Magnetic field homogeneity perturbations in finite Halbach dipole magnets.
Turek, Krzysztof; Liszkowski, Piotr
2014-01-01
Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerable attention due to their applications, among others, in compact NMR and MRI systems for investigating small objects. However, a complete mathematical framework for the analysis of magnetic fields in these magnets has been developed only for their infinitely long precursors. In such a case the analysis is reduced to two-dimensions (2D). The paper details the analysis of the 3D magnetic field in the Halbach dipole cylinders of a finite length. The analysis is based on three equations in which the components of the magnetic flux density Bx, By and Bz are expanded to infinite power series of the radial coordinate r. The zeroth term in the series corresponds to a homogeneous magnetic field Bc, which is perturbed by the higher order terms due to a finite magnet length. This set of equations is supplemented with an equation for the field profile B(z) along the magnet axis, presented for the first time. It is demonstrated that the geometrical factors in the coefficients of particular powers of r, defined by intricate integrals are the coefficients of the Taylor expansion of the homogeneity profile (B(z)-Bc)/Bc. As a consequence, the components of B can be easily calculated with an arbitrary accuracy. In order to describe perturbations of the field due to segmentation, two additional equations are borrowed from the 2D theory. It is shown that the 2D approach to the perturbations generated by the segmentation can be applied to the 3D Halbach structures unless r is not too close to the inner radius of the cylinder ri. The mathematical framework presented in the paper was verified with great precision by computations of B by a highly accurate integration of the magnetostatic Coulomb law and utilized to analyze the inhomogeneity of the magnetic field in the magnet with the accuracy better than 1 ppm.
Plasma-satellite interaction driven magnetic field perturbations
Energy Technology Data Exchange (ETDEWEB)
Saeed-ur-Rehman, E-mail: surehman@ualberta.ca [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada); Theoretical Physics Division, PINSTECH, Nilore Islamabad 44000 (Pakistan); Marchand, Richard, E-mail: Richard.Marchand@ualberta.ca [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada)
2014-09-15
We report the first fully kinetic quantitative estimate of magnetic field perturbations caused by the interaction of a spacecraft with space environment. Such perturbations could affect measurements of geophysical magnetic fields made with very sensitive magnetometers on-board satellites. Our approach is illustrated with a calculation of perturbed magnetic fields near the recently launched Swarm satellites. In this case, magnetic field perturbations do not exceed 20 pT, and they are below the sensitivity threshold of the on-board magnetometers. Anticipating future missions in which satellites and instruments would be subject to more intense solar UV radiation, however, it appears that magnetic field perturbations associated with satellite interaction with space environment, might approach or exceed instruments' sensitivity thresholds.
The perturbed magnetic fields caused by mechanical stress
Institute of Scientific and Technical Information of China (English)
QIN Fei; YAN Dong-mei
2006-01-01
In the framework of the linearized magnetoelastic theory,the perturbed magnetic fields caused by mechanical stress and deformation were investigated theoretically.Governing equations and boundary conditions to determine the perturbed fields were derived.The effect of mechanical deformation on the magnetic fields was taken into account by coupling structural displacement into the perturbed magnetic field continuous conditions on the boundary of the structure.As an example,the perturbed field of a half-plane magnetized structure caused by a point force was calculated by the Fourier transform method.The results show that the calculated magnetic intensity component normal to the boundary of the structure reaches its maximum at the point force acted while the component tangent to the boundary inverses its direction sharply.The magnetic induction of the perturbed field is proportional to the applied force.Magnitude analysis proved that since the applied magnetic field has a relative weak intensity such as the Earth's magnetic field, influence of the magnetic field on deformation of the structure can be neglected.
Compensation of Gradient-Induced Magnetic Field Perturbations
Nixon, Terence W.; McIntyre, Scott; Rothman, Douglas L.; de Graaf, Robin A.
2008-01-01
Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field gradients, pulsed currents in a strong external magnetic field also generate unwanted effects like eddy currents, gradient coil vibrations and acoustic noise. While the temporal magnetic field perturbations associated with eddy currents lead to spectral line shape distortions and signal loss, the vibration-related modulations lead to anti-symmetrical sidebands of any large signal (i.e. water), thereby obliterating the signals from smaller signals (i.e. metabolites). Here the measurement, characterization and compensation of vibrations-related magnetic field perturbations is presented. Following a quantitative evaluation of the various temporal components of the main magnetic field, a digital B0 magnetic field waveform is generated which reduces all temporal variations of the main magnetic field to within the spectral noise level. PMID:18329304
Cosmological Perturbations: Vorticity, Isocurvature and Magnetic Fields
Christopherson, Adam J
2014-01-01
In this paper I review some recent, interlinked, work undertaken using cosmological perturbation theory -- a powerful technique for modelling inhomogeneities in the Universe. The common theme which underpins these pieces of work is the presence of non-adiabatic pressure, or entropy, perturbations. After a brief introduction covering the standard techniques of describing inhomogeneities in both Newtonian and relativistic cosmology, I discuss the generation of vorticity. As in classical fluid mechanics, vorticity is not present in linearized perturbation theory (unless included as an initial condition). Allowing for entropy perturbations, and working to second order in perturbation theory, I show that vorticity is generated, even in the absence of vector perturbations, by purely scalar perturbations, the source term being quadratic in the gradients of first order energy density and isocurvature, or non-adiabatic pressure perturbations. This generalizes Crocco's theorem to a cosmological setting. I then introduc...
Cosmic magnetic fields from velocity perturbations in the early Universe
Betschart, G; Marklund, M; Betschart, Gerold; Dunsby, Peter K.S.; Marklund, Mattias
2004-01-01
We show, using a covariant and gauge-invariant charged multifluid perturbation scheme, that velocity perturbations of the matter-dominated dust Friedmann-Lemaitre-Robertson-Walker (FLRW) model can lead to the generation of cosmic magnetic fields. Moreover, using cosmic microwave background (CMB) constraints, it is argued that these fields can reach strengths of between 10^{-28} and 10^{-29} G at the time the dynamo mechanism sets in, making them plausible seed field candidates.
Effects of magnetic field perturbations in the ATF torsatron
Energy Technology Data Exchange (ETDEWEB)
Colchin, R.J.; England, A.C.; Isler, R.C.; Murakami, M.; Rasmussen, D.A.; Uckan, T.; Wilgen, J.B. [Oak Ridge National Lab., TN (United States); Aceto, S.C.; Zielinski, J.J. [Rensselaer Polytechnic Inst., Troy, NY (United States)
1993-10-01
The effects of errors in the magnetic fields of tokamaks on the plasma are quite different from those in stellarators. In tokamaks, field errors can cause disruptive locked modes through the non-linear evolution of tearing modes acting on initially small error-induced islands. Scaling predictions for these effects indicate that the critical relative field error which can be tolerated becomes smaller as the tokamak size becomes larger. In stellarators, the effect is more benign, as field errors appear only to cause increased plasma transport in the vicinity of islands. Great care has been taken to minimize magnetic field errors in the most recent generation of stellarator-type magnetic plasma traps. In the past six years, several new and sensitive techniques have been developed to detect and map field errors. These methods all rely on the detection of electrons injected along magnetic field lines. During the commissioning of ATF, flux surfaces were mapped using the fluorescent screen technique. Field errors were discovered and traced to uncompensated dipoles in the helical current feeds. Prior to elimination of these errors, plasma discharges indicated centrally peaked plasma profiles. After correction of the uncompensated dipoles, flux surfaces were mapped a second time, and the island widths were found to be greatly reduced. Field errors were then deliberately introduced using a set of perturbation coils that had been added to ATF, and electron-beam mapping of the flux surfaces showed that islands several centimeters in width could easily be created by these coils. After elimination of the error fields, the measured plasma temperature and density profiles were much broader. The field-perturbation coils were then used to produce magnetic field asymmetries, and the measured plasma profiles were again shown to narrow as a result of islands.
Test particle transport in perturbed magnetic fields in tokamaks
de Rover, M.; Schilham, A.M.R.; Montvai, A.; Cardozo, N. J. L.
1999-01-01
Numerical calculations of magnetic field line trajectories in a tokamak are used to investigate the common hypotheses that (i) field lines in a chaotic field make a Gaussian random walk and (ii) that the poloidal component of the magnetic field is uniform in regions with a chaotic magnetic field. Bo
Wang, Shaojie
2016-07-01
Anomalous current pinch, in addition to the anomalous diffusion due to stochastic magnetic perturbations, is theoretically found, which may qualitatively explain the recent DIII-D experiment on resonant magnetic field perturbation. The anomalous current pinch, which may resolve the long-standing issue of seed current in a fully bootstrapped tokamak, is also discussed for the electrostatic turbulence.
A Mechanism of ELM Mitigation by External Magnetic Field Perturbations
Singh, Raghvendra; Jhang, H.; Kim, J.-H.; Hahm, T. S.
2016-10-01
We study the impact of external magnetic perturbations (EMP) on the stability of ballooning mode (BM). We use: 1) the two-step process; 2) standard four wave interactions. In two-step process, we consider EMP are long wave-length perturbations interacting with short scale BM and generating side-bands of higher harmonics. This calculates contributions from all the high toroidal mode numbers. EMP can modify the dispersion characteristics of BM - the growth spectrum becomes broader in kBM space. The increase in high kBM can lead to the mitigation of an ELM crash by increasing turbulent transport. New nonlinear instability is also found even below the BM threshold at large EMP amplitude. In four wave interaction, EMP act like a short scale pump wave interacting with BM and creating two sidebands. The side-bands couple with the pump and produce the ponderomotive force, magnetic stress at BM frequency. EMP may enhance the BM instability threshold if RMP K->BM RMP and reduce the threshold if K->BM >K->RMP .
Toroidal rotation braking with n = 1 magnetic perturbation field on JET
DEFF Research Database (Denmark)
Sun, Y; Liang, Y; Koslowski, H R;
2010-01-01
A strong toroidal rotation braking has been observed in plasmas with application of an n = 1 magnetic perturbation field on the JET tokamak. Calculation results from the momentum transport analysis show that the torque induced by the n = 1 perturbation field has a global profile. The maximal valu...
Kim, Kimin; Jeon, Y. M.; Park, J.-K.; Ko, W. H.; In, Y.; Choe, W.; Kim, J.; Lee, S. G.; Yoon, S. W.; Kwak, J. G.; Oh, Y. K.
2017-03-01
The variation of a magnetic braking profile by non-axisymmetric magnetic fields has been experimentally demonstrated and numerically validated in the KSTAR tokamak. Two types of n = 2 non-resonant magnetic fields were applied by changing the relative phase of non-axisymmetric field coils. One is even parity, of which non-resonant fields deeply penetrate into the plasma core, and the other is odd parity localized at the plasma edge. The even and odd parity produced significantly different perturbed magnetic field structures, and thereby drove global and edge-dominant toroidal rotation damping, respectively. These distinct braking profiles are consistently reproduced by drift-kinetic particle simulations, indicating the possibility of the predictive utilization of non-resonant magnetic fields for rotation profile control.
Use of Earth's magnetic field for mitigating gyroscope errors regardless of magnetic perturbation.
Afzal, Muhammad Haris; Renaudin, Valérie; Lachapelle, Gérard
2011-01-01
Most portable systems like smart-phones are equipped with low cost consumer grade sensors, making them useful as Pedestrian Navigation Systems (PNS). Measurements of these sensors are severely contaminated by errors caused due to instrumentation and environmental issues rendering the unaided navigation solution with these sensors of limited use. The overall navigation error budget associated with pedestrian navigation can be categorized into position/displacement errors and attitude/orientation errors. Most of the research is conducted for tackling and reducing the displacement errors, which either utilize Pedestrian Dead Reckoning (PDR) or special constraints like Zero velocity UPdaTes (ZUPT) and Zero Angular Rate Updates (ZARU). This article targets the orientation/attitude errors encountered in pedestrian navigation and develops a novel sensor fusion technique to utilize the Earth's magnetic field, even perturbed, for attitude and rate gyroscope error estimation in pedestrian navigation environments where it is assumed that Global Navigation Satellite System (GNSS) navigation is denied. As the Earth's magnetic field undergoes severe degradations in pedestrian navigation environments, a novel Quasi-Static magnetic Field (QSF) based attitude and angular rate error estimation technique is developed to effectively use magnetic measurements in highly perturbed environments. The QSF scheme is then used for generating the desired measurements for the proposed Extended Kalman Filter (EKF) based attitude estimator. Results indicate that the QSF measurements are capable of effectively estimating attitude and gyroscope errors, reducing the overall navigation error budget by over 80% in urban canyon environment.
Use of Earth’s Magnetic Field for Mitigating Gyroscope Errors Regardless of Magnetic Perturbation
Directory of Open Access Journals (Sweden)
Muhammad Haris Afzal
2011-11-01
Full Text Available Most portable systems like smart-phones are equipped with low cost consumer grade sensors, making them useful as Pedestrian Navigation Systems (PNS. Measurements of these sensors are severely contaminated by errors caused due to instrumentation and environmental issues rendering the unaided navigation solution with these sensors of limited use. The overall navigation error budget associated with pedestrian navigation can be categorized into position/displacement errors and attitude/orientation errors. Most of the research is conducted for tackling and reducing the displacement errors, which either utilize Pedestrian Dead Reckoning (PDR or special constraints like Zero velocity UPdaTes (ZUPT and Zero Angular Rate Updates (ZARU. This article targets the orientation/attitude errors encountered in pedestrian navigation and develops a novel sensor fusion technique to utilize the Earth’s magnetic field, even perturbed, for attitude and rate gyroscope error estimation in pedestrian navigation environments where it is assumed that Global Navigation Satellite System (GNSS navigation is denied. As the Earth’s magnetic field undergoes severe degradations in pedestrian navigation environments, a novel Quasi-Static magnetic Field (QSF based attitude and angular rate error estimation technique is developed to effectively use magnetic measurements in highly perturbed environments. The QSF scheme is then used for generating the desired measurements for the proposed Extended Kalman Filter (EKF based attitude estimator. Results indicate that the QSF measurements are capable of effectively estimating attitude and gyroscope errors, reducing the overall navigation error budget by over 80% in urban canyon environment.
Perturbed magnetic field of an infinite plate with a centered crack
Institute of Scientific and Technical Information of China (English)
Fei Qin; Yang Zhang; Ya-Nan Liu
2011-01-01
Deforming a cracked magnetoelastic body in a magnetic field induces a perturbed magnetic field around the crack.The quantitative relationship between this perturbed field and the stress around the crack is crucial in developing a new generation of magnetism-based nondestructive testing technologies.In this paper, an analytical expression of the perturbed magnetic field induced by structural deformation of an infinite ferromagnetic elastic plate containing a centered crack in a weak external magnetic field is obtained by using the linearized magnetoelastic theory and Fourier transform methods.The main finding is that the perturbed magnetic field intensity is proportional to the applied tensile stress, and is dominated by the displacement gradient on the boundary of the magnetoelastic solid.The tangential component of the perturbed magnetic-field intensity near the crack exhibits an antisymmetric distribution along the crack that reverses its direction sharply across its two faces, while the normal component shows a symmetric distribution along the crack with singular points at the crack tips.
Indian Academy of Sciences (India)
K. N. Nagendra; H. Frisch; M. Faurobert-Scholl; F. Paletou
2000-09-01
We present an application of the PALI (Polarized Approximate Lambda Iteration) method to the resonance scattering in spectral lines formed in the presence of weak magnetic fields. The method is based on an operator perturbation approach, and can efficiently give solutions for oriented vector magnetic fields in the solar atmosphere.
Primordial magnetic fields from second-order cosmological perturbations:Tight coupling approximation
Maeda, Satoshi; Kobayashi, Tsutomu; Shiromizu, Tetsuya
2008-01-01
We explore the possibility of generating large-scale magnetic fields from second-order cosmological perturbations during the pre-recombination era. The key process for this is Thomson scattering between the photons and the charged particles within the cosmic plasma. To tame the multi-component interacting fluid system, we employ the tight coupling approximation. It is shown that the source term for the magnetic field is given by the product of the first order perturbations and so the intrinsically second-order quantities do not contribute to magnetogenesis. The magnetic fields generated by this process are estimated to be \\sim 10^{-26},Gauss on the horizon scale.
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.
Most Typical 12 Resonant Perturbation of the Hydrogen Atom by Weak Electric and Magnetic Fields
Efstathiou, K.; Lukina, O. V.; Sadovskii, D. A.
2008-01-01
We study a perturbation of the hydrogen atom by small homogeneous static electric and magnetic fields in a specific mutual alignment with angle approximately pi/3 which results in the 12 resonance of the linearized Keplerian n-shell approximation. The bifurcation diagram of the classical integrable
Evolution of Cosmological Perturbations in the Presence of Primordial Magnetic Fields
Kojima, Kazuhiko
2009-01-01
Possible existence of the primordial magnetic fields has affected the structure formation of the universe. In the numerical calculations for the evolution of density perturbations with primordial magnetic fields, there has been a difficulty in solving the Einstein-Boltzmann equations which arises due to the unwanted cancellation of contributions from the magnetic fields and primordial radiations. Here this problem is solved by newly taking into account a non-relativistic matter contribution in the radiation dominated era. A complete set of equations and appropriate initial conditions in the long wavelength limit are derived in a courteous manner in the covariant approach with CDM frame. By solving these equations numerically, we derive the angular spectrum of cosmic microwave background anisotropies and the matter power spectrum with magnetic fields. We find that the amplitude of the angular power spectrum of CMB anisotropies can alter at most a order of magnitude at $l \\lesssim 3000$ compared with the previo...
Screening of resonant magnetic perturbations taking into account a self-consistent electric field
Kaveeva, E.; Rozhansky, V.
2012-05-01
Steady-state screening of resonant magnetic perturbations (RMPs) in a tokamak is analysed taking into account a self-consistent electric field. On the one hand, the self-consistent radial electric field is determined by the balance of the electron radial conductivity in a stochastic magnetic field screened by the plasma and by the neoclassical ion conductivity. On the other hand, the parallel current of electrons, the radial projection of which is balanced by the ion current, determines the screening of RMPs. In this work, the self-consistent electric field and RMP screening are calculated. Two different regimes of screening are found: the ‘ion’ branch which corresponds to the negative radial electric field and the ‘electron’ branch for which the electric field is positive. Predictions of the model are compared with the experimental data and results of the simulation with various codes. The corresponding toroidal rotation and pump-out effect are discussed.
Institute of Scientific and Technical Information of China (English)
Yuan Lin; Zhao Yun-Hui; Xu Jun; Zhou Ben-Hu; Hai Wen-Hua
2012-01-01
A variational-integral perturbation method (VIPM) is established by combining the variational perturbation with the integral perturbation.The first-order corrected wave functions are constructed,and the second-order energy corrections for the ground state and several lower excited states are calculated by applying the VIPM to the hydrogen atom in a strong uniform magnetic field.Our calculations demonstrated that the energy calculated by the VIPM only shows a negative value,which indicates that the VIPM method is more accurate than the other methods.Our study indicated that the VIPM can not only increase the accuracy of the results but also keep the convergence of the wave functions.
From charge motion in general magnetic fields to the non perturbative gyrokinetic equation
Energy Technology Data Exchange (ETDEWEB)
Di Troia, C., E-mail: claudio.ditroia@enea.it [ENEA Unità tecnica Fusione, C.R. Frascati, Via E. Fermi 45, 00044 Frascati, Rome (Italy)
2015-04-15
The exact analytical description of non relativistic charge motion in general magnetic fields is, apparently, a simple problem, even if it has not been solved until now, apart for rare cases. The key feature of the present derivation is to adopt a non perturbative magnetic field description to find new solutions of motion. Among all solutions, two are particularly important: guiding particle and gyro-particle solutions. The guiding particle has been characterized to be minimally coupled to the magnetic field; the gyro-particle has been defined to be maximally coupled to the magnetic field and, also, to move on a closed orbit. The generic charged particle motion is shown to be expressed as the sum of such particular solutions. This non perturbative approach corresponds to the description of the particle motion in the gyro-center and/or guiding center reference frame obtained at all the orders of the modern gyro-center transformation. The Boltzmann equation is analyzed with the described exact guiding center coordinates. The obtained gyrokinetic equation is solved for the Boltzmann equation at marginal stability conditions.
Anisotropic non-perturbative zero modes for passively advected magnetic fields
Lanotte, A
1999-01-01
A first analytical assessment of the role of anisotropic corrections to the isotropic anomalous scaling exponents is given for the $d$-dimensional kinematic dynamo problem in the presence of a mean magnetic field. The velocity advecting the magnetic field changes very rapidly in time and scales with a positive exponent $\\xi$. Inertial-range anisotropic contributions to the scaling exponents of magnetic correlations are associated to zero modes and have been calculated non-perturbatively. For $d=3$, the limits $\\xi\\mapsto 0$ yelds $\\zeta_n=n+ \\xi [(n+2) (2 n^2-7 n-3)]/[2 (3+2 n) (1+2 n)]$ where $n$ is the order in the Legendre polynomial decomposition. Conjectures on the fact that anisotropic components cannot change the isotropic threshold to the dynamo effect are also made.
A test of magnetic field draping induced Bz perturbations ahead of fast coronal mass ejecta
Mccomas, D. J.; Gosling, J. T.; Bame, S. J.; Smith, E. J.; Cane, H. V.
1989-01-01
ICE plasma and magnetic field data are examined to look for observational evidence of IMF draping ahead of fast coronal mass ejections (CMEs). The utility of the draping model for predicting the Bz perturbations and hence geomagnetic activity associated with the sheath regions ahead of such CMEs is also examined. A simple prediction scheme based on the upstream radial field component is developed and a set of interplanetary shock events previously associated with interplanetary type II bursts, and hence solar source locations, is used. Of 17 events the radial component predictor developed here correctly predicts the direction considered of the Bz perturbations for 13 events (76 percent). While this result is certainly not conclusive, it is considered to be supportive of the draping scenario.
Tellgren, Erik I; Fliegl, Heike
2013-10-28
In the present study a non-perturbative approach to ab initio calculations of molecules in strong, linearly varying, magnetic fields is developed. The use of London atomic orbitals (LAOs) for non-uniform magnetic fields is discussed and the standard rationale of gauge-origin invariance is generalized to invariance under arbitrary constant shifts of the magnetic vector potential. Our approach is applied to study magnetically induced anapole moments (or toroidal moments) and the related anapole susceptibilities for a test set of chiral and nonchiral molecules. For the first time numerical anapole moments are accessible on an ab initio level of theory. Our results show that the use of London atomic orbitals dramatically improves the basis set convergence also for magnetic properties related to non-uniform magnetic fields, at the cost that the Hellmann-Feynman theorem does not apply for a finite LAO basis set. It is shown that the mixed anapole susceptibility can be related to chirality, since its trace vanishes for an achiral molecule.
Destruction of Invariant Surfaces and Magnetic Coordinates for Perturbed Magnetic Fields
Energy Technology Data Exchange (ETDEWEB)
S.R. Hudson
2003-11-20
Straight-field-line coordinates are constructed for nearly integrable magnetic fields. The coordinates are based on the robust, noble-irrational rotational-transform surfaces, whose existence is determined by an application of Greene's residue criterion. A simple method to locate these surfaces is described. Sequences of surfaces with rotational-transform converging to low order rationals maximize the region of straight-field-line coordinates.
Global Perturbation Configurations in a Composite Disc System with an Isopedic Magnetic Field
Lou, Y Q
2005-01-01
We construct stationary global configurations of both aligned and unaligned logarithmic spiral perturbations in a composite disc system of stellar and isopedically magnetized gaseous singular isothermal discs (SIDs) coupled by gravity. The thin gaseous SID is threaded across by a vertical magnetic field B_z with a constant ratio of the surface gas mass density to B_z. There exist two classes of stationary magnetohydrodynamic (MHD) solutions with in-phase and out-of-phase density perturbations. For both aligned and unaligned cases with azimuthal periodicities |m|\\geq 2 (m is an integer), there may be two, one, and no solution situations, depending on the chosen parameters. For the transition criteria from an axisymmetric equilibrium to aligned secular bar-like instabilities, the corresponding T/|W| ratio can be much lower than the oft-quoted value of T/|W|\\sim 0.14, where T is the total rotational kinetic energy and W is the total gravitational potential energy plus the magnetic energy. The T/|W| ratios for th...
Sub-solar Magnetopause Observation and Simulation of a Tripolar Guide-Magnetic Field Perturbation
Eriksson, S.; Cassak, P.; Retino, A.; Mozer, F.
2015-12-01
The Polar satellite recorded two reconnection exhausts within 6 min on 1 April 2001 at a rather symmetric sub-solar magnetopause that displayed different out-of-plane signatures for similar solar wind conditions. The first case was reported by Mozer et al. [2002] and displayed a bipolar guide field supporting a quadrupole Hall field consistent with a single X-line. The second case, however, shows the first known example of a tripolar guide-field perturbation at Earth's magnetopause reminiscent of the types of solar wind exhausts that Eriksson et al. [2014; 2015] have reported to be in agreement with multiple X-lines. A dedicated particle-in-cell simulation is performed for the prevailing conditions across the magnetopause. We propose an explanation in terms of asymmetric Hall magnetic fields due to a presence of a magnetic island between two X-lines, and discuss how higher resolution MMS observations can be used to further study this problem at the magnetopause.
An advection-diffusion model for cross-field runaway electron transport in perturbed magnetic fields
Särkimäki, Konsta; Decker, Joan; Varje, Jari; Kurki-Suonio, Taina
2016-01-01
Disruption-generated runaway electrons (RE) present an outstanding issue for ITER. The predictive computational studies of RE generation rely on orbit-averaged computations and, as such, they lack the effects from the magnetic field stochasticity. Since stochasiticity is naturally present in post-disruption plasma, and externally induced stochastization offers a prominent mechanism to mitigate RE avalanche, we present an advection-diffusion model that can be used to couple an orbit-following code to an orbit-averaged tool in order to capture the cross-field transport and to overcome the latter's limitation. The transport coefficients are evaluated via a Monte Carlo method. We show that the diffusion coefficient differs significantly from the well-known Rechester-Rosenbluth result. We also demonstrate the importance of including the advection: it has a two-fold role both in modelling transport barriers created by magnetic islands and in amplifying losses in regions where the islands are not present.
Perturbation Theory for Interacting Electrons in a Quantum Dot under Strong Magnetic Field
Institute of Scientific and Technical Information of China (English)
GU Yun-Ting; RUAN Wen-Ying; LI Quan; CAI Min; CHAN Kok-Sam
2001-01-01
The quantum spectrum of interacting electrons confined in a parabolic dot in two dimensions is obtained by employing the perturbation theory. Comparison with the existing analytical results has been made. We show that while the widely used second-order perturbation significantly underestimates the ground state energies, the results including higher orders of perturbation are highly accurate within the B-field range of experimental interest.
Modelling of plasma response to 3D external magnetic field perturbations in EAST
Yang, Xu; Sun, Youwen; Liu, Yueqiang; Gu, Shuai; Liu, Yue; Wang, Huihui; Zhou, Lina; Guo, Wenfeng
2016-11-01
Sustained mitigation and/or suppression of type-I edge localized modes (ELMs) has been achieved in EAST high-confinement plasmas, utilizing the resonant magnetic perturbation (RMP) fields produced by two rows of magnetic coils located just inside the vacuum vessel. Systematic toroidal modelling of the plasma response to these RMP fields with various coil configurations (with dominant toroidal mode number n = 1, 2, 3, 4) in EAST is, for the first time, carried out by using the MARS-F code (Liu et al 2000 Phys. Plasmas 7 3681), with results reported here. In particular, the plasma response is computed with varying coil phasing (the toroidal phase difference of the coil currents) between the upper and lower rows of coils, from 0 to 360°. Four figures of merit, constructed based on the MARS-F computations, are used to determine the optimal coil phasing. The modelled results, taking into account the plasma response, agree well with the experimental observations in terms of the coil phasing for both the mitigated and the suppressed ELM cases in EAST experiments. This study provides a crucial confirmation of the role of the plasma edge peeling response in ELM control, complementing similar studies carried out for other tokamak devices.
Longitudinal Conductivity in Strong Magnetic Field in Perturbative QCD: Complete Leading Order
Hattori, Koichi; Satow, Daisuke; Yee, Ho-Ung
2016-01-01
We compute the longitudinal electrical conductivity in the presence of strong background magnetic field in complete leading order of perturbative QCD, based on the assumed hierarchy of scales $\\alpha_s eB\\ll (m_q^2,T^2)\\ll eB$. We formulate an effective kinetic theory of lowest Landau level quarks with the leading order QCD collision term arising from 1-to-2 processes that become possible due to 1+1 dimensional Landau level kinematics. In small $m_q/T\\ll 1$ regime, the longitudinal conductivity behaves as $\\sigma_{zz}\\sim e^2(eB)T/(\\alpha_s m_q^2\\log(m_q/T))$, where the quark mass dependence can be understood from the chiral anomaly with the axial charge relaxation provided by a finite quark mass $m_q$. We also present parametric estimates for the longitudinal and transverse "color conductivities" in the presence of strong magnetic field, by computing dominant damping rates for quarks and gluons that are responsible for color charge transportation. We observe that the longitudinal color conductivity is enhanc...
Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR
Schmitz, O.; Ida, K.; Kobayashi, M.; Bader, A.; Brezinsek, S.; Evans, T. E.; Funaba, H.; Goto, M.; Mitarai, O.; Morisaki, T.; Motojima, G.; Nakamura, Y.; Narushima, Y.; Nicolai, D.; Samm, U.; Tanaka, H.; Yamada, H.; Yoshinuma, M.; Xu, Y.; TEXTOR, the; LHD Experiment Groups
2016-10-01
The ability to exhaust helium as the fusion born plasma impurity is a critical requirement for burning plasmas. We demonstrate in this paper that resonant magnetic perturbation (RMP) fields can be used to actively manipulate helium exhaust characteristics. We present results from puff/pump studies at TEXTOR as example for a tokamak with a pumped limiter and from the Large Helical Device (LHD) with the closed helical divertor as example for a heliotron/stellarator device. For LHD, the effective helium confinement time τ p,\\text{He}\\ast is a factor of 7-8 higher in the low and high density regimes explored when compared to TEXTOR discharges. This is attributed to ion root impurity transport which is one particular impurity transport regime assessed experimentally at LHD and which facilitates helium penetration to the plasma core. However, when an edge magnetic island is induced by externally applied RMP fields, τ p,\\text{He}\\ast is decreased by up to 30% and hence τ p,\\text{He}\\ast values closer to those of TEXTOR can be established. The combination of TEXTOR and LHD results suggest that a magnetic island induced by the RMP field in the plasma source region is an important ingredient for improving helium exhaust. The reduction in τ p,\\text{He}\\ast seen is caused by a combination of improved helium exhaust due to an enhanced coupling to the pumping systems, increased outward transport and a reduced fueling efficiency for the helium injected and recycling from the wall elements.
Perturbative Topological Field Theory
Dijkgraaf, Robbert
We give a review of the application of perturbative techniques to topological quantum field theories, in particular three-dimensional Chern-Simons-Witten theory and its various generalizations. To this end we give an introduction to graph homology and homotopy algebras and the work of Vassiliev and Kontsevich on perturbative knot invariants.
Caprini, Chiara; Paoletti, Daniela; Riotto, Antonio
2009-01-01
We evaluate the angular bispectrum of the CMB temperature anisotropy at large angular scale due to a stochastic background of primordial magnetic fields. The shape of non-Gaussianity depends on the spectral index of the magnetic field power spectrum and is peaked in the squeezed configuration for a scale-invariant magnetic spectrum. By using the large angular part of the bispectrum generated by magnetic fields, the present bounds on non-Gaussianity set a limit on the amplitude of the primordial magnetic field of the order of 10 nGauss for the scale-invariant case and 20 nGauss for the other spectral indexes.
Energy Technology Data Exchange (ETDEWEB)
JAYAKUMAR,RJ; MAKOWSKI,MA; ALLEN,SL; AUSTIN,ME; GAROFALO,AM; LA HAYE,RJ; REIMERDES,H; RHODES,TL
2003-11-01
OAK-B135 The local oscillating component of the poloidal magnetic field in plasma associated with MHD instabilities has been measured using the motional Stark effect (MSE) diagnostic on the DIII-D tokamak. The magnetic field perturbations associated with a resistive wall mode (RWM) rotated by internal coils at 20 Hz was measured using the conventional MSE operation mode. These first observations of perturbations due to a MHD mode were obtained on multiple MSE channels covering a significant portion of the plasma and the radial profile o the amplitude of the perturbed field oscillations was obtained. The measured profile is similar to the profile of the amplitude of the electron temperature oscillation measured by electron cyclotron emission (ECE) measurements. In a new mode of measurement, the amplitude of a tearing mode rotating at a high frequency ({approx} 7 kHz) was observed using the spectral analysis of high frequency MSE data on one channel. The spectrum consists of the harmonics of the light modulation employed in the MSE diagnostics, their mutual beat frequencies and their beat frequencies with the rotation frequency of the tearing mode. The value and time variation of the frequency of the observed perturbations is in good agreement with that measured by Mirnov probes and ECE. The paper demonstrates that the MSE diagnostic can be used for observing low and high frequency phenomena such as MHD instabilities and electromagnetic turbulence.
Energy Technology Data Exchange (ETDEWEB)
Vatin, N.I.; Tananaev, A.V.
1985-12-01
A relationship is established between the correlation functions of conduction converter signals and the spatial-temporal correlation functions of fluid velocity and vorticity fluctuations. Results of an experimental study of flow in a circular duct in the wake of a transverse cylinder are presented, indicating a reduction in the attenuation of perturbations oriented along a magnetic field and an increase in their scale with distance downstream.
Xiang-Gruess, M; Duschl, W J
2009-01-01
We study global non-axisymmetric stationary perturbations of aligned and unaligned logarithmic spiral configurations in an axisymmetric composite differentially rotating disc system of scale-free stellar and isopedically magnetized gas discs coupled by gravity. The gas disc is threaded across by a vertical magnetic field $B_z$ with a constant dimensionless isopedic ratio $\\lambda\\equiv 2\\pi\\sqrt{G} \\Sigma^{(g)}/B_z$ of surface gas mass density $\\Sigma^{(g)}$ to $B_z$ with $G$ being the gravitational constant. Our exploration focuses on the relation between $\\lambda$ and the dark matter amount represented by a ratio $f\\equiv\\bar{\\Phi}/\\Phi$ in order to sustain stationary perturbation configurations, where $\\bar{\\Phi}$ is the gravitational potential of a presumed axisymmetric halo of dark matter and $\\Phi$ is the gravitational potential of the composite disc matter. High and low $\\lambda$ values correspond to relatively weak and strong magnetic fields given the same gas surface mass density, respectively. The m...
Xiong, Ying; Chen, Lunjin; Xie, Lun; Fu, Suiyan; Xia, Zhiyang; Pu, Zuyin
2017-05-01
Dayside modulated relativistic electron's butterfly pitch angle distributions (PADs) from ˜200 keV to 2.6 MeV were observed by Van Allen Probe B at L = 5.3 on 15 November 2013. They were associated with localized magnetic dip driven by hot ring current ion (60-100 keV proton and 60-200 keV helium and oxygen) injections. We reproduce the electron's butterfly PADs at satellite's location using test particle simulation. The simulation results illustrate that a negative radial flux gradient contributes primarily to the formation of the modulated electron's butterfly PADs through inward transport due to the inductive electric field, while deceleration due to the inductive electric field and pitch angle change also makes in part contribution. We suggest that localized magnetic field perturbation, which is a frequent phenomenon in the magnetosphere during magnetic disturbances, is of great importance for creating electron's butterfly PADs in the Earth's radiation belts.
Energy Technology Data Exchange (ETDEWEB)
Kasilov, Sergei V. [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, Technische Universität Graz Petersgasse 16, A–8010 Graz (Austria); Institute of Plasma Physics National Science Center “Kharkov Institute of Physics and Technology” ul. Akademicheskaya 1, 61108 Kharkov (Ukraine); Kernbichler, Winfried; Martitsch, Andreas F.; Heyn, Martin F. [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, Technische Universität Graz Petersgasse 16, A–8010 Graz (Austria); Maassberg, Henning [Max-Planck Institut für Plasmaphysik, D-17491 Greifswald (Germany)
2014-09-15
The toroidal torque driven by external non-resonant magnetic perturbations (neoclassical toroidal viscosity) is an important momentum source affecting the toroidal plasma rotation in tokamaks. The well-known force-flux relation directly links this torque to the non-ambipolar neoclassical particle fluxes arising due to the violation of the toroidal symmetry of the magnetic field. Here, a quasilinear approach for the numerical computation of these fluxes is described, which reduces the dimension of a standard neoclassical transport problem by one without model simplifications of the linearized drift kinetic equation. The only limiting condition is that the non-axisymmetric perturbation field is small enough such that the effect of the perturbation field on particle motion within the flux surface is negligible. Therefore, in addition to most of the transport regimes described by the banana (bounce averaged) kinetic equation also such regimes as, e.g., ripple-plateau and resonant diffusion regimes are naturally included in this approach. Based on this approach, a quasilinear version of the code NEO-2 [W. Kernbichler et al., Plasma Fusion Res. 3, S1061 (2008).] has been developed and benchmarked against a few analytical and numerical models. Results from NEO-2 stay in good agreement with results from these models in their pertinent range of validity.
DEFF Research Database (Denmark)
Levring, O. A.; Pedersen, Niels Falsig; Samuelsen, Mogens Rugholm
1983-01-01
The motion of a single fluxon in long Josephson-junctions of overlap and inline geometries is investigated in the presence of an applied external magnetic field. The form of the first zero-field step for various parameters is given in closed analytic forms in both cases, and the differences and s...... and similarities between the two geometries are emphasized. Journal of Applied Physics is copyrighted by The American Institute of Physics....
Waltz, R. E.; Ferraro, N. M.
2015-04-01
The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, and electric potential from low-n external resonant magnetic field perturbations (RMPs) are obtained from the collisional two-fluid M3D-C1 code [N. M. Ferraro and S. C. Jardin, J. Comput. Phys. 228, 7742 (2009)]. A newly developed post-processing RMPtran code computes the resulting quasilinear E×B and magnetic (J×B) radial transport flows with respect to the unperturbed flux surfaces in all channels. RMPtran simulations focus on ion (center of mass) particle and transient non-ambipolar current flows, as well as the toroidal angular momentum flow. The paper attempts to delineate the RMP transport mechanisms that might be responsible for the RMP density pump-out seen in DIII-D [M. A. Mahdavi and J. L. Luxon, Fusion Sci. Technol. 48, 2 (2005)]. Experimentally, the starting high toroidal rotation does not brake to a significantly lower rotation after the pump-out suggesting that convective and E×B transport mechanisms dominate. The direct J×B torque from the transient non-ambipolar radial current expected to accelerate plasma rotation is shown to cancel much of the Maxwell stress J×B torque expected to brake the plasma rotation. The dominant E×B Reynolds stress accelerates rotation at the top of the pedestal while braking rotation further down the pedestal.
Li, Shiyong; Yee, Ho-Ung
2016-01-01
We compute the jet quenching parameter $\\hat q$ of QCD plasma in the presence of strong magnetic field in both weakly and strongly coupled regimes. In weakly coupled regime, we compute $\\hat q$ in perturbative QCD at complete leading order (that is, leading log as well as the constant under the log) in QCD coupling constant $\\alpha_s$, assuming the hierarchy of scales $\\alpha_s eB\\ll T^2\\ll eB$. We consider two cases of jet orientations with respect to the magnetic field: 1) the case of jet moving parallel to the magnetic field, 2) the case jet moving perpendicular to the magnetic field. In the former case, we find $\\hat q\\sim \\alpha_s^2 (eB)T\\log(1/\\alpha_s)$, while in the latter we have $\\hat q\\sim \\alpha_s^2 (eB)T\\log(T^2/\\alpha_seB)$. In both cases, this leading order result arises from the scatterings with thermally populated lowest Landau level quarks. In strongly coupled regime described by AdS/CFT correspondence, we find $\\hat q\\sim \\sqrt{\\lambda}(eB)T$ or $\\hat q\\sim\\sqrt{\\lambda}\\sqrt{eB}T^2$ in the...
Friis-Christensen, E.; Finlay, C. C.; Hesse, M.; Laundal, K. M.
2017-02-01
In the day-side sunlit polar ionosphere the varying and IMF dependent convection creates strong ionospheric currents even during quiet geomagnetic conditions. Observations during such times are often excluded when using satellite data to model the internal geomagnetic main field. Observations from the night-side or local winter during quiet conditions are, however, also influenced by variations in the IMF. In this paper we briefly review the large scale features of the ionospheric currents in the polar regions with emphasis on the current distribution during undisturbed conditions. We examine the distribution of scalar measurements of the magnetic field intensity minus predictions from a geomagnetic field model. These `residuals' fall into two main categories. One category is consistently distributed according to the well-known ionospheric plasma convection and its associated Birkeland currents. The other category represent contributions caused by geomagnetic activity related to the substorm current wedge around local magnetic midnight. A new observation is a strong IMF By control of the residuals in the midnight sector indicating larger ionospheric currents in the substorm current wedge in the northern polar region for By > 0 and correspondingly in the southern hemisphere for By < 0.
DEFF Research Database (Denmark)
Friis-Christensen, Eigil; Finlay, Chris; Hesse, M.
2017-01-01
In the day-side sunlit polar ionosphere the varying and IMF dependent convection creates strong ionospheric currents even during quiet geomagnetic conditions. Observations during such times are often excluded when using satellite data to model the internal geomagneticmain field. Observations from...... the night-side or local winter during quiet conditions are, however, also influenced by variations in the IMF. In this paper we briefly review the large scale features of the ionospheric currents in the polar regions with emphasis on the current distribution during undisturbed conditions. We examine....... The other category represent contributions caused by geomagnetic activity related to the substorm current wedge around local magnetic midnight. A new observation is a strong IMF By control of the residuals in the midnight sector indicating larger ionospheric currentsin the substorm current wedge...
Energy Technology Data Exchange (ETDEWEB)
Munaretto, S., E-mail: smunaretto@wisc.edu; Chapman, B. E.; Nornberg, M. D.; Boguski, J.; DuBois, A. M.; Almagri, A. F.; Sarff, J. S. [Department of Physics, University of Wisconsin–Madison, 1150 University Ave, Madison, Wisconsin 53706 (United States)
2016-05-15
The orientation of 3D equilibria in the Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch can now be controlled with a resonant magnetic perturbation (RMP). Absent the RMP, the orientation of the stationary 3D equilibrium varies from shot to shot in a semi-random manner, making its diagnosis difficult. Produced with a poloidal array of saddle coils at the vertical insulated cut in MST's thick conducting shell, an m = 1 RMP with an amplitude b{sub r}/B ∼ 10% forces the 3D structure into any desired orientation relative to MST's diagnostics. This control has led to improved diagnosis, revealing enhancements in both the central electron temperature and density. With sufficient amplitude, the RMP also inhibits the generation of high-energy (>20 keV) electrons, which otherwise emerge due to a reduction in magnetic stochasticity in the core. Field line tracing reveals that the RMP reintroduces stochasticity to the core. A m = 3 RMP of similar amplitude has little effect on the magnetic topology or the high-energy electrons.
Energy Technology Data Exchange (ETDEWEB)
Efstathiou, K; Lukina, O V [Department of Mathematics, University of Groningen, Groningen 9700 AK (Netherlands); SadovskiI, D A [Departement de physique, Universite du Littoral, 59140 Dunkerque (France)], E-mail: K.Efstathiou@rug.nl, E-mail: O.Lukina@math.rug.nl, E-mail: sadovski@univ-littoral.fr
2009-02-06
We consider perturbations of the hydrogen atom by sufficiently small homogeneous static electric and magnetic fields in near-orthogonal configurations. Normalization of the Keplerian symmetry reveals that in the parameter space such systems belong in a 'zone' of systems close to the 1:1 resonance, the latter corresponding to the exactly orthogonal configuration. Integrable approximations obtained from second normalization of systems in the 1:1 zone are classified into several different qualitative types, many of which possess nontrivial monodromy. We compute monodromy of the complete three-dimensional energy-momentum map, compare the joint quantum spectrum to classical bifurcation diagrams, and show the effect of second normalization to the joint spectrum.
Institute of Scientific and Technical Information of China (English)
Banibrata Mukhopadhyay; Kanak Saha
2011-01-01
The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle.Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity.Hence, any viscosity in such systems must be due to turbulence, arguably governed by magnetorotational instability, especially when temperature T (≥)105.However, such disks around quiescent cataclysmic variables, protoplanetary and star-forming disks, and the outer regions of disks in active galactic nuclei are practically neutral in charge because of their low temperature, and thus are not expected to be coupled with magnetic fields enough to generate any transport due to the magnetorotational instability.This flow is similar to plane Couette flow including the Coriolis force, at least locally.What drives their turbulence and then transport,when such flows do not exhibit any unstable mode under linear hydrodynamic perturbation? We demonstrate that the three-dimensional secondary disturbance to the primarily perturbed flow that triggers elliptical instability may generate significant turbulent viscosity in the range 0.0001 (≤) vt (≤) 0.1, which can explain transport in accretion flows.
Energy Technology Data Exchange (ETDEWEB)
Yang, Y. M.; Geurts, M.; Smilowitz, J. B.; Bednarz, B. P., E-mail: bbednarz2@wisc.edu [Department of Medical Physics, Wisconsin Institutes for Medical Research, University of Wisconsin, Madison, Wisconsin 53703 (United States); Sterpin, E. [Molecular Imaging, Radiotherapy and Oncology, Université catholique de Louvain, Brussels, Belgium 1348 (Belgium)
2015-02-15
Purpose: Several groups are exploring the integration of magnetic resonance (MR) image guidance with radiotherapy to reduce tumor position uncertainty during photon radiotherapy. The therapeutic gain from reducing tumor position uncertainty using intrafraction MR imaging during radiotherapy could be partially offset if the negative effects of magnetic field-induced dose perturbations are not appreciated or accounted for. The authors hypothesize that a more rotationally symmetric modality such as helical tomotherapy will permit a systematic mediation of these dose perturbations. This investigation offers a unique look at the dose perturbations due to homogeneous transverse magnetic field during the delivery of Tomotherapy{sup ®} Treatment System plans under varying degrees of rotational beamlet symmetry. Methods: The authors accurately reproduced treatment plan beamlet and patient configurations using the Monte Carlo code GEANT4. This code has a thoroughly benchmarked electromagnetic particle transport physics package well-suited for the radiotherapy energy regime. The three approved clinical treatment plans for this study were for a prostate, head and neck, and lung treatment. The dose heterogeneity index metric was used to quantify the effect of the dose perturbations to the target volumes. Results: The authors demonstrate the ability to reproduce the clinical dose–volume histograms (DVH) to within 4% dose agreement at each DVH point for the target volumes and most planning structures, and therefore, are able to confidently examine the effects of transverse magnetic fields on the plans. The authors investigated field strengths of 0.35, 0.7, 1, 1.5, and 3 T. Changes to the dose heterogeneity index of 0.1% were seen in the prostate and head and neck case, reflecting negligible dose perturbations to the target volumes, a change from 5.5% to 20.1% was observed with the lung case. Conclusions: This study demonstrated that the effect of external magnetic fields can
Energy Technology Data Exchange (ETDEWEB)
Kallinikos, N.; Isliker, H.; Vlahos, L.; Meletlidou, E. [Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece)
2014-06-15
An analytical description of magnetic islands is presented for the typical case of a single perturbation mode introduced to tokamak plasma equilibrium in the large aspect ratio approximation. Following the Hamiltonian structure directly in terms of toroidal coordinates, the well known integrability of this system is exploited, laying out a precise and practical way for determining the island topology features, as required in various applications, through an analytical and exact flux surface label.
Energy Technology Data Exchange (ETDEWEB)
Kikuchi, Y [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Bock, M F M de [FOM Institute for Plasma Physics Rijnhuizen, EURATOM Association, Postbus 1207, NL-3430 BE Nieuwegein, The (Netherlands); Finken, K H [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Jakubowski, M [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Jaspers, R [FOM Institute for Plasma Physics Rijnhuizen, EURATOM Association, Postbus 1207, NL-3430 BE Nieuwegein, The (Netherlands); Koslowski, H R [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Kraemer-Flecken, A [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Lehnen, M [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Liang, Y [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Loewenbrueck, K [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Matsunaga, G [Fusion Research and Development Directorate, Japan Atomic Energy Agency, 311-0193 (Japan); Reiser, D [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Samm, U [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany); Sewell, G [Mathematics Department Texas A and M University, College Station, Texas (United States); Takamura, S [Department of Energy Engineering and Science, Graduate School of Engineering, Nagoya University, 464-8603 Nagoya (Japan); Unterberg, B; Wolf, R C; Zimmermann, O [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, D-52425 (Germany)
2007-05-15
Penetration processes of rotating helical magnetic perturbation field into tokamak plasmas have been investigated by the dynamic ergodic divertor (DED) in TEXTOR. Experimental observations of the field penetration and field amplification are performed and the data are interpreted by theoretical analyses based on a linearized two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED-field is accompanied by a change in the plasma fluid rotation. The theoretical model is also applied to the DED experiment in the small tokamak device HYBTOK-II. It is confirmed that the theoretical analyses can explain the observed radial profiles of the DED-field in the plasma by inserting small magnetic pick-up coils in HYBTOK-II.
Longcai, Zhang; Jianguo, Kong
2012-07-01
Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to AC external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay of the YBCO bulk over the NdFdB guideway used in the High-temperature superconducting maglev vehicle system with the application of the AC external magnetic field, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of the critical current density on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with lower critical current density. Therefore, we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by improving critical current density of the bulk.
Perturbed Einstein field equations using Maple
De Campos, M
2003-01-01
We obtain the perturbed components of affine connection and Ricci tensor using algebraic computation. Naturally, the perturbed Einstein field equations for the vacuum can written. The method can be used to obtain perturbed equations of the superior order.
Gregoratto, D.; Drake, J. R.; Yadikin, D.; Liu, Y. Q.; Paccagnella, R.; Brunsell, P. R.; Bolzonella, T.; Marchiori, G.; Cecconello, M.
2005-09-01
Arrays of magnetic coils and sensors in the EXTRAP T2R [P. R. Brunsell et al., Plasma Phys. Controlled Fusion 43 1457 (2001)] reversed-field pinch have been used to investigate the plasma response to an applied resonant magnetic perturbation in the range of the resistive-wall modes (RWMs). Measured RWM growth rates agree with predictions of a cylindrical ideal-plasma model. The linear growth of low-n marginally stable RWMs is related to the so-called resonant-field amplification due to a dominant ∣n∣=2 machine error field of about 2 G. The dynamics of the m =1 RWMs interacting with the applied field produced by the coils can be accurately described by a two-pole system. Estimated poles and residues are given with sufficient accuracy by the cylindrical model with a thin continuous wall.
Cosmic Electromagnetic Fields due to Perturbations in the Gravitational Field
Mongwane, Bishop; Osano, Bob
2012-01-01
We use non-linear gauge-invariant perturbation theory to study the interaction of an inflation produced seed magnetic field with density and gravitational wave perturbations in an almost Friedmann-Lema\\^itre-Robertson-Walker (FLRW) spacetime. We compare the effects of this coupling under the assumptions of poor conductivity, infinite conductivity and the case where the electric field is sourced via the coupling of velocity perturbations to the seed field in the ideal magnetohydrodynamic (MHD) regime, thus generalizing, improving on and correcting previous results. We solve our equations for long wavelength limits and numerically integrate the resulting equations to generate power spectra for the electromagnetic field variables, showing where the modes cross the horizon. We find that the rotation of the electric field dominates the power spectrum on small scales, in agreement with previous arguments.
Raikov, G D
2002-01-01
We consider the Pauli operator $H(b,V)$ acting in $L^2({\\mathbb R}^2; {\\mathbb C}^2)$. We describe a class of admissible magnetic fields $b$ such that the ground state of the unperturbed operator $H(b,0)$ which coincides with the origin, is an isolated eigenvalue of infinite multiplicity. In particular, this class includes certain almost periodic functions of non-zero mean value. Under the assumption that the matrix-valued electric potential $V$ has a definite sign and decays at infinity, we invastigate the asymptotic distribution of the discrete spectrum of $H(b,V)$ accumulating to the origin. We obtain different asymptotic formulae valid respectively in the cases of power-like decay of $V$, exponential decay of $V$, or compact support of $V$.
Resonant magnetic perturbations and divertor footprints in poloidally diverted tokamaks
Cahyna, Pavel
2010-01-01
General formula describing both the divertor strike point splitting and width of magnetic islands created by resonant magnetic perturbations (RMPs) in a poloidally diverted tokamak equilibrium is derived. Under the assumption that the RMP is produced by coils at the low-field side such as those used to control edge localized modes (ELMs) it is demonstrated that the width of islands on different magnetic surfaces at the edge and the amount of divertor splitting are related to each other. Explanation is provided of aligned maxima of the perturbation spectra with the safety factor profile - an effect empirically observed in models of many perturbation coil designs.
Multi-field inflation and cosmological perturbations
Gong, Jinn-Ouk
2016-01-01
We provide a concise review on multi-field inflation and cosmological perturbations. We discuss convenient and physically meaningful bases in terms of which perturbations can be systematically studied. We give formal accounts on the gauge fixing conditions and present the perturbation action in two gauges. We also briefly review non-linear perturbations.
DEFF Research Database (Denmark)
Olsen, Nils
2015-01-01
of the fluid flow at the top of the core. However, what is measured at or near the surface of the Earth is the superposition of the core field and fields caused by magnetized rocks in the Earth’s crust, by electric currents flowing in the ionosphere, magnetosphere, and oceans, and by currents induced......he Earth has a large and complicated magnetic field, the major part of which is produced by a self-sustaining dynamo operating in the fluid outer core. Magnetic field observations provide one of the few tools for remote sensing the Earth’s deep interior, especially regarding the dynamics...... in the Earth by time-varying external fields. These sources have their specific characteristics in terms of spatial and temporal variations, and their proper separation, based on magnetic measurements, is a major challenge. Such a separation is a prerequisite for remote sensing by means of magnetic field...
Solitary magnetic perturbations at the ELM onset
Wenninger, RP; Boom, JE; Burckhart, A; Dunne, MG; Dux, R; Eich, T; Fischer, R; Fuchs, C; Garcia-Munoz, M; Igochine, V; Hoelzl, M; Luhmann, NC; Lunt, T; Maraschek, M; Mueller, HW; Park, HK; Schneider, PA; Sommer, F; Suttrop, W; Viezzer, E
2012-01-01
Edge localised modes (ELMs) allow maintaining sufficient purity of tokamak H-mode plasmas and thus enable stationary H-mode. On the other hand in a future device ELMs may cause divertor power flux densities far in excess of tolerable material limits. The size of the energy loss per ELM is determined by saturation effects in the non-linear phase of the ELM, which at present is hardly understood. Solitary magnetic perturbations (SMPs) are identified as dominant features in the radial magnetic fluctuations below 100kHz. They are typically observed close (+-0.1ms) to the onset of pedestal erosion. SMPs are field aligned structures rotating in the electron diamagnetic drift direction with perpendicular velocities of about 10km/s. A comparison of perpendicular velocities suggests that the perturbation evoking SMPs is located at or inside the separatrix. Analysis of very pronounced examples showed that the number of peaks per toroidal turn is 1 or 2, which is clearly lower than corresponding numbers in linear stabil...
Zhang, Zhenyu
This thesis is written to summarize investigations of the mechanisms that underlie the kinetics of diatomic ligand rebinding to the iron atom of the heme group, which is chelated inside heme proteins. The family of heme proteins is a major object of studies for several branches of scientific research activity. Understanding the ligand binding mechanisms and pathways is one of the major goals for biophysics. My interests mainly focus on the physics of this ligand binding process. Therefore, to investigate the problem, isolated from the influence of the protein matrix, Fe-protophorphyrin IX is chosen as the prototype system in my studies. Myoglobin, the most extensively and intensively studied protein, is another ideal system that allows coupling the protein polypeptide matrix into the investigation. A technique to synchro-lock two laser pulse trains electronically is applied to our pump-probe spectroscopic studies. Based on this technique, a two color, fs/ps pump-probe system is developed which extends the temporal window for our investigation to 13ns and fills a gap existing in previous pump-probe investigations. In order to apply this newly-developed pump-probe laser system to implement systematic studies on the kinetics of diatomic ligand (NO, CO, O2) rebinding to heme and heme proteins, several experimental setups are utilized. In Chapter 1, the essential background knowledge, which helps to understand the iron-ligand interaction, is briefly described. In Chapter 2, in addition to a description of the preparation protocols of protein samples and details of the method for data analysis, three home-made setups are described, which include: a picosecond laser regenerative amplifier, a pump-probe application along the bore (2-inch in diameter) of a superconducting magnet and a temperature-controllable cryostat for spinning sample cell. Chapter 3 presents high magnetic field studies of several heme-ligand or protein-ligand systems. Pump-probe spectroscopy is used to
DeBock, M. F. M.; Classen, I. G. J.; Busch, C.; Jaspers, R. J. E.; Koslowski, H. R.; Unterberg, B.; TEXTOR Team
2008-01-01
For fusion reactors, based on the principle of magnetic confinement, it is important to avoid so-called magnetic islands or tearing modes. They reduce confinement and can be the cause of major disruptions. One class of magnetic islands is that of the perturbation field driven modes. This perturbation field can, for example, be the intrinsic error field. Theoretical work predicts a strong relationship between plasma rotation and the excitation of perturbation field modes. Experimentally, the theory on mode excitation and plasma rotation has been confirmed on several tokamaks. In those experiments, however, the control over the plasma rotation velocity and direction, and over the externally applied perturbation field was limited. In this paper experiments are presented that were carried out at the TEXTOR tokamak. Two tangential neutral beam injectors and a set of helical perturbation coils, called the dynamic ergodic divertor (DED), provide control over both the plasma rotation and the external perturbation field in TEXTOR. This made it possible to set up a series of experiments to test the theory on mode excitation and plasma rotation in detail. The perturbation field induced by the DED not only excites magnetic islands, it also sets up a layer near the plasma boundary where the magnetic field is stochastic. It will be shown that this stochastic field alters both the rotational response of the plasma on the perturbation field and the threshold for mode excitation. It therefore has to be included in an extended theory on mode excitation.
Controlling tokamak geometry with three-dimensional magnetic perturbations
Energy Technology Data Exchange (ETDEWEB)
Bird, T. M., E-mail: tbird@ipp.mpg.de [Max Planck Institute for Plasma Physics, EURATOM Association, Wendelsteinstr. 1, 17491 Greifswald (Germany); Hegna, C. C. [Departments of Engineering Physics and Physics, University of Wisconsin-Madison, 1500 Engineering Dr., Madison, Wisconsin 53703 (United States)
2014-10-15
It is shown that small externally applied magnetic perturbations can significantly alter important geometric properties of magnetic flux surfaces in tokamaks. Through 3D shaping, experimentally relevant perturbation levels are large enough to influence turbulent transport and MHD stability in the pedestal region. It is shown that the dominant pitch-resonant flux surface deformations are primarily induced by non-resonant 3D fields, particularly in the presence of significant axisymmetric shaping. The spectral content of the applied 3D field can be used to control these effects.
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)
2014-12-15
Resonant magnetic perturbations (RMPs) produce magnetic islands in toroidal plasmas. Self-healing (annihilation) of RMP-induced magnetic islands has been observed in helical systems, where a possible mechanism of the self-healing is shielding of RMP penetration by plasma flows, which is well known in tokamaks. Thus, fundamental physics of RMP shielding is commonly investigated in both tokamaks and helical systems. In order to check this mechanism, detailed informations of magnetic island phases are necessary. In experiments, measurement of radial magnetic responses is relatively easy. In this study, based on a theoretical model of rotating magnetic islands, behavior of radial magnetic fields during the self-healing is investigated. It is confirmed that flips of radial magnetic fields are typically observed during the self-healing. Such behavior of radial magnetic responses is also observed in LHD experiments.
Determination of wave fields from perturbed particle orbits
Skiff, Fred
1992-12-01
The linear problem of determining wave electric fields from measured perturbed particle distributions is considered. Previous work is extended to consider the case of arbitrary wave structure transverse to the magnetic field. The calculations are limited to electrostatic waves, although the ideas extend naturally to electromagnetic waves, and are illustrated in the one-dimensional case using data taken by laser-induced fluorescence.
Runaway electron drift orbits in magnetostatic perturbed fields
Papp, G.; Drevlak, M.; Fülöp, T.; Helander, P.
2011-04-01
Disruptions in large tokamaks can lead to the generation of a relativistic runaway electron beam that may cause serious damage to the first wall. To mitigate the disruption and suppress the runaway beam the application of resonant magnetic perturbations has been suggested. In this work we investigate the effect of resonant magnetic perturbations on the confinement of runaway electrons by simulating their drift orbits in magnetostatic perturbed fields and calculating the orbit losses for various initial energies and magnetic perturbation magnitudes. In the simulations we use a TEXTOR-like configuration and solve the relativistic, gyro-averaged drift equations for the runaway electrons including synchrotron radiation and collisions. The results indicate that runaway electrons are well confined in the core of the device, but the onset time of runaway losses closer to the edge is dependent on the magnetic perturbation level and thereby can affect the maximum runaway current. However, the runaway current damping rate is not sensitive to the magnetic perturbation level, in agreement with experimental observations.
Adiabatic perturbations in coupled scalar field cosmologies
Beyer, Joschka
2014-01-01
We present a comprehensive and gauge invariant treatment of perturbations around cosmological scaling solutions for two canonical scalar fields coupled through a common potential in the early universe, in the presence of neutrinos, photons and baryons, but excluding cold dark matter. This setup is relevant for analyzing cosmic perturbations in scalar field models of dark matter with a coupling to a quintessence field. We put strong restrictions on the shape of the common potential and adopt a matrix-eigensystem approach to determine the dominant perturbations modes in such models. Similar to recent results in scenarios where standard cold dark matter couples to quintessence, we show that the stability of the adiabatic perturbation mode can be an issue for this class of scalar field dark matter models, but only for specific choices of the common potential. For an exponential coupling potential, a rather common shape arising naturally in many instances, this problem can be avoided. We explicitly calculate the d...
Effective Field Theory of Cosmological Perturbations
Piazza, Federico
2013-01-01
The effective field theory of cosmological perturbations stems from considering a cosmological background solution as a state displaying spontaneous breaking of time translations and (adiabatic) perturbations as the related Nambu-Goldstone modes. With this insight, one can systematically develop a theory for the cosmological perturbations during inflation and, with minor modifications, also describe in full generality the gravitational interactions of dark energy, which are relevant for late-time cosmology. The formalism displays a unique set of Lagrangian operators containing an increasing number of cosmological perturbations and derivatives. We give an introductory description of the unitary gauge formalism for theories with broken gauge symmetry---that allows to write down the most general Lagrangian---and of the Stueckelberg "trick"---that allows to recover gauge invariance and to make the scalar field explicit. We show how to apply this formalism to gravity and cosmology and we reproduce the detailed ana...
Birkeland current effects on high-latitude groundmagnetic field perturbations
Laundal, K M; Lehtinen, N; Gjerloev, J W; Østgaard, N; Tenfjord, P; Reistad, J P; Snekvik, K; Milan, S E; Ohtani, S; Anderson, B J
2016-01-01
Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, $\\textbf{J}_{\\perp,df}$. Here we show how $\\textbf{J}_{\\perp,df}$ can be expressed as the total horizontal current $\\textbf{J}_\\perp$ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus in regions where $\\textbf{J}_\\perp = 0$, the global Birkeland current distribution alone determines the local magnetic perturbation. We show with observations from ground and space that in the polar cap, the ground magnetic field perturbations tend to align with the Birkeland current contribution in darkness but not in sunlight. We also show that in sunlight, the magnetic perturbations are typically such that the equivalent overhead current is anti-parallel to the convection, indicating that the Hall current system dominates. Thus the ground magnetic field in the polar cap relates to different c...
Cosmological scalar field perturbations can grow
Alcubierre, Miguel; Diez-Tejedor, Alberto; Torres, José M
2015-01-01
It has been argued that the small perturbations in the energy density to the homogeneous and isotropic configurations of a canonical scalar field in an expanding universe do not grow. We show that this is not true in general, and clarify the root of the misunderstanding. We revisit a simple model in which the linear perturbations grow like those in the standard cold dark matter scenario, but with the Jeans length at the scale of the Compton wavelength of the scalar particle.
Effective pinning energy landscape perturbations for propagating magnetic domain walls
Burn, D. M.; Atkinson, D.
2016-01-01
The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping ’quasi-static’ and low damping ’dynamic’ regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated. PMID:27694953
ELM mitigation via rotating resonant magnetic perturbations on MAST
Energy Technology Data Exchange (ETDEWEB)
Thornton, A.J., E-mail: andrew.thornton@ccfe.ac.uk [CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom); Kirk, A. [CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom); Cahyna, P. [Institute of Plasma Physics AS CR v.v.i, Prague (Czech Republic); Chapman, I.T.; Fishpool, G.; Harrison, J.R.; Liu, Y.Q. [CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom); Kripner, L.; Peterka, M. [Institute of Plasma Physics AS CR v.v.i, Prague (Czech Republic)
2015-08-15
The application of resonant magnetic perturbations (RMPs) produces splitting of the divertor strike point due to the interaction of the RMP field and the plasma field. The application of a rotating RMP field causes the strike point splitting to rotate, distributing the particle and heat flux evenly over the divertor. The RMP coils in MAST have been used to generate a rotating perturbation with a toroidal mode number n = 3. The ELM frequency is doubled with the application of the RMP rotating field, whilst maintaining the H mode. During mitigation, the ELM peak heat flux is seen to be reduced by 50% for a halving in the ELM energy and motion of the strike point, consistent with the rotation of the applied RMP field, is seen using high spatial resolution (1.5 mm at the target) heat flux profiles measured using infrared (IR) thermography.
ELM mitigation via rotating resonant magnetic perturbations on MAST
Thornton, A J; Cahyna, P; Chapman, I T; Fishpool, G; Harrison, J R; Liu, Y Q; Kripner, L; Peterka, M
2014-01-01
The application of resonant magnetic perturbations (RMPs) produces splitting of the divertor strike point due to the interaction of the RMP field and the plasma field. The application of a rotating RMP field causes the strike point splitting to rotate, distributing the particle and heat flux evenly over the divertor. The RMP coils in MAST have been used to generate a rotating perturbation with a toroidal mode number n=3. The ELM frequency is doubled with the application of the RMP rotating field, whilst maintaining the H mode. During mitigation, the ELM peak heat flux is seen to be reduced by 50% for a halving in the ELM energy and motion of the strike point, consistent with the rotation of the applied RMP field, is seen using high spatial resolution (1.5mm at the target) heat flux profiles measured using infrared (IR) thermography.
Cosmological Perturbations with Multiple Fluids and Fields
Hwang, J
2002-01-01
We consider the evolution of perturbed cosmological spacetime with multiple fluid and field system in Einstein gravity. Equations are presented in gauge-ready forms, and are presented using the adiabatic and isocurvature perturbation variables. We present equations in the general background with $K$ and $\\Lambda$. We also clarify the conditions for conserved adiabatic and isocurvature perturbations in the large-scale limit. One interesting conclusion is that, for ideal fluid system, although the isocurvature modes can seed the adiabatic mode in the large-scale limit, the isocurvature modes decouple from the adiabatic one which is not the case for the field system. Useful sets of equations readily applicable to the quintessence models and the warm inflation scenario can be found in this work. An application to the scaling regime with an exponential field potential is made in the Appendix.
Perturbations of ultralight vector field dark matter
Cembranos, J. A. R.; Maroto, A. L.; Núñez Jareño, S. J.
2017-02-01
We study the dynamics of cosmological perturbations in models of dark matter based on ultralight coherent vector fields. Very much as for scalar field dark matter, we find two different regimes in the evolution: for modes with {k}^2≪ Hma, we have a particle-like behaviour indistinguishable from cold dark matter, whereas for modes with {k}^2≫ Hma, we get a wave-like behaviour in which the sound speed is non-vanishing and of order c s 2 ≃ k 2/ m 2 a 2. This implies that, also in these models, structure formation could be suppressed on small scales. However, unlike the scalar case, the fact that the background evolution contains a non-vanishing homogeneous vector field implies that, in general, the evolution of the three kinds of perturbations (scalar, vector and tensor) can no longer be decoupled at the linear level. More specifically, in the particle regime, the three types of perturbations are actually decoupled, whereas in the wave regime, the three vector field perturbations generate one scalar-tensor and two vector-tensor perturbations in the metric. Also in the wave regime, we find that a non-vanishing anisotropic stress is present in the perturbed energy-momentum tensor giving rise to a gravitational slip of order ( Φ - Ψ)/ Φ ˜ c s 2 . Moreover in this regime the amplitude of the tensor to scalar ratio of the scalar-tensor modes is also h/ Φ ˜ c s 2 . This implies that small-scale density perturbations are necessarily associated to the presence of gravity waves in this model. We compare their spectrum with the sensitivity of present and future gravity waves detectors.
Near-zero-field nuclear magnetic resonance
Ledbetter, Micah; Theis, Thomas; Blanchard, John; Ring, Hattie; Ganssle, Paul; Appelt, Stephan; Bluemich, Bernhard; Pines, Alex; Budker, Dmitry
2011-01-01
We investigate nuclear magnetic resonance (NMR) in near-zero-field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction (J-coupling). This is in stark contrast to the high field case, where heteronuclear J-couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectr...
Perturbations of ultralight vector field dark matter
Cembranos, J A R; Jareño, S J Núñez
2016-01-01
We study the dynamics of cosmological perturbations in models of dark matter based on ultralight coherent vector fields. Very much as for scalar field dark matter, we find two different regimes in the evolution: for modes with $k^2\\ll {\\cal H}ma$, we have a particle-like behaviour indistinguishable from cold dark matter, whereas for modes with $k^2\\gg {\\cal H}ma$, we get a wave-like behaviour in which the sound speed is non-vanishing and of order $c_s^2\\simeq k^2/m^2a^2$. This implies that, also in these models, structure formation could be suppressed on small scales. However, unlike the scalar case, the fact that the background evolution contains a non-vanishing homogeneous vector field implies that, in general, the evolution of the three kinds of perturbations (scalar, vector and tensor) can no longer be decoupled at the linear level. More specifically, in the particle regime, the three types of perturbations are actually decoupled, whereas in the wave regime, the three vector field perturbations generate o...
Simulation of runaway electrons, transport affected by J-TEXT resonant magnetic perturbation
Jiang, Z. H.; Wang, X. H.; Chen, Z. Y.; Huang, D. W.; Sun, X. F.; Xu, T.; Zhuang, G.
2016-09-01
The topology of a magnetic field and transport properties of runaway electrons can be changed by a resonant magnetic perturbation field. The J-TEXT magnetic topology can be effectively altered via static resonant magnetic perturbation (SRMP) and dynamic resonant magnetic perturbation (DRMP). This paper studies the effect of resonant magnetic perturbation (RMP) on the confinement of runaway electrons via simulating their drift orbits in the magnetic perturbation field and calculating the orbit losses for different runaway initial energies and different runaway electrons, initial locations. The model adopted is based on Hamiltonian guiding center equations for runaway electrons, and the J-TEXT magnetic turbulences and RMP are taken into account. The simulation indicates that the loss rate of runaway electrons is sensitive to the radial position of electrons. The loss of energetic runaway beam is dominated by the shrinkage of the confinement region. Outside the shrinkage region of the runaway electrons are lost rapidly. Inside the shrinkage region the runaway beam is confined very well and is less sensitive to the magnetic perturbation. The experimental result on the response of runaway transport to the application RMP indicates that the loss of runaway electrons is dominated by the shrinkage of the confinement region, other than the external magnetic perturbation.
Magnetic field perturbartions in closed-field-line systems with zero toroidal magnetic field
Energy Technology Data Exchange (ETDEWEB)
Mauel, M; Ryutov, D; Kesner, J
2003-12-02
In some plasma confinement systems (e.g., field-reversed configurations and levitated dipoles) the confinement is provided by a closed-field-line poloidal magnetic field. We consider the influence of the magnetic field perturbations on the structure of the magnetic field in such systems and find that the effect of perturbations is quite different from that in the systems with a substantial toroidal field. In particular, even infinitesimal perturbations can, in principle, lead to large radial excursions of the field lines in FRCs and levitated dipoles. Under such circumstances, particle drifts and particle collisions may give rise to significant neoclassical transport. Introduction of a weak regular toroidal magnetic field reduces radial excursions of the field lines and neoclassical transport.
Perturbative renormalization of the electric field correlator
Christensen, C
2016-01-01
The momentum diffusion coefficient of a heavy quark in a hot QCD plasma can be extracted as a transport coefficient related to the correlator of two colour-electric fields dressing a Polyakov loop. We determine the perturbative renormalization factor for a particular lattice discretization of this correlator within Wilson's SU(3) gauge theory, finding a ~12% NLO correction for values of the bare coupling used in the current generation of simulations. The impact of this result on existing lattice determinations is commented upon, and a possibility for non-perturbative renormalization through the gradient flow is pointed out.
Perturbative renormalization of the electric field correlator
Directory of Open Access Journals (Sweden)
C. Christensen
2016-04-01
Full Text Available The momentum diffusion coefficient of a heavy quark in a hot QCD plasma can be extracted as a transport coefficient related to the correlator of two colour-electric fields dressing a Polyakov loop. We determine the perturbative renormalization factor for a particular lattice discretization of this correlator within Wilson's SU(3 gauge theory, finding a ∼12% NLO correction for values of the bare coupling used in the current generation of simulations. The impact of this result on existing lattice determinations is commented upon, and a possibility for non-perturbative renormalization through the gradient flow is pointed out.
Perturbative renormalization of the electric field correlator
Christensen, C.; Laine, M.
2016-04-01
The momentum diffusion coefficient of a heavy quark in a hot QCD plasma can be extracted as a transport coefficient related to the correlator of two colour-electric fields dressing a Polyakov loop. We determine the perturbative renormalization factor for a particular lattice discretization of this correlator within Wilson's SU(3) gauge theory, finding a ∼ 12% NLO correction for values of the bare coupling used in the current generation of simulations. The impact of this result on existing lattice determinations is commented upon, and a possibility for non-perturbative renormalization through the gradient flow is pointed out.
DEFF Research Database (Denmark)
Menvielle, M.; Primdahl, Fritz; Brauer, Peter
as characterizing its sub-surface. Magnetic fields are generated by electric currents in the planetary space environment, induced currents in the planetary interior and possibly remanent magnetism. In consequence, hardly any other single physical quantity can be used in such a variety of studies related...
Influence of resonant magnetic perturbations on transient heat load deposition and fast ion losses
Energy Technology Data Exchange (ETDEWEB)
Rack, Michael Thomas
2014-07-11
Thermonuclear fusion is the energy conversion process which keeps the sun shining. For the last six decades, researchers have been investigating the physics involved in order to enable the usage of this energy supply on Earth. The most promising candidates for fusion power plants are based on magnetic confinement of plasma to provide the ideal conditions for efficient thermonuclear fusion in well controlled surroundings. One important aspect is the control of instabilities that occur in the edge region of the plasma and lead to an ejection of huge amounts of energy. Magnetic perturbation fields which are resonant in the plasma edge are found to modify the plasma favourably and reduce the impact of these instabilities. This dissertation focuses on the effects of resonant magnetic perturbation fields on the ejected energy as well as on the drawbacks of these perturbation fields. The transient energy ejection which is triggered by the instabilities causes extreme heat loads on the wall components in fusion devices. Therefore, it is crucial to understand how resonant magnetic perturbation fields affect the heat load deposition. Furthermore, the impact of resonant magnetic perturbation fields on the confinement of fast ions is an important aspect as fast ions are still required to be well confined in order to avoid additional wall loads and increase the fusion efficiency. Recent upgrades on the Joint European Torus allow for a detailed study of the heat load deposition profiles caused by transient events. Throughout this work, the new features are used for the study of the modifications of the transient heat load depositions that occur if resonant magnetic perturbation fields are applied. This leads to a further understanding of the processes involved during the plasma edge instabilities. Additionally, an alternative method using lower hybrid waves for applying resonant magnetic perturbations is investigated. Furthermore, a new diagnostic, capable of detecting fast ion
Plasma Braking Due to External Magnetic Perturbations
Frassinetti, L.; Olofsson, Kejo; Brunsell, P. R.; Khan, M. W. M.; Drake, J. R.
2010-11-01
The RFP EXTRAP T2R is equipped with a comprehensive active feedback system (128 active saddle coils in the full-coverage array) and active control of both resonant and non-resonant MHD modes has been demonstrated. The feedback algorithms, based on modern control methodology such as reference mode tracking (both amplitude and phase), are a useful tool to improve the ``state of the art'' of the MHD mode control. But this tool can be used also to improve the understanding and the characterization of other phenomena such as the ELM mitigation with a resonant magnetic perturbation or the plasma viscosity. The present work studies plasma and mode braking due to static RMPs. Results show that a static RMP produces a global braking of the flow profile. The study of the effect of RMPs characterized by different helicities will also give information on the plasma viscosity profile. Experimental results are finally compared to theoretical models.
National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Calculator will calculate the total magnetic field, including components (declination, inclination, horizontal intensity, northerly intensity,...
Cosmological scalar field perturbations can grow
Alcubierre, Miguel; de la Macorra, Axel; Diez-Tejedor, Alberto; Torres, José M.
2015-09-01
It has been argued that the small perturbations to the homogeneous and isotropic configurations of a canonical scalar field in an expanding universe do not grow. We show that this is not true in general, and clarify the root of the misunderstanding. We revisit a simple model in which the zero mode of a free scalar field oscillates with high frequency around the minimum of the potential. Under this assumption the linear perturbations grow like those in the standard cold dark matter scenario, but with a Jeans length at the scale of the Compton wavelength of the scalar particle. Contrary to previous analyses in the literature our results do not rely on time averages and/or fluid identifications, and instead we solve both analytically (in terms of a well-defined series expansion) and numerically the linearized Einstein-Klein-Gordon system. Also, we use gauge-invariant fields, which makes the physical analysis more transparent and simplifies the comparison with previous works carried out in different gauges. As a byproduct of this study we identify a time-dependent modulation of the different physical quantities associated to the background as well as the perturbations with potential observational consequences in dark matter models.
Magnetic fields from second-order interactions
Osano, Bob
2014-01-01
It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a covariant-index-free approach, but could be done in the standard covariant indexed-approach.
Magnetic fields from second-order interactions
Osano, Bob
2014-01-01
It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a covariant-index-fre...
Energy Technology Data Exchange (ETDEWEB)
Yun, G. S.; Lee, W.; Choi, M. J.; Lee, J.; Park, H. K. [Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Domier, C. W.; Luhmann, N. C. Jr. [University of California at Davis, Davis, California 95616 (United States); Tobias, B. [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Donne, A. J. H. [FOM-Institute for Plasma Physics Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Einhoven University of Technology, 5600 MB Einhoven (Netherlands); Lee, J. H.; Jeon, Y. M.; Yoon, S. W. [National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Collaboration: KSTAR Team
2012-05-15
The temporal evolution of edge-localized modes (ELMs) has been studied using a 2-D electron cyclotron emission imaging system in the KSTAR tokamak. The ELMs are observed to evolve in three distinctive stages: the initial linear growth of multiple filamentary structures having a net poloidal rotation, the interim state of regularly spaced saturated filaments, and the final crash through a short transient phase characterized by abrupt changes in the relative amplitudes and distance among filaments. The crash phase, typically consisted of multiple bursts of a single filament, involves a complex dynamics, poloidal elongation of the bursting filament, development of a fingerlike bulge, and fast localized burst through the finger. Substantial alterations of the ELM dynamics, such as mode number, poloidal rotation, and crash time scale, have been observed under external magnetic perturbations with the toroidal mode number n= 1.
Perturbative quantum gravity in double field theory
Boels, Rutger H.; Horst, Christoph
2016-04-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Perturbative quantum gravity in double field theory
Boels, Rutger H
2015-01-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Large Field Cutoffs Make Perturbative Series Converge
Meurice, Y
2002-01-01
For lambda phi^4 problems, convergent perturbative series can be obtained by cutting off the large field configurations. The modified series converge to values exponentially close to the exact ones. For lambda larger than some critical value, the method outperforms Pade approximants and Borel summations. We discuss some aspects of the semi-classical methods used to calculate the modified Feynman rules and estimate the error associated with the procedure. We provide a simple numerical example where the procedure works despite the fact that the Borel sum has singularities on the positive real axis.
Large field cutoffs make perturbative series converge
Meurice, Yannick
2002-03-01
For λφ 4 problems, convergent perturbative series can be obtained by cutting off the large field configurations. The modified series converge to values exponentially close to the exact ones. For λ larger than some critical value, the method outperforms Padé approximants and Borel summations. We discuss some aspects of the semi-classical methods used to calculate the modified Feynman rules and estimate the error associated with the procedure. We provide a simple numerical example where the procedure works despite the fact that the Borel sum has singularities on the positive real axis.
Divertor heat load in ASDEX Upgrade L-mode in presence of external magnetic perturbation
Faitsch, M.; Sieglin, B.; Eich, T.; Herrmann, A.; Suttrop, W.; the ASDEX Upgrade Team
2017-09-01
Power exhaust is one of the major challenges for a future fusion device. Applying a non-axisymmetric external magnetic perturbation is one technique that is studied in order to mitigate or suppress large edge localized modes which accompany the high confinement regime in tokamaks. The external magnetic perturbation induces breaking in the axisymmetry of a tokamak and leads to a 2D heat flux pattern on the divertor target. The 2D heat flux pattern at the outer divertor target is studied on ASDEX Upgrade in stationary L-mode discharges. The amplitude of the 2D characteristic of the heat flux depends on the alignment between the field lines at the edge and the vacuum response of the applied magnetic perturbation spectrum. The 2D characteristic reduces with increasing density. The increasing divertor broadening, S, with increasing density is proposed as the main actuator. This is supported by a generic model using field line tracing and the vacuum field approach that is in quantitative agreement with the measured heat flux. The perturbed heat flux, averaged over a full toroidal rotation of the magnetic perturbation, is identical to the non-perturbed heat flux without magnetic perturbation. The transport qualifiers, power fall-off length {λ }q and divertor broadening, S, are the same within the uncertainty compared to the unperturbed reference. No additional cross field transport is observed.
Control of Transport-barrier relaxations by Resonant Magnetic Perturbations
Leconte, M; Garbet, X; Benkadda, S
2009-01-01
Transport-barrier relaxation oscillations in the presence of resonant magnetic perturbations are investigated using three-dimensional global fluid turbulence simulations from first principles at the edge of a tokamak. It is shown that resonant magnetic perturbations have a stabilizing effect on these relaxation oscillations and that this effect is due mainly to a modification of the pressure profile linked to the presence of both residual residual magnetic island chains and a stochastic layer.
Cosmological Electromagnetic Fields due to Gravitational Wave Perturbations
Marklund, M; Brodin, G; Marklund, Mattias; Dunsby, Peter K. S.; Brodin, Gert
2000-01-01
We consider the dynamics of electromagnetic fields in an almost-Friedmann-Robertson-Walker universe using the covariant and gauge-invariant approach of Ellis and Bruni. Focusing on the situation where deviations from the background model are generated by tensor perturbations only, we demonstrate that the coupling between gravitational waves and a weak magnetic test field can generate electromagnetic waves. We show that this coupling leads to an initial pulse of electromagnetic waves whose width and amplitude is determined by the wavelengths of the magnetic field and gravitational waves. A number of implications for cosmology are discussed, in particular we calculate an upper bound of the magnitude of this effect using limits on the quadrapole anisotropy of the Cosmic Microwave Background.
Gravitational perturbations of the Higgs field
Albareti, Franco D; Prada, Francisco
2016-01-01
We study the possible effects of classical gravitational fields on the Higgs vacuum expectation value through the modifications induced in the one-loop effective potential. We concentrate our study on the Higgs self-interactions contribution in a perturbed FRW background. For weak and slowly-varying gravitational fields, a complete set of mode solutions for the Klein-Gordon equation is obtained to leading order in the adiabatic approximation. The mode integrations are calculated using standard dimensional regularization techniques. As expected, the regularized effective potential contains the same divergences as in flat space-time, which can be renormalized without the need of additional counterterms. However, we find new finite non-local contributions which depend on the gravitational potentials, and introduce an explicit space-time dependence on the Higgs potential coefficients. Being finite, the new terms are free of renormalization ambiguities. Inhomogeneities in the effective potential translate into per...
Energy Technology Data Exchange (ETDEWEB)
Witwit, M.R.M.; Killingbeck, J.P. (Hull Univ. (United Kingdom). Dept. of Applied Mathematics)
1993-05-28
This paper studies the partitioned perturbation series for the states (1s, 2s, 2p[sub 0], 2p[sub -1], 3d[sub -1], 3d[sub -2]). Second-and third-order corrections to the energy perturbation series are calculated by using a combination of hypervirial perturbation theory and the Hylleraas variational principle. (author).
Kunze, Kerstin E
2013-01-01
Magnetic fields are observed on nearly all scales in the universe, from stars and galaxies upto galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created. Observations of the cosmic microwave background (CMB) provide a window to the early universe and might therefore be able to tell us whether cosmic magnetic fields are of primordial, cosmological origin and at the same time constrain its parameters. We will give an overview of the observational evidence of large scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.
Magnetic Field Grid Calculator
National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Properties Calculator will computes the estimated values of Earth's magnetic field(declination, inclination, vertical component, northerly...
RCD Large Aspect-Ratio Tokamak Equilibrium with Magnetic Islands: a Perturbed Approach
F. L., Braga
2013-03-01
Solutions of Grad-Shafranov (GS) equation with Reversed Current Density (RCD) profiles present magnetic islands when the magnetic flux is explicitly dependent on the poloidal angle. In this work it is shown that a typical cylindrical (large aspect-ratio) RCD equilibrium configuration perturbed by the magnetic field of a circular loop (simulating a divertor) is capable of generate magnetic islands, due to the poloidal symmetry break of the GS equilibrium solution.
Edda Lína Gunnarsdóttir 1988
2012-01-01
The Earth's magnetic field is essential for life on Earth, as we know it, to exist. It forms a magnetic shield around the planet, protecting it from high energy particles and radiation from the Sun, which can cause damage to life, power systems, orbiting satellites, astronauts and spacecrafts. This report contains a general overview of the Earth's magnetic field. The different sources that contribute to the total magnetic field are presented and the diverse variations in the field are describ...
Near-zero-field nuclear magnetic resonance
Ledbetter, Micah; Blanchard, John; Ring, Hattie; Ganssle, Paul; Appelt, Stephan; Bluemich, Bernhard; Pines, Alex; Budker, Dmitry
2011-01-01
We investigate nuclear magnetic resonance (NMR) in near-zero-field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction (J-coupling). This is in stark contrast to the high field case, where heteronuclear J-couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectra. Experimental results are in good agreement with first-order perturbation theory and with full numerical simulation when perturbation theory breaks down. We present simple rules for understanding the splitting patterns in near-zero-field NMR, which can be applied to molecules with non-trivial spectra.
Near-zero-field nuclear magnetic resonance.
Ledbetter, M P; Theis, T; Blanchard, J W; Ring, H; Ganssle, P; Appelt, S; Blümich, B; Pines, A; Budker, D
2011-09-02
We investigate nuclear magnetic resonance (NMR) in near zero field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction (J coupling). This is in stark contrast to the high-field case, where heteronuclear J couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectra. Experimental results are in good agreement with first-order perturbation theory and with full numerical simulation when perturbation theory breaks down. We present simple rules for understanding the splitting patterns in near-zero-field NMR, which can be applied to molecules with nontrivial spectra.
Perturbed soliton spin excitations by EM-field in ferromagnetic medium
Daniel, M
2003-01-01
We study nonlinear spin excitations in the form of perturbed solitons in a one dimensional inhomogeneous bilinear anisotropic Heisenberg ferromagnet and an anisotropic homogeneous biquadratic ferromagnet in the classical continuum limit when acted upon by an electromagnetic(EM)-field. Using a reductive perturbation method, we deduce the associated Landau-Lifshtiz equations coupled with Maxwell's equations to perturbed nonlinear Schroedinger equations. A perturbation analysis carried out in both cases shows that the EM-field excites the magnetization of the medium in the form of solitons with small fluctuations.
Unusual Low-frequency Magnetic Perturbations in TFTR
Energy Technology Data Exchange (ETDEWEB)
H. Takahashi; E.D. Fredrickson; M.S. Chance
2001-02-12
Low-frequency magnetic perturbations (less than or equal to 30 kHz) observed in the Tokamak Fusion Test Reactor (TFTR) tokamak do not always conform to expectations from Magneto-Hydro-Dynamic (MHD) modes. The discrepancy between observations and expectations arises from the existence of three classes of magnetic perturbations in TFTR: (1) 'Edge Originated Magnetic Perturbations' (EOMP's), (2) 'Kink-like Modes' (KLM's), and (3) Tearing Modes (TM's). The EOMP class has unusual magnetic phenomenon including up/down asymmetry in poloidal intensity variation that MHD modes alone cannot generate. The contributions of MHD modes in plasma edge regions are too small to explain the magnitude of observed EOMP perturbations. At least two-thirds, possibly nearly all, of magnetic perturbations in a typical EOMP originate from sources other than MHD modes. An EOMP has a unity toroidal harmonic number and a poloidal harmonic number close to a discharge's edge q-value. It produces little temperature fluctuations, except possibly in edge regions. The KLM class produces temperature fluctuations, mostly confined within the q=1 surface with an ideal-mode-like structure, but generates little external magnetic perturbations. The TM class conforms generally to expectations from MHD modes. We propose that current flowing in the Scrape-off-layer (SOL) plasma is a possible origin of EOMP's.
On the non-Gaussian correlation of the primordial curvature perturbation with vector fields
Jain, Rajeev Kumar
2012-01-01
We compute the three-point cross-correlation function of the primordial curvature perturbation generated during inflation with two powers of a vector field in a model where conformal invariance is broken by a direct coupling of the vector field with the inflaton. If the vector field is identified with the electromagnetic field, this correlation would be a non-Gaussian signature of primordial magnetic fields generated during inflation. We find that the signal is maximized for the flattened configuration where the wave number of the curvature perturbation is twice that of the vector field and in this limit, the magnetic non-linear parameter becomes as large as |b_{NL}| ~ 10^3. In the squeezed limit where the wave number of the curvature perturbation vanishes, our results agree with the magnetic consistency relation derived in arXiv:1207.4187.
On the non-Gaussian correlation of the primordial curvature perturbation with vector fields
Energy Technology Data Exchange (ETDEWEB)
Jain, Rajeev Kumar [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, 24, Quai E. Ansermet, CH-1211 Genève 4 (Switzerland); Sloth, Martin S., E-mail: rajeev.jain@unige.ch, E-mail: sloth@cp3.dias.sdu.dk [CP3-Origins, Centre for Cosmology and Particle Physics Phenomenology, University of Southern Denmark, Campusvej 55, 5230 Odense M (Denmark)
2013-02-01
We compute the three-point cross-correlation function of the primordial curvature perturbation generated during inflation with two powers of a vector field in a model where conformal invariance is broken by a direct coupling of the vector field with the inflaton. If the vector field is identified with the electromagnetic field, this correlation would be a non-Gaussian signature of primordial magnetic fields generated during inflation. We find that the signal is maximized for the flattened configuration where the wave number of the curvature perturbation is twice that of the vector field and in this limit, the magnetic non-linear parameter becomes as large as |b{sub NL}| ∼ O(10{sup 3}). In the squeezed limit where the wave number of the curvature perturbation vanishes, our results agree with the magnetic consistency relation derived in arXiv:1207.4187.
Signatures of core perturbations in geomagnetic field dynamics - preliminary results
Bury, Agata; Mizerski, Krzysztof
2017-04-01
Earth's magnetic field is continuously evolving in time. Research is carried out in order to understand it's characteristics and also to describe types of perturbations which can exist in the Earth's liquid core. The aim of this work is to analyze the geomagnetic ground observatory data for the occurrence of magnetohydrodynamic (MHD) waves described in literature traveling at the top of the Earth's liquid core. Hourly means data from 150 observatories collected from the World Data Center for Geomagnetism (WDC) were used in this work. Local topocentric magnetic field components: X (East), Y (North), Z (vertical), and also spherical coordinates: Br, Bθ, BΦ were analyzed. Hourly means were averaged to one day means and to one month means, missing values were interpolated by different methods. Fourier analysis and Empirical Mode Decomposition (EMD) method were applied to extract periods of oscillations visible in datasets. Similar analysis was also made for data generated from the IGRF12 model for comparison. The times associated with peaks within these data were identified for all components and plotted versus colatitude and longitude to find possible travelling perturbations. Possible candidates of MHD waves for future investigation will be presented.
Perturbation Theory of the Cosmological Log-Density Field
DEFF Research Database (Denmark)
Wang, Xin; Neyrinck, Mark; Szapudi, István
2011-01-01
, motivating an analytic study of it. In this paper, we develop cosmological perturbation theory for the power spectrum of this field. Our formalism is developed in the context of renormalized perturbation theory, which helps to regulate the convergence behavior of the perturbation series, and of the Taylor...
Beck, Rainer
2013-01-01
Most of the visible matter in the Universe is ionized, so that cosmic magnetic fields are quite easy to generate and due to the lack of magnetic monopoles hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in-situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic fie...
Large-scale weakly nonlinear perturbations of convective magnetic dynamos in a rotating layer
Chertovskih, Roman
2015-01-01
We present a new mechanism for generation of large-scale magnetic field by thermal convection which does not involve the alpha-effect. We consider weakly nonlinear perturbations of space-periodic steady convective magnetic dynamos in a rotating layer that were identified in our previous work. The perturbations have a spatial scale in the horizontal direction that is much larger than the period of the perturbed convective magnetohydrodynamic state. Following the formalism of the multiscale stability theory, we have derived the system of amplitude equations governing the evolution of the leading terms in expansion of the perturbations in power series in the scale ratio. This asymptotic analysis is more involved than in the cases considered earlier, because the kernel of the operator of linearisation has zero-mean neutral modes whose origin lies in the spatial invariance of the perturbed regime, the operator reduced on the generalised kernel has two Jordan normal form blocks of size two, and simplifying symmetri...
Combustion instability mitigation by magnetic fields
Jocher, Agnes; Pitsch, Heinz; Gomez, Thomas; Bonnety, Jérôme; Legros, Guillaume
2017-06-01
The present interdisciplinary study combines electromagnetics and combustion to unveil an original and basic experiment displaying a spontaneous flame instability that is mitigated as the non-premixed sooting flame experiences a magnetic perturbation. This magnetic instability mitigation is reproduced by direct numerical simulations to be further elucidated by a flow stability analysis. A key role in the stabilization process is attributed to the momentum and thermochemistry coupling that the magnetic force, acting mainly on paramagnetic oxygen, contributes to sustain. The spatial local stability analysis based on the numerical simulations shows that the magnetic field tends to reduce the growth rates of small flame perturbations.
The Juno Magnetic Field Investigation
DEFF Research Database (Denmark)
Connerney, J. E. P.; Benn, Mathias; Bjarnø, Jonas Bækby
2017-01-01
The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor ...
Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A
2011-01-01
We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early genera...
Energy Technology Data Exchange (ETDEWEB)
Nardon, E
2007-10-15
The present work is dedicated to one of the most promising methods of control of the ELMs (Edge Localized Modes), based on a system of coils producing Resonant Magnetic Perturbations (RMPs). Our main objectives are, on the one hand, to improve the physical understanding of the mechanisms at play, and on the other hand to propose a concrete design of ELMs control coils for ITER. In order to calculate and analyze the magnetic perturbations produced by a given set of coils, we have developed the ERGOS code. The first ERGOS calculation was for the DIII-D ELMs control coils, the I-coils. It showed that they produce magnetic islands chains which overlap at the edge of the plasma, resulting in the ergodization of the magnetic field. We have then used ERGOS for the modelling of the experiments on ELMs control using the error field correction coils at JET and MAST. In the case of JET, we have shown the existence of a correlation between the mitigation of the ELMs and the ergodization of the magnetic field at the edge, in agreement with the DIII-D result. In order to design the ELMs control coils for ITER we have used ERGOS intensively, taking the case of the DIII-D I-coils as a reference. Three candidate designs came out, which we presented at the ITER Design Review, in 2007. Recently, the ITER management decided to provide a budget for building ELMs control coils, the design of which remains to be chosen between two of the three options that we proposed. Finally, in order to understand better the non-linear magnetohydrodynamics phenomena taking place in ELMs control by RMPs, we performed numerical simulations, in particular with the JOREK code for a DIII-D case. The simulations reveal the existence of convection cells induced at the edge by the magnetic perturbations, and the possible screening of the RMPs in presence of rotation.
Energy Technology Data Exchange (ETDEWEB)
McCamey, Dane; Boehme, Christoph
2017-01-24
An organic, spin-dependent magnetic field sensor (10) includes an active stack (12) having an organic material with a spin-dependence. The sensor (10) also includes a back electrical contact (14) electrically coupled to a back of the active stack (12) and a front electrical contact (16) electrically coupled to a front of the active stack (12). A magnetic field generator (18) is oriented so as to provide an oscillating magnetic field which penetrates the active stack (12).
Non-perturbative Euler-Heisenberg Lagrangian and paraelectricity in magnetized massless QED
Energy Technology Data Exchange (ETDEWEB)
Ferrer, Efrain J. [Department of Physics, University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79968 (United States); Incera, Vivian de la, E-mail: vincera@utep.edu [Department of Physics, University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79968 (United States); Sanchez, Angel [Department of Physics, University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79968 (United States)
2012-11-21
In this paper we calculate the non-perturbative Euler-Heisenberg Lagrangian for massless QED in a strong magnetic field H, where the breaking of the chiral symmetry is dynamically catalyzed by the external magnetic field via the formation of an electro-positron condensate. This chiral condensate leads to the generation of dynamical parameters that have to be found as solutions of non-perturbative Schwinger-Dyson equations. Since the electron-positron pairing mechanism leading to the breaking of the chiral symmetry is mainly dominated by the contributions from the infrared region of momenta much smaller than {radical}(eH), the magnetic field introduces a dynamical ultraviolet cutoff in the theory that also enters in the non-perturbative Euler-Heisenberg action. Using this action, we show that the system exhibits a significant paraelectricity in the direction parallel to the magnetic field. The non-perturbative nature of this effect is reflected in the non-analytic dependence of the obtained electric susceptibility on the fine-structure constant. The strong paraelectricity in the field direction is linked to the orientation of the electric dipole moments of the pairs that form the chiral condensate. The large electric susceptibility can be used to detect the realization of the magnetic catalysis of chiral symmetry breaking in physical systems.
On the non-Gaussian correlation of the primordial curvature perturbation with vector fields
DEFF Research Database (Denmark)
Kumar Jain, Rajeev; Sloth, Martin Snoager
2013-01-01
We compute the three-point cross-correlation function of the primordial curvature perturbation generated during inflation with two powers of a vector field in a model where conformal invariance is broken by a direct coupling of the vector field with the inflaton. If the vector field is identified...... with the electromagnetic field, this correlation would be a non-Gaussian signature of primordial magnetic fields generated during inflation. We find that the signal is maximized for the flattened configuration where the wave number of the curvature perturbation is twice that of the vector field and in this limit...
Hajian, K; Sheikh-Jabbari, M M
2014-01-01
In arXiv:1310.3727 we formulated and derived the three universal laws governing Near Horizon Extremal Geometries (NHEG). In this work we focus on the Entropy Perturbation Law (EPL) which, similarly to the first law of black hole thermodynamics, relates perturbations of the charges labeling perturbations around a given NHEG to the corresponding entropy perturbation. We show that field perturbations governed by the linearized equations of motion and symmetry conditions which we carefully specify, satisfy the EPL. We also show that these perturbations are limited to those coming from difference of two NHEG solutions (i.e. variations on the NHEG solution parameter space). Our analysis and discussions shed light on the "no-dynamics" statements of arXiv:0906.2380 and arXiv:0906.2376.
Attitude dynamics of gyrostat-satellites under control by magnetic actuators at small perturbations
Doroshin, Anton V.
2017-08-01
The angular motion of gyrostat-satellites with one axial rotor is considered under control by magnetic actuators and at the action of small polyharmonic perturbations of the own dipole magnetic moment's components which are created proportionally to components of the angular velocity of the satellite. The attitude dynamics is investigated in conditions of the coincidence of the vector of magnetic induction of the external magnetic field and the initial angular momentum vector of the satellite. General and heteroclinic analytical solutions are obtained for dynamical parameters at the relative smallness of the magnetic torques. The chaotic regimes are examined on the base of the Melnikov method and Poincaré sections.
Resonant magnetic perturbation effect on tearing mode dynamics
Frassinetti, L.; Olofsson, K. E. J.; Brunsell, P. R.; Drake, J. R.
2010-03-01
The effect of a resonant magnetic perturbation (RMP) on the tearing mode (TM) dynamics is experimentally studied in the EXTRAP T2R device. EXTRAP T2R is equipped with a set of sensor coils and active coils connected by a digital controller allowing a feedback control of the magnetic instabilities. The recently upgraded feedback algorithm allows the suppression of all the error field harmonics but keeping a selected harmonic to the desired amplitude, therefore opening the possibility of a clear study of the RMP effect on the corresponding TM. The paper shows that the RMP produces two typical effects: (1) a weak oscillation in the TM amplitude and a modulation in the TM velocity or (2) a strong modulation in the TM amplitude and phase jumps. Moreover, the locking mechanism of a TM to a RMP is studied in detail. It is shown that before the locking, the TM dynamics is characterized by velocity modulation followed by phase jumps. Experimental results are reasonably explained by simulations obtained with a model.
Mechanism of Edge Localized Mode Mitigation by Resonant Magnetic Perturbations
Bécoulet, M.; Orain, F.; Huijsmans, G. T. A.; Pamela, S.; Cahyna, P.; Hoelzl, M.; Garbet, X.; Franck, E.; Sonnendrücker, E.; Dif-Pradalier, G.; Passeron, C.; Latu, G.; Morales, J.; Nardon, E.; Fil, A.; Nkonga, B.; Ratnani, A.; Grandgirard, V.
2014-09-01
A possible mechanism of edge localized modes (ELMs) mitigation by resonant magnetic perturbations (RMPs) is proposed based on the results of nonlinear resistive magnetohydrodynamic modeling using the jorek code, realistic JET-like plasma parameters and an RMP spectrum of JET error-field correction coils (EFCC) with a main toroidal number n =2 were used in the simulations. Without RMPs, a large ELM relaxation is obtained mainly due to the most unstable medium-n ballooning mode. The externally imposed RMP drives nonlinearly the modes coupled to n =2 RMP which produce small multimode relaxations, mitigated ELMs. The modes driven by RMPs exhibit a tearinglike structure and produce additional islands. Mitigated ELMs deposit energy into the divertor mainly in the structures ("footprints") created by n =2 RMPs, however, slightly modulated by other nonlinearly driven even harmonics. The divertor power flux during a ELM phase mitigated by RMPs is reduced almost by a factor of 10. The mechanism of ELM mitigation by RMPs proposed here reproduces generic features of high collisionality RMP experiments, where large ELMs are replaced by small, much more frequent ELMs or magnetic turbulence. Total ELM suppression was also demonstrated in modeling at higher RMP amplitude.
Rydberg EIT in High Magnetic Field
Ma, Lu; Anderson, David; Miller, Stephanie; Raithel, Georg
2016-05-01
We present progress towards an all-optical approach for measurements of strong magnetic fields using electromagnetically induced transparency (EIT) with Rydberg atoms in an atomic vapor. Rydberg EIT spectroscopy is a promising technique for the development of atom-based, calibration- and drift-free technology for high magnetic field sensing. In this effort, Rydberg EIT is employed to spectroscopically investigate the response of Rydberg atoms exposed to strong magnetic fields, in which Rydberg atoms are in the strong-field regime. In our setup, two neodymium block magnets are used to generate fields of about 0.8 Tesla, which strongly perturb the atoms. Information on the field strength and direction is obtained by a comparison of experimental spectra with calculated spectral maps. Investigations of magnetic-field inhomogeneities and other decoherence sources will be discussed.
EFFECTS OF LARGE-SCALE NON-AXISYMMETRIC PERTURBATIONS IN THE MEAN-FIELD SOLAR DYNAMO
Energy Technology Data Exchange (ETDEWEB)
Pipin, V. V. [Institute of Solar-Terrestrial Physics, Russian Academy of Sciences (Russian Federation); Kosovichev, A. G. [W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)
2015-11-10
We explore the response of a nonlinear non-axisymmetric mean-field solar dynamo model to shallow non-axisymmetric perturbations. After a relaxation period, the amplitude of the non-axisymmetric field depends on the initial condition, helicity conservation, and the depth of perturbation. It is found that a perturbation that is anchored at 0.9 R{sub ⊙} has a profound effect on the dynamo process, producing a transient magnetic cycle of the axisymmetric magnetic field, if it is initiated at the growing phase of the cycle. The non-symmetric, with respect to the equator, perturbation results in a hemispheric asymmetry of the magnetic activity. The evolution of the axisymmetric and non-axisymmetric fields depends on the turbulent magnetic Reynolds number R{sub m}. In the range of R{sub m} = 10{sup 4}–10{sup 6} the evolution returns to the normal course in the next cycle, in which the non-axisymmetric field is generated due to a nonlinear α-effect and magnetic buoyancy. In the stationary state, the large-scale magnetic field demonstrates a phenomenon of “active longitudes” with cyclic 180° “flip-flop” changes of the large-scale magnetic field orientation. The flip-flop effect is known from observations of solar and stellar magnetic cycles. However, this effect disappears in the model, which includes the meridional circulation pattern determined by helioseismology. The rotation rate of the non-axisymmetric field components varies during the relaxation period and carries important information about the dynamo process.
Fietz, S.; Bergmann, A.; Classen, I.; Maraschek, M.; M. García-Muñoz,; Suttrop, W.; Zohm, H.; ASDEX Upgrade team,
2015-01-01
The influence of externally applied magnetic perturbations (MPs) on neoclassical tearing modes (NTM) and the plasma rotation in general is investigated at the ASDEX Upgrade tokamak (AUG). The low n resonant components of the applied field exert local torques and influence the stability of NTMs. The
Effect of a localized magnetic perturbation on magnetic islands in a cylindrical plasma
Energy Technology Data Exchange (ETDEWEB)
Bateman, G; Morris, R N
1980-05-01
A self-consistent plasma equilibrium model is developed to study the width or ergodic regions and magnetic islands in a periodic cylindrical plasma under the influence of a localized magnetic perturbation, such as that produced by a bundle divertor or ripple coil set. It is found that localized perturbations tend to produce poloidally symmetric annular ergodic regions and poloidally elongated magnetic islands rather than simple magnetic islands. Our plasma model takes into account the flattening of the current profile across each annular ergodic region and the concommitant steepening of the current profile between ergodic regions. Using current profiles inferred from experimental data, saturated tearing mode amplitudes are computed and found to agree with the experimentally observed Mirnov oscillation amplitudes. As the applied magnetic perturbation is turned on and increased, it is observed that the steepened current profile and resulting enhancement of tearing modes produces wider ergodic regions than would be expected from the vacuum magnetic perturbation alone.
Nizic, Bene
1985-12-01
This thesis consists of two unrelated topics in perturbative quantum field theory: eighth order QED contribution to the anomalous magnetic moment of the muon and next to leading order perturbative QCD correction to (gamma)(gamma) ( --->) M('+)M('-)(M = (pi),K). In Part I we present the evaluation of the complete eighth order QED contribution to the difference of the anomalous magnetic moments of the muon and the electron, (a(,(mu)) - a(,e))('(8)), arising from 469 Feynman diagrams. Our result is 140.7(4.5)((alpha)/(pi))('4). The theoretical error represents the estimated accuracy of the required numerical integration. We have also improved the light -by-light QED contribution to (a(,(mu)) - a(,e))('(6)). With these results the difference a(,(mu)) - a(,e) through eighth order in QED is (a(,(mu)) - a(,e))('QED) = 619 551(21) x 10('-11). Adding to the present theoretical value of the electron anomaly a(,e)('QED) = 115 965 246(5) x 10(' -11), we find that the pure QED contribution to the muon anomaly is given by a(,(mu))('QED) = 116 584 797(22) x 10('-11). In Part II we present the results of our calculation of the next to leading order perturbative QCD correction to the two-photon exclusive channels (gamma)(gamma)(-- ->)M('+)M('-)(M = (pi),K) at large momentum transfer. Calculation is performed in the Feynman gauge. Dimensional regularization is used to treat both UV and (//R) divergences. The meson distribution amplitude is taken to be (PHI)(,M)(PROPORTIONAL)('(delta))(x - 1/2). In order to reduce the dependence on the particular choice of (PHI)(,M), similarity of (gamma)(gamma)(--->)M('+)M(' -) and meson electromagnetic form-factor is employed. One loop correction to the (gamma)(gamma)(--->)M('+)M('-) cross section is obtained. In the MS renormalization scheme this correction is found not to be large.
Magnetization reversal in ultrashort magnetic field pulses
Bauer, M; Fassbender, J; Hillebrands, B
2000-01-01
We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4 ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization ...
Effect of a static external magnetic perturbation on resistive mode stability in tokamaks
Energy Technology Data Exchange (ETDEWEB)
Fitzpatrick, R. [Univ. of Texas, Austin, TX (United States). Institute for Fusion Studies; Hender, T.C. [Univ. of Texas, Austin, TX (United States). Institute for Fusion Studies]|[Culham Lab., Abingdon (United Kingdom)
1994-03-01
The influence of a general static external magnetic perturbation on the stability of resistive modes in a tokamak plasma is examined. There are three main parts to this investigation. Firstly, the vacuum perturbation is expanded as a set of well-behaved toroidal ring functions and is, thereafter, specified by the coefficients of this expansion. Secondly, a dispersion relation is derived for resistive plasma instabilities in the presence of a general external perturbation and finally, this dispersion relation is solved for the amplitudes of the tearing and twisting modes driven in the plasma by a specific perturbation. It is found that the amplitudes of driven tearing and twisting modes are negligible until a certain critical perturbation strength is exceeded. Only tearing modes are driven in low-{beta} plasmas with {epsilon}{beta}{sub p} << 1. However, twisting modes may also be driven if {epsilon}{beta}{sub p}{approx}>1. For error-field perturbations made up of a large number of different poloidal and toroidal harmonics the critical strength to drive locked modes has a {open_quote}staircase{close_quote} variation with edge-q, characterized by strong discontinuities as coupled rational surfaces enter or leave the plasma. For single harmonic perturbations the variation with edge-q is far smoother. Both types of behaviour have been observed experimentally. The critical perturbation strength is found to decrease strongly close to an ideal external kink stability boundary. This is also in agreement with experimental observations.
Cosmological perturbations from a Spectator field during inflation
Wang, Lingfei
2013-01-01
In this paper we will discuss analytically the perturbations created from a slowly rolling subdominant spectator field which decays much before the end of inflation. The quantum fluctuations of such a spectator field can seed perturbations on very large scales and explain the temperature anisotropy in the cosmic microwave background radiation with moderate non-Gaussianity, provided the relevant modes leave the Hubble patch while the spectator is slowly rolling. Furthermore, the perturbations are purely {\\it adiabatic} since the inflaton decay dominates and creates all the Standard Model degrees of freedom. We will provide two examples for the spectator field potential, one with a step function profile, and the other with an inflection point. In both the cases we will compute higher order curvature perturbations, i.e.\\ local bispectrum and trispectrum, which can be constrained by the forthcoming Planck data.
Perturbation Theory of the Cosmological Log-Density Field
Wang, Xin; Szapudi, István; Szalay, Alex; Chen, Xuelei; Lesgourgues, Julien; Riotto, Antonio; Sloth, Martin; 10.1088/0004-637X/735/1/32
2011-01-01
The matter density field exhibits a nearly lognormal probability density distribution (PDF) after entering into the nonlinear regime. Recently, it has been shown that the shape of the power spectrum of a logarithmically transformed density field is very close to the linear density power spectrum, motivating an analytic study of it. In this paper, we develop cosmological perturbation theory for the power spectrum of this field. Our formalism is developed in the context of renormalized perturbation theory, which helps to regulate the convergence behavior of the perturbation series, and of the Taylor- series expansion we use of the logarithmic mapping. This approach allows us to handle the critical issue of density smoothing in a straightforward way. We also compare our perturbative results with simulation measurements.
Berdyugina, Svetlana
2015-08-01
Molecules probe cool matter in the Universe and various astrophysical objects. Their ability to sense magnetic fields provides new insights into magnetic properties of these objects. During the past fifteen years we have carried out a theoretical study of molecular magnetic effects such as the Zeeman, Paschen-Back and Hanle effects and their applications for inferring magnetic structures and spatial inhomogeneities on the Sun, cool stars, brown dwarfs, and exoplanets from molecular spectro-polarimetry (e.g., Berdyugina 2011). Here, we present an overview of this study and compare our theoretical predictions with recent laboratory measurements of magnetic properties of some molecules. We present also a new web-based tool to compute molecular magnetic effects and polarized spectra which is supported by the ERC Advanced Grant HotMol.
Mechanics of magnetic fluid column in strong magnetic fields
Polunin, V. M.; Ryapolov, P. A.; Platonov, V. B.
2017-06-01
Elastic-and magnetic properties of magnetic fluid confined by ponderomotive force in a tube fixed in horizontal position are considered. The system is placed in a strong magnetic field under the influence of external static and dynamic perturbations. An experimental setup has been developed. A theoretical basis of the processes of magnetic colloid elastic deformation has been proposed. The values of the static ponderomotive elasticity coefficient and the elasticity coefficient under dynamic action are experimentally determined. The calculations of the saturation magnetization for two magnetic fluid samples, carried out according to the equation containing the dynamic elasticity coefficient, are in good agreement with the experimental magnetization curve. The described method is of interest when studying magnetophoresis and aggregation of nanoparticles in magnetic colloids.
Non-perturbative Euler-Heisenberg Lagrangian and Paraelectricity in Magnetized Massless QED
Ferrer, Efrain J; Sanchez, Angel
2012-01-01
Using the non-perturbative Euler-Heisenberg Lagrangian for massless QED in a strong magnetic field, we show that the chiral-symmetry-broken phase of massless QED in the presence of a magnetic field exhibits significant paraelectricity. A large anisotropic electric susceptibility develops in the strong-field region, where most of the fermions are confined to their lowest Landau level, and dynamical mass and anomalous magnetic moment are generated via the magnetic catalysis mechanism. The nonperturbative nature of this effect is reflected in the non-analytic dependence of the electric susceptibility on the fine-structure constant. The strong paraelectricity is linked to the electric dipole moments of the particle/anti-particle pairs that form the chiral condensate. The large electric susceptibility can be used to detect the realization of the magnetic catalysis of chiral symmetry breaking in physical systems.
Consistency relation for cosmic magnetic fields
DEFF Research Database (Denmark)
Jain, R. K.; Sloth, M. S.
2012-01-01
to be extremely useful to test some recent calculations in the literature. Apart from primordial non-Gaussianity induced by the curvature perturbations, such a cross correlation might provide a new observational probe of inflation and can in principle reveal the primordial nature of cosmic magnetic fields. DOI...
Tellgren, E I; Teale, A M; Furness, J W; Lange, K K; Ekström, U; Helgaker, T
2014-01-21
We present a novel implementation of Kohn-Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals-the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.
Energy Technology Data Exchange (ETDEWEB)
Tellgren, E. I., E-mail: erik.tellgren@kjemi.uio.no; Lange, K. K.; Ekström, U.; Helgaker, T. [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Teale, A. M., E-mail: andrew.teale@nottingham.ac.uk [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Furness, J. W. [School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)
2014-01-21
We present a novel implementation of Kohn–Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals—the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.
Bouwman, Job G; Bakker, Chris J G
2012-08-01
Forward calculation of the susceptibility induced field shift by Fourier-based procedures requires spatial zero-padding to prevent aliasing artifacts (periodic wrap-around). Padding with a factor of two gives accurate results, however, halves the maximal attainable resolution, and slows down the calculation, which may hamper the feasibility of real-time calculations. Herein is proposed to first perform the calculation at the original resolution--allowing aliasing-and to remove aliasing with an additional convolution in a lower resolution, to alleviate these restrictions regarding memory size and calculation speed, a procedure we termed "virtual" zero-padding. Virtual zero-padding was numerically and experimentally tested and validated with conventional zero-padding and the analytical solution (in the case of spheres) on several phantoms. A demonstration of the increased efficiency is given by implementing virtual zero-padding in a dynamic calculation procedure. The improved efficiency is expected to be relevant regarding the ongoing increase in spatial and temporal resolution in ultra-high-field MRI. Procedures are presented for circular convolution using the discrete Green's function and k-space filtering using the continuous Green's function.
Joint development in perturbed stress fields near faults
Rawnsley, K. D.; Rives, T.; Petti, J.-P.; Hencher, S. R.; Lumsden, A. C.
1992-09-01
Field evidence is presented for complex spatial and temporal perturbations of an otherwise systematic joint pattern around faults from well exposed faulted rock platforms. Joints propagating in perturbed stress fields will curve to follow the directions of the stress field trajectories. A progressive change in joint direction is observed from unperturbed regions away from faults, to strongly perturbed zones adjacent to faults. This indicates that the joint pattern can reflect perturbations of the regional stress field around faults. In the examples, the stress field perturbations are probably due to points of high friction on the fault plane which concentrate stress and distort the stress field in the surrounding rock. The corresponding joints converge at these points and are sub-parallel to the fault along the remainder of the fault plane. The possibility that a fault plane acts as a free surface contained within an elastic body is considered. In this situation the fault plane induces a rotation of the principal stress axes to become either perpendicular or parallel to the fault. The free surface model seems to explain the metre-scale curvature of joints in the vicinity of existing joints, but at the kilometre scale of a large fault plane the model becomes unrealistic unless the fault is open at the Earth's surface. Two examples are investigated from the Lias of Great Britain; at Nash Point and Robin Hood's Bay. Both comprise sub-horizontal strata of relatively homogeneous lithology and bed thickness, which provide striking examples of joints developed near faults.
Energy Technology Data Exchange (ETDEWEB)
Seth, Michael, E-mail: mseth@ucalgary.ca [Department of Chemistry, University of Calgary, University Drive 2500, Calgary, AB T2N-1N4 (Canada); Ziegler, Tom, E-mail: ziegler@ucalgary.ca [Department of Chemistry, University of Calgary, University Drive 2500, Calgary, AB T2N-1N4 (Canada)
2012-02-20
The theory of calculating magnetic circular dichroism in the presence of zero-field splitting is presented and illustrated with applications to small and medium-sized systems. Highlights: Black-Right-Pointing-Pointer ZFS and MCD calculated with DFT are combined. Black-Right-Pointing-Pointer Influence of ZFS on the MCD spectra of group 15 hydrides analyzed. Black-Right-Pointing-Pointer Absorption and MCD spectra of Fe-EDTA-peroxide complex calculated. Black-Right-Pointing-Pointer ZFS does not appear to influence MCD spectra qualitatively. Black-Right-Pointing-Pointer Quantitative effects are present and difficult to model. - Abstract: An implementation into the ADF program of a method for calculating zero-field splitting (ZFS) of molecules with spin degenerate ground states and S > 1/2 is reported. ZFS can influence temperature-dependent magnetic circular dichroism (MCD) intensity. Previously published equations for the calculation of MCD with time-dependent density functional theory are modified to take zero-field splitting into account. The MCD spectra of the group 15 hydrides and the complex formed from iron (III), ethylenediaminetetraacetate and peroxide, [Fe(III)(EDTA)O{sub 2}]{sup 3-} are simulated. These spectra are analyzed with particular reference to the influence of ZFS on the MCD intensity.
1983-01-01
There were 37 (normal) + 3 (special) Radial Field magnets in the ISR to adjust vertically the closed orbit. Gap heights and strengths were 200 mm and .12 Tm in the normal magnets, 220 mm and .18 Tm in the special ones. The core length was 430 mm in both types. Due to their small length as compared to the gap heights the end fringe field errors were very important and had to be compensated by suitably shaping the poles. In order to save on cables, as these magnets were located very far from their power supplies, the coils of the normal type magnets were formed by many turns of solid cpper conductor with some interleaved layers of hollow conductor directly cooled by circulating water
Perturbative algebraic quantum field theory at finite temperature
Energy Technology Data Exchange (ETDEWEB)
Lindner, Falk
2013-08-15
We present the algebraic approach to perturbative quantum field theory for the real scalar field in Minkowski spacetime. In this work we put a special emphasis on the inherent state-independence of the framework and provide a detailed analysis of the state space. The dynamics of the interacting system is constructed in a novel way by virtue of the time-slice axiom in causal perturbation theory. This method sheds new light in the connection between quantum statistical dynamics and perturbative quantum field theory. In particular it allows the explicit construction of the KMS and vacuum state for the interacting, massive Klein-Gordon field which implies the absence of infrared divergences of the interacting theory at finite temperature, in particular for the interacting Wightman and time-ordered functions.
Kronberg, Philipp P
2016-01-01
Magnetic fields are important in the Universe and their effects contain the key to many astrophysical phenomena that are otherwise impossible to understand. This book presents an up-to-date overview of this fast-growing topic and its interconnections to plasma processes, astroparticle physics, high energy astrophysics, and cosmic evolution. The phenomenology and impact of magnetic fields are described in diverse astrophysical contexts within the Universe, from galaxies to the filaments and voids of the intergalactic medium, and out to the largest redshifts. The presentation of mathematical formulae is accessible and is designed to add insight into the broad range of topics discussed. Written for graduate students and researchers in astrophysics and related disciplines, this volume will inspire readers to devise new ways of thinking about magnetic fields in space on galaxy scales and beyond.
Gauge invariant cosmological perturbations for the nonminimally coupled inflaton field
Weenink, J.; Prokopec, T.
2010-01-01
We construct the gauge invariant free action for cosmological perturbations for the nonminimally coupled inflaton field in the Jordan frame. For this the phase space formalism is used, which keeps track of all the dynamical and constraint fields. We perform explicit conformal transformations to demo
Creating perturbations from a decaying field during inflation
DEFF Research Database (Denmark)
Mazumdar, A.; Wang, L.
2013-01-01
Typically, the fluctuations generated from a decaying field during inflation do not contribute to the large scale structures. In this paper, we provide an example where it is possible for a field which slowly rolls and then decays during inflation to create all the matter perturbations...
Perturbation of near-field scan from connected cables
DEFF Research Database (Denmark)
Sørensen, Morten; Franek, Ondrej; Pedersen, Gert Frølund;
2012-01-01
The perturbation of near-fields scan from connected cables are investigated and how to handle the cables is discussed. A connected cable induced small but theoretical detectable changes in the near-field. This change can be seen in Huygens’ box simulations (equivalent source currents on a box...
Indian Academy of Sciences (India)
J. O. Stenflo
2008-03-01
Since the structuring and variability of the Sun and other stars are governed by magnetic fields, much of present-day stellar physics centers around the measurement and understanding of the magnetic fields and their interactions. The Sun, being a prototypical star, plays a unique role in astrophysics, since its proximity allows the fundamental processes to be explored in detail. The PRL anniversary gives us an opportunity to look back at past milestones and try to identify the main unsolved issues that will be addressed in the future.
Hood, Alan W
2011-01-01
This review provides an introduction to the generation and evolution of the Sun's magnetic field, summarising both observational evidence and theoretical models. The eleven year solar cycle, which is well known from a variety of observed quantities, strongly supports the idea of a large-scale solar dynamo. Current theoretical ideas on the location and mechanism of this dynamo are presented. The solar cycle influences the behaviour of the global coronal magnetic field and it is the eruptions of this field that can impact on the Earth's environment. These global coronal variations can be modelled to a surprising degree of accuracy. Recent high resolution observations of the Sun's magnetic field in quiet regions, away from sunspots, show that there is a continual evolution of a small-scale magnetic field, presumably produced by small-scale dynamo action in the solar interior. Sunspots, a natural consequence of the large-scale dynamo, emerge, evolve and disperse over a period of several days. Numerical simulation...
Ground Vehicle Navigation Using Magnetic Field Variation
Shockley, Jeremiah A.
The Earth's magnetic field has been the bedrock of navigation for centuries. The latest research highlights the uniqueness of magnetic field measurements based on position due to large scale variations as well as localized perturbations. These observable changes in the Earth's magnetic field as a function of position provide distinct information which can be used for navigation. This dissertation describes ground vehicle navigation exploiting variation in Earth's magnetic field using a self-contained navigation system consisting of only a magnetometer and magnetic field maps. In order to achieve navigation, effective calibration enables repeatable magnetic field measurements from different vehicles and facilitates mapping of the observable magnetic field as a function of position. A new modified ellipsoid calibration technique for strapdown magnetometers in large vehicles is described, as well as analysis of position measurement generation comparing a multitude of measurement compositions using existing and newly developed likelihood techniques. Finally, navigation solutions are presented using both a position measurement and direct incorporation of the magnetometer measurements via a particle filter to demonstrate road navigation in three different environments. Emphatically, the results affirm that navigation using magnetic field variation in ground vehicles is viable and achieves adequate performance for road level navigation.
Chishtie, F A
2002-01-01
Pade approximants (PA) have been widely applied in practically all areas of physics. This thesis focuses on developing PA as tools for both perturbative and non- perturbative quantum field theory (QFT). In perturbative QFT, we systematically estimate higher (unknown) loop terms via the asymptotic formula devised by Samuel et al. This algorithm, generally denoted as the asymptotic Pade approximation procedure (APAP), has greatly enhanced scope when it is applied to renormalization-group-(RG-) invariant quantities. A presently-unknown higher-loop quantity can then be matched with the approximant over the entire momentum region of phenomenological interest. Furthermore, the predicted value of the RG coefficients can be compared with the RG-accessible coefficients (at the higher-loop order), allowing a clearer indication of the accuracy of the predicted RG-inaccessible term. This methodology is applied to hadronic Higgs decay rates (H → bb¯ and H → gg, both within the Standard Model and...
Early time perturbations behaviour in scalar field cosmologies
Perrotta, F; Perrotta, Francesca; Baccigalupi, Carlo
1999-01-01
We consider the problem of the initial conditions and behaviour of the perturbations in scalar field cosmology with general potential. We use the general definition of adiabatic and isocurvature conditions to set the appropriate initial values for the perturbation in the scalar field and in the ordinary matter and radiation components. In both the cases of initial adiabaticity and isocurvature, we solve the Einstein and fluid equation at early times and on superhorizon scales to find the initial behaviour of the relevant quantities. In particular, in the isocurvature case, we consider models in which the initial perturbation arises from the matter as well as from the scalar field itself, provided that the initial value of the gauge invariant curvature is zero. We extend the standard code to include all these cases, and we show some results concerning the power spectrum of the cosmic microwave background temperature anisotropies. In particular, it turns out that the acoustic peaks follow opposite behaviours in...
Approach to exact solutions of cosmological perturbations: Tachyon field inflation
Herrera, Ramón; Pérez, Roberto G.
2016-03-01
An inflationary universe scenario in the context of a tachyon field is studied. This study is carried out using an ansatz for the effective potential of cosmological perturbations U (η ). We describe in great detail the analytical solutions of the scalar and tensor perturbations for two different Ansätze for the effective potential of cosmological perturbations: Easther's model and an effective potential similar to power-law inflation. Also, we find from the background equations that the effective tachyonic potentials V (φ ) in both models satisfy the properties of a tachyonic potential. We consider the recent data from the Planck to constrain the parameters in our effective potential generating the cosmological perturbations.
Nonperturbative Physics in a Magnetic Field
de la Incera, Vivian
2010-01-01
Non-Perturbative Quantum Field Theory has played an important role in the study of phenomena where a fermion condensate can appear under certain physical conditions. The familiar phenomenon of electric superconductivity, the color superconductivity of very dense quark matter, and the chiral symmetry breaking of low energy effective chiral theories are all examples of that sort. Often one is interested in the behavior of these systems in the presence of an external magnetic field. In this talk I will outline the effects of an external magnetic field on theories with either fermion-fermion or fermion-antifermion condensates.
High field superconducting magnets
Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)
2011-01-01
A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.
Abdullaev, Sadrilla
2014-01-01
This is the first book to systematically consider the modern aspects of chaotic dynamics of magnetic field lines and charged particles in magnetically confined fusion plasmas. The analytical models describing the generic features of equilibrium magnetic fields and magnetic perturbations in modern fusion devices are presented. It describes mathematical and physical aspects of onset of chaos, generic properties of the structure of stochastic magnetic fields, transport of charged particles in tokamaks induced by magnetic perturbations, new aspects of particle turbulent transport, etc. The presentation is based on the classical and new unique mathematical tools of Hamiltonian dynamics, like the action--angle formalism, classical perturbation theory, canonical transformations of variables, symplectic mappings, the Poincaré-Melnikov integrals. They are extensively used for analytical studies as well as for numerical simulations of magnetic field lines, particle dynamics, their spatial structures and statisti...
The nucleon in a periodic magnetic field
Agadjanov, Andria; Rusetsky, Akaki
2016-01-01
The energy shift of a nucleon in a static periodic magnetic field is evaluated at second order in the external field strength in perturbation theory. It is shown that the measurement of this energy shift on the lattice allows one to determine the unknown subtraction function in the forward doubly-virtual Compton scattering amplitude. The limits of applicability of the obtained formula for the energy shift are discussed.
Primordial magnetic fields from the string network
Horiguchi, Kouichirou; Ichiki, Kiyotomo; Sugiyama, Naoshi
2016-08-01
Cosmic strings are a type of cosmic defect formed by a symmetry-breaking phase transition in the early universe. Individual strings would have gathered to build a network, and their dynamical motion would induce scalar-, vector-, and tensor-type perturbations. In this paper, we focus on the vector mode perturbations arising from the string network based on the one scale model and calculate the time evolution and the power spectrum of the associated magnetic fields. We show that the relative velocity between photon and baryon fluids induced by the string network can generate magnetic fields over a wide range of scales based on standard cosmology. We obtain the magnetic field spectrum before recombination as aB(k,z)~4×10Gμ/1k)3.5 gauss on super-horizon scales, and aB(k,z)~2.4×10Gμ/1k)2.5 gauss on sub-horizon scales in co-moving coordinates. This magnetic field grows up to the end of recombination, and has a final amplitude of approximately B~10Gμ gauss at the k~1 Mpc scale today. This field might serve as a seed for cosmological magnetic fields.
Missile launch detection electric field perturbation experiment. Final report
Energy Technology Data Exchange (ETDEWEB)
Kane, R.J.; Rynne, T.M.
1993-04-28
The Lawrence Livermore National Laboratory and SARA Inc. participated in the ATMD missile launch activities that occurred at WSMR during January 1993. LLNL and SARA deployed sensors for monitoring of basic phenomena. An attempt was made to measure perturbations of the earth geo-potential during the launch of a Lance missile. The occurrence of the perturbation is expected from the conducting body of the missile and the exhaust plume. A set of voltage-probe antennas were used to monitor the local electric field perturbation from the launch at ranges of approximately 1 km. Examination of the data acquired during the launch period failed to show identifiable correlation of the field variations with the launch event. Three reasons are ascribed to this lack of event data: (1) The electric field potential variations have a limited spatial correlation length - the fields measured in one region have little correlation to measurements made at distances of a kilometer away. The potential variations are related to localized atmospheric disturbances and are generally unpredictable. A value for the spatial correlation length is also not known. (2) The conductivity of the plume and missile body are not adequate to produce a field perturbation of adequate magnitude. Phenomena related to the exhaust plume and missile may exist and be outside of the collection range of the equipment employed for these measurements. (3) The presence of 60 Hz power line noise was of sufficient magnitude to irreversibly contaminate measurements.
Effect of Island Overlap on ELM Suppression by Resonant Magnetic Perturbations in DIII-D
Energy Technology Data Exchange (ETDEWEB)
Fenstermacher, M E; Evans, T E; Osborne, T H; Schaffer, M J; Aldan, M P; deGrassie, J S; Gohil, P; Joseph, I; Moyer, R A; Snyder, P B; Groebner, R J; Jakubowski, M; Leonard, A W; Schmitz, O
2007-11-08
Recent DIII-D [J.L. Luxon, et al., Nucl. Fusion 43, 1813 (2003)] experiments show a correlation between the extent of overlap of magnetic islands induced in the edge plasma by perturbation coils and complete suppression of Type-I edge localized modes (ELMs) in plasmas with ITER-like electron pedestal collisionality {nu}*{sub e} {approx} 0.1, flux surface shape and low edge safety factor (q{sub 95} {approx} 3.6). With fixed n = 3 resonant magnetic perturbation (RMP) strength, ELM suppression is obtained only in a finite window in the edge safety factor (q{sub 95}) consistent with maximizing the resonant component of the applied helical field. ELM suppression is obtained over an increasing range of q{sub 95} by either increasing the n = 3 RMP strength, or by adding n = 1 perturbations to 'fill in' gaps between islands across the edge plasma. The suppression of Type-I ELMs correlates with a minimum width of the edge region having magnetic islands with Chirikov parameter >1.0, based on vacuum calculations of RMP mode components excluding the plasma response or rotational shielding. The fraction of vacuum magnetic field lines that are lost from the plasma, with connection length to the divertor targets comparable to an electron-ion collisional mean free path, increases throughout the island overlap region in the ELM suppressed case compared with the ELMing case.
Penetration of a resonant magnetic perturbation in an adiabatically rippled plasma slab
Dewar, Robert L; Bhattacharjee, Amitava; Yoshida, Zensho
2016-01-01
The adiabatic limit of a recently proposed dynamical extension of Taylor relaxation, \\emph{multi-region relaxed magnetohydrodynamics} (MRxMHD) is summarized, with special attention to the appropriate definition of relative magnetic helicity. The formalism is illustrated using a simple two-region, sheared-magnetic-field model similar to the Hahm--Kulsrud--Taylor (HKT) rippled-boundary slab model. In MRxMHD a linear Grad--Shafranov equation applies, even at finite ripple amplitude. The adiabatic switching on of boundary ripple excites a shielding current sheet opposing reconnection at a resonant surface. The perturbed magnetic field as a function of ripple amplitude is calculated by invoking conservation of magnetic helicity in the two regions separated by the current sheet. At low ripple amplitude "half islands" appear on each side of the current sheet, locking the rotational transform at the resonant value. Beyond a critical amplitude these islands disappear and the rotational transform develops a discontinui...
Magnetic fields in diffuse media
Pino, Elisabete; Melioli, Claudio
2015-01-01
This volume presents the current knowledge of magnetic fields in diffuse astrophysical media. Starting with an overview of 21st century instrumentation to observe astrophysical magnetic fields, the chapters cover observational techniques, origin of magnetic fields, magnetic turbulence, basic processes in magnetized fluids, the role of magnetic fields for cosmic rays, in the interstellar medium and for star formation. Written by a group of leading experts the book represents an excellent overview of the field. Nonspecialists will find sufficient background to enter the field and be able to appreciate the state of the art.
Perturbation Theory of Massive Yang-Mills Fields
Veltman, M.
1968-08-01
Perturbation theory of massive Yang-Mills fields is investigated with the help of the Bell-Treiman transformation. Diagrams containing one closed loop are shown to be convergent if there are more than four external vector boson lines. The investigation presented does not exclude the possibility that the theory is renormalizable.
Non perturbative methods in two dimensional quantum field theory
Abdalla, Elcio; Rothe, Klaus D
1991-01-01
This book is a survey of methods used in the study of two-dimensional models in quantum field theory as well as applications of these theories in physics. It covers the subject since the first model, studied in the fifties, up to modern developments in string theories, and includes exact solutions, non-perturbative methods of study, and nonlinear sigma models.
Basics of thermal field theory - a tutorial on perturbative computations
Laine, Mikko; Vuorinen, Aleksi
2017-01-01
These lecture notes, suitable for a two-semester introductory course or self-study, offer an elementary and self-contained exposition of the basic tools and concepts that are encountered in practical computations in perturbative thermal field theory. Selected applications to heavy ion collision physics and cosmology are outlined in the last chapter.
Perturbation theory of massive Yang-Mills fields
Veltman, M.J.G.
1968-01-01
Perturbation theory of massive Yang-Mills fields is investigated with the help of the Bell-Treiman transformation. Primitive diagrams containing one closed loop are shown to be convergent if there are more than four external vector boson lines. The investigation presented does not exclude the possib
Torsional oscillations of neutron stars with highly tangled magnetic fields
Sotani, Hajime
2015-01-01
To determine the frequencies of magnetic oscillations in the neutron stars with highly tangled magnetic fields, we derive the perturbation equations. We assume that the field strength of the global magnetic structure is so small that such fields are negligible compared with the tangled fields, which may still be far from a realistic configuration. Then, we systematically examine the spectra of the magnetic oscillations, as varying the magnetic field strength and stellar mass. The frequencies without crust elasticity are completely proportional to the strength of magnetic field, whose proportionality constant depends strongly on the stellar mass. On the other hand, the oscillation spectra with crust elasticity become more complicated, where the frequencies even for weak magnetic fields are different from the crustal torsional oscillations without magnetic fields. For discussing the spectra, the critical field strength can play an important role, which is determined in such a way that the shear velocity is equi...
Campione, Salvatore; Warne, Larry K; Sinclair, Michael B
2014-01-01
In this paper we describe a methodology for tailoring the design of metamaterial dielectric resonators, which represent a promising path toward low-loss metamaterials at optical frequencies. We first describe a procedure to decompose the far field scattered by subwavelength resonators in terms of multipolar field components, providing explicit expressions for the multipolar far fields. We apply this formulation to confirm that an isolated high-permittivity cube resonator possesses frequency separated electric and magnetic dipole resonances, as well as a magnetic quadrupole resonance in close proximity to the electric dipole resonance. We then introduce multiple dielectric gaps to the resonator geometry in a manner suggested by perturbation theory, and demonstrate the ability to overlap the electric and magnetic dipole resonances, thereby enabling directional scattering by satisfying the first Kerker condition. We further demonstrate the ability to push the quadrupole resonance away from the degenerate dipole ...
Non-gaussianity from the trispectrum and vector field perturbations
Valenzuela-Toledo, Cesar A
2009-01-01
We use the \\delta N formalism to study the trispectrum T_\\zeta of the primordial curvature perturbation \\zeta when the latter is generated by vector field perturbations, considering the tree-level and one-loop contributions. The level of non-gaussianity in the trispectrum, \\tau_{NL}, is calculated in this scenario and related to the level of non-gaussianity in the bispectrum, f_{NL}, and the level of statistical anisotropy in the power spectrum, g_\\zeta. Such consistency relations will put under test this scenario against future observations. Comparison with the expected observational bound on \\tau_{NL} from WMAP, for generic inflationary models, is done.
Primordial Magnetic Field at the Photon Last Scattering Surface
Energy Technology Data Exchange (ETDEWEB)
Yamazaki, D.G. [Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033 (Japan); National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 (Japan); Ichiki, K. [Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033 (Japan); National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 (Japan); Kajino, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 (Japan); Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033 (Japan)
2005-07-25
We construct the original method and numerical code to calculate the effects of magnetic field on CMB at the last scattering surface (LSS). In order to investigate the specific nature of the magnetic field effects on the CMB, we compare our calculated perturbation and the WMAP data.
Perturbations of single-field inflation in modified gravity theory
Directory of Open Access Journals (Sweden)
Taotao Qiu
2015-05-01
Full Text Available In this paper, we study the case of single field inflation within the framework of modified gravity theory where the gravity part has an arbitrary form f(R. Via a conformal transformation, this case can be transformed into its Einstein frame where it looks like a two-field inflation model. However, due to the existence of the isocurvature modes in such a multi-degree-of-freedom (m.d.o.f. system, the (curvature perturbations are not equivalent in two frames, so despite of its convenience, it is illegal to treat the perturbations in its Einstein frame as the “real” ones as we always do for pure f(R theory or single field with nonminimal coupling. Here by pulling the results of curvature perturbations back into its original Jordan frame, we show explicitly the power spectrum and spectral index of the perturbations in the Jordan frame, as well as how it differs from the Einstein frame. We also fit our results with the newest Planck data. Since there is large parameter space in these models, we show that it is easy to fit the data very well.
Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete
2017-09-01
Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.
Willensdorfer, M.; Denk, S. S.; Strumberger, E.; Suttrop, W.; Vanovac, B.; Brida, D.; Cavedon, M.; Classen, I.; Dunne, M.; Fietz, S.; Fischer, R.; Kirk, A.; Laggner, F. M.; Liu, Y. Q.; Odstrcil, T.; Ryan, D. A.; Viezzer, E.; Zohm, H.; Luhmann, I. C.; ASDEX Upgrade team,; EUROfusion MST1 Team,
2016-01-01
The plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation
Perturbations of the Yang-Mills field in the universe
Institute of Scientific and Technical Information of China (English)
Wen Zhao
2009-01-01
It has been suggested that the Yang-Mills (YM) field can be a kind of candidate for the inflationary field at high energy scales or dark energy at very low energy scales, which can naturally give the equation of state -1 <ω< 0 or ω<-1. We discuss the zero order and first order Einstein equations and YM field kinetic energy equations of the free YM field models. From the zero order equations, we find that ω+1 ∝α-2, from which it follows that the equation of state of the YM field always goes to - 1, independent of the initial conditions. By solving the first order Einstein equations and the YM field equations, we find that in the YM field inflationary models, the scale-invariant primordial perturbation power spectrum cannot be generated. Therefore, only using this kind of YM field is not enough to account for inflationary sources. However, as a kind of candidate for dark energy, the YM field has the 'sound speed' cs2 = -1/3 < 0, which makes the perturbation φ have a damping behavior at large scales. This provides a way to distinguish the YM field dark energy models from other kinds of models.
Using Gravitational Waves to put limits on Primordial Magnetic Fields
Garrison, David
2016-01-01
We describe a technique for using simulated tensor perturbations in order to place upper limits on the intensity of magnetic fields in the early universe. As an example, we apply this technique to the beginning of primordial nucleosynthesis. We determined that any magnetic seed fields that existed before that time were still in the process of being amplified. In the future, we plan to apply this technique to a wider range of initial magnetic fields and cosmological epochs.
Perturbative Quantum Field Theory in the String-Inspired Formalism
Schubert, C
2001-01-01
We review the status and present range of applications of the ``string-inspired'' approach to perturbative quantum field theory. This formalism offers the possibility of computing effective actions and S-matrix elements in a way which is similar in spirit to string perturbation theory, and bypasses much of the apparatus of standard second-quantized field theory. Its development was initiated by Bern and Kosower, originally with the aim of simplifying the calculation of scattering amplitudes in quantum chromodynamics and quantum gravity. We give a short account of the original derivation of the Bern-Kosower rules from string theory. Strassler's alternative approach in terms of first-quantized particle path integrals is then used to generalize the formalism to more general field theories, and, in the abelian case, also to higher loop orders. A considerable number of sample calculations are presented in detail, with an emphasis on quantum electrodynamics.
Proton Radiography as an electromagnetic field and density perturbation diagnostic
Energy Technology Data Exchange (ETDEWEB)
Mackinnon, A; Patel, P; Town, R; Edwards, M; Phillips, T; Lerner, S; Price, D; Hicks, D; Key, M; Hatchett, S; Wilks, S; King, J; Snavely, R; Freeman, R; Boehlly, T; Koenig, M; Martinolli, E; Lepape, S; Benuzzi-Mounaix, A; Audebert, P; Gauthier, J; Borghesi, M; Romagnani, L; Toncian, T; Pretzler, G; Willi, O
2004-04-15
Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with MeV protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter . PACS numbers: 52.50.Jm, 52.40.Nk, 52.40.Mj, 52.70.Kz
Magnetic Field Topology in Jets
Gardiner, T. A.; Frank, A.
2000-01-01
We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.
Magnetic-perturbation-induced plasma transport in H-mode pedestals
Callen, J. D.; Cole, A. J.; Hegna, C. C.
2012-03-01
Plasma toroidal rotation can prevent reconnection of externally applied resonant magnetic perturbation (RMP) fields on rational surfaces and hence magnetic island formation and stochasticity in the edge of tokamak H-mode plasmas. However, magnetic flutter induced by RMPs off the rational surfaces causes a radial electron heat diffusivity χe^RMP˜(δBr/B0)^2χ| F(x) in which χ|˜vTe^2/νe is an effective parallel electron heat diffusivity and F is a spatially varying factor [1]. The flutter also diffuses electrons radially and causes a factor of about 3 smaller increases in density diffusion. Since the electron density transport is non-ambipolar, this flutter process also modifies the radial electric field and plasma toroidal rotation. This work extends the previously developed periodic cylinder screw pinch model [1] of RMP-flutter-induced plasma transport to a full toroidal model which is axisymmetric to lowest order plus gyroradius-small magnetic field perturbations. The possible role of the RMP-flutter-induced plasma transport in reducing pressure gradients in H-mode pedestals and thereby suppressing ELMs will be discussed.[4pt] [1] J.D. Callen et al., UW-CPTC 11-13, http://www.cptc.wisc.edu (submitted to Nucl. Fusion.)
Two charges on plane in a magnetic field: II. Moving neutral quantum system across magnetic field
Escobar-Ruiz, M A
2014-01-01
The moving neutral system of two Coulomb charges on a plane subject to a constant magnetic field $B$ perpendicular to the plane is considered. It is shown that the composite system of finite total mass is bound for any center-of-mass momentum $P$ and magnetic field strength; the energy of the ground state is calculated accurately using a variational approach. Their accuracy is cross-checked in Lagrange-mesh method for $B=1$\\,a.u. and in a perturbation theory at small $B$ and $P$. The constructed trial function has a property to be a uniform approximation of the exact eigenfunction. For Hydrogen atom and Positronium a double perturbation theory in $B$ and $P$ is developed and the first corrections are found algebraically. A phenomenon of a sharp change of energy behavior for a certain center-of-mass momentum but a fixed magnetic field is indicated.
Magnetic field switchable dry adhesives.
Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo
2015-02-01
A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field.
Limits for primordial magnetic fields
Caprini, Chiara
2011-01-01
A possible explanation for the origin of the magnetic fields observed today in matter structures is that they were generated in the primordial universe. After briefly revising the model of a primordial stochastic magnetic field and sketching the main features of its time evolution in the primordial plasma, we illustrate the current upper bounds on the magnetic field amplitude and spectral index from Cosmic Microwave Background observations and gravitational wave production. We conclude that a primordial magnetic field generated by a non-causal process such as inflation with a red spectrum seems to be favoured as a seed for the magnetic fields observed today in structures.
Tearing mode velocity braking due to resonant magnetic perturbations
Frassinetti, L.; Menmuir, S.; Olofsson, K. E. J.; Brunsell, P. R.; Drake, J. R.
2012-10-01
The effect of resonant magnetic perturbations (RMPs) on the tearing mode (TM) velocity is studied in EXTRAP T2R. Experimental results show that the RMP produces TM braking until a new steady velocity or wall locking is reached. The braking is initially localized at the TM resonance and then spreads to the other TMs and to the rest of the plasma producing a global velocity reduction via the viscous torque. The process has been used to experimentally estimate the kinematic viscosity profile, in the range 2-40 m2 s-1, and the electromagnetic torque produced by the RMP, which is strongly localized at the TM resonance. Experimental results are then compared with a theoretical model which gives a reasonable qualitative explanation of the entire process.
Primordial magnetic fields from the string network
Horiguchi, Kouichirou; Sugiyama, Naoshi
2016-01-01
Cosmic strings are a type of cosmic defect formed by a symmetry-breaking phase transition in the early universe. Individual strings would have gathered to build a network, and their dynamical motion would induce scalar--, vector-- and tensor--type perturbations. In this paper, we focus on the vector mode perturbations arising from the string network based on the one scale model and calculate the time evolution and the power spectrum of the associated magnetic fields. We show that the relative velocity between photon and baryon fluids induced by the string network can generate magnetic fields over a wide range of scales based on standard cosmology. We obtain the magnetic field spectrum before recombination as $a^2B(k,z)\\sim4\\times10^{-16}G\\mu/((1+z)/1000)^{4.25}(k/{\\rm Mpc}^{-1})^{3.5}$ Gauss on super-horizon scales, and $a^2B(k,z)\\sim2.4\\times10^{-17}G\\mu/((1+z)/1000)^{3.5}(k/{\\rm Mpc}^{-1})^{2.5}$ Gauss on sub-horizon scales in co-moving coordinates. This magnetic field grows up to the end of recombination, ...
Using Perturbation theory to reduce noise in diffusion tensor fields.
Bansal, Ravi; Staib, Lawrence H; Xu, Dongrong; Laine, Andrew F; Liu, Jun; Peterson, Bradley S
2009-08-01
We propose the use of Perturbation theory to reduce noise in Diffusion Tensor (DT) fields. Diffusion Tensor Imaging (DTI) encodes the diffusion of water molecules along different spatial directions in a positive definite, 3 x 3 symmetric tensor. Eigenvectors and eigenvalues of DTs allow the in vivo visualization and quantitative analysis of white matter fiber bundles across the brain. The validity and reliability of these analyses are limited, however, by the low spatial resolution and low Signal-to-Noise Ratio (SNR) in DTI datasets. Our procedures can be applied to improve the validity and reliability of these quantitative analyses by reducing noise in the tensor fields. We model a tensor field as a three-dimensional Markov Random Field and then compute the likelihood and the prior terms of this model using Perturbation theory. The prior term constrains the tensor field to be smooth, whereas the likelihood term constrains the smoothed tensor field to be similar to the original field. Thus, the proposed method generates a smoothed field that is close in structure to the original tensor field. We evaluate the performance of our method both visually and quantitatively using synthetic and real-world datasets. We quantitatively assess the performance of our method by computing the SNR for eigenvalues and the coherence measures for eigenvectors of DTs across tensor fields. In addition, we quantitatively compare the performance of our procedures with the performance of one method that uses a Riemannian distance to compute the similarity between two tensors, and with another method that reduces noise in tensor fields by anisotropically filtering the diffusion weighted images that are used to estimate diffusion tensors. These experiments demonstrate that our method significantly increases the coherence of the eigenvectors and the SNR of the eigenvalues, while simultaneously preserving the fine structure and boundaries between homogeneous regions, in the smoothed tensor
Cosmological perturbations in coherent oscillating scalar field models
Energy Technology Data Exchange (ETDEWEB)
Cembranos, J.A.R.; Maroto, A.L.; Jareño, S.J. Núñez [Departamento de Física Teórica I, Universidad Complutense de Madrid,Avenida Complutense s/n, Madrid (Spain)
2016-03-03
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V(ϕ)=λ|ϕ|{sup n}/n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c{sub eff}{sup 2}=ω=(n−2)/(n+2) with ω the effective equation of state. We also obtain the first order correction in k{sup 2}/ω{sub eff}{sup 2}, when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω{sub eff}. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet’s theorem.
Cosmological perturbations in coherent oscillating scalar field models
Cembranos, J A R; Jareño, S J Núñez
2015-01-01
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials $V(\\phi)=\\lambda \\vert\\phi\\vert^{n}/n$. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained $c_{\\text{eff}}^2 = \\omega=(n-2)/(n+2)$ with $\\omega$ the effective equation of state. We also obtain the first order correction in $k^2/\\omega_{\\text{eff}}^2$, when the wavenumber $k$ of the perturbations is much smaller than the background oscillation frequency, $\\omega_{\\text{eff}}$. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the nat...
Cosmological perturbations in coherent oscillating scalar field models
Cembranos, J. A. R.; Maroto, A. L.; Jareño, S. J. Núñez
2016-03-01
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V( ϕ) = λ| ϕ| n /n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c eff 2 = ω = ( n - 2)/( n + 2) with ω the effective equation of state. We also obtain the first order correction in k 2/ ω eff 2 , when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω eff. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet's theorem.
Campanelli, Leonardo
2015-01-01
[Abridged] We analyze the evolution of superhorizon-scale magnetic fields from the end of inflation till today. Whatever is the mechanism responsible for their generation during inflation, we find that a given magnetic mode with wavenumber $k$ evolves, after inflation, according to the values of $k\\eta_e$, $n_{\\mathbf{k}}$, and $\\Omega_k$, where $\\eta_e$ is the conformal time at the end of inflation, $n_{\\mathbf{k}}$ is the number density spectrum of inflation-produced photons, and $\\Omega_k$ is the phase difference between the two Bogolubov coefficients which characterize the state of that mode at the end of inflation. For any realistic inflationary magnetogenesis scenario, we find that $n_{\\mathbf{k}}^{-1} \\ll |k\\eta_e| \\ll 1$, and three evolutionary scenarios are possible: ($i$) $|\\Omega_k \\mp \\pi| = \\mathcal{O}(1)$, in which case the evolution of the magnetic spectrum $B_k(\\eta)$ is adiabatic, $a^2B_k(\\eta) = \\mbox{const}$, with $a$ being the expansion parameter; ($ii$) $|\\Omega_k \\mp \\pi| \\ll |k\\eta_e|$,...
Bera, Prasanta
2016-01-01
In the presence of a strong magnetic field a stellar equilibrium configuration, aided by the Lorentz force, can support a larger mass than a non-magnetic one. This has been considered a possible explanation of the super-Chandrasekhar mass white dwarfs giving rise to over-luminous Type-Ia supernovae. We present here linear and non-linear perturbation studies of such strongly magetised configurations and show that axisymmetric configurations with poloidal or toroidal fields are unstable. The numerical evolution of the perturbations shows instability after about an Alfv\\'en crossing time. This time scale is very short for the magnetically supported super-Chandrasekhar mass white dwarfs. Uniform rotation about the symmetry axis can reduce the growth rate but can not stabilize the super-massive configurations. It is concluded that long-lived super-Chandrasekhar mass white dwarfs supported by magnetic field are unlikely to occur in Nature.
Primordial magnetic fields from self-ordering scalar fields
Horiguchi, Kouichirou; Sekiguchi, Toyokazu; Sugiyama, Naoshi
2015-01-01
A symmetry-breaking phase transition in the early universe could have led to the formation of cosmic defects. Because these defects dynamically excite not only scalar and tensor type cosmological perturbations but also vector type ones, they may serve as a source of primordial magnetic fields. In this study, we calculate the time evolution and the spectrum of magnetic fields that are generated by a type of cosmic defects, called global textures, using the non-linear sigma (NLSM) model. Based on the standard cosmological perturbation theory, we show, both analytically and numerically, that a vector-mode relative velocity between photon and baryon fluids is induced by textures, which inevitably leads to the generation of magnetic fields over a wide range of scales. We find that the amplitude of the magnetic fields is given by $B\\sim{10^{-9}}{((1+z)/10^3)^{-2.5}}({v}/{m_{\\rm pl}})^2({k}/{\\rm Mpc^{-1}})^{3.5}/{\\sqrt{N}}$ Gauss in the radiation dominated era for $k\\lesssim 1$ Mpc$^{-1}$, with $v$ being the vacuum ...
Resonant-magnetic-perturbation-induced plasma transport in H-mode pedestals
Energy Technology Data Exchange (ETDEWEB)
Callen, J. D.; Hegna, C. C. [University of Wisconsin, 1500 Engineering Drive, Madison, Wisconsin 53706-1609 (United States); Cole, A. J. [Columbia University, 201 S.W. Mudd, New York, New York 10027 (United States)
2012-11-15
Plasma toroidal rotation reduces reconnection of externally applied resonant magnetic perturbation (RMP) fields {delta}B on rational (q = m/n) magnetic flux surfaces. Hence, it causes radial perturbations {delta}B{sub {rho}m/n} to be small there, and thus inhibits magnetic island formation and stochasticity in the edge of high (H-) mode confinement tokamak plasmas. However, electron collisional damping combined with the spatial magnetic flutter {delta}B{sub {rho}m/n} induced by RMPs in the vicinity of rational surfaces causes a radial electron heat diffusivity in which {chi}{sub e Parallel-To }{sup eff}{approx}(v{sub Te}{sup 2}/{nu}{sub e})/(1+x{sup 2}/{delta}{sub Parallel-To }{sup 2}) is an effective parallel electron thermal diffusivity. These effects are reduced by magnetic shear effects at a distance x from rational surfaces for |x|>{delta}{sub Parallel-To} but amplified for {delta}B-caret{sub {rho}m/n}(x)>{delta}B-caret{sub {rho}m/n}(0). A kinetic, toroidal model of these RMP-flutter-induced plasma transport effects is developed and compared to a previously developed cylindrical model. The RMP-induced increases in plasma transport can be large enough to reduce plasma gradients in H-mode pedestals. Thus, they may contribute to suppressing edge localized modes in tokamak plasmas.
Resonant magnetic perturbations of edge-plasmas in toroidal confinement devices
Evans, T. E.
2015-12-01
Controlling the boundary layer in fusion-grade, high-performance, plasma discharges is essential for the successful development of toroidal magnetic confinement power generating systems. A promising approach for controlling the boundary plasma is based on the use of small, externally applied, edge resonant magnetic perturbation (RMP) fields (δ b\\bot\\text{ext}≈ {{10}-4}\\to {{10}-3}~\\text{T} ). A long-term focus area in tokamak fusion research has been to find methods, involving the use of non-axisymmetric magnetic perturbations to reduce the intense particle and heat fluxes to the wall. Experimental RMP research has progressed from the early pioneering work on tokamaks with material limiters in the 1970s, to present day research in separatrix-limited tokamaks operated in high-confinement mode, which is primarily aimed at the mitigation of the intermittent fluxes due edge localized modes (ELMs). At the same time, theoretical research has evolved from analytical models to numerical simulations, including the full 3D complexities of the problem. Following the first demonstration of ELM suppression in the DIII-D tokamak during 2003, there has been a rapid worldwide growth in theoretical, numerical and experimental edge RMP research resulting in the addition of ELM control coils to the ITER baseline design (Loarte et al 2014 Nucl. Fusion 54 033007). This review provides an overview of edge RMP research including a summary of the early theoretical and numerical background along with recent experimental results on improved particle and energy confinement in tokamaks triggered by edge RMP fields. The topics covered make up the basic elements needed for developing a better understanding of 3D magnetic perturbation physics, which is required in order to utilize the full potential of edge RMP fields in fusion relevant high performance, H-mode, plasmas.
SCUPOL Magnetic Field Analysis
Poidevin, Frederick; Kowal, Grzegorz; Pino, Elisabete de Gouveia Dal; Magalhaes, Antonio-Mario
2013-01-01
We present an extensive analysis of the 850 microns polarization maps of the SCUPOL Catalog produced by Matthews et al. (2009), focusing exclusively on the molecular clouds and star-forming regions. For the sufficiently sampled regions, we characterize the depolarization properties and the turbulent-to-mean magnetic field ratio of each region. Similar sets of parameters are calculated from 2D synthetic maps of dust emission polarization produced with 3D MHD numerical simulations scaled to the S106, OMC-2/3, W49 and DR21 molecular clouds polarization maps. For these specific regions the turbulent MHD regimes retrieved from the simulations, as described by the turbulent Alfv\\`en and sonic Mach numbers, are consistent within a factor 1 to 2 with the values of the same turbulent regimes estimated from the analysis of Zeeman measurements data provided by Crutcher (1999). Constraints on the values of the inclination angle of the mean magnetic field with respect to the LOS are also given. The values obtained from th...
Magnetic Fields: Visible and Permanent.
Winkeljohn, Dorothy R.; Earl, Robert D.
1983-01-01
Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)
Magnetic field contribution to the last electron-photon scattering
Giovannini, Massimo
2010-01-01
When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tens...
Reduction of magnetic perturbation for SR-POEM
Patla, B. R.
2016-02-01
SR-POEM is a Galilean test of the weak equivalence principle that aims to measure the fractional acceleration difference η with a mission uncertainty σ (η )=1× {10}-17 for a pair of test substances. It is to be conducted during the low-drag free fall portion of a sounding rocket flight. The interaction of the magnetic field gradient with tiny remanent magnetic moments of the test masses will produce a spurious acceleration that is not sufficiently reduced by a single Mu-metal shield. In this paper, we study configurations with two and three shields. Approximate analytic formulae are used to study the shielding factor as a function of geometry. We use finite element analysis (FEA) to determine the magnetic field and gradient for certain cases that satisfy the mission requirements. FEA results are compared with analytic expressions wherever appropriate. Several configurations reduce both axial and transverse magnetic field within the shielding volume by at least the required factor of 4× {10}5.
Reduction of magnetic perturbation for SR-POEM
Patla, Bijunath R; Reasenberg, Robert D
2014-01-01
SR-POEM is a Galilean test of the weak equivalence principle (WEP) that aims to measure the fractional acceleration difference $\\eta$ with a mission uncertainty $\\sigma(\\eta)=2\\times 10^{-17}$ for a pair of test substances. It is to be conducted during the low-drag free fall portion of a sounding rocket flight. The interaction of the magnetic field gradient with the (small) magnetic moment of the test masses (TMs) will produce a spurious acceleration that is not sufficiently reduced by a single Mu-metal shield. In this paper, we study configurations with two and three shields. Approximate analytic formulae are used to study the shielding factor as a function of the geometry. We use finite element analysis (FEA) to determine the magnetic field and gradient in chosen cases. The analytic and FEA results are compared. Several configurations reduce both the axial and transverse magnetic field by at least the required factor of $4\\times 10^5$.
Detailed ultraviolet asymptotics for AdS scalar field perturbations
Evnin, Oleg
2016-01-01
We present a range of methods suitable for accurate evaluation of the leading asymptotics for integrals of products of Jacobi polynomials in limits when the degrees of some or all polynomials inside the integral become large. The structures in question have recently emerged in the context of effective descriptions of small amplitude perturbations in anti-de Sitter (AdS) spacetime. The limit of high degree polynomials corresponds in this situation to effective interactions involving extreme short-wavelength modes, whose dynamics is crucial for the turbulent instabilities that determine the ultimate fate of small AdS perturbations. We explicitly apply the relevant asymptotic techniques to the case of a self-interacting probe scalar field in AdS and extract a detailed form of the leading large degree behavior, including closed form analytic expressions for the numerical coefficients appearing in the asymptotics.
Detailed ultraviolet asymptotics for AdS scalar field perturbations
Energy Technology Data Exchange (ETDEWEB)
Evnin, Oleg [Department of Physics, Faculty of Science, Chulalongkorn University,Thanon Phayathai, Pathumwan, Bangkok 10330 (Thailand); Theoretische Natuurkunde, Vrije Universiteit Brussel and The International Solvay Institutes,Pleinlaan 2, B-1050 Brussels (Belgium); Jai-akson, Puttarak [Department of Physics, Faculty of Science, Chulalongkorn University,Thanon Phayathai, Pathumwan, Bangkok 10330 (Thailand)
2016-04-11
We present a range of methods suitable for accurate evaluation of the leading asymptotics for integrals of products of Jacobi polynomials in limits when the degrees of some or all polynomials inside the integral become large. The structures in question have recently emerged in the context of effective descriptions of small amplitude perturbations in anti-de Sitter (AdS) spacetime. The limit of high degree polynomials corresponds in this situation to effective interactions involving extreme short-wavelength modes, whose dynamics is crucial for the turbulent instabilities that determine the ultimate fate of small AdS perturbations. We explicitly apply the relevant asymptotic techniques to the case of a self-interacting probe scalar field in AdS and extract a detailed form of the leading large degree behavior, including closed form analytic expressions for the numerical coefficients appearing in the asymptotics.
Diffusion of magnetic field lines in a confined RFP plasma
Energy Technology Data Exchange (ETDEWEB)
Bazzani, A. [Bologna Univ. (Italy). Dip. di Fisica; INFN, Istituto Nazionale di Fisica Nucleare, Bologna (Italy); Lab. di Tecnologia dei Materiali, Bologna (Italy); Di Sebastiano, A. [Bologna Univ. (Italy). Dip. di Fisica; Bologna Univ. (Italy). Dip. di Matematica; Turchetti, G. [Bologna Univ. (Italy). Dip. di Fisica
1998-12-01
A volume-preserving symplectic map is proposed to describe the magnetic field lines when the Taylor equilibrium is perturbed in a generic way. The standard scenario is observed by varying the perturbation strength, but the statistical properties in the chaotic regions are not simple due to the presence of boundaries and remnants of invariant structures. Simpler models of volume-preserving maps are proposed. The slowly modulated standard map captures the basic topological and statistical features. The diffusion is analytically described for large perturbations in terms of correlation functions and for small perturbations using the adiabatic theory, provided that the modulation is sufficiently slow.
Reconnection of Magnetic Fields
Birn, J.; Priest, E. R.
2007-01-01
Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.
Perturbative algebraic quantum field theory an introduction for mathematicians
Rejzner, Kasia
2016-01-01
Perturbative Algebraic Quantum Field Theory (pAQFT), the subject of this book, is a complete and mathematically rigorous treatment of perturbative quantum field theory (pQFT) that doesn’t require the use of divergent quantities. We discuss in detail the examples of scalar fields and gauge theories and generalize them to QFT on curved spacetimes. pQFT models describe a wide range of physical phenomena and have remarkable agreement with experimental results. Despite this success, the theory suffers from many conceptual problems. pAQFT is a good candidate to solve many, if not all of these conceptual problems. Chapters 1-3 provide some background in mathematics and physics. Chapter 4 concerns classical theory of the scalar field, which is subsequently quantized in chapters 5 and 6. Chapter 7 covers gauge theory and chapter 8 discusses QFT on curved spacetimes and effective quantum gravity. The book aims to be accessible researchers and graduate students interested in the mathematical foundations of pQFT are th...
Mirus, Kevin Andrew
In this thesis, the possibility of controlling low- and high-dimensional chaotic systems by periodically driving an accessible system parameter is examined. This method has been carried out on several numerical systems and the MST Reversed Field Pinch. The numerical systems investigated include the logistic equation, the Lorenz equations, the Rossler equations, a coupled lattice of logistic equations, a coupled lattice of Lorenz equations, the Yoshida equations, which model tearing mode fluctuations in a plasma, and a neural net model for magnetic fluctuations on MST. This method was tested on the MST by sinusoidally driving a magnetic flux through the toroidal gap of the device. Numerically, periodic drives were found to be most effective at producing limit cycle behavior or significantly reducing the dimension of the system when the perturbation frequency was near natural frequencies of unstable periodic orbits embedded in the attractor of the unperturbed system. Several different unstable periodic orbits have been stabilized in this way for the low-dimensional numerical systems, sometimes with perturbation amplitudes that were less than 5% of the nominal value of the parameter being perturbed. In high- dimensional systems, limit cycle behavior and significant decreases in the system dimension were also achieved using perturbations with frequencies near the natural unstable periodic orbit frequencies. Results for the MST were not this encouraging, most likely because of an insufficient drive amplitude, the extremely high dimension of the plasma behavior, large amounts of noise, and a lack of stationarity in the transient plasma pulses.
Dissipation function in a magnetic field (Review)
Gurevich, V. L.
2015-07-01
The dissipation function is introduced to describe the behavior of the system of harmonic oscillations interacting with the environment (thermostat). This is a quadratic function of generalized velocities, which determines the rate of dissipation of the mechanical energy in the system. It was assumed earlier (Landau, Lifshitz) that the dissipation function can be introduced only in the absence of magnetic field. In the present review based on the author's studies, it has been shown how the dissipation function can be introduced in the presence of a magnetic field B. In a magnetic field, both dissipative and nondissipative responses arise as a response to perturbation and are expressed in terms of kinetic coefficients. The matrix of nondissipative coefficients can be obtained to determine an additional term formally including it into the equations of motion, which still satisfy the energy conservation law. Then, the dissipative part of the matrix can be considered in exactly the same way as without magnetic field, i.e., it defines the dissipation loss. As examples, the propagation and absorption of ultrasound in a metal or a semiconductor in a magnetic field have been considered using two methods: (i) the method based on the phenomenological theory using the equations of the theory of elasticity and (ii) the method based on the microscopic approach by analyzing and solving the kinetic equation. Both examples are used to illustrate the approach with the dissipation function.
Effect of magnetic perturbations on the 3D MHD self-organization of shaped tokamak plasmas
Bonfiglio, D; Veranda, M; Chacón, L; Escande, D F
2016-01-01
The effect of magnetic perturbations (MPs) on the helical self-organization of shaped tokamak plasmas is discussed in the framework of the nonlinear 3D MHD model. Numerical simulations performed in toroidal geometry with the \\textsc{pixie3d} code [L. Chac\\'on, Phys. Plasmas {\\bf 15}, 056103 (2008)] show that $n=1$ MPs significantly affect the spontaneous quasi-periodic sawtoothing activity of such plasmas. In particular, the mitigation of sawtooth oscillations is induced by $m/n=1/1$ and $2/1$ MPs. These numerical findings provide a confirmation of previous circular tokamak simulations, and are in agreement with tokamak experiments in the RFX-mod and DIII-D devices. Sawtooth mitigation via MPs has also been observed in reversed-field pinch simulations and experiments. The effect of MPs on the stochastization of the edge magnetic field is also discussed.
Perturbed soliton excitations of Rao-dust Alfvén waves in magnetized dusty plasmas
Energy Technology Data Exchange (ETDEWEB)
Kavitha, L., E-mail: louiskavitha@yahoo.co.in [Department of Physics, School of Basic and Applied Sciences, Central University of Tamil Nadu, Thiruvarur 610 101 (India); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Lavanya, C.; Senthil Kumar, V. [Department of Physics, Periyar University, Salem, Tamil Nadu 636 011 (India); Gopi, D. [Department of Chemistry, Periyar University, Salem 636 011 (India); Center for Nanoscience and Nanotechnology, Periyar University, Salem, Tamil Nadu 636 011 (India); Pasqua, A. [Department of Physics, University of Trieste, Trieste (Italy)
2016-04-15
We investigate the propagation dynamics of the perturbed soliton excitations in a three component fully ionized dusty magnetoplasma consisting of electrons, ions, and heavy charged dust particulates. We derive the governing equation of motion for the two dimensional Rao-dust magnetohydrodynamic (R-D-MHD) wave by employing the inertialess electron equation of motion, inertial ion equation of motion, the continuity equations in a plasma with immobile charged dust grains, together with the Maxwell's equations, by assuming quasi neutrality and neglecting the displacement current in Ampere's law. Furthermore, we assume the massive dust particles are practically immobile since we are interested in timescales much shorter than the dusty plasma period, thereby neglecting any damping of the modes due to the grain charge fluctuations. We invoke the reductive perturbation method to represent the governing dynamics by a perturbed cubic nonlinear Schrödinger (pCNLS) equation. We solve the pCNLS, along the lines of Kodama-Ablowitz multiple scale nonlinear perturbation technique and explored the R-D-MHD waves as solitary wave excitations in a magnetized dusty plasma. Since Alfvén waves play an important role in energy transport in driving field-aligned currents, particle acceleration and heating, solar flares, and the solar wind, this representation of R-D-MHD waves as soliton excitations may have extensive applications to study the lower part of the earth's ionosphere.
Basics of thermal field theory a tutorial on perturbative computations
Laine, Mikko
2016-01-01
This book presents thermal field theory techniques, which can be applied in both cosmology and the theoretical description of the QCD plasma generated in heavy-ion collision experiments. It focuses on gauge interactions (whether weak or strong), which are essential in both contexts. As well as the many differences in the physics questions posed and in the microscopic forces playing a central role, the authors also explain the similarities and the techniques, such as the resummations, that are needed for developing a formally consistent perturbative expansion. The formalism is developed step by step, starting from quantum mechanics; introducing scalar, fermionic and gauge fields; describing the issues of infrared divergences; resummations and effective field theories; and incorporating systems with finite chemical potentials. With this machinery in place, the important class of real-time (dynamic) observables is treated in some detail. This is followed by an overview of a number of applications, ranging from t...
Tearing mode dynamics and locking in the presence of external magnetic perturbations
Fridström, R.; Munaretto, S.; Frassinetti, L.; Chapman, B. E.; Brunsell, P. R.; Sarff, J. S.
2016-06-01
In normal operation, Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch plasmas exhibit several rotating tearing modes (TMs). Application of a resonant magnetic perturbation (RMP) results in braking of mode rotation and, if the perturbation amplitude is sufficiently high, in a wall-locked state. The coils that produce the magnetic perturbation in MST give rise to RMPs with several toroidal harmonics. As a result, simultaneous deceleration of all modes is observed. The measured TM dynamics is shown to be in qualitative agreement with a magnetohydrodynamical model of the RMP interaction with the TM [R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)] adapted to MST. To correctly model the TM dynamics, the electromagnetic torque acting on several TMs is included. Quantitative agreement of the TM slowing-down time was obtained for a kinematic viscosity in the order of νki n≈10 -20 m2/s. Analysis of discharges with different plasma densities shows an increase of the locking threshold with increasing density. Modeling results show good agreement with the experimental trend, assuming a density-independent kinematic viscosity. Comparison of the viscosity estimates in this paper to those made previously with other techniques in MST plasmas suggests the possibility that the RMP technique may allow for estimates of the viscosity over a broad range of plasmas in MST and other devices.
Vestibular stimulation by magnetic fields
Ward, Bryan K.; Roberts, Dale C.; Della Santina, Charles C.; Carey, John P.; Zee, David S.
2015-01-01
Individuals working next to strong static magnetic fields occasionally report disorientation and vertigo. With the increasing strength of magnetic fields used for magnetic resonance imaging (MRI) studies, these reports have become more common. It was recently learned that humans, mice and zebrafish all demonstrate behaviors consistent with constant peripheral vestibular stimulation while inside a strong, static magnetic field. The proposed mechanism for this effect involves a Lorentz force resulting from the interaction of a strong static magnetic field with naturally occurring ionic currents flowing through the inner ear endolymph into vestibular hair cells. The resulting force within the endolymph is strong enough to displace the lateral semicircular canal cupula, inducing vertigo and the horizontal nystagmus seen in normal mice and in humans. This review explores the evidence for interactions of magnetic fields with the vestibular system. PMID:25735662
Magnetic response to applied electrostatic field in external magnetic field
Energy Technology Data Exchange (ETDEWEB)
Adorno, T.C. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil); University of Florida, Department of Physics, Gainesville, FL (United States); Gitman, D.M. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil); Tomsk State University, Department of Physics, Tomsk (Russian Federation); Shabad, A.E. [P. N. Lebedev Physics Institute, Moscow (Russian Federation)
2014-04-15
We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics. (orig.)
Magnetic response to applied electrostatic field in external magnetic field
Adorno, T C; Shabad, A E
2014-01-01
We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to a simple example of a spherically-symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space, the pattern of lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.
Effects of compressional magnetic perturbation on kinetic Alfven waves
Dong, Ge; Bhattacharjee, Amitava; Lin, Zhihong
2016-10-01
Kinetic Alfven waves play a very important role in the dynamics of fusion as well as space and astrophysical plasmas. The compressional magnetic perturbation δB|| can play important role in kinetic Alfven waves (KAW) and various instabilities at large plasma β. It could affect the nonlinear behavior of these modes significantly even at small β. In this study, we have implemented δB|| in gyrokinetic toroidal code (GTC). The perpendicular Ampere's law is solved as a force balance equation. Double gyroaveraging is incorporated in the code to treat the finite Larmor radius effects related to δB|| terms. KAW is studied in slab geometry as a benchmark case. A scan in β for the KAW dispersion relation shows that as β approaches 1 (>0.3), the effects of δB|| becomes important. Connections are made with other existing studies of KAWs in the fusion and space plasma literature. This new capability of including δB|| in GTC could be applied to nonlinear simulations of modes such as kinetic ballooning and tearing modes. This research is supported by DOE Contract No. DE-AC02-09CH11466.
Precise numerical estimation of the magnetic field generated around recombination
Fidler, Christian; Pettinari, Guido; Pitrou, Cyril
2016-05-01
We investigate the generation of magnetic fields from nonlinear effects around recombination. As tight-coupling is gradually lost when approaching z ≃1100 , the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: (i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; (ii) the magnetic field is generated up to z ≃10 ; (iii) it is in practice impossible to compute the magnetic field with a Boltzmann code for scales smaller than 1 Mpc. Finally we confirm that for scales of a few Mpc, this magnetic field is of order 2 ×10-29 G , many orders of magnitude smaller than what is currently observed on intergalactic scales.
On the conservation of second-order cosmological perturbations in a scalar field dominated universe
Vernizzi, F
2005-01-01
We discuss second-order cosmological perturbations on super-Hubble scales, in a scalar field dominated universe, such as during single field inflation. In this contest we show that the gauge-invariant curvature perturbations defined on the uniform density and comoving hypersurfaces coincide and that perturbations are adiabatic in the large scale limit. Since it has been recently shown that the uniform curvature perturbation is conserved on large scales if perturbations are adiabatic, we conclude that both the uniform and comoving curvature perturbations at second-order in a scalar field dominated universe are conserved.
The perturbative structure of spin glass field theory
Temesvári, T.
2014-03-01
Cubic replicated field theory is used to study the glassy phase of the short-range Ising spin glass just below the transition temperature, and for systems above, at, and slightly below the upper critical dimension six. The order parameter function is computed up to two-loop order. There are two, well-separated bands in the mass spectrum, just as in mean field theory. The small mass band acts as an infrared cutoff, whereas contributions from the large mass region can be computed perturbatively (d>6), or interpreted by the ɛ-expansion around the critical fixed point (d=6-ɛ). The one-loop calculation of the (momentum-dependent) longitudinal mass, and the whole replicon sector is also presented. The innocuous behavior of the replicon masses while crossing the upper critical dimension shows that the ultrametric replica symmetry broken phase remains stable below six dimensions.
The perturbative structure of spin glass field theory
Energy Technology Data Exchange (ETDEWEB)
Temesvári, T., E-mail: temtam@helios.elte.hu
2014-03-15
Cubic replicated field theory is used to study the glassy phase of the short-range Ising spin glass just below the transition temperature, and for systems above, at, and slightly below the upper critical dimension six. The order parameter function is computed up to two-loop order. There are two, well-separated bands in the mass spectrum, just as in mean field theory. The small mass band acts as an infrared cutoff, whereas contributions from the large mass region can be computed perturbatively (d>6), or interpreted by the ϵ-expansion around the critical fixed point (d=6−ϵ). The one-loop calculation of the (momentum-dependent) longitudinal mass, and the whole replicon sector is also presented. The innocuous behavior of the replicon masses while crossing the upper critical dimension shows that the ultrametric replica symmetry broken phase remains stable below six dimensions.
Abou-Hamad, Edy
2011-09-01
Nuclear magnetic resonance (NMR) experiments in pulsed magnetic fields up to 30.4 T focused on 1H and 93Nb nuclei are reported. Here we discuss the advantage and limitation of pulsed field NMR and why this technique is able to become a promising research tool. © 2011 Elsevier Inc. All Rights Reserved.
Lepton asymmetries and the growth of cosmological seed magnetic fields
2007-01-01
Primordial cosmological hypermagnetic fields polarize the early Universe plasma prior to the electroweak phase transition (EWPT). As a result of the long range parity violating gauge interaction present in the Standard Model their magnitude gets amplified, opening a new, perturbative way, of accounting for the observed intergalactic magnetic fields.
The MAVEN Magnetic Field Investigation
Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.
2014-01-01
The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.
Impact of Resonant Magnetic Perturbations on the L-H Transition on MAST
Scannell, R; Carr, M; Hawke, J; Henderson, S S; O'Gorman, T; Patel, A; Shaw, A; Thornton, A
2014-01-01
The impact of resonant magnetic perturbations (RMPs) on the power required to access H-mode is examined experimentally on MAST. Applying RMP in n=2,3,4 and 6 configurations causes significant delays to the timing of the L-H transition at low applied fields and prevents the transition at high fields. The experiment was primarily performed at RMP fields sufficient to cause moderate increases in ELM frequency, f mitigated/f natural~3. To obtain H-mode with RMPs at this field, an increase of injected beam power is required of at least 50% for n=3 and n=4 RMP and 100% for n=6 RMP. In terms of power threshold, this corresponds to increases of at least 20% for n=3 and n=4 RMPs and 60% for n=6 RMPs. This 'RMP affected' power threshold is found to increase with RMP magnitude above a certain minimum perturbed field, below which there is no impact on the power threshold. Extrapolations from these results indicate large increases in the L-H power threshold will be required for discharges requiring large mitigated ELM fre...
Quantum well electronic states in a tilted magnetic field
Trallero-Giner, C.; Padilha, J. X.; Lopez-Richard, V.; Marques, G. E.; Castelano, L. K.
2017-08-01
We report the energy spectrum and the eigenstates of conduction and uncoupled valence bands of a quantum well under the influence of a tilted magnetic field. In the framework of the envelope approximation, we implement two analytical approaches to obtain the nontrivial solutions of the tilted magnetic field: (a) the Bubnov-Galerkin spectral method and b) the perturbation theory. We discuss the validity of each method for a broad range of magnetic field intensity and orientation as well as quantum well thickness. By estimating the accuracy of the perturbation method, we provide explicit analytical solutions for quantum wells in a tilted magnetic field configuration that can be employed to study several quantitative phenomena.
Schmitz, O.; Becoulet, M.; Cahyna, P.; Evans, T. E.; Feng, Y.; Frerichs, H.; Loarte, A.; Pitts, R. A.; Reiser, D.; Fenstermacher, M. E.; Harting, D.; Kirschner, A.; Kukushkin, A.; Lunt, T.; Saibene, G.; Reiter, D.; Samm, U.; Wiesen, S.
2016-06-01
Results from three-dimensional modeling of plasma edge transport and plasma-wall interactions during application of resonant magnetic perturbation (RMP) fields for control of edge-localized modes in the ITER standard 15 MA Q = 10 H-mode are presented. The full 3D plasma fluid and kinetic neutral transport code EMC3-EIRENE is used for the modeling. Four characteristic perturbed magnetic topologies are considered and discussed with reference to the axisymmetric case without RMP fields. Two perturbation field amplitudes at full and half of the ITER ELM control coil current capability using the vacuum approximation are compared to a case including a strongly screening plasma response. In addition, a vacuum field case at high q 95 = 4.2 featuring increased magnetic shear has been modeled. Formation of a three-dimensional plasma boundary is seen for all four perturbed magnetic topologies. The resonant field amplitudes and the effective radial magnetic field at the separatrix define the shape and extension of the 3D plasma boundary. Opening of the magnetic field lines from inside the separatrix establishes scrape-off layer-like channels of direct parallel particle and heat flux towards the divertor yielding a reduction of the main plasma thermal and particle confinement. This impact on confinement is most accentuated at full RMP current and is strongly reduced when screened RMP fields are considered, as well as for the reduced coil current cases. The divertor fluxes are redirected into a three-dimensional pattern of helical magnetic footprints on the divertor target tiles. At maximum perturbation strength, these fingers stretch out as far as 60 cm across the divertor targets, yielding heat flux spreading and the reduction of peak heat fluxes by 30%. However, at the same time substantial and highly localized heat fluxes reach divertor areas well outside of the axisymmetric heat flux decay profile. Reduced RMP amplitudes due to screening or reduced RMP
On perturbative field theory and twistor string theory
Bedford, James
2007-01-01
It is well-known that perturbative calculations in field theory can lead to far simpler answers than the Feynman diagram approach might suggest. In some cases scattering amplitudes can be constructed for processes with any desired number of external legs yielding compact expressions which are inaccessible from the point of view of conventional perturbation theory. In this thesis we discuss some attempts to address the nature of this underlying simplicity and then use the results to calculate some previously unknown amplitudes of interest. Witten's twistor string theory is introduced and the CSW rules at tree-level and one-loop are described. We use these techniques to calculate the one-loop gluonic MHV amplitudes in N=1 super-Yang-Mills as a verification of their validity and then proceed to evaluate the general MHV amplitudes in pure Yang-Mills with a scalar running in the loop. This latter amplitude is a new result in QCD. In addition to this, we review some recent on-shell recursion relations for tree-leve...
Magnetic fields in ring galaxies
Moss, D; Silchenko, O; Sokoloff, D; Horellou, C; Beck, R
2016-01-01
Many galaxies contain magnetic fields supported by galactic dynamo action. However, nothing definitive is known about magnetic fields in ring galaxies. Here we investigate large-scale magnetic fields in a previously unexplored context, namely ring galaxies, and concentrate our efforts on the structures that appear most promising for galactic dynamo action, i.e. outer star-forming rings in visually unbarred galaxies. We use tested methods for modelling $\\alpha-\\Omega$ galactic dynamos, taking into account the available observational information concerning ionized interstellar matter in ring galaxies. Our main result is that dynamo drivers in ring galaxies are strong enough to excite large-scale magnetic fields in the ring galaxies studied. The variety of dynamo driven magnetic configurations in ring galaxies obtained in our modelling is much richer than that found in classical spiral galaxies. In particular, various long-lived transients are possible. An especially interesting case is that of NGC 4513 where th...
Rotating superconductor magnet for producing rotating lobed magnetic field lines
Hilal, Sadek K.; Sampson, William B.; Leonard, Edward F.
1978-01-01
This invention provides a rotating superconductor magnet for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet.
Magnetic field contribution to the last electron-photon scattering
Giovannini, Massimo
2010-01-01
When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.
Magnetic field contribution to the last electron-photon scattering
Energy Technology Data Exchange (ETDEWEB)
Giovannini, Massimo, E-mail: massimo.giovannini@cern.c [Department of Physics, Theory Division, CERN, 1211 Geneva 23 (Switzerland); INFN, Section of Milan-Bicocca, 20126 Milan (Italy)
2010-11-21
When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.
Magnetic field contribution to the last electron-photon scattering
Giovannini, Massimo
2010-11-01
When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.
Scalar field perturbation on six-dimensional ultra-spinning black holes
Morisawa, Y; Morisawa, Yoshiyuki; Ida, Daisuke
2004-01-01
We studied the stability of scalar field perturbation on six-dimensional ultra-spinning black holes. We numerically calculated the quasinormal modes. Our results suggest that such perturbations are stable.
Low Cost Magnetic Field Controller
Malafronte, Alexandre A
2005-01-01
The Physics Institute of the University of São Paulo (IFUSP) is building a continuous wave (cw) racetrack microtron. This machine has several dipole magnets, like the first and second stage recirculators, and a number of smaller ones in the transport line. These magnets must produce very stable magnetic fields to allow the beam to recirculate along very precise orbits and paths. Furthermore, the fields must be reproducible with great accuracy to allow an easier setup of the machine, though the effects of hysteresis tend to jeopardize the reproducibility. If the magnetic field is chosen by setting the current in the coils, temperature effects over the magnet and power supply tend to change the field. This work describes an inexpensive magnetic field controller that allows a direct measure of the magnetic field through an Hall probe. It includes a microcontroller running a feedback algorithm to control the power supply, in order to keep the field stable and reproducible. The controller can also execu...
Transverse Field Perturbation For PIP-II SRF Cavities
Energy Technology Data Exchange (ETDEWEB)
Berrutti, Paolo [Fermilab; Khabiboulline, Timergali N. [Fermilab; Lebedev, Valeri [Fermilab; Yakovlev, Vyacheslav P. [Fermilab
2015-06-01
Proton Improvement Plan II (PIP-II) consists in a plan for upgrading the Fermilab proton accelerator complex to a beam power capability of at least 1 MW delivered to the neutrino production target. A room temperature section accelerates H⁻ ions to 2.1 MeV and creates the desired bunch structure for injection into the superconducting (SC) linac. Five cavity types, operating at three different frequencies 162.5, 325 and 650 MHz, provide acceleration to 800 MeV. This paper presents the studies on transverse field perturbation on particle dynamic for all the superconducting cavities in the linac. The effects studied include quadrupole defocusing for coaxial resonators, and dipole kick due to couplers for elliptical cavities. A multipole expansion has been performed for each of the cavity designs including effects up to octupole.
Exploring perturbative conformal field theory in Mellin space
Nizami, Amin A.; Rudra, Arnab; Sarkar, Sourav; Verma, Mritunjay
2017-01-01
We explore the Mellin representation of correlation functions in conformal field theories in the weak coupling regime. We provide a complete proof for a set of Feynman rules to write the Mellin amplitude for a general tree level Feynman diagram involving only scalar operators. We find a factorised form involving beta functions associated to the propagators, similar to tree level Feynman rules in momentum space for ordinary QFTs. We also briefly consider the case where a generic scalar perturbation of the free CFT breaks conformal invariance. Mellin space still has some utility and one can consider non-conformal Mellin representations. In this context, we find that the beta function corresponding to conformal propagator uplifts to a hypergeometric function.
Exploring Perturbative Conformal Field Theory in Mellin space
Nizami, Amin A; Sarkar, Sourav; Verma, Mritunjay
2016-01-01
We explore the Mellin representation of correlation functions in conformal field theories in the weak coupling regime. We provide a complete proof for a set of Feynman rules to write the Mellin amplitude for a general tree level Feynman diagram involving only scalar operators. We find a factorised form involving beta functions associated to the propagators, similar to tree level Feynman rules in momentum space for ordinary QFTs. We also briefly consider the case where a generic scalar perturbation of the free CFT breaks conformal invariance. Mellin space still has some utility and one can consider non-conformal Mellin representations. In this context, we find that the beta function corresponding to conformal propagator uplifts to a hypergeometric function.
Active control of edge localized modes with a low n perturbation fields in the JET tokamak
Energy Technology Data Exchange (ETDEWEB)
Liang, Y., E-mail: y.liang@fz-juelich.d [Association EURATOM-FZJ, Forschungszentrum Juelich GmbH, Institute of Energy Research IEF-4: Plasma Physics, Partner in the Trilateral Euregio Cluster, 52425 Juelich (Germany); Jachmich, S. [Association EURATOM-Belgian State, Koninklijke Militaire School - Ecole Royale Militaire, B-1000 Brussels (Belgium); Koslowski, H.R. [Association EURATOM-FZJ, Forschungszentrum Juelich GmbH, Institute of Energy Research IEF-4: Plasma Physics, Partner in the Trilateral Euregio Cluster, 52425 Juelich (Germany); Nardon, E. [EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB Abingdon, OXON (United Kingdom); Alfier, A. [Associazione EURATOM-ENEA sulla Fusione, Consorzio RFX Padova (Italy); Baranov, Y. [EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB Abingdon, OXON (United Kingdom); De La Luna, E. [Asociacion EURATOM-CIEMAT, Avenida Complutense 22, E-28040 Madrid (Spain); Vries, P. de [EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB Abingdon, OXON (United Kingdom); Eich, T. [Association EURATOM-Max-Planck-Institut fuer Plasmaphysik, D-85748 Garching (Germany); Esser, H.G.; Harting, D. [Association EURATOM-FZJ, Forschungszentrum Juelich GmbH, Inst. of Energy Research IEF-4: Plasma Physics, Partner in the Trilateral Euregio Cluster, 52425 Juelich (Germany); Kiptily, V. [EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB Abingdon, OXON (United Kingdom); Kreter, A. [Association EURATOM-FZJ, Forschungszentrum Juelich GmbH, Inst. of Energy Research IEF-4: Plasma Physics, Partner in the Trilateral Euregio Cluster, 52425 Juelich (Germany); Gerasimov, S.; Gryaznevich, M.P.; Howell, D. [EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB Abingdon, OXON (United Kingdom); Sergienko, G. [Association EURATOM-FZJ, Forschungszentrum Juelich GmbH, Inst. of Energy Research IEF-4: Plasma Physics, Partner in the Trilateral Euregio Cluster, 52425 Juelich (Germany)
2009-06-15
Active control of edge localized modes (ELMs) by using static external magnetic perturbation fields with low toroidal mode number, n, has been demonstrated for both, ITER baseline (q{sub 95}approx3) and high beta advanced tokamak scenarios at the JET tokamak. During the application of the low n field the ELM frequency increased by a factor up to approx4-5. Reduction in carbon erosion and ELM peak heat fluxes on the divertor target by roughly the same factor as the increase of the ELM frequency has been observed. The frequency of the mitigated ELMs using a low n field is found to increase proportional to the total input heating power. Compensation of the density pump-out effect observed when the external low n field is applied has been achieved by gas fueling in low triangularity plasmas.
Generation of magnetic fields in Einstein-aether gravity
Saga, Shohei; Shiraishi, Maresuke; Ichiki, Kiyotomo; Sugiyama, Naoshi
2013-05-01
Recently the lower bounds of the intergalactic magnetic fields 10-16˜10-20G are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector-mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in general relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-aether gravity model, in which the aether field can act as a new source of vector metric perturbations. The vector metric perturbations induce the velocity difference between baryons and photons which then generate magnetic fields. This velocity difference arises from effects at the second order in the tight-coupling approximation. We estimate the angular power spectra of temperature and B-mode polarization of the cosmic microwave background anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the power spectrum of associated magnetic fields around the recombination epoch within this limit. It is found that the spectrum has a characteristic peak at k=0.1hMpc-1, and at that scale the amplitude can be as large as B˜10-22G where the upper bound comes from cosmic microwave background temperature anisotropies. The magnetic fields with this amplitude can be seeds of large scale magnetic fields observed today if the sufficient dynamo mechanism takes place. Analytic interpretation for the power spectra is also given.
Resonant magnetic fields from inflation
Byrnes, Christian T; Jain, Rajeev Kumar; Urban, Federico R
2012-01-01
We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of ${\\cal O}(10^{-15}\\, \\Gauss)$ today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.
Static magnetic fields enhance turbulence
Pothérat, Alban
2015-01-01
More often than not, turbulence occurs under the influence of external fields, mostly rotation and magnetic fields generated either by planets, stellar objects or by an industrial environment. Their effect on the anisotropy and the dissipative behaviour of turbulence is recognised but complex, and it is still difficult to even tell whether they enhance or dampen turbulence. For example, externally imposed magnetic fields suppress free turbulence in electrically conducting fluids (Moffatt 1967), and make it two-dimensional (2D) (Sommeria & Moreau 1982); but their effect on the intensity of forced turbulence, as in pipes, convective flows or otherwise, is not clear. We shall prove that since two-dimensionalisation preferentially affects larger scales, these undergo much less dissipation and sustain intense turbulent fluctuations. When higher magnetic fields are imposed, quasi-2D structures retain more kinetic energy, so that rather than suppressing forced turbulence, external magnetic fields indirectly enha...
Origin of cosmic magnetic fields
Rees, M. J.
2006-06-01
The first significant cosmic fields, and the seed field for galactic dynamos probably developed after the formation of the first non-linear structures. The history of star formation and the intergalactic medium is controlled, at least in part, by how and when galaxies and their precursors acquired their fields. The amplification of fields behind shocks, and the diffusivity of the magnetic flux, are crucial to the interpretation of radio sources, gamma ray burst afterglows, and other energetic cosmic phenomena. The build-up of magnetic fields is an important aspect of the overall cosmogonic process.
Lyons, B. C.; Ferraro, N. M.; Paz-Soldan, C.; Nazikian, R.; Wingen, A.
2017-04-01
In order to understand the effect of rotation on the response of a plasma to three-dimensional magnetic perturbations, we perform a systematic scan of the zero-crossing of the rotation profile in a DIII-D ITER-similar shape equilibrium using linear, time-independent modeling with the M3D-C1 extended magnetohydrodynamics code. We confirm that the local resonant magnetic field generally increases as the rotation decreases at a rational surface. Multiple peaks in the resonant field are observed near rational surfaces, however, and the maximum resonant field does not always correspond to zero rotation at the surface. Furthermore, we show that non-resonant current can be driven at zero-crossings not aligned with rational surfaces if there is sufficient shear in the rotation profile there, leading to amplification of near-resonant Fourier harmonics of the perturbed magnetic field and a decrease in the far-off-resonant harmonics. The quasilinear electromagnetic torque induced by this non-resonant plasma response provides drive to flatten the rotation, possibly allowing for increased transport in the pedestal by the destabilization of turbulent modes. In addition, this torque acts to drive the rotation zero-crossing to dynamically stable points near rational surfaces, which would allow for increased resonant penetration. By one or both of these mechanisms, this torque may play an important role in bifurcations into suppression of edge-localized modes. Finally, we discuss how these changes to the plasma response could be detected by tokamak diagnostics. In particular, we show that the changes to the resonant field discussed here have a significant impact on the external perturbed magnetic field, which should be observable by magnetic sensors on the high-field side of tokamaks but not on the low-field side. In addition, TRIP3D-MAFOT simulations show that none of the changes to the plasma response described here substantially affects the divertor footprint structure.
Atomic and magnetic configurational energetics by the generalized perturbation method
DEFF Research Database (Denmark)
Ruban, Andrei V.; Shallcross, Sam; Simak, S.I.
2004-01-01
It is shown that, using the generalized perturbation method (GPM) with screened Coulomb interactions that ensures its consistency with the force theorem, one is able to obtain effective interactions that yield an accurate and physically transparent description of configurational energetics...
Weisberg, D. B.; Paz-Soldan, C.; Lanctot, M. J.; Strait, E. J.; Evans, T. E.
2016-10-01
The plasma response to proposed 3D coil geometries in the DIII-D tokamak is investigated using the linear MHD plasma response code MARS-F. An extensive examination of low- and high-field side coil arrangements shows the potential to optimize the coupling between imposed non-axisymmetric magnetic perturbations and the total plasma response by varying the toroidal and poloidal spectral content of the applied field. Previous work has shown that n=2 and n=3 perturbations can suppress edge-localized modes (ELMs) in cases where the applied field's coupling to resonant surfaces is enhanced by amplifying marginally-stable kink modes. This research is extended to higher n-number configurations of 2 to 3 rows with up to 12 coils each in order to advance the physical understanding and optimization of both the resonant and non-resonant responses. Both in- and ex-vessel configurations are considered. The plasma braking torque is also analyzed, and coil geometries with favorable plasma coupling characteristics are discussed. Work supported by GA internal funds.
Energy Technology Data Exchange (ETDEWEB)
Stoschus, Henning
2011-10-13
Small three-dimensional (3D) magnetic perturbations can be used as a tool to control the edge plasma parameters in magnetically confined plasmas in high confinement mode (''H-mode'') to suppress edge instabilities inherent to this regime, the Edge Localized Modes (ELMs). In this work, the impact of rotating 3D resonant magnetic perturbation (RMP) fields on the edge plasma structure characterized by electron density and temperature fields is investigated. We study a low confinement (L-mode) edge plasma (r/a>0.9) with high resistivity (edge electron collisionality {nu}{sup *}{sub e}>4) at the TEXTOR tokamak. The plasma structure in the plasma edge is measured by a set of high resolution diagnostics: a fast CCD camera ({delta}t=20 {mu}s) is set up in order to visualize the plasma structure in terms of electron density variations. A supersonic helium beam diagnostic is established as standard diagnostic at TEXTOR to measure electron density n{sub e} and temperature T{sub e} with high spatial ({delta}r=2 mm) and temporal resolution ({delta}t=20 {mu}s). The measured plasma structure is compared to modeling results from the fluid plasma and kinetic neutral transport code EMC3-EIRENE. A sequence of five new observations is discussed: (1) Imaging of electron density variations in the plasma edge shows that a fast rotating RMP field imposes an edge plasma structure, which rotates with the external RMP rotation frequency of vertical stroke {nu}{sub RMP} vertical stroke =1 kHz. (2) Measurements of the electron density and temperature provide strong experimental evidence that in the far edge a rotating 3D scrape-off layer (SOL) exists with helical exhaust channels to the plasma wall components. (3) Radially inward, the plasma structure at the next rational flux surface is found to depend on the relative rotation between external RMP field and intrinsic plasma rotation. For low relative rotation the plasma structure is dominated by a particle and energy loss
Measuring Earth's Magnetic Field Simply.
Stewart, Gay B.
2000-01-01
Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)
1975-01-01
The experimental apparatus used at intersection 4 around the Split-Field Magnet by the CERN-Bologna Collaboration (experiment R406). The plastic scintillator telescopes are used for precise pulse-height and time-of-flight measurements.
What Are Electric and Magnetic Fields? (EMF)
... take for granted. What are electric and magnetic fields? Electric and magnetic fields (EMF) are invisible lines of ... humans. AC electric power produces electric and magnetic fields that create weak electric currents in humans. Being exposed to some kinds ...
The Juno Magnetic Field Investigation
Connerney, J. E. P.; Benn, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.; Murphy, S.; Odom, J.; Oliversen, R.; Schnurr, R.; Sheppard, D.; Smith, E. J.
2017-02-01
The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ˜20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 × 106 nT per axis) with a resolution of ˜0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of
The Juno Magnetic Field Investigation
Connerney, J. E. P.; Benna, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.;
2017-01-01
The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to approx. 20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 x 10(exp. 6) nT per axis) with a resolution of approx. 0.05 nT in the most sensitive dynamic range (+/-1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through
Topics in perturbative quantum field theory: eighth order QED contribution to the anomalous magnetic moment of the muon and next to leading order QCD correction to. gamma gamma -->. M/sup +/M/sup -/(M =. pi. , K)
Energy Technology Data Exchange (ETDEWEB)
Nizic, B.
1985-01-01
In Part I the evaluation of the complete eighth order QED contribution to the difference of the anomalous magnetic moments of the muon and the electron, (a/sub ..mu../ - a/sub e/, arising from 469 Feynman diagrams is presented. The result is 140.7(4.5)(..cap alpha../..pi..). The theoretical error represents the estimated accuracy of the required numerical integration. The light-by-light QED contribution to (a/sub ..mu../ - a/sub e/) has also been improved. With these results the difference a/sub ..mu../ - a/sub e/ through eighth order in QED is (a/sub ..mu../ - a/sub e/)/sup QED/ = 619,551(21) x 10/sup -11/. Adding to the present theoretical value of the electron anomaly a/sub e//sup QED/ = 115,965,246(5) x 10/sup -11/, it was found that the pure QED contribution to the muon anomaly is given by a/sub ..mu..//sup QED/ = 116,584,797(22) x 10/sup -11/. In Part II the results of the calculation of the next to leading order perturbative QCD correction to the two-photon exclusive channels ..gamma gamma -->..M/sup +/M/sup -/(M = ..pi..,K) at large momentum transfer is presented. Calculation is performed in the Feynman gauge. Dimensional regularization is used to treat both UV and the set of reals divergences. One loop correction to the ..gamma gamma -->..M/sup +/M/sup -/ cross section is obtained. In the mean MS renormalization scheme this correction is found not to be large.
Magnetic-Field Hazards Bibliography.
1985-09-01
produced during pulsed- magnetic-field therapy for non-union of the tibia." Med. Biol. Eng. Comput., Vol. 20, pp. 501-511 (1982). 32. Miller, D. A...Phenum Publishing Co. (1983). 40. Topper, R. F., "Electromagnetic shielding feasibility study," ASD -TDR-63-194 (Armour Research Foundation, Chicago...mammalian cells by strong magnetic fields (1976). 93. Malins, D. C., and Collier, T. K., "Xenobiotic interactions in aquatic organisms-effects on
Non-radial oscillations of the magnetized rotating stars with purely toroidal magnetic fields
Asai, Hidetaka; Yoshida, Shijun
2015-01-01
We calculate non-axisymmetric oscillations of uniformly rotating polytropes magnetized with a purely toroidal magnetic field, taking account of the effects of the deformation due to the magnetic field. As for rotation, we consider only the effects of Coriolis force on the oscillation modes, ignoring those of the centrifugal force, that is, of the rotational deformation of the star. Since separation of variables is not possible for the oscillation of rotating magnetized stars, we employ finite series expansions for the perturbations using spherical harmonic functions. We calculate magnetically modified normal modes such as $g$-, $f$-, $p$-, $r$-, and inertial modes. In the lowest order, the frequency shifts produced by the magnetic field scale with the square of the characteristic Alfv\\'en frequency. As a measure of the effects of the magnetic field, we calculate the proportionality constant for the frequency shifts for various oscillation modes. We find that the effects of the deformation are significant for ...
Cosmological perturbations in SFT inspired non-local scalar field models
Energy Technology Data Exchange (ETDEWEB)
Koshelev, Alexey S. [Vrije Universiteit Brussel and The International Solvay Institutes, Theoretische Natuurkunde, Brussels (Belgium); Vernov, Sergey Yu. [Instituto de Ciencias del Espacio (ICE/CSIC) and Institut d' Estudis Espacials de Catalunya (IEEC), Bellaterra, Barcelona (Spain); Lomonosov Moscow State University, Theoretical High Energy Physics Division, Skobeltsyn Institute of Nuclear Physics, Moscow (Russian Federation)
2012-10-15
We study cosmological perturbations in models with a single non-local scalar field originating from the string field theory description of the rolling tachyon dynamics. We construct the equation for the energy density perturbations of the non-local scalar field and explicitly prove that for the free field it is identical to a system of local cosmological perturbation equations in a particular model with multiple (maybe infinitely many) local free scalar fields. We also show that vector and tensor perturbations are absent in this set-up. (orig.)
Fluctuation conductivity of disordered superconductors in magnetic fields
Tarasinski, Brian; Schwiete, Georg
2013-07-01
We calculate fluctuation corrections to the longitudinal conductivity of disordered superconductors subject to an external magnetic field. We derive analytic expressions that are valid in the entire metallic part of the temperature-magnetic field phase diagram as long as the effect of the magnetic field on the spin degrees of freedom of the electrons may be neglected. Our calculations are based on a kinetic equation approach. For the special case of superconducting films and wires in parallel magnetic fields, we perform a detailed comparison with results that were previously obtained with diagrammatic perturbation theory in the imaginary-time formalism. As an application, we study the fluctuation conductivity of films in tilted magnetic fields with a special focus on the low-temperature regime. We present a detailed discussion of the phenomenon of the nonmonotonic magnetoresistance and find that it displays a pronounced dependence on the tilting angle.
Electric Current Filamentation at a Non-potential Magnetic Null-point Due to Pressure Perturbation
Jelínek, P.; Karlický, M.; Murawski, K.
2015-10-01
An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with a plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh-Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.
ELECTRIC CURRENT FILAMENTATION AT A NON-POTENTIAL MAGNETIC NULL-POINT DUE TO PRESSURE PERTURBATION
Energy Technology Data Exchange (ETDEWEB)
Jelínek, P. [University of South Bohemia, Faculty of Science, Institute of Physics and Biophysics, Branišovská 10, CZ-37005 České Budějovice (Czech Republic); Karlický, M. [Academy of Sciences of the Czech Republic, v. v. i., Astronomical Institute, Fričova 258, CZ-25165 Ondřejov (Czech Republic); Murawski, K., E-mail: pjelinek@prf.jcu.cz [Maria Curie-Skłodowska University, Institute of Physics, Group of Astrophysics, Radziszewskiego 10, PL-20031 Lublin (Poland)
2015-10-20
An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with a plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh–Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.
RCD Large Aspect-Ratio Tokamak Equilibrium with Magnetic Islands: a Perturbed Approach
Institute of Scientific and Technical Information of China (English)
F.L.Braga
2013-01-01
Solutions of Grad-Shafranov (GS) equation with Reversed Current Density (RCD) profiles present magnetic islands when the magnetic flux is explicitly dependent on the poloidal angle.In this work it is shown that a typical cylindrical (large aspect-ratio) RCD equilibrium configuration perturbed by the magnetic tield of a circular loop (simulating a divertor) is capable of generate magnetic islands,due to the poloidal symmetry break of the GS equilibrium solution.
Magnetic fields in spiral galaxies
Beck, Rainer
2015-12-01
Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 \\upmu G) and in central starburst regions (50-100 \\upmu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15 \\upmu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.—Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with
Nanometric alternating magnetic field generator.
Espejo, A P; Tejo, F; Vidal-Silva, N; Escrig, J
2017-07-05
In this work we introduce an alternating magnetic field generator in a cylindrical nanostructure. This field appears due to the rotation of a magnetic domain wall located at some position, generating a magnetic region that varies its direction of magnetization alternately, thus inducing an alternating magnetic flux in its vicinity. This phenomenon occurs due to the competition between a spin-polarized current and a magnetic field, which allows to control both the angular velocity and the pinning position of the domain wall. As proof of concept, we study the particular case of a diameter-modulated nanowire with a spin-polarized current along its axis and the demagnetizing field produced by its modulation. This inhomogeneous field allows one to control the angular velocity of the domain wall as a function of its position along the nanowire allowing frequencies in the GHz range to be achieved. This generator could be used in telecommunications for devices in the range of radiofrequencies or, following Faraday's induction law, could also induce an electromotive force and be used as a movable alternate voltage source in future nanodevices.
The Stability of Magnetized Rotating Plasmas with Superthermal Fields
DEFF Research Database (Denmark)
Pessah, Martin Elias; Psaltis, Dimitrios
2005-01-01
findings for the stability of cold, magnetically dominated, rotating fluids and argue that, for these systems, the curvature of toroidal field lines cannot be neglected even when short wavelength perturbations are considered. We also comment on the implications of our results for the validity of shearing...
Linear metric and temperature fluctuations of a charged plasma in a primordial magnetic field
Haba, Z
2015-01-01
We discuss tensor metric perturbations in a magnetic field around the homogeneous Juttner equilibrium of massless particles in an expanding universe. We solve the Liouville equation and derive the energy-momentum tensor up to linear terms in the metric and in the magnetic field.The term linear in the magnetic field is different from zero if the total charge of the primordial plasma is non-zero. We obtain an analytic formula for temperature fluctuations treating the tensor metric perturbations and the magnetic field as independent random variables. Assuming a cutoff on large momenta of the magnetic spectral function we show that the presence of the magnetic field can discriminate only low multipoles in the multipole expansion of temperature fluctuations. In such a case the term linear in the magnetic field can be more important than the quadratic one (corresponding to the fluctuations of the pure magnetic field).
Analysis of geomagnetic data and cosmic ray variations in periods of magnetic perturbations
Mandrikova, Oksana; Zalyaev, Timur; Solovev, Igor; Shevtsov, Boris
magnetic storms. Using the combination of the wavelet transform and neural networks, we have developed a technique of approximating the time variation of cosmic-ray data. This technique allows us to perform detailed analysis of geomagnetic data and detect anomalies in periods of high solar activity. Approximations of large-scale time variation components of cosmic-ray data have been obtained in the following form: [ c_{j,n+1}(t)=\\varphi^3_m Biggl (sum_i omega^3_{mi}\\varphi^2_i biggl (sum_l omega^2_{il}\\varphi^1_lBigl(sum_n omega^1_{ln}c_{j,n}(t)Bigr )biggr ) Biggr ) ] where c_{j,n}= ;phi_{j,n}=2(j/2) phi(2(j(t)-n)) is the scaling function, omega(1_{ln}) are the weights of the neurons of the network input layer l,omega(2_{il}) are the weights of the neurons of the network hidden layer i, omega(3_{mi}) are the weights of the neurons of the network output layer m, varphi(1_l(z)=varphi^2_i(z)=(2)/(1+exp(-2z))-1) ,varphi(3_m(z)) =a*z+b. Coefficients c_{j,n} are the result of transforming of the original function y to the space with the scale j. Analysis of long geomagnetic data from the Paratunka observatory (Kamchatka region, Russia) provided quantitative estimates of the storminess degree of the geomagnetic field before and during magnetic storms. Furthermore, we have managed to identify local weak increases of the field perturbations prior to the main phase of storms. The intensity of field perturbations rises on average 2.5 days before the onset of a storm. Abnormal time periods connected with increased solar activity have been detected in the flow of cosmic rays. Comparison of the results with the geomagnetic data has shown that the anomalies in the cosmic ray variations occur in periods of strong geomagnetic perturbations. The tools and techniques suggested in the present work, together with other methods of data -analysis will help forecast space weather, estimate more accurately the condition of the Earth’s magnetic field, and identify periods when the intensity of
Energy Technology Data Exchange (ETDEWEB)
Zimbardo, G.; Veltri, P. [Arcavacata di Rende, Cosenza, Univ. della Calabria (Italy). Dipt. di Fisica
1997-11-01
The magnetic fluctuations due to, e.g., magnetohydrodynamic turbulence cause a magnetic-field line random walk that influences many cosmic plasma phenomena. The results of a three-dimensional numerical simulation of a turbulent magnetic field in plane geometry are presented here. Magnetic percolation, Levy flights, and non-Gaussian random walk of the magnetic-field lines are found for moderate perturbation levels. In such a case plasma transport can be anomalous, i.e., either super diffusive or sub diffusive. Increasing the perturbation level a Gaussian diffusion regime is attained. The implications on the structure of the electron fore shock and of planetary magneto pauses are discussed.
Magnetic Field Generation in Stars
Ferrario, Lilia; Zrake, Jonathan
2015-01-01
Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a ...
Cahyna, Pavel; Huijsmans, Guido T A; Orain, Francois; Morales, Jorge; Kirk, Andrew; Thornton, Andrew J; Pamela, Stanislas; Panek, Radomir; Hoelzl, Matthias
2016-01-01
Resonant magnetic perturbations (RMPs) can mitigate the edge-localized modes (ELMs), i.e. cause a change of the ELM character towards smaller energy loss and higher frequency. During mitigation a change of the spatial structure of ELM loads on divertor was observed on DIII-D and MAST: the power is deposited predominantly in the footprint structures formed by the magnetic perturbation. In the present contribution we develop a theory explaining this effect, based on the idea that part of the ELM loss is caused by parallel transport in the homoclinic tangle formed by the magnetic perturbation of the ELM. The modified tangle resulting from the combination of the ELM perturbation and the applied RMP has the expected property of bringing open field lines in the same areas as the tangle from the RMP alone. We show that this explanation is consistent with features of the mitigated ELMs on MAST. We in addition validated our theory by an analysis of simulations of mitigated ELMs using the code JOREK. We produced detail...
Probing correlations of early magnetic fields using mu-distortion
DEFF Research Database (Denmark)
Ganc, Jonathan; Sloth, Martin Snoager
2014-01-01
\\rangle$ of this distortion with the temperature anisotropy $T$ of the CMB to search for a correlation $\\langle B^2\\zeta\\rangle$ between the magnetic field $B$ and the curvature perturbation $\\zeta$; knowing the $\\langle B^2\\zeta\\rangle$ correlation would help us distinguish between different models of magnetogenesis. Since......_\\mu\\gtrsim 1$ nG, one would have to consider the specifics of the inflationary magnetogenesis model. We also discuss the potential post-magnetogenesis sources of a $\\langle B^2\\zeta\\rangle$ correlation and explain why there will be no contribution from the evolution of the magnetic field in response...... the perturbations which produce the $\\mu$-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of $\\langle B^2\\zeta\\rangle$, which is naturally parameterized by $b_{\\text{NL}}$ (a parameter defined analogously to $f...
Commissioning of the magnetic field in the ATLAS muon spectrometer
Arnaud, M; Bergsma, F; Bobbink, G; Bruni, A; Chevalier, L; Ennes, P; Fleischmann, P; Fontaine, M; Formica, A; Gautard, V; Groenstege, H; Guyot, C; Hart, R; Kozanecki, W; Iengo, P; Legendre, M; Nikitina, T; Perepelkin, E; Ponsot, P; Richardson, A; Vorozhtsov, A; Vorozthsov, S
2008-01-01
ATLAS is a general-purpose detector at the 14 TeV proton-proton Large Hadron Collider at CERN. The muon spectrometer will operate in the magnetic field provided by a large, eight-coil barrel toroid magnet bracketed by two smaller toroidal end-caps. The toroidal field is non-uniform, with an average value of about 0.5 T in the barrel region, and is monitored using three-dimensional Hall sensors which must be accurate to 1 mT. The barrel coils were installed in the cavern from 2004 to 2006, and recently powered up to their nominal current. The Hall-sensor measurements are compared with calculations to validate the magnetic models, and used to reconstruct the position and shape of the coil windings. Field perturbations by the magnetic materials surrounding the muon spectrometer are found in reasonable agreement with finite-element magnetic-field simulations.
Pellet fuelling of plasmas with ELM mitigation by resonant magnetic perturbations in MAST
Valovic, M; Garzotti, L; Gurl, C; Kirk, A; Naylor, G; Patel, A; Scannell, R; Thornton, A J
2013-01-01
Shallow fuelling pellets are injected from the high field side into plasmas in which ELMs have been mitigated using external magnetic perturbation coils. The data are compared with ideal assumptions in the ITER fuelling model, namely that mitigated ELMs are not affected by fuelling pellets. Firstly it is shown that during the pellet evaporation an ELM is triggered, during which the amount particle loss could be larger (factor ~1.5) than the particle loss during an ELM which was not induced by pellet. Secondly, a favourable example is shown in which post-pellet particle losses due to mitigated ELMs are similar to the non-pellet case, however unfavourable counter-examples also exist.
Regular black holes in de Sitter universe: scalar field perturbations and quasinormal modes
Fernando, Sharmanthie
2015-01-01
The purpose of this paper is to study quasinormal modes (QNM) of a regular black hole with a cosmological constant due to scalar perturbations. A detailed study of the QNM frequencies for the massless scalar field were done by varying the parameters of the theory such as the mass, magnetic charge, cosmological constant, and the spherical harmonic index. We have employed the sixth order WKB approximation to compute the QNM frequencies. We have also proved analytically that the $l=0$ mode for the massless field reach a constant value at late times. We have approximated the near-extreme regular-de Sitter black hole potential with the P$\\ddot{o}$schl-Teller potential to obtain exact frequencies. The null geodesics of the regular-de Sitter black hole is employed to describe the QNM frequencies at the eikonal limit ($ l >>1$).
Indoor localization using magnetic fields
Pathapati Subbu, Kalyan Sasidhar
Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing
Generation of magnetic fields in Einstein-Aether gravity
Saga, Shohei; Ichiki, Kiyotomo; Sugiyama, Naoshi
2013-01-01
Recently the lower bounds of the intergalactic magnetic fields $10^{-16} \\sim 10^{-20}$ Gauss are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in General Relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-Aether gravity model, in which the aether field can act as a new source of vector metric perturbations and thus of magnetic fields. We estimate the angular power spectra of temperature and B-mode polarization of the Cosmic Microwave Background (CMB) Anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the pow...
Magnetic Fields in Spiral Galaxies
Beck, Rainer
2015-01-01
Radio synchrotron emission is a powerful tool to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30\\mu G) and in central starburst regions (50-100\\mu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15\\mu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the interg...
Popov, Aleksey
2013-04-01
The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws
Magnetic fields of neutron stars
Reisenegger, Andreas
2013-01-01
Neutron stars contain the strongest magnetic fields known in the Universe. In this paper, I discuss briefly how these magnetic fields are inferred from observations, as well as the evidence for their time-evolution. I show how these extremely strong fields are actually weak in terms of their effects on the stellar structure, as is also the case for magnetic stars on the upper main sequence and magnetic white dwarfs, which have similar total magnetic fluxes. I propose a scenario in which a stable hydromagnetic equilibrium (containing a poloidal and a toroidal field component) is established soon after the birth of the neutron star, aided by the strong compositional stratification of neutron star matter, and this state is slowly eroded by non-ideal magnetohydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long time scales, the fluid in the neutron star core will behave as if it were barotropic, becau...
Magnetic fields during galaxy mergers
Rodenbeck, Kai
2016-01-01
Galaxy mergers are expected to play a central role for the evolution of galaxies, and may have a strong impact on their magnetic fields. We present the first grid-based 3D magneto-hydrodynamical simulations investigating the evolution of magnetic fields during merger events. For this purpose, we employ a simplified model considering the merger event of magnetized gaseous disks in the absence of stellar feedback and without a stellar or dark matter component. We show that our model naturally leads to the production of two peaks in the evolution of the average magnetic field strength within 5 kpc, within 25 kpc and on scales in between 5 and 25 kpc. The latter is consistent with the peak in the magnetic field strength reported by Drzazga et al. (2011) in a merger sequence of observed galaxies. We show that the peak on the galactic scale and in the outer regions is likely due to geometrical effects, as the core of one galaxy enters the outskirts of the other one. In addition, there is a physical enhancement of t...
Zero magnetic field type magnetic field sensor. Reijikaigata jikai sensor
Energy Technology Data Exchange (ETDEWEB)
Sonoda, T.; Ueda, R. (Kyushu Institute of Technology, Fukuoka (Japan))
1990-11-20
It is shown in this paper that a new type of sensor with excellent characteristics can be made by demagnetizing the sensor core toward a zero field state and then detecting an unknown field to be detected by the demagnetizing current. The core operates equivalently in a zero magnetic field so that the detection sensitivity is determined by the coil constant including the number of turns of the solenoid for demagnetization required to offset the field to be detected. Therefore the detection sensitivity does not depend on its configuration and magnetization characteristics and does not depend on the temperature. It is thereby considered that these characteristics can largely reduce such problems at present as the aging deterioration of magnetic materials or the quality control accompanied by manufacturing. In addition, the following points have been clarified: (1) The upper limit of the detectable range does not exist in principle. (2) The accuracy of the detection is 0.02% to the full scale 20kA/m. (3) The magnetization property required to the core used as a sensor is that it has a rectangular B-H loop which is as sharp as possible. 14 refs., 13 figs., 2 tabs.
Heisenberg necklace model in a magnetic field
Tsvelik, A. M.; Zaliznyak, I. A.
2016-08-01
We study the low-energy sector of the Heisenberg necklace model. Using the field-theory methods, we estimate how the coupling of the electronic spins with the paramagnetic Kondo spins affects the overall spin dynamics and evaluate its dependence on a magnetic field. We are motivated by the experimental realizations of the spin-1/2 Heisenberg chains in SrCuO2 and Sr2CuO3 cuprates, which remain one-dimensional Luttinger liquids down to temperatures much lower than the in-chain exchange coupling J . We consider the perturbation of the energy spectrum caused by the interaction γ with nuclear spins (I =3 /2 ) present on the same sites. We find that the resulting necklace model has a characteristic energy scale, Λ ˜J1 /3(γI ) 2 /3 , at which the coupling between (nuclear) spins of the necklace and the spins of the Heisenberg chain becomes strong. This energy scale is insensitive to a magnetic field B . For μBB >Λ we find two gapless bosonic modes that have different velocities, whose ratio at strong fields approaches a universal number, √{2 }+1 .
Li, Hao-Song; Chen, Xiao-Lin; Deng, Wei-Zhen; Zhu, Shi-Lin
2016-01-01
We have systematically investigated the magnetic moments and magnetic form factors of the decuplet baryons to the next-to-next-leading order in the framework of the heavy baryon chiral perturbation theory. Our calculation includes the contributions from both the intermediate decuplet and octet baryon states in the loops. We also calculate the charge and magnetic dipole form factors of the decuplet baryons. Our results may be useful to the chiral extrapolation of the lattice simulations of the decuplet electromagnetic properties.
Effect of resonant magnetic perturbations on ELMs in connected double null plasmas in MAST
Kirk, A.; Liu, Yueqiang; Chapman, I. T.; Harrison, J.; Nardon, E.; Scannell, R.; Thornton, A. J.; the MAST Team
2013-04-01
The application of resonant magnetic perturbations (RMPs) with a toroidal mode number of n = 3 to connected double null plasmas in the MAST tokamak produces up to a factor of 9 increase in edge-localized mode (ELM) frequency and reduction in plasma energy loss associated with type-I ELMs. A threshold current for ELM mitigation is observed above which the ELM frequency increases approximately linearly with current in the coils. The effect of the RMPs is found to be scenario dependent. In one scenario the mitigation is only due to a large density pump out event and if the density is recovered by gas puffing a return to type-I ELMs is observed. In another scenario sustained ELM mitigation can be achieved irrespective of the amount of fuelling. Despite a large scan of parameters complete ELM suppression has not been achieved. The results are compared with modelling performed using either the vacuum approximation or including the plasma response. The requirement for a resonant condition, that is an optimum alignment of the perturbation with the plasma, is confirmed by performing a scan in the pitch angle of the applied field.
Sawtooth mitigation in 3D MHD tokamak modelling with applied magnetic perturbations
Bonfiglio, D.; Veranda, M.; Cappello, S.; Chacón, L.; Escande, D. F.
2017-01-01
The effect of magnetic perturbations (MPs) on the sawtoothing dynamics of the internal kink mode in the tokamak is discussed in the framework of nonlinear 3D MHD modelling. Numerical simulations are performed with the pixie3d code (Chacón 2008 Phys. Plasmas 15 056103) based on a D-shaped configuration in toroidal geometry. MPs are applied as produced by two sets of coils distributed along the toroidal direction, one set located above and the other set below the outboard midplane, like in experimental devices such as DIII-D and ASDEX Upgrade. The capability of n = 1 MPs to affect quasi-periodic sawteeth is shown to depend on the toroidal phase difference Δ φ between the perturbations produced by the two sets of coils. In particular, sawtooth mitigation is obtained for the Δ φ =π phasing, whereas no significant effect is observed for Δ φ =0 . Numerical findings are explained by the interplay between different poloidal harmonics in the spectrum of applied MPs, and appear to be consistent with experiments performed in the DIII-D device. Sawtooth mitigation and stimulation of self-organized helical states by applied MPs have been previously demonstrated in both circular tokamak and reversed-field pinch (RFP) experiments in the RFX-mod device, and in related 3D MHD modelling.
Corrections to halo model in presence of primordial magnetic field
Varalakshmi, Cheera; Nigam, Rahul
2017-01-01
We study the role played by the primordial magnetic field in the process of structure formation in the early universe. We have compared the halo mass abundance in the presence and absence of the magnetic field. We derive a modified Press-Schechter formula in presence of another source for matter perturbation and use it to study how this extra source affects halo count. This other source is the magnetic field with a given power spectrum. We find the ranges for the magnetic field strength over which the field enhances the halo formation for a mass range for spectral index nb = -2.95. We found that for field strength less than or equal to B = 7.0 nG, which we call the cut-off field strength, the presence of magnetic field enhances halo formation at low mass scale while it disrupts for a stronger field. We further investigate the dependence of halo count on the spectral index of the magnetic field power spectrum. We observe that at the cut-off field strength, halo formation is disrupted for a spectral index larger than -2.9. We carry out similar investigation for the more generic ellipsoidal collapse where the mass function is given by the Sheth-Tormen formula. For this case we find the cut-off field strength is 5.5 nG.
Asunta, Otto; Kurki-Suonio, Taina; Koskela, Tuomas; Sipilä, Seppo; Snicker, Antti; Garcia-Muñoz, Manuel
2015-01-01
The effect of ASDEX Upgrade (AUG) ELM mitigation coils on fast ion wall loads was studied with the fast particle following Monte Carlo code ASCOT. Neutral beam injected (NBI) particles were simulated in two AUG discharges both in the presence and in the absence of the magnetic field perturbation induced by the eight newly installed in-vessel coils. In one of the discharges (#26476) beams were applied individually, making it a useful basis for investigating the effect of the coils on different beams. However, no ELM mitigation was observed in #26476, probably due to the low plasma density. Therefore, another discharge (#26895) demonstrating clear ELM mitigation was also studied. The magnetic perturbation due to the in-vessel coils has a significant effect on the fast particle confinement, but only when total magnetic field, $B_{tot}$, is low. When $B_{tot}$ was high, the perturbation did not increase the losses, but merely resulted in redistribution of the wall power loads. Hence, it seems to be possible to ac...
Suttrop, W.; Kirk, A.; Nazikian, R.; Leuthold, N.; Strumberger, E.; Willensdorfer, M.; Cavedon, M.; Dunne, M.; Fischer, R.; Fietz, S.; Fuchs, J. C.; Liu, Y. Q.; McDermott, R. M.; Orain, F.; Ryan, D. A.; Viezzer, E.; The ASDEX Upgrade Team; The DIII-D Team; The Eurofusion MST1 Team
2017-01-01
The interaction of externally applied small non-axisymmetric magnetic perturbations (MP) with tokamak high-confinement mode (H-mode) plasmas is reviewed and illustrated by recent experiments in ASDEX Upgrade. The plasma response to the vacuum MP field is amplified by stable ideal kink modes with low toroidal mode number n driven by the H-mode edge pressure gradient (and associated bootstrap current) which is experimentally evidenced by an observable shift of the poloidal mode number m away from field alignment (m = qn, with q being the safety factor) at the response maximum. A torque scan experiment demonstrates the importance of the perpendicular electron flow for shielding of the resonant magnetic perturbation, as expected from a two-fluid MHD picture. Two significant effects of MP occur in H-mode plasmas at low pedestal collisionality, ν \\text{ped}\\ast≤slant 0.4 : (a) a reduction of the global plasma density by up to 61 % and (b) a reduction of the energy loss associated with edge localised modes (ELMs) by a factor of up to 9. A comprehensive database of ELM mitigation pulses at low {ν\\ast} in ASDEX Upgrade shows that the degree of ELM mitigation correlates with the reduction of pedestal pressure which in turn is limited and defined by the onset of ELMs, i. e. a modification of the ELM stability limit by the magnetic perturbation.
Frassinetti, L.; Sun, Y.; Fridström, R.; Menmuir, S.; Olofsson, K. E. J.; Brunsell, P. R.; Khan, M. W. M.; Liang, Y.; Drake, J. R.
2015-09-01
The non-resonant magnetic perturbation (MP) braking is studied in the EXTRAP T2R reversed-field pinch (RFP) and the experimental braking torque is compared with the torque expected by the neoclassical toroidal viscosity (NTV) theory. The EXTRAP T2R active coils can apply magnetic perturbations with a single harmonic, either resonant or non-resonant. The non-resonant MP produces velocity braking with an experimental torque that affects a large part of the core region. The experimental torque is clearly related to the plasma displacement, consistent with a quadratic dependence as expected by the NTV theory. The work show a good qualitative agreement between the experimental torque in a RFP machine and NTV torque concerning both the torque density radial profile and the dependence on the non-resonant MP harmonic.
Sun, Y; Liang, Y; Liu, Y Q; Gu, S; Yang, X; Guo, W; Shi, T; Jia, M; Wang, L; Lyu, B; Zhou, C; Liu, A; Zang, Q; Liu, H; Chu, N; Wang, H H; Zhang, T; Qian, J; Xu, L; He, K; Chen, D; Shen, B; Gong, X; Ji, X; Wang, S; Qi, M; Song, Y; Yuan, Q; Sheng, Z; Gao, G; Fu, P; Wan, B
2016-09-01
Evidence of a nonlinear transition from mitigation to suppression of the edge localized mode (ELM) by using resonant magnetic perturbations (RMPs) in the EAST tokamak is presented. This is the first demonstration of ELM suppression with RMPs in slowly rotating plasmas with dominant radio-frequency wave heating. Changes of edge magnetic topology after the transition are indicated by a gradual phase shift in the plasma response field from a linear magneto hydro dynamics modeling result to a vacuum one and a sudden increase of three-dimensional particle flux to the divertor. The transition threshold depends on the spectrum of RMPs and plasma rotation as well as perturbation amplitude. This means that edge topological changes resulting from nonlinear plasma response plays a key role in the suppression of ELM with RMPs.
Theorems on Estimating Perturbative Coefficients in Quantum Field Theory and Statistical Physics
Energy Technology Data Exchange (ETDEWEB)
Samuel, Mark
2003-06-25
The authors present rigorous proofs for several theorems on using Pade approximants to estimate coefficients in Perturbative Quantum Field Theory and Statistical Physics. As a result, they find new trigonometric and other identities where the estimates based on this approach are exact. They discuss hypergeometric functions, as well as series from both Perturbative Quantum Field Theory and Statistical Physics.
Primordial Magnetic Fields and Causality
Durrer, R; Durrer, Ruth; Caprini, Chiara
2003-01-01
In this letter we discuss the implications of causality on a primordial magnetic field. We show that the residual field on large scales is much stronger suppressed than usually assumed and that a helical component is even suppressed even more than the parity even part. We show that due to this strong suppression, even maximal primordial fields generated at the electroweak phase transition can just marginally seed the fields in galaxies and clusters, but they cannot leave any detectable imprint on the cosmic microwave background.
Magnetic field intensification by three-dimensional explosion process
Hotta, H; Yokoyama, T
2012-01-01
We investigate an intensification mechanism for the magnetic field near the base of the solar convection zone that does not rely on differential rotation. Such mechanism in addition to differential rotation has been suggested by studies of flux emergence, which typically require field strength in excess of those provided by differential rotation alone. We study here a process in which potential energy of the superadiabatically stratified convection zone is converted into magnetic energy. This mechanism, know as explosion of magnetic flux tubes, has been previously studied in the thin flux tube approximation as well as two-dimensional MHD simulations, we expand the investigation to three-dimensional MHD simulations. Our main result is that enough intensification can be achieved in a three-dimensional magnetic flux sheet as long as the spatial scale of the imposed perturbation normal to the magnetic field is sufficiently large. When this spatial scale is small, the flux sheet tends to rise toward the surface, r...
Heat pulse propagation in chaotic 3-dimensional magnetic fields
del-Castillo-Negrete, D
2014-01-01
Heat pulse propagation in $3$-D chaotic magnetic fields is studied by solving the parallel heat transport equation using a Lagrangian-Green's function (LG) method. The LG method provides an efficient and accurate technique that circumvents limitations of finite elements and finite difference methods. The main two problems addressed are: (i) The dependence of the radial transport on the magnetic field stochasticity (controlled by the amplitude of the perturbation, $\\epsilon$); and (ii) The role of reversed shear configurations on pulse propagation. In all the cases considered there are no magnetic flux surfaces. However, radial transport is observed to depend strongly on $\\epsilon$ due to the presence of high-order magnetic islands and Cantori that act as quasi-transport barriers that preclude the radial penetration of heat pulses within physically relevant time scale. The dependence of the magnetic field connection length, $\\ell_B$, on $\\epsilon$ is studied in detail. The decay rate of the temperature maximum...
Recombination era magnetic fields from axion dark matter
Banik, Nilanjan; Christopherson, Adam J.
2016-02-01
We introduce a new mechanism for generating magnetic fields in the recombination era. This Harrison-like mechanism utilizes vorticity in baryons that is sourced through the Bose-Einstein condensate of axions via gravitational interactions. The magnetic fields generated are on galactic scales ˜10 kpc and have a magnitude of the order of B ˜1 0-23G today. The field has a greater magnitude than those generated from other mechanisms relying on second-order perturbation theory, and is sufficient to provide a seed for battery mechanisms.
Recombination era magnetic fields from axion dark matter
Banik, Nilanjan
2015-01-01
We introduce a new mechanism for generating magnetic fields in the recombination era. This Harrison-like mechanism utilizes vorticity in baryons that is sourced through the Bose-Einstein condensate of axions via gravitational interactions. The magnetic fields generated are on the galactic scales $\\sim 10\\,{\\rm kpc}$ and have a magnitude of the order of $B\\sim10^{-23}\\,{\\rm G}$ today. The field has a greater magnitude than those generated from other mechanisms relying on second order perturbation theory, and is sufficient to provide a seed for battery mechanisms.
Magnetic fields around black holes
Garofalo, David A. G.
Active Galactic Nuclei are the most powerful long-lived objects in the universe. They are thought to harbor supermassive black holes that range from 1 million solar masses to 1000 times that value and possibly greater. Theory and observation are converging on a model for these objects that involves the conversion of gravitational potential energy of accreting gas to radiation as well as Poynting flux produced by the interaction of the rotating spacetime and the electromagnetic fields originating in the ionized accretion flow. The presence of black holes in astrophysics is taking center stage, with the output from AGN in various forms such as winds and jets influencing the formation and evolution of the host galaxy. This dissertation addresses some of the basic unanswered questions that plague our current understanding of how rotating black holes interact with their surrounding magnetized accretion disks to produce the enormous observed energy. Two magnetic configurations are examined. The first involves magnetic fields connecting the black hole with the inner accretion disk and the other involves large scale magnetic fields threading the disk and the hole. We study the effects of the former type by establishing the consequences that magnetic torques between the black hole and the inner accretion disk have on the energy dissipation profile. We attempt a plausible explanation to the observed "Deep Minimum" state in the Seyfert galaxy MCG-6- 30-15. For the latter type of magnetic geometry, we study the effects of the strength of the magnetic field threading the black hole within the context of the cherished Blandford & Znajek mechanism for black hole spin energy extraction. We begin by addressing the problem in the non-relativistic regime where we find that the black hole-threading magnetic field is stronger for greater disk thickness, larger magnetic Prandtl number, and for a larger accretion disk. We then study the problem in full relativity where we show that our
Muthukrishnaveni, M.; Srinivasan, N.
2016-09-01
The polarizability and diamagnetic susceptibility values of a shallow donor in Si are computed. These values are obtained for the cases bar{E}allel bar{B} and bar{E} bot bar{B}. The anisotropy introduced by these perturbations are properly taken care of in the expressions derived for polarizability and magnetic susceptibility. Our results show that the numerical value of the contribution from electric field to diamagnetic susceptibility is several orders smaller than that of the magnetic field effect. Polarizability values are obtained in a magnetic field by two different methods. The polarizability values decrease as the intensity of magnetic field increases. Using the Clausius-Mossotti relation, the anisotropic values of the refractive indices for different magnetic fields are estimated.
Chiral transition with magnetic fields
Ayala, Alejandro; Mizher, Ana Julia; Rojas, Juan Cristobal; Villavicencio, Cristian
2014-01-01
We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses, taken as functions of the order parameter, can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling const...
Magnetic Fields of Neutron Stars
Indian Academy of Sciences (India)
Sushan Konar
2017-09-01
This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars.
Directory of Open Access Journals (Sweden)
Felix Tobias Kurz
2016-12-01
Full Text Available In biological tissue, an accumulation of similarly shaped objects with a susceptibility difference to the surrounding tissue generates a local distortion of the external magnetic field in magnetic resonance imaging. It induces stochastic field fluctuations that characteristically influence proton spin diffusion in the vicinity of these magnetic perturbers. The magnetic field correlation that is associated with such local magnetic field inhomogeneities can be expressed in the form of a dynamic frequency autocorrelation function that is related to the time evolution of the measured magnetization. Here, an eigenfunction expansion for two simple magnetic perturber shapes, that of spheres and cylinders, is considered for restricted spin diffusion in a simple model geometry. Then, the concept of generalized moment analysis, an approximation technique that is applied in the study of (non-reactive processes that involve Brownian motion, allows to provide analytical expressions for the correlation function for different exponential decay forms. Results for the biexponential decay for both spherical and cylindrical magnetized objects are derived and compared with the frequently used (less accurate monoexponential decay forms. They are in asymptotic agreement with the numerically exact value of the correlation function for long and short times.
Kurz, Felix; Kampf, Thomas; Buschle, Lukas; Schlemmer, Heinz-Peter; Bendszus, Martin; Heiland, Sabine; Ziener, Christian
2016-12-01
In biological tissue, an accumulation of similarly shaped objects with a susceptibility difference to the surrounding tissue generates a local distortion of the external magnetic field in magnetic resonance imaging. It induces stochastic field fluctuations that characteristically influence proton spin diffusion in the vicinity of these magnetic perturbers. The magnetic field correlation that is associated with such local magnetic field inhomogeneities can be expressed in the form of a dynamic frequency autocorrelation function that is related to the time evolution of the measured magnetization. Here, an eigenfunction expansion for two simple magnetic perturber shapes, that of spheres and cylinders, is considered for restricted spin diffusion in a simple model geometry. Then, the concept of generalized moment analysis, an approximation technique that is applied in the study of (non-)reactive processes that involve Brownian motion, allows to provide analytical expressions for the correlation function for different exponential decay forms. Results for the biexponential decay for both spherical and cylindrical magnetized objects are derived and compared with the frequently used (less accurate) monoexponential decay forms. They are in asymptotic agreement with the numerically exact value of the correlation function for long and short times.
Development of electric currents in a magnetic field configuration containing a magnetic null point
Santos, J. C.; Büchner, J.; Otto, A.
2011-01-01
Context. In the past the role of magnetic null points in the generation of electric currents was investigated mainly in the close vicinity of the null, with perturbations being applied at nearby boundaries, or for a magnetic null configuration with a dome-shaped fan. In the solar atmosphere, however, electric currents are generated by perturbations originating at the photosphere, far away from coronal 3D nulls, and the occurence of magnetic nulls with a dome-shaped fan is apparently not common. Aims: We investigate the consequences of photospheric motion for the development of electric currents in a coronal magnetic field configuration containing a null, located far away from the boundaries, and the influence of topological structures on the spatial distribution of the currents. Methods: We use a 3D resistive MHD code to investigate the consequences of photospheric plasma motion for the generation of currents in a coronal magnetic field containing a null. The plasma is considered fully compressible and is initially in hydrostatic equilibrium. The initial magnetic field is potential (current free). Results: The photospheric plasma motion causes magnetic field perturbations that propagate to the corona along the field lines at the local Alfvén speed. The Alfvénic wave perturbations correspond to a propagating current directed mainly parallel to the magnetic field. Perpendicular currents connect to return currents to close the current system. The magnetic perturbations eventually reach the vicinity of the null. However, the currents forming in and around the null, near the fan surface or near the spine field lines, are not always the strongest currents developing in the simulation box. In our simulation, the strongest currents develop close to the bottom boundary, where the plasma is moved, and below the null point, in a region where field line connectivity considerably changes. Conclusions: Our simulation shows that the presence of a magnetic null point does not
Alien calculus and non perturbative effects in Quantum Field Theory
Bellon, Marc P.
2016-12-01
In many domains of physics, methods for dealing with non-perturbative aspects are required. Here, I want to argue that a good approach for this is to work on the Borel transforms of the quantities of interest, the singularities of which give non-perturbative contributions. These singularities in many cases can be largely determined by using the alien calculus developed by Jean Écalle. My main example will be the two point function of a massless theory given as a solution of a renormalization group equation.
Magnetic fields in spiral galaxies
Krause, Marita
2015-03-01
The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).
Primordial Magnetic Fields that Last?
Carroll, S M; Carroll, Sean M.; Field, George B.
1998-01-01
The magnetic fields we observe in galaxies today may have their origins in the very early universe. While a number of mechanisms have been proposed which lead to an appreciable field amplitude at early times, the subsequent evolution of the field is of crucial importance, especially whether the correlation length of the field can grow as large as the size of a protogalaxy. This talk is a report on work in progress, in which we consider the fate of one specific primordial field scenario, driven by pseudoscalar effects near the electroweak phase transition. We argue that such a scenario has a number of attractive features, although it is still uncertain whether a field of appropriate size can survive until late times.
Magnetic Properties of Erbium Gallium Gallate under High Magnetic Field
Institute of Scientific and Technical Information of China (English)
Zhang Xijuan; Cheng Haiying; Yang Cuihong; Wang Wei
2004-01-01
A theoretical investigation on the magnetic properties of rare-earth Er3+ in Er3 Ga5 O12 was reported. The average magnetic moments(M) for applied magnetic field H parallel to the [001 ], [ 100], [ 110], [ 111 ] direction was studied based on the quantum theory. Temperature dependence of the magnetic properties is analyzed for H applied parallel to the [ 100] and [ 111 ] crystallographic directions. The magnetization decreases with increasing temperature,showing good agreement with thermal effect. A strong anisotropy of the magnetization is found under high magnetic field, but when the magnetic field is small, M and H are proportional.
Modeling and analysis of magnetic dipoles in weak magnetic field
Institute of Scientific and Technical Information of China (English)
2008-01-01
The magnetic leakage field distribution resulting from linear defects of a tube sample in the geomagnetic field is modeled according to the magnetic dipole theory.The formula to compute the normal component of the weak magnetic field is deduced based on the spatial distribution of the magnetic dipole.The shape and characteristics of the zero line (an important criterion for magnetic memory testing) of the normal field is analyzed under different longitudinal magnetizations.Results show that the characteristics of the zero line should be considered when the metal magnetic memory testing method is used to find and locate the defect.
Impact of resistive MHD plasma response on perturbation field sidebands
Orlov, D. M.; Evans, T. E.; Moyer, R. A.; Lyons, B. C.; Ferraro, N. M.; Park, G.-Y.
2016-07-01
Single fluid linear simulations of a KSTAR RMP ELM suppressed discharge with the M3D-C1 resistive magnetohydrodynamic code have been performed for the first time. The simulations show that the application of the n = 1 perturbation using the KSTAR in-vessel control coils (IVCC), which apply modest levels of n = 3 sidebands (~20% of the n = 1), leads to levels of n = 3 sideband that are comparable to the n = 1 when plasma response is included. This is due to the reduced level of screening of the rational-surface-resonant n = 3 component relative to the rational-surface-resonant n = 1 component. The n = 3 sidebands could play a similar role in ELM suppression on KSTAR as the toroidal sidebands (n = 1, 2, 4) in DIII-D n = 3 ELM suppression with missing I-coil segments (Paz Soldan et al 2014 Nucl. Fusion 54 073013). This result may help to explain the uniqueness of ELM suppression with n = 1 perturbations in KSTAR since the effective perturbation is a mixed n = 1/n = 3 perturbation similar to n = 3 ELM suppression in DIII-D.
A New Detector for Perturbations in Gravitational Field
Directory of Open Access Journals (Sweden)
Smirnov V. N.
2008-04-01
Full Text Available The paper presents design, principles of operation, and examples of registrations carried out by original device developed and constructed by V. N. Smirnov. The device manifested the possibility to register very weak gravitational perturbations of non-seismic kind both from celestial bodies and from the internal processed in the terrestrial globe.
Time-periodic solutions of massive scalar fields in AdS background: perturbative constructions
Kim, Nakwoo
2014-01-01
We consider scalar fields which are coupled to Einstein gravity with a negative cosmological constant, and construct periodic solutions perturbatively. In particular, we study tachyonic scalar fields whose mass is at or above the Breitenlohner-Freedman bound in four, five, and seven spacetime dimensions. The critical amplitude of the leading order perturbation, for which the perturbative expansion breaks down, increases as we consider less massive fields. We present various examples including a model with a self-interacting scalar field which is derived from a consistent truncation of IIB supergravity.
Energy Technology Data Exchange (ETDEWEB)
Kim, Nakwoo, E-mail: nkim@khu.ac.kr
2015-03-06
We consider scalar fields which are coupled to Einstein gravity with a negative cosmological constant, and construct periodic solutions perturbatively. In particular, we study tachyonic scalar fields whose mass is at or above the Breitenlohner–Freedman bound in four, five, and seven spacetime dimensions. The critical amplitude of the leading order perturbation, for which the perturbative expansion breaks down, increases as we consider less massive fields. We present various examples including a model with a self-interacting scalar field which is derived from a consistent truncation of IIB supergravity.
Quasinormal modes of gravitational field perturbation of regular phantom black holes
Li, Jin; Wen, Hao
2016-01-01
We study the gravitational quasi-normal modes (QNMs) for a kind of regular black hole named as phantom black hole (BH), which is a solution of a self-gravitating minimally coupled scalar field with an arbitrary potential.The parameter conditions of such BH are investigated in asymptotically flat, de sitter (dS), and anti de sitter (AdS) spacetimes separately. Considering the standard odd parity and even parity of gravitational perturbation, the corresponding master equations are derived and quasi-normal perturbation are discussed in asymptotically flat and dS spacetimes. The dynamic evolution of the perturbation field indicates the stability of gravitational perturbation directly. On the whole in asymptotically flat and dS spacetimes, the gravitational perturbations have the similar characteristics for odd and even parities. The decay speed of perturbation is strongly dependent on the scale $b$. Furthermore through the analysis of Hawking radiation, the thermodynamics of such regular phantom black hole is als...
Evolution of cosmological perturbations in a stage dominated by an oscillatory scalar field
Kodama, H; Kodama, Hideo; Hamazaki, Takashi
1996-01-01
In the investigation of the evolution of cosmological perturbations in inflationary universe models the behavior of perturbations during the reheating stage is the most unclear point. In particular in the early reheating phase in which a rapidly oscillating scalar field dominates the energy density, the behavior of perturbations is not known well because their evolution equation expressed in terms of the curvature perturbation becomes singular. In this paper it is shown that in spite of this singular behavior of the evolution equation the Bardeen parameter stays constant in a good accuracy during this stage for superhorizon-scale perturbations except for a sequence of negligibly short intervals around the zero points of the time derivative of the scalar field. This justifies the conventional formula relating the amplitudes of quantum fluctuations during inflation and those of adiabatic perturbations at horizon crossing in the Friedmann stage, except for possible corrections produced by the energy transfer fro...
Galactic and intergalactic magnetic fields
Klein, Ulrich
2014-01-01
This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible.In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later c
ELM Suppression in DIII-D ITER-like Plasmas Using n = 2 Magnetic Perturbations
Nazikian, R.; Grierson, B. A.; Okabayashi, M.; Tobias, B. J.; Eldon, D.; Evans, T. E.; Ferraro, N. M.; Groebner, R. J.; Paz-Soldan, C.; Strait, E. J.; Haskey, S. R.; King, J. D.; McKee, G. R.; Moyer, R. A.; Orlov, D. M.; Shafer, M. W.
2014-10-01
A robust window of edge localized mode (ELM) suppression was observed at elevated magnetic safety factor (q95 ~ 4.1) in ITER-like plasmas with even parity n = 2 resonant magnetic perturbation (RMP) using the internal I-coils. Variation of the upper and lower I-coil phasing was used to explore the importance of pitch alignment vs kink alignment for ELM suppression. Both the pedestal density and ELM suppression were strongly dependent on I-coil phasing and a large variation in the plasma response amplitude was measured on multiple diagnostics. Surprisingly, toroidal rotation of the even parity n = 2 RMP led to the loss of ELM suppression, indicating that components of the residual error field orthogonal to the kink mode may be important near the threshold for ELM suppression. Work supported by the US Department of Energy under DE-AC02-09CH11466, DE-FC02-04ER54698, DE-AC05-06OR23100, DE-FG02-89ER53296, DE-FG02-08ER54999, DE-FG02-07ER54917, and DE-AC05-00OR22725.
Effect of resonant magnetic perturbations on microturbulence in DIII-D pedestal
Holod, I.; Lin, Z.; Taimourzadeh, S.; Nazikian, R.; Spong, D.; Wingen, A.
2017-01-01
Vacuum resonant magnetic perturbations (RMP) applied to otherwise axisymmetric tokamak plasmas produce in general a combination of non-resonant effects that preserve closed flux surfaces (kink response) and resonant effects that introduce magnetic islands and/or stochasticity (tearing response). The effect of the plasma kink response on the linear stability and nonlinear transport of edge turbulence is studied using the gyrokinetic toroidal code GTC for a DIII-D plasma with applied n = 2 vacuum RMP. GTC simulations use the 3D equilibrium of DIII-D discharge 158103 (Nazikian et al 2015 Phys. Rev. Lett. 114 105002), which is provided by nonlinear ideal MHD VMEC equilibrium solver in order to include the effect of the plasma kink response to the external field but to exclude island formation at rational surfaces. Analysis using the GTC simulation results reveal no increase of growth rates for the electrostatic drift wave instability and for the electromagnetic kinetic-ballooning mode in the presence of the plasma kink response to the RMP. Furthermore, nonlinear electrostatic simulations show that the effect of the 3D equilibrium on zonal flow damping is very weak and found to be insufficient to modify turbulent transport in the electrostatic turbulence.
Fast magnetic twister and plasma perturbations in a three-dimensional coronal arcade
Energy Technology Data Exchange (ETDEWEB)
Murawski, K. [Group of Astrophysics, UMCS, ul. Radziszewskiego 10, 20-031 Lublin (Poland); Srivastava, A. K. [Department of Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi-221005 (India); Musielak, Z. E., E-mail: kmur@kft.umcs.lublin.pl, E-mail: asrivastava.app@iitbhu.ac.in, E-mail: zmusielak@uta.edu, E-mail: musielak@kis.uni-freiburg.de [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States)
2014-06-10
We present results of three-dimensional (3D) numerical simulations of a fast magnetic twister excited above a foot-point of the potential solar coronal arcade that is embedded in the solar atmosphere with the initial VAL-IIIC temperature profile, which is smoothly extended into the solar corona. With the use of the FLASH code, we solve 3D ideal magnetohydrodynamic equations by specifying a twist in the azimuthal component of magnetic field in the solar chromosphere. The imposed perturbation generates torsional Alfvén waves as well as plasma swirls that reach the other foot-point of the arcade and partially reflect back from the transition region. The two vortex channels are evident in the generated twisted flux-tube with a fragmentation near its apex which results from the initial twist as well as from the morphology of the tube. The numerical results are compared to observational data of plasma motions in a solar prominence. The comparison shows that the numerical results and the data qualitatively agree even though the observed plasma motions occur over comparatively large spatio-temporal scales in the prominence.
Fast Magnetic Twister and Plasma Perturbations in a 3-D Coronal Arcade
Murawski, K; Musielak, Z E
2014-01-01
We present results of 3-D numerical simulations of a fast magnetic twister excited above a foot-point of the potential solar coronal arcade that is embedded in the solar atmosphere with the initial VAL-IIIC temperature profile, which is smoothly extended into the solar corona. With the use of the FLASH code, we solve 3-D ideal magnetohydrodynamic equations by specifying a twist in the azimuthal component of magnetic field in the solar chromosphere. The imposed perturbation generates torsional Alfv\\'en waves as well as plasma swirls that reach the other foot-point of the arcade and partially reflect back from the transition region. The two vortex channels are evident in the generated twisted flux-tube with a fragmentation near its apex that results from the initial twist as well as from the morphology of the tube. The numerical results are compared to observational data of plasma motions in a solar prominence. The comparison shows that the numerical results and the data qualitatively agree even though the obse...
Stress Field of Straight Edge Dislocation in Magnetic Field
Institute of Scientific and Technical Information of China (English)
LIU Zhao-long; HU Hai-yun; FAN Tian-you
2007-01-01
To study the changes in mechanical properties of materials within magnetic fields and the motion of dislocations,stress fields of dislocation in magnetic field need to be calculated.The straight edge dislocation is of basic importance in various defects.The stress field of straight edge dislocation in an external static magnetic field is determined by the theory of elasticity and electrodynamics according to the Volterra dislocation model for continuous media.This reduces to the known stress field when the magnet field is zero.The results can be used for further study on the strain energy of dislocations and the interactions between dislocations in magnetic fields.
Angeli, Celestino; Calzado, Carmen J
2012-07-21
The use of multireference perturbation theory (MRPT) for the calculation of the magnetic coupling in binuclear complexes has shown to give poor results if applied on a minimal active space complete active space self-consistent field (CASSCF) wavefunction. In this work, we identify the origin of this problem in the starting CASSCF orbitals, which are exceedingly localized on the metal atoms. Focusing on the case of antiferromagnetic systems, it is shown that the form of the active orbitals has a dramatic effect on the relative description of the neutral and ionic structures. Finally, a simple and computational inexpensive strategy is proposed for the calculation of a set of magnetic orbitals describing in a more balanced way the neutral and ionic structures. The use of these orbitals, instead the CASSCF ones, in minimal active space MRPT2 calculations leads to a marked improvement of the J values, which become in reasonable agreement with those obtained with the expensive high level difference dedicated configuration interaction approach and with the experimental values.
Diagnosis of solar chromospheric magnetic field
Institute of Scientific and Technical Information of China (English)
ZHANG; Hongqi(张洪起)
2002-01-01
This paper discusses the measurements of the chromospheric magnetic field and the spatial configuration of the field at the lower solar atmosphere inferred by the distribution of the solar photospheric and chromospheric magnetic fields. Some questions in the study of the chromospheric magnetic field are also presented.
The HMI Magnetic Field Pipeline
Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI Science Team
2009-05-01
The Helioseismic and Magnetic Imager (HMI) will provide frequent full-disk magnetic field data after launch of the Solar Dynamics Observatory (SDO), currently scheduled for fall 2009. 16 megapixel line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A full set of polarized filtergrams needed to determine the vector magnetic field requires 90 seconds. Quick-look data will be available within a few minutes of observation. Quick-look space weather and browse products must have identified users, and the list currently includes full disk magnetograms, feature identification and movies, 12-minute disambiguated vector fields in active region patches, time evolution of AR indices, synoptic synchronic frames, potential and MHD model results, and 1 AU predictions. A more complete set of definitive science data products will be offered about a day later and come in three types. "Pipeline” products, such as full disk vector magnetograms, will be computed for all data on an appropriate cadence. A larger menu of "On Demand” products, such as Non-Linear Force Free Field snapshots of an evolving active region, will be produced whenever a user wants them. Less commonly needed "On Request” products that require significant project resources, such as a high resolution MHD simulation of the global corona, will be created subject to availability of resources. Further information can be found at the SDO Joint Science Operations Center web page, jsoc.stanford.edu
A Vorticity-Magnetic Field Dynamo Instability
1997-01-01
We generalize the mean field magnetic dynamo to include local evolution of the mean vorticity in addition to the mean magnetic field. The coupled equations exhibit a general mean field dynamo instability that enables the transfer of turbulent energy to the magnetic field and vorticity on larger scales. The growth of the vorticity and magnetic field both require helical turbulence which can be supplied by an underlying global rotation. The dynamo coefficients are derived including the backreac...
Willensdorfer, M; Strumberger, E; Suttrop, W; Vanovac, B; Brida, D; Cavedon, M; Classen, I; Dunne, M; Fietz, S; Fischer, R; Kirk, A; Laggner, F M; Liu, Y Q; Odstrcil, T; Ryan, D A; Viezzer, E; Zohm, H; Luhmann, I C
2016-01-01
The plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC. The measured amplitudes of the helical displacement in the midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the vacuum field calculations and indicate the presence of an amplified kink response at the edge. Although the calculated magnetic structure of this edge kink peaks at poloidal mode numbers larger than the resonant components |m| > |nq|, the displacement measured by ECE-I is almost resonant |m| ~ |nq|. This is expected from ideal MHD in the proximity of rational surfaces. VMEC and MARS-...
Williams, P Stephen; Carpino, Francesca; Zborowski, Maciej
2010-09-28
Quadrupole magnetic field-flow fractionation is a relatively new technique for the separation and characterization of magnetic nanoparticles. Magnetic nanoparticles are often of composite nature having a magnetic component, which may be a very finely divided material, and a polymeric or other material coating that incorporates this magnetic material and stabilizes the particles in suspension. There may be other components such as antibodies on the surface for specific binding to biological cells, or chemotherapeutic drugs for magnetic drug delivery. Magnetic field-flow fractionation (MgFFF) has the potential for determining the distribution of the magnetic material among the particles in a given sample. MgFFF differs from most other forms of field-flow fractionation in that the magnetic field that brings about particle separation induces magnetic dipole moments in the nanoparticles, and these potentially can interact with one another and perturb the separation. This aspect is examined in the present work. Samples of magnetic nanoparticles were analysed under different experimental conditions to determine the sensitivity of the method to variation of conditions. The results are shown to be consistent and insensitive to conditions, although magnetite content appeared to be somewhat higher than expected.
Magnetic field of a combined plasma trap
Kotenko, V. G.; Moiseenko, V. E.; Ågren, O.
2012-06-01
This paper presents numerical simulations performed on the structure of a magnetic field created by the magnetic system of a combined plasma trap. The magnetic system includes the stellarator-type magnetic system and one of the mirror-type. For the stellarator type magnetic system the numeric model contains a magnetic system of an l=2 torsatron with the coils of an additional toroidal magnetic field. The mirror-type magnetic system element is considered as being single current-carrying turn enveloping the region of existence of closed magnetic surfaces of the torsatron. The calculations indicate the existence of a vast area of the values of the additional magnetic field magnitude and magnetic field of the single turn where, in principle, the implementation of the closed magnetic surface configuration is quite feasible.
ANALYTIC EXPRESSION OF MAGNETIC FIELD DISTRIBUTION OF RECTANGULAR PERMANENT MAGNETS
Institute of Scientific and Technical Information of China (English)
苟晓凡; 杨勇; 郑晓静
2004-01-01
From the molecular current viewpoint,an analytic expression exactly describing magnetic field distribution of rectangular permanent magnets magnetized sufficiently in one direction was derived from the Biot-Savart's law. This expression is useful not only for the case of one rectangular permanent magnet bulk, but also for that of several rectangular permanent magnet bulks. By using this expression,the relations between magnetic field distribution and the size of rectangular permanent magnets as well as the magnitude of magnetic field and the distance from the point in the space to the top (or bottom) surface of rectangular permanent magnets were discussed in detail. All the calculating results are consistent with experimental ones. For transverse magnetic field which is a main magnetic field of rectangular permanent magnets,in order to describe its distribution,two quantities,one is the uniformity in magnitude and the other is the uniformity in distribution of magnetic field,were defined. Furthermore, the relations between them and the geometric size of the magnet as well as the distance from the surface of permanent magnets were investigated by these formulas. The numerical results show that the geometric size and the distance have a visible influence on the uniformity in magnitude and the uniformity in distribution of the magnetic field.
Cosmic Ray Small Scale Anisotropies and Local Turbulent Magnetic Fields
López-Barquero, Vanessa; Xu, S; Desiati, P; Lazarian, A
2015-01-01
Cosmic ray anisotropy is observed in a wide energy range and at different angular scales by a variety of experiments. However, a comprehensive and satisfactory explanation has been elusive for over a decade now. The arrival distribution of cosmic rays on Earth is the convolution of the distribution of their sources and of the effects of geometry and properties of the magnetic field through which particles propagate. It is generally believed that the anisotropy topology at the largest angular scale is adiabatically shaped by diffusion in the structured interstellar magnetic field. On the contrary, the medium and small angular scale structure could be an effect of non diffusive propagation of cosmic rays in perturbed magnetic fields. In particular, a possible explanation of the observed small scale anisotropy observed at TeV energy scale, may come from the effect of particle scattering in turbulent magnetized plasmas. We perform numerical integration of test particle trajectories in low-$\\beta$ compressible mag...
Firpo, Marie-Christine; 10.1063/1.3562493
2011-01-01
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 non-axisymmetric 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 possibl...
Twist, writhe and energy from the helicity of magnetic perturbed vortex filaments
de Andrade, Luiz Carlos Garcia
2007-01-01
The twist and writhe numbers and magnetic energy of an orthogonally perturbed vortex filaments are obtained from the computation of the magnetic helicity of geodesic and abnormal magnetohydrodynamical (MHD) vortex filament solutions. Twist is computed from a formula recently derived by Berger and Prior [J. Phys. A 39 (2006) 8321] and finally writhe is computed from the theorem that the helicity is proportional to the sum of twist and writhe. The writhe number is proportional to the total tors...
Field and Thermal Characteristics of Magnetizing Fixture
Institute of Scientific and Technical Information of China (English)
2000-01-01
This paper describes field modeling and thermal modeling for magnetizing fixture. As the detailed characteristics of magnetizing fixture can be obtained, the efficient design of magnetizer which produce desired magnet will be possible using our modeling. For field modeling finite-element analysis is used as part of the design and analysis process for magnetizing fixture. The thermal modeling method of magnetizing fixture resistor uses multi-lumped model with equivalent thermal resistance and thermal capacitance.
Full particle orbit effects in regular and stochastic magnetic fields
Ogawa, Shun; Cambon, Benjamin; Leoncini, Xavier; Vittot, Michel; del Castillo-Negrete, Diego; Dif-Pradalier, Guilhem; Garbet, Xavier
2016-07-01
We present a numerical study of charged particle motion in a time-independent magnetic field in cylindrical geometry. The magnetic field model consists of an unperturbed reversed-shear (non-monotonic q-profile) helical part and a perturbation consisting of a superposition of modes. Contrary to most of the previous studies, the particle trajectories are computed by directly solving the full Lorentz force equations of motion in a six-dimensional phase space using a sixth-order, implicit, symplectic Gauss-Legendre method. The level of stochasticity in the particle orbits is diagnosed using averaged, effective Poincare sections. It is shown that when only one mode is present, the particle orbits can be stochastic even though the magnetic field line orbits are not stochastic (i.e., fully integrable). The lack of integrability of the particle orbits in this case is related to separatrix crossing and the breakdown of the global conservation of the magnetic moment. Some perturbation consisting of two modes creates resonance overlapping, leading to Hamiltonian chaos in magnetic field lines. Then, the particle orbits exhibit a nontrivial dynamics depending on their energy and pitch angle. It is shown that the regions where the particle motion is stochastic decrease as the energy increases. The non-monotonicity of the q-profile implies the existence of magnetic ITBs (internal transport barriers) which correspond to shearless flux surfaces located in the vicinity of the q-profile minimum. It is shown that depending on the energy, these magnetic ITBs might or might not confine particles. That is, magnetic ITBs act as an energy-dependent particle confinement filter. Magnetic field lines in reversed-shear configurations exhibit topological bifurcations (from homoclinic to heteroclinic) due to separatrix reconnection. We show that a similar but more complex scenario appears in the case of particle orbits that depend in a non-trivial way on the energy and pitch angle of the
Full particle orbit effects in regular and stochastic magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Ogawa, Shun, E-mail: shun.ogawa@cpt.univ-mrs.fr [Aix Marseille Univ., Univ. Toulon, CNRS, CPT, Marseille (France); CEA, IRFM, F-13108 St. Paul-lez-Durance Cedex (France); Cambon, Benjamin; Leoncini, Xavier; Vittot, Michel [Aix Marseille Univ., Univ. Toulon, CNRS, CPT, Marseille (France); Castillo-Negrete, Diego del [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6169 (United States); Dif-Pradalier, Guilhem; Garbet, Xavier [CEA, IRFM, F-13108 St. Paul-lez-Durance Cedex (France)
2016-07-15
We present a numerical study of charged particle motion in a time-independent magnetic field in cylindrical geometry. The magnetic field model consists of an unperturbed reversed-shear (non-monotonic q-profile) helical part and a perturbation consisting of a superposition of modes. Contrary to most of the previous studies, the particle trajectories are computed by directly solving the full Lorentz force equations of motion in a six-dimensional phase space using a sixth-order, implicit, symplectic Gauss-Legendre method. The level of stochasticity in the particle orbits is diagnosed using averaged, effective Poincare sections. It is shown that when only one mode is present, the particle orbits can be stochastic even though the magnetic field line orbits are not stochastic (i.e., fully integrable). The lack of integrability of the particle orbits in this case is related to separatrix crossing and the breakdown of the global conservation of the magnetic moment. Some perturbation consisting of two modes creates resonance overlapping, leading to Hamiltonian chaos in magnetic field lines. Then, the particle orbits exhibit a nontrivial dynamics depending on their energy and pitch angle. It is shown that the regions where the particle motion is stochastic decrease as the energy increases. The non-monotonicity of the q-profile implies the existence of magnetic ITBs (internal transport barriers) which correspond to shearless flux surfaces located in the vicinity of the q-profile minimum. It is shown that depending on the energy, these magnetic ITBs might or might not confine particles. That is, magnetic ITBs act as an energy-dependent particle confinement filter. Magnetic field lines in reversed-shear configurations exhibit topological bifurcations (from homoclinic to heteroclinic) due to separatrix reconnection. We show that a similar but more complex scenario appears in the case of particle orbits that depend in a non-trivial way on the energy and pitch angle of the
Magnetic fields for fluid motion.
Weston, Melissa C; Gerner, Matthew D; Fritsch, Ingrid
2010-05-01
Three forces induced by magnetic fields offer unique control of fluid motion and new opportunities in microfluidics. This article describes magnetoconvective phenomena in terms of the theory and controversy, tuning by redox processes at electrodes, early-stage applications in analytical chemistry, mature applications in disciplines far afield, and future directions for micro total analysis systems. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html .).
On the ambiguity of field correlators represented by asymptotic perturbation expansions
Energy Technology Data Exchange (ETDEWEB)
Caprini, Irinel [National Institute of Physics and Nuclear Engineering, Bucharest POB MG-6, R-077125 Romania (Romania); Fischer, Jan [Institute of Physics, Academy of Sciences of the Czech Republic, CZ-182 21 Prague 8 (Czech Republic); Vrkoc, Ivo [Mathematical Institute, Academy of Sciences of the Czech Republic, CZ-115 67 Prague 1 (Czech Republic)
2009-10-02
Starting from the divergence pattern of perturbation expansions in quantum field theory and the (assumed) asymptotic character of the series, we address the problem of ambiguity of a function determined by the perturbation expansion. We consider functions represented by an integral of the Laplace-Borel type along a general contour in the Borel complex plane. Proving a modified form of Watson's lemma, we obtain a large class of functions having the same asymptotic perturbation expansion. Some remarks on perturbative QCD are made, using the particular case of the Adler function.
Quark deconfinement and gluon condensate in a weak magnetic field
Ayala, Alejandro; Hernandez, L A; Loewe, M; Rojas, Juan Cristobal; Villavicencio, Cristian
2015-01-01
We study QCD finite energy sum rules (FESR) for the axial-vector current correlator in the presence of a magnetic field, in the weak field limit and at zero temperature. We find that the perturbative QCD as well as the hadronic contribution to the sum rules get explicit magnetic field-dependent corrections and that these in turn induce a magnetic field dependence on the deconfinement phenomenological parameter s_0 and on the gluon condensate. The leading corrections turn out to be quadratic in the field strength. We find from the dimension d=2 first FESR that the magnetic field dependence of s_0 is proportional to the absolute value of the light-quark condensate. Hence, it increases with increasing field strength. This implies that the parameters describing chiral symmetry restoration and deconfinement behave similarly as functions of the magnetic filed. Thus, at zero temperature the magnetic field is a catalysing agent of both chiral symmetry breaking and confinement. From the dimension d=4 second FESR we ob...
Generation of primordial magnetic fields on linear overdensity scales.
Naoz, Smadar; Narayan, Ramesh
2013-08-02
Magnetic fields appear to be present in all galaxies and galaxy clusters. Recent measurements indicate that a weak magnetic field may be present even in the smooth low density intergalactic medium. One explanation for these observations is that a seed magnetic field was generated by some unknown mechanism early in the life of the Universe, and was later amplified by various dynamos in nonlinear objects like galaxies and clusters. We show that a primordial magnetic field is expected to be generated in the early Universe on purely linear scales through vorticity induced by scale-dependent temperature fluctuations, or equivalently, a spatially varying speed of sound of the gas. Residual free electrons left over after recombination tap into this vorticity to generate magnetic field via the Biermann battery process. Although the battery operates even in the absence of any relative velocity between dark matter and gas at the time of recombination, the presence of such a relative velocity modifies the predicted spatial power spectrum of the magnetic field. At redshifts of order a few tens, we estimate a root mean square field strength of order 10(-25)-10(-24) G on comoving scales ~10 kpc. This field, which is generated purely from linear perturbations, is expected to be amplified significantly after reionization, and to be further boosted by dynamo processes during nonlinear structure formation.
Investigation of ELM [edge localized mode] Dynamics with the Resonant Magnetic Perturbation Effects
Energy Technology Data Exchange (ETDEWEB)
Pankin, Alexei Y.; Kritz, Arnold H.
2011-07-19
Topics covered are: anomalous transport and E x B flow shear effects in the H-mode pedestal; RMP (resonant magnetic perturbation) effects in NSTX discharges; development of a scaling of H-mode pedestal in tokamak plasmas with type I ELMs (edge localized modes); and divertor heat load studies.
Deformation of Water by a Magnetic Field
Chen, Zijun; Dahlberg, E. Dan
2011-03-01
After the discovery that superconducting magnets could levitate diamagnetic objects,1,2 researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields,3-5 which was given the name "The Moses Effect."5 Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary were produced by superconducting magnets.
Wiggle Instability of Galactic Spiral Shocks: Effects of Magnetic Fields
Kim, Yonghwi; Elmegreen, Bruce G
2015-01-01
It has been suggested that the wiggle instability (WI) of spiral shocks in a galactic disk is responsible for the formation of gaseous feathers observed in grand-design spiral galaxies. We perform both a linear stability analysis and numerical simulations to investigate the effect of magnetic fields on the WI. The disk is assumed to be infinitesimally-thin, isothermal, and non-self-gravitating. We control the strengths of magnetic fields and spiral-arm forcing using the dimensionless parameters $\\beta$ and $\\mathcal{F}$, respectively. By solving the perturbation equations as a boundary-eigenvalue problem, we obtain dispersion relations of the WI for various values of $\\beta=1-\\infty$ and $\\mathcal{F}=5\\%$ and $10\\%$. We find that the WI arising from the accumulation of potential vorticity at disturbed shocks is suppressed, albeit not completely, by magnetic fields. The stabilizing effect of magnetic fields is not from the perturbed fields but from the unperturbed fields that reduce the density compression fac...
Kim, Juhyung; Kim, S. S.; Jhang, Hogun
2016-09-01
Numerical studies are made of the effects of resistivity on linear plasma responses to resonant magnetic perturbations (RMPs) in tokamaks based on a reduced magnetohydrodynamic model. From a local two-field model, it is suggested that the ratio of the poloidal electron advection to the resistivity diffusion rate α m can be a figure of merit parameter in linear RMP penetration physics. The shielding efficiency is governed by α m , and when α m ≳ 1 , RMPs are effectively shielded. Global simulations using a four-field model [Hazeltine and Meiss, Phys. Rep. 121, 1 (1985)] show that there exists an effective threshold of the perpendicular electron flow ( Ve , ⊥ c ) beyond which RMPs cannot penetrate. Resistivity is found to determine Ve , ⊥ c which increases as resistivity becomes higher, making RMP penetration easier. At low resistivity, small Ve , ⊥ c renders the RMP penetration sensitive to ion collisionality and the change in q95. The kink response is observed to be closely related to the residual level of RMPs at rational surfaces and can be also strongly affected by resistivity.
Impact of resonant magnetic perturbations on nonlinearly driven modes in drift-wave turbulence
Energy Technology Data Exchange (ETDEWEB)
Leconte, M. [WCI Center for Fusion Theory, NFRI (Korea, Republic of); Diamond, P. H. [WCI Center for Fusion Theory, NFRI (Korea, Republic of); CMTFO and CASS, UCSD, California 92093 (United States)
2012-05-15
In this work, we study the effects of resonant magnetic perturbations (RMPs) on turbulence, flows, and confinement in the framework of resistive drift wave turbulence. We extend the Hasegawa-Wakatani model to include RMP fields. The effect of the RMPs is to induce a linear coupling between the zonal electric field and the zonal density gradient, which drives the system to a state of electron radial force balance for large ({delta}B{sub r}/B{sub 0}). Both the vorticity flux (Reynolds stress) and particle flux are modulated. We derive an extended predator prey model which couples zonal potential and density dynamics to the evolution of turbulence intensity. This model has both turbulence drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. We find states that are similar to the ZF-dominated state of the standard predator-prey model, but for which the power threshold is now a function of the RMP strength. For small RMP amplitude, the energy of zonal flows decreases and the turbulence energy increases with ({delta}B{sub r}/B{sub 0}), corresponding to a damping of zonal flows.
Effect of resonant magnetic perturbations on secondary structures in drift-wave turbulence
Energy Technology Data Exchange (ETDEWEB)
Leconte, M. [WCI Center for Fusion Theory, NFRI, Daejeon (Korea, Republic of); Diamond, P. H. [WCI Center for Fusion Theory, NFRI, Daejeon (Korea, Republic of); CMTFO and CASS, UCSD, California 92093 (United States)
2011-08-15
Recent experiments showed a decrease of long range correlations during the application of resonant magnetic perturbations (RMPs) [Y. Xu et al., Nucl. Fusion 51, 063020 (2011)]. This finding suggests that RMPs damp zonal flows. To elucidate the effect of the RMPs on zonal structures in drift wave turbulence, we construct a generalized Hasegawa-Wakatani model including RMP fields. The effect of the RMPs is to induce a linear coupling between the zonal electric field and the zonal density gradient, which drives the system to a state of electron radial force balance for large RMP amplitude. A predator-prey model coupling the primary drift wave dynamics to the zonal modes evolution is derived. This model has both turbulence drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. The novel regime has a power threshold which increases with RMP amplitude as {gamma}{sub c}{approx}[({delta}B{sub r}/B)]{sup 2}.
Inter-ELM pedestal evolution on MAST and impact of Resonant Magnetic Perturbations
Scannell, R; Chapman, I T; 10.1088/0741-3335/55/3/035013
2013-01-01
The peak pressure gradient in the pedestal (dPe/d{\\psi}) on MAST varies little between edge localized modes (ELMs), although it varies between discharges due factors such as gas fuelling and plasma current. The pressure pedestal width in flux space on the high-field side (HFS), both during the inter-ELM period and amongst different plasma discharges is consistent with a scaling of . In flux space very similar dPe/d{\\psi} and {\\Delta}pe are observed on the HFS and low-field side (LFS) in single null configuration. This symmetry is broken by the application of resonant magnetic perturbations (RMPs). During ELM mitigation by application of RMPs changes in the edge transport barrier position and width are observed. These changes are dependent on the intensity of the RMP and on the toroidal location with respect to the RMP phase. An outward displacement of up to 30 mm and increase in the edge pedestal width of up to 50% with respect to the coils case off are observed. Increased particle transport causes a decrease...
Passive Magnetic Shielding in Gradient Fields
Bidinosti, C P
2013-01-01
The effect of passive magnetic shielding on dc magnetic field gradients imposed by both external and internal sources is studied. It is found that for concentric cylindrical or spherical shells of high permeability material, higher order multipoles in the magnetic field are shielded progressively better, by a factor related to the order of the multipole. In regard to the design of internal coil systems for the generation of uniform internal fields, we show how one can take advantage of the coupling of the coils to the innermost magnetic shield to further optimize the uniformity of the field. These results demonstrate quantitatively a phenomenon that was previously well-known qualitatively: that the resultant magnetic field within a passively magnetically shielded region can be much more uniform than the applied magnetic field itself. Furthermore we provide formulae relevant to active magnetic compensation systems which attempt to stabilize the interior fields by sensing and cancelling the exterior fields clos...
Magnetic Field Effect on the Phase Transition in AdS Soliton Spacetime
Cai, Rong-Gen; Zhang, Hai-Qing; Zhang, Yun-Long
2011-01-01
We investigate the scalar perturbations in an AdS soliton background coupled to a Maxwell field via marginally stable modes. In the probe limit, we study the magnetic field effect on the holographic insulator/superconductor phase transition numerically and analytically. The condensate will be localized in a finite circular region for any finite constant magnetic field. Near the critical point, we find that there exists a simple relation among the critical chemical potential, magnetic field, the charge and mass of the scalar field. This relation indicates that the presence of the magnetic field causes the phase transition hard.
Frassinetti, L.; Olofsson, K. E. J.; Brunsell, P. R.; Drake, J. R.
2011-06-01
The EXTRAP T2R feedback system (active coils, sensor coils and controller) is used to study and develop new tools for advanced control of the MHD instabilities in fusion plasmas. New feedback algorithms developed in EXTRAP T2R reversed-field pinch allow flexible and independent control of each magnetic harmonic. Methods developed in control theory and applied to EXTRAP T2R allow a closed-loop identification of the machine plant and of the resistive wall modes growth rates. The plant identification is the starting point for the development of output-tracking algorithms which enable the generation of external magnetic perturbations. These algorithms will then be used to study the effect of a resonant magnetic perturbation (RMP) on the tearing mode (TM) dynamics. It will be shown that the stationary RMP can induce oscillations in the amplitude and jumps in the phase of the rotating TM. It will be shown that the RMP strongly affects the magnetic island position.
Evidence and relevance of spatially chaotic magnetic field lines in MCF devices
Firpo, M.-C.; Lifschitz, A. F.; Ettoumi, W.; Farengo, R.; Ferrari, H. E.; García-Martínez, P. L.
2017-03-01
Numerical evidence for the existence of spatially chaotic magnetic field lines about the collapse phase of tokamak sawteeth with incomplete reconnection is presented. This uses the results of extensive test particle simulations in different sets of electromagnetic perturbations tested against experimental JET measurements. In tokamak sawteeth, that form a laboratory prototype of magnetic reconnection, the relative magnetic perturbation δ B/B may reach a few percents. This does not apply to tokamak operating regimes dominated by turbulence where δ B/B is usually not larger than {10}-4. However, this small magnetic perturbation being sustained by a large spectrum of modes is shown to be sufficient to ensure the existence of stochastic magnetic field lines. This has important consequences for magnetic confinement fusion where electrons are dominantly governed by the magnetic force. Indeed some overlap between magnetic resonances can locally induce chaotic magnetic field lines enabling the spatial redistribution of the electron population and of its thermal content. As they are the swiftest plasma particles, electrons feed back the most rapid perturbations of the magnetic field.
Fridström, R.; Frassinetti, L.; Brunsell, P. R.
2015-10-01
The physical mechanisms behind the hysteresis in the tearing mode locking and unlocking to a resonant magnetic perturbation (RMP) are experimentally studied in EXTRAP T2R reversed-field pinch. The experiments show that the electromagnetic and the viscous torque increase with increasing perturbation amplitude until the mode locks to the wall. At the wall-locking, the plasma velocity reduction profile is peaked at the radius where the RMP is resonant. Thereafter, the viscous torque drops due to the relaxation of the velocity in the central plasma. This is the main reason for the hysteresis in the RMP locking and unlocking amplitude. The increased amplitude of the locked tearing mode produces further deepening of the hysteresis. Both experimental results are in qualitative agreement with the model in Fitzpatrick et al (2001 Phys. Plasmas 8 4489)
Bats respond to very weak magnetic fields.
Directory of Open Access Journals (Sweden)
Lan-Xiang Tian
Full Text Available How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here, the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT, despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05. Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.
Adaptive control of rotating magnetic perturbations in HBT-EP using GPU processing
Rath, N.; Angelini, S.; Bialek, J.; Byrne, P. J.; DeBono, B.; Hughes, P.; Levesque, J. P.; Mauel, M. E.; Navratil, G. A.; Peng, Q.; Rhodes, D.; Stoafer, C.
2013-08-01
Feedback control has become a crucial tool in the research on magnetic confinement of plasmas for achieving controlled nuclear fusion. We present the first experimental results from a novel feedback control system that, for the first time, employs a graphics processing unit (GPU) for microsecond-latency, real-time control computations. The system was tested on the HBT-EP tokamak using an adaptive control algorithm for control of rotating magnetic perturbations. The algorithm assumes that perturbations of known shape are rotating rigidly, but dynamically derives and updates the rotation frequency to improve phase and gain accuracy of the control signals. Experiments were set up to control four rotating n = 1 perturbations at different poloidal angles. The perturbations are treated as coupled in frequency but independent of amplitude and phase, so that the system effectively controls a helical n = 1 perturbation with unknown poloidal spectrum. The control system suppresses the amplitude of the dominant 8 kHz mode by up to 60%. Deviation from the optimal feedback phase combines suppression with a speed up or slow down of the mode rotation frequency. The feedback performance is found to exceed previous results obtained with an FPGA- and Kalman-filter based control system without requiring any tuning of system model parameters.
Hybrid Shielding for Magnetic Fields
Mullins, David; Royal, Kevin
2017-01-01
Precision symmetry measurements such as the search for the electric dipole moment of the neutron require magnetic shielding rooms to reduce the ambient field to the pT scale. The massive mu-metal sheets and large separation between layers make these shield rooms bulky and expensive. Active field cancellation systems used to reduce the surrounding field are limited in uniformity of cancellation. A novel approach to reducing the space between shield layers and increasing the effectiveness of active cancellation is to combine the two systems into a hybrid system, with active and passive layers interspersed. We demonstrate this idea in a prototype with an active layer sandwiched between two passive layers of shielding.
Manifestations of Magnetic Field Inhomogeneities
Indian Academy of Sciences (India)
Lawrence Rudnick
2011-12-01
Both observations and simulations reveal large inhomogeneities in magnetic field distributions in diffuse plasmas. Incorporating these inhomogeneities into various calculations can significantly change the inferred physical conditions. In extragalactic sources, e.g., these can compromise analyses of spectral ageing, which I will illustrate with some current work on cluster relics. I also briefly re-examine the old issue of how inhomogeneous fields affect particle lifetimes; perhaps not surprisingly, the next generation of radio telescopes are unlikely to find many sources that can extend their lifetimes from putting relativistic electrons into a low-field ‘freezer’. Finally, I preview some new EVLA results on the complex relic in Abell 2256, with implications for the interspersing of its relativistic and thermal plasmas.
Magnetic exchange couplings from noncollinear perturbation theory: dinuclear CuII complexes.
Phillips, Jordan J; Peralta, Juan E
2014-08-07
To benchmark the performance of a new method based on noncollinear coupled-perturbed density functional theory [J. Chem. Phys. 138, 174115 (2013)], we calculate the magnetic exchange couplings in a series of triply bridged ferromagnetic dinuclear Cu(II) complexes that have been recently synthesized [Phys. Chem. Chem. Phys. 15, 1966 (2013)]. We find that for any basis-set the couplings from our noncollinear coupled-perturbed methodology are practically identical to those of spin-projected energy-differences when a hybrid density functional approximation is employed. This demonstrates that our methodology properly recovers a Heisenberg description for these systems, and is robust in its predictive power of magnetic couplings. Furthermore, this indicates that the failure of density functional theory to capture the subtle variation of the exchange couplings in these complexes is not simply an artifact of broken-symmetry methods, but rather a fundamental weakness of current approximate density functionals for the description of magnetic couplings.
Effects of magnetic field on fluidization properties of magnetic pearls
Institute of Scientific and Technical Information of China (English)
Maoming Fan; Zhenfu Luo; Yuemin Zhao; Qingru Chen; Daniel Tao; Xiuxiang Tao; Zhenqiang Chen
2007-01-01
An experimental study of the influence of external magnetic field on the fluidization behavior of magnetic pearls was carried out. Magnetic pearls are a magnetic form of iron oxide that mainly consists of Fe2O3 which are recovered from a high-volume power plant fly ash from pulverized coal combustion. Due to its abundance, low price and particular physical and chemical properties, magnetic pearls can be used as a heavy medium for minerals or solid waste dry separation based on density difference. This paper introduces the properties of magnetic pearls and compares the performance of magnetic pearls fluidised bed operation with or without an external magnetic field. Experimental results show that an external magnetic field significantly improves the fluidization performance of magnetic pearls such as uniformity and stability.
Post-processing scheme for modelling the lithospheric magnetic field
Directory of Open Access Journals (Sweden)
V. Lesur
2013-03-01
Full Text Available We investigated how the noise in satellite magnetic data affects magnetic lithospheric field models derived from these data in the special case where this noise is correlated along satellite orbit tracks. For this we describe the satellite data noise as a perturbation magnetic field scaled independently for each orbit, where the scaling factor is a random variable, normally distributed with zero mean. Under this assumption, we have been able to derive a model for errors in lithospheric models generated by the correlated satellite data noise. Unless the perturbation field is known, estimating the noise in the lithospheric field model is a non-linear inverse problem. We therefore proposed an iterative post-processing technique to estimate both the lithospheric field model and its associated noise model. The technique has been successfully applied to derive a lithospheric field model from CHAMP satellite data up to spherical harmonic degree 120. The model is in agreement with other existing models. The technique can, in principle, be extended to all sorts of potential field data with "along-track" correlated errors.
Gauge-invariant perturbations at second order: multiple scalar fields on large scales
Malik, K A
2005-01-01
We derive the governing equations for multiple scalar fields minimally coupled to gravity in a flat Friedmann-Robertson-Walker (FRW) background spacetime on large scales. We include scalar perturbations up to second order and write the equations in terms of physically transparent gauge-invariant variables at first and second order. This allows us to write the perturbed Klein-Gordon equation at second order solely in terms of the field fluctuations on flat slices at first and second order.
A note on second-order perturbations of non-canonical scalar fields
Appignani, Corrado; Shankaranarayanan, S
2009-01-01
We study second-order perturbations for a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. By employing different approaches to cosmological perturbation theory, we show that, even in this simplified set-up, there arise ambiguities in the expressions of physically relevant quantities, such as the effective speed of the perturbations, and the stress tensor and energy density display a potential instability which is not present at linear order. We also discuss the significance of our analysis in light of the possible linearization instability of these fields about the FRW background.
Magnetic Helicity and Large Scale Magnetic Fields: A Primer
Blackman, Eric G
2014-01-01
Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. H...
Interaction between two magnetic dipoles in a uniform magnetic field
Directory of Open Access Journals (Sweden)
J. G. Ku
2016-02-01
Full Text Available A new formula for the interaction force between two magnetic dipoles in a uniform magnetic field is derived taking their mutual magnetic interaction into consideration and used to simulate their relative motion. Results show that when the angle β between the direction of external magnetic field and the centerline of two magnetic dipoles is 0 ° or 90 °, magnetic dipoles approach each other or move away from each other in a straight line, respectively. And the time required for them to contact each other from the initial position is related to the specific susceptibility and the diameter of magnetic particles, medium viscosity and magnetic field strength. When β is between 0 ° and 90 °, magnetic dipole pair performs approximate elliptical motion, and the motion trajectory is affected by the specific susceptibility, diameter and medium viscosity but not magnetic field strength. However, time required for magnetic dipoles to complete the same motion trajectory is shorter when adopting stronger magnetic field. Moreover, the subsequent motion trajectory of magnetic dipoles is ascertained once the initial position is set in a predetermined motion trajectory. Additionally, magnetic potential energy of magnetic dipole pairs is transformed into kinetic energy and friction energy during the motion.
Azimuthal field perturbations in the jovian magnetosphere: ulysses observations
Directory of Open Access Journals (Sweden)
T. M. Edwards
2000-01-01
Full Text Available Las perturbaciones azimutales del campo magn etico observadas por el sat elite Ulysses durante la entrada y salida de la magnet osfera joviana son comparadas con los valores calculados con la tranferencia de momento angular de la ion osfera a la magnet osfera debido a plasma magnetosf erico que no est a corrotando. Durante la entrada se observ o una con guraci on \\retrasada" del campo, correspondiente a ujos con subcorrotaci on. Se encontr o que los valores m aximos del campo azimutal disminuyen con la distancia como r
Effective magnetic moment of neutrinos in strong magnetic fields
Pérez, A; Masood, S S; Gaitan, R; Rodríguez, S
2002-01-01
In this paper we compute the effective magnetic moment of neutrinos propagating in dense high magnetized medium. Taking typical values of magnetic field and densities of astrophysical objects (such as the cores of supernovae and neutron stars) we obtain an effective type of dipole magnetic moment in agreement with astrophysical and cosmological bounds. (Author)
Microbially assisted recording of the Earth's magnetic field in sediment.
Zhao, Xiangyu; Egli, Ramon; Gilder, Stuart A; Müller, Sebastian
2016-02-11
Sediments continuously record variations of the Earth's magnetic field and thus provide an important archive for studying the geodynamo. The recording process occurs as magnetic grains partially align with the geomagnetic field during and after sediment deposition, generating a depositional remanent magnetization (DRM) or post-DRM (PDRM). (P)DRM acquisition mechanisms have been investigated for over 50 years, yet many aspects remain unclear. A key issue concerns the controversial role of bioturbation, that is, the mechanical disturbance of sediment by benthic organisms, during PDRM acquisition. A recent theory on bioturbation-driven PDRM appears to solve many inconsistencies between laboratory experiments and palaeomagnetic records, yet it lacks experimental proof. Here we fill this gap by documenting the important role of bioturbation-induced rotational diffusion for (P)DRM acquisition, including the control exerted on the recorded inclination and intensity, as determined by the equilibrium between aligning and perturbing torques acting on magnetic particles.
Probing correlations of early magnetic fields using $\\mu$-distortion
Ganc, Jonathan
2014-01-01
The damping of a non-uniform magnetic field between the redshifts of about $10^4$ and $10^6$ injects energy into the photon-baryon plasma and causes the CMB to deviate from a perfect blackbody spectrum, producing a so-called $\\mu$-distortion. We can calculate the correlation $\\langle\\mu T\\rangle$ of this distortion with the temperature anisotropy $T$ of the CMB to search for a correlation $\\langle B^2\\zeta\\rangle$ between the magnetic field $B$ and the curvature perturbation $\\zeta$. Since the perturbations which produce the $\\mu$-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of $\\langle B^2\\zeta\\rangle$, which is naturally parameterized by $b_{\\text{NL}}$ (a parameter defined analogously to $f_{\\text{NL}}$). We find that a PIXIE-like CMB experiments has a signal to noise $S/N\\approx 1.0 \\times b_{\\text{NL}} (\\tilde B_\\mu/10\\text{ nG})^2$, where $\\tilde B_\\mu$ is the magnetic field's strength on $\\mu$-disto...
Zero-temperature perturbative calculation of the magnetic susceptibility of the free fermion system
Energy Technology Data Exchange (ETDEWEB)
Ciccariello, Salvino; De Col, Alvise [Dipartimento di Fisica ' G Galilei' and Unita INFM, Padova (Italy)
2001-11-01
Using the zero-temperature perturbative expansion, we show how to obtain the correct value of the magnetic susceptibility of a system of free fermions at zero temperature. To this aim, it is first observed that the Feynman rules for the perturbative expansion of the Green function substantially do not change when the ground state is substituted with a generic eigenstate of the unperturbed system. Then, the requirement that the resulting Green function has the correct Lehmann representation uniquely determines the unperturbed eigenstate which yields the interacting ground state by adiabatically switching on the interaction. (author)
Effect of 3D magnetic perturbations on the plasma rotation in ASDEX Upgrade
Martitsch, A. F.; Kasilov, S. V.; Kernbichler, W.; Kapper, G.; Albert, C. G.; Heyn, M. F.; Smith, H. M.; Strumberger, E.; Fietz, S.; Suttrop, W.; Landreman, M.; The ASDEX Upgrade Team; the EUROfusion MST1 Team
2016-07-01
The toroidal torque due to the non-resonant interaction with external magnetic perturbations (TF ripple and perturbations from ELM mitigation coils) in ASDEX Upgrade is modelled with help of the NEO-2 and SFINCS codes and compared to semi-analytical models. It is shown that almost all non-axisymmetric transport regimes contributing to neoclassical toroidal viscosity (NTV) are realized within a single discharge at different radial positions. The NTV torque is obtained to be roughly a quarter of the NBI torque. This indicates the presence of other important momentum sources. The role of these momentum sources and possible integral torque balance measurements are briefly discussed.
SU(3)-breaking corrections to the baryon-octet magnetic moments in chiral perturbation theory
Camalich, J Martin; Geng, L S; Vacas, M J Vicente
2009-01-01
We report a calculation of the baryon magnetic moments using covariant chiral perturbation theory within the extended-on-mass-shell renormalization scheme including intermediate octet and decuplet contributions. By fitting the two available low-energy constants, we improve the Coleman-Glashow description of the data when we include the leading SU(3) breaking effects coming from the lowest-order loops. We compare with previous attempts at the same order using heavy-baryon and covariant infrared chiral perturbation theory, and discuss the source of the differences.
Strike point splitting induced by the application of magnetic perturbations on MAST
Cahyna, P; Kirk, A; Thornton, A; Harrison, J; Muir, D; Panek, R
2012-01-01
Divertor strike point splitting induced by resonant magnetic perturbations (RMPs) has been observed on MAST for a variety of RMP configurations in a plasma scenario with Ip=750kA where those configurations all have similar resonant components. Complementary measurements have been obtained with divertor Langmuir probes and an infrared camera. Clear splitting consistently appears in this scenario only in the even configuration of the perturbation coils, similarly to the density pump-out. These results present a challenge for models of plasma response to RMPs.
Magnetic field penetration of erosion switch plasmas
Mason, Rodney J.; Jones, Michael E.; Grossmann, John M.; Ottinger, Paul F.
1988-10-01
Computer simulations demonstrate that the entrainment (or advection) of magnetic field with the flow of cathode-emitted electrons can constitute a dominant mechanism for the magnetic field penetration of erosion switch plasmas. Cross-field drift in the accelerating electric field near the cathode starts the penetration process. Plasma erosion propagates the point for emission and magnetic field injection along the cathode toward the load-for the possibility of rapid switch opening.
Magnetic field reversals and galactic dynamos
2012-01-01
We argue that global magnetic field reversals similar to those observed in the Milky Way occur quite frequently in mean-field galactic dynamo models that have relatively strong, random, seed magnetic fields that are localized in discrete regions. The number of reversals decreases to zero with reduction of the seed strength, efficiency of the galactic dynamo and size of the spots of the seed field. A systematic observational search for magnetic field reversals in a representative sample of spi...
Perturbative unitarity of Lee-Wick quantum field theory
Anselmi, Damiano; Piva, Marco
2017-08-01
We study the perturbative unitarity of the Lee-Wick models, formulated as nonanalytically Wick rotated Euclidean theories. The complex energy plane is divided into disconnected regions and the values of a loop integral in the various regions are related to one another by a nonanalytic procedure. We show that the one-loop diagrams satisfy the expected, unitary cutting equations in each region: only the physical d.o.f. propagate through the cuts. The goal can be achieved by working in suitable subsets of each region and proving that the cutting equations can be analytically continued as a whole. We make explicit calculations in the cases of the bubble and triangle diagrams and address the generality of our approach. We also show that the same higher-derivative models violate unitarity if they are formulated directly in Minkowski spacetime.
Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field
Ratushnaya, Valeria
2016-12-17
We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.
Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field
Ratushnaya, Valeria; Samtaney, Ravi
2016-12-01
We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.
Probing correlations of early magnetic fields using μ-distortion
Energy Technology Data Exchange (ETDEWEB)
Ganc, Jonathan; Sloth, Martin S., E-mail: ganc@cp3.dias.sdu.dk, E-mail: sloth@cp3.dias.sdu.dk [CP" 3-Origins, Center for Cosmology and Particle Physics Phenomenology, University of Southern Denmark, Campusvej 55, 5230 Odense M (Denmark)
2014-08-01
The damping of a non-uniform magnetic field between the redshifts of about 10{sup 4} and 10{sup 6} injects energy into the photon-baryon plasma and causes the CMB to deviate from a perfect blackbody spectrum, producing a so-called μ-distortion. We can calculate the correlation (μ T) of this distortion with the temperature anisotropy T of the CMB to search for a correlation ( B{sup 2}ζ) between the magnetic field B and the curvature perturbation ζ; knowing the ( B{sup 2}ζ) correlation would help us distinguish between different models of magnetogenesis. Since the perturbations which produce the μ-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of ( B{sup 2}ζ), which is naturally parameterized by b{sub NL} (a parameter defined analogously to f{sub NL}). We find that a PIXIE-like CMB experiments has a signal to noise S/N≈ 1.0 × b{sub NL} ( B-tilde {sub μ}/10nG){sup 2}, where B-tilde {sub μ} is the magnetic field's strength on μ-distortion scales normalized to today's redshift; thus, a 10 nG field would be detectable with b{sub NL}=O(1). However, if the field is of inflationary origin, we generically expect it to be accompanied by a curvature bispectrum (ζ{sup 3}) induced by the magnetic field. For sufficiently small magnetic fields, the signal ( B{sup 2} ζ) will dominate, but for B-tilde {sub μ}∼> 1 nG, one would have to consider the specifics of the inflationary magnetogenesis model. We also discuss the potential post-magnetogenesis sources of a ( B{sup 2}ζ) correlation and explain why there will be no contribution from the evolution of the magnetic field in response to the curvature perturbation.
Towards understanding edge localised mode mitigation by resonant magnetic perturbations in MAST
Chapman, I T; Ham, C J; Harrison, J R; Liu, Y Q; Saarelma, S; Scannell, R; Thornton, A J; Becoulet, M; Orain, F; Cooper, W A; Pamela, S
2013-01-01
Type-I Edge Localised Modes (ELMs) have been mitigated in MAST through the application of n = 3, 4 and 6 resonant magnetic perturbations (RMPs). For each toroidal mode number of the non-axisymmetric applied fields, the frequency of the ELMs has been increased significantly, and the peak heat flux on the divertor plates reduced commensurately. This increase in ELM frequency occurs despite a significant drop in the edge pressure gradient, which would be expected to stabilise the peeling-ballooning modes thought to be responsible for type-I ELMs. Various mechanisms which could cause a destabilisation of the peeling-ballooning modes are presented, including pedestal widening, plasma rotation braking, three dimensional corrugation of the plasma boundary and the existence of radially extended lobe structures near to the X-point. This leads to a model aimed at resolving the apparent dichotomy of ELM control, that is to say ELM suppression occurring due to the pedestal pressure reduction below the peeling-ballooning ...
Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations
Energy Technology Data Exchange (ETDEWEB)
Orain, F.; Bécoulet, M.; Dif-Pradalier, G.; Nardon, E.; Passeron, C.; Latu, G.; Grandgirard, V.; Fil, A.; Ratnani, A. [CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France); Huijsmans, G. [ITER Organization, Route de Vinon, F-13115 Saint-Paul-Lez-Durance (France); Pamela, S. [IIFS-PIIM. Aix Marseille Université - CNRS, 13397 Marseille Cedex20 (France); Chapman, I.; Kirk, A.; Thornton, A. [EURATOM/CCFE Fusion Association, Culham Science Centre, Oxon OX14 3DB (United Kingdom); Hoelzl, M. [Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching (Germany); Cahyna, P. [Association EURATOM/IPP.CR, Prague (Czech Republic)
2013-10-15
The interaction of static Resonant Magnetic Perturbations (RMPs) with the plasma flows is modeled in toroidal geometry, using the non-linear resistive MHD code JOREK, which includes the X-point and the scrape-off-layer. Two-fluid diamagnetic effects, the neoclassical poloidal friction and a source of toroidal rotation are introduced in the model to describe realistic plasma flows. RMP penetration is studied taking self-consistently into account the effects of these flows and the radial electric field evolution. JET-like, MAST, and ITER parameters are used in modeling. For JET-like parameters, three regimes of plasma response are found depending on the plasma resistivity and the diamagnetic rotation: at high resistivity and slow rotation, the islands generated by the RMPs at the edge resonant surfaces rotate in the ion diamagnetic direction and their size oscillates. At faster rotation, the generated islands are static and are more screened by the plasma. An intermediate regime with static islands which slightly oscillate is found at lower resistivity. In ITER simulations, the RMPs generate static islands, which forms an ergodic layer at the very edge (ψ≥0.96) characterized by lobe structures near the X-point and results in a small strike point splitting on the divertor targets. In MAST Double Null Divertor geometry, lobes are also found near the X-point and the 3D-deformation of the density and temperature profiles is observed.
Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations
Orain, F.; Bécoulet, M.; Dif-Pradalier, G.; Huijsmans, G.; Pamela, S.; Nardon, E.; Passeron, C.; Latu, G.; Grandgirard, V.; Fil, A.; Ratnani, A.; Chapman, I.; Kirk, A.; Thornton, A.; Hoelzl, M.; Cahyna, P.
2013-10-01
The interaction of static Resonant Magnetic Perturbations (RMPs) with the plasma flows is modeled in toroidal geometry, using the non-linear resistive MHD code JOREK, which includes the X-point and the scrape-off-layer. Two-fluid diamagnetic effects, the neoclassical poloidal friction and a source of toroidal rotation are introduced in the model to describe realistic plasma flows. RMP penetration is studied taking self-consistently into account the effects of these flows and the radial electric field evolution. JET-like, MAST, and ITER parameters are used in modeling. For JET-like parameters, three regimes of plasma response are found depending on the plasma resistivity and the diamagnetic rotation: at high resistivity and slow rotation, the islands generated by the RMPs at the edge resonant surfaces rotate in the ion diamagnetic direction and their size oscillates. At faster rotation, the generated islands are static and are more screened by the plasma. An intermediate regime with static islands which slightly oscillate is found at lower resistivity. In ITER simulations, the RMPs generate static islands, which forms an ergodic layer at the very edge (ψ ≥0.96) characterized by lobe structures near the X-point and results in a small strike point splitting on the divertor targets. In MAST Double Null Divertor geometry, lobes are also found near the X-point and the 3D-deformation of the density and temperature profiles is observed.
Suzuki, H
2003-01-01
We derive the superpotential of gauge theories having matter fields in the fundamental representation of gauge fields by using the method of Dijkgraaf and Vafa. We treat the theories with one flavour and reproduce a well-known non-perturbative superpotential for meson field.
Lie Symmetries of Quasihomogeneous Polynomial Planar Vector Fields and Certain Perturbations
Institute of Scientific and Technical Information of China (English)
Javier CHAVARRIGA; Isaac A. GARC(I)A
2005-01-01
In this work we study Lie symmetries of planar quasihomogeneous polynomial vector fields from different points of view, showing its integrability. Additionally, we show that certain perturbations of such vector fields which generalize the so-called degenerate infinity vector fields are also integrable.
Microscopic Processes in Global Relativistic Jets Containing Helical Magnetic Fields
Nishikawa, Ken-Ichi; Niemiec, Jacek; Kobzar, Oleh; Pohl, Martin; Gomez, Jose L; Dutan, Ioana; Pe'er, Asaf; Frederiksen, Jacob Trier; Nordlund, AAke; Meli, Athina; Sol, Helene; Hardee, Philip E; Hartmann, Dieter H
2016-01-01
In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron$-$proton ($e^{-}-p^{+}$) and electron$-$positron ($e^{\\pm}$) relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of "global" jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the Mushroom instability (MI). In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the $e^{-}-p^{+}$ jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the $e^{\\pm}$ jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to ...
Near-Field Magnetic Dipole Moment Analysis
Harris, Patrick K.
2003-01-01
This paper describes the data analysis technique used for magnetic testing at the NASA Goddard Space Flight Center (GSFC). Excellent results have been obtained using this technique to convert a spacecraft s measured magnetic field data into its respective magnetic dipole moment model. The model is most accurate with the earth s geomagnetic field cancelled in a spherical region bounded by the measurement magnetometers with a minimum radius large enough to enclose the magnetic source. Considerably enhanced spacecraft magnetic testing is offered by using this technique in conjunction with a computer-controlled magnetic field measurement system. Such a system, with real-time magnetic field display capabilities, has been incorporated into other existing magnetic measurement facilities and is also used at remote locations where transport to a magnetics test facility is impractical.
Magnetic Fields from the Electroweak Phase Transition
Törnkvist, O
1998-01-01
I review some of the mechanisms through which primordial magnetic fields may be created in the electroweak phase transition. I show that no magnetic fields are produced initially from two-bubble collisions in a first-order transition. The initial field produced in a three-bubble collision is computed. The evolution of fields at later times is discussed.
Strong and superstrong pulsed magnetic fields generation
Shneerson, German A; Krivosheev, Sergey I
2014-01-01
Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.
Deformation of Water by a Magnetic Field
Chen, Zijun; Dahlberg, E. Dan
2011-01-01
After the discovery that superconducting magnets could levitate diamagnetic objects, researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields, which was given the name "The Moses Effect." Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary…
Exploring Magnetic Fields with a Compass
Lunk, Brandon; Beichner, Robert
2011-01-01
A compass is an excellent classroom tool for the exploration of magnetic fields. Any student can tell you that a compass is used to determine which direction is north, but when paired with some basic trigonometry, the compass can be used to actually measure the strength of the magnetic field due to a nearby magnet or current-carrying wire. In this…
Biological Effect of Magnetic Field in Mice
Institute of Scientific and Technical Information of China (English)
Zhao-Wei ZENG
2005-01-01
Objective: To study the biological effect of magnetic field in mice bodies. Method: With a piece of permanent magnet embeded in mice bodies beside the femoral artery and vein to measure the electrophoretic velocity(um/s). Result: The magnetic field in mice bodies on the experiment group that the electrophoretic velocity is faster more than control and free group.Conclusion:The magnetic field in animal's body can raise the negative electric charges on the surface of erythrocyte to improve the microcirculation, this is the biological effect of magnetic field.
The Magnetic Field Effect on Planetary Nebulae
Institute of Scientific and Technical Information of China (English)
A. R. Khesali; K. Kokabi
2006-01-01
In our previous work on the 3-dimensional dynamical structure of planetary nebulae the effect of magnetic field was not considered. Recently Jordan et al. have directly detected magnetic fields in the central stars of some planetary nebulae. This discovery supports the hypothesis that the non-spherical shape of most planetary nebulae is caused by magnetic fields in AGB stars. In this study we focus on the role of initially weak toroidal magnetic fields embedded in a stellar wind in altering the shape of the PN. We found that magnetic pressure is probably influential on the observed shape of most PNe.
Magnetic field concentrator for probing optical magnetic metamaterials.
Antosiewicz, Tomasz J; Wróbel, Piotr; Szoplik, Tomasz
2010-12-06
Development of all dielectric and plasmonic metamaterials with a tunable optical frequency magnetic response creates a need for new inspection techniques. We propose a method of measuring magnetic responses of such metamaterials within a wide range of optical frequencies with a single probe. A tapered fiber probe with a radially corrugated metal coating concentrates azimuthally polarized light in the near-field into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one. The active probe may be used in a future scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of metamaterials.
Electrolytic tiltmeters inside magnetic fields: Some observations
Energy Technology Data Exchange (ETDEWEB)
Alberdi, J. [CIEMAT, Madrid (Spain); Arce, P. [CIEMAT, Madrid (Spain); Barcala, J.M. [CIEMAT, Madrid (Spain); Calvo, E. [CIEMAT, Madrid (Spain); Ferrando, A. [CIEMAT, Madrid (Spain)]. E-mail: antonio.ferrando@ciemat.es; Josa, M.I. [CIEMAT, Madrid (Spain); Luque, J.M. [CIEMAT, Madrid (Spain); Molinero, A. [CIEMAT, Madrid (Spain); Navarrete, J. [CIEMAT, Madrid (Spain); Oller, J.C. [CIEMAT, Madrid (Spain); Yuste, C. [CIEMAT, Madrid (Spain); Calderon, A. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Garcia-Moral, L.A. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Gomez, G. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Gonzalez-Sanchez, F.J. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Martinez-Rivero, C. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Matorras, F. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Rodrigo, T. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Ruiz-Arbol, P. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Scodellaro, L. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Sobron, M. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Vila, I. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Virto, A.L. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain)
2007-04-21
We present observations of the electrolytic clinometers behaviour inside magnetic field environments introducing phenomenological expressions to account for the measured output voltage variations as functions of field gradients and field strengths.
From Inverse to Delayed Magnetic Catalysis in Strong Magnetic Field
Mao, Shijun
2016-01-01
We study magnetic field effect on chiral phase transition in a Nambu--Jona-Lasinio model. In comparison with mean field approximation containing quarks only, including mesons as quantum fluctuations in the model leads to a transition from inverse to delayed magnetic catalysis at finite temperature and delays the transition at finite baryon chemical potential. The location of the critical end point depends on the the magnetic field non-monotonously.
Dynamic shielding of the magnetic fields
Directory of Open Access Journals (Sweden)
RAU, M.
2010-11-01
Full Text Available The paper presents a comparative study of the methods used to control and compensate the direct and alternative magnetic fields. Two frequently used methods in the electromagnetic compatibility of the complex biomagnetism installations were analyzed. The two methods refer to the use of inductive magnetic field sensors (only for alternative fields and of fluxgate magnetometers as active transducers which measures both the direct and alternative components of the magnetic field. The applications of the dynamic control of the magnetic field are: control of the magnetic field of the military ships, control of parasite magnetic field produced by power transformers and the electrical networks, protection of the mass spectrometers, electronic microscopes, SQUID and optical pumping magnetometers for applications in biomagnetism.
Masses and magnetic moments of ground-state baryons in covariant baryon chiral perturbation theory
Geng, L S; Alvarez-Ruso, L; Vicente-Vacas, M J
2012-01-01
We report on some recent developments in our understanding of the light-quark mass dependence and the SU(3) flavor symmetry breaking corrections to the magnetic moments of the ground-state baryons in a covariant formulation of baryon chiral perturbation theory, the so-called EOMS formulation. We show that this covariant ChPT exhibits some promising features compared to its heavy-baryon and infrared counterparts.
Perturbative Expansion around the Gaussian Effective Potential of the Fermion Field Theory
Lee, G H; Yee, J H; Lee, Geon Hyoung; Lee, Tack Hwi; Yee, Jae Hyung
1998-01-01
We have extended the perturbative expansion method around the Gaussian effective action to the fermionic field theory, by taking the 2-dimensional Gross-Neveu model as an example. We have computed both the zero temperature and the finite temperature effective potentials of the Gross-Neveu model up to the first perturbative correction terms, and have found that the critical temperature, at which dynamically broken symmetry is restored, is significantly improved for small value of the flavour number.
Interaction Between Massive and Massless Gravitons by Perturbing Topological Field Theory
Institute of Scientific and Technical Information of China (English)
E. Koorambas
2012-01-01
We test the Wu gauge theory of gravity with massive gravitons in the perturbing topological field theory framework. We show that the computation of the correlation function between massive and massless gravitons is reported up to 4-loop and appears to be unaffected by radiative correction. This result ensures the stability of the linking number between massive and massless gravitons with respect to the local perturbation, a result with potential wider applications in cosmology.
Field free line magnetic particle imaging
Erbe, Marlitt
2014-01-01
Marlitt Erbe provides a detailed introduction into the young research field of Magnetic Particle Imaging (MPI) and field free line (FFL) imaging in particular. She derives a mathematical description of magnetic field generation for FFL imaging in MPI. To substantiate the simulation studies on magnetic FFL generation with a proof-of-concept, the author introduces the FFL field demonstrator, which provides the world's first experimentally generated rotated and translated magnetic FFL field complying with the requirements for FFL reconstruction. Furthermore, she proposes a scanner design of consi
Leading-order decuplet contributions to the baryon magnetic moments in chiral perturbation theory
Energy Technology Data Exchange (ETDEWEB)
Geng, L.S. [Departamento de Fisica Teorica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigacion de Paterna, 46071-Valencia (Spain); Camalich, J. Martin [Departamento de Fisica Teorica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigacion de Paterna, 46071-Valencia (Spain)], E-mail: camalich@ific.uv.es; Vacas, M.J. Vicente [Departamento de Fisica Teorica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigacion de Paterna, 46071-Valencia (Spain)
2009-06-01
We extend an earlier study of the baryon magnetic moments in chiral perturbation theory by the explicit inclusion of the spin-3/2 decuplet resonances. We find that the corrections induced by these heavier degrees of freedom are relatively small in a covariant framework where unphysical spin-1/2 modes are removed. Consequently, implementing the leading SU(3)-breaking corrections given by both the baryon and decuplet contributions, we obtain a description of the baryon-octet magnetic moments that is better than the Coleman-Glashow relations. Finally, we discuss the uncertainties and compare between heavy baryon and covariant approaches.
Leading-order decuplet contributions to the baryon magnetic moments in Chiral Perturbation Theory
Geng, L S; Vacas, M J Vicente
2009-01-01
We extend an earlier study of the baryon magnetic moments in chiral perturbation theory by the explicit inclusion of the spin-3/2 decuplet resonances. We find that the corrections induced by these heavier degrees of freedom are relatively small in a covariant framework where unphysical spin-1/2 modes are removed. Consequently, implementing the leading SU(3)-breaking corrections given by both the baryon and decuplet contributions, we obtain a description of the baryon-octet magnetic moments that is better than the Coleman-Glashow relations. Finally, we discuss the uncertainties and compare between heavy baryon and covariant approaches.
Full particle orbit effects in regular and stochastic magnetic fields
Ogawa, Shun; Leoncini, Xavier; Vittot, Michel; del Castillo-Negrete, Diego; Dif-Pradalier, Guilhem; Garbet, Xavier
2016-01-01
We study numerically the motion of a charged particle evolving in a periodic cylindric static magnetic field, in order to investigate a magnetic model of internal transport barrier (ITB). Starting from an initial ideal configuration with a given q-profile, we perturb the magnetic structure by adding first only one mode, and then two modes. In the first two considered cases magnetic field lines are integrable, while they become chaotic when two modes are present. Regarding the particle motion, while it is integrable in the ideal configuration, we show that generic chaotic motion arises as soon as one of the magnetic mode is present. Given the presence of two conserved quantities, the existence of chaos in phase space implies that a conserved quantity related to the magnetic moment cannot exist globally in phase space. Regarding the motion when two modes are present and magnetic field lines are chaotic, the particles trajectory analysis indicates that the regions where chaotic motion occurs decreases as the ene...
Magnetic field mapper based on rotating coils
AUTHOR|(CDS)2087244; Arpaia, Pasquale
This thesis presents a magnetic field mapper based on rotating coils. The requirements, the architecture, the conceptual design, and the prototype for straight magnets were shown. The proposed system is made up of a rotating coil transducer and a train-like system for longitudinal motion and positioning inside magnet bore. The mapper allows a localized measurement of magnetic fields and the variation of the harmonic multipole content in the magnet ends. The proof-of-principle demonstration and the experimental characterization of the rotating-coil transducer specifically conceived for mapping validated the main objective of satisfying the magnetic measurement needs of the next generation of compact accelerators.
Magnetic Fields and Star Formation
Van Loo, S; Falle, S A E G
2012-01-01
Research performed in the 1950s and 1960s by Leon Mestel on the roles of magnetic fields in star formation established the framework within which he and other key figures have conducted subsequent investigations on the subject. This short tribute to Leon contains a brief summary of some, but not all, of his ground breaking contributions in the area. It also mentions of some of the relevant problems that have received attention in the last few years. The coverage is not comprehensive, and the authors have drawn on their own results more and touched more briefly on those of others than they would in a normal review. Theirs is a personal contribution to the issue honouring Leon, one of the truly great gentlemen, wits, and most insightful of astrophysicists.
Nonequilibrium Transport through a Kondo-dot in a Magnetic Field
DEFF Research Database (Denmark)
Wölfle, Peter; Rosch, Achim; Paaske, Jens;
2002-01-01
Electron transport through a quantum-dot in the Coulomb blockade regime is modeled by a Kondo-type hamiltonian describing spin-dependent tunneling and exchange interaction with the local spin. We consider the regime of large transport voltage V and magnetic field B with max(V, B) » Tk, the Kondo...... temperature, and show that a renormalized perturbation theory can be formulated describing the local magnetization M and the differential conductance G quantitatively. Based on the structure of leading logarithmic corrections in bare perturbation theory we argue that the perturbative renormalization group has...
Electron thermal self-energy in a magnetic field
Persson, D
1995-01-01
Using the general form of the static energy solutions to the Dirac equation with a magnetic field, we calculate a general self-energy matrix in the Furry-picture. In the limit of high temperatures, but even higher magnetic fields, a self-consistent dispersion relation is solved. In contrast to the high temperature limit, this merely results in a small mass shift. The electron anomalous magnetic moment is calculated. The contribution from thermal fermions is found to be different from the corresponding contribution using perturbation theory and plane-wave external states. In the low temperature limit the self-energy is shown to exhibit de Haas--van Alphen oscillations. In the limit of low temperatures and high densities, the self-energy becomes very large.
Ambitwistor Strings: Worldsheet Approaches to perturbative Quantum Field Theories
Geyer, Yvonne
2016-01-01
Tree-level scattering amplitudes in massless theories not only exhibit a simplicity entirely unexpected from Feynman diagrams, but also an underlying structure remarkably reminiscent of worldsheet theory correlators. These features can be explained by ambitwistor strings - two-dimensional chiral conformal field theories in an auxiliary target space, the complexified phase space of null geodesics. The aim of this thesis is to explore the ambitwistor string approach to understand these structures in amplitudes, and thereby provide a new angle on quantum field theories. The first part of the thesis provides a user-friendly introduction to ambitwistor strings, as well as a condensed overview over the literature and some novel results. Emphasising the study of tree-level amplitudes, we then explore the wide-ranging impact of ambitwistor strings for an extensive family of massless theories, and discuss the duality between asymptotic symmetries and the low energy behaviour of a theory from the point of view of the w...
DC-based magnetic field controller
Energy Technology Data Exchange (ETDEWEB)
Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)
1994-01-01
A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.
DC-based magnetic field controller
Energy Technology Data Exchange (ETDEWEB)
Kotter, D.K.; Rankin, R.A.; Morgan, J.P.
1994-05-31
A magnetic field controller is described for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a Hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage. 1 fig.
High magnetic fields science and technology
Miura, Noboru
2003-01-01
This three-volume book provides a comprehensive review of experiments in very strong magnetic fields that can only be generated with very special magnets. The first volume is entirely devoted to the technology of laboratory magnets: permanent, superconducting, high-power water-cooled and hybrid; pulsed magnets, both nondestructive and destructive (megagauss fields). Volumes 2 and 3 contain reviews of the different areas of research where strong magnetic fields are an essential research tool. These volumes deal primarily with solid-state physics; other research areas covered are biological syst
Trapped magnetic field measurements on HTS bulk by peak controlled pulsed field magnetization
Energy Technology Data Exchange (ETDEWEB)
Ida, Tetsuya; Watasaki, Masahiro [Department of Electronic Control Engineering, Hiroshima National College of Maritime Technology, 4272-1, Higashino, Ohsakikamijima-cho, Toyota-gun, Hiroshima 725-0231 (Japan); Kimura, Yosuke [Kawasaki Heavy Industries, Ltd. Technical Institute System Technology Development Centre 1-1, Kawasaki-cho, Akashi-shi, Hyogo 673-8666 (Japan); Miki, Motohiro; Izumi, Mitsuru, E-mail: ida@hiroshima-cmt.ac.j [Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, 2-1-6, Etchu-jima, Koto-ku, Tokyo 135-8533 (Japan)
2010-06-01
For the past several years, we have studied the high-temperature superconducting (HTS) synchronous motor assembled with melt-textured Gd-Ba-Cu-O bulk magnets. If the single pulse field magnetizes a bulk effectively, size of electrical motor will become small for the strong magnetic field of the HTS magnets without reducing output power of motor. In the previous study, we showed that the HTS bulk was magnetized to excellent cone-shape magnetic field distribution by using the waveform control pulse magnetization (WCPM) method. The WCPM technique made possible the active control of the waveform on which magnetic flux motion depended. We generated the pulse waveform with controlled risetime for HTS bulk magnetization to suppress the magnetic flux motion which decreases magnetization efficiency. The pulsed maximum magnetic flux density with slow risetime is not beyond the maximum magnetic flux density which is trapped by the static field magnetization. But, as for applying the pulse which has fast risetime, the magnetic flux which exceed greatly the threshold penetrates the bulk and causes the disorder of the trapped magnetic distribution. This fact suggests the possibility that the threshold at pulsed magnetization influences the dynamic magnetic flux motion. In this study, Gd-Ba-Cu-O bulk is magnetized by the controlled arbitrary trapezoidal shape pulse, of which the maximum magnetic flux density is controlled not to exceed the threshold. We will present the trapped magnetic characteristics and the technique to generate the controlled pulsed field.
Magnetic field evolution in tidal disruption events
Bonnerot, Clément; Lodato, Giuseppe; Rossi, Elena M
2016-01-01
When a star gets tidally disrupted by a supermassive black hole, its magnetic field is expected to be transmitted to the debris. In this paper, we study this process via smoothed particle magnetohydrodynamical simulations of the disruption and early debris evolution including the stellar magnetic field. As the gas stretches into a stream, we show that the magnetic field evolution is strongly dependent on its orientation with respect to the stretching direction. In particular, an alignment of the field lines with the direction of stretching induces an increase of the magnetic energy. For disruptions happening well within the tidal radius, the star compression causes the magnetic field strength to sharply increase by an order of magnitude at the time of pericentre passage. If the disruption is partial, we find evidence for a dynamo process occurring inside the surviving core due to the formation of vortices. This causes an amplification of the magnetic field strength by a factor of $\\sim 10$. However, this valu...
Synchrotron Applications of High Magnetic Fields
Energy Technology Data Exchange (ETDEWEB)
NONE
2006-07-01
This workshop aims at discussing the scientific potential of X-ray diffraction and spectroscopy in magnetic fields above 30 T. Pulsed magnetic fields in the range of 30 to 40 T have recently become available at Spring-8 and the ESRF (European synchrotron radiation facility). This document gathers the transparencies of the 6 following presentations: 1) pulsed magnetic fields at ESRF: first results; 2) X-ray spectroscopy and diffraction experiments by using mini-coils: applications to valence state transition and frustrated magnet; 3) R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}: an ideal system to be studied in X-ray under high magnetic field?; 4) high field studies at the Advanced Photon Source: present status and future plans; 5) synchrotron X-ray diffraction studies under extreme conditions; and 6) projects for pulsed and steady high magnetic fields at the ESRF.
Demagnetizing fields in active magnetic regenerators
DEFF Research Database (Denmark)
Nielsen, Kaspar Kirstein; Bahl, Christian R.H.; Smith, Anders
2014-01-01
is in general both a function of the overall shape of the regenerator and its morphology (packed particles, parallel plates etc.) as well as the magnetization of the material. Due to the pronounced temperature dependence of the magnetization near the Curie temperature, the demagnetization field is also......A magnetic material in an externally applied magnetic field will in general experience a spatially varying internal magnetic field due to demagnetizing effects. When the performance of active magnetic regenerators (AMRs) is evaluated using numerical models the internal field is often assumed...... temperature dependent. We propose a relatively straightforward method to correct sufficiently for the demagnetizing field in AMR models. We discuss how the demagnetizing field behaves in regenerators made of packed spheres under realistic operation conditions....
New knowledge of the Galactic magnetic fields
Han, J L
2009-01-01
The magnetic fields of our Milky Way galaxy are the main agent for cosmic rays to transport. In the last decade, much new knowledge has been gained from measurements of the Galactic magnetic fields. In the Galactic disk, from the RMs of a large number of newly discovered pulsars, the large-scale magnetic fields along the spiral arms have been delineated in a much larger region than ever before, with alternating directions in the arm and interarm regions. The toroidal fields in the Galactic halo were revealed to have opposite directions below and above the Galactic plane, which is an indication of an A0 mode dynamo operating in the halo. The strength of large-scale fields obtained from pulsar RM data has been found to increase exponentially towards the Galactic center. Compared to the steep Kolmogorov spectrum of magnetic energy at small scales, the large-scale magnetic fields show a shallow broken spatial magnetic energy spectrum.
Behaviour of ferrocholesterics under external magnetic fields
Petrescu, Emil; Motoc, Cornelia
2001-08-01
The influence of an external magnetic field on the orientational behaviour of a ferrocholesteric with a positive magnetic anisotropy is investigated. Both the phenomena arising when the field was switched on or switched off are considered. It is found that the field needed for a ferrocholesteric-ferronematic transition BFC↑ is higher when compared to that obtained for the pure cholesteric ( BC↑). A similar result was obtained when estimating the critical field for the homeotropic ferronematic-ferrocholesteric (focal conic) transition, occurring when the magnetic field was decreased or switched off. We found that BFC↓> BC↓. These results are explained when considering that the magnetic moments of the magnetic powder are not oriented parallel to the liquid crystal molecular directors, therefore hindering their orientation under a magnetic field.
Coulomb crystals in the magnetic field
Baiko, D A
2009-01-01
The body-centered cubic Coulomb crystal of ions in the presence of a uniform magnetic field is studied using the rigid electron background approximation. The phonon mode spectra are calculated for a wide range of magnetic field strengths and for several orientations of the field in the crystal. The phonon spectra are used to calculate the phonon contribution to the crystal energy, entropy, specific heat, Debye-Waller factor of ions, and the rms ion displacements from the lattice nodes for a broad range of densities, temperatures, chemical compositions, and magnetic fields. Strong magnetic field dramatically alters the properties of quantum crystals. The phonon specific heat increases by many orders of magnitude. The ion displacements from their equilibrium positions become strongly anisotropic. The results can be relevant for dusty plasmas, ion plasmas in Penning traps, and especially for the crust of magnetars (neutron stars with superstrong magnetic fields $B \\gtrsim 10^{14}$ G). The effect of the magnetic ...
Generating the optimal magnetic field for magnetic refrigeration
DEFF Research Database (Denmark)
Bjørk, Rasmus; Insinga, Andrea Roberto; Smith, Anders
2016-01-01
remanence distribution for any desired magnetic field. The method is based on the reciprocity theorem, which through the use of virtual magnets can be used to calculate the optimal remanence distribution. Furthermore, we present a method for segmenting a given magnet design that always results...
Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane
Pant, Bharat B. (Inventor); Wan, Hong (Inventor)
2001-01-01
A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.
Three-dimensional photogrammetric measurement of magnetic field lines in the WEGA stellarator
Energy Technology Data Exchange (ETDEWEB)
Drewelow, Peter; Braeuer, Torsten; Otte, Matthias; Wagner, Friedrich; Werner, Andreas [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Wendelsteinstr. 1, D-17491 Greifswald (Germany)
2009-12-15
The magnetic confinement of plasmas in fusion experiments can significantly degrade due to perturbations of the magnetic field. A precise analysis of the magnetic field in a stellarator-type experiment utilizes electrons as test particles following the magnetic field line. The usual fluorescent detector for this electron beam limits the provided information to two-dimensional cut views at certain toroidal positions. However, the technique described in this article allows measuring the three-dimensional structure of the magnetic field by means of close-range photogrammetry. After testing and optimizing the main diagnostic components, measurements of the magnetic field lines were accomplished with a spatial resolution of 5 mm. The results agree with numeric calculations, qualifying this technique as an additional tool to investigate magnetic field configurations in a stellarator. For a possible future application, ways are indicated on how to reduce experimental error sources.
Three-dimensional photogrammetric measurement of magnetic field lines in the WEGA stellarator.
Drewelow, Peter; Bräuer, Torsten; Otte, Matthias; Wagner, Friedrich; Werner, Andreas
2009-12-01
The magnetic confinement of plasmas in fusion experiments can significantly degrade due to perturbations of the magnetic field. A precise analysis of the magnetic field in a stellarator-type experiment utilizes electrons as test particles following the magnetic field line. The usual fluorescent detector for this electron beam limits the provided information to two-dimensional cut views at certain toroidal positions. However, the technique described in this article allows measuring the three-dimensional structure of the magnetic field by means of close-range photogrammetry. After testing and optimizing the main diagnostic components, measurements of the magnetic field lines were accomplished with a spatial resolution of 5 mm. The results agree with numeric calculations, qualifying this technique as an additional tool to investigate magnetic field configurations in a stellarator. For a possible future application, ways are indicated on how to reduce experimental error sources.
Nonlinear energy dissipation of magnetic nanoparticles in oscillating magnetic fields
Soto-Aquino, D.; Rinaldi, C.
2015-11-01
The heating of magnetic nanoparticle suspensions subjected to alternating magnetic fields enables a variety of emerging applications such as magnetic fluid hyperthermia and triggered drug release. Rosensweig (2002) [25] obtained a model for the heat dissipation rate of a collection of non-interacting particles. However, the assumptions made in this analysis make it rigorously valid only in the limit of small applied magnetic field amplitude and frequency (i.e., values of the Langevin parameter that are much less than unity and frequencies below the inverse relaxation time). In this contribution we approach the problem from an alternative point of view by solving the phenomenological magnetization relaxation equation exactly for the case of arbitrary magnetic field amplitude and frequency and by solving a more accurate magnetization relaxation equation numerically. We also use rotational Brownian dynamics simulations of non-interacting magnetic nanoparticles subjected to an alternating magnetic field to estimate the rate of energy dissipation and compare the results of the phenomenological theories to the particle-scale simulations. The results are summarized in terms of a normalized energy dissipation rate and show that Rosensweig's expression provides an upper bound on the energy dissipation rate achieved at high field frequency and amplitude. Estimates of the predicted dependence of energy dissipation rate, quantified as specific absorption rate (SAR), on magnetic field amplitude and frequency, and particle core and hydrodynamic diameter, are also given.
Beam Transport in Toroidal Magnetic Field
Joshi, N; Meusel, O; Ratzinger, U
2016-01-01
The concept of a storage ring with toroidal magnetic field was presented in the two previous EPAC conferences. Here we report the first results of experiments performed with beam transport in toroidal magnetic fields and details of the injection system. The beam transport experiments were carried out with 30 degree toroidal segments with an axial magnetic field of 0.6T. The multi turn injection system relies on a transverse injection coil together with an electric kicker system.
Microscopic Processes in Global Relativistic Jets Containing Helical Magnetic Fields
Directory of Open Access Journals (Sweden)
Ken-Ichi Nishikawa
2016-09-01
Full Text Available In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron–proton ( e − – p + and electron–positron ( e ± relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of “global” jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI and the Mushroom instability (MI. In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the e − – p + jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the e ± jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to a simulation without helical magnetic field. Simulations using much larger systems are required in order to thoroughly follow the evolution of global jets containing helical magnetic fields.
Effect of Resonant Magnetic Perturbations on 3D equilibria in the MST RFP
Munaretto, Stefano
2015-11-01
The orientation of 3D, stellarator-like equilibria in the MST RFP can now be controlled with application of an m = 1 RMP. This has led to greatly improved diagnosis, revealing enhancements in both the central electron temperature and density. Coupled to a recent advance in the V3FIT code, reconstructions of the 3D equilibria have also been dramatically improved. The RMP also inhibits the generation of high-energy >20 keV electrons that is otherwise common with the 3D state. This state occurs when the normally broad spectrum of core-resonant m = 1 tearing modes condenses, with the innermost resonant mode growing to large amplitude, reaching ~ 8% of the axisymmetric field strength. This occurs in plasmas of sufficiently large Lundquist number ~ IpTe3/2, and the duration of the state is maximized with zero applied Bt (infinite toroidal beta). As the dominant mode grows, eddy current in MST's conducting shell slows the mode's rotation. This leads to locking of the 3D structure, but with an orientation that varies randomly shot to shot, making diagnosis difficult. An m = 1 RMP can now be applied with an array of saddle coils at the vertical insulated cut in the shell. With an amplitude br/B ~ 10% and a tailored temporal waveform, the RMP can force the 3D structure into any desired orientation relative to MST's diagnostics. A recent advance in V3FIT allows calculation of the substantial helical image current flowing in MST's shell, which has in turn allowed self-consistent utilization of both external and internal (Faraday rotation) measurements of the magnetic field. The ORBIT code predicts reduced stochasticity and improved confinement of high-energy electrons within the 3D structure. The suppression of these electrons by the m = 1 RMP may reflect a change to the central magnetic topology. The generation of these electrons is unaffected by non-resonant perturbations, such as m = 3. Supported by the US DOE.
Magnetically modified bioсells in constant magnetic field
Abramov, E. G.; Panina, L. K.; Kolikov, V. A.; Bogomolova, E. V.; Snetov, V. N.; Cherepkova, I. A.; Kiselev, A. A.
2017-02-01
Paper addresses the inverse problem in determining the area, where the external constant magnetic field captures the biological cells modified by the magnetic nanoparticles. Zero velocity isolines, in area where the modified cells are captured by the magnetic field were determined by numerical method for two locations of the magnet. The problem was solved taking into account the gravitational field, magnetic induction, density of medium, concentration and size of cells, and size and magnetization of nanoparticles attached to the cell. Increase in the number of the nanoparticles attached to the cell and decrease in the cell' size, enlarges the area, where the modified cells are captured and concentrated by the magnet. Solution is confirmed by the visible pattern formation of the modified cells Saccharomyces cerevisiae.
On Second Order Gauge Invariant Perturbations in Multi-Field Inflationary Models
Rigopoulos, G I
2002-01-01
In a recent letter [1] Acquaviva et. al presented results from a second order calculation for a single field inflationary model. In this paper we elaborate on their approach. We present equations for the second order superhorizon perturbations of a generic multi field model. We utilise a change of coordinates in field space - first presented in [2] and given a more geometrical flavour here - to separate isocurvature and adiabatic perturbations and construct gauge invariant variables related to them to second order. Explicit relations are given for two scalar fields on a flat field manifold although the results can be generalised to curved field manifolds and an arbitrary number of fields. This is an outline of a possible procedure to study nonlinear and nongaussian effects during multifield inflation. For a more detailed discussion we refer to a future publication [12].
Statistical Perturbation Theory of Cosmic Fields; 1, Basic Formalism and Second-order Theory
Matsubara, T
2000-01-01
We formulate a general method for perturbative evaluations of statistics of smoothed cosmic fields, which we call as ``Statistical Perturbation Theory''. The formalism is an extensive generalization of the method used by Matsubara (1994) who derived a weakly nonlinear formula of the genus statistic in a 3D density field. After describing the general method, we apply the formalism especially to analyses of more general genus statistics, level-crossing statistics, Minkowski functionals, and a density extrema statistic, regardless of the dimensions in which each statistic is defined. The relation between the Minkowski functionals and other geometrical statistics is clearly described. These examples are applied to some cosmic fields, including 3D density field, 3D velocity field, 2D projected density field, and 2D weak lensing field. The results are detailed for second order theory of the formalism. The reason why the genus curves etc. in CDM-like models exhibit smaller deviations from Gaussian predictions when t...
Minimizing magnetic fields for precision experiments
Altarev, I; Lins, T; Marino, M G; Nießen, B; Petzoldt, G; Reisner, M; Stuiber, S; Sturm, M; Singh, J T; Taubenheim, B; Rohrer, H K; Schläpfer, U
2015-01-01
An increasing number of measurements in fundamental and applied physics rely on magnetically shielded environments with sub nano-Tesla residual magnetic fields. State of the art magnetically shielded rooms (MSRs) consist of up to seven layers of high permeability materials in combination with highly conductive shields. Proper magnetic equilibration is crucial to obtain such low magnetic fields with small gradients in any MSR. Here we report on a scheme to magnetically equilibrate MSRs with a 10 times reduced duration of the magnetic equilibration sequence and a significantly lower magnetic field with improved homogeneity. For the search of the neutron's electric dipole moment, our finding corresponds to a linear improvement in the systematic reach and a 40 % improvement of the statistical reach of the measurement. However, this versatile procedure can improve the performance of any MSR for any application.
Magnetic field evolution in tidal disruption events
Bonnerot, Clément; Price, Daniel J.; Lodato, Giuseppe; Rossi, Elena M.
2017-08-01
When a star gets tidally disrupted by a supermassive black hole, its magnetic field is expected to pervade its debris. In this paper, we study this process via smoothed particle magnetohydrodynamical simulations of the disruption and early debris evolution including the stellar magnetic field. As the gas stretches into a stream, we show that the magnetic field evolution is strongly dependent on its orientation with respect to the stretching direction. In particular, an alignment of the field lines with the direction of stretching induces an increase of the magnetic energy. For disruptions happening well within the tidal radius, the star compression causes the magnetic field strength to sharply increase by an order of magnitude at the time of pericentre passage. If the disruption is partial, we find evidence for a dynamo process occurring inside the surviving core due to the formation of vortices. This causes an amplification of the magnetic field strength by a factor of ˜10. However, this value represents a lower limit since it increases with numerical resolution. For an initial field strength of 1 G, the magnetic field never becomes dynamically important. Instead, the disruption of a star with a strong 1 MG magnetic field produces a debris stream within which magnetic pressure becomes similar to gas pressure a few tens of hours after disruption. If the remnant of one or multiple partial disruptions is eventually fully disrupted, its magnetic field could be large enough to magnetically power the relativistic jet detected from Swift J1644+57. Magnetized streams could also be significantly thickened by magnetic pressure when it overcomes the confining effect of self-gravity.
Magnetic field screening effect in electroweak model
Bakry, A; Zhang, P M; Zou, L P
2014-01-01
It is shown that in the Weinberg-Salam model a magnetic field screening effect for static magnetic solutions takes place. The origin of that phenomenon is conditioned by features of the electro-weak interaction, namely, there is mutual cancellation of Abelian magnetic fields created by the SU(2) gauge fields and Higgs boson. The effect implies monopole charge screening in finite energy system of monopoles and antimonopoles. We consider another manifestation of the screening effect which leads to an essential energy decrease of magnetic solutions. Applying variational method we have found a magnetic field configuration with a topological azimuthal magnetic flux which minimizes the energy functional and possesses a total energy of order 1 TeV. We suppose that corresponding magnetic bound state exists in the electroweak theory and can be detected in experiment.
Numerical Simulation of Level Magnetic Field
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
According to Maxwell electromagnetic field theory and magnetic vector potential integral equation, a mathematical model of LMF (Level Magnetic Field) for EMBR (Electromagnetic brake) was proposed, and the reliable software for LMF calculation was developed. The distribution of magnetic flux density given by numerical simulation shows that the magnetic flux density is greater in the magnet and magnetic leakage is observed in the gap. The magnetic flux density is uniform in horizontal plane and a peak is observed in vertical plane. Furthermore, the effects of electromagnetic and structural parameters on magnetic flux density were discussed. The relationship between magnetic flux, electromagnetic parameters and structural parameters is obtained by dimensional analysis, simulation experiment and least square method.
Perturbations of slowly rotating black holes: massive vector fields in the Kerr metric
Pani, Paolo; Gualtieri, Leonardo; Berti, Emanuele; Ishibashi, Akihiro
2012-01-01
We discuss a general method to study linear perturbations of slowly rotating black holes which is valid for any perturbation field, and particularly advantageous when the field equations are not separable. As an illustration of the method we investigate massive vector (Proca) perturbations in the Kerr metric, which do not appear to be separable in the standard Teukolsky formalism. Working in a perturbative scheme, we discuss two important effects induced by rotation: a Zeeman-like shift of nonaxisymmetric quasinormal modes and bound states with different azimuthal number m, and the coupling between axial and polar modes with different multipolar index l. We explicitly compute the perturbation equations up to second order in rotation, but in principle the method can be extended to any order. Working at first order in rotation we show that polar and axial Proca modes can be computed by solving two decoupled sets of equations, and we derive a single master equation describing axial perturbations of spin s=0 and ...
Khoury, Justin
2009-01-01
The universe can be made flat and smooth by undergoing a phase of ultra-slow (ekpyrotic) contraction with equation of state w >> 1, a condition that is achievable with a single, canonical scalar field and conventional general relativity. It has been argued, though, that another goal, generating scale-invariant density perturbations, requires at least two scalar fields and a two-step process that first produces entropy fluctuations and then converts them to curvature perturbations. In this paper, we exploit a loophole in the argument and introduce an ekpyrotic model based on a single, canonical scalar field that utilizes a purely "adiabatic mechanism" to generate nearly scale-invariant curvature fluctuations. The curvature perturbation tends to a constant at long wavelengths, indicating that the background evolution is a dynamical attractor. The resulting spectrum is slightly red with distinctive non-gaussian fluctuations.
Optical fibers with composite magnetic coating for magnetic field sensing
Energy Technology Data Exchange (ETDEWEB)
Radojevic, V.; Nedeljkovic, D.; Talijan, N. E-mail: ntalijan@elab.tmf.bg.ac.yu; Trifunovic, D.; Aleksic, R
2004-05-01
The investigated system for optical fiber sensor was multi-mode optical fiber with magnetic composite coating. Polymer component of composite coating was poly (ethylene-co-vinyl acetate)-EVA, and the magnetic component was powder of SmCo{sub 5} permanent magnet in form of single domain particles. The influence of the applied external magnetic field on the change of intensity of the light signal propagated through optical fiber was investigated.
Optical fibers with composite magnetic coating for magnetic field sensing
Radojevic, V.; Nedeljkovic, D.; Talijan, N.; Trifunovic, D.; Aleksic, R.
2004-05-01
The investigated system for optical fiber sensor was multi-mode optical fiber with magnetic composite coating. Polymer component of composite coating was poly (ethylene-co-vinyl acetate)-EVA, and the magnetic component was powder of SmCo5 permanent magnet in form of single domain particles. The influence of the applied external magnetic field on the change of intensity of the light signal propagated through optical fiber was investigated.
Nakamura, Kouji
2008-01-01
Some formulae for the perturbations of the matter fields are summarized within the framework of the second-order gauge-invariant cosmological perturbation theory in a four dimensional homogeneous isotropic universe, which is developed in the papers [K. Nakamura, Prog. Theor. Phys. {\\bf 117} (2005), 17.]. We derive the formulae for the perturbations of the energy momentum tensors and equations of motion in the cases of a perfect fluid, an imperfect fluid, and a signle scalar field, and show that all equations are derived in terms of gauge-invariant variables without any gauge fixing.
Gauge-invariant perturbations at second order in two-field inflation
Energy Technology Data Exchange (ETDEWEB)
Tzavara, Eleftheria; Tent, Bartjan van, E-mail: Eleftheria.Tzavara@th.u-psud.fr, E-mail: Bartjan.Van-Tent@th.u-psud.fr [Laboratoire de Physique Théorique, Université Paris-Sud 11 and CNRS, Bâtiment 210, 91405 Orsay Cedex (France)
2012-08-01
We study the second-order gauge-invariant adiabatic and isocurvature perturbations in terms of the scalar fields present during inflation, along with the related fully non-linear space gradient of these quantities. We discuss the relation with other perturbation quantities defined in the literature. We also construct the exact cubic action of the second-order perturbations (beyond any slow-roll or super-horizon approximations and including tensor perturbations), both in the uniform energy-density gauge and the flat gauge in order to settle various gauge-related issues. We thus provide the tool to calculate the exact non-Gaussianity beyond slow-roll and at any scale.
Gauge-invariant perturbations at second order in two-field inflation
Tzavara, Eleftheria
2011-01-01
We study the second-order gauge-invariant adiabatic and isocurvature perturbations in terms of the scalar fields present during inflation, along with the related fully non-linear space gradient of these quantities. We discuss the relation with other perturbation quantities defined in the literature. We also construct the exact cubic action of the second-order perturbations (beyond any slow-roll or super-horizon approximations and including tensor perturbations), both in the uniform energy density gauge and the flat gauge in order to settle various gauge-related issues. We thus provide the tool to calculate the exact non-Gaussianity beyond slow-roll and at any scale.
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
An Intergalactic Magnetic Field from Quasar Outflows
Furlanetto, S; Furlanetto, Steven; Loeb, Abraham
2001-01-01
Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and calculate their distribution as a function magnetic field strength at different redshifts. We find that by a redshift z ~ 3, about 5-80% of the IGM volume is filled by magnetic fields with an energy density > 10% of the mean thermal energy density of a photo-ionized IGM (at ~ 10^4 K). As massive galaxies and X-ray clusters condense out of the magnetized IGM, the adiabatic compression of the magnetic field could result in the fields observed in these systems without a need for further dynamo amplification.
Nanoscale magnetic field mapping with a single spin scanning probe magnetometer
Energy Technology Data Exchange (ETDEWEB)
Rondin, L.; Tetienne, J.-P.; Spinicelli, P.; Roch, J.-F.; Jacques, V. [Laboratoire de Photonique Quantique et Moleculaire, Ecole Normale Superieure de Cachan and CNRS UMR 8537, 94235 Cachan Cedex (France); Dal Savio, C.; Karrai, K. [Attocube systems AG, Koeniginstrasse 11A RGB, Munich 80539 (Germany); Dantelle, G. [Laboratoire de Physique de la Matiere Condensee, Ecole Polytechnique and CNRS UMR 7643, 91128 Palaiseau (France); Thiaville, A.; Rohart, S. [Laboratoire de Physique des Solides, Universite Paris-Sud and CNRS UMR 8502, 91405 Orsay (France)
2012-04-09
We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics.
Dynamics of Peccei-Quinn breaking field after inflation and axion isocurvature perturbations
Energy Technology Data Exchange (ETDEWEB)
Harigaya, Keisuke; Ibe, Masahiro; Kawasaki, Masahiro [ICRR, University of Tokyo,Kashiwa, Chiba 277-8582 (Japan); Kavli IPMU (WPI), UTIAS, University of Tokyo,Kashiwa, Chiba 277-8583 (Japan); Yanagida, Tsutomu T. [Kavli IPMU (WPI), UTIAS, University of Tokyo,Kashiwa, Chiba 277-8583 (Japan)
2015-11-04
The Peccei-Quinn mechanism suffers from the problem of the isocurvature perturbations. The isocurvature perturbations are suppressed if the Peccei-Quinn breaking scale is large during inflation. The oscillation of the Peccei-Quinn breaking field after inflation, however, leads to the formation of domain walls due to the parametric resonance effect. In this paper, we discuss the evolution of the Peccei-Quinn breaking field after inflation in detail, and propose a model where the parametric resonance is ineffective and hence domain walls are not formed. We also discuss consistency of our model with supersymmetric theory.
SUSY sine-Gordon theory as a perturbed conformal field theory and finite size effects
Bajnok, Z; Palla, L; Takács, G; Wagner, F
2004-01-01
We consider SUSY sine-Gordon theory in the framework of perturbed conformal field theory. Using an argument from Zamolodchikov, we obtain the vacuum structure and the kink adjacency diagram of the theory, which is cross-checked against the exact S matrix prediction, first-order perturbed conformal field theory (PCFT), the NLIE method and truncated conformal space approach. We provide evidence for consistency between the usual Lagrangian description and PCFT on the one hand, and between PCFT, NLIE and a massgap formula conjectured by Baseilhac and Fateev, on the other. In addition, we extend the NLIE description to all the vacua of the theory.
MDI Synoptic Charts of Magnetic Field: Interpolation of Polar Fields
Liu, Yang; Hoeksema, J. T.; Zhao, X.; Larson, R. M.
2007-05-01
In this poster, we compare various methods for interpolation of polar field for the MDI synoptic charts of magnetic field. By examining the coronal and heliospheric magnetic field computed from the synoptic charts based on a Potential Field Source Surface model (PFSS), and by comparing the heliospheric current sheets and footpoints of open fields with the observations, we conclude that the coronal and heliospheric fields calculated from the synoptic charts are sensitive to the polar field interpolation, and a time-dependent interpolation method using the observed polar fields is the best among the seven methods investigated.
Efficient magnetic fields for supporting toroidal plasmas
Landreman, Matt
2016-01-01
The magnetic field that supports tokamak and stellarator plasmas must be produced by coils well separated from the plasma. However the larger the separation, the more difficult it is to produce a given magnetic field in the plasma region, so plasma configurations should be chosen that can be supported as efficiently as possible by distant coils. The properties of curl-free magnetic fields allow magnetic field distributions to be ranked in order of their difficulty of production from a distance. Plasma shapes with low curvature and spectral width may be difficult to support, whereas plasma shapes with sharp edges may be efficiently supported by distant coils. Two measures of difficulty, which correctly identify such differences in difficulty, will be examined. These measures, which can be expressed as matrices, relate the externally-produced normal magnetic field on the plasma surface to the either the normal field or current on a distant control surface. A singular value decomposition (SVD) of either matrix y...
Torque measurements on ferrofluid cylinders in rotating magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Rinaldi, Carlos [Department of Chemical Engineering, University of Puerto Rico, PO Box 9046, Mayagueez, PR 00680 (United States)]. E-mail: crinaldi@uprm.edu; Gutman, Fernando [Department of Chemical Engineering, University of Puerto Rico, PO Box 9046, Mayagueez, PR 00680 (United States); He Xiaowei [Laboratory for Electromagnetic and Electronic Systems, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139 (United States); Rosenthal, Adam D. [Laboratory for Electromagnetic and Electronic Systems, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139 (United States); Zahn, Markus [Laboratory for Electromagnetic and Electronic Systems, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139 (United States)
2005-03-15
We study the response of magnetic nanoparticle suspensions (ferrofluids) to uniform rotating magnetic fields generated by a two-pole three-phase magnetic induction motor stator winding. Measurements of the torque required to rotate a polycarbonate spindle submerged in ferrofluid subjected to co-rotating and counter-rotating fields yield experimental observations of negative magnetoviscosity in a cylindrical Couette geometry, conceptually similar to the observations of Bacri et al. (Phys. Rev. Lett. 75 (1995) 2128) in a Poiseuille flow under an oscillating magnetic field. Further measurements are presented for the torque required to restrain a spindle when it is (i) entirely filled with ferrofluid (ii) entirely surrounded with ferrofluid, and (iii) both entirely filled and surrounded with ferrofluid. Some of the results for the spindle either entirely filled or entirely surrounded with ferrofluid are compared to theoretical expressions obtained from the ferrohydrodynamic equations using a rigorous regular perturbation expansion in the small parameter {omega}{tau}, where {omega} is the applied field frequency and {tau} is the effective magnetic relaxation time of the suspension.
The Evolution of the Earth's Magnetic Field.
Bloxham, Jeremy; Gubbins, David
1989-01-01
Describes the change of earth's magnetic field at the boundary between the outer core and the mantle. Measurement techniques used during the last 300 years are considered. Discusses the theories and research for explaining the field change. (YP)
Marcus, F A; Fuhr, G; Monnier, A; Benkadda, S
2014-01-01
With the resonant magnetic perturbations (RMPs) consolidating as an important tool to control the transport barrier relaxation, the mechanism on how they work is still a subject to be clearly understood. In this work we investigate the equilibrium states in the presence of RMPs for a reduced MHD model using 3D electromagnetic fluid numerical code (EMEDGE3D) with a single harmonic RMP (single magnetic island chain) and multiple harmonics RMPs in cylindrical and toroidal geometry. Two different equilibrium states were found in the presence of the RMPs with different characteristics for each of the geometries used. For the cylindrical geometry in the presence of a single RMP, the equilibrium state is characterized by a strong convective radial thermal flux and the generation of a mean poloidal velocity shear. In contrast, for toroidal geometry the thermal flux is dominated by the magnetic flutter. For multiple RMPs, the high amplitude of the convective flux and poloidal rotation are basically the same in cylindr...
The Physics of Attraction and Repulsion: Magnetism and Magnetic Fields
Nakotte, Heinz
2001-11-01
The development of new materials with improved magnetic properties completely changed the modern world in the past decades. Recent progress is predominantly due to a better understanding of magnetism that has gone far beyond compass needles rotating in a magnetic field and bar magnets attracting or repelling each other. New magnetic materials are used to build smaller and smaller read/write heads and hard disks with increased storage capacity, developments that are responsible the revolution in the computer industry. Another example is the field of magnetic levitation that became feasible for commercial applications with the discovery of new superconducting materials, and a prototype train is under development in Japan. In medicine, the development of magnetic resonance imaging (MRI) provides an alternative to other (destructive) radiation techniques.
Assembly of magnetic spheres in strong homogeneous magnetic field
Messina, René; Stanković, Igor
2017-01-01
The assembly in two dimensions of spherical magnets in strong magnetic field is addressed theoretically. It is shown that the attraction and assembly of parallel magnetic chains is the result of a delicate interplay of dipole-dipole interactions and short ranged excluded volume correlations. Minimal energy structures are obtained by numerical optimization procedure as well as analytical considerations. For a small number of constitutive magnets Ntot ≤ 26, a straight chain is found to be the ground state. In the regime of larger Ntot ≥ 27, the magnets form two touching chains with equally long tails at both ends. We succeed to identify the transition from two to three touching chains at Ntot = 129. Overall, this study sheds light on the mechanisms of the recently experimentally observed ribbon formation of superparamagnetic colloids via lateral aggregation of magnetic chains in magnetic field (Darras et al., 2016).
Evolution of Neutron Star Magnetic Fields
Indian Academy of Sciences (India)
Dipankar Bhattacharya
2002-03-01
This paper reviews the current status of the theoretical models of the evolution of the magnetic fields of neutron stars other than magnetars. It appears that the magnetic fields of neutron stars decay significantly only if they are in binary systems. Three major physical models for this, namely spindown-induced flux expulsion, ohmic evolution of crustal field and diamagnetic screening of the field by accreted plasma, are reviewed.
Nonlinear energy dissipation of magnetic nanoparticles in oscillating magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Soto-Aquino, D. [ERC Incorporated, Air Force Research Laboratory, 10 E. Saturn Blvd., Edwards AFB, CA 93524 (United States); Rinaldi, C., E-mail: carlos.rinaldi@bme.ufl.edu [J. Crayton Pruitt Family Department of Biomedical Engineering and Department of Chemical Engineering, University of Florida, PO Box 116131, Gainesville, FL 32611-6131 (United States)
2015-11-01
The heating of magnetic nanoparticle suspensions subjected to alternating magnetic fields enables a variety of emerging applications such as magnetic fluid hyperthermia and triggered drug release. Rosensweig (2002) [25] obtained a model for the heat dissipation rate of a collection of non-interacting particles. However, the assumptions made in this analysis make it rigorously valid only in the limit of small applied magnetic field amplitude and frequency (i.e., values of the Langevin parameter that are much less than unity and frequencies below the inverse relaxation time). In this contribution we approach the problem from an alternative point of view by solving the phenomenological magnetization relaxation equation exactly for the case of arbitrary magnetic field amplitude and frequency and by solving a more accurate magnetization relaxation equation numerically. We also use rotational Brownian dynamics simulations of non-interacting magnetic nanoparticles subjected to an alternating magnetic field to estimate the rate of energy dissipation and compare the results of the phenomenological theories to the particle-scale simulations. The results are summarized in terms of a normalized energy dissipation rate and show that Rosensweig's expression provides an upper bound on the energy dissipation rate achieved at high field frequency and amplitude. Estimates of the predicted dependence of energy dissipation rate, quantified as specific absorption rate (SAR), on magnetic field amplitude and frequency, and particle core and hydrodynamic diameter, are also given. - Highlights: • Rosensweig's model for SAR was extended to high fields. • The MRSh relaxation equation was used to predict SAR at high fields. • Rotational Brownian dynamics simulations were used to predict SAR. • The results of these models were compared. • Predictions of effect of size and field conditions on SAR are presented.
Two-axis magnetic field sensor
Jander, Albrecht (Inventor); Nordman, Catherine A. (Inventor); Qian, Zhenghong (Inventor); Smith, Carl H. (Inventor)
2006-01-01
A ferromagnetic thin-film based magnetic field sensor with first and second sensitive direction sensing structures each having a nonmagnetic intermediate layer with two major surfaces on opposite sides thereof having a magnetization reference layer on one and an anisotropic ferromagnetic material sensing layer on the other having a length in a selected length direction and a smaller width perpendicular thereto and parallel to the relatively fixed magnetization direction. The relatively fixed magnetization direction of said magnetization reference layer in each is oriented in substantially parallel to the substrate but substantially perpendicular to that of the other. An annealing process is used to form the desired magnetization directions.
Magnetic fields and rotation of spiral galaxies
Battaner, E; Florido, E
1998-01-01
We present a simplified model in which we suggest that two important galactic problems -the magnetic field configuration at large scales and the flat rotation curve- may be simultaneously explained. A highly convective disc produces a high turbulent magnetic diffusion in the vertical direction, stablishing a merging of extragalactic and galactic magnetic fields. The outer disc may then adquire a magnetic energy gradient very close to the gradient required to explain the rotation curve, without the hypothesis of galactic dark matter. Our model predicts symmetries of the galactic field in noticeable agreement with the large scale structure of our galaxy.
Rotating artificial gauge magnetic and electric fields
Lembessis, V E; Alshamari, S; Siddig, A; Aldossary, O M
2016-01-01
We consider the creation of artificial gauge magnetic and electric fields created when a two-level atom interacts with an optical Ferris wheel light field.These fields have the spatial structure of the optical Ferris wheel field intensity profile. If this optical field pattern is made to rotate in space then we have the creation of artificial electromagnetic fields which propagate in closed paths. The properties of such fields are presented and discussed
Non-gaussianity at tree- and one-loop levels from vector field perturbations
Valenzuela-Toledo, Cesar A; Lyth, David H
2009-01-01
We study the spectrum P_\\zeta and bispectrum B_\\zeta of the primordial curvature perturbation \\zeta when the latter is generated by scalar and vector field perturbations. The tree-level and one-loop contributions from vector field perturbations are worked out considering the possibility that the one-loop contributions may be dominant over the tree level terms (both (either) in P_\\zeta and (or) in B_\\zeta) and viceversa. The level of non-gaussianity in the bispectrum, f_{NL}, is calculated and related to the level of statistical anisotropy in the power spectrum, g_\\zeta. For very small amounts of statistical anisotropy in the power spectrum, the level of non-gaussianity may be very high, in some cases exceeding the current observational limit.
Magnetic fields in Neutron Stars
Viganò, Daniele; Miralles, Juan A; Rea, Nanda
2015-01-01
Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.
Earth magnetism a guided tour through magnetic fields
Campbell, Wallace H
2001-01-01
An introductory guide to global magnetic field properties, Earth Magnetism addresses, in non-technical prose, many of the frequently asked questions about Earth''s magnetic field. Magnetism surrounds and penetrates our Earth in ways basic science courses can rarely address. It affects navigation, communication, and even the growth of crystals. As we observe and experience an 11-year solar maximum, we may witness spectacular satellite-destroying solar storms as they interact with our magnetic field. Written by an acknowledged expert in the field, this book will enrich courses in earth science, atmospheric science, geology, meteorology, geomagnetism, and geophysics. Contains nearly 200 original illustrations and eight pages of full-color plates.* Largely mathematics-free and with a wide breadth of material suitable for general readers* Integrates material from geomagnetism, paleomagnetism, and solar-terrestrial space physics.* Features nearly 200 original illustrations and 4 pages of colour plates
DEFF Research Database (Denmark)
Hubrig, S.; Gonzalez, J. F.; Ilyin, I.
2012-01-01
Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have fai...
Lattice Planar QED in external magnetic field
Cea, Paolo; Giudice, Pietro; Papa, Alessandro
2011-01-01
We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.
Helical Magnetic Fields in AGN Jets
Indian Academy of Sciences (India)
Y. J. Chen; G.-Y. Zhao; Z.-Q. Shen
2014-09-01
We establish a simple model to describe the helical magnetic 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 observation of many blazar objects, suggesting the existence of helical magnetic fields in these sources.
Magnetic Fields at the Center of Coils
Binder, Philippe; Hui, Kaleonui; Goldman, Jesse
2014-01-01
In this note we synthesize and extend expressions for the magnetic field at the center of very short and very long current-carrying coils. Elementary physics textbooks present the following equation for the magnetic field inside a very long current-carrying coil (solenoid): B[subscript sol] = µ[subscript 0] (N/L) I, (1) where I is the current, N…
Magnetic Fields in Stars: Origin and Impact
Langer, N
2013-01-01
Various types of magnetic fields occur in stars: small scale fields, large scale fields, and internal toroidal fields. While the latter may be ubiquitous in stars due to differential rotation, small scale fields (spots) may be associated with envelop convection in all low and high mass stars. The stable large scale fields found in only about 10 per cent of intermediate mass and massive stars may be understood as a consequence of dynamical binary interaction, e.g., the merging of two stars in a binary. We relate these ideas to magnetic fields in white dwarfs and neutron stars, and to their role in core-collapse and thermonuclear supernova explosions.
Classical theory of electric and magnetic fields
Good, Roland H
1971-01-01
Classical Theory of Electric and Magnetic Fields is a textbook on the principles of electricity and magnetism. This book discusses mathematical techniques, calculations, with examples of physical reasoning, that are generally applied in theoretical physics. This text reviews the classical theory of electric and magnetic fields, Maxwell's Equations, Lorentz Force, and Faraday's Law of Induction. The book also focuses on electrostatics and the general methods for solving electrostatic problems concerning images, inversion, complex variable, or separation of variables. The text also explains ma
Pair annihilation in superstrong magnetic fields
Daugherty, J. K.; Bussard, R. W.
1980-01-01
The kinematical and dynamical aspects of the annihilation processes in superstrong magnetic fields are studied. The feasibility and potential significance of detecting from magnetic neutron stars are discussed. The discussion proceeds from the derivation of the fully relativistic differential cross sections and annihilation rates for both one- and two-photon emission from a ground-state gas of electrons and positrons in a static, uniform magnetic field.
On the regularity of the Hausdorff distance between spectra of perturbed magnetic Hamiltonians
DEFF Research Database (Denmark)
Cornean, Horia; Purice, Radu
2012-01-01
We study the regularity properties of the Hausdorff distance between spectra of continuous Harper-like operators. As a special case we obtain Hölder continuity of this Hausdorff distance with respect to the intensity of the magnetic field for a large class of magnetic elliptic (pseudo)differentia...
Tuning the pseudo-Zeeman splitting in graphene cones by magnetic field
Energy Technology Data Exchange (ETDEWEB)
Kandemir, B.S.; Akay, D.
2015-06-15
The effect of a homogeneous magnetic field on the energy spectrum of gapped graphene cones with long range charged Coulomb impurity is investigated within the framework of the perturbation theory. It is found that, besides lifting the degeneracy of angular momentum channels due to topological defects, the size of the corresponding splitting is enhanced by the introduction of a homogeneous magnetic field. This indicates that the level splitting may be controlled by the strength of a magnetic field in topological cones. Therefore, our results show that the magnetic field may be used as a tool to tune the pseudo-Zeeman splitting in graphene cones. - Highlights: • The size of level splitting in angular momentum channels is enhanced by introduction of a homogenous magnetic field. • Pseudo-Zeeman splitting in graphene can be controlled by hydrogenic impurities. • Pseudo-Zeeman splitting may be controlled by the strength of magnetic field in topological cones.
Turbulent amplification of supernova magnetic fields in the laboratory
Gregori, Gianluca
2014-10-01
X-ray and radio observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. Field coincident with the outer shock probably arises through a non-linear feedback process involving cosmic rays. The origin of the large magnetic field in the interior of the remnant is less clear but it is probably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas. However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar cloud bank formed prior to the supernova explosion. We have conducted a series of laboratory experiments using high power laser facilities in order to reproduce the essential features of the supernova shock interacting with strong density perturbations. Our results indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. These experiments provide an example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena.
Delayed quarkonium formation in a magnetic field
Suzuki, Kei
2016-01-01
Formation time of heavy quarkonia in a homogeneous magnetic field is analyzed by using a phenomenological ansatz of the vector current correlator. Because the existence of a magnetic field mixes vector quarkonia ($J/\\psi$, $\\psi^\\prime$) and their pseudoscalar partners ($\\eta_c$, $\\eta_c^\\prime$), the properties of the quarkonia can be modified through such a spin mixing. This means that the formation time of quarkonia is also changed by the magnetic field. We show the formation time of vector quarkonia is delayed by an idealized constant magnetic field, where the formation time of the excited state becomes longer than that of the ground state. As a more realistic situation in heavy-ion collisions, effects by a time-dependent magnetic field are also discussed.
Structure of magnetic fields in intracluster cavities
Gourgouliatos, Konstantinos Nektarios; Lyutikov, Maxim
2010-01-01
Observations of clusters of galaxies show ubiquitous presence of X-ray cavities, presumably blown by the AGN jets. We consider magnetic field structures of these cavities. Stability requires that they contain both toroidal and poloidal magnetic fields, while realistic configurations should have vanishing magnetic field on the boundary. For axisymmetric configurations embedded in unmagnetized plasma, the continuity of poloidal and toroidal magnetic field components on the surface of the bubble then requires solving the elliptical Grad-Shafranov equation with both Dirichlet and Neumann boundary conditions. This leads to a double eigenvalue problem, relating the pressure gradients and the toroidal magnetic field to the radius of the bubble. We have found fully analytical stable solutions. This result is confirmed by numerical simulation. We present synthetic X-ray images and synchrotron emission profiles and evaluate the rotation measure for radiation traversing the bubble.
Probing Magnetic Fields of Early Galaxies
Kohler, Susanna
2017-06-01
How do magnetic fields form and evolve in early galaxies? A new study has provided some clever observations to help us answer this question.The Puzzle of Growing FieldsDynamo theory is the primary model describing how magnetic fields develop in galaxies. In this picture, magnetic fields start out as weak seed fields that are small and unordered. These fields then become ordered and amplified by large-scale rotation and turbulence in galaxy disks and halos, eventually leading to the magnetic fields we observe in galaxies today.Schematic showinghow to indirectly measure protogalactic magnetic fields. The measured polarization of a background quasar is altered by the fields in a foreground protogalaxy. Click for a closer look! [Farnes et al. 2017/Adolf Schaller/STSCI/NRAO/AUI/NSF]To test this model, we need observations of the magnetic fields in young protogalaxies. Unfortunately, we dont have the sensitivity to be able to measure these fields directly but a team of scientists led by Jamie Farnes (Radboud University in the Netherlands) have come up with a creative alternative.The key is to find early protogalaxies that absorb the light of more distant background objects. If a protogalaxy lies between us and a distant quasar, then magnetic fields of the protogalaxy if present will affect the polarization measurements of the background quasar.Observing Galactic Building BlocksTop: Redshift distribution for the background quasars in the authors sample. Bottom: Redshift distribution for the foreground protogalaxies the authors are exploring. [Farnes et al. 2017]Farnes and collaborators examined two types of foreground protogalaxies: Damped Lyman-Alpha Absorbers (DLAs) and Lyman Limit Systems (LLSs). They obtained polarimetric data for a sample of 114 distant quasars with nothing in the foreground (the control sample), 19 quasars with DLAs in the foreground, and 27 quasars with LLSs in the foreground. They then used statistical analysis techniques to draw conclusions about
Mostert, W.
2015-10-06
The effects of seed magnetic fields on the Richtmyer-Meshkov instability driven by converging cylindrical and spherical implosions in ideal magnetohydrodynamics are investigated. Two different seed field configurations at various strengths are applied over a cylindrical or spherical density interface which has a single-dominant-mode perturbation. The shocks that excite the instability are generated with appropriate Riemann problems in a numerical formulation and the effect of the seed field on the growth rate and symmetry of the perturbations on the density interface is examined. We find reduced perturbation growth for both field configurations and all tested strengths. The extent of growth suppression increases with seed field strength but varies with the angle of the field to interface. The seed field configuration does not significantly affect extent of suppression of the instability, allowing it to be chosen to minimize its effect on implosion distortion. However, stronger seed fields are required in three dimensions to suppress the instability effectively.
Formation of magnetically anisotropic composite films at low magnetic fields
Ghazi Zahedi, Maryam; Ennen, Inga; Marchi, Sophie; Barthel, Markus J.; Hütten, Andreas; Athanassiou, Athanassia; Fragouli, Despina
2017-04-01
We present a straightforward two-step technique for the fabrication of poly (methyl methacrylate) composites with embedded aligned magnetic chains. First, ferromagnetic microwires are realized in a poly (methyl methacrylate) solution by assembling iron nanoparticles in a methyl methacrylate solution under heat in an external magnetic field of 160 mT. The simultaneous thermal polymerization of the monomer throughout the wires is responsible for their permanent linkage and stability. Next, the polymer solution containing the randomly dispersed microwires is casted on a solid substrate in the presence of a low magnetic field (20–40 mT) which induces the final alignment of the microwires into long magnetic chains upon evaporation of the solvent. We prove that the presence of the nanoparticles assembled in the form of microwires is a key factor for the formation of the anisotropic films under low magnetic fields. In fact, such low fields are not capable of driving and assembling dispersed magnetic nanoparticles in the same type of polymer solutions. Hence, this innovative approach can be utilized for the synthesis of magnetically anisotropic nanocomposite films at low magnetic fields.
Teaching Representation Translations with Magnetic Field Experiments
Tillotson, Wilson Andrew; McCaskey, Timothy; Nasser, Luis
2017-01-01
We have developed a laboratory exercise designed to help students translate between different field representations. It starts with students qualitatively mapping field lines for various bar magnet configurations and continues with a Hall probe experiment in which students execute a series of scaffolded tasks, culminating in the prediction and measurement of the spatial variation of magnetic field components along a line near magnets. We describe the experimental tasks, various difficulties students have throughout, and ways this lab makes even their incorrect predictions better. We suggest that developing lab activities of this nature brings a new dimension to the ways students learn and interact with field concepts.
DEFF Research Database (Denmark)
Hubrig, S.; González, J. F.; Ilyin, I.
2012-01-01
Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have...... failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. Aims. We re-analyse the available spectropolarimetric material...
Warm inflation in presence of magnetic fields
Piccinelli, Gabriella; Ayala, Alejandro; Mizher, Ana Julia
2013-01-01
We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales, which rises the possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger proper time method.
Instability of Non-uniform Toroidal Magnetic Fields in Accretion Disks
Hirabayashi, Kota
2016-01-01
A new type of instability that is expected to drive magnetohydrodynamic (MHD) turbulence from a purely toroidal magnetic field in an accretion disk is presented. It is already known that in a differentially rotating system, the uniform toroidal magnetic field is unstable due to a magnetorotational instability (MRI) under a non-axisymmetric and vertical perturbation, while it is stable under a purely vertical perturbation. Contrary to the previous study, this paper proposes an unstable mode completely confined to the equatorial plane, driven by the expansive nature of the magnetic pressure gradient force under a non-uniform toroidal field. The basic nature of this growing eigenmode, to which we give a name "magneto-gradient driven instability", is studied using linear analysis, and the corresponding nonlinear evolution is then investigated using two-dimensional ideal MHD simulations. Although a single localized magnetic field channel alone cannot provide sufficient Maxwell stress to contribute significantly to...
Strong Magnetic field effects on Neutron Stars within $f(T)$ theory of gravity
Ganiou, M G; Houndjo, M J S; Tossa, J
2016-01-01
We investigate in this paper the structures of neutron stars under the strong magnetic field in the framework of $f(T)$ gravity where $T$ denotes the scalar torsion. The TOV equations in this theory of gravity have been considered and numerical resolution of these equations has been performed within perturbative approach taking into account the equation of state of neutron dense matter in magnetic field. We simplify the problem by considering the very strong magnetic field which affects considerably the dense matter; and for quadratic and cubic corrections to Teleparallel term, one finds that the mass of neutron stars can increase for different values of the perturbation parameter. The deviation from Teleparallel for different values of magnetic field is found out and this feature is very appreciable in the case of cubic correction. Our results are related to the hadronic particles description with very small hyperon contributions and the mass-radius evolution is consistency with the observational data.
Leading SU(3)-breaking corrections to the baryon magnetic moments in chiral perturbation theory.
Geng, L S; Camalich, J Martin; Alvarez-Ruso, L; Vacas, M J Vicente
2008-11-28
We calculate the baryon magnetic moments using covariant chiral perturbation theory (chiPT) within the extended-on-mass-shell renormalization scheme. By fitting the two available low-energy constants, we improve the Coleman-Glashow description of the data when we include the leading SU(3)-breaking effects coming from the lowest-order loops. This success is in dramatic contrast with previous attempts at the same order using heavy-baryon chiPT and covariant infrared chiPT. We also analyze the source of this improvement with particular attention to the comparison between the covariant results.
Energy Technology Data Exchange (ETDEWEB)
Leitner, Peter; Heyn, Martin F.; Kernbichler, Winfried [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, TU Graz, Petersgasse 16, A-8010 Graz (Austria); Ivanov, Ivan B. [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, TU Graz, Petersgasse 16, A-8010 Graz (Austria); St. Petersburg State University, Institute of Physics, Ulyanovskaya 1, Petrodvoretz 198504 (Russian Federation); Petersburg Nuclear Physics Institute, 188300 Gatchina, Leningrad Oblast (Russian Federation); Kasilov, Sergei V. [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, TU Graz, Petersgasse 16, A-8010 Graz (Austria); Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology,” Ul. Akademicheskaya 1, 61108 Kharkov (Ukraine)
2014-06-15
In this paper, the impact of momentum and energy conservation of the collision operator in the kinetic description for Resonant Magnetic Perturbations (RMPs) in a tokamak is studied. The particle conserving differential collision operator of Ornstein-Uhlenbeck type is supplemented with integral parts such that energy and momentum are conserved. The application to RMP penetration in a tokamak shows that energy conservation in the electron collision operator is important for the quantitative description of plasma shielding effects at the resonant surface. On the other hand, momentum conservation in the ion collision operator does not significantly change the results.
Field Mapping System for Solenoid Magnet
Park, K. H.; Jung, Y. K.; Kim, D. E.; Lee, H. G.; Park, S. J.; Chung, C. W.; Kang, B. K.
2007-01-01
A three-dimensional Hall probe mapping system for measuring the solenoid magnet of PLS photo-cathode RF e-gun has been developed. It can map the solenoid field either in Cartesian or in cylindrical coordinate system with a measurement reproducibility better than 5 × 10-5 T. The system has three axis motors: one for the azimuthal direction and the other two for the x and z direction. This architecture makes the measuring system simple in fabrication. The magnetic center was calculated using the measured axial component of magnetic field Bz in Cartesian coordinate system because the accuracy of magnetic axis measurement could be improved significantly by using Bz, instead of the radial component of magnetic field Br. This paper describes the measurement system and summarizes the measurement results for the solenoid magnetic of PLS photo-cathode RF e-gun.
Magnetic-field-controlled reconfigurable semiconductor logic.
Joo, Sungjung; Kim, Taeyueb; Shin, Sang Hoon; Lim, Ju Young; Hong, Jinki; Song, Jin Dong; Chang, Joonyeon; Lee, Hyun-Woo; Rhie, Kungwon; Han, Suk Hee; Shin, Kyung-Ho; Johnson, Mark
2013-02-07
Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices.
Solar Force-free Magnetic Fields
Wiegelmann, Thomas
2012-01-01
The structure and dynamics of the solar corona is dominated by the magnetic field. In most areas in the corona magnetic forces are so dominant that all non-magnetic forces like plasma pressure gradient and gravity can be neglected in the lowest order. This model assumption is called the force-free field assumption, as the Lorentz force vanishes. This can be obtained by either vanishing electric currents (leading to potential fields) or the currents are co-aligned with the magnetic field lines. First we discuss a mathematically simpler approach that the magnetic field and currents are proportional with one global constant, the so-called linear force-free field approximation. In the generic case, however, the relation between magnetic fields and electric currents is nonlinear and analytic solutions have been only found for special cases, like 1D or 2D configurations. For constructing realistic nonlinear force-free coronal magnetic field models in 3D, sophisticated numerical computations are required and boundar...
Magnetic monopole field exposed by electrons
Béché, A; Van Tendeloo, G; Verbeeck, J
2013-01-01
Magnetic monopoles have provided a rich field of study, leading to a wide area of research in particle physics, solid state physics, ultra-cold gases, superconductors, cosmology, and gauge theory. So far, no true magnetic monopoles were found experimentally. Using the Aharonov-Bohm effect, one of the central results of quantum physics, shows however, that an effective monopole field can be produced. Understanding the effects of such a monopole field on its surroundings is crucial to its observation and provides a better grasp of fundamental physical theory. We realize the diffraction of fast electrons at a magnetic monopole field generated by a nanoscopic magnetized ferromagnetic needle. Previous studies have been limited to theoretical semiclassical optical calculations of the motion of electrons in such a monopole field. Solid state systems like the recently studied 'spin ice' provide a constrained system to study similar fields, but make it impossible to separate the monopole from the material. Free space ...
Perturbative self-interacting scalar field theory: a differential equation approach
Rocha, R; Coimbra-Araujo, C H
2005-01-01
We revisit the investigation about the partition function related to a \\phi^4-scalar field theory on a n-dimensional Minkowski spacetime, which is shown to be a self-interacting scalar field theory at least in 4-dimensional Minkowski spacetime. After rederiving the analytical calculation of the perturbative expansion coefficients and also the approximate values for suitable limits using Stirling's formulae, which consists of Witten's proposed questions, solved by P. Deligne, D. Freed, L. Jeffrey, and S. Wu, we investigate a spherically symmetric scalar field in a n-dimensional Minkowski spacetime. For the first perturbative expansion coefficient it is shown how it can be derived a modified Bessel equation (MBE), which solutions are investigated in one, four, and eleven-dimensional Minkowski spacetime. The solutions of MBE are the first expansion coefficient of the series associated with the partition function of \\phi^4-scalar field theory.
Matrix method for the solution of RF field perturbations due to local frequency shifts
Institute of Scientific and Technical Information of China (English)
SUN Zhi-Rui; PENG Jun; FU Shi-Nian
2009-01-01
To tune the accelerating field to the design value in a periodical radio frequency accelerating structure, Slater's perturbation theorem is commonly used. This theorem solves a second-order differential equation to obtain the electrical field variation due to a local frequency shift. The solution becomes very difficult for a complex distribution of the local frequency shifts. Noticing the similarity between the field perturbation equation and the equation describing the transverse motion of a particle in a quadrupole channel, we propose in this paper a new method in which the transfer matrix method is applied to the field calculation instead of directly solving the differential equation. The advantage of the matrix method is illustrated in examples.
External-field-free magnetic biosensor
Energy Technology Data Exchange (ETDEWEB)
Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
2014-03-24
In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6 dB from one iron oxide magnetic nanoparticle with 8 nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200 nm × 200 nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3 dB is achieved for 30 μl magnetic nanoparticles suspension (30 nm iron oxide particles, 1 mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.
Interplanetary magnetic field and geomagnetic Dst variations.
Patel, V. L.; Desai, U. D.
1973-01-01
The interplanetary magnetic field has been shown to influence the ring current field represented by Dst. Explorer 28 hourly magnetic field observations have been used with the hourly Dst values. The moderate geomagnetic storms of 60 gammas and quiet-time fluctuations of 10 to 30 gammas are correlated with the north to south change of the interplanetary field component perpendicular to the ecliptic. This change in the interplanetary field occurs one to three hours earlier than the corresponding change in the Dst field.
Polarized radiation diagnostics of stellar magnetic fields
Mathys, Gautier
The main techniques used to diagnose magnetic fields in stars from polarimetric observations are presented. First, a summary of the physics of spectral line formation in the presence of a magnetic field is given. Departures from the simple case of linear Zeeman effect are briefly considered: partial Paschen-Back effect, contribution of hyperfine structure, and combined Stark and Zeeman effects. Important approximate solutions of the equation of transfer of polarized light in spectral lines are introduced. The procedure for disk-integration of emergent Stokes profiles, which is central to stellar magnetic field studies, is described, with special attention to the treatment of stellar rotation. This formalism is used to discuss the determination of the mean longitudinal magnetic field (through the photographic technique and through Balmer line photopolarimetry). This is done within the specific framework of Ap stars, which, with their unique large-scale organized magnetic fields, are an ideal laboratory for studies of stellar magnetism. Special attention is paid to those Ap stars whose magnetically split line components are resolved in high-dispersion Stokes I spectra, and to the determination of their mean magnetic field modulus. Various techniques of exploitation of the information contained in polarized spectral line profiles are reviewed: the moment technique (in particular, the determination of the crossover and of the mean quadratic field), Zeeman-Doppler imaging, and least-squares deconvolution. The prospects that these methods open for linear polarization studies are sketched. The way in which linear polarization diagnostics complement their Stokes I and V counterparts is emphasized by consideration of the results of broad band linear polarization measurements. Illustrations of the use of various diagnostics to derive properties of the magnetic fields of Ap stars are given. This is used to show the interest of deriving more physically realistic models of the
Scattering in a magnetic field
Energy Technology Data Exchange (ETDEWEB)
David C. Carey
2002-08-19
The fixed target program at Fermilab has come to an end. New projects are in the planning stage. Among them is a muon storage ring. Up to the present, all storage rings in high-energy physics have carried stable particles, namely the electron and proton and their antiparticles. The muon is unstable and decays with a mean lifetime of 2.0 x 10{sup -6} sec. Two types of cooling have been used in the past. One is stochastic cooling where an electrode is used to detect the positions of the particles and send a signal to another position across the ring. Through successive applications of this technique, the phase space is ultimately greatly reduced and beams can be made to collide with a useful event rate. The second type of cooling is electron cooling. Here protons and electrons are made to travel together for a short distance. Equipartition causes transfer of transverse energy of the protons to that of the electrons. Neither of these methods is fast enough to allow acceleration of a sufficient number of muons up to maximum energy before they decay. A new method known as ionization cooling has been proposed.[1] The muons are cooled by passing them through a container of liquid hydrogen. The energy loss reduces both transverse and longitudinal momentum. The longitudinal momentum is restored with RF cavities. The net result is to maintain the longitudinal momentum while cooling the transverse momentum. To minimize the total travel distance of the muons the liquid hydrogen is placed inside the focusing solenoids. The question arises as to whether the presence of the solenoids influences the phase space occupied by the muons. After the muon scatters it has transverse momentum. In a constant longitudinal magnetic field the trajectory wraps around the field lines and coincides in momentum and position with a particle which scatters one cycle later. Here we calculate the change in emittance for both a drift space and a solenoid. We find that the presence of the solenoid does
Barnes, Daniel; Braxton-Gravin, Asiha; Jenkins, Jade; Ali, Halima; Punjabi, Alkesh
2013-10-01
The double-null map is the simplest symplectic map that has the generic magnetic topology of double-null divertor tokamaks. The generating function of the double-null map is given by S (x , y) = x2 /2 +y2 /2-y4/4. The equilibrium magnetic surfaces of the double-null map are calculated from the generating function. 0 1/4 gives open surfaces. The scaling of safety factor on the magnetic axis, q0, with map parameter k is calculated. The scaling of root mean square deviation of energy on the q95 surface with map parameter k is calculated and taken as the estimate of magnetic asymmetry to represent the magnetic perturbation. The results of this work will be reported. These results are used to calculate heteroclinic tangles of the separatrix of double-null map. This work is supported by grants DE-FG02-01ER54624, DE-FG02-04ER54793, and DE-FG02-07ER54937.
Compact low field magnetic resonance imaging magnet: Design and optimization
Sciandrone, M.; Placidi, G.; Testa, L.; Sotgiu, A.
2000-03-01
Magnetic resonance imaging (MRI) is performed with a very large instrument that allows the patient to be inserted into a region of uniform magnetic field. The field is generated either by an electromagnet (resistive or superconductive) or by a permanent magnet. Electromagnets are designed as air cored solenoids of cylindrical symmetry, with an inner bore of 80-100 cm in diameter. In clinical analysis of peripheral regions of the body (legs, arms, foot, knee, etc.) it would be better to adopt much less expensive magnets leaving the most expensive instruments to applications that require the insertion of the patient in the magnet (head, thorax, abdomen, etc.). These "dedicated" apparati could be smaller and based on resistive magnets that are manufactured and operated at very low cost, particularly if they utilize an iron yoke to reduce power requirements. In order to obtain good field uniformity without the use of a set of shimming coils, we propose both particular construction of a dedicated magnet, using four independently controlled pairs of coils, and an optimization-based strategy for computing, a posteriori, the optimal current values. The optimization phase could be viewed as a low-cost shimming procedure for obtaining the desired magnetic field configuration. Some experimental measurements, confirming the effectiveness of the proposed approach (construction and optimization), have also been reported. In particular, it has been shown that the adoption of the proposed optimization based strategy has allowed the achievement of good uniformity of the magnetic field in about one fourth of the magnet length and about one half of its bore. On the basis of the good experimental results, the dedicated magnet can be used for MRI of peripheral regions of the body and for animal experimentation at very low cost.
The complex-mass scheme and unitarity in perturbative quantum field theory
Energy Technology Data Exchange (ETDEWEB)
Denner, Ansgar; Lang, Jean-Nicolas [Universitaet Wuerzburg, Institut fuer Theoretische Physik und Astrophysik, Wuerzburg (Germany)
2015-08-15
We investigate unitarity within the complex-mass scheme, a convenient universal scheme for perturbative calculations involving unstable particles in quantum field theory which guarantees exact gauge invariance. Since this scheme requires one to introduce complex masses and complex couplings, the Cutkosky cutting rules, which express perturbative unitarity in theories of stable particles, are no longer valid. We derive corresponding rules for scalar theories with unstable particles based on Veltman's largest-time equation and prove unitarity in this framework. (orig.)
Kovtun, Pavel; Ünsal, Mithat; Yaffe, Laurence G.
2003-12-01
We prove an equivalence, in the large N limit, between certain U(N) gauge theories containing adjoint representation matter fields and their orbifold projections. Lattice regularization is used to provide a non-perturbative definition of these theories; our proof applies in the strong coupling, large mass phase of the theories. Equivalence is demonstrated by constructing and comparing the loop equations for a parent theory and its orbifold projections. Loop equations for both expectation values of single-trace observables, and for connected correlators of such observables, are considered; hence the demonstrated non-perturbative equivalence applies to the large N limits of both string tensions and particle spectra.
Hyperfine magnetic fields in substituted Finemet alloys
Energy Technology Data Exchange (ETDEWEB)
Brzózka, K., E-mail: k.brzozka@uthrad.pl [University of Technology and Humanities in Radom, Department of Physics (Poland); Sovák, P. [P.J. Šafárik University, Institute of Physics (Slovakia); Szumiata, T.; Gawroński, M.; Górka, B. [University of Technology and Humanities in Radom, Department of Physics (Poland)
2016-12-15
Transmission Mössbauer spectroscopy was used to determine the hyperfine fields of Finemet-type alloys in form of ribbons, substituted alternatively by Mn, Ni, Co, Al, Zn, V or Ge of various concentration. The comparative analysis of magnetic hyperfine fields was carried out which enabled to understand the role of added elements in as-quenched as well as annealed samples. Moreover, the influence of the substitution on the mean direction of the local hyperfine magnetic field was examined.
Comment on "Perturbative method to solve fourth-order gravity field equations"
Campanelli, M
1995-01-01
We reconsider the cosmic string perturbative solution to the classical fourth-order gravity field equations, obtained in Ref.\\cite{CLA94}, and we obtain that static, cylindricaly symmetric gauge cosmic strings, with constant energy density, can contain only \\beta-terms in the first order corrections to the interior gravitational field, while the exact exterior solution is a conical spacetime with deficit angle D=8\\pi\\mu.
Magnetic fields in Local Group dwarf irregulars
Chyzy, Krzysztof T; Beck, Rainer; Bomans, Dominik J
2011-01-01
We clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and what is the role of dwarf galaxies in the magnetization of the Universe. We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100m Effelsberg telescope at 2.64 and 4.85GHz. Magnetic fields in LG dwarfs are three times weaker than in the normal spirals (6muG) are observed only in dwarfs of extreme characteristics while typical LG dwarfs are not suitable objects for efficient supply of magnetic fields to the intergalactic medium.
Using optical soliton stability for magnetic field measurement
Şchiopu, IonuÅ£ Romeo; ǎgulinescu, Andrei, Dr; Marinescu, Andrei
2015-02-01
In this paper we propose a novel optical method for measuring the circular magnetic field. In practice, many situations may appear in which there are difficulties in measuring the magnetic field, as inside coils, motors etc., where the magnetic field lines are circular or elliptical. The proposed method, applied for measuring the current on high voltage lines, strongly benefits from the advantages that it offers as compared to classical solutions based on the inductive principle. Some of the advantages of optoelectronic and optic measurement methods have a real importance. These advantages consist in: avoiding the use of energy intensive materials (Cu, Fe etc.), reducing the weight of the measuring system, reducing at the minimum the fire danger due to the use of paper-oil insulation in high voltage devices etc. The novelty of our proposed method consists in using the electromagnetic radiation in ultrashort pulses, having a relatively large frequency band and a much improved resistance to external perturbations, for measuring the circular magnetic field generated from the current of high voltage lines, inside power transformers or high power motors.
Instability of strong magnetic field and neutrino magnetic dipole moment
Lee, Hyun Kyu
2016-01-01
Vacuum instability of the strong electromagnetic field has been discussed since long time ago. The instability of the strong electric field due to creation of electron pairs is one of the examples, which is known as Schwinger process. What matters are the coupling of particles to the electromagnetic field and the mass of the particle to be produced. The critical electric field for electrons in the minimal coupling is ~ m^2/e . Spin 1/2 neutral particles but with magnetic dipole moments can interact with the electromagnetic field through Pauli coupling. The instability of the particular vacuum under the strong magnetic field can be formulated as the emergence of imaginary parts of the effective potential. In this talk, the development of the imaginary part in the effective potential as a function of the magnetic field strength is discussed for the configurations of the uniform magnetic field and the inhomogeneous magnetic field. Neutrinos are the lightest particle(if not photon or gluon) in the "standard model...
Computation of magnetic fields in hysteretic media
Energy Technology Data Exchange (ETDEWEB)
Adly, A.A.; Mayergoyz, I.D.; Gomez, R.D.; Burke, E.R. (Univ. of Maryland, College Park, MD (United States))
1993-11-01
A newly developed vector Preisach-type model of hysteresis is applied to the computation of static magnetic fields in media with hysteresis. Time stepping technique is used to trace the time evolution of local magnetic fields which form the history of magnetizing process. At each time step, the magnetostatic problem is formulated in terms of an integral equation and an efficient iterative algorithm is employed for solving this problem. The technique has been used to simulate some magnetic recording processes. Sample results of these simulations are given in the paper.
Magnetosphere of a Kerr black hole immersed in magnetized plasma and its perturbative mode structure
Yang, Huan; Lehner, Luis
2015-01-01
This work studies jet-like electromagnetic configurations surrounding a slowly-spinning black-hole immersed in a uniformly magnetized force-free plasma. In the first part of this work, we present a family of stationary solutions that are jet-capable. While these solutions all satisfy the force-free equations and the appropriate boundary conditions, our numerical experiments show a unique relaxed state starting from different initial data, and so one member of the family is likely preferred over the others. In the second part of this work, we analyze the perturbations of this family of jet-like solutions, and show that the perturbative modes exhibit a similar split into the trapped and traveling categories previously found for perturbed Blandford-Znajek solutions. In the eikonal limit, the trapped modes can be identified with the fast magnetosonic waves in the force-free plasma and the traveling waves are essentially the Alfven waves. Moreover, within the scope of our analysis, we have not seen signs of unstab...
On the Stability of a General Magnetic Field Topology in Stellar Radiative Zones
Augustson, Kyle; Strugarek, Antoine
2016-01-01
This paper provides a brief overview of the formation of stellar fossil magnetic fields and what potential instabilities may occur given certain configurations of the magnetic field. In particular, a purely magnetic instability can occur for poloidal, toroidal, and mixed poloidal-toroidal axisymmetric magnetic field configurations as originally studied in Tayler (1973), Markey & Tayler (1973), and Tayler (1980). However, most of the magnetic field configurations observed at the surface of massive stars are non- axisymmetric. Thus, extending earlier studies of the axisymmetric Tayler instability in spherical geometry (Goossens, 1980), we introduce a formulation for the global change in the potential energy contained in a convectively-stable region given an arbitrary Lagrangian perturbation, which permits the inclusion of both axisymmetric and non-axisymmetric magnetic fields. With this tool in hand, a path is shown by which more general stability criterion can be established.
On The Stability of A General Magnetic Field Topology In Stellar Radiative Zones
Augustson, Kyle; Mathis, Stéphane; Strugarek, Antoine
2016-10-01
This paper provides a brief overview of the formation of stellar fossil magnetic fields and what potential instabilities may occur given certain configurations of the magnetic field. In particular, a purely magnetic instability can occur for poloidal, toroidal, and mixed poloidal-toroidal axisymmetric magnetic field configurations as originally studied in Tayler (1973), Markey & Tayler (1973), and Tayler (1980). However, most of the magnetic field configurations observed at the surface of massive stars are non- axisymmetric. Thus, extending earlier studies of the axisymmetric Tayler instability in spherical geometry (Goossens, 1980), we introduce a formulation for the global change in the potential energy contained in a convectively-stable region given an arbitrary Lagrangian perturbation, which permits the inclusion of both axisymmetric and non-axisymmetric magnetic fields. With this tool in hand, a path is shown by which more general stability criterion can be established.
Growth rate of matter perturbations as a probe of large-scale magnetism
Giovannini, Massimo
2011-01-01
The growth rate of matter perturbations is computed in a magnetized environment for the LambdaCDM and wCDM paradigms. It is argued that the baryons do not necessarily follow into the dark matter potential wells after they are released from the drag of the photons. The baryonic evolution equations inherit a forcing term whose explicit form depends on the plasma description and can be deduced, for instance, in the resistive magnetohydrodynamical approximation. After deriving an analytical expression for the growth rate applicable when dark energy does not cluster, the effects of relativistic corrections and of the inhomogeneities associated with the other species of the plasma are taken into account numerically. The spectral amplitudes and slopes of the stochastic magnetic background are selected to avoid appreciable distortions in the measured temperature and polarization anisotropies of the Cosmic Microwave Background. The growth of structures in the current paradigms of structure formation represents a compl...
Manganotti, Paolo; Del Felice, Alessandra
2013-01-01
Transcranial magnetic stimulation (TMS) evolved from a simple method to stimulate the motor cortex to an invaluable tool for multiple diagnostic, research, and therapeutic applications. A further development of this noninvasive brain stimulation technique is concomitant electroencephalographic (EEG) recording during TMS. The theoretical underpinnings and the technological innovation of TMS-EEG co-registration have opened new ways to study brain excitability in neurological conditions previously investigated with conventional EEG alone. A further advance in TMS research applications is the perturbational approach: magnetic pulses can interfere not only with dynamic, often pathological rhythms in epilepsy or altered consciousness states, but also modulate physiological states such as sleep and sleep deprivation. So applied, TMS-EEG co-registration can reveal different neurophysiological and behavioral patterns in the awake state, sleep or sleep deprivation. In this review, we discuss the use of TMS and TMS-EEG co-registration in epilepsy, a still rather limited although promising area of study.
Orain, François; Bécoulet, M.; Morales, J.; Huijsmans, G. T. A.; Dif-Pradalier, G.; Hoelzl, M.; Garbet, X.; Pamela, S.; Nardon, E.; Passeron, C.; Latu, G.; Fil, A.; Cahyna, P.
2015-01-01
The dynamics of a multi-edge localized mode (ELM) cycle as well as the ELM mitigation by resonant magnetic perturbations (RMPs) are modeled in realistic tokamak X-point geometry with the non-linear reduced MHD code JOREK. The diamagnetic rotation is found to be a key parameter enabling us to reproduce the cyclical dynamics of the plasma relaxations and to model the near-symmetric ELM power deposition on the inner and outer divertor target plates consistently with experimental measurements. Moreover, the non-linear coupling of the RMPs with unstable modes are found to modify the edge magnetic topology and induce a continuous MHD activity in place of a large ELM crash, resulting in the mitigation of the ELMs. At larger diamagnetic rotation, a bifurcation from unmitigated ELMs—at low RMP current—towards fully suppressed ELMs—at large RMP current—is obtained.