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)
Resonant helical fields in the TBR tokamak
International Nuclear Information System (INIS)
Bender, O.W.
1986-01-01
The influence of external resonant helical fields (RHF) in the tokamak TBR plasma discharges was investigated. These fields were created by helical windings wounded on the TBR vessel with the same helicity of rational magnetic surfaces, producing resonant efects on these surfaces. The characteristics of the MHZ activity (amplitude, frequency and poloidal and toroidal wave numbers, m=2,3,4 and n=1, respectively) during the plasma discharges were modified by eletrical winding currents of the order of 2% of the plasma current. These characterisitics were measured for diferent discharges safety factors at the limiter (q) between 3 and 4, with and without the RHF, with the atenuation of the oscillation amplitudes and the increasing of their frequencies. The existente of expontaneous and induced magnetic islands were investigated. The data were compared with results obtained in other tokamaks. (author) [pt
Effects of Resonant Helical Field on Toroidal Field Ripple in IR-T1 Tokamak
Mahdavipour, B.; Salar Elahi, A.; Ghoranneviss, M.
2018-02-01
The toroidal magnetic field which is created by toroidal coils has the ripple in torus space. This magnetic field ripple has an importance in plasma equilibrium and stability studies in tokamak. In this paper, we present the investigation of the interaction between the toroidal magnetic field ripple and resonant helical field (RHF). We have estimated the amplitude of toroidal field ripples without and with RHF (with different q = m/n) ( m = 2, m = 3, m = 4, m = 5, m = 2 & 3, n = 1) using “Comsol Multiphysics” software. The simulations show that RHF has effects on the toroidal ripples.
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
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
International Nuclear Information System (INIS)
Taniguchi, Satoshi; Yamazaki, Kozo; Oishi, Tetsutarou; Arimoto, Hideki; Shoji, Tatsuo
2010-01-01
On tokamak plasmas like ITER, it is necessary to stabilize neoclassical tearing mode (NTM) because the NTM reduces plasma temperature and fusion power output. For the analysis of stabilizing NTM in fusion plasmas, the electron cyclotron current drive (ECCD) and the non-resonant external helical field (NRHF) application are simulated using the 1.5-dimensional equilibrium/transport simulation code (TOTAL code). The 3/2 NTM is stabilized by only external helical field, but the 2/1 mode is not stabilized by only external helical field in the present model. The stabilization time becomes shorter by the combination of ECCD and NRHF than that by ECCD alone. (author)
Influence of the helical resonant fields on the plasma potential in the TBR-1 Tokamak
International Nuclear Information System (INIS)
Ribeiro, C.; Silva, R.P. da; Caldas, I.L.; Fagundes, A.N.; Sanada, E.K.
1990-01-01
This work describes an experimental work that are in progress in TBR-1 tokamak about the influence of resonant helical fields on the plasma potential. TBR-1 is a small tokamak in operation in the Physics Institute of University of Sao Paulo and used for basic research, diagnostic development and personal formation. Its main parameters are: R(Major Radius) = 0.30 m; a v (Vessel Radius) = 0.11 m; a(Plasma Radius) = 0.08 m; R/a(Aspect Ratio) = 3.75; B φ (Toroidal Field) = 5 kG; n e0 (Central Electron Density) ≅ 7 x 10 18 m -3 ; T e0 (central electron temperature) ≅ 200 eV. (Author)
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
Energy Technology Data Exchange (ETDEWEB)
Volino, F [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1969-07-01
We show that helices can be used as resonant systems. Their properties are theoretically and experimentally studied. We describe resonant helices for electron paramagnetic resonance in X-band and develop a comparison between their sensitivity and the sensitivity of a normal resonant cavity. For cylindrical samples less than 3 mm diameter, the helix is more sensitive and can produce more intense microwave magnetic fields. (author) [French] Il est montre que les helices peuvent etre utilisees comme systeme resonnant. Leurs proprietes sont discutees theoriquement et experimentalement. Des helices resonnantes en bande X pour la resonance paramagnetique electronique sont decrites et leur sensibilite est comparee a celle des cavites resonnantes. Pour des echantillons cylindriques de moins de 3 mm de diametre, l'helice est plus sensible et peut produire des champs magnetiques hyper fins plus intenses. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Volino, F. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1969-07-01
We show that helices can be used as resonant systems. Their properties are theoretically and experimentally studied. We describe resonant helices for electron paramagnetic resonance in X-band and develop a comparison between their sensitivity and the sensitivity of a normal resonant cavity. For cylindrical samples less than 3 mm diameter, the helix is more sensitive and can produce more intense microwave magnetic fields. (author) [French] Il est montre que les helices peuvent etre utilisees comme systeme resonnant. Leurs proprietes sont discutees theoriquement et experimentalement. Des helices resonnantes en bande X pour la resonance paramagnetique electronique sont decrites et leur sensibilite est comparee a celle des cavites resonnantes. Pour des echantillons cylindriques de moins de 3 mm de diametre, l'helice est plus sensible et peut produire des champs magnetiques hyper fins plus intenses. (auteur)
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 )
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.
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
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.
Weaving Knotted Vector Fields with Tunable Helicity.
Kedia, Hridesh; Foster, David; Dennis, Mark R; Irvine, William T M
2016-12-30
We present a general construction of divergence-free knotted vector fields from complex scalar fields, whose closed field lines encode many kinds of knots and links, including torus knots, their cables, the figure-8 knot, and its generalizations. As finite-energy physical fields, they represent initial states for fields such as the magnetic field in a plasma, or the vorticity field in a fluid. We give a systematic procedure for calculating the vector potential, starting from complex scalar functions with knotted zero filaments, thus enabling an explicit computation of the helicity of these knotted fields. The construction can be used to generate isolated knotted flux tubes, filled by knots encoded in the lines of the vector field. Lastly, we give examples of manifestly knotted vector fields with vanishing helicity. Our results provide building blocks for analytical models and simulations alike.
Helicity amplitudes and electromagnetic decays of hyperon resonances
International Nuclear Information System (INIS)
Cauteren, T. van; Ryckebusch, J.; Metsch, B.; Petry, H.R.
2005-01-01
We present results for the helicity amplitudes of the lowest-lying hyperon resonances Y * , computed within the framework of the Bonn Constituent-Quark model, which is based on the Bethe-Salpeter approach. The seven parameters entering the model were fitted to the best-known baryon masses. Accordingly, the results for the helicity amplitudes are genuine predictions. Some hyperon resonances are seen to couple more strongly to a virtual photon with finite Q 2 than to a real photon. Other Y * 's, such as the S 01 (1670) Λ-resonance or the S 11 (1620) Σ-resonance, couple very strongly to real photons. We present a qualitative argument for predicting the behaviour of the helicity asymmetries of baryon resonances at high Q 2 . (orig.)
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.
Determining the helicity structure of third generation resonances
International Nuclear Information System (INIS)
Papaefstathiou, Andreas
2011-11-01
We examine methods that have been proposed for determining the helicity structure of decays of new resonances to third generation quarks and/or leptons. We present analytical and semi-analytical predictions and assess the applicability of the relevant variables in realistic reconstruction scenarios using Monte Carlo-generated events, including the effects of QCD radiation and multiple parton interactions, combinatoric ambiguities and fast detector simulation. (orig.)
Numerical modeling of formation of helical structures in reversed-field-pinch plasma
International Nuclear Information System (INIS)
Mizuguchi, N.; Ichiguchi, K.; Todo, Y.; Sanpei, A.; Oki, K.; Masamune, S.; Himura, H.
2012-11-01
Nonlinear three-dimensional magnetohydrodynamic(MHD) simulations have been executed for the low-aspect-ratio reversed-field-pinch (RFP) plasma to reveal the physical mechanism of the formation processes of helical structures. The simulation results show a clear formation of n=4 structure as a result of dominant growth of resistive modes, where n represents the toroidal mode number. The resultant relaxed helical state consists of a unique bean-shaped and hollow pressure profile in the poloidal cross section for both cases of resonant and non-resonant triggering instability modes. The results are partially comparable to the experimental observations. The physical mechanisms of those processes are examined. (author)
Helicity and isospin asymmetries in the electroproduction of nucleon resonances
International Nuclear Information System (INIS)
Warns, M.; Pfeil, W.; Rollnik, H.
1989-10-01
We investigate the helicity asymmetries and isospin ratios of ratiative transition amplitudes for nucleon resonances electroproduced off proton and neutron targets at momentum transfers of Q 2 ≤3 GeV 2 . Calculations were done in the framework of a relativized constituent quark model which includes many-body effects due to the quark interaction potential and to a relativistic treatment of the center-of-mass motion of the three quark system. We find significant deviations from the predictions of the nonrelativistic quark models and the SU(6) W algebraic approach based on the single quark transition hypothesis. Our calculated relativistic corrections lead to an overall better agreement with the experimental data. The question if some of the low-lying P-wave baryons are of hermaphrodite nature is briefly discussed. Finally we analyse the electroexcitation of the missing [20,1 + ] P-wave resonances. (orig.)
Neutrino's helicity in a gravitational field
International Nuclear Information System (INIS)
Pansart, J.P.
1996-01-01
By using approximated solutions of Dirac's equation, we show that there is no helicity reversal for light neutrinos in the Schwarzschild metric nor in an expanding universe. The actual coupling between a particle spin and the angular momentum of a heavy rotating body induces a possible helicity reversal but with an unobservable probability proportional to m 2 p / E 2 , where m p is the particle mass and E its energy. In these calculations, the helicity is defined through the spin orientation with respect to the current and not with respect to the linear momentum. This definition gives simple expressions and is equal to the usual definition in the case of a flat space. (N.T.)
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)
Radiation Field of a Square, Helical Beam Antenna
DEFF Research Database (Denmark)
Knudsen, Hans Lottrup
1952-01-01
square helices are used. Further, in connection with corresponding rigorous formulas for the field from a circular, helical antenna with a uniformly progressing current wave of constant amplitude the present formulas may be used for an investigation of the magnitude of the error introduced in Kraus......' approximate calculation of the field from a circular, helical antenna by replacing this antenna with an ``equivalent'' square helix. This investigation is carried out by means of a numerical example. The investigation shows that Kraus' approximate method of calculation yields results in fair agreement...
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.
Study of electric field pulsation in helical plasmas
International Nuclear Information System (INIS)
Toda, S; Itoh, K
2011-01-01
A model for the experimental results of the periodic oscillation of the electric field, so-called the electric field pulsation, observed in the Compact Helical Device (Fujisawa et al 1998 Phys. Rev. Lett. 81 2256) and the Large Helical Device (Shimizu et al 2010 Plasma Fusion Res. 5 S1015) is presented. A self-generated oscillation of the radial electric field is shown as the simulation result in helical plasmas. The reduction of the anomalous transport diffusivity in the core region is observed due to the strong shear of the radial electric field when the positive electric field is shown in the core region in the periodic oscillation of E r . Two different time scales are found in the self-generated oscillation, which are the transport time scale and the fast time scale at the transition of the radial electric field. This oscillation because of the hysteresis characteristic is attributed to the electric field pulsation observed in helical plasmas. The parameter region of the condition for the self-generated oscillation is derived. It is shown that the multiple solutions of the radial electric field for the ambipolar condition are necessary but not sufficient for obtaining the self-generated oscillation.
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
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)
Overview of quasi single helicity experiments in reversed field pinches
International Nuclear Information System (INIS)
Martin, P.; Marrelli, L.; Spizzo, G.
2003-01-01
We report the results of an experimental and theoretical project dedicated to the study of Quasi Single Helicity Reversed Field Pinch plasmas. The project has involved several RFP devices and numerical codes. It appears that QSH spectra are a feature common to all the experiments. (author)
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.
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)
Suppression and control of leakage field in electromagnetic helical microwiggler
Energy Technology Data Exchange (ETDEWEB)
Ohigashi, N. [Kansai Univ., Osaka (Japan); Tsunawaki, Y. [Osaka Sangyo Univ. (Japan); Imasaki, K. [Institute for Laser Technology, Osaka (Japan)] [and others
1995-12-31
Shortening the period of electromagnetic wiggler introduces both the radical increase of the leakage field and the decrease of the field in the gap region. The leakage field is severer problem in planar electromagnetic wiggler than in helical wiggler. Hence, in order to develop a short period electromagnetic wiggler, we have adopted {open_quotes}three poles per period{close_quotes} type electromagnetic helical microwiggler. In this work, we inserted the permanent magnet (PM) blocks with specific magnetized directions in the space between magnetic poles, for suppressing the leakage field flowing out from a pole face to the neighboring pole face. These PM-blocks must have higher intrinsic coersive force than saturation field of pole material. The gap field due to each pole is adjustable by controlling the leakage fields, that is, controlling the position of each iron screw set in each retainer fixing the PM-blocks. At present time, a test wiggler with period 7.8mm, periodical number 10 and gap length 4.6mm has been manufactured. Because the ratio of PM-block aperture to gap length is important parameter to suppress the leakage field, the parameter has been surveyed experimentally for PM-blocks with several dimensions of aperture. The field strength of 3-5kG (K=0.2-0.4) would be expected in the wiggler.
The velocity field induced by a helical vortex tube
DEFF Research Database (Denmark)
Fukumoto, Y.; Okulov, Valery
2005-01-01
The influence of finite-core thickness on the velocity field around a vortex tube is addressed. An asymptotic expansion of the Biot-Savart law is made to a higher order in a small parameter, the ratio of core radius to curvature radius, which consists of the velocity field due to lines of monopoles...... and dipoles arranged on the centerline of the tube. The former is associated with an infinitely thin core and is featured by the circulation alone. The distribution of vorticity in the core reflects on the strength of dipole. This result is applied to a helical vortex tube, and the induced velocity due...
The effect of materials properties on the Q of high Tc helical and coaxial resonators
International Nuclear Information System (INIS)
Peterson, G.E.; Fleming, D.A.; Johnson, D.W. Jr.; Rhodes, W.W.
1990-01-01
High T c helical and coaxial resonators have applications in U.H.F. radio receivers. We have employed a variety of techniques to study the superconducting materials used to form such resonators. These include, X-ray diffraction, SEM, density, dilatometry and sedigraph. We have correlated our data with resonator Q and frequency and have determined optimum conditions for highest Q. Our best resonators perform better than their all copper counterparts by a factor of 10 at 77K and at frequencies below 1,000 MHz. We have used these resonators in local oscillators and Butterworth filters in U.H.F. receivers
Transport analysis of radial electric field in helical plasmas
International Nuclear Information System (INIS)
Toda, S.; Itoh, K.
2004-01-01
A set of transport equations is analyzed which induces the radial transition of the electric field. A temperature profile which is related with the transport barrier is obtained by use of the theoretical model for the anomalous transport diffusivities. A dependence on the different initial condition is found even if the same values of the control parameters are used in calculations. A study of the temporal evolution of E r is done. We examine the test of the adopted theoretical model for the anomalous transport diffusivities compared with the experimental result in Large Helical Device (LHD). (authors)
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...
Epicyclic helical channels for parametric resonance ionization cooling
Energy Technology Data Exchange (ETDEWEB)
Johson, Rolland Paul [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Derbenev, Yaroslav [Muons, Inc., Batavia, IL (United States)
2015-08-23
Proposed next-generation muon colliders will require major technical advances to achieve rapid muon beam cooling requirements. Parametric-resonance Ionization Cooling (PIC) is proposed as the final 6D cooling stage of a high-luminosity muon collider. In PIC, a half-integer parametric resonance causes strong focusing of a muon beam at appropriately placed energy absorbers while ionization cooling limits the beam’s angular spread. Combining muon ionization cooling with parametric resonant dynamics in this way should then allow much smaller final transverse muon beam sizes than conventional ionization cooling alone. One of the PIC challenges is compensation of beam aberrations over a sufficiently wide parameter range while maintaining the dynamical stability with correlated behavior of the horizontal and vertical betatron motion and dispersion. We explore use of a coupling resonance to reduce the dimensionality of the problem and to shift the dynamics away from non-linear resonances. PIC simulations are presented.
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)
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.
Low field magnetic resonance imaging
Pines, Alexander; Sakellariou, Dimitrios; Meriles, Carlos A.; Trabesinger, Andreas H.
2010-07-13
A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.
International Nuclear Information System (INIS)
Takagaki, Y.
2015-01-01
The helical edge states of two-dimensional topological insulators (TIs) experience appreciable quantum mechanical scattering in narrow channels when the width changes abruptly. The interference of the geometry scattering in narrow-wide-narrow waveguide structures is shown to give rise to the strong suppression of transmission when the incident energy is barely above the propagation threshold. Periodic resonant transmission takes place in this high reflection regime while the length of the wide section is varied. The resonance condition is governed by the transverse confinement in the wide section, where the form of quantization is manifested to differ for the two orthogonal directions. The confined energy levels in TI quantum dots are derived based on this observation. In addition, the off-diagonal spin-orbit term is found to produce an anomalous resonance state, which merges with the bottom ordinary resonance state to annihilate
Shape resonances in molecular fields
International Nuclear Information System (INIS)
Dehmer, J.L.
1984-01-01
A shape resonance is a quasibound state in which a particle is temporarily trapped by a potential barrier (i.e., the shape of the potential), through which it may eventually tunnel and escape. This simple mechanism plays a prominent role in a variety of excitation processes in molecules, ranging from vibrational excitation by slow electrons to ionization of deep core levels by x-rays. Moreover, their localized nature makes shape resonances a unifying link between otherwise dissimilar circumstances. One example is the close connection between shape resonances in electron-molecule scattering and in molecular photoionization. Another is the frequent persistence of free-molecule shape resonant behavior upon adsorption on a surface or condensation into a molecular solid. The main focus of this article is a discussion of the basic properties of shape resonances in molecular fields, illustrated by the more transparent examples studied over the last ten years. Other aspects to be discussed are vibrational effects of shape resonances, connections between shape resonances in different physical settings, and examples of shape resonant behavior in more complex cases, which form current challenges in this field
Review on resonance cone fields
International Nuclear Information System (INIS)
Ohnuma, Toshiro.
1980-02-01
Resonance cone fields and lower hybrid heating are reviewed in this report. The resonance cone fields were reported by Fisher and Gould, and they proposed the use of the measurement of resonance cones and structure as a diagnostic tool to determine the plasma density and electron temperature in magnetoplasma. After the resonance cone, a wave-like disturbance persists. Ohnuma et al. have measured bending, reflection and ducting of resonance cones in detail. The thermal modes in inhomogeneous magnetoplasma were seen. The reflection of thermal mode near an electron plasma frequency layer and an insulating plate has been observed. The non-linear effects of resonance cones is reported. Monochromatic electron beam produces the noise of broad band whistler mode. Lower hybrid waves have been the subject of propagation from the edge of plasma to the lower hybrid layer. Linear lower hybrid waves were studied. The lower hybrid and ion acoustic waves radiated from a point source were observed. The parametric decay of finite-extent, cold electron plasma waves was studied. The lower hybrid cone radiated from a point source going along magnetic field lines was observed. Several experimental data on the lower hybrid heating in tokamak devices have been reported. The theories on resonance cones and lower hybrid waves are introduced in this report. (Kato, T.)
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.
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.
Interactions between Radial Electric Field, Transport and Structure in Helical Plasmas
International Nuclear Information System (INIS)
Ida, Katsumi and others
2006-01-01
Control of the radial electric field is considered to be important in helical plasmas, because the radial electric field and its shear are expected to reduce neoclassical and anomalous transport, respectively. Particle and heat transport, that determines the radial structure of density and electron profiles, sensitive to the structure of radial electric field. On the other hand, the radial electric field itself is determined by the plasma parameters. In general, the sign of the radial electric field is determined by the plasma collisionality, while the magnitude of the radial electric field is determined by the temperature and/or density gradients. Therefore the structure of radial electric field and temperature and density are strongly coupled through the particle and heat transport and formation mechanism of radial electric field. Interactions between radial electric field, transport and structure in helical plasmas is discussed based on the experiments on Large Helical Device
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)
Field-theoretic calculation of kinetic helicity flux
Indian Academy of Sciences (India)
Given all these practical aspects, kinetic helicity is an important quantity to study in fluid turbulence. Turbulence involves millions of interacting modes. It is very difficult to analyze these modes theoretically as well as numerically. In recent times, a new numeri- cal procedure called 'large eddy simulations' (LES) has become ...
International Nuclear Information System (INIS)
Veranda, M; Bonfiglio, D; Cappello, S; Chacón, L; Escande, D F
2013-01-01
Helical self-organized reversed-field pinch (RFP) regimes emerge both numerically—in 3D visco-resistive magnetohydrodynamic (MHD) simulations—and experimentally, as in the RFX-mod device at high current (I P above 1 MA). These states, called quasi-single helicity (QSH) states, are characterized by the action of a MHD mode that impresses a quasi-helical symmetry to the system, thus allowing a high degree of magnetic chaos healing. This is in contrast with the multiple helicity (MH) states, where magnetic fluctuations create a chaotic magnetic field degrading the confinement properties of the RFP. This paper reports an extensive numerical study performed in the frame of 3D visco-resistive MHD which considers the effect of helical magnetic boundary conditions, i.e. of a finite value of the radial magnetic field at the edge (magnetic perturbation, MP). We show that the system can be driven to a selected QSH state starting from both spontaneous QSH and MH regimes. In particular, a high enough MP can force a QSH helical self-organization with a helicity different from the spontaneous one. Moreover, MH states can be turned into QSH states with a selected helicity. A threshold in the amplitude of MP is observed above which is able to influence the system. Analysis of the magnetic topology of these simulations indicates that the dominant helical mode is able to temporarily sustain conserved magnetic structures in the core of the plasma. The region occupied by conserved magnetic surfaces increases reducing secondary modes' amplitude to experimental-like values. (paper)
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.
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
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.)
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)
Improvement of the density limit with an external helical field on JFT-2M tokamak
International Nuclear Information System (INIS)
Tamai, H.; Shoji, T.; Nagashima, K.; Miura, Y.; Yamauchi, T.; Ogawa, H.; Kawashima, H.; Matsuda, T.; Mori, M.; Ida, K.; Ohdachi, S.
1995-01-01
The density limit is increased by the application of an external helical field in the JFT-2M tokamak. The effect of the magnetic stochasticity due to the external field is investigated to study the mechanism of the improved density limit related to the edge plasma behaviour. The improvement is correlated with the retardation of the increase in the plasma inductance. At the improved density limit, local radiation loss is modified by the helical field, in which that from the vicinity of separatrix X-point is remarkably reduced, while that from outboard edge is slightly increased. The formation of a positive radial electric field at the plasma edge is also observed in the presence of the helical field. ((orig.))
International Nuclear Information System (INIS)
Motojima, Osamu; Shishkin, A.A.; Inagaki, Shigeru; Watanabe, Kiyomasa
1999-08-01
The possibility of controlling the radial electric field of toroidal plasmas by injecting high energy electrons along the reversible loss cone orbit of the helical magnetic traps is investigated. It is well known that the radial electric field plays an important role in the confinement improvement scenario especially in the low collisional regime under the physics picture of neoclassical theory. For this purpose, it is made clear that the most suitable particles are transit particles, which show a transition from helically trapped orbits to blocked ones. It is also found that a parallel AC electric field launched from outside assists this transition and makes it possible for particles to penetrate deeply into the plasma. In addition we clarify that the viscosity of the plasma coupled with the helical field configuration provide a bifurcation of plasma states and its stable solution results in confinement improvement. (author)
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)
A Field Theory Approach to Modeling Helical FCG's
International Nuclear Information System (INIS)
Fortgang, C.M.
1998-01-01
Often helical flux-compressor generator (FCG) design codes are essentially circuit codes which utilize known equations for parameterizing circuit elements such as armature and stator inductance. The authors present an analytical model that is based more on first principals. The stator inductance is calculated using a definition of inductance in terms of the magnetic vector-potential. The calculation accounts for winding-pitch, bifurcations, and works for any ratio of length to diameter. The currents on the armature are calculated self-consistently and are not assumed to simply 'mirror' the stator currents. Resistive losses and magnetic diffusion losses are calculated less rigorously but they are working on better methods. Details of the model and comparison with experiment will be presented
International Nuclear Information System (INIS)
Irvine, William T M
2010-01-01
Maxwell's equations allow for some remarkable solutions consisting of pulsed beams of light which have linked and knotted field lines. The preservation of the topological structure of the field lines in these solutions has previously been ascribed to the fact that the electric and magnetic helicities, a measure of the degree of linking and knotting between field lines, are conserved. Here we show that the elegant evolution of the field is due to the stricter condition that the electric and magnetic fields be everywhere orthogonal. The field lines then satisfy a 'frozen field' condition and evolve as if they were unbreakable filaments embedded in a fluid. The preservation of the orthogonality of the electric and magnetic field lines is guaranteed for null, shear-free fields such as the ones considered here by a theorem of Robinson. We calculate the flow field of a particular solution and find it to have the form of a Hopf fibration moving at the speed of light in a direction opposite to the propagation of the pulsed light beam, a familiar structure in this type of solution. The difference between smooth evolution of individual field lines and conservation of electric and magnetic helicities is illustrated by considering a further example in which the helicities are conserved, but the field lines are not everywhere orthogonal. The field line configuration at time t = 0 corresponds to a nested family of torus knots but unravels upon evolution.
Formation of positive radial electric field by electron cyclotron heating in compact helical system
International Nuclear Information System (INIS)
Idei, H.; Ida, K.; Sanuki, H.
1994-07-01
The radial electric field is driven to positive value by off-axis second harmonic electron cyclotron heating (ECH) in the Compact Helical System. The observed positive electric field is associated with the outward particle flux enhanced with ECH. The enhanced particle flux triggered by the production of the electrons accelerated perpendicularly to the magnetic field with ECH results in the change of the electric field. (author)
Plasma equilibrium profiles with applied resonant fields on TBR-1 tokamak
International Nuclear Information System (INIS)
Castro, R.M. de; Heller, M.V.A.P.; Caldas, I.L.; Silva, R.P. da; Brasilio, Z.A.; Oda, G.A.
1995-01-01
In this work we present the measurements of the plasma potential, in the edge and in the scrape-off layer regions of plasma, with and without the presence of the magnetic field perturbations produced by resonant helical windings. (author). 6 refs., 6 figs
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.
International Nuclear Information System (INIS)
Toi, K; Ohdachi, S; Watanabe, F; Narihara, K; Morisaki, T; Sakakibara, S; Morita, S; Goto, M; Ida, K; Masuzaki, S; Miyazawa, K; Tanaka, K; Tokuzawa, T; Watanabe, K W; Yoshinuma, M
2006-01-01
On the Large Helical Device (LHD), low to high confinement (L-H) transition and edge transport barrier (ETB) formation were observed in the low beta regime ((β dia ) dia ): volume-averaged beta derived from diamagnetic measurement) as well as in relatively high beta regime (>1.5%). In most of ETB plasmas electron density preferentially increases in the edge region without a substantial rise of the edge electron temperature. The ETB zone develops inside the ergodic field layer calculated in the vacuum field. The ETB formation strongly destabilizes edge coherent modes such as m/n = 2/3 or 1/2 (m, n: poloidal and toroidal mode numbers), because the plasma edge region is in the magnetic hill. The ETB is partially destroyed by the combination of these edge MHD modes and ELM-like activities. For a particular experimental condition, the forced generation of a sizable m/n = 1/1 magnetic island near the edge by application of external field perturbations facilitates the L-H transition at a lower electron density and suppresses edge MHD modes and ELM-like activities to lower levels
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)
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.
Theoretical transport analysis of density limit with radial electric field in helical plasmas
International Nuclear Information System (INIS)
Toda, S.; Itoh, K.
2010-11-01
The confinement property in helical toroidal plasmas is clarified. The analysis is performed by use of the one-dimensional transport equations with the effect of the radiative loss and the radial profile of the electric field. The analytical results in the edge region show the steep gradient in the electron temperature, which indicates the transport barrier formation. Because of the rapid increase of the radiative loss at the low electron temperature, the anomalous heat diffusivity is reduced near the edge. Next, the efficiency of the heating power input in the presence of the radiative loss is studied. The scaling of the critical density in helical devices is also derived. (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.
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.
Frassinetti, L; Predebon, I; Koguchi, H; Yagi, Y; Hirano, Y; Sakakita, H; Spizzo, G; White, R B
2006-10-27
The quasi-single-helicity (QSH) state of a reversed-field pinch (RFP) plasma is a regime in which the RFP configuration can be sustained by a dynamo produced mainly by a single tearing mode and in which a helical structure with well-defined magnetic flux surfaces arises. In this Letter, we show that spontaneous transitions to the QSH regime enhance the particle confinement. This improvement is originated by the simultaneous and cooperative action of the increase of the magnetic island and the reduction of the magnetic stochasticity.
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)
Petrie, Gordon; McMaken, Tyler C.
2017-08-01
The solar active region (AR), NOAA 12192, appeared in 2014 October as the largest AR in 24 years. Here we examine the counterintuitive nature of two diffusion-driven processes in the region: the role of helicity buildup in the formation of a major filament, and the relationship between the effects of supergranular diffusion and meridional flow on the AR and on the polar field. Quantitatively, calculations of current helicity and magnetic twist from Helioseismic and Magnetic Imager (HMI) vector magnetograms indicate that, though AR 12192 emerged with negative helicity, positive helicity from subsequent flux emergence, consistent with the hemispheric sign-preference of helicity, increased over time within large-scale, weak-field regions such as those near the polarity inversion line (PIL). Morphologically, Atmospheric Imaging Assembly observations of filament barbs, sigmoidal patterns, and bases of Fe xii stalks initially exhibited signatures of negative helicity, and the long filament that subsequently formed had a strong positive helicity consistent with the helicity buildup along the PIL. We find from full-disk HMI magnetograms that AR 12192's leading positive flux was initially closer to the equator but, owing either to the region’s magnetic surroundings or to its asymmetric flux density distribution, was transported poleward more quickly on average than its trailing negative flux, contrary to the canonical pattern of bipole flux transport. This behavior caused the AR to have a smaller effect on the polar fields than expected and enabled the formation of the very long neutral line where the filament formed.
Investigation of Horizontal Velocity Fields in Stirred Vessels with Helical Coils by PIV
Directory of Open Access Journals (Sweden)
Volker Bliem
2014-01-01
Full Text Available Horizontal velocity flow fields were measured by particle image velocimetry for a stirred vessel with baffles and two helical coils for enlargement of heat transfer area. The investigation was carried out in a cylindrical vessel with flat base and two different stirrers (radial-flow Rushton turbine and axial-flow propeller stirrer. Combined velocity plots for flow fields at different locations are presented. It was found that helical coils change the flow pattern significantly. Measurements for the axial-flow Rushton turbine showed a strong deflection by the coils, leading to a mainly tangential flow pattern. Behind baffles large areas of unused heat transfer area were found. First results for the axial-flow propeller reveal an extensive absence of fluid movement in the horizontal plane. Improved design considerations for enhanced heat transfer by more compatible equipment compilation are proposed.
Phase diagram of structure of radial electric field in helical plasmas
International Nuclear Information System (INIS)
Toda, S.; Itoh, K.
2002-01-01
A set of transport equations in toroidal helical plasmas is analyzed, including the bifurcation of the radial electric field. Multiple solutions of E r for the ambipolar condition induces domains of different electric polarities. A structure of the domain interface is analyzed and a phase diagram is obtained in the space of the external control parameters. The region of the reduction of the anomalous transport is identified. (author)
Theoretical and experimental studies on electric field and confinement in helical systems
International Nuclear Information System (INIS)
Sanuki, H.; Itoh, K.; Todoroki, J.; Ida, K.; Idei, H.; Iguchi, H.; Yamada, H.
1994-06-01
The present study consists of two parts. The first part is oriented to a theoretical model of selfconsistent analysis to determine simultaneously the electric field and loss cone boundary in heliotron/torsatron configurations under the influence of nonclassical particle losses. The second part is referred to the analysis on NBI heated and ECH plasmas in Compact Helical System (CHS) device. A comparison is made between theoretical results and experimental observations. (author)
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.
International Nuclear Information System (INIS)
Yamazaki, K.; Kawahata, K.; Ando, R.
1986-09-01
Disruptive behavior of magnetic field configuration leading to tokamak major disruption is found to be controlled by a mild ''mini-disruption'' which is induced by the compact external modular multipole-field coils with m = 3/n = 2 dominant helical field component in the JIPP T-IIU tokamak. This mini-disruption ergodizes the m = 2/n = 1 magnetic island quickly but mildly and then prevents the profile of electron temperature from flattening. This quick profile-reorganization is effective to avoid the two-step disruption (pre- and major disuptions) responsible for the chatastrophic current termination. (author)
Resonant fields created by spiral electric currents in Tokamaks
International Nuclear Information System (INIS)
Fernandes, A.S.; Caldas, I.L.
1985-01-01
The influence of the resonant magnetic perturbations, created by electric currents in spirals, on the plasma confinement in a tokamak with circular section and large aspect ratio is investigated. These perturbations create magnetic islands around the rational magnetic surface which has the helicity of the helicoidal currents. The intensities of these currents are calculated in order to the magnetic islands reach the limiter or others rational surfaces, what could provoke the plasma disrupture. The electric current intensities are estimated, in two spiral sets with different helicities, which create a predominantly stocastic region among the rational magnetic surfaces with these helicities. (L.C.) [pt
Vorticity field, helicity integral and persistence of entanglement in reaction-diffusion systems
International Nuclear Information System (INIS)
Trueba, J L; Arrayas, M
2009-01-01
We show that a global description of the stability of entangled structures in reaction-diffusion systems can be made by means of a helicity integral. A vorticity vector field is defined for these systems, as in electromagnetism or fluid dynamics. We have found under which conditions the helicity is conserved or lost through the boundaries of the medium, so the entanglement of structures observed is preserved or disappears during time evolution. We illustrate the theory with an example of knotted entanglement in a FitzHugh-Nagumo model. For this model, we introduce new non-trivial initial conditions using the Hopf fibration and follow the time evolution of the entanglement. (fast track communication)
Vorticity field, helicity integral and persistence of entanglement in reaction-diffusion systems
Energy Technology Data Exchange (ETDEWEB)
Trueba, J L; Arrayas, M [Area de Electromagnetismo, Universidad Rey Juan Carlos, Camino del Molino s/n, 28943 Fuenlabrada, Madrid (Spain)
2009-07-17
We show that a global description of the stability of entangled structures in reaction-diffusion systems can be made by means of a helicity integral. A vorticity vector field is defined for these systems, as in electromagnetism or fluid dynamics. We have found under which conditions the helicity is conserved or lost through the boundaries of the medium, so the entanglement of structures observed is preserved or disappears during time evolution. We illustrate the theory with an example of knotted entanglement in a FitzHugh-Nagumo model. For this model, we introduce new non-trivial initial conditions using the Hopf fibration and follow the time evolution of the entanglement. (fast track communication)
Highlights from the assembly of the helical field coils for the Advanced Toroidal Facility
International Nuclear Information System (INIS)
Benson, R.D.
1985-01-01
The helical field (HF) coils in the Advanced Toroidal Facility (ATF) device consist of a set of 24 identical segments connected to form a continuous pair of helical coils wrapped around a toroidal vacuum vessel. Each segment weighs approximately 1364 kg (3000 lb) and is composed of 14 water-cooled copper plate conductors bolted to a cast stainless steel structural support member with a T-shape cross section (known as the structural tee). The segment components are electrically insulated with Kapton adhesive tape, G-10, Tefzel, and rubber to withstand 2.5 kV. As a final insulator and structural support, the entire segment is vacuum impregnated with epoxy. This paper offers a brief overview of the processes used to assemble the component parts into a completed segment, including identification of items that required special attention. 4 figs
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
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.
Issues of effective field theories with resonances
International Nuclear Information System (INIS)
Gegelia, J.; Japaridze, G.
2014-01-01
We address some issues of renormalization and symmetries of effective field theories with unstable particles - resonances. We also calculate anomalous contributions in the divergence of the singlet axial current in an effective field theory of massive SU(N) Yang-Mills fields interacting with fermions and discuss their possible relevance to the strong CP problem. (author)
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.
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.
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
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.
Mean-field Ohm's law and coaxial helicity injection in force-free plasmas
International Nuclear Information System (INIS)
Weening, R. H.
2011-01-01
A theoretical analysis of steady-state coaxial helicity injection (CHI) in force-free plasmas is presented using a parallel mean-field Ohm's law that includes resistivity η and hyper-resistivity Λ terms. Using Boozer coordinates, a partial differential equation is derived for the time evolution of the mean-field poloidal magnetic flux, or magnetic Hamiltonian function, from the parallel mean-field Ohm's law. A general expression is obtained from the mean-field theory for the efficiency of CHI current drive in force-free plasmas. Inductances of internal energy, magnetic helicity, and poloidal magnetic flux are used to characterize axisymmetric plasma equilibria that have a model current profile. Using the model current profile, a method is suggested to determine the level of magnetohydrodynamic activity at the magnetic axis and the consequent deviation from the completely relaxed Taylor state. The mean-field Ohm's law model suggests that steady-state CHI can be viewed most simply as a boundary layer problem.
Helicity dependence of the γ {sup 3}He → πX reactions in the Δ(1232) resonance region
Energy Technology Data Exchange (ETDEWEB)
Costanza, S.; Rigamonti, F. [INFN, Sezione di Pavia, Pavia (Italy); Universita di Pavia, Dipartimento di Fisica, Pavia (Italy); Mushkarenkov, A.; Braghieri, A.; Pedroni, P. [INFN, Sezione di Pavia, Pavia (Italy); Romaniuk, M.; Mandaglio, G. [INFN, Sezione di Catania, Catania (Italy); Universita di Messina, Dipartimento di Fisica e Scienze della Terra, Messina (Italy); Aguar Bartolome, P.; Ahrens, J.; Arends, H.J.; Heid, E.; Jahn, O.; Kashevarov, V.L.; Ostrick, M.; Ortega, H.; Otte, P.B.; Oussena, B.; Schumann, S.; Thomas, A.; Unverzagt, M. [Universitaet Mainz, Institut fuer Kernphysik, Mainz (Germany); Annand, J.R.M.; Hamilton, D.; Howdle, D.; Livingston, K.; MacGregor, I.J.D.; Mancell, J.; McGeorge, J.C.; Rosner, G. [University of Glasgow, SUPA School of Physics and Astronomy, Glasgow (United Kingdom); Beck, R. [University of Bonn, Helmholtz-Institut fuer Strahlen und Kernphysik, Bonn (Germany); Bekrenev, V.; Kruglov, S.; Kulbardis, A. [Petersburg Nuclear Physics Institute, Gatchina (Russian Federation); Berghaeuser, H.; Drexler, P.; Metag, V.; Thiel, M. [University of Giessen, II Physikalisches Institut, Giessen (Germany); Briscoe, W.J.; Downie, E.J. [The George Washington University, Washington, DC (United States); Cherepnya, S.N.; Fil' kov, L.V.; Lisin, V.; Polonski, A. [Institute for Nuclear Research, Moscow (Russian Federation); Collicott, C. [Dalhousie University, Halifax, NS (Canada); Saint Mary' s University, Halifax, NS (Canada); Fix, A. [Tomsk Polytechnic University, Tomsk (Russian Federation); Glazier, D.I. [University of Glasgow, SUPA School of Physics and Astronomy, Glasgow (United Kingdom); University of Edinburgh, SUPA School of Physics and Astronomy, Edinburgh (United Kingdom); Heil, W.; Krimmer, J. [Universitaet Mainz, Institut fuer Physik, Mainz (Germany); Hornidge, D.; Middleton, D.G. [Mount Allison University, Sackville, NB (Canada); Jaegle, I.; Keshelashvili, I.; Krusche, B.; Oberle, M.; Pheron, F.; Rostomyan, T.; Werthmueller, D. [University of Basel, Institut fuer Physik, Basel (Switzerland); Huber, G.M. [University of Regina, Regina, SK (Canada); Jude, T.; Watts, D.P. [University of Edinburgh, SUPA School of Physics and Astronomy, Edinburgh (United Kingdom); Kondratiev, R. [Lebedev Physical Institute, Moscow (Russian Federation); Korolija, M.; Supek, I. [Rudjer Boskovic Institute, Zagreb (Croatia); Manley, D.M. [Kent State University, Kent, Ohio (United States); Nefkens, B.M.K.; Starostin, A. [University of California, Los Angeles, California (United States); Nikolaev, A. [Universita di Pavia, Dipartimento di Fisica, Pavia (Italy); Prakhov, S. [Universitaet Mainz, Institut fuer Kernphysik, Mainz (Germany); The George Washington University, Washington, DC (United States); University of California, Los Angeles, California (United States); Sarty, A.J. [Saint Mary' s University, Halifax, NS (Canada); Collaboration: A2 Collaboration
2014-11-15
The helicity dependences of the differential cross sections for the semi-inclusive γ {sup 3}He → π{sup 0} X and γ {sup 3}He → π{sup ±} X reactions have been measured for the first time in the energy region 200 < E{sub γ} 450 MeV. The experiment was performed at the tagged photon beam facility of the MAMI accelerator in Mainz using a longitudinally polarised high-pressure {sup 3}He gas target. Hadronic products were measured with the large-acceptance Crystal Ball detector complemented with additional devices for charged-particle tracking and identification. Unpolarised differential cross sections and their helicity dependence are compared with theoretical calculations using the Fix-Arenhoevel model. The effect of the intermediate excitation of the Δ(1232) resonance can be clearly seen from this comparison, especially for the polarised case, where nuclear effects are relatively small. The model provides a better theoretical description of the unpolarised charged pion photoproduction data than the neutral pion channel. It does significantly better in describing the helicity-dependent data in both channels. These comparisons provide new information on the mechanisms involved in pion photoproduction on {sup 3}He and suggest that a polarised {sup 3}He target can provide valuable information on the corresponding polarised quasi-free neutron reactions. (orig.)
Helicity dependence of the γ 3He → πX reactions in the Δ(1232) resonance region
International Nuclear Information System (INIS)
Costanza, S.; Rigamonti, F.; Mushkarenkov, A.; Braghieri, A.; Pedroni, P.; Romaniuk, M.; Mandaglio, G.; Aguar Bartolome, P.; Ahrens, J.; Arends, H.J.; Heid, E.; Jahn, O.; Kashevarov, V.L.; Ostrick, M.; Ortega, H.; Otte, P.B.; Oussena, B.; Schumann, S.; Thomas, A.; Unverzagt, M.; Annand, J.R.M.; Hamilton, D.; Howdle, D.; Livingston, K.; MacGregor, I.J.D.; Mancell, J.; McGeorge, J.C.; Rosner, G.; Beck, R.; Bekrenev, V.; Kruglov, S.; Kulbardis, A.; Berghaeuser, H.; Drexler, P.; Metag, V.; Thiel, M.; Briscoe, W.J.; Downie, E.J.; Cherepnya, S.N.; Fil'kov, L.V.; Lisin, V.; Polonski, A.; Collicott, C.; Fix, A.; Glazier, D.I.; Heil, W.; Krimmer, J.; Hornidge, D.; Middleton, D.G.; Jaegle, I.; Keshelashvili, I.; Krusche, B.; Oberle, M.; Pheron, F.; Rostomyan, T.; Werthmueller, D.; Huber, G.M.; Jude, T.; Watts, D.P.; Kondratiev, R.; Korolija, M.; Supek, I.; Manley, D.M.; Nefkens, B.M.K.; Starostin, A.; Nikolaev, A.; Prakhov, S.; Sarty, A.J.
2014-01-01
The helicity dependences of the differential cross sections for the semi-inclusive γ 3 He → π 0 X and γ 3 He → π ± X reactions have been measured for the first time in the energy region 200 γ 450 MeV. The experiment was performed at the tagged photon beam facility of the MAMI accelerator in Mainz using a longitudinally polarised high-pressure 3 He gas target. Hadronic products were measured with the large-acceptance Crystal Ball detector complemented with additional devices for charged-particle tracking and identification. Unpolarised differential cross sections and their helicity dependence are compared with theoretical calculations using the Fix-Arenhoevel model. The effect of the intermediate excitation of the Δ(1232) resonance can be clearly seen from this comparison, especially for the polarised case, where nuclear effects are relatively small. The model provides a better theoretical description of the unpolarised charged pion photoproduction data than the neutral pion channel. It does significantly better in describing the helicity-dependent data in both channels. These comparisons provide new information on the mechanisms involved in pion photoproduction on 3 He and suggest that a polarised 3 He target can provide valuable information on the corresponding polarised quasi-free neutron reactions. (orig.)
Diffusion with finite-helicity field tensor: A mechanism of generating heterogeneity
Sato, N.; Yoshida, Z.
2018-02-01
Topological constraints on a dynamical system often manifest themselves as breaking of the Hamiltonian structure; well-known examples are nonholonomic constraints on Lagrangian mechanics. The statistical mechanics under such topological constraints is the subject of this study. Conventional arguments based on phase spaces, Jacobi identity, invariant measure, or the H theorem are no longer applicable since all these notions stem from the symplectic geometry underlying canonical Hamiltonian systems. Remembering that Hamiltonian systems are endowed with field tensors (canonical 2-forms) that have zero helicity, our mission is to extend the scope toward the class of systems governed by finite-helicity field tensors. Here, we introduce a class of field tensors that are characterized by Beltrami vectors. We prove an H theorem for this Beltrami class. The most general class of energy-conserving systems are non-Beltrami, for which we identify the "field charge" that prevents the entropy to maximize, resulting in creation of heterogeneous distributions. The essence of the theory can be delineated by classifying three-dimensional dynamics. We then generalize to arbitrary (finite) dimensions.
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.
Resonant Alfven waves on auroral field lines
International Nuclear Information System (INIS)
Chiu, Y.T.
1987-01-01
It is shown that resonant Alfven waves on dipole magnetic field geometry and plasma distributions suitable for auroral field lines can be conveniently treated in the theory of Mathieu functions. Resurgent interest in invoking large-scale Alfven waves to structure some elements of auroral electrodynamics calls for interpretation of measured perpendicular electric and magnetic disturbance fields in terms of Alfven waves. The ability to express the resonant eigenmodes in closed form in terms of Mathieu functions allows for convenient tests of the Alfven wave structuring hypothesis. Implications for current vector electric and magnetic disturbance measurements are discussed
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
Reducing Field Distortion in Magnetic Resonance Imaging
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2010-01-01
A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T
Energy Technology Data Exchange (ETDEWEB)
McMaken, Tyler C. [National Solar Observatory REU Program, 3665 Discovery Drive, 3rd Floor, Boulder, CO 80303 (United States); Petrie, Gordon J. D., E-mail: tmcmaken@gmail.com, E-mail: gpetrie@noao.edu [National Solar Observatory, 3665 Discovery Drive, 3rd Floor, Boulder, CO 80303 (United States)
2017-05-10
The solar active region (AR), NOAA 12192, appeared in 2014 October as the largest AR in 24 years. Here we examine the counterintuitive nature of two diffusion-driven processes in the region: the role of helicity buildup in the formation of a major filament, and the relationship between the effects of supergranular diffusion and meridional flow on the AR and on the polar field. Quantitatively, calculations of current helicity and magnetic twist from Helioseismic and Magnetic Imager (HMI) vector magnetograms indicate that, though AR 12192 emerged with negative helicity, positive helicity from subsequent flux emergence, consistent with the hemispheric sign-preference of helicity, increased over time within large-scale, weak-field regions such as those near the polarity inversion line (PIL). Morphologically, Atmospheric Imaging Assembly observations of filament barbs, sigmoidal patterns, and bases of Fe xii stalks initially exhibited signatures of negative helicity, and the long filament that subsequently formed had a strong positive helicity consistent with the helicity buildup along the PIL. We find from full-disk HMI magnetograms that AR 12192's leading positive flux was initially closer to the equator but, owing either to the region’s magnetic surroundings or to its asymmetric flux density distribution, was transported poleward more quickly on average than its trailing negative flux, contrary to the canonical pattern of bipole flux transport. This behavior caused the AR to have a smaller effect on the polar fields than expected and enabled the formation of the very long neutral line where the filament formed.
Coaxial plasma gun in the high density regime and injection into a helical field
Energy Technology Data Exchange (ETDEWEB)
Schaer, S.F. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)
1994-02-01
A modified coaxial gun in the high density regime of 20-70 mT of He restgas, energized by a 1200 HV sinusoidally damped capacitor discharge with peak currents of 86 kA in a potential range of 10-15 kV, was investigated. The acceleration of the current sheet inside the gun was studied, and an MHD current element model derived, in good agreement with experiment, indicating that thermal diffusion can be neglected during the acceleration phase and furthermore explains the sheet velocity limitation. At the muzzle the plasma is magnetized by inducing a toroidal current through a permanent radial field, generating poloidal field. The injection of the generated current-carrying plasma torus into the driftspace was studied by means of a diamagnetic probe array, for 1) toroidal bias field, and 2) helical bias field. The inner electrode (negative polarity) is continued into the driftspace by a considerably thinner, pyrex insulated central conductor, generating the toroidal bias. Quasi-Tokamak geometry is reached in the helical case. The necessary axial bias field strength was then calculated. Second half-period breakdown was observed, thus a positive electrode was present most of the time. This is a unique way to achieve autopreionisation. Plasma gun operation is very much breakdown dependent, specially in the region of the muzzle. This made it necessary to construct a special compensation coil for the axial field coil. The mean torus speed in the driftspace was 2.2 cm/{mu}sec. The tori were azimuthally homogeneous and exhibited enhanced stability. Transverse expansion at ejection and in the driftspace is prevented by a unique rarefaction wave-pattern resulting from the Mach 50 flow. The toroidal current was observed to decay continuously, not abruptly. No n type or oscillatory instabilities were encountered. These findings are important for future designs of guns where a stable and homogenous torus is needed, such as magnetic confinement injectors. (author) 39 figs., 38 refs.
Coaxial plasma gun in the high density regime and injection into a helical field
International Nuclear Information System (INIS)
Schaer, S.F.
1994-02-01
A modified coaxial gun in the high density regime of 20-70 mT of He restgas, energized by a 1200 HV sinusoidally damped capacitor discharge with peak currents of 86 kA in the potential range of 10-15 kV, was investigated. The acceleration of the current sheet inside the gun was studied, and an MHD current element model derived, in good agreement with experiment, indicating that thermal diffusion can be neglected during the acceleration phase and furthermore explains the sheet velocity limitation. At the muzzle the plasma is magnetized by inducing a toroidal current through a permanent radial field, generating poloidal field. The injection of the generated current-carrying plasma torus into the driftspace was studied by means of a diamagnetic probe array, for 1) toroidal bias field, and 2) helical bias field. The inner electrode (negative polarity) is continued into the driftspace by a considerably thinner, pyrex insulated central conductor, generating the toroidal bias. Quasi-Tokamak geometry is reached in the helical case. The necessary axial bias field strength was then calculated. Second half-period breakdown was observed, thus a positive electrode was present most of the time. This is a unique way to achieve autopreionisation. Plasma gun operation is very much breakdown dependent, specially in the region of the muzzle. This made it necessary to construct a special compensation coil for the axial field coil. The mean torus speed in the driftspace was 2.2 cm/μsec. The tori were azimuthally homogeneous and exhibited enhanced stability. Transverse expansion at ejection and in the driftspace is prevented by a unique rarefaction wave-pattern resulting from the Mach 50 flow. The toroidal current was observed to decay continuously, not abruptly. No n type or oscillatory instabilities were encountered. These findings are important for future designs of guns where a stable and homogenous torus is needed, such as magnetic confinement injectors. (author) 39 figs., 38 refs
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.
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)
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)
Numerical study of whisker field lines in the periphery of the Large Helical Device
International Nuclear Information System (INIS)
Akao, Hideki
1990-01-01
The behavior of periphery magnetic field lines in the standard Large-Helical Device (l=2 heliotron/torsatron type) configuration is studied numerically. Three different types of behavior are found, corresponding to three different regions: the stochastic region near the outermost magnetic surface, the whisker region, and the inter-whisker region outside the stochastic region. The behavior of whisker and inter-whisker field lines is specifically analyzed. It is found that whisker field lines exhibit both regular and irregular types of behavior, whereas inter-whisker field lines exhibit only regular behavior. The connection lengths for the whisker field lines are usually as long as several tens of toroidal pitches, whereas those for the inter-whisker field lines are usually less than ten toroidal pitch lengths. Whisker field lines are characterized by three fundamental processes; stretching, folding, and nesting associated with the motion of a residual X-point of the separatrix. Simple modeling is performed to reproduce these three fundamental processes. (author)
Helicity dependence of the {gamma}d{yields} {pi}NN reactions in the {delta}-resonance region
Energy Technology Data Exchange (ETDEWEB)
Ahrens, J.; Arends, H.J.; Beck, R.; Heid, E.; Jahn, O.; Lang, M.; Martinez-Fabregate, M.; Schwamb, M.; Tamas, G.; Thomas, A. [Universitaet Mainz, Institut fuer Kernphysik, Mainz (Germany); Altieri, S.; Panzeri, A.; Pinelli, T. [INFN, Pavia (Italy); Universita di Pavia, Dipartimento di Fisica Nucleare e Teorica, Pavia (Italy); Annand, J.R.M.; McGeorge, J.C.; Protopopescu, D.; Rosner, G. [University of Glasgow, Department of Physics and Astronomy, Glasgow (United Kingdom); Blackston, M.A.; Weller, H.R. [Duke University, Department of Physics, Durham, NC (United States); Bradtke, C.; Dutz, H.; Klein, F.; Rohlof, C. [Universitaet Bonn, Physikalisches Institut, Bonn (Germany); Braghieri, A.; Pedroni, P. [INFN, Sezione di Pavia, Pavia (Italy); Hose, N. d' [DSM/DAPNIA/SPhN, CEA Saclay, Gif-sur-Yvette Cedex (France); Fix, A. [Tomsk Polytechnic University, Laboratory of Mathematical Physics, Tomsk (Russian Federation); Kondratiev, R.; Lisin, V. [Academy of Science, INR, Moscow (Russian Federation); Meyer, W.; Reicherz, G. [Ruhr-Universitaet Bochum, Insitut fuer Experimentalphysik, Bochum (Germany); Rostomyan, T. [Universiteit Gent, Subatomaire en Stralingsfysica, Gent (Belgium); INFN, Pavia (Italy); Ryckbosch, D. [Universiteit Gent, Subatomaire en Stralingsfysica, Gent (Belgium)
2010-05-15
The helicity dependence of the differential cross-section for the {gamma}d{yields}{pi}NN reactions has been measured for the first time in the {delta} -resonance region. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. The data show that the main reaction mechanisms for the {pi}{sup {+-}} NN channels are the quasi-free N {pi} processes on one bound nucleon with nuclear dynamics playing a minor role. On the contrary, for the {pi}{sup 0}np channel nuclear mechanisms involving the reabsorption of the photoproduced {pi}{sup 0} by the np pair have to be taken into account to reproduce the experimental data. (orig.)
Helicity dependence of the γd→ πNN reactions in the Δ-resonance region
International Nuclear Information System (INIS)
Ahrens, J.; Arends, H.J.; Beck, R.; Heid, E.; Jahn, O.; Lang, M.; Martinez-Fabregate, M.; Schwamb, M.; Tamas, G.; Thomas, A.; Altieri, S.; Panzeri, A.; Pinelli, T.; Annand, J.R.M.; McGeorge, J.C.; Protopopescu, D.; Rosner, G.; Blackston, M.A.; Weller, H.R.; Bradtke, C.; Dutz, H.; Klein, F.; Rohlof, C.; Braghieri, A.; Pedroni, P.; Hose, N. d'; Fix, A.; Kondratiev, R.; Lisin, V.; Meyer, W.; Reicherz, G.; Rostomyan, T.; Ryckbosch, D.
2010-01-01
The helicity dependence of the differential cross-section for the γd→πNN reactions has been measured for the first time in the Δ -resonance region. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. The data show that the main reaction mechanisms for the π ± NN channels are the quasi-free N π processes on one bound nucleon with nuclear dynamics playing a minor role. On the contrary, for the π 0 np channel nuclear mechanisms involving the reabsorption of the photoproduced π 0 by the np pair have to be taken into account to reproduce the experimental data. (orig.)
DEFF Research Database (Denmark)
Lysenko, Alexander; Volk, Iurii; Serozhko, Anastasia
2017-01-01
We have carried out the research of plural three-wave resonances of space charge wave (SCW) harmonics in the transit section of the klystron type two-stream superheterodyne free-electron laser (TSFEL) with helical electron beam in cubic non-linear approximation. We have found out that two...
Nuclear magnetic resonance and earth magnetic field
International Nuclear Information System (INIS)
Anon.
1998-01-01
Nuclear magnetic resonance concerns nuclei whose spin is different from 0. These nuclei exposed to a magnetic field is comparable to a peg top spinning around its axis while being moved by a precession movement called Larmor precession. This article presents an experiment whose aim is to reveal nuclear magnetism of nuclei by observing Larmor precession phenomena due to the earth magnetic field. The earth magnetic field being too weak, it is necessary to increase the magnetization of the sample during a polarization phase. First the sample is submitted to a magnetic field B perpendicular to the earth magnetic field B 0 , then B is cut off and the nuclei move back to their equilibrium position by executing a precession movement due to B 0 field. (A.C.)
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
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.
Azimuthal electric fields and ambipolarity in a multiple-helicity torsatron
International Nuclear Information System (INIS)
Hastings, D.E.; Shaing, K.C.
1985-01-01
In a torsatron there are multiple solutions to the ambipolarity relationship for the electric field. If the electric field is small over some region of space then the self-consistent poloidal electric field can be important and lead to potential islands. If the plasma is in the superbanana plateau regime, then slow resonant particles limit the rate of change of the electric field and, hence, give a minimum width for the spatial zone where the plasma is changing roots of the ambipolarity relationship
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.
Non-solenoidal Startup with High-Field-Side Local Helicity Injection on the Pegasus ST
Perry, J. M.; Bodner, G. M.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Pachicano, J. L.; Pierren, C.; Richner, N. J.; Rodriguez Sanchez, C.; Schlossberg, D. J.; Reusch, J. A.; Weberski, J. D.
2017-10-01
Local Helicity Injection (LHI) is a non-solenoidal startup technique utilizing electron current injectors at the plasma edge to initiate a tokamak-like plasma at high Ip . Recent experiments on Pegasus explore the inherent tradeoffs between high-field-side (HFS) injection in the lower divertor region and low-field-side (LFS) injection at the outboard midplane. Trade-offs include the relative current drive contributions of HI and poloidal induction, and the magnetic geometry required for relaxation to a tokamak-like state. HFS injection using a set of two increased-area injectors (Ainj = 4 cm2, Vinj 1.5 kV, and Iinj 8 kA) in the lower divertor is demonstrated over the full range of toroidal field available on Pegasus (BT 0 = 10) attainable with LHI and the favorable stability of the ultra-low aspect ratio, low-li LHI-driven plasmas allow access to high βt-up to 100 % , as indicated by kinetically-constrained equilibrium reconstructions. Work supported by US DOE Grant DE-FG02-96ER54375.
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 ...
Cyclotron resonance cooling by strong laser field
International Nuclear Information System (INIS)
Tagcuhi, Toshihiro; Mima, Kunioka
1995-01-01
Reduction of energy spread of electron beam is very important to increase a total output radiation power in free electron lasers. Although several cooling systems of particle beams such as a stochastic cooling are successfully operated in the accelerator physics, these cooling mechanisms are very slow and they are only applicable to high energy charged particle beams of ring accelerators. We propose here a new concept of laser cooling system by means of cyclotron resonance. Electrons being in cyclotron motion under a strong magnetic field can resonate with circular polarized electromagnetic field, and the resonance take place selectively depending on the velocity of the electrons. If cyclotron frequency of electrons is equal to the frequency of the electromagnetic field, they absorb the electromagnetic field energy strongly, but the other electrons remain unchanged. The absorbed energy will be converted to transverse kinetic energy, and the energy will be dumped into the radiation energy through bremastrahlung. To build a cooling system, we must use two laser beams, where one of them is counter-propagating and the other is co-propagating with electron beam. When the frequency of the counter-propagating laser is tuned with the cyclotron frequency of fast electrons and the co-propagating laser is tuned with the cyclotron frequency of slow electrons, the energy of two groups will approach and the cooling will be achieved. We solve relativistic motions of electrons with relativistic radiation dumping force, and estimate the cooling rate of this mechanism. We will report optimum parameters for the electron beam cooling system for free electron lasers
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)
Ultra high field magnetic resonance imaging
International Nuclear Information System (INIS)
Lethimonnier, F.; Vedrine, P.
2007-01-01
Understanding human brain function, brain development and brain dysfunction is one of the great challenges of the twenty first century. Biomedical imaging has now run up against a number of technical constraints that are exposing limits to its potential. In order to overcome the current limits to high-field magnetic resonance cerebral imaging (MRI) and unleash its fullest potential, the Cea has built NeuroSpin, an ultra-high-field neuroimaging facility at its Saclay centre (in the Essonne). NeuroSpin already boasts three fully operational MRI systems. The first is a 3-tesla high-field system and the second is a very-high-field 7-tesla system, both of which are dedicated to clinical studies and investigations in humans, while the third is an ultra-high-field 17.65-tesla system designed for studies on small animals. In 2011, NeuroSpin will be commissioning an 11.7-tesla ultra-high-field system of unprecedented power that is designed for research on human subjects. The level of the magnetic field and the scale required will make this joint French-German project to build the magnet a breakthrough in the international arena. (authors)
Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch
Frassinetti, L.; Brunsell, P. R.; Drake, J. R.; Menmuir, S.; Cecconello, M.
2007-11-01
In recent years, good progress toward a better understanding and control of the plasma performance in reversed-field pinch devices has been made. These improvements consist both of the discovery of spontaneous plasma regimes, termed the quasi single helicity (QSH) regime, in which part of the plasma core is no longer stochastic, and of the development of techniques for active control of plasma instabilities. In this paper, a systematic study of spontaneous QSH in the EXTRAP T2R device [P. R. Brunsell, H. Bergsaker, M. Cecconello et al., Plasma Phys. Control. Fusion 43, 1457 (2001)] is presented. In this device, QSH states can occur spontaneously and it is associated with magnetic and thermal structures. A statistical analysis to determine the most favorable experimental conditions to have a transition to the QSH regime will be presented. The results described here are useful to understand the underlying properties of QSH regimes in view of future applications of the QSH active control in EXTRAP T2R; they are also important to have a comparison with the QSH studied in other devices.
International Nuclear Information System (INIS)
Nelson, B.E.; Bryan, W.E.; Goranson, P.L.; Warwick, J.E.
1985-01-01
The helical field (HF) coil set for the Advanced Toroidal Facility (ATF) is an M = 12, l = 2, constant-ratio torsatron winding consisting of 2 coils, each with 14 turns of heavy copper conductor. The coils are divided into 24 identical segments to facilitate fabrication and minimize the assembly schedule. The segments are connected across through-bolted lap joints that must carry up to 124,000 A per turn for 5 s or 62,500 A steady-state. In addition, the joints must carry the high magnetic and thermal loads induced in the conductor and still fit within the basic 140- by 30-mm copper envelope. Extensive testing and development were undertaken to verify and refine the basic joint design. Tests included assembly force and clamping force for various types of misalignment; joint resistance as a function of clamping force; clamp bolt relaxation due to thermal cycling; fatigue testing of full-size, multiturn joint prototypes; and low-cycle fatigue and tensile tests of annealed CDA102 copper. The required performance parameters and actual test results, as well as the final joint configuration, are presented. 2 refs., 9 figs., 4 tabs
Ohdachi, Satoshi; Watanabe, Kiyomasa; Sakakibara, Satoru; Suzuki, Yasuhiro; Tsuchiya, Hayato; Ming, Tingfeng; Du, Xiaodi; LHD Expriment Group Team
2014-10-01
In the Large Helical Device (LHD), the plasma is surrounded by the so-called magnetic stochastic region, where the Kolmogorov length of the magnetic field lines is very short, from several tens of meters and to thousands meters. Finite pressure gradient are formed in this region and MHD instabilities localized in this region is observed since the edge region of the LHD is always unstable against the pressure driven mode. Therefore, the saturation level of the instabilities is the key issue in order to evaluate the risk of this kind of MHD instabilities. The saturation level depends on the pressure gradient and on the magnetic Reynolds number; there results are similar to the MHD mode in the closed magnetic surface region. The saturation level in the stochastic region is affected also by the stocasticity itself. Parameter dependence of the saturation level of the MHD activities in the region is discussed in detail. It is supported by NIFS budget code ULPP021, 028 and is also partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research 26249144, by the JSPS-NRF-NSFC A3 Foresight Program NSFC: No. 11261140328.
Resonance broadening in an intense light field
International Nuclear Information System (INIS)
Andreev, S.P.; Lisitsa, V.S.
1977-01-01
Collisions of identical atoms in a strong resonance radiation field E 0 cosωt, for which the atomic oscillation period is comparable to the collision time of the atoms, are considered. The problem is treated in terms of the simplest two-level atomic model. The problem of light absorption in such collisions is reduced to the problem of inelastic transitions in a three-level compound system of two atoms and an electromagnetic field. Corresponding probabilities and inelastic scattering integral cross sections for transitions between energy levels in such a system are calculated for two extreme cases- the impact (rapid collisions) and the static one (slow collisions). In the general case the cross sections depend nonlinearly on Esub(0). For small Esub(0) as compared to a certain critical Esub(0)* the results are similar to those of the well-known linear theory of resonance broadening. For Esub(0)>>Esub(0)* the absorption in the line wing is found to decrease (with increase of Esub(0)-the medium becomes more ''transparent''). The kinetics of light absorption in the medium of identical atoms with constant absorption capacity is analysed
Energy Technology Data Exchange (ETDEWEB)
Takahashi, H., E-mail: takahashi.hiromi@LHD.nifs.ac.jp; Shimozuma, T.; Kubo, S.; Yoshimura, Y.; Igami, H.; Ito, S.; Kobayashi, S.; Mizuno, Y.; Okada, K.; Mutoh, T.; Nagaoka, K.; Osakabe, M.; Yamada, I.; Nakano, H.; Yokoyama, M.; Ido, T.; Shimizu, A.; Seki, R.; Ida, K.; Yoshinuma, M. [National Institute for Fusion Science, Toki 509-5292 (Japan); and others
2014-06-15
Enhancement of the output power per gyrotron has been planned in the Large Helical Device (LHD). Three 77-GHz gyrotrons with an output power of more than 1 MW have been operated. In addition, a high power gyrotron with the frequency of 154 GHz (1 MW/5 s, 0.5 MW/CW) was newly installed in 2012, and the total injection power of Electron cyclotron resonance heating (ECRH) reached 4.6 MW. The operational regime of ECRH plasma on the LHD has been extended due to the upgraded ECRH system such as the central electron temperature of 13.5 keV with the line-averaged electron density n{sub e-fir} = 1 × 10{sup 19} m{sup −3}. The electron thermal confinement clearly improved inside the electron internal transport barrier, and the electron thermal diffusivity reached neoclassical level. The global energy confinement time increased with increase of n{sub e-fir}. The plasma stored energy of 530 kJ with n{sub e-fir} = 3.2 × 10{sup 19} m{sup −3}, which is 1.7 times larger than the previous record in the ECRH plasma in the LHD, has been successfully achieved.
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)
Kato, A.; Nakamura, Y.; Wakatani, M.
1990-07-01
L = 2 torsatrons are studied to improve the high energy trapped particle confinement with additional l = 1 and/or l = 3 helical coils. The winding laws are selected in two ways. One is to realize 'σ - optimization' by the additional helical coils, but this approach loses magnetic well region. The other selection is to produce or deepen the magnetic well by the additional helical coils. L=3 helical coils are usable to this end. In this case the improvement of the trapped particle confinement depends on magnetic axis position. Radial electric field producing sheared rotational motion is also considered to improve the trapped particle confinement in a standard l = 2 torsatron. By excluding cancellation between E x B and ΔB drift motion occurred for the parabolic potential profiles, all deeply trapped particles can be confined in the central region. Degradation of the trapped particle confinement by the Shafranov shift is mitigated by shifting the magnetic axis inside in the vacuum configuration. (author)
Directory of Open Access Journals (Sweden)
Manuel Arrayás
2018-03-01
Full Text Available We calculate analytically the spin-orbital decomposition of the angular momentum using completely nonparaxial fields that have a certain degree of linkage of electric and magnetic lines. The split of the angular momentum into spin-orbital components is worked out for non-null knotted electromagnetic fields. The relation between magnetic and electric helicities and spin-orbital decomposition of the angular momentum is considered. We demonstrate that even if the total angular momentum and the values of the spin and orbital momentum are the same, the behavior of the local angular momentum density is rather different. By taking cases with constant and non-constant electric and magnetic helicities, we show that the total angular momentum density presents different characteristics during time evolution.
Far-field superresolution by imaging of resonance scattering
Schuster, Gerard T.; Huang, Y.
2014-01-01
We show that superresolution imaging in the far-field region of the sources and receivers is theoretically and practically possible if migration of resonant multiples is employed. A resonant multiple is one that bounces back and forth between two
Directory of Open Access Journals (Sweden)
A. H. ELBATRAN
2015-07-01
Full Text Available Helical channels have a wide range of applications in petroleum engineering, nuclear, heat exchanger, chemical, mineral and polymer industries. They are used in the separation processes for fluids of different densities. The centrifugal force, free surface and geometrical effects of the helical channel make the flow pattern more complicated; hence it is very difficult to perform physical experiment to predict channel performance. Computational Fluid Dynamics (CFD can be suitable alternative for studying the flow pattern characteristics in helical channels. The different ranges of dimensional parameters, such as curvature and torsion, often cause various flow regimes in the helical channels. In this study, the effects of physical parameters such as curvature, torsion, Reynolds number, Froude number and Dean Number on the characteristics of the turbulent flow in helical rectangular channels have been investigated numerically, using a finite volume RANSE code Fluent of Ansys workbench 10.1 UTM licensed. The physical parameters were reported for range of curvature (δ of 0.16 to 0.51 and torsion (λ of 0.032 to 0.1 .The numerical results of this study showed that the decrease in the channel curvature and the increase in the channel torsion numbers led to the increase of the flow velocity inside the channel and the change in the shape of water free surface at given Dean, Reynolds and Froude numbers.
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
Very low field magnetic resonance imaging
International Nuclear Information System (INIS)
Herreros, Quentin
2013-01-01
The aim of this thesis is to perform Magnetic Resonance Imaging at very low field (from 1 mT to 10 mT). A new kind of sensor called 'mixed sensor' has been used to achieve a good detectivity at low frequencies. Combining a superconducting loop and a giant magnetoresistance, those detectors have a competitive equivalent field noise compared to existing devices (Tuned coils, SQUIDs and Atomic Magnetometers). They have been combined with flux transformers to increase the coupling between the sample and the sensor. A complete study has been performed to adapt it to mixed sensors and then maximize the gain. This set has been incorporated in an existing small MRI device to test its robustness in real conditions. In parallel, several MRI sequences (GE, SE, FLASH, EPI,...) have been integrated and adapted to very low field requirements. They have been used to perform in-vivo three dimensional imaging and relaxometry studies on well known products to test their reliability. Finally, a larger setup adapted for full-head imaging has been designed and built to perform images on a larger working volume. (author) [fr
Thermal and electrical joint test for the helical field coils in the Advanced Toroidal Facility
International Nuclear Information System (INIS)
Brown, R.L.; Johnson, R.L.
1985-01-01
Initial feasibility studies of a number of configurations for the Advanced Toroidal Facility (ATF) resulted in the selection of a resistive copper continuous-coil torsatron as the optimum device considering the physics program, cost, and schedule. Further conceptual design work was directed toward optimization of this configuration and, if possible, a shorter schedule. It soon became obvious that in order to shorten the schedule, a number of design and fabrication activities should proceed in parallel. This was most critical for the vacuum vessel and the helical field (HF) coils. If the HF coils were wound in place on a completed vacuum vessel, the overall schedule would be significantly (greater than or equal to12 months) longer. The approach of parallel scheduel paths requires that the HF coils be segmented into parts of less than or equal to180 0 of poloidal angle and that joints be made on a turn-by-turn basis when the segments are installed. It was obvious from the outset that the compact and complex geometry of the joint design presented a special challenge in the areas of reliability, assembly, maintenance, disassembly, and cost. Also, electrical, thermal, and force excursions are significant for these joints. A number of soldered, welded, brazed, electroplated, and bolted joints were evaluated. The evaluations examined fabrication feasibility and complexity, thermal-electrical performance at approximately two-thirds of the steady-state design conditions, and installation and assembly processes. Results of the thermal-electrical tests were analyzed and extrapolated to predict performance at peak design parameters. The final selection was a lap-type joint clamped with insulated bolts that pass through the winding packing. 3 refs., 4 figs
Neutrino`s helicity in a gravitational field; Helicite des neutrinos dans un champ gravitationnel
Energy Technology Data Exchange (ETDEWEB)
Pansart, J.P.
1996-12-31
By using approximated solutions of Dirac`s equation, we show that there is no helicity reversal for light neutrinos in the Schwarzschild metric nor in an expanding universe. The actual coupling between a particle spin and the angular momentum of a heavy rotating body induces a possible helicity reversal but with an unobservable probability proportional to m{sup 2}{sub p} / E{sup 2}, where m{sub p} is the particle mass and E its energy. In these calculations, the helicity is defined through the spin orientation with respect to the current and not with respect to the linear momentum. This definition gives simple expressions and is equal to the usual definition in the case of a flat space. (N.T.). 10 refs.
Large field-of-view transmission line resonator for high field MRI
DEFF Research Database (Denmark)
Zhurbenko, Vitaliy; Johannesson, Kristjan Sundgaard; Boer, Vincent
2016-01-01
Transmission line resonators is often a preferable choice for coils in high field magnetic resonance imaging (MRI), because they provide a number of advantages over traditional loop coils. The size of such resonators, however, is limited to shorter than half a wavelength due to high standing wave....... Achieved magnetic field distribution is compared to the conventional transmission line resonator. Imaging experiments are performed using 7 Tesla MRI system. The developed resonator is useful for building coils with large field-of-view....
Molecular structure and motion in zero field magnetic resonance
International Nuclear Information System (INIS)
Jarvie, T.P.
1989-10-01
Zero field magnetic resonance is well suited for the determination of molecular structure and the study of motion in disordered materials. Experiments performed in zero applied magnetic field avoid the anisotropic broadening in high field nuclear magnetic resonance (NMR) experiments. As a result, molecular structure and subtle effects of motion are more readily observed
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.
On field line resonances of hydromagnetic Alfven waves in dipole magnetic field
International Nuclear Information System (INIS)
Chen, Liu; Cowley, S.C.
1989-07-01
Using the dipole magnetic field model, we have developed the theory of field line resonances of hydromagnetic Alfven waves in general magnetic field geometries. In this model, the Alfven speed thus varies both perpendicular and parallel to the magnetic field. Specifically, it is found that field line resonances do persist in the dipole model. The corresponding singular solutions near the resonant field lines as well as the natural definition of standing shear Alfven eigenfunctions have also been systematically derived. 11 refs
In-line production of a bi-circular field for generation of helically polarized high-order harmonics
Energy Technology Data Exchange (ETDEWEB)
Kfir, Ofer, E-mail: ofertx@technion.ac.il, E-mail: oren@si.technion.ac.il; Bordo, Eliyahu; Ilan Haham, Gil; Lahav, Oren; Cohen, Oren, E-mail: ofertx@technion.ac.il, E-mail: oren@si.technion.ac.il [Solid State Institute and Physics Department, Technion, Haifa 32000 (Israel); Fleischer, Avner [Solid State Institute and Physics Department, Technion, Haifa 32000 (Israel); Department of Physics and Optical Engineering, Ort Braude College, Karmiel 21982 (Israel)
2016-05-23
The recent demonstration of bright circularly polarized high-order harmonics of a bi-circular pump field gave rise to new opportunities in ultrafast chiral science. In previous works, the required nontrivial bi-circular pump field was produced using a relatively complicated and sensitive Mach-Zehnder-like interferometer. We propose a compact and stable in-line apparatus for converting a quasi-monochromatic linearly polarized ultrashort driving laser field into a bi-circular field and employ it for generation of helically polarized high-harmonics. Furthermore, utilizing the apparatus for a spectroscopic spin-mixing measurement, we identify the photon spins of the bi-circular weak component field that are annihilated during the high harmonics process.
Detection of internal fields in double-metal terahertz resonators
DEFF Research Database (Denmark)
Mitrofanov, Oleg; Han, Zhanghua; Ding, Fei
2017-01-01
Terahertz (THz) double-metal plasmonic resonators enable enhanced light-matter coupling by exploiting strong field confinement. The double-metal design however restricts access to the internal fields. We propose and demonstrate a method for spatial mapping and spectroscopic analysis of the internal...... electromagnetic fields in double-metal plasmonic resonators. We use the concept of image charges and aperture-type scanning near-field THz time-domain microscopy to probe the fields confined within the closed resonator. The experimental method opens doors to studies of light-matter coupling in deeply sub...
Propagation characteristics of resonance cone in a nonuniform magnetic field
International Nuclear Information System (INIS)
Ohnuma, T.; Sanuki, H.
1984-01-01
Propagation characteristics of resonance cone field for frequencies below the electron cyclotron frequency are described in a mirror magnetic field on the basis of fluid equation. Theoretical results are compared qualitatively with those of experiment
Chkhetiani, O G; Jurcisinova, E; Jurcisin, M; Mazzino, A; Repasan, M
2005-01-01
The advection of a passive scalar quantity by incompressible helical turbulent flow has been investigated in the framework of an extended Kraichnan model. Statistical fluctuations of the velocity field are assumed to have the Gaussian distribution with zero mean and defined noise with finite-time correlation. Actual calculations have been done up to two-loop approximation in the framework of the field-theoretic renormalization group approach. It turned out that the space parity violation (helicity) of a stochastic environment does not affect anomalous scaling which is the peculiar attribute of a corresponding model without helicity. However, stability of asymptotic regimes, where anomalous scaling takes place, and the effective diffusivity strongly depend on the amount of helicity.
Effects of finite-β and radial electric fields on neoclassical transport in the Large Helical Device
International Nuclear Information System (INIS)
Kanno, R.; Nakajima, N.; Sugama, H.; Okamoto, M.; Ogawa, Y.
1997-01-01
Effects of finite-β and radial electric fields on the neoclassical transport in the Large Helical Device are investigated with the DKES (Drift Kinetic Equation Solver) code. In the finite-β configuration, even orbits of deeply trapped particles deviate significantly from magnetic flux surfaces. Thus, neoclassical ripple transport coefficients in the finite-β configuration are several times larger than those in the vacuum configuration under the same condition of temperatures and radial electric fields. When the plasma temperature is several keV, a bifurcation of the electric fields appears under the ambipolarity condition, and sufficient large radial electric fields can be generated. As a result, the ExB drift rectifies orbits of particles and improves significantly the transport coefficients in the finite-β configuration. (author)
Energy Technology Data Exchange (ETDEWEB)
Ahrens, J.; Altieri, S.; Annand, J.R.M.; Anton, G.; Arends, H.-J.; Aulenbacher, K.; Beck, R.; Bradtke, C.; Braghieri, A.; Degrande, N.; D' Hose, N.; Dutz, H.; Goertz, S.; Grabmayr, P.; Hansen, K.; Harmsen, J.; Harrach, D. von; Hasegawa, S.; Hasegawa, T.; Heid, E.; Helbing, K.; Holvoet, H.; Van Hoorebeke, L.; Horikawa, N.; Iwata, T.; Jahn, O.; Jennewein, P.; Kageya, T.; Kiel, B.; Klein, F.; Kondratiev, R.; Kossert, K.; Krimmer, J.; Lang, M.; Lannoy, B.; Leukel, R.; Lisin, V.; Matsuda, T.; McGeorge, J.C.; Meier, A.; Menze, D.; Meyer, W.; Michel, T.; Naumann, J.; Panzeri, A.; Pedroni, P.; Pinelli, T.; Preobrajenski, I.; Radtke, E.; Reichert, E.; Reicherz, G.; Rohlof, Ch.; Rosner, G.; Rostomyan, T.; Rovelli, C.; Ryckbosch, D.; Sauer, M.; Schoch, B.; Schumacher, M.; Seitz, B.; Speckner, T.; Takabayashi, N.; Tamas, G.; Thomas, A.; Vyver, R. van de; Wakai, A.; Weihofen, W.; Wissmann, F.; Zapadtka, F.; Zeitler, G
2003-01-02
The helicity dependence of the total cross section for the {gamma}{yields}p{yields}{yields}n{pi}{sup +}{pi}{sup 0} reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D{sub 13} resonance.
Energy Technology Data Exchange (ETDEWEB)
Airapetian, A. [Giessen Univ. (Germany). 2. Physikalisches Inst.; Michigan Univ., Ann Arbor, MI (United States). Randall Laboratory of Physics; Akopov, N. [Yerevan Physics Institute (Argentina); Aschenauer, E.C. [DESY Zeuthen (Germany)] [and others; Collaboration: HERMES Collaboration
2013-10-15
The beam-helicity asymmetry in associated electroproduction of real photons, ep {yields} e{gamma}{pi}N, in the {Delta}(1232)-resonance region is measured using the longitudinally polarized HERA positron beam and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, ep {yields} e{gamma}{pi}{sup 0}p and ep {yields} e{gamma}{pi}{sup +}n, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.
Kamada, Kohei
2018-05-01
It has been considered that baryogenesis models without a generation of B -L asymmetry such as the GUT baryogenesis do not work since the asymmetry is washed out by the electroweak sphalerons. Here, we point out that helical hypermagnetic fields can be generated through the chiral magnetic effect with a chiral asymmetry generated in such baryogenesis models. The helical hypermagnetic fields then produce baryon asymmetry mainly at the electroweak symmetry breaking, which remains until today. Therefore, the baryogenesis models without B -L asymmetry can still be the origin of the present baryon asymmetry. In particular, if it can produce chiral asymmetry mainly carried by right-handed electrons of order of 10-3 in terms of the chemical potential to temperature ratio, the resultant present-day baryon asymmetry can be consistent with our Universe, although simple realizations of the GUT baryogenesis are hard to satisfy the condition. We also argue the way to overcome the difficulty in the GUT baryogenesis. The intergalactic magnetic fields with B0˜10-16 - 17 G and λ0˜10-2 - 3 pc are the smoking gun of the baryogenesis scenario as discussed before.
Analysis of transverse field distributions in Porro prism resonators
Litvin, Igor A.; Burger, Liesl; Forbes, Andrew
2007-05-01
A model to describe the transverse field distribution of the output beam from porro prism resonators is proposed. The model allows the prediction of the output transverse field distribution by assuming that the main areas of loss are located at the apexes of the porro prisms. Experimental work on a particular system showed some interested correlations between the time domain behavior of the resonator and the transverse field output. These findings are presented and discussed.
Resonant tunneling in a pulsed phonon field
DEFF Research Database (Denmark)
Kral, P.; Jauho, Antti-Pekka
1999-01-01
, The nonequilibrium spectral function for the resonance displays the formation and decay of the phonon sidebands on ultrashort time scales. The time-dependent tunneling current through the individual phonon satellites reflects this quasiparticle formation by oscillations, whose time scale is set by the frequency...
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)
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
International Nuclear Information System (INIS)
Bialynicki-Birula, I.; Newmann, E.T.; Porter, J.; Winicour, J.; Lukacs, B.; Perjes, Z.; Sebestyen, A.
1981-03-01
The authors give a formal definition of the helicity operator for integral spin fields, which does not involve their momentum-space decomposition. The discussion is based upon a representation of the Pauli-Lubanski operator in terms of the action on tensor fields by the Killing vectors associated with the generators of the Poincare group. This leads to an identification of the helicity operator with the duality operator defined by the space-time alternating tensor. Helicity eigenstates then correspond to self-dual or anti-self-dual fields, in agreement with usage implicit in the literature. In addiition, the relationship between helicity eigenstates which are intrinsically non-classical, and states of right or left circular polarization in classical electrodynamics are discussed. (author)
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
NMR magnetic field controller for pulsed nuclear magnetic resonance experiments
International Nuclear Information System (INIS)
Scheler, G.; Anacker, M.
1975-01-01
A nuclear magnetic resonance controller for magnetic fields, which can also be used for pulsed NMR investigations, is described. A longtime stability of 10 -7 is achieved. The control signal is generated by a modified time sharing circuit with resonance at the first side band of the 2 H signal. An exact calibration of the magnetic field is achieved by the variation of the H 1 - or of the time-sharing frequency. (author)
Structure of magnetic field in Tokamaks
International Nuclear Information System (INIS)
Heller, M.V.A.P.; Caldas, I.L.
1990-01-01
Magnetic surfaces, necessary to plasma confinement, can be extinguished by resonant helical perturbations with small intensities due to plasma oscillations or external helical currents. The mapping of magnetic field is obtained intergrating numerically the differential equation of its lines. Criteria which evaluate the chaotic distribution of lines between resonant magnetic islands are presented. (M.C.K.) [pt
Far-field super-resolution imaging of resonant multiples
Guo, Bowen
2016-05-20
We demonstrate for the first time that seismic resonant multiples, usually considered as noise, can be used for super-resolution imaging in the far-field region of sources and receivers. Tests with both synthetic data and field data show that resonant multiples can image reflector boundaries with resolutions more than twice the classical resolution limit. Resolution increases with the order of the resonant multiples. This procedure has important applications in earthquake and exploration seismology, radar, sonar, LIDAR (light detection and ranging), and ultrasound imaging, where the multiples can be used to make high-resolution images.
Characterization of complementary electric field coupled resonant surfaces
Hand, Thomas H.; Gollub, Jonah; Sajuyigbe, Soji; Smith, David R.; Cummer, Steven A.
2008-11-01
We present angle-resolved free-space transmission and reflection measurements of a surface composed of complementary electric inductive-capacitive (CELC) resonators. By measuring the reflection and transmission coefficients of a CELC surface with different polarizations and particle orientations, we show that the CELC only responds to in-plane magnetic fields. This confirms the Babinet particle duality between the CELC and its complement, the electric field coupled LC resonator. Characterization of the CELC structure serves to expand the current library of resonant elements metamaterial designers can draw upon to make unique materials and surfaces.
Resonant scattering in the presence of an electromagnetic field
International Nuclear Information System (INIS)
Rosenberg, L.
1983-01-01
The theory of resonant reactions, in the projection-operator formulation of Feshbach, is generalized to account for the presence of an external electromagnetic field. The theory is used as the basis for the construction of low-frequency approximations for the transition amplitude. Results obtained here for scattering in a laser field confirm earlier versions of the low-frequency approximation when the resonances are isolated. However, if there are several closely spaced resonances additional terms must be included (their importance magnified by the appearance of near singularities) which account for the effect of radiative transitions between pairs of nearly degenerate resonant states. The weak-field limit of this result yields a low-frequency approximation for single-photon spontaneous bremsstrahlung which, through the inclusion of correction terms associated with closely spaced resonances, provides an improvement over the Feshbach-Yennie version derived some time ago. A separate treatment is required to deal with the limiting case of a static external field and this is worked out here in the context of a time-dependent formulation of the scattering problem. Linear and quadratic Stark splitting of the resonance positions, and resonance broadening due to the tunneling mechanism, are expected to play a significant role in the static limit and these effects are included in the approximation derived here for the transition amplitude
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.
Magnetic field induced incommensurate resonance in cuprate superconductors
International Nuclear Information System (INIS)
Zhang Jingge; Cheng Li; Guo Huaiming; Feng Shiping
2009-01-01
The influence of a uniform external magnetic field on the dynamical spin response of cuprate superconductors in the superconducting state is studied based on the kinetic energy driven superconducting mechanism. It is shown that the magnetic scattering around low and intermediate energies is dramatically changed with a modest external magnetic field. With increasing the external magnetic field, although the incommensurate magnetic scattering from both low and high energies is rather robust, the commensurate magnetic resonance scattering peak is broadened. The part of the spin excitation dispersion seems to be an hourglass-like dispersion, which breaks down at the heavily low energy regime. The theory also predicts that the commensurate resonance scattering at zero external magnetic field is induced into the incommensurate resonance scattering by applying an external magnetic field large enough
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.
Magnetic resonance imaging: effects of magnetic field strength
International Nuclear Information System (INIS)
Crooks, L.E.; Arakawa, M.; Hoenninger, J.; McCarten, B.; Watts, J.; Kaufman, L.
1984-01-01
Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. For any one spin echo sequence, gray/white matter contrast decreases and muscle/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then change more slowly, actually dropping for muscle. The optimum field for magnetic resonance imaging depends on tissue type, body part, and imaging sequence, so that it does not have a unique value. Magnetic resonance systems that operate in the 3.0-5.0 kgauss range achieve most or all of the gains that can be achieved by higher magnetic fields
Resonances of the helium atom in a strong magnetic field
DEFF Research Database (Denmark)
Lühr, Armin Christian; Al-Hujaj, Omar-Alexander; Schmelcher, Peter
2007-01-01
We present an investigation of the resonances of a doubly excited helium atom in a strong magnetic field covering the regime B=0–100 a.u. A full-interaction approach which is based on an anisotropic Gaussian basis set of one-particle functions being nonlinearly optimized for each field strength...
Magnetic Field Dependence and Q of the Josephson Plasma Resonance
DEFF Research Database (Denmark)
Pedersen, Niels Falsig; Finnegan, T. F.; Langenberg, D. N.
1972-01-01
of supercurrent density which is not observed in conventional measurements of the field-dependent critical current. The frequency and field dependence of the plasma-resonance linewidth are interpreted as evidence that the previously unobserved quasiparticle-pair-interference tunnel current predicted by Josephson...
Radiofrequency solutions in clinical high field magnetic resonance
Andreychenko, A.
2013-01-01
Magnetic resonance imaging (MRI) and spectroscopy (MRS) benefit from the sensitivity gain at high field (≥7T). However, high field brings also certain challenges associated with growing frequency and spectral dispersion. Frequency growth results in degraded performance of large volume radiofrequency
DIELECTRIC WAKE FIELD RESONATOR ACCELERATOR MODULE
Energy Technology Data Exchange (ETDEWEB)
Hirshfield, Jay L.
2013-11-06
Results are presented from experiments, and numerical analysis of wake fields set up by electron bunches passing through a cylindrical or rectangular dielectric-lined structure. These bunches excite many TM-modes, with Ez components of the wake fields sharply localized on the axis of the structure periodically behind the bunches. The experiment with the cylindrical structure, carried out at ATF Brookhaven National Laboratory, used up to three 50 MeV bunches spaced by one wake field period (21 cm) to study the superposition of wake fields by measuring the energy loss of each bunch after it passed through the 53-cm long dielectric element. The millimeter-wave spectrum of radiation excited by the passage of bunches is also studied. Numerical analysis was aimed not only to simulate the behavior of our device, but in general to predict dielectric wake field accelerator performance. It is shown that one needs to match the radius of the cylindrical dielectric channel with the bunch longitudinal rms-length to achieve optimal performance.
International Nuclear Information System (INIS)
Chang, Albert J.; Richardson, Susan; Grigsby, Perry W.; Schwarz, Julie K.
2012-01-01
Objective: The objective of this study was to investigate the chronic toxicity, response to therapy, and survival outcomes of patients with cervical cancer treated with definitive pelvic irradiation delivered by helical tomotherapy (HT), with or without concurrent chemotherapy. Methods and Materials: There were 15 patients with a new diagnosis of cervical cancer evaluated in this study from April 2006 to February 2007. The clinical stages of their disease were Stage Ib1 in 3 patients, Ib2 in 3, IIa in 2, IIb in 4, IIIb in 2, and IVa in 1 patient. Fluorodeoxyglucose–positron emission tomography/computed tomography (FDG-PET/CT) simulation was performed in all patients. All patients received pelvic irradiation delivered by HT and high-dose-rate (HDR) brachytherapy. Four patients also received para-aortic irradiation delivered by HT. Thirteen patients received concurrent chemotherapy. Patients were monitored for chronic toxicity using the Common Terminology Criteria for Adverse Events version 3.0 criteria. Results: The median age of the cohort was 51 years (range, 29-87 years), and the median follow-up for all patients alive at time of last follow-up was 35 months. The median overall radiation treatment time was 54 days. One patient developed a chronic Grade 3 GI complication. No other Grade 3 or 4 complications were observed. At last follow-up, 3 patients had developed a recurrence, with 1 patient dying of disease progression. The 3-year progression-free and cause-specific survival estimates for all patients were 80% and 93%, respectively. Conclusion: Intensity-modulated radiation therapy delivered with HT and HDR brachytherapy with or without chemotherapy for definitive treatment of cervical cancer is feasible, with acceptable levels of chronic toxicity.
Theoretical study of structure of electric field in helical toroidal plasmas
International Nuclear Information System (INIS)
Toda, S.; Itoh, K.
2001-06-01
A set of transport equations is analyzed, including the bifurcation of the electric field. The structure of the electric field is studied by use of the theoretical model for the anomalous transport diffusivities. The steep gradient of the electric field is obtained at the electric domain. The suppression of the anomalous transport diffusivity is studied in the presence of the strong shear of the electric field. The hard transition with the multiple ambipolar solutions is examined in the structure of the radial electric field. The details of the structure of the electric domain interface are investigated. (author)
Wilcox, R. S.; Rhodes, T. L.; Shafer, M. W.; Sugiyama, L. E.; Ferraro, N. M.; Lyons, B. C.; McKee, G. R.; Paz-Soldan, C.; Wingen, A.; Zeng, L.
2018-05-01
Small 3D perturbations to the magnetic field in DIII-D ( δB /B ˜2 ×10-4 ) result in large modulations of density fluctuation amplitudes in the pedestal, which are shown using Doppler backscattering measurements to vary by a factor of 2. Helical perturbations of equilibrium density within flux surfaces have previously been observed in the pedestal of DIII-D plasmas when 3D fields are applied and were correlated with density fluctuation asymmetries in the pedestal. These intra-surface density and pressure variations are shown through two fluid MHD modeling studies using the M3D-C1 code to be due to the misalignment of the density and temperature equilibrium iso-surfaces in the pedestal region. This modeling demonstrates that the phase shift between the two iso-surfaces corresponds to the diamagnetic direction of the two species, with the mass density surfaces shifted in the ion diamagnetic direction relative to the temperature and magnetic flux iso-surfaces. The resulting pedestal density, potential, and turbulence asymmetries within flux surfaces near the separatrix may be at least partially responsible for several poorly understood phenomena that occur with the application of 3D fields in tokamaks, including density pump out and the increase in power required to transition from L- to H-mode.
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
Slotted cage resonator for high-field magnetic resonance imaging of rodents
Energy Technology Data Exchange (ETDEWEB)
Marrufo, O; Vasquez, F; Solis, S E; Rodriguez, A O, E-mail: arog@xanum.uam.mx [Departamento de Ingenieria Electrica, Universidad Autonoma Metropolitana Iztapalapa, Mexico, DF 09340 (Mexico)
2011-04-20
A variation of the high-frequency cavity resonator coil was experimentally developed according to the theoretical frame proposed by Mansfield in 1990. Circular slots were used instead of cavities to form the coil endplates and it was called the slotted cage resonator coil. The theoretical principles were validated via a coil equivalent circuit and also experimentally with a coil prototype. The radio frequency magnetic field, B1, produced by several coil configurations was numerically simulated using the finite-element approach to investigate their performances. A transceiver coil, 8 cm long and 7.6 cm in diameter, and composed of 4 circular slots with a 15 mm diameter on both endplates, was built to operate at 300 MHz and quadrature driven. Experimental results obtained with the slotted cage resonator coil were presented and showed very good agreement with the theoretical expectations for the resonant frequency as a function of the coil dimensions and slots. A standard birdcage coil was also built for performance comparison purposes. Phantom images were then acquired to compute the signal-to-noise ratio of both coils showing an important improvement of the slotted cage coil over the birdcage coil. The whole-body images of the mouse were also obtained showing high-quality images. Volume resonator coils can be reliably built following the physical principles of the cavity resonator design for high-field magnetic resonance imaging applications of rodents.
Photocurrent mapping of near-field optical antenna resonances
Barnard, Edward S.; Pala, Ragip A.; Brongersma, Mark L.
2011-01-01
An increasing number of photonics applications make use of nanoscale optical antennas that exhibit a strong, resonant interaction with photons of a specific frequency. The resonant properties of such antennas are conventionally characterized by far-field light-scattering techniques. However, many applications require quantitative knowledge of the near-field behaviour, and existing local field measurement techniques provide only relative, rather than absolute, data. Here, we demonstrate a photodetector platform that uses a silicon-on-insulator substrate to spectrally and spatially map the absolute values of enhanced fields near any type of optical antenna by transducing local electric fields into photocurrent. We are able to quantify the resonant optical and materials properties of nanoscale (∼50nm) and wavelength-scale (∼1μm) metallic antennas as well as high-refractive-index semiconductor antennas. The data agree well with light-scattering measurements, full-field simulations and intuitive resonator models. © 2011 Macmillan Publishers Limited. All rights reserved.
Photocurrent mapping of near-field optical antenna resonances
Barnard, Edward S.
2011-08-21
An increasing number of photonics applications make use of nanoscale optical antennas that exhibit a strong, resonant interaction with photons of a specific frequency. The resonant properties of such antennas are conventionally characterized by far-field light-scattering techniques. However, many applications require quantitative knowledge of the near-field behaviour, and existing local field measurement techniques provide only relative, rather than absolute, data. Here, we demonstrate a photodetector platform that uses a silicon-on-insulator substrate to spectrally and spatially map the absolute values of enhanced fields near any type of optical antenna by transducing local electric fields into photocurrent. We are able to quantify the resonant optical and materials properties of nanoscale (∼50nm) and wavelength-scale (∼1μm) metallic antennas as well as high-refractive-index semiconductor antennas. The data agree well with light-scattering measurements, full-field simulations and intuitive resonator models. © 2011 Macmillan Publishers Limited. All rights reserved.
DEFF Research Database (Denmark)
Petersen, Nils Holger
2014-01-01
A chapter in a book about terminology within the field of medievalism: the chapter discusses the resonance of medieval music and ritual in modern (classical) music culture and liturgical practice.......A chapter in a book about terminology within the field of medievalism: the chapter discusses the resonance of medieval music and ritual in modern (classical) music culture and liturgical practice....
Helicity coherence in binary neutron star mergers and nonlinear feedback
Chatelain, Amélie; Volpe, Cristina
2017-02-01
Neutrino flavor conversion studies based on astrophysical environments usually implement neutrino mixings, neutrino interactions with matter, and neutrino self-interactions. In anisotropic media, the most general mean-field treatment includes neutrino mass contributions as well, which introduce a coupling between neutrinos and antineutrinos termed helicity or spin coherence. We discuss resonance conditions for helicity coherence for Dirac and Majorana neutrinos. We explore the role of these mean-field contributions on flavor evolution in the context of a binary neutron star merger remnant. We find that resonance conditions can be satisfied in neutron star merger scenarios while adiabaticity is not sufficient for efficient flavor conversion. We analyze our numerical findings by discussing general conditions to have multiple Mikheyev-Smirnov-Wolfenstein-like resonances, in the presence of nonlinear feedback, in astrophysical environments.
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)
Bifurcation of equilibria between with and without a large island in the large helical device
Energy Technology Data Exchange (ETDEWEB)
Ohyabu, N; Narushima, Y; Nagayama, Y; Narihara, K; Morisaki, T; Komori, A [National Institute for Fusion Science, Toki, Gifu, 509-5292 (Japan)
2005-09-01
A rapid bifurcation of the equilibria with and without a large island (n/m = 1/1) has been observed in the medium to high beta large helical device discharges. A large island imposed by an external resonant field is suddenly suppressed nearly perfectly by the plasma effects when the beta at the {iota}/2{pi} = 1 surface exceeds a critical value. The critical beta value is nearly proportional to the externally imposed resonant field normalized by the main field strength.
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)
Ultrasound versus high field magnetic resonance imaging in rheumatoid arthritis
DEFF Research Database (Denmark)
Tan, York Kiat; Østergaard, Mikkel; Bird, Paul
2014-01-01
Over the past decade there have been significant advances in the field of musculoskeletal imaging, especially in the application of ultrasound (US) and magnetic resonance imaging (MRI) to the management of rheumatoid arthritis (RA). Both modalities offer significant advantages over the previous...
Directory of Open Access Journals (Sweden)
Xiaoliang Zhang
2011-07-01
Full Text Available In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintain the homogeneity of the RF field. To investigate the design method, the common-mode resonator was realized by using a microstrip line which was split along the central to become a pair of parallel transmission lines within which common-mode currents exist. Eight common-mode resonators were placed equidistantly along the circumference of a low loss dielectric cylinder to form a volume coil. Theoretical analysis and comparison between the 16-strut common-mode volume coil and a conventional 16-strut volume coil in terms of RF field homogeneity and efficiency was performed using Finite-Difference Time-Domain (FDTD method at 298.2 MHz. MR imaging experiments were performed by using a prototype of the common-mode volume coil on a whole body 7 Tesla scanner. FDTD simulation results showed the reduced number of resonant modes of the common-mode volume coil over the conventional volume coil, while the RF field homogeneity of the two type volume coils was kept at the same level. MR imaging of a water phantom and a kiwi fruit showing the feasibility of the proposed method for simplifying the volume coil design is also presented.
Non-resonant terahertz field enhancement in periodically arranged nanoslits
DEFF Research Database (Denmark)
Novitsky, Andrey; Ivinskaya, Aliaksandra; Zalkovskij, Maksim
2012-01-01
We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength λ of the impinging radiatio...... by the microscopic Drude-Lorentz model taking into account retardation processes in the metal film and validated by the finite difference frequency domain method. We expect sensor and modulation applications of the predicted giant broadband field enhancement.......We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength λ of the impinging radiation...... approaches the THz wavelength but before entering the Raleigh-Wood anomaly, the field enhancement in nanoslit stays close to that in a single isolated slit, i.e., the well-known inversefrequency dependence. Both regimes are non-resonant and thus extremely broadband for P
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.
Interaction of magnetic resonators studied by the magnetic field enhancement
Directory of Open Access Journals (Sweden)
Yumin Hou
2013-12-01
Full Text Available It is the first time that the magnetic field enhancement (MFE is used to study the interaction of magnetic resonators (MRs, which is more sensitive than previous parameters–shift and damping of resonance frequency. To avoid the coherence of lattice and the effect of Bloch wave, the interaction is simulated between two MRs with same primary phase when the distance is changed in the range of several resonance wavelengths, which is also compared with periodic structure. The calculated MFE oscillating and decaying with distance with the period equal to resonance wavelength directly shows the retardation effect. Simulation also shows that the interaction at normal incidence is sensitive to the phase correlation which is related with retardation effect and is ultra-long-distance interaction when the two MRs are strongly localized. When the distance is very short, the amplitude of magnetic resonance is oppressed by the strong interaction and thus the MFE can be much lower than that of single MR. This study provides the design rules of metamaterials for engineering resonant properties of MRs.
Electromagnetically induced transparency resonances inverted in magnetic field
Energy Technology Data Exchange (ETDEWEB)
Sargsyan, A.; Sarkisyan, D., E-mail: davsark@yahoo.com, E-mail: david@ipr.sci.am [National Academy of Sciences of Armenia, Institute for Physical Research (Armenia); Pashayan-Leroy, Y.; Leroy, C. [Université de Bourgogne-Dijon, Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS (France); Cartaleva, S. [Bulgarian Academy of Sciences, Institute of Electronics (Bulgaria); Wilson-Gordon, A. D. [Bar-Ilan University Ramat Gan, Department of Chemistry (Israel); Auzinsh, M. [University of Latvia, Department of Physics (Latvia)
2015-12-15
The phenomenon of electromagnetically induced transparency (EIT) is investigated in a Λ-system of the {sup 87}Rb D{sub 1} line in an external transverse magnetic field. Two spectroscopic cells having strongly different values of the relaxation rates γ{sub rel} are used: an Rb cell with antirelaxation coating (L ∼ 1 cm) and an Rb nanometric- thin cell (nanocell) with a thickness of the atomic vapor column L = 795 nm. For the EIT in the nanocell, we have the usual EIT resonances characterized by a reduction in the absorption (dark resonance (DR)), whereas for the EIT in the Rb cell with an antirelaxation coating, the resonances demonstrate an increase in the absorption (bright resonances (BR)). We suppose that such an unusual behavior of the EIT resonances (i.e., the reversal of the sign from DR to BR) is caused by the influence of an alignment process. The influence of alignment strongly depends on the configuration of the coupling and probe frequencies as well as on the configuration of the magnetic field.
Parahydrogen-enhanced zero-field nuclear magnetic resonance
Theis, T.; Ganssle, P.; Kervern, G.; Knappe, S.; Kitching, J.; Ledbetter, M. P.; Budker, D.; Pines, A.
2011-07-01
Nuclear magnetic resonance, conventionally detected in magnetic fields of several tesla, is a powerful analytical tool for the determination of molecular identity, structure and function. With the advent of prepolarization methods and detection schemes using atomic magnetometers or superconducting quantum interference devices, interest in NMR in fields comparable to the Earth's magnetic field and below (down to zero field) has been revived. Despite the use of superconducting quantum interference devices or atomic magnetometers, low-field NMR typically suffers from low sensitivity compared with conventional high-field NMR. Here we demonstrate direct detection of zero-field NMR signals generated through parahydrogen-induced polarization, enabling high-resolution NMR without the use of any magnets. The sensitivity is sufficient to observe spectra exhibiting 13C-1H scalar nuclear spin-spin couplings (known as J couplings) in compounds with 13C in natural abundance, without the need for signal averaging. The resulting spectra show distinct features that aid chemical fingerprinting.
Development and applications of NMR [nuclear magnetic resonance] in low fields and zero field
International Nuclear Information System (INIS)
Bielecki, A.
1987-05-01
This dissertation is about nuclear magnetic resonance (NMR) spectroscopy in the absence of applied magnetic fields. NMR is usually done in large magnetic fields, often as large as can be practically attained. The motivation for going the opposite way, toward zero field, is that for certain types of materials, particularly powdered or polycrystalline solids, the NMR spectra in zero field are easier to interpret than those obtained in high field. 92 refs., 60 figs., 1 tab
Low-Field Magnetic Resonance Imaging of Canine Hydrocephalus
Directory of Open Access Journals (Sweden)
Z. Adamiak* and M. Jaskólska and A. Pomianowski1
2012-01-01
Full Text Available The aim of presented study was to evaluate selected surface spine coil, and low-field magnetic resonance (MR selected sequences in diagnosing hydrocephalus in dogs. This paper discusses 19 dogs (14 canine patients with hydrocephalus and 5 healthy dogs, of five breeds, subjected to low-field magnetic resonance imaging (MRI of hydrocephalus. Area of the lateral ventricles and brain were examined in dogs with hydrocephalus using low-field MRI (at 0.25 Tesla. The MRI of FSE REL, SE, FLAIR, STIR, 3D HYCE, T3DT1, GE STIR 3D and 3D SHARC sequences with an indication of the most effective sequences are described. Additionally, coils for MR were compared, and models for infusion anesthesia were described. As a result of performed study all estimated sequences were diagnostically useful. However, spinal coil No. 2 (ESAOTE was the most optimal for examining and positioning the cranium.
Parallel inhomogeneity and the Alfven resonance. 1: Open field lines
Hansen, P. J.; Harrold, B. G.
1994-01-01
In light of a recent demonstration of the general nonexistence of a singularity at the Alfven resonance in cold, ideal, linearized magnetohydrodynamics, we examine the effect of a small density gradient parallel to uniform, open ambient magnetic field lines. To lowest order, energy deposition is quantitatively unaffected but occurs continuously over a thickened layer. This effect is illustrated in a numerical analysis of a plasma sheet boundary layer model with perfectly absorbing boundary conditions. Consequences of the results are discussed, both for the open field line approximation and for the ensuing closed field line analysis.
Magnetic resonance signal moment determination using the Earth's magnetic field
Fridjonsson, Einar Orn; Creber, Sarah A.; Vrouwenvelder, Johannes S.; Johns, Michael L.
2015-01-01
We demonstrate a method to manipulate magnetic resonance data such that the moments of the signal spatial distribution are readily accessible. Usually, magnetic resonance imaging relies on data acquired in so-called k-space which is subsequently Fourier transformed to render an image. Here, via analysis of the complex signal in the vicinity of the centre of k-space we are able to access the first three moments of the signal spatial distribution, ultimately in multiple directions. This is demonstrated for biofouling of a reverse osmosis (RO) membrane module, rendering unique information and an early warning of the onset of fouling. The analysis is particularly applicable for the use of mobile magnetic resonance spectrometers; here we demonstrate it using an Earth's magnetic field system.
Magnetic resonance signal moment determination using the Earth's magnetic field
Fridjonsson, Einar Orn
2015-03-01
We demonstrate a method to manipulate magnetic resonance data such that the moments of the signal spatial distribution are readily accessible. Usually, magnetic resonance imaging relies on data acquired in so-called k-space which is subsequently Fourier transformed to render an image. Here, via analysis of the complex signal in the vicinity of the centre of k-space we are able to access the first three moments of the signal spatial distribution, ultimately in multiple directions. This is demonstrated for biofouling of a reverse osmosis (RO) membrane module, rendering unique information and an early warning of the onset of fouling. The analysis is particularly applicable for the use of mobile magnetic resonance spectrometers; here we demonstrate it using an Earth\\'s magnetic field system.
SQUID-detected magnetic resonance imaging in microtesla magnetic fields
International Nuclear Information System (INIS)
McDermott, Robert; Kelso, Nathan; Lee, SeungKyun; Moessle, Michael; Mueck, Michael; Myers, Whittier; Haken, Bernard ten; Seton, H.C.; Trabesinger, Andreas H.; Pines, Alex; Clarke, John
2003-01-01
We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (∼1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a 31P nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and 31P nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mm resolution. In further experiments we demonstrate T1-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T1. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging
Directory of Open Access Journals (Sweden)
K. Bartušek
2003-01-01
Full Text Available This paper describes a method for measuring of the gradient magnetic field in Nuclear Magnetic Resonance (NMR tomography, which is one of the modern medical diagnostic methods. A very important prerequisite for high quality imaging is a gradient magnetic field in the instrument with exactly defined properties. Nuclear magnetic resonance enables us to measure the pulse gradient magnetic field characteristics with high accuracy. These interesting precise methods were designed, realised, and tested at the Institute of Scientific Instruments (ISI of the Academy of Sciences of the Czech Republic. The first of them was the Instantaneous Frequency (IF method, which was developed into the Instantaneous Frequency of Spin Echo (IFSE and the Instantaneous Frequency of Spin Echo Series (IFSES methods. The above named methods are described in this paper and their a comparison is also presented.
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
Far-field superresolution by imaging of resonance scattering
Schuster, Gerard T.
2014-10-31
We show that superresolution imaging in the far-field region of the sources and receivers is theoretically and practically possible if migration of resonant multiples is employed. A resonant multiple is one that bounces back and forth between two scattering points; it can also be the multiple between two smoothly varying interfaces as long as the reflection wave paths partially overlap and reflect from the same Fresnel zone. For a source with frequency f, compared to a one-way trip, N round trips in propagating between two scatterers increase the effective frequency by 2N × f and decrease the effective wavelength by λ/(2N). Thus, multiples can, in principle, be used as high-frequency probes to estimate detailed properties of layers. Tests with both synthetic and field data validate this claim. Improved resolution by multiple imaging is not only feasible for crustal reflections, but might be applicable to mantle and core reverberations recorded by earthquake seismologists.
Longitudinal and transverse electric field measurements in resonant cavities
International Nuclear Information System (INIS)
Tong Dechun; Chen Linfeng; Zheng Xiaoyue
1994-01-01
The paper presents a measuring technique for the electric field distribution of high order modes in resonant cavities. A perturbing bead-like cage made with metallic wires are developed for S-band field measurements, which can be used to detect a small electric field component in the presence of other strong electric or magnetic field components (That means high sensitivity and high directivity). In order to avoid orientation error for the cage with very high directivity, two parallel threads were used for supporting the perturbing cage. A simple mechanical set-up is described. The cage can be driven into the cavity on-axis or off-axis in any azimuth for the longitudinal and transverse electric field measurements
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)
Resonance double magnetic bremsstrahlung in a strong magnetic field
International Nuclear Information System (INIS)
Fomin, P.I.; Kholodov, R.I.
2003-01-01
The possibility of resonance double magnetic bremsstrahlung in the approximation of weakly excited electron states in a strong external magnetic field is analyzed. The differential probability of this process in the Breit-Wigner form is obtained. The probability of double magnetic bremsstrahlung (second-order process of perturbation theory) is compared with the probability of magnetic bremsstrahlung (first-order process of perturbation theory)
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....
Resonance properties of the biological objects in the RF field
International Nuclear Information System (INIS)
Cocherova, E; Kupec, P; Stofanik, V
2011-01-01
Irradiation of people with electromagnetic fields emitted from miscellaneous devices working in the radio-frequency (RF) range may have influence, for example may affect brain processes. The question of health impact of RF electromagnetic fields on population is still not closed. This article is devoted to an investigation of resonance phenomena of RF field absorption in the models of whole human body and body parts (a head) of different size and shape. The values of specific absorption rate (SAR) are evaluated for models of the different shapes: spherical, cylindrical, realistic shape and for different size of the model, that represents the case of new-born, child and adult person. In the RF frequency region, absorption depends nonlinearly on frequency. Under certain conditions (E-polarization), absorption reaches maximum at frequency, that is called r esonance frequency . The whole body absorption and the resonance frequency depends on many further parameters, that are not comprehensively clarified. The simulation results showed the dependence of the whole-body average SAR and resonance frequency on the body dimensions, as well as the influence of the body shape.
Resonance and Chaotic Trajectories in Magnetic Field Reversed Configuration
Energy Technology Data Exchange (ETDEWEB)
A.S. Landsman; S.A. Cohen; M. Edelman; G.M. Zaslavsky
2005-04-13
The nonlinear dynamics of a single ion in a field-reversed configuration (FRC) were investigated. FRC is a toroidal fusion device which uses a specific type of magnetic field to confine ions. As a result of angular invariance, the full three-dimensional Hamiltonian system can be expressed as two coupled, highly nonlinear oscillators. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved canonical angular momentum and the geometry of the fusion vessel. Perturbation theory and averaging were used to derive the unperturbed Hamiltonian and frequencies of the two degrees of freedom. The derived equations were then used to find resonances and compare to Poincar{copyright} surface-of-section plots. A regime was found where the nonlinear resonances were clearly separated by KAM [Kolmogorov-Arnold-Mosher] curves. The structure of the observed island chains was explained. The condition for the destruction of KAM curves and the onset of strong chaos was derived, using Chirikov island overlap criterion, and shown qualitatively to depend both on the canonical angular momentum and geometry of the device. After a brief discussion of the adiabatic regime the paper goes on to explore the degenerate regime that sets in at higher values of angular momenta. In this regime, the unperturbed Hamiltonian can be approximated as two uncoupled linear oscillators. In this case, the system is near-integrable, except in cases of a universal resonance, which results in large island structures, due to the smallness of nonlinear terms, which bound the resonance. The linear force constants, dominant in this regime, were derived and the geometry for a large one-to-one resonance identified. The above analysis showed good agreement with numerical simulations and was able to explain characteristic features of the dynamics.
Resonance and Chaotic Trajectories in Magnetic Field Reversed Configuration
International Nuclear Information System (INIS)
Landsman, A.S.; Cohen, S.A.; Edelman, M.; Zaslavsky, G.M.
2005-01-01
The nonlinear dynamics of a single ion in a field-reversed configuration (FRC) were investigated. FRC is a toroidal fusion device which uses a specific type of magnetic field to confine ions. As a result of angular invariance, the full three-dimensional Hamiltonian system can be expressed as two coupled, highly nonlinear oscillators. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved canonical angular momentum and the geometry of the fusion vessel. Perturbation theory and averaging were used to derive the unperturbed Hamiltonian and frequencies of the two degrees of freedom. The derived equations were then used to find resonances and compare to Poincar(copyright) surface-of-section plots. A regime was found where the nonlinear resonances were clearly separated by KAM [Kolmogorov-Arnold-Mosher] curves. The structure of the observed island chains was explained. The condition for the destruction of KAM curves and the onset of strong chaos was derived, using Chirikov island overlap criterion, and shown qualitatively to depend both on the canonical angular momentum and geometry of the device. After a brief discussion of the adiabatic regime the paper goes on to explore the degenerate regime that sets in at higher values of angular momenta. In this regime, the unperturbed Hamiltonian can be approximated as two uncoupled linear oscillators. In this case, the system is near-integrable, except in cases of a universal resonance, which results in large island structures, due to the smallness of nonlinear terms, which bound the resonance. The linear force constants, dominant in this regime, were derived and the geometry for a large one-to-one resonance identified. The above analysis showed good agreement with numerical simulations and was able to explain characteristic features of the dynamics
Magnetic resonance of field-frozen and zero-field-frozen magnetic fluids
International Nuclear Information System (INIS)
Pereira, A.R.; Pelegrini, F.; Neto, K. Skeff; Buske, N.; Morais, P.C.
2004-01-01
In this study magnetic resonance was used to investigate magnetic fluid samples frozen under zero and non-zero (15 kG) external fields. The magnetite-based sample containing 2x10 17 particle/cm 3 was investigated from 100 to 400 K. Analysis of the temperature dependence of the resonance field revealed bigger magnetic structures in the frozen state than in the liquid phase. Also, differences in the mesoscopic organization in the frozen state may explain the data obtained from samples frozen under zero and non-zero fields
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)
Functional magnetic resonance imaging with ultra-high fields
International Nuclear Information System (INIS)
Windischberger, C.; Schoepf, V.; Sladky, R.; Moser, E.; Fischmeister, F.P.S.
2010-01-01
Functional magnetic resonance imaging (fMRI) is currently the primary method for non-invasive functional localization in the brain. With the emergence of MR systems with field strengths of 4 Tesla and above, neuronal activation may be studied with unprecedented accuracy. In this article we present different approaches to use the improved sensitivity and specificity for expanding current fMRT resolution limits in space and time based on several 7 Tesla studies. In addition to the challenges that arise with ultra-high magnetic fields possible solutions will be discussed. (orig.) [de
Near-Field Resonance Microwave Tomography and Holography
Gaikovich, K. P.; Smirnov, A. I.; Yanin, D. V.
2018-02-01
We develop the methods of electromagnetic computer near-field microwave tomography of distributed subsurface inhomogeneities of complex dielectric permittivity and of holography (shape retrieval) of internally homogeneous subsurface objects. The methods are based on the solution of the near-field inverse scattering problem from measurements of the resonance-parameter variations of microwave probes above the medium surface. The capabilities of the proposed diagnostic technique are demonstrated in the numerical simulation for sensors with a cylindrical capacitor as a probe element, the edge capacitance of which is sensitive to subsurface inhomogeneities.
International Nuclear Information System (INIS)
Araujo, M.S.T. de.
1991-01-01
The effect of resonant helical fields (CHR) on the plasma confined by the TBR-1 tokamak was investigated. The external perturbations were created by a set of windings located around the vacuum vessel. The field helicity corresponding to the components m/n = 2/1, m/n = 3/1 and m/n = 4/1 could be chosen, from two existing panels beside the tokamak. The main diagnostic used was a set of 10 Mirnov magnetic coils. For this work, a computer program, called MHD-FOUR, was created to Fourier-analyse the detected MHD oscillations. Therefore, the time evolution of every component ranging from m = to m = 4 could be separately obtained. The Spectral Analysis done on some parts of the discharges showed that two or more modes were coupled, and this coupling could justify the disruptive instability that occurred afterwards, while rather intense helical currents (I hel ≅ 400 - 500 A) were applied. The major disruptions were frequently observed to be preceded by a dominant m = 2 mode while, for the minor disruptions, besides the m = 2, also the m 3 component was found to be equally dominant. The modes growth rates were calculated using experimental data taken just before the occurrence of a disruptive instability. The results confirmed the resistive nature of the perturbations. The rational magnetic surfaces positions and the half-width of the corresponding islands were also estimated. The Chirikov criterion showed that the minor disruptions were preceded by an ergodization of the external part of the plasma column while before the major disruption the ergodization also comprised the internal region. This total ergodization of the plasma column was, most probably, the main cause for the destruction of the confinement. (author)
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)
Resonant Magnetic Field Sensors Based On MEMS Technology
Directory of Open Access Journals (Sweden)
Elías Manjarrez
2009-09-01
Full Text Available Microelectromechanical systems (MEMS technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration.
Resonant Magnetic Field Sensors Based On MEMS Technology
Herrera-May, Agustín L.; Aguilera-Cortés, Luz A.; García-Ramírez, Pedro J.; Manjarrez, Elías
2009-01-01
Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration. PMID:22408480
Nonlinear resonance and dynamical chaos in a diatomic molecule driven by a resonant ir field
International Nuclear Information System (INIS)
Berman, G.P.; Bulgakov, E.N.; Holm, D.D.
1995-01-01
We consider the transition from regular motion to dynamical chaos in a classical model of a diatomic molecule which is driven by a circularly polarized resonant ir field. Under the conditions of a nearly two-dimensional case, the Hamiltonian reduces to that for the nonintegrable motion of a charged particle in an electromagnetic wave [A. J. Lichtenberg and M. A. Lieberman, Regular and Stochastic Motion (Springer-Verlag, City, 1983)]. In the general case, the transition to chaos is connected with the overlapping of vibrational-rotational nonlinear resonances and appears even at rather low radiation field intensity, S approx-gt 1 GW/cm 2 . We also discuss the possibility of experimentally observing this transition
International Nuclear Information System (INIS)
Du, X.D.; Toi, K.; Osakabe, M.
2014-10-01
A resistive interchange mode with bursting behavior and rapid frequency chirping in the range less than 10 kHz is observed for the first time in the magnetic hill region of net current-free, low beta LHD (Large Helical Device) plasmas during high power injection of perpendicular neutral beams. The mode resonates with the precession motion of helically trapped energetic beam ions, following the resonant condition. The radial mode structure is found to be very similar to that of usual pressure-driven interchange mode, of which radial displacement eigenfunction has an even function around the rational surface. This beam driven mode is excited when the beta value of helically trapped energetic ions exceed a certain threshold. The radial transport of helically trapped energetic ions induced by the mode transiently generates significant radial electric field near the plasma peripheral region. Thus generated radial electric field clearly suppresses micro turbulence and improves bulk plasma confinement, suggesting strong flow shear generation. (author)
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...
Resonant tunnelling from nanometre-scale silicon field emission cathodes
International Nuclear Information System (INIS)
Johnson, S.; Markwitz, A.
2005-01-01
In this paper we report the field emission properties of self-assembled silicon nanostructures formed on an n-type silicon (100) substrate by electron beam annealing. The nanostructures are square based, with an average height of 8 nm and are distributed randomly over the entire substrate surface. Following conditioning, the silicon nanostructure field emission characteristics become stable and reproducible with electron emission occurring for fields as low as 3 Vμm-1. At higher fields, a superimposed on a background current well described by conventional Fowler-Nordheim theory. These current peaks are understood to result from enhanced tunnelling through resonant states formed at the substrate-nanostructure and nanostructure-vacuum interface. (author). 13 refs., 3 figs
Magnetic resonance imaging and spectroscopy at ultra high fields
International Nuclear Information System (INIS)
Neuberger, Thomas
2009-01-01
The goal of the work presented in this thesis was to explore the possibilities and limitations of MRI / MRS using an ultra high field of 17.6 tesla. A broad range of specific applications and MR methods, from MRI to MRSI and MRS were investigated. The main foci were on sodium magnetic resonance spectroscopic imaging of rodents, magnetic resonance spectroscopy of the mouse brain, and the detection of small amounts of iron labeled stem cells in the rat brain using MRI Sodium spectroscopic imaging was explored since it benefits tremendously from the high magnetic field. Due to the intrinsically low signal in vivo, originating from the low concentrations and short transverse relaxation times, only limited results have been achieved by other researchers until now. Results in the literature include studies conducted on large animals such as dogs to animals as small as rats. No studies performed on mice have been reported, despite the fact that the mouse is the most important laboratory animal due to the ready availability of transgenic strains. Hence, this study concentrated on sodium MRSI of small rodents, mostly mice (brain, heart, and kidney), and in the case of the brain on young rats. The second part of this work concentrated on proton magnetic resonance spectroscopy of the rodent brain. Due to the high magnetic field strength not only the increasing signal but also the extended spectral resolution was advantageous for such kind of studies. The difficulties/limitations of ultra high field MRS were also investigated. In the last part of the presented work detection limits of iron labeled stem cells in vivo using magnetic resonance imaging were explored. The studies provided very useful benchmarks for future researchers in terms of the number of labeled stem cells that are required for high-field MRI studies. Overall this work has shown many of the benefits and the areas that need special attention of ultra high fields in MR. Three topics in MRI, MRS and MRSI were
Magnetic resonance imaging and spectroscopy at ultra high fields
Energy Technology Data Exchange (ETDEWEB)
Neuberger, Thomas
2009-06-23
The goal of the work presented in this thesis was to explore the possibilities and limitations of MRI / MRS using an ultra high field of 17.6 tesla. A broad range of specific applications and MR methods, from MRI to MRSI and MRS were investigated. The main foci were on sodium magnetic resonance spectroscopic imaging of rodents, magnetic resonance spectroscopy of the mouse brain, and the detection of small amounts of iron labeled stem cells in the rat brain using MRI Sodium spectroscopic imaging was explored since it benefits tremendously from the high magnetic field. Due to the intrinsically low signal in vivo, originating from the low concentrations and short transverse relaxation times, only limited results have been achieved by other researchers until now. Results in the literature include studies conducted on large animals such as dogs to animals as small as rats. No studies performed on mice have been reported, despite the fact that the mouse is the most important laboratory animal due to the ready availability of transgenic strains. Hence, this study concentrated on sodium MRSI of small rodents, mostly mice (brain, heart, and kidney), and in the case of the brain on young rats. The second part of this work concentrated on proton magnetic resonance spectroscopy of the rodent brain. Due to the high magnetic field strength not only the increasing signal but also the extended spectral resolution was advantageous for such kind of studies. The difficulties/limitations of ultra high field MRS were also investigated. In the last part of the presented work detection limits of iron labeled stem cells in vivo using magnetic resonance imaging were explored. The studies provided very useful benchmarks for future researchers in terms of the number of labeled stem cells that are required for high-field MRI studies. Overall this work has shown many of the benefits and the areas that need special attention of ultra high fields in MR. Three topics in MRI, MRS and MRSI were
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
Mett, Richard R.; Anderson, James R.; Sidabras, Jason W.; Hyde, James S.
2005-09-01
Magnetic field modulation is often introduced into a cylindrical TE011 electron paramagnetic resonance (EPR) cavity through silver plating over a nonconductive substrate. The plating thickness must be many times the skin depth of the rf and smaller than the skin depth of the modulation. We derive a parameter that quantifies the modulation field penetration and find that it also depends on resonator dimensions. Design criteria based on this parameter are presented graphically. This parameter is then used to predict the behavior of eddy currents in substrates of moderate conductivity, such as graphite. The conductivity of the graphite permits improved plating uniformity and permits use of electric discharge machining (EDM) techniques to make the resonator. EDM offers precision tolerances of 0.005 mm and is suitable for small, complicated shapes that are difficult to machine by other methods. Analytic predictions of the modulation penetration are compared with the results of finite-element simulations. Simulated magnetic field modulation uniformity and penetration are shown for several elemental coils and structures including the plated graphite TE011 cavity. Fabrication and experimental testing of the structure are discussed. Spatial inhomogeneity of the modulation phase is also investigated by computer simulation. We find that the modulation phase is uniform to within 1% over the TE011 cavity. Structures of lower symmetry have increased phase nonuniformity.
Manipulation of resonant Auger processes with strong optical fields
Picón, Antonio; Buth, Christian; Doumy, Gilles; Krässig, Bertold; Young, Linda; Southworth, Stephen
2013-05-01
We recently reported on the optical control of core-excited states of a resonant Auger process in neon. We have focused on the resonant excitation 1 s --> 1s-1 3 p , while a strong optical field may resonantly couple two core-excited states (1s-1 3 p and 1s-1 3 s) in the Rydberg manifold as well as dressing the continuum. There is a clear signature in the Auger electron spectrum of the inner-shell dynamics induced by the strong optical field: i) the Auger electron spectrum is modified by the rapid optical-induced population transfer from the 1s-1 3 p state to the 1s-1 3 s state during their decay. ii) The angular anisotropy parameter, defining the angular distribution of the Auger electron, is manifested in the envelope of the (angle-integrated) sidebands. This work is funded by the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, under Contract No. DE-AC02-06CH11357.
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.
Diamagnetic (cyclotron) resonance in semiconductors using strong magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Sosniak, J
1962-07-01
Diamagnetic (cyclotron) resonance experiments have been carried out in the semiconductors indium-antimonide (InSb), the indium-arsenide (InAs). Pulsed magnetic fields up to 300,000 gauss and monochromatic infrared radiation of 9 to 13.5 microns wavelength were used to measure the effective mass of the conduction electrons in those materials. The samples were n-type single crystals, with a room temperature electron concentration of 1.9 x 10{sup 16} and 6 x 10{sup 16} per cm{sup 3} in InSb and InAs respectively. Both the InSb and InAs samples showed a strong dependence of the effective mass on the magnetic field. The results show that the conduction bands in those solids are highly non-parabolic. Measurements were also made of the resonance absorption coefficients, which were found to be considerably smaller than the values obtained from simple theory. The effect is explained by assuming that the magnetic field reduces the intrinsic electron density, and that the absorption coefficient depends on the shape of the conduction band. It is postulated as a consequence that the relaxation time of diamagnetic energy levels at high magnetic fields does not differ appreciably from the relaxation time used in the description of conduction processes. (author)
The resonant wake field transformer (RWT)-collider
International Nuclear Information System (INIS)
Weiland, T.; Holtkamp, N.; Schuett, P.; Wanzenberg, R.
1990-01-01
Future e + e - Linear Colliders with center of mass energies of 2 TeV need average accelerating gradients of 100 MeV/m to be built within a length of 20 km. The gradients required by colliders at this energy range can be economically provided by resonant Wake Field Transformers. At the Wake Field Experiment at DESY (Deutsches Elektronen-Synchrotron) a 20 cm long transformer section was investigated and the most recent results are presented. The second part gives a short overview of the present status of research concerning the proposed next stage of a multibunch driver linac with superconducting cavities and long Wake Field Transformer sections. (author) 9 refs.; 5 figs.; 1 tab
Safety aspects in high-field magnetic resonance imaging
International Nuclear Information System (INIS)
Muehlenweg, M.; Trattnig, S.; Schaefers, G.
2008-01-01
With more and more 3 Tesla high-field magnetic resonance (MR) scanners entering clinical routine, the safety notion in MR imaging has also reached a new dimension. The first part of this paper deals with the three most important sources of physical interaction (static magnetic field, gradient and HF fields). The paper discusses the differences compared with the traditional clinical 1.5 T standard scanners, the impact on human beings, the interactions with metallic objects and the relevant safety standards. The second part of the paper examines the issue of MR safety as seen in clinical practice and tries to demonstrate optimization potentials. This includes structural optimization in information distribution and hospital organization as well as test standards and labeling guidelines. (orig.) [de
International Nuclear Information System (INIS)
Baldin, V.I.; Stepanov, A.P.
1976-01-01
Spectrometer double-frequency resonance cell construction of a double nuclear electron resonance for operation in 120-350 Gs magnetic fields is described. The cell has been developed from a special decimeter resonator with a concentrated capacitance. The electric and magnetic components of a high frequency field are efficiently divided in the separator. Therefore, the insertion of a measuring coil and a sample in the maximum of the magnetic component of the field does not practically affect the distribution and parameters of the high-frequency field. The double-frequency resonance cell proposed provides for a higher accuracy of measuring amplifications of the nuclear magnetic resonance signals when there is the overhauzer effect for 120-350 Gs magnetic fields
Kinetic theory of rf current drive and helicity injection
International Nuclear Information System (INIS)
Mett, R.R.
1992-01-01
Current drive and helicity injection by plasma waves are examined with the use of kinetic theory. The Vlasov equation yields a general current drive formula that contains resonant and nonresonant (ponderomotivelike) contributions. Standard quasilinear current drive is described by the former, while helicity current drive may be contained in the latter. Since direct analytical comparison of the sizes of the two terms is, in general, difficult, a new approach is taken. Solution of the drift-kinetic equation shows that the standard Landau damping/transit time magnetic pumping quasilinear diffusion coefficient is the only contribution to steady-state current drive to leading order in ε=ρ L /l, where ρ L is the Larmor radius and l is the inhomogeneity scale length. All nonresonant contributions, including the helicity, appear at higher order, after averages are taken over a flux surface, over azimuth, and over time. Consequently, at wave frequencies well below the electron cyclotron frequency, a wave helicity flux perpendicular to the magnetic field does not influence the parallel motion of electrons to leading order and therefore will not drive a significant current. Any current associated with a wave helicity flux is then either ion current (and thus inefficient) or electron current stemming from effects not included in the drift-kinetic treatment, such as cyclotron, collisional, or nonlinear (i.e., not quasilinear)
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
Energy Technology Data Exchange (ETDEWEB)
Li, Hai-ming; Liu, Shao-bin, E-mail: lsb@nuaa.edu.cn; Liu, Si-yuan; Zhang, Hai-feng; Bian, Bo-rui; Kong, Xiang-kun [Key Laboratory of Radar Imaging and Microwave Photonics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Wang, Shen-yun [Research Center of Applied Electromagnetics, Nanjing University of Information Science and Technology, Nanjing 210044 (China)
2015-03-16
In this paper, we numerically and experimentally demonstrate electromagnetically induced transparency (EIT)-like spectral response with magnetic resonance near field coupling to electric resonance. Six split-ring resonators and a cut wire are chosen as the bright and dark resonator, respectively. An EIT-like transmission peak located between two dips can be observed with incident magnetic field excitation. A large delay bandwidth product (0.39) is obtained, which has potential application in quantum optics and communications. The experimental results are in good agreement with simulated results.
Firpo, M.-C.; Constantinescu, D.
2011-03-01
The issue of magnetic confinement in magnetic fusion devices is addressed within a purely magnetic approach. Using some Hamiltonian models for the magnetic field lines, the dual impact of low magnetic shear is shown in a unified way. Away from resonances, it induces a drastic enhancement of magnetic confinement that favors robust internal transport barriers (ITBs) and stochastic transport reduction. When low shear occurs for values of the winding of the magnetic field lines close to low-order rationals, the amplitude thresholds of the resonant modes that break internal transport barriers by allowing a radial stochastic transport of the magnetic field lines may be quite low. The approach can be applied to assess the robustness versus magnetic perturbations of general (almost) integrable magnetic steady states, including nonaxisymmetric ones such as the important single-helicity steady states. This analysis puts a constraint on the tolerable mode amplitudes compatible with ITBs and may be proposed as a possible explanation of diverse experimental and numerical signatures of their collapses.
Electric-field-modified Feshbach resonances in ultracold atom–molecule collision
International Nuclear Information System (INIS)
Cheng Dong; Li Ya; Feng Eryin; Huang Wuying
2017-01-01
We present a detailed analysis of near zero-energy Feshbach resonances in ultracold collisions of atom and molecule, taking the He–PH system as an example, subject to superimposed electric and magnetic static fields. We find that the electric field can induce Feshbach resonance which cannot occur when only a magnetic field is applied, through couplings of the adjacent rotational states of different parities. We show that the electric field can shift the position of the magnetic Feshbach resonance, and change the amplitude of resonance significantly. Finally, we demonstrate that, for narrow magnetic Feshbach resonance as in most cases of ultracold atom–molecule collision, the electric field may be used to modulate the resonance, because the width of resonance in electric field scale is relatively larger than that in magnetic field scale. (paper)
Ida, K; Funaba, H; Kado, S; Narihara, K; Tanaka, K; Takeiri, Y; Nakamura, Y; Ohyabu, N; Yamazaki, K; Yokoyama, M; Murakami, S; Ashikawa, N; deVries, P C; Emoto, M; Goto, M; Idei, H; Ikeda, K; Inagaki, S; Inoue, N; Isobe, M; Itoh, K; Kaneko, O; Kawahata, K; Khlopenkov, K; Komori, A; Kubo, S; Kumazawa, R; Liang, Y; Masuzaki, S; Minami, T; Miyazawa, J; Morisaki, T; Morita, S; Mutoh, T; Muto, S; Nagayama, Y; Nakanishi, H; Nishimura, K; Noda, N; Notake, T; Kobuchi, T; Ohdachi, S; Ohkubo, K; Oka, Y; Osakabe, M; Ozaki, T; Pavlichenko, R O; Peterson, B J; Sagara, A; Saito, K; Sakakibara, S; Sakamoto, R; Sanuki, H; Sasao, H; Sasao, M; Sato, K; Sato, M; Seki, T; Shimozuma, T; Shoji, M; Suzuki, H; Sudo, S; Tamura, N; Toi, K; Tokuzawa, T; Torii, Y; Tsumori, K; Yamamoto, T; Yamada, H; Yamada, I; Yamaguchi, S; Yamamoto, S; Yoshimura, Y; Watanabe, K Y; Watari, T; Hamada, Y; Motojima, O; Fujiwara, M
2001-06-04
Recent large helical device experiments revealed that the transition from ion root to electron root occurred for the first time in neutral-beam-heated discharges, where no nonthermal electrons exist. The measured values of the radial electric field were found to be in qualitative agreement with those estimated by neoclassical theory. A clear reduction of ion thermal diffusivity was observed after the mode transition from ion root to electron root as predicted by neoclassical theory when the neoclassical ion loss is more dominant than the anomalous ion loss.
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.
Pulsed magnetic field generation suited for low-field unilateral nuclear magnetic resonance systems
Gaunkar, Neelam Prabhu; Selvaraj, Jayaprakash; Theh, Wei-Shen; Weber, Robert; Mina, Mani
2018-05-01
Pulsed magnetic fields can be used to provide instantaneous localized magnetic field variations. In presence of static fields, pulsed field variations are often used to apply torques and in-effect to measure behavior of magnetic moments in different states. In this work, the design and experimental performance of a pulsed magnetic field generator suited for low static field nuclear magnetic resonance (NMR) applications is presented. One of the challenges of low bias field NMR measurements is low signal to noise ratio due to the comparable nature of the bias field and the pulsed field. Therefore, a circuit is designed to apply pulsed currents through an inductive load, leading to generation of pulsed magnetic fields which can temporarily overpower the effect of the bias field on magnetic moments. The designed circuit will be tuned to operate at the precession frequency of 1H (protons) placed in a bias field produced by permanent magnets. The designed circuit parameters may be tuned to operate under different bias conditions. Therefore, low field NMR measurements can be performed for different bias fields. Circuit simulations were used to determine design parameters, corresponding experimental measurements will be presented in this work.
Vector network analyzer ferromagnetic resonance spectrometer with field differential detection
Tamaru, S.; Tsunegi, S.; Kubota, H.; Yuasa, S.
2018-05-01
This work presents a vector network analyzer ferromagnetic resonance (VNA-FMR) spectrometer with field differential detection. This technique differentiates the S-parameter by applying a small binary modulation field in addition to the DC bias field to the sample. By setting the modulation frequency sufficiently high, slow sensitivity fluctuations of the VNA, i.e., low-frequency components of the trace noise, which limit the signal-to-noise ratio of the conventional VNA-FMR spectrometer, can be effectively removed, resulting in a very clean FMR signal. This paper presents the details of the hardware implementation and measurement sequence as well as the data processing and analysis algorithms tailored for the FMR spectrum obtained with this technique. Because the VNA measures a complex S-parameter, it is possible to estimate the Gilbert damping parameter from the slope of the phase variation of the S-parameter with respect to the bias field. We show that this algorithm is more robust against noise than the conventional algorithm based on the linewidth.
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
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)
Zeverino, Michele, E-mail: michele.zeverino@istge.it [Medical Physics Department, IRCCS, Istituto Nazionale per la Ricerca sul cancro, Genoa (Italy); Agostinelli, Stefano; Taccini, Gianni; Cavagnetto, Francesca; Garelli, Stefania; Gusinu, Marco [Medical Physics Department, IRCCS, Istituto Nazionale per la Ricerca sul cancro, Genoa (Italy); Vagge, Stefano; Barra, Salvina; Corvo, Renzo [Radiation Oncology Department, IRCCS, Istituto Nazionale per la Ricerca sul cancro, Genoa (Italy)
2012-10-01
Given the limitations in the travel ability of the helical tomotherapy (HT) couch, total marrow irradiation (TMI) has to be split in 2 segments, with the lower limbs treated with feet first orientation. The aim of this work is to present a planning technique useful to reduce the dose inhomogeneity resulting from the matching of the 2 helical dose distributions. Three HT plans were generated for each of the 18 patients enrolled. Upper TMI (UTMI) and lower TMI (LTMI) were planned onto the whole-body computed tomography (CT) and on the lower-limb CT, respectively. A twin lower TMI plan (tLTMI) was designed on the whole-body CT. Agreement between LTMI and tLTMI plans was assessed by computing for each dose-volume histogram (DVH) structure the {gamma} index scored with 1% of dose and volume difference thresholds. UTMI and tLTMI plans were summed together on the whole-body CT, enabling the evaluation of dose inhomogeneity. Moreover, a couple of transition volumes were used to improve the dose uniformity in the abutment region. For every DVH, a number of points >99% passed the {gamma} analysis, validating the method used to generate the twin plan. The planned dose inhomogeneity at the junction level resulted within {+-}10% of the prescribed dose. Median dose reduction to organs at risk ranged from 30-80% of the prescribed dose. Mean conformity index was 1.41 (range 1.36-1.44) for the whole-body target. The technique provided a 'full helical' dose distribution for TMI treatments, which can be considered effective only if the dose agreement between LTMI and tLTMI plans is met. The planning of TMI with HT for the whole body with adequate dose homogeneity and conformity was shown to be feasible.
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)
High field nuclear magnetic resonance application to polysaccharide chemistry
International Nuclear Information System (INIS)
Vincendon, Marc
1972-01-01
Nuclear magnetic resonance has been applied to polysaccharide chemistry using time averaging technique and high fields (100 and 250 MHz). The three methyl signals of methyl cellulose and cellulose triacetate are separated, and the C-6 substituent has been identified. Biosynthesis of bacterial cellulose has been performed using deuterium labelled D-glucose and Acetobacter xylinum. Per-acetylated derivative of bacterial cellulose has been studied by NMR; this study permitted us to determine the quantity of deuterium on each position of the anhydro-glucose unit in the polymer. NMR has also been used to see the anomeric end chain of cellulose and amylose derivatives and to show the fixation of bromine and t-butyl group on the free anomeric end chain of cellulose triacetate. (author) [fr
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.
SQUID-Detected Magnetic Resonance Imaging in MicroteslaFields
Energy Technology Data Exchange (ETDEWEB)
Moessle, Michael; Hatridge, Michael; Clarke, John
2006-08-14
Magnetic resonance imaging (MRI) has developed into a powerful clinical tool for imaging the human body (1). This technique is based on nuclear magnetic resonance (NMR) of protons (2, 3) in a static magnetic field B{sub 0}. An applied radiofrequency pulse causes the protons to precess about B{sub 0} at their Larmor frequency {nu}{sub 0} = ({gamma}/2{pi})B{sub 0}, where {gamma} is the gyromagnetic ratio; {gamma}/2{pi} = 42.58 MHz/tesla. The precessing protons generate an oscillating magnetic field and hence a voltage in a nearby coil that is amplified and recorded. The application of three-dimensional magnetic field gradients specifies a unique magnetic field and thus an NMR frequency in each voxel of the subject, so that with appropriate encoding of the signals one can acquire a complete image (4). Most clinical MRI systems involve magnetic fields generated by superconducting magnets, and the current trend is to higher magnetic fields than the widely used 1.5-T systems (5). Nonetheless, there is ongoing interest in the development of less expensive imagers operating at lower fields. Commercially available 0.2-T systems based on permanent magnets offer both lower cost and a more open access than their higher-field counterparts, at the expense of signal-to-noise-ratio (SNR) and spatial resolution. At the still lower field of 0.03 mT maintained by a conventional, room-temperature solenoid, Connolly and co-workers (6, 7) obtain good spatial resolution and signal-to-noise ratio (SNR) by prepolarizing the protons in a field B{sub p} of 0.3 T. Prepolarization (8) enhances the magnetic moment of an ensemble of protons over that produced by the lower precession field; after the polarizing field is removed, the higher magnetic moment produces a correspondingly larger signal during its precession in B{sub 0}. Using the same method, Stepisnik et al. (9) obtained MR images in the Earth's magnetic field ({approx} 50 {micro}T). Alternatively, one can enhance the signal
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.
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.
Resonant effects on the low frequency vlasov stability of axisymmetric field reversed configurations
International Nuclear Information System (INIS)
Finn, J.M.; Sudan, R.N.
We investigate the effect of particle resonances on low frequency MHD modes in field-reversed geometries, e.g., an ion ring. It is shown that, for sufficiently high field reversal, modes which are hydromagnetically stable can be driven unstable by ion resonances. The stabilizing effect of a toroidal magnetic field is discussed
Optimum condition for spatial ion cyclotron resonance in a multiple magnetic mirror field
International Nuclear Information System (INIS)
Mieno, Tetsu; Hatakeyama, Rikizo; Sato, Noriyoshi
1988-01-01
A Spatial cyclotron resonance of ion beams passing through a multiple magnetic mirror field is investigated experimentally by varying parameters of the multiple mirror field. The optimum resonance condition is realized with a decrease in the cell length of the multiple mirror along the beams to satisfy the local condition of the spatial ion cyclotron resonance. The results show a remarkable increase of nonadiabatic transfer of the beam energy into the transverse direction to the magnetic field. (author)
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
Determination of the electromagnetic field in a high-Tc linear superconducting resonator
International Nuclear Information System (INIS)
Trotel, A.; Sautrot, S.; Pyee, M.
1994-01-01
In this paper, the electromagnetic field configuration in a linear SHTC resonator is described. Two areas are considered: 1) the superconducting strip, 2) the dielectric around the strip. The calculation is based on the current density given by Bowers for an infinite superconducting line. The current density in the resonator is defined by these relations and the resonance conditions. (orig.)
Self-Biased 215MHz Magnetoelectric NEMS Resonator for Ultra-Sensitive DC Magnetic Field Detection
Nan, Tianxiang; Hui, Yu; Rinaldi, Matteo; Sun, Nian X.
2013-06-01
High sensitivity magnetoelectric sensors with their electromechanical resonance frequencies electromechanical systems (NEMS) resonator with an electromechanical resonance frequency of 215 MHz based on an AlN/(FeGaB/Al2O3) × 10 magnetoelectric heterostructure for detecting DC magnetic fields. This magnetoelectric NEMS resonator showed a high quality factor of 735, and strong magnetoelectric coupling with a large voltage tunable sensitivity. The admittance of the magnetoelectric NEMS resonator was very sensitive to DC magnetic fields at its electromechanical resonance, which led to a new detection mechanism for ultra-sensitive self-biased RF NEMS magnetoelectric sensor with a low limit of detection of DC magnetic fields of ~300 picoTelsa. The magnetic/piezoelectric heterostructure based RF NEMS magnetoelectric sensor is compact, power efficient and readily integrated with CMOS technology, which represents a new class of ultra-sensitive magnetometers for DC and low frequency AC magnetic fields.
Energy Technology Data Exchange (ETDEWEB)
Hod, Shahar, E-mail: shaharhod@gmail.com [The Ruppin Academic Center, Emeq Hefer 40250 (Israel); The Hadassah Academic College, Jerusalem 91010 (Israel)
2017-05-10
We study analytically the characteristic resonance spectrum of charged massive scalar fields linearly coupled to a spherically symmetric charged reflecting shell. In particular, we use analytical techniques in order to solve the Klein–Gordon wave equation for the composed charged-shell–charged-massive-scalar-field system. Interestingly, it is proved that the resonant oscillation frequencies of this composed physical system are determined by the characteristic zeroes of the confluent hypergeometric function. Following this observation, we derive a remarkably compact analytical formula for the resonant oscillation frequencies which characterize the marginally-bound charged massive scalar field configurations. The analytically derived resonance spectrum is confirmed by numerical computations.
Wake-Field Wave Resonant Excitation in Magnetized Plasmas by Electromagnetic Pulse
International Nuclear Information System (INIS)
Milant'ev, V.P.; Turikov, V.A.
2006-01-01
In this paper the space charge wave excitation process at electromagnetic pulse propagation along external magnetic field in vicinity of electron cyclotron resonance. In hydrodynamic approach it is obtained an equation for plasma density under ponderomotive force action. With help of this equation we investigated a wake-field wave amplitude dependence from resonance detuning. The numerical simulation using a PIC method electromagnetic pulse propagation process in the resonant conditions was done
The permittivity of a plasma at cyclotron resonance in large amplitude e.m. fields
Schram, D.C.
1970-01-01
The permittivity of a collisionless plasma as a function of field parameters is measured in standing and in travelling waves. In both experiments the permittivity remains finite at cyclotron resonance; the resonance is broadened and shifted towards higher values of the magnetic field strength. The
Optical field emission from resonant gold nanorods driven by femtosecond mid-infrared pulses
Energy Technology Data Exchange (ETDEWEB)
Kusa, F. [Department of Applied Physics, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei Tokyo 184-8588 (Japan); Institute of Industrial Science, the University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Echternkamp, K. E.; Herink, G.; Ropers, C. [4th Physical Institute – Solids and Nanostructures, University of Göttingen, 37077 Göttingen (Germany); Ashihara, S., E-mail: ashihara@iis.u-tokyo.ac.jp [Institute of Industrial Science, the University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)
2015-07-15
We demonstrate strong-field photoelectron emission from gold nanorods driven by femtosecond mid-infrared optical pulses. The maximum photoelectron yield is reached at the localized surface plasmon resonance, indicating that the photoemission is governed by the resonantly-enhanced optical near-field. The wavelength- and field-dependent photoemission yield allows for a noninvasive determination of local field enhancements, and we obtain intensity enhancement factors close to 1300, in good agreement with finite-difference time domain computations.
Field-angle dependence of magnetic resonance in Pt/NiFe films
International Nuclear Information System (INIS)
Inoue, H.Y.; Harii, K.; Saitoh, E.
2007-01-01
Ferromagnetic resonance in NiFe/ amorphous Pt bilayer thin films was investigated with changing the external field direction. The spectral width of the ferromagnetic resonance depends critically on the external-magnetic-field direction. We found that the sample dependence of the spectral width is enhanced with deviation of external field direction from the direction along the film plain, implying an important role of spin directions in field-induced spin-decoherence mechanism in Pt
Energy Technology Data Exchange (ETDEWEB)
Schmitz, O., E-mail: o.schmitz@fz-juelich.de [Forschungszentrum Jülich, IEK-4, Association EURATOM-FZJ, Jülich (Germany); Becoulet, M. [CEA/IRFM, Cadarache, 13108 St. Paul-lez-Durance Cedex (France); Cahyna, P. [IPP AS CR, Za Slovankou 3, 18200 Prague 8 (Czech Republic); Evans, T.E. [General Atomics, P.O. Box 85608, San Diego, CA 92186-5608 (United States); Feng, Y. [Max-Planck-Institut für Plasmaphysik, Greifswald (Germany); Frerichs, H.; Kirschner, A. [Forschungszentrum Jülich, IEK-4, Association EURATOM-FZJ, Jülich (Germany); Kukushkin, A. [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France); Laengner, R. [Forschungszentrum Jülich, IEK-4, Association EURATOM-FZJ, Jülich (Germany); Lunt, T. [Max-Planck-Institut für Plasmaphysik, Greifswald (Germany); Loarte, A.; Pitts, R. [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France); Reiser, D.; Reiter, D. [Forschungszentrum Jülich, IEK-4, Association EURATOM-FZJ, Jülich (Germany); Saibene, G. [Fusion for Energy Joint Undertaking, Barcelona (Spain); Samm, U. [Forschungszentrum Jülich, IEK-4, Association EURATOM-FZJ, Jülich (Germany)
2013-07-15
First results from three-dimensional modeling of the divertor heat and particle flux pattern during application of resonant magnetic perturbation fields as ELM control scheme in ITER with the EMC3-Eirene fluid plasma and kinetic neutral transport code are discussed. The formation of a helical magnetic footprint breaks the toroidal symmetry of the heat and particle fluxes. Expansion of the flux pattern as far as 60 cm away from the unperturbed strike line is seen with vacuum RMP fields, resulting in a preferable heat flux spreading. Inclusion of plasma response reduces the radial extension of the heat and particle fluxes and results in a heat flux peaking closer to the unperturbed level. A strong reduction of the particle confinement is found. 3D flow channels are identified as a consistent reason due to direct parallel outflow from inside of the separatrix. Their radial inward expansion and hence the level of particle pump out is shown to be dependent on the perturbation level.
Influence of external fields and environment on the dynamics of a phase-qubit-resonator system
International Nuclear Information System (INIS)
Berman, G. P.; Chumak, A. A.
2011-01-01
We analyze the dynamics of a qubit-resonator system coupled with a thermal bath and external electromagnetic fields. Using the evolution equations for the set of Heisenberg operators that describe the whole system, we derive an expression for the resonator field, accounting for the resonator-drive, -bath, and -qubit interaction. The renormalization of the resonator frequency caused by the qubit-resonator interaction is accounted for. Using solutions for the resonator field, we derive the equation describing qubit dynamics. The influence of the qubit evolution during measurement time on the fidelity of a single-shot measurement is studied. The relation between fidelity and measurement time is shown explicitly. Also, an expression describing relaxation of the superposition qubit state toward its stationary value is derived. The possibility of controlling this state by varying the amplitude and frequency of drive is shown.
Helical muon beam cooling channel engineering design
International Nuclear Information System (INIS)
Johnson, Rolland
2015-01-01
The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb 3 Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb 3 Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb 3 Sn solenoid as originally planned. Instead, a complementary project was approved by the
Helical muon beam cooling channel engineering design
Energy Technology Data Exchange (ETDEWEB)
Johnson, Rolland [Muons, Inc., Batavia, IL (United States)
2015-08-07
The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb_{3}Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb_{3}Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb_{3}Sn solenoid as originally planned. Instead, a complementary
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.
Extended abstract: ergodic magnetic limiter experiments on TEXT with a 7/3 resonance
International Nuclear Information System (INIS)
deGrassie, J.S.; Ohyabu, N.; Brooks, N.H.
1984-05-01
The ergodic magnetic limiter coils on TEXT have been reconfigured to produce the primary helical perturbation resonance at m = 7 / n = 3. The experiments continue to demonstrate that the weak resonant perturbations modify the edge conditions in keeping with model predictions. We observe a reduction in the intrinsic impurity levels accompanying the helical current pulse, presumably the result of a reduction in the electron temperature in the edge. Heat follows the perturbed field lines to the limiter, generating heat load patterns which reflect the geometry of a magnetic island - limiter intersection. A strong spatial modulation of the electron density in the scrape-off-layer also reflects the helical mode structure
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
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)
Hsu, J.Y.; Chan, V.S.; Harvey, R.W.; Prater, R.; Wong, S.K.
1984-01-01
The perpendicular heating in cyclotron waves tends to pile up the resonant particles toward the low magnetic field side with their banana tips localized to the resonant surface. A poloidal electric field with an E x B drift comparable to the ion vertical drift in a toroidal magnetic field may result. With the assumption of anomalous electron and neoclassical ion transport, density variations due to wave heating are discussed
Method of shaping fields of controlled extension in a resonator with a large electrical length
International Nuclear Information System (INIS)
Bomko, V.A.; Rudiak, B.I.
A method is discussed for controlling the energy of particles accelerated in a linear accelerator consisting of a volume resonator with drift tubes. Results are described for experimental studies of problems with field shaping of controlled extension of fields in an accelerating structure having drift tubes and a large electrical length. The possibility of shaping the field in a resonator using a stabilizing system of the ''antipode'' type is considered
Three-dimensional tokamak equilibria in the presence of resonant field errors
International Nuclear Information System (INIS)
Reiman, A.; Monticello, D.
1992-01-01
Numerical solutions are described for three-dimensional MHD equilibria in the presence of resonant magnetic field perturbations. The effects of a realistic spectrum of resonant field errors are calculated for a range of current profiles. It is found that field errors of the magnitude existing in present day devices, and contemplated for future devices, can produce a set of magnetic islands occupying a significant fraction of the plasma cross-section
International Nuclear Information System (INIS)
Rebreyend, D.; Pignol, G.; Baeßler, S.; Nesvizhevsky, V. V.; Protasov, K.; Voronin, A.
2014-01-01
Gravitational resonance spectroscopy consists in measuring the energy spectrum of bouncing ultracold neutrons above a mirror by inducing resonant transitions between different discrete quantum levels. We discuss how to induce the resonances with a flow through arrangement in the GRANIT spectrometer, excited by an oscillating magnetic field gradient. The spectroscopy could be realized in two distinct modes (so called DC and AC) using the same device to produce the magnetic excitation. We present calculations demonstrating the feasibility of the newly proposed AC mode
Resonant frequencies of massless scalar field in rotating black-brane spacetime
Institute of Scientific and Technical Information of China (English)
Jing Ji-Liang; Pan Qi-Yuan
2008-01-01
This paper investigates the resonant frequencies of the massless scalar field in the near extremal Kerr-like black-brahe spacetime. It is shown that the different angular quantum number will present different resonant frequencies. It is also shown that the real part of the resonant frequencies increases as the compact dimensions parameter μi increases, but the magnitude of the imaginary part decreases as μi increases.
International Nuclear Information System (INIS)
Owada, Kimio.
1989-01-01
Helical type vacuum containers in the prior art lack in considerations for thermal expansion stresses to helical coils, and there is a possibility of coil ruptures. The object of the present invention is to avoid the rupture of helical coils wound around the outer surface of a vacuum container against heat expansion if any. That is, bellows or heat expansion absorbing means are disposed to a cross section of a helical type vacuum container. With such a constitution, thermal expansion of helical coils per se due to temperature elevation of the coils during electric supply can be absorbed by expansion of the bellows or absorption of the heat expansion absorbing means. Further, this can be attained by arranging shear pins in the direction perpendicular to the bellows axis so that the bellows are not distorted when the helical coils are wound around the helical type vacuum container. (I.S.)
International Nuclear Information System (INIS)
Takizuka, T.; Tokunaga, S.; Hoshino, K.; Shimizu, K.; Asakura, N.
2015-01-01
Edge localized modes (ELMs) in the H-mode operation of tokamak reactors may be suppressed/mitigated by the resonant magnetic perturbation (RMP), but RMP coils are considered incompatible with DEMO reactors under the strong neutron flux. We propose an innovative concept of the RMP without installing coils but inserting ferritic steels of the helical configuration. Helically perturbed field is naturally formed in the axisymmetric toroidal field through the helical ferritic steel inserts (FSIs). When ELMs are avoided, large stationary heat load on divertor plates can be reduced by adopting a flux-tube-expansion (FTE) divertor like an X divertor. Separatrix shape and divertor-plate inclination are similar to those of a simple long-leg divertor configuration. Combination of the helical FSIs and the FTE divertor is a suitable method for the heat control to avoid transient ELM heat pulse and to reduce stationary divertor heat load in a tokamak DEMO reactor
On dynamics of resonant charged particles in cyclotron electromagnetic wave field
International Nuclear Information System (INIS)
Shyutte, N.M.; Izhovkina, N.I.
1989-01-01
The model of time and spatial separation of resonance and nonresonance particles with quasimonochromatic wave packets during their propagation in the magnetosphere is presented. In regions with elevated geomagnetic field gradients and.or in waveguide channels such separation can result in diffusion increase of resonance particles by the pitch angle and create ''little peaks'' in the distribution function tail
Communication patterns in the field of nuclear magnetic resonance
International Nuclear Information System (INIS)
Tomov, D.; Filipov, F.; Kolev, N.
1986-01-01
A scientometric analysis of publications presented in four secondary information sources on the problem of nuclear magnetic resonance in physics, biomedicine and technology was carried out. A dynamic growth of the number of articles in biomedicine over 1982 to 1984 was established. Secondary publications play an important role in scientific communications as revealed by citation analysis. (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.
International Nuclear Information System (INIS)
Zhang, Fan; Wu, Chenyun; Yang, Hong; Hu, Xiaoyong; Gong, Qihuang
2014-01-01
Composite modulation of Fano resonance by using electric-field and microcavity simultaneously is realized in a plasmonic microstructure, which consists of a gold nanowire grating inserted into a Fabry-Perot microcavity composited of a liquid crystal layer sandwiched between two indium tin oxide layers. The Fano resonance wavelength varies with the applied voltage and the microcavity resonance. A large shift of 48 nm in the Fano resonance wavelength is achieved when the applied voltage is 20 V. This may provide a new way for the study of multi-functional integrated photonic circuits and chips based on plasmonic microstructures
Energy Technology Data Exchange (ETDEWEB)
Zhang, Fan; Wu, Chenyun; Yang, Hong [State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871 (China); Hu, Xiaoyong, E-mail: xiaoyonghu@pku.edu.cn; Gong, Qihuang [State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100871 (China)
2014-11-03
Composite modulation of Fano resonance by using electric-field and microcavity simultaneously is realized in a plasmonic microstructure, which consists of a gold nanowire grating inserted into a Fabry-Perot microcavity composited of a liquid crystal layer sandwiched between two indium tin oxide layers. The Fano resonance wavelength varies with the applied voltage and the microcavity resonance. A large shift of 48 nm in the Fano resonance wavelength is achieved when the applied voltage is 20 V. This may provide a new way for the study of multi-functional integrated photonic circuits and chips based on plasmonic microstructures.
Novel 1H low field nuclear magnetic resonance applications for the field of biodiesel
2013-01-01
Background Biodiesel production has increased dramatically over the last decade, raising the need for new rapid and non-destructive analytical tools and technologies. 1H Low Field Nuclear Magnetic Resonance (LF-NMR) applications, which offer great potential to the field of biodiesel, have been developed by the Phyto Lipid Biotechnology Lab research team in the last few years. Results Supervised and un-supervised chemometric tools are suggested for screening new alternative biodiesel feedstocks according to oil content and viscosity. The tools allowed assignment into viscosity groups of biodiesel-petrodiesel samples whose viscosity is unknown, and uncovered biodiesel samples that have residues of unreacted acylglycerol and/or methanol, and poorly separated and cleaned glycerol and water. In the case of composite materials, relaxation time distribution, and cross-correlation methods were successfully applied to differentiate components. Continuous distributed methods were also applied to calculate the yield of the transesterification reaction, and thus monitor the progress of the common and in-situ transesterification reactions, offering a tool for optimization of reaction parameters. Conclusions Comprehensive applied tools are detailed for the characterization of new alternative biodiesel resources in their whole conformation, monitoring of the biodiesel transesterification reaction, and quality evaluation of the final product, using a non-invasive and non-destructive technology that is new to the biodiesel research area. A new integrated computational-experimental approach for analysis of 1H LF-NMR relaxometry data is also presented, suggesting improved solution stability and peak resolution. PMID:23590829
On effect of stability of magnetic resonance position by harmonized field
International Nuclear Information System (INIS)
Ivanchenko, E.A.; Tolstoluzhsky, A.P.
2006-01-01
The formalism of density matrix in a two level system is used to study the time-periodic modulation of the magnetic field stabilizating the magnetic resonance position. An exact solution for density matrix at resonance is found. It is shown that the fundamental resonance is stable with respect to consistent variations of longitudinal and transversal magnetic fields. A differential equation for the transition probability is obtained. The dependence of time-averaged spin flip probability on the normalized Larmor frequency was numerically researched in different parameter regimes with account of dissipation and decoherence. It is shown that the position of the main resonance is independent of field deformation and dissipation; only the width of resonance line changes upon field deformation and dissipation. The odd parametric (multi-photon) resonance transitions is studied. Static magnetization induced by time-periodic modulated magnetic field is considered. The results of the investigation may be useful for analysis of interference experiments, improvement of magnetic spectrometers and in the field of quantum computing manipulation of q-bits
Quantum averaging and resonances: two-level atom in a one-mode classical laser field
Directory of Open Access Journals (Sweden)
M. Amniat-Talab
2007-06-01
Full Text Available We use a nonperturbative method based on quantum averaging and an adapted from of resonant transformations to treat the resonances of the Hamiltonian of a two-level atom interacting with a one-mode classical field in Floquet formalism. We illustrate this method by extraction of effective Hamiltonians of the system in two regimes of weak and strong coupling. The results obtained in the strong-coupling regime, are valid in the whole range of the coupling constant for the one-photon zero-field resonance.
Low field magnetic resonance experiments in superfluid 3He--A
International Nuclear Information System (INIS)
Gully, W.J. Jr.
1976-01-01
Measurements of the longitudinal and transverse nuclear magnetic resonance signals have been made on the A phase of liquid 3 He. They were performed on a sample of 3 He self-cooled by the Pomeranchuk effect to the critical temperature of the superfluid at 2.7 m 0 K. The longitudinal resonance is a magnetic mode of the liquid excited by radio frequency magnetic fields applied in the direction of the static magnetic field. Frequency profiles of this resonance were indirectly obtained by contour techniques from signals recorded by sweeping the temperature. Its frequency is found to be related to the frequency shift of the transverse resonance in agreement with theoretical predictions for the ABM pairing state. Its linewidth also agrees with theoretical predictions based upon dissipative phenomena peculiar to the superfluid phase. An analysis of the linewidth of the longitudinal resonance yields a value for the quasiparticle collision time. Transverse NMR lines were also studied. In low magnetic fields (20 Oersted) these lines were found to become extremely broad. This is shown to be a manifestation of the same collisional processes that broaden the longitudinal resonance lines. Also, the effects of various textures on the resonance lines are discussed, including the results of an attempt to create a single domain of 3 He with crossed electric and magnetic fields
Radiation characteristics of helical tomotherapy
International Nuclear Information System (INIS)
Jeraj, Robert; Mackie, Thomas R.; Balog, John; Olivera, Gustavo; Pearson, Dave; Kapatoes, Jeff; Ruchala, Ken; Reckwerdt, Paul
2004-01-01
Helical tomotherapy is a dedicated intensity modulated radiation therapy (IMRT) system with on-board imaging capability (MVCT) and therefore differs from conventional treatment units. Different design goals resulted in some distinctive radiation field characteristics. The most significant differences in the design are the lack of flattening filter, increased shielding of the collimators, treatment and imaging operation modes and narrow fan beam delivery. Radiation characteristics of the helical tomotherapy system, sensitivity studies of various incident electron beam parameters and radiation safety analyses are presented here. It was determined that the photon beam energy spectrum of helical tomotherapy is similar to that of more conventional radiation treatment units. The two operational modes of the system result in different nominal energies of the incident electron beam with approximately 6 MeV and 3.5 MeV in the treatment and imaging modes, respectively. The off-axis mean energy dependence is much lower than in conventional radiotherapy units with less than 5% variation across the field, which is the consequence of the absent flattening filter. For the same reason the transverse profile exhibits the characteristic conical shape resulting in a 2-fold increase of the beam intensity in the center. The radiation leakage outside the field was found to be negligible at less than 0.05% because of the increased shielding of the collimators. At this level the in-field scattering is a dominant source of the radiation outside the field and thus a narrow field treatment does not result in the increased leakage. The sensitivity studies showed increased sensitivity on the incident electron position because of the narrow fan beam delivery and high sensitivity on the incident electron energy, as common to other treatment systems. All in all, it was determined that helical tomotherapy is a system with some unique radiation characteristics, which have been to a large extent
Near resonant absorption by atoms in intense fluctuating laser fields
International Nuclear Information System (INIS)
Smith, S.J.
1994-01-01
The objective of this program was to make quantitative measurements of the effects of higher-order phase/frequency correlations in a laser beam on nonlinear optical absorption processes in atoms. The success of this program was due in large part to a unique experimental capability for modulating the extracavity beam of a stabilized (approx-lt 200 kHz) continuous-wave laser with statistically-well-characterized stochastic phase (or frequency) fluctuations, in order to synthesize laser bandwidths to ∼20 MHz (depending on noise amplitude), with profiles variable between Gaussian and Lorentzian (depending on noise bandwidth). Laser driven processes investigated included the following: (1) the optical Autler-Towns effect in the 3S 1/2 (F = 2, M F = 2) → 3P 3/2 (F = 3, M F = 3) two- level Na resonance, using a weak probe to the 4D 5/2 level; (2) the variance and spectra of fluorescence intensity fluctuations in the two-level Na resonance; (3) the Hanle effect in the 1 S 0 - 3 P 1 , transition at λ = 555.6 nm in 174 Yb; (4) absorption (and gain) of a weak probe, when the probe is a time-delayed replica of the resonant (with the two-level Na transition) pump laser; and (5) four-wave-mixing in a phase-conjugate geometry, in a sodium cell, and, finally, in a diffuse atomic sodium beam. The experimental results from these several studies have provided important confirmation of advanced theoretical methods
Resonances and reactions from mean-field dynamics
Directory of Open Access Journals (Sweden)
Stevenson P. D.
2016-01-01
Full Text Available The time-dependent version of nuclear density functional theory, using functionals derived from Skyrme interactions, is able to approximately describe nuclear dynamics. We present time-dependent results of calculations of dipole resonances, concentrating on excitations of valence neutrons against a proton plus neutron core in the neutron-rich doubly-magic 132Sn nucleus, and results of collision dynamics, highlighting potential routes to ternary fusion, with the example of a collision of 48Ca+48Ca+208Pb resulting in a compound nucleus of element 120 stable against immediate fission.
Analysis of transverse field distributions in Porro prism resonators
CSIR Research Space (South Africa)
Litvin, IA
2007-01-01
Full Text Available in 1962 by Gould et al1 as a means to overcome misalignment problems in optical resonators employing Fabry-Perot cavities, by replacing the end face mirrors with crossed roof prisms. Lasers based on this principle have been developed over the years2... Optronics for the use of their laser and for making experimental data available to us. We would also like to thank Dr Dieter Preussler and Mr Daniel Esser for useful discussions. REFERENCES 1. G. Gould, S. Jacobs, P. Rabinowitz and T. Shultz...
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.
HEMISPHERIC HELICITY TREND FOR SOLAR CYCLE 24
International Nuclear Information System (INIS)
Hao Juan; Zhang Mei
2011-01-01
Using vector magnetograms obtained with the Spectro-polarimeter (SP) on board Hinode satellite, we studied two helicity parameters (local twist and current helicity) of 64 active regions that occurred in the descending phase of solar cycle 23 and the ascending phase of solar cycle 24. Our analysis gives the following results. (1) The 34 active regions of the solar cycle 24 follow the so-called hemispheric helicity rule, whereas the 30 active regions of the solar cycle 23 do not. (2) When combining all 64 active regions as one sample, they follow the hemispheric helicity sign rule as in most other observations. (3) Despite the so-far most accurate measurement of vector magnetic field given by SP/Hinode, the rule is still weak with large scatters. (4) The data show evidence of different helicity signs between strong and weak fields, confirming previous result from a large sample of ground-based observations. (5) With two example sunspots we show that the helicity parameters change sign from the inner umbra to the outer penumbra, where the sign of penumbra agrees with the sign of the active region as a whole. From these results, we speculate that both the Σ-effect (turbulent convection) and the dynamo have contributed in the generation of helicity, whereas in both cases turbulence in the convection zone has played a significant role.
ICRF heating on helical devices
International Nuclear Information System (INIS)
Rasmussen, D.A.; Lyon, J.F.; Hoffman, D.J.; Murakami, M.; England, A.C.; Wilgen, J.B.; Jaeger, E.F.; Wang, C.; Batchelor, D.B.
1995-01-01
Ion cyclotron range of frequency (ICRF) heating is currently in use on CHS and W7-AS and is a major element of the heating planned for steady state helical devices. In helical devices, the lack of a toroidal current eliminates both disruptions and the need for ICRF current drive, simplifying the design of antenna structures as compared to tokamak applications. However the survivability of plasma facing components and steady state cooling issues are directly applicable to tokamak devices. Results from LHD steady state experiments should be available on a time scale to strongly influence the next generation of steady state tokamak experiments. The helical plasma geometry provides challenges not faced with tokamak ICRF heating, including the potential for enhanced fast ion losses, impurity accumulation, limited access for antenna structures, and open magnetic field lines in the plasma edge. The present results and near term plans provide the basis for steady state ICRF heating of larger helical devices. An approach which includes direct electron, mode conversion, ion minority and ion Bernstein wave heating addresses these issues
ICRF heating on helical devices
International Nuclear Information System (INIS)
Rasmussen, D.A.; Lyon, J.F.; Hoffman, D.J.
1995-01-01
Ion cyclotron range of frequency (ICRF) heating is currently in use on CHS and W7AS and is a major element of the heating planned for steady state helical devices. In helical devices, the lack of a toroidal current eliminates both disruptions and the need for ICRF current drive, simplifying the design of antenna structures as compared to tokamak applications. However the survivability of plasma facing components and steady state cooling issues are directly applicable to tokamak devices. Results from LHD steady state experiments should be available on a time scale to strongly influence the next generation of steady state tokamak experiments. The helical plasma geometry provides challenges not faced with tokamak ICRF heating, including the potential for enhanced fast ion losses, impurity accumulation, limited access for antenna structures, and open magnetic field lines in the plasma edge. The present results and near term plans provide the basis for steady state ICRF heating of larger helical devices. An approach which includes direct electron, mode conversion, ion minority and ion Bernstein wave heating addresses these issues
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
Endogenous fields enhanced stochastic resonance in a randomly coupled neuronal network
International Nuclear Information System (INIS)
Deng, Bin; Wang, Lin; Wang, Jiang; Wei, Xi-le; Yu, Hai-tao
2014-01-01
Highlights: • We study effects of endogenous fields on stochastic resonance in a neural network. • Stochastic resonance can be notably enhanced by endogenous field feedback. • Endogenous field feedback delay plays a vital role in stochastic resonance. • The parameters of low-passed filter play a subtle role in SR. - Abstract: Endogenous field, evoked by structured neuronal network activity in vivo, is correlated with many vital neuronal processes. In this paper, the effects of endogenous fields on stochastic resonance (SR) in a randomly connected neuronal network are investigated. The network consists of excitatory and inhibitory neurons and the axonal conduction delays between neurons are also considered. Numerical results elucidate that endogenous field feedback results in more rhythmic macroscope activation of the network for proper time delay and feedback coefficient. The response of the network to the weak periodic stimulation can be notably enhanced by endogenous field feedback. Moreover, the endogenous field feedback delay plays a vital role in SR. We reveal that appropriately tuned delays of the feedback can either induce the enhancement of SR, appearing at every integer multiple of the weak input signal’s oscillation period, or the depression of SR, appearing at every integer multiple of half the weak input signal’s oscillation period for the same feedback coefficient. Interestingly, the parameters of low-passed filter which is used in obtaining the endogenous field feedback signal play a subtle role in SR
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
Narrowing the Zero-Field Tunneling Resonance by Decreasing the Crystal Symmetry of Mn12 Acetate.
Espín, Jordi; Zarzuela, Ricardo; Statuto, Nahuel; Juanhuix, Jordi; Maspoch, Daniel; Imaz, Inhar; Chudnovsky, Eugene; Tejada, Javier
2016-07-27
We report the discovery of a less symmetric crystalline phase of Mn12 acetate, a triclinic phase, resulting from recrystallizing the original tetragonal phase reported by Lis in acetonitrile and toluene. This new phase exhibits the same structure of Mn12 acetate clusters and the same positions of tunneling resonances on the magnetic field as the conventional tetragonal phase. However, the width of the zero-field resonance is at least 1 order of magnitude smaller-can be as low as 50 Oe-indicating very small inhomogeneous broadening due to dipolar and nuclear fields.
Resonant e+e- production by time-varying electromagnetic field
International Nuclear Information System (INIS)
Farakos, K.; Koutsoumbas, G.; Tiktopoulos, G.
1990-01-01
As pointed out by Cornwall and Tiktopoulos (CT) strong, time-varying electric fields may produce e + e - pairs in a resonant fashion. This effect could be related to the sharp peaks in the e + e - spectrum observed in the GSI heavy-ion collision experiments. We attempt to go beyond the case of spatially uniform fields discussed by CT. We find that resonant e + e - production indeed takes place for electric fields derived from four-potentials of the form A 1 =A 2 =A 0 =0, A 3 =δ(t)b(x 3 ) provided by b(x) has discontinuities with a jump at least equal to π. (orig.)
Resonance fluorescence spectra of a three-level atom driven by two strong laser fields
International Nuclear Information System (INIS)
Peng Jinsheng.
1986-12-01
The resonance fluorescence of a three-level atom interacted with two high-power laser fields is investigated in strong field approximation. The fluorescence distribution is obtained by means of the theory of dressing transformation. (author). 15 refs, 2 figs
Principles of nuclear magnetic resonance imaging using an inhomogeneous polarizing field
International Nuclear Information System (INIS)
Briguet, A.; Chaillout, J.; Goldman, M.
1985-01-01
In this paper, it is indicated how to reconstruct nuclear magnetic resonance images acquired in an inhomogeneous static magnetic field without the previous knowledge of its spatial distribution. The method provides also the map of the static magnetic field through the sample volume; furthermore it allows the use of non uniform but spatially controlled encoding gradients [fr
Nonlinear interactions of focused resonance cone fields with plasmas
International Nuclear Information System (INIS)
Stenzel, R.L.; Gekelman, W.
1977-01-01
A simple yet novel rf exciter structure has been developed for generating remotely intense rf fields in a magnetoplasma. It is a circular line source of radius R in a plane perpendicularB 0 driven with an rf signal at ω 0 E/sub rf/ 2 /nkT/sub e/>0.2, a strong density depression in the focal region (deltan/n>40%) is observed. The density perturbation modifies the cone angle and field distribution. This nonlinear interaction leads to a rapid growth of ion acoustic wave turbulence and a corresponding random rf field distribution in a broadened focal region. The development of the interaction is mapped in space and time
Resonator as high frequency electromagnetic field oscillation generator
International Nuclear Information System (INIS)
Svoroba, O.V.; Scherbina, V.O.
2007-01-01
The problem of finding the u(x-vector) field potential in a specific waveguide with generalized corrugated core geometry is considered. The perturbation is brought to the system by high energy electron beam, injected in a waveguide. It is shown that the Neumann spectral problem can be reduced to finding Green approximation solution, and how it can be solved by the discretization technique. Considered parameterization allow to optimize the u(x-vector) field for specific frequency tuning. This method can be used as plasma heating method for thermonuclear temperature control
Matlashov, Andrei Nikolaevich; Urbaitis, Algis V.; Savukov, Igor Mykhaylovich; Espy, Michelle A.; Volegov, Petr Lvovich; Kraus, Jr., Robert Henry
2013-03-05
Method comprising obtaining an NMR measurement from a sample wherein an ultra-low field NMR system probes the sample and produces the NMR measurement and wherein a sampling temperature, prepolarizing field, and measurement field are known; detecting the NMR measurement by means of inductive coils; analyzing the NMR measurement to obtain at least one measurement feature wherein the measurement feature comprises T1, T2, T1.rho., or the frequency dependence thereof; and, searching for the at least one measurement feature within a database comprising NMR reference data for at least one material to determine if the sample comprises a material of interest.
RF Magnetic Field Uniformity of Rectangular Planar Coils for Resonance Imaging
2016-02-04
magnetic, potassium chlorate , nuclear quadrupole resonance, uniform field, coil, surface coil I. INTRODUCTION QR is a magnetic resonance phenomenon...material that will be used is this investigation is potassium chlorate (KCLO3). This paper utilizes the NQR signals detection from KCLO3 to determine the...frequency of potassium chlorate (KCLO3), and matched to a 50 ohm input impedance using L-network circuit of capacitors. Fig.1 shows a diagram of the
Double giant resonances in time-dependent relativistic mean-field theory
International Nuclear Information System (INIS)
Ring, P.; Podobnik, B.
1996-01-01
Collective vibrations in spherical nuclei are described in the framework of time-dependent relativistic mean-field theory (RMFT). Isoscalar quadrupole and isovector dipole oscillations that correspond to giant resonances are studied, and possible excitations of higher modes are investigated. We find evidence for modes which can be interpreted as double resonances. In a quantized RMFT they correspond to two-phonon states. (orig.)
Sherkunov, Yury
2018-03-01
We study theoretically the van der Waals interaction between two atoms out of equilibrium with an isotropic electromagnetic field. We demonstrate that at large interatomic separations, the van der Waals forces are resonant, spatially oscillating, and nonreciprocal due to resonance absorption and emission of virtual photons. We suggest that the van der Waals forces can be controlled and manipulated by tuning the spectrum of artificially created random light.
Electron scattering by an atom in the field of resonant laser radiation
International Nuclear Information System (INIS)
Agre, M.; Rapoport, L.
1982-01-01
The collision of an electron with an atom in the field of intense electromagnetic radiation that is at resonance with two atomic multiplets is investigated theoretically. Expressions are obtained for the amplitudes of the elastic and inelastic scattering with emission (absorption) of photons. The case of a ground state at resonance with a doublet is considered in detail. It is shown that photon absorption takes place predominantly in the case of resonance in inelastic transitions from a state of the lower multiplet, and photon emission takes place in transitions from a state of the upper multiplet
International Nuclear Information System (INIS)
Choe, W.; Ono, M.; Chang, C.S.
1994-11-01
The temperature anisotropy generated by cyclotron resonance heating of tokamak plasmas is calculated and the poloidal equilibrium electric field due to the anisotropy is studied. For the calculation of anisotropic temperatures, bounce-averaged Fokker-Planck equation with a bi-Maxwellian distribution function of heated particles is solved, assuming a moderate wave power and a constant quasilinear cyclotron resonance diffusion coefficient. The poloidal electrostatic potential variation is found to be proportional to the particle density and the degree of temperature anisotropy of warm species created by cyclotron resonance heating
Modelling of helical current filaments induced by LHW on EAST
Energy Technology Data Exchange (ETDEWEB)
Rack, Michael; Denner, Peter; Liang, Yunfeng [Institute of Energy and Climate Research - Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Partner in the Trilateral Euregio Cluster, D-52425 Juelich (Germany); Zeng, Long [Institute of Energy and Climate Research - Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Partner in the Trilateral Euregio Cluster, D-52425 Juelich (Germany); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Gong, Xianzu; Gan, Kaifu; Wang, Liang; Liu, Fukun; Qian, Jinping; Shen, Biao; Li, Jiangang [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Gauthier, Eric [Association EURATOM-CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Collaboration: the EAST Team
2013-07-01
Helical radiation belts have been observed in the scrape-off layer (SOL) of the plasma during the application of lower hybrid wave (LHW) heating at the superconducting tokamak EAST. Modelled SOL field lines, starting in-front of the LHW antennas, show agreement in position and pitch angle to the experimental observed radiation belts. A splitting of the strike-line can be observed on the outer divertor plates during the application of LHW heating. Agreement in the comparison of the Mirnov coil signals and a modelled electric current flow along these SOL field lines was found. A lower hybrid current drive can induce such an electric current flow near the plasma edge. This electric current flow causes a change of the plasma topology which could result in the splitting of the strike-line as known from the application of resonant magnetic perturbation fields. Comparisons of modelled footprint structures and experimental observed heat load patterns in the divertor region are discussed.
Hints for electric-field compensation in multicell resonant structures
Energy Technology Data Exchange (ETDEWEB)
Fernandes, P; Parodi, R
1981-03-31
We propose a lumped-parameter equivalent circuit for a TM/sub 01/ multicell standing wave accelerating structure with full end cells. By the suggested model we can predict the amount of end cell frequency compensation needed to achieve field flatness in the highest mode of the structure.
Effect of an additional magnetic field on Hanle-type absorption resonances
International Nuclear Information System (INIS)
Singh Grewal, Raghwinder; Pattabiraman, M
2014-01-01
We computationally compare Hanle-type resonances for a F g =1→F e =0 transition of the 87 RbD 2 line for magnetic field scans parallel (longitudinal scan) and perpendicular (transverse scan) to the direction of propagation of the optical field in the presence of an additional transverse magnetic field (TMF). For a linearly polarized light, the coherent population trapping (CPT) resonances split at line centre and are identical for both longitudinal and transverse scans. When the probe beam ellipticity is varied, the effect of the TMF is found to be opposite for longitudinal and transverse scans. For a longitudinal scan, the splitting observed in the CPT resonance evolves into an enhanced absorption resonance with an increase in ellipticity. For a transverse scan, the splitting vanishes at higher ellipticities. This can be understood in terms of population redistribution in the ground state sublevels and near-neighbor ground state coherences created by the TMF. We also show that the enhanced absorption signal that splits the CPT resonance strongly depends on transit time, and the CPT resonance strength depends on the excited state dephasing rate. (paper)
Directory of Open Access Journals (Sweden)
Emmanuel Frenod
2002-01-01
Full Text Available We study the qualitative behavior of solutions to the Vlasov equation with strong external magnetic field and oscillating electric field. This model is relevant to the understanding of isotop resonant separation. We show that the effective equation is a kinetic equation with a memory term. This memory term involves a pseudo-differential operator whose kernel is characterized by an integral equation involving Bessel functions. The kernel is explicitly given in some particular cases.
Poloidal field effects on fundamental minority ion cyclotron resonance heating in a tokamak plasma
International Nuclear Information System (INIS)
Jun, S. C.; Imre, Kaya; Stevens, D. C.; Weitzner, Harold; Chang, C. S.
2000-01-01
Minority ion fundamental cyclotron resonance is studied in a large tokamak in which the geometrical optics approximation applies off resonance and the minority average speed is less than the wave phase speeds. Poloidal equilibrium magnetic field effects are included, which lead to nontrivially nonlocal integrodifferential equations for the wave fields. Exact reciprocity relation is given as well as explicit analytic solutions for the transmission coefficients for both the high and low field side incidences. Numerical solutions are needed only for the high field side incident reflection coefficient. Numerical schemes are described and numerical results are presented together with a reliable error bound. Typically, energy absorption increases with poloidal field. The energy absorption increases with minority density at low values of minority density. However, it decreases at high minority density. Poloidal field effects weaken the dependence of energy absorption on the toroidal wave number. (c) 2000 American Institute of Physics
Resonant geomagnetic field oscillations and Birkeland currents in the morning sector
International Nuclear Information System (INIS)
Potemra, T.A.; Zanetti, L.J.; Bythrow, P.F.; Erlandson, R.E.; Lundin, R.; Marklund, G.T.; Block, L.P.; Lindqvist, P.A.
1988-01-01
Magnetic field, electric field, and particle measurements acquired by the Viking satellite and magnetic field measurements acquired by the Active Magnetosphere Particle Tracer Explorers (AMPTE) CCE satellite have been used to study the relationship between large-scale Birkeland currents and resonant oscillations in the Earth's magnetic field. Region 1, region 2, and northward B Z (NBZ) Birkeland currents were identified with the data acquired by the Viking magnetic field instrument. Magnetic field oscillations, present in each of the 10 consecutive Viking passes studied here, have periods between 1 min. and 6 min. and amplitudes from 5 nT to 60 nT. These oscillations extend from lower L shells where they correlate with the CCCE observations up to at least the interface between the region 1 and region 2 Birkeland current system. The Viking particle observations confirm that the region 1/region 2 interface maps closely to the interface between the low-latitude boundary layer (LLBL) and the central plasma sheet (CPS). Electric and magnetic field variations are closely correlated in the region 1 Birkeland current. In the region 2 system of Birkeland currents, the northward electric and eastward magnetic field components show the same resonance oscillations with the electric field variations leading the magnetic field by approximately 90 degree. There is evidence that the amplitudes of the oscillations observed by Viking are correlated with interplanetary magnetic field (IMF) cone angle. In one case, the energy-time dispersion signature of temporal magnetosheath plasma injection into the low-latitude boundary layer was associated with the resonant oscillations. These relationships and the presence of the resonant oscillations on field lines up to the region 1/region 2 (LLBL/CPS) interface lead us to conclude that there are several features in the solar wind and the direction of the IMF that can initiate magnetospheric pulsations
Effect of inhomogeneous temperature fields on acoustic streaming structures in resonators.
Červenka, Milan; Bednařík, Michal
2017-06-01
Acoustic streaming in 2D rectangular resonant channels filled with a fluid with a spatial temperature distribution is studied within this work. An inertial force is assumed for driving the acoustic field; the temperature inhomogeneity is introduced by resonator walls with prescribed temperature distribution. The method of successive approximations is employed to derive linear equations for calculation of primary acoustic and time-averaged secondary fields including the streaming velocity. The model equations have a standard form which allows their numerical integration using a universal solver; in this case, COMSOL Multiphysics was employed. The numerical results show that fluid temperature variations in the direction perpendicular to the resonator axis influence strongly the streaming field if the ratio of the channel width and the viscous boundary layer thickness is big enough; the streaming in the Rayleigh vortices can be supported as well as opposed, which can ultimately lead to the appearance of additional vortices.
de Graaf, S E; Danilov, A V; Adamyan, A; Kubatkin, S E
2013-02-01
We report on the design and performance of a cryogenic (300 mK) near-field scanning microwave microscope. It uses a microwave resonator as the near-field sensor, operating at a frequency of 6 GHz and microwave probing amplitudes down to 100 μV, approaching low enough photon population (N ∼ 1000) of the resonator such that coherent quantum manipulation becomes feasible. The resonator is made out of a miniaturized distributed fractal superconducting circuit that is integrated with the probing tip, micromachined to be compact enough such that it can be mounted directly on a quartz tuning-fork, and used for parallel operation as an atomic force microscope (AFM). The resonator is magnetically coupled to a transmission line for readout, and to achieve enhanced sensitivity we employ a Pound-Drever-Hall measurement scheme to lock to the resonance frequency. We achieve a well localized near-field around the tip such that the microwave resolution is comparable to the AFM resolution, and a capacitive sensitivity down to 6.4 × 10(-20) F/Hz, limited by mechanical noise. We believe that the results presented here are a significant step towards probing quantum systems at the nanoscale using near-field scanning microwave microscopy.
Monte Carlo simulation study of the ICRF minority heating in the Large Helical Device
International Nuclear Information System (INIS)
Murakami, S.; Okamoto, M.; Nakajima, N.; Ohnishi, M.; Okada, H.
1993-10-01
A Monte Carlo simulation code is developed for the ICRF heating in helical systems, which takes into account finite beta effects, complicated orbits of high energetic particles, Coulomb collisions, and interactions between the particles and the applied waves. The code is used to investigate the ICRF minority heating in the Large Helical Device. The configuration of the magnetic fields changes significantly due to finite beta effects in the Large Helical Device. The resonance layer position is found to be crucial to the heating efficiency as the plasma beta increases. When the strength of the resonance magnetic field is set to the value at the magnetic axis, the higher heat efficiency is obtained and no clear difference of the heat efficiency due to the finite beta effects is found at the high ICRF wave power region. However the radial profile of the transferred power to majority ions and electrons from minority ions changes by the deformation of the trapped particle orbits due to the finite beta effects. The heat efficiency is improved if the radial electric field, E r , is positive (E r is directed radially outward) and it is also improved by supplying 3 He minority ions rather than proton minority ions. (author)
Lin, Jian Hung; Tseng, Chun-Yen; Lee, Ching-Ting; Young, Jeff F; Kan, Hung-Chih; Hsu, Chia Chen
2014-02-10
Guided mode resonance (GMR) enhanced second- and third-harmonic generation (SHG and THG) is demonstrated in an azo-polymer resonant waveguide grating (RWG), comprised of a poled azo-polymer layer on top of a textured SU8 substrate with a thin intervening layer of TiO2. Strong SHG and THG outputs are observed by matching either in-coming fundamental- or out-going harmonic-wavelength to the GMR wavelengths of the azo-polymer RWG. Without the azo-polymer coating, pure TiO2 RWGs, do not generate any detectable SHG using a fundamental beam peak intensity of 2 MW/cm(2). Without the textured TiO2 layer, a planar poled azo-polymer layer results in 3650 times less SHG than the full nonlinear RWG structure under identical excitation conditions. Rigorous coupled-wave analysis calculations confirm that this enhancement of the nonlinear conversion is due to strong local electric fields that are generated at the interfaces of the TiO2 and azo-polymer layers when the RWG is excited at resonant wavelengths associated with both SHG and THG conversion processes.
Direct imaging of neural currents using ultra-low field magnetic resonance techniques
Volegov, Petr L [Los Alamos, NM; Matlashov, Andrei N [Los Alamos, NM; Mosher, John C [Los Alamos, NM; Espy, Michelle A [Los Alamos, NM; Kraus, Jr., Robert H.
2009-08-11
Using resonant interactions to directly and tomographically image neural activity in the human brain using magnetic resonance imaging (MRI) techniques at ultra-low field (ULF), the present inventors have established an approach that is sensitive to magnetic field distributions local to the spin population in cortex at the Larmor frequency of the measurement field. Because the Larmor frequency can be readily manipulated (through varying B.sub.m), one can also envision using ULF-DNI to image the frequency distribution of the local fields in cortex. Such information, taken together with simultaneous acquisition of MEG and ULF-NMR signals, enables non-invasive exploration of the correlation between local fields induced by neural activity in cortex and more `distant` measures of brain activity such as MEG and EEG.
On the frequency and field linewidth conversion of ferromagnetic resonance spectra
International Nuclear Information System (INIS)
Wei, Yajun; Svedlindh, Peter; Liang Chin, Shin
2015-01-01
Both frequency swept and field swept ferromagnetic resonance measurements have been carried out for a number of different samples with negligible, moderate and significant extrinsic frequency independent linewidth contribution to analyze the correlation between the experimentally measured frequency and field linewidths. Contrary to the belief commonly held by many researchers, it is found that the frequency and field linewidth conversion relation does not hold for all cases. Instead it holds only for samples with negligible frequency independent linewidth contributions. For samples with non-negligible frequency independent linewidth contribution, the field linewidth values converted from the measured frequency linewidth are larger than the experimentally measured field linewidth. A close examination of the literature reveals that previously reported results support our findings, with successful conversions related to samples with negligible frequency independent linewidth contributions and unsuccessful conversions related to samples with significant frequency independent linewidth. The findings are important in providing guidance in ferromagnetic resonance linewidth conversions. (paper)
International Nuclear Information System (INIS)
Wei, Zhiliang; Yang, Jian; Lin, Yanqin; Chen, Zhong; Chen, Youhe
2015-01-01
Nuclear magnetic resonance spectroscopy serves as an important tool for analyzing chemicals and biological metabolites. However, its performance is subject to the magnetic-field homogeneity. Under inhomogeneous fields, peaks are broadened to overlap each other, introducing difficulties for assignments. Here, we propose a method termed as line broadening interference (LBI) to provide high-resolution information under inhomogeneous magnetic fields by employing certain gradients in the indirect dimension to interfere the magnetic-field inhomogeneity. The conventional spectral-line broadening is thus interfered to be non-diagonal, avoiding the overlapping among adjacent resonances. Furthermore, an inhomogeneity correction algorithm is developed based on pattern recognition to recover the high-resolution information from LBI spectra. Theoretical deductions are performed to offer systematic and detailed analyses on the proposed method. Moreover, experiments are conducted to prove the feasibility of the proposed method for yielding high-resolution spectra in inhomogeneous magnetic fields
Internal transport barrier physics in helical systems
International Nuclear Information System (INIS)
Yokoyama, M.; Minami, T.; Fujisawa, A.; Herranz, J.; Ida, K.; Yamagishi, O.; Yamada, H.; Maaberg, H.; Beidler, C.D.; Dinklage, A.; Estrada, T.; Castejon, F.; Murakami, S.
2005-01-01
The electron internal transport barrier (eITB) has been observed in wide range of helical systems, such as CHS [eg.,1], LHD [eg., 2], TJ-II [eg., 3] and W7-AS [eg., 4]. The eITB isA defined as highly peaked electron temperature (Te) profile with strongly positive radial electric field (Er) in the central region. These observations are reviewed in this paper to understand the device-independent common findings and also to draw the main differences. This is the first report from the International Stellarator Profile Database Activity. The formation of the strong central positive Er has been understood mainly as a result of the ambipolarity of neoclassical electron and ion fluxes, although some additional convective electron flux such as driven by ECRH is required in some situations. This 'neoclassical' physics peculiar to low collisional regime of helical plasmas provides the commonly observed existence of the ECRH power threshold (which is also depending on the density). This is contrastive characteristics to the ITB observed in tokamaks. The dependence of the ECRH power threshold on the magnetic configuration and on the heating scenario among these devices are currently being examined by taking the effective ripple and the trapped particle fraction as parameters to achieve the comprehensive understanding. The roles of low order rational surfaces on the onset of eITB formation and also on its radial size (location of the footpoint of the eITB) have been indicated in inward shifted configurations in LHD (depending on the relative locations of heating position and 2/1 island) and TJ-II (eITB becomes possible at higher density when 3/2 rational is introduced in the plasma core region). It is speculated that, for the latter case, the resonance causes an extra electron flux to trigger the positive Er. The interplay between low order rational surfaces and the formation of eITB still waits for the systematic experiment and theoretical analysis. The external controllability
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
Dynamics of moving interacting atoms in a laser radiation field and optical size resonances
International Nuclear Information System (INIS)
Gadomskii, O.N.; Glukhov, A.G.
2005-01-01
The forces acting on interacting moving atoms exposed to resonant laser radiation are calculated. It is shown that the forces acting on the atoms include the radiation pressure forces as well as the external and internal bias forces. The dependences of the forces on the atomic spacing, polarization, and laser radiation frequency are given. It is found that the internal bias force associated with the interaction of atomic dipoles via the reemitted field may play an important role in the dynamics of dense atomic ensembles in a light field. It is shown that optical size resonances appear in the system of interacting atoms at frequencies differing substantially from transition frequencies in the spectrum of atoms. It is noted that optical size resonances as well as the Doppler frequency shift in the spectrum of interacting atoms play a significant role in the processes of laser-radiation-controlled motion of the atoms
International Nuclear Information System (INIS)
Sun, J. D.; Qin, H.; Yang, X. X.; Zhang, Z. P.; Li, X. X.; Zhang, X. Y.; Cai, Y.; Wu, D. M.; Zhang, B. S.; Lewis, R. A.; Sun, Y. F.
2015-01-01
The effect of the symmetries in the terahertz (THz) field distribution and the field-effect channel on THz photoresponse is examined. Resonant excitation of cavity plasmon modes and nonresonant self-mixing of THz waves are demonstrated in a GaN/AlGaN two-dimensional electron gas with symmetrically designed nanogates, antennas, and filters. We found that the self-mixing signal can be effectively suppressed by the symmetric design and the resonant response benefits from the residual asymmetry. The findings suggest that a single detector may provide both high sensitivity from the self-mixing mechanism and spectral resolution from the resonant response by optimizing the degree of geometrical and/or electronic symmetries
International Nuclear Information System (INIS)
Minaif, Karine; Ajzen, Sergio; Shigueoka, David Carlos; Minami, Cintia Cristina Satie; Sales, Danilo Moulin; Szejnfeld, Jacob; Ruano, Jose Maria Cordeiro; Noguti, Alberto Sinhiti
2008-01-01
Objective: to compare low-field (0.2 T) with high-field (1.5 T) magnetic resonance imaging in the assessment of pelvic endometriosis and adenomyosis. Materials and methods: twenty-seven female patients with clinically suspected endometriosis were prospectively evaluated by means of high-field and low-field magnetic resonance imaging. The reading of the images was performed by a single radiologist, initiating by the low-field, followed by the high-field images. High-field magnetic resonance imaging was utilized as the golden-standard. Results: among the 27 patients included in the present study, 18 (66.7%) had some type of lesion suggesting the presence of endometriosis demonstrated at high-field images. In 14 of these patients the diagnosis was correctly established by low-field magnetic resonance imaging. Endometriomas, tubal lesions, and endometriotic foci > 7 mm identified at the high-field images were also identified at low-field images with 100% accuracy, sensitivity and specificity. Among the nine patients diagnosed with adenomyosis by high-field images, eight were correctly diagnosed by low-field images with 88.9% accuracy, specificity and sensitivity. Conclusion: low-field magnetic resonance imaging demonstrated a low sensitivity in the detection of small endometriotic foci, high sensitivity in the detection of endometriomas and large endometriotic foci, and high accuracy in the detection of adenomyosis when compared with high-field magnetic resonance imaging. (author)
Energy Technology Data Exchange (ETDEWEB)
Minaif, Karine; Ajzen, Sergio [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Dept. of Imaging Diagnosis]. E-mail: kminaif@uol.com.br; Shigueoka, David Carlos; Minami, Cintia Cristina Satie; Sales, Danilo Moulin; Szejnfeld, Jacob [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Dept. of Imaging Diagnosis. Unit of Abdomen; Ruano, Jose Maria Cordeiro [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Dept. of General Gynecology. Sector of Videlaparoscopy; Noguti, Alberto Sinhiti [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Dept. of General Gynecology
2008-11-15
Objective: to compare low-field (0.2 T) with high-field (1.5 T) magnetic resonance imaging in the assessment of pelvic endometriosis and adenomyosis. Materials and methods: twenty-seven female patients with clinically suspected endometriosis were prospectively evaluated by means of high-field and low-field magnetic resonance imaging. The reading of the images was performed by a single radiologist, initiating by the low-field, followed by the high-field images. High-field magnetic resonance imaging was utilized as the golden-standard. Results: among the 27 patients included in the present study, 18 (66.7%) had some type of lesion suggesting the presence of endometriosis demonstrated at high-field images. In 14 of these patients the diagnosis was correctly established by low-field magnetic resonance imaging. Endometriomas, tubal lesions, and endometriotic foci > 7 mm identified at the high-field images were also identified at low-field images with 100% accuracy, sensitivity and specificity. Among the nine patients diagnosed with adenomyosis by high-field images, eight were correctly diagnosed by low-field images with 88.9% accuracy, specificity and sensitivity. Conclusion: low-field magnetic resonance imaging demonstrated a low sensitivity in the detection of small endometriotic foci, high sensitivity in the detection of endometriomas and large endometriotic foci, and high accuracy in the detection of adenomyosis when compared with high-field magnetic resonance imaging. (author)
Influence of external resonant magnetic perturbation field on edge plasma of small tokamak HYBTOK-II
Energy Technology Data Exchange (ETDEWEB)
Hayashi, Y., E-mail: hayashi-yuki13@ees.nagoya-u.ac.jp [Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Suzuki, Y.; Ohno, N. [Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Okamoto, M. [Ishikawa National College of Technology, Kitachujo, Tsubata-cho, Kahoku-gun, Ishikawa 929-0392 (Japan); Kikuchi, Y. [University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280 (Japan); Sakakibara, S.; Watanabe, K.; Takemura, Y. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292 (Japan)
2015-08-15
Radial profile of externally applied resonant magnetic perturbation (RMP) field with mode numbers of m = 6 and n = 2 in a small tokamak device HYBTOK-II have been investigated using a magnetic probe array, which is able to measure the radial profile of magnetic field perturbation induced by applying RMP. Results of RMP penetration into the plasma show that the RMP decreased toward the plasma center, while they were amplified around the resonant surface with a safety factor q = 3 due to the formation of magnetic islands. This suggests that RMP fields for controlling edge plasmas may trigger some kind of MHD instabilities. In addition, simulation results, based on a linearized four-field model, which agrees with the experimental ones, indicates that the penetration and amplification process of RMP strongly depend on a Doppler-shifted frequency between the RMP and plasma rotation.
Li, Si-Yu; Liu, Haiwen; Qiao, Jia-Bin; Jiang, Hua; He, Lin
2018-03-01
Negative differential conductance (NDC), characterized by the decreasing current with increasing voltage, has attracted continuous attention for its various novel applications. The NDC typically exists in a certain range of bias voltages for a selected system and controlling the regions of NDC in curves of current versus voltage (I -V ) is experimentally challenging. Here, we demonstrate a magnetic-field-controlled NDC in scanning tunneling spectroscopy of graphene npn junction resonators. The magnetic field not only can switch on and off the NDC, but also can continuously tune the regions of the NDC in the I -V curves. In the graphene npn junction resonators, magnetic fields generate sharp and pronounced Landau-level peaks with the help of the Klein tunneling of massless Dirac fermions. A tip of scanning tunneling microscope induces a relatively shift of the Landau levels in graphene beneath the tip. Tunneling between the misaligned Landau levels results in the magnetic-field-controlled NDC.
A Method for Eddy Current Field Measurement in Permanent Magnet Magnetic Resonance Imaging Systems
Directory of Open Access Journals (Sweden)
SONG Rui
2018-03-01
Full Text Available Magnetic resonance imaging (MRI is a widely used medical imaging technique. In MRI system, gradient magnetic fields are used to code spatial information. However, the fast-switching electric currents in the gradients coils used to generate gradient fields also induce vortex electric field, often referred as eddy current, in the surrounding metal conductors. In this paper, a method for eddy current field measurement was proposed. Based on the Faraday law of electromagnetic induction, an eddy current field measuring device was designed. Combining hardware acquisition and software processing, the eddy current field was obtained by subtracting the ideal gradient field from the magnetic field measured experimentally, whose waveform could be displayed in real time. The proposed method was verified by experimental results.
Evaluation Method for Fieldlike-Torque Efficiency by Modulation of the Resonance Field
Kim, Changsoo; Kim, Dongseuk; Chun, Byong Sun; Moon, Kyoung-Woong; Hwang, Chanyong
2018-05-01
The spin Hall effect has attracted a lot of interest in spintronics because it offers the possibility of a faster switching route with an electric current than with a spin-transfer-torque device. Recently, fieldlike spin-orbit torque has been shown to play an important role in the magnetization switching mechanism. However, there is no simple method for observing the fieldlike spin-orbit torque efficiency. We suggest a method for measuring fieldlike spin-orbit torque using a linear change in the resonance field in spectra of direct-current (dc)-tuned spin-torque ferromagnetic resonance. The fieldlike spin-orbit torque efficiency can be obtained in both a macrospin simulation and in experiments by simply subtracting the Oersted field from the shifted amount of resonance field. This method analyzes the effect of fieldlike torque using dc in a normal metal; therefore, only the dc resistivity and the dimensions of each layer are considered in estimating the fieldlike spin-torque efficiency. The evaluation of fieldlike-torque efficiency of a newly emerging material by modulation of the resonance field provides a shortcut in the development of an alternative magnetization switching device.
Near field wireless power transfer using curved relay resonators for extended transfer distance
International Nuclear Information System (INIS)
Zhu, D; Beeby, S P; Clare, L; Stark, B H
2015-01-01
This paper investigates the performance of a near field wireless power transfer system that uses curved relay resonator to extend transfer distance. Near field wireless power transfer operates based on the near-field electromagnetic coupling of coils. Such a system can transfer energy over a relatively short distance which is of the same order of dimensions of the coupled coils. The energy transfer distance can be increased using flat relay resonators. Recent developments in printing electronics and e-textiles have seen increasing demand of embedding electronics into fabrics. Near field wireless power transfer is one of the most promising methods to power electronics on fabrics. The concept can be applied to body-worn textiles by, for example, integrating a transmitter coil into upholstery, and a flexible receiver coil into garments. Flexible textile coils take on the shape of the supporting materials such as garments, and therefore curved resonator and receiver coils are investigated in this work. Experimental results showed that using curved relay resonator can effectively extend the wireless power transfer distance. However, as the curvature of the coil increases, the performance of the wireless power transfer, especially the maximum received power, deteriorates. (paper)
DEFF Research Database (Denmark)
Iwaszczuk, Krzysztof; Zalkovskij, Maksim; Strikwerda, Andrew C.
2015-01-01
Summary form only given. Ultrafast electron field emission from gold resonant antennas induced by strong terahertz (THz) transient is investigated using two THz pulse experiments. It is shown that UV emission from nitrogen plasma generated by liberated electrons is a good indication of the local...
Theory of Electric-Field Effects on Electron-Spin-Resonance Hyperfine Couplings
International Nuclear Information System (INIS)
Karna, S.P.
1997-01-01
A quantum mechanical theory of the effects of a uniform electric field on electron-spin-resonance hyperfine couplings is presented. The electric-field effects are described in terms of perturbation coefficients which can be used to probe the local symmetry as well as the strength of the electric field at paramagnetic sites in a solid. Results are presented for the first-order perturbation coefficients describing the Bloembergen effect (linear electric-field effect on hyperfine coupling tensor) for the O atom and the OH radical. copyright 1997 The American Physical Society
High-sensitivity dc field magnetometer using nonlinear resonance magnetoelectric effect
International Nuclear Information System (INIS)
Burdin, D.A.; Chashin, D.V.; Ekonomov, N.A.; Fetisov, Y.K.; Stashkevich, A.A.
2016-01-01
The design and operation principle of dc field magnetometer using nonlinear resonance magnetoelectric effect in a ferromagnetic–piezoelectric structure are described. It is shown that under action of ac pumping magnetic field the structure generates the output voltage containing higher harmonics whose amplitudes depend on the dc magnetic field. Best performance of the device is obtained if the signal of the third harmonics is used for the dc field measurement. The sensitivity can be considerably (by approximately three orders of magnitude) increased if advantage is taken of the acoustic resonance of the structure at this frequency. There exists the optimal pumping field ensuring the highest sensitivity. Further increasing of this field expands the range of measurable dc fields at the expense of deteriorated sensitivity. The magnetometer fabricated on the basis of a planar langatate-Metglas structure had sensitivity up to ~1 V/Oe and allowed detection of the fields as low as ~10"−"5 Oe. - Highlights: • Operational principle and design of new type dc field magnetometer is described. • Magnetometer uses nonlinear magnetoelectric effect in a langatate-Metglas structure. • Magnetometer has sensitivity of ~1 V/Oe and detects fields as low as 10"−"5 Oe. • The proposed magnetometer can compete with well known fluxgate sensors.
High-sensitivity dc field magnetometer using nonlinear resonance magnetoelectric effect
Energy Technology Data Exchange (ETDEWEB)
Burdin, D.A.; Chashin, D.V.; Ekonomov, N.A. [Moscow State University of Information Technologies, Radio Engineering and Electronics, Moscow (Russian Federation); Fetisov, Y.K., E-mail: fetisov@mirea.ru [Moscow State University of Information Technologies, Radio Engineering and Electronics, Moscow (Russian Federation); Stashkevich, A.A. [LSPM (CNRS-UPR 3407), Université Paris 13, Sorbonne Paris Cité, 93430 Villetaneuse (France)
2016-05-01
The design and operation principle of dc field magnetometer using nonlinear resonance magnetoelectric effect in a ferromagnetic–piezoelectric structure are described. It is shown that under action of ac pumping magnetic field the structure generates the output voltage containing higher harmonics whose amplitudes depend on the dc magnetic field. Best performance of the device is obtained if the signal of the third harmonics is used for the dc field measurement. The sensitivity can be considerably (by approximately three orders of magnitude) increased if advantage is taken of the acoustic resonance of the structure at this frequency. There exists the optimal pumping field ensuring the highest sensitivity. Further increasing of this field expands the range of measurable dc fields at the expense of deteriorated sensitivity. The magnetometer fabricated on the basis of a planar langatate-Metglas structure had sensitivity up to ~1 V/Oe and allowed detection of the fields as low as ~10{sup −5} Oe. - Highlights: • Operational principle and design of new type dc field magnetometer is described. • Magnetometer uses nonlinear magnetoelectric effect in a langatate-Metglas structure. • Magnetometer has sensitivity of ~1 V/Oe and detects fields as low as 10{sup −5} Oe. • The proposed magnetometer can compete with well known fluxgate sensors.
Assili, Mohamed; Haddad, Sonia; Kang, Woun
2015-01-01
A double peak structure in the magneto-phonon resonance (MPR) spectrum of uniaxial strained graphene, under crossed electric and magnetic fields, is predicted. We focus on the $\\Gamma$ point optical phonon modes coupled to the inter-Landau level transitions $0 \\leftrightarrows \\pm 1$ where MPR is expected to be more pronounced at high magnetic field. We derive the frequency shifts and the broadenings of the longitudinal (LO) and transverse (TO) optical phonon modes taking into account the eff...
Directory of Open Access Journals (Sweden)
I.I. Gimazov, Yu.I. Talanov
2015-12-01
Full Text Available The results of the electron spin resonance study of the La1-xCaxMnO3 manganite and the diphenyl-picrylhydrazyl thin films for the magnetic field parallel and perpendicular to plane of the films are presented. The temperature dependence of the demagnetizing field is obtained. The parameters of the Curie-Weiss law are estimated for the paramagnetic thin film.
International Nuclear Information System (INIS)
Ferrando, R.; Fiorini, G.; Beghello, A.; Cicio, G.R.; Derchi, L.E.; Consigliere, M.; Resasco, M.; Tornago, S.
1999-01-01
The purpose of this work is to investigate the possible role of Helical CT defecography in pelvic floor disorders by comparing the results of the investigations with those of conventional defecography. The series analyzed consisted of 90 patients, namely 62 women and 28 men, ranging in age 24-82 years. They were all submitted to conventional defecography, and 18 questionable cases were also studied with Helical CT defecography. The conventional examination was performed during the 4 standard phases of resting, squeezing, Valsalva and straining; it is used a remote-control unit. The parameters for Helical CT defecography were: 5 mm beam collimation, pitch 2, 120 KV, 250 m As and 18-20 degrees gantry inclination to acquire coronal images of the pelvic floor. The rectal ampulla was distended with a bolus of 300 mL nonionic iodinated contrast agent (dilution: 3g/cc). The patient wore a napkin and was seated on the table, except for those who could not hold the position and were thus examined supine. Twenty-second helical scans were performed at rest and during evacuation; multiplanar reconstructions were obtained especially on the sagittal plane for comparison with conventional defecographic images. Coronal Helical CT defecography images permitted to map the perineal floor muscles, while sagittal reconstructions provided information on the ampulla and the levator ani. To conclude, Helical CT defecography performed well in study of pelvic floor disorders and can follow conventional defecography especially in questionable cases [it
Medical Imaging Field of Magnetic Resonance Imaging: Identification of Specialties within the Field
Grey, Michael L.
2009-01-01
This study was conducted to determine if specialty areas are emerging in the magnetic resonance imaging (MRI) profession due to advancements made in the medical sciences, imaging technology, and clinical applications used in MRI that would require new developments in education/training programs and national registry examinations. In this…
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.
International Nuclear Information System (INIS)
Kranjc, Matej; Miklavcic, Damijan; Bajd, Franci; Serša, Igor
2013-01-01
Electroporation is a phenomenon caused by externally applied electric field to cells that results in an increase of cell membrane permeability to various molecules. Accurate coverage of the tissue with a sufficiently large electric field presents one of the most important conditions for successful membrane permeabilization. Applications based on electroporation would greatly benefit with a method for monitoring the electric field, especially if it could be done in situ. As the membrane electroporation is a consequence of an induced transmembrane potential, which is directly proportional to the local electric field, we have been investigating current density imaging and magnetic resonance electrical impedance tomography techniques to determine the electric field distribution during electroporation. In this paper, we present comparison of current density and electric field distribution in an agar phantom and in a liver tissue exposed to electroporation pulses. As expected, a region of increased electrical conductivity was observed in the liver tissue exposed to sufficiently high electric field but not in agar phantom.
Equilibrium studies of helical axis stellarators
International Nuclear Information System (INIS)
Hender, T.C.; Carreras, B.A.; Garcia, L.; Harris, J.H.; Rome, J.A.; Cantrell, J.L.; Lynch, V.E.
1984-01-01
The equilibrium properties of helical axis stellarators are studied with a 3-D equilibrium code and with an average method (2-D). The helical axis ATF is shown to have a toroidally dominated equilibrium shift and good equilibria up to at least 10% peak beta. Low aspect ratio heliacs, with relatively large toroidal shifts, are shown to have low equilibrium beta limits (approx. 5%). Increasing the aspect ratio and number of field periods proportionally is found to improve the equilibrium beta limit. Alternatively, increasing the number of field periods at fixed aspect ratio which raises and lowers the toroidal shift improves the equilibrium beta limit
Fan, Non Q.; Clarke, John
1993-01-01
A spectrometer for measuring the nuclear quadrupole resonance spectra or the zero-field nuclear magnetic resonance spectra generated by a sample is disclosed. The spectrometer uses an amplifier having a dc SQUID operating in a flux-locked loop for generating an amplified output as a function of the intensity of the signal generated by the sample. The flux-locked loop circuit includes an integrator. The amplifier also includes means for preventing the integrator from being driven into saturation. As a result, the time for the flux-locked loop to recover from the excitation pulses generated by the spectrometer is reduced.
International Nuclear Information System (INIS)
Vertij, A.A.; Gavrilov, S.P.; Shestopalov, V.P.
1990-01-01
Interaction of incident nuclear particle beam with J = 1/2 (neutrons) spin and (J = 1/2) protons with the target substance is considered. It is shown that neutron polarization at the target exit and neutron transparency (G) of the target depend significantly on incident wave amplitude level and physical parameter values which characterize the target, such as target temperature, resonator mirror reflection factor, number of spins interacting with the field, etc. Under interaction of neutrons with a target resonator which features a high mirror reflection factor and low losses for absorption which is not related to magnetic dipole absorption, a bistable response of neutron polarization and G manifests itself. 1 ref
Biot-Savart helicity versus physical helicity: A topological description of ideal flows
Sahihi, Taliya; Eshraghi, Homayoon
2014-08-01
For an isentropic (thus compressible) flow, fluid trajectories are considered as orbits of a family of one parameter, smooth, orientation-preserving, and nonsingular diffeomorphisms on a compact and smooth-boundary domain in the Euclidian 3-space which necessarily preserve a finite measure, later interpreted as the fluid mass. Under such diffeomorphisms the Biot-Savart helicity of the pushforward of a divergence-free and tangent to the boundary vector field is proved to be conserved and since these circumstances present an isentropic flow, the conservation of the "Biot-Savart helicity" is established for such flows. On the other hand, the well known helicity conservation in ideal flows which here we call it "physical helicity" is found to be an independent constant with respect to the Biot-Savart helicity. The difference between these two helicities reflects some topological features of the domain as well as the velocity and vorticity fields which is discussed and is shown for simply connected domains the two helicities coincide. The energy variation of the vorticity field is shown to be formally the same as for the incompressible flow obtained before. For fluid domains consisting of several disjoint solid tori, at each time, the harmonic knot subspace of smooth vector fields on the fluid domain is found to have two independent base sets with a special type of orthogonality between these two bases by which a topological description of the vortex and velocity fields depending on the helicity difference is achieved since this difference is shown to depend only on the harmonic knot parts of velocity, vorticity, and its Biot-Savart vector field. For an ideal magnetohydrodynamics (MHD) flow three independent constant helicities are reviewed while the helicity of magnetic potential is generalized for non-simply connected domains by inserting a special harmonic knot field in the dynamics of the magnetic potential. It is proved that the harmonic knot part of the vorticity
International Nuclear Information System (INIS)
Hong, Liu; He, X.T.; Chen, S.G.; Zhang, W.Y.; He, X.T.; Hong, Liu
2004-01-01
We propose a new particle acceleration mechanism. Electrons can be accelerated to relativistic energy within a few electromagnetic wave cycles through the mechanism which is named electromagnetic and magnetic field resonance acceleration (EMRA). We find that the electron acceleration depends not only on the electromagnetic wave intensity, but also on the ratio between electron Larmor frequency and electromagnetic wave frequency. As the ratio approaches to unity, a clear resonance peak is observed, corresponding to the EMRA. Near the resonance regime, the strong magnetic fields still affect the electron acceleration dramatically. We derive an approximate analytical solution of the relativistic electron energy in adiabatic limit, which provides a full understanding of this phenomenon. In typical parameters of pulsar magnetospheres, the mechanism allows particles to increase their energies through the resonance of high magnetic field and high frequency electromagnetic wave in each electromagnetic wave period. The energy spectra of the accelerated particles exhibit the synchrotron radiation behavior. These can help to understand the remaining emission of high energy electron from radio pulsar within supernova remnant. The other potential application of our theory in fast ignition scheme of inertial confinement fusion is also discussed. (authors)
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.
High speed resonant frequency determination applied to field mapping using perturbation techniques
International Nuclear Information System (INIS)
Smith, B.H.; Burton, R.J.; Hutcheon, R.M.
1992-01-01
Perturbation techniques are commonly used for measuring electric and magnetic field distributions in resonant structures. A field measurement system has been assembled using a Hewlett Packard model 8753C network analyzer interfaced via an HPIB bus to a personal computer to form an accurate, rapid and flexible system for data acquisition, control, and analysis of such measurements. Characterization of long linac structures (up to 3 m) is accomplished in about three minutes, minimizing thermal drift effects. This paper describes the system, its application and its extension to applications such as confirming the presence of weak, off-axis quadrupole fields in an on-axis coupled linac. (Author) 5 figs., 10 refs
Investigation of Condensed Media in Weak Fields by the Method of Nuclear Magnetic Resonance
Davydov, V. V.; Myazin, N. S.; Dudkin, V. I.; Velichko, E. N.
2018-05-01
A compact design of a rapid-response nuclear magnetic spectrometer for investigation of condensed media in weak fields is reported. As a result of investigation of different condensed media, special features of recording a nuclear magnetic resonance (NMR) signal in a weak magnetic field from a small volume of the medium under study are established. For the first time the NMR absorption spectra of condensed media in a weak field are collected. Based on the results of experimental studies, the potential of using a compact NMR-spectrometer for condensed media monitoring in a rapid response mode is determined.
Zero-field optical magnetic resonance study of phosphorus donors in 28-silicon
Morse, Kevin J.; Dluhy, Phillip; Huber, Julian; Salvail, Jeff Z.; Saeedi, Kamyar; Riemann, Helge; Abrosimov, Nikolay V.; Becker, Peter; Pohl, Hans-Joachim; Simmons, S.; Thewalt, M. L. W.
2018-03-01
Donor spins in silicon are some of the most promising qubits for upcoming solid-state quantum technologies. The nuclear spins of phosphorus donors in enriched silicon have among the longest coherence times of any solid-state system as well as simultaneous high fidelity qubit initialization, manipulation, and readout. Here we characterize the phosphorus in silicon system in the regime of "zero" magnetic field, where a singlet-triplet spin clock transition can be accessed, using laser spectroscopy and magnetic resonance methods. We show the system can be optically hyperpolarized and has ˜10 s Hahn echo coherence times, even for applied static magnetic fields below Earth's field.
One phonon resonant Raman scattering in semiconductor quantum wires: Magnetic field effect
Energy Technology Data Exchange (ETDEWEB)
Betancourt-Riera, Re., E-mail: rbriera@posgrado.cifus.uson.mx [Instituto Tecnologico de Hermosillo, Avenida Tecnologico S/N, Colonia Sahuaro, C.P. 83170, Hermosillo, Sonor, (Mexico); Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-088, C.P. 83190, Hermosillo, Sonora (Mexico); Betancourt-Riera, Ri. [Instituto Tecnologico de Hermosillo, Avenida Tecnologico S/N, Colonia Sahuaro, C.P. 83170, Hermosillo, Sonora (Mexico); Nieto Jalil, J.M. [Tecnologico de Monterrey-Campus Sonora Norte, Bulevar Enrique Mazon Lopez No. 965, C.P. 83000, Hermosillo, Sonora (Mexico); Riera, R. [Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-088, C.P. 83190, Hermosillo, Sonora (Mexico)
2013-02-01
We have developed a theory of one phonon resonant Raman scattering in a semiconductor quantum wire of cylindrical geometry in the presence of an external magnetic field distribution, parallel to the cylinder axis. The effect of the magnetic field in the electron and hole states, and in the Raman scattering efficiency, is determinate. We consider the electron-phonon interaction using a Froehlich-type Hamiltonian, deduced for the case of complete confinement phonon modes by Comas and his collaborators. We also assume T=0 K, a single parabolic conduction and valence bands. The spectra are discussed for different magnetic field values and the selection rules for the processes are also studied.
Fano resonance of the ultrasensitve optical force excited by Gaussian evanescent field
International Nuclear Information System (INIS)
Yang, Yang; Li, Jiafang; Li, Zhi-Yuan
2015-01-01
In this paper, we study the angle-dependent Fano-like optical force spectra of plasmonic Ag nanoparticles, which exhibit extraordinary transformation from Lorentzian resonance to Fano resonance when excited by a Gaussian evanescent wave. We systematically analyze the behavior of this asymmetric scattering induced optical force under different conditions and find that this Fano interference-induced force is ultrasensitive to the excitation wavelength, incident angle and particle size, as well as the core–shell configuration, which could be useful for wavelength- and angle-dependent size-selective optical manipulation. The origin of this Fano resonance is further identified as the interference between the two adjacent-order multipolar plasmonic modes excited in the Ag particle under the excitation of an inhomogeneously distributed evanescent field. (paper)
Energy Technology Data Exchange (ETDEWEB)
Ciovati, Gianluigi [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Dhakal, Pashupati [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Gurevich, Alexander V. [Old Dominion University, Norfolk, VA (United States)
2014-03-03
Measurements of the quality factor, Q, of Nb superconducting microwave resonators often show that Q increases by {approx_equal} 10%–30% with increasing radio-frequency (rf) field, H, up to {approx} 15-20 mT. Recent high temperature heat treatments can amplify this rf field-induced increase of Q up to {approx_equal} 50%–100% and extend it to much higher fields, but the mechanisms of the enhancement of Q(H) remain unclear. Here, we suggest a method to reveal these mechanisms by measuring temperature dependencies of Q at different rf field amplitudes. We show that the increase of Q(H) does not come from a field dependent quasi-particles activation energy or residual resistance, but rather results from the smearing of the density of state by the rf field.
International Nuclear Information System (INIS)
Casini, Roberto
2005-01-01
We derive a formalism for the computation of resonance-scattering polarization of hydrogen lines in the presence of simultaneous magnetic and electric fields, within a framework of the quantum theory of polarized line formation in the limit of complete frequency redistribution and of collisionless regime. Quantum interferences between fine-structure levels are included in this formalism. In the presence of a magnetic field, these interferences affect, together with the magnetic Hanle effect, the polarization of the atomic levels. In the presence of an electric field, interferences between distinct orbital configurations are also induced, further affecting the polarization of the hydrogen levels. In turn, the electric field is expected to affect the polarization of the atomic levels (electric Hanle effect), in a way analogous to the magnetic Hanle effect. We find that the simultaneous action of electric and magnetic fields give rise to complicated patterns of polarization and depolarization regimes, for varying geometries and field strengths
Energy Technology Data Exchange (ETDEWEB)
Samanta, Kousik [Department of Chemistry, Rice University, Houston, TX 77005 (United States); Yeager, Danny L. [Department of Chemistry, Texas A and M University, College Station, TX 77843 (United States)
2015-01-22
Resonances are temporarily bound states which lie in the continuum part of the Hamiltonian. If the electronic coordinates of the Hamiltonian are scaled (“dilated”) by a complex parameter, η = αe{sup iθ} (α, θ real), then its complex eigenvalues represent the scattering states (resonant and non-resonant) while the eigenvalues corresponding to the bound states and the ionization and the excitation thresholds remain real and unmodified. These make the study of these transient species amenable to the bound state methods. We developed a quadratically convergent multiconfigurational self-consistent field method (MCSCF), a well-established bound-state technique, combined with a dilated Hamiltonian to investigate resonances. This is made possible by the adoption of a second quantization algebra suitable for a set of “complex conjugate biorthonormal” spin orbitals and a modified step-length constraining algorithm to control the walk on the complex energy hypersurface while searching for the stationary point using a multidimensional Newton-Raphson scheme. We present our computational results for the {sup 2}PBe{sup −} shape resonances using two different computationally efficient methods that utilize complex scaled MCSCF (i.e., CMCSCF). These two methods are to straightforwardly use CMCSCF energy differences and to obtain energy differences using an approximation to the complex multiconfigurational electron propagator. It is found that, differing from previous computational studies by others, there are actually two {sup 2}PBe{sup −} shape resonances very close in energy. In addition, N{sub 2} resonances are examined using one of these methods.
DEFF Research Database (Denmark)
an impetus or drive to that account: change, innovation, rupture, or discontinuity. Resonances: Historical Essays on Continuity and Change explores the historiographical question of the modes of interrelation between these motifs in historical narratives. The essays in the collection attempt to realize...
Electromagnetic Resonance in Biological Form: A Role for Fields in Morphogenesis
International Nuclear Information System (INIS)
Pietak, Alexis M
2011-01-01
In morphogenesis, the mechanisms through which homogeneous, symmetric collectives of self-same cells are able to consistently and precisely establish long-range pattern remain an open question of scientific research. This work explores the hypothesis of developing biological structures as dielectric microwave resonators, using plant leaves as a working example. A finite element analysis (FEA) model was designed to determine if suitable resonant modes were physically possible for geometric and electrical parameters similar to those of developing leaf tissue. Using the FEA model, resonant EM modes with patterns of relevance to developing leaf vein modalities were detected. Here I show how the single physical mechanism of EM resonance can self-consistently account for different kinds of key symmetry-breaking operations characteristic of a variety of leaf vascular patterns. On account of the existence of shared geometric signatures in a leaf's vascular pattern and the electric field component of EM resonant modes supported by a leaf-like structure, further theoretical and experimental investigations are warranted. Significantly, this hypothesis is not limited to leaf vascular patterning, but may be applicable to a variety of morphogenetic phenomena in a number of living systems.
Directory of Open Access Journals (Sweden)
N. I. Polzikova
2018-05-01
Full Text Available We report on the first observation of microvolt-scale inverse spin Hall effect (ISHE dc voltage driven by an acoustic spin pumping (ASP in a bulk acoustic wave (BAW resonator formed by a Al-ZnO-Al-YIG(1-GGG-YIG(2-Pt structure. When 2 mW power is applied to an Al-ZnO-Al transducer, the voltage VISHE ∼ 4 μV in the Pt film is observed as a result of resonant ASP from YIG(2 to Pt in the area ∼ 170 μm. The results of frequency and magnetic field mapping of VISHE(f,H together with reflectivity of the resonator show an obvious agreement between the positions of the voltage maxima and BAW resonance frequencies fn(H on the (f, H plane. At the same time a significant asymmetry of the VISHE(fn(H value in reference to the magnetoelastic resonance (MER line fMER(H position is revealed, which is explained by asymmetry of the magnetoelastic waves dispersion law.
Polzikova, N. I.; Alekseev, S. G.; Pyataikin, I. I.; Luzanov, V. A.; Raevskiy, A. O.; Kotov, V. A.
2018-05-01
We report on the first observation of microvolt-scale inverse spin Hall effect (ISHE) dc voltage driven by an acoustic spin pumping (ASP) in a bulk acoustic wave (BAW) resonator formed by a Al-ZnO-Al-YIG(1)-GGG-YIG(2)-Pt structure. When 2 mW power is applied to an Al-ZnO-Al transducer, the voltage VISHE ˜ 4 μV in the Pt film is observed as a result of resonant ASP from YIG(2) to Pt in the area ˜ 170 μm. The results of frequency and magnetic field mapping of VISHE(f,H) together with reflectivity of the resonator show an obvious agreement between the positions of the voltage maxima and BAW resonance frequencies fn(H) on the (f, H) plane. At the same time a significant asymmetry of the VISHE(fn(H)) value in reference to the magnetoelastic resonance (MER) line fMER(H) position is revealed, which is explained by asymmetry of the magnetoelastic waves dispersion law.
Resonant excitation and the decay of autoionization states in a strong electromagnetic field
International Nuclear Information System (INIS)
Andryushin, A.I.; Kazakov, A.E.; Fedorov, M.V.
1985-01-01
Photoionization of atoms involving resonant excitation of the auto-ionization state is studied. The evolution of the total ionization probability, its dependence on the frequency of the resonance radiation and also the photoelectron energy spectrum are investigated. It is shown that the energy of the final state of the system may be localized either in the vicinity of E approximately Esub(α), where Esub(α) is the auto-ionization energy, or in the vicinity of E approximately Esub(α)+h/2πω where h/2πω is the quantum energy of the resonance radiation. The photoelectron specturum in the region E approximately Esub(α)+h/2πω as a whole is similar to the electron spectrum on photoionization of atoms involving resonance excitation of the bound state. A strong effect on the photoelectron spectrum in the region E approximately Esub(α) is exerted by interference of various decay channels of the ground state in the resonance field which leads to the appearance in the spectrum of a characteristic structure of the Fano type. Interence also affects the widths of the two spectral curves, the relatve amount of electrons in the two energy ranges and also other characteristics of the ionization process. It is shown that the presence of a noninterfering photoionization channel of the autoionization state ensures the finiteness of the swidths and heights of the spectral curves and the absence of complete ''coherency merging''
Effects of multi-photon interferences from internally generated fields in strongly resonant systems
International Nuclear Information System (INIS)
Deng, Lu; Payne, Marvin G.; Garrett, William R.
2006-01-01
In studies of various nonlinear optical phenomena, strong resonant features in the atomic or molecular response to multi-photon driven processes have been used to greatly enhance the visibility of otherwise weak higher-order processes. However, there are well defined circumstances where a multi-photon-resonant response of a target system leads to the generation of one or more new electromagnetic fields that can drastically change the overall system response from what would be expected from the imposed laser fields alone. New effects can occur and dominate some aspects of the nonlinear optical response because of the constructive or destructive interference between transition amplitudes along multiple excitation pathways between a given set of optically coupled states, where one of the pathways involve internally generated field(s). Under destructive interference some resonant enhancements can become completely canceled (suppressed). This review focuses on the class of optical interference effects associated with internally generated fields, that have been found to be capable of influencing a very significant number of basic physical phenomena in gas or vapor phase systems. It provides a historical overview of experimental and theoretical developments and a modern understanding of the underlying physics and its various manifestations that include: suppression of multi-photon excitation processes, suppression of stimulated emissions (Raman, hyper-Raman, and optically pumped stimulated emissions), saturation of parametric wave-mixing, pressure and beam-geometry dependent shifting of multi-photon-resonant absorption lines, and the suppression of Autler-Townes splitting and ac-stark shifts. Additionally, optical interference effects in some modern contexts, such as achieving multi-photon induced transparency, establishing single-photon self-interference based induced transparency, and generating entangled single photon states, are reviewed
Panaro, Simone; Proietti Zaccaria, Remo; Toma, Andrea
2017-02-01
Spintronics and spin-based technology rely on the ultra-fast unbalance of the electronic spin population in quite localized spatial regions. However, as a matter of fact, the low susceptibility of conventional materials at high frequencies strongly limits these phenomena, rendering the efficiency of magnetically active devices insufficient for application purposes. Among the possible strategies which can be envisaged, plasmonics offers a direct approach to increase the effect of local electronic unbalancing processes. By confining and enhancing free radiation in nm-size spatial regions, plasmonic nano-assemblies have demonstrated to support very intense electric and magnetic hot-spots. In particular, very recent studies have proven the fine control of magnetic fields in Fano resonance condition. The near-field-induced out-of-phase oscillation of localized surface plasmons has manifested itself with the arising of magnetic sub-diffractive hot-spots. Here, we show how this effect can be further boosted in the mid-infrared regime via the introduction of higher order plasmonic modes. The investigated system, namely Moon Trimer Resonator (MTR), combines the high efficiency of a strongly coupled nano-assembly in Fano interferential condition with the elevated tunability of the quadrupolar resonance supported by a moon-like geometry. The fine control of the apical gap in this unique nanostructure, characterizes a plasmonic device able to tune its resonance without any consequence on the magnetic hot-spot size, thus enabling an efficient squeezing in the infrared.
Coupling between core and cladding modes in a helical core fiber with large core offset
International Nuclear Information System (INIS)
Napiorkowski, Maciej; Urbanczyk, Waclaw
2016-01-01
We analyzed the effect of resonant coupling between core and cladding modes in a helical core fiber with large core offset using the fully vectorial method based on the transformation optics formalism. Our study revealed that the resonant couplings to lower order cladding modes predicted by perturbative methods and observed experimentally in fibers with small core offsets are in fact prohibited for larger core offsets. This effect is related to the lack of phase matching caused by elongation of the optical path of the fundamental modes in the helical core. Moreover, strong couplings to the cladding modes of the azimuthal modal number much higher than predicted by perturbative methods may be observed for large core offsets, as the core offset introduces higher order angular harmonics in the field distribution of the fundamental modes. Finally, in contrast to previous studies, we demonstrate the existence of spectrally broad polarization sensitive couplings to the cladding modes suggesting that helical core fibers with large core offsets may be used as broadband circular polarizers. (paper)
Gabrys, Charles M; Qiang, Wei; Sun, Yan; Xie, Li; Schmick, Scott D; Weliky, David P
2013-10-03
Fusion of the human immunodeficiency virus (HIV) membrane and the host cell membrane is an initial step of infection of the host cell. Fusion is catalyzed by gp41, which is an integral membrane protein of HIV. The fusion peptide (FP) is the ∼25 N-terminal residues of gp41 and is a domain of gp41 that plays a key role in fusion catalysis likely through interaction with the host cell membrane. Much of our understanding of the FP domain has been accomplished with studies of "HFP", i.e., a ∼25-residue peptide composed of the FP sequence but lacking the rest of gp41. HFP catalyzes fusion between membrane vesicles and serves as a model system to understand fusion catalysis. HFP binds to membranes and the membrane location of HFP is likely a significant determinant of fusion catalysis perhaps because the consequent membrane perturbation reduces the fusion activation energy. In the present study, many HFPs were synthesized and differed in the residue position that was (13)CO backbone labeled. Samples were then prepared that each contained a singly (13)CO labeled HFP incorporated into membranes that lacked cholesterol. HFP had distinct molecular populations with either α helical or oligomeric β sheet structure. Proximity between the HFP (13)CO nuclei and (31)P nuclei in the membrane headgroups was probed by solid-state NMR (SSNMR) rotational-echo double-resonance (REDOR) measurements. For many samples, there were distinct (13)CO shifts for the α helical and β sheet structures so that the proximities to (31)P nuclei could be determined for each structure. Data from several differently labeled HFPs were then incorporated into a membrane location model for the particular structure. In addition to the (13)CO labeled residue position, the HFPs also differed in sequence and/or chemical structure. "HFPmn" was a linear peptide that contained the 23 N-terminal residues of gp41. "HFPmn_V2E" contained the V2E mutation that for HIV leads to greatly reduced extent of fusion and
Resistive internal helical mode near the instability threshold
International Nuclear Information System (INIS)
Gal'vao, R.M.; Sakanaka, P.Kh.
1979-01-01
The behaviour of a resistive internal helical mode is examined on condition that its resonance surface is located on a magnetic axis, i.e., at the stability boundary. In this case the mode increment is shown to have the scale (tausub(R)tausub(H))sup(1/2), where: 1) tausub(H)=rsub(o)/Vsub(THETA), Vsub(THETA) = Bsub(THETA)(q'rsub(o)/q)/(4πrho)sup(1/2), rho is a matter density, q'=dq/dr and Vsub(THETA) is calculated at r=rsub(o)) (rsub(o) is a radium on which q(rsub(o)=1), 2)tausub(R)=4πrsub(o)sup(2)/etacsup(2) - time of field diffusion (eta-plasma resistance)
Field-swept pulsed electron paramagnetic resonance of Cr3+-doped ZBLAN fluoride glass
International Nuclear Information System (INIS)
Drew, S.C.; Pilbrow, J.R.; Newman, P.J.; MacFarlane, D.R.
2001-01-01
Field-swept pulsed electron paramagnetic resonance (EPR) spectra of a ZBLAN fluoride glass doped with a low concentration of Cr 3+ are obtained using echo-detected EPR and hole-burning free induction decay detection. We review the utility of the pulsed EPR technique in generating field-swept EPR spectra, as well as some of the distorting effects that are peculiar to the pulsed detection method. The application of this technique to Cr 3+ -doped ZBLAN reveals that much of the broad resonance extending from g eff =5.1 to g eff =1.97, characteristic of X-band continuous wave EPR of Cr 3+ in glasses, is absent. We attribute this largely to the variation in nutation frequencies across the spectrum that result from sites possessing large fine structure interactions. The description of the spin dynamics of such sites is complicated and we discuss some possible approaches to the simulation of the pulsed EPR spectra. (author)
Resonance tuning due to Coulomb interaction in strong near-field coupled metamaterials
International Nuclear Information System (INIS)
Roy Chowdhury, Dibakar; Xu, Ningning; Zhang, Weili; Singh, Ranjan
2015-01-01
Coulomb's law is one of the most fundamental laws of physics that describes the electrostatic interaction between two like or unlike point charges. Here, we experimentally observe a strong effect of Coulomb interaction in tightly coupled terahertz metamaterials where the split-ring resonator dimers in a unit cell are coupled through their near fields across the capacitive split gaps. Using a simple analytical model, we evaluated the Coulomb parameter that switched its sign from negative to positive values indicating the transition in the nature of Coulomb force from being repulsive to attractive depending upon the near field coupling between the split ring resonators. Apart from showing interesting effects in the strong coupling regime between meta-atoms, Coulomb interaction also allows an additional degree of freedom to achieve frequency tunable dynamic metamaterials
International Nuclear Information System (INIS)
Costa, Paula de M.; Tavares, Maria I.B.
2005-01-01
Blends of natural and synthetic polymers represent a new class of materials with better mechanical properties and biocompatibility than those of the single components. Collagen and poly(vinylpyrrolidone) are well known for their important biological properties. The blending of collagen with poly(vinylpyrrolidone) makes it possible to obtain new materials in which strong interactions between the synthetic and biological components occur. Do to the excellent biocompatibility of these polymers, this blend has been much studied intending biomedical applications. And a one technique that can provide important information on molecular mobility, compatibility and even evaluate the interactions that can occur with these polymers is the Low Field Nuclear Magnetic Resonance Spectroscopy. Thus, the purpose of this work is to evaluate collagen and poly(vinylpyrrolidone) by Low Field Nuclear Magnetic Resonance Spectroscopy. From the values of relaxation times obtained, we can conclude that these materials have different interactions, and different mobility domains, confirming the heterogeneity and complexity of these materials. (author)
Probing two-field open inflation by resonant signals in correlation functions
Energy Technology Data Exchange (ETDEWEB)
Battefeld, Thorsten; Niemeyer, Jens C.; Vlaykov, Dimitar, E-mail: tbattefe@astro.physik.uni-goettingen.de, E-mail: niemeyer@astro.physik.uni-goettingen.de, E-mail: vlaykov@astro.physik.uni-goettingen.de [Institute for Astrophysics, University of Goettingen, Friedrich Hund Platz 1, D-37077 Goettingen (Germany)
2013-05-01
We derive oscillatory signals in correlation functions in two-field open inflation by means of the in-in formalism; such signatures are caused by resonances between oscillations in the tunnelling field and fluctuations in the inflaton during the curvature dominated, intermediate and subsequent inflationary regime. While amplitudes are model-dependent, we find distinct oscillations in the power and bi-spectrum that can act as a direct probe of the curvature dominated phase and thus, indirectly, strengthen the claim of the string landscape if they were observed. We comment on the prospects of detecting these tell-tale signs in current experiments, which is challenging, but not impossible. At the technical level, we pay special attention to the applicability conditions for truncating fluctuations to the light (inflaton) field and derive upper limits on the oscillation amplitude of the heavy field. A violation of these bounds requires a multi-field analysis at the perturbed level.
International Nuclear Information System (INIS)
Zivkovic, D.; Hrnjak, M.; Ivanovic, C.
1997-01-01
Medical personnel working with magnetic resonance imaging (MRI) devices could be exposed to static magnetic (M) field, time-varying M fields and radiofrequency (RF) radiation. The aim of work was to investigate the density of magnetic flux of static magnetic field and the power density of RF radiation which appear in the working environment around the 0.5 T MRI unit in one hospital. The density of magnetic flux of static magnetic field was measured with Hall Effect Gauss meter - Magnetech (Great Britain), and the power density of RF radiation was measured with broadband isotropic meter - The Narda Microwave Corp. (USA). The results of measurement show that the density of magnetic flux of static M field on working places are below threshold limit of exposure and the intensities of RF radiation are far below maximum permissible level. (author)
International Nuclear Information System (INIS)
Ertl-Wagner, B.B.; Reith, W.; Sartor, K.
2001-01-01
As low-field MR imaging is becoming a widely used imaging technique, we aimed at a prospective assessment of differences in imaging quality between low- and high-field MR imaging in multiple sclerosis patients possibly interfering with diagnostic or therapeutic decision making. Twenty patients with clinically proven multiple sclerosis were examined with optimized imaging protocols in a 1.5- and a 0.23-T MR scanner within 48 h. Images were assessed independently by two neuroradiologists. No statistically significant interrater discrepancies were observed. A significantly lower number of white matter lesions could be identified in low-field MR imaging both on T1- and on T2-weighted images (T2: high field 700, low field 481; T1: high field 253, low field 177). A total of 114 enhancing lesions were discerned in the high-field MR imaging as opposed to 45 enhancing lesions in low-field MR imaging. Blood-brain barrier disruption was identified in 11 of 20 patients in the high-field MR imaging, but only in 4 of 20 patients in low-field MR imaging. Since a significantly lower lesion load is identified in low-field MR imaging than in high-field MR imaging, and blood-brain barrier disruption is frequently missed, caution must be exercised in interpreting a normal low-field MR imaging scan in a patient with clinical signs of multiple sclerosis and in interpreting a scan without enhancing lesions in a patient with known multiple sclerosis and clinical signs of exacerbation. (orig.)
Non-Weyl resonance asymptotics for quantum graphs in a magnetic field
Czech Academy of Sciences Publication Activity Database
Exner, Pavel; Lipovský, J.
2011-01-01
Roč. 375, č. 4 (2011), s. 805-807 ISSN 0375-9601 R&D Projects: GA MŠk LC06002; GA ČR GAP203/11/0701 Institutional research plan: CEZ:AV0Z10480505 Keywords : Quantum graphs * Magnetic field * Resonances Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.632, year: 2011
Czech Academy of Sciences Publication Activity Database
Kortunov, P.; Vasenkov, S.; Kärger, J.; Fé Elía, M.; Perez, M.; Stöcker, M.; Papadopoulos, G. K.; Theodorou, D.; Drescher, B.; McElhiney, G.; Bernauer, B.; Krystl, V.; Kočiřík, Milan; Zikánová, Arlette; Jirglová, Hana; Berger, C.; Gläser, R.; Weitkamp, J.; Hansen, E. W.
2005-01-01
Roč. 23, č. 2 (2005), s. 233-237 ISSN 0730-725X Grant - others:TROCAT project - European Community(DE) G5RD-CT-2001-00520 Institutional research plan: CEZ:AV0Z40400503 Keywords : pulsed-field gradient * nuclear magnetic resonance * fluid catalytic cracking catalyst Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.361, year: 2005
Xiong, Caiqiao; Zhou, Xiaoyu; Zhang, Ning; Zhan, Lingpeng; Chen, Yongtai; Nie, Zongxiu
2016-02-01
The nonlinear harmonics within the ion motion are the fingerprint of the nonlinear fields. They are exclusively introduced by these nonlinear fields and are responsible to some specific nonlinear effects such as nonlinear resonance effect. In this article, the ion motion in the quadrupole field with a weak superimposed octopole component, described by the nonlinear Mathieu equation (NME), was studied by using the analytical harmonic balance (HB) method. Good accuracy of the HB method, which was comparable with that of the numerical fourth-order Runge-Kutta (4th RK), was achieved in the entire first stability region, except for the points at the stability boundary (i.e., β = 1) and at the nonlinear resonance condition (i.e., β = 0.5). Using the HB method, the nonlinear 3β harmonic series introduced by the octopole component and the resultant nonlinear resonance effect were characterized. At nonlinear resonance, obvious resonant peaks were observed in the nonlinear 3β series of ion motion, but were not found in the natural harmonics. In addition, both resonant excitation and absorption peaks could be observed, simultaneously. These are two unique features of the nonlinear resonance, distinguishing it from the normal resonance. Finally, an approximation equation was given to describe the corresponding working parameter, q nr , at nonlinear resonance. This equation can help avoid the sensitivity degradation due to the operation of ion traps at the nonlinear resonance condition.
A resonant magnetic field microsensor with high quality factor at atmospheric pressure
International Nuclear Information System (INIS)
Herrera-May, A L; García-Ramírez, P J; Martínez-Castillo, J; Sauceda-Carvajal, A; García-González, L; Aguilera-Cortés, L A; Figueras-Costa, E
2009-01-01
A resonant magnetic field microsensor with a high quality factor at atmospheric pressure has been designed, fabricated and tested. This microsensor does not require vacuum packaging to operate efficiently and presents a compact and simple geometrical configuration of silicon. This geometry permits us to decrease the size of the structure and facilities its fabrication and operation. It is constructed of a seesaw plate (400 × 150 × 15 µm 3 ), two torsional beams (60 × 40 × 15 µm 3 ), four flexural beams (130 × 12 × 15 µm 3 ) and a Wheatstone bridge with four p-type piezoresistors. The resonant device exploits the Lorentz force principle and operates at its first resonant frequency (136.52 kHz). A sinusoidal excitation current of 22.0 mA with a frequency of 136.52 kHz and magnetic fields from 1 to 400 G are considered. The mechanical response of the microsensor is modeled with the finite element method (FEM). The structure of the microsensor registered a maximum von Mises stress of 53.8 MPa between the flexural and the torsional beams. Additionally, a maximum deflection (372.5 nm) is obtained at the extreme end of the plate. The proposed microsensor has the maximum magnetic sensitivity of 40.3 µV G −1 (magnetic fields −1/2 , theoretical resolution of 1.43 mG Hz −1/2 and power consumption less than 10.0 mW
Field angle dependence of voltage-induced ferromagnetic resonance under DC bias voltage
International Nuclear Information System (INIS)
Shiota, Yoichi; Miwa, Shinji; Tamaru, Shingo; Nozaki, Takayuki; Kubota, Hitoshi; Fukushima, Akio; Suzuki, Yoshishige; Yuasa, Shinji
2016-01-01
We studied the rectification function of microwaves in CoFeB/MgO-based magnetic tunnel junctions using voltage-induced ferromagnetic resonance (FMR). Our findings reveal that the shape of the structure of the spectrum depends on the rotation angle of the external magnetic field, providing clear evidence that FMR dynamics are excited by voltage-induced magnetic anisotropy changes. Further, enhancement of the rectified voltage was demonstrated under a DC bias voltage. In our experiments, the highest microwave detection sensitivity obtained was 350 mV/mW, at an RF frequency of 1.0 GHz and field angle of θ_H=80°, ϕ_H=0°. The experimental results correlated with those obtained via simulation, and the calculated results revealed the magnetization dynamics at the resonance state. - Highlights: • Examined voltage-induced ferromagnetic resonance (FMR) under various field angles. • FMR dynamics are excited by voltage-induced magnetic anisotropy changes. • Microwave detection sensitivity depends on input RF and elevation angle. • Microwave detection sensitivity=350 mV/mW at RF=1.0 GHz, θ_H=80°, ϕ_H=0°.
Uniform field loop-gap resonator and rectangular TEU02 for aqueous sample EPR at 94 GHz
Sidabras, Jason W.; Sarna, Tadeusz; Mett, Richard R.; Hyde, James S.
2017-09-01
In this work we present the design and implementation of two uniform-field resonators: a seven-loop-six-gap loop-gap resonator (LGR) and a rectangular TEU02 cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94 GHz. The LGR geometry employs low-loss Rexolite end-sections to improve the field homogeneity over a 3 mm sample region-of-interest from near-cosine distribution to 90% uniform. The LGR was designed to accommodate large degassable Polytetrafluorethylen (PTFE) tubes (0.81 mm O.D.; 0.25 mm I.D.) for aqueous samples. Additionally, field modulation slots are designed for uniform 100 kHz field modulation incident at the sample. Experiments using a point sample of lithium phthalocyanine (LiPC) were performed to measure both the uniformity of the microwave magnetic field and 100 kHz field modulation, and confirm simulations. The rectangular TEU02 cavity resonator employs over-sized end-sections with sample shielding to provide an 87% uniform field for a 0.1 × 2 × 6 mm3 sample geometry. An evanescent slotted window was designed for light access to irradiate 90% of the sample volume. A novel dual-slot iris was used to minimize microwave magnetic field perturbations and maintain cross-sectional uniformity. Practical EPR experiments using the application of light irradiated rose bengal (4,5,6,7-tetrachloro-2‧,4‧,5‧,7‧-tetraiodofluorescein) were performed in the TEU02 cavity. The implementation of these geometries providing a practical designs for uniform field resonators that continue resonator advancements towards quantitative EPR spectroscopy.
Elnaggar, Sameh Y.; Tervo, Richard; Mattar, Saba M.
2014-01-01
Probes consisting of a dielectric resonator (DR) inserted in a cavity are important integral components of electron paramagnetic resonance (EPR) spectrometers because of their high signal-to-noise ratio. This article studies the behavior of this system, based on the coupling between its dielectric and cavity modes. Coupled-mode theory (CMT) is used to determine the frequencies and electromagnetic fields of this coupled system. General expressions for the frequencies and field distributions are derived for both the resulting symmetric and anti-symmetric modes. These expressions are applicable to a wide range of frequencies (from MHz to THz). The coupling of cavities and DRs of various sizes and their resonant frequencies are studied in detail. Since the DR is situated within the cavity then the coupling between them is strong. In some cases the coupling coefficient, κ, is found to be as high as 0.4 even though the frequency difference between the uncoupled modes is large. This is directly attributed to the strong overlap between the fields of the uncoupled DR and cavity modes. In most cases, this improves the signal to noise ratio of the spectrometer. When the DR and the cavity have the same frequency, the coupled electromagnetic fields are found to contain equal contributions from the fields of the two uncoupled modes. This situation is ideal for the excitation of the probe through an iris on the cavity wall. To verify and validate the results, finite element simulations are carried out. This is achieved by simulating the coupling between a cylindrical cavity's TE011 and the dielectric insert's TE01δ modes. Coupling between the modes of higher order is also investigated and discussed. Based on CMT, closed form expressions for the fields of the coupled system are proposed. These expressions are crucial in the analysis of the probe's performance.
Resonance properties of a three-level atom with quantized field modes
International Nuclear Information System (INIS)
Yoo, H.I.
1984-01-01
A system of one three-level atom and one or two quantized electro-magnetic field modes coupled to each other by the dipole interaction, with the rotating wave approximation is studied. All three atomic configurations, i.e., cascade Lambda- and V-types, are treated simultaneously. The system is treated as closed, i.e., no interaction with the external radiation field modes, to reveal the internal structures and symmetries in the system. The general dynamics of the system are investigated under several distinct initial conditions and their similarities and differences with the dynamics of the Jaynes-Cummings model are revealed. Also investigated is the possibility of so-called coherent trapping of the atom in the quantized field modes in a resonator. An atomic state of coherent trapping exists only for limited cases, and it generally requires the field to be in some special states, depending on the system. The discussion of coherent trapping is extended into a system of M identical three-level atoms. The stability of a coherent-trapping state when fluorescence can take place is discussed. The distinction between a system with resonator field modes and one with ideal laser modes is made clear, and the atomic relaxation to the coherent-trapping atomic state when a Lambda-type atom is irradiated by two ideal laser beams is studied. The experimental prospects to observe the collapse-revival phenomena in the atomic occupation probabilities, which is characteristic of a system with quantized resonator field modes is discussed
Low-frequency current drive and helicity injection
International Nuclear Information System (INIS)
Chan, V.S.; Miller, R.L.; Ohkawa, T.
1990-01-01
For ω much-lt Ω i , where Ω i is the ion cyclotron frequency, circularly polarized waves can drive current far exceeding the current resulting from linearly polarized waves. Further, the efficiency can be independent of plasma density. In some cases, this circular polarization may be interpreted in terms of helicity injection. For tokamak applications, where the wavenumber in the toroidal direction is a real quantity, wave helicity is injected only with finite E z waves, where z is the direction of the static magnetic field. The Alfven waves are possible current drive candidates but, in the cylindrical model considered, the compressional wave is weakly damped because E z =0, while the shear Alfven wave is totally absorbed at the surface because of finite E z . A mixture of the two modes is shown to drive an oscillatory surface current even though the efficiency is high and independent of density. A more promising current drive candidate is a fast wave that propagates to the plasma interior and is damped by the minority cyclotron resonance. Near the minority mode conversion region, the fast wave is left-handed circularly polarized and it has a small but finite E z component at high electron temperatures. The current drive efficiency, although not as high as that of the Alfven wave, is still good and independent of density, making it attractive for fusion reactors
Adaptive radiotherapy using helical tomotherapy system
International Nuclear Information System (INIS)
Jeswani, Sam; Ruchala, Kenneth; Olivera, Gustavo; Mackie, T.R.
2008-01-01
As commonly known in the field, adaptive radiation therapy (ART) is the use of feedback to modify a radiotherapy treatment. There are numerous ways in which this feedback can be received and used, and this presentation will discuss some of the implementations of ART being investigated with a helical TomoTherapy system
Improved method for measuring the electric fields in microwave cavity resonators
International Nuclear Information System (INIS)
Amato, J.C.; Herrmann, H.
1985-01-01
The electric field distribution in microwave cavities is commonly measured by frequency perturbation techniques. For many cavity modes which are important in accelerator applications, the standard bead-pulling technique cannot provide adequate discrimination between fields parallel and perpendicular to the particle trajectory, leading to inaccurate and ambiguous results. A method is described which substantially increases the directivity of the measurements. The method has been successfully used to determine the accelerator-related cavity parameters at frequencies up to three times the fundamental resonant frequency
International Nuclear Information System (INIS)
Park, Kyoung-Duck; Park, Doo-Jae; Jeong, Mun-Seok; Choi, Geun-Chang; Lee, Seung-Gol; Byeon, Clare-Chisu; Choi, Soo-Bong
2014-01-01
We report on a successful topographical and optical imaging of various cancer cells in liquid and in air by using a stable wet near-field scanning optical microscope that utilizes a resonance tracking method. We observed a clear dehydration which gives rise to a decrease in the cell volume down to 51%. In addition, a micro-ball lens effect due to the round-shaped young cancer cells was observed from near-field imaging, where the refractive index of young cancer cells was deduced.
Energy Technology Data Exchange (ETDEWEB)
Park, Kyoung-Duck [Sungkyunkwan University, Suwon (Korea, Republic of); Inha University, Incheon (Korea, Republic of); Park, Doo-Jae; Jeong, Mun-Seok [Sungkyunkwan University, Suwon (Korea, Republic of); Choi, Geun-Chang [Seoul National University, Seoul (Korea, Republic of); Lee, Seung-Gol [Inha University, Incheon (Korea, Republic of); Byeon, Clare-Chisu [Kyungpook National University, Daegu (Korea, Republic of); Choi, Soo-Bong [Incheon National University, Incheon (Korea, Republic of)
2014-05-15
We report on a successful topographical and optical imaging of various cancer cells in liquid and in air by using a stable wet near-field scanning optical microscope that utilizes a resonance tracking method. We observed a clear dehydration which gives rise to a decrease in the cell volume down to 51%. In addition, a micro-ball lens effect due to the round-shaped young cancer cells was observed from near-field imaging, where the refractive index of young cancer cells was deduced.
Review of the helicity formalism
International Nuclear Information System (INIS)
Barreiro, F.; Cerrada, M.; Fernandez, E.
1972-01-01
Our purpose in these notes has been to present a brief and general review of the helicity formalism. We begin by discussing Lorentz invariance, spin and helicity ideas, in section 1 . In section 2 we deal with the construction of relativistic states and scattering amplitudes in the helicity basis and we study their transformation properties under discrete symmetries. Finally we present some more sophisticated topics like kinematical singularities of helicity amplitudes, kinematical constraints and crossing relations 3, 4, 5 respectively. (Author) 8 refs
Introduction to the m = 1 helicity source
International Nuclear Information System (INIS)
Platts, D.A.; Jarboe, T.R.; Wright, B.L.
1985-01-01
The m = 1 Helicity Source, formerly called the Kinked Z-pinch, was developed as part of the Electrode Studies program at Los Alamos. The Electrode Studies program was initiated to study the control of electrode erosion in long discharge duration spheromak sources. Erosion control is necessary to reduce plasma impurities and to obtain adequate electrode lifetimes. The first task of the Electrode Studies program is to determine, from among a variety of configurations including the coaxial one, a helicity source geometry with good prospects for erosion control. The more efficient the helicity source the easier it will be to control erosion, but the source most also be easy to diagnose and modify if it is to be a useful test bed. The various erosion control techniques which have been proposed will require extensive experimentation to evaluate and optimize. Proposed techniques include, using refractory metals, profiling of the electrodes and magnetic fields, and various gas injection schemes including porous electrodes. It is considered necessary to do these experiments on an optimized helicity source so that the electrode geometries and plasma properties will be relevant. Therefore the present Electrode Studies program is aimed at developing an improved helicity source design
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.
International Nuclear Information System (INIS)
Boyanovsky, D.; Holman, R.; Hutasoit, Jimmy A.
2009-01-01
Motivated by slow-roll inflationary cosmology we study a scalar unparticle weakly coupled to a Higgs field in the broken symmetry phase. The mixing between the unparticle and the Higgs field results in a seesaw type matrix and the mixing angles feature a Mikheyev-Smirnov-Wolfenstein (MSW) effect as a consequence of the unparticle field being noncanonical. We find two (MSW) resonances for small and large spacelike momenta. The unparticlelike mode features a nearly flat potential with spinodal instabilities and a large expectation value. An effective potential for the unparticlelike field is generated from the Higgs potential, but with couplings suppressed by a large power of the small seesaw ratio. The dispersion relation for the Higgs-like mode features an imaginary part even at ''tree level'' as a consequence of the fact that the unparticle field describes a multiparticle continuum. Mixed unparticle-Higgs propagators reveal the possibility of oscillations, albeit with short coherence lengths. The results are generalized to the case in which the unparticle features a mass gap, in which case a low energy MSW resonance may occur for lightlike momenta depending on the scales. Unparticle-Higgs mixing leads to an effective unparticle potential of the new-inflation form. Slow-roll variables are suppressed by seesaw ratios and the anomalous dimensions and favor a red spectrum of scalar perturbations consistent with cosmic microwave background data.
Boyanovsky, D.; Holman, R.; Hutasoit, Jimmy A.
2009-04-01
Motivated by slow-roll inflationary cosmology we study a scalar unparticle weakly coupled to a Higgs field in the broken symmetry phase. The mixing between the unparticle and the Higgs field results in a seesaw type matrix and the mixing angles feature a Mikheyev-Smirnov-Wolfenstein (MSW) effect as a consequence of the unparticle field being noncanonical. We find two (MSW) resonances for small and large spacelike momenta. The unparticlelike mode features a nearly flat potential with spinodal instabilities and a large expectation value. An effective potential for the unparticlelike field is generated from the Higgs potential, but with couplings suppressed by a large power of the small seesaw ratio. The dispersion relation for the Higgs-like mode features an imaginary part even at “tree level” as a consequence of the fact that the unparticle field describes a multiparticle continuum. Mixed unparticle-Higgs propagators reveal the possibility of oscillations, albeit with short coherence lengths. The results are generalized to the case in which the unparticle features a mass gap, in which case a low energy MSW resonance may occur for lightlike momenta depending on the scales. Unparticle-Higgs mixing leads to an effective unparticle potential of the new-inflation form. Slow-roll variables are suppressed by seesaw ratios and the anomalous dimensions and favor a red spectrum of scalar perturbations consistent with cosmic microwave background data.
Single-superfield helical-phase inflation
Energy Technology Data Exchange (ETDEWEB)
Ketov, Sergei V., E-mail: ketov@tmu.ac.jp [Department of Physics, Tokyo Metropolitan University, Minami-ohsawa 1-1, Hachioji-shi, Tokyo 192-0397 (Japan); Kavli Institute for the Physics and Mathematics of the Universe (IPMU), The University of Tokyo, Chiba 277-8568 (Japan); Institute of Physics and Technology, Tomsk Polytechnic University, 30 Lenin Ave., Tomsk 634050 (Russian Federation); Terada, Takahiro, E-mail: takahiro@hep-th.phys.s.u-tokyo.ac.jp [Department of Physics, The University of Tokyo, Tokyo 113-0033 (Japan); Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg (Germany)
2016-01-10
Large-field inflation in supergravity requires the approximate global symmetry needed to protect flatness of the scalar potential. In helical-phase inflation, the U(1) symmetry of the Kähler potential is assumed, the phase part of the complex scalar of a chiral superfield plays the role of inflaton, and the radial part is strongly stabilized. The original model of helical phase inflation, proposed by Li, Li and Nanopoulos (LLN), employs an extra (stabilizer) superfield. We propose a more economical new class of the helical phase inflationary models without a stabilizer superfield. As the specific examples, the quadratic, the natural, and the Starobinsky-type inflationary models are studied in our approach.
Field and frequency modulated sub-THz electron spin resonance spectrometer
Directory of Open Access Journals (Sweden)
Christian Caspers
2016-05-01
Full Text Available 260-GHz radiation is used for a quasi-optical electron spin resonance (ESR spectrometer which features both field and frequency modulation. Free space propagation is used to implement Martin-Puplett interferometry with quasi-optical isolation, mirror beam focusing, and electronic polarization control. Computer-aided design and polarization pathway simulation lead to the design of a compact interferometer, featuring lateral dimensions less than a foot and high mechanical stability, with all components rated for power levels of several Watts suitable for gyrotron radiation. Benchmark results were obtained with ESR standards (BDPA, DPPH using field modulation. Original high-field ESR of 4f electrons in Sm3+-doped Ceria was detected using frequency modulation. Distinct combinations of field and modulation frequency reach a signal-to-noise ratio of 35 dB in spectra of BDPA, corresponding to a detection limit of about 1014 spins.
Turbulent Helicity in the Atmospheric Boundary Layer
Chkhetiani, Otto G.; Kurgansky, Michael V.; Vazaeva, Natalia V.
2018-05-01
We consider the assumption postulated by Deusebio and Lindborg (J Fluid Mech 755:654-671, 2014) that the helicity injected into the Ekman boundary layer undergoes a cascade, with preservation of its sign (right- or alternatively left-handedness), which is a signature of the system rotation, from large to small scales, down to the Kolmogorov microscale of turbulence. At the same time, recent direct field measurements of turbulent helicity in the steppe region of southern Russia near Tsimlyansk Reservoir show the opposite sign of helicity from that expected. A possible explanation for this phenomenon may be the joint action of different scales of atmospheric flows within the boundary layer, including the sea-breeze circulation over the test site. In this regard, we consider a superposition of the classic Ekman spiral solution and Prandtl's jet-like slope-wind profile to describe the planetary boundary-layer wind structure. The latter solution mimics a hydrostatic shallow breeze circulation over a non-uniformly heated surface. A 180°-wide sector on the hodograph plane exists, within which the relative orientation of the Ekman and Prandtl velocity profiles favours the left rotation with height of the resulting wind velocity vector in the lowermost part of the boundary layer. This explains the negative (left-handed) helicity cascade toward small-scale turbulent motions, which agrees with the direct field measurements of turbulent helicity in Tsimlyansk. A simple turbulent relaxation model is proposed that explains the measured positive values of the relatively minor contribution to turbulent helicity from the vertical components of velocity and vorticity.
Energy Technology Data Exchange (ETDEWEB)
Wang Shumin; Duyn, Jeff H [Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive, 10/B1D728, Bethesda, MD 20892 (United States)
2006-06-21
We present the combined field integral equation (CFIE) method for analysing radio-frequency coil arrays in high-field magnetic resonance imaging (MRI). Three-dimensional models of coils and the human body were used to take into account the electromagnetic coupling. In the method of moments formulation, we applied triangular patches and the Rao-Wilton-Glisson basis functions to model arbitrarily shaped geometries. We first examined a rectangular loop coil to verify the CFIE method and also demonstrate its efficiency and accuracy. We then studied several eight-channel receive-only head coil arrays for 7.0 T SENSE functional MRI. Numerical results show that the signal dropout and the average SNR are two major concerns in SENSE coil array design. A good design should be a balance of these two factors.
Chzhan, Michael; Kuppusamy, Periannan; Samouilov, Alexandre; He, Guanglong; Zweier, Jay L.
1999-04-01
There has been a need for development of microwave resonator designs optimized to provide high sensitivity and high stability for EPR spectroscopy and imaging measurements ofin vivosystems. The design and construction of a novel reentrant resonator with transversely oriented electric field (TERR) and rectangular sample opening cross section for EPR spectroscopy and imaging ofin vivobiological samples, such as the whole body of mice and rats, is described. This design with its transversely oriented capacitive element enables wide and simple setting of the center frequency by trimming the dimensions of the capacitive plate over the range 100-900 MHz with unloadedQvalues of approximately 1100 at 750 MHz, while the mechanical adjustment mechanism allows smooth continuous frequency tuning in the range ±50 MHz. This orientation of the capacitive element limits the electric field based loss of resonatorQobserved with large lossy samples, and it facilitates the use of capacitive coupling. Both microwave performance data and EPR measurements of aqueous samples demonstrate high sensitivity and stability of the design, which make it well suited forin vivoapplications.
INTRODUCTION One proposed mechanism of action of electromagnetic fields (EMFs) on biological systems is the Ion Parametric Resonance (IPR) model, which has been experimentally validated in neuronal PC-12 cells [1, 2]. It proposes that when applied EMFs are tuned to resonate with...
Directory of Open Access Journals (Sweden)
Agustín Leobardo Herrera-May
2016-08-01
Full Text Available Microelectromechanical systems (MEMS resonators have allowed the development of magnetic field sensors with potential applications such as biomedicine, automotive industry, navigation systems, space satellites, telecommunications and non-destructive testing. We present a review of recent magnetic field sensors based on MEMS resonators, which operate with Lorentz force. These sensors have a compact structure, wide measurement range, low energy consumption, high sensitivity and suitable performance. The design methodology, simulation tools, damping sources, sensing techniques and future applications of magnetic field sensors are discussed. The design process is fundamental in achieving correct selection of the operation principle, sensing technique, materials, fabrication process and readout systems of the sensors. In addition, the description of the main sensing systems and challenges of the MEMS sensors are discussed. To develop the best devices, researches of their mechanical reliability, vacuum packaging, design optimization and temperature compensation circuits are needed. Future applications will require multifunctional sensors for monitoring several physical parameters (e.g., magnetic field, acceleration, angular ratio, humidity, temperature and gases.
Least Squares Magnetic-Field Optimization for Portable Nuclear Magnetic Resonance Magnet Design
International Nuclear Information System (INIS)
Paulsen, Jeffrey L; Franck, John; Demas, Vasiliki; Bouchard, Louis-S.
2008-01-01
Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum in a cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16,100 ppm across a 1.9 cc volume located 1.5 cm above the top of the magnets and homogeneous to 32,200 ppm over a 7.6 cc volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable 'sensitive volumes'
Kovalev, A S
2002-01-01
The resonance activation of eigenmodes for a finite 2D easy-plane ferromagnet is considered to treat theoretically by the vortex switching in magnetic nanodots due to the action of external circular magnetic field. It is shown analytically that if the anisotropy is weak, i.e. the vortex has a nonzero polarity (total magnization along the z-axis), the process of the field action has a complicated nature. The circular field acts in a resonance way upon azimuthal system eigenmodes, in which magnetization depends on the azimuthal coordinate (as a direct resonance at the eigenfrequencies of these modes). The interaction of the azimuthal and symmetric modes (in which the magnetization does not depend on the azimuthal coordinate) via the applied field gives rise to complex parametric resonance at multifrequencies. The results obtained are compared with the data of previous numerical calculations.
Internal additive noise effects in stochastic resonance using organic field effect transistor
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Yoshiharu; Asakawa, Naoki [Division of Molecular Science, Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan); Matsubara, Kiyohiko [KOOROGI LLC, 6-1585-1-B Sakaino-cho, Kiryu, Gunma 376-0002 (Japan)
2016-08-29
Stochastic resonance phenomenon was observed in organic field effect transistor using poly(3-hexylthiophene), which enhances performance of signal transmission with application of noise. The enhancement of correlation coefficient between the input and output signals was low, and the variation of correlation coefficient was not remarkable with respect to the intensity of external noise, which was due to the existence of internal additive noise following the nonlinear threshold response. In other words, internal additive noise plays a positive role on the capability of approximately constant signal transmission regardless of noise intensity, which can be said “homeostatic” behavior or “noise robustness” against external noise. Furthermore, internal additive noise causes emergence of the stochastic resonance effect even on the threshold unit without internal additive noise on which the correlation coefficient usually decreases monotonically.
Near resonant absorption by atoms in intense, fluctuating fields: [Progress report
International Nuclear Information System (INIS)
1989-01-01
During the present grant period preparations for photon echo studies of the role of phase fluctuations of an optical driving field resonant with the 1 S 0 - 3 P 1 transition in 174 Yb are moving forward. This experimental study emphasizes the role of fluctuations as a decorrelating mechanism on a phased array of excited atoms. Improvements in laser stabilization and in the quality of the fluctuation spectrum have been carried out and the first spectroscopic measurements will be carried out during this grant year. In response to an important recent theoretical study we have also applied the phase fluctuation synthesizing capability to the study of the atomic sodium resonance fluorescence line profile, driven by a phase fluctuating laser. The measured fluctuations in the fluorescence, characterized in terms of the standard deviation of the fluorescence intensity, have an unexpected and strong dependence on detuning of the driving laser
Collisional approach to dynamics of resonance atomic states in an external field
International Nuclear Information System (INIS)
Urnov, A.M.; Uskov, D.B.
1993-01-01
The following aspects of the dynamics of an atomic state in an external stationary field are assessed: (i) the rearrangement problem; (ii) the description of the appropriate final-channel wavefunctions; (iii) the analytical properties of the transition amplitude into the continuum. The rearrangement problem was solved by the introduction of the effective Hamiltonian, the eigenstates of which include both the initial state and final states ('modified states of continuum spectrum' MSCS) which describe the potential part of the exact wavefunction of the scattering problem. It is shown that the amplitude of decay and transition into MSCS as functions of time have an exact representation as a sum of resonance terms defined by a set of resonance states and the matrix elements of the shift R-matrix operator. (author)
International Nuclear Information System (INIS)
Sushilov, N.V.; Kholodkevich, E.D.
1995-01-01
An analytical expression is derived for the polarization induced by a weak probe field with periodically modulated amplitude in a two-level medium saturated by a strong amplitude-and phase-modulated resonance field. It is shown that the absorption spectrum of the probe field includes parametric resonances, the maxima corresponding to the condition δ= 2nΓ-Ω w and the minima to that of δ= (2n + 1)Γ- w , where δ is the probe-field detuning front the resonance frequency, Ω w is the modulation frequency of the probe-field amplitude, and Γ is the transition line width, n = 1, 2, 3, hor-ellipsis. At the specific modulation parameters, a substantial region of negative values (i.e., the region of amplification without the population inversion) exists in the absorption spectrum of the probe field
Anderson, David A.; Paradis, Eric G.; Raithel, Georg
2018-01-01
We present a hybrid atomic sensor that realizes radio-frequency electric field detection with intrinsic field amplification and polarization selectivity for robust high-sensitivity field measurement. The hybrid sensor incorporates a passive resonator element integrated with an atomic vapor cell that provides amplification and polarization selectivity for detection of incident radio-frequency fields. The amplified intra-cavity radio-frequency field is measured by atoms using a quantum-optical ...
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.
Energy fluxes in helical magnetohydrodynamics and dynamo action
Indian Academy of Sciences (India)
Kinetic and magnetic helicities do not affect the renormalized parameters, ... Generation of magnetic field in plasma, usually referred to as 'dynamo', is one of the ..... energy fluxes for the inertial-range wave numbers where the same power.
Field-aligned plasma-potential structure formed by local electron cyclotron resonance
International Nuclear Information System (INIS)
Hatakeyama, Rikizo; Kaneko, Toshiro; Sato, Noriyoshi
2001-01-01
The significance of basic experiments on field-aligned plasma-potential structure formed by local electron cyclotron resonance (ECR) is claimed based on the historical development of the investigation on electric double layer and electrostatic potential confinement of open-ended fusion-oriented plasmas. In the presence of a single ECR point in simple mirror-type configurations of magnetic field, a potential dip (thermal barrier) appears around this point, being followed by a subsequent potential hump (plug potential) along a collisionless plasma flow. The observed phenomenon gives a clear-cut physics to the formation of field-aligned plug potential with thermal barrier, which is closely related to the double layer formation triggered by a negative dip. (author)
Directory of Open Access Journals (Sweden)
Fenglong Wang
2016-11-01
Full Text Available Herein, we experimentally investigate the effect of temperature on the electric field tunable ferromagnetic resonance (FMR in a ferroelectric/ferromagnetic heterostructure, and demonstrate the tuning of abnormal change in FMR using the polarization of the ferroelectric layer above 200 K. The FMR was found to be almost unchanged under different electric field strength at 100 K owing to frozen polarization, which causes extremely weak magnetoelectric coupling. More interestingly, negative effective linewidth was observed when an electric field greater than 10 kV/cm was applied above 220 K. The simultaneous electrical control of magnetization and its damping via FMR based on linear magnetoelectric coupling are directly relevant to use of composite multiferroics for a wide range of devices.
Bongers, Suzan|info:eu-repo/dai/nl/313874050; Christopher, Yvette|info:eu-repo/dai/nl/27590184X; Engels, Hans; Slottje, Pauline|info:eu-repo/dai/nl/299345351; Kromhout, Hans|info:eu-repo/dai/nl/074385224
2014-01-01
At present, the relationship between chronic exposure to static magnetic fields (SMF) and health effects is unclear. We developed a task-based deterministic model for estimating historical electromagnetic field exposure from the static B-field (B0) of magnetic resonance imaging (MRI) systems, for a
Stimuli-Directed Helical Chirality Inversion and Bio-Applications
Directory of Open Access Journals (Sweden)
Ziyu Lv
2016-08-01
Full Text Available Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for helical polymeric materials, is how to design smart systems with controllable helical chirality, and further use them to develop chiral functional materials and promote their applications in biology, biochemistry, medicine, and nanotechnology fields. This review summarizes the recent progress in the development of high-performance systems with tunable helical chirality on receiving external stimuli and discusses advances in their applications as drug delivery vesicles, sensors, molecular switches, and liquid crystals. Challenges and opportunities in this emerging area are also presented in the conclusion.
Coulomb double helical structure
Kamimura, Tetsuo; Ishihara, Osamu
2012-01-01
Structures of Coulomb clusters formed by dust particles in a plasma are studied by numerical simulation. Our study reveals the presence of various types of self-organized structures of a cluster confined in a prolate spheroidal electrostatic potential. The stable configurations depend on a prolateness parameter for the confining potential as well as on the number of dust particles in a cluster. One-dimensional string, two-dimensional zigzag structure and three-dimensional double helical structure are found as a result of the transition controlled by the prolateness parameter. The formation of stable double helical structures resulted from the transition associated with the instability of angular perturbations on double strings. Analytical perturbation study supports the findings of numerical simulations.
International Nuclear Information System (INIS)
Bennati, Marina; Prisner, Thomas F
2005-01-01
Recent developments in microwave technologies have led to a renaissance of electron paramagnetic resonance (EPR) due to the implementation of new spectrometers operating at frequencies ≥90 GHz. EPR at high fields and high frequencies (HF-EPR) has been established up to THz (very high frequency (VHF) EPR) in continuous wave (cw) operation and up to about 300 GHz in pulsed operation. To date, its most prominent application field is structural biology. This review article first gives an overview of the theoretical basics and the technical aspects of HF-EPR methodologies, such as cw and pulsed HF-EPR, as well as electron nuclear double resonance at high fields (HF-ENDOR). In the second part, the article illustrates different application areas of HF-EPR in studies of protein structure and function. In particular, HF-EPR has delivered essential contributions to disentangling complex spectra of radical cofactors or reaction intermediates in photosynthetic reaction centres, radical enzymes (such as ribonucleotide reductase) and in metalloproteins. Furthermore, HF-EPR combined with site-directed spin labelling in membranes and soluble proteins provides new methods of investigating complex molecular dynamics and intermolecular distances
Monte Carlo simulation study of ICRF minority heating in the large helical device
International Nuclear Information System (INIS)
Murakami, S.; Okamoto, M.; Ohnishi, M.; Okada, H.
1994-01-01
A Monte Carlo simulation code is developed for ion cyclotron range of frequencies (ICRF) heating in helical systems, which takes into account finite beta effects, complicated orbits of high energetic particles, Coulomb collisions and interactions between particles and the applied waves. The code is used to investigate ICRF minority heating in the Large Helical Device (LHD). The configuration of the magnetic fields changes significantly due to finite beta effects in the LHD. The resonance layer position is found to be crucial to the heating efficiency as the plasma beta increases. When the strength of the resonance magnetic field is set to the value at the magnetic axis, a higher heat efficiency is obtained and no clear difference of the heat efficiency due to finite beta effects is found in the high ICRF wave power region. However, the radial profile of the power transferred to majority ions and electrons from minority ions changes because of the deformation of the trapped particle due to the finite beta effects. The heat efficiency is improved if the radial electric field, E r , is positive (E r is directed radially outward) and it is also improved by supplying 3 He minority ions rather than proton minority ions. (author). 26 refs, 11 figs, 2 tabs
Resonant shallow donor magnetopolaron effect in a GaAs/AlGaAs quantum dot in high magnetic fields
International Nuclear Information System (INIS)
Zhu Kadi.
1993-11-01
Resonant shallow donor magnetopolaron effect in a GaAs/AlGaAs quantum dot in high magnetic fields is investigated by the variational treatment. It is shown that both the cyclotron resonant frequency ω * c+ due to the 1s-p+ hydrogenic transition and the cyclotron resonant frequency ω * c- due to the 1s-p - hydrogenic transition increase with the decrease of the dot size. The cyclotron resonant frequency ω * c+ is always larger than the bulk LO-phonon frequency ω LO , while the cyclotron resonant frequency ω * c- is lower than ω LO for larger quantum dots (l 0 > 2.0.r 0 , r 0 is the polaron radius). The results also show that the Coulomb interaction effect on the resonant frequencies is significant. (author). 26 refs, 3 figs
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.
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.
Functional magnetic resonance imaging of the frontal eye fields during saccadic eye movements
International Nuclear Information System (INIS)
Miki, Atsushi; Takagi, Mineo; Abe, Haruki; Nakajima, Takashi; Miyauchi, Satoru.
1996-01-01
We evaluated activity-induced signal intensity changes in the human cerebral cortex during horizontal saccadic eye movements using functional magnetic resonance imaging (fMRI) based on the blood-oxygenation-level-dependent (BOLD) contrast method. Compared with central fixation, significant signal increases were observed bilaterally in the middle frontal gyrus (Brodmann area 8) during saccadic conditions. The location of the activated area was consistent with that of previously reported frontal eye fields (FEF). These results suggest that fMRI has potential merit for the study of cortical control of eye movements in humans. (author)
Zero-range effective field theory for resonant wino dark matter. Part III. Annihilation effects
Braaten, Eric; Johnson, Evan; Zhang, Hong
2018-01-01
Near a critical value of the wino mass where there is a zero-energy S-wave resonance at the neutral-wino-pair threshold, low-energy winos can be described by a zero-range effective field theory (ZREFT) in which the winos interact nonperturbatively through a contact interaction and through Coulomb interactions. The effects of wino-pair annihilation into electroweak gauge bosons are taken into account through the analytic continuation of the real parameters for the contact interaction to comple...
DEFF Research Database (Denmark)
Göksu, Cihan; Scheffler, Klaus; Ehses, Philipp
2017-01-01
Purpose: Clinical use of magnetic resonance electrical impedance tomography (MREIT) still requires significant sensitivity improvements. Here, the measurement of the current-induced magnetic field (DBz,c) is improved using systematic efficiency analyses and optimization of multi-echo spin echo...... (MESE) and steady-state free precession free induction decay (SSFP-FID) sequences. Theory and Methods: Considering T1, T2, and T 2 relaxation in the signal-to-noise ratios (SNRs) of the MR magnitude images, the efficiency of MESE and SSFP-FID MREIT experiments, and its dependence on the sequence...
Energy Technology Data Exchange (ETDEWEB)
Xu, Ling-Fang; Feng, Xing; Sun, Kang; Liang, Ze-Yu; Xu, Qian; Liang, Jia-Yu; Yang, Chang-Ping [Hubei University, Hubei Key Laboratory of Ferro and Piezoelectric Materials and Devices, Faculty of Physics and Electronic Science, Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Wuhan (China)
2017-07-15
Sandwich magnetoelectric composites of PZT/NFO/PZT (PNP) have been prepared by laminating PZT5, NiFe{sub 2}O{sub 4}, and PZT5 ceramics in turn with polyvinyl alcohol (PVA) paste. A systematic study of structural, magnetic and ferroelectric properties is undertaken. Structural studies carried out by X-ray diffraction indicate formation of cubic perovskite phase of PZT5 ceramic and cubic spinel phase of NiFe{sub 2}O{sub 4} ceramic. As increasing the content of PZT5 phase, ferroelectric loops and magnetic loops of PNP composites showed increasing remnant electric polarizations and decreasing remnant magnetic moments separately. Both external magnetic fields and bias voltages could regulate the basal radial resonance frequency of the composites, which should be originated with the transformation and coupling of the stress between the piezoelectric phase and magnetostrictive phase. Such magnetoelectric composite provides great opportunities for electrostatically tunable devices. (orig.)
Topology of helical fluid flow
DEFF Research Database (Denmark)
Andersen, Morten; Brøns, Morten
2014-01-01
function for the topology of the streamline pattern in incompressible flows. On this basis, we perform a comprehensive study of the topology of the flow field generated by a helical vortex filament in an ideal fluid. The classical expression for the stream function obtained by Hardin (Hardin, J. C. 1982...... the zeroes of a single real function of one variable, and we show that three different flow topologies can occur, depending on a single dimensionless parameter. By including the self-induced velocity on the vortex filament by a localised induction approximation, the stream function is slightly modified...... and an extra parameter is introduced. In this setting two new flow topologies arise, but not more than two critical points occur for any combination of parameters....
The quantum Hall effect helicity
Energy Technology Data Exchange (ETDEWEB)
Shrivastava, Keshav N., E-mail: keshav1001@yahoo.com [Department of Physics, University of Malaya, Kuala Lumpur 50603 (Malaysia); School of Physics, University of Hyderabad, Hyderabad 500046 (India)
2015-04-16
The quantum Hall effect in semiconductor heterostructures is explained by two signs in the angular momentum j=l±s and g=(2j+1)/(2l+1) along with the Landau factor (n+1/2). These modifications in the existing theories explain all of the fractional charges. The helicity which is the sign of the product of the linear momentum with the spin p.s plays an important role for the understanding of the data at high magnetic fields. In particular it is found that particles with positive sign in the spin move in one direction and those with negative sign move in another direction which explains the up and down stream motion of the particles.
International Nuclear Information System (INIS)
Takahashi, Minoru; Momozaki, Yoichi
2000-01-01
For the reduction of a large magneto-hydrodynamic (MHD) pressure drop of a liquid metal single-phase flow, a liquid metal two-phase flow cooling system has been proposed. As a fundamental study, MHD pressure drops and heat transfer characteristics of a mercury single-phase flow and an air-mercury two-phase flow were experimentally investigated. A strong transverse magnetic field relevant to the fusion reactor conditions was applied to the mercury single-phase flow and the air-mercury two-phase flow in a helically coiled tube that was inserted in the vertical bore of a solenoidal superconducting magnet. It was found that MHD pressure drops of a mercury single-phase flow in the helically coiled tube were nearly equal to those in a straight tube. The Nusselt number at an outside wall was higher than that at an inside wall both in the mercury single-phase flow in the absence and presence of a magnetic field. The Nusselt number of the mercury single-phase flow decreased, increased and again decreased with an increase in the magnetic flux density. MHD pressure drops did not decrease appreciably by injecting air into a mercury flow and changing the mercury flow into the air-mercury two-phase flow. Remarkable heat transfer enhancement did not appear by the air injection. The injection of air into the mercury flow enhanced heat transfer in the ranges of high mercury flow rate and low magnetic flux density, possibly due to the agitation effect of air bubbles. The air injection deteriorated heat transfer in the range of low mercury flow rates possibly because of the occupation of air near heating wall
Xiao, W W; Evans, T E; Tynan, G R; Yoon, S W; Jeon, Y M; Ko, W H; Nam, Y U; Oh, Y K
2017-11-17
The propagation dynamics of resonant magnetic perturbation fields in KSTAR H-mode plasmas with injection of small edge perturbations produced by a supersonic molecular beam injection is reported for the first time. The results show that the perturbation field first excites a plasma response on the q=3 magnetic surface and then propagates inward to the q=2 surface with a radially averaged propagation velocity of resonant magnetic perturbations field equal to 32.5 m/ s. As a result, the perturbation field brakes the toroidal rotation on the q=3 surface first causing a momentum transport perturbation that propagates both inward and outward. A higher density fluctuation level is observed. The propagation velocity of the resonant magnetic perturbations field is larger than the radial propagation velocity of the perturbation in the toroidal rotation.
Field emission studies of silver nanoparticles synthesized by electron cyclotron resonance plasma
International Nuclear Information System (INIS)
Purohit, Vishwas; Mazumder, Baishakhi; Bhise, A.B.; Poddar, Pankaj; Joag, D.S.; Bhoraskar, S.V.
2011-01-01
Field emission has been studied for silver nanoparticles (25-200 nm), deposited within a cylindrical silver target in an electron cyclotron resonance (ECR) plasma. Particle size distribution was controlled by optimum biasing voltages between the chamber and the target. Presence of non-oxidized silver was confirmed from the X-Ray diffraction analysis; however, thin protective layer of oxide was identified from the selective area electron diffraction pattern obtained with transmission electron microscopy. The silver nanoparticles were seen to exhibit hilly pointed like structures when viewed under the atomic force microscopy (AFM). The emissive properties of these particles were investigated by field emission microscopy. It is found that this technique of deposition is ideal for formation of nanoparticles films on different substrate geometries with size controllability as well as its application to emission devices.
Resonant Wave Energy Converters: Small-scale field experiments and first full-scale prototype
International Nuclear Information System (INIS)
Arena, Felice; Fiamma, Vincenzo; Iannolo, Roberto; Laface, Valentina; Malara, Giovanni; Romolo, Alessandra; Strati Federica Maria
2015-01-01
The Resonant Wave Energy Converter 3 (REWEC3) is a device belonging to the family of Oscillating Water Columns (OWCs), that can convert the energy of incident waves into electrical energy via turbines. In contrast to classical OWCs, it incorporates a small vertical U-shaped duct to connect the water column to the open wave field. This article shows the results of a small-scale field experiment involving a REWEC3 designed for working with a 2 kW turbine. Then, the next experimental activity on a REWEC3 installed in the NOEL laboratory with the collaboration of ENEA, is presented. Finally, the first prototype of ReWEC3 under construction in Civitavecchia (Rome, Italy) is shown. The crucial features of the construction stage are discussed and some initial performances are provided. [it
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-09-01
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.
International Nuclear Information System (INIS)
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-01-01
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems
Reconstruction of an acoustic pressure field in a resonance tube by particle image velocimetry.
Kuzuu, K; Hasegawa, S
2015-11-01
A technique for estimating an acoustic field in a resonance tube is suggested. The estimation of an acoustic field in a resonance tube is important for the development of the thermoacoustic engine, and can be conducted employing two sensors to measure pressure. While this measurement technique is known as the two-sensor method, care needs to be taken with the location of pressure sensors when conducting pressure measurements. In the present study, particle image velocimetry (PIV) is employed instead of a pressure measurement by a sensor, and two-dimensional velocity vector images are extracted as sequential data from only a one- time recording made by a video camera of PIV. The spatial velocity amplitude is obtained from those images, and a pressure distribution is calculated from velocity amplitudes at two points by extending the equations derived for the two-sensor method. By means of this method, problems relating to the locations and calibrations of multiple pressure sensors are avoided. Furthermore, to verify the accuracy of the present method, the experiments are conducted employing the conventional two-sensor method and laser Doppler velocimetry (LDV). Then, results by the proposed method are compared with those obtained with the two-sensor method and LDV.
Experimental benchmarking of quantum control in zero-field nuclear magnetic resonance.
Jiang, Min; Wu, Teng; Blanchard, John W; Feng, Guanru; Peng, Xinhua; Budker, Dmitry
2018-06-01
Demonstration of coherent control and characterization of the control fidelity is important for the development of quantum architectures such as nuclear magnetic resonance (NMR). We introduce an experimental approach to realize universal quantum control, and benchmarking thereof, in zero-field NMR, an analog of conventional high-field NMR that features less-constrained spin dynamics. We design a composite pulse technique for both arbitrary one-spin rotations and a two-spin controlled-not (CNOT) gate in a heteronuclear two-spin system at zero field, which experimentally demonstrates universal quantum control in such a system. Moreover, using quantum information-inspired randomized benchmarking and partial quantum process tomography, we evaluate the quality of the control, achieving single-spin control for 13 C with an average fidelity of 0.9960(2) and two-spin control via a CNOT gate with a fidelity of 0.9877(2). Our method can also be extended to more general multispin heteronuclear systems at zero field. The realization of universal quantum control in zero-field NMR is important for quantum state/coherence preparation, pulse sequence design, and is an essential step toward applications to materials science, chemical analysis, and fundamental physics.
Wang, Chang; Qin, Xin; Liu, Yan; Zhang, Wenchao
2016-06-01
An adaptive inertia weight particle swarm algorithm is proposed in this study to solve the local optimal problem with the method of traditional particle swarm optimization in the process of estimating magnetic resonance(MR)image bias field.An indicator measuring the degree of premature convergence was designed for the defect of traditional particle swarm optimization algorithm.The inertia weight was adjusted adaptively based on this indicator to ensure particle swarm to be optimized globally and to avoid it from falling into local optimum.The Legendre polynomial was used to fit bias field,the polynomial parameters were optimized globally,and finally the bias field was estimated and corrected.Compared to those with the improved entropy minimum algorithm,the entropy of corrected image was smaller and the estimated bias field was more accurate in this study.Then the corrected image was segmented and the segmentation accuracy obtained in this research was 10% higher than that with improved entropy minimum algorithm.This algorithm can be applied to the correction of MR image bias field.
Directory of Open Access Journals (Sweden)
Karen Falke
Full Text Available PURPOSE: The case reports presented here were compiled to demonstrate the potential for improved diagnosis and monitoring of disease progress of intraocular lesions using ultrahigh-field magnetic resonance microscopy (MRM at 7.1 Tesla. METHODS: High-resolution ex vivo ocular magnetic resonance (MR images were acquired on an ultrahigh-field MR system (7.1 Tesla, ClinScan, Bruker BioScan, Germany using a 2-channel coil with 4 coil elements and T2-weighted turbo spin echo (TSE sequences of human eyes enucleated because of different intraocular lesions. Imaging parameters were: 40×40 mm field of view, 512×512 matrix, and 700 µm slice thickness. The results were correlated with in vivo ultrasound and histology of the enucleated eyes. RESULTS: Imaging was performed in enucleated eyes with choroidal melanoma, malignant melanoma of iris and ciliary body with scleral perforation, ciliary body melanoma, intraocular metastasis of esophageal cancer, subretinal bleeding in the presence of perforated corneal ulcer, hemorrhagic choroidal detachment, and premature retinopathy with phthisis and ossification of bulbar structures. MR imaging allowed differentiation between solid and cystic tumor components. In case of hemorrhage, fluid-fluid levels were identified. Melanin and calcifications caused significant hypointensity. Microstructural features of eye lesions identified by MRM were confirmed by histology. CONCLUSION: This study demonstrates the potential of MRM for the visualization and differential diagnosis of intraocular lesions. At present, the narrow bore of the magnet still limits the use of this technology in humans in vivo. Further advances in ultrahigh-field MR imaging will permit visualization of tumor extent and evaluation of nonclassified intraocular structures in the near future.
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.
Plasmoid behavior in helical plasmas
International Nuclear Information System (INIS)
Ishizaki, R.; Nakajima, N.
2009-01-01
Full text: It is well known that an ablation cloud; a high density and low temperature plasmoid, drifts to the lower field side in tokamak plasmas, which leads to a good performance on fueling in tokamak. Such a good performance, however, has not been obtained yet in the planar axis heliotron; Large Helical Device (LHD) experiments, even if a pellet has been injected from the high field side. The purpose of the study is to clarify the difference on the plasmoid motion between tokamak and LHD plasmas by using the MHD simulation including ablation processes. It is found in tokamaks that the drift motion is induced by a tire tube force and 1/R force in the major radius direction, and that the pressure and density of the plasmoid have oscillation due to fast compressional Alfven wave. On the other hand, the upper and lower portions surrounding the plasmoid center drift to the higher field side, because 1/R force by magnetic field becomes negative in the major radius direction since the magnetic field surrounding the plasmoid is accumulated by the extremely large ablation pressure and the magnetic pressure perturbation becomes positive. It is also found that the plasmoid does not drift when the perturbation of the plasmoid is small. In addition, the motion of the plasmoid is investigated in LHD plasmas in four cases that the plasmoids are initially located at the inner and outer sides of the torus on the vertically and horizontally elongated poloidal cross sections. The plasmoids drift to the lower field sides in all cases. However, in the case that it is located at the inner side of the torus on the horizontally elongated poloidal cross section, it is found that the plasmoid drifts in the negative direction of the major radius and subsequently drifts in the positive direction of it. In other words, the plasmoid finally drifts in the positive direction of the major radius the same as the plasmoid located at the outer side of the torus. This fact might be one of the
International Nuclear Information System (INIS)
Yamazaki, K.; Yamada, I.; Taniguchi, S.; Oishi, T.
2009-01-01
Full text: The high performance plasma behavior is required to realize economic and environmental-friendly fusion reactors compatible with conventional power plant systems. To improve plasma confinement, the formation of internal transport barrier (ITB) is anticipated, and its behavior is analyzed by the simulation code TOTAL (Toroidal Transport Linkage Analysis). This TOTAL code comprises a 2- or 3-dimensional equilibrium and 1-dimensional predictive transport code for both tokamak and helical systems. In the tokamak code TOTAL-T, the external current drive, bootstrap current, sawtooth oscillation, ballooning mode and neoclassical tearing mode (NTM) analyses are included. The steady-state burning plasma operation is achieved by the feedback control of pellet injection fuelling and external heating power control. The impurity dynamics of iron and tungsten is also included in this code. The NTM effects are evaluated using the modified Rutherford Model with the stabilization of the ECCD current drive. The excitation of m=2/n=1 NTM leads to the 20 % reduction in the central temperature in ITER-like reactors. Recently, the external non-resonant helical field application is analyzed and its stabilization properties are evaluated. The pellet injection effects on ITB formation is also clarified in tokamak and helical plasmas. Relationship between sawtooth oscillation and impurity ejection is recently simulated in comparison with experimental data. In this conference, we will show above-stated new results on MHD instability effects on burning plasma transport. (author)
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.
Nuclear magnetic resonance studies of quadrupolar nuclei and dipolar field effects
International Nuclear Information System (INIS)
Urban, Jeffry Todd
2004-01-01
Experimental and theoretical research conducted in two areas in the field of nuclear magnetic resonance (NMR) spectroscopy is presented: (1) studies of the coherent quantum-mechanical control of the angular momentum dynamics of quadrupolar (spin I > 1/2) nuclei and its application to the determination of molecular structure; and (2) applications of the long-range nuclear dipolar field to novel NMR detection methodologies.The dissertation is organized into six chapters. The first two chapters and associated appendices are intended to be pedagogical and include an introduction to the quantum mechanical theory of pulsed NMR spectroscopy and the time dependent theory of quantum mechanics. The third chapter describes investigations of the solid-state multiple-quantum magic angle spinning (MQMAS) NMR experiment applied to I 5/2 quadrupolar nuclei. This work reports the use of rotary resonance-matched radiofrequency irradiation for sensitivity enhancement of the I = 5/2 MQMAS experiment. These experiments exhibited certain selective line narrowing effects which were investigated theoretically.The fourth chapter extends the discussion of multiple quantum spectroscopy of quadrupolar nuclei to a mostly theoretical study of the feasibility of enhancing the resolution of nitrogen-14 NMR of large biomolecules in solution via double-quantum spectroscopy. The fifth chapter continues to extend the principles of multiple quantum NMR spectroscopy of quadrupolar nuclei to make analogies between experiments in NMR/nuclear quadrupolar resonance (NQR) and experiments in atomic/molecular optics (AMO). These analogies are made through the Hamiltonian and density operator formalism of angular momentum dynamics in the presence of electric and magnetic fields.The sixth chapter investigates the use of the macroscopic nuclear dipolar field to encode the NMR spectrum of an analyte nucleus indirectly in the magnetization of a sensor nucleus. This technique could potentially serve as an encoding
Nuclear magnetic resonance studies of quadrupolar nuclei and dipolar field effects
Energy Technology Data Exchange (ETDEWEB)
Urban, Jeffry Todd [Univ. of California, Berkeley, CA (United States)
2004-01-01
Experimental and theoretical research conducted in two areas in the field of nuclear magnetic resonance (NMR) spectroscopy is presented: (1) studies of the coherent quantum-mechanical control of the angular momentum dynamics of quadrupolar (spin I > 1/2) nuclei and its application to the determination of molecular structure; and (2) applications of the long-range nuclear dipolar field to novel NMR detection methodologies.The dissertation is organized into six chapters. The first two chapters and associated appendices are intended to be pedagogical and include an introduction to the quantum mechanical theory of pulsed NMR spectroscopy and the time dependent theory of quantum mechanics. The third chapter describes investigations of the solid-state multiple-quantum magic angle spinning (MQMAS) NMR experiment applied to I = 5/2 quadrupolar nuclei. This work reports the use of rotary resonance-matched radiofrequency irradiation for sensitivity enhancement of the I = 5/2 MQMAS experiment. These experiments exhibited certain selective line narrowing effects which were investigated theoretically.The fourth chapter extends the discussion of multiple quantum spectroscopy of quadrupolar nuclei to a mostly theoretical study of the feasibility of enhancing the resolution of nitrogen-14 NMR of large biomolecules in solution via double-quantum spectroscopy. The fifth chapter continues to extend the principles of multiple quantum NMR spectroscopy of quadrupolar nuclei to make analogies between experiments in NMR/nuclear quadrupolar resonance (NQR) and experiments in atomic/molecular optics (AMO). These analogies are made through the Hamiltonian and density operator formalism of angular momentum dynamics in the presence of electric and magnetic fields.The sixth chapter investigates the use of the macroscopic nuclear dipolar field to encode the NMR spectrum of an analyte nucleus indirectly in the magnetization of a sensor nucleus. This technique could potentially serve as an
Total scalp irradiation using helical tomotherapy
International Nuclear Information System (INIS)
Orton, Nigel; Jaradat, Hazim; Welsh, James; Tome, Wolfgang
2005-01-01
Homogeneous irradiation of the scalp poses technical and dosimetric challenges due to the extensive, superficial, curved treatment volume. Conventional treatments on a linear accelerator use multiple matched electron fields or a combination of electron and photon fields. Problems with these techniques include dose heterogeneity in the target due to varying source-to-skin distance (SSD) and angle of beam incidence, significant dose to the brain, and the potential for overdose or underdose at match lines between the fields. Linac-based intensity-modulated radiation therapy (IMRT) plans have similar problems. This work presents treatment plans for total scalp irradiation on a helical tomotherapy machine. Helical tomotherapy is well-suited for scalp irradiation because it has the ability to deliver beamlets that are tangential to the scalp at all points. Helical tomotherapy also avoids problems associated with field matching and use of more than one modality. Tomotherapy treatment plans were generated and are compared to plans for treatment of the same patient on a linac. The resulting tomotherapy plans show more homogeneous target dose and improved critical structure dose when compared to state-of-the-art linac techniques. Target equivalent uniform dose (EUD) for the best tomotherapy plan was slightly higher than for the linac plan, while the volume of brain tissue receiving over 30 Gy was reduced by two thirds. Furthermore, the tomotherapy plan can be more reliably delivered than linac treatments, because the patient is aligned prior to each treatment based on megavoltage computed tomography (MVCT)
Shi, Yifei
2013-08-01
Internal resonant modes are always observed in the marching-on-in-time (MOT) solution of the time domain electric field integral equation (EFIE), although \\'relaxed initial conditions,\\' which are enforced at the beginning of time marching, should in theory prevent these spurious modes from appearing. It has been conjectured that, numerical errors built up during time marching establish the necessary initial conditions and induce the internal resonant modes. However, this conjecture has never been proved by systematic numerical experiments. Our numerical results in this communication demonstrate that, the internal resonant modes\\' amplitudes are indeed dictated by the numerical errors. Additionally, it is shown that in a few cases, the internal resonant modes can be made \\'invisible\\' by significantly suppressing the numerical errors. These tests prove the conjecture that the internal resonant modes are induced by numerical errors when the time domain EFIE is solved by the MOT method. © 2013 IEEE.
Shi, Yifei; Bagci, Hakan; Lu, Mingyu
2013-01-01
Internal resonant modes are always observed in the marching-on-in-time (MOT) solution of the time domain electric field integral equation (EFIE), although 'relaxed initial conditions,' which are enforced at the beginning of time marching, should in theory prevent these spurious modes from appearing. It has been conjectured that, numerical errors built up during time marching establish the necessary initial conditions and induce the internal resonant modes. However, this conjecture has never been proved by systematic numerical experiments. Our numerical results in this communication demonstrate that, the internal resonant modes' amplitudes are indeed dictated by the numerical errors. Additionally, it is shown that in a few cases, the internal resonant modes can be made 'invisible' by significantly suppressing the numerical errors. These tests prove the conjecture that the internal resonant modes are induced by numerical errors when the time domain EFIE is solved by the MOT method. © 2013 IEEE.
DEFF Research Database (Denmark)
Lange, Simon Lehnskov; Iwaszczuk, Krzysztof; Hoffmann, Matthias
2016-01-01
We present here a novel design for a coupled split ring resonator antenna optimized for time-domain electric field enhancement in the 0.1 to 1 terahertz (THz) range. The antenna is designed to be sensitive to the incident field polarization and seeks to avoid metal damage due to electron bombardm...
Linear and Nonlinear Response of a Rotating Tokamak Plasma to a Resonant Error-Field
Fitzpatrick, Richard
2014-10-01
An in-depth investigation of the effect of a resonant error-field on a rotating, quasi-cylindrical, tokamak plasma is preformed within the context of resistive-MHD theory. General expressions for the response of the plasma at the rational surface to the error-field are derived in both the linear and nonlinear regimes, and the extents of these regimes mapped out in parameter space. Torque-balance equations are also obtained in both regimes. These equations are used to determine the steady-state plasma rotation at the rational surface in the presence of the error-field. It is found that, provided the intrinsic plasma rotation is sufficiently large, the torque-balance equations possess dynamically stable low-rotation and high-rotation solution branches, separated by a forbidden band of dynamically unstable solutions. Moreover, bifurcations between the two stable solution branches are triggered as the amplitude of the error-field is varied. A low- to high-rotation bifurcation is invariably associated with a significant reduction in the width of the magnetic island chain driven at the rational surface, and vice versa. General expressions for the bifurcation thresholds are derived, and their domains of validity mapped out in parameter space. This research was funded by the U.S. Department of Energy under Contract DE-FG02-04ER-54742.
Assili, Mohamed; Haddad, Sonia; Kang, Woun
2015-03-01
A double peak structure in the magnetophonon resonance (MPR) spectrum of uniaxial strained graphene, under crossed electric and magnetic fields, is predicted. We focus on the Γ point optical phonon modes coupled to the inter-Landau level transitions 0 ⇆±1 where MPR is expected to be more pronounced at high magnetic field. We derive the frequency shifts and the broadenings of the longitudinal and transverse optical phonon modes taking into account the effect of the strain modified electronic spectrum on the electron-phonon coupling. We show that the MPR line for a given phonon mode acquires a double peak structure originating from the twofold valley degeneracy lifting. The latter is due to the different Landau level spacings in the two Dirac valleys resulting from the simultaneous action of the inplane electric field and the strain-induced Dirac cone tilt. We discuss the role of some key parameters such as disorder, strain, doping, and electric field amplitude on the emergence of the double peak structure.
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.
Optimization of AGS Polarized Proton Operation with the Warm Helical Snake
Takano, Junpei; Bai, Mei; Brown, Kevin A; Gardner, Chris J; Glenn, Joseph; Hattori, Toshiyuki; Huang, Haixin; Luccio, Alfredo U; MacKay, William W; Okamura, Masahiro; Roser, Thomas; Tepikian, Steven; Tsoupas, Nicholaos
2005-01-01
A normal conducting helical dipole partial Siberian snake (Warm Snake) has been installed in the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL) for overcoming all of imperfection depolarizing resonances and reducing the transverse coupling resonances caused by the solenoidal Siberian snake which had been operated in AGS before the last polarized run. The polarized proton beam has been accelerated successfully with the warm snake and the polarization at extraction of the AGS was increased to 50% as opposed to 40% with the solenoidal snake. The magnetic field and beam trajectory in the warm snake was calculated by using the OPERA-3D/TOSCA software. We present optimization of the warm snake with beam during RUN5.
Spatial Variations of Poloidal and Toroidal Mode Field Line Resonances Observed by MMS
Le, G.; Chi, P. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Anderson, B. J.; Kepko, L.; Nakamura, R.; Plaschke, F.; Torbert, R. B.
2017-12-01
Field line resonances (FLRs) are magnetosphere's responses to solar wind forcing and internal instabilities generated by solar wind-magnetospheric interactions. They are standing waves along the Earth's magnetic field lines oscillating in either poloidal or toroidal modes. The two types of waves have their unique frequency characteristics. The eigenfrequency of FLRs is determined by the length of the field line and the plasma density, and thus gradually changes with L. For toroidal mode oscillations with magnetic field perturbations in the azimuthal direction, ideal MHD predicts that each field line oscillates independently with its own eigenfrequency. For poloidal mode waves with field lines oscillating radially, their frequency cannot change with L easily as L shells need to oscillate in sync to avoid efficient damping due to phase mixing. Observations, mainly during quiet times, indeed show that poloidal mode waves often exhibit nearly constant frequency across L shells. Our recent observations, on the other hand, reveal a clear L-dependent frequency trend for a long lasting storm-time poloidal wave event, indicating the wave can maintain its power with changing frequencies for an extended period [Le et al., 2017]. The spatial variation of the frequency shows discrete spatial structures. The frequency remains constant within each discrete structure that spans about 1 REalong L, and changes discretely. We present a follow-up study to investigate spatial variations of wave frequencies using the Wigner-Ville distribution. We examine both poloidal and toroidal waves under different geomagnetic conditions using multipoint observations from MMS, and compare their frequency and occurrence characteristics for insights into their generation mechanisms. Reference: Le, G., et al. (2017), Global observations of magnetospheric high-m poloidal waves during the 22 June 2015 magnetic storm, Geophys. Res. Lett., 44, 3456-3464, doi:10.1002/2017GL073048.
[Patient exposure to electromagnetic fields in magnetic resonance scanners: a review].
Guibelalde del Castillo, E
2013-12-01
The use of non-ionizing electromagnetic fields in the low frequency end of the electromagnetic spectrum and static fields, radiofrequencies (RF), and microwaves is fundamental both in modern communication systems and in diagnostic medical imaging techniques like magnetic resonance imaging (MRI). The proliferation of these applications in recent decades has led to intense activity in developing regulations to guarantee their safety and to the establishment of guidelines and legal recommendations for the public, workers, and patients. In April 2012 it was foreseen that the European Parliament and Council would approve and publish a directive on the minimum health and safety requirements regarding the exposure of workers to the risks arising from electromagnetic fields, which would modify Directive 2004/40/EC. New studies related to the exposure to electromagnetic radiation and its impact on health published in recent years have led to a new postponement, and it is now foreseen that the directive will come into effect in October 2013. One of the most noteworthy aspects of the new version of the directive is the exclusion of the limits of occupational exposure to electromagnetic fields in the clinical use of MRI. In exchange for this exception, physicians and experts in protection against non-ionizing radiation are asked to make additional efforts to train workers exposed to non-ionizing radiation and to establish mechanisms to guarantee the correct application of non-ionizing electromagnetic fields in patients, along similar lines to the principles of justification and optimization established for ionizing radiation. On the basis of the most recently published studies, this article reviews some safety-related aspects to take into account when examining patients with MRI with high magnetic fields. Copyright © 2013 SERAM. Published by Elsevier Espana. All rights reserved.
Helical Tomotherapy Quality Assurance
International Nuclear Information System (INIS)
Balog, John; Soisson, Emilie
2008-01-01
Helical tomotherapy uses a dynamic delivery in which the gantry, treatment couch, and multileaf collimator leaves are all in motion during treatment. This results in highly conformal radiotherapy, but the complexity of the delivery is partially hidden from the end-user because of the extensive integration and automation of the tomotherapy control systems. This presents a challenge to the medical physicist who is expected to be both a system user and an expert, capable of verifying relevant aspects of treatment delivery. A related issue is that a clinical tomotherapy planning system arrives at a customer's site already commissioned by the manufacturer, not by the clinical physicist. The clinical physicist and the manufacturer's representative verify the commissioning at the customer site before acceptance. Theoretically, treatment could begin immediately after acceptance. However, the clinical physicist is responsible for the safe and proper use of the machine. In addition, the therapists and radiation oncologists need to understand the important machine characteristics before treatment can proceed. Typically, treatment begins about 2 weeks after acceptance. This report presents an overview of the tomotherapy system. Helical tomotherapy has unique dosimetry characteristics, and some of those features are emphasized. The integrated treatment planning, delivery, and patient-plan quality assurance process is described. A quality assurance protocol is proposed, with an emphasis on what a clinical medical physicist could and should check. Additionally, aspects of a tomotherapy quality assurance program that could be checked automatically and remotely because of its inherent imaging system and integrated database are discussed
Glushkov, A. V.; Gurskaya, M. Yu; Ignatenko, A. V.; Smirnov, A. V.; Serga, I. N.; Svinarenko, A. A.; Ternovsky, E. V.
2017-10-01
The consistent relativistic energy approach to the finite Fermi-systems (atoms and nuclei) in a strong realistic laser field is presented and applied to computing the multiphoton resonances parameters in some atoms and nuclei. The approach is based on the Gell-Mann and Low S-matrix formalism, multiphoton resonance lines moments technique and advanced Ivanov-Ivanova algorithm of calculating the Green’s function of the Dirac equation. The data for multiphoton resonance width and shift for the Cs atom and the 57Fe nucleus in dependence upon the laser intensity are listed.
Tokamak startup using point-source dc helicity injection.
Battaglia, D J; Bongard, M W; Fonck, R J; Redd, A J; Sontag, A C
2009-06-05
Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation.
Directory of Open Access Journals (Sweden)
Xinyu Li
2016-01-01
Full Text Available Water plays a very important role in wood and wood products. The molecular motion of water in wood is susceptible to thermal activation. Thermal energy makes water molecules more active and weakens the force between water and wood; therefore, the water molecules dynamic properties are greatly influenced. Molecular dynamics study is important for wood drying; this paper therefore focuses on water molecular dynamics in wood through fast field cycling nuclear magnetic resonance relaxometry techniques. The results show that the spin-lattice relaxation rate decreases with the Larmor frequency. Nuclear magnetic resonance dispersion profiles at different temperatures could separate the relaxation contribution of water in bigger pores and smaller pores. The T1 distribution from wide to narrow at 10 MHz Larmor frequency reflects the shrinkage of pore size with the higher temperature. The dependence of spin-lattice relaxation rate on correlation time for water molecular motion based on BPP (proposed by Bloembergen, Purcell, and Pound theory shows that water correlation time increases with higher temperature, and its activation energy, calculated using the Arrhenius transformation equation, is 9.06±0.53 kJ/mol.
Ion heating at the cyclotron resonance in plasmas magnetically confined in a toroidal octupole field
International Nuclear Information System (INIS)
Barter, J.D.
1976-01-01
Ion temperatures as high as 600 eV have been produced using rf wave heating at the ion cyclotron resonance frequency in a toroidal octupole magnetic field. Rf is coupled to the plasma with an externally driven ''fifth'' hoop which forms the inductive leg of an oscillator tank circuit. Power levels up to 1 MW at 1 to 3 MHz have been applied for periods up to 2 msec. Plasmas produced either by ECRH or by gun injection are simulated with a computer program in which known particle and energy production and loss mechanisms are used to predict the spatially averaged time behaviour of the plasma in the presence of the applied ion heating. The program can be used to calculate the consequences of the heating model in the presence of many cooling mechanisms which may each have a separate dependence on instantaneous plasma parameters. Experimental quantities compared to computer predictions include density, ion temperature, and loading of the hoop by the plasma, both resistive and reactive, and neutral reflux from the wall by electron and ion impact. Wave penetration to the resonance zone is good up to the highest densities available (6 x 10 12 cm -3 by gun injection) in good agreement with theory. Neutral reflux from the walls and the large charge exchange cooling which results is the dominant loss mechanism at the higher hoop voltages
High-energy localized eigenstates in a Fabry-Perot graphene resonator in a magnetic field
Zalipaev, V. V.
2012-06-01
A semiclassical analysis of the high-energy eigenstates of Dirac fermions inside a graphene monolayer nanoribbon resonator of Fabry-Perot type in a magnetic field with zigzag boundary conditions is discussed. A semiclassical asymptotic method of construction of Maslov spectral series of energy spectrum and eigenfunctions, localized in an asymptotically small neighborhood of a periodic orbit, is developed for the graphene Dirac system. The isolated periodic orbit is confined between two flat boundaries. The analysis involves constructing a localized asymptotic solution to the Dirac system (electron-hole Gaussian beam). Then, the stability of a continuous family of periodic orbits (POs) confined between reflecting boundaries of the resonator is studied. The asymptotics of the eigenfunctions are constructed as a superposition of two Gaussian beams propagating in opposite directions between two reflecting points of the periodic orbit. The asymptotics of the energy spectrum are obtained by means of the generalized Bohr-Sommerfeld quantization condition only for stable POs. It provides two parts of semiclassical Maslov spectral series with positive and negative energies, for electrons and holes, correspondingly, with two different Hamiltonian dynamics and families of classical trajectories. The presence of electrostatic potential is vital as it makes a family of periodic orbit stable. For one subclass of lens-shaped periodic orbits, for a piecewise linear potential, localized eigenstates were computed numerically by the finite element method using COMSOL, and proved to be in very good agreement with the ones computed semiclassically.
High magnetic field observation of the resonance donor states of S in InSb
International Nuclear Information System (INIS)
Porowski, S.; Konczewicz, L.; Kowalski, J.
1981-01-01
Electrical transport measurements in InSb heavily doped with sulfur (n approximately 5x10 18 cm -3 ) are performed. At T = 4.2 K the Hall coefficient and transverse magnetoresistivity are measured as a function of pressure up to 2100 MPa and magnetic field up to 18 T. At the highest pressure, a decrease of the frequency and a decrease of the damping of Shubnikov-de Haas oscillations are observed. These effects are explained as a result of the transfer of electrons from the conduction band to the resonance states of sulfur. At atmospheric pressure these states are 0.55 eV above the bottom of conduction band. In the lower pressure range, the experimental dependence of the effective Dingle temperature T*sub(D) = Tsub(D) + Tsub(i) can be explained by the model in which the scattering by ionized impurities and short-range potentials are taken into account. At the highest pressures a change of inhomogeneity of carrier concentration due to the transfer of electrons to the resonance states has to be considered. (author)
A novel noncontact electromagnetic field-based sensor for the monitoring of resonant fatigue tests
International Nuclear Information System (INIS)
Nam, Si-Byung; Yun, Gun Jin; Binienda, Wieslaw; Carletta, Joan; Kim, Dong-Han
2011-01-01
In this paper, a prototype of an electromagnetic field-based (EFB) vibration sensor that uses a novel sensing technique to monitor the resonant fatigue testing of a conductive and/or ferromagnetic target specimen is presented. The distance from the target to a coil within the sensor affects the impedance of the coil. The electronic circuitry for the sensor consists of a relaxation oscillator, an embedded microprocessor module and a high-speed digital-to-analog converter. The impedance of the coil determines the frequency of oscillation of the relaxation oscillator's output, so that vibration of the target causes changes in the oscillation frequency. A timer in the embedded microprocessor module is used to count the oscillations, producing a digital signal that indicates the coil-to-target distance. The digital signal is instantaneously converted to an analog signal to produce the sensor's output. The key technologies proposed include: (1) a novel timer counting method using the input capture functionality and timer of the embedded microprocessor module and (2) significant simplification of the analog electronic circuitry. The performance of the proposed sensor has been verified using AISI 1095 carbon steel and Al6061–T6 aluminum alloy specimens during resonant fatigue tests. The sensor shows a good linearity between displacement amplitudes and output voltages
Helical bifurcation and tearing mode in a plasma—a description based on Casimir foliation
International Nuclear Information System (INIS)
Yoshida, Z; Dewar, R L
2012-01-01
The relation between the helical bifurcation of a Taylor relaxed state (a Beltrami equilibrium) and a tearing mode is analyzed in a Hamiltonian framework. Invoking an Eulerian representation of the Hamiltonian, the symplectic operator (defining a Poisson bracket) becomes non-canonical, i.e. the symplectic operator has a nontrivial cokernel (dual to its nullspace), foliating the phase space into level sets of Casimir invariants. A Taylor relaxed state is an equilibrium point on a Casimir (helicity) leaf. Changing the helicity, equilibrium points may bifurcate to produce helical relaxed states; a necessary and sufficient condition for bifurcation is derived. Tearing yields a helical perturbation on an unstable equilibrium, producing a helical structure approximately similar to a helical relaxed state. A slight discrepancy found between the helically bifurcated relaxed state and the linear tearing mode viewed as a perturbed, singular equilibrium state is attributed to a Casimir element (named ‘helical flux’) pertinent to a ‘resonance singularity’ of the non-canonical symplectic operator. While the helical bifurcation can occur at discrete eigenvalues of the Beltrami parameter, the tearing mode, being a singular eigenfunction, exists for an arbitrary Beltrami parameter. Bifurcated Beltrami equilibria appearing on the same helicity leaf are isolated by the helical-flux Casimir foliation. The obstacle preventing the tearing mode to develop in the ideal limit turns out to be the shielding current sheet on the resonant surface, preventing the release of the ‘potential energy’. When this current is dissipated by resistivity, reconnection is allowed and tearing instability occurs. The Δ′ criterion for linear tearing instability of Beltrami equilibria is shown to be directly related to the spectrum of the curl operator. (paper)
Lack of dependence on resonant error field of locked mode island size in ohmic plasmas in DIII-D
La Haye, R. J.; Paz-Soldan, C.; Strait, E. J.
2015-02-01
DIII-D experiments show that fully penetrated resonant n = 1 error field locked modes in ohmic plasmas with safety factor q95 ≳ 3 grow to similar large disruptive size, independent of resonant error field correction. Relatively small resonant (m/n = 2/1) static error fields are shielded in ohmic plasmas by the natural rotation at the electron diamagnetic drift frequency. However, the drag from error fields can lower rotation such that a bifurcation results, from nearly complete shielding to full penetration, i.e., to a driven locked mode island that can induce disruption. Error field correction (EFC) is performed on DIII-D (in ITER relevant shape and safety factor q95 ≳ 3) with either the n = 1 C-coil (no handedness) or the n = 1 I-coil (with ‘dominantly’ resonant field pitch). Despite EFC, which allows significantly lower plasma density (a ‘figure of merit’) before penetration occurs, the resulting saturated islands have similar large size; they differ only in the phase of the locked mode after typically being pulled (by up to 30° toroidally) in the electron diamagnetic drift direction as they grow to saturation. Island amplification and phase shift are explained by a second change-of-state in which the classical tearing index changes from stable to marginal by the presence of the island, which changes the current density profile. The eventual island size is thus governed by the inherent stability and saturation mechanism rather than the driving error field.
International Nuclear Information System (INIS)
Rodrigues, George; Yartsev, Slav; Tay, Keng Yeow; Pond, Gregory R; Lagerwaard, Frank; Bauman, Glenn
2012-01-01
Our research group has previously published a dosimetric planning study that demonstrated that a 60 Gy/10 fractions intralesional boost with whole-brain radiotherapy (WBRT) to 30 Gy/10 fractions was biologically equivalent with a stereotactic radiosurgery (SRS) boost of 18 Gy/1 fraction with 30 Gy/10 fractions WBRT. Helical tomotherapy (HT) was found to be dosimetrically equivalent to SRS in terms of target coverage and superior to SRS in terms of normal tissue tolerance. A phase I trial has been now completed at our institution with a total of 60 enrolled patients and 48 evaluable patients. The phase II dose has been determined to be the final phase I cohort dose of 60 Gy/10 fractions. The objective of this clinical trial is to subject the final phase I cohort dose to a phase II assessment of the endpoints of overall survival, intracranial control (ICC) and intralesional control (ILC). We hypothesize HT would be considered unsuitable for further study if the median OS for patients treated with the HT SIB technique is degraded by 2 months, or the intracranial progression-free rates (ICC and ILC) are inferior by 10% or greater compared to the expected results with treatment by whole brain plus SRS as defined by the RTOG randomized trial. A sample size of 93 patients was calculated based on these parameters as well as the statistical assumptions of alpha = 0.025 and beta = 0.1 due to multiple statistical testing. Secondary assessments of toxicity, health-related quality-of-life, cognitive changes, and tumor response are also integrated into this research protocol. To summarize, the purpose of this phase II trial is to assess this non-invasive alternative to SRS in terms of central nervous system (CNS) control when compared to SRS historical controls. A follow-up phase III trial may be required depending on the results of this trial in order to definitively assess non-inferiority/superiority of this approach. Ultimately, the purpose of this line of research is to
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.
Employing Helicity Amplitudes for Resummation
Moult, I.; Stewart, I.W.; Tackmann, F.J.; Waalewijn, W.J.
2015-01-01
Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are
International Nuclear Information System (INIS)
Kim, Yonghee; Heo, Myoung-Sun; Moon, Geol; Kim, Ji-Hyoun; Jhe, Wonho; Noh, Heung-Ryoul
2010-01-01
We experimentally demonstrate resonant symmetry lifting in a parametrically modulated magneto-optical trap of cold 85 Rb atoms. This is achieved by applying a weak additional modulation at half the frequency of the strong parametric modulation, which acts as an effective static bias field to the system. We measure the system response by varying the amplitude of the additional fictitious bias as well as the relative phase between the bias and the parametric drive, and the results are in good agreement with theory. The additional modulation provides an additional degree of freedom to control the system, which is useful for investigating system properties such as susceptibility, dynamic response, and related critical phenomena. We also have measured the amplitude of the response to higher harmonics of the additional modulation frequency, which allows more precise understanding of the system dynamics.
International Nuclear Information System (INIS)
Cheng, M C; Yan, B P; Lee, K H; Ma, Q Y; Yang, E S
2005-01-01
High temperature superconductor (HTS) thin films have been applied in making a low loss RF receiver coil for improving magnetic resonance imaging image quality. However, the application of these coils is severely limited by their limited field of view (FOV). Stringent fabrication environment requirements and high cost are further limitations. In this paper, we propose a simpler method for designing and fabricating HTS coils. Using industrial silver alloy sheathed Bi (2-x) Pb x Sr 2 Ca 2 Cu 3 O 10 (Bi-2223) HTS tapes, a five-inch single-turn HTS solenoid coil has been developed, and human wrist images have been acquired with this coil. The HTS tape coil has demonstrated an enhanced FOV over a six-inch YBCO thin film surface coil at 77 K with comparable signal-to-noise ratio
Oval gradient coils for an open magnetic resonance imaging system with a vertical magnetic field.
Matsuzawa, Koki; Abe, Mitsushi; Kose, Katsumi; Terada, Yasuhiko
2017-05-01
Existing open magnetic resonance imaging (MRI) systems use biplanar gradient coils for the spatial encoding of signals. We propose using novel oval gradient coils for an open vertical-field MRI. We designed oval gradients for a 0.3T open MRI system and showed that such a system could outperform a traditional biplanar gradient system while maintaining adequate gradient homogeneity and subject accessibility. Such oval gradient coils would exhibit high efficiency, low inductance and resistance, and high switching capability. Although the designed oval Y and Z coils showed more heat dissipation and less cooling capability than biplanar coils with the same gap, they showed an efficient heat-dissipation path to the surrounding air, which would alleviate the heat problem. The performance of the designed oval-coil system was demonstrated experimentally by imaging a human hand. Copyright © 2017 Elsevier Inc. All rights reserved.
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.
Spatial Steering of Cyclotron-Resonance Maser Array Antenna by Magnetic Fields
International Nuclear Information System (INIS)
Kesar, A.; Jerby, E.
2001-01-01
The novel concept of radiation lobe generation and steering by cyclotron-resonance maser (CRM) array is presented. In this scheme the gain and phase of each CRM-element in the array are tuned by magnetic fields which control the cyclotron synchronism condition and the pitch-ratio of each CRM-element. These operating parameters are controlled by the magnetic fields of the solenoid and the kicker, respectively. A numerical example of a CRM-array operating in a gyro-TWT mode is presented. The radiation pattern of a 10-element CRM phased array (15 kV, 1A each) is calculated. The radiation lobe steering by the magnetic field controls is demonstrated in this analysis. A 40 lobe steering range is shown for the 10-element CRM-array at 7.3 GHz. An experimental device is built in our laboratory to demonstrate the active CRM-array antenna concept. Preliminary experimental results of gain and phase-delay of a single CRM-element, as function of electron-beam parameters are presented. These results are compared to the numerical model
Coordinated observation of field line resonance in the mid-tail
Directory of Open Access Journals (Sweden)
Y. Zheng
2006-03-01
Full Text Available Standing Alfvén waves of 1.1 mHz (~15 min in period were observed by the Cluster satellites in the mid-tail during 06:00-07:00 UT on 8 August 2003. Pulsations with the same frequency were also observed at several ground stations near Cluster's footpoint. The standing wave properties were determined from the electric and magnetic field measurements of Cluster. Data from the ground magnetometers indicated a latitudinal amplitude and phase structure consistent with the driven field line resonance (FLR at 1.1 mHz. Simultaneously, quasi-periodic oscillations at different frequencies were observed in the post-midnight/early morning sector by GOES 12 (l_{0}≈8.7, Polar (l_{0}≈11-14 and Geotail (l_{0}≈9.8. The 8 August 2003 event yields rare and interesting datasets. It provides, for the first time, coordinated in situ and ground-based observations of a very low frequency FLR in the mid-tail on stretched field lines.
Niendorf, Thoralf; Graessl, Andreas; Thalhammer, Christof; Dieringer, Matthias A; Kraus, Oliver; Santoro, Davide; Fuchs, Katharina; Hezel, Fabian; Waiczies, Sonia; Ittermann, Bernd; Winter, Lukas
2013-04-01
A growing number of reports eloquently speak about explorations into cardiac magnetic resonance (CMR) at ultrahigh magnetic fields (B0≥7.0 T). Realizing the progress, promises and challenges of ultrahigh field (UHF) CMR this perspective outlines current trends in enabling MR technology tailored for cardiac MR in the short wavelength regime. For this purpose many channel radiofrequency (RF) technology concepts are outlined. Basic principles of mapping and shimming of transmission fields including RF power deposition considerations are presented. Explorations motivated by the safe operation of UHF-CMR even in the presence of conductive implants are described together with the physics, numerical simulations and experiments, all of which detailing antenna effects and RF heating induced by intracoronary stents at 7.0 T. Early applications of CMR at 7.0 T and their clinical implications for explorations into cardiovascular diseases are explored including assessment of cardiac function, myocardial tissue characterization, MR angiography of large and small vessels as well as heteronuclear MR of the heart and the skin. A concluding section ventures a glance beyond the horizon and explores future directions. The goal here is not to be comprehensive but to inspire the biomedical and diagnostic imaging communities to throw further weight behind the solution of the many remaining unsolved problems and technical obstacles of UHF-CMR with the goal to transfer MR physics driven methodological advancements into extra clinical value. Copyright © 2012 Elsevier Inc. All rights reserved.
Pseudo-field line resonances in ground Pc5 pulsation events
Directory of Open Access Journals (Sweden)
D. V. Sarafopoulos
2005-02-01
Full Text Available In this work we study four representative cases of Pc5 ground pulsation events with discrete and remarkably stable frequencies extended at least in a high-latitude range of ~20°; a feature that erroneously gives the impression for an oscillation mode with "one resonant field line". Additionally, the presented events show characteristic changes in polarization sense, for a meridian chain of stations from the IMAGE array, and maximize their amplitude at or close to the supposed resonant magnetic field shell, much like the typical FLR. Nevertheless, they are not authentic FLRs, but pseudo-FLRs, as they are called. These structures are produced by repetitive and tilted twin-vortex structures caused by magnetopause surface waves, which are probably imposed by solar wind pressure waves. The latter is confirmed with in-situ measurements obtained by the Cluster satellites, as well as the Geotail, Wind, ACE, and LANL 1994-084 satellites. This research effort is largely based on two recent works: first, Sarafopoulos (2004a has observationally established that a solar wind pressure pulse (stepwise pressure variation produces a twin-vortex (single vortex current system over the ionosphere; second, Sarafopoulos (2004b has studied ground events with characteristic dispersive latitude-dependent structures and showed that these are associated with twin-vortex ionosphere current systems. In this work, we show that each pseudo-FLR event is associated with successive and tilted large-scale twin-vortex current systems corresponding to a magnetopause surface wave with wavelength 10-20RE. We infer that between an authentic FLR, which is a spatially localized structure with an extent 0.5RE in the magnetospheric equatorial plane, and the magnetopause surface wavelength, there is a scale factor of 20-40. A chief observational finding, in this work, is that there are Pc5 ground pulsation events showing two gradual and latitude dependent phase-shifts of 180°, at the
Theory of dynamics in long pulse helical plasmas
International Nuclear Information System (INIS)
Itoh, K.; Sanuki, H.; Toda, S.; Yokoyama, M.; Itoh, S.-I.; Yagi, M.; Fukuyama, A.
2001-01-01
Self-organized dynamics of toroidal helical plasma, which is induced by the nonlinear transport property, is discussed. Neoclassical ripple diffusion is a dominant mechanism that drives the radial electric field. The bifurcation nature of the electric field generation gives rise to the electric field domain interface, across which the electric field changes strongly. This domain interface is an origin of internal transport barrier in helical systems. This nonlinearity gives rise to the self-organized oscillations; the electric field pulsation is one of the examples. Based on the model of density limit, in which the competition between the transport loss and radiation loss is analyzed, dynamics near the density limit of helical systems is also discussed. (author)
Helical type thermonuclear device and control method
International Nuclear Information System (INIS)
Ishigaki, Yukio.
1990-01-01
In a conventional helical type thermonuclear device, electric current flows in the toroidal direction under magnetic fields of helical coils and vertical magnetic coils, by which a circulating electric field is caused. Therefore, there is a problem that electrons as a seed are generated by cosmic rays, etc., the electrons are confined in a magnetic field boundary, are accelerated by the circulating electric field, to reach a high energy level, collide against structures in a vacuum vessel and emit a great amount of X-rays. Then, compensation coils for offsetting the magnetic fields generated upon energization and deenergization of the vertical magnetic coils and the power source therefor are disposed at the positions opposing to each other on both sides of the vertical magnetic coils for controlling the variation coefficient rate of electric current upon energization and deenergization of the vertical magnetic coils. Since the compensation coils also offset the magnetic field generated upon energization and deenergization of the vertical magnetic field coils by this control, the circulating magnetic field is not caused in the vacuum vessel to reduce the X-ray radiation by electrons at high energy level. (N.H.)
International Nuclear Information System (INIS)
Freire, Geison Moreira; Dias, Rodrigo Souza; Giordani, Adelmo Jose; Segreto, Helena Regina Comodo; Segreto, Roberto Araujo; Ribalta, Julisa Chamorro Lascasas
2010-01-01
Objective: to evaluate, by means of magnetic resonance imaging, the standardized field borders in radiotherapy for malignant neoplasm of uterine cervix, and to determine the role of this method in the reduction of possible planning errors related to the conventional technique. Materials and methods: magnetic resonance imaging studies for planning of treatment of 51 patients with uterine cervix cancer were retrospectively analyzed. The parameters assessed were the anterior and posterior field borders on sagittal section. Results: The anterior field border was inappropriate in 20 (39.2%) patients and geographic miss was observed in 37.3% of cases in the posterior border. The inappropriateness of both field borders did not correlate with clinical parameters such as patients' age, tumor staging, histological type and degree. Conclusion: the evaluation of standardized field borders with the use of magnetic resonance imaging has demonstrated high indices of inappropriateness of the lateral field borders, as well as the relevant role of magnetic resonance imaging in the radiotherapy planning for patients with uterine cervix cancer with a view to reduce the occurrence of geographic miss of the target volume. (author)
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.
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)
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)
Cyclotron resonance in InAs/AlSb quantum wells in magnetic fields up to 45 T
Energy Technology Data Exchange (ETDEWEB)
Spirin, K. E., E-mail: spirink@ipmras.ru; Krishtopenko, S. S. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Sadofyev, Yu. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Drachenko, O. [Laboratoire National des Champs Magn’etiques Intenses (France); Helm, M. [Forschungszentrum Dresden–Rossendorf, Dresden High-Magnetic-Field Laboratory and Institute of Ion-Beam Physics and Materials Research (Germany); Teppe, F.; Knap, W. [GIS-TERALAB Universite Montpellier II, Laboratoire Charles Coulomb UMR CNRS 5221 (L2C) (France); Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)
2015-12-15
Electron cyclotron resonance in InAs/AlSb heterostructures with quantum wells of various widths in pulsed magnetic fields up to 45 T are investigated. Our experimental cyclotron energies are in satisfactory agreement with the results of theoretical calculations performed using the eight-band kp Hamiltonian. The shift of the cyclotron resonance (CR) line, which corresponds to the transition from the lowest Landau level to the low magnetic-field region, is found upon varying the electron concentration due to the negative persistent photoconductivity effect. It is shown that the observed shift of the CR lines is associated with the finite width of the density of states at the Landau levels.
DEFF Research Database (Denmark)
Mortensen, Asger; Rønnow, Henrik Moodysson; Bruus, Henrik
2000-01-01
The magnetic resonance at 41 meV observed in neutron scattering studies of YBa2Cu3O7 holds a key position in the understanding of high-T-c, superconductivity. Within the SO(5) model for superconductivity and antiferromagnetism, we have calculated the effect of an applied magnetic field on the neu......The magnetic resonance at 41 meV observed in neutron scattering studies of YBa2Cu3O7 holds a key position in the understanding of high-T-c, superconductivity. Within the SO(5) model for superconductivity and antiferromagnetism, we have calculated the effect of an applied magnetic field...
Rybicki, F J; Hrovat, M I; Patz, S
2000-09-01
We have proposed a two-dimensional PERiodic-Linear (PERL) magnetic encoding field geometry B(x,y) = g(y)y cos(q(x)x) and a magnetic resonance imaging pulse sequence which incorporates two fields to image a two-dimensional spin density: a standard linear gradient in the x dimension, and the PERL field. Because of its periodicity, the PERL field produces a signal where the phase of the two dimensions is functionally different. The x dimension is encoded linearly, but the y dimension appears as the argument of a sinusoidal phase term. Thus, the time-domain signal and image spin density are not related by a two-dimensional Fourier transform. They are related by a one-dimensional Fourier transform in the x dimension and a new Bessel function integral transform (the PERL transform) in the y dimension. The inverse of the PERL transform provides a reconstruction algorithm for the y dimension of the spin density from the signal space. To date, the inverse transform has been computed numerically by a Bessel function expansion over its basis functions. This numerical solution used a finite sum to approximate an infinite summation and thus introduced a truncation error. This work analytically determines the basis functions for the PERL transform and incorporates them into the reconstruction algorithm. The improved algorithm is demonstrated by (1) direct comparison between the numerically and analytically computed basis functions, and (2) reconstruction of a known spin density. The new solution for the basis functions also lends proof of the system function for the PERL transform under specific conditions.
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
Microstrip Resonator for High Field MRI with Capacitor-Segmented Strip and Ground Plane
DEFF Research Database (Denmark)
Zhurbenko, Vitaliy; Boer, Vincent; Petersen, Esben Thade
2017-01-01
) segmenting stripe and ground plane of the resonator with series capacitors. The design equations for capacitors providing symmetric current distribution are derived. The performance of two types of segmented resonators are investigated experimentally. To authors’ knowledge, a microstrip resonator, where both......, strip and ground plane are capacitor-segmented, is shown here for the first time....
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.
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.
Fourier Transfrom Ion Cyclotron Resonance Mass Spectrometry at High Magnetic Field
Marshall, Alan G.
1998-03-01
At high magnetic field (9.4 tesla at NHMFL), Fourier transform ion cyclotron resonance mass spectrometry performance improves dramatically: mass resolving power, axialization efficiency, and scan speed (each proportional to B), maximum ion mass, dynamic range, ion trapping period, kinetic energy, and electron self-cooling rate for sympathetic cooling (each proportional to B^2), and ion coalescence tendency (proportional 1/B^2). These advantages may apply singly (e.g., unit mass resolution for proteins of >100,000 Da), or compound (e.g., 10-fold improvement in S/N ratio for 9.4 T vs. 6 T at the same resolving power). Examples range from direct determination of molecular formulas of diesel fuel components by accurate mass measurement (=B10.1 ppm) to protein structure and dynamics probed by H/D exchange. This work was supported by N.S.F. (CHE-93-22824; CHE-94-13008), N.I.H. (GM-31683), Florida State University, and the National High Magnetic Field Laboratory in Tallahassee, FL.
Energy Technology Data Exchange (ETDEWEB)
Windischberger, C.; Schoepf, V.; Sladky, R.; Moser, E. [Medizinische Universitaet Wien, Exzellenzzentrum Hochfeld-MR, Wien (Austria); Medizinische Universitaet Wien, Zentrum fuer Medizinische Physik und Biomedizinische Technik, Wien (Austria); Fischmeister, F.P.S. [Medizinische Universitaet Wien, Exzellenzzentrum Hochfeld-MR, Wien (Austria); Universitaet Wien, Fakultaet fuer Psychologie, Wien (Austria)
2010-02-15
Functional magnetic resonance imaging (fMRI) is currently the primary method for non-invasive functional localization in the brain. With the emergence of MR systems with field strengths of 4 Tesla and above, neuronal activation may be studied with unprecedented accuracy. In this article we present different approaches to use the improved sensitivity and specificity for expanding current fMRT resolution limits in space and time based on several 7 Tesla studies. In addition to the challenges that arise with ultra-high magnetic fields possible solutions will be discussed. (orig.) [German] Die funktionelle Magnetresonanztomographie (fMRT) stellt zurzeit die wichtigste Methode zur nichtinvasiven Funktionslokalisation im Gehirn dar. Mit der Verfuegbarkeit von MRT-Geraeten mit Magnetfeldstaerken von 4 Tesla (T) und darueber ergeben sich neue Moeglichkeiten, mittels fMRT die neuronale Aktivitaet in bislang unerreichter Genauigkeit zu untersuchen. In diesem Artikel zeigen wir anhand mehrerer Studien bei 7 T, in wieweit die Zugewinne an Sensitivitaet und Spezifitaet verwendet werden koennen, um die bisherigen Grenzen der fMRT-Aufloesung in raeumlicher und zeitlicher Hinsicht auszuweiten. Die neuen Herausforderungen, die mit dem Schritt zu ultrahohen Magnetfeldern einhergehen, werden dabei ebenso diskutiert wie moegliche Ansaetze zu deren Loesung. (orig.)
International Nuclear Information System (INIS)
Park, G.; Chang, C. S.; Joseph, I.; Moyer, R. A.
2010-01-01
A kinetic transport simulation for the first 4 ms of the vacuum resonant magnetic perturbations (RMPs) application has been performed for the first time in realistic diverted DIII-D tokamak geometry [J. Luxon, Nucl. Fusion 42, 614 (2002)], with the self-consistent evaluation of the radial electric field and the plasma rotation. It is found that, due to the kinetic effects, the stochastic parallel thermal transport is significantly reduced when compared to the standard analytic model [A. B. Rechester and M. N. Rosenbluth, Phys. Rev. Lett. 40, 38 (1978)] and the nonaxisymmetric perpendicular radial particle transport is significantly enhanced from the axisymmetric level. These trends agree with recent experimental result trends [T. E. Evans, R. A. Moyer, K. H. Burrell et al., Nat. Phys. 2, 419 (2006)]. It is also found, as a side product, that an artificial local reduction of the vacuum RMP fields in the vicinity of the magnetic separatrix can bring the kinetic simulation results to a more detailed agreement with experimental plasma profiles.
Miller, Renee; Kolipaka, Arunark; Nash, Martyn P; Young, Alistair A
2018-03-12
Magnetic resonance elastography (MRE) has been used to estimate isotropic myocardial stiffness. However, anisotropic stiffness estimates may give insight into structural changes that occur in the myocardium as a result of pathologies such as diastolic heart failure. The virtual fields method (VFM) has been proposed for estimating material stiffness from image data. This study applied the optimised VFM to identify transversely isotropic material properties from both simulated harmonic displacements in a left ventricular (LV) model with a fibre field measured from histology as well as isotropic phantom MRE data. Two material model formulations were implemented, estimating either 3 or 5 material properties. The 3-parameter formulation writes the transversely isotropic constitutive relation in a way that dissociates the bulk modulus from other parameters. Accurate identification of transversely isotropic material properties in the LV model was shown to be dependent on the loading condition applied, amount of Gaussian noise in the signal, and frequency of excitation. Parameter sensitivity values showed that shear moduli are less sensitive to noise than the other parameters. This preliminary investigation showed the feasibility and limitations of using the VFM to identify transversely isotropic material properties from MRE images of a phantom as well as simulated harmonic displacements in an LV geometry. Copyright © 2018 John Wiley & Sons, Ltd.
Wu, Yong; Wu, Xundong; Lu, Rong; Zhang, Jin; Toro, Ligia; Stefani, Enrico
2015-10-01
Photobleaching is a major limitation of superresolution Stimulated Depletion Emission (STED) microscopy. Fast scanning has long been considered an effective means to reduce photobleaching in fluorescence microscopy, but a careful quantitative study of this issue is missing. In this paper, we show that the photobleaching rate in STED microscopy can be slowed down and the fluorescence yield be enhanced by scanning with high speed, enabled by using large field of view in a custom-built resonant-scanning STED microscope. The effect of scanning speed on photobleaching and fluorescence yield is more remarkable at higher levels of depletion laser irradiance, and virtually disappears in conventional confocal microscopy. With ≥6 GW∙cm(-2) depletion irradiance, we were able to extend the fluorophore survival time of Atto 647N and Abberior STAR 635P by ~80% with 8-fold wider field of view. We confirm that STED Photobleaching is primarily caused by the depletion light acting upon the excited fluorophores. Experimental data agree with a theoretical model. Our results encourage further increasing the linear scanning speed for photobleaching reduction in STED microscopy.
International Nuclear Information System (INIS)
Dino, Wilson Agerico; Kasai, Hideaki; Rodulfo, Emmanuel Tapas; Nishi, Mayuko
2006-01-01
Manifestations of the Kondo effect on an atomic length scale on and around a magnetic atom adsorbed on a nonmagnetic surface differ depending on the spectroscopic mode of operation of the scanning tunneling microscope. Two prominent signatures of the Kondo effect that can be observed at surfaces are the development of a sharp resonance (Yosida-Kondo resonance) at the Fermi level, which broadens with increasing temperature, and the splitting of this sharp resonance upon application of an external magnetic field. Until recently, observing the temperature and magnetic field dependence has been a challenge, because the experimental conditions strongly depend on the system's critical temperature, the so-called Kondo temperature T K . In order to clearly observe the temperature dependence, one needs to choose a system with a large T K . One can thus perform the experiments at temperatures T K . However, because the applied external magnetic field necessary to observe the magnetic field dependence scales with T K , one needs to choose a system with a very small T K . This in turn means that one should perform the experiments at very low temperatures, e.g., in the mK range. Here we discuss the temperature and magnetic field dependence of the Yosida-Kondo resonance for a single magnetic atom on a metal surface, in relation to recent experimental developments
International Nuclear Information System (INIS)
Miura, N.
1999-01-01
Full text: We present a review on the recent advances in physics of magneto-optical spectroscopy in the visible range and of infrared cyclotron resonance in pulsed high magnetic fields, which are produced by electromagnetic flux compression up to 500T, by the single-turn coil technique up to 200T or by conventional non-destructive long pulse magnets up to 50T. We discuss the recent results on the spectroscopy of low dimensional excitons in quantum wells and short period superlattices. In very high fields up to 500T, we observed anomalous field dependence of the exciton absorption lines and the 2D - 3D cross-over effects in GaAs/AlAs quantum wells. In GaP/AlP short period superlattices, it was found that the exciton photoluminescence intensity shows a dramatic decrease and the diamagnetic shift was negative when high magnetic fields were applied parallel to the growth direction. We observed also remarkable effects of uniaxial stress, which are ascribed to the cross-over effect between the two inequivalent valleys at the X points. Cyclotron resonance was measured by using various molecular gas lasers as radiation sources in the range 5 - 119 m . We present the results of cyclotron resonance in GaAs/AlGaAs quantum wells with tilted magnetic fields from the growth direction. It was found that the resonant field and the peak intensity show many different features depending on the extent of the Landau level-subband coupling and on the relation between the photon energy and the barrier height. A large hysteresis was observed between the rising and the falling sweeps of the magnetic field, when the cyclotron resonance energy became comparable with the subband spacing. In a diluted magnetic semiconductor CdFeS, we observed anomalous temperature dependence of the effective mass, suggestive of the magnetic polaron effect
International Nuclear Information System (INIS)
Onofri, M.; Malara, F.
2013-01-01
Compressible magnetohydrodynamics simulations of the reversed-field pinch (RFP) are presented. Previous simulations of the RFP, including density and pressure evolution, showed that a stationary state with a reversed toroidal magnetic field could not be obtained, contrary to the results produced with numerical codes neglecting density and pressure dynamics. The simulations described in the present paper show that including density and pressure evolution, a stationary RFP configuration can be obtained if the resistivity has a radial profile steeply increasing close to the wall. Such resistivity profile is more realistic than a uniform resistivity, since the temperature at the wall is lower than in the plasma core
Effect of loss cone on confinement in toroidal helical device
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.-I.; Fukuyama, A.; Hanatani, K.
1988-12-01
Analytical estimation is given on the loss cone in the toroidal helical devices in the presence of the radial electric field and the modulation of the helical ripple. The minimum energy of particles entering the loss cone is calculated. The modulation is not always effective in reducing the loss in the presence of the radial electric field. The plasma loss due to the loss cone is estimated in the collisionless limit. The radial electric field is estimated in the presence of the loss cone. It is found that the transition to the solution with positive radial electric field, which is necessary to achieve the high-ion-temperature mode, becomes difficult. This difficulty is large for the systems with the small helical ripple. (author)
ADDITIVE SELF-HELICITY AS A KINK MODE THRESHOLD
International Nuclear Information System (INIS)
Malanushenko, A.; Longcope, D. W.; Fan, Y.; Gibson, S. E.
2009-01-01
In this paper, we propose that additive self-helicity, introduced by Longcope and Malanushenko, plays a role in the kink instability for complex equilibria, similar to twist helicity for thin flux tubes. We support this hypothesis by a calculation of additive self-helicity of a twisted flux tube from the simulation of Fan and Gibson. As more twist gets introduced, the additive self-helicity increases, and the kink instability of the tube coincides with the drop of additive self-helicity, after the latter reaches the value of H A /Φ 2 ∼ 1.5 (where Φ is the flux of the tube and H A is the additive self-helicity). We compare the additive self-helicity to twist for a thin subportion of the tube to illustrate that H A /Φ 2 is equal to the twist number, studied by Berger and Field, when the thin flux tube approximation is applicable. We suggest that the quantity H A /Φ 2 could be treated as a generalization of a twist number, when the thin flux tube approximation is not applicable. A threshold on a generalized twist number might prove extremely useful studying complex equilibria, just as the twist number itself has proven useful studying idealized thin flux tubes. We explicitly describe a numerical method for calculating additive self-helicity, which includes an algorithm for identifying a domain occupied by a flux bundle and a method of calculating potential magnetic field confined to this domain. We also describe a numerical method to calculate twist of a thin flux tube, using a frame parallelly transported along the axis of the tube.
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)
Effects of the radial electric field resonances on the particle orbits and loss cones in TJ-II
International Nuclear Information System (INIS)
Guasp, J.; Liniers, M.
1997-07-01
The effects of the radial electric field resonances on the trapping and confinement of low and intermediate energy ions (0.1-1 keV) for the Reference configuration of TJ-II have been analysed. In TJ-II these resonances appear for electric potentials that grow with pitch and with the square root of the initial kinetic energy and are placed inside strips whose width increases with the initial radius and with the absolute value of initial pitch. The 0-Resonance is the most important one for particle trapping, it appears for high electric potential (between 1000 and 3000 V for 0.5 keV ions) with the same sign than pitch, inside very wide strips (several thousands of V). Along these band periphery, for potential intensities below the central resonant values, there exists a very strong increase of particle trapping. Instead, around the resonance center, the trapping is inhibited and a very strong increase of the passing particle population appears. This increase is higher for the torus external side (Theta approximately 0 degree centigree) and for small initial radius. For peripherical particles wide loss strips appear along the border of the resonant band corresponding to more positive potential. The 2-Resonance has small effect on trapping but affects strongly to the of peripherical passing particles. It appears for moderate electric potential (between 400 and 1000 V for 0.5 keV ions) with sign opposite than pitch and inside narrow bands than the 0-Resonance. In this case a loss of peripherical passing particles appears, placed also along the more positive potential band side. The other Resonances (except the -4) have much less effect on particle trapping and confinement. All these phenomena have been explained by the action of magnetic barriers and different mechanisms for particle orbit modification. (Author) 8 refs
Functional magnetic resonance imaging in a low-field intraoperative scanner.
Schulder, Michael; Azmi, Hooman; Biswal, Bharat
2003-01-01
Functional magnetic resonance imaging (fMRI) has been used for preoperative planning and intraoperative surgical navigation. However, most experience to date has been with preoperative images acquired on high-field echoplanar MRI units. We explored the feasibility of acquiring fMRI of the motor cortex with a dedicated low-field intraoperative MRI (iMRI). Five healthy volunteers were scanned with the 0.12-tesla PoleStar N-10 iMRI (Odin Medical Technologies, Israel). A finger-tapping motor paradigm was performed with sequential scans, acquired alternately at rest and during activity. In addition, scans were obtained during breath holding alternating with normal breathing. The same paradigms were repeated using a 3-tesla MRI (Siemens Corp., Allandale, N.J., USA). Statistical analysis was performed offline using cross-correlation and cluster techniques. Data were resampled using the 'jackknife' process. The location, number of activated voxels and degrees of statistical significance between the two scanners were compared. With both the 0.12- and 3-tesla imagers, motor cortex activation was seen in all subjects to a significance of p < 0.02 or greater. No clustered pixels were seen outside the sensorimotor cortex. The resampled correlation coefficients were normally distributed, with a mean of 0.56 for both the 0.12- and 3-tesla scanners (standard deviations 0.11 and 0.08, respectively). The breath holding paradigm confirmed that the expected diffuse activation was seen on 0.12- and 3-tesla scans. Accurate fMRI with a low-field iMRI is feasible. Such data could be acquired immediately before or even during surgery. This would increase the utility of iMRI and allow for updated intraoperative functional imaging, free of the limitations of brain shift. Copyright 2003 S. Karger AG, Basel
Usefulness of intraoperative ultra low-field magnetic resonance imaging in glioma surgery.
Senft, Christian; Seifert, Volker; Hermann, Elvis; Franz, Kea; Gasser, Thomas
2008-10-01
The aim of this study was to demonstrate the usefulness of a mobile, intraoperative 0.15-T magnetic resonance imaging (MRI) scanner in glioma surgery. We analyzed our prospectively collected database of patients with glial tumors who underwent tumor resection with the use of an intraoperative ultra low-field MRI scanner (PoleStar N-20; Odin Medical Technologies, Yokneam, Israel/Medtronic, Louisville, CO). Sixty-three patients with World Health Organization Grade II to IV tumors were included in the study. All patients were subjected to postoperative 1.5-T imaging to confirm the extent of resection. Intraoperative image quality was sufficient for navigation and resection control in both high- and low-grade tumors. Primarily enhancing tumors were best detected on T1-weighted imaging, whereas fluid-attenuated inversion recovery sequences proved best for nonenhancing tumors. Intraoperative resection control led to further tumor resection in 12 (28.6%) of 42 patients with contrast-enhancing tumors and in 10 (47.6%) of 21 patients with noncontrast-enhancing tumors. In contrast-enhancing tumors, further resection led to an increased rate of complete tumor resection (71.2 versus 52.4%), and the surgical goal of gross total removal or subtotal resection was achieved in all cases (100.0%). In patients with noncontrast-enhancing tumors, the surgical goal was achieved in 19 (90.5%) of 21 cases, as intraoperative MRI findings were inconsistent with postoperative high-field imaging in 2 cases. The use of the PoleStar N-20 intraoperative ultra low-field MRI scanner helps to evaluate the extent of resection in glioma surgery. Further tumor resection after intraoperative scanning leads to an increased rate of complete tumor resection, especially in patients with contrast-enhancing tumors. However, in noncontrast- enhancing tumors, the intraoperative visualization of a complete resection seems less specific, when compared with postoperative 1.5-T MRI.
A high-resolution EPR-CT microscope using cavity-resonators equipped with small field gradient coils
International Nuclear Information System (INIS)
Miki, T.; Murata, T.; Kumai, H.; Yamashiro, A.
1996-01-01
Cylindrical cavity resonators equipped with field gradient coils were developed for two-dimensional EPR-CT microscope systems. The field gradient coils lie in four (or six) thin metal tubes placed along the direction of the microwave magnetic field in the cavity to minimize impact on the resonator's quality factor. Two pairs of the tubes carry a 100 kHz current for magnetic field modulation. This cavity has high spin-detection sensitivity and can provide EPR images with submillimeter resolution. In order to reconstruct better images from fewer projections, we used an algebraic reconstruction technique (ART) for the two-dimensional image reconstruction. The ART method may be suitable for not only spectral-spatial two-dimensional EPR imaging, but also spatio-temporal EPR imaging in dynamic spin systems. (author)
International Nuclear Information System (INIS)
Kuo, S.C.; Kuo, S.P.
1996-01-01
Electron behavior in an electron cyclotron resonance microwave discharge sustained by TM 11 mode fields of a cylindrical waveguide has been investigated via a Monte Carlo simulation. The time averaged, spatially dependent electron energy distribution is computed self-consistently. At low pressures (∼0.5 mTorr), the temperature of the tail portion of the electron energy distribution exceeds 40 eV, and the sheath potential is about -250 V. These results, which are about twice as high as the previous results for TM 01 mode fields [S. C. Kuo, E. E. Kunhardt, and S. P. Kuo, J. Appl. Phys. 73, 4197 (1993)], suggest that TM 11 mode fields have a stronger electron cyclotron resonance effect than TM 01 mode fields in a cylindrical waveguide. copyright 1996 American Institute of Physics
Hayashi, Akihiro; Shibamoto, Yuta; Hattori, Yukiko; Tamura, Takeshi; Iwabuchi, Michio; Otsuka, Shinya; Sugie, Chikao; Yanagi, Takeshi
2015-03-01
We treated prostate cancer patients with static 5-field intensity-modulated radiation therapy (IMRT) using linac 18-MV X-rays or tomotherapy with 6-MV X-rays. As X-ray energies differ, we hypothesized that 18-MV photon IMRT may be better for large patients and tomotherapy may be more suitable for small patients. Thus, we compared dose-volume parameters for the planning target volume (PTV) and organs at risk (OARs) in 59 patients with T1-3 N0M0 prostate cancer who had been treated using 5-field IMRT. For these same patients, tomotherapy plans were also prepared for comparison. In addition, plans of 18 patients who were actually treated with tomotherapy were analyzed. The evaluated parameters were homogeneity indicies and a conformity index for the PTVs, and D2 (dose received by 2% of the PTV in Gy), D98, Dmean and V10-70 Gy (%) for OARs. To evaluate differences by body size, patients with a known body mass index were grouped by that index ( 25 kg/m(2)). For the PTV, all parameters were higher in the tomotherapy plans compared with the 5-field IMRT plans. For the rectum, V10 Gy and V60 Gy were higher, whereas V20 Gy and V30 Gy were lower in the tomotherapy plans. For the bladder, all parameters were higher in the tomotherapy plans. However, both plans were considered clinically acceptable. Similar trends were observed in 18 patients treated with tomotherapy. Obvious trends were not observed for body size. Tomotherapy provides equivalent dose distributions for PTVs and OARs compared with 18-MV 5-field IMRT. Tomotherapy could be used as a substitute for high-energy photon IMRT for prostate cancer regardless of body size. © The Author 2015. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.
Pseudo-field line resonances in ground Pc5 pulsation events
Directory of Open Access Journals (Sweden)
D. V. Sarafopoulos
2005-02-01
Full Text Available In this work we study four representative cases of Pc5 ground pulsation events with discrete and remarkably stable frequencies extended at least in a high-latitude range of ~20°; a feature that erroneously gives the impression for an oscillation mode with "one resonant field line". Additionally, the presented events show characteristic changes in polarization sense, for a meridian chain of stations from the IMAGE array, and maximize their amplitude at or close to the supposed resonant magnetic field shell, much like the typical FLR. Nevertheless, they are not authentic FLRs, but pseudo-FLRs, as they are called. These structures are produced by repetitive and tilted twin-vortex structures caused by magnetopause surface waves, which are probably imposed by solar wind pressure waves. The latter is confirmed with in-situ measurements obtained by the Cluster satellites, as well as the Geotail, Wind, ACE, and LANL 1994-084 satellites. This research effort is largely based on two recent works: first, Sarafopoulos (2004a has observationally established that a solar wind pressure pulse (stepwise pressure variation produces a twin-vortex (single vortex current system over the ionosphere; second, Sarafopoulos (2004b has studied ground events with characteristic dispersive latitude-dependent structures and showed that these are associated with twin-vortex ionosphere current systems. In this work, we show that each pseudo-FLR event is associated with successive and tilted large-scale twin-vortex current systems corresponding to a magnetopause surface wave with wavelength 10-20R_{E}. We infer that between an authentic FLR, which is a spatially localized structure with an extent 0.5R_{E} in the magnetospheric equatorial plane, and the magnetopause surface wavelength, there is a scale factor of 20-40. A chief observational finding, in this work, is that there are Pc5 ground pulsation events showing two gradual and latitude
International Nuclear Information System (INIS)
Ebbers, T.
2001-01-01
Cardiovascular blood flow is highly complex and incompletely understood. Blood flow patterns are expected to influence the opening and closing of normal and prosthetic heart valves, the efficiency of cardiac filling and ejection, and the resistance to thrombus formation within the heart. Conventional diagnostic techniques are poorly suited to the study of the three-dimensional (3D) blood flow patterns in the heart chambers and large vessels. Noninvasive methods have also been inadequate in studying intracardiac pressure differences, which are the driving force of flow and are critical in the evaluation of many cardiovascular abnormalities. This thesis focuses on the development of non-invasive methods for analysis of 3D cardiovascular blood flow. Simultaneous study of cardiovascular fluid dynamics allowed knowledge exchange across the two disciplines, facilitating the development process and broadening the applicability of the methods. A time-resolved 3D phase-contrast Magnetic Resonance Imaging (MRI) technique was used to acquire the velocity vector field in a 3D volume encompassing the entire heart or a large vessel. Cardiovascular blood flow patterns were visualized by use of particle traces, which revealed, for instance, vortical flow patterns in the left atrium. By applying the Navier-Stokes equation along a user-defined line in the 3D velocity vector field, the relative pressure could be obtained as an excellent supplement to the flow pattern visualization. Using a delineation of the blood pool, the time-varying 3D relative pressure field in the human left ventricle was obtained from the velocity field by use of the pressure Poisson equation. A delineation of the heart muscle, a task that is almost impossible to perform on 3D MRI either automatically or manually, was also achieved by usage of particle traces. This segmentation allows automatic calculation of the 3D relative pressure field, as well as calculation of well-established parameters such as
Energy Technology Data Exchange (ETDEWEB)
Ebbers, T
2001-05-01
Cardiovascular blood flow is highly complex and incompletely understood. Blood flow patterns are expected to influence the opening and closing of normal and prosthetic heart valves, the efficiency of cardiac filling and ejection, and the resistance to thrombus formation within the heart. Conventional diagnostic techniques are poorly suited to the study of the three-dimensional (3D) blood flow patterns in the heart chambers and large vessels. Noninvasive methods have also been inadequate in studying intracardiac pressure differences, which are the driving force of flow and are critical in the evaluation of many cardiovascular abnormalities. This thesis focuses on the development of non-invasive methods for analysis of 3D cardiovascular blood flow. Simultaneous study of cardiovascular fluid dynamics allowed knowledge exchange across the two disciplines, facilitating the development process and broadening the applicability of the methods. A time-resolved 3D phase-contrast Magnetic Resonance Imaging (MRI) technique was used to acquire the velocity vector field in a 3D volume encompassing the entire heart or a large vessel. Cardiovascular blood flow patterns were visualized by use of particle traces, which revealed, for instance, vortical flow patterns in the left atrium. By applying the Navier-Stokes equation along a user-defined line in the 3D velocity vector field, the relative pressure could be obtained as an excellent supplement to the flow pattern visualization. Using a delineation of the blood pool, the time-varying 3D relative pressure field in the human left ventricle was obtained from the velocity field by use of the pressure Poisson equation. A delineation of the heart muscle, a task that is almost impossible to perform on 3D MRI either automatically or manually, was also achieved by usage of particle traces. This segmentation allows automatic calculation of the 3D relative pressure field, as well as calculation of well-established parameters such as
Near-field probing of Mie resonances in single TiO.sub.2./sub. microspheres at terahertz frequencies
Czech Academy of Sciences Publication Activity Database
Mitrofanov, O.; Dominec, Filip; Kužel, Petr; Reno, J.L.; Brener, I.; Chung, U.-C.; Elissalde, C.; Maglione, M.; Mounaix, P.
2014-01-01
Roč. 22, č. 19 (2014), s. 23034-23042 ISSN 1094-4087 R&D Projects: GA ČR(CZ) GA14-25639S EU Projects: European Commission(XE) 607521 - NOTEDEV Institutional support: RVO:68378271 Keywords : metamaterials * near-field microscopy * resonators * terahertz imaging Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.488, year: 2014
Jose, J.; Segerink, Franciscus B.; Korterik, Jeroen P.; Offerhaus, Herman L.
2008-01-01
We report the near-field observation of the phase shifts associated with total internal reflection on a glass-air interface and surface plasmon resonance on a glass-gold-air system. The phase of the evanescent waves on glass and gold surfaces, as a function of incident angle, is measured using a
DEFF Research Database (Denmark)
Kristensen, B.H.; Laursen, F.J.; Logager, V.
2008-01-01
Background and purpose: Magnetic resonance (MR) imaging is superior to computed tomography (CT) in radiotherapy of brain tumours. In this study an open low-field MR-simulator is evaluated in order to eliminate the cost of and time spent on additional CT scanning. Materials and methods: Eleven...
DEFF Research Database (Denmark)
Sørensen, Joan Solgaard; Kjaer, Per; Jensen, Tue Secher
2006-01-01
PURPOSE: To determine the intra- and interobserver reliability in grading disc and muscle parameters using low-field magnetic resonance imaging (MRI). MATERIAL AND METHODS: MRI scans of 100 subjects representative of the general population were evaluated blindly by two radiologists. Criteria......: Convincing reliability was found in the evaluation of disc- and muscle-related MRI variables....
Plasma edge control by chaotic magnetic field structures. Book of abstracts
International Nuclear Information System (INIS)
2013-01-01
The following topics were dealt with: Formation of stochastic magnetic layers and plasma response to external, non-axisymmetric magnetic perturbations, energy and particle transport in stochastic magnetic fields and 3D equilibria, application of resonant magnetic perturbations for ELM control and implications for ITER, transport and exhaust in helical and island divertors. (HSI)
Helicity multiplexed broadband metasurface holograms.
Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Pun, Edwin Yue Bun; Zhang, Shuang; Chen, Xianzhong
2015-09-10
Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices.
International Nuclear Information System (INIS)
Casado-Pascual, Jesus
2010-01-01
Graphical abstract: In this paper, we investigate the role of a high-frequency magnetic field in the resonant behavior displayed by a spin-1/2 particle under the influence of a rotating magnetic field. We propose two alternative methods for analyzing the system dynamics, namely, the averaging method and the multiple scale method. - Abstract: In this paper, we investigate the role of a high-frequency magnetic field in the resonant behavior displayed by a spin-1/2 particle under the influence of a rotating magnetic field. We propose two alternative methods for analyzing the system dynamics, namely, the averaging method and the multiple scale method. The analytical results achieved by applying these two methods are compared with those obtained from the numerical solution of the Schroedinger equation. This comparison leads to the conclusion that the multiple scale method provides a better understanding of the system dynamics than the averaging method. In particular, the averaging method predicts the complete destruction of the resonant behavior by an appropriate choice of the parameter values of the high-frequency magnetic field. This conclusion is disproved both by the numerical results, and also by the results obtained from the multiple scale method.
Imploding to equilibrium of helically symmetric theta pinches
International Nuclear Information System (INIS)
Sharky, N.N.
1978-01-01
The time-dependent, single-fluid, dissipative magnetohydrodynamic equations are solved in helical coordinates (r,phi), where phi = THETA-kz, k = 2π/L and L is the periodicity length in the z-direction. The two-dimensional numerical calculations simulate theta pinches which have an l = 1 helical field added to them. Given the applied magnetic fields and the initial state of the plasma, we study the time evolution of the system. The plasma is found to experience two kinds of oscillations, occurring on different time scales. These are the radial compression oscillations, and the slower helical oscillations of the plasma column. The plasma motion is followed until these oscillations disappear and an equilibrium is nearly reached. Hence given the amplitude and the rise time of the applied magnetic fields, the calculations allow one to relate the initial state of a cold, homogeneous plasma to its final equilibrium state where it is heated and compressed
Employing helicity amplitudes for resummation
International Nuclear Information System (INIS)
Moult, Ian; Stewart, Iain W.; Tackmann, Frank J.; Waalewijn, Wouter J.; Amsterdam Univ.
2015-08-01
Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of color-ordered helicity amplitudes. Using this basis allows one to seamlessly combine fixed-order helicity amplitudes at any order they are known with a resummation of higher-order logarithmic corrections. In particular, the virtual loop amplitudes can be employed in factorization theorems to make predictions for exclusive jet cross sections without the use of numerical subtraction schemes to handle real-virtual infrared cancellations. We also discuss matching onto SCET in renormalization schemes with helicities in 4- and d-dimensions. To demonstrate that our helicity operator basis is easy to use, we provide an explicit construction of the operator basis, as well as results for the hard matching coefficients, for pp → H+0,1,2 jets, pp → W/Z/γ+0,1,2 jets, and pp → 2,3 jets. These operator bases are completely crossing symmetric, so the results can easily be applied to processes with e + e - and e - p collisions.