Xinlei; Zhang, Lingjiao; Cowburn, Russell P; Lesniak, Maciej S
2016-02-10
Magnetic particles that can be precisely controlled under a magnetic field and transduce energy from the applied field open the way for innovative cancer treatment. Although these particles represent an area of active development for drug delivery and magnetic hyperthermia, the in vivo anti-tumor effect under a low-frequency magnetic field using magnetic particles has not yet been demonstrated. To-date, induced cancer cell death via the oscillation of nanoparticles under a low-frequency magnetic field has only been observed in vitro. In this report, we demonstrate the successful use of spin-vortex, disk-shaped permalloy magnetic particles in a low-frequency, rotating magnetic field for the in vitro and in vivo destruction of glioma cells. The internalized nanomagnets align themselves to the plane of the rotating magnetic field, creating a strong mechanical force which damages the cancer cell structure inducing programmed cell death. In vivo, the magnetic field treatment successfully reduces brain tumor size and increases the survival rate of mice bearing intracranial glioma xenografts, without adverse side effects. This study demonstrates a novel approach of controlling magnetic particles for treating malignant glioma that should be applicable to treat a wide range of cancers. Copyright © 2015 Elsevier B.V. All rights reserved.
Rotation and magnetism in intermediate-mass stars
Quentin, Léo G.; Tout, Christopher A.
2018-06-01
Rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. Surface magnetic fields from a few to 20 000 G have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars. Stellar remnants such as white dwarfs have been observed with fields from a few to more than 109 G. We investigate the origin of and the evolution, on thermal and nuclear rather than dynamical time-scales, of an averaged large-scale magnetic field throughout a star's life and its coupling to stellar rotation. Large-scale magnetic fields sustained until late stages of stellar evolution with conservation of magnetic flux could explain the very high fields observed in white dwarfs. We include these effects in the Cambridge stellar evolution code using three time-dependant advection-diffusion equations coupled to the structural and composition equations of stars to model the evolution of angular momentum and the two components of the magnetic field. We present the evolution in various cases for a 3 M_{⊙} star from the beginning to the late stages of its life. Our particular model assumes that turbulent motions, including convection, favour small-scale field at the expense of large-scale field. As a result, the large-scale field concentrates in radiative zones of the star and so is exchanged between the core and the envelope of the star as it evolves. The field is sustained until the end of the asymptotic giant branch, when it concentrates in the degenerate core.
Energy Technology Data Exchange (ETDEWEB)
Ye, Bo, E-mail: yebo@hubu.edu.cn [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); School of Computer Science and Information Engineering, HuBei University, Wuhan 430062 (China); Zhang, Wei [Department of Mechanical Engineering, Hubei University of Automotive Technology, Shiyan 442002 (China); Sun, Zhen-jun [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); Guo, Lin [School of Computer Science and Information Engineering, HuBei University, Wuhan 430062 (China); Deng, Chao [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); Chen, Ya-qi [Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030 (China); Zhang, Hong-hai [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); Liu, Sheng [School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072 (China)
2015-12-01
In this paper, the authors propose rotating an external permanent magnet (EPM) to manipulate the synchronous rotation of a magnetic spiral-type wireless capsule endoscope (WCE), and the synchronous rotation of the WCE is converted to its translational motion in intestinal tract. In order to preliminarily verify the feasibility of this method, a handheld actuator (HA) controlled by micro controller unit, a magnetic spiral-type WCE and a bracket were fabricated, theoretical analysis and simulations about the control distance of this method were performed, and in ex-vivo tests were examined in porcine small intestine to verify the control distance and control performances of this method. It was demonstrated that this method showed good performances in controlling the translational motion of the magnetic spiral-type WCE, and this method has great potential to be used in clinical application. - Highlights: • A new magnetic control method for spiral-type wireless capsule endoscope is proposed. • Wireless capsule endoscope rotates synchronously with external permanent magnet. • The method controls the wireless capsule endoscope well in porcine small intestine. • Long control distance makes the method may be used in future medical application. • Experimental setup has great advantages: high cost performance and easy operation.
Helicity content and tokamak applications of helicity
International Nuclear Information System (INIS)
Boozer, A.H.
1986-05-01
Magnetic helicity is approximately conserved by the turbulence associated with resistive instabilities of plasmas. To generalize the application of the concept of helicity, the helicity content of an arbitrary bounded region of space will be defined. The definition has the virtues that both the helicity content and its time derivative have simple expressions in terms of the poloidal and toroidal magnetic fluxes, the average toroidal loop voltage and the electric potential on the bounding surface, and the volume integral of E-B. The application of the helicity concept to tokamak plasmas is illustrated by a discussion of so-called MHD current drive, an example of a stable tokamak q profile with q less than one in the center, and a discussion of the possibility of a natural steady-state tokamak due to the bootstrap current coupling to tearing instabilities
Tissue discrimination in magnetic resonance imaging of the rotator cuff
International Nuclear Information System (INIS)
Meschino, G J; Comas, D S; González, M A; Ballarin, V L; Capiel, C
2016-01-01
Evaluation and diagnosis of diseases of the muscles within the rotator cuff can be done using different modalities, being the Magnetic Resonance the method more widely used. There are criteria to evaluate the degree of fat infiltration and muscle atrophy, but these have low accuracy and show great variability inter and intra observer. In this paper, an analysis of the texture features of the rotator cuff muscles is performed to classify them and other tissues. A general supervised classification approach was used, combining forward-search as feature selection method with kNN as classification rule. Sections of Magnetic Resonance Images of the tissues of interest were selected by specialist doctors and they were considered as Gold Standard. Accuracies obtained were of 93% for T1-weighted images and 92% for T2-weighted images. As an immediate future work, the combination of both sequences of images will be considered, expecting to improve the results, as well as the use of other sequences of Magnetic Resonance Images. This work represents an initial point for the classification and quantification of fat infiltration and muscle atrophy degree. From this initial point, it is expected to make an accurate and objective system which will result in benefits for future research and for patients’ health. (paper)
Tissue discrimination in magnetic resonance imaging of the rotator cuff
Meschino, G. J.; Comas, D. S.; González, M. A.; Capiel, C.; Ballarin, V. L.
2016-04-01
Evaluation and diagnosis of diseases of the muscles within the rotator cuff can be done using different modalities, being the Magnetic Resonance the method more widely used. There are criteria to evaluate the degree of fat infiltration and muscle atrophy, but these have low accuracy and show great variability inter and intra observer. In this paper, an analysis of the texture features of the rotator cuff muscles is performed to classify them and other tissues. A general supervised classification approach was used, combining forward-search as feature selection method with kNN as classification rule. Sections of Magnetic Resonance Images of the tissues of interest were selected by specialist doctors and they were considered as Gold Standard. Accuracies obtained were of 93% for T1-weighted images and 92% for T2-weighted images. As an immediate future work, the combination of both sequences of images will be considered, expecting to improve the results, as well as the use of other sequences of Magnetic Resonance Images. This work represents an initial point for the classification and quantification of fat infiltration and muscle atrophy degree. From this initial point, it is expected to make an accurate and objective system which will result in benefits for future research and for patients’ health.
Spinning rate decay of levitated high-Tc superconductors in rotational magnetic field
Energy Technology Data Exchange (ETDEWEB)
Terentiev, A.N.; Kutukova, E.O.; Kuznetsov, A.A. (Inst. of Chemical Physics, Academy of Sciences, Moscow (Russia)); Mozhaev, A.P. (Moscow State Univ., Dept. of Chemistry (Russia))
1992-04-01
The rotation damping of a levitated superconductor was examined in the static field of a ring-shaped magnet and in the rotating field of coils. It was demonstrated that the pinning force mainly contributed to magnetic friction while the influence of a viscous component was negligible. The rotating magnetic field created a torque, reducing the angular deceleration under relaxation. Dependence of the rotational field-induced torque on the field-intensity was step-like. A relationship between the step-like behavior of rotational field-induced torque and pinning center distribution is discussed. The origins of friction torque and rotational field-produced torque are discussed. (orig.).
Bouchard, Louis-Serge; Pines, Alexander; Demas, Vasiliki
2014-01-21
A system and method for Fourier encoding a nuclear magnetic resonance (NMR) signal is disclosed. A static magnetic field B.sub.0 is provided along a first direction. An NMR signal from the sample is Fourier encoded by applying a rotating-frame gradient field B.sub.G superimposed on the B.sub.0, where the B.sub.G comprises a vector component rotating in a plane perpendicular to the first direction at an angular frequency .omega.in a laboratory frame. The Fourier-encoded NMR signal is detected.
Momentum transfer to rotating magnetized plasma from gun plasma injection
International Nuclear Information System (INIS)
Shamim, Imran; Hassam, A. B.; Ellis, R. F.; Witherspoon, F. D.; Phillips, M. W.
2006-01-01
Numerical simulations are carried out to investigate the penetration and momentum coupling of a gun-injected plasma slug into a rotating magnetized plasma. An experiment along these lines is envisioned for the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et al., Phys. Plasmas 8, 2057 (2001)] using a coaxial plasma accelerator gun developed by HyperV Technologies Corp. [F. D. Witherspoon et al., Bull. Am. Phys. Soc. 50, LP1 87 (2005)]. The plasma gun would be located in the axial midplane and fired off-axis into the rotating MCX plasma annulus. The numerical simulation is set up so that the initial momentum in the injected plasma slug is of the order of the initial momentum of the target plasma. Several numerical firings are done into the cylindrical rotating plasma. Axial symmetry is assumed. The slug is seen to penetrate readily and deform into a mushroom, characteristic of interchange deformations. It is found that up to 25% of the momentum in the slug can be transferred to the background plasma in one pass across a cylindrical chord. For the same initial momentum, a high-speed low density slug gives more momentum transfer than a low-speed high density slug. Details of the numerical simulations and a scaling study are presented
The rotational hysteresis losses in thin films with unidirectional magnetic anisotropy
Mucha, J. M.; Vatskichev, L.; Vatskicheva, M.
1992-03-01
Using the Planar Hall Effect (PHE) the rotational hysteresis losses in NiFeGe thin magnetic films were measured. The calculation of the critical field for magnetization and rotational hysteresis losses based on extended Stoner-Wohlfarth theory including an exchange magnetic field is given.
Energy Technology Data Exchange (ETDEWEB)
Singh, Chandra B.; Pino, Elisabete M. de Gouveia Dal [Department of Astronomy (IAG-USP), University of São Paulo, São Paulo (Brazil); Mizuno, Yosuke, E-mail: csingh@iag.usp.br, E-mail: dalpino@iag.usp.br, E-mail: mizuno@th.physik.uni-frankfurt.de [Institute for Theoretical Physics, Goethe University, D-60438, Frankfurt am Main (Germany)
2016-06-10
Using the three-dimensional relativistic magnetohydrodynamic code RAISHIN, we investigated the influence of the radial density profile on the spatial development of the current-driven kink instability along magnetized rotating, relativistic jets. For the purposes of our study, we used a nonperiodic computational box, the jet flow is initially established across the computational grid, and a precessional perturbation at the inlet triggers the growth of the kink instability. We studied light and heavy jets with respect to the environment depending on the density profile. Different angular velocity amplitudes have been also tested. The results show the propagation of a helically kinked structure along the jet and a relatively stable configuration for the lighter jets. The jets appear to be collimated by the magnetic field, and the flow is accelerated owing to conversion of electromagnetic into kinetic energy. We also identify regions of high current density in filamentary current sheets, indicative of magnetic reconnection, which are associated with the kink-unstable regions and correlated with the decrease of the sigma parameter of the flow. We discuss the implications of our findings for Poynting-flux-dominated jets in connection with magnetic reconnection processes. We find that fast magnetic reconnection may be driven by the kink-instability turbulence and govern the transformation of magnetic into kinetic energy, thus providing an efficient way to power and accelerate particles in active galactic nucleus and gamma-ray-burst relativistic jets.
Energy Technology Data Exchange (ETDEWEB)
Morii, Y.; Sukedai, M. [Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680 (Japan); Ohashi, S., E-mail: ohashi@kansai-u.ac.jp [Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680 (Japan)
2011-11-15
The hybrid magnetic bearing has been developed. In the hybrid system, effect of the pinning force becomes smaller. Influence of the vibration and the gradient angle in the resonance state is large. The resonance frequency becomes small in the hybrid bearing system. The hybrid magnetic bearing using permanent magnets and the high-Tc bulk superconductor (HTSC) has been developed. Repulsive force of the permanent magnet is introduced to increase the load weight of the magnetic bearing. Effect of the hybrid system has been shown. In this paper, influence of the hybrid system on the dynamic characteristics of the rotor is studied. The rotational characteristics in the mechanical resonance state are studied, and the equivalent magnetic spring coefficient is estimated from the experimental results of the load weight. The resonance frequency is measured by the rotation experiments. The rotor achieves stable levitation even in the resonance state. In the hybrid system, effect of the pinning force becomes smaller than that of the lateral force generated by the repulsive force between the two permanent magnets at the smaller air gap. Thus influence of the lateral vibration and the gradient angle in the resonance state becomes larger at a smaller air gap. The equivalent magnetic spring coefficient becomes also small, and the resonance frequency becomes small in the hybrid bearing system.
An Air Bearing Rotating Coil Magnetic Measurement System
Gottschalk, Stephen C; Taylor, David J; Thayer, William
2005-01-01
This paper describes a rotating coil magnetic measurement system supported on air bearings. The design is optimized for measurements of 0.1micron magnetic centerline changes on long, small aperture quadrupoles. Graphite impregnated epoxy resin is used for the coil holder and coil winding forms. Coil holder diameter is 11 mm with a length between supports of 750mm. A pair of coils is used to permit quadrupole bucking during centerline measurements. Coil length is 616mm, inner radius 1.82mm, outer radius 4.74mm. The key features of the mechanical system are simplicity; air bearings for accurate, repeatable measurements without needing warm up time and a vibration isolated stand that uses a steel-topped Newport optical table with air suspension. Coil rotation is achieved by a low noise servo motor controlled by a standalone Ethernet servo board running custom servo software. Coil calibration procedures that correct wire placement errors, tests for mechanical resonances, and other system checks will also be discu...
Belinsky, Moisey I
2016-05-02
The rotation behavior of the vector chirality κ, scalar chirality χ, and magnetization M in the rotating magnetic field H1 is considered for the V3 and Cu3 nanomagnets, in which the Dzialoshinsky-Moriya coupling is active. The polar rotation of the field H1 of the given strength H1 results in the energy spectrum characterized by different vector and scalar chiralities in the ground and excited states. The magnetochiral correlations between the vector and scalar chiralities, energy, and magnetization in the rotating field were considered. Under the uniform polar rotation of the field H1, the ground-state chirality vector κI performs sawtooth oscillations and the magnetization vector MI performs the sawtooth oscillating rotation that is accompanied by the correlated transformation of the scalar chirality χI. This demonstrates the magnetochiral effect of the joint rotation behavior and simultaneous frustrations of the spin chiralities and magnetization in the rotating field, which are governed by the correlation between the chiralities and magnetization.
Numerical analysis on the action of centrifuge force in magnetic fluid rotating shaft seals
Zou, Jibin; Li, Xuehui; Lu, Yongping; Hu, Jianhui
2002-11-01
The magnetic fluid seal is suitable for high-speed rotating shaft seal applications. Centrifuge force will have evident influence on magnetic fluid rotating shaft seals. The seal capacity of the rotating shaft seal can be improved or increased by some measures. Through hydrodynamic analysis the moving status of the magnetic fluid is worked out. By numerical method, the magnetic field and the isobars in the magnetic fluid of a seal device are computed. Then the influence of the centrifuge force on the magnetic fluid seal is calculated quantitatively.
Numerical analysis on the action of centrifuge force in magnetic fluid rotating shaft seals
International Nuclear Information System (INIS)
Zou Jibin; Li Xuehui; Lu Yongping; Hu Jianhui
2002-01-01
The magnetic fluid seal is suitable for high-speed rotating shaft seal applications. Centrifuge force will have evident influence on magnetic fluid rotating shaft seals. The seal capacity of the rotating shaft seal can be improved or increased by some measures. Through hydrodynamic analysis the moving status of the magnetic fluid is worked out. By numerical method, the magnetic field and the isobars in the magnetic fluid of a seal device are computed. Then the influence of the centrifuge force on the magnetic fluid seal is calculated quantitatively
Influence of the shaft rotation on the stability of magnetic fluid shaft seal characteristics
Krakov, M. S.; Nikiforov, I. V.
2008-12-01
Distribution of the magnetic particles concentration in a magnetic fluid shaft seal is studied numerically for a rotating shaft. It is revealed that the shaft rotation causes not only an azimuthal flow of the magnetic fluid, but a meridional flow as well. This meridional flow prevents the growth of magnetic particle concentration in the gap of the magnetic fluid shaft seal. As a result, the burst pressure of the magnetic fluid shaft seal for the rotating shaft is stable and does not change with time. Figs 6, Refs 7.
Directory of Open Access Journals (Sweden)
Ivo Doležel
2014-04-01
Full Text Available An advanced way of induction heating of nonmagnetic billets is discussed and modeled. The billet rotates in a stationary magnetic field produced by unmoving high-parameter permanent magnets fixed on magnetic circuit of an appropriate shape. The mathematical model of the problem consisting of two coupled partial differential equations is solved numerically, in the monolithic formulation. Computations are carried out using our own code Agros2D based on a fully adaptive higher-order finite element method. The most important results are verified experimentally on our own laboratory device.
Energy Technology Data Exchange (ETDEWEB)
Dobák, Samuel, E-mail: samuel.dobak@student.upjs.sk [Institute of Physics, Faculty of Science, Pavol Jozef Šafárik University, Park Angelinum 9, 041 54 Košice (Slovakia); Füzer, Ján; Kollár, Peter [Institute of Physics, Faculty of Science, Pavol Jozef Šafárik University, Park Angelinum 9, 041 54 Košice (Slovakia); Fáberová, Mária; Bureš, Radovan [Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 043 53 Košice (Slovakia)
2017-03-15
This study sheds light on the dynamic magnetization process in iron/resin soft magnetic composites from the viewpoint of quantitative decomposition of their complex permeability spectra into the viscous domain wall motion and magnetization rotation. We present a comprehensive view on this phenomenon over the broad family of samples with different average particles dimension and dielectric matrix content. The results reveal the pure relaxation nature of magnetization processes without observation of spin resonance. The smaller particles and higher amount of insulating resin result in the prevalence of rotations over domain wall movement. The findings are elucidated in terms of demagnetizing effects rising from the heterogeneity of composite materials. - Highlights: • A first decomposition of complex permeability into domain wall and rotation parts in soft magnetic composites. • A pure relaxation nature of dynamic magnetization processes. • A complete loss separation in soft magnetic composites. • The domain walls activity is considerably suppressed in composites with smaller iron particles and higher matrix content. • The demagnetizing field acts as a significant factor at the dynamic magnetization process.
Research on single-chip microcomputer controlled rotating magnetic field mineralization model
Li, Yang; Qi, Yulin; Yang, Junxiao; Li, Na
2017-08-01
As one of the method of selecting ore, the magnetic separation method has the advantages of stable operation, simple process flow, high beneficiation efficiency and no chemical environment pollution. But the existing magnetic separator are more mechanical, the operation is not flexible, and can not change the magnetic field parameters according to the precision of the ore needed. Based on the existing magnetic separator is mechanical, the rotating magnetic field can be used for single chip microcomputer control as the research object, design and trial a rotating magnetic field processing prototype, and through the single-chip PWM pulse output to control the rotation of the magnetic field strength and rotating magnetic field speed. This method of using pure software to generate PWM pulse to control rotary magnetic field beneficiation, with higher flexibility, accuracy and lower cost, can give full play to the performance of single-chip.
Energy Technology Data Exchange (ETDEWEB)
Li, Xun [State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructure, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China); State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China); Xu, Zheng, E-mail: zhengxu@nju.edu.cn [State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructure, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China)
2012-12-15
Graphical abstract: The helical, straight and hollow carbon nanofibers can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. Display Omitted Highlights: ► CNFs were synthesized via pyrolysis of acetylene on copper NPs. ► The helical, straight, hollow and N-doped CNFs can be selectively synthesized. ► The growth mechanism of different types of CNFs was proposed. -- Abstract: Carbon nanofibers (CNFs) with various morphologies were synthesized by catalytic pyrolysis of acetylene on copper nanoparticles which were generated from the in situ decomposition of copper acetylacetonate. The morphology of the pristine and acid-washed CNFs was investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. Helical, straight and hollow CNFs can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. The growth mechanism for these three types of CNFs was proposed.
Explosion of optimal high-beta operation regime by magnetic axis swing in the Large Helical Device
International Nuclear Information System (INIS)
Sakakibara, S.; Ohdachi, S.; Watanabe, K.Y.
2010-11-01
In Large Helical Device (LHD), the volume averaged beta value dia > as high as 5.1% was achieved in FY2007-2008 experiments. High beta operation regime was explorated by the programmed control of magnetic axis position, which characterizes MHD equilibrium, stability and transport. This control became enable by increasing capability of poloidal coil power supply. The experiments made clear the effect of magnetic hill on MHD activities in high-beta plasmas with more than 4%. Also it enabled to access the ideal stability boundary with keeping high-beta state. The strong m/n=2/1 mode leading minor collapse in core plasma appeared with the inward shift of the magnetic axis. (author)
Energy Technology Data Exchange (ETDEWEB)
Cheung, Mark C. M.; Pontieu, B. De; Tarbell, T. D.; Fu, Y.; Martínez-Sykora, J.; Boerner, P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N. [Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street Bldg. 252, Palo Alto, CA 94304 (United States); Tian, H.; Testa, P.; Reeves, K. K.; Golub, L.; McKillop, S.; Saar, S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kleint, L. [University of Applied Sciences and Arts Northwestern Switzerland, Bahnhofstr. 6, 5210 Windisch (Switzerland); Kankelborg, C.; Jaeggli, S. [Department of Physics, Montana State University, Bozeman, P.O. Box 173840, Bozeman, MT 59717 (United States); Carlsson, M., E-mail: cheung@lmsal.com [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, NO-0315 Oslo (Norway); and others
2015-03-10
We report on observations of recurrent jets by instruments on board the Interface Region Imaging Spectrograph, Solar Dynamics Observatory (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21, recurrent coronal jets were observed to emanate from NOAA Active Region 11793. Far-ultraviolet spectra probing plasma at transition region temperatures show evidence of oppositely directed flows with components reaching Doppler velocities of ±100 km s{sup −1}. Raster Doppler maps using a Si iv transition region line show all four jets to have helical motion of the same sense. Simultaneous observations of the region by SDO and Hinode show that the jets emanate from a source region comprising a pore embedded in the interior of a supergranule. The parasitic pore has opposite polarity flux compared to the surrounding network field. This leads to a spine-fan magnetic topology in the coronal field that is amenable to jet formation. Time-dependent data-driven simulations are used to investigate the underlying drivers for the jets. These numerical experiments show that the emergence of current-carrying magnetic field in the vicinity of the pore supplies the magnetic twist needed for recurrent helical jet formation.
Helical Tomotherapy Planning for Lung Cancer Based on Ventilation Magnetic Resonance Imaging
Energy Technology Data Exchange (ETDEWEB)
Cai Jing; McLawhorn, Robert [Department of Radiation Oncology, University of Virginia, Charlottesville, VA (United States); Altes, Tallisa A.; Lange, Eduard de [Department of Radiology, University of Virginia, Charlottesville, VA (United States); Read, Paul W.; Larner, James M.; Benedict, Stanley H. [Department of Radiation Oncology, University of Virginia, Charlottesville, VA (United States); Sheng Ke, E-mail: ks2mc@virginia.edu [Department of Radiation Oncology, University of Virginia, Charlottesville, VA (United States)
2011-01-01
To investigate the feasibility of lung ventilation-based treatment planning, computed tomography and hyperpolarized (HP) helium-3 (He-3) magnetic resonance imaging (MRI) ventilation images of 6 subjects were coregistered for intensity-modulated radiation therapy planning in Tomotherapy. Highly-functional lungs (HFL) and less-functional lungs (LFL) were contoured based on their ventilation image intensities, and a cylindrical planning-target-volume was simulated at locations adjacent to both HFL and LFL. Annals of an anatomy-based plan (Plan 1) and a ventilation-based plan (Plan 2) were generated. The following dosimetric parameters were determined and compared between the 2 plans: percentage of total/HFL volume receiving {>=}20 Gy, 15 Gy, 10 Gy, and 5 Gy (TLV{sub 20}, HFLV{sub 20}, TLV{sub 15}, HFLV{sub 15}, TLV{sub 10}, HFLV{sub 10}, TLV{sub 5}, HFLV{sub 5}), mean total/HFL dose (MTLD/HFLD), maximum doses to all organs at risk (OARs), and target dose conformality. Compared with Plan 1, Plan 2 reduced mean HFLD (mean reduction, 0.8 Gy), MTLD (mean reduction, 0.6 Gy), HFLV{sub 20} (mean reduction, 1.9%), TLV{sub 20} (mean reduction, 1.5%), TLV{sub 15} (mean reduction, 1.7%), and TLV{sub 10} (mean reduction, 2.1%). P-values of the above comparisons are less than 0.05 using the Wilcoxon signed rank test. For HFLV{sub 15}, HFLV{sub 10}, TLV{sub 5}, and HTLV{sub 5}, Plan 2 resulted in lower values than plan 1 but the differences are not significant (P-value range, 0.063-0.219). Plan 2 did not significantly change maximum doses to OARs (P-value range, 0.063-0.563) and target conformality (P = 1.000). HP He-3 MRI of patients with lung disease shows a highly heterogeneous ventilation capacity that can be utilized for functional treatment planning. Moderate but statistically significant improvements in sparing functional lungs were achieved using helical tomotherapy plans.
Magnetism, planetary rotation and convection in the solar system
1985-01-01
On the 6th, 7th' and 8th April 1983, a conference entitled "Magnetism, planetary rotation and convection in the Solar System" was held in the School of Physics at the University of Newcastle upon Tyne. The purpose of the meeting was to celebrate the 60th birthday of Prof. Stanley Keith Runcorn and his, and his students' and associates', several decades of scientific achievement. The social programme, which consisted of excursions in Northumberland and Durham with visits to ancient castles and churches, to Hexham Abbey and Durham Cathedral, and dinners in Newcastle and Durham, was greatly enjoyed by those attending the meeting and by their guests. The success ofthe scientific programme can be judged by this special edition of Geophysical Surveys which is derived mainly from the papers given at the meeting. The story starts in the late 1940s when the question of the origin of the magnetic field of the Earth and such other heavenly bodies as had at that time been discovered as having a magnetic field, was exerci...
Experimental and numerical results of a high frequency rotating active magnetic refrigerator
DEFF Research Database (Denmark)
Lozano, Jaime; Engelbrecht, Kurt; Bahl, Christian
2012-01-01
Experimental results for a recently developed prototype magnetic refrigeration device at The Technical University of Denmark (DTU) were obtained and compared with numerical simulation results. A continuously rotating active magnetic regenerator (AMR) using 2.8 kg packed sphere regenerators...
Experimental and numerical results of a high frequency rotating active magnetic refrigerator
DEFF Research Database (Denmark)
Lozano, Jaime; Engelbrecht, Kurt; Bahl, Christian R.H.
2014-01-01
Experimental results for a recently developed prototype magnetic refrigeration device at the Technical University of Denmark (DTU) were obtained and compared with numerical simulation results. A continuously rotating active magnetic regenerator (AMR) using 2.8 kg packed sphere regenerators...
A SCILAB Program for Computing Rotating Magnetic Compact Objects
Papasotiriou, P. J.; Geroyannis, V. S.
We implement the so-called ``complex-plane iterative technique'' (CIT) to the computation of classical differentially rotating magnetic white dwarf and neutron star models. The program has been written in SCILAB (© INRIA-ENPC), a matrix-oriented high-level programming language, which can be downloaded free of charge from the site http://www-rocq.inria.fr/scilab. Due to the advanced capabilities of this language, the code is short and understandable. Highlights of the program are: (a) time-saving character, (b) easy use due to the built-in graphics user interface, (c) easy interfacing with Fortran via online dynamic link. We interpret our numerical results in various ways by extensively using the graphics environment of SCILAB.
Magnetic resonance imaging in acute and chronic rotator cuff tears
International Nuclear Information System (INIS)
Buirski, G.
1990-01-01
Magnetic resonance imaging has been assessed in patients with acute rotator cuff tears and normal radiographs (9 cases) and those with chronic tears and changes of cuff arthropathy (9 cases). All images were obtained using a low field strength system (FONAR 0.3 T). Particular attention was placed on the appearances of the tendon and the cuff muscles themselves. Six complete acute tears were clearly identified, but MRI failed to demonstrate two partial tears. Muscle bulk was preserved in all patients in this group. In contrast, all patients with cuff arthropathy had complete tears of the supraspinatus tendon with marked tendon retraction and associated muscle atrophy: These changes precluded primary surgical repair. MRI should be used to assess muscle atrophy preoperatively in those patients with acute tears. When plain radiographs demonstrate cuff arthropathy, the MRI appearances are predictable and primary repair is unlikely to be successful. Further imaging is therefore not indicated. (orig.)
Structural looseness investigation in slow rotating permanent magnet generators
DEFF Research Database (Denmark)
Skrimpas, Georgios Alexandros; Mijatovic, Nenad; Sweeney, Christian Walsted
2016-01-01
Structural looseness in electric machines is a condition influencing the alignment of the machine and thus the overall bearing health. In this work, assessment of the above mentioned failure mode is tested on a slow rotating (running speed equal to 0.7Hz) permanent magnet generator (PMG), while...... collecting vibration and current data in order to cross-reference the indications from the two monitoring techniques. It is found that electric signature analysis shows no response even when two hold down bolts are untightened, whereas the analysis results from the vibration data exhibit superior performance....... The vibration-based condition indicators with the best response are the stator slot pass frequency, which can be directly related to the cogging torque in PMGs, and the 4th electric frequency harmonic, whose amplitudes increase due to the overall lower structure damping coefficient under looseness...
Magneto-Rayleigh-Taylor instability driven by a rotating magnetic field
Duan, Shuchao; Xie, Weiping; Cao, Jintao; Li, Ding
2018-04-01
In this paper, we analyze theoretically the magneto-Rayleigh-Taylor instability driven by a rotating magnetic field. Slab configurations of finite thickness are treated both with and without using the Wenzel-Kramers-Brillouin approximation. Regardless of the slab thickness, the directional rotation of the driving magnetic field contributes to suppressing these instabilities. The two factors of the finite thickness and directional rotation of the magnetic field cooperate to enhance suppression, with the finite thickness playing a role only when the orientation of the magnetic field is time varying. The suppression becomes stronger as the driving magnetic field rotates faster, and all modes are suppressed, in contrast to the case of a non-rotating magnetic field, for which the vertical mode cannot be suppressed. This implies that the dynamically alternate configuration of a Theta-pinch and a Z-pinch may be applicable to the concept of Theta-Z liner inertial fusion.
Acromial Findings Associated with Rotator cuff's Lesions in Magnetic Resonance
International Nuclear Information System (INIS)
Avila, Mercedes; Atencio, Elizabeth; Moreno, Franklin
2008-01-01
The objective is to evaluate by means of magnetic resonance the acromial alterations associated to rotator cuff (RC) lesions (MR). Materials and methods: A prospective, descriptive and cross-sectional type study was performed in 30 patients aged between 40 and 70 years who attended the Resomer imaging center during the period comprised between October-December 2007, with clinical diagnosis of RC lesion, using a 1.5 T magnet. Results: Most of the studied population were females (66.67%), the mean age being of 56.93 years with a typical deviation of 8.75, with partial lesions in 63.33%, Type II acromion was the dominant acromion in 50%, of anterior orientation (90%), with absent os acromiale (96.66%). Likewise, clavicular and acromial articular hypertrophy was demonstrated in 93.33% of cases. The glenoid-acromion distance had a mean value of 3.15 cm and a typical deviation of 0.55 while the glenoid-humeral distance was 4.65 cm with a typical deviation of 0.46 and the acromial index of 0.67. The humeral-acromion space exhibited a mean value of 6.3 mm with a typical deviation of 1.72. Conclusion: The predominantly degenerative acromial alterations are a conditioning factor of compression resulting from incarceration in the clamp form with a larger > supraspinous tendon wear-out with later affectation to the remaining tendons of the RC as the exposure evolves.
Electrodeless plasma acceleration system using rotating magnetic field method
Directory of Open Access Journals (Sweden)
T. Furukawa
2017-11-01
Full Text Available We have proposed Rotating Magnetic Field (RMF acceleration method as one of electrodeless plasma accelerations. In our experimental scheme, plasma generated by an rf (radio frequency antenna, is accelerated by RMF antennas, which consist of two-pair, opposed, facing coils, and these antennas are outside of a discharge tube. Therefore, there is no wear of electrodes, degrading the propulsion performance. Here, we will introduce our RMF acceleration system developed, including the experimental device, e.g., external antennas, a tapered quartz tube, a vacuum chamber, external magnets, and a pumping system. In addition, we can change RMF operation parameters (RMF applied current IRMF and RMF current phase difference ϕ, focusing on RMF current frequency fRMF by adjusting matching conditions of RMF, and investigate the dependencies on plasma parameters (electron density ne and ion velocity vi; e.g., higher increases of ne and vi (∼360 % and 55 %, respectively than previous experimental results were obtained by decreasing fRMF from 5 MHz to 0.7 MHz, whose RMF penetration condition was better according to Milroy’s expression. Moreover, time-varying component of RMF has been measured directly to survey the penetration condition experimentally.
International Nuclear Information System (INIS)
Sakakibara, S; Suzuki, Y; Narushima, Y; Watanabe, K Y; Ohdachi, S; Ida, K; Yoshinuma, M; Narihara, K; Yamada, I; Tanaka, K; Tokuzawa, T; Yamada, H; Takemura, Y
2013-01-01
The effect of resonant magnetic perturbation (RMP) on MHD characteristics is investigated in high-beta plasmas of the Large Helical Device. The ramp-up and static m/n = 1/1 RMP field are applied in medium- (∼2%) and high- (∼4%) beta plasmas in order to find beta dependences of mode penetration, MHD activities and confinement. The results show that the threshold of mode penetration linearly increases with the beta value and/or plasma collisionality. The threshold of mode penetration in the RMP ramp-up experiments is roughly consistent with the static RMP case. The beta value gradually decreases with the RMP field strength before mode penetration, which is caused by a reduction in the pressure inside the ι/2π = 1 resonance. The width of the magnetic island after the penetration becomes larger than the given RMP field, and it is further enhanced by the increment of the beta value. (paper)
Solution of magnetic field and eddy current problem induced by rotating magnetic poles (abstract)
Liu, Z. J.; Low, T. S.
1996-04-01
The magnetic field and eddy current problems induced by rotating permanent magnet poles occur in electromagnetic dampers, magnetic couplings, and many other devices. Whereas numerical techniques, for example, finite element methods can be exploited to study various features of these problems, such as heat generation and drag torque development, etc., the analytical solution is always of interest to the designers since it helps them to gain the insight into the interdependence of the parameters involved and provides an efficient tool for designing. Some of the previous work showed that the solution of the eddy current problem due to the linearly moving magnet poles can give satisfactory approximation for the eddy current problem due to rotating fields. However, in many practical cases, especially when the number of magnet poles is small, there is significant effect of flux focusing due to the geometry. The above approximation can therefore lead to marked errors in the theoretical predictions of the device performance. Bernot et al. recently described an analytical solution in a polar coordinate system where the radial field is excited by a time-varying source. A discussion of an analytical solution of the magnetic field and eddy current problems induced by moving magnet poles in radial field machines will be given in this article. The theoretical predictions obtained from this method is compared with the results obtained from finite element calculations. The validity of the method is also checked by the comparison of the theoretical predictions and the measurements from a test machine. It is shown that the introduced solution leads to a significant improvement in the air gap field prediction as compared with the results obtained from the analytical solution that models the eddy current problems induced by linearly moving magnet poles.
Response of plasma rotation to resonant magnetic perturbations in J-TEXT tokamak
Yan, W.; Chen, Z. Y.; Huang, D. W.; Hu, Q. M.; Shi, Y. J.; Ding, Y. H.; Cheng, Z. F.; Yang, Z. J.; Pan, X. M.; Lee, S. G.; Tong, R. H.; Wei, Y. N.; Dong, Y. B.; J-TEXT Team
2018-03-01
The response of plasma toroidal rotation to the external resonant magnetic perturbations (RMP) has been investigated in Joint Texas Experimental Tokamak (J-TEXT) ohmic heating plasmas. For the J-TEXT’s plasmas without the application of RMP, the core toroidal rotation is in the counter-current direction while the edge rotation is near zero or slightly in the co-current direction. Both static RMP experiments and rotating RMP experiments have been applied to investigate the plasma toroidal rotation. The core toroidal rotation decreases to lower level with static RMP. At the same time, the edge rotation can spin to more than 20 km s-1 in co-current direction. On the other hand, the core plasma rotation can be slowed down or be accelerated with the rotating RMP. When the rotating RMP frequency is higher than mode frequency, the plasma rotation can be accelerated to the rotating RMP frequency. The plasma confinement is improved with high frequency rotating RMP. The plasma rotation is decelerated to the rotating RMP frequency when the rotating RMP frequency is lower than the mode frequency. The plasma confinement also degrades with low frequency rotating RMP.
Toroidal Flux Ropes with Elliptical Cross Sections and Their Magnetic Helicity
Czech Academy of Sciences Publication Activity Database
Vandas, Marek; Romashets, E.
2017-01-01
Roč. 292, č. 9 (2017), 129/1-129/23 ISSN 0038-0938 R&D Projects: GA ČR(CZ) GA14-19376S; GA ČR(CZ) GA17-06065S Institutional support: RVO:67985815 Keywords : coronal mass ejections * interplanetary * helicity Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 2.682, year: 2016
Teodorescu, C; Young, W C; Swan, G W S; Ellis, R F; Hassam, A B; Romero-Talamas, C A
2010-08-20
Interferometric density measurements in plasmas rotating in shaped, open magnetic fields demonstrate strong confinement of plasma parallel to the magnetic field, with density drops of more than a factor of 10. Taken together with spectroscopic measurements of supersonic E × B rotation of sonic Mach 2, these measurements are in agreement with ideal MHD theory which predicts large parallel pressure drops balanced by centrifugal forces in supersonically rotating plasmas.
Liquid metal flow in a finite-length cylinder with a rotating magnetic field
International Nuclear Information System (INIS)
Gelfgat, Yu.M.; Gorbunov, L.A.; Kolevzon, V.
1993-01-01
A liquid metal flow induced by a rotating magnetic field in a cylindrical container of finite height was investigated experimentally. It was demonstrated that the flow in a rotating magnetic field is similar to geophysical flows: the fluid rotates uniformly with depth and the Ekman layer exists at the container bottom. Near the vertical wall the flow is depicted in the form of a confined jet whose thickness determines the instability onset in a rotating magnetic field. It was shown that the critical Reynolds number can be found by using the jet velocity u 0 for Re cr =u 2 0 /ν∂u/∂r. The effect of frequency of a magnetic field on the fluid flow was also studied. An approximate theoretical model is presented for describing the fluid flow in a uniform rotating magnetic field. (orig.)
EVOLUTION OF SPINNING AND BRAIDING HELICITY FLUXES IN SOLAR ACTIVE REGION NOAA 10930
Energy Technology Data Exchange (ETDEWEB)
Ravindra, B. [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India); Yoshimura, Keiji [Department of Physics, Montana State University Bozeman, MT 59717 (United States); Dasso, Sergio, E-mail: ravindra@iiap.res.in, E-mail: yosimura@solar.physics.montana.edu, E-mail: dasso@df.uba.ar [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA), 1428 Buenos Aires (Argentina)
2011-12-10
The line-of-sight magnetograms from Solar Optical Telescope Narrowband Filter Imager observations of NOAA Active Region 10930 have been used to study the evolution of spinning and braiding helicities over a period of five days starting from 2006 December 9. The north (N) polarity sunspot was the follower and the south (S) polarity sunspot was the leader. The N-polarity sunspot in the active region was rotating in the counterclockwise direction. The rate of rotation was small during the first two days of observations and it increased up to 8 Degree-Sign hr{sup -1} on the third day of the observations. On the fourth and fifth days it remained at 4 Degree-Sign hr{sup -1} with small undulations in its magnitude. The sunspot rotated about 260 Degree-Sign in the last three days. The S-polarity sunspot did not complete more than 20 Degree-Sign in five days. However, it changed its direction of rotation five times over a period of five days and injected both the positive and negative type of spin helicity fluxes into the corona. Through the five days, both the positive and negative sunspot regions injected equal amounts of spin helicity. The total injected helicity is predominantly negative in sign. However, the sign of the spin and braiding helicity fluxes computed over all the regions were reversed from negative to positive five times during the five-day period of observations. The reversal in spinning helicity flux was found before the onset of the X3.4-class flare, too. Though, the rotating sunspot has been observed in this active region, the braiding helicity has contributed more to the total accumulated helicity than the spinning helicity. The accumulated helicity is in excess of -7 Multiplication-Sign 10{sup 43} Mx{sup 2} over a period of five days. Before the X3.4-class flare that occurred on 2006 December 13, the rotation speed and spin helicity flux increased in the S-polarity sunspot. Before the flare, the total injected helicity was larger than -6
Planar rotational magnetic micromotors with integrated shaft encoder and magnetic rotor levitation
Guckel, Henry; Christenson, T. R.; Skrobis, K. J.; Klein, J.; Karnowsky, M.
1994-01-01
Deep x-ray lithography and electroplating may be combined to form a fabrication tool for micromechanical devices with large structural heights, to 500 micron, and extreme edge acuities, less than 0.1 micron-run-out per 100 micron of height. This process concept which originated in Germany as LIGA may be further extended by adding surface micromachining. This extension permits the fabrication of precision metal and plastic parts which may be assembled into three-dimensional micromechanical components and systems. The processing tool may be used to fabricate devices from ferromagnetic material such as nickel and nickel-iron alloys. These materials when properly heat treated exhibit acceptable magnetic behavior for current to flux conversion and marginal behavior for permanent magnet applications. The tool and materials have been tested via planar, magnetic, rotational micromotor fabrication. Three phase reluctance machines of the 6:4 configuration with 280 micron diameter rotors have been tested and analyzed. Stable rotational speeds to 34,000 rpm with output torques above 10 x 10(exp -9) N-m have been obtained. The behavior is monitored with integrated shaft encoders which are photodiodes which measure the rotor response. Magnetic levitation of the rotor via reluctance forces has been achieved and has reduced frictional torque losses to less than 1 percent of the available torque. The results indicate that high speed limits of these actuators are related to torque ripple. Hysteresis motors with magnetic bearings are under consideration and will produce high speed rotational machines with excellent sensor application potential.
CURRENT AND KINETIC HELICITY OF LONG-LIVED ACTIVITY COMPLEXES
International Nuclear Information System (INIS)
Komm, Rudolf; Gosain, Sanjay
2015-01-01
We study long-lived activity complexes and their current helicity at the solar surface and their kinetic helicity below the surface. The current helicity has been determined from synoptic vector magnetograms from the NSO/SOLIS facility, and the kinetic helicity of subsurface flows has been determined with ring-diagram analysis applied to full-disk Dopplergrams from NSO/GONG and SDO/HMI. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values (78%; 78%, respectively, with a 95% confidence level of 31%) in the southern hemisphere and negative ones (80%; 93%, respectively, with a 95% confidence level of 22% and 14%, respectively) in the northern hemisphere. The locations with the dominant sign of kinetic helicity derived from Global Oscillation Network Group (GONG) and SDO/HMI data are more organized than those of the secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. This is the case for both hemispheres even for the northern one where it is not as obvious visually due to the large amount of magnetic activity present as compared to the southern hemisphere. The current helicity shows a similar behavior. The dominant sign of current helicity is the same as that of kinetic helicity for the majority of the activity complexes (83% with a 95% confidence level of 15%). During the 24 Carrington rotations analyzed here, there is at least one longitude in each hemisphere where activity complexes occur repeatedly throughout the epoch. These ''active'' longitudes are identifiable as locations of strong current and kinetic helicity of the same sign
International Nuclear Information System (INIS)
Duez, Matthew D.; Liu, Yuk Tung; Shapiro, Stuart L.; Stephens, Branson C.; Shibata, Masaru
2006-01-01
We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can be formed in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both act on differentially rotating stars to redistribute angular momentum. Simulations of these stars are carried out in axisymmetry using our recently developed codes which integrate the coupled Einstein-Maxwell-MHD equations. We consider stars with two different equations of state (EOS), a gamma-law EOS with Γ=2, and a more realistic hybrid EOS, and we evolve them adiabatically. Our simulations show that the fate of the star depends on its mass and spin. For initial data, we consider three categories of differentially rotating, equilibrium configurations, which we label normal, hypermassive and ultraspinning. Normal configurations have rest masses below the maximum achievable with uniform rotation, and angular momentum below the maximum for uniform rotation at the same rest mass. Hypermassive stars have rest masses exceeding the mass limit for uniform rotation. Ultraspinning stars are not hypermassive, but have angular momentum exceeding the maximum for uniform rotation at the same rest mass. We show that a normal star will evolve to a uniformly rotating equilibrium configuration. An ultraspinning star evolves to an equilibrium state consisting of a nearly uniformly rotating central core, surrounded by a differentially rotating torus with constant angular velocity along magnetic field lines, so that differential rotation ceases to wind the magnetic field. In addition, the final state is stable against the MRI, although it has differential rotation. For a hypermassive neutron star, the MHD-driven angular momentum transport leads to catastrophic collapse of the core. The resulting rotating black hole is surrounded by a hot, massive, magnetized torus undergoing quasistationary accretion, and a magnetic field collimated along
Centrifugal Force Based Magnetic Micro-Pump Driven by Rotating Magnetic Fields
International Nuclear Information System (INIS)
Kim, S H; Hashi, S; Ishiyama, K
2011-01-01
This paper presents a centrifugal force based magnetic micro-pump for the pumping of blood. Most blood pumps are driven by an electrical motor with wired control. To develop a wireless and battery-free blood pump, the proposed pump is controlled by external rotating magnetic fields with a synchronized impeller. Synchronization occurs because the rotor is divided into multi-stage impeller parts and NdFeB permanent magnet. Finally, liquid is discharged by the centrifugal force of multi-stage impeller. The proposed pump length is 30 mm long and 19 mm in diameter which much smaller than currently pumps; however, its pumping ability satisfies the requirement for a blood pump. The maximum pressure is 120 mmHg and the maximum flow rate is 5000ml/min at 100 Hz. The advantage of the proposed pump is that the general mechanical problems of a normal blood pump are eliminated by the proposed driving mechanism.
Centrifugal Force Based Magnetic Micro-Pump Driven by Rotating Magnetic Fields
Kim, S. H.; Hashi, S.; Ishiyama, K.
2011-01-01
This paper presents a centrifugal force based magnetic micro-pump for the pumping of blood. Most blood pumps are driven by an electrical motor with wired control. To develop a wireless and battery-free blood pump, the proposed pump is controlled by external rotating magnetic fields with a synchronized impeller. Synchronization occurs because the rotor is divided into multi-stage impeller parts and NdFeB permanent magnet. Finally, liquid is discharged by the centrifugal force of multi-stage impeller. The proposed pump length is 30 mm long and19 mm in diameter which much smaller than currently pumps; however, its pumping ability satisfies the requirement for a blood pump. The maximum pressure is 120 mmHg and the maximum flow rate is 5000ml/min at 100 Hz. The advantage of the proposed pump is that the general mechanical problems of a normal blood pump are eliminated by the proposed driving mechanism.
Apparatus and method for generating a magnetic field by rotation of a charge holding object
Gerald, II, Rex E.; Vukovic, Lela [Westchester, IL; Rathke, Jerome W [Homer Glenn, IL
2009-10-13
A device and a method for the production of a magnetic field using a Charge Holding Object that is mechanically rotated. In a preferred embodiment, a Charge Holding Object surrounding a sample rotates and subjects the sample to one or more magnetic fields. The one or more magnetic fields are used by NMR Electronics connected to an NMR Conductor positioned within the Charge Holding Object to perform NMR analysis of the sample.
DEFF Research Database (Denmark)
Juul-Kristensen, B.; Bojsen-Møller, Finn; Holst, E.
2000-01-01
Anatomy, biomechanics, cross-section, magnetic resonance imaging, method comparison, rotator cuff muscles, ultrasound......Anatomy, biomechanics, cross-section, magnetic resonance imaging, method comparison, rotator cuff muscles, ultrasound...
Modeling and Swimming Property Characterizations of Scaled-Up Helical Microswimmers.
Xu , Tiantian; Hwang , Gilgueng; Andreff , Nicolas; Régnier , Stéphane
2014-01-01
International audience; Micro- and nanorobots capable of controlled propulsion at low Reynolds number are foreseen to change many aspects of medicine by enabling targeted diagnosis and therapy, and minimally invasive surgery. Several kinds of helical swimmers with different heads actuated by a rotating magnetic field have been proposed in prior works. Beyond these proofs of concepts, this paper aims to obtain an optimized design of the helical swimmers adapted to low Reynolds numbers. For thi...
3-D explosions: a meditation on rotation (and magnetic fields)
Wheeler, J. C.
This is the text of an introduction to a workshop on asymmetric explosions held in Austin in June, 2003. The great progress in supernova research over thirty-odd years is briefly reviewed. The context in which the meeting was called is then summarized. The theoretical success of the intrinsically multidimensional delayed detonation paradigm in explaining the nature of Type Ia supernovae coupled with new techniques of observations in the near IR and with spectropolarimetry promise great advances in understanding binary progenitors, the explosion physics, and the ever more accurate application to cosmology. Spectropolarimetry has also revealed the strongly asymmetric nature of core collapse and given valuable perspectives on the supernova - gamma-ray burst connection. The capability of the magneto-rotational instability to rapidly create strong toroidal magnetic fields in the core collapse ambiance is outlined. This physics may be the precursor to driving MHD jets that play a role in asymmetric supernovae. Welcome to the brave new world of three-dimensional explosions!
Energy Technology Data Exchange (ETDEWEB)
Azreg-Ainou, Mustapha [Baskent University, Department of Mathematics, Ankara (Turkey)
2014-05-15
We derive a shortcut stationary metric formula for generating imperfect fluid rotating solutions, in Boyer-Lindquist coordinates, from spherically symmetric static ones. We explore the properties of the curvature scalar and stress-energy tensor for all types of rotating regular solutions we can generate without restricting ourselves to specific examples of regular solutions (regular black holes or wormholes). We show through examples how it is generally possible to generate an imperfect fluid regular rotating solution via radial coordinate transformations. We derive rotating wormholes that are modeled as imperfect fluids and discuss their physical properties. These are independent on the way the stress-energy tensor is interpreted. A solution modeling an imperfect fluid rotating loop black hole is briefly discussed. We then specialize to the recently discussed stable exotic dust Ellis wormhole as emerged in a source-free radial electric or magnetic field, and we generate its, conjecturally stable, rotating counterpart. This turns out to be an exotic imperfect fluid wormhole, and we determine the stress-energy tensor of both the imperfect fluid and the electric or magnetic field. (orig.)
International Nuclear Information System (INIS)
Azreg-Ainou, Mustapha
2014-01-01
We derive a shortcut stationary metric formula for generating imperfect fluid rotating solutions, in Boyer-Lindquist coordinates, from spherically symmetric static ones. We explore the properties of the curvature scalar and stress-energy tensor for all types of rotating regular solutions we can generate without restricting ourselves to specific examples of regular solutions (regular black holes or wormholes). We show through examples how it is generally possible to generate an imperfect fluid regular rotating solution via radial coordinate transformations. We derive rotating wormholes that are modeled as imperfect fluids and discuss their physical properties. These are independent on the way the stress-energy tensor is interpreted. A solution modeling an imperfect fluid rotating loop black hole is briefly discussed. We then specialize to the recently discussed stable exotic dust Ellis wormhole as emerged in a source-free radial electric or magnetic field, and we generate its, conjecturally stable, rotating counterpart. This turns out to be an exotic imperfect fluid wormhole, and we determine the stress-energy tensor of both the imperfect fluid and the electric or magnetic field. (orig.)
International Nuclear Information System (INIS)
Alizadeh Pahlavani, M.R.; Shoulaie, A.
2010-01-01
In this paper, formulas are proposed for the self and mutual inductance calculations of the helical toroidal coil (HTC) by the direct and indirect methods at superconductivity conditions. The direct method is based on the Neumann's equation and the indirect approach is based on the toroidal and the poloidal components of the magnetic flux density. Numerical calculations show that the direct method is more accurate than the indirect approach at the expense of its longer computational time. Implementation of some engineering assumptions in the indirect method is shown to reduce the computational time without loss of accuracy. Comparison between the experimental measurements and simulated results for inductance, using the direct and the indirect methods indicates that the proposed formulas have high reliability. It is also shown that the self inductance and the mutual inductance could be calculated in the same way, provided that the radius of curvature is >0.4 of the minor radius, and that the definition of the geometric mean radius in the superconductivity conditions is used. Plotting contours for the magnetic flux density and the inductance show that the inductance formulas of helical toroidal coil could be used as the basis for coil optimal design. Optimization target functions such as maximization of the ratio of stored magnetic energy with respect to the volume of the toroid or the conductor's mass, the elimination or the balance of stress in some coordinate directions, and the attenuation of leakage flux could be considered. The finite element (FE) approach is employed to present an algorithm to study the three-dimensional leakage flux distribution pattern of the coil and to draw the magnetic flux density lines of the HTC. The presented algorithm, due to its simplicity in analysis and ease of implementation of the non-symmetrical and three-dimensional objects, is advantageous to the commercial software such as ANSYS, MAXWELL, and FLUX. Finally, using the
DARK MATTER, MAGNETIC FIELDS, AND THE ROTATION CURVE OF THE MILKY WAY
International Nuclear Information System (INIS)
Ruiz-Granados, B.; Battaner, E.; Florido, E.; Calvo, J.; Rubiño-Martín, J. A.
2012-01-01
The study of the disk rotation curve of our Galaxy at large distances provides an interesting scenario for us to test whether magnetic fields should be considered as a non-negligible dynamical ingredient. By assuming a bulge, an exponential disk for the stellar and gaseous distributions, and a dark halo and disk magnetic fields, we fit the rotation velocity of the Milky Way. In general, when the magnetic contribution is added to the dynamics, a better description of the rotation curve is obtained. Our main conclusion is that magnetic fields should be taken into account for the Milky Way dynamics. Azimuthal magnetic field strengths of B φ ∼ 2 μG at distances of ∼2 R 0 (16 kpc) are able to explain the rise-up for the rotation curve in the outer disk.
Sustained turbulence and magnetic energy in non-rotating shear flows
DEFF Research Database (Denmark)
Nauman, Farrukh; Blackman, Eric G.
2017-01-01
From numerical simulations, we show that non-rotating magnetohydrodynamic shear flows are unstable to finite amplitude velocity perturbations and become turbulent, leading to the growth and sustenance of magnetic energy, including large scale fields. This supports the concept that sustained...... magnetic energy from turbulence is independent of the driving mechanism for large enough magnetic Reynolds numbers....
Schröder, Femke F; Huis In't Veld, Rianne; den Otter, Lydia A; van Raak, Sjoerd M; Ten Haken, Bennie; Vochteloo, Anne J H
2018-04-01
The rate of retear after rotator cuff surgery is 17%. Magnetic resonance imaging (MRI) scans are used for confirmative diagnosis of retear. However, because of the presence of titanium suture anchors, metal artefacts on the MRI are common. The present study evaluated the diagnostic value of MRI after rotator cuff tendon surgery with respect to assessing the integrity as well as the degeneration and atrophy of the rotator cuff tendons when titanium anchors are in place. Twenty patients who underwent revision surgery of the rotator cuff as a result of a clinically suspected retear between 2013 and 2015 were included. The MRI scans of these patients were retrospectively analyzed by four specialized shoulder surgeons and compared with intra-operative findings (gold standard). Sensitivity and interobserver agreement among the surgeons in assessing retears as well as the Goutallier and Warner classification were examined. In 36% (range 15% to 50%) of the pre-operative MRI scans, the observers could not review the rotator cuff tendons. When the rotator cuff tendons were assessable, a diagnostic accuracy with a mean sensitivity of 0.84 (0.70 to 1.0) across the surgeons was found, with poor interobserver agreement (kappa = 0.12). Metal artefacts prevented accurate diagnosis from MRI scans of rotator cuff retear in 36% of the patients studied.
High-n helicity-induced shear Alfven eigenmodes
International Nuclear Information System (INIS)
Nakajima, N.; Cheng, C.Z.; Okamoto, M.
1992-05-01
The high-n Helicity-induced shear Alfven Eigenmodes (HAE) are considered both analytically and numerically for the straight helical magnetic system, where n is the toroidal mode number. The eigenmode equation for the high-n HAE modes is derived along the field line and with the aid of the averaging method is shown to reduce to the Mathieu equation asymptotically. The discrete HAE modes are shown to exist inside the continuum spectrum gaps. The continuous spectrum gaps appear around ω 2 = ω A 2 [N(lι-m)/2] 2 for N = 1,2,.., where ω A is the toroidal Alfven transit frequency, and l, m, and ι are the polarity of helical coils, the toroidal pitch number of helical coils, and the rotational transform, respectively. For the same ω A and ι, the frequency of the helical continuum gap is larger than that of the continuum gap in tokamak plasmas by |l-ι -1 m|. The polarity of helical coils l plays a crucial role in determining the spectrum gaps and the properties of the high-n HAE modes. The spectrum gaps near the magnetic axis are created by the helical ripple with circular flux surfaces for l = 1, and ≥ 3 helicals. For l = 2 helical systems, the spectrum gaps are created by the ellipticity of the flux surfaces. These analytical results for the continuum gaps and the existence of the high-n HAE modes in the continuum gaps are confirmed numerically for the l = 2 case, and we find that the HAE modes exist for mode structures with the even and the odd parities. (author)
International Nuclear Information System (INIS)
Misra, K.D.; Mishra, P.K.
2002-01-01
A self-consistent theory of a free-electron laser is developed by the kinetic approach, using the method of characteristics in helical wiggler and guide magnetic fields. The detailed relativistic particle trajectories obtained in wiggler and guide magnetic fields are used in linearized Vlasov-Maxwell equations having variations in perpendicular and parallel momenta to obtain the perturbed distribution function in terms of perturbed electric and magnetic fields deviating from the vector potential approach. The perturbed distribution function thus obtained, having variations in perpendicular and parallel momenta for an arbitrary distribution function, is used to obtain current, conductivity and dielectric tensors. The full dispersion relation (FDR) and Compton dispersion relation (CDR) have been obtained. The dispersion diagram has been obtained and the interaction of the negative longitudinal space charge with the electromagnetic wave has been shown. The temporal growth rates obtained from the full dispersion relation and Compton dispersion relation for the tenuous cold relativistic beam in microwave region have been discussed
International Nuclear Information System (INIS)
Ida, K.; Nagaoka, K.; Kasahara, H.; Yoshinuma, M.; Ohdachi, S.; Osakabe, M.; Kobayashi, M.; Sudo, S.; Yamada, H.; Takeiri, Y.; Mutoh, T.; Imagawa, S.; Mito, T.; Nagayama, Y.; Watanabe, K.Y.; Kaneko, O.; Komori, A.; Inagaki, S.; Evans, T.; Kamiya, Kensaku
2014-10-01
The progress of physics understanding and concurrent parameter extension since the last IAEA-FEC 2012 in the Large Helical Device is overviewed. High ion and electron temperature plasma (T i (0) ∼ T e (0) ∼ 6 keV) with simultaneous ion and electron internal transport barrier (ITB) is obtained by controlling recycling and heating deposition. Associated with the formation of a transport barrier, a sign flip of the non-diffusive term of impurity/momentum transport (residual stress and convection flow) is observed. The impact of the topology of 3-D magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum and particle/impurity transport and MHD stability is also discussed. In the steady state operation, a 48 min discharge with a line-averaged electron density of 1x10 19 m -3 and with high electron and ion temperatures (T i (0) ∼ T e (0) ∼ 2 keV) resulting in 3.36 GJ of input energy is achieved. (author)
Observation of plasma rotation driven by static nonaxisymmetric magnetic fields in a tokamak.
Garofalo, A M; Burrell, K H; DeBoo, J C; deGrassie, J S; Jackson, G L; Lanctot, M; Reimerdes, H; Schaffer, M J; Solomon, W M; Strait, E J
2008-11-07
We present the first evidence for the existence of a neoclassical toroidal rotation driven in a direction counter to the plasma current by nonaxisymmetric, nonresonant magnetic fields. At high beta and with large injected neutral beam momentum, the nonresonant field torque slows down the plasma toward the neoclassical "offset" rotation rate. With small injected neutral beam momentum, the toroidal rotation is accelerated toward the offset rotation, with resulting improvement in the global energy confinement time. The observed magnitude, direction, and radial profile of the offset rotation are consistent with neoclassical theory predictions.
Field of a helical Siberian Snake
Energy Technology Data Exchange (ETDEWEB)
Luccio, A. [Brookhaven National Lab., Upton, NY (United States)
1995-02-01
To preserve the spin polarization of a beam of high energy protons in a circular accelerator, magnets with periodic magnetic field, called Siberian Snakes are being used. Recently, it was proposed to build Siberian Snakes with superconducting helical dipoles. In a helical, or twisted dipole, the magnetic field is perpendicular to the axis of the helix and rotates around it as one proceeds along the magnet. In an engineering study of a 4 Tesla helical snake, the coil geometry is derived, by twisting, from the geometry of a cosine superconducting dipole. While waiting for magnetic measurement data on such a prototype, an analytical expression for the field of the helice is important, to calculate the particle trajectories and the spin precession in the helix. This model will also allow to determine the optical characteristics of the snake, as an insertion in the lattice of the accelerator. In particular, one can calculate the integrated multipoles through the magnet and the equivalent transfer matrix. An expression for the field in the helix body, i.e., excluding the fringe field was given in a classical paper. An alternate expression can be found by elaborating on the treatment of the field of a transverse wiggler obtained under the rather general conditions that the variables are separable. This expression exactly satisfies Maxwell`s div and curl equations for a stationary field, {del} {center_dot} B = 0, {del} x B = 0. This approach is useful in that it will allow one to use much of the work already done on the problem of inserting wigglers and undulators in the lattice of a circular accelerator.
Magnetic pseudo-fields in a rotating electron-nuclear spin system
Wood, A. A.; Lilette, E.; Fein, Y. Y.; Perunicic, V. S.; Hollenberg, L. C. L.; Scholten, R. E.; Martin, A. M.
2017-11-01
Analogous to the precession of a Foucault pendulum observed on the rotating Earth, a precessing spin observed in a rotating frame of reference appears frequency-shifted. This can be understood as arising from a magnetic pseudo-field in the rotating frame that nevertheless has physically significant consequences, such as the Barnett effect. To detect these pseudo-fields, a rotating-frame sensor is required. Here we use quantum sensors, nitrogen-vacancy (NV) centres, in a rapidly rotating diamond to detect pseudo-fields in the rotating frame. Whereas conventional magnetic fields induce precession at a rate proportional to the gyromagnetic ratio, rotation shifts the precession of all spins equally, and thus primarily affect 13C nuclear spins in the sample. We are thus able to explore these effects via quantum sensing in a rapidly rotating frame, and define a new approach to quantum control using rotationally induced nuclear spin-selective magnetic fields. This work provides an integral step towards realizing precision rotation sensing and quantum spin gyroscopes.
Rotational Evolution and Magnetic Field of AP Stars
Xiaojun, C.; Matsuura, O. T.
1990-11-01
RESUMO. Prop6e- se qLie 0 campo de estrelas Ap pode ser 9cr ado pelo mecanismo de na base clo envelope c 0 fl V C C t V 0, C t r a ri S p 0 r t a d C) p a r a a S LI p e r f C 1 e p e I a Instabllidade de boiament 0 na ase de Haya hi. Campos cibservados permit em est imar uma perda de momento durante a ase pr -Seque%nC:ia P r ri C: p a I a ci ni p a t V C I C: C) m a s C) b s e r V a nT C 5. E S t r C I a S A normals, que ro t a ao , ria0 most ram camp Os :os superficia; importantes e isto pode ac:oriteaer C LIma protoestrela evolue para Sequencia Principal em passar pela fase de Hayashi. ABSTRACT: It 5 proposed that the ma9netic field o Ap stars may be enerated by the dynamo at the base of the convective envelope, arid transported to the surface b y t h C i ri s t a b iii t y C) f b LI 0 y a n c y i n t h C H a y a s hi p h a s e. Observed surface ma9netic fields allow to estimate a 1055 of an9ular momentum during the pre-Main Sequence phase compatible with the observations. apidIy rotating normal A stars do not shciw important surface magnetic fields and this may occur if a protostar evcilves to Main Sequence skipping the Hayashi phase. Key words: HYDROMAGNETICS - STARS-PECULIAR A
Specific features of the motion of neutrons in a medium with a helical magnetic structure
International Nuclear Information System (INIS)
Fraerman, A. A.; Udalov, O. G.
2007-01-01
The specific features of the motion of neutrons in a noncoplanar magnetic field are considered by an example of the magnetization distribution in the form of a conical helix. The reflection coefficients of neutrons from holmium crystals are calculated. It is shown that, for a noncoplanar distribution of a magnetic field in a crystal, the reflection coefficient of neutrons with spin flip exhibits an additional feature
International Nuclear Information System (INIS)
Iguchi, H.; Ida, K.; Yamada, H.
1994-01-01
Radial particle transport has been experimentally studied in the low-aspect-ratio heliotron/torsatron device CHS. A non-diffusive outward particle flow (inverse pinch) is observed in the magnetic configuration with the magnetic axis shifted outward, while an inward pinch, like in tokamaks, is observed with the magnetic axis shifted inward. This change in the direction of anomalous particle flow is not due to the reversal of temperature gradient nor the radial electric field. The observation suggests that the particle pinch velocity is sensitive to the magnetic field structure. (author)
The anisotropic magnetic property and Faraday rotation in Er3Ga5O12 under high magnetic field
International Nuclear Information System (INIS)
Wang Wei; Zhang Xijuan; Liu Gongqiang
2005-01-01
A theoretical investigation on the anisotropic magnetic property and Faraday rotation in Er 3 Ga 5 O 12 (ErGaG) is presented. With particular consideration of the anisotropy of the exchange interaction between rare-earth ions (Er 3+ ), the magnetization, based on the quantum theory, in ErGaG under high magnetic field (HMF) is calculated. Theoretical calculations show that the appropriate choice of the crystal field (CF) parameters is of great importance. A novel three-level model is presented, and in terms of this model the Faraday rotation under HMF is calculated. In addition, it is demonstrated that the Faraday rotation (θ) depends not only on the magnetization (M) but also on the magnetic field (H e ). The theory is in good agreement with the experiment
International Nuclear Information System (INIS)
Schaffer, M.J.
1997-08-01
A stabilized pinch configuration is described, consisting of a D-shaped plasma cross section wrapped tightly around a guiding axis. The open-quotes helical-Dclose quotes geometry produces a very large axial (toroidal) transform of magnetic line direction that reverses the pitch of the magnetic lines without the need of azimuthal (poloidal) plasma current. Thus, there is no need of a open-quotes dynamoclose quotes process and its associated fluctuations. The resulting configuration has the high magnetic shear and pitch reversal of the reversed field pinch (RFP). (Pitch = P = qR, where R = major radius). A helical-D pinch might demonstrate good confinement at q << 1
Suwa, Masayori; Nakano, Yusuke; Tsukahara, Satoshi; Watarai, Hitoshi
2013-05-21
We have constructed an experimental setup for Faraday rotation dispersion imaging and demonstrated the performance of a novel imaging principle. By using a pulsed magnetic field and a polarized light synchronized to the magnetic field, quantitative Faraday rotation images of diamagnetic organic liquids in glass capillaries were observed. Nonaromatic hydrocarbons, benzene derivatives, and naphthalene derivatives were clearly distinguished by the Faraday rotation images due to the difference in Verdet constants. From the wavelength dispersion of the Faraday rotation images in the visible region, it was found that the resonance wavelength in the UV region, which was estimated based on the Faraday B-term, could be used as characteristic parameters for the imaging of the liquids. Furthermore, simultaneous acquisition of Faraday rotation image and natural optical rotation image was demonstrated for chiral organic liquids.
Some consequences of shear on galactic dynamos with helicity fluxes
Zhou, Hongzhe; Blackman, Eric G.
2017-08-01
Galactic dynamo models sustained by supernova (SN) driven turbulence and differential rotation have revealed that the sustenance of large-scale fields requires a flux of small-scale magnetic helicity to be viable. Here we generalize a minimalist analytic version of such galactic dynamos to explore some heretofore unincluded contributions from shear on the total turbulent energy and turbulent correlation time, with the helicity fluxes maintained by either winds, diffusion or magnetic buoyancy. We construct an analytic framework for modelling the turbulent energy and correlation time as a function of SN rate and shear. We compare our prescription with previous approaches that include only rotation. The solutions depend separately on the rotation period and the eddy turnover time and not just on their ratio (the Rossby number). We consider models in which these two time-scales are allowed to be independent and also a case in which they are mutually dependent on radius when a radial-dependent SN rate model is invoked. For the case of a fixed rotation period (or a fixed radius), we show that the influence of shear is dramatic for low Rossby numbers, reducing the correlation time of the turbulence, which, in turn, strongly reduces the saturation value of the dynamo compared to the case when the shear is ignored. We also show that even in the absence of winds or diffusive fluxes, magnetic buoyancy may be able to sustain sufficient helicity fluxes to avoid quenching.
Kinetic theory of instabilities responsible for magnetic turbulence in laboratory rotating plasma
International Nuclear Information System (INIS)
Mikhailovskii, A.B.; Lominadze, J.G.; Churikov, A.P.; Pustovitov, V.D.; Erokhin, N.N.; Konovalov, S.V.
2008-01-01
The problem of instabilities responsible for magnetic turbulence in collisionless laboratory rotating plasma is investigated. It is shown that the standard mechanism of driving the magnetorotational instability (MRI), due to negative rotation frequency gradient, disappears in such a plasma. Instead of it, a new driving mechanism due to plasma pressure gradient is predicted
International Nuclear Information System (INIS)
Sosenko, P.; Pierre, Th.; Zagorodny, A.
2004-01-01
The linear and non-linear properties of global low-frequency oscillations in cylindrical weakly ionized magnetized plasmas are investigated analytically for the conditions of equilibrium plasma rotation. The theoretical results are compared with the experimental observations of rotating plasmas in laboratory devices, such as Mistral and Mirabelle in France, and KIWI in Germany. (authors)
Energy Technology Data Exchange (ETDEWEB)
Klein, Kristopher G.; Howes, Gregory G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); TenBarge, Jason M. [IREAP, University of Maryland, College Park, MD 20742 (United States); Podesta, John J., E-mail: kristopher-klein@uiowa.edu [Center for Space Plasma Physics, Space Science Institute, Boulder, CO 80301 (United States)
2014-04-20
Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.
International Nuclear Information System (INIS)
Klein, Kristopher G.; Howes, Gregory G.; TenBarge, Jason M.; Podesta, John J.
2014-01-01
Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.
Directory of Open Access Journals (Sweden)
D. J. Scott
2007-03-01
Full Text Available A comparison of possible undulator designs for the International Linear Collider positron source has resulted in a superconducting bifilar wire design being selected. After a comprehensive paper study and fabrication of the two preeminent designs, the superconducting undulator was chosen instead of the permanent magnet alternative. This was because of its superior performance in terms of magnetic field strength and quality, operational flexibility, risk of radiation damage, ease in achieving the required vacuum, and cost. The superconducting undulator design will now be developed into a complete system design for the full 200 m long magnet that is required.
Mamatsashvili, G.; Stefani, F.; Guseva, A.; Avila, M.
2018-01-01
Magnetorotational instability (MRI) is one of the fundamental processes in astrophysics, driving angular momentum transport and mass accretion in a wide variety of cosmic objects. Despite much theoretical/numerical and experimental efforts over the last decades, its saturation mechanism and amplitude, which sets the angular momentum transport rate, remains not well understood, especially in the limit of high resistivity, or small magnetic Prandtl numbers typical to interiors (dead zones) of protoplanetary disks, liquid cores of planets and liquid metals in laboratory. Using direct numerical simulations, in this paper we investigate the nonlinear development and saturation properties of the helical magnetorotational instability (HMRI)—a relative of the standard MRI—in a magnetized Taylor-Couette flow at very low magnetic Prandtl number (correspondingly at low magnetic Reynolds number) relevant to liquid metals. For simplicity, the ratio of azimuthal field to axial field is kept fixed. From the linear theory of HMRI, it is known that the Elsasser number, or interaction parameter determines its growth rate and plays a special role in the dynamics. We show that this parameter is also important in the nonlinear problem. By increasing its value, a sudden transition from weakly nonlinear, where the system is slightly above the linear stability threshold, to strongly nonlinear, or turbulent regime occurs. We calculate the azimuthal and axial energy spectra corresponding to these two regimes and show that they differ qualitatively. Remarkably, the nonlinear state remains in all cases nearly axisymmetric suggesting that this HMRI-driven turbulence is quasi two-dimensional in nature. Although the contribution of non-axisymmetric modes increases moderately with the Elsasser number, their total energy remains much smaller than that of the axisymmetric ones.
ROTATION RATE DIFFERENCES OF POSITIVE AND NEGATIVE SOLAR MAGNETIC FIELDS BETWEEN ±60° LATITUDES
Energy Technology Data Exchange (ETDEWEB)
Shi, X. J.; Xie, J. L., E-mail: shixiangjun@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China)
2015-04-15
Based on a cross-correlation analysis of the Carrington synoptic maps of solar photospheric magnetic fields from Carrington Rotations Nos. 1625 to 2135 (from 1975 February to 2013 March), the sidereal rotation rates of the positive and negative magnetic fields in the latitude range of ±60° are obtained, and the rotation rate differences between them are investigated. The time–latitude distribution of the rate differences is shown, which looks like a butterfly diagram at the low and middle latitudes. For comparison, the time–latitude distribution of the longitudinally averaged photospheric magnetic fields is shown. We conclude that the magnetic fields having the same polarity as the leading sunspots at a given hemisphere rotate faster than those exhibiting the opposite polarity at low and middle latitudes. However, at higher latitudes, the magnetic fields having the same polarity as the leading sunspots at a given hemisphere do not always rotate faster than those with the opposite polarity. Furthermore, the relationship between the rotation rate differences and solar magnetic fields is studied through a correlation analysis. Our result shows that the correlation coefficients between them reach maximum values at 13° (14°) latitude in the northern (southern) hemisphere, and change sign at 28° latitude in both hemispheres, then reach their minimum values at 58° (53°) latitude in the northern (southern) hemisphere.
International Nuclear Information System (INIS)
Gisin, B V
2002-01-01
We consider the anomalous magnetic moment from an 'optical viewpoint' using an analogy between the motion of a particle with a magnetic moment in a magnetic field and the propagation of an optical pulse through an electro-optical crystal in an electric field. We show that an optical experiment similar to electron magnetic resonance is possible in some electro-optical crystals possessing the Faraday effect. This phenomenon is described by an analogue of the Pauli equation extracted from the Maxwell equation in the slowly varied amplitude approximation. In such an experiment the modulation by rotating fields plays a significant role. From the optical viewpoint the modulation assumes introducing the concept of a point rotation frame with the rotation axis at every point originated from the concept of the optical indicatrix (index ellipsoid). We discuss the connection between the non-classical transformation by transition from one such frame to another and an anomalous magnetic moment
Design and Test Results of Superconducting Magnet for Heavy-Ion Rotating Gantry
Takayama, S.; Koyanagi, K.; Miyazaki, H.; Takami, S.; Orikasa, T.; Ishii, Y.; Kurusu, T.; Iwata, Y.; Noda, K.; Obana, T.; Suzuki, K.; Ogitsu, T.; Amemiya, N.
2017-07-01
Heavy-ion radiotherapy has a high curative effect in cancer treatment and also can reduce the burden on patients. These advantages have been generally recognized. Furthermore, a rotating gantry can irradiate a tumor with ions from any direction without changing the position of the patient. This can reduce the physical dose on normal cells, and is thus commonly used in proton radiotherapy. However, because of the high magnetic rigidity of carbon ions, the weight of the rotating gantry for heavy-ion therapy is about three-times heavier than those used for proton cancer therapy, according to our estimation. To overcome this issue, we developed a small and lightweight rotating gantry in collaboration with the National Institute of Radiological Sciences (NIRS). The compact rotating gantry was composed of ten low-temperature superconducting (LTS) magnets that were designed from the viewpoint of beam optics. These LTS magnets have a surface-winding coil-structure and provide both dipole and quadrupole fields. The maximum dipole and quadrupole magnetic field of the magnets were 2.88 T and 9.3 T/m, respectively. The rotating gantry was installed at NIRS, and beam commissioning is in progress to achieve the required beam quality. In the three years since 2013, in a project supported by the Ministry of Economy, Trade and Industry (METI) and the Japan Agency for Medical Research and Development (AMED), we have been developing high-temperature superconducting (HTS) magnets with the aim of a further size reduction of the rotating gantry. To develop fundamental technologies for designing and fabricating HTS magnets, a model magnet was manufactured. The model magnet was composed of 24 saddle-shaped HTS coils and generated a magnetic field of 1.2 T. In the presentation, recent progress in this research will be reported.
Features of the mass transfer in magnetic cataclysmic variables with fast-rotating white dwarfs
Directory of Open Access Journals (Sweden)
Isakova Polina
2014-01-01
Full Text Available The flow structure in magnetic cataclysmic variables was investigated taking into account the effects of strong magnetic field and fast rotation of the white dwarf. We modeled the AE Aqr system as a unique object that has the rotation period of the white dwarf is about 1000 times shorter than the orbital period of the binary system. Observations show that in spite of fast rotation of the white dwarf some part of the stream from the inner Lagrange point comes into the Roche lobe region. We analyzed possible mechanisms preventing material to outflow from the system.
International Nuclear Information System (INIS)
Song, M.C.; Lee, K.J.
2004-01-01
Most of the insoluble radioactive corrosion products have the characteristic of showing strong ferrimagnetism. Along with the new development and production of permanent magnets which generate much stronger magnetic field than conventional permanent magnets, new type of magnetic filter that can separate radioactive corrosion products efficiently and eventually reduce the radiation exposure of the personnel at a nuclear power plant is suggested. This new type of separator with novel geometry consists of an inner and an outer magnet assembly, a coolant channel and a container surrounding the outer magnet assembly. The particulates are separated from the coolant by the alternating magnetic fields that are generated by shift arrangement of permanent magnets. This study describes of experimental results performed with the different flow rates, rotation velocities of magnet assemblies, particle size and various materials. The efficiency of magnetic filter tends to increase as the flow rate is lower, and particle size is bigger. The rotating velocity of magnet assembly has also some influences on the separation efficiency. This new magnetic filter shows good performance results in filtering magnetite, cobalt ferrite and nickel ferrite except hematite, which is a kind of anti-ferromagnetic material, from aqueous coolant simulation. At the above 5 μm of particle size, the separation efficiencies are over than 90%. (author)
Influence of end-joint methods on magnetization loss in striated helical conductors
International Nuclear Information System (INIS)
Kim, Woo Seok; Kim, Yung Il; Choi, Kyeong Dal; Lee, Ji Kwang
2013-01-01
To reduce the magnetization loss of a coated conductor, the striation and the transposition have to be accomplished for magnetic decoupling. The loss reduction effect in incomplete as well as complete striated YBCO CCs was reported in previous research. At the case of the incomplete striated sample, the end region of the sample is non-striated. So, it is not jointed with each other. In power applications, the joint is needed because current leads must be connected with HTS coils. In this research, the influence of end-joint methods with copper and superconducting joint on magnetization loss in striated YBCO CC and spiral winding samples are presented and compared with non-striated measured result.
Applications of 2D helical vortex dynamics
DEFF Research Database (Denmark)
Okulov, Valery; Sørensen, Jens Nørkær
2010-01-01
In the paper, we show how the assumption of helical symmetry in the context of 2D helical vortices can be exploited to analyse and to model various cases of rotating flows. From theory, examples of three basic applications of 2D dynamics of helical vortices embedded in flows with helical symmetry...... of the vorticity field are addressed. These included some of the problems related to vortex breakdown, instability of far wakes behind rotors and vortex theory of ideal rotors....
A rotation/magnetism analogy for the quark–gluon plasma
Directory of Open Access Journals (Sweden)
Brett McInnes
2016-10-01
Full Text Available In peripheral heavy ion collisions, the Quark–Gluon Plasma that may be formed often has a large angular momentum per unit energy. This angular momentum may take the form of (local rotation. In many physical systems, rotation can have effects analogous to those produced by a magnetic field; thus, there is a risk that the effects of local rotation in the QGP might be mistaken for those of the large genuine magnetic fields which are also known to arise in these systems. Here we use the gauge-gravity duality to investigate this, and we find indeed that, with realistic parameter values, local rotation has effects on the QGP (at high values of the baryonic chemical potential which are not only of the same kind as those produced by magnetic fields, but which can in fact be substantially larger. Furthermore, the combined effect of rotation and magnetism is to change the shape of the main quark matter phase transition line in an interesting way, reducing the magnitude of its curvature; again, local rotation contributes to this phenomenon at least as strongly as magnetism.
A rotation/magnetism analogy for the quark–gluon plasma
Energy Technology Data Exchange (ETDEWEB)
McInnes, Brett, E-mail: matmcinn@nus.edu.sg
2016-10-15
In peripheral heavy ion collisions, the Quark–Gluon Plasma that may be formed often has a large angular momentum per unit energy. This angular momentum may take the form of (local) rotation. In many physical systems, rotation can have effects analogous to those produced by a magnetic field; thus, there is a risk that the effects of local rotation in the QGP might be mistaken for those of the large genuine magnetic fields which are also known to arise in these systems. Here we use the gauge-gravity duality to investigate this, and we find indeed that, with realistic parameter values, local rotation has effects on the QGP (at high values of the baryonic chemical potential) which are not only of the same kind as those produced by magnetic fields, but which can in fact be substantially larger. Furthermore, the combined effect of rotation and magnetism is to change the shape of the main quark matter phase transition line in an interesting way, reducing the magnitude of its curvature; again, local rotation contributes to this phenomenon at least as strongly as magnetism.
Effect of magnetic field on the Rayleigh Taylor instability of rotating and stratified plasma
International Nuclear Information System (INIS)
Sharma, PK; Tiwari, Anita; Argal, Shraddha
2017-01-01
In the present study the effect of magnetic field and rotation have been carried out on the Rayleigh Taylor instability of conducting and rotating plasma, which is assumed to be incompressible and confined between two rigid planes z = 0 and z = h. The dispersion relation of the problem is obtained by solving the basic MHD equations of the problem with the help normal mode technique and appropriate boundary conditions. The dispersion relation of the medium is analysed and the effect of magnetic field and angular velocity (rotation effect) have been examined on the growth rate of Rayleigh Taylor instability. It is found that the magnetic field and angular velocity (rotation effect) have stabilizing influence on the Rayleigh Taylor instability. (paper)
Effect of rotation on Jeans instability of magnetized radiative quantum plasma
Joshi, H.; Pensia, R. K.
2017-03-01
The influence of rotation on the Jeans instability of homogeneous magnetized radiative quantum plasma is investigated. The basic equations of the problem are constructed and linearized by using the Quantum Magnetohydrodynamics (QMHD) model. The general dispersion relation is obtained by using the normal mode analysis technique, which is reduced for both the transverse and the longitudinal mode of propagations and further it is reduced for the axis of rotation parallel and perpendicular to the magnetic field. We found that the stabilizing effects of rotation are decreases for a strong magnetic field which is shown in the graphical representation. We also found that the quantum correction modified the condition of Jeans instability in both modes of propagation. The stabilizing effect of rotation is more increased in the presence of quantum correction.
International Nuclear Information System (INIS)
Hase, T.P.A.; Fulthorpe, B.D.; Wilkins, S.B.; Tanner, B.K.; Marrows, C.H.; Hickey, B.J.
2001-01-01
We report the observation of magnetic viscosity in the intensity of resonant magnetic soft X-ray scattering during rotational magnetisation processes in antiferromagnetically coupled Co/Cu multilayers. The hysteretic time-dependent component of the signal can be fitted to a single-exponential function that varies as a function of magnetising field
Faraday rotation and magneto-optical figure of merit for the magnetite magnetic fluids
Directory of Open Access Journals (Sweden)
Kalandadze L.
2011-05-01
Full Text Available In the present paper, using magnetite magnetic fluids as examples, we consider the optical and magneto-optical properties of magnetic fluids based on particles of magnetic oxides, for the optical constants of the material of which, n and k , the relation k2 ≺≺ n2 holds. In this work the Faraday rotation is represented within the theoretical Maxwell-Garnett model. A theoretical analysis has shown that Faraday rotation for magnetic fluids is related to the Faraday rotation on the material of particles by the simple relation. According to this result in specific experimental conditions the values of the Faraday rotation prorate to q , which is the occupancy of the volume of the magnetic fluid with magnetic particles and spectral dependences of effect in magnetic fluid and in the proper bulk magnetic are similar. We also show that the values of the magneto-optical figure of merit for ultrafine medium and for the bulk material are equal.
Synthesis and magnetic properties of a 1-D helical chain derived ...
Indian Academy of Sciences (India)
mounted on the tip of a glass pin using mineral oil and placed in the cold .... applied magnetic field of 0.5 Tesla, between 2–300 K. (figure 4). .... edges CSIR for financial support. ... Seo J S, Whang D, Lee H, Jun S I, Oh J, Jeon Y J and. Kim K ...
Formation of helical electron beams by electrostatic pumping
International Nuclear Information System (INIS)
Barroso, J.J.; Spassovsky, L.P.; Stellati, C.
1993-01-01
A non-adiabatic gun for a 35 GHz, 100 kw gyrotron is presented. A 50 kV, 10 A laminar helical electron beam has been achieved with a perpendicular to parallel velocity ratio of 1.9. A non-adiabatic change of the pumping electric field is used to impart rotational velocity to the beam particles which are extracted at the cathode surface in a direction parallel to the guiding magnetic field. (author)
Alternating-current ohmic heating in a helical stellarator
International Nuclear Information System (INIS)
Funato, Yasuyuki; Kitajima, Sumio; Watanabe, Hiroshige
1984-01-01
A toroidal plasma is generated successively by an alternating-current discharge in a helical or non-planar torus, and is confined quasi-stationarily by a longitudinal magnetic field with a high rotational transform angle. The particle confinement time obtained experimentally is estimated to be 3-10 ms, which is compared with theoretical values for this system, and is much larger than the time of pulse interval of the plasma production. (author)
International Nuclear Information System (INIS)
Carvalho-Santos, Vagson L.; Dandoloff, Rossen
2012-01-01
We study the nonlinear σ-model in an external magnetic field applied on curved surfaces with rotational symmetry. The Euler–Lagrange equations derived from the Hamiltonian yield the double sine-Gordon equation (DSG) provided the magnetic field is tuned with the curvature of the surface. A 2π skyrmion appears like a solution for this model and surface deformations are predicted at the sector where the spins point in the opposite direction to the magnetic field. We also study some specific examples by applying the model on three rotationally symmetric surfaces: the cylinder, the catenoid and the hyperboloid.
Tools and setups for experiments with AC and rotating magnetic fields
International Nuclear Information System (INIS)
Ponikvar, D
2010-01-01
A rotating magnetic field is the basis for the transformation of electrical energy to mechanical energy. School experiments on the rotating magnetic field are rare since they require the use of specially prepared mechanical setups and/or relatively large, three-phase power supplies to achieve strong magnetic fields. This paper proposes several experiments and describes setups and tools which are easy to obtain and work with. Free software is offered to generate the required signals by a personal computer. The experiments can be implemented in introductory physics courses on electromagnetism for undergraduates or specialized courses at high schools.
Interplay between intrinsic plasma rotation and magnetic island evolution in disruptive discharges
Energy Technology Data Exchange (ETDEWEB)
Ronchi, G.; Severo, J. H. F. [Universidade de São Paulo, Instituto de Física (Brazil); Salzedas, F. [Universidade do Porto, Faculdade de Engenharia (Portugal); Galvão, R. M. O., E-mail: rgalvao@if.usp.br; Sanada, E. K. [Universidade de São Paulo, Instituto de Física (Brazil)
2016-05-15
The behavior of the intrinsic toroidal rotation of the plasma column during the growth and eventual saturation of m/n = 2/1 magnetic islands, triggered by programmed density rise, has been carefully investigated in disruptive discharges in TCABR. The results show that, as the island starts to grow and rotate at a speed larger than that of the plasma column, the angular frequency of the intrinsic toroidal rotation increases and that of the island decreases, following the expectation of synchronization. As the island saturates at a large size, just before a major disruption, the angular speed of the intrinsic rotation decreases quite rapidly, even though the island keeps still rotating at a reduced speed. This decrease of the toroidal rotation is quite reproducible and can be considered as an indicative of disruption.
A brief review of intruder rotational bands and magnetic rotation in the A = 110 mass region
Banerjee, P.
2018-05-01
Nuclei in the A ∼ 110 mass region exhibit interesting structural features. One of these relates to the process by which specific configurations, built on the excitation of one or more protons across the Z = 50 shell-gap, manifest as collective rotational bands at intermediate spins and gradually lose their collectivity with increase in spin and terminate in a non-collective state at the maximum spin which the configuration can support. These bands are called terminating bands that co-exist with spherical states. Some of these bands are said to terminate smoothly underlining the continuous character of the process by which the band evolves from significant collectivity at low spin to a pure particle-hole non-collective state at the highest spin. The neutron-deficient A ∼ 110 mass region provides the best examples of smoothly terminating bands. The present experimental and theoretical status of such bands in several nuclei with 48 ≤ Z ≤ 52 spanning the 106 ≤ A ≤ 119 mass region have been reviewed in this article. The other noteworthy feature of nuclei in the A ∼ 110 mass region is the observation of regular rotation-like sequences of strongly enhanced magnetic dipole transitions in near-spherical nuclei. These bands, unlike the well-studied rotational sequences in deformed nuclei, arise from a spontaneous symmetry breaking by the anisotropic currents of a few high-j excited particles and holes. This mode of excitation is called magnetic rotation and was first reported in the Pb region. Evidence in favor of the existence of such structures, also called shears bands, are reported in the literature for a large number of Cd, In, Sn and Sb isotope with A ∼ 110. The present article provides a general overview of these reported structures across this mass region. The review also discusses antimagnetic rotation bands and a few cases of octupole correlations in the A = 110 mass region.
Study on impurity screening in stochastic magnetic boundary of the Large Helical Device
International Nuclear Information System (INIS)
Kobayashi, M.; Morita, S.; Feng, Y.
2008-10-01
The impurity transport characteristics in the scrape-off layer associated with a stochastic magnetic boundary of LHD are analyzed. The remnant islands with very small internal field line pitch in the stochastic region play a key role in reducing the impurity influx. The thermal force driven impurity influx is significantly suppressed when the perpendicular energy flux exceeds the parallel one inside the islands due to the small pitch. Application of the 3D edge transport code, EMC3-EIRENE, confirmed the impurity retention (screening) effect in the edge region. It is also found that the edge surface layers are the most effective region to retain (screen) impurities because of the flow acceleration and plasma cooling via short flux tubes. The carbon emission obtained in experiments is in good agreement with the modelling results, showing the impurity retention (screening) potential of the stochastic magnetic boundary. (author)
Swimming Characteristics of Bioinspired Helical Microswimmers Based on Soft Lotus-Root Fibers
Directory of Open Access Journals (Sweden)
Jia Liu
2017-11-01
Full Text Available Various kinds of helical swimmers inspired by E. coli bacteria have been developed continually in many types of researches, but most of them are proposed by the rigid bodies. For the targeted drug delivery, the rigid body may hurt soft tissues of the working region with organs. Due to this problem, the biomedical applications of helical swimmers may be restricted. However, the helical microswimmers with the soft and deformable body are appropriate and highly adaptive in a confined environment. Thus, this paper presents a lotus-root-based helical microswimmer, which is fabricated by the fibers of lotus-root coated with magnetic nanoparticles to active under the magnetic fields. The helical microstructures are derived from the intrinsic biological structures of the fibers of the lotus-root. This paper aims to study the swimming characteristic of lotus-root-based microswimmers with deformable helical bodies. In the initial step under the uniform magnetic actuation, the helical microswimmers are bent lightly due to the heterogeneous distribution of the internal stress, and then they undergo a swimming motion which is a spindle-like rotation locomotion. Our experiments report that the microswimmers with soft bodies can locomote faster than those with rigid bodies. Moreover, we also find that the curvature of the shape decreases as a function of actuating field frequency which is related to the deformability of lotus-root fibers.
Domain walls dynamics in the amorphous ribbon with a helical magnetic anisotropy
International Nuclear Information System (INIS)
Zhmetko, D.N.; Savin, V.V.; Lemish, P.V.; Troschenkov, Y.N.
2006-01-01
The damping mechanism for motion of domain walls, which form the sandwich structure and move from the middle plane of the ribbon to opposite surfaces during the dynamic magnetization reversal, have been investigated. The difference between the real and ideal sandwich domain structure, the actual distribution of the anisotropy easy directions through the ribbon thickness and the M-bar s deviation from local easy directions under the action of applied magnetic field have been taken into account. It was revealed that the maximum of the total damping coefficient β tot (x) near the half-way of the domain wall run is due to the influence of the magnetic stray fields. These fields have a character of irregular oscillations and are directed approximately perpendicular to the local easy direction of the ribbon layer through which the domain wall propagates. The damping coefficient β e.c. (x) determined by eddy-currents has the maximal value close to the ribbon middle and decreases linearly to zero when the domain wall approaches the ribbon surface
International Nuclear Information System (INIS)
Kondo, Shintaro; Isayama, Hiroyuki; Akahane, Masaaki; Toda, Nobuo; Sasahira, Naoki; Nakai, Yosuke; Yamamoto, Natsuyo; Hirano, Kenji; Komatsu, Yutaka; Tada, Minoru; Yoshida, Haruhiko; Kawabe, Takao; Ohtomo, Kuni; Omata, Masao
2005-01-01
Objectives: New modalities, namely, endoscopic ultrasonography (EUS), magnetic resonance cholangiopancreatography (MRCP), and helical computed-tomographic cholangiography (HCT-C), have been introduced recently for the detection of common bile duct (CBD) stones and shown improved detectability compared to conventional ultrasound or computed tomography. We conducted this study to compare the diagnostic ability of EUS, MRCP, and HCT-C in patients with suspected choledocholithiasis. Methods: Twenty-eight patients clinically suspected of having CBD stones were enrolled, excluding those with cholangitis or a definite history of choledocholithiasis. Each patient underwent EUS, MRCP, and HCT-C prior to endoscopic retrograde cholangio-pancreatography (ERCP), the result of which served as the diagnostic gold standard. Results: CBD stones were detected in 24 (86%) of 28 patients by ERCP/IDUS. The sensitivity of EUS, MRCP, and HCT-C was 100%, 88%, and 88%, respectively. False negative cases for MRCP and HCT-C had a CBD stone smaller than 5 mm in diameter. No serious complications occurred while one patient complained of itching in the eyelids after the infusion of contrast agent on HCT-C. Conclusions: When examination can be scheduled, MRCP or HCT-C will be the first choice because they were less invasive than EUS. MRCP and HCT-C had similar detectability but the former may be preferable considering the possibility of allergic reaction in the latter. When MRCP is negative, EUS is recommended to check for small CBD stones
International Nuclear Information System (INIS)
Kikuchi, Y; Finken, K H; Jakubowski, M; Lehnen, M; Reiser, D; Sewell, G; Wolf, R C
2006-01-01
The error-field penetration process of the dynamic ergodic divertor (DED) on the TEXTOR tokamak has been investigated analytically in terms of a single fluid MHD model with a finite plasma resistivity and viscosity in a cylindrical geometry. The linear model produces a localization of the induced current at the resonance surface and predicts a vortex structure of the velocity field near the resonance layer. Moreover, effects of the Alfven resonance for the error-field penetration are identified by two peaks in the radial profiles of the perturbed toroidal current and the perturbed magnetic flux when the relative rotation velocity between the DED and the rotating tokamak plasma is set to large. Fine structures of the vorticity induced by the DED in the vicinity of the rational surface disappear by introducing a finite plasma perpendicular viscosity. In addition, it is shown that the two peaks of the perturbed toroidal current overlap by an anomalous plasma perpendicular viscosity. Likewise, a bifurcation of the penetration process from the suppressed to the excited state is obtained by a quasi-linear approach taking into account modifications of the radial profiles of the equilibrium current and the plasma rotation due to the DED. A comparison with real experimental results of the DED on the TEXTOR tokamak is shown
Vogel, Michael W; Giorni, Andrea; Vegh, Viktor; Pellicer-Guridi, Ruben; Reutens, David C
2016-01-01
We studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability. The finite element method (COMSOL®) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field. A concentric small permanent magnet array can be used to generate strong sample pre-polarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20-50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres. A dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably.
Seismometer using a vertical long natural-period rotational pendulum with magnetic levitation
International Nuclear Information System (INIS)
Otake, Yuji; Araya, Akito; Hidano, Kazuo
2005-01-01
We have demonstrated a highly sensitive/wideband vertical-component seismometer using an astatic rotational pendulum to obtain a long natural period. This seismometer employs magnetic levitation for removing any parasitic resonances of a spring to support a weight due to gravity and the thermal dependence of the spring constant. The pendulum has a cylindrical plunger-type permanent magnet that has a weight at one side of its end edge. The plunger magnet is inserted into a uniform magnetic field generated by a window-frame-type permanent magnet, and attached to two crossed-leaf spring hinges as a rotational axis outside of the bore of the magnet. Magnetic forces applied to the plunger magnet counterbalance the gravitational force at the weight. To realize stable operation of the rotational pendulum without any unnecessary movements of the plunger magnet, a tilt of lines of the magnetic force in the bore of the window-frame magnet was compensated by a tilted magnetic-pole surface near to its opening. The field uniformity reached 10 -4 owing to this compensation. The thermal dependence of a magnetic field strength of about 10 -3 /K was also compensated by as much as 9x10 -5 /K by Ni-Fe metal having a negative permeability coefficient. The metal was attached along the sidewalls of the window-frame magnet. To determine the feedback control parameters for a feedback control seismometer, the natural period of a prototype rotational pendulum was measured. It was more than 8 s, and was able to be changed from 5 to 8 s by using an additional magnetic spring, similar to the voice coil actuator of a speaker. This change was in accordance with theoretical calculations, and showed that the pendulum movement did not include a big nonlinearity caused by the tilt of the lines of the magnetic force. No parasitic resonances were found during experiments. A velocity feedback-control circuit and a capacitance position detector to measure the weight position were applied to the
Energy Technology Data Exchange (ETDEWEB)
Yang, Y. M.; Geurts, M.; Smilowitz, J. B.; Bednarz, B. P., E-mail: bbednarz2@wisc.edu [Department of Medical Physics, Wisconsin Institutes for Medical Research, University of Wisconsin, Madison, Wisconsin 53703 (United States); Sterpin, E. [Molecular Imaging, Radiotherapy and Oncology, Université catholique de Louvain, Brussels, Belgium 1348 (Belgium)
2015-02-15
Purpose: Several groups are exploring the integration of magnetic resonance (MR) image guidance with radiotherapy to reduce tumor position uncertainty during photon radiotherapy. The therapeutic gain from reducing tumor position uncertainty using intrafraction MR imaging during radiotherapy could be partially offset if the negative effects of magnetic field-induced dose perturbations are not appreciated or accounted for. The authors hypothesize that a more rotationally symmetric modality such as helical tomotherapy will permit a systematic mediation of these dose perturbations. This investigation offers a unique look at the dose perturbations due to homogeneous transverse magnetic field during the delivery of Tomotherapy{sup ®} Treatment System plans under varying degrees of rotational beamlet symmetry. Methods: The authors accurately reproduced treatment plan beamlet and patient configurations using the Monte Carlo code GEANT4. This code has a thoroughly benchmarked electromagnetic particle transport physics package well-suited for the radiotherapy energy regime. The three approved clinical treatment plans for this study were for a prostate, head and neck, and lung treatment. The dose heterogeneity index metric was used to quantify the effect of the dose perturbations to the target volumes. Results: The authors demonstrate the ability to reproduce the clinical dose–volume histograms (DVH) to within 4% dose agreement at each DVH point for the target volumes and most planning structures, and therefore, are able to confidently examine the effects of transverse magnetic fields on the plans. The authors investigated field strengths of 0.35, 0.7, 1, 1.5, and 3 T. Changes to the dose heterogeneity index of 0.1% were seen in the prostate and head and neck case, reflecting negligible dose perturbations to the target volumes, a change from 5.5% to 20.1% was observed with the lung case. Conclusions: This study demonstrated that the effect of external magnetic fields can
ROTATION AND MAGNETIC ACTIVITY IN A SAMPLE OF M-DWARFS
International Nuclear Information System (INIS)
Browning, Matthew K.; Basri, Gibor; Marcy, Geoffrey W.; Zhang Jiahao; West, Andrew A.
2010-01-01
We have analyzed the rotational broadening and chromospheric activity in a sample of 123 M-dwarfs, using spectra taken at the W.M. Keck Observatory as part of the California Planet Search program. We find that only seven of these stars are rotating more rapidly than our detection threshold of v sin i ∼ 2.5 km s -1 . Rotation appears to be more common in stars later than M3 than in the M0-M2.5 mass range: we estimate that less than 10% of early-M stars are detectably rotating, whereas roughly a third of those later than M4 show signs of rotation. These findings lend support to the view that rotational braking becomes less effective in fully convective stars. By measuring the equivalent widths of the Ca II H and K lines for the stars in our sample, and converting these to approximate L Ca /L bol measurements, we also provide constraints on the connection between rotation and magnetic activity. Measurable rotation is a sufficient, but not necessary condition for activity in our sample: all the detectable rotators show strong Ca II emission, but so too do a small number of non-rotating stars, which we presume may lie at high inclination angles relative to our line of sight. Our data are consistent with a 'saturation-type' rotation-activity relationship, with activity roughly independent of rotation above a threshold velocity of less than 6 km s -1 . We also find weak evidence for a 'gap' in L Ca /L bol between a highly active population of stars, which typically are detected as rotators, and another much less active group.
Drag and lift forces between a rotating conductive sphere and a cylindrical magnet
Nurge, Mark A.; Youngquist, Robert C.; Starr, Stanley O.
2018-06-01
Modeling the interaction between a non-uniform magnetic field and a rotating conductive object provides insight into the drag force, which is used in applications such as eddy current braking and linear induction motors, as well as the transition to a repulsive force, which is the basis for magnetic levitation systems. Here, we study the interaction between a non-uniform field generated by a cylindrical magnet and a rotating conductive sphere. Each eddy current in the sphere generates a magnetic field which in turn generates another eddy current, eventually feeding back on itself. A two-step mathematical process is developed to find a closed-form solution in terms of only three eddy currents. However, the complete solution requires decomposition of the magnetic field into a summation of spherical harmonics, making it more suitable for a graduate-level electromagnetism lecture or lab. Finally, the forces associated with these currents are calculated and then verified experimentally.
Damping and non-linearity of a levitating magnet in rotation above a superconductor
International Nuclear Information System (INIS)
Druge, J; Jean, C; Laurent, O; Méasson, M-A; Favero, I
2014-01-01
We study the dissipation of moving magnets in levitation above a superconductor. The rotation motion is analyzed using optical tracking techniques. It displays a remarkable regularity together with long damping time up to several hours. The magnetic contribution to the damping is investigated in detail by comparing 14 distinct magnetic configurations and points towards amplitude-dependent dissipation mechanisms. The non-linear dynamics of the mechanical rotation motion is also revealed and described with an effective Duffing model. The magnetic mechanical damping is consistent with measured hysteretic cycles M(H) that are discussed within a modified critical state model. The obtained picture of the coupling of levitating magnets to their environment sheds light on their potential as ultra-low dissipation mechanical oscillators for high precision physics. (paper)
Drag and Lift Forces Between a Rotating Conductive Sphere and a Cylindrical Magnet
Nurge, Mark A.; Youngquist, Robert C.
2017-01-01
Modeling the interaction between a non-uniform magnetic field and a rotating conductive object allows study of the drag force which is used in applications such as eddy current braking and linear induction motors as well as the transition to a repulsive force that is the basis for magnetic levitation systems. Here, we study the interaction between a non-uniform field generated by a cylindrical magnet and a rotating conductive sphere. Each eddy current in the sphere generates a magnetic field which in turn generates another eddy current, eventually feeding back on itself. A two step mathematics process is developed to find a closed form solution in terms of only two eddy currents. However, the complete solution requires decomposition of the magnetic field into a summation of spherical harmonics, making it more suitable for a graduate level electromagnetism lecture or lab. Finally, the forces associated with these currents are calculated and then verified experimentally.
International Nuclear Information System (INIS)
Gierster, L.; Ünal, A.A.; Pape, L.; Radu, F.; Kronast, F.
2015-01-01
We investigate laser induced magnetic switching in a ferrimagnetic thin film of Tb_2_2Fe_6_9Co_9 by PEEM. Using a small laser beam with a spot size of 3–5 µm in diameter in combination with high resolution magnetic soft X-ray microscopy we are able to discriminate between different effects that govern the microscopic switching process, namely the influence of the laser heating, of the helicity dependent momentum transfer, and of the dipolar coupling. Applying a sequence of femtosecond laser pulses to a previously saturated TbFeCo film leads to the formation of ring shaped magnetic structures in which all three effects can be observed. Laser helicity assisted switching is only observed in a narrow region within the Gaussian profile of the laser spot. Whereas in the center of the laser spot we find clear evidence for thermal demagnetization and in the outermost areas magnetic switching is determined by dipolar coupling with the surrounding film. Our findings demonstrate that by reducing the laser spot size the influence of dipolar coupling on laser induced switching is becoming increasingly important. - Highlights: • With a new PEEM sample holder a laser spot size of 3–5 µm in diameter is reached. • Spatial resolved imaging of laser induced magnetization reversal. • A single femtosecond laser pulse leads to a multi-domain state in TbFeCo. • A pulse sequence results in a ring-shaped magnetic pattern caused by dipolar fields. • Laser helicity dependent effects appear only in a narrow fluence region.
Generation of zonal flows in rotating fluids and magnetized plasmas
DEFF Research Database (Denmark)
Juul Rasmussen, J.; Garcia, O.E.; Naulin, V.
2006-01-01
The spontaneous generation of large-scale flows by the rectification of small-scale turbulent fluctuations is of great importance both in geophysical flows and in magnetically confined plasmas. These flows regulate the turbulence and may set up effective transport barriers. In the present....... The analogy to large-scale flow generation in drift-wave turbulence dynamics in magnetized plasma is briefly discussed....
Energy Technology Data Exchange (ETDEWEB)
Maldonado-Velázquez, M. [Posgrado en Ciencias Físicas, Universidad Nacional Autónoma de México, 04510 (Mexico); Barrón-Palos, L., E-mail: libertad@fisica.unam.mx [Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, 01000 (Mexico); Crawford, C. [University of Kentucky, Lexington, KY 40506 (United States); Snow, W.M. [Indiana University, Bloomington, IN 47405 (United States)
2017-05-11
The neutron spin is a critical degree of freedom for many precision measurements using low-energy neutrons. Fundamental symmetries and interactions can be studied using polarized neutrons. Parity-violation (PV) in the hadronic weak interaction and the search for exotic forces that depend on the relative spin and velocity, are two questions of fundamental physics that can be studied via the neutron spin rotations that arise from the interaction of polarized cold neutrons and unpolarized matter. The Neutron Spin Rotation (NSR) collaboration developed a neutron polarimeter, capable of determining neutron spin rotations of the order of 10{sup −7} rad per meter of traversed material. This paper describes two key components of the NSR apparatus, responsible for the transport and manipulation of the spin of the neutrons before and after the target region, which is surrounded by magnetic shielding and where residual magnetic fields need to be below 100 μG. These magnetic field devices, called input and output coils, provide the magnetic field for adiabatic transport of the neutron spin in the regions outside the magnetic shielding while producing a sharp nonadiabatic transition of the neutron spin when entering/exiting the low-magnetic-field region. In addition, the coils are self contained, forcing the return magnetic flux into a compact region of space to minimize fringe fields outside. The design of the input and output coils is based on the magnetic scalar potential method.
Power system stabilization by superconducting magnetic energystorage connected to rotating exciter
Mitani, Yasunori; Tsuji, K
1993-01-01
The authors describe a combination of a rotating exciter and a superconducting magnetic energy storage (SMES) system for efficient power system stabilization. A SMES system connected to an exciter rotating with a turbine-rotor shaft is proposed. The exciter is installed exclusively to supply current for the SMES. Since electrical power output from the SMES is converted into a mechanical torque of the generator directly by the exciter, it is expected that power swings of the generator will be ...
Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment
Energy Technology Data Exchange (ETDEWEB)
Fonseca, I. C.; Bakke, K., E-mail: kbakke@fisica.ufpb.br [Departamento de Física, Universidade Federal da Paraíba, Caixa Postal 5008, João Pessoa, PB 58051-970 (Brazil)
2016-01-07
Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels.
Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment
Fonseca, I. C.; Bakke, K.
2016-01-01
Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels.
Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment
International Nuclear Information System (INIS)
Fonseca, I. C.; Bakke, K.
2016-01-01
Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels
Surface geometry of a rotating black hole in a magnetic field
International Nuclear Information System (INIS)
Kulkarni, R.; Dadhich, N.
1986-01-01
We study the intrinsic geometry of the surface of a rotating black hole in a uniform magnetic field, using a metric discovered by Ernst and Wild. Rotating black holes are analogous to material rotating bodies according to Smarr since black holes also tend to become more oblate on being spun up. Our study shows that the presence of a strong magnetic field ensures that a black hole actually becomes increasingly prolate on being spun up. Studying the intrinsic geometry of the black-hole surface also gives rise to an interesting embedding problem. Smarr shows that a Kerr black hole cannot be globally isometrically embedded in R 3 if its specific angular momentum a exceeds (√3 /2)mapprox.0.866. . .m. We show that in the presence of a magnetic field of strength B, satisfying 2- √3 2 m 2 3 for all values of the angular momentum
Rigid-body rotation of an electron cloud in divergent magnetic fields
International Nuclear Information System (INIS)
Fruchtman, A.; Gueroult, R.; Fisch, N. J.
2013-01-01
For a given voltage across a divergent poloidal magnetic field, two electric potential distributions, each supported by a rigid-rotor electron cloud rotating with a different frequency, are found analytically. The two rotation frequencies correspond to the slow and fast rotation frequencies known in uniform plasma. Due to the centrifugal force, the equipotential surfaces, that correspond to the two electric potential distributions, diverge more than the magnetic surfaces do, the equipotential surfaces in the fast mode diverge largely in particular. The departure of the equipotential surfaces from the magnetic field surfaces may have a significant focusing effect on the ions accelerated by the electric field. The focusing effect could be important for laboratory plasma accelerators as well as for collimation of astrophysical jets
Energy Technology Data Exchange (ETDEWEB)
Kameno, H.; Miyagawa, Y.; Takahata, R.; Ueyama, H. [Koyo Seiko Co., Ltd., Osaka (Japan)
1999-11-25
In order to clarify the rotation loss and levitation force reduction characteristics of two kinds of radial and axial-type superconducting magnetic bearings (SMB) consisting of a ring-shaped YBCO and a permanent magnet composite, we measured rotation losses and levitation forces of each SMB with a new rotation-loss measuring device using active magnetic bearings. The rotation loss of the SMB increased with increased initial load of the SMB. The levitation force of the SMB decreased remarkably just after activating the initial load to the SMB and during acceleration of the rotor suspended by the SMB. The reduction in levitation force was improved by means of applying a pre-load, that means a temporary load, before the initial load against the SMB. But the rotation loss of the SMB was increased as pre-load was increased. When the YBCO was cooled down from 77 to 66 K, the rotation loss of the SMB decreased as the temperature of the SC decreased. (author)
Energy Technology Data Exchange (ETDEWEB)
Vanderbemden, P [SUPRATECS and Department of Electrical Engineering and Computer Science B28, Sart-Tilman, B-4000 Liege (Belgium); Hong, Z [Centre for Advanced Photonics and Electronics, Engineering Department, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Coombs, T A [Centre for Advanced Photonics and Electronics, Engineering Department, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Ausloos, M [SUPRATECS and Department of Physics B5, Sart-Tilman, B-4000 Liege (Belgium); Babu, N Hari [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Cardwell, D A [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Campbell, A M [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom)
2007-09-15
Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety of high-field permanent-magnet-like applications, such as the rotor of a brushless motor. When used in rotating devices of this kind, however, the YBCO can be subjected to both transient and alternating magnetic fields that are not parallel to the direction of magnetization and which have a detrimental effect on the trapped field. These effects may lead to long-term decay of the magnetization of the bulk sample. In the present work, we analyze both experimentally and numerically the remagnetization process of a melt-processed YBCO single domain that has been partially demagnetized by a magnetic field applied orthogonal to the initial direction of trapped flux. Magnetic torque measurements are used as a tool to probe changes in the remanent magnetization during various sequences of applied field. The application of a small magnetic field between the transverse cycles parallel to the direction of original magnetization results in partial remagnetization of the sample. Rotating the applied field, however, is found to be much more efficient at remagnetizing the bulk material than applying a magnetizing field pulse of the same amplitude. The principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law. Finally, the remagnetization process is shown to result from the complex modification of current distribution within the cross-section of the bulk sample.
International Nuclear Information System (INIS)
Vanderbemden, P; Hong, Z; Coombs, T A; Ausloos, M; Babu, N Hari; Cardwell, D A; Campbell, A M
2007-01-01
Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety of high-field permanent-magnet-like applications, such as the rotor of a brushless motor. When used in rotating devices of this kind, however, the YBCO can be subjected to both transient and alternating magnetic fields that are not parallel to the direction of magnetization and which have a detrimental effect on the trapped field. These effects may lead to long-term decay of the magnetization of the bulk sample. In the present work, we analyze both experimentally and numerically the remagnetization process of a melt-processed YBCO single domain that has been partially demagnetized by a magnetic field applied orthogonal to the initial direction of trapped flux. Magnetic torque measurements are used as a tool to probe changes in the remanent magnetization during various sequences of applied field. The application of a small magnetic field between the transverse cycles parallel to the direction of original magnetization results in partial remagnetization of the sample. Rotating the applied field, however, is found to be much more efficient at remagnetizing the bulk material than applying a magnetizing field pulse of the same amplitude. The principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law. Finally, the remagnetization process is shown to result from the complex modification of current distribution within the cross-section of the bulk sample
Differential detection for measurements of Faraday rotation by means of ac magnetic fields
International Nuclear Information System (INIS)
Valev, V K; Wouters, J; Verbiest, T
2008-01-01
We demonstrate that by using a combination of a Wollaston prism and two photodiodes the accuracy in the measurements of Faraday rotation with ac magnetic fields can be greatly improved. Our experiments were performed on microscope cover glass plates with thicknesses between 0.13 and 0.16 mm. We show that our setup is capable of distinguishing between the Faraday rotation signals of glass plates having a difference in thickness of a few micrometers, corresponding to Faraday rotations of hundreds of microdegrees per Tesla only
Magnetic rotational hysteresis study on spherical 85-160 nm Fe3O4 particles
Schmidbauer, E.
1988-05-01
Rotational hysteresis losses Wr were determined as a function of magnetic field H for dispensed spherical Fe3O4 particles of mean grain sizes 85 nm, 127 nm and 162 nm between 78 K and 294 K. The observed Wr-H curves are compared with theoretical curves for single domain particles. The analysed particles reveal centers of high magnetic anisotropy. Such centers can be of importance during the generation of a thermoremanent magnetization, as they may be the origin of enhanced magnetic stability.
Activity of an enzyme immobilized on superparamagnetic particles in a rotational magnetic field
Energy Technology Data Exchange (ETDEWEB)
Mizuki, Toru; Watanabe, Noriyuki; Nagaoka, Yutaka [Bio-Nano Electronics Research Centre, Toyo University, Saitama 350-8585 (Japan); Fukushima, Tadamasa [Shimadzu GLC Ltd., Phenomenex Support Centre, Tokyo 110-0016 (Japan); Morimoto, Hisao; Usami, Ron [Bio-Nano Electronics Research Centre, Toyo University, Saitama 350-8585 (Japan); Maekawa, Toru, E-mail: maekawa@toyonet.toyo.ac.jp [Bio-Nano Electronics Research Centre, Toyo University, Saitama 350-8585 (Japan)
2010-03-19
We immobilize {alpha}-amylase extracted from Bacillus Iicheniformis on the surfaces of superparamagnetic particles and investigate the effect of a rotational magnetic field on the enzyme's activity. We find that the activity of the enzyme molecules immobilized on superparamagnetic particles increases in the rotational magnetic field and reaches maximum at a certain frequency. We clarify the effect of the cluster structures formed by the superparamagnetic particles on the activity. Enzyme reactions are enhanced even in a tiny volume of solution using the present method, which is very important for the development of efficient micro reactors and micro total analysis systems ({mu}-TAS).
The effect of sheared toroidal rotation on pressure driven magnetic islands in toroidal plasmas
Energy Technology Data Exchange (ETDEWEB)
Hegna, C. C. [Departments of Engineering Physics and Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2016-05-15
The impact of sheared toroidal rotation on the evolution of pressure driven magnetic islands in tokamak plasmas is investigated using a resistive magnetohydrodynamics model augmented by a neoclassical Ohm's law. Particular attention is paid to the asymptotic matching data as the Mercier indices are altered in the presence of sheared flow. Analysis of the nonlinear island Grad-Shafranov equation shows that sheared flows tend to amplify the stabilizing pressure/curvature contribution to pressure driven islands in toroidal tokamaks relative to the island bootstrap current contribution. As such, sheared toroidal rotation tends to reduce saturated magnetic island widths.
Energy Technology Data Exchange (ETDEWEB)
Wei, Xing, E-mail: xing.wei@sjtu.edu.cn [Institute of Natural Sciences and Department of Physics and Astronomy, Shanghai Jiao Tong University (China); Princeton University Observatory, Princeton, NJ 08544 (United States)
2016-09-01
To understand magnetic effects on dynamical tides, we study the rotating magnetohydrodynamic (MHD) flow driven by harmonic forcing. The linear responses are analytically derived in a periodic box under the local WKB approximation. Both the kinetic and Ohmic dissipations at the resonant frequencies are calculated, and the various parameters are investigated. Although magnetic pressure may be negligible compared to thermal pressure, the magnetic field can be important for the first-order perturbation, e.g., dynamical tides. It is found that the magnetic field splits the resonant frequency, namely the rotating hydrodynamic flow has only one resonant frequency, but the rotating MHD flow has two, one positive and the other negative. In the weak field regime the dissipations are asymmetric around the two resonant frequencies and this asymmetry is more striking with a weaker magnetic field. It is also found that both the kinetic and Ohmic dissipations at the resonant frequencies are inversely proportional to the Ekman number and the square of the wavenumber. The dissipation at the resonant frequency on small scales is almost equal to the dissipation at the non-resonant frequencies, namely the resonance takes its effect on the dissipation at intermediate length scales. Moreover, the waves with phase propagation that is perpendicular to the magnetic field are much more damped. It is also interesting to find that the frequency-averaged dissipation is constant. This result suggests that in compact objects, magnetic effects on tidal dissipation should be considered.
Jeans instability of rotating magnetized quantum plasma: Influence of radiation
Energy Technology Data Exchange (ETDEWEB)
Joshi, H., E-mail: hjoshi8525@yahoo.com [Department of Physics, Mewar University, Chittorgarh (Raj.) India (India); Pensia, R. K. [Department of Physics, Govt. Girls College, Neemuch (M.P.) India (India)
2015-07-31
The effect of radiative heat-loss function and rotation on the Jeans instability of quantum plasma is investigated. The basic set of equations for this problem is constructed by considering quantum magnetohydrodynamic (QMHD) model. Using normal mode analysis, the general dispersion relation is obtained. This dispersion relation is studied in both, longitudinal and transverse direction of propagations. In both case of longitudinal and transverse direction of propagation, the Jeans instability criterion is modified due to presence of radiative heat-loss function and quantum correction.
Resonant helical fields in tokamaks
International Nuclear Information System (INIS)
Okano, V.
1990-01-01
Poincare maps of magnetic field lines of a toroidal helical system were made. The magnetic field is a linear superposition of the magnetic fields produced by a toroidal plasma in equilibrium and by external helical currents. Analytical expression for the Poincare maps was no obtained since the magnetic field do not have symmetry. In order to obtain the maps, the equation minus derivative of l vector times B vector = 0 was numerically integrated. In the Poincare maps, the principal and the secondary magnetic island were observed. (author)
A procedure for combining rotating-coil measurements of large-aperture accelerator magnets
Energy Technology Data Exchange (ETDEWEB)
Köster, Oliver, E-mail: oliver.koester@cern.ch; Fiscarelli, Lucio, E-mail: lucio.fiscarelli@cern.ch; Russenschuck, Stephan, E-mail: stephan.russenschuck@cern.ch
2016-05-11
The rotating search coil is a precise and widely used tool for measuring the magnetic field harmonics of accelerator magnets. This paper deals with combining several such multipole measurements, in order to cover magnet apertures largely exceeding the diameter of the available search coil. The method relies on the scaling laws for multipole coefficients and on the method of analytic continuation along zero-homotopic paths. By acquiring several measurements of the integrated magnetic flux density at different transverse positions within the bore of the accelerator magnet, the uncertainty on the field harmonics can be reduced at the expense of tight tolerances on the positioning. These positioning tolerances can be kept under control by mounting the rotating coil and its motor-drive unit on precision alignment stages. Therefore, the proposed technique is able to yield even more precise results for the higher-order field components than a dedicated rotating search coil of larger diameter. Moreover, the versatility of the measurement bench is enhanced by avoiding the construction of rotating search coils of different measurement radii.
Five-dimensional rotating black hole in a uniform magnetic field: The gyromagnetic ratio
International Nuclear Information System (INIS)
Aliev, A.N.; Frolov, Valeri P.
2004-01-01
In four-dimensional general relativity, the fact that a Killing vector in a vacuum spacetime serves as a vector potential for a test Maxwell field provides one with an elegant way of describing the behavior of electromagnetic fields near a rotating Kerr black hole immersed in a uniform magnetic field. We use a similar approach to examine the case of a five-dimensional rotating black hole placed in a uniform magnetic field of configuration with biazimuthal symmetry that is aligned with the angular momenta of the Myers-Perry spacetime. Assuming that the black hole may also possess a small electric charge we construct the five-vector potential of the electromagnetic field in the Myers-Perry metric using its three commuting Killing vector fields. We show that, like its four-dimensional counterparts, the five-dimensional Myers-Perry black hole rotating in a uniform magnetic field produces an inductive potential difference between the event horizon and an infinitely distant surface. This potential difference is determined by a superposition of two independent Coulomb fields consistent with the two angular momenta of the black hole and two nonvanishing components of the magnetic field. We also show that a weakly charged rotating black hole in five dimensions possesses two independent magnetic dipole moments specified in terms of its electric charge, mass, and angular momentum parameters. We prove that a five-dimensional weakly charged Myers-Perry black hole must have the value of the gyromagnetic ratio g=3
The magnetic early B-type stars I: magnetometry and rotation
Shultz, M. E.; Wade, G. A.; Rivinius, Th; Neiner, C.; Alecian, E.; Bohlender, D.; Monin, D.; Sikora, J.; MiMeS Collaboration; BinaMIcS Collaboration
2018-04-01
The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the Magnetism in Massive Stars and Binarity and Magnetic Interactions in various classes of Stars collaborations have collected extensive high-dispersion spectropolarimetric data sets of these targets. We present longitudinal magnetic field measurements for 52 early B-type stars (B5-B0), with which we attempt to determine their rotational periods Prot. Supplemented with high-resolution spectroscopy, low-resolution Dominion Astrophysical Observatory circular spectropolarimetry, and archival Hipparcos photometry, we determined Prot for 10 stars, leaving only five stars for which Prot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of Prot is very similar to that observed for the cooler Ap/Bp stars. We also measured v sin i and vmac for all stars. Comparison to non-magnetic stars shows that v sin i is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that vmac is lower for magnetic stars. Least-squares deconvolution profiles extracted using single-element masks revealed widespread, systematic discrepancies in between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in six stars for which this has not previously been reported; however, in all six cases, the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.
White-dwarf rotational equilibria in magnetic cataclysmic variable stars
Energy Technology Data Exchange (ETDEWEB)
Warner, B. (Cape Town Univ. (South Africa). Dept. of Astronomy Australian National Univ., Canberra (Australia). Dept. of Mathematics); Wickramasinghe, D.T. (Australian National Univ., Canberra (Australia). Dept. of Mathematics)
1991-02-01
The magnetic cataclysmic variable stars (polars, intermediate polars and DQ Her stars) are grouped about three lines in the orbital period-spin period diagram. This segregation is shown to be the consequence of competition between braking and accretion torques when combined with the effects of cyclical variations in rate of mass transfer. (author).
Magnetic layers and neutral points near a rotating black hole
Czech Academy of Sciences Publication Activity Database
Karas, Vladimír; Kopáček, Ondřej
2009-01-01
Roč. 26, č. 2 (2009), s. 1-9 ISSN 0264-9381 R&D Projects: GA ČR GA205/07/0052 Institutional research plan: CEZ:AV0Z10030501 Keywords : black holes * magnetic fields Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.029, year: 2009
The behavior of the magnetic lines of a rotating system
International Nuclear Information System (INIS)
Evangelidis, E.
1977-01-01
The behaviour of a magnetic line has been studied under continuous injection of plasma. Under increasing density the existence of three zones of possible concentration has been shown. For values greater than a critical value D=0, with D suitably defined, one zone disappears, whilst the other two degenerate into one. (Auth.)
Zhang, Li; Zhang, Peng; Zhao, Lang; Wu, Jianfeng; Guo, Mei; Tang, Jinkui
2016-06-28
An unprecedented octanuclear dysprosium(iii) cluster with the formula [Dy8L6(μ3-OH)4(μ2-CH3O)2(CH3OH)6(H2O)2]·6H2O·10CH3OH·2CH3CN () based on a nonlinearly tritopic aroylhydrazone ligand H3L has been isolated, realizing the successful linking of pairwise interesting triangular Dy3 SMMs. It is noteworthy that two enantiomers (Λ and Δ configurations) individually behaving as a coordination-induced chirality presented in the Dy3 helicate are connected in the meso Dy8 cluster. Remarkably, alternating-current magnetic susceptibility measurements revealed that the Dy8 cluster shows typical SMM behavior inherited from its Dy3 helical precursor. It is one of the rare polynuclear Lnn SMMs (n > 7) under zero dc field.
Magnetic resonance described in the excitation dependent rotating frame of reference.
Tahayori, Bahman; Johnston, Leigh A; Mareels, Iven M Y; Farrell, Peter M
2008-01-01
An excitation dependent rotating frame of reference to observe the magnetic resonance phenomenon is introduced in this paper that, to the best of our knowledge, has not been used previously in the nuclear magnetic resonance context. The mathematical framework for this new rotating frame of reference is presented based on time scaling the Bloch equation after transformation to the classical rotating frame of reference whose transverse plane is rotating at the Larmor frequency. To this end, the Bloch equation is rewritten in terms of a magnetisation vector observed from the excitation dependent rotating frame of reference. The resultant Bloch equation is referred to as the time scaled Bloch equation. In the excitation dependent rotating frame of reference whose coordinates are rotating at the instantaneous Rabi frequency the observed magnetisation vector is a much slower signal than the true magnetisation in the rotating frame of reference. As a result the ordinary differential equation solvers have the ability to solve the time scaled version of the Bloch equation with a larger step size resulting in a smaller number of samples for solving the equation to a desired level of accuracy. The simulation results for different types of excitation are presented in this paper. This method may be used in true Bloch simulators in order to reduce the simulation time or increase the accuracy of the numerical solution. Moreover, the time scaled Bloch equation may be employed to determine the optimal excitation pattern in magnetic resonance imaging as well as designing pulses with better slice selectivity which is an active area of research in this field.
Temporal Variation of the Rotation of the Solar Mean Magnetic Field
Energy Technology Data Exchange (ETDEWEB)
Xie, J. L.; Shi, X. J.; Xu, J. C., E-mail: xiejinglan@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China)
2017-04-01
Based on continuous wavelet transformation analysis, the daily solar mean magnetic field (SMMF) from 1975 May 16 to 2014 July 31 is analyzed to reveal its rotational behavior. Both the recurrent plot in Bartels form and the continuous wavelet transformation analysis show the existence of rotational modulation in the variation of the daily SMMF. The dependence of the rotational cycle lengths on solar cycle phase is also studied, which indicates that the yearly mean rotational cycle lengths generally seem to be longer during the rising phase of solar cycles and shorter during the declining phase. The mean rotational cycle length for the rising phase of all of the solar cycles in the considered time is 28.28 ± 0.67 days, while for the declining phase it is 27.32 ± 0.64 days. The difference of the mean rotational cycle lengths between the rising phase and the declining phase is 0.96 days. The periodicity analysis, through the use of an auto-correlation function, indicates that the rotational cycle lengths have a significant period of about 10.1 years. Furthermore, the cross-correlation analysis indicates that there exists a phase difference between the rotational cycle lengths and solar activity.
MAGNETIC RESONANCE IMAGING EVALUATION OF ROTATOR CUFF IMPINGEMENT
Directory of Open Access Journals (Sweden)
Chandrakanth K. S
2017-06-01
Full Text Available BACKGROUND Shoulder pain is a common clinical problem. Impingement syndrome of the shoulder is believed to be the most common cause of shoulder pain. The term ‘impingement syndrome’ was first used by Neer to describe a condition of shoulder pain associated with chronic bursitis and partial thickness tear of Rotator Cuff (RC. The incidence of Rotator Cuff (RC tear is estimated to be about 20.7% in the general population. This study is intended to analyse various extrinsic and intrinsic causes of shoulder impingement. MATERIALS AND METHODS 110 consecutive patients referred for MRI with clinical suspicion of shoulder impingement were prospectively studied. All the patients were evaluated for Rotator Cuff (RC degeneration and various extrinsic factors that lead to degeneration like acromial shape, down-sloping acromion, Acromioclavicular (AC joint degeneration and acromial enthesophyte. Intrinsic factors like degeneration and its correlation with age of the patients were evaluated. RESULTS Of the total 110 patients, 19 (17.3% patients had FT RC tear and 31 (28.2% had PT (both bursal and articular surface tears. There was no statistically significant correlation (p=0.76 between acromion types and RC tear. Down-sloping acromion and enthesophytes had statistically significant association with RC tear (p=0.008 and 0.008, respectively. Statistically significant (0.008 correlation between the severity of AC joint degeneration and RC tears was noted. AC joint degeneration and RC pathologies also showed a correlation with the age of the patients with p values of <0.001 and 0.001, respectively. CONCLUSION No statistically significant correlation between RC pathologies with hooked acromion was found, that makes the role played by hooked acromion in FT RC tear questionable. AC joint degeneration association with RC tear is due to the association of both RC tear and AC joint degeneration with age of the patient. Down-sloping acromion, AC joint degeneration
X-ray tube incorporating a rotating anode with magnetic bearings
International Nuclear Information System (INIS)
1979-01-01
This patent describes an X-ray tube incorporating a rotating anode. The rotor consists of a single, soft-magnetic dish which is fixed on the axis and which seals the magnetic yoke of the stator. Looking in the direction of the axis, one side is equipped with two circular pole surfaces, one at least of which is provided with circular pole-shoes, separated from one another by concentric grooves. (T.P.)
A Rigidly Rotating Magnetosphere Model for the Circumstellar Environments of Magnetic OB Stars
Townsend, R.; Owocki, S.; Groote, D.
2005-11-01
We report on a new model for the circumstellar environments of rotating, magnetic hot stars. This model predicts the channeling of wind plasma into a corotating magnetosphere, where -- supported against gravity by centrifugal forces -- it can steadily accumulate over time. We apply the model to the B2p star σ Ori E, demonstrating that it can simultaneously reproduce the spectroscopic, photometric and magnetic variations exhibited by the star.
Helical-tokamak hybridization concepts for compact configuration exploration and MHD stabilization
International Nuclear Information System (INIS)
Oishi, T.; Yamazaki, K.; Arimoto, H.; Baba, K.; Hasegawa, M.; Ozeki, H.; Shoji, T.; Mikhailov, M.I.
2010-11-01
To search for low-aspect-ratio torus systems, a lot of exotic confinement concepts are proposed so far historically. One of the authors previously proposed the tokamak-helical hybrid called TOKASTAR (Tokamak-Stellarator Hybrid) to improve the magnetic local shear near the bad curvature region. This is characterized by simple and compact coil systems with enough divertor space relevant to reactor designs. Based on this TOKASTAR concept, a toroidal mode number N=2 C (compact) -TOKASTAR machine (R - 35 mm) was constructed. The rotational transform of this compact helical configuration is rather small to confine hot ions, but can be utilized as a compact electron plasma machine for multi-purposes. The C-TOKASTAR has a pair of spherically winding helical coils and a pair of poloidal coils. Existence of magnetic surface and electron confinement property in C-TOKASTAR device were investigated by an electron-emission impedance method. Calculation of the particle orbit also supports that closed magnetic surface is formed in the cases that the ratio between poloidal and helical coil current is appropriate. Another aspect of the research using TOKASTAR configuration includes the evaluation of the effect of the outboard helical field application to tokamak plasmas. It is considered that outboard helical field has roles to assist the initiation of plasma current, to improve MHD stability, and so on. To check these roles, we made TOKASTAR-2 machine (R - 0.12 m, B - 1 kG) with ohmic heating central coil, eight toroidal field coils, a pair of vertical field coils and two outboard helical field coil segments. The electron cyclotron heating plasma start-up and plasma current disruption control experiments might be expected in this machine. Calculation of magnetic field line tracing has revealed that magnetic surface can be formed using additional outer helical coils. (author)
Three-dimensional rotational plasma flows near solid surfaces in an axial magnetic field
Energy Technology Data Exchange (ETDEWEB)
Gorshunov, N. M., E-mail: gorshunov-nm@nrcki.ru; Potanin, E. P., E-mail: potanin45@yandex.ru [National Research Center Kurchatov Institute (Russian Federation)
2016-11-15
A rotational flow of a conducting viscous medium near an extended dielectric disk in a uniform axial magnetic field is analyzed in the magnetohydrodynamic (MHD) approach. An analytical solution to the system of nonlinear differential MHD equations of motion in the boundary layer for the general case of different rotation velocities of the disk and medium is obtained using a modified Slezkin–Targ method. A particular case of a medium rotating near a stationary disk imitating the end surface of a laboratory device is considered. The characteristics of a hydrodynamic flow near the disk surface are calculated within the model of a finite-thickness boundary layer. The influence of the magnetic field on the intensity of the secondary flow is studied. Calculations are performed for a weakly ionized dense plasma flow without allowance for the Hall effect and plasma compressibility. An MHD flow in a rotating cylinder bounded from above by a retarding cap is considered. The results obtained can be used to estimate the influence of the end surfaces on the main azimuthal flow, as well as the intensities of circulating flows in various devices with rotating plasmas, in particular, in plasma centrifuges and laboratory devices designed to study instabilities of rotating plasmas.
Overview of results from the Large Helical Device
International Nuclear Information System (INIS)
Yamada, H.
2010-11-01
The physical understanding of net-current free helical plasmas has progressed in the Large Helical Device (LHD) since the last Fusion Energy Conference in Geneva, 2008. The experimental results from LHD have promoted detailed physical documentation of features specific to net-current-free 3-D helical plasmas as well as complementary to the tokamak approach. The primary heating source is NBI with a heating power of 23 MW, and ECH with 3.7 MW plays an important role in local heating and power modulation in transport studies. The maximum central density has reached 1.2 x 10 21 m -3 due to the formation of an Internal Diffusion Barrier (IDB) at the magnetic field of 2.5 T. The IDB has been maintained for 3 s by refueling with repetitive pellet injection. The plasma with a central ion temperature reaching 5.6 keV exhibits the formation of an Internal Transport Barrier (ITB). The ion thermal diffusivity decreases to the level predicted by neoclassical transport. This ITB is accompanied by spontaneous toroidal rotation and an Impurity Hole which generates an impurity-free core. Impurity Hole is due to a large outward convection of impurities in spite of the negative radial electric field. The magnitude of the Impurity Hole is enhanced in the magnetic configuration with larger helical ripple and for higher Z impurities. Another mechanism to suppress impurity contamination has been identified at the plasma edge with a stochastic magnetic field. A helical system shares common physics issues with tokamaks such as 3-D equilibria, transport in a stochastic magnetic field, plasma response to a Resonant Magnetic Perturbation (RMP), divertor physics, and the role of radial electric field and meso-scale structure. (author)
Toroidal rotation braking with n = 1 magnetic perturbation field on JET
DEFF Research Database (Denmark)
Sun, Y; Liang, Y; Koslowski, H R
2010-01-01
A strong toroidal rotation braking has been observed in plasmas with application of an n = 1 magnetic perturbation field on the JET tokamak. Calculation results from the momentum transport analysis show that the torque induced by the n = 1 perturbation field has a global profile. The maximal value...
Rotating structures in low temperature magnetized plasmas - Insight from particle simulations
Directory of Open Access Journals (Sweden)
Jean-Pierre eBoeuf
2014-12-01
Full Text Available The EXB configuration of various low temperature plasma devices is often responsible for the formation of rotating structures and instabilities leading to anomalous electron transport across the magnetic field. In these devices, electrons are strongly magnetized while ions are weakly or not magnetized and this leads to specific physical phenomena that are not present in fusion plasmas where both electrons and ions are strongly magnetized. In this paper we describe basic phenomena involving rotating plasma structures in simple configurations of low temperature EXB plasma devices on the basis of PIC-MCC (Particle-In-Cell Monte Carlo Collisions simulations. We focus on three examples: rotating electron vortices and rotating spokes in cylindrical magnetrons, and azimuthal electron-cyclotron drift instability in Hall thrusters. The simulations are not intended to give definite answers to the many physics issues related to low temperature EXB plasma devices but are used to illustrate and discuss some of the basic questions that need further studies.
Spin current pumped by a rotating magnetic field in zigzag graphene nanoribbons
International Nuclear Information System (INIS)
Wang, J; Chan, K S
2010-01-01
We study electron spin resonance in zigzag graphene nanoribbons by applying a rotating magnetic field on the system without any bias. By using the nonequilibrium Green's function technique, the spin-resolved pumped current is explicitly derived in a rotating reference frame. The pumped spin current density increases with the system size and the intensity of the transverse rotating magnetic field. For graphene nanoribbons with an even number of zigzag chains, there is a nonzero pumped charge current in addition to the pumped spin current owing to the broken spatial inversion symmetry of the system, but its magnitude is much smaller than the spin current. The short-ranged static disorder from either impurities or defects in the ribbon can depress the spin current greatly due to the localization effect, whereas the long-ranged disorder from charge impurities can avoid inter-valley scattering so that the spin current can survive in the strong disorder for the single-energy mode.
Magnetism of iron and nickel from rotationally invariant Hirsch-Fye quantum Monte Carlo calculations
Belozerov, A. S.; Leonov, I.; Anisimov, V. I.
2013-03-01
We present a rotationally invariant Hirsch-Fye quantum Monte Carlo algorithm in which the spin rotational invariance of Hund's exchange is approximated by averaging over all possible directions of the spin quantization axis. We employ this technique to perform benchmark calculations for the two- and three-band Hubbard models on the infinite-dimensional Bethe lattice. Our results agree quantitatively well with those obtained using the continuous-time quantum Monte Carlo method with rotationally invariant Coulomb interaction. The proposed approach is employed to compute the electronic and magnetic properties of paramagnetic α iron and nickel. The obtained Curie temperatures agree well with experiment. Our results indicate that the magnetic transition temperature is significantly overestimated by using the density-density type of Coulomb interaction.
Energy Technology Data Exchange (ETDEWEB)
Santos-Lima, R.; De Gouveia Dal Pino, E. M. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, R. do Matao, 1226, Sao Paulo, SP 05508-090 (Brazil); Lazarian, A. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)
2012-03-01
The formation of protostellar disks out of molecular cloud cores is still not fully understood. Under ideal MHD conditions, the removal of angular momentum from the disk progenitor by the typically embedded magnetic field may prevent the formation of a rotationally supported disk during the main protostellar accretion phase of low-mass stars. This has been known as the magnetic braking problem and the most investigated mechanism to alleviate this problem and help remove the excess of magnetic flux during the star formation process, the so-called ambipolar diffusion (AD), has been shown to be not sufficient to weaken the magnetic braking at least at this stage of the disk formation. In this work, motivated by recent progress in the understanding of magnetic reconnection in turbulent environments, we appeal to the diffusion of magnetic field mediated by magnetic reconnection as an alternative mechanism for removing magnetic flux. We investigate numerically this mechanism during the later phases of the protostellar disk formation and show its high efficiency. By means of fully three-dimensional MHD simulations, we show that the diffusivity arising from turbulent magnetic reconnection is able to transport magnetic flux to the outskirts of the disk progenitor at timescales compatible with the collapse, allowing the formation of a rotationally supported disk around the protostar of dimensions {approx}100 AU, with a nearly Keplerian profile in the early accretion phase. Since MHD turbulence is expected to be present in protostellar disks, this is a natural mechanism for removing magnetic flux excess and allowing the formation of these disks. This mechanism dismisses the necessity of postulating a hypothetical increase of the ohmic resistivity as discussed in the literature. Together with our earlier work which showed that magnetic flux removal from molecular cloud cores is very efficient, this work calls for reconsidering the relative role of AD in the processes of star
Faraday rotation, stochastic magnetic fields and CMB maps
Giovannini, Massimo
2008-01-01
The high- and low-frequency descriptions of the pre-decoupling plasma are deduced from the Vlasov-Landau treatment generalized to curved space-times and in the presence of the relativistic fluctuations of the geometry. It is demonstrated that the interplay between one-fluid and two-fluid treatments is mandatory for a complete and reliable calculation of the polarization observables. The Einstein-Boltzmann hierarchy is generalized to handle the dispersive propagation of the electromagnetic disturbances in the pre-decoupling plasma. Given the improved physical and numerical framework, the polarization observables are computed within the magnetized $\\Lambda$CDM paradigm (m$\\Lambda$CDM). In particular, the Faraday-induced B-mode is consistently estimated by taking into account the effects of the magnetic fields on the initial conditions of the Boltzmann hierarchy, on the dynamical equations and on the dispersion relations. The complete calculations of the angular power spectra constitutes the first step for the d...
Evaluation of post-exercise magnetic resonance images of the rotator cuff
International Nuclear Information System (INIS)
Cahoy, P.M.; Orwin, J.F.; Tuite, M.J.
1996-01-01
Objective. To examine the effect of strenuous exercise on the magnetic resonance imaging (MRI) characteristics of the rotator cuff tendon. A second objective was to define an optimal time to image the rotator cuff and possibly eliminate exercise-induced false positives. Design and patients. Five male subjects from 24 to 38 years old with normal rotator cuffs by history, physical examination, and screening MRI underwent a rotator cuff exercise session on the Biodex System 2 (Biodex, Shirley, New York). The exercise sessions were followed by sequential MRI scans of the exercised shoulder. These were performed immediately and at 8 h and 24 h after exercise. Results and conclusions. The rotator cuff tendon and subacromial-subdeltoid bursal signal remained unchanged from the pre-exercise through the 24-h post-exercise scans. The rotator cuff muscle signal was increased in five of five subjects on the immediate post-exercise fat-suppressed T2-weighted images. This signal returned to baseline by the 8-h scan. Positive findings of rotator cuff pathology on MRI after strenuous athletic activity should not be discounted as normal exercise-induced changes. Also, diagnostic MRI scanning may take place after a practice session without an increased risk of false positives. (orig.). With 1 fig
Evaluation of post-exercise magnetic resonance images of the rotator cuff
Energy Technology Data Exchange (ETDEWEB)
Cahoy, P M [Division of Orthopedic Surgery G5/358, University of Wisconsin Hospital and Clinics, Madison, WI (United States); Orwin, J F [Division of Orthopedic Surgery G5/358, University of Wisconsin Hospital and Clinics, Madison, WI (United States); Tuite, M J [Department of Radiology, University of Wisconsin Hospital and Clinics, Madison, WI (United States)
1996-11-01
Objective. To examine the effect of strenuous exercise on the magnetic resonance imaging (MRI) characteristics of the rotator cuff tendon. A second objective was to define an optimal time to image the rotator cuff and possibly eliminate exercise-induced false positives. Design and patients. Five male subjects from 24 to 38 years old with normal rotator cuffs by history, physical examination, and screening MRI underwent a rotator cuff exercise session on the Biodex System 2 (Biodex, Shirley, New York). The exercise sessions were followed by sequential MRI scans of the exercised shoulder. These were performed immediately and at 8 h and 24 h after exercise. Results and conclusions. The rotator cuff tendon and subacromial-subdeltoid bursal signal remained unchanged from the pre-exercise through the 24-h post-exercise scans. The rotator cuff muscle signal was increased in five of five subjects on the immediate post-exercise fat-suppressed T2-weighted images. This signal returned to baseline by the 8-h scan. Positive findings of rotator cuff pathology on MRI after strenuous athletic activity should not be discounted as normal exercise-induced changes. Also, diagnostic MRI scanning may take place after a practice session without an increased risk of false positives. (orig.). With 1 fig.
Combining rotating-coil measurements of large-aperture accelerator magnets
AUTHOR|(CDS)2089510
2016-10-05
The rotating coil is a widely used tool to measure the magnetic field and the field errors in accelerator magnets. The coil has a length that exceeds the entire magnetic field along the longitudinal dimension of the magnet and gives therefore a two-dimensional representation of the integrated field. Having a very good precision, the rotating coil lacks in versatility. The fixed dimensions make it impractical and inapplicable in situations, when the radial coil dimension is much smaller than the aperture or when the aperture is only little covered by the coil. That being the case for rectangular apertures with large aspect ratio, where a basic measurement by the rotating coil describes the field only in a small area of the magnet. A combination of several measurements at different positions is the topic of this work. Very important for a combination is the error distribution on the measured field harmonics. To preserve the good precision of the higher-order harmonics, the combination must not rely on the main ...
International Nuclear Information System (INIS)
Carvalho-Santos, Vagson L.; Dandoloff, Rossen
2013-01-01
We study the Heisenberg model in an external magnetic field on curved surfaces with rotational symmetry. The Euler-Lagrange static equations, derived from the Hamiltonian, lead to the inhomogeneous double sine-Gordon equation. Nonetheless, if the magnetic field is coupled to the metric elements of the surface, and consequently to its curvature, the homogeneous double sine-Gordon equation emerges and a 2π-soliton solution is obtained. In order to satisfy the self-dual equations, surface deformations are predicted to appear at the sector where the spin direction is opposite to the magnetic field. On the basis of the model, we find the characteristic length of the 2π-soliton for three specific rotationally symmetric surfaces: the cylinder, the catenoid, and the hyperboloid. On finite surfaces, such as the sphere, torus, and barrels, fractional 2π-solitons are predicted to appear. (author)
SPECTRAL VARIATIONS OF Of?p OBLIQUE MAGNETIC ROTATOR CANDIDATES IN THE MAGELLANIC CLOUDS
Energy Technology Data Exchange (ETDEWEB)
Walborn, Nolan R. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Morrell, Nidia I. [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile); Nazé, Yaël [GAPHE, Département AGO, Université de Liège, Allée du 6 Août 19c, Bat. B5C, B-4000-Liège (Belgium); Wade, Gregg A. [Department of Physics, Royal Military College of Canada, P.O. Box 17000 Station Forces, Kingston, ON, Canada K7K 7B4 (Canada); Bagnulo, Stefano [Armagh Observatory, College Hill, Armagh BT61 9DG (United Kingdom); Barbá, Rodolfo H. [Departamento de Física y Astronomía, Universidad de La Serena, Cisternas 1200 Norte, La Serena (Chile); Apellániz, Jesús Maíz [Centro de Astrobiología, CSIC-INTA, Campus ESAC, Apartado Postal 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Howarth, Ian D. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Evans, Christopher J. [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Sota, Alfredo, E-mail: walborn@stsci.edu, E-mail: nmorrell@lco.cl, E-mail: naze@astro.ulg.ac.be, E-mail: wade-g@rmc.ca, E-mail: sba@arm.ac.uk, E-mail: rbarba@dfuls.cl, E-mail: jmaiz@cab.inta-csic.es, E-mail: idh@star.ucl.ac.uk [Instituto de Astrofísica de Andalucía—CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain)
2015-10-15
Optical spectroscopic monitoring has been conducted of two O stars in the SMC and one in the LMC, the spectral characteristics of which place them in the Of?p category, which has been established in the Galaxy to consist of oblique magnetic rotators. All of these Magellanic stars show systematic spectral variations typical of the Of?p class, further strengthening their magnetic candidacy to the point of virtual certainty. The spectral variations are related to photometric variations derived from Optical Gravitational Lensing Experiment data by Nazé et al. in a parallel study, which yields rotational periods for two of them. Now circular spectropolarimetry is required to measure their fields, and ultraviolet spectroscopy to further characterize their low-metallicity, magnetically confined winds, in support of hydrodynamical analyses.
SPECTRAL VARIATIONS OF Of?p OBLIQUE MAGNETIC ROTATOR CANDIDATES IN THE MAGELLANIC CLOUDS
International Nuclear Information System (INIS)
Walborn, Nolan R.; Morrell, Nidia I.; Nazé, Yaël; Wade, Gregg A.; Bagnulo, Stefano; Barbá, Rodolfo H.; Apellániz, Jesús Maíz; Howarth, Ian D.; Evans, Christopher J.; Sota, Alfredo
2015-01-01
Optical spectroscopic monitoring has been conducted of two O stars in the SMC and one in the LMC, the spectral characteristics of which place them in the Of?p category, which has been established in the Galaxy to consist of oblique magnetic rotators. All of these Magellanic stars show systematic spectral variations typical of the Of?p class, further strengthening their magnetic candidacy to the point of virtual certainty. The spectral variations are related to photometric variations derived from Optical Gravitational Lensing Experiment data by Nazé et al. in a parallel study, which yields rotational periods for two of them. Now circular spectropolarimetry is required to measure their fields, and ultraviolet spectroscopy to further characterize their low-metallicity, magnetically confined winds, in support of hydrodynamical analyses
Abdoli-Arani, A.; Ramezani-Arani, R.
2012-11-01
The dielectric permittivity tensor elements of a rotating cold collisionless plasma spheroid in an external magnetic field with toroidal and axial components are obtained. The effects of inhomogeneity in the densities of charged particles and the initial toroidal velocity on the dielectric permittivity tensor and field equations are investigated. The field components in terms of their toroidal components are calculated and it is shown that the toroidal components of the electric and magnetic fields are coupled by two differential equations. The influence of thermal and collisional effects on the dielectric tensor and field equations in the rotating plasma spheroid are also investigated. In the limiting spherical case, the dielectric tensor of a stationary magnetized collisionless cold plasma sphere is presented.
Design of Rotating Moving-Magnet-Type VCM Actuator for Miniaturized Mobile Robot
Energy Technology Data Exchange (ETDEWEB)
Shin, Bu Hyun [Hanbat Nat' l Univ., Daejeon (Korea, Republic of); Lee, Seungyop [Sogana Univ., Seoul (Korea, Republic of); Lee, Kyungmin [Korean Intellectual Property Office, Seoul (Korea, Republic of); Oh, Dongho [Chungnam Nat' l Univ., Daejeon (Korea, Republic of)
2013-12-15
A voice coil actuator with a rotating moving magnet has been developed for a miniaturized mobile robot. The actuator has simple structure comprising a magnet, a coil, and a yoke. Actuator performance is predicted using a linearized theoretical model, and dynamic performance based on the air-gap between the magnet and the coil is predicted using motor constant and restoring constant obtained through finite element simulations. The theoretical model was verified using a prototype with 60 Hz resonance and 80 Hz bandwidth. We found that an input of 1.5 V can make the actuator rotate by 20 .deg. statically. The driving configuration of the proposed actuator can be simplified because of its implementation of open-loop control.
International Nuclear Information System (INIS)
Bazaliy, Y. B.; Jones, B. A.
2002-01-01
''Spin-transfer'' torque is created when electric current is passed through metallic ferromagnets and may have interesting applications in spintronics. So far it was experimentally studied in ''collinear'' geometries, where it is difficult to predict whether magnetization will coherently rotate or spin-waves will be generated. Here we propose an easy modification of existing experiment in which the spin-polarization of incoming current will no longer be collinear with magnetization and recalculate the switching behavior of the device. We expect that a better agreement with the magnetization rotation theory will be achieved. That can be an important step in reconciling alternative points of view on the effect of spin-transfer torque
Helical waves in easy-plane antiferromagnets
Semenov, Yuriy G.; Li, Xi-Lai; Xu, Xinyi; Kim, Ki Wook
2017-12-01
Effective spin torques can generate the Néel vector oscillations in antiferromagnets (AFMs). Here, it is theoretically shown that these torques applied at one end of a normal AFM strip can excite a helical type of spin wave in the strip whose properties are drastically different from characteristic spin waves. An analysis based on both a Néel vector dynamical equation and the micromagnetic simulation identifies the direction of magnetic anisotropy and the damping factor as the two key parameters determining the dynamics. Helical wave propagation requires the hard axis of the easy-plane AFM to be aligned with the traveling direction, while the damping limits its spatial extent. If the damping is neglected, the calculation leads to a uniform periodic domain wall structure. On the other hand, finite damping decelerates the helical wave rotation around the hard axis, ultimately causing stoppage of its propagation along the strip. With the group velocity staying close to spin-wave velocity at the wave front, the wavelength becomes correspondingly longer away from the excitation point. In a sufficiently short strip, a steady-state oscillation can be established whose frequency is controlled by the waveguide length as well as the excitation energy or torque.
Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes
Energy Technology Data Exchange (ETDEWEB)
Emeriau-Viard, Constance; Brun, Allan Sacha, E-mail: constance.emeriau@cea.fr, E-mail: sacha.brun@cea.fr [Laboratoire AIM Paris-Saclay CEA/DSM—CNRS—Université Paris Diderot, IRFU/DAp CEA Paris-Saclay, F-91191 Gif-sur-Yvette Cedex (France)
2017-09-01
During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing a seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.
Energy Technology Data Exchange (ETDEWEB)
Jarboe, T. R.; Nelson, B. A.; Sutherland, D. A. [University of Washington, Seattle, Washington 98195 (United States)
2015-07-15
An analysis of imposed dynamo current drive (IDCD) [T.R. Jarboe et al., Nucl. Fusion 52 083017 (2012)] reveals: (a) current drive on closed flux surfaces seems possible without relaxation, reconnection, or other flux-surface-breaking large events; (b) the scale size of the key physics may be smaller than is often computationally resolved; (c) helicity can be sustained across closed flux; and (d) IDCD current drive is parallel to the current which crosses the magnetic field to produce the current driving force. In addition to agreeing with spheromak data, IDCD agrees with selected tokamak data.
Directory of Open Access Journals (Sweden)
N. C. LENIN
2017-01-01
Full Text Available This paper presents the application of Soft Magnetic Composite (SMC material in Outer Rotating Switched Reluctance Motor (ORSRM. The presented stator core of the Switched Reluctance Motor was made of two types of material, the classical laminated silicon steel sheet and the soft magnetic composite material. First, the stator core made of laminated steel has been analysed. The next step is to analyse the identical geometry SRM with the soft magnetic composite material, SOMALOY for its stator core. The comparisons of both cores include the calculated torque and torque ripple, magnetic conditions, simplicity of fabrication and cost. The finite element method has been used to analyse the magnetic conditions and the calculated torque. Finally, tested results shows that SMC is a better choice for SRM in terms of torque ripple and power density.
Controlling the structure of forced convective flow by means of rotating magnetic-field inductors
International Nuclear Information System (INIS)
Sorkin, M.Z.; Mozgirs, O.Kh.
1993-01-01
The forced convective flow generated by a rotating magnetic-field inductor is used in a melt as a means of controlling the transfer of mass and heat in the case of directed crystallization. An obvious advantage in using a rotating field is the generation of azimuthal twisting of the fluid, this providing for an evening out of the crystallization conditions in the azimuthal direction under nonsymmetrical boundary conditions in an actual technological process. From the standpoint of affecting the crystallization processes it would be preferable to use an inductor which would allow alteration of the intensity and of the direction of the meridional flow. Mixing in the form of velocity pulsations generated by the inductor within the melt would be if interest from the standpoint of affecting the crystallization processes, in particular to intensify the crystallization purification. The authors propose the use of a double magnetohydrodynmic rotator which consists of two rotating magnetic-field inductors, separated in altitude, with separate power supplies. The supply of power to the inductors with various current loads allows the generation of a controllable nonuniformity in field distribution and in the azimuthal velocity through the altitude and thus allows control of both the intensity and configuration of the meridional flows. The dual rotator makes it possible to purposefully control the structure of the meridional flows and the pulsation component of velocity and can be recommended for use in processes of directed crystallization as well as in crystallization purification. 4 refs., 3 figs
Generalized helicity and its time derivative
International Nuclear Information System (INIS)
Jarboe, T.R.; Marklin, G.J.
1985-01-01
Spheromaks can be sustained against resistive decay by helicity injection because they tend to obey the minimum energy principle. This principle states that a plasma-laden magnetic configuration will relax to a state of minimum energy subject to the constraint that the magnetic helicity is conserved. Use of helicity as a constraint on the minimization of energy was first proposed by Woltjer in connection with astrophysical phenomena. Helicity does decay on the resistive diffusion time. However, if helicity is created and made to flow continuoiusly into a confinement geometry, these additional linked fluxes can relax and sustain the configuration indefinitely against the resistive decay. In this paper we will present an extension of the definition of helicity to include systems where B vector can penetrate the boundary and the penetration can be varying in time. We then discuss the sustainment of RFPs and spheromaks in terms of helicity injection
Sensorless interior permanent magnet synchronous motor control with rotational inertia adjustment
Directory of Open Access Journals (Sweden)
Yongle Mao
2016-12-01
Full Text Available Mechanical model is generally required in high dynamic sensorless motor control schemes for zero phase lag estimation of rotor position and speed. However, the rotational inertia uncertainty will cause dynamic estimation errors, eventually resulting in performance deterioration of the sensorless control system. Therefore, this article proposes a high dynamic performance sensorless control strategy with online adjustment of the rotational inertia. Based on a synthetic back electromotive force model, the voltage equation of interior permanent magnet synchronous motor is transformed to that of an equivalent non-salient permanent magnet synchronous motor. Then, an extended nonlinear observer is designed for interior permanent magnet synchronous motor in the stator-fixed coordinate frame, with rotor position, speed and load torque simultaneously estimated. The effect of inaccurate rotational inertia on the estimation of rotor position and speed is investigated, and a novel rotational inertia adjustment approach that employs the gradient descent algorithm is proposed to suppress the dynamic estimation errors. The effectiveness of the proposed control strategy is demonstrated by experimental tests.
A MODEL OF MAGNETIC BRAKING OF SOLAR ROTATION THAT SATISFIES OBSERVATIONAL CONSTRAINTS
International Nuclear Information System (INIS)
Denissenkov, Pavel A.
2010-01-01
The model of magnetic braking of solar rotation considered by Charbonneau and MacGregor has been modified so that it is able to reproduce for the first time the rotational evolution of both the fastest and slowest rotators among solar-type stars in open clusters of different ages, without coming into conflict with other observational constraints, such as the time evolution of the atmospheric Li abundance in solar twins and the thinness of the solar tachocline. This new model assumes that rotation-driven turbulent diffusion, which is thought to amplify the viscosity and magnetic diffusivity in stellar radiative zones, is strongly anisotropic with the horizontal components of the transport coefficients strongly dominating over those in the vertical direction. Also taken into account is the poloidal field decay that helps to confine the width of the tachocline at the solar age. The model's properties are investigated by numerically solving the azimuthal components of the coupled momentum and magnetic induction equations in two dimensions using a finite element method.
Superconducting magnets for induction linac phase-rotation in a neutrino factory
International Nuclear Information System (INIS)
Green, M.A.; Yu, S.
2001-01-01
The neutrino factory[1-3] consists of a target section where pions are produced and captured in a solenoidal magnetic field. Pions in a range of energies from 100 Mev to 400 MeV decay into muons in an 18-meter long channel of 1.25 T superconducting solenoids. The warm bore diameter of these solenoids is about 600 mm. The phase rotation section slows down the high-energy muon and speeds up the low energy muons to an average momentum of 200 MeV/c. The phase-rotation channel consists of three induction linac channels with a short cooling section and a magnetic flux reversal section between the first and second induction linacs and a drift space between the second and third induction linacs. The length of the phase rotation channel will be about 320 meters. The superconducting coils in the channel are 0.36 m long with a gap of 0.14 m between the coils. The magnetic induction within the channel will be 1.25. For 260 meters of the 320-meter long channel, the solenoids are inside the induction linac. This paper discusses the design parameters for the superconducting solenoids in the neutrino factory phase-rotation channel
New Methodology For Use in Rotating Field Nuclear MagneticResonance
Energy Technology Data Exchange (ETDEWEB)
Jachmann, Rebecca C. [Univ. of California, Berkeley, CA (United States)
2007-01-01
High-resolution NMR spectra of samples with anisotropicbroadening are simplified to their isotropic spectra by fast rotation ofthe sample at the magic angle 54.7 circ. This dissertation concerns thedevelopment of novel Nuclear Magnetic Resonance (NMR) methodologies basedwhich would rotate the magnetic field instead of the sample, rotatingfield NMR. It provides an over of the NMR concepts, procedures, andexperiments needed to understand the methodologies that will be used forrotating field NMR. A simple two-dimensional shimming method based onharmonic corrector rings which can provide arbitrary multiple ordershimming corrections were developed for rotating field systems, but couldbe used in shimming other systems as well. Those results demonstrate, forexample, that quadrupolar order shimming improves the linewidth by up toan order of magnitude. An additional order of magnitude reduction is inprinciple achievable by utilizing this shimming method for z-gradientcorrection and higher order xy gradients. A specialized pulse sequencefor the rotating field NMR experiment is under development. The pulsesequence allows for spinning away from the magic angle and spinningslower than the anisotropic broadening. This pulse sequence is acombination of the projected magic angle spinning (p-MAS) and magic angleturning (MAT) pulse sequences. This will be useful to rotating field NMRbecause there are limits on how fast a field can be spun and spin at themagic angle is difficult. One of the goals of this project is forrotating field NMR to be used on biological systems. The p-MAS pulsesequence was successfully tested on bovine tissue samples which suggeststhat it will be a viable methodology to use in a rotating field set up. Aside experiment on steering magnetic particle by MRI gradients was alsocarried out. Some movement was seen in these experiment, but for totalcontrol over steering further experiments would need to bedone.
New Methodology For Use in Rotating Field Nuclear MagneticResonance
Energy Technology Data Exchange (ETDEWEB)
Jachmann, Rebecca C. [Univ. of California, Berkeley, CA (United States)
2007-05-18
High-resolution NMR spectra of samples with anisotropicbroadening are simplified to their isotropic spectra by fast rotation ofthe sample at the magic angle 54.7 circ. This dissertation concerns thedevelopment of novel Nuclear Magnetic Resonance (NMR) methodologies basedwhich would rotate the magnetic field instead of the sample, rotatingfield NMR. It provides an over of the NMR concepts, procedures, andexperiments needed to understand the methodologies that will be used forrotating field NMR. A simple two-dimensional shimming method based onharmonic corrector rings which can provide arbitrary multiple ordershimming corrections were developed for rotating field systems, but couldbe used in shimming other systems as well. Those results demonstrate, forexample, that quadrupolar order shimming improves the linewidth by up toan order of magnitude. An additional order of magnitude reduction is inprinciple achievable by utilizing this shimming method for z-gradientcorrection and higher order xy gradients. A specialized pulse sequencefor the rotating field NMR experiment is under development. The pulsesequence allows for spinning away from the magic angle and spinningslower than the anisotropic broadening. This pulse sequence is acombination of the projected magic angle spinning (p-MAS) and magic angleturning (MAT) pulse sequences. This will be useful to rotating field NMRbecause there are limits on how fast a field can be spun and spin at themagic angle is difficult. One of the goals of this project is forrotating field NMR to be used on biological systems. The p-MAS pulsesequence was successfully tested on bovine tissue samples which suggeststhat it will be a viable methodology to use in a rotating field set up. Aside experiment on steering magnetic particle by MRI gradients was alsocarried out. Some movement was seen in these experiment, but for totalcontrol over steering further experiments would need to bedone.
Analysis on the Viscous Pumping in a Magnetic Fluid Seal Under a Rotating Load and the Seal Design
長屋, 幸助; 大沼, 浩身; 佐藤, 淳
1990-01-01
This paper discusses effects of viscous pumping in a magnetic fluid seal under a rotating load. The Reynolds equation was presented for the seal based on magnetic fluid mechanics, and the expressions for obtaining pressures in the seal, eccentricities of the rotating shaft due to the viscous pumping and seal pressures were given. Numerical Calculations were carried out for some sample problems, and the effect of magnetic flux densities on the pressure in the seal and the seal pressures were c...
DEFF Research Database (Denmark)
Cheng, Shuangyin; Luo, Derong; Huang, Shoudao
2015-01-01
This study presents an investigation into the control of an axial-flux permanent magnet synchronous machine (PMSM) with contra-rotating rotors fed by a single inverter, which corresponds to two PMSM connected in series. In this study, the mathematic model of the PMSM with contra-rotating rotors...... water vehicle propulsions. The control strategy is implemented on a DSP 28335 processor featured hardware platform and is tested on a 1.2 kW prototype machine. Experimental results validate the correctness of the analysis and control strategy....
A Method to Measure the Transverse Magnetic Field and Orient the Rotational Axis of Stars
Energy Technology Data Exchange (ETDEWEB)
Leone, Francesco; Scalia, Cesare; Gangi, Manuele; Giarrusso, Marina [Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, I-95123 Catania (Italy); Munari, Matteo; Scuderi, Salvatore; Trigilio, Corrado [INAF—Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania (Italy); Stift, Martin J. [Armagh Observatory, College Hill, Armagh BT61 9DG. Northern Ireland (United Kingdom)
2017-10-20
Direct measurements of stellar magnetic fields are based on the splitting of spectral lines into polarized Zeeman components. With a few exceptions, Zeeman signatures are hidden in data noise, and a number of methods have been developed to measure the average, over the visible stellar disk, of longitudinal components of the magnetic field. At present, faint stars are only observable via low-resolution spectropolarimetry, which is a method based on the regression of the Stokes V signal against the first derivative of Stokes I . Here, we present an extension of this method to obtain a direct measurement of the transverse component of stellar magnetic fields by the regression of high-resolution Stokes Q and U as a function of the second derivative of Stokes I . We also show that it is possible to determine the orientation in the sky of the rotation axis of a star on the basis of the periodic variability of the transverse component due to its rotation. The method is applied to data, obtained with the Catania Astrophysical Observatory Spectropolarimeter along the rotational period of the well known magnetic star β CrB.
Directory of Open Access Journals (Sweden)
Manh-Huong Phan
2016-12-01
Full Text Available A new type of rotary coolers based on the temperature change (ΔTrot of an anisotropic superconductor when rotated in a constant magnetic field is proposed. We show that at low temperature the Sommerfeld coefficient γ(B,Θ of a single crystalline superconductor, such as MgB2 and NbS2, sensitively depends on the applied magnetic field (B and the orientation of the crystal axis (Θ, which is related to the electronic entropy (SE and temperature (T via the expression: SE=γT. A simple rotation of the crystal from one axis to one another in a constant magnetic field results in a change in γ and hence SE: ΔSE=ΔγT. A temperature change −ΔTrot ∼ 0.94 K from a bath temperature of 2.5 K is achieved by simply rotating the single crystal MgB2 by 90° with respect to the c-axis direction in a fixed field of 2 T. ΔTrot can be tuned by adjusting the strength of B within a wide magnetic field range. Our study paves the way for development of new materials and cryogenic refrigerators that are potentially more energy-efficient, simplified, and compact.
Hyperthermia with rotating magnetic nanowires inducing heat into tumor by fluid friction
Energy Technology Data Exchange (ETDEWEB)
Egolf, Peter W.; Pawlowski, Anne-Gabrielle; Tsague, Paulin; Marco, Bastien de; Bovy, William; Tucev, Sinisa [Institute of Thermal Sciences and Engineering, University of Applied Sciences of Western Switzerland, CH 1401 Yverdon-les-Bains (Switzerland); Shamsudhin, Naveen, E-mail: snaveen@ethz.ch; Pané, Salvador; Pokki, Juho; Ansari, M. H. D.; Nelson, Bradley J. [Multi-Scale Robotics Lab, Institute of Robotics and Intelligent Systems, ETH Zurich, CH 8092 Zurich (Switzerland); Vuarnoz, Didier [Ecole Polytechnique Fédérale de Lausanne (EPFL), EPFL Fribourg, CH 1701 Fribourg (Switzerland)
2016-08-14
A magnetic hyperthermia cancer treatment strategy that does not operate by means of conventional heating mechanisms is presented. The proposed approach consists of injecting a gel with homogeneously distributed magnetic nanowires into a tumor. Upon the application of a low-frequency rotating or circularly polarized magnetic field, nanowires spin around their center of viscous drag due to torque generated by shape anisotropy. As a result of external rotational forcing and fluid friction in the nanoparticle's boundary layer, heating occurs. The nanowire dynamics is theoretically and experimentally investigated, and different feasibility proofs of the principle by physical modeling, which adhere to medical guidelines, are presented. The magnetic nanorotors exhibit rotations and oscillations with quite a steady center of gravity, which proves an immobile behavior and guarantees a time-independent homogeneity of the spatial particle distribution in the tumor. Furthermore, a fluid dynamic and thermodynamic heating model is briefly introduced. This model is a generalization of Penne's model that for this method reveals theoretic heating rates that are sufficiently high, and fits well into medical limits defined by present standards.
A special correcting winding for the l = 2 torsatron with split-type helical coils
International Nuclear Information System (INIS)
Kotenko, V.G.
2012-01-01
A split-type special correcting winding (split-type SCW) for the l = 2 torsatron toroidal magnetic system with split-type helical coils is considered. The split-type SCW gives the possibility of controlling the position of the magnetic surface configuration in the direction perpendicular to the torus equatorial plane. Numerical simulations were carried out to investigate the influence of the split-type SCW magnetic field on centered and distant relative to the torus surface magnetic surface configuration with a plane magnetic axis, being promising for the fusion reactor. The configuration is realized in the l = 2 torsatron with split-type helical coils and with the coils of an additional toroidal magnetic field. The calculations show that the split-type SCW magnetic field influence on the initial magnetic surface configuration leads mainly to the magnetic surface configuration displacement along the straight z axis of torus rotation. The displacement of ∼0.1a, a is the minor radius of the torus, has no critical effect on the magnetic surface parameters. An idea on the split-type SCW magnetic field structure is obtained by numerical simulations of the effect of this field as a minority magnetic field imposed on the magnetic field of a well-known configuration. The split-type SCW magnetic field is directed, predominantly along the major radius of the torus within its volume. The displacement range of the closed magnetic surface configuration depends on the split-type SCW magnetic field value.
International Nuclear Information System (INIS)
Dahmani, Ch.; Mykhaylyk, O.; Helling, Fl.; Götz, St.; Weyh, Th.; Herzog, H.-G.; Plank, Ch.
2013-01-01
The association of magnetic nanoparticles with gene delivery vectors in combination with the use of gradient magnetic fields (magnetofection) enables improved and synchronised gene delivery to cells. In this paper, we report a system comprising rotating permanent magnets to generate defined magnetic field pulses with frequencies from 2.66 to 133 Hz and a field amplitude of 190 or 310 mT at the location of the cells. Low-frequency pulses of 2.66–10 Hz with a magnetic flux density of 190 mT were applied to the examined cells for 30–120 s after magnetofection. These pulses resulted in a 1.5–1.9-fold enhancement in the transfection efficiency compared with magnetofection with only a static magnetic field in both adherent and suspension cells. The magnetic field amplitudes of 190 and 310 mT had similar effects on the transfection efficacy. No increase in the percentage of transgene-expressing suspension cells and no cytotoxic effects (based on the results of the MTT assay) were observed after applying alternating magnetic fields. - Highlights: ► We developed a magnetic system capable of generating defined magnetic pulses based on permanent magnets. ► The main advantage of the system is the lack of heat-induced fluctuations in the working parameters. ► Our system succeeded in enhancing the transfection of adherent human lung epithelial cells and human suspension cells. ► The enhancement in the transfection efficiency compared with static magnetic field is due to the magnetic field pulses. ► The approach could be used as a complementary method for drug targeting
Monte-Carlo calculation of perpendicular neutral-beam injection in helical systems
International Nuclear Information System (INIS)
Hanatani, K.; Wakatani, M.; Uo, K.
1981-01-01
The effect of a helical field ripple on the slowing-down process of the fast ions created by neutral injection is investigated numerically. For this purpose, the guiding-centre orbits are followed in a model magnetic field without plasma current, on the assumption that the slowing-down process is to be classical. Optimum injection angles in two types of helical magnetic traps are compared. One is the Heliotron-E configuration with a large rotational transform and deep helical ripple; the other one is the conventional stellarator field with a small rotational transform and shallow helical ripple. In contrast to the stellarator, the heating efficiency as calculated for Heliotron-E does not decrease monotonically when the injection angle is perpendicular to the toroidal direction; a heating efficiency of above 70% was obtained for perpendicular injection into a high-density plasma with negligible charge-exchange loss. The difference in heating efficiency versus injection angle between heliotron and conventional stellarator fields is explained by a difference in drift motion of the helically trapped fast ions. (author)
Helically symmetric experiment, (HSX) goals, design and status
International Nuclear Information System (INIS)
Anderson, F.S.B.; Almagri, A.F.; Anderson, D.T.; Matthews, P.G.; Talmadge, J.N.; Shohet, J.L.
1995-01-01
HSX is a quasi-helically symmetric (QHS) stellarator currently under construction at the Torsatron-Stellarator Laboratory of the University of Wisconsin-Madison. This device is unique in its magnetic design in that the magnetic field spectrum possesses only a single dominant (helical) component. This design avoids the large direct orbit losses and the low-collisionality neoclassical losses associated with conventional stellarators. The restoration of symmetry to the confining magnetic field makes the neoclassical confinement in this device analogous to an axisymmetric q=1/3 tokamak. The HSX device has been designed with a clear set of primary physics goals: demonstrate the feasibility of construction of a QHS device, examine single particle confinement of injected ions with regard to magnetic field symmetry breaking, compare density and temperature profiles in this helically symmetric system to those for axisymmetric tokamaks and conventional stellarators, examine electric fields and plasma rotation with edge biasing in relation to L-H transitions in symmetric versus non-symmetric stellarator systems, investigate QHS effects on 1/v regime electron confinement, and examine how greatly-reduced neoclassical electron thermal conductivity compares to the experimental χ e profile. 3 refs., 4 figs., 1 tab
Energy Technology Data Exchange (ETDEWEB)
Abo-Dahab, S. M. [Taif University, Taif (Saudi Arabia); Abd-Alla, A. M. [SVU, Qena (Egypt); Khan, Aftab [Sohag University, Sohag (Egypt)
2015-08-15
The aim of this paper is to study the propagation of surface waves in a rotating fibre-reinforced viscoelastic media of higher order under the influence of magnetic field. The general surface wave speeds derived to study the effects of rotation and magnetic field on surface waves. Particular cases for Stoneley, Love and Rayleigh waves are also discussed and dispersion relation for the waves has been deduced. The results obtained in this investigation are more general in the sense that some earlier published results are obtained from our result as special cases. For order zero our results are well agreement to fibre-reinforced materials. Also by neglecting the reinforced elastic parameters, the results reduce to well known isotropic medium. It is observed that in a rotating medium the surface waves are dispersive. Also magnetic effects play a significant roll. It is observed that Love wave remain unaffected in a rotating medium but remain under the influence of magnetic field. Rayleigh waves are affected by rotation and magnetic field whereas Stoneley waves are independent of Maxwell stresses. It is also observed that, surface waves cannot propagate in a fast rotating medium or in the presence of magnetic field of high intensity. Numerical results for particular materials are given and illustrated graphically. The results indicate that the effect of rotation and magnetic field are very pronounced.
International Nuclear Information System (INIS)
Abo-Dahab, S. M.; Abd-Alla, A. M.; Khan, Aftab
2015-01-01
The aim of this paper is to study the propagation of surface waves in a rotating fibre-reinforced viscoelastic media of higher order under the influence of magnetic field. The general surface wave speeds derived to study the effects of rotation and magnetic field on surface waves. Particular cases for Stoneley, Love and Rayleigh waves are also discussed and dispersion relation for the waves has been deduced. The results obtained in this investigation are more general in the sense that some earlier published results are obtained from our result as special cases. For order zero our results are well agreement to fibre-reinforced materials. Also by neglecting the reinforced elastic parameters, the results reduce to well known isotropic medium. It is observed that in a rotating medium the surface waves are dispersive. Also magnetic effects play a significant roll. It is observed that Love wave remain unaffected in a rotating medium but remain under the influence of magnetic field. Rayleigh waves are affected by rotation and magnetic field whereas Stoneley waves are independent of Maxwell stresses. It is also observed that, surface waves cannot propagate in a fast rotating medium or in the presence of magnetic field of high intensity. Numerical results for particular materials are given and illustrated graphically. The results indicate that the effect of rotation and magnetic field are very pronounced.
Reyes, Bryan A; Hull, Brandon R; Kurth, Alexander B; Kukowski, Nathan R; Mulligan, Edward P; Khazzam, Michael S
2017-11-01
Many patients with rotator cuff tears suffer from nocturnal shoulder pain, resulting in sleep disturbance. To determine whether rotator cuff tear size correlated with sleep disturbance in patients with full-thickness rotator cuff tears. Cross-sectional study; Level of evidence, 3. Patients with a diagnosis of unilateral full-thickness rotator cuff tears (diagnosed via magnetic resonance imaging [MRI]) completed the Pittsburgh Sleep Quality Index (PSQI), a visual analog scale (VAS) quantifying their shoulder pain, and the American Shoulder and Elbow Surgeons (ASES) questionnaire. Shoulder MRI scans were analyzed for anterior-posterior tear size (mm), tendon retraction (mm), Goutallier grade (0-4), number of tendons involved (1-4), muscle atrophy (none, mild, moderate, or severe), and humeral head rise (present or absent). Bivariate correlations were calculated between the MRI characteristics and baseline survey results. A total of 209 patients with unilateral full-thickness rotator cuff tears were included in this study: 112 (54%) female and 97 (46%) male (mean age, 64.1 years). On average, shoulder pain had been present for 24 months. The mean PSQI score was 9.8, and the mean VAS score was 5.0. No significant correlations were found between any of the rotator cuff tear characteristics and sleep quality. Only tendon retraction had a significant correlation with pain. Although rotator cuff tears are frequently associated with nocturnal pain and sleep disruption, this study demonstrated that morphological characteristics of full-thickness rotator cuff tears, such as size and tendon retraction, do not correlate with sleep disturbance and have little to no correlation with pain levels.
International Nuclear Information System (INIS)
Toi, K; Yamamoto, S; Nakajima, N; Ohdachi, S; Sakakibara, S; Osakabe, M; Murakami, S; Watanabe, K Y; Goto, M; Kawahata, K; Kolesnichenko, Ya I; Masuzaki, S; Morita, S; Narihara, K; Narushima, Y; Takeiri, Y; Tanaka, K; Tokuzawa, T; Yamada, H; Yamada, I; Yamazaki, K
2004-01-01
In the Large Helical Device (LHD), energetic ion driven Alfven eigenmodes (AEs) and their impact on energetic ion transport have been studied. The magnetic configuration of the LHD is three-dimensional and has negative magnetic shear over a whole plasma radius in the low beta regime. These features introduce the characteristic structures of the shear Alfven spectrum. In particular, a core-localized type of toroidicity-induced AE (TAE) is most likely because the TAE gap frequency rapidly increases towards the plasma edge. Moreover, helicity-induced AEs (HAEs) can be generated through a toroidal mode coupling as well as poloidal one in the three-dimensional configuration. The following experimental results have been obtained in LHD plasmas heated by tangential neutral beam injection: (1) observation of core-localized TAEs having odd as well as even parity, (2) eigenmode transition of the core-localized TAE to global AEs (GAEs), which phenomenon is very similar to that in a reversed shear tokamak, (3) observation of HAEs of which the frequency is about eight times higher than the TAE gap frequency, (4) enhanced radial transport/loss of energetic ions caused by bursting TAEs in a relatively high beta regime, and (5) seed formation of internal transport barriers induced by TAE-induced energetic ion transport. These results will be important and interesting information for AE physics in toroidal plasmas
A Peristaltic Micro Pump Driven by a Rotating Motor with Magnetically Attracted Steel Balls
Directory of Open Access Journals (Sweden)
Zhaoying Zhou
2009-04-01
Full Text Available In this paper, we present a membrane peristaltic micro pump driven by a rotating motor with magnetically attracted steel balls for lab-on-a-chip applications. The fabrication process is based on standard soft lithography technology and bonding of a PDMS layer with a PMMA substrate. A linear flow rate range ~490 μL/min was obtained by simply varying the rotation speed of a DC motor, and a maximum back pressure of 592 Pa was achieved at a rotation speed of 43 rpm. The flow rate of the pump can also be adjusted by using steel balls with different diameters or changing the number of balls. Nevertheless, the micro pump can also work in high speed mode. A high back pressure up to 10 kPa was achieved at 500 rpm using a high speed DC motor, and an utmost flow rate up to 5 mL/min was reached.
Measurements of plasma rotation in an axially magnetized MPD arc-jet
Energy Technology Data Exchange (ETDEWEB)
Tobari, Hiroyuki; Ashino, Masashi; Yoshino, Kyohei; Sagi, Yukiko; Yoshinuma, Mikirou; Hattori, Kunihiko; Ando, Akira; Inutake, Masaaki [Department of Electrical Engineering, Graduate School of Engineering, Tohoku University, Sendai, Miyagi (Japan)
2001-01-24
Characteristics of an axially magnetized MPD (magneto-plasma-dynamic) arcjet plasma are investigated by spectroscopy on the HITOP (High density of Tohoku Plasma) device in Tohoku University. Plasma flow and rotational velocity and temperature of He ion and atom near the muzzle region of MPD arcjet are measured by Doppler shift and broadening of the HeI ({lambda}=578.56 nm) and HeII ({lambda}=468.58 nm) lines. From the measured radial profile of rotational velocity and temperature of He ion, the radial profiles of electrical field and space potential are calculated and it has been found that the potential profile in the core region is parabolic, which shows the plasma rotates as a rigid body. (author)
Rotating and propagating LIB stabilized by self-induced magnetic field
International Nuclear Information System (INIS)
Murakami, H.; Aoki, T.; Kawata, S.; Niu, K.
1984-01-01
Rotating motion of a propagating LIB is analyzed in order to suppress the mixed mode of the Kelvin-Helmholtz instability, the tearing instability and the sausage instability by the action of a self-induced magnetic field in the axial direction. The beams are assumed to be charge-neutralized but not current-neutralized. The steady-state solutions of a propagating LIB with rotation are first obtained numerically. Through the dispersion relation with respect to the ikonal type of perturbations, which are added to the steady-state solutions, the growth rates of instabilities appearing in an LIB are obtained. It is concluded that if the mean rotating velocity of an LIB is comparable to the propagation velocity, the instability disappears in the propagating ion beam. (author)
Functional and magnetic resonance imaging evaluation after single-tendon rotator cuff reconstruction
DEFF Research Database (Denmark)
Knudsen, H B; Gelineck, J; Søjbjerg, Jens Ole
1999-01-01
The aim of this study was to investigate tendon integrity after surgical repair of single-tendon rotator cuff lesions. In 31 patients, 31 single-tendon repairs were evaluated. Thirty-one patients were available for clinical assessment and magnetic resonance imaging (MRI) at follow-up. A standard...... series of MR images was obtained for each. The results of functional assessment were scored according to the system of Constant. According to MRI evaluation, 21 (68%) patients had an intact or thinned rotator cuff and 10 (32%) had recurrence of a full-thickness cuff defect at follow-up. Patients...... with an intact or thinned rotator cuff had a median Constant score of 75.5 points; patients with a full-thickness cuff defect had a median score of 62 points. There was no correlation between tendon integrity on postoperative MR images and functional outcome. Patients with intact or thinned cuffs did not have...
The influence of magnetic field on the inertial deposition of a particle on a rotating disk
International Nuclear Information System (INIS)
Tsatsin, P O; Beskachko, V P
2008-01-01
The problem of inertial deposition attracts considerable attention in the connection with the separating of detrimental impurities and the refining of liquid metals. In the present investigation the deposition of particles suspended in a conducting melt on the rotating disk in the presence of axial uniform magnetic field is considered. The field of the fluid velocities is computed by means of the MHD-analogue of Karman reduction, which makes possible to reduce initial governing nonlinear partial differential equations to a two-point boundary value problem for the set of ordinary differential equations. The influence of magnetic field on dia-and paramagnetic particle deposition effect was estimated. The results reveal that magnetic field has significant effect on particle parameters, especially for magnetic particles
North–South Asymmetry of the Rotation of the Solar Magnetic Field
Xie, Jinglan; Shi, Xiangjun; Qu, Zhining
2018-03-01
Using the rotation rates of the solar magnetic field during solar cycles 21 to 23 obtained by Chu et al. by analyzing the synoptic magnetic maps produced by the NSO/Kitt Peak and SOHO/MDI during the years 1975 to 2008, the temporal variation of the equatorial rotation rate (A) and the latitude gradient of rotation (B) in the northern and southern hemispheres are studied separately. The results indicate that the rotation is more differential (about 4.3%) in the southern hemisphere in the considered time frame. It is found that the north–south asymmetry of A and the asymmetry of B show increasing trends in the considered time frame, while the north–south asymmetry of the solar activity shows a decreasing trend. There exists a significant negative correlation (at 95% confidence level) between the asymmetry of B and the asymmetry of the solar activity, and this may be due to stronger magnetic activity in a certain hemisphere that may suppress the differential rotation to some extent. The periodicities in the variation of A and B are also studied, and periods of about 5.0 and 10.5 yr (5.5 and 10.4 yr) can be found for the variation of the northern (southern) hemisphere B. Moreover, the north–south asymmetry of A and the asymmetry of B have similar periods of about 2.6–2.7 and 5.2–5.3 yr. Further, cross-correlation analysis indicates that there exists a phase difference (about eight months) between the northern and southern hemisphere B, and this means that the northern hemisphere B generally leads by about eight months.
Waltz, R. E.; Waelbroeck, F. L.
2012-03-01
Static external resonant magnetic field perturbations (RMPs) have been added to the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J. Comp. Phys. 186, 545 (2003)]. This allows nonlinear gyrokinetic simulations of the nonambipolar radial current flow jr, and the corresponding j→×B→ plasma torque (density) R[jrBp/c], induced by magnetic islands that break the toroidal symmetry of a tokamak. This extends the previous GYRO formulation for the transport of toroidal angular momentum (TAM) [R. E. Waltz, G. M. Staebler, J. Candy, and F. L. Hinton, Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)]. The focus is on electrostatic full torus radial slice simulations of externally induced q =m/n=6/3 islands with widths 5% of the minor radius or about 20 ion gyroradii. Up to moderately strong E ×B rotation, the island torque scales with the radial electric field at the resonant surface Er, the island width w, and the intensity I of the high-n micro-turbulence, as Erw√I . The radial current inside the island is carried (entirely in the n =3 component) and almost entirely by the ion E ×B flux, since the electron E ×B and magnetic flutter particle fluxes are cancelled. The net island torque is null at zero Er rather than at zero toroidal rotation. This means that while the expected magnetic braking of the toroidal plasma rotation occurs at strong co- and counter-current rotation, at null toroidal rotation, there is a small co-directed magnetic acceleration up to the small diamagnetic (ion pressure gradient driven) co-rotation corresponding to the zero Er and null torque. This could be called the residual stress from an externally induced island. At zero Er, the only effect is the expected partial flattening of the electron temperature gradient within the island. Finite-beta GYRO simulations demonstrate almost complete RMP field screening and n =3 mode unlocking at strong Er.
Test of Magnetic Rotation near the band head in ^197,198Pb
Krücken, R.; Clark, R. M.; Deleplanque, M. A.; Diamond, R. M.; Fallon, P.; Macchiavelli, A. O.; Lee, I. Y.; Schmid, G. J.; Stephens, F. S.; Vetter, K.; Dewald, A.; Peusquens, R.; von Brentano, P.; Baldsiefen, G.; Chmel, S.; Hübel, H.; Becker, J. A.; Bernstein, L. A.; Hauschild, K.
1998-04-01
The concept of magnetic rotation is tested near the band head of shears-bands in ^197,198Pb by means of a lifetime experiment with the recoil distance method (RDM). The experiment was performed using the Gammasphere array in conjunction with the Cologne Plunger. The B(M1) values extracted from the measured lifetimes can prove the applicability of the concept of magnetic rotation for the states near the band head of these shears bands. The RDM results are compared with tilted axis cranking and shell model calculations. Furthermore the results will be used to test earlier DSAM lifetime measurements for states at higher spins. Preliminary results of this topic will be presented. This work is supported by DOE grant numbers DE-AC03-76SF00098 (LBNL), DE-FG02-91ER40609 (Yale), W-7405-ENG-48 (LLNL) and by the German BMBF for Cologne (No. 06 OK 668) and Bonn.
Large-scale flows, sheet plumes and strong magnetic fields in a rapidly rotating spherical dynamo
Takahashi, F.
2011-12-01
Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell is investigated. Bearing dynamos of the Eartn and planets in mind, the Ekman number is set at 10-5. A strong dipolar solution with magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, convection structure consists of a few large-scale retrograde flows in the azimuthal direction and sporadic thin sheet-like plumes. The magnetic field is amplified through stretching of magnetic lines, which occurs typically through three types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, and the prograde azimuthal flow near the rim of the tangent cylinder induced by the downwelling flow. It is found that either structure of current loops or current sheets is accompanied in each flow structure. Current loops emerge as a result of stretching the magnetic lines along the magnetic field, wheres the current sheets are formed to counterbalance the Coriolis force. Convection structure and processes of magnetic field generation found in the present model are distinct from those in models at larger/smaller Ekman number.
Demonstrating multibit magnetic memory in the Fe8 high-spin molecule by muon spin rotation
Shafir, Oren; Keren, Amit; Maegawa, Satoru; Ueda, Miki; Amato, Alex; Baines, Chris
2005-09-01
We develop a method to detect the quantum nature of high-spin molecules using muon spin rotation and a three-step field cycle ending always with the same field. We use this method to demonstrate that the Fe8 molecule can remember six (possibly eight) different histories (bits). A wide range of fields can be used to write a particular bit, and the information is stored in discrete states. Therefore, Fe8 can be used as a model compound for multibit magnetic memory. Our experiment also paves the way for magnetic quantum tunneling detection in films.
Directory of Open Access Journals (Sweden)
Peter Cimalla
2017-04-01
Full Text Available In this paper, we present a reliable and robust method for magnetomotive optical coherence tomography (MM-OCT imaging of single cells labeled with iron oxide particles. This method employs modulated longitudinal and transverse magnetic fields to evoke alignment and rotation of anisotropic magnetic structures in the sample volume. Experimental evidence suggests that magnetic particles assemble themselves in elongated chains when exposed to a permanent magnetic field. Magnetomotion in the intracellular space was detected and visualized by means of 3D OCT as well as laser speckle reflectometry as a 2D reference imaging method. Our experiments on mesenchymal stem cells embedded in agar scaffolds show that the magnetomotive signal in rotational MM-OCT is significantly increased by a factor of ~3 compared to previous pulsed MM-OCT, although the solenoid’s power consumption was 16 times lower. Finally, we use our novel method to image ARPE-19 cells, a human retinal pigment epithelium cell line. Our results permit magnetomotive imaging with higher sensitivity and the use of low power magnetic fields or larger working distances for future three-dimensional cell tracking in target tissues and organs.
Magnetic fields produced by rotating symmetrical bodies with homogeneous surface charge density
International Nuclear Information System (INIS)
Espejel-Morales, R; Murguía-Romero, G; Calles, A; Cabrera-Bravo, E; Morán-López, J L
2016-01-01
We present a numerical calculation for the stationary magnetic field produced by different rotating bodies with homogeneous and constant surface charge density. The calculation is done by superposing the magnetic field produced by a set of loops of current which mimic the magnetic field produced by belts of current defined by slices of fixed width. We consider the cases of a sphere, ellipsoids, open and closed cylinders and a combination of these in a dumbbell -like shell. We also plot their magnetic field lines using a technique that make use of the Runge–Kutta fourth-order method. Up to our knowledge, the case of closed cylinders was not calculated before. In contrast to previous results, we find that the magnetic field inside finite hollow bodies is homogeneous only in the case of a sphere. This is consequence of the fact that, for the sphere, the surface of any slice taken perpendicularly to the rotation axis, depends only on its thickness, like in the case of an infinite cylinder. (paper)
SOLAR MAGNETIZED TORNADOES: ROTATIONAL MOTION IN A TORNADO-LIKE PROMINENCE
International Nuclear Information System (INIS)
Su, Yang; Veronig, Astrid; Temmer, Manuela; Vanninathan, Kamalam; Gömöry, Peter; Wang, Tongjiang; Gan, Weiqun; Li, YouPing
2014-01-01
Su et al. proposed a new explanation for filament formation and eruption, where filament barbs are rotating magnetic structures driven by underlying vortices on the surface. Such structures have been noticed as tornado-like prominences when they appear above the limb. They may play a key role as the source of plasma and twist in filaments. However, no observations have successfully distinguished rotational motion of the magnetic structures in tornado-like prominences from other motions such as oscillation and counter-streaming plasma flows. Here we report evidence of rotational motions in a tornado-like prominence. The spectroscopic observations in two coronal lines were obtained from a specifically designed Hinode/EIS observing program. The data revealed the existence of both cold and million-degree-hot plasma in the prominence leg, supporting the so-called prominence-corona transition region. The opposite velocities at the two sides of the prominence and their persistent time evolution, together with the periodic motions evident in SDO/AIA dark structures, indicate a rotational motion of both cold and hot plasma with a speed of ∼5 km s –1
Solar Magnetized Tornadoes: Rotational Motion in a Tornado-like Prominence
Su, Yang; Gömöry, Peter; Veronig, Astrid; Temmer, Manuela; Wang, Tongjiang; Vanninathan, Kamalam; Gan, Weiqun; Li, YouPing
2014-04-01
Su et al. proposed a new explanation for filament formation and eruption, where filament barbs are rotating magnetic structures driven by underlying vortices on the surface. Such structures have been noticed as tornado-like prominences when they appear above the limb. They may play a key role as the source of plasma and twist in filaments. However, no observations have successfully distinguished rotational motion of the magnetic structures in tornado-like prominences from other motions such as oscillation and counter-streaming plasma flows. Here we report evidence of rotational motions in a tornado-like prominence. The spectroscopic observations in two coronal lines were obtained from a specifically designed Hinode/EIS observing program. The data revealed the existence of both cold and million-degree-hot plasma in the prominence leg, supporting the so-called prominence-corona transition region. The opposite velocities at the two sides of the prominence and their persistent time evolution, together with the periodic motions evident in SDO/AIA dark structures, indicate a rotational motion of both cold and hot plasma with a speed of ~5 km s-1.
SOLAR MAGNETIZED TORNADOES: ROTATIONAL MOTION IN A TORNADO-LIKE PROMINENCE
Energy Technology Data Exchange (ETDEWEB)
Su, Yang; Veronig, Astrid; Temmer, Manuela; Vanninathan, Kamalam [IGAM-Kanzelhöhe Observatory, Institute of Physics, University of Graz, Universitätsplatz 5, A-8010 Graz (Austria); Gömöry, Peter [Astronomical Institute of the Slovak Academy of Sciences, SK-05960 Tatranská Lomnica (Slovakia); Wang, Tongjiang [Department of Physics, the Catholic University of America, Washington, DC 20064 (United States); Gan, Weiqun; Li, YouPing, E-mail: yang.su@uni-graz.at [Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
2014-04-10
Su et al. proposed a new explanation for filament formation and eruption, where filament barbs are rotating magnetic structures driven by underlying vortices on the surface. Such structures have been noticed as tornado-like prominences when they appear above the limb. They may play a key role as the source of plasma and twist in filaments. However, no observations have successfully distinguished rotational motion of the magnetic structures in tornado-like prominences from other motions such as oscillation and counter-streaming plasma flows. Here we report evidence of rotational motions in a tornado-like prominence. The spectroscopic observations in two coronal lines were obtained from a specifically designed Hinode/EIS observing program. The data revealed the existence of both cold and million-degree-hot plasma in the prominence leg, supporting the so-called prominence-corona transition region. The opposite velocities at the two sides of the prominence and their persistent time evolution, together with the periodic motions evident in SDO/AIA dark structures, indicate a rotational motion of both cold and hot plasma with a speed of ∼5 km s{sup –1}.
Calorimetric method of ac loss measurement in a rotating magnetic field
Energy Technology Data Exchange (ETDEWEB)
Ghoshal, P. K. [Oxford Instruments NanoScience, Abingdon, Oxfordshire OX13 5QX (United Kingdom); Coombs, T. A.; Campbell, A. M. [Department of Engineering, Electrical Engineering, University of Cambridge, Cambridge CB3 0FA (United Kingdom)
2010-07-15
A method is described for calorimetric ac-loss measurements of high-T{sub c} superconductors (HTS) at 80 K. It is based on a technique used at 4.2 K for conventional superconducting wires that allows an easy loss measurement in parallel or perpendicular external field orientation. This paper focuses on ac loss measurement setup and calibration in a rotating magnetic field. This experimental setup is to demonstrate measuring loss using a temperature rise method under the influence of a rotating magnetic field. The slight temperature increase of the sample in an ac-field is used as a measure of losses. The aim is to simulate the loss in rotating machines using HTS. This is a unique technique to measure total ac loss in HTS at power frequencies. The sample is mounted on to a cold finger extended from a liquid nitrogen heat exchanger (HEX). The thermal insulation between the HEX and sample is provided by a material of low thermal conductivity, and low eddy current heating sample holder in vacuum vessel. A temperature sensor and noninductive heater have been incorporated in the sample holder allowing a rapid sample change. The main part of the data is obtained in the calorimetric measurement is used for calibration. The focus is on the accuracy and calibrations required to predict the actual ac losses in HTS. This setup has the advantage of being able to measure the total ac loss under the influence of a continuous moving field as experienced by any rotating machines.
Magnetic cycles and rotation periods of late-type stars from photometric time series
Suárez Mascareño, A.; Rebolo, R.; González Hernández, J. I.
2016-10-01
Aims: We investigate the photometric modulation induced by magnetic activity cycles and study the relationship between rotation period and activity cycle(s) in late-type (FGKM) stars. Methods: We analysed light curves, spanning up to nine years, of 125 nearby stars provided by the All Sky Automated Survey (ASAS). The sample is mainly composed of low-activity, main-sequence late-A to mid-M-type stars. We performed a search for short (days) and long-term (years) periodic variations in the photometry. We modelled the light curves with combinations of sinusoids to measure the properties of these periodic signals. To provide a better statistical interpretation of our results, we complement our new results with results from previous similar works. Results: We have been able to measure long-term photometric cycles of 47 stars, out of which 39 have been derived with false alarm probabilities (FAP) of less than 0.1 per cent. Rotational modulation was also detected and rotational periods were measured in 36 stars. For 28 stars we have simultaneous measurements of activity cycles and rotational periods, 17 of which are M-type stars. We measured both photometric amplitudes and periods from sinusoidal fits. The measured cycle periods range from 2 to 14 yr with photometric amplitudes in the range of 5-20 mmag. We found that the distribution of cycle lengths for the different spectral types is similar, as the mean cycle is 9.5 yr for F-type stars, 6.7 yr for G-type stars, 8.5 yr for K-type stars, 6.0 yr for early M-type stars, and 7.1 yr for mid-M-type stars. On the other hand, the distribution of rotation periods is completely different, trending to longer periods for later type stars, from a mean rotation of 8.6 days for F-type stars to 85.4 days in mid-M-type stars. The amplitudes induced by magnetic cycles and rotation show a clear correlation. A trend of photometric amplitudes with rotation period is also outlined in the data. The amplitudes of the photometric variability
International Nuclear Information System (INIS)
Toi, K.; Ohdachi, S.; Watanabe, F.
2006-10-01
In a helical divertor configuration of the Large Helical Device (LHD), transport barrier was formed through low to high confinement (L-H) transition in the plasma edge region including ergodic field layer of which region is in the magnetic hill. The plasma stored energy or the averaged bulk plasma beta dia > (derived from diamagnetic measurement) starts to increase just after the transition. In the case that both dia > and line-averaged electron density e > at the transition are relatively high as dia >≥1.5% and e >≥2x10 19 m -3 , the increase is hampered by rapid growth of edge MHD modes and/or small ELM like activities just after the transition. On the other hand, the transition at lower e > (≤1.5x10 19 m -3 ) and dia > (<2%) leads to a continuous increase in the stored energy with a time scale longer than the global energy confinement time, without suffering from these MHD activities near the edge. The ETB typically formed in electron density profile extends into ergodic field layer defined in the vacuum field. The width of ETB is almost independent of the toroidal field strength from 0.5T to 1.5T and is much larger than the poloidal ion gyro-radius. When resonant helical field perturbations are applied to expand a magnetic island size at the rational surface of the rotational transform ι/2π=1 near the edge, the L-H transition is triggered at lower electron density compared with the case without the field perturbations. The application of large helical field perturbations also suppresses edge MHD modes and ELM like activities. (author)
Magnetic resonance imaging findings associated with surgically proven rotator interval lesions
Energy Technology Data Exchange (ETDEWEB)
Vinson, Emily N.; Major, Nancy M. [Duke University Medical Center, Department of Radiology, P.O. Box 3808, Durham, NC (United States); Higgins, Laurence D. [Brigham and Women' s Hospital, Department of Orthopedic Surgery, Boston, MA (United States)
2007-05-15
To identify shoulder magnetic resonance imaging (MRI) findings associated with surgically proven rotator interval abnormalities. The preoperative MRI examinations of five patients with surgically proven rotator interval (RI) lesions requiring closure were retrospectively evaluated by three musculoskeletal-trained radiologists in consensus. We assessed the structures in the RI, including the coracohumeral ligament, superior glenohumeral ligament, fat tissue, biceps tendon, and capsule for variations in size and signal alteration. In addition, we noted associated findings of rotator cuff and labral pathology. Three of three of the MR arthrogram studies demonstrated extension of gadolinium to the cortex of the undersurface of the coracoid process compared with the control images, seen best on the sagittal oblique images. Four of five of the studies demonstrated subjective thickening of the coracohumeral ligament, and three of five of the studies demonstrated subjective thickening of the superior glenohumeral ligament. Five of five of the studies demonstrated a labral tear. The MRI arthrogram finding of gadolinium extending to the cortex of the undersurface of the coracoid process was noted on the studies of those patients with rotator interval lesions at surgery in this series. Noting this finding - especially in the presence of a labral tear and/or thickening of the coracohumeral ligament or superior glenohumeral ligament - may be helpful in the preoperative diagnosis of rotator interval lesions. (orig.)
4 K to 20 K rotational-cooling magnetic refrigerator capable of 1-mW to >1-W operation
International Nuclear Information System (INIS)
Barclay, J.A.
1980-02-01
The low-temperature, magnetic entropy of certain single-crystal paramagnetic materials, such as DyPO 4 , changes dramatically as the crystal rotates in a magnetic field. A new magnetic refrigerator design based on the anisotropic nature of such materials is presented. The key advantages of the rotational-cooling concept are (1) a single, rotary motion is required, (2) magnetic field shaping is not a problem because the entire working material is in a constant field, and (3) the refrigerator can be smaller than comparable magnetic refrigerators because the working material is entirely inside the magnet at all times. The main disadvantage of the rotational-cooling concept is that small-dimension single crystals are required
Energy Technology Data Exchange (ETDEWEB)
Azimi, Neda; Rahimi, Masoud, E-mail: masoudrahimi@yahoo.com
2017-01-15
Rotating magnetic field (RMF) was applied on a micromixer to break the laminar flow and induce chaotic flow to enhance mass transfer between two-immiscible organic and aqueous phases. The results of RMF were compared to those of static magnetic field (SMF). For this purpose, experiments were carried out in a T-micromixer at equal volumetric flow rates of organic and aqueous phases. Fe{sub 3}O{sub 4} nanoparticles were synthesized by co-precipitation technique and they were dissolved in organic phase. Results obtained from RMF and SMF were compared in terms of overall volumetric mass transfer coefficient (K{sub L}a) and extraction efficiency (E) at various Reynolds numbers. Generally, RMF showed higher effect in mass transfer characteristics enhancement compared with SMF. The influence of rotational speeds of magnets (ω) in RMF was investigated, and measurable enhancements of K{sub L}a and E were observed. In RMF, the effect of magnetic field induction (B) was investigated. The results reveal that at constant concentration of nanoparticles, by increasing of B, mass transfer characteristics will be enhanced. The effect of various nanoparticles concentrations (ϕ) within 0.002–0.01 (w/v) on K{sub L}a and E at maximum induction of RMF (B=76 mT) was evaluated. Maximum values of K{sub L}a (2.1±0.001) and E (0.884±0.001) were achieved for the layout of RMF (B=76 mT), ω=16 rad/s and MNPs concentration of 0.008–0.01 (w/v). - Highlights: • Magnetic nanoparticles used for mixing of two immiscible liquids in a micromixer. • Extraction efficiency of rotating magnetic field (RMF) is compared with static one. • In RMF, the effect of the angular speed on KLa and E enhancement is reported. • In RMF, at a selected magnet distance effect of nanoparticle concentration is reported.
Energy Technology Data Exchange (ETDEWEB)
Barbieri, Nicholas; Lim, Khan; Durand, Magali; Baudelet, Matthieu; Richardson, Martin [Townes Laser Institute, CREOL—The College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816 (United States); Hosseinimakarem, Zahra; Johnson, Eric [Micro-Photonics Laboratory – Center for Optical Material Science, Clemson, Anderson, South Carolina 29634 (United States)
2014-06-30
The shaping of laser-induced filamenting plasma channels into helical structures by guiding the process with a non-diffracting beam is demonstrated. This was achieved using a Bessel beam superposition to control the phase of an ultrafast laser beam possessing intensities sufficient to induce Kerr effect driven non-linear self-focusing. Several experimental methods were used to characterize the resulting beams and confirm the observed structures are laser air filaments.
Energy Technology Data Exchange (ETDEWEB)
Armour, N.; Dost, S. [Crystal Growth Laboratory, University of Victoria, Victoria, BC, V8W 3P6 (Canada)
2010-04-15
The effect of applied rotating and combined (rotating and static) magnetic fields on silicon transport during the liquid phase diffusion growth of SiGe was experimentally studied. 72-hour growth periods produced some single crystal sections. Single and polycrystalline sections of the processed samples were examined for silicon composition. Results show that the application of a rotating magnetic field enhances silicon transport in the melt. It also has a slight positive effect on flattening the initial growth interface. For comparison, growth experiments were also conducted under combined (rotating and static) magnetic fields. The processed samples revealed that the addition of static field altered the thermal characteristics of the system significantly and led to a complete melt back of the germanium seed. Silicon transport in the melt was also enhanced under combined fields compared with experiments with no magnetic field. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
A magnetic levitation rotating plate model based on high-Tc superconducting technology
Zheng, Jun; Li, Jipeng; Sun, Ruixue; Qian, Nan; Deng, Zigang
2017-09-01
With the wide requirements of the training aids and display models of science, technology and even industrial products for the public like schools, museums and pleasure grounds, a simple-structure and long-term stable-levitation technology is needed for these exhibitions. Opportunely, high temperature superconducting (HTS) technology using bulk superconductors indeed has prominent advantages on magnetic levitation and suspension for its self-stable characteristic in an applied magnetic field without any external power or control. This paper explores the feasibility of designing a rotatable magnetic levitation (maglev) plate model with HTS bulks placed beneath a permanent magnet (PM) plate. The model is featured with HTS bulks together with their essential cryogenic equipment above and PMs below, therefore it eliminates the unclear visual effects by spray due to the low temperature coolant such as liquid nitrogen (LN2) and additional levitation weight of the cryogenic equipment. Besides that, a matched LN2 automation filling system is adopted to help achieving a long-term working state of the rotatable maglev plate. The key low-temperature working condition for HTS bulks is maintained by repeatedly opening a solenoid valve and automatically filling LN2 under the monitoring of a temperature sensor inside the cryostat. With the support of the cryogenic devices, the HTS maglev system can meet all requirements of the levitating display model for exhibitions, and may enlighten the research work on HTS maglev applications.
Energy Technology Data Exchange (ETDEWEB)
Dieckhoff, Jan, E-mail: j.dieckhoff@tu-bs.de [Institut fuer Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Braunschweig (Germany); Schrittwieser, Stefan; Schotter, Joerg [Molecular Diagnostics, AIT Austrian Institute of Technology, Vienna (Austria); Remmer, Hilke; Schilling, Meinhard; Ludwig, Frank [Institut fuer Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Braunschweig (Germany)
2015-04-15
In this work, we report on the effect of the magnetic nanoparticle (MNP) concentration on the quantitative detection of proteins in solution with a rotating magnetic field (RMF) based homogeneous bioassay. Here, the phase lag between 30 nm iron oxide single-core particles and the RMF is analyzed with a fluxgate-based measurement system. As a test analyte anti-human IgG is applied which binds to the protein G functionalized MNP shell and causes a change of the phase lag. The measured phase lag changes for a fixed MNP and a varying analyte concentration are modeled with logistic functions. A change of the MNP concentration results in a nonlinear shift of the logistic function with the analyte concentration. This effect results from the law of mass action. Furthermore, the bioassay results are used to determine the association constant of the binding reaction. - Highlights: • A rotating magnetic field based homogeneous bioassay concept was presented. • Here, single-core iron oxide nanoparticles are applied as markers. • The impact of the particle concentration on the bioassay results is investigated. • The relation between particle concentration and bioassay sensitivity is nonlinear. • This finding can be reasonably explained by the law of mass action.
Energy Technology Data Exchange (ETDEWEB)
Emoto, Kozo; Sugiyama, Ryo; Takagi, Shogo; Ohashi, Shunsuke, E-mail: k145676@kansai-u.ac.jp
2013-11-15
Highlights: •We have developed the HTS-permanent magnet hybrid bearing system. •Three dimensional numerical analysis is undertaken to get the effective hybrid configuration. •Repulsive force and pinning force are combined effectively. •The hybrid system shows better levitation characteristics than the non-hybrid one. •In the mechanical resonance state, vibration of the rotor in the hybrid system is small. -- Abstract: We have developed the hybrid magnetic bearing using permanent magnets and the high-T{sub c} bulk superconductor (HTSC). Pinning force of the HTSC is used for the levitation and the guidance. Repulsive force of the permanent magnets is introduced to increase the load weight of the magnetic bearing. In this system, the stator side permanent magnet has the ring type structure so that both pinning force and repulsive force are used effectively. In this paper, influence of the hybrid system on dynamic characteristics of the rotor is studied. The rotor which is supported by the hybrid magnetic bearing is rotated. Then, vibration and the gradient angle of the rotor are measured until the rotor reaches to the end of the resonance state. Three dimensional numerical analysis of the flux which penetrates on the surface of the HTSC is undertaken. The relation between the dynamic characteristics and the flux is considered, and that of the hybrid system is compared with the non-hybrid one. In the hybrid system, the flux is changed by the influences of the stator side permanent magnet. Vibration and the gradient angle of the hybrid system are shown to be smaller than that of the non-hybrid one.
International Nuclear Information System (INIS)
Emoto, Kozo; Sugiyama, Ryo; Takagi, Shogo; Ohashi, Shunsuke
2013-01-01
Highlights: •We have developed the HTS-permanent magnet hybrid bearing system. •Three dimensional numerical analysis is undertaken to get the effective hybrid configuration. •Repulsive force and pinning force are combined effectively. •The hybrid system shows better levitation characteristics than the non-hybrid one. •In the mechanical resonance state, vibration of the rotor in the hybrid system is small. -- Abstract: We have developed the hybrid magnetic bearing using permanent magnets and the high-T c bulk superconductor (HTSC). Pinning force of the HTSC is used for the levitation and the guidance. Repulsive force of the permanent magnets is introduced to increase the load weight of the magnetic bearing. In this system, the stator side permanent magnet has the ring type structure so that both pinning force and repulsive force are used effectively. In this paper, influence of the hybrid system on dynamic characteristics of the rotor is studied. The rotor which is supported by the hybrid magnetic bearing is rotated. Then, vibration and the gradient angle of the rotor are measured until the rotor reaches to the end of the resonance state. Three dimensional numerical analysis of the flux which penetrates on the surface of the HTSC is undertaken. The relation between the dynamic characteristics and the flux is considered, and that of the hybrid system is compared with the non-hybrid one. In the hybrid system, the flux is changed by the influences of the stator side permanent magnet. Vibration and the gradient angle of the hybrid system are shown to be smaller than that of the non-hybrid one
SUN-LIKE MAGNETIC CYCLES IN THE RAPIDLY ROTATING YOUNG SOLAR ANALOG HD 30495
International Nuclear Information System (INIS)
Egeland, Ricky; Metcalfe, Travis S.; Hall, Jeffrey C.; Henry, Gregory W.
2015-01-01
A growing body of evidence suggests that multiple dynamo mechanisms can drive magnetic variability on different timescales, not only in the Sun but also in other stars. Many solar activity proxies exhibit a quasi-biennial (∼2 year) variation, which is superimposed upon the dominant 11 year cycle. A well-characterized stellar sample suggests at least two different relationships between rotation period and cycle period, with some stars exhibiting long and short cycles simultaneously. Within this sample, the solar cycle periods are typical of a more rapidly rotating star, implying that the Sun might be in a transitional state or that it has an unusual evolutionary history. In this work, we present new and archival observations of dual magnetic cycles in the young solar analog HD 30495, a ∼1 Gyr old G1.5 V star with a rotation period near 11 days. This star falls squarely on the relationships established by the broader stellar sample, with short-period variations at ∼1.7 years and a long cycle of ∼12 years. We measure three individual long-period cycles and find durations ranging from 9.6 to 15.5 years. We find the short-term variability to be intermittent, but present throughout the majority of the time series, though its occurrence and amplitude are uncorrelated with the longer cycle. These essentially solar-like variations occur in a Sun-like star with more rapid rotation, though surface differential rotation measurements leave open the possibility of a solar equivalence
International Nuclear Information System (INIS)
Hugrass, W.N.; Grimm, R.C.
1980-07-01
The generation of a steady azimuthal current in a cylindrical plasma column using a rotating magnetic field is numerically investigated. The mixed initial-boundary-value problem is solved using a finite difference method. It is shown that substantial azimuthal current can be driven provided that the amplitude of the rotating magnetic field is greater than a certain threshold value which depends on the plasma resistivity
Nonlinear magneto-optical rotation with modulated light in tilted magnetic fields
International Nuclear Information System (INIS)
Pustelny, S.; Gawlik, W.; Rochester, S. M.; Kimball, D. F. Jackson; Yashchuk, V. V.; Budker, D.
2006-01-01
Larmor precession of laser-polarized atoms contained in antirelaxation-coated cells, detected via nonlinear magneto-optical rotation (NMOR), is a promising technique for a new generation of ultrasensitive atomic magnetometers. For magnetic fields directed along the light propagation direction, resonances in NMOR appear when linearly polarized light is frequency or amplitude modulated at twice the Larmor frequency. Because the frequency of these resonances depends on the magnitude but not the direction of the field, they are useful for scalar magnetometry. Additional NMOR resonances at the Larmor frequency appear when the magnetic field is tilted away from the light propagation direction in the plane defined by the light propagation and polarization vectors. These resonances, studied both experimentally and with a density matrix calculation in the present work, offer a convenient method of achieving additional information about a direction of the magnetic field
International Nuclear Information System (INIS)
Sugiyama, Jun; Ikedo, Yutaka; Mukai, Kazuhiko; Nozaki, Hiroshi; Russo, Peter L.; Ansaldo, Eduardo J.; Brewer, Jess H.; Andreica, Daniel; Amato, Alex
2009-01-01
In order to elucidate the nature of layered cobalt dioxides A x CoO 2 , we have investigated their microscopic magnetism by means of positive muon-spin rotation and relaxation (μ + SR) spectroscopy, in particular for A=Li, Na, and K. The dome-shaped magnetic phase diagram for Na x CoO 2 with x≥0.75 suggests the competition between the spin concentration and geometrical frustration on the two-dimensional triangular lattice of the CoO 2 plane. The additional experiment on Li x CoO 2 and K x CoO 2 indicates both a weakly coupled regime for the d electrons in the CoO 2 plane and an ignorable weak effect of the inter-plane interaction on their magnetic order at low T.
International Nuclear Information System (INIS)
Calderon, Oscar G; Melle, Sonia
2002-01-01
We study theoretically the dynamics of a system of two magnetizable particles suspended in a non-magnetic fluid subject to a rotating magnetic field when a modulation on the Mason number (ratio of viscous to magnetic forces) is applied. We find, using a periodic modulation, that a resonant-like phenomenon between the periodic modulation of the Mason number and the intrinsic radial oscillation of the system without modulation occurs. For a random perturbation of the Mason number, we obtain an optimum noise strength at which the average interparticle distance reaches the lowest value. When a weak periodic modulation and a noise source are included in the Mason number, stochastic resonance (SR) is found for different frequencies and amplitudes of the modulation. An interpretation of this SR phenomenon is made by means of a threshold crossing mechanism
Compact torus equilibria set up in the rotamak by rotating magnetic fields
International Nuclear Information System (INIS)
Storer, R.G.
1983-01-01
In the Rotamak, a rotating magnetic field is used to drive a steady toroidal current in a compact torus device. High power, short duration (approx.=80 μs) and low power, long duration experiments (approx.=3 ms) have been studied. In both of these experiments a steady phase exists which is well described by the assumption that the plasma is in an averaged magnetohydrodynamic pressure balance situation. Using a model based on this assumption, self-consistency imposes conditions relating the temperature and density of the plasma to the steady components of the internal magnetic fields. In the high power experiment, this steady phase evolves into a second steady phase, with lower toroidal current, which has a #betta#=1, mirror-like configuration which also appears to satisfy local pressure balance but with the magnetic axis (minimum of the poloidal flux) at the centre of the spherical vessel. (orig.)
360° deterministic magnetization rotation in a three-ellipse magnetoelectric heterostructure
Kundu, Auni A.; Chavez, Andres C.; Keller, Scott M.; Carman, Gregory P.; Lynch, Christopher S.
2018-03-01
A magnetic dipole-coupled magnetoelectric heterostructure comprised of three closely spaced ellipse shapes was designed and shown to be capable of achieving deterministic in-plane magnetization rotation. The design approach used a combination of conventional micromagnetic simulations to obtain preliminary configurations followed by simulations using a fully strain-coupled, time domain micromagnetic code for a detailed assessment of performance. The conventional micromagnetic code has short run times and was used to refine the ellipse shape and orientation, but it does not accurately capture the effects of the strain gradients present in the piezoelectric and magnetostrictive layers that contribute to magnetization reorientation. The fully coupled code was used to assess the effects of strain and magnetic field gradients on precessional switching in the side ellipses and on the resulting dipole-field driven magnetization reorientation in the center ellipse. The work led to a geometry with a CoFeB ellipse (125 nm × 95 nm × 4 nm) positioned between two smaller CoFeB ellipses (75 nm × 50 nm × 4 nm) on a 500 nm PZT-5H film substrate clamped at its bottom surface. The smaller ellipses were oriented at 45° and positioned at 70° and 250° about the central ellipse due to the film deposition on a thick substrate. A 7.3 V pulse applied to the PZT for 0.22 ns produced 180° switching of the magnetization in the outer ellipses that then drove switching in the center ellipse through dipole-dipole coupling. Full 360° deterministic rotation was achieved with a second pulse. The temporal response of the resulting design is discussed.
Plasma rotation by electric and magnetic fields in a discharge cylinder
Wilhelm, H. E.; Hong, S. H.
1977-01-01
A theoretical model for an electric discharge consisting of a spatially diverging plasma sustained electrically between a small ring cathode and a larger ring anode in a cylindrical chamber with an axial magnetic field is developed to study the rotation of the discharge plasma in the crossed electric and magnetic fields. The associated boundary-value problem for the coupled partial differential equations which describe the electric potential and the plasma velocity fields is solved in closed form. The electric field, current density, and velocity distributions are discussed in terms of the Hartmann number and the Hall coefficient. As a result of Lorentz forces, the plasma rotates with speeds as high as 1 million cm/sec around its axis of symmetry at typical conditions. As an application, it is noted that rotating discharges of this type could be used to develop a high-density plasma-ultracentrifuge driven by j x B forces, in which the lighter (heavier) ion and atom components would be enriched in (off) the center of the discharge cylinder.
Twin Rotating Coils for Cold Magnetic Measurements of 15 m Long LHC Dipoles
Billan, J; Buzio, M; D'Angelo, G; Deferne, G; Dunkel, O; Legrand, P; Rijllart, A; Siemko, A; Sievers, P; Schloss, S; Walckiers, L
2000-01-01
We describe here a new harmonic coil system for the field measurement of the superconducting, twin aperture LHC dipoles and the associated corrector magnets. Besides field measurements the system can be used as an antenna to localize the quench origin. The main component is a 16 m long rotating shaft, made up of 13 ceramic segments, each carrying two tangential coils plus a central radial coil, all working in parallel. The segments are connected with flexible Ti-alloy bellows, allowing the piecewise straight shaft to follow the curvature of the dipole while maintaining high torsional rigidity. At each interconnection the structure is supported by rollers and ball bearings, necessary for the axial movement for installation and for the rotation of the coil during measurement. Two such shafts are simultaneously driven by a twin-rotating unit, thus measuring both apertures of a dipole at the same time. This arrangement allows very short measurement times (typically 10 s) and is essential to perform cold magnetic ...
Flexible helical yarn swimmers.
Zakharov, A P; Leshansky, A M; Pismen, L M
2016-09-01
We investigate the motion of a flexible Stokesian flagellar swimmer realised as a yarn made of two intertwined elastomer fibres, one active, that can reversibly change its length in response to a local excitation causing transition to the nematic state or swelling, and the other one, a passive isotropic elastomer with identical mechanical properties. A propagating chemical wave may provide an excitation mechanism ensuring a constant length of the excited region. Generally, the swimmer moves along a helical trajectory, and the propagation and rotation velocity are very sensitive to the ratio of the excited region to the pitch of the yarn, as well as to the size of a carried load. External excitation by a moving actuating beam is less effective, unless the direction of the beam is adjusted to rotation of the swimmer.
Helical axis stellarator equilibrium model
International Nuclear Information System (INIS)
Koniges, A.E.; Johnson, J.L.
1985-02-01
An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift
International Nuclear Information System (INIS)
Abd-Alla, A.M.; Abo-Dahab, S.M.
2015-01-01
In this paper, the peristaltic flow of a Jeffrey fluid in an asymmetric rotating channel is studied. Mathematical modeling is carried out by utilizing long wavelength and low Reynolds number assumptions. Closed form expressions for the pressure gradient, pressure rise, streamlines, axial velocity and shear stress on the channel walls have been computed numerically. Effects of Hartmann number, the ratio of relaxation to retardation times, time-mean flow, rotation and the phase angle on the pressure gradient, pressure rise, streamline, axial velocity and shear stress are discussed in detail and shown graphically. The results indicate that the effect of the Hartmann number, the ratio of relaxation to retardation times, time-mean flow, rotation and the phase angle are very pronounced in the phenomena. Comparison was made with the results obtained in the asymmetric channel and symmetric channel. - Highlights: • The peristaltic flow of a Jeffrey fluid in an asymmetric rotating channel with magnetic field. • Mathematical modeling for long wavelength and low Reynolds number assumptions. • Closed form expressions for the pressure gradient, pressure rise, stream function, axial velocity and shear stress
Asynchronous Magnetic Bead Rotation (AMBR Microviscometer for Label-Free DNA Analysis
Directory of Open Access Journals (Sweden)
Yunzi Li
2014-03-01
Full Text Available We have developed a label-free viscosity-based DNA detection system, using paramagnetic beads as an asynchronous magnetic bead rotation (AMBR microviscometer. We have demonstrated experimentally that the bead rotation period is linearly proportional to the viscosity of a DNA solution surrounding the paramagnetic bead, as expected theoretically. Simple optical measurement of asynchronous microbead motion determines solution viscosity precisely in microscale volumes, thus allowing an estimate of DNA concentration or average fragment length. The response of the AMBR microviscometer yields reproducible measurement of DNA solutions, enzymatic digestion reactions, and PCR systems at template concentrations across a 5000-fold range. The results demonstrate the feasibility of viscosity-based DNA detection using AMBR in microscale aqueous volumes.
Pinning, rotation, and metastability of BiFeO3 cycloidal domains in a magnetic field
Fishman, Randy S.
2018-01-01
Earlier models for the room-temperature multiferroic BiFeO3 implicitly assumed that a very strong anisotropy restricts the domain wave vectors q to the threefold-symmetric axis normal to the static polarization P . However, recent measurements demonstrate that the domain wave vectors q rotate within the hexagonal plane normal to P away from the magnetic field orientation m . We show that the previously neglected threefold anisotropy K3 restricts the wave vectors to lie along the threefold axis in zero field. Taking m to lie along a threefold axis, the domain with q parallel to m remains metastable below Bc 1≈7 T. Due to the pinning of domains by nonmagnetic impurities, the wave vectors of the other two domains start to rotate away from m above 5.6 T, when the component of the torque τ =M ×B along P exceeds a threshold value τpin. Since τ =0 when m ⊥q , the wave vectors of those domains never become completely perpendicular to the magnetic field. Our results explain recent measurements of the critical field as a function of field orientation, small-angle neutron scattering measurements of the wave vectors, as well as spectroscopic measurements with m along a threefold axis. The model developed in this paper also explains how the three multiferroic domains of BiFeO3 for a fixed P can be manipulated by a magnetic field.
Magnetic Resonance Imaging of Rotator Cuff Tears in Shoulder Impingement Syndrome
International Nuclear Information System (INIS)
Freygant, Magdalena; Dziurzyńska-Białek, Ewa; Guz, Wiesław; Samojedny, Antoni; Gołofit, Andrzej; Kostkiewicz, Agnieszka; Terpin, Krzysztof
2014-01-01
Shoulder joint is a common site of musculoskeletal pain caused, among other things, by rotator cuff tears due to narrowing of subacromial space, acute trauma or chronic shoulder overload. Magnetic resonance imaging (MRI) is an excellent modality for imaging of soft tissues of the shoulder joint considering a possibility of multiplanar image acquisition and non-invasive nature of the study. The aim of this study was to evaluate the prevalence of partial and complete rotator cuff tears in magnetic resonance images of patients with shoulder impingement syndrome and to review the literature on the causes and classification of rotator cuff tears. We retrospectively analyzed the results of 137 shoulder MRI examinations performed in 57 women and 72 men in Magnetic Resonance facility of the Department of Radiology and Diagnostic Imaging at the St. Jadwiga the Queen Regional Hospital No. 2 in Rzeszow between June 2010 and February 2013. Examinations were performed using Philips Achieva 1.5T device, including spin echo and gradient echo sequences with T1-, T2- and PD-weighted as well as fat saturation sequences in transverse, frontal and sagittal oblique planes. Patients were referred from hospital wards as well as from outpatient clinics of the subcarpathian province. The most frequently reported injuries included partial supraspinatus tendon tear and complete tearing most commonly involved the supraspinatus muscle tendon. The smallest group comprised patients with complete tear of subscapularis muscle tendon. Among 137 patients in the study population, 129 patients suffered from shoulder pain, including 57 patients who reported a history of trauma. There was 44% women and 56% men in a group of patients with shoulder pain. Posttraumatic shoulder pain was predominantly reported by men, while women comprised a larger group of patients with shoulder pain not preceded by injury. Rotator cuff injury is a very common pathology in patients with shoulder impingement syndrome
Adjustable Permanent Quadrupoles Using Rotating Magnet Material Rods for the Next Linear Collider
International Nuclear Information System (INIS)
Spencer, Cherrill M
2002-01-01
The proposed Next Linear Collider (NLC) will require over 1400 adjustable quadrupoles between the main linacs' accelerator structures. These 12.7 mm bore quadrupoles will have a range of integrated strength from 0.6 to 132 Tesla, with a maximum gradient of 135 Tesla per meter, an adjustment range of +0 -20% and effective lengths from 324 mm to 972 mm. The magnetic center must remain stable to within 1 micrometer during the 20% adjustment. In an effort to reduce estimated costs and increase reliability, several designs using hybrid permanent magnets have been developed. All magnets have iron poles and use either Samarium Cobalt or Neodymium Iron to provide the magnetic fields. Two prototypes use rotating rods containing permanent magnetic material to vary the gradient. Gradient changes of 20% and center shifts of less than 20 microns have been measured. These data are compared to an equivalent electromagnet prototype. See High Reliability Prototype Quadrupole for the Next Linear Collider by C.E Rago, C.M SPENCER, Z. Wolf submitted to this conference
Adjustable Permanent Quadrupoles Using Rotating Magnet Material Rods for the Next Linear Collider.
Spencer, C M
2002-01-01
The proposed Next Linear Collider (NLC) will require over 1400 adjustable quadrupoles between the main linacs' accelerator structures. These 12.7 mm bore quadrupoles will have a range of integrated strength from 0.6 to 132 Tesla, with a maximum gradient of 135 Tesla per meter, an adjustment range of +0 -20% and effective lengths from 324 mm to 972 mm. The magnetic center must remain stable to within 1 micrometer during the 20% adjustment. In an effort to reduce estimated costs and increase reliability, several designs using hybrid permanent magnets have been developed. All magnets have iron poles and use either Samarium Cobalt or Neodymium Iron to provide the magnetic fields. Two prototypes use rotating rods containing permanent magnetic material to vary the gradient. Gradient changes of 20% and center shifts of less than 20 microns have been measured. These data are compared to an equivalent electromagnet prototype. See High Reliability Prototype Quadrupole for the Next Linear Collider by C.E Rago, C.M SPENC...
Energy Technology Data Exchange (ETDEWEB)
Mao, S. A. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); McClure-Griffiths, N. M.; McConnell, D. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Epping, NSW 1710 (Australia); Gaensler, B. M. [Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Haverkorn, M. [Department of Astrophysics, Radboud University, P.O. Box 9010, 6500-GL Nijmegen (Netherlands); Beck, R. [Max-Planck-Institut fuer Radioastronomie, D-53121 Bonn (Germany); Wolleben, M. [Square Kilometre Array South Africa, The Park, Pinelands 7405 (South Africa); Stanimirovic, S. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States); Dickey, J. M. [Physics Department, University of Tasmania, Hobart, TAS 7001 (Australia); Staveley-Smith, L., E-mail: mao@astro.wisc.edu [International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, Crawley, WA 6009 (Australia)
2012-11-01
We present a study of the magnetic field of the Large Magellanic Cloud (LMC), carried out using diffuse polarized synchrotron emission data at 1.4 GHz acquired at the Parkes Radio Telescope and the Australia Telescope Compact Array. The observed diffuse polarized emission is likely to originate above the LMC disk on the near side of the galaxy. Consistent negative rotation measures (RMs) derived from the diffuse emission indicate that the line-of-sight magnetic field in the LMC's near-side halo is directed coherently away from us. In combination with RMs of extragalactic sources that lie behind the galaxy, we show that the LMC's large-scale magnetic field is likely to be of quadrupolar geometry, consistent with the prediction of dynamo theory. On smaller scales, we identify two brightly polarized filaments southeast of the LMC, associated with neutral hydrogen arms. The filaments' magnetic field potentially aligns with the direction toward the Small Magellanic Cloud (SMC). We suggest that tidal interactions between the SMC and the LMC in the past 10{sup 9} years are likely to have shaped the magnetic field in these filaments.
Directory of Open Access Journals (Sweden)
C. W. Su
2013-07-01
Full Text Available An experimental approach of inclined incidence magneto-optic Faraday effect observed in the polar plane is applied. Three samples containing ferromagnetic cobalt ultrathin films on a semiconductor zinc oxide (0001 single crystal substrate with in-plane and out-of-plane anisotropy are evaluated. Through the fine adjustment of crossed polarizers in the magneto-optic effect measurement completely recorded the detail optical and magneto-optical responses from the birefringent crystal substrate and the magnetic film, especially for the signal induced from the substrate with uniaxial optical axis. The angle dependency of interference phenomena periodically from the optical and magneto-optical responses is attributed to the birefringence even in the absence of a magnetic field. The new type of observation finds that the transmission Faraday intensity in the oblique incidence includes a combination of polarization rotations, which results from optical compensation from the substrate and magneto-optical Faraday effects from the film. The samples grown at different rates and examined by this method exhibit magnetic structure discriminations. This result can be applied in the advanced polarized-light technologies to enhance the spatial resolution of magnetic surfaces with microstructural information under various magnetic field direction.
Energy Technology Data Exchange (ETDEWEB)
Llera, María [Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires (Argentina); Codnia, Jorge [Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires (Argentina); Centro de Investigaciones en Láseres y Aplicaciones, CITEDEF-CONICET, Buenos Aires (Argentina); Jorge, Guillermo A., E-mail: gjorge@ungs.edu.ar [Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires (Argentina)
2015-06-15
We present a dynamic study of soft magnetic, commercial Fe and Ni micrometer-sized particles dispersed in oleic acid and subjected to a variable (rotating) magnetic field in the horizontal plane. A very complex structure is formed after the particles decant towards the bottom liquid–solid interface and the magnetic field is applied for several minutes. The dynamics of structure formation was studied by means of the registration and analysis of microscopic video images, through a Matlab image analysis script. Several parameters, such as the number of clusters, the perimeter-based fractal dimension and circularity, were calculated as a function of time. The time evolution of the number of clusters was found to follow a power-law behavior, with an exponent consistent with that found in other studies for magnetic systems, whereas the typical formation time depends on the particle diameter and field configuration. Complementarily, the magnetic properties of the formed structure were studied, reproducing the experiment with liquid paraffin as the containing fluid, and then letting it solidify. The sample obtained was studied by vibrating sample magnetometry. The magnetization curves show that the material obtained is a planar magnetically anisotropic material, which could eventually be used as an anisotropic magnetic sensor or actuator. - Highlights: • Dynamic study of Fe and Ni particles in oleic acid under rotating fields. • A very complex system of interconnected clusters was observed. • Larger particles had a smaller aggregation time. • A power law behavior of the number of clusters vs. time. • A Fe-paraffin sample with planar anisotropy characterized.
International Nuclear Information System (INIS)
Llera, María; Codnia, Jorge; Jorge, Guillermo A.
2015-01-01
We present a dynamic study of soft magnetic, commercial Fe and Ni micrometer-sized particles dispersed in oleic acid and subjected to a variable (rotating) magnetic field in the horizontal plane. A very complex structure is formed after the particles decant towards the bottom liquid–solid interface and the magnetic field is applied for several minutes. The dynamics of structure formation was studied by means of the registration and analysis of microscopic video images, through a Matlab image analysis script. Several parameters, such as the number of clusters, the perimeter-based fractal dimension and circularity, were calculated as a function of time. The time evolution of the number of clusters was found to follow a power-law behavior, with an exponent consistent with that found in other studies for magnetic systems, whereas the typical formation time depends on the particle diameter and field configuration. Complementarily, the magnetic properties of the formed structure were studied, reproducing the experiment with liquid paraffin as the containing fluid, and then letting it solidify. The sample obtained was studied by vibrating sample magnetometry. The magnetization curves show that the material obtained is a planar magnetically anisotropic material, which could eventually be used as an anisotropic magnetic sensor or actuator. - Highlights: • Dynamic study of Fe and Ni particles in oleic acid under rotating fields. • A very complex system of interconnected clusters was observed. • Larger particles had a smaller aggregation time. • A power law behavior of the number of clusters vs. time. • A Fe-paraffin sample with planar anisotropy characterized
Dikpati, Mausumi; McIntosh, Scott W.; Bothun, Gregory; Cally, Paul S.; Ghosh, Siddhartha S.; Gilman, Peter A.; Umurhan, Orkan M.
2018-02-01
We present a nonlinear magnetohydrodynamic shallow-water model for the solar tachocline (MHD-SWT) that generates quasi-periodic tachocline nonlinear oscillations (TNOs) that can be identified with the recently discovered solar “seasons.” We discuss the properties of the hydrodynamic and magnetohydrodynamic Rossby waves that interact with the differential rotation and toroidal fields to sustain these oscillations, which occur due to back-and-forth energy exchanges among potential, kinetic, and magnetic energies. We perform model simulations for a few years, for selected example cases, in both hydrodynamic and magnetohydrodynamic regimes and show that the TNOs are robust features of the MHD-SWT model, occurring with periods of 2–20 months. We find that in certain cases multiple unstable shallow-water modes govern the dynamics, and TNO periods vary with time. In hydrodynamically governed TNOs, the energy exchange mechanism is simple, occurring between the Rossby waves and differential rotation. But in MHD cases, energy exchange becomes much more complex, involving energy flow among six energy reservoirs by means of eight different energy conversion processes. For toroidal magnetic bands of 5 and 35 kG peak amplitudes, both placed at 45° latitude and oppositely directed in north and south hemispheres, we show that the energy transfers responsible for TNO, as well as westward phase propagation, are evident in synoptic maps of the flow, magnetic field, and tachocline top-surface deformations. Nonlinear mode–mode interaction is particularly dramatic in the strong-field case. We also find that the TNO period increases with a decrease in rotation rate, implying that the younger Sun had more frequent seasons.
Top, Can Barış; Ilbey, Serhat; Güven, Hüseyin Emre
2017-12-01
We propose a coil arrangement for open bore field-free line (FFL) magnetic particle imaging (MPI) system, which is suitable for accessing the subject from the sides. The purpose of this study is twofold, to show that the FFL can be rotated and translated electronically in a volume of interest with this arrangement and to analyze the current, voltage and power requirements for a 1 T/m gradient human sized scanner for a 200 mm diameter × 200 mm height cylindrical field of view (FOV). We used split coils side by side with alternating current directions to generate a field-free line. Employing two of these coil groups, one of which is rotated 90 degrees with respect to the other, a rotating FFL was generated. We conducted numerical simulations to show the feasibility of this arrangement for three-dimensional (3D) electronical scan of the FFL. Using simulations, we obtained images of a two-dimensional (2D) in silico dot phantom for a human size scanner with system matrix-based reconstruction. Simulations showed that the FFL can be generated and rotated in one plane and can be translated in two axes, allowing for 3D imaging of a large subject with the proposed arrangement. Human sized scanner required 63-215 kW power for the selection field coils to scan the focus inside the FOV. The proposed setup is suitable for FFL MPI imaging with an open bore configuration without the need for mechanical rotation, which is preferable for clinical usage in terms of imaging time and patient access. Further studies are necessary to determine the limitations imposed by peripheral nerve stimulation, and to optimize the system parameters and the sequence design. © 2017 American Association of Physicists in Medicine.
Glatzmaier, Gary
2013-01-01
This book provides readers with the skills they need to write computer codes that simulate convection, internal gravity waves, and magnetic field generation in the interiors and atmospheres of rotating planets and stars. Using a teaching method perfected in the classroom, Gary Glatzmaier begins by offering a step-by-step guide on how to design codes for simulating nonlinear time-dependent thermal convection in a two-dimensional box using Fourier expansions in the horizontal direction and finite differences in the vertical direction. He then describes how to implement more efficient and accura
International Nuclear Information System (INIS)
Matsuyama, Shoichiro; Shinohara, Shunjiro
2001-01-01
A large density profile modification was successfully obtained by voltage biasing to electrodes inserted in a RF (radio frequency) produced, magnetized plasma, and formation of strong shear of azimuthal plasma rotation velocity in a supersonic regime was found. For the case of biasing to an electrode near the central plasma region, two types of density transitions were observed in the outer plasma region: one was an oscillatory transition between two states, and the other was a transition from high to low density states with a large reduction of density fluctuations. (author)
Energy Technology Data Exchange (ETDEWEB)
Matsuyama, Shoichiro; Shinohara, Shunjiro [Kyushu Univ., Interdisciplinary Graduate School of Engineering Sciences, Fukuoka (Japan)
2001-07-01
A large density profile modification was successfully obtained by voltage biasing to electrodes inserted in a RF (radio frequency) produced, magnetized plasma, and formation of strong shear of azimuthal plasma rotation velocity in a supersonic regime was found. For the case of biasing to an electrode near the central plasma region, two types of density transitions were observed in the outer plasma region: one was an oscillatory transition between two states, and the other was a transition from high to low density states with a large reduction of density fluctuations. (author)
International Nuclear Information System (INIS)
Gorican, Viktor; Hamler, Anton; Jesenik, Marko; Stumberger, Bojan; Trlep, Mladen
2004-01-01
The magnetic properties of grain-oriented material under rotational magnetic flux condition were measured, using two different pairs of B coils with different angle with respect to the rolling direction. It is known that induced voltages in two perpendicularly positioned B coils do not represent the actual amplitude and the angular speed of vector B in the measuring region. Consequently, the control of the induced voltages in the B coils at different positions means that the sample is measured under different magnetic flux condition. This leads to a difference between the results of vector H and the rotational loss
Borisevich, V. D.; Potanin, E. P.
2017-07-01
The possibility of using a rotating magnetic field (RMF) in a plasma centrifuge (PC), with axial circulation to multiply the radial separation effect in an axial direction, is considered. For the first time, a traveling magnetic field (TMF) is proposed to drive an axial circulation flow in a PC. The longitudinal separation effect is calculated for a notional model, using specified operational parameters and the properties of a plasma, comprising an isotopic mixture of 20Ne-22Ne and generated by a high frequency discharge. The optimal intensity of a circulation flow, in which the longitudinal separation effect reaches its maximum value, is studied. The optimal parameters of the RMF and TMF for effective separation, as well as the centrifuge performance, are calculated.
Toroidal rotation braking with n = 1 magnetic perturbation field on JET
International Nuclear Information System (INIS)
Sun, Y; Liang, Y; Koslowski, H R; Harting, D; Wiegmann, C; Wiesen, S; Jachmich, S; Alfier, A; Asunta, O; Corrigan, G; Giroud, C; Gryaznevich, M P; Hender, T; Nardon, E; Parail, V; Naulin, V; Tala, T
2010-01-01
A strong toroidal rotation braking has been observed in plasmas with application of an n = 1 magnetic perturbation field on the JET tokamak. Calculation results from the momentum transport analysis show that the torque induced by the n = 1 perturbation field has a global profile. The maximal value of this torque is at the plasma core region (ρ - √ν regime in the plasma core, but it is close to the transition between the 1/ν and ν - √ν regimes. The neoclassical toroidal viscosity (NTV) torque in the 1/ν and ν - √ν regimes is calculated. The observed torque is of a magnitude in between that of the NTV torque in the 1/ν and ν - √ν regimes. The NTV torque in the ν - √ν regimes is enhanced using the Lagrangian variation of the magnetic field strength. However, it is still smaller than the observed torque by one order of magnitude.
Shielding of External Magnetic Perturbations By Torque In Rotating Tokamak Plasmas
International Nuclear Information System (INIS)
Park, Jong-Kyu; Boozer, Allen H.; Menard, Jonathan E.; Gerhardt, Stefan P.; Sabbagh, Steve A.
2009-01-01
The imposition of a nonaxisymmetric magnetic perturbation on a rotating tokamak plasma requires energy and toroidal torque. Fundamental electrodynamics implies that the torque is essentially limited and must be consistent with the external response of a plasma equilibrium (rvec f) = (rvec j) x (rvec B). Here magnetic measurements on National Spherical Torus eXperiment (NSTX) device are used to derive the energy and the torque, and these empirical evaluations are compared with theoretical calculations based on perturbed scalar pressure equilibria (rvec f) = (rvec (del))p coupled with the theory of nonambipolar transport. The measurement and the theory are consistent within acceptable uncertainties, but can be largely inconsistent when the torque is comparable to the energy. This is expected since the currents associated with the torque are ignored in scalar pressure equilibria, but these currents tend to shield the perturbation.
Directory of Open Access Journals (Sweden)
Fijałkowski Karol
2017-06-01
Full Text Available The aim of the present study was to evaluate the impact of a rotating magnetic field (RMF on cellular and biochemical properties of Gluconacetobacter xylinus during the process of cellulose synthesis by these bacteria. The application of the RMF during bacterial cellulose (BC production intensified the biochemical processes in G. xylinus as compared to the RMF-unexposed cultures. Moreover, the RMF had a positive impact on the growth of cellulose-producing bacteria. Furthermore, the application of RMF did not increase the number of mutants unable to produce cellulose. In terms of BC production efficacy, the most favorable properties were found in the setting where RMF generator was switched off for the first 72 h of cultivation and switched on for the further 72 h. The results obtained can be used in subsequent studies concerning the optimization of BC production using different types of magnetic fields including RMF, especially.
Shot noise of charge current in a quantum dot responded by rotating and oscillating magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Zhao, Hong-Kang, E-mail: zhaohonk@yahoo.com; Zou, Wei-Ke [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Chen, Qiao [Department of Maths and Physics, Hunan Institute of Engineering, Xiangtan 411104 (China)
2014-09-07
We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle θ of RMF. The magnitude of shot noise increases as the photon energy ℏω of OMF increases, and its valley eventually is reversed to peaks as the photon energy is large enough. Double-peak structure of Fano factor is exhibited as the frequency of OMF increases to cover a large regime. The Zeeman energy μ{sub 0}B{sub 0} acts as an effective gate bias to exhibit resonant behavior, and novel peak emerges associated with the applied OMF.
Hamano, Noritaka; Yamamoto, Atsushi; Shitara, Hitoshi; Ichinose, Tsuyoshi; Shimoyama, Daisuke; Sasaki, Tsuyoshi; Kobayashi, Tsutomu; Kakuta, Yohei; Osawa, Toshihisa; Takagishi, Kenji
2017-06-01
Muscle atrophy and fatty infiltration in the rotator cuff muscles are often observed in patients with chronic rotator cuff tears. The recovery from these conditions has not been clarified. Ninety-four patients were included in this study. The improvement in muscle atrophy and fatty infiltration in successfully repaired rotator cuff tears was evaluated by magnetic resonance imaging at 1 year and 2 years after surgery and was compared with muscle atrophy and fatty infiltration observed on magnetic resonance imaging at 2 weeks after surgery to discount any changes due to the medial retraction of the torn tendon. The patients' muscle strength was evaluated in abduction and external rotation. Muscle atrophy and fatty infiltration of the supraspinatus were significantly improved at 2 years after surgery in comparison to 2 weeks after surgery. The subjects' abduction and external rotation strength was also significantly improved at 2 years after surgery in comparison to the preoperative values. Patients whose occupation ratio was improved had a better abduction range of motion, stronger abduction strength, and higher Constant score. Patients whose fatty infiltration was improved had a better range of motion in flexion and abduction, whereas the improvements of muscle strength and the Constant score were similar in the group that showed an improvement of fatty infiltration and the group that did not. Muscle atrophy and fatty infiltration can improve after rotator cuff repair. The strengths of abduction and external rotation were also improved at 2 years after surgery. Copyright © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.
International Nuclear Information System (INIS)
Zhmetko, D.N.; Zhmetko, S.D.
2009-01-01
The damping of the motion of domain walls of a sandwich domain structure by the eddy currents magnetic fields, the stray fields and the hysteresis friction fields is investigated. The blocking of the motion of domain walls by the eddy currents magnetic fields is discovered.
Long pulse FRC sustainment with enhanced edge driven rotating magnetic field current drive
International Nuclear Information System (INIS)
Hoffman, A.L.; Guo, H.Y.; Miller, K.E.; Milroy, R.D.
2005-01-01
FRCs have been formed and sustained for up to 50 normal flux decay times by Rotating Magnetic Fields (RMF) in the TCS experiment. For these longer pulse times a new phenomenon has been observed: switching to a higher performance mode delineated by shallower RMF penetration, higher ratios of generated poloidal to RMF drive field, and lower overall plasma resistivity. This global data is not explainable by previous RMF theory based on uniform electron rotational velocities or by numerical calculations based on uniform plasma resistivity, but agrees in many respects with new calculations made using strongly varying resistivity profiles. In order to more realistically model RMF driven FRCs with such non-uniform resistivity profiles, a double rigid rotor model has been developed with separate inner and outer electron rotational velocities and resistivities. The results of this modeling suggest that the RMF drive results in very high resistivity in a narrow edge layer, and that the higher performance mode is characterized by a sharp reduction in resistivity over the bulk of the FRC. (author)
Radial modes of slowly rotating compact stars in the presence of magnetic field
Energy Technology Data Exchange (ETDEWEB)
Panda, N.R. [Institute of Physics, Bhubaneswar (India); Siksha ' O' Anusandhan University, Bhubaneswar (India); Mohanta, K.K. [Rairangpur College, Rairangpur, Odisha (India); Sahu, P.K. [Institute of Physics, Bhubaneswar (India)
2016-09-15
Compact stars are composed of very high-density hadron matter. When the matter is above nuclear matter density, then there is a chance of different phases of matter such as hadron matter to quark matter. There is a possible phase which, having the quark core surrounded by a mixed phase followed by hadronic matter, may be considered as a hybrid phase inside the stars called hybrid star (HS). The star which consists of only u, d and s quarks is called quark star (QS) and the star which has only hadronic matter is called neutron star (NS). For the equation of state (EOS) of hadronic matter, we have considered the Relativistic Mean Field (RMF) theory and we incorporated the effect of strong magnetic fields. For the EOS of the quark phase we use the simple MIT bag model. We have assumed Gaussian parametrization to make the density dependent for both bag pressure in quark matter and magnetic field. We have constructed the intermediate mixed phase by using the Glendenning conjecture. Eigenfrequencies of radial pulsations of slowly rotating magnetized compact stars (NS, QS, HS) are calculated in a general relativistic formalism given by Chandrasekhar and Friedman. We have studied the effect of central density on the square of the frequencies of the compact stars in the presence of zero and strong magnetic field. (orig.)
Backe, H; Engfer, R; Kankeleit, E; Link, R; Michaelsen, R; Petitjean, C; Schellenberg, L; Schneuwly, H; Schröder, W U; Vuilleumier, J L; Walter, H K; Zehnder, A
1973-01-01
The lowest states in muonic atoms are rather sensitive to the spatial distribution of the nuclear magnetization density, and several results were deduced from the broadening of the muonic 2p/sub 1/2/-1s/sub 1/2/ and 3d/sub 3/2/-2p/sub 1/2/ transitions. By measuring low energetic transitions such as the 2s/sub 1/2/-2p/sub 1/2/ transition or nuclear gamma -transitions, it is possible to resolve the magnetic hyperfine splittings. The magnetic hf splitting of the 2s/sub 1/2/-2p/sub 1/2/ transition in mu /sup 115/In and of the 3/2/sup +/-1/2/sup +/ nuclear gamma -transitions in mu /sup 203/Tl at 279 keV, and in mu /sup 205/Tl at 204 keV, have been resolved. For the 2/sup +/-0/sup +/ nuclear gamma -transition in mu /sup 190,192/Os at 187 keV and 206 keV, respectively, the magnetic hf splitting of the 2/sup +/ rotational levels and the intensities of the hf components were determined from a nearly resolved doublet splitting. (7 refs).
Spin, quadrupole moment, and deformation of the magnetic-rotational band head in Pb193
Balabanski, D. L.; Ionescu-Bujor, M.; Iordachescu, A.; Bazzacco, D.; Brandolini, F.; Bucurescu, D.; Chmel, S.; Danchev, M.; de Poli, M.; Georgiev, G.; Haas, H.; Hübel, H.; Marginean, N.; Menegazzo, R.; Neyens, G.; Pavan, P.; Rossi Alvarez, C.; Ur, C. A.; Vyvey, K.; Frauendorf, S.
2011-01-01
The spectroscopic quadrupole moment of the T1/2=9.4(5) ns isomer in Pb193 at an excitation energy Eex=(2585+x) keV is measured by the time-differential perturbed angular distribution method as |Qs|=2.6(3) e b. Spin and parity Iπ=27/2- are assigned to it based on angular distribution measurements. This state is the band head of a magnetic-rotational band, described by the 1i13/2 subshell with the (3s1/2-21h9/21i13/2)11- proton excitation. The pairing-plus-quadrupole tilted-axis cranking calculations reproduce the measured quadrupole moment with a moderate oblate deformation ɛ2=-0.11, similar to that of the 11-proton intruder states, which nuclei in the region. This is the first direct measurement of a quadrupole moment and thus of the deformation of a magnetic-rotational band head.
Spin, quadrupole moment, and deformation of the magnetic-rotational band head in (193)Pb
Balabanski, D L; Iordachescu, A; Bazzacco, D; Brandolini, F; Bucurescu, D; Chmel, S; Danchev, M; De Poli, M; Georgiev, G; Haas, H; Hubel, H; Marginean, N; Menegazzo, R; Neyens, G; Pavan, P; Rossi Alvarez, C; Ur, C A; Vyvey, K; Frauendorf, S
2011-01-01
The spectroscopic quadrupole moment of the T(1/2) = 9.4(5) ns isomer in (193)Pb at an excitation energy E(ex) = (2585 + x) keV is measured by the time-differential perturbed angular distribution method as vertical bar Q(s)vertical bar = 2.6(3) e b. Spin and parity I(pi) = 27/2(-) are assigned to it based on angular distribution measurements. This state is the band head of a magnetic-rotational band, described by the coupling of a neutron hole in the 1i(13/2) subshell with the (3s(1/2)(-2)1h(9/2)1i(13/2))(11-) proton excitation. The pairing-plus-quadrupole tilted-axis cranking calculations reproduce the measured quadrupole moment with a moderate oblate deformation epsilon(2) = -0.11, similar to that of the 11(-)proton intruder states, which occur in the even-even Pb nuclei in the region. This is the first direct measurement of a quadrupole moment and thus of the deformation of a magnetic-rotational band head.
Grants, Ilmars; Gerbeth, Gunter
2010-07-01
The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by a rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilize the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. These rolls can only be excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this nonlinear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and nonlinear components of this transition by direct numerical simulation of the flow response to noise. It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.
Waltz, R. E.; Waelbroeck, F. L.
2012-03-01
Static external resonant magnetic perturbations (RMPs) have been added to the δf gyrokinetic code GYRO. This allows nonlinear gyrokinetic simulations of the nonambipolar radial current flow jr and the corresponding plasma torque (density) R[jrBθ/c], induced by islands that break the toroidal symmetry of a tokamak. This extends previous GYRO simulations for the transport of toroidal angular momentum (TAM) [1,2]. The focus is on full torus radial slice electrostatic simulations of induced q=m/n=6/3 islands with widths 5% of the minor radius. The island torque scales with the radial electric field Er the island width w, and the intensity I of the high-n micro-turbulence, as wErI^1/2. The net island torque is null at zero Er rather than at zero toroidal rotation. This means that there is a small co-directed magnetic acceleration to the small diamagnetic co-rotation corresponding to the zero Er which can be called the residual stress [2] from an externally induced island. Finite-beta GYRO simulations of a core radial slice demonstrate island unlocking and the RMP screening. 6pt[1] R.E. Waltz, et al., Phys. Plasmas 14, 122507 (2007). [2] R.E. Waltz, et al., Phys. Plasmas 18, 042504 (2011).
Evidence of magnetic field in plasma focus by means of Faraday rotation measurements
International Nuclear Information System (INIS)
Fischfeld, G.
1982-01-01
Preliminary results of Faraday rotation measurements on a beam of laser light crossing the plasma column in the axial direction. are repacted. The presence of intense axial magnetic field Bsup(z) in the column both before and during the pinch phase is demonstrated. The experiments were performed on the Mather type Frascati 1 MJ plasma Focus, operated at 250 KJ 3 torr D 2 filling pressure. Is is used in the measurements a Quantel YG 49 YAG laser, frecuency doubled by means of KD*P crystal, which delivers about 60 mJ in 3 ns at = 530 nm. The beam polarization is analized by Wollaston prism. The electronic density is determined by Mach-Zender insterferometry. Two measurements are taken at time close to the end of the radial collapse phase, yielding Faraday rotation angles of 0.25 +- 0.05 rd and 0.56 +- o.05 rd which correspond to values, of axial magnetic fields of b(sup z) = 500 KG and B(sub z) = 400 KG. (Author) [pt
Ireland, Lewis G.; Browning, Matthew K.
2018-04-01
Some low-mass stars appear to have larger radii than predicted by standard 1D structure models; prior work has suggested that inefficient convective heat transport, due to rotation and/or magnetism, may ultimately be responsible. We examine this issue using 1D stellar models constructed using Modules for Experiments in Stellar Astrophysics (MESA). First, we consider standard models that do not explicitly include rotational/magnetic effects, with convective inhibition modeled by decreasing a depth-independent mixing length theory (MLT) parameter α MLT. We provide formulae linking changes in α MLT to changes in the interior specific entropy, and hence to the stellar radius. Next, we modify the MLT formulation in MESA to mimic explicitly the influence of rotation and magnetism, using formulations suggested by Stevenson and MacDonald & Mullan, respectively. We find rapid rotation in these models has a negligible impact on stellar structure, primarily because a star’s adiabat, and hence its radius, is predominantly affected by layers near the surface; convection is rapid and largely uninfluenced by rotation there. Magnetic fields, if they influenced convective transport in the manner described by MacDonald & Mullan, could lead to more noticeable radius inflation. Finally, we show that these non-standard effects on stellar structure can be fabricated using a depth-dependent α MLT: a non-magnetic, non-rotating model can be produced that is virtually indistinguishable from one that explicitly parameterizes rotation and/or magnetism using the two formulations above. We provide formulae linking the radially variable α MLT to these putative MLT reformulations.
Directory of Open Access Journals (Sweden)
Assaf Rotem
Full Text Available Transcranial Magnetic Stimulation (TMS is a promising technology for both neurology and psychiatry. Positive treatment outcome has been reported, for instance in double blind, multi-center studies on depression. Nonetheless, the application of TMS towards studying and treating brain disorders is still limited by inter-subject variability and lack of model systems accessible to TMS. The latter are required to obtain a deeper understanding of the biophysical foundations of TMS so that the stimulus protocol can be optimized for maximal brain response, while inter-subject variability hinders precise and reliable delivery of stimuli across subjects. Recent studies showed that both of these limitations are in part due to the angular sensitivity of TMS. Thus, a technique that would eradicate the need for precise angular orientation of the coil would improve both the inter-subject reliability of TMS and its effectiveness in model systems. We show here how rotation of the stimulating field relieves the angular sensitivity of TMS and provides improvements in both issues. Field rotation is attained by superposing the fields of two coils positioned orthogonal to each other and operated with a relative phase shift in time. Rotating field TMS (rfTMS efficiently stimulates both cultured hippocampal networks and rat motor cortex, two neuronal systems that are notoriously difficult to excite magnetically. This opens the possibility of pharmacological and invasive TMS experiments in these model systems. Application of rfTMS to human subjects overcomes the orientation dependence of standard TMS. Thus, rfTMS yields optimal targeting of brain regions where correct orientation cannot be determined (e.g., via motor feedback and will enable stimulation in brain regions where a preferred axonal orientation does not exist.
The helical tomotherapy thread effect
International Nuclear Information System (INIS)
Kissick, M.W.; Fenwick, J.; James, J.A.; Jeraj, R.; Kapatoes, J.M.; Keller, H.; Mackie, T.R.; Olivera, G.; Soisson, E.T.
2005-01-01
Inherent to helical tomotherapy is a dose variation pattern that manifests as a 'ripple' (peak-to-trough relative to the average). This ripple is the result of helical beam junctioning, completely unique to helical tomotherapy. Pitch is defined as in helical CT, the couch travel distance for a complete gantry rotation relative to the axial beam width at the axis of rotation. Without scattering or beam divergence, an analytical posing of the problem as a simple integral predicts minima near a pitch of 1/n where n is an integer. A convolution-superposition dose calculator (TomoTherapy, Inc.) included all the physics needed to explore the ripple magnitude versus pitch and beam width. The results of the dose calculator and some benchmark measurements demonstrate that the ripple has sharp minima near p=0.86(1/n). The 0.86 factor is empirical and caused by a beam junctioning of the off-axis dose profiles which differ from the axial profiles as well as a long scatter tail of the profiles at depth. For very strong intensity modulation, the 0.86 factor may vary. The authors propose choosing particular minima pitches or using a second delivery that starts 180 deg off-phase from the first to reduce these ripples: 'Double threading'. For current typical pitches and beam widths, however, this effect is small and not clinically important for most situations. Certain extremely large field or high pitch cases, however, may benefit from mitigation of this effect
Feonychev, A. I.
It is well known that numerous experiments on crystal growth by the Bridgman method in space had met with only limited success. Because of this, only floating zone method is promising at present. However, realization of this method demands solution of some problems, in particular reduction of dopant micro- and macrosegregation. Rotating magnetic field is efficient method for control of flow in electrically conducting fluid and transfer processes. Investigation of rotating magnetic field had initiated in RIAME MAI in 1994 /3/. Results of the last investigations had been presented in /4/. Mathematical model of flow generated by rotating magnetic field and computer program were verified by comparison with experiment in area of developed oscillatory flow. Nonlinear analysis of flow stability under combination of thermocapillary convection and secondary flow generated by rotating magnetic field shows that boundary of transition from laminar to oscillatory flow is nonmonotone function in the plane of Marangoni number (Ma) - combined parameter Reω Ha2 (Ha is Hartman number, Reω is dimensionless velocity of magnetic field rotation). These data give additional knowledge of mechanism of onset of oscillations. In this case, there is reason to believe that the cause is Eckman's viscous stresses in rotating fluid on solid end-walls. It was shown that there is a possibility to increase stability of thermocapillary convection and in doing so to remove the main cause of dopant microsegregation. In doing so, if parameters of rotating magnetic field had been incorrectly chosen the dangerous pulsating oscillations are to develop. Radial macrosegregation of dopant can result from correct choosing of parameters of rotating magnetic field. As example, optimization of rotating magnetic field had been carried out for Ge(Ga) under three values of Marangoni number in weightlessness conditions. In the case when rotating magnetic field is used in terrestrial conditions, under combination of
LIM, M.; PARK, Y.; Jung, H.; SHIN, Y.; Rim, H.; PARK, C.
2017-12-01
To measure all components of a physical property, for example the magnetic field, is more useful than to measure its magnitude only in interpretation and application thereafter. To convert the physical property measured in 3 components on a random coordinate system, for example on moving magnetic sensor body's coordinate system, into 3 components on a fixed coordinate system, for example on geographical coordinate system, by the rotations of coordinate system around Euler angles for example, we should have the attitude values of the sensor body in time series, which could be acquired by an INS-GNSS system of which the axes are installed coincident with those of the sensor body. But if we want to install some magnetic sensors in array at sea floor but without attitude acquisition facility of the magnetic sensors and to monitor the variation of magnetic fields in time, we should have also some way to estimate the relation between the geographical coordinate system and each sensor body's coordinate system by comparison of the vectors only measured on both coordinate systems on the assumption that the directions of the measured magnetic field on both coordinate systems are the same. For that estimation, we have at least 3 ways. The first one is to calculate 3 Euler angles phi, theta, psi from the equation Vgeograph = Rx(phi) Ry(theta) Rz(psi) Vrandom, where Vgeograph is the vector on geographical coordinate system etc. and Rx(phi) is the rotation matrix around the x axis by the angle phi etc. The second one is to calculate the difference of inclination and declination between the 2 vectors on spherical coordinate system. The third one, used by us for this study, is to calculate the angle of rotation along a great circle around the rotation axis, and the direction of the rotation axis. We installed no. 1 and no. 2 FVM-400 fluxgate magnetometers in array near Cheongyang Geomagnetic Observatory (IAGA code CYG) and acquired time series of magnetic fields for CYG and for
International Nuclear Information System (INIS)
Castejon M, F.
1989-01-01
The study of the Linear Theory microwave propagation and absorption in the the frequency range of electron cyclotron resonance, in a magnetized plasma, is developed. This study is particularized to the flexible heliac TJ-II, whose main characteristics are dsetailed in a memory chapter, as an interesting case example for its peculiar magnetic configuration. As a preliminary phase, a cold plasma model is useds to analyze the resonance accessibility and the approximated density limits which will be obtainable in each electron cyclotron resonance harmonic. This analysis was used to find the suitable positions for the microwave injection in TJ-II. An analytical weakly relativistic model for the dielectric tensor is developed, valid for oblique propagation, that takes account of the effect of superthermal electrons. Second order Larmor radius effects are included, so that the Quasi-Electrostatic branch of X mode can be studied. A numerical study is then presented on the absorption properties of TJ-II. Since the TJ-II geometry is complex and its magnetic field distribution is very different from that of a tokamak, ray tracing calculations are necessary to consider refraction effects. The ray tracing codse RAYS, developed in the Oak Ridge National Laboratory (U.S.A.), was take and adapted to the helical magnetic configuration of the TJ-II. The absorption model described above was then included in RAYS. For completeness, an introduction to the Quasi Linear Theory, natural prolongation of this work, is included at the end of the memory, ands the effects of taking into account the quasi linear evolution of the distribution function are described. (Author)
Helicity and Filament Channels? The Straight Twist!
Antiochos, Spiro K.
2010-01-01
One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at special locations, photospheric polarity inversions lines where the non-potentiality is observed as a filament channel. This characteristic feature of the closed-field corona is highly unexpected given that photospheric motions continuously tangle its magnetic field. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. We propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries, polarity inversion lines, creating filament channels. We describe how the helicity is injected and transported and calculate the relevant rates. We argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field.
Bayones, F. S.; Abd-Alla, A. M.
2018-06-01
The prime objective of the present paper is to analyze the effect of magnetic field and rotation on the free vibrations of an elastic hollow sphere. The one-dimensional equation of motion is solved in terms of radial displacement. The frequency equation is obtained when the boundaries are free and fixed boundary conditions. The determination is concerned with the eigenvalues of the natural frequency of the free vibrations in the case of harmonic vibrations. The natural frequencies and the mode shapes are calculated numericall and the effects of rotation and magnetic field are discussed. It was shown that the dispersion curves of waves were significantly influenced by the magnetic field and rotation of the elastic sphere.
Multiple helical modes of vortex breakdown
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Naumov, I. V.; Okulov, Valery
2011-01-01
Experimental observations of vortex breakdown in a rotating lid-driven cavity are presented. The results show that vortex breakdown for cavities with high aspect ratios is associated with the appearance of stable helical vortex multiplets. By using results from stability theory generalizing Kelvi......’s problem on vortex polygon stability, and systematically exploring the cavity flow, we succeeded in identifying two new stable vortex breakdown states consisting of triple and quadruple helical multiplets....
Kinetic equilibrium for an asymmetric tangential layer with rotation of the magnetic field
Belmont, Gérard; Dorville, Nicolas; Aunai, Nicolas; Rezeau, Laurence
2015-04-01
Finding kinetic equilibria for tangential current layers is a key issue for modeling plasma phenomena such as magnetic reconnection instabilities, for which theoretical and numerical studies have to start from steady-state current layers. Until 2012, all theoretical models -starting with the most famous "Harris" one- relied on distribution functions built as mono-valued functions of the trajectories invariants. For a coplanar anti-symmetric magnetic field and in absence of electric field, these models were only able to model symmetric variations of the plasma, so precluding any modeling of "magnetopause-like'' layers, which separate two plasmas of different densities and temperatures. Recently, the "BAS" model was presented (Belmont et al., 2012), where multi-valued functions were taken into account. This new tool is made necessary each time the magnetic field reversal occurs on scales larger than the particle Larmor radii, and therefore guaranties a logical transition with the MHD modeling of large scales. The BAS model so provides a new asymmetric equilibrium. It has been validated in a hybrid simulation by Aunai et al (2013), and more recently in a fully kinetic simulation as well. For this original equilibrium to be computed, the magnetic field had to stay coplanar inside the layer. We present here an important generalization, where the magnetic field rotates inside the layer (although restricted to a 180° rotation hitherto). The tangential layers so obtained are thus closer to those encountered at the real magnetopause. This will be necessary, in the future, for comparing directly the theoretical profiles with the experimental ones for the various physical parameters. As it was done previously, the equilibrium is presently tested with a hybrid simulation. Belmont, G.; Aunai, N.; Smets, R., Kinetic equilibrium for an asymmetric tangential layer, Physics of Plasmas, Volume 19, Issue 2, pp. 022108-022118-10, 2012 Aunai, N.; Belmont, G.; Smets, R., First
International Nuclear Information System (INIS)
Sonier, J E
2007-01-01
The focus of this paper is on recent progress in muon spin rotation (μSR) studies of the vortex cores in type-II superconductors. By comparison of μSR measurements of the vortex core size in a variety of materials with results from techniques that directly probe electronic states, the effect of delocalized quasiparticles on the spatial variation of field in a lattice of interacting vortices has been determined for both single-band and multi-band superconductors. These studies demonstrate the remarkable accuracy of what some still consider an exotic technique. In recent years μSR has also been used to search for magnetism in and around the vortex cores of high-temperature superconductors. As a local probe μSR is specially suited for detecting static or quasistatic magnetism having short-range or random spatial correlations. As discussed in this review, μSR experiments support a generic phase diagram of competing superconducting and magnetic order parameters, characterized by a quantum phase transition to a state where the competing order is spatially nonuniform
International Nuclear Information System (INIS)
Ohyabu, N.; Watanabe, T.; Ji Hantao
1993-07-01
The Large Helical Device (LHD) now under construction is a heliotron/torsatron device with a closed divertor system. The edge LHD magnetic structure has been studied in detail. A peculiar feature of the configuration is existence of edge surface layers, a complicated three dimensional magnetic structure which does not, however, seem to hamper the expected divertor functions. Two divertor operational modes are being considered for the LHD experiment, high density, cold radiative divertor operation as a safe heat removal scheme and high temperature divertor plasma operation. In the latter operation, a divertor plasma with temperature of a few kev, generated by efficient pumping, expects to lead to significant improvement in core plasma confinement. Conceptual designs of the LHD divertor components are under way. (author)
Polymorphic transformation of helical flagella of bacteria
Lim, Sookkyung; Howard Berg Collaboration; William Ko Collaboration; Yongsam Kim Collaboration; Wanho Lee Collaboration; Charles Peskin Collaboration
2016-11-01
Bacteria such as E. coli swim in an aqueous environment by utilizing the rotation of flagellar motors and alternate two modes of motility, runs and tumbles. Runs are steady forward swimming driven by bundles of flagellar filaments whose motors are turning CCW; tumbles involve a reorientation of the direction of swimming triggered by motor reversals. During tumbling, the helical flagellum undergoes polymorphic transformations, which is a local change in helical pitch, helical radius, and handedness. In this work, we investigate the underlying mechanism of structural conformation and how this polymorphic transition plays a role in bacterial swimming. National Science Foundation.
International Nuclear Information System (INIS)
Andreev, Pavel A.
2015-01-01
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction
Spencer, Charles S.; Gayles, Jacob; Porter, Nicholas A.; Sugimoto, Satoshi; Aslam, Zabeada; Kinane, Christian J.; Charlton, Timothy R.; Freimuth, Frank; Chadov, Stanislav; Langridge, Sean; Sinova, Jairo; Felser, Claudia; Blügel, Stefan; Mokrousov, Yuriy; Marrows, Christopher H.
2018-06-01
Epitaxial films of the B20-structure compound Fe1 -yCoyGe were grown by molecular beam epitaxy on Si (111) substrates. The magnetization varied smoothly from the bulklike values of one Bohr magneton per Fe atom for FeGe to zero for nonmagnetic CoGe. The chiral lattice structure leads to a Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground state was confirmed using polarized neutron reflectometry measurements. The pitch of the spin helix, measured by this method, varies with Co content y and diverges at y ˜0.45 . This indicates a zero crossing of the DMI, which we reproduced in calculations using first-principles methods. We also measured the longitudinal and Hall resistivity of our films as a function of magnetic field, temperature, and Co content y . The Hall resistivity is expected to contain contributions from the ordinary, anomalous, and topological Hall effects. Both the anomalous and topological Hall resistivities show peaks around y ˜0.5 . Our first-principles calculations show a peak in the topological Hall constant at this value of y , related to the strong spin polarization predicted for intermediate values of y . Our calculations predict half-metallicity for y =0.6 , consistent with the experimentally observed linear magnetoresistance at this composition, and potentially related to the other unusual transport properties for intermediate value of y . While it is possible to reconcile theory with experiment for the various Hall effects for FeGe, the large topological Hall resistivities for y ˜0.5 are much larger than expected when the very small emergent fields associated with the divergence in the DMI are taken into account.
Transport barrier in Helical system
International Nuclear Information System (INIS)
Ida, Katsumi
1998-01-01
Experiments on the transport barrier in Helical plasmas are reviewed. There are two mechanisms of transport improvement, that results in the formation of the transport barrier. One is the improvement of neoclassical transport by reducing the ripple loss with radial electric field, which exist only in helical plasma. The other is the improvement of anomalous transport due to the suppression of fluctuations associated with a radial electric field shear both in tokamak and helical plasma. The formation of the transport barrier can be triggered by the radial electric field shear associated with the transition of the radial electric field (L/H transition or ion-electron root transition) or the peaked density or the optimization of magnetic field shear. The mechanisms of transport barrier formation are also discussed. (author). 60 refs
Generalized helicity and Beltrami fields
Energy Technology Data Exchange (ETDEWEB)
Buniy, Roman V., E-mail: roman.buniy@gmail.com [Schmid College of Science, Chapman University, Orange, CA 92866 (United States); Isaac Newton Institute, University of Cambridge, Cambridge, CB3 0EH (United Kingdom); Kephart, Thomas W., E-mail: tom.kephart@gmail.com [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Isaac Newton Institute, University of Cambridge, Cambridge, CB3 0EH (United Kingdom)
2014-05-15
We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫{sub Ω}trF{sub μν}F{sup μν}d{sup 4}x subject to the local constraint ε{sup μναβ}trF{sub μν}F{sub αβ}=0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity.
Generalized helicity and Beltrami fields
International Nuclear Information System (INIS)
Buniy, Roman V.; Kephart, Thomas W.
2014-01-01
We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫ Ω trF μν F μν d 4 x subject to the local constraint ε μναβ trF μν F αβ =0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity
NuSTAR and swift observations of the fast rotating magnetized white dwarf AE Aquarii
DEFF Research Database (Denmark)
Kitaguchi, Takao; An, Hongjun; Beloborodov, Andrei M.
2014-01-01
AE Aquarii is a cataclysmic variable with the fastest known rotating magnetized white dwarf (P-spin = 33.08 s). Compared to many intermediate polars, AE Aquarii shows a soft X-ray spectrum with a very low luminosity (L-X similar to 10(31) erg s(-1)). We have analyzed overlapping observations...... of this system with the NuSTAR and the Swift X-ray observatories in 2012 September. We find the 0.5-30 keV spectra to be well fitted by either an optically thin thermal plasma model with three temperatures of 0.75(-0.45)(+0.18), 2.29(-0.82)(+0.96), and 9.33(-2.18)(+6.07) keV, or an optically thin thermal plasma...
International Nuclear Information System (INIS)
Yang, J.; Kondoh, T.; Kan, K.; Kozawa, T.; Yoshida, Y.; Tagawa, S.
2006-01-01
A femtosecond (fs) electron bunching was observed in a photoinjector with a magnetic compressor by rotating the bunch in longitudinal phase space. The bunch length was obtained by measuring Cherenkov radiation of the electron beam with a femtosecond streak camera technique. A single electron bunch with rms bunch length of 98 fs was observed for a 32 MeV electron beam at a charge of 0.17 nC. The relative energy spread and the normalized transverse emittance of the electron beam were 0.2% and 3.8 mm-mrad, respectively. The effect of space charge on the bunch compression was investigated experimentally for charges from 0.17 to 1.25 nC. The dependences of the relative energy spread and the normalized beam transverse emittance on the bunch charge were measured
Use of an arc plasma rotating in a magnetic field for metal coating glass substrates
International Nuclear Information System (INIS)
Vukanovic, V.; Butler, S.; Kapur, S.; Krakower, E.; Allston, T.; Belfield, K.; Gibson, G.
1983-01-01
First results are reported about deposition of metals on glass substrate using a low current arc plasma source at atmospheric pressure. The arc source consists of a graphite cathode rod placed on the axis of a graphite anode cylinder aligned in a magnetic field. The carrier gas is argon. The deposition material, zinc or gold, is evaporated from a reservoir in the cathode. Depositions on flat substrates positioned on the periphery of the rotating plasma within the anode tube and in a jet outside the anode have been investigated. The investigations are planned to lead towards laser fusion target pusher layer fabrication. This fabrication would be facilitated by a high pressure deposition process where target levitation is readily performed
Local study of helical magnetorotational instability in viscous Keplerian disks
MahdaviGharavi, M.; Hajisharifi, K.; Mehidan, H.
2018-03-01
In this paper, regarding the recent detection of significant azimuthal magnetic field in some accretion disks such as protostellar (Donati et al. in Nature 438:466, 2005), the multi-fluid model has been employed to analysis the stability of Keplerian rotational viscous dusty plasma system in a current-free helical magnetic field structure. Using the fluid-Maxwell equations, the general dispersion relation of the excited modes in the system has been obtained by applying the local approximation method in the linear perturbation theory. The typical numerical analysis of the obtained dispersion relation in the high-frequency regime shows that the presence of azimuthal magnetic field component in Keplerian flow has a considerable role in the stability conditions of the system. It also shows that the magnetic field helicity has a stabilization role against the magnetorotational instability (MRI) in the system due to contraction of the unstable wavelength region and decreasing the maximum growth rate of the instability. In this sense, the stabilization role of the viscosity term is more considerable for HMRI (instability in the presence of azimuthal magnetic field component) than the corresponding MRI (instability in the absence of azimuthal magnetic field component). Moreover, considering the discovered azimuthal magnetic field in these systems, the MRI can be arisen in the over-all range of dust grains construction values in contract with traditional MRI. This investigation can greatly contribute to better understanding the physics of some astrophysical phenomena, such as the main source of turbulence and angular momentum transport in protostellar and the other sufficiently ionized astrophysical disks, where the azimuthal magnetic field component in these systems can play a significant role.
THE EFFECTS OF CLOSE COMPANIONS (AND ROTATION) ON THE MAGNETIC ACTIVITY OF M DWARFS
International Nuclear Information System (INIS)
Morgan, Dylan P.; West, Andrew A.; Dhital, Saurav; Fuchs, Miriam; Garcés, Ane; Catalán, Silvia; Silvestri, Nicole M.
2012-01-01
We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf main-sequence binaries from Rebassa-Mansergas et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space. Then using the SDSS Data Release 8 spectroscopic database, we construct a sample of 1756 WD+dM high-quality pairs from our color cuts and previous catalogs. We separate the individual WD and dM from each spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the Hα emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types ≤ M7. Our results show that early-type M dwarfs (≤M4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems become more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully convective stars. Using the WD components of the pairs, we find WD cooling ages to use as an additional constraint on the age-activity relation for our sample. We find that, on average, active early-type dMs tend to be younger and that active late-type dMs span a much broader age regime making them
Doppler-Zeeman Mapping of the Rapidly Rotating Magnetic CP Star HD37776
Khokhlova, V. L.; Vasilchenko, D. V.; Stepanov, V. V.; Romanyuk, I. I.
2000-03-01
We present the results of our analysis of magnetic-field configuration and abundance anomalies on the surface of the rapidly rotating, chemically peculiar helium-strong variable B2 V star HD37776 with unresolved Zeeman components of spectral lines. Simultaneous inversion of the observed Stokes I and V profiles, which realizes the method of Doppler-Zeeman mapping (Vasilchenko et al. 1996), has been applied for the first time. Spectroscopic observations were carried out with the Main stellar spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a Zeeman analyzer and a CCD array, which allowed spectra in right- and left-hand circularly polarized light to be taken simultaneously at a signal-to-noise ratio S/N > 200 (Romanyuk et al. 1999). The profile width of winged spectral lines (reaching 5 A) is determined by Zeeman line splitting; however, the observed Zeeman components are blurred and unresolved because of the rapid stellar rotation. When solving the inverse problem, we sought for the magnetic-field configuration in the form of a combination of arbitrarily oriented dipole, quadrupole, and octupole placed at the stellar center. The observed Stokes I and V profiles for eight spectral lines of He, OII, AlIII, SiIII, and FeIII averaged over the visible stellar surface were used as input data. We constructed a model of the magnetic field from the condition of coincidence of magnetic maps obtained from different lines of different chemical elements and from the condition of a minimum profile residual. This model is a combination of centered coaxial dipole and quadrupole with the dominant quadrupole component at 30 deg < i < 50 deg, beta = 40 deg, and a maximum surface field strength H_s = 60 kG. A comparison of our abundance maps with the field configuration shows that the He concentration is at a maximum in the regions of maximum radial field, while the maximum concentrations of O, Al, Si, and Fe coincide with the regions of maximum
Static magnetic Faraday rotation spectroscopy combined with a differential scheme for OH detection
Zhao, Weixiong; Deng, Lunhua; Qian, Xiaodong; Fang, Bo; Gai, Yanbo; Chen, Weidong; Gao, Xiaoming; Zhang, Weijun
2015-04-01
The hydroxyl (OH) radical plays a critical role in atmospheric chemistry due to its high reactivity with volatile organic compounds (VOCs) and other trace gaseous species. Because of its very short life time and very low concentration in the atmosphere, interference-free high sensitivity in-situ OH monitoring by laser spectroscopy represents a real challenge. Faraday rotation spectroscopy (FRS) relies on the particular magneto-optic effect observed for paramagnetic species, which makes it capable of enhancing the detection sensitivity and mitigation of spectral interferences from diamagnetic species in the atmosphere. When an AC magnetic field is used, the Zeeman splitting of the molecular absorption line (and thus the magnetic circular birefringence) is modulated. This provides an 'internal modulation' of the sample, which permits to suppress the external noise like interference fringes. An alternative FRS detection scheme is to use a static magnetic field (DC-field) associated with laser wavelength modulation to effectively modulate the Zeeman splitting of the absorption lines. In the DC field case, wavelength modulation of the laser frequency can provide excellent performance compared to most of the sensing systems based on direct absorption and wavelength modulation spectroscopy. The dimension of the DC solenoid is not limited by the resonant frequency of the RLC circuit, which makes large dimension solenoid coil achievable and the absorption base length could be further increased. By employing a combination of the environmental photochemical reactor or smog chamber with multipass absorption cell, one can lower the minimum detection limit for high accuracy atmospheric chemistry studies. In this paper, we report on the development of a DC field based FRS in conjunction with a balanced detection scheme for OH radical detection at 2.8 μm and the construction of OH chemistry research platform which combined a large dimension superconducting magnetic coil with the
Characterization of magnetic field profiles at RFX-mod by Faraday rotation measurements
Auriemma, Fulvio; Brombin, Matteo; Canton, Alessandra; Giudicotti, Leonardo; Innocente, Paolo; Zilli, Enrico
2009-11-01
A multichannel far-infrared (FIR, λ=118.8 μm) polarimeter has been recently upgraded and re-installed on RFX-mod to measure the Faraday rotation angle along five vertical chords. Polarimetric data, associated with electron density profile, allow the reconstruction of the poloidal magnetic field profile. In this work the setup of the diagnostic is presented and the first Faraday rotation measurements are analyzed. The measurements have been performed at plasma current above 1.2 MA and electron density between 2 and 6x10^19 m-3. The actual S/N ratio is slightly lower than the expected one, due to electromagnetic coupling of the detectors with the saddle coils close to the polarimeter position. Due to this limit, only average information in the flat-top phase of the discharge could be so far obtained. The experimental data have been compared with the result of the μ&p equilibrium model [1], showing a good agreement between experiment and model, whereas the main differences are in the external region of the plasma. A different parameterization of the μ=μ0 J.B/B^2 profile has been proposed to enhance the agreement between model and experiment. [0pt] [1] Ortolani and Snack, World Scientific (1993) Singapore
Viscosity estimation utilizing flow velocity field measurements in a rotating magnetized plasma
International Nuclear Information System (INIS)
Yoshimura, Shinji; Tanaka, Masayoshi Y.
2008-01-01
The importance of viscosity in determining plasma flow structures has been widely recognized. In laboratory plasmas, however, viscosity measurements have been seldom performed so far. In this paper we present and discuss an estimation method of effective plasma kinematic viscosity utilizing flow velocity field measurements. Imposing steady and axisymmetric conditions, we derive the expression for radial flow velocity from the azimuthal component of the ion fluid equation. The expression contains kinematic viscosity, vorticity of azimuthal rotation and its derivative, collision frequency, azimuthal flow velocity and ion cyclotron frequency. Therefore all quantities except the viscosity are given provided that the flow field can be measured. We applied this method to a rotating magnetized argon plasma produced by the Hyper-I device. The flow velocity field measurements were carried out using a directional Langmuir probe installed in a tilting motor drive unit. The inward ion flow in radial direction, which is not driven in collisionless inviscid plasmas, was clearly observed. As a result, we found the anomalous viscosity, the value of which is two orders of magnitude larger than the classical one. (author)
Effects from magnetic boundary conditions in superconducting-magnetic proximity systems
Directory of Open Access Journals (Sweden)
Thomas E. Baker
2016-05-01
Full Text Available A superconductor-magnetic proximity system displays singlet-triplet pair correlations in the magnetization as a function of inhomogeneities of the magnetic profile. We discuss how the magnetic boundary conditions affects differently the curvature and winding number of rotating magnetizations in the three commonly used structures to generate long range triplet components: an exchange spring, a helical structure and a misaligned magnetic multilayer. We conclude that the choice of the system is dictated by the goal one wishes to achieve in designing a spintronic device but note that only the exchange spring presently offers an experimentally realizable magnetic profile that is tunable.
International Nuclear Information System (INIS)
Rudnick, J.J.; Filipkowski, M.E.; Tan, Z.; Chamberland, B.; Niedermayer, C.; Weidinger, A.; Golnik, A.; Simon, R.; Rauer, M.; Recknagel, E.; Gluckler, H.; Baines, C.
1990-01-01
In this paper the authors review results of a series of muon spin rotation (μSR) studies extending down to milli Kelvin temperatures in order to explore the existence of magnetic correlations below T C in the La 2-x Sr x CuO 4 system. Evidence is presented for the existence of local magnetic fields thought to originate from Cu electronic moments in both superconducting La 2-x Sr x CuO 4 and in superconducting oxygen deficient YBa 2 Cu 3 O 6.6 . μSR results are also presented for oxygen deficient and superconducting GdBa 2 Cu 3 O 6+x samples. Some discussion of the relevance of these results to recent proposals for pairing mechanisms is presented
International Nuclear Information System (INIS)
Tietze, Thomas Hermann
2014-01-01
significant shape dependence was observed. This part of the thesis provides a microscopic understanding of the electronic and magnetic properties of Ni nanocluster on graphene and the cluster/graphene interaction. The resulting strong change in the Ni d states is very important concerning the choice of suitable materials for graphene based spintronic devices. The second part of this thesis is dedicated to the indirect influence of the nanoparticle size on the magnetic properties of an oxide system. In particular the origin of ferromagnetism in actual nonmagnetic ZnO is discussed. The reason for ferromagnetism in ZnO depends strongly on its microscopic properties. Nanocrystalline samples with adequate small grains are mandatory. The key parameter is the so called specific grain boundary area which is defined as ratio of grain surface to grain volume. If this value exceeds a certain threshold limit, ZnO can become ferromagnetic even without doping atoms. Here the ferromagnetic coupling is suggested to occur within the grain boundaries itself. A direct proof of this hypothesis is difficult. Measurement methods like SQUID do not provide information on the microscopic origin of the sample magnetization. Therefore, this problem was addressed using low energy muon spin rotation (μSR). Here, the magnetic moment of the muon is utilized as a local magnetic probe. Three different sample systems were investigated, varying the respective grain size. Two nanograined samples with an average grain size of 31 nm and 65 nm were compared to a nonmagnetic reference ZnO single crystal. A detailed TEM analysis of the grain size distribution showed that in both nanograined samples a significant fraction of grains is smaller than the threshold condition. SQUID and μSR measurements show a clear relation between magnetization respectively magnetic volume fraction and the sample volume occupied by grain boundaries. For larger grain boundary volume a larger saturation magnetization and μSR related
Kesseli, Aurora Y.; Muirhead, Philip S.; Mann, Andrew W.; Mace, Greg
2018-06-01
Main-sequence, fully convective M dwarfs in eclipsing binaries are observed to be larger than stellar evolutionary models predict by as much as 10%–15%. A proposed explanation for this discrepancy involves effects from strong magnetic fields, induced by rapid rotation via the dynamo process. Although, a handful of single, slowly rotating M dwarfs with radius measurements from interferometry also appear to be larger than models predict, suggesting that rotation or binarity specifically may not be the sole cause of the discrepancy. We test whether single, rapidly rotating, fully convective stars are also larger than expected by measuring their R\\sin i distribution. We combine photometric rotation periods from the literature with rotational broadening (v\\sin i) measurements reported in this work for a sample of 88 rapidly rotating M dwarf stars. Using a Bayesian framework, we find that stellar evolutionary models underestimate the radii by 10 % {--}15{ % }-2.5+3, but that at higher masses (0.18 theory is 13%–18%, and we argue that the discrepancy is unlikely to be due to effects from age. Furthermore, we find no statistically significant radius discrepancy between our sample and the handful of M dwarfs with interferometric radii. We conclude that neither rotation nor binarity are responsible for the inflated radii of fully convective M dwarfs, and that all fully convective M dwarfs are larger than models predict.
Metamorphosis of helical magnetorotational instability in the presence of axial electric current.
Priede, Jānis
2015-03-01
This paper presents numerical linear stability analysis of a cylindrical Taylor-Couette flow of liquid metal carrying axial electric current in a generally helical external magnetic field. Axially symmetric disturbances are considered in the inductionless approximation corresponding to zero magnetic Prandtl number. Axial symmetry allows us to reveal an entirely new electromagnetic instability. First, we show that the electric current passing through the liquid can extend the range of helical magnetorotational instability (HMRI) indefinitely by transforming it into a purely electromagnetic instability. Two different electromagnetic instability mechanisms are identified. The first is an internal pinch-type instability, which is due to the interaction of the electric current with its own magnetic field. Axisymmetric mode of this instability requires a free-space component of the azimuthal magnetic field. When the azimuthal component of the magnetic field is purely rotational and the axial component is nonzero, a new kind of electromagnetic instability emerges. The latter, driven by the interaction of electric current with a weak collinear magnetic field in a quiescent fluid, gives rise to a steady meridional circulation coupled with azimuthal rotation.
International Nuclear Information System (INIS)
Kumano, Seishi; Okada, Masahiro; Murakami, Takamichi; Uemura, Masahiko; Haraikawa, Toyoaki; Hirata, Masaaki; Kikuchi, Keiichi; Mochizuki, Teruhito; Kim, Tonsok
2009-01-01
The aim of this study was to evaluate the efficacy of double arterial phase dynamic magnetic resonance imaging (MRI) with the sensitivity encoding technique (SENSE dynamic MRI) for detection of hypervascular hepatocellular carcinoma (HCC) in comparison with double arterial phase dynamic multidetector-row helical computed tomography (dynamic MDCT). A total of 28 patients with 66 hypervascular HCCs underwent both double arterial SENSE dynamic MRI and dynamic MDCT. The diagnosis of HCC was based on surgical resection (n=7), biopsy (n=10), or a combination of CT during arterial portography (CTAP), CT during hepatic arteriography (CTA), and/or the 6-month follow-up CT (n=49). Based on alternative-free response receiving operating characteristic (ROC) analysis, the diagnostic performance for detecting HCC was compared between double arterial phase SENSE dynamic MRI and double arterial phase dynamic MDCT. The mean sensitivity, positive predictive value, and mean A Z values for hypervascular HCCs were 72%, 80%, and 0.79, respectively, for SENSE dynamic MRI and 66%, 92%, and 0.78, respectively, for dynamic MDCT. The mean sensitivity for double arterial phase SENSE dynamic MRI was higher than that for double arterial phase dynamic MDCT, but the difference was not statistically significant. Double arterial phase SENSE dynamic MRI is as valuable as double arterial phase dynamic MDCT for detecting hypervascular HCCs. (author)
Dong, Dapeng; Yu, Naisen; Zhao, Haiyan; Liu, Dedi; Liu, Jia; Li, Zhenghua; Liu, Dongping
2016-01-01
A novel homochiral manganese (III) Mn(5-Brsalen) coordination polymer with left-handed helical character by spontaneous resolution on crystallization by using Mn(5-Brsalen) and 4,4-bipyridine, [MnIII(5-Brsalen)(4,4-bipy)]·ClO4·CH3OH (1) (4,4-bipy = 4,4-bipyridine) has been synthesized and structurally characterized by X-ray single-crystal diffraction, elemental analysis and infrared spectroscopy. In compound 1, each manganese(III) anion is six-coordinate octahedral being bonded to four atoms of 5-Brsalen ligand in an equatorial plane and two nitrogen atoms from a 4,4-bipyridine ligand in axial positions. The structure of compound 1 can be described a supramolecular 2D-like structure which was formed by the intermolecular π-stacking interactions between the neighboring chains of the aromatic rings of 4,4-bipyridine and 5-Brsalen molecules. UV-vis absorption spectrum, electrochemistry and magnetic properties of the compound 1 have also been studied.
International Nuclear Information System (INIS)
Abd-Alla, A.M.; Abo-Dahab, S.M.; Al-Simery, R.D.
2013-01-01
In this paper, the effects of both rotation and magnetic field of a micropolar fluid through a porous medium induced by sinusoidal peristaltic waves traveling down the channel walls are studied analytically and computed numerically. Closed-form solutions under the consideration of long wavelength and low-Reynolds number is presented. The analytical expressions for axial velocity, pressure rise per wavelength, mechanical efficiency, spin velocity, stream function and pressure gradient are obtained in the physical domain. The effect of the rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude in the wave frame is analyzed theoretically and computed numerically. Numerical results are given and illustrated graphically in each case considered. Comparison was made with the results obtained in the presence and absence of rotation and magnetic field. The results indicate that the effect of rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude are very pronounced in the phenomena. - Highlights: • The effects of induced magnetic field and rotation in peristaltic motion of a two dimensional of a micropolar fluid through a porous medium • The exact and closed form solutions are presented • Different wave shapes are considered to observe the behavior of the axial velocity, pressure rise, mechanical efficiency, spin velocity, stream function and pressure gradient