Excitation of global Alfven Eigenmodes by RF heating in JET
Kerner, W.; Borba, D.; Gormezano, C.; Huysmans, G.; Porcelli, F.; Start, D. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Fasoli, A. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Sharapov, S. [Kurchatov Institute, Moscow (Russian Federation)
1994-07-01
The alpha-particle confinement of future D-T experiments at JET can be severely degraded by Global Alfven Eigenmodes (AE). Scenarios for the excitation of Alfven Eigenmodes in usual (e.g. D-D) plasmas are proposed, which provide a MHD diagnostic and allow the study of the transport of super-Alfvenic ions. Active studies with separate control of TAE amplitude and energetic particle destabilization, measuring the plasma response, give more information than passive studies, in particular concerning the damping mechanisms. The TAE excitation can be achieved by means of the saddle coil and the ICRH antenna. The experimental method is introduced together with a theoretical model for RF excitation. (authors). 6 refs., 3 figs.
Characteristics of Short Wavelength Compressional Alfven Eigenmodes
Fredrickson, E D; Podesta, M; Bortolon, A; Crocker, N A; Gerhardt, S P; Bell, R E; Diallo, A; LeBlanc, B; Levinton, F M
2012-12-19
Most Alfvenic activity in the frequency range between Toroidal Alfven Eigenmodes and roughly one half of the ion cyclotron frequency on NSTX [M. Ono, et al., Nucl. Fusion 40 (2000) 557], that is, approximately 0.3 MHz up to ≈ 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n=1 kink-like mode. In this paper we present measurements of the spectrum of these high frequency CAE (hfCAE), and their mode structure. We compare those measurements to a simple model of CAE and present evidence of a curious non-linear coupling of the hfCAE and the low frequency kink-like mode.
Non-linear modulation of short wavelength compressional Alfven eigenmodes
Fredrickson, E. D.; Gorelenkov, N. N.; Podesta, M.; Gerhardt, S. P.; Bell, R. E.; Diallo, A.; LeBlanc, B. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Bortolon, A. [University of California, Irvine, California 92697 (United States); Crocker, N. A. [University of California, Los Angeles, California 90095 (United States); Levinton, F. M.; Yuh, H. [Nova Photonics, Princeton, New Jersey 08543 (United States)
2013-04-15
Most Alfvenic activity in the frequency range between toroidal Alfven eigenmodes and roughly one half of the ion cyclotron frequency on National Spherical Torus eXperiment [Ono et al., Nucl. Fusion 40, 557 (2000)], that is, approximately 0.3 MHz up to Almost-Equal-To 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n = 1 kink-like mode. In this paper, we present measurements of the spectrum of these high frequency CAE (hfCAE) and their mode structure. We compare those measurements to a simple model of CAE and present a predator-prey type model of the curious non-linear coupling of the hfCAE and the low frequency kink-like mode.
Alfven eigenmode structure during off-axis neutral beam injection
Tobias, B.; Bass, E. M.; Classen, I.G.J.; Domier, C.W.; Grierson, B. A.; Heidbrink, W. W.; N C Luhmann Jr.,; Nazikian, R.; Park, H. K.; Spong, D. A.; VanZeeland, M. A.
2012-01-01
The spatial structure of Alfven eigenmodes on the DIII-D tokamak is compared for contrasting fast ion deposition profiles resulting from on- and off-axis neutral beam injection (NBI). In both cases, poloidal mode rotation and eigenmode twist, or radial phase variation, are correlated with the direct
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
N.N. Gorelenkov, G.J. Kramer, and R. Nazikian
2011-05-23
A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
Destabilization of Alfven eigenmodes by fast particles in W7-AS
Zegenhagen, S.
2006-02-15
In the present thesis, a systematic study of beam driven Alfven eigenmodes in high-density and low-temperature plasmas of the W7-AS stellarator is performed. The goal of this thesis is twofold: (I) identification and description of fast particle driven Alfven instabilities in W7-AS, and (II) study of energetic particle losses induced by Alfven instabilities. A total of 133 different Alfven eigenmodes is studied in discharges from different experimental campaigns. The discharges are characterized by high density, n{sub e}=5 x 1019 m{sup -3} to 2.5 x 1020 m{sup -3} at relatively low temperatures of T{sub e}=T{sub i}=150..600 eV. Additional 13 events are found to have frequencies inside the EAE gap and could possibly be EAEs. Evidence for high-frequency Alfven eigenmodes (mirror- and helicity-induced Alfven eigenmodes) is seen, but can not be proven rigorously due to uncertain mode numbers and the complexity of the Alfven continuum. The remaining 41 Alfven eigenmodes can not be classified to be one of the above cases. (orig.)
Existence of Weakly Damped Kinetic Alfven Eigenmodes in Reversed Shear Tokamak
N. N. Gorelenkov
2008-08-12
A kinetic theory of weakly damped Alfven Eigenmode (AE) solutions strongly interacting with the continuum is developed for tokamak plasmas with reversed magnetic shear. We show that the ideal MHD model is not sufficient for the eigenmode solutions if the standard causality condition bypass rule is applied. Finite Larmor radius effects are required, which introduce multiple kinetic subeigenmodes and collisionless radiative damping. The theory explains the existence of experimentally observed Alfvenic instabilities with frequencies sweeping down and reaching their minimum (bottom).
VanZeeland, M. A.; Heidbrink, W. W.; Fisher, R. K.; Munoz, M. G.; Kramer, G. J.; Pace, D. C.; White, R. B.; Akaslompolo, S.; Austin, M. E.; Boom, J. E.; Classen, I.G.J.; da Graca, S.; Geiger, B.; Gorelenkova, M.; Gorelenkov, N. N.; Hyatt, A. W.; Luhmann, N.; Maraschek, M.; McKee, G. R.; Moyer, R. A.; Muscatello, C. M.; Nazikian, R.; Park, H.; Sharapov, S.; Suttrop, W.; Tardini, G.; Tobias, B. J.; Zhu, Y. B.
2011-01-01
Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas produces a variety of Alfvenic activity including toroidicity-induced Alfven eigenmodes and reversed shear Alfven eigenmodes (RSAEs). These modes are studied during the discharge current ramp phase when incomplete c
Gorelenkov, N.N. [Princeton Plasma Physics Laboratory, Princeton University (United States)], E-mail: ngorelen@pppl.gov; Berk, H.L. [IFS, Austin, Texas (United States); Fredrickson, E. [Princeton Plasma Physics Laboratory, Princeton University (United States); Sharapov, S.E. [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire (United States)
2007-10-08
New global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfven-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high-beta >20%. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfven coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.
Perturbative Study of Energetic Particle Redistribution by Alfven Eigenmodes in ITER
N.N. Gorelenkov and R.B. White
2012-10-29
The modification of particle distributions by magnetohydrodynamic modes is an important topic for magnetically confined plasmas. Low amplitude modes are known to be capable of producing significant modification of injected neutral beam profiles. Flattening of a distribution due to phase mixing in an island or due to portions of phase space becoming stochastic is a process extremely rapid on the time scale of an experiment. In this paper we examine the effect of toroidal Alfven eigenmodes (TAE) and reversed shear Alfven eigenmodes (RSAE) in ITER on alpha particle and injected beam distributions using theoretically predicted mode amplitudes. It is found that for the equilibrium of a hybrid scenario even at ten times the predicted saturation level the modes have negligible effect on these distributions. A strongly reversed shear (or advanced) scenario, having a spectrum of modes that are much more global, is somewhat more susceptible to induced loss due to mode resonance, with alpha particle losses of over one percent with predicted amplitudes and somewhat larger with the assistance of toroidal field ripple. The elevated q profile contributes to stronger TAE (RSAE) drive and more unstable modes. An analysis of the existing mode-particle resonances is carried out to determine which modes are responsible for the profile modification and induced loss. We find that losses are entirely due to resonance with the counter-moving and trapped particle populations, with co-moving passing particles participating in resonances only deep within the plasma and not leading to loss.
Pressure-gradient-induced Alfven eigenmodes: 2. Kinetic excitation with ion temperature gradient
Bierwage, Andreas; Zonca, Fulvio
2009-01-01
The kinetic excitation of ideal magnetohydrodynamic (MHD) discrete Alfven eigenmodes in the second MHD ballooning stable domain is studied in the presence of a thermal ion temperature gradient (ITG), using linear gyrokinetic particle-in-cell simulations of a local flux tube in shifted-circle tokamak geometry. The instabilities are identified as alpha-induced toroidal Alfven eigenmodes (alphaTAE); that is, bound states trapped between pressure-gradient-induced potential barriers of the Schroedinger equation for shear Alfven waves. Using numerical tools, we examine in detail the effect of kinetic thermal ion compression on alphaTAEs; both non-resonant coupling to ion sound waves and wave-particle resonances. It is shown that the Alfvenic ITG instability thresholds (e.g., the critical temperature gradient) are determined by two resonant absorption mechanisms: Landau damping and continuum damping. The numerical results are interpreted on the basis of a theoretical framework previously derived from a variational f...
The effect of toroidal plasma rotation on low-frequency reversed shear Alfven eigenmodes in tokamaks
Haverkort, J. W.
2012-01-01
The influence of toroidal plasma rotation on the existence of reversed shear Alfven eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence of RSAEs. Th
Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging
Tobias, B. J.; Classen, I.G.J.; Domier, C.W.; Heidbrink, W. W.; N C Luhmann Jr.,; Nazikian, R.; Park, H. K.; Spong, D. A.; VanZeeland, M. A.
2011-01-01
Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the o
Calculation of continuum damping of Alfv\\'en eigenmodes in 2D and 3D cases
Bowden, G W; Könies, A
2015-01-01
In ideal MHD, shear Alfv\\'{e}n eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfv\\'{e}n continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfv\\'{e}n eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD code CKA . ...
Tholerus, Emmi; Hellsten, Torbjörn
2016-01-01
FOXTAIL is a new hybrid magnetohydrodynamic-kinetic code used to describe interactions between energetic particles and Alfv\\'en eigenmodes in tokamaks with realistic geometries. The code simulates the nonlinear dynamics of the amplitudes of individual eigenmodes and of a set of discrete markers in five-dimensional phase space representing the energetic particle distribution. Action-angle coordinates of the equilibrium system are used for efficient tracing of energetic particles, and the particle acceleration by the wave fields of the eigenmodes is Fourier decomposed in the same angles. The eigenmodes are described using temporally constant eigenfunctions with dynamic complex amplitudes. Possible applications of the code are presented, e.g., making a quantitative validity evaluation of the one-dimensional bump-on-tail approximation of the system. Expected effects of the fulfillment of the Chirikov criterion in two-mode scenarios have also been verified.
Sensitivity of alpha-particle-driven Alfven eigenmodes to q-profile variation in ITER scenarios
Rodrigues, P; Fazendeiro, L; Ferreira, J; Coelho, R; Nabais, F; Borba, D; Polevoi, N F Loureiro A R; Pinches, S D; Sharapov, S E
2016-01-01
An hybrid ideal-MHD/drift-kinetic approach to assess the stability of alpha-particle-driven Alfven eigenmodes in burning plasmas is used to show that certain foreseen ITER scenarios, namely the $I_\\mathrm{p} = 15$ MA baseline scenario with very low and broad core magnetic shear, are sensitive to small changes in the background magnetic equilibrium. Slight perturbations (of the order of 1%) in the total plasma current are seen to cause large variations in the growth rate, toroidal mode number, and radial location of the most unstable eigenmodes found. The observed sensitivity is shown to proceed from the very low magnetic shear values attained throughout the plasma core.
Testa, D. [CRPP, Switzerland; Spong, Donald A [ORNL; Panis, T. [CRPP, Switzerland; Blanchard, P. [CRPP, Switzerland; Fasoli, A. [CRPP, Switzerland
2011-01-01
This paper reports the results of recent experiments performed on the JET tokamak on Alfven eigenmodes (AEs) with toroidal mode number (n) in the range n = 3-15. The stability properties of these medium-n AEs are investigated experimentally using a new set of compact in-vessel antennas, providing a direct and real-time measurement of the frequency, damping rate and amplitude for each individual toroidal mode number. We report here the quantitative analysis of the measurements of the damping rate for stable n = 3 toroidal AEs as a function of the edge plasma elongation, and the theoretical analysis of these data with the TAEFL code. The TAEFL results are in excellent qualitative agreement with the measurements, reproducing well the experimental scaling of increasing damping rate versus increasing edge elongation, and in many cases are also quantitatively correct, with a difference with respect to the measurements below 30%, particularly for magnetic configurations that have a larger edge magnetic shear.
Analysis of Alfven Eigenmodes destabilization by fast particles in Large Helical Device
Varela, Jacobo; Spong, Donald; Garcia, Luis
2016-10-01
Fast particle populations in nuclear fusion experiments can destabilize Alfven Eigenmodes through inverse Landau damping and couplings with gap modes in the shear Alfven continua. We use the reduced MHD equations to describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles. We add the Landau damping and resonant destabilization effects by a closure relation. We apply this model to study the Alfven modes stability in Large Helical Device (LHD) equilibria for inward configurations, performing a parametric analysis along a range of realistic values of fast particle β (βfp), ratios of thermal/Alfven velocities (Vth/Vao), magnetic Lundquist numbers (S) and dominant toroidal (n) modes families. The n = 1 and n =2 toroidal families show the largest growth rates for parameters closer to a real LHD scenario (S = 5E6, βfp = 0.02 and Vth/Vao = 0.5), particularly the modes n/m = 1/2 and 2/4 located the inner and middle plasma (ρ = 0.25 - 0.5 with ρ the normalized minor radius). The n = 3 and n = 4 toroidal families are weakly perturbed by fast particles.
Effects of energetic particles on zonal flow generation by toroidal Alfven eigenmode
Qiu, Zhiyong; Zonca, Fulvio
2016-01-01
Generation of zonal ow (ZF) by energetic particle (EP) driven toroidal Alfven eigenmode (TAE) is investigated using nonlinear gyrokinetic theory. It is found that, nonlinear resonant EP contri- bution dominates over the usual Reynolds and Maxwell stresses due to thermal plasma nonlinear response. ZF can be forced driven in the linear growth stage of TAE, with the growth rate being twice the TAE growth rate. The ZF generation mechanism is shown to be related to polarization induced by resonant EP nonlinearity. The generated ZF has both the usual meso-scale and micro- scale radial structures. Possible consequences of this forced driven ZF on the nonlinear dynamics of TAE are also discussed.
Fine Structure Zonal Flow Excitation by Beta-induced Alfven Eigenmode
Qiu, Zhiyong; Zonca, Fulvio
2016-01-01
Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced Alfven eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It is found that electrostatic zonal flow (ZF), rather than zonal current, is preferentially excited by finite amplitude BAE. In addition to the well-known meso-scale radial envelope structure, ZF is also found to exhibit fine radial structure due to the localization of BAE with respect to mode rational surfaces. Specifically, the zonal electric field has an even mode structure at the rational surface where radial envelope peaks.
Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging
Tobias, Ben [University of California, Davis; Classen, I.G.J. [FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands; Domier, C. W. [University of California, Davis; Heidbrink, W. [University of California, Irvine; Luhmann, N.C. [University of California, Davis; Nazikian, Raffi [Princeton Plasma Physics Laboratory (PPPL); Park, H.K. [Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea; Spong, Donald A [ORNL; Van Zeeland, Michael [General Atomics
2011-01-01
Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.
Stability of Global Alfven Waves (Tae, Eae) in Jet Tritium Discharges
Kerner, W.; Borba, D.; Huysmans, G. T. A.; Porcelli, F.; Poedts, S.; Goedbloed, J. P.; Betti, R.
1994-01-01
The interaction of alpha-particles in JET tritium discharges with global Alfven waves via inverse Landau damping is analysed. It is found that alpha-particle driven eigenmodes were stable in the PTE1 and should also be stable in a future 50:50 deuterium-tritium mix discharge aiming at Q(DT) = 1,
Podesta, M; Fredrickson, E D; Gorelenkov, N N; LeBlanc, B P; Heidbrink, W W; Crocker, N A; Kubota, S
2010-08-19
The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Reversed Shear Alfv'en Eigenmode Stabilization by Localized Electron Cyclotron Heating
van Zeeland, M. A.; Lohr, J.; Heidbrink, W. W.; Nazikian, R.; Solomon, W. M.; Gorelenkov, N. N.; Kramer, G. J.; Austin, M. E.; Rhodes, T. L.; Holcomb, C.; Makowski, M. A.; McKee, G. R.; Sharapov, S. E.
2007-11-01
Reversed shear Alfv'en eigenmode (RSAE) activity in DIII-D is observed to be stabilized by electron cyclotron heating (ECH) near the minimum of the safety factor (qmin) in neutral beam heated discharges with reversed magnetic shear. The degree of RSAE stabilization and the volume averaged neutron production (Sn) are highly dependent on ECH deposition location relative to qmin. Ideal MHD simulations predict RSAE existence during ECH, indicating that the mode disappearance is due to kinetic effects not taken into account by the ideal MHD model. While discharges with ECH stabilization of RSAEs have higher Sn than discharges with significant RSAE activity, neutron production remains strongly reduced (up to 60%), indicating the bulk of the deficit is not due to RSAEs alone.
Experimental Evaluation of Energy Transfer between Fast Ions and Alfven Eigenmodes
Nagaoka, Kenichi; Osakabe, Masaki; Isobe, Mitsutaka; Ogawa, Kunihiro; Suzuki, Yasuhiro; Kobayashi, Shinji; Yamamoto, Satoshi; Miyoshi, Yoshizumi; Katoh, Yuto; Fontdecaba, Josep Maria; Ascasibar, Enrique; LHD Team
2016-10-01
Recently, a new wave-particle analyzer was proposed to identify interaction between fast ions and Alfven eigenmodes [K. Nagaoka, 67th annual meeting of APS-DPP, savanna, 2015]. A data acquisition system for the wave-particle interaction analysis was developed for particle counting mode operation of neutral particle detectors. We recently applied the system to the Si-FNA detector signals in LHD and Heliotron J, and NPA signals in TJ-II. The first experimental results obtained in three devices are presented and the importance of the optimization of line of sight will be discussed. This research was supported by NIFS/NINS under the project of 'Promotion of International Network for Scientific Collaboration', NIFS Collaboration Research program (NIFS16KUHL068) and JSPS KAKENHI Grani-in-Aid for Young Scientists (A) 26709071.
Stochastic Orbit Loss of Neutral Beam Ions From NSTX Due to Toroidal Alfven Eigenmode Avalanches
Darrow, D S; Fredrickson, E D; Gorelenkov, N N; Gorelenkova, M; Kubota, S; Medley, S S; Podesta, M; Shi, L
2012-07-11
Short toroidal Alfven eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and sometimes a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions occurs. When beam ion orbits are followed with a guiding center code that incorporates plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are similar to those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary.
Bierwage, Andreas; Spong, Donald A.
2009-05-01
Hybrid-MHD-Gyrokinetic Code (HMGC) [1] and the gyrofluid code TAEFL [2,3] are used for nonlinear simulation of Alfven Eigenmodes in Tokamak plasma. We compare results obtained in two cases: (I) a case designed for cross-code benchmark of TAE excitation; (II) a case based on a dedicated DIII-D shot #132707 where RSAE and TAE activity is observed. Differences between the numerical simulation results are discussed and future directions are outlined. [1] S. Briguglio, G. Vlad, F. Zonca and C. Kar, Phys. Plasmas 2 (1995) 3711. [2] D.A. Spong, B.A. Carreras and C.L. Hedrick, Phys. Fluids B4 (1992) 3316. [3] D.A. Spong, B.A. Carreras and C.L. Hedrick, Phys. Plasmas 1 (1994) 1503.
The Berk-Breizman Model as a Paradigm for Energetic Particle-driven Alfven Eigenmodes
Lesur, Maxime
2011-01-01
The achievement of sustained nuclear fusion in magnetically confined plasma relies on efficient confinement of high-energy ions produced by the fusion reaction. Such particles can excite Alfven Eigenmodes (AEs), which significantly degrade their confinement and threatens the vacuum vessel of future reactors. To develop diagnostics and control schemes, a better understanding of linear and nonlinear features of resonant interactions between plasma waves and high-energy particles, is required. In the case of an isolated single resonance, the problem is homothetic to the so-called Berk-Breizman (BB) problem, which is an extension of the classic bump-on-tail electrostatic problem, including external damping to a thermal plasma, and collisions. A semi-Lagrangian simulation code, COBBLES, is developed to solve the initial-value BB problem. The nonlinear behavior of instabilities in experimentally-relevant conditions is categorized into steady-state, periodic, chaotic, and frequency-sweeping (chirping) regimes. The c...
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
Batha, S.H.; Levinton, F.M. [Fusion Physics and Technology, Torrance, CA (United States); Spong, D.A. [Oak Ridge National Lab., TN (United States)] [and others
1995-07-01
Experiments to destabilize the Toroidicity-induced Alfven Eigenmode (TAE) by energetic alpha particles were performed on the Tokamak Fusion Test Reactor using deuterium and tritium fuel. To decrease the alpha particle pressure instability threshold, discharges with an elevated value of q(0) > 1.5 were used. By raising q(0), the radial location of the low toroidal-mode-number TAE gaps moves toward the magnetic axis and into alignment with the region of maximum alpha pressure gradient, thereby (in theory) lowering the value of {beta}{sub {alpha}}(0) required for instability. No TAE activity was observed when the central alpha particle {beta}{sub {alpha}} reached 0.08% in a discharge with fusion power of 2.4 MW. Calculations show that the fusion power is within a factor of 1.5 to 3 of the instability threshold.
Stability of the toroidicity-induced Alfven eigenmode in axisymmetric toroidal equilibria
Fu, G.Y.; Cheng, C.Z.; Wong, K.L.
1993-09-01
The stability of toroidicity-induced Alfven eigenmodes (TAE) is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. For the trapped hot particles, the finite orbit width is found to be stabilizing. For the circulating hot particles, the finite orbit width effect is stabilizing for larger values of v{sub h}/v{sub A} (> 1) and destabilizing for smaller values of v{sub h}/v{sub A} (< 1), where v{sub h} is the hot particle speed and v{sub A} is the Alfven speed. The collisional damping of the trapped electrons is found to have a much weaker dependence on the collision frequency than the previous analytic results. The contribution of the curvature term to the trapped electron collisional damping is negligible compared to that of the parallel electric field term for typical parameters. The calculated critical hot particle beta values for the TAE instability are consistent with the experimental measurements.
Alfven eigenmode stability and fast ion loss in DIII-D and ITER reversed magnetic shear plasmas
Van Zeeland, Michael [General Atomics; Gorelenkov, Nikolai [Princeton Plasma Physics Laboratory (PPPL); Heidbrink, W. [University of California, Irvine; Kramer, G. [Princeton Plasma Physics Laboratory (PPPL); Spong, Donald A [ORNL; Austin, M. E. [University of Texas, Austin; Fisher, R K [General Atomics, San Diego; Munoz, M G [Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Garching, Germany; Gorelenkova, M. [Princeton Plasma Physics Laboratory (PPPL); Luhmann, N.C. [University of California, Davis; Murakami, Masanori [ORNL; Nazikian, Raffi [Princeton Plasma Physics Laboratory (PPPL); Park, J. M. [Oak Ridge National Laboratory (ORNL); Tobias, Ben [University of California, Davis; White, R. [Princeton Plasma Physics Laboratory (PPPL)
2012-01-01
Neutral beam injection into reversed-magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including toroidicity-induced Alfven eigenmodes (TAEs) and reversed shear Alfven eigenmodes (RSAEs). With measured equilibrium profiles as inputs, the ideal MHD code NOVA is used to calculate eigenmodes of these plasmas. The postprocessor code NOVA-K is then used to perturbatively calculate the actual stability of the modes, including finite orbit width and finite Larmor radius effects, and reasonable agreement with the spectrum of observed modes is found. Using experimentally measured mode amplitudes, fast ion orbit following simulations have been carried out in the presence of the NOVA calculated eigenmodes and are found to reproduce the dominant energy, pitch and temporal evolution of the losses measured using a large bandwidth scintillator diagnostic. The same analysis techniques applied to a DT 8 MA ITER steady-state plasma scenario with reversed-magnetic shear and both beam ion and alpha populations show Alfven eigenmode instability. Both RSAEs and TAEs are found to be unstable with maximum growth rates occurring for toroidal mode number n = 6 and the majority of the drive coming from fast ions injected by the 1MeV negative ion beams. AE instability due to beam ion drive is confirmed by the non-perturbative code TAEFL. Initial fast ion orbit following simulations using the unstable modes with a range of amplitudes (delta B/B = 10(-5)-10(-3)) have been carried out and show negligible fast ion loss. The lack of fast ion loss is a result of loss boundaries being limited to large radii and significantly removed from the actual modes themselves.
Stability analysis of toroidicity-induced Alfven eigenmodes in TFTR DT experiments
Fu, G.Y.; Cheng, C.Z.; Budny, R.; Chang, Z.; Darrow, D.S.; Fredrickson, E.; Mazzucato, E.; Nazikian, R.; Zweben, S.
1995-05-15
The toroidicity-induced Alfvin eigenmodes (TAE) with radially extended structure are found to be stable in the Tokamak Fusion Test Reactor Deuterium-Tritium plasmas. A core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta, which can be destabilized by energetic alpha particles on TFTR. With additional instability drive from fast minority ions powered by ICRH, both the global and the core localized TAE modes can be readily destabilized.
Biglari, H.; Zonca, F.; Chen, L.
1991-10-01
Toroidal Alfven eigenmodes are shown to be resonantly destabilized by both circulating and trapped energetic ions/alpha particles. In particular, the energetic circulating ions are shown to resonate with the mode not only at the Alfven speed ({upsilon}{sub A}), but also one-third of this speed, while resonances exist between trapped energetic ions and the wave when {upsilon} = {upsilon}{sub A}/21{epsilon}{sup {1/2}} (l=integer, {epsilon}=r/R is the local inverse aspect ratio), although the instability becomes weaker for resonances other than the fundamental. The oft-quoted criterion that instability requires super-Alfvenic ion velocities is thus sufficient but not necessary. 14 refs.
Figueiredo, A C A; Borba, D; Coelho, R; Fazendeiro, L; Ferreira, J; Loureiro, N F; Nabais, F; Pinches, S D; Polevoi, A R; Sharapov, S E
2016-01-01
The linear stability of Alfv\\'en eigenmodes in the presence of fusion-born alpha particles is thoroughly assessed for two variants of an ITER baseline scenario, which differ significantly in their core and pedestal temperatures. A systematic approach is used that considers all possible eigenmodes for a given magnetic equilibrium and determines their growth rates due to alpha-particle drive and Landau damping on fuel ions, helium ashes and electrons. This extensive stability study is efficiently conducted through the use of a specialized workflow that profits from the performance of the hybrid MHD drift-kinetic code $\\mbox{CASTOR-K}$ (Borba D. and Kerner W. 1999 J. Comput. Phys. ${\\bf 153}$ 101; Nabais F. ${\\it et\\,al}$ 2015 Plasma Sci. Technol. ${\\bf 17}$ 89), which can rapidly evaluate the linear growth rate of an eigenmode. It is found that the fastest growing instabilities in the aforementioned ITER scenario are core-localized, low-shear toroidal Alfv\\'en eigenmodes. The largest growth-rates occur in the s...
On Properties of Compressional Alfven Eigenmode Instability Driven by Superalfvinic Ions
N.N. Gorelenkov; C.Z. Cheng
2002-02-06
Properties of the instability of Compressional Alfven Eigenmodes (CAE) in tokamak plasmas are studied in the cold plasma approximation with an emphasis on the instability driven by the energetic minority Ion Cyclotron Resonance Heating (ICRH) ions. We apply earlier developed theory [N.N. Gorelenkov and C.Z. Cheng, Nuclear Fusion 35 (1995) 1743] to compare two cases: Ion Cyclotron Emission (ICE) driven by charged fusion products and ICRH Minority driven ICE (MICE) [J. Cottrell, Phys. Rev. Lett. (2000)] recently observed on JET [Joint European Torus]. Particularly in MICE spectrum, only instabilities with even harmonics of deuterium-cyclotron frequency at the low-field-side plasma edge were reported. Odd deuterium-cyclotron frequency harmonics of ICE spectrum between the cyclotron harmonics of protons can be driven only via the Doppler-shifted cyclotron wave-particle resonance of CAEs with fusion products, but are shown to be damped due to the electron Landau damping in experiments on MI CE. Excitation of odd harmonics of MICE with high-field-side heating is predicted. Dependencies of the instability on the electron temperature is studied and is shown to be strong. Low electron temperature is required to excite odd harmonics in MICE.
Predictions and observations of global beta-induced Alfven-acoustic modes in JET and NSTX
Gorelenkov, N N [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Berk, H L [Institute for Fusion Studies, University of Texas, Austin, TX 78712 (United States); Crocker, N A [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Fredrickson, E D [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kaye, S [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kubota, S [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Park, H [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Peebles, W [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Sabbagh, S A [Department of Applied Physics, Columbia University, New York, NY 10027-6902 (United States); Sharapov, S E [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom); Stutmat, D [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Tritz, K [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Levinton, F M [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States); Yuh, H [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States)
2007-12-15
In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfven-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.
Lestz, Jeff; Belova, Elena; Gorelenkov, Nikolai; Tang, Shawn; Crocker, Neal
2016-10-01
High frequency compressional (CAE) and global (GAE) Alfvén eigenmodes are often driven unstable by super-Alfvénic beam ions in NSTX, and have been linked to anomalous electron temperature profile flattening at high beam power [D. Stutman, PRL 2009]. A large set of 3D MHD- δf hybrid simulations show that GAE are ubiquitous at beam energies Vb /VA > 2.5 , while CAE are not excited until Vb /VA > 4 . The frequency of the most unstable GAE changes significantly with the normalized beam energy, consistent with trends described by its dispersion and resonance condition. These simulation results are analyzed and compared with a new, extensive experimental survey of NSTX discharges, as well as analytic studies. Interestingly, simulations find no case where counter-propagating CAE are more unstable than co-CAE, whereas experiments routinely observe both co- and counter-CAE. Moreover, simulations find co-GAE to be very unstable for beams peaked around λ <= 0.5 , yet these modes have not yet been thoroughly investigated experimentally. Preliminary predictions are also made for the CAE/GAE instability in ITER-like plasmas, which are expected to operate near similar values of Vb /VA as those studied for NSTX. This work supported by DOE contracts DE-AC02-09CH11466 and DE-SC0011810.
Yamaguchi, Y [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Ichimura, M [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Higaki, H [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Kakimoto, S [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Nakagome, K [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Nemoto, K [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Katano, M [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Nakajima, H [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Fukuyama, A [Department of Nuclear Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan); Cho, T [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan)
2006-08-15
The formation of eigenmodes with the m = 1 fast Alfven waves in the ion-cyclotron range of frequency are investigated in the axisymmetric central cell of the GAMMA 10 tandem mirror. When the fast waves with frequencies near the fundamental ion-cyclotron frequency have been used for the plasma production, the saturation in the density has been observed. The spatial structure of the excited wave field is calculated in the central cell using a two-dimensional full wave code. The results of numerical analysis indicate that the increase in plasma density depends strongly on the eigenmode formations associated with the boundary conditions. The results of numerical analysis are compared with the results of measurements of the waves with magnetic probes. A very good degree of agreement is found between the theoretical results and the experimental results. It is suggested that the simultaneous excitation of several radial eigenmodes with high-harmonic fast waves is effective for higher density plasma production.
Rodrigues, P; Ferreira, J; Coelho, R; Nabais, F; Borba, D; Loureiro, N F; Oliver, H J C; Sharapov, S E
2014-01-01
A systematic approach to assess the linear stability of Alfv\\'en eigenmodes in the presence of fusion-born alpha particles is described. Because experimental results for ITER are not available yet, it is not known beforehand which Alfv\\'en eigenmodes will interact more intensively with the alpha-particle population. Therefore, the number of modes that need to be considered in stability assessments becomes quite large and care must be exercised when choosing the numerical tools to work with, which must be fast and efficient. In the presented approach, all possible eigenmodes are first found after intensively scanning a suitable frequency range. Each solution found is then tested to find if its discretization over the radial grid in use is adequate. Finally, the interaction between the identified eigenmodes and the alpha-particle population is evaluated with the drift-kinetic code CASTOR-K, in order to assess their growth rates and hence their linear stability. The described approach enables one to single out t...
Weiland, Markus; Geiger, Benedikt; Bilato, Roberto; Schneider, Philip; Tardini, Giovanni; Lauber, Philipp; Ryter, Francois; Schneller, Mirjam [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); Collaboration: ASDEX Upgrade Team
2015-05-01
Fast, supra-thermal ions are created in the tokamak ASDEX Upgrade by neutral beam injection and ion cyclotron resonance heating (ICRH) and they are needed for plasma heating and current drive. A possibility to study them is the spectroscopic observation of line radiation (fast-ion D-alpha, FIDA), which emerges from charge exchange reactions. Here, the fast ions can be distinguished from the thermal particles through there strong Doppler-shift, and their radial density profile can be measured and compared to theoretical models. An analysis of the whole Doppler spectrum yields information about the 2D velocity distribution f(v {sub parallel}, v {sub perpendicular} {sub to}). Observation from different viewing angles allows consequently a tomographic reconstruction of f(v {sub parallel}, v {sub perpendicular} {sub to}). For this purpose, the FIDA diagnostic at ASDEX Upgrade has been extended from two to five views, and the spectrometer setup was improved to allow a simultaneous measurement of blue and red Doppler shifts. These recently developed diagnostic capabilities are used to study changes in the fast-ion distribution, which are caused by Alfven eigenmodes. Moreover, the further acceleration of fast ions through 2{sup nd} harmonic ICRH is investigated and compared to theoretical predictions.
Ogawa, K. [Nagoya University, Japan; Isobe, M. [National Institute for Fusion Science, Toki, Japan; Watanabe, F. [Kyoto University, Japan; Spong, Donald A [ORNL; Shimizu, A. [National Institute for Fusion Science, Toki, Japan; Osakabe, M. [National Institute for Fusion Science, Toki, Japan; Ohdachi, S. [National Institute for Fusion Science, Toki, Japan; Sakakibara, S. [National Institute for Fusion Science, Toki, Japan
2012-01-01
Beam-ion losses induced by fast-ion-driven toroidal Alfven eigenmodes (TAE) were measured with a scintillator-based lost fast-ion probe (SLIP) in the large helical device (LHD). The SLIP gave simultaneously the energy E and the pitch angle chi = arccos(v(parallel to)/v) distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of R{sub ax{_}vac} = 3.60 m, 3.75 m, and 3.90 m, where R{sub ax{_}vac} is the magnetic axis position of the vacuum field. Dominant losses induced by TAEs in these three configurations were observed in the E/chi regions of 50 similar to 190 keV/40 degrees, 40 similar to 170 keV/25 degrees, and 30 similar to 190 keV/30 degrees, respectively. Lost-ion fluxes induced by TAEs depend clearly on the amplitude of TAE magnetic fluctuations, R{sub ax{_}vac} and the toroidal field strength B{sub t}. The increment of the loss fluxes has the dependence of (b{sub TAE}/B{sub t}){sup s}. The power s increases from s = 1 to 3 with the increase of the magnetic axis position in finite beta plasmas.
Spong, D. A. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States); Bass, E. M. [Department of Physics, University of California, San Diego, California 192093 (United States); Deng, W.; Heidbrink, W. W.; Lin, Z. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Tobias, B. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 085430 (United States); Van Zeeland, M. A. [General Atomics, San Diego, California 92121 (United States); Austin, M. E. [Institute for Fusion Studies, University of Texas, Austin, Texas 78712 (United States); Domier, C. W.; Luhmann, N. C. Jr. [Department of Electrical and Computer Engineering and Department of Applied Science, University of California, Davis, California 95616 (United States)
2012-08-15
A verification and validation study is carried out for a sequence of reversed shear Alfven instability time slices. The mode frequency increases in time as the minimum (q{sub min}) in the safety factor profile decreases. Profiles and equilibria are based upon reconstructions of DIII-D discharge (no. 142111) in which many such frequency up-sweeping modes were observed. Calculations of the frequency and mode structure evolution from two gyrokinetic codes, GTC and GYRO, and a gyro-Landau fluid code TAEFL are compared. The experimental mode structure of the instability was measured using time-resolved two-dimensional electron cyclotron emission imaging. The three models reproduce the frequency upsweep event within {+-}10% of each other, and the average of the code predictions is within {+-}8% of the measurements; growth rates are predicted that are consistent with the observed spectral line widths. The mode structures qualitatively agree with respect to radial location and width, dominant poloidal mode number, ballooning structure, and the up-down asymmetry, with some remaining differences in the details. Such similarities and differences between the predictions of the different models and the experimental results are a valuable part of the verification/validation process and help to guide future development of the modeling efforts.
Alfven Eigenmode And Ion Bernstein Wave Studies For Controlling Fusion Alpha Particles
Heeter, R F
1999-01-01
In magnetic confinement fusion reactor plasmas, the charged fusion products (such as alpha particles in deuterium-tritium plasmas) will be the dominant power source, and by controlling these charged fusion products using wave-particle interactions the reactor performance could be optimized. This thesis studies two candidate waves: Mode-Converted Ion Bernstein Waves (MCIBWs) and Alfvén Eigenmodes (AEs). Rates of MCIBW-driven losses of alpha-like fast deuterons, previously observed in the Tokamak Fusion Test Reactor (TFTR), are reproduced by a new model so that the wave-particle diffusion coefficient can be deduced. The MCIBW power in TFTR is found to be ∼ 1/3 that needed for collisionless alpha particle control. A reasonable reactor power scaling is derived. To study AEs, existing magnetic fluctuation probes at the Joint European Torus (JET) have been absolutely calibrated from 30–500 kHz for the first time, allowing fluctuation measurements with &vbm0;dBpol&vbm0;/B0&am...
G.J. Kramer; S.E. Sharapov; R. Nazikian; N.N. Gorelenkov; R. Budny; JET-EFDA contributors
2003-01-15
Experimental evidence is presented for the existence of the theoretically predicted odd Torodicity-induced Alfven Eigenmode (TAEs) from the simultaneous appearance of odd and even TAEs in a normal shear discharge. The modes are observed in low central magnetic shear plasmas created by injecting lower hybrid current drive. A fast ion population was created by applying ion cyclotron heating at the high field side to excite the TAEs in the weak magnetic shear region. The odd TAEs were identified from their frequency, mode number, and timing relative to the even TAEs.
Panis, T.
2010-12-15
Direct damping rate measurements of Alfven eigenmodes (AE) are obtained using the active MHD spectroscopy system installed on the JET tokamak. The system was recently equipped with new antennas, designed to study especially the modes of intermediate toroidal mode number n, ¦n¦ = 3 -- 15, as the AEs of this range are most prone to destabilization by the fast particles in JET and in future burning plasma experiments such as ITER. The broad n-spectrum that is driven by the new antennas and the more localized structure of intermediate-n AEs has important implications for the ability to measure damping rates of intermediate n. To obtain an extended database of high accuracy individual-n measurements, experimental work on technical and engineering aspects was indispensable both on the excitation side and on the detection side. On the excitation side, the electrical model of the AE exciter has been constructed during this thesis. The model is used to determine the operational capabilities of the exciter with the new antennas, to optimize the antenna currents and to design the relevant impedance matching circuits. On the detection side, the excitation of multiple-n, degenerate AEs at close frequencies prompted for a sophisticated method to correctly estimate the n-spectrum of the plasma response. To this end, a sparse spectrum representation method was adapted to deal with the complex and real-time data produced by the active MHD spectroscopy system. The n-decomposition of the plasma response requires an accurate relative calibration of the magnetic pick-up coils. An in situ method was developed and applied for the calibration of the coils using the direct coupling to the new AE antennas. A large collection of damping rate measurements of, mainly, toroidal AEs (TAEs) was obtained during the 2008/2009 JET experimental campaigns following the technical optimization of the antenna system. Selected measurements of ¦n¦ = 3, 4 and ¦n¦ = 7 TAEs are compared to the plasma
Global Alfven Waves in Solar Physics: Coronal Heating
de Azevedo, C. A.; de Assis, A. S.
1990-11-01
RESUMEN. Se ha demostrado que Ia onda discreta de Alfven puede generar por lo memos un 20% de la energia coronal requerida con densidad de flujo de lO- erg 5 . Las ondas discretas de Alfven son una nueva clase `de ondas de Alfven las cuales pueden describirse por el modelo con que incluye un i6n finito, con frecuencia ciclotr6nica ( /uci # 0) y los efectos del equilibrio de plasma mostrados por Appert, Vaclavik and Villar 1984. ABSTRACT. It has been shown that the Discrete Alfven wave can power at least 20% of the required coronal energy flux density iO- Discrete Alfven waves are a new class of Alfven waves wich can be described by the model with the inclusion of finite ion cyclotron frequency (w/wci 0) and the equilibrium plasma current effects as shown by Appert, Vaclavik and Villar 1984. o,t :, HYDROMAGNETICS - SUN-CORONA
Global Structures of Alfven-Ballooning Modes in Magnetospheric Plasmas.
Vetoulis, Georgios
1995-01-01
The problem of radial localization of kinetically excited Alfven-type waves in the terrestial magnetosphere is examined using WKB approximations in the radial direction. These modes have been called drift Alfven ballooning modes (DABM) by CHEN and HASEGAWA, (1991)^1 and are the prime candidates to explain Pc4-Pc5 waves observed during storms. Pc4-5 type geomagnetic oscillations are long-lasting pulsations with large amplitudes and periods on the order of 500 sec. They are typically observed in the inner magnetosphere. Up to now, work on the theory of these pulsations has been done in one dimension, along the equilibrium magnetic field. In this dissertation, we include the effects of both parallel and perpendicular plasma inhomogeneities and investigate the issue of whether such a wave can be radially localized. In the first part, we formulate the theoretical approach neglecting the wave -particle resonances and using the one-fluid MHD limit. A local dispersion relationship is found on each flux surface of the equilibrium, and a global quantization condition is derived. To each flux surface correspond certain characteristic frequencies, (determined as eigenvalues of appropriate one-dimensional problems along the equilibrium magnetic field), and if the appropriate frequency matches the global mode frequency, then this surface is called resonant. In the picture developed here, the global mode is trapped at the outer side of a storm-time ring current by a steep pressure gradient. At the same time, energy from it tunnels through a barrier, and gets absorbed at its corresponding resonant flux surface, which in space physics terminology is called field line resonance. This energy absorption would lead to the damping of the mode, in the absence of an excitation mechanism. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. First, it is found that the equilibrium pressure gradient has to be steeper
Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields II. Global Alfv\\'en Modes
Sotani, H; Stergioulas, N; Vavoulidis, M
2006-01-01
We investigate torsional Alfv\\'{e}n modes of relativistic stars with a global dipole magnetic field. It has been noted recently (Glampedakis et al. 2006) that such oscillation modes could serve as as an alternative explanation (in contrast to torsional crustal modes) for the SGR phenomenon, if the magnetic field is not confined to the crust. We compute global Alfv\\'{e}n modes for a representative sample of equations of state and magnetar masses, in the ideal MHD approximation and ignoring $\\ell \\pm 2$ terms in the eigenfunction. We find that the presence of a realistic crust has a negligible effect on Alfv\\'{e}n modes for $B > 4\\times 10^{15}$ G. Furthermore, we find strong avoided crossings between torsional Alfv\\'{e}n modes and torsional crust modes. For magnetar-like magnetic field strengths, the spacing between consecutive Alfv\\'{e}n modes is of the same order as the gap of avoided crossings. As a result, it is not possible to identify modes of predominantly crustal character and all oscillations are pred...
Coupling of global toroidal Alfvén eigenmodes and reversed shear Alfvén eigenmodes in DIII-Da)
Van Zeeland, M. A.; Austin, M. E.; Gorelenkov, N. N.; Heidbrink, W. W.; Kramer, G. J.; Makowski, M. A.; McKee, G. R.; Nazikian, R.; Ruskov, E.; Turnbull, A. D.
2007-05-01
Reversed shear Alfvén eigenmodes (RSAEs) are typically thought of as being localized near the minima in the magnetic safety factor profile, however, their spatial coupling to global toroidal Alfvén eigenmodes (TAEs) has been observed in DIII-D discharges. For a decreasing minimum magnetic safety factor, the RSAE frequency chirps up through that of stable and unstable TAEs. Coupling creates a small gap at the frequency degeneracy point forming two distinct global modes. The core-localized RSAE mode structure changes and becomes temporarily global. Similarly, near the mode frequency crossing point, the global TAE extends deeper into the plasma core. The frequency splitting and spatial structure of the two modes throughout the various coupling stages, as measured by an array of internal fluctuation diagnostics, are in close agreement with linear ideal MHD calculations using the NOVA code. The implications of this coupling for eigenmode stability is also investigated and marked changes are noted throughout the coupling process.
Low-n shear Alfven spectra in axisymmetric toroidal plasmas
Cheng, C.Z.; Chance, M.S.
1985-11-01
In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfven continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfven eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfven eigenmodes on plasma heating and instabilities are addressed. 17 refs., 4 figs.
Alfven frequency modes at the edge of TFTR plasmas
Chang, Z.; Fredrickson, E.D.; Zweben, S.J. [and others
1995-07-01
An Alfven frequency mode (AFM) is very often seen in TFTR neutral beam heated plasmas as well as ohmic plasmas. This quasi-coherent mode is so far only seen on the magnetic fluctuation diagnostics (Mirnov coils). A close correlation between the plasma edge density and the mode activity (frequency and amplitude) has been observed, which indicates that the AFM is an edge localized mode with r/a > 0.85. No direct impact of this mode on the plasma global performance or fast ion loss (e.g., the {alpha}-particles in DT experiments) has been observed. This mode is apparently not the conventional TAE (toroidicity-induced Alfven eigenmodes). The present TAE theory cannot explain the observation. Other possible explanations are discussed.
Beam Distribution Modification By Alfven Modes
White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.
2010-01-25
Modification of a deuterium beam distribution in the presence of low amplitude Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes in a toroidal magnetic confinement device is examined. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam transport, and that the experimental amplitudes are only slightly above this threshold. The modes produce a substantial central flattening of the beam distribution.
Beam Distribution Modification by Alfven Modes
White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.
2010-04-03
Modification of a deuterium beam distribution in the presence of low amplitude Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes in a toroidal magnetic confinement device is examined. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam transport, and that the experimental amplitudes are only slightly above this threshold. The modes produce a substantial central flattening of the beam distribution.
Linear gyrokinetic particle-in-cell simulations of Alfven instabilities in tokamaks
Biancalani, A; Briguglio, S; Koenies, A; Lauber, Ph; Mishchenko, A; Poli, E; Scott, B D; Zonca, F
2015-01-01
The linear dynamics of Alfven modes in tokamaks is investigated here by means of the global gyrokinetic particle-in-cell code NEMORB. The model equations are shown and the local shear Alfven wave dispersion relation is derived, recovering the continuous spectrum in the incompressible ideal MHD limit. A verification and benchmark analysis is performed for continuum modes in a cylinder and for toroidicity-induced Alfven Eigenmodes. Modes in a reversed-shear equilibrium are also investigated, and the dependence of the spatial structure in the poloidal plane on the equilibrium parameters is described. In particular, a phase-shift in the poloidal angle is found to be present for modes whose frequency touches the continuum, whereas a radial symmetry is found to be characteristic of modes in the continuum gap.
Garcia-Munoz, M.; Hicks, N.; van Voornveld, R.; Classen, I.G.J.; Bilato, R.; Bobkov, V.; Bruedgam, M.; Fahrbach, H. U.; Igochine, V.; Jaemsae, S.; Maraschek, M.; Sassenberg, K.
2010-01-01
We present here the first phase-space characterization of convective and diffusive energetic particle losses induced by shear Alfven waves in a magnetically confined fusion plasma. While single toroidal Alfven eigenmodes (TAE) and Alfven cascades (AC) eject resonant fast ions in a convective process
Horváth, Ivan
2005-03-01
The structure of QCD vacuum can be studied from first principles using lattice-regularized theory. This line of research entered a qualitatively new phase recently, wherein the space-time structure (at least for some quantities) can be directly observed in configurations dominating the QCD path integral, i.e., without any subjective processing of typical configurations. This approach to QCD vacuum structure does not rely on any proposed picture of QCD vacuum but rather attempts to characterize this structure in a model-independent manner, so that a coherent physical picture of the vacuum can emerge when such unbiased numerical information accumulates to a sufficient degree. An important part of this program is to develop a set of suitable quantitative characteristics describing the space-time structure in a meaningful and physically relevant manner. One of the basic pertinent issues here is whether QCD vacuum dynamics can be understood in terms of localized vacuum objects, or whether such objects behave as inherently global entities. The first direct studies of vacuum structure strongly support the latter. In this paper, we develop a formal framework which allows to answer this question in a quantitative manner. We discuss in detail how to apply this approach to Dirac eigenmodes and to basic scalar and pseudoscalar composites of gauge fields (action density and topological charge density). The approach is illustrated numerically on overlap Dirac zero modes and near-zero modes. This illustrative data provides direct quantitative evidence supporting our earlier arguments for the global nature of QCD Dirac eigenmodes.
A global 3-D MHD model of the solar wind with Alfven waves
Usmanov, A. V.
1995-01-01
A fully three-dimensional solar wind model that incorporates momentum and heat addition from Alfven waves is developed. The proposed model upgrades the previous one by considering self-consistently the total system consisting of Alfven waves propagating outward from the Sun and the mean polytropic solar wind flow. The simulation region extends from the coronal base (1 R(sub s) out to beyond 1 AU. The fully 3-D MHD equations written in spherical coordinates are solved in the frame of reference corotating with the Sun. At the inner boundary, the photospheric magnetic field observations are taken as boundary condition and wave energy influx is prescribed to be proportional to the magnetic field strength. The results of the model application for several time intervals are presented.
Shukla, P K
2012-01-01
It is shown that a three-dimensional (3D) modified-kinetic Alfv\\'en waves (m-KAWs) can propagate in the form of Alfv\\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \\ll \\beta \\ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\\beta =4 \\pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unperturbed plasma number density, $k_B$ the Boltzmann constant, $T_e (T_e)$ the electron (ion) temperature, and $B_0$ the strength of the ambient magnetic field. The 3D m-KAW equation admits solutions in the form of a Laguerre-Gauss (LG) Alfv\\'enic vortex beam or Alfv\\'enic tornadoes with plasma density whirls that support the dynamics of Alfv\\'en magnetic flux ropes.
Shukla, P. K.
2012-01-01
It is shown that a three-dimensional (3D) modified-kinetic Alfv\\'en waves (m-KAWs) can propagate in the form of Alfv\\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \\ll \\beta \\ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\\beta =4 \\pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unpert...
Cai, DongSheng; Lembege, Bertrand; Nishikawa, Ken-ichi
2017-04-01
Using a global 3D PIC simulation, the solar-terrestrial magnetosphere interaction has been analyzed focusing on the 3D magnetic cusp region. Our recent global simulation results (Cai et al., JGR 2015) have reproduced the main features of the magnetic cusp under a northward IMF configuration comparing with the three-year statistical observations of Cluster satellites (Lavraud et al., JGR, 2005). One of the most important features found in our simulation is the existence of the Alfven Transition Layer (ATL) where Alfven Mach number is nearly zero almost adjacent to the upper stagnant exterior cusp (SEC). Its width measured near the SEC within the meridian plane varies from 1 to 4 Re. From the magnetosheath to SEC, the plasma flows transit from super to sub-Alfvenic regime. Striking features observed in the simulation is the unique depleted funnel shape ATL starting from the high altitude dusk to low altitude dawn above the magnetic cusp in a northward IMF. Both the ion and electron flux enter and spiral into the cups region through this depleted ATL with possibly a curvature drift. Varying IMF from north to south through dusk-dawn direction, this ATL persists although it drastically shrinks. Especially, in the southward IMF, the ion flux enters into the cusp region through the complicated ATL and bounce back to the magnetosheath. ATL can help us to investigate the complex structures of the magnetic cusp.
Alfven cyclotron instability and ion cyclotron emission
Gorelenkov, N.N.; Cheng, C.Z.
1995-07-01
Two-dimensional solutions of compressional Alfven eigenmodes (CAE) are studied in the cold plasma approximation. For finite inverse aspect ratio tokamak plasmas the two-dimensional eigenmode envelope is localized at the low magnetic field side with the radial and poloidal localization on the order of a/{radical}m and a/(fourth root of m), respectively, where m is the dominant poloidal mode number. Charged fusion product driven Alfven Cyclotron Instability (ACI) of the compressional Alfven eigenmodes provides the explanation for the ion cyclotron emission (ICE) spectrum observed in tokamak experiments. The ACI is excited by fast charged fusion products via Doppler shifted cyclotron wave-particle resonances. The ion cyclotron and electron Landau dampings and fast particle instability drive are calculated perturbatively for deuterium-deuterium (DD) and deuterium-tritium (DT) plasmas. Near the plasma edge at the low field side the velocity distribution function of charged fusion products is localized in both pitch angle and velocity. The poloidal localization of the eigenmode enhances the ACI growth rates by a factor of {radical}m in comparison with the previous results without poloidal envelope. The thermal ion cyclotron damping determines that only modes with eigenfrequencies at multiples of the edge cyclotron frequency of the background ions can be easily excited and form an ICE spectrum similar to the experimental observations. Theoretical understanding is given for the results of TFTR DD and DT experiments with {upsilon}{sub {alpha}0}/{upsilon}{sub A} < 1 and JET experiments with {upsilon}{sub {alpha}0}/{upsilon}{sub A} > 1.
Simulation of the interaction between Alfven waves and fast particles
Feher, Tamas Bela
2014-02-18
There is a wide variety of Alfven waves in tokamak and stellarator plasmas. While most of them are damped, some of the global eigenmodes can be driven unstable when they interact with energetic particles. By coupling the MHD code CKA with the gyrokinetic code EUTERPE, a hybrid kinetic-MHD model is created to describe this wave-particle interaction in stellarator geometry. In this thesis, the CKA-EUTERPE code package is presented. This numerical tool can be used for linear perturbative stability analysis of Alfven waves in the presence of energetic particles. The equations for the hybrid model are based on the gyrokinetic equations. The fast particles are described with linearized gyrokinetic equations. The reduced MHD equations are derived by taking velocity moments of the gyrokinetic equations. An equation for describing the Alfven waves is derived by combining the reduced MHD equations. The Alfven wave equation can retain kinetic corrections. Considering the energy transfer between the particles and the waves, the stability of the waves can be calculated. Numerically, the Alfven waves are calculated using the CKA code. The equations are solved as an eigenvalue problem to determine the frequency spectrum and the mode structure of the waves. The results of the MHD model are in good agreement with other sophisticated MHD codes. CKA results are shown for a JET and a W7-AS example. The linear version of the EUTERPE code is used to study the motion of energetic particles in the wavefield with fixed spatial structure, and harmonic oscillations in time. In EUTERPE, the gyrokinetic equations are discretized with a PIC scheme using the delta-f method, and both full orbit width and finite Larmor radius effects are included. The code is modified to be able to use the wavefield calculated externally by CKA. Different slowing-down distribution functions are also implemented. The work done by the electric field on the particles is measured to calculate the energy transfer
Tang, S.; Crocker, N. A.; Carter, T. A.; Fredrickson, E. D.; Gorelenkov, N. N.; Guttenfelder, W.
2016-10-01
The leading candidates for anomalous electron transport in NSTX with increasing beam power are high-frequency Alfvén eigenmodes excited through Doppler-shifted cyclotron resonance with beam ions. However, there exists no current model for predicting the spectra, structure, and amplitude of these modes, which consist of compressional (CAE) and global (GAE) Alfvén eigenmodes. An existing database of neutral beam heated NSTX shots spanning a broad range of plasma parameters is extended to include measurements of CAE/GAE activity in order to statistically investigate the physics parameters controlling the characteristics of these modes and how they contribute to anomalous electron transport. Mode power is found to scale with beam power as |dB| P2.6. Average frequency is shown to correlate strongly with average toroidal mode number (|n| decreases as f increases) across a wide range of beam powers. This correlation might be explained by the parallel resonance condition expected to govern the instability of these modes. Central electron temperature is also found to correlate with mode frequency. A possible explanation is that the higher frequency, lower |n| modes are more effective at electron thermal transport. The physical causes of these correlations require further investigation. Supported by US DOE Contracts DE-SC0011810 & DE-AC02-09CH11466.
Evans, R. M. [NASA Goddard Space Flight Center, Space Weather Lab, Greenbelt, MD 20771 (United States); Opher, M. [Astronomy Department, Boston University, 675 Commonwealth Avenue, Boston, MA 02215 (United States); Oran, R.; Van der Holst, B.; Sokolov, I. V.; Frazin, R.; Gombosi, T. I. [Center for Space Environment Modeling, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States); Vasquez, A., E-mail: Rebekah.e.frolov@nasa.gov [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA) and FCEN (UBA), CC 67, Suc 28, Ciudad de Buenos Aires (Argentina)
2012-09-10
The heating and acceleration of the solar wind is an active area of research. Alfven waves, because of their ability to accelerate and heat the plasma, are a likely candidate in both processes. Many models have explored wave dissipation mechanisms which act either in closed or open magnetic field regions. In this work, we emphasize the boundary between these regions, drawing on observations which indicate unique heating is present there. We utilize a new solar corona component of the Space Weather Modeling Framework, in which Alfven wave energy transport is self-consistently coupled to the magnetohydrodynamic equations. In this solar wind model, the wave pressure gradient accelerates and wave dissipation heats the plasma. Kolmogorov-like wave dissipation as expressed by Hollweg along open magnetic field lines was presented in van der Holst et al. Here, we introduce an additional dissipation mechanism: surface Alfven wave (SAW) damping, which occurs in regions with transverse (with respect to the magnetic field) gradients in the local Alfven speed. For solar minimum conditions, we find that SAW dissipation is weak in the polar regions (where Hollweg dissipation is strong), and strong in subpolar latitudes and the boundaries of open and closed magnetic fields (where Hollweg dissipation is weak). We show that SAW damping reproduces regions of enhanced temperature at the boundaries of open and closed magnetic fields seen in tomographic reconstructions in the low corona. Also, we argue that Ulysses data in the heliosphere show enhanced temperatures at the boundaries of fast and slow solar wind, which is reproduced by SAW dissipation. Therefore, the model's temperature distribution shows best agreement with these observations when both dissipation mechanisms are considered. Lastly, we use observational constraints of shock formation in the low corona to assess the Alfven speed profile in the model. We find that, compared to a polytropic solar wind model, the wave
Gap eigenmode of radially localised helicon waves in a periodic structure
Chang, Lei; Hole, Matthew J
2012-01-01
An ElectroMagnetic Solver (EMS) [Chen et al., Phys. Plasmas, 13, 123507 (2006)] is employed to model a spectral gap and a gap eigenmode in a periodic structure in the whistler frequency range. A Radially Localised Helicon (RLH) mode [Breizman and Arefiev, Phys. Rev. Lett, 84, 3863 (2000)] is considered. We demonstrate that the computed gap frequency and gap width agree well with a theoretical analysis, and find a discrete eigenmode inside the gap by introducing a defect to the system's periodicity. The axial wavelength of the gap eigenmode is close to twice the system's periodicity, which is consistent with Bragg's law. Such an eigenmode could be excited by energetic electrons, similar to the excitation of Toroidal Alfv\\'{e}n Eigenmodes (TAE) by energetic ions in tokamaks.
Nonlinear interplay of Alfven instabilities and energetic particles in tokamaks
Biancalani, A; Cole, M; Di Troia, C; Lauber, Ph; Mishchenko, A; Scott, B; Zonca, F
2016-01-01
The confinement of energetic particles (EP) is crucial for an efficient heating of tokamak plasmas. Plasma instabilities such as Alfven Eigenmodes (AE) can redistribute the EP population making the plasma heating less effective, and leading to additional loads on the walls. The nonlinear dynamics of toroidicity induced AE (TAE) is investigated by means of the global gyrokinetic particle-in-cell code ORB5, within the NEMORB project. The nonperturbative nonlinear interplay of TAEs and EP due to the wave-particle nonlinearity is studied. In particular, we focus on the nonlinear modification of the frequency, growth rate and radial structure of the TAE, depending on the evolution of the EP distribution in phase space. For the ITPA benchmark case, we find that the frequency increases when the growth rate decreases, and the mode shrinks radially. This nonlinear evolution is found to be correctly reproduced by means of a quasilinear model, namely a model where the linear effects of the nonlinearly modified EP distri...
Alfven Wave Solar Model: Part 1, Coronal Heating
van der Holst, Bart; Meng, Xing; Jin, Meng; Manchester, Ward B; Toth, Gabor; Gombosi, Tamas I
2013-01-01
We present the new Alfven Wave Solar Model (AWSoM), a global model from the upper chromosphere to the corona and the heliosphere. The coronal heating and solar wind acceleration are addressed with low-frequency Alfven wave turbulence. The injection of Alfven wave energy at the inner boundary is such that the Poynting flux is proportional to the magnetic field strength. The three-dimensional magnetic field topology is simulated using data from photospheric magnetic field measurements. This model does not impose open-closed magnetic field boundaries; those develop self-consistently. The physics includes: (1) The model employs three different temperatures, namely the isotropic electron temperature and the parallel and perpendicular ion temperatures. The firehose, mirror, and ion-cyclotron instabilities due to the developing ion temperature anisotropy are accounted for. (2) The Alfven waves are partially reflected by the Alfven speed gradient and the vorticity along the field lines. The resulting counter-propagat...
Eigenmode characteristics of the double tearing mode in the presence of shear flows
Mao Aohua [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011 (Japan); Li Jiquan; Kishimoto, Y. [Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011 (Japan); Liu Jinyuan [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)
2013-02-15
The double tearing mode (DTM) is characterized by two eigen states with antisymmetric or symmetric magnetic island structure, referred to as the even or odd DTM. In this work, we systematically revisit the DTM instabilities in the presence of an antisymmetric shear flow with a focus on eigenmode characteristics as well as the stabilization or destabilization mechanism in a wide parameter region. Both initial value simulation and eigenvalue analysis are performed based on reduced resistive MHD model in slab geometry. A degenerated eigen state is found at a critical flow amplitude v{sub c}. The even (or odd) DTM is stabilized (or destabilized) by weak shear flow below v{sub c} through the distortion of magnetic islands mainly due to the global effect of shear flow rather than the local flow shear. The distortion can be quantified by the phase angles of the perturbed flux, showing a perfect correspondence to the growth rates. As the shear flow increases above v{sub c}, the degenerated eigen state bifurcates into two eigen modes with the same growth rate but opposite propagating direction, resulting in an oscillatory growth of fluctuation energy. It is identified that two eigen modes show the single tearing mode structure due to the Alfven resonance (AR) occurring on one current sheet. Most importantly, the AR can destabilize the DTMs through enhancing the plasma flow exerting on the remaining island. Meanwhile, the local flow shear plays a remarkable stabilizing role in this region. In addition, the eigenmode characteristic of the electromagnetic Kelvin-Helmholtz instability is also discussed.
The eigenmode perspective of NMR spin relaxation in proteins
Shapiro, Yury E., E-mail: shapiro@nmrsgi4.ls.biu.ac.il, E-mail: eva.meirovitch@biu.ac.il; Meirovitch, Eva, E-mail: shapiro@nmrsgi4.ls.biu.ac.il, E-mail: eva.meirovitch@biu.ac.il [The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900-02 (Israel)
2013-12-14
We developed in recent years the two-body (protein and probe) coupled-rotator slowly relaxing local structure (SRLS) approach for elucidating protein dynamics from NMR spin relaxation. So far we used as descriptors the set of physical parameters that enter the SRLS model. They include the global (protein-related) diffusion tensor, D{sub 1}, the local (probe-related) diffusion tensor, D{sub 2}, and the local coupling/ordering potential, u. As common in analyzes based on mesoscopic dynamic models, these parameters have been determined with data-fitting techniques. In this study, we describe structural dynamics in terms of the eigenmodes comprising the SRLS time correlation functions (TCFs) generated by using the best-fit parameters as input to the Smoluchowski equation. An eigenmode is a weighted exponential with decay constant given by an eigenvalue of the Smoluchowski operator, and weighting factor determined by the corresponding eigenvector. Obviously, both quantities depend on the SRLS parameters as determined by the SRLS model. Unlike the set of best-fit parameters, the eigenmodes represent patterns of motion of the probe-protein system. The following new information is obtained for the typical probe, the {sup 15}N−{sup 1}H bond. Two eigenmodes, associated with the protein and the probe, dominate when the time scale separation is large (i.e., D{sub 2} ≫ D{sub 1}), the tensorial properties are simple, and the local potential is either very strong or very weak. When the potential exceeds these limits while the remaining conditions are preserved, new eigenmodes arise. The multi-exponentiality of the TCFs is associated in this case with the restricted nature of the local motion. When the time scale separation is no longer large, the rotational degrees of freedom of the protein and the probe become statistically dependent (coupled dynamically). The multi-exponentiality of the TCFs is associated in this case with the restricted nature of both the local and the
Measuring Kinetic Plasma Eigenmodes
Mattingly, Sean; Berumen, Jorge; Chu, Feng; Hood, Ryan; Skiff, Fred
2015-11-01
We present a method for measuring kinetic plasma eigenmodes of a cylindrical axially magnetized (1 kG) laboratory plasma (n ~109cm-3 , Te ~ 5eV , Ti ~ 0 . 06eV) by measuring velocity space correlation functions. This method simultaneously observes two separate laser induced fluorescence schemes. Each scheme has its own indepedently tunable laser and its own set of collection optics. With this setup, we are able to measure the time - averaged correlation function as a function of position on the cylindrical axis parallel to the magnetic field (z) and velocity on the deconvolved ion velocity distribution function (v) : C (z , v ,z' ,v' , τ) = t. The freedom of two lasers allows us to measure a two dimensional velocity correlation matrix. This matrix is investigated with the Vlasov equation in the collisionless and weakly collisional regime. The former case, which is continuous, is diagonalized with an integral transform defined by P. J. Morrison while the latter case, which is discrete, is diagonalized through the use of Hermite polynomials.
Multi-mode Alfv\\'enic Fast Particle Transport and Losses: Numerical vs. Experimental Observation
Schneller, Mirjam; Bilato, Roberto; García-Muñoz, Manuel; Brüdgam, Michael; Günter, Sibylle
2013-01-01
In many discharges at ASDEX Upgrade fast particle losses can be observed due to Alfv\\'enic gap modes, Reversed Shear Alfv\\'en Eigenmodes or core-localized Beta Alfv\\'en Eigenmodes. For the first time, simulations of experimental conditions in the ASDEX Upgrade fusion device are performed for different plasma equilibria (particularly for different, also non-monotonic q profiles). The numerical tool is the extended version of the HAGIS code [Pinches'98, Br\\"udgam PhD Thesis, 2010], which also computes the particle motion in the vacuum region between vessel wall in addition to the internal plasma volume. For this work, a consistent fast particle distribution function was implemented to represent the strongly anisotropic fast particle population as generated by ICRH minority heating. Furthermore, HAGIS was extended to use more realistic eigenfunctions, calculated by the gyrokinetic eigenvalue solver LIGKA [Lauber'07]. The main aim of these simulations is to allow fast ion loss measurements to be interpreted with ...
Cohen, Ofer
2015-01-01
The potential field approximation has been providing a fast, and computationally inexpensive estimation for the solar corona's global magnetic field geometry for several decades. In contrast, more physics-based global magnetohydrodynamic (MHD) models have been used for a similar purpose, while being much more computationally expensive. Here, we investigate the difference in the field geometry between a global MHD model and the potential field source surface model (PFSSM) by tracing individual magnetic field lines in the MHD model from the Alfven surface (AS), through the source surface (SS), all the way to the field line footpoint, and then back to the source surface in the PFSSM. We also compare the flux-tube expansion at two points at the SS and the AS along the same radial line. We study the effect of solar cycle variations, the order of the potential field harmonic expansion, and different magnetogram sources. We find that the flux-tube expansion factor is consistently smaller at the AS than at the SS for...
Clustered frequency analysis of shear Alfven modes in stellarators
Spong, Donald A [ORNL; D' Azevedo, Ed F [ORNL; Todo, Yasushi [National Institute for Fusion Science, Toki, Japan
2010-01-01
The shear Alfven spectrum in three-dimensional configurations, such as stellarators and rippled tokamaks, is more densely populated due to the larger number of mode couplings caused by the variation in the magnetic field in the toroidal dimension. This implies more significant computational requirements that can rapidly become prohibitive as more resolution is requested. Alfven eigenfrequencies and mode structures are a primary point of contact between theory and experiment. A new algorithm based on the Jacobi-Davidson method is developed here and applied for a reduced magnetohydrodynamics model to several stellarator configurations. This technique focuses on finding a subset of eigenmodes clustered about a specified input frequency. This approach can be especially useful in modeling experimental observations, where the mode frequency can generally be measured with good accuracy and several different simultaneous frequency lines may be of interest. For cases considered in this paper, it can be a factor of 10{sup 2}-10{sup 3} times faster than more conventional methods.
Formation of quasiparallel Alfven solitons
Hamilton, R. L.; Kennel, C. F.; Mjolhus, E.
1992-01-01
The formation of quasi-parallel Alfven solitons is investigated through the inverse scattering transformation (IST) for the derivative nonlinear Schroedinger (DNLS) equation. The DNLS has a rich complement of soliton solutions consisting of a two-parameter soliton family and a one-parameter bright/dark soliton family. In this paper, the physical roles and origins of these soliton families are inferred through an analytic study of the scattering data generated by the IST for a set of initial profiles. The DNLS equation has as limiting forms the nonlinear Schroedinger (NLS), Korteweg-de-Vries (KdV) and modified Korteweg-de-Vries (MKdV) equations. Each of these limits is briefly reviewed in the physical context of quasi-parallel Alfven waves. The existence of these limiting forms serves as a natural framework for discussing the formation of Alfven solitons.
2D continuous spectrum of shear Alfven waves in the presence of a magnetic island
Biancalani, Alessandro; Pegoraro, Francesco; Zonca, Fulvio
2010-01-01
The radial structure of the continuous spectrum of shear Alfven modes is calculated in the presence of a magnetic island in tokamak plasmas. Modes with the same helicity of the magnetic island are considered in a slab model approximation. In this framework, with an appropriate rotation of the coordinates the problem reduces to 2 dimensions. Geometrical effects due to the shape of the flux surfaceâs cross section are retained to all orders. On the other hand, we keep only curvature effects responsible of the beta induced gap in the low-frequency part of the continuous spectrum. New continuum accumulation points are found at the O-point of the magnetic island. The beta-induced Alfven Eigenmodes (BAE) continuum accumulation point is found to be positioned at the separatrix flux surface. The most remarkable result is the nonlinear modification of the BAE continuum accumulation point frequency.
Sotani, Hajime; Stergioulas, Nikolaos
2007-01-01
We investigate torsional Alfv\\'en oscillations of relativistic stars with a global dipole magnetic field, via two-dimensional numerical simulations. We find that a) there exist two families of quasi-periodic oscillations (QPOs) with harmonics at integer multiples of the fundamental frequency, b) the lower-frequency QPO is related to the region of closed field lines, near the equator, while the higher-frequency QPO is generated near the magnetic axis, c) the QPOs are long-lived, d) for the chosen form of dipolar magnetic field, the frequency ratio of the lower to upper fundamental QPOs is ~0.6, independent of the equilibrium model or of the strength of the magnetic field, and e) within a representative sample of equations of state and of various magnetar masses, the Alfv\\'en QPO frequencies are given by accurate empirical relations that depend only on the compactness of the star and on the magnetic field strength. The lower and upper QPOs can be interpreted as corresponding to the edges or turning points of an...
Highly Alfvenic Slow Solar Wind
Roberts, D. Aaron
2010-01-01
It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.
Dirac eigenmodes at the QCD Anderson transition
Giordano, Matteo; Pittler, Ferenc; Ujfalusi, Laszlo; Varga, Imre
2014-01-01
Recently we found an Anderson-type localization-delocalization transition in the QCD Dirac spectrum at high temperature. Using spectral statistics we obtained a critical exponent compatible with that of the corresponding Anderson model. Here we study the spatial structure of the eigenmodes both in the localized and the transition region. Based on previous studies in the Anderson model, at the critical point, the eigenmodes are expected to have a scale invariant multifractal structure. We verify the scale invariance of Dirac eigenmodes at the critical point.
Skew chicane based betatron eigenmode exchange module
Douglas, David
2010-12-28
A skewed chicane eigenmode exchange module (SCEEM) that combines in a single beamline segment the separate functionalities of a skew quad eigenmode exchange module and a magnetic chicane. This module allows the exchange of independent betatron eigenmodes, alters electron beam orbit geometry, and provides longitudinal parameter control with dispersion management in a single beamline segment with stable betatron behavior. It thus reduces the spatial requirements for multiple beam dynamic functions, reduces required component counts and thus reduces costs, and allows the use of more compact accelerator configurations than prior art design methods.
James Clerk Maxwell Prize for Plasma Physics Talk: On Nonlinear Physics of Shear Alfv'en Waves
Chen, Liu
2012-10-01
Shear Alfv'en Waves (SAW) are electromagnetic oscillations prevalent in laboratory and nature magnetized plasmas. Due to its anisotropic propagation property, it is well known that the linear wave propagation and dispersiveness of SAW are fundamentally affected by plasma nonuniformities and magnetic field geometries; for example, the existence of continuous spectrum, spectral gaps, and discrete eigenmodes in toroidal plasmas. This talk will discuss the crucial roles that nonuniformity and geometry could also play in the physics of nonlinear SAW interactions. More specifically, the focus will be on the Alfv'enic state and its breaking up by finite compressibility, non-ideal kinetic effects, and geometry. In the case of compressibility, finite ion-Larmor-radius effects are shown to qualitatively and quantitatively modify the three-wave parametric decays via the ion-sound perturbations. In the case of geometry, the spontaneous excitation of zonal structures by toroidal Alfv'en eigenmodes is investigated; demonstrating that, for realistic tokamak geometries, zonal current dominates over zonal flow. [4pt] Present address: Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China.
Attractors of magnetohydrodynamic flows in an Alfvenic state
Nunez, Manuel; Sanz, Javier [Departamento de Analisis Matematico, Universidad de Valladolid, Valladolid (Spain)
1999-08-13
We present a simplified form of the magnetohydrodynamic system which describes the evolution of a plasma where the small-scale velocity and magnetic field are aligned in the form of Alfven waves, such as happens in several turbulent situations. Bounds on the dimension of the global attractor are found, and are shown to be an improvement of the standard ones for the full magnetohydrodynamic equations. (author)
Alfven Wave Tomography for Cold MHD Plasmas
I.Y. Dodin; N.J. Fisch
2001-09-07
Alfven waves propagation in slightly nonuniform cold plasmas is studied by means of ideal magnetohydrodynamics (MHD) nonlinear equations. The evolution of the MHD spectrum is shown to be governed by a matrix linear differential equation with constant coefficients determined by the spectrum of quasi-static plasma density perturbations. The Alfven waves are shown not to affect the plasma density inhomogeneities, as they scatter off of them. The application of the MHD spectrum evolution equation to the inverse scattering problem allows tomographic measurements of the plasma density profile by scanning the plasma volume with Alfven radiation.
Eigenmodes of decay and discrete fragmentation processes
Giraud, B G; Giraud, B G; Peschanski, R
1994-01-01
Linear rate equations are used to describe the cascading decay of an initial heavy cluster into fragments. This representation is based upon a triangular matrix of transition rates. We expand the state vector of mass multiplicities, which describes the process, into the biorthonormal basis of eigenmodes provided by the triangular matrix. When the transition rates have a scaling property in terms of mass ratios at binary fragmentation vertices, we obtain solvable models with explicit mathematical properties for the eigenmodes. A suitable continuous limit provides an interpolation between the solvable models. It gives a general relationship between the decay products and the elementary transition rates.
Interchange Reconnection Alfven Wave Generation
Lynch, B J; Li, Y
2014-01-01
Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfven waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly-open field lines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high frequency component associated with the current sheet/reconnection site and an extended low frequency component associ...
Nonlinear Landau damping and Alfven wave dissipation
Vinas, Adolfo F.; Miller, James A.
1995-01-01
Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.
Alfven Wave-Driven Supernova Explosion
Suzuki, T K; Yamada, S
2007-01-01
We investigate the role of Alfven waves in the core-collapse supernova (SN) explosion. We assume that Alfven waves are generated by convections inside a proto-neutron star (PNS) and emitted from its surface. Then these waves propagate outwards and dissipate via nonlinear processes and heat up matter around a stalled prompt shock. To quantitatively assess the importance of this process for revival of the stalled shock, we perform 1D time-dependent hydrodynamical simulations, taking into account the heating via the dissipation of Alfven waves. We show that the shock revival occurs if the surface field strength is larger than ~2x10^{15}G and if the amplitude of velocity fluctuation at the PNS surface is larger than ~ 20% of the local sound speed. Interestingly, the Alfven wave mechanism is self-regulating in the sense that the explosion energy is not very sensitive to the surface field strength and initial amplitude of Alfven waves as long as they are larger than the threshold values given above. It should be em...
Sub-Alfvenic reduced equations in a tokamak
Sengupta, Wrick
Magnetized fusion experiments generally perform under conditions where ideal Alfvenic modes are stable. It is therefore desirable to develop a reduced formalism which would order out Alfvenic frequencies. This is challenging because sub-Alfvenic phenomena are sensitive to magnetic geometries. In this work an attempt has been made to develop a formalism to study plasma phenomena on time scales much longer than the Alfvenic time scales. (Abstract shortened by ProQuest.).
Eigenmode analysis of advective-diffusive transport in micromixers by the diffusive mapping method
Anderson, Patrick; Speetjens, Michel; Gorodetskyi, Oleksandr; Giona, Max; Mixing Collaboration
2013-11-01
Advective-diffusive transport in microflows is studied by means of the diffusive map- ping method, a recent extension of the mapping method by Gorodetskyi et al. (Phys. Fluids 24, 2012) that includes molecular diffusion. This greatly expands the application area of the mapping technique and makes the powerful concepts of eigenmode decompo- sition and spectral analysis of scalar transport accessible to an important class of flows: inline micromixers with diffusion. The staggered herringbone micro-mixer is adopted as a prototypical three-dimensional micro mixer. Simulations with the diffusive mapping method are in close agreement with experimental observations in literature and expose a strong impact of diffusion on the transport. Diffusion enables crossing of Lagrangian trans- port barriers and thus smoothens concentration gradients and accelerates homogenization. Spectral analysis of the mapping matrix reveals this already occurs on a modal level in that individual eigenmodes progressively smoothen and spread out across transport bar- riers with stronger diffusion. Concurrently, the corresponding eigenvalues diminish and thus fundamentally alter the mixing process by invariably causing homogenization, irre- spective of the Lagrangian flow structure. This happens faster and exhibits an earlier emergence of the dominant eigenmode the stronger the diffusion. Lagrangian structures may still affect the spectral properties in that flows comprising both islands and chaotic seas typically result in a richer set of eigenmodes compared to cases with global chaos.
Kinetic Alfven wave turbulence in space plasmas
Sharma, R.P. [Plasma Simulation Laboratory, Centre for Energy Studies, Indian Institute of Technology, Delhi-110016, New Delhi (India); Kumar, Sachin, E-mail: dynamicalfven@gmail.co [Plasma Simulation Laboratory, Centre for Energy Studies, Indian Institute of Technology, Delhi-110016, New Delhi (India)
2010-07-26
This work presents the derivation of nonlinear coupled equations for the evolution of solar wind turbulence. These equations are governing the coupled dynamics of kinetic Alfven wave and ion acoustic wave. Numerical simulation of these equations is also presented. The ponderomotive nonlinearity is incorporated in the wave dynamics. Filamentation of kinetic Alfven wave and the turbulent spectra are presented in intermediate-{beta} plasmas at heliocentric distances (0.3 AU{<=}r<1.0 AU). The growing filaments and steeper turbulent spectra (of power law k{sup -S}, 5/3{<=}S{<=}3) can be responsible for plasma heating and particle acceleration in solar wind.
Nonlinear Landau damping of Alfven waves.
Hollweg, J. V.
1971-01-01
Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.
Analysis of Magnetic Fields in Inertial Alfven Wave Collisions
Drake, Dereth J; Shanken, Brian C; Howes, Gregory G; Skiff, Frederick; Kletzing, Craig A; Carter, Troy A; Dorfman, Seth
2014-01-01
Turbulence in astrophysical and space plasmas is dominated by the nonlinear interaction of counterpropagating Alfven waves. Most Alfven wave turbulence theories have been based on ideal plasma models, such as incompressible MHD, for Alfven waves at large scales. However, in the inertial Alfven wave regime (vA > vthe), relevant to magnetospheric plasmas, how the turbulent nonlinear interactions are modified by the dispersive nature of the waves remains to be explored. Here we present the first laboratory evidence of the nonlinear interaction in the inertial regime. A comparison is made with the theory for MHD Alfven waves.
Nonlinear Evolution of Alfvenic Wave Packets
Buti, B.; Jayanti, V.; Vinas, A. F.; Ghosh, S.; Goldstein, M. L.; Roberts, D. A.; Lakhina, G. S.; Tsurutani, B. T.
1998-01-01
Alfven waves are a ubiquitous feature of the solar wind. One approach to studying the evolution of such waves has been to study exact solutions to approximate evolution equations. Here we compare soliton solutions of the Derivative Nonlinear Schrodinger evolution equation (DNLS) to solutions of the compressible MHD equations.
Spectral stability of Alfven filament chains
Bergmans, J.; Kuvshinov, B. N.; Lakhin, V. P.; Schep, T. J.
2000-01-01
The two-fluid model of nonlinear Alfven perturbations has singular solutions in the form of current-vortex filaments. We investigate analytically and numerically the spectral stability of single and double rows of filaments. Staggered and non-staggered double rows (von Karman streets) are studied. I
Spectral stability of Alfven filament configurations
Bergmans, J.; Kuvshinov, B. N.; Lakhin, V. P.; Schep, T. J.
2000-01-01
The two-fluid plasma equations that describe nonlinear Alfven perturbations have singular solutions in the form of current-vortex filaments. These filaments are analogous to point vortices in ideal hydrodynamics and geostrophic fluids. In this work the spectral (linear) stability of current-vortex f
The Eigenmode Analysis of Human Motion
Park, Juyong; Gonzalez, Marta C
2016-01-01
Rapid advances in modern communication technology are enabling the accumulation of large-scale, high-resolution observational data of spatiotemporal movements of humans. Classification and prediction of human mobility based on the analysis of such data carry great potential in applications such as urban planning as well as being of theoretical interest. A robust theoretical framework is therefore required to study and properly understand human motion. Here we perform the eigenmode analysis of human motion data gathered from mobile communication records, which allows us to explore the scaling properties and characteristics of human motion.
The eigenmode analysis of human motion
Park, Juyong; Lee, Deok-Sun; González, Marta C.
2010-11-01
Rapid advances in modern communication technology are enabling the accumulation of large-scale, high-resolution observational data of the spatiotemporal movements of humans. Classification and prediction of human mobility based on the analysis of such data has great potential in applications such as urban planning in addition to being a subject of theoretical interest. A robust theoretical framework is therefore required to study and properly understand human motion. Here we perform the eigenmode analysis of human motion data gathered from mobile communication records, which allows us to explore the scaling properties and characteristics of human motion.
Ultra-high Q even eigenmode resonance in terahertz metamaterials
Al-Naib, Ibraheem; Yang, Yuping; Dignam, Marc M.; Zhang, Weili; Singh, Ranjan
2015-01-01
We report the simultaneous excitation of the odd and the even eigenmode resonances in a periodic array of square split-ring resonators, with four resonators per unit cell. When the electric field is parallel to their gaps, only the two well-studied odd eigenmodes are excited. As the resonators are rotated relative to one another, we observe the emergence and excitation of an extremely sharp even eigenmode. In uncoupled split-ring resonators, this even eigenmode is typically radiative in nature with a broad resonance linewidth and low Q-factor. However, in our coupled system, for specific range of rotation angles, our simulations revealed a remarkably high quality factor (Q ˜ 100) for this eigenmode, which has sub-radiant characteristics. This type of quad-supercell metamaterial offers the advantage of enabling access to all the three distinct resonance features of the split-ring resonator, which consists of two odd eigenmodes in addition to the high-Q even eigenmode, which could be exploited for high performance multiband filters and absorbers. The high Q even eigenmode could find applications in designing label free bio-sensors and for studying the enhanced light matter interaction effects.
Neutral beam excitation of Alfven continua in the madison symmetric torus reversed field pinch
Koliner, Jonathan Jay
Alfven continua and Alfven eigenmodes (AEs) have been generated for reversed-field pinch (RFP) plasma equilibria in Madison Symmetric Torus (MST). Data gathered from the extensive suite of diagnostics on MST was used to generate equilibria using MSTFIT and VMEC. Three dimensional equilibria for spontaneous helical states were generated using the equilibrium reconstruction code V3FIT. The reduced-MHD codes AE3D and STELLGAP were run on all generated equilibria to calculate the continua and AEs. All continuum solutions contain a toroidicity-induced Alfven gap at 200-400 kHz, within which AE solutions appear by coupling of m=0,1 at medium n. The first observation of beam-driven instabilities on the RFP was performed using MST magnetics during neutral beam injection (NBI). Spatially coherent bursts with n=5,m=1 were observed in plasmas with edge safety factor q_a=0. The bursts oscillate at 65 kHz, and reach maximum amplitude and decay away within 100 mus. These bursts persist for the duration of NBI. Secondary n=-1 and n=4 bursts are coupled in time, reaching maximum amplitude with 50 mus after the n=5 peak amplitude. While the n=5 bursts scale weakly with the electron density n_e and strongly with the beam velocity v_beam, the n=4 bursts scale with the Alfven speed v_A. The burst frequencies are well below those of the calculated AEs and the modes are driven even with v_ beam plasmas. In reversed plasmas, the temporally changing q profile changes the burst resonances, bringing n=6 into resonance halfway through the sawtooth cycle. The n=5 mode switches from its frequency in non-reversed plasmas to a higher frequency at the end of the sawtooth cycle. In deeply reversed plasmas, the bursts are weaker and display chirping behavior as the plasma reversal increases. During the transition to a helical state, the bursts increase in frequency as q on-axis changes, altering the parallel wavenumber k_||. When the helical state is established, the bursts terminate.
Calibration of higher eigenmodes of cantilevers
Labuda, Aleksander; Kocun, Marta; Walsh, Tim; Meinhold, Jieh; Proksch, Tania; Meinhold, Waiman; Anderson, Caleb; Proksch, Roger [Asylum Research, an Oxford Instruments Company, Santa Barbara, California 93117 (United States); Lysy, Martin [Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada)
2016-07-15
A method is presented for calibrating the higher eigenmodes (resonant modes) of atomic force microscopy cantilevers that can be performed prior to any tip-sample interaction. The method leverages recent efforts in accurately calibrating the first eigenmode by providing the higher-mode stiffness as a ratio to the first mode stiffness. A one-time calibration routine must be performed for every cantilever type to determine a power-law relationship between stiffness and frequency, which is then stored for future use on similar cantilevers. Then, future calibrations only require a measurement of the ratio of resonant frequencies and the stiffness of the first mode. This method is verified through stiffness measurements using three independent approaches: interferometric measurement, AC approach-curve calibration, and finite element analysis simulation. Power-law values for calibrating higher-mode stiffnesses are reported for several cantilever models. Once the higher-mode stiffnesses are known, the amplitude of each mode can also be calibrated from the thermal spectrum by application of the equipartition theorem.
Reese, D; Rieutord, M
2004-01-01
We carry out numerical and mathematical investigations of shear Alfven waves inside of a spherical shell filled with an incompressible conducting fluid, and bathed in a strong dipolar magnetic field. We focus on axisymmetric toroidal and non-axisymmetric modes, in continuation of a previous work by Rincon & Rieutord (2003). Analytical expressions are obtained for toroidal eigenmodes and their corresponding frequencies at low diffusivities. These oscillations behave like magnetic shear layers, in which the magnetic poles play a key role, and hence become singular when diffusivities vanish. It is also demonstrated that non-axisymmetric modes are split into two categories, namely poloidal or toroidal types, following similar asymptotic behaviours as their axisymmetric counterparts when the diffusivities become arbitrarily small.
Torsional Alfven waves in stratified and expanding magnetic flux tubes
2011-01-01
The effects of both density stratification and magnetic field expansion on torsional Alfven waves in magnetic flux tubes are studied. The frequencies, the period ratio P1/P2 of the fundamental and its first-overtone, and eigenfunctions of torsional Alfven modes are obtained. Our numerical results show that the density stratification and magnetic field expansion have opposite effects on the oscillating properties of torsional Alfven waves.
Adiabatic trapping in coupled kinetic Alfven-acoustic waves
Shah, H. A.; Ali, Z. [Department of Physics, G.C. University, 54000 Lahore (Pakistan); Masood, W. [COMSATS, Institute of Information Technology, Park Road, Chak Shahzad, Islamabad 44000 (Pakistan); National Centre for Physics (NCP), Shahdara Valley Road, 44000 Islamabad (Pakistan); Theoretical Plasma Physics Division, P. O. Nilore, Islamabad (Pakistan)
2013-03-15
In the present work, we have discussed the effects of adiabatic trapping of electrons on obliquely propagating Alfven waves in a low {beta} plasma. Using the two potential theory and employing the Sagdeev potential approach, we have investigated the existence of arbitrary amplitude coupled kinetic Alfven-acoustic solitary waves in both the sub and super Alfvenic cases. The results obtained have been analyzed and presented graphically and can be applied to regions of space where the low {beta} assumption holds true.
Riemann solvers and Alfven waves in black hole magnetospheres
Punsly, Brian; Balsara, Dinshaw; Kim, Jinho; Garain, Sudip
2016-09-01
In the magnetosphere of a rotating black hole, an inner Alfven critical surface (IACS) must be crossed by inflowing plasma. Inside the IACS, Alfven waves are inward directed toward the black hole. The majority of the proper volume of the active region of spacetime (the ergosphere) is inside of the IACS. The charge and the totally transverse momentum flux (the momentum flux transverse to both the wave normal and the unperturbed magnetic field) are both determined exclusively by the Alfven polarization. Thus, it is important for numerical simulations of black hole magnetospheres to minimize the dissipation of Alfven waves. Elements of the dissipated wave emerge in adjacent cells regardless of the IACS, there is no mechanism to prevent Alfvenic information from crossing outward. Thus, numerical dissipation can affect how simulated magnetospheres attain the substantial Goldreich-Julian charge density associated with the rotating magnetic field. In order to help minimize dissipation of Alfven waves in relativistic numerical simulations we have formulated a one-dimensional Riemann solver, called HLLI, which incorporates the Alfven discontinuity and the contact discontinuity. We have also formulated a multidimensional Riemann solver, called MuSIC, that enables low dissipation propagation of Alfven waves in multiple dimensions. The importance of higher order schemes in lowering the numerical dissipation of Alfven waves is also catalogued.
Eigenmodes of three-dimensional magnetic arcades in the Sun's corona
Jain, Bradley W Hindman Rekha
2015-01-01
We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger 3-D magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3-D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3-D waveguide if the Alfv\\'en speed increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1-D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade posse...
An improved perfectly matched layer for the eigenmode expansion technique
Gregersen, Niels; Mørk, Jesper
2008-01-01
When performing optical simulations for rotationally symmetric geometries using the eigenmode expansion technique, it is necessary to place the geometry under investigation inside a cylinder with perfectly conducting walls. The parasitic reflections at the boundary of the computational domain can...
MIMO Identical Eigenmode Transmission System (IETS) - A Channel Decomposition Perspective
Shakir, M Zeeshan
2010-01-01
In the past few years considerable attention has been given to the design of Multiple-Input Multiple-Output (MIMO) Eigenmode Transmission Systems (EMTS). This paper presents an in-depth analysis of a new MIMO eigenmode transmission strategy. The non-linear decomposition technique called Geometric Mean Decomposition (GMD) is employed for the formation of eigenmodes over MIMO flatfading channel. Exploiting GMD technique, identical, parallel and independent transmission pipes are created for data transmission at higher rate. The system based on such decomposition technique is referred to as MIMO Identical Eigenmode Transmission System (IETS). The comparative analysis of the MIMO transceiver design exploiting nonlinear and linear decomposition techniques for variable constellation is presented in this paper. The new transmission strategy is tested in combination with the Vertical Bell Labs Layered Space Time (V-BLAST) decoding scheme using different number of antennas on both sides of the communication link. The ...
Radial Eigenmodes for a Toroidal Waveguide with Rectangular Cross Section
Rui Li
2012-07-01
In applying mode expansion to solve the CSR impedance for a section of toroidal vacuum chamber with rectangular cross section, we identify the eigenvalue problem for the radial eigenmodes which is different from that for cylindrical structures. In this paper, we present the general expressions of the radial eigenmodes, and discuss the properties of the eigenvalues on the basis of the Sturm-Liouville theory.
Nonlinear propagation of short wavelength drift-Alfven waves
Shukla, P. K.; Pecseli, H. L.; Juul Rasmussen, Jens
1986-01-01
Making use of a kinetic ion and a hydrodynamic electron description together with the Maxwell equation, the authors derive a set of nonlinear equations which governs the dynamics of short wavelength ion drift-Alfven waves. It is shown that the nonlinear drift-Alfven waves can propagate as two...
HLL Riemann Solvers and Alfven Waves in Black Hole Magnetospheres
Punsly, Brian; Kim, Jinho; Garain, Sudip
2016-01-01
In the magnetosphere of a rotating black hole, an inner Alfven critical surface (IACS) must be crossed by inflowing plasma. Inside the IACS, Alfven waves are inward directed toward the black hole. The majority of the proper volume of the active region of spacetime (the ergosphere) is inside of the IACS. The charge and the totally transverse momentum flux (the momentum flux transverse to both the wave normal and the unperturbed magnetic field) are both determined exclusively by the Alfven polarization. However, numerical simulations of black hole magnetospheres are often based on 1-D HLL Riemann solvers that readily dissipate Alfven waves. Elements of the dissipated wave emerge in adjacent cells regardless of the IACS, there is no mechanism to prevent Alfvenic information from crossing outward. Thus, it is unclear how simulated magnetospheres attain the substantial Goldreich-Julian charge density associated with the rotating magnetic field. The HLL Riemann solver is also notorious for producing large recurring...
Damping of visco-resistive Alfven waves in solar spicules
Z Fazel
2014-12-01
Full Text Available Interaction of Alfven waves with plasma inhomogeneity generates phase mixing which can cause the dissipation of Alfven waves. We investigated the dissipation of standing Alfven waves due to phase mixing at the presence of steady flow and sheared magnetic field in solar spicules. Moreover, the transition region between chromosphere and corona was considered. Our numerical simulation showed that the phase mixing and dissipation rate of Alfven waves are enhanced relative to viscosity and resistivity gradients. Comparison of the results of our models with and without these gradients illustrated a significant difference between them. In other words, with these assumptions, Alfven waves may transfer the photospheric energy to the corona during timescales corresponding to the observed lifetimes of spicules. It should be noted that the results of our numerical simulation were in good agreement with observational scaling law obtained by Kuridze et al. [1
Alfven wave in higher dimensional space time
Panigrahi, D; Chatterjee, S
2009-01-01
Following the wellknown spacetime decomposition technique as applied to (d+1) dimensions we write down the equations of magnetohydrodynamics (MHD) in a spatially at generalised FRW universe. Assuming an equation of state for the background cosmic fluid we find solutions in turn for acous- tic waves and also for Alfven waves in a warm (cold) magnetised plasma. Interestingly the different plasma modes closely resemble the at space coun- terparts except that here the field variables all redshift with their time due to the expansion of the background. It is observed that in the ultrarelativistic limit the field parameters all scale as the free photon. The situation changes in the prerelativistic limit where the frequencies change in a bizarre fashion depending on initial conditions. It is observed that for a fixed magnetic field in a particular medium the Alfven wave velocity decreases with the number of dimensions, being the maximum in the usual 4D. Further for a fixed dimension the velocity attenuation is more ...
Excitation of Alfven Cyclotron Instability by charged fusion products in tokamaks
Gorelenkov, N.N.; Cheng, C.Z.
1994-08-01
The spectrum of ion cyclotron emission (ICE) observed in tokamak experiments shows narrow peaks at multiples of the edge cyclotron frequency of background ions. A possible mechanism of ICE based on the fast Alfven Cyclotron Instability (ACI) resonantly excited by high energy charged products ({alpha}-particles or protons) is studied here. The two-dimensional ACI eigenmode structure and eigenfrequency are obtained in the large tokamak aspect ratio limit. The ACI is excited via wave-particle resonances in phase space by tapping the fast ion velocity space free energy. The instability growth rates are computed perturbatively from the perturbed fast particle distribution function, which is obtained by integrating the high frequency gyrokinetic equation along the particle orbit. Numerical examples of ACI growth rates are presented for TFTR plasmas. The fast ion distribution function is assumed to be singular in pitch angle near the plasma edge. The results are employed to understand the ICE in Deuterium-Deuterium (DD) and Deuterium-tritium (DT) tokamak experiments.
Nonlinear evolution of parallel propagating Alfven waves: Vlasov - MHD simulation
Nariyuki, Y; Kumashiro, T; Hada, T
2009-01-01
Nonlinear evolution of circularly polarized Alfv\\'en waves are discussed by using the recently developed Vlasov-MHD code, which is a generalized Landau-fluid model. The numerical results indicate that as far as the nonlinearity in the system is not so large, the Vlasov-MHD model can validly solve time evolution of the Alfv\\'enic turbulence both in the linear and nonlinear stages. The present Vlasov-MHD model is proper to discuss the solar coronal heating and solar wind acceleration by Alfve\\'n waves propagating from the photosphere.
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
Bowden, G. W.; Hole, M. J. [Plasma Theory and Modelling, Research School of Physics and Engineering, Australian National University, Acton 2601, Australian Capital Territory (Australia); Könies, A. [Max-Planck-Institut für Plasmaphysik, EURATOM-Association, D-17491 Greifswald (Germany)
2015-09-15
In an ideal magnetohydrodynamic (MHD) plasma, shear Alfvén eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfvén continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfvén eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD Code for Kinetic Alfvén waves. In this paper, we discuss the application of the complex contour technique to calculate the continuum damping of global modes in tokamak as well as torsatron, W7-X and H-1NF stellarator cases. To the authors' knowledge, these stellarator calculations represent the first calculation of continuum damping for eigenmodes in fully three-dimensional equilibria. The continuum damping of global modes in W7-X and H-1NF stellarator configurations investigated is found to depend sensitively on coupling to numerous poloidal and toroidal harmonics.
Numerical Simulation of Solitary Kinetic Alfven Waves
DING Jian; LI Yi; WANG Shui
2008-01-01
Using the two-fluid model in the case of α1 (α=β/2Q, β is the ratio of thermal pressure to magnetic pressure, and Q=m,e/m,I), we numerically investigate the interactions between two solitary kinetic Alfven waves (SKAWs) and between an SKAW and a density discontinuity. The results show that the two SKAWs would remain in their original shapes and propagate at their initiating speeds, which indicates that SKAWs behave just like standard solitons. The simulation also shows that SKAWs will reflect and refract when crossing a discontinuity and propagating into a higher density region. The transmission wave is an SKAW with increasing density, and the reverberation is a disturbance with lower amplitude.
Collisionless magnetic reconnection via Alfvén eigenmodes.
Dai, Lei
2009-06-19
We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfvén eigenmodes' generation and dissipation. Alfvén eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh;{2} potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n = 1 mode. The prediction of the n = 1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields.
Eigenmode Splitting in all Hydrogenated Amorphous Silicon Nitride Coupled Microcavity
ZHANG Xian-Gao; HUANG Xin-Fan; CHEN Kun-Ji; QIAN Bo; CHEN San; DING Hong-Lin; LIU Sui; WANG Xiang; XU Jun; LI Wei
2008-01-01
Hydrogenated amorphous silicon nitride based coupled optical microcavity is investigated theoretically and experimentally. The theoretical calculation of the transmittance spectra of optical microcavity with one cavity and coupled microcavity with two-cavity is performed.The optical eigenmode splitting for coupled microcavity is found due to the interaction between the neighbouring localized cavities.Experimentally,the coupled cavity samples are prepared by plasma enhanced chemical vapour deposition and characterized by photoluminescence measurements.It is found that the photoluminescence peak wavelength agrees well with the cavity mode in the calculated transmittance spectra.This eigenmode splitting is analogous to the electron state energy splitting in diatom molecules.
A laboratory search for plasma erosion by Alfven waves
Vincena, S.; Gekelman, W.; Pribyl, P.
2007-12-01
Obliquely propagating shear Alfven waves with transverse wavelengths on the order of the electron inertial length or even the ion gyro-radius are commonly observed in the earth's low-altitude auroral zones. These regions are also replete with observations of electron beams and transversely heated ions. A kinetic treatment of shear Alfven wave-particle interaction reveals how these waves can be responsible for some of the observed particle acceleration. The auroral plasma environment is further enriched by the presence of field-aligned depletions in plasma density, and it has been suggested* that the Alfven waves may, in fact, be the cause of the erosion of ionospheric density. In this laboratory experiment, shear waves will be launched using a variety of proven antennas, and also allowed to grow spontaneously as Drift-Alfven modes in seeded density depletions**. Detailed measurements of the wave magnetic fields in the perpendicular density gradient regions will be presented which demonstrate the generation of short perpendicular wave scales due to the perpendicular gradient in parallel wave phase speed. Miniature in-situ particle diagnostics will also be used to look for electron and ion acceleration. The waves will also be launched into an increasing region of background magnetic field in an attempt to model the ratios of Alfven speed to electron thermal speed, and density gradient scale length to electron inertial length appropriate to the earth's auroral zone. Preliminary results will be presented on the efficacy of shear Alfven waves to self-generate plasma density depletions, or deepen ambient density inhomogeneities. The experiments are conducted at UCLA's Basic Plasma Science Facility in the Large Plasma Device. *Chaston, et al., "Ionospheric erosion by Alfven Waves," JGR, V 111, A03206, 2006. **Penano, et al., "Drift-Alfven fluctuations associated with a narrow pressure striation," Phys. Plasmas, V 7, Issue 1, pp. 144-157 (2000).
Emission of radiation induced by pervading Alfven waves
Zhao, G. Q. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Wu, C. S. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China); Institute of Space Science, National Central University, Zhongli, Taiwan (China)
2013-03-15
It is shown that under certain conditions, propagating Alfven waves can energize electrons so that consequently a new cyclotron maser instability is born. The necessary condition is that the plasma frequency is lower than electron gyrofrequency. This condition implies high Alfven speed, which can pitch-angle scatter electrons effectively and therefore the electrons are able to acquire free energy which are needed for the instability.
Eigenmode expansion of the polarization for a spherical sample of two-level atoms
Friedberg, Richard [Physics Department, Columbia University, New York, NY 10027 (United States); Manassah, Jamal T., E-mail: jmanassah@gmail.co [HMS Consultants, Inc., PO Box 592, New York, NY 10028 (United States)
2009-12-07
We derive pseudo-orthogonality relations for both the magnetic and electric eigenmodes of a system of two-level atoms in a sphere configuration. We verify numerically that an arbitrary vector field can be reconstructed to a great accuracy from these eigenmode expansions. We apply this eigenmode analysis to explore superradiance from a sphere with initially uniform polarization.
Fast-ion transport induced by Alfvén eigenmodes in the ASDEX Upgrade tokamak
Garcia-Munoz, M.; Classen, I.G.J.; Geiger, B.
2011-01-01
A comprehensive suite of diagnostics has allowed detailed measurements of the Alfvén eigenmode (AE) spatial structure and subsequent fast-ion transport in the ASDEX Upgrade (AUG) tokamak [1]. Reversed shear Alfvén eigenmodes (RSAEs) and toroidal induced Alfvén eigenmodes (TAEs) have been driven u...
Belova, Elena; Gorelenkov, N. N.; Crocker, N. A.; Lestz, J. B.; Fredrickson, E. D.; Tang, S.
2016-10-01
Results of 3D nonlinear simulations of neutral-beam-driven compressional Alfvén eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX) are presented. Hybrid MHD-particle simulations for the H-mode NSTX discharge (shot 141398) using the HYM code show unstable CAE modes for a range of toroidal mode numbers, n =4-9, and frequencies below the ion cyclotron frequency. It is found that the essential feature of CAEs is their coupling to kinetic Alfven wave (KAW) that occurs on the high-field side at the Alfven resonance location. Nonlinear simulations demonstrate that CAEs can channel the energy of the beam ions from the injection region near the magnetic axis to the location of the resonant mode conversion at the edge of the beam density profile. This mechanism provides an alternative explanation to the observed reduced heating of the plasma core in the NSTX. A set of nonlinear simulations show that the CAE instability saturates due to nonlinear particle trapping, and a large fraction of beam energy can be transferred to several unstable CAEs of relatively large amplitudes and absorbed at the resonant location. Absorption rate shows a strong scaling with the beam power. This research was supported by the U.S. DOE contract # DE-AC02-09CH11466.
Eigenmodes of misaligned unstable optical resonators with circular mirrors.
Bowers, M S
1992-03-20
It is shown numerically that the diffractive transverse (Fox-Li) eigenmodes supported by an unstable cavity with tilted end mirrors can be computed by expanding these modes in terms of the fully aligned (aberration-free) eigenmodes of the same cavity. Circular mirror resonators are considered in which the aligned cavity eigenmodes can be decomposed into different azimuthal components. The biorthogonality property of the aligned cavity eigenmodes is used to obtain the coefficients in the modal expansion of the misaligned modes. Results are given for two different resonators: a conventional hard-edge unstable cavity with a small tilt of the output coupler and one that uses a graded reflectivity output mirror with a small tilt of the primary mirror. It is shown that the series expansion of the misaligned modes in terms of the aligned modes converges, and the converged eigenvalues are virtually identical to those computed by using the Prony method. Symmetry considerations and other new insights into the effects of a mirror tilt on the modes of a resonator are also discussed.
An improved perfectly matched layer in the eigenmode expansion technique
Gregersen, Niels; Mørk, Jesper
2008-01-01
When employing the eigenmode expansion technique (EET), parasitic reflections at the boundary of the computational domain can be suppressed by introducing a perfectly matched layer (PML). However, the traditional PML, suffers from an artificial field divergence limiting its usefulness. We propose...
Strange eigenmodes of chaotic granular flow in a tumbler
Christov, Ivan C.; Ottino, Julio M.; Lueptow, Richard M.
2011-11-01
Through a combined computational-experimental study of monodisperse granular flow in a slowly-rotating quasi-two-dimensional container we show the presence of naturally-persistent mixing patterns, i.e., ``strange'' eigenmodes of the advection- diffusion operator governing the mixing process in the Eulerian frame. A comparative analysis of the structure of eigenmodes and the corresponding Poincaré section and finite-time Lyapunov exponent field of the flow highlights the relationship between the Eulerian and Lagrangian descriptions of mixing. In addition, we show how the mapping method for scalar transport can be modified to include diffusive effects, which are more significant in a granular flow (in laboratory size equipment) than in a similar fluid flow. This allow us to examine (for the first time in a granular flow) the change in shape, lifespan, and eventual decay of eigenmodes due to diffusive effects at larger numbers of revolutions. Finally, it is shown that segregation patterns in bidisperse mixtures correspond to permanently-excited eigenmodes. This work was supported, in part, by NSF Grant CMMI-1000469.
On reflection of Alfven waves in the solar wind
Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Moore, R. L.; Nerney, S. F.
1993-01-01
We have revisited the problem of propagation of toroidal and linear Alfven waves formulated by Heinemann and Olbert (1980) to compare WKB and non-WKB waves and their effects on the solar wind. They considered two solar wind models and showed that reflection is important for Alfven waves with periods of the order of one day and longer, and that non-WKB Alfven waves are no more effective in accelerating the solar wind than WKB waves. There are several recently published papers which seem to indicate that Alfven waves with periods of the order of several minutes should be treated as non-WKB waves and that these non-WKB waves exert a stronger acceleration force than WKB waves. The purpose of this paper is to study the origin of these discrepancies by performing parametric studies of the behavior of the waves under a variety of different conditions. In addition, we want to investigate two problems that have not been addressed by Heinemann and Olbert, namely, calculate the efficiency of Alfven wave reflection by using the reflection coefficient and identify the region of strongest wave reflection in different wind models. To achieve these goals, we investigated the influence of temperature, electron density distribution, wind velocity and magnetic field strength on the waves. The obtained results clearly demonstrate that Alfven wave reflection is strongly model dependent and that the strongest reflection can be expected in models with the base temperatures higher than 10(exp 6) K and with the base densities lower than 7 x 10(exp 7) cm(exp -3). In these models as well as in the models with lower temperatures and higher densities, Alfven waves with periods as short as several minutes have negligible reflection so that they can be treated as WKB waves; however, for Alfven waves with periods of the order of one hour or longer reflection is significant, requiring a non-WKB treatment. We also show that non-WKB, linear Alfven waves are always less effective in accelerating the
Toi, K. [National Institute for Fusion Science, Toki, Japan; Ogawa, K. [Nagoya University, Japan; Isobe, M. [National Institute for Fusion Science, Toki, Japan; Osakabe, M. [National Institute for Fusion Science, Toki, Japan; Spong, Donald A [ORNL; Todo, Yasushi [National Institute for Fusion Science, Toki, Japan
2011-01-01
Comprehensive understanding of energetic-ion-driven global instabilities such as Alfven eigenmodes (AEs) and their impact on energetic ions and bulk plasma is crucially important for tokamak and stellarator/helical plasmas and in the future for deuterium-tritium (DT) burning plasma experiments. Various types of global modes and their associated enhanced energetic ion transport are commonly observed in toroidal plasmas. Toroidicity-induced AEs and ellipticity-induced AEs, whose gaps are generated through poloidal mode coupling, are observed in both tokamak and stellarator/helical plasmas. Global AEs and reversed shear AEs, where toroidal couplings are not as dominant were also observed in those plasmas. Helicity induced AEs that exist only in 3D plasmas are observed in the large helical device (LHD) and Wendelstein 7 Advanced Stellarator plasmas. In addition, the geodesic acoustic mode that comes from plasma compressibility is destabilized by energetic ions in both tokamak and LHD plasmas. Nonlinear interaction of these modes and their influence on the confinement of the bulk plasma as well as energetic ions are observed in both plasmas. In this paper, the similarities and differences in these instabilities and their consequences for tokamak and stellarator/helical plasmas are summarized through comparison with the data sets obtained in LHD. In particular, this paper focuses on the differences caused by the rotational transform profile and the 2D or 3D geometrical structure of the plasma equilibrium. Important issues left for future study are listed.
Gyrokinetic particle simulations of reversed shear Alfvén eigenmode in DIII-D tokamak
Deng, Wenjun
2011-10-01
Simulations of reversed shear Alfvén eigenmode (RSAE) in DIII-D discharge 142111 near 750 ms have been successfully performed using the global gyrokinetic toroidal code (GTC). The background plasma pressure raises the mode frequency due to the elevation of the Alfvén continuum by the geodesic compressibility. The non-perturbative contributions from the fast ions and kinetic thermal ions modify the mode structure relative to the ideal magnetohydrodynamic (MHD) theory due to the breaking of radial symmetry, in qualitative agreement with XHMGC and TAEFL simulations and recent 2D imaging of RSAE mode structure in DIII- D tokamak. Various RSAE damping mechanisms are identified and measured in the simulations. The mode structure, frequency, and growth rate obtained from GTC simulations are close to those given by GYRO and TAEFL simulations. The frequency up-chirping of the RSAE and the mode transition from RSAE to toroidal Alfvén eigenmode (TAE) are revealed to be close to the experimental results when scanning qmin values in our simulations. Study of nonlinear effects of the RSAE is in progress. This work is in collaboration with Z. Lin, I. Holod, X. Wang, Z. Wang, Y. Xiao, H. Zhang, W. Zhang, E. Bass, D. Spong, and M. Van Zeeland and is supported by SciDAC GSEP Center.
Testa, D [CRPP, Association EURATOM-Confederation Suisse, EPFL, Lausanne (Switzerland); Fasoli, A [CRPP, Association EURATOM-Confederation Suisse, EPFL, Lausanne (Switzerland); Borba, D [Associacao EURATOM/IST (Portugal); EDFA-CSU, Culham Science Centre (United Kingdom); Baar, M de [FOM-Instituut Voor Plasmafysica, Rijnhuizen (Netherlands); Bigi, M [Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon (United Kingdom); Brzozowski, J [NADA VR-Euratom Association, Royal Institute of Technology, Stockholm (Sweden); Vries, P de [Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon (United Kingdom)
2004-07-01
We have investigated the effect of different ion cyclotron resonance frequency (ICRF) heating schemes, of error field modes, of the plasma shape and edge magnetic shear, and of the ion {nabla}B drift direction on the stability of Alfven eigenmodes (AEs). The use of multi-frequency or 2nd harmonic minority ICRF heating at high plasma density gives rise to a lower fast ion pressure gradient in the plasma core and to a reduced mode activity in the Alfven frequency range. Externally excited low-amplitude error fields lead to a much larger AE instability threshold, which we attribute to a moderate radial redistribution of the fast ions. The edge plasma shape has a clear stabilizing effect on high-n, radially localized AEs. The damping rate of n = 1 toroidal AEs is a factor 3 higher when the ion {nabla}B drift is directed towards the divertor. These results represent a useful step towards the extrapolation of current scenarios to the inclusion of fusion-born alpha particles in ITER, with possible application for feedback control schemes for the various ITER operating regimes.
Discrete Alfvén eigenmodes in high performance discharges in the D Ⅲ-D tokamak%DⅢ-D高性能运行参数下的离散阿尔芬本征模
王一如; 胡双辉; 姚龙宝; 陈淑平
2012-01-01
The physical features of the discrete Alfven eigenmodes are investigated in the DⅢ-D tokamak plasmas for the high performance discharge conditions, including the negative magnetic shear configuration, the high power heating, the co- and counter- neutral beam injection (NBI), the internal transport barrier, the high bootstrap current fraction case, and the VH-mode discharge. These Alfven eigenmodes exist in a wide radial range of the DⅢ-D plasma with a broad frequency spectrum in the advanced operation regime with the negative magnetic shear. The high power heating, the co-NBI, and the internal transport barrier can help form multiple deep potential wells, thus efficiently trapping the Alfven eigenmodes. These Alfven bound states can be found in even more extended radial range with relatively high frequencies for both the high bootstrap fraction discharge and the VH-mode discharge. These discrete Alfven eigenmodes, developed during the DⅢ-D high performance discharges with a broad scope of operating parameters, would be the potential instability which can exist widely in the experiments on the large similar tokamaks.%采用本征模式的数值打靶方法研究了离散阿尔芬本征模在DⅢ-D高性能运行条件下的物理特性,包括负磁剪切位形、高性能加热、正反中性束注入、内部输运垒以及高自举电流和甚高约束运行状态对这种阿尔芬模式的影响.在DⅢ-D托卡马克装置负磁剪切位形及先进运行状态实验参数下这些离散阿尔芬本征模存在于宽的径向区域,且具有广泛的本征频谱；高性能加热、同向中性束注入以及内部输运垒的存在有利于产生多个较深的气球模驱动势阱,由之得以很好地形成这种阿尔芬束缚态本征模；在高自举电流和甚高约束运行条件下这些离散阿尔芬本征模束缚态能够在更广的径向区域存在,且可具有较高的本征频率.另外,参照DⅢ-D装置放电实验数据的时间演
Diffusive shock acceleration with magnetic field amplification and Alfvenic drift
Kang, Hyesung
2012-01-01
We explore how wave-particle interactions affect diffusive shock acceleration (DSA) at astrophysical shocks by performing time-dependent kinetic simulations, in which phenomenological models for magnetic field amplification (MFA), Alfvenic drift, thermal leakage injection, Bohm-like diffusion, and a free escape boundary are implemented. If the injection fraction of cosmic-ray (CR) particles is greater than 2x10^{-4}, for the shock parameters relevant for young supernova remnants, DSA is efficient enough to develop a significant shock precursor due to CR feedback, and magnetic field can be amplified up to a factor of 20 via CR streaming instability in the upstream region. If scattering centers drift with Alfven speed in the amplified magnetic field, the CR energy spectrum can be steepened significantly and the acceleration efficiency is reduced. Nonlinear DSA with self-consistent MFA and Alfvenic drift predicts that the postshock CR pressure saturates roughly at 10 % of the shock ram pressure for strong shocks...
Chiral transition, eigenmode localisation and Anderson-like models
Giordano, Matteo; Pittler, Ferenc
2016-01-01
We discuss chiral symmetry restoration and eigenmode localisation in finite-temperature QCD by looking at the lattice Dirac operator as a random Hamiltonian. We argue that the features of QCD relevant to both phenomena are the presence of order in the Polyakov line configuration, and the correlations that this induces between spatial links across time slices. This ties the fate of chiral symmetry and of localisation of the lowest Dirac eigenmodes to the confining properties of the theory. We then show numerical results obtained in a QCD-inspired Anderson-like toy model, derived by radically simplifying the QCD dynamics while keeping the important features mentioned above. The toy model reproduces all the important qualitative aspects of chiral symmetry breaking and localisation in QCD, thus supporting the central role played by the confinement/deconfinement transition in triggering both phenomena.
Cooperative eigenmodes and scattering in 1D atomic arrays
Bettles, R J; Adams, C S
2016-01-01
Using a classical coupled dipole model, we numerically investigate the cooperative behavior of a one dimensional array of atomic dipoles driven by a weak laser field. Changing the polarization and direction of the driving field allows us to separately address superradiant, subradiant, red shifted, and blue shifted eigenmodes, as well as observe strong Fano-like interferences between different modes. The cooperative eigenvectors can be characterized by the phase difference between nearest neighbor dipoles, ranging from all oscillating in phase to all oscillating out of phase with their nearest neighbors. Investigating the eigenvalue behavior as a function of atom number and lattice spacing, we find that certain eigenmodes of an infinite atomic chain have the same decay rate as a single atom between two mirrors.
Dichromatic nonlinear eigenmodes in slab waveguide with chi(2) nonlinearity.
Darmanyan, S A; Nevière, M
2001-03-01
The existence of purely nonlinear eigenmodes in a waveguiding structure composed of a slab with quadratic nonlinearity surrounded by (non)linear claddings is reported. Modes having bright and dark solitonlike shapes and consisting of two mutually locked harmonics are identified. Asymmetrical modes are shown to exist in symmetrical environments. Constraints for the existence of the modes are derived in terms of parameters of guiding structure materials.
Detection of Ionospheric Alfven Resonator Signatures Onboard C/NOFS: Implications for IRI Modeling
Simoes, F.; Klenzing, J.; Ivanov, S.; Pfaff, R.; Rowland, D.; Bilitza, D.
2011-01-01
The 2008-2009 long-lasting solar minimum activity has been the one of its kind since the dawn of space age, offering exceptional conditions for investigating space weather in the near-Earth environment. First ever detection of Ionospheric Alfven Resonator (IAR) signatures in orbit offers new means for investigating ionospheric electrodynamics, namely MHD (MagnetoHydroDynamics) wave propagation, aeronomy processes, ionospheric dynamics, and Sun-Earth connection mechanisms at a local scale. Local and global plasma density heterogeneities in the ionosphere and magnetosphere allow for formation of waveguides and resonators where magnetosonic and shear Alfven waves propagate. The ionospheric magnetosonic waveguide results from complete magnetosonic wave reflection about the ionospheric F-region peak, where the Alfven index of refraction presents a maximum. MHD waves can also be partially trapped in the vertical direction between the lower boundary of the ionosphere and the magnetosphere, a resonance mechanism known as IAR. In this work we present C/NOFS (Communications/Navigation Outage Forecasting System) Extremely Low Frequency (ELF) electric field measurements related to IAR signatures, discuss the resonance and wave propagation mechanisms in the ionosphere, and address the electromagnetic inverse problem from which electron/ion distributions can be derived. These peculiar IAR electric field measurements provide new, complementary methodologies for inferring ionospheric electron and ion density profiles, and also contribute for the investigation of ionosphere dynamics and space weather monitoring. Specifically, IAR spectral signatures measured by C/NOFS contribute for improving the International Reference Ionosphere (IRI) model, namely electron density and ion composition.
The impact of localized overlap eigenmodes on RMT measurements and topology
Hasenfratz, Anna; Schaefer, Stefan
2007-01-01
The low energy eigenmodes of the continuum QCD Dirac operator are extended, but on the lattice, due to discretization effects, the Dirac operator can have localized eigenmodes. These non-physical modes can introduce strong lattice artifacts for observables that are sensitive to chiral symmetry, especially in mixed action simulations. We study how these lattice artifacts depend on the parameters of the overlap operator and their affect on the distribution on the Dirac eigenmodes and the topological susceptibility.
ALFVEN WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA
Soler, R.; Ballester, J. L.; Terradas, J. [Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Carbonell, M., E-mail: roberto.soler@uib.es, E-mail: joseluis.ballester@uib.es, E-mail: jaume.terradas@uib.es, E-mail: marc.carbonell@uib.es [Departament de Matematiques i Informatica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)
2013-04-20
Alfven waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfven waves is affected by the interaction between ionized and neutral species. Here we study Alfven waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible, we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cutoff values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mode approach and solve the initial-value problem in order to study the time-dependent evolution of the wave perturbations in the two fluids. An application to Alfven waves in the low solar atmospheric plasma is performed and the implication of partial ionization for the energy flux is discussed.
Quantum effects on compressional Alfven waves in compensated semiconductors
Amin, M. R. [Department of Electronics and Communications Engineering, East West University, Aftabnagar, Dhaka 1212 (Bangladesh)
2015-03-15
Amplitude modulation of a compressional Alfven wave in compensated electron-hole semiconductor plasmas is considered in the quantum magnetohydrodynamic regime in this paper. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential in the momentum balance equations of the charge carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the compressional Alfven wave by employing the standard reductive perturbation technique. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the linear and nonlinear dispersions of the compressional Alfven wave. Detailed analysis of the modulation instability in the long-wavelength regime is presented. For typical parameter ranges of the semiconductor plasmas and at the long-wavelength regime, it is found that the wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the effect of the Bohm potential may be neglected in comparison with the effect of the exchange-correlation potential in the linear and nonlinear dispersions of the compressional Alfven wave.
Direct excitation of resonant torsional Alfven waves by footpoint motions
Ruderman, M. S.; Berghmans, D.; Goossens, M.; Poedts, S.
1997-01-01
The present paper studies the heating of coronal loops by linear resonant Alfven waves that are excited by the motions of the photospheric footpoints of the magnetic field lines. The analysis is restricted to torsionally polarised footpoint motions in an axially symmetric system so that only
The role of torsional Alfven waves in coronal heating
Antolin, P
2009-01-01
In the context of coronal heating, among the zoo of MHD waves that exist in the solar atmosphere, Alfven waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption or turbulent cascade in order to heat the plasma. New observations with polarimetric, spectroscopic and imaging instruments such as those on board of the japanese satellite Hinode, or the SST or CoMP, are bringing strong evidence for the existence of energetic Alfven waves in the solar corona. In order to assess the role of Alfven waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfven wave heating through the mode conversion mechanism. Using a 1.5-dimensional MHD code we carry out a paramete...
Swirling astrophysical flows - efficient amplifiers of Alfven waves
Rogava, A D; Bodo, G; Massaglia, S; Rogava, Andria D.; Mahajan, Swadesh M.; Bodo, Gianluigi; Massaglia, Silvano
2003-01-01
We show that a helical shear flow of a magnetized plasma may serve as an efficient amplifier of Alfven waves. We find that even when the flow is purely ejectional (i.e., when no rotation is present) Alfven waves are amplified through the transient, shear-induced, algebraic amplification process. Series of transient amplifications, taking place sequentially along the flow, may result in a cascade amplification of these waves. However, when a flow is swirling or helical (i.e., some rotation is imposed on the plasma motion), Alfven waves become subject to new, much more powerful shear instabilities. In this case, depending on the type of differential rotation, both usual and parametric instabilities may appear. We claim that these phenomena may lead to the generation of large amplitude Alfven waves and the mechanism may account for the appearance of such waves in the solar atmosphere, in accretion-ejecion flows and in accretion columns. These processes may also serve as an important initial (linear and nonmodal)...
Localized eigenmodes of the overlap operator and their impact on the eigenvalue distribution
Hasenfratz, Anna; Schaefer, Stefan
2007-01-01
In a system where chiral symmetry is spontaneously broken, the low energy eigenmodes of the continuum Dirac operator are extended. On the lattice, due to discretization effects, the Dirac operator can have localized eigenmodes that affect physical quantities sensitive to chiral symmetry. While the infrared eigenmodes of the Wilson Dirac operator are usually extended even on coarse lattices, the chiral overlap operator has many localized eigenmodes in the physical region, especially in mixed action simulations. Depending on their density, these modes can introduce strong lattice artifacts. The effect can be controlled by changing the parameters of the overlap operator, in particular the clover improvement term and the center of the overlap projection.
Localized eigenmodes of the overlap operator and their impact on the eigenvalue distribution
Hasenfratz, A.; Hoffmann, R. [Colorado Univ., Boulder, CO (United States). Department of Physics; Schaefer, S. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC
2007-09-15
In a system where chiral symmetry is spontaneously broken, the low energy eigenmodes of the continuum Dirac operator are extended. On the lattice, due to discretization effects, the Dirac operator can have localized eigenmodes that affect physical quantities sensitive to chiral symmetry. While the infrared eigenmodes of the Wilson Dirac operator are usually extended even on coarse lattices, the chiral overlap operator has many localized eigenmodes in the physical region, especially in mixed action simulations. Depending on their density, these modes can introduce strong lattice artifacts. The effect can be controlled by changing the parameters of the overlap operator, in particular the clover improvement term and the center of the overlap projection. (orig.)
Measurement of erythrocyte membrane elasticity by flicker eigenmode decomposition.
Strey, H; Peterson, M; Sackmann, E
1995-08-01
We have studied the flickering of erythrocytes at wavelengths comparable to the cell dimension. To do this we have analyzed the edge fluctuations of the cell to a resolution of 5 nm by combining phase contrast microscopy with fast image processing. By measuring the edge excitations simultaneously at four orthogonal positions around the cell, the eigenmodes of equal azimuthal mode numbers m = 0,1,2 could be separated. From a continuous time sequence of 100 s of video frames taken at 40 ms time intervals, we determined the time-auto correlation function for the modes m = 0,1,2 and calculated their mean square amplitudes as well as their decay times tau m. To explain the results we also present the theoretically calculated energy eigenmodes of an erythrocyte, accounting for the constraint that the cell is in contact with the substrate along an annular ring, which agreed well with the experimental findings. We found that the softest mode is a "hindered translational" mode with m = 1 of the adhered cell, which is almost insensitive to the shear elastic modulus. Comparison of the calculated and measured amplitudes yielded an average value for the bending stiffness of kc = 4 x 10(-19) J, which is much larger than the value obtained by flicker analysis at short wavelengths (kc = 2.3 x 10(-20) J). It would, however, agree well with the value expected from the red cell membrane area compressibility modulus of K = 4.5 x 10(-1)N/m, which corresponds to a lipid bilayer containing approximately 50 mol % of cholesterol. In contradiction to our theoretical expectations we found that the flicker eigenmodes seemed not to be influenced by the membrane shear elasticity, which will be discussed in terms of an unusual coupling between the lipid bilayer and the cytoskeleton.
Optical Control of Fluorescence through Plasmonic Eigenmode Extinction
Xu, Xiaoying; Li, Quanshui; Zhang, Zhili; Ivanov, Ilia N; Li, Yuan; Wang, Wenbin; Gu, Baohua; Zhang, Zhenyu; Hsueh, Chun-Hway; Snijders, Paul C; Seal, Katyayani
2015-01-01
We introduce the concept of optical control of the fluorescence yield of CdSe quantum dots through plasmon-induced structural changes in random semicontinuous nanostructured gold films. We demonstrate that the wavelength- and polarization dependent coupling between quantum dots and the semicontinuous films, and thus the fluorescent emission spectrum, can be controlled and significantly increased through the optical extinction of a selective band of eigenmodes in the films. This optical method of effecting controlled changes in the metal nanostructure allows for versatile functionality in a single sample and opens a pathway to in situ control over the fluorescence spectrum.
Kinetic theory of the eigenmodes of classical fluids and neutron scattering
Cohen, E.G.D.; Schepper, I.M. de; Zuilhof, M.J.
1984-01-01
The lowest lying eigenmodes of a classical fluid have been approximately determined for a wide range of densities and wavenumbers. The most important eigenmodes are direct extensions of the three hydrodynamic heat and sound modes to much larger wavenumbers. A new and consistent interpretation of neu
Recent Alfvén Eigenmode measurements on JET
Aslanyan, V.; Porkolab, M.; Woskov, P.; Puglia, P.; Pires de Sa, W.; Galvao, R.; Ruchko, L.; Sharapov, S.; Dorling, S.; Dowson, S.; Graham, M.; Blackman, T.; Jones, G.; Goodyear, A.; Blanchard, P.; Fasoli, A.; Testa, D.; Figueiredo, J.; Perez von Thun, C.; JET Collaboration
2016-10-01
Alfvén Eigenmodes (AE) have been observed in the latest JET campaigns, excited by ICRH-driven fast particles in D and DH plasmas. The detection of AEs allows determination of isotope abundance in recent experiments with mixed ion composition plasmas. A major upgrade to the Toroidal Alfvén Eigenmode Active Antenna diagnostic at JET has opened the possibility to probe AEs with a wide range of toroidal mode numbers n and quantify their damping rate. A new 4 kW amplifier has been installed for each of six antennas to increase the output power and allow real time control of the relative phasing between the antennas. The diagnostic will be used to study the damping of alpha-driven AEs during the DT campaign planned on JET in support of ITER. Simulations with the MISHKA code are used to interpret the frequencies and radial localization of AEs. This work has been carried out within the framework of the EUROfusion Consortium Grant 633053. Support for the US group was provided by the US DOE, the Brazilian group from the FAPESP Project 2011/50773-0, and the Swiss group in part by the Swiss NSF.
Cooperative eigenmodes and scattering in one-dimensional atomic arrays
Bettles, Robert J.; Gardiner, Simon A.; Adams, Charles S.
2016-10-01
Collective coupling between dipoles can dramatically modify the optical response of a medium. Such effects depend strongly on the geometry of the medium and the polarization of the light. Using a classical coupled dipole model, here we investigate the simplest case of one-dimensional arrays of interacting atomic dipoles driven by a weak laser field. Changing the polarization and direction of the driving field allows us to separately address superradiant, subradiant, redshifted, and blueshifted eigenmodes, as well as observe strong Fano-like interferences between different modes. The cooperative eigenvectors can be characterized by the phase difference between nearest-neighbor dipoles, ranging from all oscillating in phase to all oscillating out of phase with their nearest neighbors. Investigating the eigenvalue behavior as a function of atom number and lattice spacing, we find that certain eigenmodes of an infinite atomic chain have the same decay rate as a single atom between two mirrors. The effects we observe provide a framework for collective control of the optical response of a medium, giving insight into the behavior of more complicated geometries, as well as providing further evidence for the dipolar analog of cavity QED.
Interacting Eigenmodes of a plasma diode with a density gradient
Loefgren, T.; Gunell, H.
1997-08-01
The formation of narrow high frequency electric field spikes in plasma density gradients is investigated using one-dimensional particle in cell simulations. It is found that the shape of the plasma density gradient is very important for the spike formation. The spike appears also in simulations with immobile ions showing that a coupling to the ion motion, as for example in wave interactions, is not necessary for the formation of HF spikes. However, the HF spike influences the ion motion, and ion waves are seen in the simulations. It has been found, in experiments and simulations, that the electron velocity distribution function deviates from the Maxwellian distribution. Dispersion relations are calculated using realistic distribution functions. The spike can be seen as a coupled system of two Eigenmodes of a plasma diode fed by the beam-plasma interaction. Based on a simplified fluid description of such Eigenmodes, explanations for the localization of the spike, spatially and in frequency, are given. The density amplitude is comparable with the DC density level close to the cathode. Space charge limits of waves in this region seem to determine the amplitude of the spike through the Poisson`s equation. 12 refs, 19 figs.
Tuan, P. H.; Wen, C. P.; Yu, Y. T.; Liang, H. C.; Huang, K. F.; Chen, Y. F.
2014-02-01
Experimentally resonant modes are commonly presumed to correspond to eigenmodes in the same bounded domain. However, the one-to-one correspondence between theoretical eigenmodes and experimental observations is never reached. Theoretically, eigenmodes in numerous classical and quantum systems are the solutions of the homogeneous Helmholtz equation, whereas resonant modes should be solved from the inhomogeneous Helmholtz equation. In the present paper we employ the eigenmode expansion method to derive the wave functions for manifesting the distinction between eigenmodes and resonant modes. The derived wave functions are successfully used to reconstruct a variety of experimental results including Chladni figures generated from the vibrating plate, resonant patterns excited from microwave cavities, and lasing modes emitted from the vertical cavity.
Sub-Alfvenic inlet boundary conditions for axisymmetric MHD nozzles
Cassibry, J T [Propulsion Research Center, University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Wu, S T [Center for Space Plasma and Aeronomy Research, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
2007-09-07
There are numerous electromagnetic accelerator concepts which require plasma expansion through a magnetic nozzle. If the inlet flow is slower than one or all of the outgoing characteristics, namely, the Alfven, slow and fast magnetosonic speeds, then the number of inlet conditions which could be arbitrarily specified are reduced by the number of outgoing characteristics (up to three). We derive the axisymmetric compatibility equations using the method of projected characteristics for the inlet conditions in the z-plane to assure the boundary conditions being consistent with flow properties. We make simplifications to the equations assuming that the inlet Alfven speed is much faster than the sonic and slow magnetosonic speeds. We compare results for various inlet boundary conditions, including a modified Lax-Wendroff implementation of the compatibility equations, first order extrapolation and arbitrarily specifying the inlet conditions, in order to assess the stability and accuracy of various approaches.
Cortical geometry as a determinant of brain activity eigenmodes: Neural field analysis
Gabay, Natasha C.; Robinson, P. A.
2017-09-01
Perturbation analysis of neural field theory is used to derive eigenmodes of neural activity on a cortical hemisphere, which have previously been calculated numerically and found to be close analogs of spherical harmonics, despite heavy cortical folding. The present perturbation method treats cortical folding as a first-order perturbation from a spherical geometry. The first nine spatial eigenmodes on a population-averaged cortical hemisphere are derived and compared with previous numerical solutions. These eigenmodes contribute most to brain activity patterns such as those seen in electroencephalography and functional magnetic resonance imaging. The eigenvalues of these eigenmodes are found to agree with the previous numerical solutions to within their uncertainties. Also in agreement with the previous numerics, all eigenmodes are found to closely resemble spherical harmonics. The first seven eigenmodes exhibit a one-to-one correspondence with their numerical counterparts, with overlaps that are close to unity. The next two eigenmodes overlap the corresponding pair of numerical eigenmodes, having been rotated within the subspace spanned by that pair, likely due to second-order effects. The spatial orientations of the eigenmodes are found to be fixed by gross cortical shape rather than finer-scale cortical properties, which is consistent with the observed intersubject consistency of functional connectivity patterns. However, the eigenvalues depend more sensitively on finer-scale cortical structure, implying that the eigenfrequencies and consequent dynamical properties of functional connectivity depend more strongly on details of individual cortical folding. Overall, these results imply that well-established tools from perturbation theory and spherical harmonic analysis can be used to calculate the main properties and dynamics of low-order brain eigenmodes.
Phase Mixing of Alfv\\'en Waves Near a 2D Magnetic Null Point
McLaughlin, J A
2014-01-01
The propagation of linear Alfv\\'en wave pulses in an inhomogeneous plasma near a 2D coronal null point is investigated. When a uniform plasma density is considered, it is seen that an initially planar Alfv\\'en wavefront remains planar, despite the varying equilibrium Alfv\\'en speed, and that all the wave collects at the separatrices. Thus, in the non-ideal case, these Alfv\\'enic disturbances preferentially dissipate their energy at these locations. For a non-uniform equilibrium density, it is found that the Alfv\\'en wavefront is significantly distorted away from the initially planar geometry, inviting the possibility of dissipation due to phase mixing. Despite this however, we conclude that for the Alfv\\'en wave, current density accumulation and preferential heating still primarily occur at the separatrices, even when an extremely non-uniform density profile is considered.
Kuridze, D
2007-01-01
Nonlinear coupling between 3-minute oscillations and Alfven waves in the solar lower atmosphere is studied. 3-minute oscillations are considered as acoustic waves trapped in a chromospheric cavity and oscillating along transversally inhomogeneous vertical magnetic field. It is shown that under the action of the oscillations the temporal dynamics of Alfven waves is governed by Mathieu equation. Consequently, the harmonics of Alfven waves with twice period and wavelength of 3-minute oscillations grow exponentially in time near the layer where the sound and Alfven speeds equal. Thus the 3-minute oscillations are resonantly absorbed by pure Alfven waves near this resonant layer. The resonant Alfven waves may penetrate into the solar corona taking energy from the chromosphere. Therefore the layer c_s=v_A may play a role of energy channel for otherwise trapped acoustic oscillations.
Nonlinear Alfv\\'en waves in extended magnetohydrodynamics
Abdelhamid, Hamdi M
2015-01-01
Large-amplitude Alfv\\'en waves are observed in various systems in space and laboratories, demonstrating an interesting property that the wave shapes are stable even in the nonlinear regime. The ideal magnetohydrodynamics (MHD) model predicts that an Alfv\\'en wave keeps an arbitrary shape constant when it propagates on a homogeneous ambient magnetic field. However, such arbitrariness is an artifact of the idealized model that omits the dispersive effects. Only special wave forms, consisting of two component sinusoidal functions, can maintain the shape; we derive fully nonlinear Alfv\\'en waves by an extended MHD model that includes both the Hall and electron inertia effects. Interestingly, these \\small-scale effects" change the picture completely; the large-scale component of the wave cannot be independent of the small scale component, and the coexistence of them forbids the large scale component to have a free wave form. This is a manifestation of the nonlinearity-dispersion interplay, which is somewhat differ...
Alfven waves in a partially ionized two-fluid plasma
Soler, R; Ballester, J L; Terradas, J
2013-01-01
Alfv\\'en waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfv\\'en waves is affected by the interaction between ionized and neutral species. Here we study Alfv\\'en waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cut-off values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mo...
Kelvin-Helmholtz instability in an Alfven resonant layer of a solar coronal loop
Uchimoto, E.; Strauss, H. R.; Lawson, W. S.
1991-01-01
A Kelvin-Helmholtz instability has been identified numerically on an azimuthally symmetric Alfven resonant layer in an axially bounded, straight cylindrical coronal loop. The set of equations is solved numerically as an initial value problem. The linear growth rate of this instability is shown to be approximately proportional to the Alfven driving amplitude and inversely proportional to the width of the Alfven resonant layer. It is also shown that the linear growth rate increases linearly with m - 1 up to a certain m, reaches its maximum value for the mode whose half wavelength is comparable to the Alfven resonant layer width, and decreases at higher azimuthal mode number.
Multiple regimes of operation in bimodal AFM: understanding the energy of cantilever eigenmodes.
Kiracofe, Daniel; Raman, Arvind; Yablon, Dalia
2013-01-01
One of the key goals in atomic force microscopy (AFM) imaging is to enhance material property contrast with high resolution. Bimodal AFM, where two eigenmodes are simultaneously excited, confers significant advantages over conventional single-frequency tapping mode AFM due to its ability to provide contrast between regions with different material properties under gentle imaging conditions. Bimodal AFM traditionally uses the first two eigenmodes of the AFM cantilever. In this work, the authors explore the use of higher eigenmodes in bimodal AFM (e.g., exciting the first and fourth eigenmodes). It is found that such operation leads to interesting contrast reversals compared to traditional bimodal AFM. A series of experiments and numerical simulations shows that the primary cause of the contrast reversals is not the choice of eigenmode itself (e.g., second versus fourth), but rather the relative kinetic energy between the higher eigenmode and the first eigenmode. This leads to the identification of three distinct imaging regimes in bimodal AFM. This result, which is applicable even to traditional bimodal AFM, should allow researchers to choose cantilever and operating parameters in a more rational manner in order to optimize resolution and contrast during nanoscale imaging of materials.
Variational analysis of eigenmodes of integrated optical waveguides and applications
祝宁华
1995-01-01
An iterative procedure is proposed for the variational analysis of Ti:LiNbO3 optical waveguides. A trial solution for the dominant electric field profile of arbitrary-order eigenmodes in strip waveguides and two coupled waveguides is proposed and its parameters are determined using the variational method. The results calculated using this method agree well with those obtained using the finite-element method. The present method has been used to check the accuracy of the effective index method as well as a quasi-analytical technique based on the effective index method. The results show that the effective index method is generally accurate for the fundamental mode and becomes less accurate for higher-order vertical modes.
K. OGAWA; M. ISOBE; K. TOI; F. WATANABE; D. A. SPONG; A. SHIMIZU; M. OSAKABE; D. S. DARROW; S. OHDACHI; S. SAKAKIBARA; LHD Experiment -Group
2012-01-01
Beam-ion losses induced by fast-ion-driven toroidal Alfven eigenmodes （TAE） were measured with a scintillator-based lost fast-ion probe （SLIP） in the large helical device （LHD）. The SLIP gave simultaneously the energy E and the pitch angle X=arccos（v///v） distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of Rax-vac=3.60 m, 3.75 m. and 3.90 m, where Rax-vac is the magnetic axis position of the vacuum field. Dominant losses induced by TAEs in these three configurations were observed in the E/X regions of 50-190 keV/40°, 40-170 keV/25°, and 30-190 keV/30°, respectively. Lost-ion fluxes induced by TAEs depend clearly on the amplitude of TAE magnetic fluctuations, Rax-vac and the toroidal field strength Bt. The increment of the loss fluxes has the dependence of （bTAE/Bt）s. The power s increases from s = 1 to 3 with the increase of the magnetic axis position in finite beta plasmas.
Relativistic particle acceleration in developing Alfv\\'{e}n turbulence
Matsukiyo, S; 10.1088/0004-637X/692/2/1004
2009-01-01
A new particle acceleration process in a developing Alfv\\'{e}n turbulence in the course of successive parametric instabilities of a relativistic pair plasma is investigated by utilyzing one-dimensional electromagnetic full particle code. Coherent wave-particle interactions result in efficient particle acceleration leading to a power-law like energy distribution function. In the simulation high energy particles having large relativistic masses are preferentially accelerated as the turbulence spectrum evolves in time. Main acceleration mechanism is simultaneous relativistic resonance between a particle and two different waves. An analytical expression of maximum attainable energy in such wave-particle interactions is derived.
Lohmeyer, Manfred
2004-01-01
The propagation of guided and nonconfined optical waves at fixed frequency through dielectric structures with piecewise constant, rectangular permittivity is considered in two spatial dimensions. Bidirectional versions of eigenmodes, computed for sequences of multilayer slab waveguides, constitute t
Lohmeyer, Manfred; Honsa, R.; Richter, L.
2003-01-01
Superpositions of two perpendicularly oriented bidirectional eigenmode propagation (BEP) fields, composed of basis modes that satisfy Dirichlet boundary conditions, can establish rigorous semianalytical solutions for problems of 2-D fixed-frequency wave propagation on unbounded, cross-shaped domains
Alfven waves in the solar atmosphere. III - Nonlinear waves on open flux tubes
Hollweg, J. V.; Jackson, S.; Galloway, D.
1982-01-01
Consideration is given the nonlinear propagation of Alfven waves on solar magnetic flux tubes, where the tubes are taken to be vertical, axisymmetric and initially untwisted and the Alfven waves are time-dependent axisymmetric twists. The propagation of the waves into the chromosphere and corona is investigated through the numerical solution of a set of nonlinear, time-dependent equations coupling the Alfven waves into motions that are parallel to the initial magnetic field. It is concluded that Alfven waves can steepen into fast shocks in the chromosphere, pass through the transition region to produce high-velocity pulses, and then enter the corona, which they heat. The transition region pulses have amplitudes of about 60 km/sec, and durations of a few tens of seconds. In addition, the Alfven waves exhibit a tendency to drive upward flows, with many of the properties of spicules.
The scaling dimension of low lying Dirac eigenmodes and of the topological charge density
Aubin, C. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Bernard, C. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Gottlieb, Steven [Department of Physics, Indiana Univerity, Bloomington, IN 47405 (United States); Gregory, E.B. [Department of Physics, University of Arizona, Tucson, AZ 85721 (United States); Heller, Urs M. [American Physical Society, One Research Road, Box 9000, Ridge, NY 11961 (United States); Hetrick, J.E. [Physics Department, University of the Pacific, Stockton, CA 95211 (United States); Osborn, J.; Sugar, R. [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Forcrand, Ph. de [Institute for Theoretical Physics, ETH Zuerich, CH-8093 Zurich (Switzerland); CERN, Theory Division, CH-1211 Geneva 23 (Switzerland); Jahn, O. [Center for Theoretical Physics, MIT, Cambridge, MA 02139 (United States)
2005-03-15
As a quantitative measure of localization, the inverse participation ratio of low lying Dirac eigenmodes and topological charge density is calculated on quenched lattices over a wide range of lattice spacings and volumes. Since different topological objects (instantons, vortices, monopoles, and artifacts) have different co-dimension, scaling analysis provides information on the amount of each present and their correlation with the localization of low lying eigenmodes.
Inductive Eigenmodes of a resistive toroidal surface in vacuum
Lo Surdo, C. [ENEA, Centro Ricerche Frascati, Rome (Italy). Dipt. Innovazione
1999-07-01
In this paper it has been studied the Electro-Magnetic (EM) Eigenmodes, sufficiently slow as to legitimate the pre-Maxwell approximation of Maxwell's system (or inductive Eigenmodes), of a given smooth, toroidal-un knotted, electrically resistive surface {tau} with given smooth (surface) resistivity 0 < {rho}{sub d}egree < {infinity}, and lying in the (empty) R{sup 3}. Within the above limitations (to be made more precise), the geometry of {tau} is arbitrary. With the eigenvalue associated with the generic Eigenmode being defined as the opposite of its logarithmic time-derivative, one expects that the resulting spectrum be discrete and strictly positive. It shall be interested into the degenerate case where {tau} be cut (i.e. electrically broken) along one or more of its irreducible cycles. This case will be analyzed autonomously, rather than as a limit (for {rho}{sub d}egree {yields} {infinity} along the cuts) of the regular case. Without cuts, the Eigenproblem under consideration is nothing but the two-dimensional (2-dim) generalization of the classical case of a smooth, unknotted, electrically conductive, simple coil in infinite vacuum. Its analysis hinges on the classical potential theory, and turns out to be a special application of the linear, integrodifferential (elliptic) equation theory on a compact, multiply connected, 2-dim manifold. The attention and approach will be confined to strong (or classical) solutions, both in {tau} and C {tau} = R{sup 3} / {tau}. This study is divided in two parts: a General Part (Sects 1 divided 4) is devoted to the case of generic {tau} and {rho}{sub d}egree (within the convenient smoothness requirements), whereas a Special Part (Sects 5 divided 7) deals with the (more or less formal) discussion of a couple of particular cases ({tau} {identical_to} a canonical torus), both of which with uniform {rho}{sub d}egree. Some propaedeutical/supplementary information is provided in a number of Appendices. [Italian] Il presente
Rankin, R.; Sydorenko, D.
2015-12-01
Results from a 3D global numerical model of Alfven wave propagation in a warm multi-species plasma in Earth's magnetosphere are presented. The model uses spherical coordinates, accounts for a non-dipole magnetic field, vertical structure of the ionosphere, and an air gap below the ionosphere. A realistic density model is used. Below the exobase altitude (2000 km) the densities and the temperatures of electrons, ions, and neutrals are obtained from the IRI and MSIS models. Above the exobase, ballistic (originating from the ionosphere and returning to ionosphere) and trapped (bouncing between two reflection points above the ionosphere) electron populations are considered similar to [Pierrard and Stegen (2008), JGR, v.113, A10209]. Plasma parameters at the exobase provided by the IRI are the boundary conditions for the ballistic electrons while the [Carpenter and Anderson (1992), JGR, v.97, p.1097] model of equatorial electron density defines parameters of the trapped electron population. In the simulations that are presented, Alfven waves with frequencies from 1 Hz to 0.01 Hz and finite azimuthal wavenumbers are excited in the magnetosphere and compared with Van Allen Probes data and ground-based observations from the CARISMA array of ground magnetometers. When short perpendicular scale waves reflect form the ionosphere, compressional Alfven waves are observed to propagate across the geomagnetic field in the ionospheric waveguide [e.g., Lysak (1999), JGR, v.104, p.10017]. Signals produced by the waves on the ground are discussed. The wave model is also applied to interpret recent Van Allen Probes observations of kinetic scale ULF waves that are associated with radiation belt electron dynamics and energetic particle injections.
Xie, Ming [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2000-05-18
Exact solution and variational approximation of eigenmodes in high gain FELs are presented. These eigenmodes specify transverse profiles and exponential growth rates of the laser field before saturation. They are self-consistent solutions of coupled Maxwell–Vlasov equations describing FEL interaction taking into account the effects due to energy spread, emittance and betatron oscillations of the electron beam, as well as diffraction and optical guiding of the laser field. A new formalism of scaling is introduced and based on which solutions in various limiting cases are discussed. Additionally, a fitting formula is obtained from interpolating the variational solution for quick calculation of exponential growth rate of the fundamental mode.
Compressional Alfvén eigenmodes in rotating spherical tokamak plasmas
Smith, H. M.; Fredrickson, E. D.
2017-03-01
Spherical tokamaks often have a considerable toroidal plasma rotation of several tens of kHz. Compressional Alfvén eigenmodes in such devices therefore experience a frequency shift, which if the plasma were rotating as a rigid body, would be a simple Doppler shift. However, since the rotation frequency depends on minor radius, the eigenmodes are affected in a more complicated way. The eigenmode solver CAE3B (Smith et al 2009 Plasma Phys. Control. Fusion 51 075001) has been extended to account for toroidal plasma rotation. The results show that the eigenfrequency shift due to rotation can be approximated by a rigid body rotation with a frequency computed from a spatial average of the real rotation profile weighted with the eigenmode amplitude. To investigate the effect of extending the computational domain to the vessel wall, a simplified eigenmode equation, yet retaining plasma rotation, is solved by a modified version of the CAE code used in Fredrickson et al (2013 Phys. Plasmas 20 042112). In summary, both solving the full eigenmode equation, as in the CAE3B code, and placing the boundary at the vessel wall, as in the CAE code, significantly influences the calculated eigenfrequencies.
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.
Cosmic Ray propagation in sub-Alfvenic magnetohydrodynamic turbulence
Cohet, Romain
2016-01-01
This work has the main objective to provide a detailed investigation of cosmic ray propagation in magnetohydrodynamic turbulent fields generated by forcing the fluid velocity field at large scales. It provides a derivation of the particle mean free path dependences in terms of the turbulence level described by the Alfv\\'enic Mach number and in terms of the particle rigidity. We use an upgrade version of the magnetohydrodynamic code {\\tt RAMSES} which includes a forcing module and a kinetic module and solve the Lorentz equation for each particle. The simulations are performed using a 3 dimension periodical box in the test-particle and magnetostatic limits. The forcing module is implemented using an Ornstein-Uhlenbeck process. An ensemble average over a large number of particle trajectories is applied to reconstruct the particle mean free paths. We derive the cosmic ray mean free paths in terms of the Alfv\\'enic Mach numbers and particle reduced rigidities in different turbulence forcing geometries. The reduced...
Characteristics of Short-wavelength Oblique Alfven and Slow waves
Zhao, J S; Yu, M Y; Lu, J Y; Wu, D J
2014-01-01
Linear properties of kinetic Alfv\\'en waves (KAWs) and kinetic slow waves (KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We obtain the wave dispersion relations that are valid in a wide range of the wave frequency {\\omega} and plasma-to-magnetic pressure ratio {\\beta}. The KAW frequency can reach and exceed the ion cyclotron frequency at ion kinetic scales, whereas the KSW frequency remains sub-cyclotron. At {\\beta}\\sim1, the plasma and magnetic pressure perturbations of both modes are in anti-phase, so that there is nearly no total pressure perturbations. However, these modes exhibit several different properties. At high {\\beta}, the electric field polarization of KAW and KSW is opposite at the ion gyroradius scale, where KAWs are polarized in sense of electron gyration (right-hand polarized) and KSWs are left-hand polarized. The magnetic helicity {\\sigma}\\sim1 for KAWs and {\\sigma}\\sim-1 for KSWs, and the ion Alfv\\'en ratio R_{Ai}\\ll 1 for KAWs and R_{Ai}\\gg 1 for KSWs. We also found...
Plasma heating inside ICMEs by Alfvenic fluctuations dissipation
Li, Hui; He, Jiansen; Zhang, Lingqian; Richardson, John D; Belcher, John W; Tu, Cui
2016-01-01
Nonlinear cascade of low-frequency Alfvenic fluctuations (AFs) is regarded as one candidate of the energy sources to heat plasma during the non-adiabatic expansion of interplanetary coronal mass ejections (ICMEs). However, AFs inside ICMEs were seldom reported in the literature. In this study, we investigate AFs inside ICMEs using observations from Voyager 2 between 1 and 6 au. It is found that AFs with high degree of Alfvenicity frequently occurred inside ICMEs, for almost all the identified ICMEs (30 out of 33 ICMEs), and 12.6% of ICME time interval. As ICMEs expand and move outward, the percentage of AF duration decays linearly in general. The occurrence rate of AFs inside ICMEs is much less than that in ambient solar wind, especially within 4 au. AFs inside ICMEs are more frequently presented in the center and at the boundaries of ICMEs. In addition, the proton temperature inside ICME has a similar distribution. These findings suggest significant contribution of AFs on local plasma heating inside ICMEs.
Superdiffusion versus Alfvenic collapse: plasma flow bounding and penetration
Savin, S.; Amata, A.; Zelenyi, L.; Budaev, V.; Kuznetsov, E. A.; Consolini, G.; Blecki, J.; Buechner, J.; Rauch, J. L.
2009-04-01
A geophysical flow is the solar plasma one around the Earth's magnetosphere. We discuss an anomalous MHD plasma mixing with concentrated kinetic energy bursts - ‘plasma jets' - in view of common features of the geophysical flows, along with the laboratory and astrophysical plasma ones. While the plasma flows are quite dilute, they probably can lead to electric power system collapses on the ground, radiation hazards in space, including geostationary spacecraft faults, and communication interrupts etc. We would like to concentrate on a unique case of plasma mixing by the jets in the streamlining flow with quite effective transport barrier , most probably, due to Alfvenic collapse of the magnetic field at the interface of their streaming and stagnant plasma ahead the Earth magnetopause on February 2, 2003 from the Cluster spacecraft data. On the basis of outer magnetospheric spacecraft observations in the magnetosheath (MSH) we provide evidence for the temporary existence of the anomalously concentrated plasma jets as well in the region close to the bow shock (BS) as near the magnetopause (MP). Disturbed zones of duration of up to 2 hours are regularly detected in the MSH, preferably downstream of the quasi-parallel and oblique BS with average energy density well above that of the un-shocked solar wind (SW). These zones are similar to high-latitude MSH near the MP, known as the ‘turbulent boundary layer' (TBL), which is the result of the interaction of the MSH flow with the throat of the cusp. In both these disturbed zones the field and plasma fluctuations have comparable intensity and similar spectral properties. Determination of the structure functions of the magnetic field and ion flux also reveals similar multifractal and intermittent properties. The same holds for fitting a Log-Poisson cascade model. A new phenomenon - Alfvenic collapse - is discussed as a ‘tool' for separating of the MHD flows: in the MHD limit it predicts infinite field rising due to
Similon, Philippe L.; Sudan, R. N.
1989-01-01
The importance of field line geometry for shear Alfven wave dissipation in coronal arches is demonstrated. An eikonal formulation makes it possible to account for the complicated magnetic geometry typical in coronal loops. An interpretation of Alfven wave resonance is given in terms of gradient steepening, and dissipation efficiencies are studied for two configurations: the well-known slab model with a straight magnetic field, and a new model with stochastic field lines. It is shown that a large fraction of the Alfven wave energy flux can be effectively dissipated in the corona.
Behavior of Torsional Alfven Waves and Field Line Resonance on Rotating Magnetars
Kojima, T O Y
2005-01-01
Torsional Alfven waves are likely excited with bursts in rotating magnetars. These waves are probably propagated through corotating atmospheres toward a vacuum exterior. We have studied the physical effects of the azimuthal wave number and the characteristic height of the plasma medium on wave transmission. In this work, explicit calculations were carried out based on the three-layered cylindrical model. We found that the coupling strength between the internal shear and the external Alfven modes is drastically enhanced, when resonance occurs in the corotating plasma cavity. The spatial structure of the electromagnetic fields in the resonance cavity is also investigated when Alfven waves exhibit resonance.
Eigenmodes of brain activity: Neural field theory predictions and comparison with experiment.
Robinson, P A; Zhao, X; Aquino, K M; Griffiths, J D; Sarkar, S; Mehta-Pandejee, Grishma
2016-11-15
Neural field theory of the corticothalamic system is applied to predict and analyze the activity eigenmodes of the bihemispheric brain, focusing particularly on their spatial structure. The eigenmodes of a single brain hemisphere are found to be close analogs of spherical harmonics, which are the natural modes of the sphere. Instead of multiple eigenvalues being equal, as in the spherical case, cortical folding splits them to have distinct values. Inclusion of interhemispheric connections between homologous regions via the corpus callosum leads to further splitting that depends on symmetry or antisymmetry of activity between brain hemispheres, and the strength and sign of the interhemispheric connections. Symmetry properties of the lowest observed eigenmodes strongly constrain the interhemispheric connectivity strengths and unihemispheric mode spectra, and it is predicted that most spontaneous brain activity will be symmetric between hemispheres, consistent with observations. Comparison with the eigenmodes of an experimental anatomical connectivity matrix confirms these results, permits the relative strengths of intrahemispheric and interhemispheric connectivities to be approximately inferred from their eigenvalues, and lays the foundation for further experimental tests. The results are consistent with brain activity being in corticothalamic eigenmodes, rather than discrete "networks" and open the way to new approaches to brain analysis. Copyright © 2016 Elsevier Inc. All rights reserved.
Drake, D J; Howes, G G; Kletzing, C A; Skiff, F; Carter, T A; Auerbach, D W
2013-01-01
Turbulence is a phenomenon found throughout space and astrophysical plasmas. It plays an important role in solar coronal heating, acceleration of the solar wind, and heating of the interstellar medium. Turbulence in these regimes is dominated by Alfven waves. Most turbulence theories have been established using ideal plasma models, such as incompressible MHD. However, there has been no experimental evidence to support the use of such models for weakly to moderately collisional plasmas which are relevant to various space and astrophysical plasma environments. We present the first experiment to measure the nonlinear interaction between two counterpropagating Alfven waves, which is the building block for astrophysical turbulence theories. We present here four distinct tests that demonstrate conclusively that we have indeed measured the daughter Alfven wave generated nonlinearly by a collision between counterpropagating Alfven waves.
Drift-Alfven instabilities of a finite beta plasma shear flow along a magnetic field
Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June
2016-02-01
It was derived that the drift-Alfven instabilities with the shear flow parallel to the magnetic field have significant difference from the drift-Alfven instabilities of a shearless plasma when the ion temperature is comparable with electron temperature for a finite plasma beta. The velocity shear not only modifies the frequency and the growth rate of the known drift-Alfven instability, which develops due to the inverse electron Landau damping, but also triggers a combined effect of the velocity shear and the inverse ion Landau damping, which manifests the development of the ion kinetic shear-flow-driven drift-Alfven instability. The excited unstable waves have the phase velocities along the magnetic field comparable with the ion thermal velocity, and the growth rate is comparable with the frequency. The development of this instability may be the efficient mechanism of the ion energization in shear flows.
Parametric instabilities of large-amplitude parallel propagating Alfven waves: 2-D PIC simulation
Nariyuki, Yasuhiro; Hada, Tohru
2008-01-01
We discuss the parametric instabilities of large-amplitude parallel propagating Alfven waves using the 2-D PIC simulation code. First, we confirmed the results in the past study [Sakai et al, 2005] that the electrons are heated due to the modified two stream instability and that the ions are heated by the parallel propagating ion acoustic waves. However, although the past study argued that such parallel propagating longitudinal waves are excited by transverse modulation of parent Alfven wave, we consider these waves are more likely to be generated by the usual, parallel decay instability. Further, we performed other simulation runs with different polarization of the parent Alfven waves or the different ion thermal velocity. Numerical results suggest that the electron heating by the modified two stream instability due to the large amplitude Alfven waves is unimportant with most parameter sets.
Alfven. Symphony No 5 in A minor, Op. 54 / Robert Layton
Layton, Robert
1994-01-01
Uuest heliplaadist "Alfven. Symphony No 5 in A minor, Op. 54. The Mountain King - Suite, Gustav II Adolf, Op. 49 - Elegy. Royal Stockholm Philarmonic Orchestra / Neeme Järvi. BIS CD 585 (68 minutes) Recorded in association with Trygg Hansa"
Alfven. Symphony No 5 in A minor, Op. 54 / Robert Layton
Layton, Robert
1994-01-01
Uuest heliplaadist "Alfven. Symphony No 5 in A minor, Op. 54. The Mountain King - Suite, Gustav II Adolf, Op. 49 - Elegy. Royal Stockholm Philarmonic Orchestra / Neeme Järvi. BIS CD 585 (68 minutes) Recorded in association with Trygg Hansa"
Alfven Waves in a Plasma Sheet Boundary Layer Associated with Near-Tail Magnetic Reconnection
YUAN Zhi-Gang; DENG Xiao-Hua; PANG Ye; LI Shi-You; WANG Jing-Fang
2007-01-01
We report observations from Geotail satellite showing that large Poynting fluxes associated with Alfven waves in the plasma sheet boundary layer(PSBL) occur in the vicinity of the near-tail reconnection region on 10 December 1996.During the period of large Poynting fluxex,Geotail also observed strong tailward plasma flws.These observations demonstrate the importance of near-tail reconnection process as the energy source of Alfven waves in the PSBL.Strong tailward(Earthward)plasma flows ought to be an important candidate in generating Alfven waves.Furthermore,the strong pertutbations not only of the magnetic field but also of the electric field observed in the PSBL indicate that the PSBL plays an important role in the generation and propagation of the energy flux associated with Alfven waves.
Heating of the Solar Corona by Alfven Waves: Self-Induced Opacity
Zahariev, N I
2011-01-01
There have been derived equations describing the static distributions of temperature and wind velocity at the transition region within the framework of the magnetohydrodynamics (MHD) of fully ionized hydrogen plasma . We have also calculated the width of the transition between the chromosphere and corona as a self-induced opacity of the high-frequency Alfven waves (AWs). The domain wall is a direct consequence of the self-consistent MHD treatment of AWs propagation. We predict considerable spectral density of the high-frequency AWs in the photosphere. The idea that Alfven waves might heat the solar corona belong to Alfven - we simply derived the corresponding MHD equations. The comparison of the solutions to those equations with the observational/measured data will be crucial for revealing the heating mechanism. The analysis of those solutions will explain how Alfven waves brick unto the corona and dissipate their energy there.
Transfer of Energy, Potential, and Current by Alfv\\'en Waves in Solar Flares
Melrose, D B
2013-01-01
Alfv\\'en waves play three related roles in the impulsive phase of a solar flare: they transport energy from a generator region to an acceleration region; they map the cross-field potential (associated with the driven energy release) from the generator region onto the acceleration region; and within the acceleration region they damp by setting up a parallel electric field that accelerates electrons and transfers the wave energy to them. The Alfv\\'en waves may also be regarded as setting up new closed current loops, with field-aligned currents that close across field lines at boundaries. A model is developed for large-amplitude Alfv\\'en waves that shows how Alfv\\'en waves play these roles in solar flares. A picket-fence structure for the current flow is incorporated into the model to account for the "number problem" and the energy of the accelerated electrons.
Dipole AlfvenVortex with Finite Ion Larmor Radius in a Low-Beta Plasma
WANG Xu-Yu; HE Xian-Tu; LIU Zhen-Xing; CAO Jin-Bin
2000-01-01
A set of nonlinear fluid equations which include the effects of ion gyroradius is derived to describe Alfven vortex. The correction of finite ion gyroradius to the Alfven vortex in the inertial region is much more significant than that in the kinetic region. The amplitude of the vortex is enhanced in both regions. The scale of the vortex in the kinetic region becomes larger whereas it becomes smaller in the inertial region.
Eigenmodes and field distribution of a nanosphere-in-a-nanoshell metallodielectric nanostructure
Manassah, Jamal T., E-mail: jmanassah@gmail.com [Department of Electrical Engineering, City College of New York, New York, NY 10031 (United States)
2012-08-06
I compute the plasmonic eigenmodes of a nanostructure consisting of a metallic sphere surrounded by a layer of dielectric C (d{sub C}) and a metallic shell on top embedded in a dielectric A (d{sub A}). Using the continuity conditions of the tangential components of the magnetic flux density and of the electric field at the interfaces and the Drude model, I obtain the equations relating the dominant three plasmonic eigenfrequencies and decay rates, to the nanostructure geometric parameters and the indices of refraction of d{sub A} and d{sub C}. I also compute the electric and magnetic fields' configurations for the dominant eigenmodes. -- Highlights: ► Compute the eigenmodes, resonance frequencies and decay rates, for a metallic nanosphere in a nanoshell. ► Full Maxwell treatment. No quasi-static approximation. ► Computationally direct and accurate. ► Method can be easily generalized to any multilayers spherical structure.
Eigenmodes of a hydrodynamically coupled micron-size multiple-particle ring
di Leonardo, R.; Keen, S.; Leach, J.; Saunter, C. D.; Love, G. D.; Ruocco, G.; Padgett, M. J.
2007-12-01
We use a continuous acquisition, high-speed camera with integrated centroid tracking to simultaneously measure the positions of a ring of micron-sized particles held in holographic optical tweezers. Hydrodynamic coupling between the particles gives a set of eigenmodes, each one independently relaxing with a characteristic decay rate (eigenvalue) that can be measured using our positional data. Despite the finite particle size, we find an excellent agreement between the measured eigenvalues and those numerically predicted by Oseen theory applied to the two-dimensional (2D) ring geometry. Particle motions are also analyzed in terms of the alternative eigenmode set obtained by wrapping onto the ring the eigenmodes of a 1D periodic chain. We identify the modes for which the periodic chain is a good approximation to the ring and those for which it is not.
Cossu, Guido
2016-01-01
We investigate the properties of the background gauge field configurations that act as disorder for the Anderson localization mechanism in the Dirac spectrum of QCD at high temperatures. We compute the eigenmodes of the M\\"obius domain-wall fermion operator on configurations generated for the $SU(3)$ gauge theory with two flavors of fermions, in the temperature range $[0.9,1.9]T_c$. We identify the source of localization of the eigenmodes with gauge configurations that are self-dual and support negative fluctuations of the Polyakov loop $P_L$, in the high temperature sea of $P_L\\sim 1$. The dependence of these observations on the boundary conditions of the valence operator is studied. We also investigate the spatial overlap of the left-handed and right-handed projected eigenmodes in correlation with the localization and the corresponding eigenvalue. We discuss an interpretation of the results in terms of monopole-instanton structures.
Nasr, Mamdouh H; Eshrah, Islam A; Abuelfadl, Tamer M
2016-01-01
An eigenmode projection technique (EPT) is developed and employed to solve problems of electromagnetic resonance in closed cavities and scattering from discontinuities in guided-wave structures. The EPT invokes the eigenmodes of a canonical predefined cavity in the solution procedure and uses the expansion of these eigenmodes to solve Maxwell's equations, in conjunction with a convenient choice of port boundary conditions. For closed cavities, resonance frequencies of arbitrary-shaped cavities are accurately determined with a robust and efficient separation method of spurious modes. For waveguide scattering problems, the EPT is combined with the generalized scattering matrix approach to solve problems involving waveguide discontinuities with arbitrary dielectric profiles. Convergence studies show stable solutions for a relatively small number of expansion modes, and the proposed method shows great robustness over conventional solvers in analyzing electromagnetic problems with inhomogeneous materials.
Eigenfrequencies and eigenmodes of a beam with periodically continuously varying spatial properties
Sorokin, Vladislav S.; Thomsen, Jon Juel
2015-01-01
A beam with periodically continuously varying spatial properties is analyzed. This structure is a generic model for various systems widely used in industry, e.g. risers, rotor blades, and similar. The aim is to reveal effects of periodic spatial modulation both on the beam eigenfrequencies...... and eigenmodes. Special attention is given to "mid-frequency" eigenmodes having period of the same order as the period of modulation, which cannot be captured by the conventional analytical methods. In particular, the paper addresses prediction of bandgaps and their influence on the distribution...... of modulation on eigenfrequencies, and that modulations of the beam mass per unit length and of the beam stiffness affect them oppositely. It is shown that eigenmodes having a period close to the period of modulation comprise a long-wave component; this illustrates the capacity of non-uniform structures...
Threaded-Field-Lines Model for the Low Solar Corona Powered by the Alfven Wave Turbulence
Sokolov, Igor V; Manchester, Ward B; Ozturk, Doga Can Su; Szente, Judit; Taktakishvili, Aleksandre; Tóth, Gabor; Jin, Meng; Gombosi, Tamas I
2016-01-01
We present an updated global model of the solar corona, including the transition region. We simulate the realistic tree-dimensional (3D) magnetic field using the data from the photospheric magnetic field measurements and assume the magnetohydrodynamic (MHD) Alfv\\'en wave turbulence and its non-linear dissipation to be the only source for heating the coronal plasma and driving the solar wind. In closed field regions the dissipation efficiency in a balanced turbulence is enhanced. In the coronal holes we account for a reflection of the outward propagating waves, which is accompanied by generation of weaker counter-propagating waves. The non-linear cascade rate degrades in strongly imbalanced turbulence, thus resulting in colder coronal holes. The distinctive feature of the presented model is the description of the low corona as almost-steady-state low-beta plasma motion and heat flux transfer along the magnetic field lines. We trace the magnetic field lines through each grid point of the lower boundary of the g...
Anomalous flow deflection at planetary bow shocks in the low Alfven Mach number regime
Nishino, Masaki N.; Fujimoto, Masaki; Tai, Phan-Duc; Mukai, Toshifumi; Saito, Yoshifumi; Kuznetsova, Masha M.; Rastaetter, Lutz
A planetary magnetosphere is an obstacle to the super-sonic solar wind and the bow shock is formed in the front-side of it. In ordinary hydro-dynamics, the flow decelerated at the shock is diverted around the obstacle symmetrically about the planet-Sun line, which is indeed observed in the magnetosheath most of the time. Here we show a case under a very low density solar wind in which duskward flow was observed in the dawnside magnetosheath of the Earth's magnetosphere. A Rankine-Hugoniot test across the bow shock shows that the magnetic effect is crucial for this "wrong flow" to appear. A full three-dimensional Magneto- Hydro-Dynamics (MHD) simulation of the situation in this previously unexplored parameter regime is also performed. It is illustrated that in addition to the "wrong flow" feature, various peculiar characteristics appear in the global picture of the MHD flow interaction with the obstacle. The magnetic effect at the bow shock should become more conspicuously around the Mercury's magnetosphere, because stronger interplanetary magnetic field and slower solar wind around the Mercury let the Alfven Mach number low. Resultant strong deformation of the magnetosphere induced by the "wrong flow" will cause more complex interaction between the solar wind and the Mercury.
Anomalous Flattening of the Fast-Ion Profile during Alfvén-Eigenmode Activity
Heidbrink, W. W.; Gorelenkov, N. N.; Luo, Y.; van Zeeland, M. A.; White, R. B.; Austin, M. E.; Burrell, K. H.; Kramer, G. J.; Makowski, M. A.; McKee, G. R.; Nazikian, R.
2007-12-01
Neutral-beam injection into plasmas with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The first application of fast-ion Dα (FIDA) spectroscopy to Alfvén-eigenmode physics shows that the central fast-ion profile is anomalously flat in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The current density driven by fast ions is also strongly modified. Calculations based on the measured mode amplitudes do not explain the observed fast-ion transport.
Violation of chirality of the M\\"obius domain-wall Dirac operator from the eigenmodes
Cossu, Guido; Hashimoto, Shoji; Tomiya, Akio
2015-01-01
We investigate the effects of the violation of the Ginsparg-Wilson (GW) relation in the M\\"obius domain-wall fermion formulation on the lattice with finite fifth dimension. Using a decomposion in terms of the eigenmodes of its four-dimensional effective Dirac operator, we isolate the GW-violating terms for various physical quantities including the residual mass and the meson susceptibilities relevant for the effective restoration of the axial U(1) symmetry at finite temperature. Numerical result shows that the GW-violating effect is more significant, or even overwhelming, for the quantities that are dominated by the low-lying eigenmodes.
Randomly phase-locked microlaser arrays and fuzzy eigenmodes with stochastic phasing.
Riyopoulos, S
2006-10-30
Deviations in the cold cavity parameters, random or systematic, produce incoherently phased-locked laser arrays with unevenly distributed phase difference and intensity. The collective radiation fields constitute "fuzzy" eigenmodes; the phasing among cavities is constant in time but changes randomly from site-to-site. The existence and structure of such eigenmodes is demonstrated numerically and analyzed theoretically using the rate equations for coupled semiconductor laser cavities. Active coupling, whereby one cavity's radiation field modulates the complex gain of nearby cavities (cross-cavity hole burning), is essential for the frequency pulling allowing synchronization of the laser operating frequencies.
INFLUENCE OF DAMPING SUSPENSION ON THE VIBRATION EIGENMODES OF RAILWAY VEHICLES
Mădălina DUMITRIU
2013-05-01
Full Text Available The dynamic performance of the railway vehicle, mainly the rolling comfort, strongly depends on thelevel of vibrations. The suspension, when its characteristics are properly adopted, has the ability to maintain thevibration behavior at a level that will provide the passengers with comfort, even though velocities increase. Thevertical vibration eigenmodes, the bounce, the pitch and the bending of the carbody are essential for comfort.The paper proves that the level of the accelerations derived from these vibration eigenmodes is influenced by theextent of the suspension damping.
范玮丽
2008-01-01
This paper mainly talks about the currently hot topic-globalization. Firstly, it brings out the general trend about globalization and how to better understand its implication. Secondly, it largely focuses on how to deal with it properly, especially for international marketers. Then, facing with the overwhelming trend, it is time for us to think about seriously what has globalization brought to us. Last but not least, it summarized the author's personal view about the future of globalization and how should we go.
Tulio Rosembuj
2006-12-01
Full Text Available There is no singular globalization, nor is the result of an individual agent. We could start by saying that global action has different angles and subjects who perform it are different, as well as its objectives. The global is an invisible invasion of materials and immediate effects.
Carrion, P.M.; Hasegawa, A.; Patton, W.; Prakash, M.
1988-06-01
A set of linearized magnetohydrodynamic equations was reduced to the reflectivity equation for the compressional magnetic perturbations in the framework of the Radoski model. It is shown that the reflection coeficient is a function of the inhomogeneities of the magnetic field, and the inhomogeneities of the Alfven velocity. An interesting property of the reflectivity equation is that, near Alfven resonant magnetic-force lines, this equation reduces to the curvature-free Budden equation. Near Alfven resonances, the curvature does not play a significant role and Budden's asymptotics in time can be applied to the wave field near the magnetic-force lines where the Alfven dispersion relation holds.
Sabeen, A.; Masood, W.; Qureshi, M. N. S.; Shah, H. A.
2017-07-01
In this paper, linear and nonlinear coupling of kinetic Alfven and acoustic waves has been studied in a dusty plasma in the presence of trapping and self-gravitation effects. In this regard, we have derived the linear dispersion relations for positively and negatively coupled dust kinetic Alfven-acoustic waves. Stability analysis of the coupled dust kinetic Alfven-acoustic wave has also been presented. The formation of solitary structures has been investigated following the Sagdeev potential approach by using the two-potential theory. Numerical results show that the solitary structures can be obtained only for sub-Alfvenic regimes in the scenario of space plasmas.
Generation of Alfvenic Waves and Turbulence in Magnetic Reconnection Jets
Hoshino, M.
2014-12-01
The magneto-hydro-dynamic (MHD) linear stability for the plasma sheet with a localized bulk plasma flow parallel to the neutral sheet is investigated. We find three different unstable modes propagating parallel to the anti-parallel magnetic field line, and we call them as "streaming tearing'', "streaming sausage'', and "streaming kink'' mode. The streaming tearing and sausage modes have the tearing mode-like structure with symmetric density fluctuation to the neutral sheet, and the streaming kink mode has the asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing the magnetic Reynolds number, while those of the streaming sausage and kink modes do not strongly depend on the Reynolds number. The wavelengths of these unstable modes are of the order of the thickness of plasma sheet, which behavior is almost same as the standard tearing mode with no bulk flow. Roughly speaking the growth rates of three modes become faster than the standard tearing mode. The situation of the plasma sheet with the bulk flow can be realized in the reconnection exhaust with the Alfvenic reconnection jet, and the unstable modes may be regarded as one of the generation processes of Alfvenic turbulence in the plasma sheet during magnetic reconnection.
Maruta, Kazuki; Iwakuni, Tatsuhiko; Ohta, Atsushi; Arai, Takuto; Shirato, Yushi; Kurosaki, Satoshi; Iizuka, Masataka
2016-07-08
Drastic improvements in transmission rate and system capacity are required towards 5th generation mobile communications (5G). One promising approach, utilizing the millimeter wave band for its rich spectrum resources, suffers area coverage shortfalls due to its large propagation loss. Fortunately, massive multiple-input multiple-output (MIMO) can offset this shortfall as well as offer high order spatial multiplexing gain. Multiuser MIMO is also effective in further enhancing system capacity by multiplexing spatially de-correlated users. However, the transmission performance of multiuser MIMO is strongly degraded by channel time variation, which causes inter-user interference since null steering must be performed at the transmitter. This paper first addresses the effectiveness of multiuser massive MIMO transmission that exploits the first eigenmode for each user. In Line-of-Sight (LoS) dominant channel environments, the first eigenmode is chiefly formed by the LoS component, which is highly correlated with user movement. Therefore, the first eigenmode provided by a large antenna array can improve the robustness against the channel time variation. In addition, we propose a simplified beamforming scheme based on high efficient channel state information (CSI) estimation that extracts the LoS component. We also show that this approximate beamforming can achieve throughput performance comparable to that of the rigorous first eigenmode transmission. Our proposed multiuser massive MIMO scheme can open the door for practical millimeter wave communication with enhanced system capacity.
Detection of a flow induced magnetic field eigenmode in the Riga dynamo facility
Gailitis, A; Dementev, S; Platacis, E; Cifersons, A; Gerbeth, G; Gundrum, T; Stefani, F; Christen, M; Hänel, H; Will, G; Gailitis, Agris; Lielausis, Olgerts; Dement'ev, Sergej; Platacis, Ernests; Cifersons, Arnis; Gerbeth, Gunter; Gundrum, Thomas; Stefani, Frank; Christen, Michael; Hänel, Heiko; Will, Gotthard
2000-01-01
In an experiment at the Riga sodium dynamo facility, a slowly growing magnetic field eigenmode has been detected over a period of about 15 seconds. For a slightly decreased propeller rotation rate, additional measurements showed a slow decay of this mode. The measured results correspond satisfactory with numerical predictions for the growth rates and frequencies.
Tikan, A. M.; Vatnik, I. D.; Churkin, D. V.; Sukhorukov, A. A.
2017-02-01
A method based on optical heterodyning is proposed for measuring relative optical phases of pulses circulating in synthetic photonic lattices (SPL). The knowledge of the phases can be further used for qualitative reconstruction of an eigenmode excitation spectrum in the SPL.
Kazuki Maruta
2016-07-01
Full Text Available Drastic improvements in transmission rate and system capacity are required towards 5th generation mobile communications (5G. One promising approach, utilizing the millimeter wave band for its rich spectrum resources, suffers area coverage shortfalls due to its large propagation loss. Fortunately, massive multiple-input multiple-output (MIMO can offset this shortfall as well as offer high order spatial multiplexing gain. Multiuser MIMO is also effective in further enhancing system capacity by multiplexing spatially de-correlated users. However, the transmission performance of multiuser MIMO is strongly degraded by channel time variation, which causes inter-user interference since null steering must be performed at the transmitter. This paper first addresses the effectiveness of multiuser massive MIMO transmission that exploits the first eigenmode for each user. In Line-of-Sight (LoS dominant channel environments, the first eigenmode is chiefly formed by the LoS component, which is highly correlated with user movement. Therefore, the first eigenmode provided by a large antenna array can improve the robustness against the channel time variation. In addition, we propose a simplified beamforming scheme based on high efficient channel state information (CSI estimation that extracts the LoS component. We also show that this approximate beamforming can achieve throughput performance comparable to that of the rigorous first eigenmode transmission. Our proposed multiuser massive MIMO scheme can open the door for practical millimeter wave communication with enhanced system capacity.
Nonlinear Alfv\\'en wave dynamics at a 2D magnetic null point: ponderomotive force
Thurgood, J O
2013-01-01
Context : In the linear, {\\beta}=0 MHD regime, the transient properties of MHD waves in the vicinity of 2D null points are well known. The waves are decoupled and accumulate at predictable parts of the magnetic topology: fast waves accumulate at the null point; whereas Alfv\\'en waves cannot cross the separatricies. However, in nonlinear MHD mode conversion can occur at regions of inhomogeneous Alfv\\'en speed, suggesting that the decoupled nature of waves may not extend to the nonlinear regime. Aims: We investigate the behaviour of low-amplitude Alfv\\'en waves about a 2D magnetic null point in nonlinear, {\\beta}= 0 MHD. Methods: We numerically simulate the introduction of low-amplitude Alfv\\'en waves into the vicinity of a magnetic null point using the nonlinear LARE2D code. Results: Unlike in the linear regime, we find that the Alfv\\'en wave sustains cospatial daughter disturbances, manifest in the transverse and longitudinal fluid velocity, owing to the action of nonlinear magnetic pressure gradients (viz. t...
Disperson relation of finite amplitude Alfven wave in a relativistic electron- positron plasma
Hada, T; Muñoz, V; Hada, Tohru; Matsukiyo, Shuichi; Munoz, Victor
2004-01-01
The linear dispersion relation of a finite amplitude, parallel, circularly polarized Alfv\\'en wave in a relativistic electron-positron plasma is derived. In the nonrelativistic regime, the dispersion relation has two branches, one electromagnetic wave, with a low frequency cutoff at $\\sqrt{1+2\\omega_p^2/\\Omega_p^2}$ (where $\\omega_p=(4\\pi n e^2/m)^{1/2}$ is the electron/positron plasma frequency), and an Alfv\\'en wave, with high frequency cutoff at the positron gyrofrequency $\\Omega_p$. There is only one forward propagating mode for a given frequency. However, due to relativistic effects, there is no low frequency cutoff for the electromagnetic branch, and there appears a critical wave number above which the Alfv\\'en wave ceases to exist. This critical wave number is given by $ck_c/\\Omega_p=a/\\eta$, where $a=\\omega_p^2/\\Omega_p^2$ and $\\eta$ is the ratio between the Alfv\\'en wave magnetic field amplitude and the background magnetic field. In this case, for each frequency in the Alfv\\'en branch, two additional...
Zaqarashvili, T V; Soler, R
2012-01-01
Ion-neutral collisions may lead to the damping of Alfven waves in chromospheric and prominence plasmas. Neutral helium atoms enhance the damping in certain temperature interval, where the ratio of neutral helium and neutral hydrogen atoms is increased. Therefore, the height-dependence of ionization degrees of hydrogen and helium may influence the damping rate of Alfven waves. We aim to study the effect of neutral helium in the damping of Alfven waves in stratified partially ionized plasma of the solar chromosphere. We consider a magnetic flux tube, which is expanded up to 1000 km height and then becomes vertical due to merging with neighboring tubes, and study the dynamics of linear torsional Alfven waves in the presence of neutral hydrogen and neutral helium atoms. We start with three-fluid description of plasma and consequently derive single-fluid magnetohydrodynamic (MHD) equations for torsional Alfven waves. Thin flux tube approximation allows to obtain the dispersion relation of the waves in the lower pa...
Pulse-driven nonlinear Alfv\\'en waves and their role in the spectral line broadening
Chmielewski, P; Murawski, K; Musielak, Z E
2012-01-01
We study the impulsively generated non-linear Alfv\\'en waves in the solar atmosphere, and describe their most likely role in the observed non-thermal broadening of some spectral lines in solar coronal holes. We solve numerically the time-dependent magnetohydrodynamic equations to find temporal signatures of large-amplitude Alfv\\'en waves in the model atmosphere of open and expanding magnetic field configuration, with a realistic temperature distribution. We calculate the temporally and spatially averaged, instantaneous transversal velocity of non-linear Alfv\\'en waves at different heights of the model atmosphere, and estimate its contribution to the unresolved non-thermal motions caused by the waves. We find that the pulse-driven nonlinear Alfv\\'en waves with the amplitude $A_{\\rm v}$=50 km s$^{-1}$ are the most likely candidates for the non-thermal broadening of Si VIII $\\lambda$1445.75 \\AA\\ line profiles in the polar coronal hole as reported by Banerjee et al. (1998). We also demonstrate that the Alfv\\'en w...
Impulsively Generated Linear and Non-linear Alfven Waves in the Coronal Funnels
Chmielewski, P; Murawski, K; Musielak, Z E
2014-01-01
We present simulation results of the impulsively generated linear and non-linear Alfven waves in the weakly curved coronal magnetic flux-tubes (coronal funnels) and discuss their implications for the coronal heating and solar wind acceleration. We solve numerically the time-dependent magnetohydrodynamic equations to find the temporal signatures of the small and large-amplitude Alfven waves in the model atmosphere of open and expanding magnetic field configuration with a realistic temperature distribution. We compute the maximum transversal velocity of both linear and non-linear Alfven waves at different heights of the model atmosphere, and study their response in the solar corona during the time of their propagation. We infer that the pulse-driven non-linear Alfven waves may carry sufficient wave energy fluxes to heat the coronal funnels and also to power the solar wind that originates in these funnels. Our study of linear Alfven waves show that they can contribute only to the plasma dynamics and heating of t...
Numerical simulations of impulsively generated Alfv\\'en waves in solar magnetic arcades
Chmielewski, P; Musielak, Z E; Srivastava, A K
2014-01-01
We perform numerical simulations of impulsively generated Alfv\\'en waves in an isolated solar arcade, which is gravitationally stratified and magnetically confined. We study numerically the propagation of Alfv\\'en waves along such magnetic structure that extends from the lower chromosphere, where the waves are generated, to the solar corona, and analyze influence of the arcade size and width of the initial pulses on the wave propagation and reflection. Our model of the solar atmosphere is constructed by adopting the temperature distribution based on the semi-empirical VAL-C model and specifying the curved magnetic field lines that constitute the asymmetric magnetic arcade. The propagation and reflection of Alfv\\'en waves in this arcade is described by 2.5D magnetohydrodynamic equations that are numerically solved by the FLASH code. Our numerical simulations reveal that the Alfv\\'en wave amplitude decreases as a result of a partial reflection of Alfv\\'en waves in the solar transition region, and that the waves...
Medina-Tanco, G. A.; Opher, R.
1990-11-01
RESUMEN. Se presentan resultados numericos para un modelo hidrodinamico de cuatro componentes (plasma de fondo, particulas energeticas, ondas de Alfven autogeneradas y campo magnetico) para choques oblicuos. ABSTRACT. Numerical results of a four component hydrodynamic model (background plasma, energetic particles, self-generated Alfven waves and magnetic field) for oblique shocks are presented. Keq wo't : COSMIC RAY-GENERAL - PLASMAS - SHOCK WAVES
Small amplitude Kinetic Alfven waves in a superthermal electron-positron-ion plasma
Adnan, Muhammad; Mahmood, Sahahzad; Qamar, Anisa; Tribeche, Mouloud
2016-11-01
We are investigating the propagating properties of coupled Kinetic Alfven-acoustic waves in a low beta plasma having superthermal electrons and positrons. Using the standard reductive perturbation method, a nonlinear Korteweg-de Vries (KdV) type equation is derived which describes the evolution of Kinetic Alfven waves. It is found that nonlinearity and Larmor radius effects can compromise and give rise to solitary structures. The parametric role of superthermality and positron content on the characteristics of solitary wave structures is also investigated. It is found that only sub-Alfvenic and compressive solitons are supported in the present model. The present study may find applications in a low β electron-positron-ion plasma having superthermal electrons and positrons.
Alfv\\'enic Wave Heating of the Upper Chromosphere in Flares
Reep, Jeffrey W
2016-01-01
We have developed a numerical model of flare heating due to the dissipation of Alfv\\'enic waves propagating from the corona to the chromosphere. With this model, we present an investigation of the key parameters of these waves on the energy transport, heating, and subsequent dynamics. For sufficiently high frequencies and perpendicular wave numbers, the waves dissipate significantly in the upper chromosphere, strongly heating it to flare temperatures. This heating can then drive strong chromospheric evaporation, bringing hot and dense plasma to the corona. We therefore find three important conclusions: (1) Alfv\\'enic waves, propagating from the corona to the chromosphere, are capable of heating the upper chromosphere and the corona, (2) the atmospheric response to heating due to the dissipation of Alfv\\'enic waves can be strikingly similar to heating by an electron beam, and (3) this heating can produce explosive evaporation.
Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited
Burkhart, Blakesley; Leao, I C; de Medeiros, J R; Esquivel, A
2014-01-01
The dynamics of the interstellar medium (ISM) are strongly affected by turbulence, which shows increased anisotropy in the presence of a magnetic field. We expand upon the Esquivel & Lazarian method to estimate the Alfven Mach number using the structure function anisotropy in velocity centroid data from position-position-velocity maps. We utilize 3D magnetohydrodynamic (MHD) simulations of fully developed turbulence, with a large range of sonic and Alfvenic Mach numbers, to produce synthetic observations of velocity centroids with observational characteristics such as thermal broadening, cloud boundaries, noise, and radiative transfer effects of carbon monoxide. In addition, we investigate how the resulting anisotropy-Alfven Mach number dependency found in Esquivel & Lazarian (2011) might change when taking the second moment of the position-position-velocity cube or when using different expressions to calculate the velocity centroids. We find that the degree of anisotropy is related primarily to the m...
Observation of an Alfv\\'en Wave Parametric Instability in a Laboratory Plasma
Dorfman, S
2016-01-01
A shear Alfv\\'en wave parametric instability is observed for the first time in the laboratory. When a single finite $\\omega/\\Omega_i$ kinetic Alfv\\'en wave (KAW) is launched in the Large Plasma Device above a threshold amplitude, three daughter modes are produced. These daughter modes have frequencies and parallel wave numbers that are consistent with copropagating KAW sidebands and a low frequency nonresonant mode. The observed process is parametric in nature, with the frequency of the daughter modes varying as a function of pump wave amplitude. The daughter modes are spatially localized on a gradient of the pump wave magnetic field amplitude in the plane perpendicular to the background field, suggesting that perpendicular nonlinear forces (and therefore $k_{\\perp}$ of the pump wave) play an important role in the instability process. Despite this, modulational instability theory with $k_{\\perp}=0$ has several features in common with the observed nonresonant mode and Alfv\\'en wave sidebands.
Exploring the Use of Alfven Waves in Magnetometer Calibration at Geosynchronous Orbit
Bentley, John; Sheppard, David; RIch, Frederick; Redmon, Robert; Loto'aniu, Paul; Chu, Donald
2016-01-01
An Alfven wave is a type magnetohydrodynamicwave that travels through a conducting fluid under the influence of a magnetic field. Researchers have successfully calculated offset vectors of magnetometers in interplanetary space by optimizing the offset to maximize certain Alfvenic properties of observed waves (Leinweber, Belcher). If suitable Alfven waves can be found in the magnetosphere at geosynchronous altitude then these techniques could be used to augment the overall calibration plan for magnetometers in this region such as on the GOES spacecraft, possibly increasing the time between regular maneuvers. Calibration maneuvers may be undesirable because they disrupt the activities of other instruments. Various algorithms to calculate an offset using Alfven waves were considered. A new variation of the Davis-Smith method was derived because it can be mathematically shown that the Davis-Smith method tolerates filtered data, which expands potential applications. The variant developed was designed to find only the offset in the plane normal to the main field because the overall direction of Earth's magnetic field rarely changes, and theory suggests the Alfvenic disturbances occur transverse to the main field. Other variations of the Davis-Smith method encounter problems with data containing waves that propagate in mostly the same direction. A searching algorithm was then designed to look for periods of time with potential Alfven waves in GOES 15 data based on parameters requiring that disturbances be normal to the main field and not change field magnitude. Final waves for calculation were hand-selected. These waves produced credible two-dimensional offset vectors when input to the Davis-Smith method. Multiple two-dimensional solutions in different planes can be combined to get a measurement of the complete offset. The resulting three dimensional offset did not show sufficient precision over several years to be used as a primary calibration method, but reflected
Effects of electron drift on the collisionless damping of kinetic Alfv\\'en waves in the solar wind
Tong, Yuguang; Chen, Christopher H K; Salem, Chadi S; Verscharen, Daniel
2015-01-01
The collisionless dissipation of anisotropic Alfv\\'enic turbulence is a promising candidate to solve the solar wind heating problem. Extensive studies examined the kinetic properties of Alfv\\'en waves in simple Maxwellian or bi-Maxwellian plasmas. However, the observed electron velocity distribution functions in the solar wind are more complex. In this study, we analyze the properties of kinetic Alfv\\'en waves in a plasma with two drifting electron populations. We numerically solve the linearized Maxwell-Vlasov equations and find that the damping rate and the proton-electron energy partition for kinetic Alfv\\'en waves are significantly modified in such plasmas, compared to plasmas without electron drifts. We suggest that electron drift is an important factor to take into account when considering the dissipation of Alfv\\'enic turbulence in the solar wind or other $\\beta \\sim 1$ astrophysical plasmas.
Nariyuki, Y; Nariyuki, Yasuhiro; Hada, Tohru
2006-01-01
Nonlinear relations among frequencies and phases in modulational instability of circularly polarized Alfven waves are discussed, within the context of one dimensional, dissipation-less, unforced fluid system. We show that generation of phase coherence is a natural consequence of the modulational instability of Alfven waves. Furthermore, we quantitatively evaluate intensity of wave-wave interaction by using bi-coherence, and also by computing energy flow among wave modes, and demonstrate that the energy flow is directly related to the phase coherence generation.
Quantum Treatment of Kinetic Alfv\\'en Waves instability in a dusty plasma: Magnetized ions
Rubab, N
2016-01-01
The dispersion relation of kinetic Alfv\\'en wave in inertial regime is studied in a three component non-degenerate streaming plasma. A lin- ear dispersion relation using fluid- Vlasov equation for quantum plasma is also derived. The quantum correction CQ raised due to the insertion of Bohm potential in Vlasov model causes the suppression in the Alfven wave frequency and the growth rates of instability. A number of analytical expressions are derived for various modes of propagation. It is also found that many system parameters, i.e, streaming velocity, dust charge, num- ber density and quantum correction significantly influence the dispersion relation and the growth rate of instability.
Fast-Particle-Driven Alfvenic Modes in a Reversed Field Pinch
Koliner, J. J. [University of Wisconsin, Madison; Forest, C. B. [University of Wisconsin, Madison; Sarff, J. S. [University of Wisconsin, Madison; Anderson, J. [University of Wisconsin, Madison; Liu, D [University of Wisconsin, Madison; Nomberg, M. D. [University of Wisconsin, Madison; Waksman, J. [University of Wisconsin, Madison; Lin, L. [University of California, Los Angeles; Brower, D. L. [University of California, Los Angeles; Ding, W. X. [University of California, Los Angeles; Spong, Donald A [ORNL
2012-01-01
Alfvenic modes are observed due to neutral beam injection for the first time in a reversed field pinch plasma. Modeling of the beam deposition and slowing down shows that the velocity and radial localization are high. This allows instability drive from inverse Landau damping of a bump-on-tail in the parallel distribution function or from free energy in the fast ion density gradient. Mode switching from a lower frequency toroidal mode number n = 5 mode that scales with beam injection velocity to a higher frequency n = 4 mode with Alfvenic scaling is observed.
A self-consistent theory of collective alpha particle losses induced by Alfvenic turbulence
Biglari, H. (Princeton Univ., NJ (United States). Plasma Physics Lab.); Diamond, P.H. (California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics)
1992-01-01
The nonlinear dynamics of kinetic Alfven waves, resonantly excited by energetic ions/alpha particles, is investigated. It is shown that {alpha}-particles govern both linear instability and nonlinear saturation dynamics, while the background MHD turbulence results only in a nonlinear real frequency shift. The most efficient saturation mechanism is found to be self-induced profile modification. Expressions for the fluctuation amplitudes and the {alpha}-particle radial flux are self-consistently derived. The work represents the first self-consistent, turbulent treatment of collective {alpha}-particle losses by Alfvenic fluctuations.
Fierros Palacios, Angel [Instituto de Investigaciones Electricas, Temixco, Morelos (Mexico)
2001-02-01
In this work the complete set of differential field equations which describes the dynamic state of a continuos conducting media which flow in presence of a perturbed magnetic field is obtained. Then, the thermic equation of state, the wave equation and the conservation law of energy for the Alfven MHD waves are obtained. [Spanish] Es este trabajo se obtiene el conjunto completo de ecuaciones diferenciales de campo que describen el estado dinamico de un medio continuo conductor que se mueve en presencia de un campo magnetico externo perturbado. Asi, se obtiene la ecuacion termica de estado, la ecuacion de onda y la ley de la conservacion de la energia para las ondas de Alfven de la MHD.
Plum, Maja
Globalization is often referred to as external to education - a state of affair facing the modern curriculum with numerous challenges. In this paper it is examined as internal to curriculum; analysed as a problematization in a Foucaultian sense. That is, as a complex of attentions, worries, ways...... of reasoning, producing curricular variables. The analysis is made through an example of early childhood curriculum in Danish Pre-school, and the way the curricular variable of the pre-school child comes into being through globalization as a problematization, carried forth by the comparative practices of PISA...
Park, Jae Seok [Doosan Heavy Industries and Construction, Changwon (Korea, Republic of); Jang, Chang Heui [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Lee, Jong Po [ANSCO Corp., Daejeon (Korea, Republic of)
2010-06-15
Based on the idea of eigen-mode expansion, a method to analyze the reflection of Lamb wave from a finite vertical discontinuity of plate is theoretically derived and verified by experiment. The theoretical prediction is in good agreement with the experimental result, and this strongly suggests that eigen-mode expansion method could be used for solution of inverse scattering problem for ultrasonic testing using Lamb wave
Remnant index theorem and low-lying eigenmodes for twisted mass fermions
Gattringer, C; Gattringer, Christof; Solbrig, Stefan
2005-01-01
We analyze the low-lying spectrum and eigenmodes of lattice Dirac operators with a twisted mass term. The twist term expels the eigenvalues from a strip in the complex plane and all eigenmodes obtain a non-vanishing matrix element with gamma-5. For a twisted Ginsparg-Wilson operator the spectrum is located on two arcs in the complex plane. Modes due to non-trivial topological charge of the underlying gauge field have their eigenvalues at the edges of these arcs and obey a remnant index theorem. For configurations in the confined phase we find that the twist mainly affects the zero modes, while the bulk of the spectrum is essentially unchanged.
Cavity-enhanced eigenmode and angular hybrid multiplexing in holographic data storage systems.
Miller, Bo E; Takashima, Yuzuru
2016-12-26
Resonant optical cavities have been demonstrated to improve energy efficiencies in Holographic Data Storage Systems (HDSS). The orthogonal reference beams supported as cavity eigenmodes can provide another multiplexing degree of freedom to push storage densities toward the limit of 3D optical data storage. While keeping the increased energy efficiency of a cavity enhanced reference arm, image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe:LiNbO3 medium with a 532 nm laser at two Bragg angles. We experimentally confirmed write rates are enhanced by an average factor of 1.1, and page crosstalk is about 2.5%. This hybrid multiplexing opens up a pathway to increase storage density while minimizing modification of current angular multiplexing HDSS.
Miriţoiu, C. M.; Stănescu, M. M.; Burada, C. O.; Bolcu, D.; Roşca, V.
2015-11-01
For modal identification, the single-point excitation method has been widely used in modal tests and it consists in applying a force in a given point and recording the vibratory structure response in all interest points, including the excitation point. There will be presented the experimental recordings for the studied bars (with Kevlar-carbon or carbon fibers), the frequency response function in Cartesian and polar coordinates. By using the frequency response functions we determine the eigenparameters for each bar. We present the final panel of the eigenmodes (with the damping factors, eigenfrequencies and critical damping) for each considered bar. Using the eigenfrequency of the first determined eigenmode, the bars stiffness has been determined. The presented bars can be used in practical engineering for: car or bus body parts, planes body parts, bullet-proof vests, reinforcements for sandwich beams, and so on.
General Framework and Advanced Information Theoretical Results on Eigenmode MIMO Channel Inversion
J. Sykora
2005-09-01
Full Text Available This paper provides general and deep investigation of adaptationstrategies based on the channel inversion policy regarding wide varietyof channel modes. Our novel approach to the eigenmode space MIMOchannel inversion policy relies on the eigenmode space reductionproviding zero transmission outage probability regardless of theinstantaneous channel fading realization. Very detailed survey of thefeatures of channel capacity is provided in analytical closed formexpressions supported by many particular numerical results (Alamoutischeme is included. The correlated MIMO channel is involved into ourtreatment as well. We also address the trade-off between the capacityand transmission outage probability. The novel results are developed inthe general framework with exhaustive summary of well known SISO andSIMO results.
Goos-Hänchen induced vector eigenmodes in a dome cavity.
Foster, David H; Cook, Andrew K; Nöckel, Jens U
2007-06-15
We demonstrate numerically calculated electromagnetic eigenmodes of a 3D dome cavity resonator that owe their shape and character entirely to the Goos-Hänchen effect. The V-shaped modes, which have purely TE or TM polarization, are well described by a 2D billiard map with the Goos-Hänchen shift included. A phase space plot of this augmented billiard map reveals a saddle-node bifurcation; the stable periodic orbit that is created in the bifurcation corresponds to the numerically calculated eigenmode, dictating the angle of its 'V.' A transition from a fundamental Gaussian to a TM V mode has been observed as the cavity is lengthened to become nearly hemispherical.
Frequency splitting of polarization eigenmodes in microscopic Fabry-Perot cavities
Uphoff, Manuel; Rempe, Gerhard; Ritter, Stephan
2014-01-01
We study the frequency splitting of the polarization eigenmodes of the fundamental transverse mode in CO2 laser-machined, high-finesse optical Fabry-Perot cavities and investigate the influence of the geometry of the cavity mirrors. Their highly reflective surfaces are typically not rotationally symmetric, but have slightly different radii of curvature along two principal axes. We observe that the eccentricity of such elliptical mirrors lifts the degeneracy of the polarization eigenmodes. The impact of the eccentricity increases for smaller radii of curvature. A model derived from corrections to the paraxial resonator theory is in excellent agreement with measurements, showing that geometric effects are the main source of the frequency splitting of polarization modes for the studied type of microscopic cavity. By rotation of one of the mirrors around the cavity axis, the splitting can be tuned. In the case of an identical differential phase shift per mirror it can even be eliminated, despite a nonvanishing ec...
Observations of toroidicity-induced Alfvén eigenmodes in a reversed field pinch plasma
Regnoli, G.; Bergsâker, H.; Tennfors, E.; Zonca, F.; Martines, E.; Serianni, G.; Spolaore, M.; Vianello, N.; Cecconello, M.; Antoni, V.; Cavazzana, R.; Malmberg, J.-A.
2005-04-01
High frequency peaks in the spectra of magnetic field signals have been detected at the edge of Extrap-T2R [P. R. Brunsell, H. Bergsåker, M. Cecconello, J. R. Drake, R. M. Gravestijn, A. Hedqvist, and J.-A. Malmberg, Plasma Phys. Controlled Fusion, 43, 1457 (2001)]. The measured fluctuation is found to be mainly polarized along the toroidal direction, with high toroidal periodicity n and Alfvénic scaling (f∝B/√mini ). Calculations for a reversed field pinch plasma predict the existence of an edge resonant, high frequency, high-n number toroidicity-induced Alfvén eigenmode with the observed frequency scaling. In addition, gas puffing experiments show that edge density fluctuations are responsible for the rapid changes of mode frequency. Finally a coupling with the electron drift turbulence is proposed as drive mechanism for the eigenmode.
Duan, Wenbo; Kirby, Ray; Mudge, Peter; Gan, Tat-Hean
2016-12-01
Ultrasonic guided waves are often used in the detection of defects in oil and gas pipelines. It is common for these pipelines to be buried underground and this may restrict the length of the pipe that can be successfully tested. This is because acoustic energy travelling along the pipe walls may radiate out into the surrounding medium. Accordingly, it is important to develop a better understanding of the way in which elastic waves propagate along the walls of buried pipes, and so in this article a numerical model is developed that is suitable for computing the eigenmodes for uncoated and coated buried pipes. This is achieved by combining a one dimensional eigensolution based on the semi-analytic finite element (SAFE) method, with a perfectly matched layer (PML) for the infinite medium surrounding the pipe. This article also explores an alternative exponential complex coordinate stretching function for the PML in order to improve solution convergence. It is shown for buried pipelines that accurate solutions may be obtained over the entire frequency range typically used in long range ultrasonic testing (LRUT) using a PML layer with a thickness equal to the pipe wall thickness. This delivers a fast and computationally efficient method and it is shown for pipes buried in sand or soil that relevant eigenmodes can be computed and sorted in less than one second using relatively modest computer hardware. The method is also used to find eigenmodes for a buried pipe coated with the viscoelastic material bitumen. It was recently observed in the literature that a viscoelastic coating may effectively isolate particular eigenmodes so that energy does not radiate from these modes into the surrounding [elastic] medium. A similar effect is also observed in this article and it is shown that this occurs even for a relatively thin layer of bitumen, and when the shear impedance of the coating material is larger than that of the surrounding medium.
Zhang, Pei [Manchester Univ. (United Kingdom). School of Physics and Astronomy; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Baboi, Nicoleta [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Jones, Roger M. [Manchester Univ. (United Kingdom). School of Physics and Astronomy; The Cockcroft Institute, Daresbury, Warrington (United Kingdom)
2012-06-15
The third harmonic nine-cell cavity (3.9 GHz) for FLASH and the European XFEL has been investigated using simulations performed with the computer code CST Microwave Studio registered. The band structure of monopole, dipole, quadrupole and sextupole modes for an ideal cavity has been studied. The higher order modes for the nine-cell structure are compared with that of the cavity mid-cell. The R/Q of these eigenmodes are calculated.
FAN Hong-Yi; FAN Yue
2003-01-01
By introducing a convenient complex form of the α-th 2-dimensional fractional Fourier transform (CFFT) operation we find that it possesses new eigenmodes which are two-mode Hermite polynomials. We prove the eigenvalues of propagation in quadratic graded-index medium over a definite distance are the same as the eigenvalues of the α-th CFFT, which means that our definition of the α-th CFFT is physically meaningful.
Miccio, Luis A; Kummali, Mohammed M; Schwartz, Gustavo A; Alegría, Ángel; Colmenero, Juan
2014-11-01
In the last years, a new AFM based dielectric spectroscopy approach has been developed for measuring the dielectric relaxation of materials at the nanoscale, the so called nanoDielectric Spectroscopy (nDS). In spite of the effort done so far, some experimental aspects of this technique remain still unclear. In particular, one of these aspects is the possibility of extending the experimental frequency range, to date limited at high frequencies by the resonance frequency of the AFM cantilever as a main factor. In order to overcome this limitation, the electrical excitation of cantilever higher eigenmodes for measuring the dielectric relaxation is here explored. Thus, in this work we present a detailed experimental analysis of the electrical excitation of the cantilever second eigenmode. Based on this analysis we show that the experimental frequency range of the AFM based dielectric spectroscopy can be extended by nearly two decades with a good signal-to-noise ratio. By using the combination of first and second cantilever eigenmodes we study dissipation processes on well known PVAc based polymeric samples. Both, relaxation spectra and images with molecular dynamics contrast were thus obtained over this broader frequency range.
The upgraded JET toroidal Alfvén eigenmode diagnostic system
Puglia, P.; Pires de Sa, W.; Blanchard, P.; Dorling, S.; Dowson, S.; Fasoli, A.; Figueiredo, J.; Galvão, R.; Graham, M.; Jones, G.; Perez von Thun, C.; Porkolab, M.; Ruchko, L.; Testa, D.; Woskov, P.; Albarracin-Manrique, M. A.; Contributors, JET
2016-11-01
The main characteristics of toroidal Alfvén eigenmodes (TAEs) have been successfully investigated in JET (Joint European Torus) using the scheme of sweeping-frequency external excitation with tracking of the synchronously-detected resonances. However, due to technical limitations, only modes with low values of the toroidal mode number n≤slant 7 could be effectively excited and unambiguously identified by the Alfvén Eigenmode Active Diagnostic (AEAD) system. This represents a serious restriction because theoretical models indicate that medium-n Alfvén eigenmodes (AEs) are the most prone to be destabilized by energetic particles in ignited plasmas and, therefore, reliable measurement of their damping rates remains a relevant issue to properly access their effect in ignited plasmas. For this reason, a major upgrade of the AEAD system has been carried out aiming at providing a state-of-the-art excitation and real-time detection system for the planned DT campaign in JET. This required the development of a new type of radio frequency amplifier and filter, not commercially available, and also a control system. In this paper, details of the concepts that are relevant to understand the operation of the new system in the next experimental campaigns are presented, as are the results of numerical simulations to model its performance.
Electromagnetic transport components and sheared flows in drift-Alfven turbulence
Naulin, V.
2003-01-01
Results from three-dimensional numerical simulations of drift-Alfven turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma beta we...
Heating and Acceleration of the Fast Solar Wind by Alfv\\'{e}n Wave Turbulence
van Ballegooijen, A A
2016-01-01
We present numerical simulations of reduced magnetohydrodynamic (RMHD) turbulence in a magnetic flux tube at the center of a polar coronal hole. The model for the background atmosphere is a solution of the momentum equation, and includes the effects of wave pressure on the solar wind outflow. Alfv\\'{e}n waves are launched at the coronal base, and reflect at various heights due to variations in Alfv\\'{e}n speed and outflow velocity. The turbulence is driven by nonlinear interactions between the counter-propagating Alfv\\'{e}n waves. Results are presented for two models of the background atmosphere. In the first model the plasma density and Alfv\\'{e}n speed vary smoothly with height, resulting in minimal wave reflections and low energy dissipation rates. We find that the dissipation rate is insufficient to maintain the temperature of the background atmosphere. The standard phenomenological formula for the dissipation rate significantly overestimates the rate derived from our RMHD simulations, and a revised formu...
Alfv\\'en Wave Driven High Frequency Waves in the Solar Atmosphere: Implications for Ion Heating
Kaghashvili, Edisher Kh
2014-01-01
This work is an extension of Kaghashvili [1999] where ion-cyclotron wave dissipation channel for Alfv\\'en waves was discussed. While our earlier study dealt with the mode coupling in the commonly discussed sense, here we study changes in the initial waveform due to interaction of the initial driver Alfv\\'en wave and the plasma inhomogeneity, which are implicitly present in the equations, but were not elaborated in Kaghashvili [1999]. Using a cold plasma approximation, we show how high frequency waves (higher than the initial driver Alfv\\'en wave frequency) are generated in the inhomogeneous solar plasma flow. The generation of the high frequency forward and backward propagating modified fast magnetosonic/whistler waves as well as the generation of the driven Alfv\\'en waves is discussed in the solar atmosphere. The generated high frequency waves have a shorter dissipation timescale, and they can also resonant interact with particles using both the normal cyclotron and anomalous cyclotron interaction channels. ...
Current-vortex filament model of nonlinear Alfven perturbations in a finite-pressure plasma
Lakhin, V. P.; Schep, T. J.; Westerhof, E.
1998-01-01
A low-beta, two-fluid model is shown to possess solutions in the form of current-vortex filaments. The model can be viewed as that of reduced magnetohydrodynamics, extended with electron inertia, the Hall term and parallel electron pressure. These drift-Alfven filaments are the plasma analogs of poi
Experimental evidence of Alfv\\'en wave propagation in a Gallium alloy
Alboussiere, Thierry; Debray, François; La Rizza, Patrick; Masson, Jean-Paul; Plunian, Franck; Ribeiro, Adolfo; Schmitt, Denys
2011-01-01
Experiments with a liquid metal alloy, galinstan, are reported and show clear evidence of Alfv\\'en wave propagation as well as resonance of Alfv\\'en modes. Galinstan is liquid at room temperature, and although its electrical conductivity is not as large as that of liquid sodium or NaK, it has still been possible to study Alfv\\'en waves, thanks to the use of intense magnetic fi elds, up to 13 teslas. The maximal values of Lundquist number, around 60, are similar to that of the reference experimental study by Jameson [1]. The generation mechanism for Alfv\\'en waves and their refl ection is studied carefully. Numerical simulations have been performed and have been able to reproduce the experimental results despite the fact that the simulated magnetic Prandtl number was much larger than that of galinstan. An originality of the present study is that a poloidal disturbance (magnetic and velocity fields) is generated, allowing us to track its propagation from outside the conducting domain, hence without interfering.
Cut-off wavenumber of Alfven waves in partially ionized plasmas of the solar atmosphere
Zaqarashvili, T V; Ballester, J L; Khodachenko, M L
2012-01-01
Alfven wave dynamics in partially ionized plasmas of the solar atmosphere shows that there is indeed a cut-off wavenumber, i.e. the Alfven waves with wavenumbers higher than the cut-off value are evanescent. The cut-off wavenumber appears in single-fluid magnetohydrodynamic (MHD) approximation but it is absent in a multi-fluid approach. Up to now, an explanation for the existence of the cut-off wavenumber is still missing. The aim of this paper is to point out the reason for the appearance of a cut-off wavenumber in single-fluid MHD. Beginning with three-fluid equations (with electrons, protons and neutral hydrogen atoms), we performed consecutive approximations until we obtained the usual single-fluid description is obtained. We solved the dispersion relation of linear Alfven waves at each step and sought the approximation responsible of the cut-off wavenumber appearance. We have found that neglecting inertial terms significantly reduces the real part of the Alfven frequency although it never becomes zero. T...
Overdamped Alfven waves due to ion-neutral collisions in the solar chromosphere
Soler, R; Zaqarashvili, T V
2014-01-01
Alfvenic waves are ubiquitous in the solar atmosphere and their dissipation may play an important role in atmospheric heating. In the partially ionized solar chromosphere, collisions between ions and neutrals are an efficient dissipative mechanism for Alfven waves with frequencies near the ion-neutral collision frequency. The collision frequency is proportional to the ion-neutral collision cross section for momentum transfer. Here, we investigate Alfven wave damping as a function of height in a simplified chromospheric model and compare the results for two sets of collision cross sections, namely those of the classic hard-sphere model and those based on recent quantum-mechanical computations. We find important differences between the results for the two sets of cross sections. There is a critical interval of wavelengths for which impulsively excited Alfven waves are overdamped as a result of the strong ion-neutral dissipation. The critical wavelengths are in the range from 1 km to 50 km for the hard-sphere cr...
Alfven wave coupled with flow-driven fluid instability in interpenetrating plasmas
Vranjes, J
2015-01-01
The Alfven wave is analyzed in case of one quasineutral plasma propagating with some constant speed $v_0$ through another static quasineutral plasma. A dispersion equation is derived describing the Alfven wave coupled with the flow driven mode $\\omega= k v_0$ and solutions are discussed analytically and numerically. The usual solutions for two oppositely propagating Alfv\\'en waves are substantially modified due to the flowing plasma. More profound is modification of the solution propagating in the negative direction with respect to the magnetic field and the plasma flow. For a large enough flow speed (exceeding the Alfven speed in the static plasma), this negative solution may become non-propagating, with frequency equal to zero. In this case it represents a spatial variation of the electromagnetic field. For greater flow speed it becomes a forward mode, and it may merge with the positive one. This merging of the two modes represents the starting point for a flow-driven instability, with two complex-conjugate...
Alfven, Hugo. Die drei Schwedischen Rhapsodien op. 19, 24 und 47 / Andreas Meyer
Meyer, Andreas
1995-01-01
Uuest heliplaadist "Alfven, Hugo. Die drei Schwedischen Rhapsodien op. 19, 24 und 47, En skärgardssägen op. 20, Suite aus Der Berkönig. Königliche Stockholmer Philharmoniker, Neeme Järvi". AD: 1987-1992. BIS?Disco-Center CD 725 (WD: 77'00")
Arbitrary amplitude kinetic Alfven solitary waves in two temperature electron superthermal plasma
Singh, Manpreet; Singh Saini, Nareshpal; Ghai, Yashika
2016-07-01
Through various satellite missions it is observed that superthermal velocity distribution for particles is more appropriate for describing space and astrophysical plasmas. So it is appropriate to use superthermal distribution, which in the limiting case when spectral index κ is very large ( i.e. κ→∞), shifts to Maxwellian distribution. Two temperature electron plasmas have been observed in auroral regions by FAST satellite mission, and also by GEOTAIL and POLAR satellite in the magnetosphere. Kinetic Alfven waves arise when finite Larmor radius effect modifies the dispersion relation or characteristic perpendicular wavelength is comparable to electron inertial length. We have studied the kinetic Alfven waves (KAWs) in a plasma comprising of positively charged ions, superthermal hot electrons and Maxwellian distributed cold electrons. Sagdeev pseudo-potential has been employed to derive an energy balance equation. The critical Mach number has been determined from the expression of Sagdeev pseudo-potential to see the existence of solitary structures. It is observed that sub-Alfvenic compressive solitons and super-Alfvenic rarefactive solitons exist in this plasma model. It is also observed that various parameters such as superthermality of hot electrons, relative concentration of cold and hot electron species, Mach number, plasma beta, ion to cold electron temperature ratio and ion to hot electron temperature ratio have significant effect on the amplitude and width of the KAWs. Findings of this investigation may be useful to understand the dynamics of coherent non-linear structures (i.e. KAWs) in space and astrophysical plasmas.
Benchmarking Fast-to-Alfven Mode Conversion in a Cold MHD Plasma
Cally, Paul S
2011-01-01
Alfv\\'en waves may be generated via mode conversion from fast magneto-acoustic waves near their reflection level in the solar atmosphere, with implications both for coronal oscillations and for active region helio-seismology. In active regions this reflection typically occurs high enough that the Alfv\\'en speed $a$ greatly exceeds the sound speed $c$, well above the $a=c$ level where the fast and slow modes interact. In order to focus on the fundamental characteristics of fast/Alfv\\'en conversion, stripped of unnecessary detail, it is therefore useful to freeze out the slow mode by adopting the gravitationally stratified cold MHD model $c\\to0$. This provides a benchmark for fast-to-Alfv\\'en mode conversion in more complex atmospheres. Assuming a uniform inclined magnetic field and an exponential Alfv\\'en speed profile with density scale height $h$, the Alfv\\'en conversion coefficient depends on three variables only; the dimensionless transverse-to-the-stratification wavenumber $\\kappa=kh$, the magnetic field ...
Prokopov, P. A.; Zakharov, Yu P.; Tishchenko, V. N.; Shaikhislamov, I. F.; Boyarintsev, E. L.; Melekhov, A. V.; Ponomarenko, A. G.; Posukh, V. G.; Terekhin, V. A.
2016-11-01
Generation of Alfven waves propagating along external magnetic field B0 and Collisionless Shock Waves propagating across B0 are studied in experiments with laser- produced plasma and magnetized background plasma. The collisionless interaction of interpenetrating plasma flows takes place through a so-called Magnetic Laminar Mechanism (MLM) or Larmor Coupling. At the edge of diamagnetic cavity LP-ions produce induction electric field Eφ which accelerates BP-ions while LP-ions rotate in opposite direction. The ions movement generates sheared azimuthal magnetic field Bφ which could launches torsional Alfven wave. In previous experiments at KI-1 large scale facility a generation of strong perturbations propagating across B0 with magnetosonic speed has been studied at a moderate value of interaction parameter δ∼0.3. In the present work we report on experiments at conditions of 5∼R2 and large Alfven-Mach number MA∼10 in which strong transverse perturbations traveling at a scale of ∼1 m in background plasma at a density of ∼3*1013 cm-3 is observed. At the same conditions but smaller MA ∼ 2 a generation, the structure and dynamic of Alfven wave with wavelength ∼0.5 m propagating along fields B0∼100÷500 G for a distance of ∼2.5 m is studied.
Inbound waves in the solar corona: a direct indicator of Alfv\\'en Surface location
DeForest, C E; McComas, D J
2014-01-01
The tenuous supersonic solar wind that streams from the top of the corona passes through a natural boundary -- the Alfv\\'en surface -- that marks the causal disconnection of individual packets of plasma and magnetic flux from the Sun itself. The Alfv\\'en surface is the locus where the radial motion of the accelerating solar wind passes the radial Alfv\\'en speed, and therefore any displacement of material cannot carry information back down into the corona. It is thus the natural outer boundary of the solar corona, and the inner boundary of interplanetary space. Using a new and unique motion analysis to separate inbound and outbound motions in synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft, we have identified inbound wave motion in the outer corona beyond 6 solar radii for the first time, and used it to determine that the Alfv\\'en surface is at least 12.5 solar radii from the Sun over the polar coronal holes and 17 solar radii in the streamer belt, well beyond ...
Energy densities of Alfven waves between 0.7 and 1.6 AU. [in interplanetary medium
Belcher, J. W.; Burchsted, R.
1974-01-01
Plasma and field data from Mariner 4 and 5 between 0.7 and 1.6 AU are used to study the radial dependence of the levels of microscale fluctuation associated with interplanetary Alfven waves. The observed decrease of these levels with increasing distance from the sun is consistent with little or no local generation or damping of the ambient Alfven waves over this range of radial distance.
Eigenmode Analysis of Boundary Conditions for One-Dimensional Preconditioned Euler Equations
Darmofal, David L.
1998-01-01
An analysis of the effect of local preconditioning on boundary conditions for the subsonic, one-dimensional Euler equations is presented. Decay rates for the eigenmodes of the initial boundary value problem are determined for different boundary conditions. Riemann invariant boundary conditions based on the unpreconditioned Euler equations are shown to be reflective with preconditioning, and, at low Mach numbers, disturbances do not decay. Other boundary conditions are investigated which are non-reflective with preconditioning and numerical results are presented confirming the analysis.
Eigenmodes of 3-dimensional spherical spaces and their application to cosmology
Lehoucq, R; Uzan, J P; Gausmann, E; Luminet, Jean Pierre; Lehoucq, Roland; Weeks, Jeffrey; Uzan, Jean-Philippe; Gausmann, Evelise; Luminet, Jean-Pierre
2002-01-01
This article investigates the computation of the eigenmodes of the Laplacian operator in multi-connected three-dimensional spherical spaces. General mathematical results and analytical solutions for lens and prism spaces are presented. Three complementary numerical methods are developed and compared with our analytic results and previous investigations. The cosmological applications of these results are discussed, focusing on the cosmic microwave background (CMB) anisotropies. In particular, whereas in the Euclidean case too small universes are excluded by present CMB data, in the spherical case there will always exist candidate topologies even if the total energy density parameter of the universe is very close to unity.
Electrical model of the Alfvén eigenmode exciter on JET
Panis, Theodoros; Fasoli, Ambrogio; Klein, Alex; Testa, Duccio
2008-01-01
The TAE antenna system on JET is used to drive intermediate and high n Alfvén Eigenmodes (AEs) into the plasma so as to study their properties and estimate their stability by measuring their damping rates as a function of the various plasma parameters. In order to bring the system to full and optimized operation in terms of driving higher current into the antennas and hence higher magnetic perturbations into the plasma, the design of a matching unit was considered. The latter required a compl...
Drift-Alfven turbulence of a parallel shearing flow of the finite beta plasma with warm ions
Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June
2016-09-01
It was predicted [Mikhailenko et al., Phys. Plasmas 23, 020701 (2016)] that two distinct drift-Alfven instabilities may be developed in the parallel shearing flow of finite beta plasmas ( 1 ≫β≫me/mi ) with comparable ion and electron temperatures. The first one is the shear-flow-modified drift-Alfven instability, which develops due to the inverse electron Landau damping and exists in the shearless plasma as well. The second one is the shear-flow-driven drift-Alfven instability, which develops due to the combined effect of the velocity shear and ion Landau damping and is absent in the shearless plasma flows. In the present paper, these drift-Alfven instabilities are examined numerically and analytically by including the electromagnetic response of the ions. The levels of the drift-Alfven turbulence, resulted from the development of both instabilities, are determined from the renormalized nonlinear dispersion equation, which accounts for the nonlinear effect of ion scattering by the electromagnetic turbulence. The renormalized quasilinear equation for the ion distribution function, which accounts for the same nonlinear effect of ion scattering, is derived and employed for the analysis of the ion viscosity and ions heating resulting from the interactions of ions with drift-Alfven turbulence.
Nariyuki, Y; Nariyuki, Yasuhiro; Hada, Tohru
2006-01-01
Parametric instabilities of parallel propagating,circularly polarized Alfv\\'en waves in a uniform background plasma is studied, within a framework of one-dimensional Vlasov equation for ions and massless electron fluid, so that kinetic perturbations in the longitudinal direction (ion Landau damping) are included. The present formulation also includes the Hall effect. The obtained results agree well with relevant analysis in the past, suggesting that kinetic effects in the longitudinal direction play essential roles in the parametric instabilities of Alfven waves when the kinetic effects react "passively". Furthermore, existence of the kinetic parametric instabilities is confirmed for the regime with small wave number daughter waves. Growth rates of these instabilities are sensitive to ion temperature.
Phenomenology of non-Alfvenic turbulence in a uniformly expanding medium
Matthaeus, W. H.; Zank, G. P.
1995-01-01
Transport and decay of magnetohydrodynamic (MHD) turbulence in a weakly inhomogeneous uniformly expanding medium involves a fairly complex formalism, even for the case where no spectral information is required. Here we argue that the phenomenology for decay simplifies greatly if: (1) the cross helicity (Alfvenicity) is small, (2) the dynamical influence of the large scale magnetic field is negligible either because of spectral anisotropy or because the expansion speed is much greater than the corresponding Alfven speed, and (3) the ratio of kinetic energy to magnetic energy for the fluctuations is either unity or some other constant. These conditions are acceptable as an approximation to solar wind turbulence in the outer heliosphere. In these circumstances a reasonable MHD energy-containing phenomenology is essentially that of locally homogeneous Kolmogoroff turbulence in a uniformly expanding medium. Analytical solutions for this model are presented for both undriven and driven cases.
Reflection and dissipation of Alfv\\'en waves in interstellar clouds
Pinto, C; Galli, D; Velli, M
2012-01-01
Context: Supersonic nonthermal motions in molecular clouds are often interpreted as long-lived magnetohydrodynamic (MHD) waves. The propagation and amplitude of these waves is affected by local physical characteristics, most importantly the gas density and the ionization fraction. Aims: We study the propagation, reflection and dissipation of Alfv\\'en waves in molecular clouds deriving the behavior of observable quantities such as the amplitudes of velocity fluctuations and the rate of energy dissipation. Methods: We formulated the problem in terms of Els\\"asser variables for transverse MHD waves propagating in a one-dimensional inhomogeneous medium, including the dissipation due to collisions between ions and neutrals and to a nonlinear turbulent cascade treated in a phenomenological way. We considered both steady-state and time-dependent situations and solved the equations of the problem numerically with an iterative method and a Lax-Wendroff scheme, respectively. Results: Alfv\\'en waves incident on overdens...
Bi-directional Alfv\\'en Cyclotron Instabilities in the Mega-Amp Spherical Tokamak
Sharapov, S E; Akers, R; Ayed, N Ben; Cecconello, M; Cook, J W C; Cunningham, G; Verwichte, E; Tea, the MAST
2014-01-01
Alfv\\'en cyclotron instabilities excited by velocity gradients of energetic beam ions were investigated in MAST experiments with super-Alfv\\'enic NBI over a wide range of toroidal magnetic fields from ~0.34 T to ~0.585 T. In MAST discharges with high magnetic field, a discrete spectrum of modes in the sub-cyclotron frequency range is excited toroidally propagating counter to the beam and plasma current (toroidal mode numbers n < 0).
Alfvenic drift Kelvin-Helmholtz instability in the presence of an equilibrium electric field
Sharma, Avadhesh C.; Srivastava, Krishna M.
1992-01-01
The Alfvenic drift Kelvin-Helmholtz instability of a high-beta plasma in the presence of equilibrium magnetic and electric fields perpendicular to each other are studied. The plasma components are assumed to have 2D sheared velocity in y and z directions. The dispersion relation is derived, and the instability criterion is determined. It is shown that the equilibrium electric field has either stabilizing or destabilizing effect depending on certain conditions discussed in the paper.
Study of Nonlinear Interaction and Turbulence of Alfven Waves in LAPD Experiments
Boldyrev, Stanislav; Perez, Jean Carlos
2013-11-29
The complete project had two major goals — investigate MHD turbulence generated by counterpropagating Alfven modes, and study such processes in the LAPD device. In order to study MHD turbulence in numerical simulations, two codes have been used: full MHD, and reduced MHD developed specialy for this project. Quantitative numerical results are obtained through high-resolution simulations of strong MHD turbulence, performed through the 2010 DOE INCITE allocation. We addressed the questions of the spectrum of turbulence, its universality, and the value of the so-called Kolmogorov constant (the normalization coefficient of the spectrum). In these simulations we measured with unprecedented accuracy the energy spectra of magnetic and velocity fluctuations. We also studied the so-called residual energy, that is, the difference between kinetic and magnetic energies in turbulent fluctuations. In our analytic work we explained generation of residual energy in weak MHD turbulence, in the process of random collisions of counterpropagating Alfven waves. We then generalized these results for the case of strong MHD turbulence. The developed model explained generation of residual energy is strong MHD turbulence, and verified the results in numerical simulations. We then analyzed the imbalanced case, where more Alfven waves propagate in one direction. We found that spectral properties of the residual energy are similar for both balanced and imbalanced cases. We then compared strong MHD turbulence observed in the solar wind with turbulence generated in numerical simulations. Nonlinear interaction of Alfv´en waves has been studied in the upgraded Large Plasma Device (LAPD). We have simulated the collision of the Alfven modes in the settings close to the experiment. We have created a train of wave packets with the apltitudes closed to those observed n the experiment, and allowed them to collide. We then saw the generation of the second harmonic, resembling that observed in the
3D Alfven wave behaviour around proper and improper magnetic null points
Thurgood, J O
2013-01-01
Context: MHD waves and magnetic null points are both prevalent in many astrophysical plasmas, including the solar atmosphere. Interaction between waves and null points has been implicated as a possible mechanism for localised heating events. Aims: Here we investigate the transient behaviour of the Alfven wave about fully 3D proper and improper 3D magnetic null points. Previously, the behaviour of fast magnetoacoustic waves at null points in 3D, cold MHD was considered by Thurgood & McLaughlin (Astronomy & Astrophysics, 2012, 545, A9). Methods: We introduce an Alfven wave into the vicinity of both proper and improper null points by numerically solving the ideal, $\\beta=0$ MHD equations using the LARE3D code. A magnetic fieldline and flux-based coordinate system permits the isolation of resulting wave-modes and the analysis of their interaction. Results: We find that the Alfven wave propagates throughout the region and accumulates near the fan-plane, causing current build up. For different values of nul...
On the reflection of Alfv\\'en waves and its implication for Earth's core modeling
Schaeffer, Nathanaël; Cardin, Philippe; Marie, Drouard
2011-01-01
Alfv\\'en waves propagate in electrically conducting fluids in the presence of a magnetic field. Their reflection properties depend on the ratio between the kinematic viscosity and the magnetic diffusivity of the fluid, also known as the magnetic Prandtl number Pm. In the special case Pm=1, there is no reflection on an insulating, no-slip boundary, and the wave energy is entirely dissipated in the boundary layer. We investigate the consequences of this remarkable behaviour for the numerical modeling of torsional Alfv\\'en waves (also known as torsional oscillations), which represent a special class of Alfv\\'en waves, in rapidly rotating spherical shells. They consist of geostrophic motions and are thought to exist in the fluid cores of planets with internal magnetic field. In the geophysical limit Pm 0.3, which is the range of values for which geodynamo numerical models operate. As a result, geodynamo models with no-slip boundary conditions cannot exhibit torsional oscillation normal modes.
Kinetic Alfv\\'en waves generation by large-scale phase-mixing
Vasconez, C L; Valentini, F; Servidio, S; Matthaeus, W H; Malara, F
2015-01-01
One view of the solar-wind turbulence is that the observed highly anisotropic fluctuations at spatial scales near the proton inertial length $d_p$ may be considered as Kinetic Alfv\\'en waves (KAWs). In the present paper, we show how phase-mixing of large-scale parallel propagating Alfv\\'en waves is an efficient mechanism for the production of KAWs at wavelengths close to $d_p$ and at large propagation angle with respect to the magnetic field. Magnetohydrodynamic (MHD), Hall-Magnetohydrodynamic (HMHD), and hybrid Vlasov-Maxwell (HVM) simulations modeling the propagation of Alfv\\'en waves in inhomogeneous plasmas are performed. In linear regime, the role of dispersive effects is singled out by comparing MHD and HMHD results. Fluctuations produced by phase-mixing are identified as KAWs through a comparison of polarization of magnetic fluctuations and wave group velocity with analytical linear predictions. In the nonlinear regime, comparison of HMHD and HVM simulations allows to point out the role of kinetic effe...
Dissipative MHD solutions for resonant Alfven waves in 1-dimensional magnetic flux tubes
Goossens, Marcel; Ruderman, Michail S.; Hollweg, Joseph V.
1995-01-01
The present paper extends the analysis by Sakurai, Goossens, and Hollweg (1991) on resonant Alfven waves in nonuniform magnetic flux tubes. It proves that the fundamental conservation law for resonant Alfven waves found in ideal MHD by Sakurai, Goossens, and Hollweg remains valid in dissipative MHD. This guarantees that the jump conditions of Sakurai, Goossens, and Hollweg, that connect the ideal MHD solutions for xi(sub r), and P' across the dissipative layer, are correct. In addition, the present paper replaces the complicated dissipative MHD solutions obtained by Sakurai, Goossens, and Hollweg for xi(sub r), and P' in terms of double integrals of Hankel functions of complex argument of order 1/3 with compact analytical solutions that allow a straight- forward mathematical and physical interpretation. Finally, it presents an analytical dissipative MHD solution for the component of the Lagrangian displacement in the magnetic surfaces perpen- dicular to the magnetic field lines xi(sub perpendicular) which enables us to determine the dominant dynamics of resonant Alfven waves in dissipative MHD.
Small scales formation via Alfven wave propagation in compressible nonuniform media
Malara, F.; Primavera, L.; Veltri, P.
1995-01-01
In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. The possibility to produce small scales has been studied by Malara et al. in the case of MHD disturbances propagating in an incompressible and inhomogeneous medium, for a strictly 2D geometry. We extend the work of Malara et al. to include both compressibility and the third component for vector quantities. Using numerical simulations we show that, when an Alfven wave propagates in a compressible nonuniform medium, the two dynamical effects responsible for the small scales formation in the incompressible case are still at work: energy pinching and phase-mixing. Moreover, the interaction between the initial Alfven wave and the inhomogeneity gives rise to the formation of compressible perturbations (fast and slow waves or a static entropy wave). Some of these compressive fluctuations are subject to the steepening of the wave front and become shock waves, which are extremely efficient in dissipating their energy, their dissipation being independent of the Reynolds number. A rough estimate of the typical times which the various dynamical processes take to produce small scales and then to dissipate the energy show that these times are consistent with those required to dissipate inside the solar corona the energy of Alfven waves of photospheric origin.
Torsional Alfven Waves in Solar Magnetic Flux Tubes of Axial Symmetry
Murawski, K; Musielak, Z E; Srivastava, A K; Kraskiewicz, J
2015-01-01
Aims: Propagation and energy transfer of torsional Alfv\\'en waves in solar magnetic flux tubes of axial symmetry is studied. Methods: An analytical model of a solar magnetic flux tube of axial symmetry is developed by specifying a magnetic flux and deriving general analytical formulae for the equilibrium mass density and a gas pressure. The main advantage of this model is that it can be easily adopted to any axisymmetric magnetic structure. The model is used to simulate numerically the propagation of nonlinear Alfv\\'en waves in such 2D flux tubes of axial symmetry embedded in the solar atmosphere. The waves are excited by a localized pulse in the azimuthal component of velocity and launched at the top of the solar photosphere, and they propagate through the solar chromosphere, transition region, and into the solar corona. Results: The results of our numerical simulations reveal a complex scenario of twisted magnetic field lines and flows associated with torsional Alfv\\'en waves as well as energy transfer to t...
Sunward-propagating Alfv\\'enic fluctuations observed in the heliosphere
Li, H; Belcher, J W; He, J S; Richardson, J D
2016-01-01
The mixture/interaction of anti-sunward-propagating Alfv\\'enic fluctuations (AFs) and sunward-propagating Alfv\\'enic fluctuations (SAFs) is believed to result in the decrease of the Alfv\\'enicity of solar wind fluctuations with increasing heliocentric distance. However, SAFs are rarely observed at 1 au and solar wind AFs are found to be generally outward. Using the measurements from Voyager 2 and Wind, we perform a statistical survey of SAFs in the heliosphere inside 6 au. We first report two SAF events observed by Voyager 2. One is in the anti-sunward magnetic sector with a strong positive correlation between the fluctuations of magnetic field and solar wind velocity. The other one is in the sunward magnetic sector with a strong negative magnetic field-velocity correlation. Statistically, the percentage of SAFs increases gradually with heliocentric distance, from about 2.7% at 1.0 au to about 8.7% at 5.5 au. These results provide new clues for understanding the generation mechanism of SAFs.
Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets V: Alfv\\'{e}n Ionization
Stark, Craig R; Diver, Declan A; Rimmer, Paul B
2013-01-01
Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbour localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfv\\'{e}n ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization ($\\geq10^{-7}$) that they constitute plasmas. We outline the criteria required for Alfv\\'{e}n ionization and demonstrate it's applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs and M-dwarfs for both solar and sub-solar metallicities. We find that Alfv\\'{e}n ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neut...
Statistical Evidence for the Existence of Alfv\\'enic Turbulence in Solar Coronal Loops
Liu, Jiajia; De Moortel, Ineke; Threlfall, James; Bethge, Christian
2014-01-01
Recent observations have demonstrated that waves which are capable of carrying large amounts of energy are ubiquitous throughout the solar corona. However, the question of how this wave energy is dissipated (on which time and length scales) and released into the plasma remains largely unanswered. Both analytic and numerical models have previously shown that Alfv\\'enic turbulence may play a key role not only in the generation of the fast solar wind, but in the heating of coronal loops. In an effort to bridge the gap between theory and observations, we expand on a recent study [De Moortel et al., ApJL, 782:L34, 2014] by analyzing thirty-seven clearly isolated coronal loops using data from the Coronal Multi-channel Polarimeter (CoMP) instrument. We observe Alfv\\'enic perturbations with phase speeds which range from 250-750 km/s and periods from 140-270 s for the chosen loops. While excesses of high frequency wave-power are observed near the apex of some loops (tentatively supporting the onset of Alfv\\'enic turbu...
Alfv\\'en Wave Heating of the Solar Chromosphere: 1.5D models
Arber, T D; Shelyag, S
2015-01-01
Physical processes which may lead to solar chromospheric heating are analyzed using high-resolution 1.5D non-ideal MHD modelling. We demonstrate that it is possible to heat the chromospheric plasma by direct resistive dissipation of high-frequency Alfv\\'en waves through Pedersen resistivity. However this is unlikely to be sufficient to balance radiative and conductive losses unless unrealistic field strengths or photospheric velocities are used. The precise heating profile is determined by the input driving spectrum since in 1.5D there is no possibility of Alfv\\'en wave turbulence. The inclusion of the Hall term does not affect the heating rates. If plasma compressibility is taken into account, shocks are produced through the ponderomotive coupling of Alfv\\'en waves to slow modes and shock heating dominates the resistive dissipation. In 1.5D shock coalescence amplifies the effects of shocks and for compressible simulations with realistic driver spectra the heating rate exceeds that required to match radiative...
The formation heights of coronal shocks from 2D density and Alfv\\'en speed maps
Zucca, Pietro; Bloomfield, D Shaun; Gallagher, Peter T
2014-01-01
Super-Alfv\\'enic shock waves associated with coronal mass ejections (CMEs) can produce radio emission known as Type II bursts. In the absence of direct imaging, accurate estimates of coronal electron densities, magnetic field strengths and Alfv\\'en speeds are required in order to calculate the kinematics of shocks. To date, 1D radial models have been used, but these are not appropriate for shocks propagating in non-radial directions. Here, we study a coronal shock wave associated with a CME and Type II radio burst using 2D electron density and Alfv\\'en speed maps to determine the locations that shocks are excited as the CME expands through the corona. Coronal density maps were obtained from emission measures derived from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory ($SDO$) and polarized brightness measurements from the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory ($SOHO$). Alfv\\'en speed maps were calculated using these dens...
The Modulation of Ionospheric Alfven Resonator on Heating HF Waves and the Doppler Effect
NiBin-bin; ZhaoZheng-yu; XieShu-guo
2003-01-01
The propagation of HF waves in IAR can produce many nonlinear effects, including the modulation effect of IAR on HF waves and the Doppler effect. To start with the dependence of the ionospheric electron temperature varia-tions on the Alfven resonant field, We discuss the mechanism of the modulation effect and lucubrate possible reasons for the Doppler effect. The results show that the Alfven resonant field can have an observable modulation effect on HF waves while its mechanism is quite different from that of Schumann resonant field on HF waves. The depth of modulation of IAR on HF waves has a quasi-quadratic relation with the Alfven field, which directly inspires the formation of cross-spectrum between ULF waves and HF waves and results in spectral peaks at some gyro-frequencies of IAR. With respect to the Doppler effect during the propagation of HF waves in IAR, it is mainly caused by the motion of the high-speed flyer and the drifting electrons and the frequency shift from the phase vari-ation of the reflected waves can be neglected when the frequency of HF incident wave is high enough.
Spectroscopic Observations and Modelling of Impulsive Alfv\\'en Waves Along a Polar Coronal Jet
Jelínek, P; Murawski, K; Kayshap, P; Dwivedi, B N
2015-01-01
Using the Hinode/EIS 2$"$ spectroscopic observations, we study the intensity, velocity, and FWHM variations of the strongest Fe XII 195.12 \\AA\\ line along the jet to find the signature of Alfv\\'en waves. We simulate numerically the impulsively generated Alfv\\'en waves within the vertical Harris current-sheet, forming the jet plasma flows, and mimicking their observational signatures. Using the FLASH code and the atmospheric model with embedded weakly expanding magnetic field configuration within a vertical Harris current-sheet, we solve the two and half-dimensional (2.5-D) ideal magnetohydrodynamic (MHD) equations to study the evolution of Alfv\\'en waves and vertical flows forming the plasma jet. At a height of $\\sim 5~\\mathrm{Mm}$ from the base of the jet, the red-shifted velocity component of Fe XII 195.12 \\AA\\ line attains its maximum ($5~\\mathrm{km\\,s}^{-1}$) which converts into a blue-shifted one between the altitude of $5-10~\\mathrm{Mm}$. The spectral intensity continously increases up to $10~\\mathrm{Mm...
Alfvenic behavior of alpha particle driven ion cyclotron emission in TFTR
Cauffman, S.; Majeski, R. [Princeton Plasma Physics Lab., NJ (United States); McClements, K.G. [UKAEA Government Division, Oxfordshire (United Kingdom). Euratom/UKAEA Fusion Association] [and others
1995-07-01
Ion cyclotron emission (ICE) has been observed during D-T discharges in the Tokamak Fusion Test Reactor (TFTR), using rf probes located near the top and bottom of the vacuum vessel. Harmonics of the alpha cyclotron frequency ({Omega}{sub {alpha}}) evaluated at the outer midplane plasma edge are observed at the onset of the beam injection phase of TFTR supershots, and persist for approximately 100-250 ms. These results are in contrast with observations of ICE in JET, in which harmonics of {Omega}{sub {alpha}} evolve with the alpha population in the plasma edge. Such differences are believed to be due to the fact that newly-born fusion alpha particles are super-Alfvenic near the edge of JET plasmas, while they are sub-Alfvenic near the edge of TFTR supershot plasmas. In TFTR discharges with edge densities such that newly-born alpha particles are super-Alfvenic, alpha cyclotron harmonics are observed to persist. These results are in qualitative agreement with numerical calculations of growth rates due to the magnetoacoustic cyclotron instability.
Observation of Kinetic Alfvén Eigenmodes with RMP Penetration in J-TEXT Tokamak
Liu, Linzi; Hu, Qiming; Zhuang, Ge; J-text Team
2016-10-01
kinetic Alfvén eigenmodes excited in J-TEXT Ohmic plasmas are observed when the penetration of external applied resonant magnetic perturbations (RMPs) occurs. These modes are identified localized in gaps (20-80kHz) triggered by kinetic thermal ion effect [Chen L and Zonca F 2016 Reviews of Modern Physics] in the Alfvén continuum. One of these modes, which have the highest frequency, is modulated by the RMP intensity, and its frequency converge to the nonlinearly modified beta-induced Alfvén eigenmode (BAE) continuum accumulation point [Biancalani A 2011 PPCF]. The experimental observation of this type of mode agrees with BAE whose frequency is proportional to the magnetic island half width. Another type of mode with lower frequency ( 35kHz) well settled down in the thermal ion transit frequency range is found that it has no relation with RMP strength and magnetic island width, as indicated in previous work [Linzi L 2015 PPCF]. The investigation of the third type of modes shows that the mode frequency is in the range of diamagnetic drift frequency (20kHz) and its damping mechanism should involve the fast particle effect. All of the modes above are observed only in low density (1 ×1019) along with slide-away discharge.
Spin wave eigenmodes in single and coupled sub-150 nm rectangular permalloy dots
Carlotti, G., E-mail: giovanni.carlotti@fisica.unipg.it; Madami, M. [Dipartimento di Fisica e Geologia, Università di Perugia, Perugia (Italy); Tacchi, S. [Istituto Officina dei Materiali del CNR (CNR-IOM), Dipartimento di Fisica e Geologia, Perugia (Italy); Gubbiotti, G.; Dey, H.; Csaba, G.; Porod, W. [Center for Nano Science and Technology, Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States)
2015-05-07
We present the results of a Brillouin light scattering investigation of thermally excited spin wave eigenmodes in square arrays of either isolated rectangular dots of permalloy or twins of dipolarly coupled elements, placed side-by-side or head-to-tail. The nanodots, fabricated by e-beam lithography and lift-off, are 20 nm thick and have the major size D in the range between 90 nm and 150 nm. The experimental spectra show the presence of two main peaks, corresponding to modes localized either at the edges or in the center of the dots. Their frequency dependence on the dot size and on the interaction with adjacent elements has been measured and successfully interpreted on the basis of dynamical micromagnetic simulations. The latter enabled us also to describe the spatial profile of the eigenmodes, putting in evidence the effects induced by the dipolar interaction between coupled dots. In particular, in twinned dots the demagnetizing field is appreciably modified in proximity of the “internal edges” if compared to the “external” ones, leading to a splitting of the edge mode. These results can be relevant for the exploitation of sub-150 nm magnetic dots in new applications, such as magnonic metamaterials, bit-patterned storage media, and nano-magnetic logic devices.
Itasse, Maxime, E-mail: Maxime.Itasse@onera.fr; Brazier, Jean-Philippe, E-mail: Jean-Philippe.Brazier@onera.fr; Léon, Olivier, E-mail: Olivier.Leon@onera.fr; Casalis, Grégoire, E-mail: Gregoire.Casalis@onera.fr [Onera - The French Aerospace Lab, F-31055 Toulouse (France)
2015-08-15
Nonlinear evolution of disturbances in an axisymmetric, high subsonic, high Reynolds number hot jet with forced eigenmodes is studied using the Parabolized Stability Equations (PSE) approach to understand how modes interact with one another. Both frequency and azimuthal harmonic interactions are analyzed by setting up one or two modes at higher initial amplitudes and various phases. While single mode excitation leads to harmonic growth and jet noise amplification, controlling the evolution of a specific mode has been made possible by forcing two modes (m{sub 1}, n{sub 1}), (m{sub 2}, n{sub 2}), such that the difference in azimuth and in frequency matches the desired “target” mode (m{sub 1} − m{sub 2}, n{sub 1} − n{sub 2}). A careful setup of the initial amplitudes and phases of the forced modes, defined as the “killer” modes, has allowed the minimizing of the initially dominant instability in the near pressure field, as well as its estimated radiated noise with a 15 dB loss. Although an increase of the overall sound pressure has been found in the range of azimuth and frequency analyzed, the present paper reveals the possibility to make the initially dominant instability ineffective acoustically using nonlinear interactions with forced eigenmodes.
Nonlinear simulations of beam-driven compressional Alfvén eigenmodes in NSTX
Belova, E. V.; Gorelenkov, N. N.; Crocker, N. A.; Lestz, J. B.; Fredrickson, E. D.; Tang, S.; Tritz, K.
2017-04-01
Results of 3D nonlinear simulations of neutral-beam-driven compressional Alfvén eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX) are presented. Hybrid MHD-particle simulations for the H-mode NSTX discharge (shot 141398) using the HYM code show unstable CAE modes for a range of toroidal mode numbers, n =4 -9 , and frequencies below the ion cyclotron frequency. It is found that the essential feature of CAEs is their coupling to kinetic Alfvén wave (KAW) that occurs on the high-field side at the Alfvén resonance location. High-frequency Alfvén eigenmodes are frequently observed in beam-heated NSTX plasmas, and have been linked to flattening of the electron temperature profiles at high beam power. Coupling between CAE and KAW suggests an energy channeling mechanism to explain these observations, in which beam-driven CAEs dissipate their energy at the resonance location, therefore significantly modifying the energy deposition profile. Nonlinear simulations demonstrate that CAEs can channel the energy of the beam ions from the injection region near the magnetic axis to the location of the resonant mode conversion at the edge of the beam density profile. A set of nonlinear simulations show that the CAE instability saturates due to nonlinear particle trapping, and a large fraction of beam energy can be transferred to several unstable CAEs of relatively large amplitudes and absorbed at the resonant location. Absorption rate shows a strong scaling with the beam power.
Karmakar, P. K.; Borah, B.
2013-09-01
We try to present a theoretical evolutionary model leading to the excitations of nonlinear pulsational eigenmodes in a planar (1D) collisional dust molecular cloud (DMC) on the Jeans scale. The basis of the adopted model is the Jeans assumption of self-gravitating homogeneous uniform medium for simplification. It is a self-gravitating multi-fluid consisting of the Boltzmann distributed warm electrons and ions, and the inertial cold dust grains with partial ionization. Dust-charge fluctuations, convections and all the possible collisions are included. The grain-charge behaves as a dynamical variable owing mainly to the attachment of the electrons and ions to the grain-surfaces randomly. The adopted technique is centered around a mathematical model based on new solitary spectral patterns within the hydrodynamic framework. The collective dynamics of the patterns is governed by driven Korteweg-de Vries ( d-KdV) and Korteweg-de Vries (KdV) equations obtained by a standard multiscale analysis. Then, simplified analytical and numerical solutions are presented. The grain-charge fluctuation and collision processes play a key role in the DMC stability. The sensitive dependence of the eigenmode amplitudes on diverse relevant plasma parameters is discussed. The significance of the main results in astrophysical, laboratory and space environments are concisely summarized.
Active and fast particle driven Alfvén eigenmodes in Alcator C-Moda)
Snipes, J. A.; Basse, N.; Boswell, C.; Edlund, E.; Fasoli, A.; Gorelenkov, N. N.; Granetz, R. S.; Lin, L.; Lin, Y.; Parker, R.; Porkolab, M.; Sears, J.; Sharapov, S.; Tang, V.; Wukitch, S.
2005-05-01
Alfvén eigenmodes (AEs) are studied to assess their stability in high density reactor relevant regimes where Ti≈Te and as a diagnostic tool. Stable AEs are excited with active magnetohydrodynamics antennas in the range of the expected AE frequency. Toroidal Alfvén eigenmode (TAE) damping rates between 0.5%<γ/ω<4.5% have been observed in diverted and limited Ohmic plasmas. Unstable AEs are excited with a fast ion tail driven by H minority ion cyclotron radio frequency (ICRF) heating with electron densities in the range of n¯e=0.5-2×1020m-3. Energetic particle modes or TAEs have been observed to decrease in frequency and mode number with time up to a large sawtooth collapse, indicating the role fast particles play in stabilizing sawteeth. In the current rise phase, unstable modes with frequencies that increase rapidly with time are observed with magnetic pick-up coils at the wall and phase contrast imaging density fluctuation measurements in the core. Modeling of these modes constrains the calculated safety factor profile to be very flat or with slightly reversed shear. AEs are found to be more stable for an inboard than for central or outboard ICRF resonances in qualitative agreement with modeling.
The effect of toroidal plasma rotation on low-frequency reversed shear Alfvén eigenmodes in tokamaks
Haverkort, J.W.
2012-01-01
The influence of toroidal plasma rotation on the existence of reversed shear Alfvén eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence of RSAEs. Th
Heidbrink, W. W. [University of California Irvine, Irvine, California 92697 (United States); Austin, M. E. [University of Texas at Austin, Austin, Texas 78712 (United States); Spong, D. A. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Tobias, B. J. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Van Zeeland, M. A. [General Atomics, San Diego, California 92186 (United States)
2013-08-15
Reversed shear Alfvén eigenmodes (RSAEs) usually sweep upward in frequency when the minimum value of the safety factor q{sub min} decreases in time. On rare occasions, RSAEs sweep downward prior to the upward sweep. Electron cyclotron emission measurements show that the radial eigenfunction during the downsweeping phase is similar to the eigenfunction of normal, upsweeping RSAEs.
Matteini, L; Pantellini, F; Velli, M; Schwartz, S J
2015-01-01
We investigate properties of the plasma fluid motion in the large amplitude low frequency fluctuations of highly Alfv\\'enic fast solar wind. We show that protons locally conserve total kinetic energy when observed from an effective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame can be reasonably identified by alpha particles, which, owing to their drift with respect to protons at about the Alfv\\'en speed along the magnetic field, do not partake in the fluid low frequency fluctuations. Using their velocity to transform proton velocity into the frame of Alfv\\'enic turbulence, we demonstrate that the resulting plasma motion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity and magnetic field vectors as expected for unidirectional Alfv\\'enic fluctuations in equilibrium. We propose that this constraint, via the correlation between velocity and magnetic field in Alfv\\'enic turbulence, is at the origin of ...
Matsumoto, Takuma
2010-01-01
We have performed MHD simulations of Alfven wave propagation along an open flux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photospheric granular motion from G-band movies of Hinode/SOT. It is shown that the total energy flux at the corona becomes larger and the transition region height becomes higher in the case when we use the observed spectrum rather than white/pink noise spectrum as the wave generator. This difference can be explained by the Alfven wave resonance between the photosphere and the transition region. After performing Fourier analysis on our numerical results, we have found that the region between the photosphere and the transition region becomes an Alfven wave resonant cavity. We have confirmed that there are at least three resonant frequencies, 1, 3 and 5 mHz, in our numerical model. Alfven wave resonance is one of the most effective mechanisms to explai...
Effects of energetic particles on zonal flow generation by toroidal Alfvén eigenmode
Qiu, Z.; Chen, L.; Zonca, F.
2016-09-01
Generation of zonal flow (ZF) by energetic particle (EP) driven toroidal Alfvén eigenmode (TAE) is investigated using nonlinear gyrokinetic theory. It is found that nonlinear resonant EP contribution dominates over the usual Reynolds and Maxwell stresses due to thermal plasma nonlinear response. ZF can be forced driven in the linear growth stage of TAE, with the growth rate being twice the TAE growth rate. The ZF generation mechanism is shown to be related to polarization induced by resonant EP nonlinearity. The generated ZF has both the usual meso-scale and micro-scale radial structures. Possible consequences of this forced driven ZF on the nonlinear dynamics of TAE are also discussed.
Eigenmode compendium of the third harmonic module of the European X-ray Free Electron Laser
Flisgen, Thomas; Galek, Tomasz, Rostock Universitaet; Shi, Liangliang; Joshi, Nirav; Baboi, Nicoletta; Jones, Roger M; van Rienen, Ursula
2017-01-01
Chains of superconducting radio-frequency resonators are key components of modern particle accelerators such as the European XFEL, which is currently under construction in the north of Germany. In addition to the accelerating mode of the resonators, their beam excited higher order modes are of special interest, because they can harm the beam quality. In contrast to the accelerating mode, these modes are in general not confined within single resonators of the cavity string. For instance, eigenmodes can be localized between adjacent cavities or can be distributed along the entire chain of cavities. Therefore, the full chain has to be considered for a reasonable investigation of its resonant spectra. Accounting for such complex structures is computationally challenging and is therefore often avoided. In this article, the challenge is faced by using the so-called state-space concatenation approach, which is a combination of domain decomposition and model-order reduction. The technique allows for a reduction of th...
Low frequency eigenmodes of thin anisotropic current sheets and Cluster observations
L. M. Zelenyi
2009-02-01
Full Text Available The eigenmodes of low frequency perturbations of thin anisotropic current sheets with a finite value of the normal magnetic field, are investigated in this paper. It is shown that two possible polarizations of symmetric and asymmetric modes (sausage and kink exist where the growth rate of instabilities is positive. In addition, we demonstrate that a tearing instability might have a positive growth rate in thin anisotropic current sheets. The class of relatively fast wavy flapping oscillations observed by Cluster is described. The main direction of wave motion coincides with the direction of the current and the typical velocity of this motion is comparable with the plasma drift velocity in the current sheet. The comparison of these characteristics with theoretical predictions of the model of anisotropic thin current sheets, demonstrates that, in principle, the theory adequately describes the observations.
Eigenmode description of Raman scattering in atomic vapors in the presence of decoherence
Chwedenczuk, Jan; Wasilewski, Wojciech
2012-01-01
A theoretical model describing the Raman scattering process in atomic vapors is constructed. Despite the incorporated decoherence effects, it allows for a direct separation of system's time evolution from its spatial degrees of freedom. The impact of noise on the temporal properties of the system is investigated. In particular, it is shown that even in the presence of decoherence, the estimation of the number of spin waves created in the process can reach sensitivity below the projection noise limit. The model is then applied in two experimentally relevant situations of ultra-cold and room-temperature atoms. In both cases, the spatial eigenmodes of the Stokes photon and atomic excitation fields and their coupling parameters are computed.
Influence of number and depth of magnetic mirror on Alfvénic gap eigenmode
Chang, Lei; Hu, Ning; Yao, Jianyao
2016-10-01
Alfvénic gap eigenmode (AGE) can eject energetic particles from confinement and thereby threaten the success of magnetically controlled fusion. A low-temperature plasma cylinder is a promising candidate to study this eigenmode, due to easy diagnostic access and simple geometry, and the idea is to arrange a periodic array of magnetic mirrors along the plasma cylinder and introduce a local defect to break the field periodicity. The present work validates this idea by reproducing a clear AGE inside a spectral gap, and more importantly details the influence of the number and depth (or modulation factor) of magnetic mirror on the characteristics of AGE. Results show that AGE is suppressed by other modes inside the spectral gap when the number of magnetic mirrors is below a certain value, which leads to a weakened Bragg’s effect. The structure and frequency of AGE remain unchanged for a decreased number of magnetic mirrors, as long as this number is enough for the AGE formation. The width of spectral gap and decay constant (inverse of decay length) of AGE are linearly proportional to the depth of magnetic mirror, implying easier observation of AGE through a bigger mirror depth. The frequency of AGE shifts to a lower range with the depth increased, possibly due to the unfrozen plasma with field line and the invalidity of small-perturbation analysis. Nevertheless, it is exciting to find that the depth of field modulation can be increased to form AGE for a very limited number of magnetic mirrors. This is of particular interest for the experimental implementation of AGE on a low-temperature plasma cylinder with limited length. Project supported by the National Natural Science Foundation of China (Grant Nos. 11405271, 11372104, 75121543, 11332013, 11372363, and 11502037).
Eigenmode compendium of the third harmonic module of the European X-ray Free Electron Laser
Flisgen, Thomas; Heller, Johann; Galek, Tomasz; Shi, Liangliang; Joshi, Nirav; Baboi, Nicoleta; Jones, Roger M.; van Rienen, Ursula
2017-04-01
Chains of superconducting radio-frequency resonators are key components of modern particle accelerators such as the European XFEL, which is currently under construction in the north of Germany. In addition to the accelerating mode of the resonators, their beam excited higher order modes are of special interest, because they can harm the beam quality. In contrast to the accelerating mode, these modes are in general not confined within single resonators of the cavity string. For instance, eigenmodes can be localized between adjacent cavities or can be distributed along the entire chain of cavities. Therefore, the full chain has to be considered for a reasonable investigation of its resonant spectra. Accounting for such complex structures is computationally challenging and is therefore often avoided. In this article, the challenge is faced by using the so-called state-space concatenation approach, which is a combination of domain decomposition and model-order reduction. The technique allows for a reduction of the number of degrees of freedom by a factor of ≈ 1.471 ×10-4 . The method is employed to generate a compendium of eigenmodes in the chain of third harmonic cavities for the European XFEL. The results are discussed in detail and are compared with experimental measurements. The compendium serves as a reference for experiments (inter alia for diagnostics based on higher order modes) at the third harmonic cavity string of the European XFEL, it allows for qualitative understanding of resonant effects appearing in chains of cavities, and it is meant to be a proof of principle of the state-space concatenation approach to handle very long and complex radio-frequency structures. To the authors' knowledge, it is the first time that a modal compendium of a structure with the given complexity is generated. The article presents geometrical details of the chain, defines quantities relevant to superconducting radio-frequency cavities, and describes the employed
Parametric instabilities of large amplitude Alfven waves with obliquely propagating sidebands
Vinas, A. F.; Goldstein, M. L.
1992-01-01
This paper presents a brief report on properties of the parametric decay and modulational, filamentation, and magnetoacoustic instabilities of a large amplitude, circularly polarized Alfven wave. We allow the daughter and sideband waves to propagate at an arbitrary angle to the background magnetic field so that the electrostatic and electromagnetic characteristics of these waves are coupled. We investigate the dependance of these instabilities on dispersion, plasma/beta, pump wave amplitude, and propagation angle. Analytical and numerical results are compared with numerical simulations to investigate the full nonlinear evolution of these instabilities.
Plastic damping of Alfv\\'en waves in magnetar flares and delayed afterglow emission
Li, Xinyu
2015-01-01
Magnetar flares generate Alfv\\'en waves bouncing in the closed magnetosphere with energy up to $\\sim 10^{46}$ erg. We show that on a 10-ms timescale the waves are transmitted into the star and form a compressed packet of high energy density. This packet strongly shears the stellar crust and initiates a plastic flow, heating the crust and melting it hundreds of meters below the surface. A fraction of the deposited plastic heat is eventually conducted to the stellar surface, contributing to the surface afterglow months to years after the flare. A large fraction of heat is lost to neutrino emission or conducted into the core of the neutron star.
Zonal Flows Driven by Small-Scale Drift-Alfven Modes
李德徽; 周登
2011-01-01
Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary modes propagating at both electron and ion diamagnetic drift directions in contrast to the assertion in previous studies that only primary modes propagating in the ion diamagnetic drift directions can drive zonal instabilities. Generally, the growth rate of the driven zonal mode is in the same order as that in previous study. However, different from the previous work, the growth rate is no longer proportional to the difference between the diamagnetic drift frequencies of electrons and ions.
Stimulated emission of fast Alfv\\'en waves within magnetically confined fusion plasmas
Cook, J W S; Chapman, S C
2016-01-01
A fast Alfv\\'en wave with finite amplitude is shown to grow by a stimulated emission process that we propose for exploitation in toroidal magnetically confined fusion plasmas. Stimulated emission occurs while the wave propagates inward through the outer mid-plane plasma, where a population inversion of the energy distribution of fusion-born ions is observed to arise naturally. Fully nonlinear first principles simulations, which self-consistently evolve particles and fields under the Maxwell-Lorentz system, demonstrate this novel "alpha-particle channelling" scenario for the first time.
Effect of Alfven resonance on low-frequency fast wave current drive
Wang, C.Y.; Batchelor, D.B.; Carter, M.D.; Jaeger, E.F.; Stallings, D.C. [Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
1995-07-01
The Alfven resonances may occur on the low- and high-field sides for a low-frequency fast wave current drive scenario proposed for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion {bold 31}, 1135 (1991)]. At the resonance on the low-field side, the fast wave may be mode converted into a short-wavelength slow wave, which can be absorbed by electrons at the plasma edge, before the fast wave propagates into the core area of the plasma. Such absorption may cause a significant parasitic power loss. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Prokopov, Pavel; Zaharov, Yuriy; Tishchenko, Vladimir; Boyarintsev, Eduard; Melehov, Aleksandr; Ponomarenko, Arnold; Posuh, Vitaliy; Shayhislamov, Ildar
2016-03-01
The paper deals with generation of Alfven plasma disturbances in magnetic flux tubes through exploding laser plasma in magnetized background plasma. Processes with similar effect of excitation of torsion-type waves seem to provide energy transfer from the solar photosphere to corona. The studies were carried out at experimental stand KI-1 represented a high-vacuum chamber of 1.2 m diameter, 5 m long, external magnetic field up to 500 Gs along the chamber axis, and up to 2×10^-6 Torr pressure in operating mode. Laser plasma was produced when focusing the CO2 laser pulse on a flat polyethylene target, and then the laser plasma propagated in θ-pinch background hydrogen (or helium) plasma. As a result, the magnetic flux tube of 15-20 cm radius was experimentally simulated along the chamber axis and the external magnetic field direction. Also, the plasma density distribution in the tube was measured. Alfven wave propagation along the magnetic field was registered from disturbance of the magnetic field transverse component B_ψ and field-aligned current J_z. The disturbances propagate at near-Alfven velocity of 70-90 km/s and they are of left-hand circular polarization of the transverse component of magnetic field. Presumably, Alfven wave is generated by the magnetic laminar mechanism of collisionless interaction between laser plasma cloud and background. The right-hand polarized high-frequency whistler predictor was registered which have been propagating before Alfven wave at 300 km/s velocity. The polarization direction changed with Alfven wave coming. Features of a slow magnetosonic wave as a sudden change in background plasma concentration along with simultaneous displacement of the external magnetic field were found. The disturbance propagates at ~20-30 km/s velocity, which is close to that of ion sound at low plasma beta value. From preliminary estimates, the disturbance transfers about 10 % of the original energy of laser plasma.
Vlasov simulations of Kinetic Alfv\\'en Waves at proton kinetic scales
Vasconez, C L; Camporeale, E; Veltri, P
2014-01-01
Kinetic Alfv\\'en waves represent an important subject in space plasma physics, since they are thought to play a crucial role in the development of the turbulent energy cascade in the solar wind plasma at short wavelengths (of the order of the proton inertial length $d_p$ and beyond). A full understanding of the physical mechanisms which govern the kinetic plasma dynamics at these scales can provide important clues on the problem of the turbulent dissipation and heating in collisionless systems. In this paper, hybrid Vlasov-Maxwell simulations are employed to analyze in detail the features of the kinetic Alfv\\'en waves at proton kinetic scales, in typical conditions of the solar wind environment. In particular, linear and nonlinear regimes of propagation of these fluctuations have been investigated in a single-wave situation, focusing on the physical processes of collisionless Landau damping and wave-particle resonant interaction. Interestingly, since for wavelengths close to $d_p$ and proton plasma beta $\\bet...
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Klein, R I; Li, P S; McKee, C F; Fisher, R
2008-04-10
Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256{sup 3} and 512{sup 3} simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li et al. (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.
Kinetic Alfv\\'{e}n solitary and rogue waves in superthermal plasmas
Bains, A; Xia, L -D
2014-01-01
We investigate the small but finite amplitude solitary Kinetic Alfv\\'{e}n waves (KAWs) in low $\\beta$ plasmas with superthermal electrons modeled by a kappa-type distribution. A nonlinear Korteweg-de Vries (KdV) equation describing the evolution of KAWs is derived by using the standard reductive perturbation method. Examining the dependence of the nonlinear and dispersion coefficients of the KdV equation on the superthermal parameter $\\kappa$, plasma $\\beta$ and obliqueness of propagation, we show that these parameters may change substantially the shape and size of solitary KAW pulses. Only sub-Alfv\\'enic, compressive solitons are supported. We then extend the study to examine kinetic Alfv\\'en rogue waves by deriving a nonlinear Schr\\"{o}dinger equation from {the KdV} equation. Rational solutions that form rogue wave envelopes are obtained. We examine how the behavior of rogue waves depends on the plasma parameters in question, finding that the rogue envelopes are lowered with increasing electron superthermal...
Observation of an MHD Alfv\\'en vortex in the slow solar wind
Roberts, Owen Wyn; Alexandrova, Olga; Li, Bo
2016-01-01
In the solar wind, magnetic field power spectra usually show several power-laws. In this paper, magnetic field data from the Cluster mission during an undisturbed interval of slow solar wind is analyzed at 0.28Hz, near the spectral break point between the ion inertial and dissipation/dispersion ranges. Assuming Taylor's frozen-in condition, it corresponds to a proton kinetic scale of $kv_A/\\Omega_p \\sim 0.38$, where $v_A$ and $\\Omega_p$ are the Alfv\\'en speed and proton angular gyrofrequency, respectively. Data show that the Cluster spacecraft passed through a series of wavepackets. A strong isolated wavepacket is found to be in accordance with the four Cluster satellites crossing an Alfv\\'en vortex, a nonlinear solution to the incompressible MHD equations. A strong agreement is seen between the data from four satellites and a model vortex with a radius of the order of $40$ times the local proton gyro-radii. The polarization at different spacecraft is compared and is found to agree with the vortex model, wher...
The role of Alfv\\'en wave heating in solar prominences
Soler, Roberto; Oliver, Ramon; Ballester, Jose Luis
2016-01-01
Observations have shown that magnetohydrodynamic waves over a large frequency range are ubiquitous in solar prominences. The waves are probably driven by photospheric motions and may transport energy up to prominences suspended in the corona. Dissipation of wave energy can lead to heating of the cool prominence plasma, so contributing to the local energy balance within the prominence. Here we discuss the role of Alfv\\'en wave dissipation as a heating mechanism for the prominence plasma. We consider a slab-like quiescent prominence model with a transverse magnetic field embedded in the solar corona. The prominence medium is modelled as a partially ionized plasma composed of a charged ion-electron single fluid and two separate neutral fluids corresponding to neutral hydrogen and neutral helium. Friction between the three fluids acts as a dissipative mechanism for the waves. The heating caused by externally-driven Alfv\\'en waves incident on the prominence slab is analytically explored. We find that the dense pro...
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Li, Pak Shing; Klein, Richard I; Fisher, Robert T
2008-01-01
Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256^3 and 512^3 simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li, McKee, & Klein (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectr...
Smith, David R.; Fonck, R. J.; McKee, G. R.; Diallo, A.; Kaye, S. M.; Leblanc, B. P.; Sabbagh, S. A.
2016-10-01
Edge localized mode (ELM) saturation mechanisms, filament dynamics, and multi-mode interactions require nonlinear models, and validation of nonlinear ELM models requires fast, localized measurements on Alfven timescales. Recently, we investigated characteristic ELM evolution patterns with Alfven-scale measurements from the NSTX/NSTX-U beam emission spectroscopy (BES) system. We applied clustering algorithms from the machine learning domain to ELM time-series data. The algorithms identified two or three groups of ELM events with distinct evolution patterns. In addition, we found that the identified ELM groups correspond to distinct parameter regimes for plasma current, shape, magnetic balance, and density pedestal profile. The observed characteristic evolution patterns and corresponding parameter regimes suggest genuine variation in the underlying physical mechanisms that influence the evolution of ELM events and motivate nonlinear MHD simulations. Here, we review the previous results for characteristic ELM evolution patterns and parameter regimes, and we report on a new effort to explore the identified ELM groups with 2D BES measurements and nonlinear MHD simulations. Supported by U.S. Department of Energy Award Numbers DE-SC0001288 and DE-AC02-09CH11466.
Burgulence and Alfv\\'en waves heating mechanism of solar corona
Mishonov, T M
2006-01-01
Heating of magnetized turbulent plasma is calculated in the framework of Burgers turbulence [A.M. Polyakov, Phys. Rev. E. 52, 6183, (1995)]. There is calculated the energy flux of Alfv\\'en waves along the magnetic field. The Alfven waves are considered as intermediary between the turbulent energy and the heat. The derived results are related to wave channel of the heating of solar corona. After incorporating dissipation of convective plasma waves instabilities [G.D. Chagelishvili, R.G. Chanishvili, T.S. Hristov, and J.G. Lominadze, Phys. Rev. E 47, 366 (1993)] and [A.D. Rogava, S.M. Mahajan, G. Bodo, and S. Marsaglia, Astronomy & Astrophysics, 399, 421-431 (2003)] the suggested model of heating can be applied to analysis of the missing viscosity of accretion discs and to reveal why the quasars are the most powerful sources of light in the universe. We suppose that applied Langevin-Burgers approach to turbulence can be helpful for other systems where we have intensive interaction between a stochastic turbu...
Goossens, Marcel; Hollweg, Joseph V.
1993-01-01
Resonant absorption of MHD waves on a nonuniform flux tube is investigated as a driven problem for a 1D cylindrical equilibrium. The variation of the fractional absorption is studied as a function of the frequency and its relation to the eigenvalue problem of the MHD radiating eigenmodes of the nonuniform flux tube is established. The optimal frequencies producing maximal fractional absorption are determined and the condition for total absorption is obtained. This condition defines an impedance matching and is fulfilled for an equilibrium that is fine tuned with respect to the incoming wave. The variation of the spatial wave solutions with respect to the frequency is explained as due to the variation of the real and imaginary parts of the dispersion relation of the MHD radiating eigenmodes with respect to the real driving frequency.
Ctyroký, Jirí; Richter, Ivan; Kwiecien, Pavel
2008-06-01
The performance of three bidirectional modal methods the "classical" bidirectional eigenmode expansion propagation method, the aperiodic rigorous coupled wave analysis (known also as the Fourier modal method), and the mode expansion method based on harmonic expansion are mutually compared using modeling tasks that include eigenmode calculation of a relatively high-contrast planar waveguide, spectral transmittance of a one-dimensional "photonic crystal" filter in a photonic wire, spectral transmittance of a surface plasmon based optical sensor, and a reflectance from a double-groove structure in a high-contrast waveguide. All methods exhibit generally comparable performance, as follows from good mutual agreement of the results and generally comparable computational time. Although all methods use perfectly matched layers as absorbing boundary conditions, their implementation in the aperiodic rigorous coupled wave analysis exhibits significantly stronger attenuation than that used in the other two methods. Thus, significant improvement of the latter methods seems possible.
Sensitivity of alpha-particle-driven Alfvén eigenmodes to q-profile variation in ITER scenarios
Rodrigues, P.; Figueiredo, A. C. A.; Borba, D.; Coelho, R.; Fazendeiro, L.; Ferreira, J.; Loureiro, N. F.; Nabais, F.; Pinches, S. D.; Polevoi, A. R.; Sharapov, S. E.
2016-11-01
A perturbative hybrid ideal-MHD/drift-kinetic approach to assess the stability of alpha-particle-driven Alfvén eigenmodes in burning plasmas is used to show that certain foreseen ITER scenarios, namely the {{I}\\text{p}}=15 MA baseline scenario with very low and broad core magnetic shear, are sensitive to small changes in the background magnetic equilibrium. Slight variations (of the order of 1% ) of the safety-factor value on axis are seen to cause large changes in the growth rate, toroidal mode number, and radial location of the most unstable eigenmodes found. The observed sensitivity is shown to proceed from the very low magnetic shear values attained throughout the plasma core, raising issues about reliable predictions of alpha-particle transport in burning plasmas.
Dokgo, Kyunghwan; Woo, Minho; Choi, Cheong-Rim; Min, Kyoung-Wook; Hwang, Junga
2016-09-01
Generation of coherent ion acoustic solitary waves (IASWs) in inhomogeneous plasmas by an odd eigenmode (OEM) of electron holes (EHs) is investigated using 1D electrostatic particle-in-cell (PIC) simulations. The OEM oscillates at a frequency comparable to the trapped electron bouncing frequency, as also demonstrated by Lewis' theoretical formalism about the linear eigenmode in Bernstein-Greene-Kruskal (BGK) equilibrium. The density gradient in the inhomogeneous plasmas causes asymmetry in the EH potential structure associated with the OEM, whose amplitude grows rapidly as it propagates through the density gradient region. As the ions interact with this asymmetric potential, which oscillates slowly enough for the ions to respond, they are ejected to the lower density side with a larger potential amplitude, forming a chain of IASWs coherently with the oscillation of the OEM.
Observations of a Pc5 global (cavity/waveguide) mode outside the plasmasphere by THEMIS
Hartinger, Michael; Angelopoulos, Vassilis; Moldwin, Mark B.
2012-01-01
Standing fast mode waves known as global modes, or cavity/waveguide modes, have been extensively studied as a potential driver of monochromatic shear Alfven waves in the Earth's magnetosphere via the field line resonance (FLR) mechanism. However, their existence outside of the plasmasphere remain...
Figueiredo, A. C. A.; Rodrigues, P.; Borba, D.; Coelho, R.; Fazendeiro, L.; Ferreira, J.; Loureiro, N. F.; Nabais, F.; Pinches, S. D.; Polevoi, A. R.; Sharapov, S. E.
2016-07-01
The linear stability of Alfvén eigenmodes in the presence of fusion-born alpha particles is thoroughly assessed for two variants of an ITER baseline scenario, which differ significantly in their core and pedestal temperatures. A systematic approach based on CASTOR-K (Borba and Kerner 1999 J. Comput. Phys. 153 101; Nabais et al 2015 Plasma Sci. Technol. 17 89) is used that considers all possible eigenmodes for a given magnetic equilibrium and determines their growth rates due to alpha-particle drive and Landau damping on fuel ions, helium ashes and electrons. It is found that the fastest growing instabilities in the aforementioned ITER scenario are core-localized, low-shear toroidal Alfvén eigenmodes. The largest growth-rates occur in the scenario variant with higher core temperatures, which has the highest alpha-particle density and density gradient, for eigenmodes with toroidal mode numbers n≈ 30 . Although these eigenmodes suffer significant radiative damping, which is also evaluated, their growth rates remain larger than those of the most unstable eigenmodes found in the variant of the ITER baseline scenario with lower core temperatures, which have n≈ 15 and are not affected by radiative damping.
Kotov, V. M.; Averin, S. V.; Kuznetsov, P. I.; Kotov, E. V.
2017-07-01
A method is proposed for two-dimensional spatial frequency filtration based on acousto-optic (AO) diffraction of two eigenmodes of a crystal on a single acoustic wave. It is shown that AO filters, based on the use of such diffraction, ensure the enhancement of the two-dimensional image edge during its optical Fourier processing. The main theoretical conclusions are experimentally confirmed using an AO paratellurite filter.
Nonlinear reflection process of linearly-polarized, broadband Alfv\\'en waves in the fast solar wind
Shoda, Munehito
2016-01-01
Using one-dimensional numerical simulations, we study the elementary process of Alfv\\'{e}n wave reflection in a uniform medium, including nonlinear effects. In the linear regime, Alfv\\'{e}n wave reflection is triggered only by the inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via nonlinear wave-wave interactions. Such nonlinear reflection (backscattering) is typified by decay instability. In most studies of decay instabilities, the initial condition has been a circularly polarized Alfv\\'{e}n wave. In this study we consider a linearly polarized Alfv\\'en wave, which drives density fluctuations by its magnetic pressure force. For generality, we also assume a broadband wave with a red-noise spectrum. In the data analysis, we decompose the fluctuations into characteristic variables using local eigenvectors, thus revealing the behaviors of the individual modes. Different from circular-polarization case, we find that the wave steepening produces a new energy channel from the parent Alfv\\...
Valentini, F; Pezzi, O; Servidio, S; Malara, F; Pucci, F
2016-01-01
Space plasmas are dominated by the presence of large-amplitude waves, large-scale inhomogeneities, kinetic effects and turbulence. Beside the homogeneous turbulence, generation of small scale fluctuations can take place also in other realistic configurations, namely, when perturbations superpose to an inhomogeneous background magnetic field. When an Alfv\\'en wave propagates in a medium where the Alfv\\'en speed varies in a direction transverse to the mean field, it undergoes phase-mixing, which progressively bends wavefronts, generating small scales in the transverse direction. As soon as transverse scales get of the order of the proton inertial length $d_p$, kinetic Alfv\\'en waves (KAWs) are naturally generated. KAWs belong to the branch of Alfv\\'en waves and propagate nearly perpendicular to the ambient magnetic field, at scales close to $d_p$. Many numerical, observational and theoretical works have suggested that these fluctuations may play a determinant role in the development of the solar-wind turbulent ...
Prompers, J J; Brüschweiler, R
2001-08-01
An approach is presented for the interpretation of heteronuclear NMR spin relaxation data in mobile protein parts in terms of reorientational eigenmode dynamics. The method is based on the covariance matrix of the spatial functions of the nuclear spin interactions that cause relaxation expressed as spherical harmonics of rank 2. The approach was applied to characterize the dynamics of a loop region of ubiquitin. The covariance matrix was determined from a conformational ensemble generated by a 5 ns molecular dynamics simulation. It was found that the time correlation functions of the dominant eigenmodes decay in good approximation with a single correlation time. From the reorientational eigenmodes, their eigenvalues, and correlation times, NMR relaxation data were calculated in accordance with Bloch-Wangsness-Redfield relaxation theory and directly compared with experimental (15)N relaxation parameters. Using a fitting procedure, agreement between calculated and experimental data was improved significantly by adjusting eigenvalues and correlation times of the dominant modes. The presented procedure provides detailed information on correlated reorientational dynamics of flexible parts in globular proteins. The covariance matrix was linked to the covariance matrix of backbone dihedral angle fluctuations, allowing one to study the motional behavior of these degrees of freedom on nano- and subnanosecond time scales.
Effects of near-zero Dirac eigenmodes on axial U(1) symmetry at finite temperature
Tomiya, Akio; Fukaya, Hidenori; Hashimoto, Shoji; Noaki, Junichi
2014-01-01
We study the axial U(1)A symmetry of Nf = 2 QCD at finite temperature using the Dirac eigenvalue spectrum. The gauge configurations are generated employing the Mobius domain-wall fermion action on 16^3x8 and 32^3x8 lattices. The physical spatial size of these lattices is around 2 fm and 4 fm, respectively, and the simulated temperature is around 200 MeV, which is slightly above the critical temperature of the chiral phase transition. Although the Mobius domain-wall Dirac operator is expected to have a good chiral symmetry and our data actually show small values of the residual mass, we observe significant violation of the Ginsparg-Wilson relation for the low- lying eigenmodes of the Mobius domain-wall Dirac operator. Using the reweighting technique, we compute the overlap-Dirac operator spectrum on the same set of configurations and find a significant difference of the spectrum between the two Dirac operators for the low-lying eigenvalues. The overlap-Dirac spectrum shows a gap from zero, which is insensitive...
Butet, Jérémy; Dutta-Gupta, Shourya; Martin, Olivier J. F.
2014-06-01
The surface second-harmonic generation from interacting spherical plasmonic nanoparticles building different clusters (symmetric and asymmetric dimers, trimers) is theoretically investigated. The plasmonic eigenmodes of the nanoparticle clusters are first determined using an ab initio approach based on the Green's functions method. This method provides the properties, such as the resonant wavelengths, of the modes sustained by a given cluster. The fundamental and second-harmonic responses of the corresponding clusters are then calculated using a surface integral method. The symmetry of both the linear and nonlinear responses is investigated, as well as their relationship. It is shown that the second-harmonic generation can be significantly enhanced when the fundamental field is such that its second harmonic matches modes with suitable symmetry. The role played by the nanogaps in second-harmonic generation is also underlined. The results presented in this article demonstrate that the properties of the second-harmonic generation from coupled metallic nanoparticles cannot be fully predicted from their linear response only, while, on the other hand, a detailed knowledge of the underlying modal structure can be used to optimize the generation of the second harmonic.
Sundararajan, Jency Pricilla; Bakharev, Pavel; Niraula, Ishwar; Kengne, Blaise Alexis Fouetio; MacPherson, Quinn; Sargent, Meredith; Hare, Brian; McIlroy, David N
2012-10-10
The photocurrent of individual gallium nitride (GaN) nanowires decorated with Au nanoparticles as function of the wavelength of light (405 nm (blue), 532 nm (green), and 632.8 nm (red)) and nanowire diameter (80 to 400 nm) is reported. The photocurrent scales with photon energy but oscillates with nanowire diameter. The oscillations are described in terms of the scattering of surface plasmon polaritons into allowed transverse magnetic electromagnetic modes of the nanowire that have maximum intensities in the undepleted region of the nanowire. These oscillations do not occur below a nanowire diameter of ~200 nm due to the depletion layer formed at the Au-GaN interface, which completely depletes the nanowire, that is, there is an insufficient density of carriers that can be excited into the conduction band. On the basis of estimations of the depletion depth and solutions of the Helmholtz equation, the maxima in the photocurrent for d > 200 nm are assigned to the two lowest azimuthally symmetric transverse magnetic eigenmodes: (m = 0, n = 1) and (m = 0, n = 2), which have maximum electric field intensities within the undepleted region of the GaN nanowire. The outcome of this work could have far reaching implications on the development of nanophotonics.
EIGENMODES OF THREE-DIMENSIONAL MAGNETIC ARCADES IN THE SUN’S CORONA
Hindman, Bradley W. [JILA, NIST and University of Colorado, Boulder, CO 80309-0440 (United States); Jain, Rekha, E-mail: hindman@solarz.colorado.edu [School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH (United Kingdom)
2015-12-01
We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger three-dimensional (3D) magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3D waveguide if the Alfvén speed increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade possessing a discontinuous density profile. The discontinuity separates a diffuse cylindrical cavity and an overlying shell of denser plasma that corresponds to the bright loops. We emphasize that all of the eigenfunctions have a discontinuous axial velocity at the density interface; hence, the interface can give rise to the Kelvin–Helmholtz instability. Further, we find that all modes have elliptical polarization with the degree of polarization changing with height. However, depending on the line of sight, only one polarization may be clearly visible.
Upper-hybrid wave driven Alfvenic turbulence in magnetized dusty plasmas
Misra, A P
2010-01-01
The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfven waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust impurities. A pair of nonlinear equations [J.Plasma Phys. 73, 3 (2006)] that describe the interaction of UH wave envelopes (including the relativistic electron mass increase) and the density as well as the compressional magnetic field perturbations associated with the AWs is solved numerically to show that many coherent solitary patterns can be excited and saturated due to modulational instability of unstable UH waves. The evolution of these solitary patterns is also shown to appear in the states of spatiotemporal coherence, temporal as well as spatiotemporal chaos due to collision and fusion among the patterns in stochastic motion. Furthermore, these spatiotemporal features are demonstrated by the analysis of wavelet power spectra. It is found that a redistribution of wave energy takes place to higher harmonic modes with small wavelengths which, in turn, ...
MHD-kinetic transition in imbalanced Alfv$\\'{e}$nic turbulence
Voitenko, Yuriy
2016-01-01
Alfvenic turbulence in space is usually imbalanced: amplitudes of waves propagating parallel and anti-parallel to the mean magnetic field $B_0$ are unequal. It is commonly accepted that the turbulence is driven by (counter-) collisions between these counter-propagating wave fractions. Contrary to this, we found a new ion-scale dynamical range of the turbulence established by (co-) collisions among waves co-propagating in the same direction along $B_0$. The turbulent cascade is accelerated there and power spectra are steep and non-universal. The spectral indexes vary around -3 (-4) in the strong (weak) turbulence, such that steeper spectra follow larger imbalances. Intermittency steepens spectra further, up to -3.7 (-4.5). Our theoretical predictions are compatible with steep variable spectra observed in the solar wind at ion kinetic scales.
The Heating of Test Particles in Numerical Simulations of Alfvenic Turbulence
Lehe, Remi; Quataert, Eliot
2009-01-01
We study the heating of charged test particles in three-dimensional numerical simulations of weakly compressible magnetohydrodynamic (MHD) turbulence (``Alfvenic turbulence''); these results are relevant to particle heating and acceleration in the solar wind, solar flares, accretion disks onto black holes, and other astrophysics and heliospheric environments. The physics of particle heating depends on whether the gyrofrequency of a particle is comparable to the frequency of a turbulent fluctuation that is resolved on the computational domain. Particles with these frequencies nearly equal undergo strong perpendicular heating (relative to the local magnetic field) and pitch angle scattering. By contrast, particles with large gyrofrequency undergo strong parallel heating. Simulations with a finite resistivity produce additional parallel heating due to parallel electric fields in small-scale current sheets. Many of our results are consistent with linear theory predictions for the particle heating produced by the ...
Plasma acceleration by the interaction of parallel propagating Alfv\\'en waves
Mottez, Fabrice
2014-01-01
It is shown that two circularly polarised Alfv\\'en waves that propagate along the ambient magnetic field in an uniform plasma trigger non oscillating electromagnetic field components when they cross each other. The non-oscilliating field components can accelerate ions and electrons with great efficiency. This work is based on particle-in-cell (PIC) numerical simulations and on analytical non-linear computations. The analytical computations are done for two counter-propagating monochromatic waves. The simulations are done with monochromatic waves and with wave packets. The simulations show parallel electromagnetic fields consistent with the theory, and they show that the particle acceleration result in plasma cavities and, if the waves amplitudes are high enough, in ion beams. These acceleration processes could be relevant in space plasmas. For instance, they could be at work in the auroral zone and in the radiation belts of the Earth magnetosphere. In particular, they may explain the origin of the deep plasma...
Kinetic Alfv\\'{e}n turbulence below and above ion-cyclotron frequency
Zhao, J S; Wu, D J; Yu, M Y
2015-01-01
Alfv\\'{e}nic turbulent cascade perpendicular and parallel to the background magnetic field is studied accounting for anisotropic dispersive effects and turbulent intermittency. The perpendicular dispersion and intermittency make the perpendicular-wavenumber magnetic spectra steeper and speed up production of high ion-cyclotron frequencies by the turbulent cascade. On the contrary, the parallel dispersion makes the spectra flatter and decelerate the frequency cascade above the ion-cyclotron frequency. Competition of the above factors results in spectral indices distributed in the interval [-2,-3], where -2 is the index of high-frequency space-filling turbulence, and -3 is the index of low-frequency intermittent turbulence formed by tube-like fluctuations. Spectra of fully intermittent turbulence fill a narrower range of spectral indices [-7/3,-3], which almost coincides with the range of indexes measured in the solar wind. This suggests that the kinetic-scale turbulent spectra are shaped mainly by dispersion a...
The Structure of Plasma Heating in Gyrokinetic Alfv\\'enic Turbulence
Navarro, A B; Told, D; Groselj, D; Crandall, P; Jenko, F
2016-01-01
We analyze plasma heating in weakly collisional kinetic Alfv\\'en wave (KAW) turbulence using high resolution gyrokinetic simulations spanning the range of scales between the ion and the electron gyroradii. Real space structures that have a higher than average heating rate are shown not to be confined to current sheets. This novel result is at odds with previous studies, which use the electromagnetic work in the local electron fluid frame, i.e. $\\mathbf{J} \\!\\cdot\\! (\\mathbf{E} + \\mathbf{v}_e\\times\\mathbf{B})$, as a proxy for turbulent dissipation to argue that heating follows the intermittent spatial structure of the electric current. Furthermore, we show that electrons are dominated by parallel heating while the ions prefer the perpendicular heating route. We comment on the implications of the results presented here.
Resonant Alfven waves in partially ionized plasmas of the solar atmosphere
Soler, R; Goossens, M
2011-01-01
Context. Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. In magnetic waveguides resonant absorption due to plasma inhomogeneity naturally transfers wave energy from large-scale motions to small-scale motions. In the cooler parts of the solar atmosphere as, e.g., the chromosphere, effects due to partial ionization may be relevant for wave dynamics and heating. Aims. We study resonant Alfven waves in partially ionized plasmas. Methods. We use the multifluid equations in the cold plasma approximation. We investigate propagating resonant MHD waves in partially ionized flux tubes. We use approximate analytical theory based on normal modes in the thin tube and thin boundary approximations along with numerical eigenvalue computations. Results. We find that the jumps of the wave perturbations across the resonant layer are the same as in fully ionized plasmas. The damping length due to resonant absorption is inversely proportional to the frequency, while that due to ion-neutral collisions is in...
Goodman, Michael L
2014-01-01
A magnetohydrodynamic model that includes a complete electrical conductivity tensor is used to estimate conditions for photospherically driven, linear, non-plane Alfvenic oscillations extending from the photosphere to the lower corona to drive a chromospheric heating rate due to Pedersen current dissipation that is comparable to the net chromospheric net radiative loss of $\\sim 10^7$ ergs-cm$^{-2}$-sec$^{-1}$. The heating rates due to electron current dissipation in the photosphere and corona are also computed. The wave amplitudes are computed self-consistently as functions of an inhomogeneous background (BG) atmosphere. The effects of the conductivity tensor are resolved numerically using a resolution of 3.33 m. The oscillations drive a chromospheric heating flux $F_{Ch} \\sim 10^7 - 10^8$ ergs-cm$^{-2}$-sec$^{-1}$ at frequencies $\
Parametric decay of parallel and oblique Alfven waves in the expanding solar wind
Del Zanna, L; Landi, S; Verdini, A; Velli, M
2014-01-01
The long-term evolution of large-amplitude Alfven waves propagating in the solar wind is investigated by performing two-dimensional MHD simulations within the expanding box model. The linear and nonlinear phases of the parametric decay instability are studied for both circularly polarized waves in parallel propagation and for arc-polarized waves in oblique propagation. The non-monochromatic case is also considered. In the oblique case, the direct excitation of daughter modes transverse to the local background field is found for the first time in an expanding environment, and this transverse cascade seems to be favored for monochromatic mother waves. The expansion effect reduces the instability growth rate, and it can even suppress its onset for the lowest frequency modes considered here, possibly explaining the persistence of these outgoing waves in the solar wind.
Solitary Kinetic Alfven Waves in a Low-β Dusty Plasma
CHEN Yin-Hua; LU Wei
2000-01-01
The nonlinear kinetic Alfven waves in a low-β(0<β<1)dusty plasma have been investigated with the fluid model of three-component plasma. The nonlinear equation governing the perturbation density of electrons in a form of the energy integral has been derived. In the approximation of small amplitude, the soliton solution for the perturbation density of electrons is found, and the characteristics of solitons in different range of plasma parameters is studied numerically. The results show that the density dip or hump can be formed in a dusty plasma for different ranges of parameters, the amplitude of density dip is enhanced and the amplitude of density hump is reduced with increasing dust grain content.
Focusing of Alfvenic wave power in the context of gamma-ray burst emissivity
Fatuzzo, Marco; Melia, Fulvio
1993-01-01
Highly dynamic magnetospheric perturbations in neutron star environments can naturally account for the features observed in gamma-ray burst spectra. The source distribution, however, appears to be extragalactic. Although noncatastrophic isotropic emission mechanisms may be ruled out on energetic and timing arguments, MHD processes can produce strongly anisotropic gamma rays with an observable flux out to distances of about 1-2 Gpc. Here we show that sheared Alfven waves propagating along open magnetospheric field lines at the poles of magnetized neutron stars transfer their energy dissipationally to the current sustaining the field misalignment and thereby focus their power into a spatial region about 1000 times smaller than that of the crustal disturbance. This produces a strong (observable) flux enhancement along certain directions. We apply this model to a source population of 'turned-off' pulsars that have nonetheless retained their strong magnetic fields and have achieved alignment at a period of approximately greater than 5 sec.
Entanglement of helicity and energy in kinetic Alfven wave/whistler turbulence
Galtier, S
2014-01-01
The role of magnetic helicity is investigated in kinetic Alfv\\'en wave and oblique whistler turbulence in presence of a relatively intense external magnetic field $b_0 {\\bf e_\\parallel}$. In this situation, turbulence is strongly anisotropic and the fluid equations describing both regimes are the reduced electron magnetohydrodynamics (REMHD) whose derivation, originally made from the gyrokinetic theory, is also obtained here from compressible Hall MHD. We use the asymptotic equations derived by Galtier \\& Bhattacharjee (2003) to study the REMHD dynamics in the weak turbulence regime. The analysis is focused on the magnetic helicity equation for which we obtain the exact solutions: they correspond to the entanglement relation, $n+\\tilde n = -6$, where $n$ and $\\tilde n$ are the power law indices of the perpendicular (to ${\\bf b_0}$) wave number magnetic energy and helicity spectra respectively. Therefore, the spectra derived in the past from the energy equation only, namely $n=-2.5$ and $\\tilde n = - 3.5$,...
Control of the higher eigenmodes of a microcantilever: Applications in atomic force microscopy
Karvinen, K.S., E-mail: kai.karvinen@uon.edu.au; Moheimani, S.O.R.
2014-02-01
While conventional techniques in dynamic mode atomic force microscopy typically involve the excitation of the first flexural mode of a microcantilever, situations arise where the excitation of higher modes may result in image artefacts. Strong nonlinear coupling between the cantilever modes in liquid environments may result in image artefacts, limiting the accuracy of the image. Similar observations have been made in high-speed contact mode AFM. To address this issue, we propose the application of the modulated–demodulated control technique to attenuate problematic modes to eliminate the image artefacts. The modulated–demodulated control technique is a high-bandwidth technique, which is well suited to the control of next generation of high-speed cantilevers. In addition to potential improvements in image quality, a high-bandwidth controller may also find application in multifrequency AFM experiments. To demonstrate the high-bandwidth nature of the control technique, we construct an amplitude modulation AFM experiment in air utilizing low amplitude setpoints, which ensures that harmonic generation and nonlinear coupling of the modes result in image artefacts. We then utilize feedback control to highlight the improvement in image quality. Such a control technique appears extremely promising in high-speed atomic force microscopy and is likely to have direct application in AFM in liquids. - Highlights: • The excitation of higher eigenmodes can potentially affect the estimated surface topography resulting in image artefacts. • We demonstrated the application of modulated–demodulated control and elimination of image artefacts resulting from the coupling of two modes. • Modulated–demodulated control is well suited to the control of high-frequency resonant dynamics and may find application in liquid/multifrequency AFM experiments.
Active and Fast Particle Driven Alfvén Eigenmodes in Alcator C-Mod
Snipes, Joseph
2004-11-01
Alfvén eigenmodes (AEs) are studied in Alcator C-Mod to assess their stability in high density reactor relevant regimes where Te ≈ Ti and as a diagnostic tool. Stable AEs are excited in Ohmic plasmas by driving a plasma resonance with (3 - 7 kW) active MHD antennas in the range of the expected AE frequency. The antennas excite a wide toroidal mode spectrum with observed modes between 4 MW) with electron densities in the range of bar ne = 0.5 - 2 × 10^20 m-3. In the current rise phase, low midnmid = 1 - 3 unstable modes are observed with magnetic pick-up coils to rotate in the ion diamagnetic drift direction with frequencies that increase rapidly with time. Phase Contrast Imaging (PCI) density fluctuation measurements, instead, show similar modes at the same time but with frequencies changing more rapidly in time. Similar modes on JET, known as Alfvén Cascades (ACs), have the slope of the frequency change in time proportional to midnmid. This indicates that the PCI on C-Mod is more sensitive to higher order modes in the plasma core. Modeling of the ACs constrains the calculated q profile to be very flat with perhaps slightly reversed shear at q_min = 3. By varying the toroidal field, ACs were found to be more stable for an inboard ICRF resonance than for an outboard resonance. In the flattop, energetic particle modes (EPMs) and TAEs have also been observed to decrease in frequency and mode number with time up to a monster sawtooth collapse, indicating the role fast particles play in stabilizing sawteeth. Modeling of these sawtooth-related TAEs indicates a broad radial structure peaked well outside the q=1 surface with midnmid = 5 - 11 and multiple poloidal modes numbers.
Resonant-state-expansion Born approximation with a correct eigen-mode normalisation
Doost, M. B.
2016-08-01
The Born approximation (Born 1926 Z. Phys. 38 802) is a fundamental result in physics, it allows the calculation of weak scattering via the Fourier transform of the scattering potential. As was done by previous authors (Ge et al 2014 New J. Phys. 16 113048) the Born approximation is extended by including in the formula the resonant-states (RSs) of the scatterer. However in this study unlike previous studies the included eigen-modes are correctly normalised with dramatic positive consequences for the accuracy of the method. The normalisation of RSs used in the previous RS expansion Born approximation or resonant-state expansion (RSE) Born approximation made in Ge et al (2014 New J. Phys. 16 113048) has been shown to be numerically unstable in Muljarov et al (2014 arXiv:1409.6877) and by analytics here. The RSs of the system can be calculated using my recently discovered RSE perturbation theory for dispersive electrodynamic scatterers (Muljarov et al 2010 Europhys. Lett. 92 50010; Doost et al 2012 Phys. Rev. A 85 023835; Doost et al 2013 Phys. Rev. A 87 043827; Armitage et al 2014 Phys. Rev. A 89; Doost et al 2014 Phys. Rev. A 90 013834) and normalised correctly to appear in spectral Green's functions and hence the RSE Born approximation via the flux-volume normalisation which I recently rigorously derived in Armitage et al (2014 Phys. Rev. A 89), Doost et al (2014 Phys. Rev. A 90 013834), Doost (2016 Phys. Rev. A 93 023835). In the case of effectively one-dimensional systems I find a RSE Born approximation alternative to the scattering matrix method.
Badawi, Ahmed M.; Weiss, Elisabeth; Sleeman, William C., IV; Hugo, Geoffrey D.
2012-01-01
The purpose of this study is to develop and evaluate a lung tumour interfraction geometric variability classification scheme as a means to guide adaptive radiotherapy and improve measurement of treatment response. Principal component analysis (PCA) was used to generate statistical shape models of the gross tumour volume (GTV) for 12 patients with weekly breath hold CT scans. Each eigenmode of the PCA model was classified as ‘trending’ or ‘non-trending’ depending on whether its contribution to the overall GTV variability included a time trend over the treatment course. Trending eigenmodes were used to reconstruct the original semi-automatically delineated GTVs into a reduced model containing only time trends. Reduced models were compared to the original GTVs by analyzing the reconstruction error in the GTV and position. Both retrospective (all weekly images) and prospective (only the first four weekly images) were evaluated. The average volume difference from the original GTV was 4.3% ± 2.4% for the trending model. The positional variability of the GTV over the treatment course, as measured by the standard deviation of the GTV centroid, was 1.9 ± 1.4 mm for the original GTVs, which was reduced to 1.2 ± 0.6 mm for the trending-only model. In 3/13 cases, the dominant eigenmode changed class between the prospective and retrospective models. The trending-only model preserved GTV and shape relative to the original GTVs, while reducing spurious positional variability. The classification scheme appears feasible for separating types of geometric variability by time trend.
Mithaiwala, Manish; Crabtree, Chris; Ganguli, Gurudas
2012-01-01
It is shown that the dispersion relation for whistler waves is identical for a high or low beta plasma. Furthermore in the high-beta solar wind plasma whistler waves meet the Landau resonance with electrons for velocities less than the thermal speed, and consequently the electric force is small compared to the mirror force. As whistlers propagate through the inhomogeneous solar wind, the perpendicular wave number increases through refraction, increasing the Landau damping rate. However, the whistlers can survive because the background kinetic Alfven wave turbulence creates a plateau by quasilinear diffusion in the solar wind electron distribution at small velocities. It is found that for whistler energy density of only ~10^-3 that of the kinetic Alfven waves, the quasilinear diffusion rate due to whistlers is comparable to KAW. Thus very small amplitude whistler turbulence can have a significant consequence on the evolution of the solar wind electron distribution function.
Clack, C T M; Douglas, M
2010-01-01
Resonant absorption of fast magnetoacoustic (FMA) waves in an inhomogeneous, weakly dissipative, one-dimensional planar, strongly anisotropic and dispersive plasma is investigated. The magnetic configuration consists of an inhomogeneous magnetic slab sandwiched between two regions of semi-infinite homogeneous magnetic plasmas. Laterally driven FMA waves penetrate the inhomogeneous slab interacting with the localised slow or Alfven waves present in the inhomogeneous layer and are partly reflected, dissipated and transmitted by this region. The presented research aims to find the coefficient of wave energy absorption under solar chromospheric and coronal conditions. Numerical results are analyzed to find the coefficient of wave energy absorption at both the slow and Alfven resonance positions. The mathematical derivations are based on the two simplifying assumptions that (i) nonlinearity is weak, and (ii) the thickness of the inhomogeneous layer is small in comparison to the wavelength of the wave, i.e. we empl...
Smirnov, V. N.; Avanov, L. A.; Waite, J.; Fuselier, S.; Vaisberg, O. L.; Six, N. Frank (Technical Monitor)
2002-01-01
The Interball/Tail spacecraft crossed the high latitude magnetopause near the cusp region under stable northward IMF conditions on 29 May 1996, with magnetic local time and magnetic latitude approx. 7.3 hours, approx. 65.4 degrees, respectively. The Interball Tail spacecraft observed quasi-steady reconnection and a relatively stable reconnection site at high latitudes. Observed sunward plasma flow and tangential stress balance indicated that reconnection occurred poleward of the magnetic cusp, above the spacecraft location. The spacecraft observed sub-alfvenic flow in the magnetosheath region adjacent to the magnetopause current layer near the reconnection site indicating that the reconnection site may have moved in the sunward direction. These observations suggest that the region of sub-alfvenic flow and stable, quasi-steady reconnection extend to very high latitudes under northward IMF conditions which is not consistent with the gas dynamic model predictions.
Friedberg, Richard [Department of Physics, Columbia University, New York, NY 10027 (United States); Manassah, Jamal T., E-mail: jmanassah@gmail.co [Department of Electrical Engineering, City College of New York, NY 10031 (United States)
2010-07-26
We explore steady states of an open, no end-mirrors, low-Q cw laser pumped above the threshold for laser oscillations. We find that the spatial field profile of the steady state just above the threshold is the same as that of the eigenmode that dominates superradiance in the late linear regime from an initially inverted state without continued pumping. The threshold pumping rate and emission frequency are related to the real and imaginary parts of the eigenvalue of this dominant mode.
Fast ion induced shearing of 2D Alfvén eigenmodes measured by electron cyclotron emission imaging.
Tobias, B J; Classen, I G J; Domier, C W; Heidbrink, W W; Luhmann, N C; Nazikian, R; Park, H K; Spong, D A; Van Zeeland, M A
2011-02-18
Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfvén eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.
Role of Convective Cells in Nonlinear Interaction of Kinetic Alfven Waves
Luk, Onnie
The convective cells are observed in the auroral ionosphere and they could play an important role in the nonlinear interaction of Alfven waves and disrupt the kinetic Alfven wave (KAW) turbulence. Zonal fields, which are analogous to convective cells, are generated by microturbulence and regulate microturbulence inside toroidally confined plasmas. It is important to understand the role of convective cells in the nonlinear interaction of KAW leading to perpendicular cascade of spectral energy. A nonlinear gyrokinetic particle simulation has been developed to study the perpendicular spectral cascade of kinetic Alfven wave. However, convective cells were excluded in the study. In this thesis project, we have modified the formulation to implement the convective cells to study their role in the nonlinear interactions of KAW. This thesis contains detail description of the code formulation and convergence tests performed, and the simulation results on the role of convective cells in the nonlinear interactions of KAW. In the single KAW pump wave simulations, we observed the pump wave energy cascades to waves with shorter wavelengths, with three of them as dominant daughter waves. Convective cells are among those dominant daughter waves and they enhance the rate of energy transfer from pump to daughter waves. When zonal fields are present, the growth rates of the dominant daughter waves are doubled. The convective cell (zonal flow) of the zonal fields is shown to play a major role in the nonlinear wave interaction, while the linear zonal vector potential has little effects. The growth rates of the daughter waves linearly depends on the pump wave amplitude and the square of perpendicular wavenumber. On the other hand, the growth rates do not depend on the parallel wavenumber in the limit where the parallel wavenumber is much smaller than the perpendicular wavenumber. The nonlinear wave interactions with various perpendicular wavenumbers are also studied in this work. When
Roles of Fast-Cyclotron and Alfven-Cyclotron Waves for the Multi-Ion Solar Wind
Xiong, Ming
2012-01-01
Using linear Vlasov theory of plasma waves and quasi-linear theory of resonant wave-particle interaction, the dispersion relations and the electromagnetic field fluctuations of fast and Alfven waves are studied for a low-beta multi-ion plasma in the inner corona. Their probable roles in heating and accelerating the solar wind via Landau and cyclotron resonances are quantified. We assume that (1) low-frequency Alfven and fast waves have the same spectral shape and the same amplitude of power spectral density; (2) these waves eventually reach ion cyclotron frequencies due to a turbulence cascade; (3) kinetic wave-particle interaction powers the solar wind. The existence of alpha particles in a dominant proton/electron plasma can trigger linear mode conversion between oblique fast-whistler and hybrid alpha-proton cyclotron waves. The fast-cyclotron waves undergo both alpha and proton cyclotron resonances. The alpha cyclotron resonance in fast-cyclotron waves is much stronger than that in Alfven-cyclotron waves. ...
Simulation of fast-ion-driven Alfvén eigenmodes on the Experimental Advanced Superconducting Tokamak
Hu, Youjun; Todo, Y.; Pei, Youbin; Li, Guoqiang; Qian, Jinping; Xiang, Nong; Zhou, Deng; Ren, Qilong; Huang, Juan; Xu, Liqing
2016-02-01
Kinetic-MHD hybrid simulations are carried out to investigate possible fast-ion-driven modes on the Experimental Advanced Superconducting Tokamak. Three typical kinds of fast-ion-driven modes, namely, toroidicity-induced Alfvén eigenmodes, reversed shear Alfvén eigenmodes, and energetic-particle continuum modes, are observed simultaneously in the simulations. The simulation results are compared with the results of an ideal MHD eigenvalue code, which shows agreement with respect to the mode frequency, dominant poloidal mode numbers, and radial location. However, the modes in the hybrid simulations take a twisted structure on the poloidal plane, which is different from the results of the ideal MHD eigenvalue code. The twist is due to the radial phase variation of the eigenfunction, which may be attributed to the non-perturbative kinetic effects of the fast ions. By varying the stored energy of fast ions to change the fast ion drive in the simulations, it is demonstrated that the twist (i.e., the radial phase variation) is positively correlated with the fast ion drive.
Explaining Signatures of Auroral Arcs based on the Stationary Inertial Alfven Wave
Nogami, Sh; Koepke, Me; Knudsen, Dj; Gillies, Dm; Donovan, E.; Vincena, S.
2016-10-01
Optical emission data from the THEMIS array of All Sky Imagers are analyzed to determine the lifetime of an auroral arc (i.e., the elapsed time during which an arc is visible). Lifetime is an important temporal signature related to the arc generation mechanism, by which arcs can be distinguished. An arc with a lifetime greater than ten minutes is consistent with arc generation by Stationary Inertial Alfven Wave (StIAW) which supports a steady-state wave electric field component parallel to a background magnetic field. An StIAW is a non-fluctuating, non-travelling, spatially periodic pattern of perturbed ion density that is static in the laboratory frame. StIAWs are the predicted result of the interaction between a magnetic-field-aligned electron current and plasma convection perpendicular to a background magnetic field. Electrostatic probes measure the fixed pattern of perturbed ion density in LAPD-U. Electron acceleration due to StIAWs is being investigated as a mechanism for the formation and support of long-lived auroral arcs. Preliminary evidence of electron acceleration from laboratory experiment is reported. This work was supported by NSF Grant PHY-130-1896, Grants from the Canadian Space Agency, and the THEMIS ASI teams at UCalgary and UC Berkeley. Facility use and experimental assistance from BaPSF is gratefully acknowledged.
Hybrid Model of Inhomogeneous Solar Wind Plasma Heating by Alfven Wave Spectrum: Parametric Studies
Ofman, L.
2010-01-01
Observations of the solar wind plasma at 0.3 AU and beyond show that a turbulent spectrum of magnetic fluctuations is present. Remote sensing observations of the corona indicate that heavy ions are hotter than protons and their temperature is anisotropic (T(sub perpindicular / T(sub parallel) >> 1). We study the heating and the acceleration of multi-ion plasma in the solar wind by a turbulent spectrum of Alfvenic fluctuations using a 2-D hybrid numerical model. In the hybrid model the protons and heavy ions are treated kinetically as particles, while the electrons are included as neutralizing background fluid. This is the first two-dimensional hybrid parametric study of the solar wind plasma that includes an input turbulent wave spectrum guided by observation with inhomogeneous background density. We also investigate the effects of He++ ion beams in the inhomogeneous background plasma density on the heating of the solar wind plasma. The 2-D hybrid model treats parallel and oblique waves, together with cross-field inhomogeneity, self-consistently. We investigate the parametric dependence of the perpendicular heating, and the temperature anisotropy in the H+-He++ solar wind plasma. It was found that the scaling of the magnetic fluctuations power spectrum steepens in the higher-density regions, and the heating is channeled to these regions from the surrounding lower-density plasma due to wave refraction. The model parameters are applicable to the expected solar wind conditions at about 10 solar radii.
Studies of the Jet in BL Lacertae. II. Superluminal Alfv\\'en Waves
Cohen, M H; Arshakian, T G; Clausen-Brown, E; Homan, D C; Hovatta, T; Kovalev, Y Y; Lister, M L; Pushkarev, A B; Richards, J L; Savolainen, T
2014-01-01
Ridge lines on the pc-scale jet of the active galactic nucleus BL Lac display transverse patterns that move superluminally downstream. The patterns are not ballistic, but are analogous to waves on a whip. Their apparent speeds $\\beta_\\mathrm{app}$ (units of $c$) range from 4.2 to 13.5, corresponding to $\\beta_\\mathrm{wave}^\\mathrm{gal}= 0.981 - 0.998$ in the galaxy frame. We show that the magnetic field in the jet is well-ordered with a strong transverse component, and assume that it is helical and that the transverse patterns are longitudinal Alfv\\'en waves. The wave-induced transverse speed of the jet is non-relativistic ($\\beta_\\mathrm{tr}^\\mathrm{gal}\\sim 0.09$) and in agreement with our assumption of low-amplitude waves. In 2010 the wave activity subsided and the jet displayed a mild wiggle that had a complex oscillatory behavior. The waves are excited by changes in the position angle of the recollimation shock, in analogy to exciting a wave on a whip by shaking it. Simple models of the system are presen...
Alfv\\'en wave phase-mixing and damping in the ion cyclotron range of frequencies
Threlfall, J W; De Moortel, I
2010-01-01
Aims. To determine the effect of the Hall term in the generalised Ohm's law on the damping and phase mixing of Alfv\\'en waves in the ion cyclotron range of frequencies in uniform and non-uniform equilibrium plasmas. Methods. Wave damping in a uniform plasma is treated analytically, whilst a Lagrangian remap code (Lare2d) is used to study Hall effects on damping and phase mixing in the presence of an equilibrium density gradient. Results. The magnetic energy associated with an initially Gaussian field perturbation in a uniform resistive plasma is shown to decay algebraically at a rate that is unaffected by the Hall term to leading order in k^2di^2 where k is wavenumber and di is ion skin depth. A similar algebraic decay law applies to whistler perturbations in the limit k^2di^2>>1. In a non-uniform plasma it is found that the spatially-integrated damping rate due to phase mixing is lower in Hall MHD than it is in MHD, but the reduction in the damping rate, which can be attributed to the effects of wave dispers...
Kinetic Alfven wave instability in a Lorentzian dusty plasma: Non-resonant particle approach
Rubab, N.; Biernat, H. K. [Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz (Austria); Institute of Physics, University of Graz, Universitaetplatz 5, A-8010 Graz (Austria); Erkaev, V. [Institute of Computational Modelling, 660036 Krasnoyarsk, Russia and Siberian Federal University, 660041 Krasnoyarsk (Russian Federation); Langmayr, D. [Virtual Vehicle Competence Center (vif), Inffeldgasse 21a, 8010 Graz (Austria)
2011-07-15
Analysis of the electromagnetic streaming instability is carried out which is related to the cross field drift of kappa distributed ions. The linear dispersion relation for electromagnetic wave using Vlasov-fluid equations in a dusty plasma is derived. Modified two stream instability (MTSI) in a dusty plasma has been discussed in the limit {omega}{sub pd}{sup 2}/c{sup 2}k{sub perpendicular}{sup 2}<<1. Numerical calculations of the growth rate of instability have been carried out. Growth rates of kinetic Alfven instability are found to be small as compared to MTSI. Maximum growth rates for both instabilities occur in oblique directions for V{sub 0}{>=}V{sub A}. It is shown that the presence of both the charged dust particles and perpendicular ion beam sensibly modify the dispersion relation of low-frequency electromagnetic wave. The dispersion characteristics are found to be insensible to the superthermal character of the ion distribution function. Applications to different intersteller regions are discussed.
Propagation of Alfv\\'enic Waves From Corona to Chromosphere and Consequences for Solar Flares
Russell, Alexander J B
2013-01-01
How do magnetohydrodynamic waves travel from the fully ionized corona, into and through the underlying partially ionized chromosphere, and what are the consequences for solar flares? To address these questions, we have developed a 2-fluid model (of plasma and neutrals) and used it to perform 1D simulations of Alfv\\'en waves in a solar atmosphere with realistic density and temperature structure. Studies of a range of solar features (faculae, plage, penumbra and umbra) show that energy transmission from corona to chromosphere can exceed 20% of incident energy for wave periods of one second or less. Damping of waves in the chromosphere depends strongly on wave frequency: waves with periods 10 seconds or longer pass through the chromosphere with relatively little damping, however, for periods of 1 second or less, a substantial fraction (37%-100%) of wave energy entering the chromosphere is damped by ion-neutral friction in the mid and upper chromosphere, with electron resistivity playing some role in the lower ch...
Study of kinetic Alfven wave (KAW) in plasma - sheet-boundary- layer
Shukla, Nidhi; Varma, P; Tiwari, M S, E-mail: tiwarims@rediffmail.co, E-mail: poornimavarma@yahoo.co, E-mail: nidhiphy.shukla@gmail.co [Department of Physics and Electronics, Dr. H. S. Gour University, Sagar (M.P.), 470003 (India)
2010-02-01
The effect of parallel electric field with general loss-cone distribution function on the dispersion relation and damping rate/growth rate of the kinetic Alfven wave (KAW) is evaluated by kinetic approach. The generation of KAW by the combined effect of parallel electric field and loss-cone distribution indices (J) at a particular range of k{sub p}erpendicular{rho}{sub i} (k{sub p}erpendicular{rho}{sub i} <1 and k{sub p}erpendicular{rho}{sub i} >1) is noticed, where k{sub p}erpendicular is perpendicular wave number and {rho}{sub i} is the ion-gyro radius. Thus the propagation of KAW and loss of the Poynting flux from plasma sheet boundary layer (PSBL) to the ionosphere can be explained on the basis of present investigation. It is found that the present study also shows that the loss-cone distribution index is an important parameter to study KAW in the PSBL.
Hybrid Model of Inhomogeneous Solar Wind Plasma Heating by Alfven Wave Spectrum: Parametric Studies
Ofman, L.
2010-01-01
Observations of the solar wind plasma at 0.3 AU and beyond show that a turbulent spectrum of magnetic fluctuations is present. Remote sensing observations of the corona indicate that heavy ions are hotter than protons and their temperature is anisotropic (T(sub perpindicular / T(sub parallel) >> 1). We study the heating and the acceleration of multi-ion plasma in the solar wind by a turbulent spectrum of Alfvenic fluctuations using a 2-D hybrid numerical model. In the hybrid model the protons and heavy ions are treated kinetically as particles, while the electrons are included as neutralizing background fluid. This is the first two-dimensional hybrid parametric study of the solar wind plasma that includes an input turbulent wave spectrum guided by observation with inhomogeneous background density. We also investigate the effects of He++ ion beams in the inhomogeneous background plasma density on the heating of the solar wind plasma. The 2-D hybrid model treats parallel and oblique waves, together with cross-field inhomogeneity, self-consistently. We investigate the parametric dependence of the perpendicular heating, and the temperature anisotropy in the H+-He++ solar wind plasma. It was found that the scaling of the magnetic fluctuations power spectrum steepens in the higher-density regions, and the heating is channeled to these regions from the surrounding lower-density plasma due to wave refraction. The model parameters are applicable to the expected solar wind conditions at about 10 solar radii.
Alfvenic Ion Temperature Gradient Activities in a Weak Magnetic Shear Plasma
Chen, W; Li, Y Y; Shi, Z B; Du, H R; Jiang, M; Yu, L M; Yuan, B S; Li, Y G; Yang, Z C; Shi, P W; Ding, X T; Dong, J Q; Liu, Yi; Xu, M; Xu, Y H; Yang, Q W; Duan, X R
2016-01-01
We report the first experimental evidence of Alfvenic ion temperature gradient (AITG) modes in HL-2A Ohmic plasmas. A group of oscillations with $f=15-40$ kHz and $n=3-6$ is detected by various diagnostics in high-density Ohmic regimes. They appear in the plasmas with peaked density profiles and weak magnetic shear, which indicates that corresponding instabilities are excited by pressure gradients. The time trace of the fluctuation spectrogram can be either a frequency staircase, with different modes excited at different times or multiple modes may simultaneously coexist. Theoretical analyses by the extended generalized fishbone-like dispersion relation (GFLDR-E) reveal that mode frequencies scale with ion diamagnetic drift frequency and $\\eta_i$, and they lie in KBM-AITG-BAE frequency ranges. AITG modes are most unstable when the magnetic shear is small in low pressure gradient regions. Numerical solutions of the AITG/KBM equation also illuminate why AITG modes can be unstable for weak shear and low pressure...
Oblique non-neutral solitary Alfven modes in weakly nonlinear pair plasmas
Verheest, Frank [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B-9000 Gent (Belgium); School of Physics, Howard College Campus, University of KwaZulu-Natal, Durban 4041 (South Africa); Lakhina, G S [Indian Institute of Geomagnetism, New Panvel, Navi Mumbai 410218 (India); Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)
2005-04-01
The equal charge-to-mass ratio for both species in pair plasmas induces a decoupling of the linear eigenmodes between waves that are charge neutral or non-neutral, also at oblique propagation with respect to a static magnetic field. While the charge-neutral linear modes have been studied in greater detail, including their weakly and strongly nonlinear counterparts, the non-neutral mode has received less attention. Here the nonlinear evolution of a solitary non-neutral mode at oblique propagation is investigated in an electron-positron plasma. Employing the framework of reductive perturbation analysis, a modified Korteweg-de Vries equation (with cubic nonlinearity) for the lowest-order wave magnetic field is obtained. In the linear approximation, the non-neutral mode has its magnetic component orthogonal to the plane spanned by the directions of wave propagation and of the static magnetic field. The linear polarization is not maintained at higher orders. The results may be relevant to the microstructure in pulsar radiation or to the subpulses.
Excitation of the beta-induced Alfvén eigenmode by a plasma flow around the magnetic island
Marchenko, V. S.; Panwar, A.; Reznik, S. N.; Ryu, C. M.
2016-10-01
It is well known that the rotation of a magnetic island in the reference frame of plasma guiding centers generates parallel electron current outside the island, which is induced by the geodesic curvature of a magnetic field (Smolyakov et al 2007 Phys. Rev. Lett. 99 055002). It is shown in the present work that the surface part of this current located at the island separatrix can drive a pair of counter-propagating, tearing-parity, beta-induced Alfvén eigenmodes, which have the same helicity as that of the magnetic island and form a standing wave in the island frame. These Alfvénic modes can accompany tearing activity in tokamak discharges without energetic particles.
Alfvén eigenmode evolution computed with the VENUS and KINX codes for the ITER baseline scenario
Isaev, M. Yu., E-mail: isaev-my@nrcki.ru [National Research Center Kurchatov Institute (Russian Federation); Medvedev, S. Yu. [Russian Academy of Sciences, Keldysh Institute (Russian Federation); Cooper, W. A. [Suisse Plasma Centre (Switzerland)
2017-02-15
A new application of the VENUS code is described, which computes alpha particle orbits in the perturbed electromagnetic fields and its resonant interaction with the toroidal Alfvén eigenmodes (TAEs) for the ITER device. The ITER baseline scenario with Q = 10 and the plasma toroidal current of 15 MA is considered as the most important and relevant for the International Tokamak Physics Activity group on energetic particles (ITPA-EP). For this scenario, typical unstable TAE-modes with the toroidal index n = 20 have been predicted that are localized in the plasma core near the surface with safety factor q = 1. The spatial structure of ballooning and antiballooning modes has been computed with the ideal MHD code KINX. The linear growth rates and the saturation levels taking into account the damping effects and the different mode frequencies have been calculated with the VENUS code for both ballooning and antiballooning TAE-modes.
Alfvén eigenmode evolution computed with the VENUS and KINX codes for the ITER baseline scenario
Isaev, M. Yu.; Medvedev, S. Yu.; Cooper, W. A.
2017-02-01
A new application of the VENUS code is described, which computes alpha particle orbits in the perturbed electromagnetic fields and its resonant interaction with the toroidal Alfvén eigenmodes (TAEs) for the ITER device. The ITER baseline scenario with Q = 10 and the plasma toroidal current of 15 MA is considered as the most important and relevant for the International Tokamak Physics Activity group on energetic particles (ITPA-EP). For this scenario, typical unstable TAE-modes with the toroidal index n = 20 have been predicted that are localized in the plasma core near the surface with safety factor q = 1. The spatial structure of ballooning and antiballooning modes has been computed with the ideal MHD code KINX. The linear growth rates and the saturation levels taking into account the damping effects and the different mode frequencies have been calculated with the VENUS code for both ballooning and antiballooning TAE-modes.
Stochastic orbit loss of neutral beam ions from NSTX due to toroidal Alfvén eigenmode avalanches
Darrow, D. S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Crocker, N. [Univ. of California, Los Angeles, CA (United States). Dept. of Physics; Fredrickson, E. D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Gorelenkov, N. N. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Gorelenkova, M. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Kubota, S. [Univ. of California, Los Angeles, CA (United States). Dept. of Physics; Medley, S. S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Podestà, M. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Shi, L. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); White, R. B. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2012-12-17
Short toroidal Alfvén eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and could also cause a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions takes place. When beam ion orbits are followed with a guiding centre code that incorporates the plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are like those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary and the trajectories along which modes may transport particles extend from the deposition volume to the loss boundary.
Edlund, E. M.; Porkolab, M.; Kramer, G. J.; Lin, L.; Lin, Y.; Wukitch, S. J.
2009-05-01
Reversed shear Alfvén eigenmodes (RSAEs) have been observed with the phase contrast imaging diagnostic and Mirnov coils during the sawtooth cycle in Alcator C-mod [M. Greenwald et al., Nucl. Fusion 45, S109 (2005)] plasmas with minority ion-cyclotron resonance heating. Both down-chirping RSAEs and up-chirping RSAEs have been observed during the sawtooth cycle. Experimental measurements of the spatial structure of the RSAEs are compared to theoretical models based on the code NOVA [C. Z. Cheng and M. S. Chance, J. Comput. Phys. 71, 124 (1987)] and used to derive constraints on the q profile. It is shown that the observed RSAEs can be understood by assuming a reversed shear q profile (up chirping) or a q profile with a local maximum (down chirping) with q ≈1.
Höllwieser, Roman; Heller, Urs M
2011-01-01
Intersections of thick, plane vortices are characterized by the topological charge $|Q|=1/2$. We compare such intersections with the distribution of zeromodes of the Dirac operator in the fundamental and adjoint representation using both the overlap and asqtad staggered fermion formulations in SU(2)-lattice gauge theory. We analyze configurations with four intersections and find that the probability density distribution of fundamental zeromodes in the intersection plane differs significantly from the one obtained analytically in [Phys.\\ Rev.\\ D 66, 85004 (2002)]. The Dirac eigenmodes are clearly sensitive to the traces of the Polyakov (Wilson) lines and do not exactly locate topological charge contributions. Although, the adjoint Dirac operator is able to produce zeromodes for configurations with topological charge $|Q|=1/2$, they do not locate single vortex intersections, as we prove by forming arbitrary linear combinations of these zeromodes - their scalar density peaks at least at two intersection points. ...
Matsumoto, Takuma
2011-01-01
We report the results of the first two-dimensional self-consistent simulations directly covering from the photosphere to the interplanetary space. We carefully set up grid points with spherical coordinate to treat Alfv\\'enic waves in the atmosphere with the huge density contrast, and successfully simulate hot coronal wind streaming out as a result of surface convective motion. Footpoint motion excites upwardly propagating Alfv\\'enic waves along an open magnetic flux tube. These waves, traveling in non-uniform medium, suffer reflection, nonlinear mode conversion to compressive modes, and turbulent cascade. Combination of these mechanisms, the Alfv\\'enic waves eventually dissipate to accelerate the solar wind. While the shock heating by the dissipation of the compressive wave plays a primary role in the coronal heating, both turbulent cascade and shock heating contribute to drive the solar wind.
Che, H; Viñas, A F
2013-01-01
The observed sub-proton scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quite-time suggest them as possible source of free energy to drive the turbulence. Using particle-in-cell simulations, we explore how free energy in energetic electrons, released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfv\\'enic and whistler waves are excited that evolve through inverse and forward magnetic energy cascades.
Xie, M. [Lawrence Berkeley Lab., CA (United States)
1995-12-31
I present an exact calculation of free-electron-laser (FEL) eigenmodes (fundamental as well as higher order modes) in the exponential-gain regime. These eigenmodes specify transverse profiles and exponential growth rates of the laser field, and they are self-consistent solutions of the coupled Maxwell-Vlasov equations describing the FEL interaction taking into account the effects due to energy spread, emittance and betatron oscillations of the electron beam, and diffraction and guiding of the laser field. The unperturbed electron distribution is assumed to be of Gaussian shape in four dimensional transverse phase space and in the energy variable, but uniform in longitudinal coordinate. The focusing of the electron beam is assumed to be matched to the natural wiggler focusing in both transverse planes. With these assumptions the eigenvalue problem can be reduced to a numerically manageable integral equation and solved exactly with a kernel iteration method. An approximate, but more efficient solution of the integral equation is also obtained for the fundamental mode by a variational technique, which is shown to agree well with the exact results. Furthermore, I present a handy formula, obtained from interpolating the numerical results, for a quick calculation of FEL exponential growth rate. Comparisons with simulation code TDA will also be presented. Application of these solutions to the design and multi-dimensional parameter space optimization for an X-ray free electron laser driven by SLAC linac will be demonstrated. In addition, a rigorous analysis of transverse mode degeneracy and hence the transverse coherence of the X-ray FEL will be presented based on the exact solutions of the higher order guided modes.
Jo, Young Hyun; Lee, Hae June; Mikhailenko, Vladimir V.; Mikhailenko, Vladimir S.
2016-01-01
It was derived that the drift-Alfven instabilities with the shear flow parallel to the magnetic field have significant difference from the drift-Alfven instabilities of a shearless plasma when the ion temperature is comparable with electron temperature for a finite plasma beta. The velocity shear not only modifies the frequency and the growth rate of the known drift-Alfven instability, which develops due to the inverse electron Landau damping, but also triggers a combined effect of the velocity shear and the inverse ion Landau damping, which manifests the development of the ion kinetic shear-flow-driven drift-Alfven instability. The excited unstable waves have the phase velocities along the magnetic field comparable with the ion thermal velocity, and the growth rate is comparable with the frequency. The development of this instability may be the efficient mechanism of the ion energization in shear flows. The levels of the drift--Alfven turbulence, resulted from the development of both instabilities, are determined from the renormalized nonlinear dispersion equation, which accounts for the nonlinear effect of the scattering of ions by the electromagnetic turbulence. The renormalized quasilinear equation for the ion distribution function, which accounts for the same effect of the scattering of ions by electromagnetic turbulence, is derived and employed for the analysis of the ion viscosity and ions heating, resulted from the interactions of ions with drift-Alfven turbulence. In the same way, the phenomena of the ion cyclotron turbulence and anomalous anisotropic heating of ions by ion cyclotron plasma turbulence has numerous practical applications in physics of the near-Earth space plasmas. Using the methodology of the shearing modes, the kinetic theory of the ion cyclotron turbulence of the plasma with transverse current with strong velocity shear has been developed.
Dorelli, John C; Collinson, Glyn; Tóth, Gábor
2015-01-01
We present high resolution Hall MHD simulations of Ganymede's magnetosphere demonstrating that Hall electric fields in ion-scale magnetic reconnection layers have significant global effects not captured in resistive MHD simulations. Consistent with local kinetic simulations of magnetic reconnection, our global simulations show the development of intense field-aligned currents along the magnetic separatrices. These currents extend all the way down to the moon's surface, where they may contribute to Ganymede's aurora. Within the magnetopause and magnetotail current sheets, Hall currents in the reconnection plane accelerate ions to the local Alfv\\'en speed in the out-of-plane direction, producing a global system of ion drift belts that circulates Jovian magnetospheric plasma throughout Ganymede's magnetosphere. We discuss some observable consequences of these Hall-induced currents and ion drifts: the appearance of a sub-Jovian "double magnetopause" structure, an Alfv\\'enic ion jet extending across the upstream m...
Dorelli, J. C.; Glocer, Alex; Collinson, Glyn; Toth, Gabor
2015-01-01
We present high-resolution Hall MHD simulations of Ganymede's magnetosphere demonstrating that Hall electric fields in ion-scale magnetic reconnection layers have significant global effects not captured in resistive MHD simulations. Consistent with local kinetic simulations of magnetic reconnection, our global simulations show the development of intense field-aligned currents along the magnetic separatrices. These currents extend all the way down to the moon's surface, where they may contribute to Ganymede's aurora. Within the magnetopause and magnetotail current sheets, Hall J x B forces accelerate ions to the local Alfven speed in the out-of-plane direction, producing a global system of ion drift belts that circulates Jovian magnetospheric plasma throughout Ganymede's magnetosphere. We discuss some observable consequences of these Hall-induced currents and ion drifts: the appearance of a sub-Jovian 'double magnetopause' structure, an Alfvenic ion jet extending across the upstream magnetopause, and an asymmetric pattern of magnetopause Kelvin-Helmholtz waves.
Metastability of collisionless current sheets. Hannes Alfven Lecture on behalf of Albert Galeev
Zelenyi, L.; Galeev, A.
2009-04-01
Complicated magnetic configurations containing numerous magnetic field reversals are widespread in nature. Each of such reversals is supported by corresponding current sheet (CS) which could often have very small thickness comparable to ion skin depth. Since the beginning of Space Age "in situ" investigations of current sheets in the Earth's magnetosphere (magnetopause and magnetotail) acquired one of the highest priorities in national space programs and became one of the cornerstones of various international activities, like ISTP, IACG, and ILWS, which appeared to be very effective. Intense theoretical efforts were undertaken by theorists all over the world to develop both equilibrium models of current sheets and analyze its stability and further nonlinear evolution. Lack of collisions and smallness of many characteristic scales in comparison with ion Larmor radius made an application of straightforward MHD approach dramatically questionable. Professor Alfven was one of the first who suggested in 1968 simple but very physical self-consistent particle model of CS. One of the most intriguing features of current sheets in collisionless plasma is their ability to accumulate tremendous amounts of magnetic energy (1015 J for magnetospheric substorms , 1024 J for solar flare associated sheets) and then suddenly sometimes almost explosively release them. We will demonstrate in this talk that such METASTABILITY is a principal intrinsic feature of current sheets in hot plasma. Very intense theoretical debates of 80-ies and late 90-ies resulted in some consensus that current sheets with the small component of magnetic field normal to their plane become overstable for spontaneous reconnection (i.e. versus the development of ion tearing mode). Analysis of INTERBALL and especially 4- point CLUSTER data have shown that real current sheets observed in the Earth's magnetotail very rarely resemble simplistic HARRIS current sheets which have been used for an early stability
Kinetic Alfven Waves and the Depletion of the Thermal Population in Extragalactic Jets
Jafelice, L. C.; Opher, R.
1990-11-01
evident that both problems are intimately related to one another. Jafe- lice and Opher (1987a)(Astrophys. Space Sci. 137, 303)showed that an abundant generation of kinetic Alfven waves (KAw) within EJ and ERS is expected. In the present work we study the chain of processes: a) KAW accelerate thermal electrons along the background magnetic field producing suprathermal runaway electrons; b) which generate Langmuir waves and c) which in turn further accelerate a fraction of the runaway electrons to moderately relativistic energies. We show that assuming that there is no other source of a thermal population but the original one, the above sequence of processes can account for the consumption of thermal electrons in a time scale the source lifetime. Key o : GALAXIES-JETS - HYDROMAGNETICS
Schneller, Mirjam Simone
2013-08-02
measurements to be interpreted with a theoretical basis. Fast particle losses are modeled and directly compared with experimental measurements. The phase space distribution and the mode-correlation signature of the fast particle losses allows them to be characterized as prompt, resonant or diffusive (non-resonant). It is found that a large number of diffuse losses occur in the lower energy range (at around 1/3 of the birth energy) particularly in multiple mode scenarios (with different mode frequencies), due to a domino-like transport process. In inverted q profile equilibria, the combination of radially extended global modes and large particle orbits leads to losses with energies down to 1/10th of the birth energy. The HAGIS code is a perturbative hybrid code, which models the nonlinear interaction between a distribution of energetic particles and a set of Alfven eigenmodes. The wave eigenfunctions are assumed to be invariant, but its amplitude and frequency evolve in time, as determined by kinetic wave-particle nonlinearities. To solve the particle equations of motion, the 6D phase space is reduced to a 5D description, using the guiding center approach. The change in the fast particle distribution function is modeled using a δf-method, to significantly reduce numerical noise and the number of simulation markers. As in ideal MHD, the HAGIS model previously neglected any parallel electric field perturbation E {sub parallel}. This approximation is dropped within this work, by implementing a non-vanishing E {sub parallel} term, employing the electric and magnetic perturbation structure given by LIGKA. In this way, a more advanced damping effect is introduced into the HAGIS model, which is not only individual for each poloidal harmonic, but is also characterized by a radial structure. The implementation of this damping is the first step towards a HAGIS-LIGKA hybrid model, which can overcome the limit of fixed radial mode structures.
Kovalev, A S
2002-01-01
The resonance activation of eigenmodes for a finite 2D easy-plane ferromagnet is considered to treat theoretically by the vortex switching in magnetic nanodots due to the action of external circular magnetic field. It is shown analytically that if the anisotropy is weak, i.e. the vortex has a nonzero polarity (total magnization along the z-axis), the process of the field action has a complicated nature. The circular field acts in a resonance way upon azimuthal system eigenmodes, in which magnetization depends on the azimuthal coordinate (as a direct resonance at the eigenfrequencies of these modes). The interaction of the azimuthal and symmetric modes (in which the magnetization does not depend on the azimuthal coordinate) via the applied field gives rise to complex parametric resonance at multifrequencies. The results obtained are compared with the data of previous numerical calculations.
Global stability analysis of axisymmetric boundary layers
Vinod, N
2016-01-01
This paper presents the linear global stability analysis of the incompressible axisymmetric boundary layer on a circular cylinder. The base flow is parallel to the axis of the cylinder at inlet. The pressure gradient is zero in the streamwise direction. The base flow velocity profile is fully non-parallel and non-similar in nature. The boundary layer grows continuously in the spatial directions. Linearized Navier-Stokes(LNS) equations are derived for the disturbance flow quantities in the cylindrical polar coordinates. The LNS equations along with homogeneous boundary conditions forms a generalized eigenvalues problem. Since the base flow is axisymmetric, the disturbances are periodic in azimuthal direction. Chebyshev spectral collocation method and Arnoldi's iterative algorithm is used for the solution of the general eigenvalues problem. The global temporal modes are computed for the range of Reynolds numbers and different azimuthal wave numbers. The largest imaginary part of the computed eigenmodes are nega...
Spong, Donald A [ORNL; Bass, Eric [General Atomics, San Diego; Deng, Wenjun [Princeton Plasma Physics Laboratory (PPPL); Heidbrink, W. [University of California, Irvine; Lin, Zhihong [University of California, Irvine; Tobias, Ben [University of California, Davis; Van Zeeland, Michael [General Atomics; Austin, M. E. [University of Texas, Austin; Domier, C. W. [University of California, Davis; Luhmann, N.C. [University of California, Davis
2012-01-01
A verification and validation study is carried out for a sequence of reversed shear Alfven instability time slices. The mode frequency increases in time as the minimum (q{sub min}) in the safety factor profile decreases. Profiles and equilibria are based upon reconstructions of DIII-D discharge (No.142111) in which many such frequency up-sweeping modes were observed. Calculations of the frequency and mode structure evolution from two gyrokinetic codes, GTC and GYRO, and a gyro-Landau fluid code TAEFL are compared. The experimental mode structure of the instability was measured using time-resolved two-dimensional electron cyclotron emission imaging. The three models reproduce the frequency upsweep event within {+-}10% of each other, and the average of the code predictions is within {+-}8% of the measurements; growth rates are predicted that are consistent with the observed spectral line widths. The mode structures qualitatively agree with respect to radial location and width, dominant poloidal mode number, ballooning structure, and the up-down asymmetry, with some remaining differences in the details. Such similarities and differences between the predictions of the different models and the experimental results are a valuable part of the verification/validation process and help to guide future development of the modeling efforts.
Yue-Jing He
2016-02-01
Full Text Available In this study, a numerical simulation method was employed to investigate and analyze superstructure fiber Bragg gratings (SFBGs with five duty cycles (50%, 33.33%, 14.28%, 12.5%, and 10%. This study focuses on demonstrating the relevance between design period and spectral characteristics of SFBGs (in the form of graphics for SFBGs of all duty cycles. Compared with complicated and hard-to-learn conventional coupled-mode theory, the result of the present study may assist beginner and expert designers in understanding the basic application aspects, optical characteristics, and design techniques of SFBGs, thereby indirectly lowering the physical concepts and mathematical skills required for entering the design field. To effectively improve the accuracy of overall computational performance and numerical calculations and to shorten the gap between simulation results and actual production, this study integrated a perfectly matched layer (PML, perfectly reflecting boundary (PRB, object meshing method (OMM, and boundary meshing method (BMM into the finite element method (FEM and eigenmode expansion method (EEM. The integrated method enables designers to easily and flexibly design optical fiber communication systems that conform to the specific spectral characteristic by using the simulation data in this paper, which includes bandwidth, number of channels, and band gap size.
Gulati, Mamta; Saini, Tarun Deep
2016-07-01
The short-wave asymptotics (WKB) of spiral density waves in self-gravitating stellar discs is well suited for the study of the dynamics of tightly-wound wavepackets. But the textbook WKB theory is not well adapted to the study of the linear eigenmodes in a collisionless self-gravitating disc because of the transcendental nature of the dispersion relation. We present a modified WKB theory of spiral density waves, for collisionless discs in the epicyclic limit, in which the perturbed gravitational potential is related to the perturbed surface density by the Poisson integral in Kalnaj's logarithmic spiral form. An integral equation is obtained for the surface density perturbation, which is seen to also reduce to the standard WKB dispersion relation. Although our formulation is general and applies to all discs, we present our analysis only for nearly Keplerian, low-mass, self-gravitating discs revolving around massive central objects, and derive an integral equation governing the slow precessional modes of such discs. For a prograde disc, the integral kernel turns out be real and symmetric, implying that all slow modes are stable. We apply the slow mode integral equation to two unperturbed disc profiles, the Jalali-Tremaine annular discs, and the Kuzmin disc. We determine eigenvalues and eigenfunctions for both m = 1 and m = 2 slow modes for these profiles and discuss their properties. Our results compare well with those of Jalali-Tremaine.
Gulati, Mamta
2016-01-01
The short--wave asymptotics (WKB) of spiral density waves in self-gravitating stellar discs is well suited for the study of the dynamics of tightly--wound wavepackets. But the textbook WKB theory is not well adapted to the study of the linear eigenmodes in a collisionless self-gravitating disc because of the transcendental nature of the dispersion relation. We present a modified WKB of spiral density waves, for collisionless discs in the epicyclic limit, in which the perturbed gravitational potential is related to the perturbed surface density by the Poisson integral in Kalnaj's logarithmic spiral form. An integral equation is obtained for the surface density perturbation, which is seen to also reduce to the standard WKB dispersion relation. We specialize to a low mass (or Keplerian) self-gravitating disc around a massive black hole, and derive an integral equation governing the eigenspectra and eigenfunctions of slow precessional modes. For a prograde disc, the integral kernel turns out be real and symmetric...
Heidbrink, W. W.; Persico, E. A. D. [University of California Irvine, Irvine, California 92697 (United States); Austin, M. E. [University of Texas, Austin, Texas 78705 (United States); Chen, Xi; Pace, D. C.; Van Zeeland, M. A. [General Atomics, San Diego, California 92186 (United States)
2016-02-15
Neutral-beam ions that are deflected onto loss orbits by Alfvén eigenmodes (AE) on their first bounce orbit and are detected by a fast-ion loss detector (FILD) satisfy the “local resonance” condition proposed by Zhang et al. [Nucl. Fusion 55, 22002 (2015)]. This theory qualitatively explains FILD observations for a wide variety of AE-particle interactions. When coherent losses are measured for multiple AE, oscillations at the sum and difference frequencies of the independent modes are often observed in the loss signal. The amplitudes of the sum and difference peaks correlate weakly with the amplitudes of the fundamental loss-signal amplitudes but do not correlate with the measured mode amplitudes. In contrast to a simple uniform-plasma theory of the interaction [Chen et al., Nucl. Fusion 54, 083005 (2014)], the loss-signal amplitude at the sum frequency is often larger than the loss-signal amplitude at the difference frequency, indicating a more detailed computation of the orbital trajectories through the mode eigenfunctions is needed.
Ma, Ruirui; Chen, Wei; He, Hongda; Yu, Liming; Ding, Xuantong
2017-10-01
The dispersion relation for high toroidal mode number n beta-induced Alfvén eigenmodes (BAEs) excited by magnetically trapped energetic ions generated with ion-cyclotron resonance heating via precessional resonance in low magnetic shear (s) tokamak plasma is investigated analytically and numerically. The dynamics of the energetic particles (EPs) is treated non-perturbatively and finite drift orbit width (FOW) effects are taken into account. It is found that, depending on the plasma parameters, the most unstable mode can be either the BAE mode or the energetic particle mode (EPM). Both modes can resonate with the trapped-particles' magnetic precessional drifts and become unstable. The mode frequencies and growth rates depend strongly on the EP parameters. FOW can stabilize high-n BAE modes by reducing the wave-particle interaction. Magnetic shear has an important effect on the growth rate of the modes. For BAE, the growth rate presents the trend of first increase and following decrease with the increase of s. The peak positions of the mode growth rate move towards small s with increasing EPs' density. Besides, the BAE growth rate increases with n for small kϑρLE , and decreases for kϑρLE>0.34 . On the other hand, the EPM becomes stable for sufficiently large s and enters into the second stability regime.
Critical Gradient Behavior of Alfvén Eigenmode Induced Fast-Ion Transport in Phase Space
Collins, C. S.; Pace, D. C.; van Zeeland, M. A.; Heidbrink, W. W.; Stagner, L.; Zhu, Y. B.; Kramer, G. J.; Podesta, M.; White, R. B.
2016-10-01
Experiments on DIII-D have shown that energetic particle (EP) transport suddenly increases when multiple Alfvén eigenmodes (AEs) cause particle orbits to become stochastic. Several key features have been observed; (1) the transport threshold is phase-space dependent and occurs above the AE linear stability threshold, (2) EP losses become intermittent above threshold and appear to depend on the types of AEs present, and (3) stiff transport causes the EP density profile to remain unchanged even if the source increases. Theoretical analysis using the NOVA and ORBIT codes shows that the threshold corresponds to when particle orbits become stochastic due to wave-particle resonances with AEs in the region of phase space measured by the diagnostics. The kick model in NUBEAM (TRANSP) is used to evolve the EP distribution function to study which modes cause the most transport and further characterize intermittent bursts of EP losses, which are associated with large scale redistribution through the domino effect. Work supported by the US DOE under DE-FC02-04ER54698.
Alfven波在微电离大气中的衰减特性研究%Attenuation of Alfven Waves in Weakly Ionized Near Earth Atmosphere
刘元涛; 赵华; 李磊; 王劲东; 周斌; 冯永勇
2011-01-01
利用简单的偶极子地磁场模型以及大气电子密度和电导率模式,分析地面产生的磁扰动以Alfven波的模式传播到近地空间区域.这种地面的磁扰动可能干扰近地空间卫星对空间磁扰动的观测.通过对地面磁扰动Alfven 波模式1000km高度内的衰减情况进行模拟,认为在近地空间采用地磁偶极子模型是合理的.由于衰减随扰动频率的增大而急剧增强,分析还得到了近地卫星能够探测到地面磁扰动的最大频率.计算结果表明,Alfven波的衰减主要集中在高度50km以下,这个区域内的大气电导率极其微弱,使Alfven波的传播受到极大衰减.0.4Hz 以下的Alfven波沿磁力线传播到1000 km高度后衰减结为原来扰动幅度的千分之一,因此频率在0.4 Hz以下的Alfven波可能会干扰低轨卫星探测磁场脉动.%Alfven waves, produced on the ground by artificial or by soundstorm, propagating to the near-earth space along the geomagnetic field lines, would decay greatly with distance.A dipole geomagnetic field model in near earth space, plasma density and conductivity models derived from observational data are used in this study to investigate the attenuation of Alfven waves below 1000 km altitude by numerical simulation methods.The frequency that would be detected by magnetometer carried by satellite was also found.The result showed that: Alfven waves will decay sharply in the height of less than 50 km for the much weak electrical conductivity in this region; it is 0.4 Hz Alfven waves, when transmitted to 1000 km, that becomes about one-thousandth of the original, so Alfven waves below 0.4 Hz can be detected by LEO satellites.
MHD MODES DESTABILIZED BY ENERGETIC IONS ON LHD
Toi, K. [National Institute for Fusion Science, Toki, Japan; Isobe, M. [National Institute for Fusion Science, Toki, Japan; Spong, Donald A [ORNL
2010-01-01
nergetic ion driven magnetohydrodynamic instabilities such as Alfven eigenmodes (AEs), energetic particle modes (EPMs), and their impacts on energetic ion confinement are being studied on the Large Helical Device (LHD). The magnetic configuration of this device is three dimensional and has negative magnetic shear over a whole radial region in the low-beta regime. Two types of toroidicity-induced Alfven eigenmodes (TAEs) are typically observed in LHD plasmas that are heated by tangential neutral beam injection: One is localized in the plasma core region near a central TAE gap and the other is a global TAE having a radially extended eigenfunction. Core-localized TAEs with even and odd radial mode parities are often observed. The global TAE is usually observed in medium- to high-beta plasmas where broad regions with low magnetic shear are present. Helicity-induced Alfven eigenmodes (HAEs), which exist in gaps unique to three-dimensional plasmas that have both toroidal and poloidal mode couplings, were detected for the first time. Recently, reversed magnetic shear Alfven eigenmodes (RSAEs) having characteristic frequency sweeping were discovered in reversed magnetic shear (RS) plasmas produced by intense counter-neutral beam current drive. In the RS plasma, the geodesic acoustic mode (GAM) excited by energetic ions, which is a global-type mode different from localized GAM excited by drift waves, was also detected for the first time in a helical plasma. Nonlinear couplings between RSAE and GAM modes and also between two TAEs were observed. Bursts of TAEs and EPMs often enhance radial transport and loss of energetic ions at low toroidal magnetic field (<0.75 T).
Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes
Collins, C. S.; Heidbrink, W. W.; Podestà, M.; White, R. B.; Kramer, G. J.; Pace, D. C.; Petty, C. C.; Stagner, L.; Van Zeeland, M. A.; Zhu, Y. B.; The DIII-D Team
2017-08-01
Experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfvén eigenmodes (AEs) cause fast-ion transport to sharply increase above a critical threshold in beam power, leading to fast-ion density profile resilience and reduced fusion performance. The threshold is above the AE linear stability limit and varies between diagnostics that are sensitive to different parts of fast-ion phase-space. Comparison with theoretical analysis using the nova and orbit codes shows that, for the neutral particle diagnostic, the threshold corresponds to the onset of stochastic particle orbits due to wave-particle resonances with AEs in the measured region of phase space. The bulk fast-ion distribution and instability behavior was manipulated through variations in beam deposition geometry, and no significant differences in the onset threshold outside of measurement uncertainties were found, in agreement with the theoretical stochastic threshold analysis. Simulations using the ‘kick model’ produce beam ion density gradients consistent with the empirically measured radial critical gradient and highlight the importance of including the energy and pitch dependence of the fast-ion distribution function in critical gradient models. The addition of electron cyclotron heating changes the types of AEs present in the experiment, comparatively increasing the measured fast-ion density and radial gradient. These studies provide the basis for understanding how to avoid AE transport that can undesirably redistribute current and cause fast-ion losses, and the measurements are being used to validate AE-induced transport models that use the critical gradient paradigm, giving greater confidence when applied to ITER.
Sheng, He; Waltz, R. E.; Staebler, G. M.
2017-07-01
The Trapped-Gyro-Landau-Fluid (TGLF) transport model is a physically realistic and comprehensive theory based on a local quasilinear transport model fitted to linear and nonlinear GYRO gyrokinetic simulations [Staebler et al., Phys. Plasmas 14, 55909 (2007)]. This work presents the first use of the TGLF model to treat low-n Alfvén eigenmode (AE) stability and energetic particle (EP) transport. TGLF accurately recovers the local GYRO toroidicity-induced AE (TAE) and energetic particle mode (EPM) linear growth and frequency rates for a fusion alpha case. With a very high grid resolution, TGLF can quickly find the critical EP pressure gradient profile for stiff EP transport based on an AE linear threshold given the background thermal plasma profiles in DIII-D. The TGLF critical gradient profile using the recipe γAE = 0, that is the linear AE growth rate without additional driving rates from the background plasma gradients, matches the more expensive linear GYRO results with a single worst toroidal mode number n. TGLF can easily find the minimum critical gradient profile with testing multiple ns. From a database of runs using a newly developed TGLFEP code, a rough but insightful parametric "power law" scaling for critical EP beta is demonstrated. An important toroidal stabilization condition on the EP pressure gradient pEP/LpEP drive is isolated: R /LpEP>CR ˜ 3 , where LpEP is the EP pressure gradient length and R is the tokamak major radius. This paper also demonstrates that relaxation of the fixed slowing down EP profile shape approximation often used to find the critical EP density profile has little effect on the resulting EP transport. The single EP species critical gradient model is generalized to handle two EP species.
Chandran, Benjamin D G; Quataert, Eliot; Bale, Stuart D
2011-01-01
We develop a 1D solar-wind model that includes separate energy equations for the electrons and protons, proton temperature anisotropy, collisional and collisionless heat flux, and an analytical treatment of low-frequency, reflection-driven, Alfven-wave turbulence. To partition the turbulent heating between electron heating, parallel proton heating, and perpendicular proton heating, we employ results from the theories of linear wave damping and nonlinear stochastic heating. We account for mirror and oblique firehose instabilities by increasing the proton pitch-angle scattering rate when the proton temperature anisotropy exceeds the threshold for either instability. We numerically integrate the equations of the model forward in time until a steady state is reached, focusing on two fast-solar-wind-like solutions. These solutions are consistent with a number of observations, supporting the idea that Alfven-wave turbulence plays an important role in the origin of the solar wind.
Hansen, Shelley C
2012-01-01
Alfv\\'en waves may be difficult to excite at the photosphere due to low ionization fraction and suffer near-total reflection at the transition region (TR). Yet they are ubiquitous in the corona and heliosphere. To overcome these difficulties, we show that they may instead be generated high in the chromosphere by conversion from reflecting fast magnetohydrodynamic waves, and that Alfv\\'enic transition region reflection is greatly reduced if the fast reflection point is within a few scale heights of the TR. The influence of mode conversion on the phase of the reflected fast wave is also explored. This phase can potentially be misinterpreted as a travel speed perturbation, with implications for the practical seismic probing of active regions.
Generalized global symmetries and dissipative magnetohydrodynamics
Grozdanov, Sašo; Iqbal, Nabil
2016-01-01
The conserved magnetic flux of U(1) electrodynamics coupled to matter in four dimensions is associated with a generalized global symmetry. We study the realization of such a symmetry at finite temperature and develop the hydrodynamic theory describing fluctuations of a conserved 2-form current around thermal equilibrium. This can be thought of as a systematic derivation of relativistic magnetohydrodynamics, constrained only by symmetries and effective field theory. We construct the entropy current and show that at first order in derivatives, there are six dissipative transport coefficients. We present a universal definition of resistivity in a theory of dynamical electromagnetism and derive a direct Kubo formula for the resistivity in terms of correlation functions of the electric field operator. We also study fluctuations and collective modes, deriving novel expressions for the dissipative widths of magnetosonic and Alfven modes. Finally, we demonstrate that a non-trivial truncation of the theory can be perf...
Myllys, M. E.; Kilpua, E.; Lavraud, B.
2015-12-01
We have investigated the effect of key solar wind driving parameters on the solar wind-magnetosphere coupling efficiency and saturation of the cross polar cap potential (CPCP) during sheath and magnetic cloud driven storms. The particular focus of the study was on the coupling efficiency dependence with Alfven Mach number (MA).Since we are studying the instantaneous coupling efficiency instead of the average efficiency over the whole solar wind structure, we needed to take into account the communication time between the solar wind and the magnetosphere. We present the results of the time delay analysis between geomagnetic indices (PCN, AE and SYM-H) and the interplanetary electric field y-component (EY, GSM coordinate system) and Newell and Borovsky functions. The study shows that the MA has a clear effect to the saturation of the PCN index, which can be used as a proxy of the polar cap potential. The higher the MA the higher the limit EY value after which the saturation starts to occur. Thus, the coupling efficiency increases as a function of MA. Also, the AE index saturates during high solar wind driving but the saturation is not MA depended. However, the results also suggest that the MA it is not the primary cause for the PCN saturation.
Tsiklauri, D
2015-01-01
Our magnetohydrodynamic (MHD) simulations and analytical calculations show that, when a background flow is present, mathematical expressions for the Alfv\\'en wave (AW) damping via phase mixing are modified by a following substitution $C_A^\\prime(x) \\to C_A^\\prime(x)+V_0^\\prime(x)$, where $C_A$ and $V_0$ are AW phase and the flow speeds and prime denotes derivative in the direction across the background magnetic field. In uniform magnetic field and over-dense plasma structures, in which $C_A$ is smaller compared to surrounding plasma, the flow, that is confined to the structure, in the same direction as the AW, reduces the effect of phase mixing, because on the edges of the structure $C_A^\\prime$ and $V_0^\\prime$ have opposite sign. Thus, the wave damps via phase mixing {\\it slower} compared to the case without the flow. This is the consequence of the co-directional flow reducing the wave front stretching in the transverse direction. Although, the result is generic and is applicable to different laboratory or ...
Shukla, Nidhi; Mishra, Ruchi; Varma, P; Tiwari, M S [Department of Physics and Electronics, Dr H S Gour University, Sagar (MP) 470003 (India)
2008-02-15
This work studies the effect of ion and electron beam on kinetic Alfven wave (KAW) with general loss-cone distribution function. The kinetic theory has been adopted to evaluate the dispersion relation and damping rate of the wave in the presence of loss-cone distribution indices J. The variations in wave frequency {omega} and damping rate with perpendicular wave number k{sub perpendicular}{rho}{sub i} (k{sub perpendicular} is perpendicular wave number and {rho}{sub i} is ion gyroradius) and parallel wave number k{sub parallel} are studied. It is found that the distribution index J and ion beam velocity enhance the wave frequency at lower k{sub perpendicular}{rho}{sub i}, whereas the electron beam velocity enhances the wave frequency at higher k{sub perpendicular}{rho}{sub i}. The calculated values of frequency correspond to the observed values in the range 0.1-4 Hz. Increase in damping rate due to higher distribution indices J and ion beam velocity is observed. The effect of electron beam is to reduce the damping rate at higher k{sub perpendicular}{rho}{sub i}. The plasma parameters appropriate to plasma sheet boundary layer are used. The results may explain the transfer of Poynting flux from the magnetosphere to the ionosphere. It is also found that in the presence of the loss-cone distribution function the ion beam becomes a sensitive parameter to reduce the Poynting flux of KAW propagating towards the ionosphere.
STAVREV, A.
2013-03-01
The uncertainty of geometric imperfections in a series of nominally equal I-beams leads to a variability of corresponding buckling loads. Its analysis requires a stochastic imperfection model, which can be derived either by the simple variation of the critical eigenmode with a scalar random variable, or with the help of the more advanced theory of random fields. The present paper first provides a concise review of the two different modeling approaches, covering theoretical background, assumptions and calibration, and illustrates their integration into commercial finite element software to conduct stochastic buckling analyses with the Monte-Carlo method. The stochastic buckling behavior of an example beam is then simulated with both stochastic models, calibrated from corresponding imperfection measurements. The simulation results show that for different load cases, the response statistics of the buckling load obtained with the eigenmode-based and the random field-based models agree very well. A comparison of our simulation results with corresponding Eurocode 3 limit loads indicates that the design standard is very conservative for compression dominated load cases. © 2013 World Scientific Publishing Company.
POSSIBLE PHASE LOOP FOR THE GLOBAL DECOUPLING.
LUO, Y.; CAMERON, P.; DELLA PENNA, A.; JONES, R.; ET AL.
2005-05-16
The two eigentunes Q{sub I} and Q{sub II}, two eigenmode amplitude ratios R{sub I} and R{sub II}, and two eignmode phase differences {Delta}{phi}{sub I} and {Delta}{phi}{sub II}, are defined as the coupling observables for the linear weak difference betatron coupling. Simulations were carried out to investigate their behaviors in global decoupling scans. It was found that the amplitude ratios R{sub I,II} are more sensitive than the tune split when the decoupling scan is approaching the global uncoupled point, and that the phase differences {Delta}{phi}{sub I,II} tell the right global decoupling direction, the right strength combination of the skew quadrupoles or families. The analytical solution to these six coupling observables is calculated through both the strict matrix approach and the perturbation Hamiltonian approach. The constant phase differences in the right decoupling direction hint a possible global decoupling phase loop. Dedicated beam experiments were carried out at the Relativistic Heavy Ion Collider (RHIC). The preliminary results from the beam experiments are presented. These six parameters can be used for the global decoupling in feed-back mode, especially on the non-stop energy ramp.
Monte-Carlo finite elements gyrokinetic simulations of Alfven modes in tokamaks
Bottino, Alberto; Biancalani, Alessandro; Palermo, Francesco; Tronko, Natalia
2016-10-01
The global gyrokinetic code ORB5 can simultaneously include electromagnetic perturbations, general ideal MHD axisymmetric equilibria, zonal-flow preserving sources, collisions, and the ability to solve the full core plasma including the magnetic axis. In this work, a Monte Carlo Particle In Cell Finite Element model, starting from a gyrokinetic discrete Lagrangian, is derived and implemented into the ORB5 code. The variations of the Lagrangian are used to obtain the time continuous equations of motion for the particles and the Finite Element approximation of the field equations. The Noether theorem for the semi-discretised system, implies a certain number of conservation properties for the final set of equation. Linear and nonlinear results, concerning Alfvén instabilities, in the presence of an energetic particle population, and microinstabilities, such as electromagnetic ion temperature gradient (ITG) driven modes and kinetic ballooning modes (KBM), will be presented and discussed. Due to losses of energetic particles, Alfvén instabilities can not only affect plasma stability and damage the walls, but also strongly impact the heating efficiency of a fusion reactor and ultimately the possibility of reaching ignition.
Sahraoui, Fouad; Goldstein, Melvyn L.
2010-01-01
Over the past few decades, large-scales solar wind (SW) turbulence has been studied extensively, both theoretically and observationally. Observed power spectra of the low frequency turbulence, which can be described in the magnetohydrodynamic (MHD) limit, are shown to obey the Kolmogorov scaling, $k"{ -5/3 }$, down the local proton gyrofrequency ($C{ci} \\sim O.l$-Hz). Turbulence at frequencies above $C{ci}$ has not been thoroughly investigated and remains far less well understood. Above $C{ ci}$ the spectrum steepens to $\\sim f"{ -2.5}$ and a debate exists as to whether the turbulence has become dominated by dispersive kinetic Alfven waves (KA W) or by whistler waves, before it is dissipated at small scales, In a case study Sahraoui et al., PRL (2009) have reported the first direct determination of the dissipation range of solar wind turbulence near the electron gyroscale using the high resolution Cluster magnetic and electric field data (up to $10"2$-Hz in the spacecraft reference frame). Above the Doppler-shifted proton scale $C{\\rho i}$ a new inertial range with a scaling $\\sim f"{ -2.3}$ has been evidenced and shown to remarkably agree with theoretical predictions of a quasi-two-dimensional cascade into KA W turbulence. Here, we use a wider sample of data sets of small scale SW turbulence under different plasma conditions, and investigate under which physical criteria the KA W (or the whistler) turbulence may be observed to carry out the cascade at small scales, These new observations/criteria are compared to the predictions on the cascade and the (kinetic) dissipation from the Vlasov theory. Implications of the results on the heating problem of the solar wind will be discussed.
Horváth, I
2004-01-01
The structure of QCD vacuum can be studied from first principles using lattice-regularized theory. This line of research entered a qualitatively new phase recently, wherein the space-time structure (at least for some quantities) can be directly observed in configurations dominating the QCD path integral, i.e. without any subjective processing of typical configurations. This approach to QCD vacuum structure does not rely on any proposed picture of QCD vacuum but rather attempts to characterize this structure in a model-independent manner, so that a coherent physical picture of the vacuum can emerge when such unbiased numerical information accumulates to a sufficient degree. An important part of this program is to develop a set of suitable quantitative characteristics describing the space-time structure in a meaningful and physically relevant manner. One of the basic pertinent issues here is whether QCD vacuum dynamics can be understood in terms of localized vacuum objects, or whether such objects behave as inh...
Height-dependent Refraction of A Global EUV Wave and Its Associated Sympathetic Eruptions
Liu, Wei; Ofman, Leon; Downs, Cooper; Schrijver, Karel
2014-06-01
The height dependence of global extreme-ultraviolet (EUV) waves in the solar corona, especially of their wave-like behaviors such as transmission and reflection, is critical to understanding their physical nature. Prior observations of such behaviors, when detected on the solar disk, were compromised because height-dependent information is lost due to the line-of-sight projection from a top-down view. We report a global EUV wave on the limb observed by SDO/AIA from a side-view that evidently shows height-dependent transmission and refraction. As the wave travels through an active region, the orientation of the low-corona wave front changes from a forward inclination toward the solar surface to a backward inclination. This indicates that the EUV wave speed is lower at higher altitudes, which is expected because of the rapid drop with height of the Alfven and fast-mode speeds in active regions, as predicted by MHD models. When traveling into the active region, the EUV wave speed in the low corona increases from ~600 km/s to ~900 km/s. In addition, in the neighborhood of the active region, sympathetic eruptions of local coronal structures take place sequentially upon the wave impact and may appear as wave reflection. Understanding propagation behaviors of global EUV waves brings us one step closer to fully utilizing them for seismological diagnostics of the global corona, such as mapping the spatial distribution of the Alfven speed and magnetic field strength.
Coffey, Victoria; Chandler, Michael; Singh, Nagendra
2008-01-01
The role that the cleft/cusp has in ionosphere/magnetosphere coupling makes it a very dynamic region having similar fundamental processes to those within the auroral regions. With Polar passing through the cusp at 1 Re in the Spring of 1996, we observe a strong correlation between ion heating and broadband ELF (BBELF) emissions. This commonly observed relationship led to the study of the coupling of large field-aligned currents, burst electric fields, and the thermal O+ ions. We demonstrate the role of these measurements to Alfvenic waves and stochastic ion heating. Finally we will show the properties of the resulting density cavities.
Marchenko, V. S.; Panwar, A.; Reznik, S. N.; Ryu, C. M.
2017-09-01
In a recent work, we have shown that the plasma flow around the magnetic island can excite the beta-induced Alfvén eigenmode (BAE) (Marchenko et al 2016 Nucl. Fusion 56 106021). In the present communication, it is shown that coupling of this primary BAE and magnetic island generates secondary geodesic acoustic mode (GAM), which has the frequency and mode structure identical to those of the primary BAE. The fixed GAM/BAE amplitude ratio, determined by the plasma neutrality, is comparable with the plasma/magnetic pressure ratio. This nonlinear coupling can be responsible for axis-symmetric modes, which accompany island-driven Alfvénic modes observed on HL-2A tokamak (Chen et al 2013 Nucl. Fusion 53 113010).
Hahn, Michael
2013-01-01
We present a measurement of the energy carried and dissipated by Alfv\\'en waves in a polar coronal hole. Alfv\\'en waves have been proposed as the energy source that heats the corona and drives the solar wind. Previous work has shown that line widths decrease with height in coronal holes, which is a signature of wave damping, but have been unable to quantify the energy lost by the waves. This is because line widths depend on both the non-thermal velocity v_nt and the ion temperature T_i. We have implemented a means to separate the T_i and v_nt contributions using the observation that at low heights the waves are undamped and the ion temperatures do not change with height. This enables us to determine the amount of energy carried by the waves at low heights, which is proportional to v_nt. We find the initial energy flux density present was 6.7 +/- 0.7 x 10^5 erg cm^-2 s^-1, which is sufficient to heat the coronal hole and acccelerate the solar wind during the 2007 - 2009 solar minimum. Additionally, we find tha...
Wang, C B; Lee, L C
2014-01-01
A scenario is proposed to explain the preferential heating of minor ions and differential streaming velocity between minor ions and protons observed in the solar corona and in the solar wind. It is demonstrated by test particle simulations that minor ions can be nearly fully picked up by intrinsic Alfv\\'en-cyclotron waves observed in the solar wind based on the observed wave energy density. Both high frequency ion-cyclotron waves and low frequency Alfv\\'en waves play crucial roles in the pickup process. A minor ion can first gain a high magnetic moment through the resonant wave-particle interaction with ion-cyclotron waves, and then this ion with a large magnetic moment can be trapped by magnetic mirror-like field structures in the presence of the lower-frequency Alfv\\'en waves. As a result, the ion is picked up by these Alfv\\'en-cyclotron waves. However, minor ions can only be partially picked up in the corona due to low wave energy density and low plasma beta. During the pickup process, minor ions are stoch...
Squire, J.; Bhattacharjee, A. [Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States)
2014-12-10
We study magnetorotational instability (MRI) using nonmodal stability techniques. Despite the spectral instability of many forms of MRI, this proves to be a natural method of analysis that is well-suited to deal with the non-self-adjoint nature of the linear MRI equations. We find that the fastest growing linear MRI structures on both local and global domains can look very different from the eigenmodes, invariably resembling waves shearing with the background flow (shear waves). In addition, such structures can grow many times faster than the least stable eigenmode over long time periods, and be localized in a completely different region of space. These ideas lead—for both axisymmetric and non-axisymmetric modes—to a natural connection between the global MRI and the local shearing box approximation. By illustrating that the fastest growing global structure is well described by the ordinary differential equations (ODEs) governing a single shear wave, we find that the shearing box is a very sensible approximation for the linear MRI, contrary to many previous claims. Since the shear wave ODEs are most naturally understood using nonmodal analysis techniques, we conclude by analyzing local MRI growth over finite timescales using these methods. The strong growth over a wide range of wave-numbers suggests that nonmodal linear physics could be of fundamental importance in MRI turbulence.
J Squire, A Bhattacharjee [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2014-07-01
We study the magnetorotational instability (MRI) (Balbus & Hawley 1998) using non-modal stability techniques.Despite the spectral instability of many forms of the MRI, this proves to be a natural method of analysis that is well-suited to deal with the non-self-adjoint nature of the linear MRI equations. We find that the fastest growing linear MRI structures on both local and global domains can look very diff erent to the eigenmodes, invariably resembling waves shearing with the background flow (shear waves). In addition, such structures can grow many times faster than the least stable eigenmode over long time periods, and be localized in a completely di fferent region of space. These ideas lead – for both axisymmetric and non-axisymmetric modes – to a natural connection between the global MRI and the local shearing box approximation. By illustrating that the fastest growing global structure is well described by the ordinary diff erential equations (ODEs) governing a single shear wave, we find that the shearing box is a very sensible approximation for the linear MRI, contrary to many previous claims. Since the shear wave ODEs are most naturally understood using non-modal analysis techniques, we conclude by analyzing local MRI growth over finite time-scales using these methods. The strong growth over a wide range of wave-numbers suggests that non-modal linear physics could be of fundamental importance in MRI turbulence (Squire & Bhattacharjee 2014).
Simulations of the Mg II k and Ca II 8542 lines from an Alfv\\'en Wave-heated flare chromosphere
Kerr, Graham S; Russell, Alexander J B; Allred, Joel C
2016-01-01
We use radiation hydrodynamic simulations to examine two models of solar flare chromospheric heating: Alfv\\'en wave dissipation and electron beam collisional losses. Both mechanisms are capable of strong chromospheric heating, and we show that the distinctive atmospheric evolution in the mid-to-upper chromosphere results in Mg II k-line emission that should be observably different between wave-heated and beam-heated simulations. We also present Ca II 8542A profiles which are formed slightly deeper in the chromosphere. The Mg II k-line profiles from our wave-heated simulation are quite different from those from a beam-heated model and are more consistent with IRIS observations. The predicted differences between the Ca II 8542A in the two models are small. We conclude that careful observational and theoretical study of lines formed in the mid-to-upper chromosphere holds genuine promise for distinguishing between competing models for chromospheric heating in flares.
Ethier, Wilfred J.
2002-01-01
This paper addresses a complex of globalization issues: the effect of globalization on the skill premium; the effect of globalization on unemployment; the relative importance of globalization and exogenous technical change; the effect of globalization on the ability of national governments to conduct independent social policies. Thinking about these topics has been dominated by a large empirical literature concluding that trade has played a relatively minor role in the rise of the skill premi...
Philipsen, Lotte; Baggesgaard, Mads Anders
2013-01-01
In order to understand globalization, we need to consider what globalization is not. That is, in order to understand the mechanisms and elements that work toward globalization, we must, in a sense, read against globalization, highlighting the limitations of the concept and its inherent conflicts....... Only by employing this as a critical practice will we be analytically able to gain a dynamic understanding of the forces of globalization as they unfold today and as they have developed historically....
Chen, X. [University of California-Irvine, Irvine, California 92697 (United States); General Atomics, P.O. Box 85608, San Diego, California 92186 (United States); Heidbrink, W. W. [University of California-Irvine, Irvine, California 92697 (United States); Kramer, G. J.; Nazikian, R.; Grierson, B. A.; Podesta, M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 (United States); Van Zeeland, M. A.; Pace, D. C.; Petty, C. C.; Fisher, R. K. [General Atomics, P.O. Box 85608, San Diego, California 92186 (United States); Zeng, L. [University of California, Los Angeles 90095, California (United States); Austin, M. E. [University of Texas-Austin, Austin, Texas 78712 (United States)
2014-08-15
Two key insights into interactions between Alfvén eigenmodes (AEs) and energetic particles in the plasma core are gained from measurements and modeling of first-orbit beam-ion loss in DIII-D. First, the neutral beam-ion first-orbit losses are enhanced by AEs and a single AE can cause large fast-ion displacement. The coherent losses are from born trapped full energy beam-ions being non-resonantly scattered by AEs onto loss orbits within their first poloidal transit. The loss amplitudes scale linearly with the mode amplitude but the slope is different for different modes. The radial displacement of fast-ions by individual AEs can be directly inferred from the measurements. Second, oscillations in the beam-ion first-orbit losses are observed at the sum, difference, and harmonic frequencies of two independent AEs. These oscillations are not plasma modes and are absent in magnetic, density, and temperature fluctuations. The origin of the non-linearity as a wave-particle coupling is confirmed through bi-coherence analysis, which is clearly observed because the coherences are preserved by the first-orbit loss mechanism. An analytic model and full orbit simulations show that the non-linear features seen in the loss signal can be explained by a non-linear interaction between the fast ions and the two independent AEs.
Cao, G. M.; Li, Y. D.; Li, Q.; Sun, P. J.; Wu, G. J.; Hu, L. Q.; the EAST Team
2015-08-01
Beta-induced Alfvén eigenmodes (BAEs) during strong tearing modes (TMs) have been frequently observed in fast-electron plasmas of EAST tokamak. The dynamics of the short-scale ({k}\\perp {ρ }s~{1.5-4.3}) density fluctuations during the activity of BAEs with strong TMs has been preliminarily investigated by a tangential CO2 laser collective scattering system. The results suggest the active, but different, response of short-scale density fluctuations to the TMs and BAEs. In the low-frequency (0-10 kHz) part of density fluctuations, there are harmonic oscillations totally corresponding to those of TMs. In the medium-high frequency (10-250 kHz) part of density fluctuations, with the appearance of the BAEs, the medium-high frequency density fluctuations begin to be dominated by several quasi-coherent (QC) modes, and the frequencies of the QC modes seem to be related to the changes of both TMs and BAEs. These results would shed some light on the understanding of the multi-scale interaction physics.
Li, Peter Ping
2013-01-01
Global strategy differs from domestic strategy in terms of content and process as well as context and structure. The content of global strategy can contain five key elements, while the process of global strategy can have six major stages. These are expounded below. Global strategy is influenced...... by rich and complementary local contexts with diverse resource pools and game rules at the national level to form a broad ecosystem at the global level. Further, global strategy dictates the interaction or balance between different entry strategies at the levels of internal and external networks....
Narula, Rajneesh
Technology and globalization are interdependent processes. Globalization has a fundamental influence on the creation and diffusion of technology, which, in turn, affects the interdependence of firms and locations. This volume examines the international aspect of this interdependence at two levels...
... globalhealth/what/default.htm) CDC protects Americans through global health. frame support disabled and/or not supported ... Public Health Emergencies More stories Infographic More infographics Global Health & You OUTBREAKS DISEASES & CONDITIONS TRAVEL CDC JOBS ...
Vivi Triana
2008-03-01
Full Text Available Pemanasan global (global warming pada dasarnya merupakan fenomena peningkatan temperature global dari tahun ke tahun karena terjadinya efek rumah kaca (greenhouse effect yang disebabkan oleh meningkatnya emisi gas-gas seperti karbondioksida (CO2, metana (CH4, dinitrooksida (N2O dan CFC sehingga energy matahari terperangkap dalam atmosfer bumi. Berbagai literatur menunjukkan kenaikan temperatur global termasuk Indonesia yang terjadi pada kisaran 1,5 – 40 °C pada akhir abad 21.
Longstreet, Wilma S., Ed.
1988-01-01
This issue contains an introduction ("The Promise and Perplexity of Globalism," by W. Longstreet) and seven articles dedicated to exploring the meaning of global education for today's schools. "Global Education: An Overview" (J. Becker) develops possible definitions, identifies objectives and skills, and addresses questions and…
1997
This document contains four papers from a symposium on global human resource development (HRD). "Globalization of Human Resource Management (HRM) in Government: A Cross-Cultural Perspective" (Pan Suk Kim) relates HRM to national cultures and addresses its specific functional aspects with a unique dimension in a global organization.…
Douglas, Ian
2011-01-01
The concept of usability has become an increasingly important consideration in the design of all kinds of technology. As more products are aimed at global markets and developed through internationally distributed teams, usability design needs to be addressed in global terms. Interest in usability as a design issue and specialist area of research and education has developed steadily in North America and Europe since the 1980's. However, it is only over the last ten years that it has emerged as a global concern. Global Usability provides an introduction to the important issues in globalizing des
Slaby, Christoph; Könies, Axel; Kleiber, Ralf
2016-09-01
The resonant interaction of shear Alfvén waves with energetic particles is investigated numerically in tokamak and stellarator geometry using a non-perturbative MHD-kinetic hybrid approach. The focus lies on toroidicity-induced Alfvén eigenmodes (TAEs), which are most easily destabilized by a fast-particle population in fusion plasmas. While the background plasma is treated within the framework of an ideal-MHD theory, the drive of the fast particles, as well as Landau damping of the background plasma, is modelled using the drift-kinetic Vlasov equation without collisions. Building on analytical theory, a fast numerical tool, STAE-K, has been developed to solve the resulting eigenvalue problem using a Riccati shooting method. The code, which can be used for parameter scans, is applied to tokamaks and the stellarator Wendelstein 7-X. High energetic-ion pressure leads to large growth rates of the TAEs and to their conversion into kinetically modified TAEs and kinetic Alfvén waves via continuum interaction. To better understand the physics of this conversion mechanism, the connections between TAEs and the shear Alfvén wave continuum are examined. It is shown that, when energetic particles are present, the continuum deforms substantially and the TAE frequency can leave the continuum gap. The interaction of the TAE with the continuum leads to singularities in the eigenfunctions. To further advance the physical model and also to eliminate the MHD continuum together with the singularities in the eigenfunctions, a fourth-order term connected to radiative damping has been included. The radiative damping term is connected to non-ideal effects of the bulk plasma and introduces higher-order derivatives to the model. Thus, it has the potential to substantially change the nature of the solution. For the first time, the fast-particle drive, Landau damping, continuum damping, and radiative damping have been modelled together in tokamak- as well as in stellarator geometry.
Varela, J.; Spong, D. A.; Garcia, L.
2017-04-01
Energetic particle populations in nuclear fusion experiments can destabilize the Alfvén Eigenmodes through inverse Landau damping and couplings with gap modes in the shear Alfvén continua. We use the reduced MHD equations to describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles. We add the Landau damping and resonant destabilization effects using a closure relation. We apply the model to study the Alfvén mode stability in the inward-shifted configurations of the Large Helical Device (LHD), performing a parametric analysis of the energetic particle β ({βf} ) in a range of realistic values, the ratios of the energetic particle thermal/Alfvén velocities ({{V}\\text{th}}/{{V}A0} ), the magnetic Lundquist numbers (S) and the toroidal modes (n). The n = 1 and n = 2 TAEs are destabilized, although the n = 3 and n = 4 TAEs are weakly perturbed. The most unstable configurations are associated with the density gradients of energetic particles in the plasma core: the TAEs are destabilized, even for small energetic particle populations, if their thermal velocity is lower than 0.4 times the Alfvén velocity. The frequency range of MHD bursts measured in the LHD are 50–70 kHz for the n = 1 and 60–80 kHz for the n = 2 TAE, which is consistent with the model predictions. ).
Busck, Ole Gunni
2015-01-01
Øgede globale økologiske distributionskonflikter i kraft af neoliberal globalisering drevet af kravet om økonomisk vækst......Øgede globale økologiske distributionskonflikter i kraft af neoliberal globalisering drevet af kravet om økonomisk vækst...
Jensen, Niels Rosendal
Antologien handler om "demokratiproblemer i den globale sammenhæng" (del I) og "demokratiproblemer i uddannelse og for de offentligt ansatte" (del II), bundet sammen af et mellemstykke, der rækker ud mod begge poler både det globale og det lokale ved at knytte det til forholdet mellem marked...
2009-01-01
The current global financial situation bluntly and brutally brings home the fact that the global and local are closely connected in times of opportunity as well as crises. The articles in this issue of Asia Insights are about ontra-action between Asia, particularly China, and the Nordic countries...
Lattice Boltzmann methods for global linear instability analysis
Pérez, José Miguel; Aguilar, Alfonso; Theofilis, Vassilis
2016-11-01
Modal global linear instability analysis is performed using, for the first time ever, the lattice Boltzmann method (LBM) to analyze incompressible flows with two and three inhomogeneous spatial directions. Four linearization models have been implemented in order to recover the linearized Navier-Stokes equations in the incompressible limit. Two of those models employ the single relaxation time and have been proposed previously in the literature as linearization of the collision operator of the lattice Boltzmann equation. Two additional models are derived herein for the first time by linearizing the local equilibrium probability distribution function. Instability analysis results are obtained in three benchmark problems, two in closed geometries and one in open flow, namely the square and cubic lid-driven cavity flow and flow in the wake of the circular cylinder. Comparisons with results delivered by classic spectral element methods verify the accuracy of the proposed new methodologies and point potential limitations particular to the LBM approach. The known issue of appearance of numerical instabilities when the SRT model is used in direct numerical simulations employing the LBM is shown to be reflected in a spurious global eigenmode when the SRT model is used in the instability analysis. Although this mode is absent in the multiple relaxation times model, other spurious instabilities can also arise and are documented herein. Areas of potential improvements in order to make the proposed methodology competitive with established approaches for global instability analysis are discussed.
Global Mindsets: Exploration and Perspectives seeks to tackle a topic that is relatively new in research and practice, and is considered by many to be critical for firms seeking to conduct global business. It argues that multiple mindsets exist (across and within organizations), that they operate...... it is important for future scholars and managers and how it could be conceptualized. Global Mindsets: Exploration and Perspectives is split into two major sections; the first examines where the literature currently is with respect to the knowledge in the field and what conceptual frameworks guide the thinking......, and should help researchers determine areas of high potential research needs in the future. Given the fluid sense of global mindsets in action, the authors of this book have adopted a flexible and wide-ranging approach. Global Mindsets: Exploration and Perspectives includes conceptual chapters that push...
Global marketing and globalization miths
2012-01-01
Global marketing and advertising: understanding cultural paradoxes, de Marieke de Mooij, 3rd ed. Thousand Oaks, CA. Sage Publications, 2010, 322p. Global marketing and advertising: understanding cultural paradoxes, de Marieke de Mooij, 3rd ed. Thousand Oaks, CA. Sage Publications, 2010, 322p.
Global Content in Global Coursebooks
Mimoun Melliti
2013-10-01
Full Text Available This study aims at exploring the issue of “globality” in global coursebooks as manifested in investing features of connectedness, avoiding inappropriacy, and preserving inclusivity. To do this exploration, two research methods, content analysis and the questionnaire, were adopted. The content of an example of global coursebooks, Headway Intermediate (H/I, in addition to the perception of 251 of its users at Institute Bourguiba for Living Languages (IBLV were investigated. The results obtained revealed that “globality,” in terms of connectedness, inappropriacy, and inclusivity is partial in H/I as learners’ perceptions of it do not map with the content in the coursebook. This study raises questions about the suitability of global coursebooks to globally diverse learners and reveals the necessity of taking measures in the direction of localizing the content of English as a foreign language (EFL coursebooks.
Is 21st-century Rome a global city? Is it part of Europe's core or periphery? This volume examines the “real city” beyond Rome's historical center, exploring the diversity and challenges of life in neighborhoods affected by immigration, neoliberalism, formal urban planning, and grassroots social...... movements. The contributors engage with themes of contemporary urban studies–the global city, the self-made city, alternative modernities, capital cities and nations, urban change from below, and sustainability. Global Rome serves as a provocative introduction to the Eternal City and makes an original...
Harrington, Brooke
2015-01-01
This study links theories of relationality and institutional change to deepen understanding of professionals’ role in globalization. In previous institutional research, it has been conventional to treat professionals as agents of firms or transnational organizations, and institutional change...... environment. It also broadens the model of agency to include invention and improvisation by individual professionals, as a counterpart to collective strategic action. The argument is based on data from a 16-nation study exploring the emergence of a particular ‘globalized localism’: the transformation...... to specify a new, more detailed model of the ways local practices and ideas develop into global institutions....
Is 21st-century Rome a global city? Is it part of Europe's core or periphery? This volume examines the “real city” beyond Rome's historical center, exploring the diversity and challenges of life in neighborhoods affected by immigration, neoliberalism, formal urban planning, and grassroots social...... movements. The contributors engage with themes of contemporary urban studies–the global city, the self-made city, alternative modernities, capital cities and nations, urban change from below, and sustainability. Global Rome serves as a provocative introduction to the Eternal City and makes an original...
Hurricane Excitation of Earth Eigenmodes
Peters, Randall D.
2005-01-01
A non-conventional vertical seismometer, with good low-frequency sensitivity, was used to study earth motions in Macon, Georgia USA during the time of hurricane Charley, August 2004. During its transitions between water and land, the powerful storm showed an interesting history of microseisms and also generated more than half-a-dozen surprisingly coherent oscillations, whose frequencies ranged from 0.9 to 3 mHz.
Sørensen, Olav Jull
2016-01-01
The concept of Global Mindset (GM) – the way to think about the global reality – is on the agenda of multinational companies concomitant with the increase in global complexity, uncertainty and diversity. In spite of a number of studies, the concept is still fluid and far from a managerial...... way of thinking about the global business reality. The other extreme is a GM as an organizational capability and process with a GM in a continuous state of becoming – and thus in a continuously alignment with a dynamic context. In addition, we argue for what we call “situational capabilities”, i.......e. the capability to sense (quickly), reflect (constructively) and act purposefully (for mutual benefit). A case on an MNC is used at the end to show the organizational manifestations of a GM....
Andersen, Torben Juul
." - Steen Parsholt, Chairman and CEO, Aon Nordic Region. "Andersen has done a wonderful job of developing a comprehensive text that deals with risk management in global markets. I would recommend this book to any student or businessman who has a need to better understand the risks and risk management...... management practice. Of particular note is the global and integrated approach chosen in this book which should be of special interest to aspiring managers active in global and international markets." - Dr Jean-Pierre Zigrand, Lecturer in Finance, London School of Economics, UK. More than 90 per cent...... management situations. Its key features include: derivatives are introduced in a global market perspective; describes major derivative pricing models for practical use, extending these principles to valuation of real options; practical applications of derivative instruments are richly illustrated...
Barakat, Livia L.; Lorenz, Melanie P.; Ramsey, Jase R.
2016-01-01
urpose: – The purpose of this paper is to examine the effect of cultural intelligence (CQ) on the job performance of global managers. Design/methodology/approach: – In total, 332 global managers were surveyed from multinational companies operating in Brazil. The mediating effect of job satisfaction...... was tested on the CQ-job performance relationship. Findings: – The findings suggest that job satisfaction transmits the effect of CQ to job performance, such that global managers high in CQ exhibit more job satisfaction in an international setting, and therefore perform better at their jobs. Practical...... implications: – Results imply that global managers should increase their CQ in order to improve their job satisfaction and ultimately perform better in an international context. Originality/value: – The authors make three primary contributions to the international business literature. First, the authors...
Milwertz, Cecilia Nathansen; Cai, Yiping
2017-01-01
Both the People’s Republic of China (PRC) and Nordic countries (Sweden, Iceland, Denmark, Norway and Finland) view gender equality as a social justice issue and are politically committed towards achieving gender equality nationally and internationally. Since China has taken a proactive position o...... on globalization and global governance, gender equality is possibly an area that China may wish to explore in collaboration with the Nordic countries....
Barakat, Livia L.; Lorenz, Melanie P.; Ramsey, Jase R.
2016-01-01
Purpose: – The purpose of this paper is to examine the effect of cultural intelligence (CQ) on the job performance of global managers. Design/methodology/approach: – In total, 332 global managers were surveyed from multinational companies operating in Brazil. The mediating effect of job satisfact...... behavior literature, it is not often explicitly associated with global managers that are working in cross-cultural settings. Finally, the authors posit that job satisfaction mediates the relationship between CQ and job performance.......Purpose: – The purpose of this paper is to examine the effect of cultural intelligence (CQ) on the job performance of global managers. Design/methodology/approach: – In total, 332 global managers were surveyed from multinational companies operating in Brazil. The mediating effect of job...... satisfaction was tested on the CQ-job performance relationship. Findings: – The findings suggest that job satisfaction transmits the effect of CQ to job performance, such that global managers high in CQ exhibit more job satisfaction in an international setting, and therefore perform better at their jobs...
Hulme, M
1998-01-01
Global warming-like deforestation, the ozone hole and the loss of species- has become one of the late 20the century icons of global environmental damage. The threat, is not the reality, of such a global climate change has motivated governments. businesses and environmental organisations, to take serious action ot try and achieve serious control of the future climate. This culminated last December in Kyoto in the agreement for legally-binding climate protocol. In this series of three lectures I will provide a perspective on the phenomenon of global warming that accepts the scientific basis for our concern, but one that also recognises the dynamic interaction between climate and society that has always exited The future will be no different. The challenge of global warning is not to pretend it is not happening (as with some pressure groups), nor to pretend it threatens global civilisation (as with other pressure groups), and it is not even a challenge to try and stop it from happening-we are too far down the ro...
General Description of Ideal Tokamak MHD Instability Ⅱ
石秉仁
2002-01-01
In this subsequent study on general description of ideal tokamak MHD instability,the part Ⅱ, by using a coordinate with rectified magnetic field lines, the eigenmode equationsdescribing the low-mode-number toroidal Alfven modes (TAE and EAE) are derived through afurther expansion of the shear Alfven equation of motion.
Pfaff, R. F.
2009-01-01
On December 14,2002, a NASA Black Brant X sounding rocket was launched equatorward from Ny Alesund, Spitzbergen (79 N) into the dayside cusp and subsequently cut across the open/closed field line boundary, reaching an apogee of771 km. The launch occurred during Bz negative conditions with strong By negative that was changing during the flight. SuperDarn (CUTLASS) radar and subsequent model patterns reveal a strong westward/poleward convection, indicating that the rocket traversed a rotational reversal in the afternoon merging cell. The payload returned DC electric and magnetic fields, plasma waves, energetic particle, suprathermal electron and ion, and thermal plasma data. We provide an overview of the main observations and focus on the DC electric field results, comparing the measured E x B plasma drifts in detail with the CUTLASS radar observations of plasma drifts gathered simultaneously in the same volume. The in situ DC electric fields reveal steady poleward flows within the cusp with strong shears at the interface of the closed/open field lines and within the boundary layer. We use the observations to discuss ionospheric signatures of the open/closed character of the cusp/low latitude boundary layer as a function of the IMF. The electric field and plasma density data also reveal the presence of very strong plasma irregularities with a large range of scales (10 m to 10 km) that exist within the open field line cusp region yet disappear when the payload was equatorward of the cusp on closed field lines. These intense low frequency wave observations are consistent with strong scintillations observed on the ground at Ny Alesund during the flight. We present detailed wave characteristics and discuss them in terms of Alfven waves and static irregularities that pervade the cusp region at all altitudes.
Integrated global digital image correlation for interface delamination characterization
Hoefnagels, Johan P.M.
2013-07-23
Interfacial delamination is a key reliability challenge in composites and micro-electronic systems due to (high-density) integration of dissimilar materials. Predictive finite element models are used to minimize delamination failures during design, but require accurate interface models to capture (irreversible) crack initiation and propagation behavior observed in experiments. Therefore, an Integrated Global Digital Image Correlation (I-GDIC) strategy is developed for accurate determination of mechanical interface behavior from in-situ delamination experiments. Recently, a novel miniature delamination setup was presented that enables in-situ microscopic characterization of interface delamination while sensitively measuring global load-displacement curves for all mode mixities. Nevertheless, extraction of detailed mechanical interface behavior from measured images is challenging, because deformations are tiny and measurement noise large. Therefore, an advanced I-GDIC methodology is developed which correlates the image patterns by only deforming the images using kinematically-admissible \\'eigenmodes\\' that correspond to the few parameters controlling the interface tractions in an analytic description of the crack tip deformation field, thereby greatly enhancing accuracy and robustness. This method is validated on virtual delamination experiments, simulated using a recently developed self-adaptive cohesive zone (CZ) finite element framework. © The Society for Experimental Mechanics, Inc. 2014.
Lindberg Christensen, Lars; Russo, P.
2009-05-01
IYA2009 is a global collaboration between almost 140 nations and more than 50 international organisations sharing the same vision. Besides the common brand, mission, vision and goals, IAU established eleven cornerstones programmes to support the different IYA2009 stakeholder to organize events, activities under a common umbrella. These are global activities centred on specific themes and are aligned with IYA2009's main goals. Whether it is the support and promotion of women in astronomy, the preservation of dark-sky sites around the world or educating and explaining the workings of the Universe to millions, the eleven Cornerstones are key elements in the success of IYA2009. However, the process of implementing global projects across cultural boundaries is challenging and needs central coordination to preserve the pre-established goals. During this talk we will examine the ups and downs of coordinating such a project and present an overview of the principal achievements for the Cornerstones so far.
Niño-Zarazúa, Miguel; Roope, Laurence; Tarp, Finn
2016-01-01
This paper measures trends in global interpersonal inequality during 1975–2010 using data from the most recent version of the World Income Inequality Database (WIID). The picture that emerges using ‘absolute,’ and even ‘centrist’ measures of inequality, is very different from the results obtained...... using standard ‘relative’ inequality measures such as the Gini coefficient or Coefficient of Variation. Relative global inequality has declined substantially over the decades. In contrast, ‘absolute’ inequality, as captured by the Standard Deviation and Absolute Gini, has increased considerably...... and unabated. Like these ‘absolute’ measures, our ‘centrist’ inequality indicators, the Krtscha measure and an intermediate Gini, also register a pronounced increase in global inequality, albeit, in the case of the latter, with a decline during 2005 to 2010. A critical question posed by our findings is whether...
Prof. Ph.D. Ion Bucur
2007-05-01
Full Text Available Finding the anachronisms and the failures of the present globalization, as well as the vitiated system of world-wide government, has stimulated the debates regarding the identification of a more equitable form of globalization to favor the acceleration of the economic increase and the reduction of poverty.The deficiency of the present international economic institutions, especially the lack of transparency and democratic responsibility, claims back with acuteness the reformation of the architecture of the international institutional system and the promotion of those economical policies which must ensure the stability world-wide economy and the amelioration of the international equity.
Cheraghi, Maryam; Schøtt, Thomas
2016-01-01
A firm may be conceived global, in the sense that, before its birth, the founding entrepreneur has a transnational network of advisors which provides an embedding for organising the upstart that may include assembling resources and marketing abroad. The purpose is to account for the entrepreneurs...... the intending, starting and operating phases, fairly constantly with only small fluctuations. The firm is conceived global in terms of the entrepreneur's transnational networking already in the pre-birth phase, when the entrepreneur is intending to start the firm. These phase effects hardly depend on attributes...
Fejerskov, Adam Moe; Rasmussen, Christel
2016-01-01
During the past decade, academic attention to the role of private foundations in international development cooperation has greatly intensified. The largest foundations have increased their global giving and moved towards strategic social impact, but we do not know if such processes have also...... occurred at a more micro level. This article explores this issue by studying the international activities of Danish foundations. It finds that grant-making on global issues is increasing, and that several foundations have undergone transformations in their approach to grantmaking, making them surprisingly...
van der Linden, M.
2009-01-01
The recent growth of the working classes in various parts of the Global South (or what was called the Tricontinent of Africa, Asia, and Latin America some years ago) has important consequences for labor historians. For a very long time labor history was mainly based in the North Atlantic region,
M.J. Mol; R.J.M. van Tulder (Rob); P.R. Beije (Paul)
2002-01-01
textabstractSince the early 1990s international - or even global - outsourcing of intermediate products from suppliers has been propagated as a key means to improve the performance of firms. It is argued that becoming more lean and internationally focused is beneficial for the buyer as
2012-01-01
Molycorp Announces Successful Close of Neo Materials Acquisition Molycorp, Inc. announced on 11 June 2012 that its acquisition of Canadian-based Neo Material Technologies Inc. has officially closed, creating a global rare earth leader with a combination of a world-class rare earth resource, ultra-high-purity rare earth processing capabilities, and full ＇mine-to-magnetics＇ vertical integration.
Wilson, Erin; Steger, Manfred; Siracusa, Joseph; Battersby, Paul
2014-01-01
The pursuit of a global order founded on universal rules extends beyond economics into the normative spheres of law, politics and justice. Justice globalists claim universal principles applicable to all societies irrespective of religion or ideology. This view privileges human rights, democracy and
Rosenstand, Claus A. Foss
2007-01-01
- idet min lillebror er blandt de anholdte; og mine forældre derfor skulle være blandt de skyldige. Hvilket har fået mig til at fare i blækhuset, med en alternativ forklaringsmodel, der ikke handler om skyld. Kulturen omkring Ungdomshuset er globalt orienteret, og derfor meget sensible overfor global...... forandringer. Den globale orientering kommer blandt andet til udtryk i det relativt store internationale netværk, som bakker de unge op i deres protester - enten ved tilstedeværelse i København eller andre sympatiaktioner. Siden den 11. september, 2001, er globale realiteter blevet eksponeret i massemedierne...... også sig selv og sin omverden igennem en global optik. Ungdommen af i dag er som børn vokset op i et samfund og dannelseskultur, der ikke har været globalt orienteret, hvor demokratiske værdier som frihed, lighed, menneskerettigheder her hersket i det socialdemokratiske projekt om sammenhængskraft. Og...
van Bottenburg, Maarten
2001-01-01
Why is soccer the sport of choice in South America, while baseball has soared to popularity in the Carribean? How did cricket become India's national sport, while China is a stronghold of table tennis? In Global Games, Maarten van Bottenburg asserts that it is the 'hidden competition' of social and
Wilson, Erin; Steger, Manfred; Siracusa, Joseph; Battersby, Paul
2014-01-01
The pursuit of a global order founded on universal rules extends beyond economics into the normative spheres of law, politics and justice. Justice globalists claim universal principles applicable to all societies irrespective of religion or ideology. This view privileges human rights, democracy and
Brewer, Thomas L.; Boyd, Gavin
An argument that globalization is an ungoverned integration process in which US firms are agents of structural change. It describes the benefits and costs (for example, generating pressure for protection of US home markets), and reviews the expansion of interdependencies between the US and others....
Rosenstand, Claus A. Foss
2007-01-01
- idet min lillebror er blandt de anholdte; og mine forældre derfor skulle være blandt de skyldige. Hvilket har fået mig til at fare i blækhuset, med en alternativ forklaringsmodel, der ikke handler om skyld. Kulturen omkring Ungdomshuset er globalt orienteret, og derfor meget sensible overfor global...... forandringer. Den globale orientering kommer blandt andet til udtryk i det relativt store internationale netværk, som bakker de unge op i deres protester - enten ved tilstedeværelse i København eller andre sympatiaktioner. Siden den 11. september, 2001, er globale realiteter blevet eksponeret i massemedierne...... også sig selv og sin omverden igennem en global optik. Ungdommen af i dag er som børn vokset op i et samfund og dannelseskultur, der ikke har været globalt orienteret, hvor demokratiske værdier som frihed, lighed, menneskerettigheder her hersket i det socialdemokratiske projekt om sammenhængskraft. Og...
Wallensteen, P.; Galtung, J.; Portales, C.
1985-01-01
This book contains 10 chapters. Some of the titles are: Military Formations and Social Formations: A Structural Analysis; Global Conflict Formations: Present Developments and Future Directions; War and the Power of Warmakers in Western Europe and Elsewhere, 1600-1980; and The Urban Type of Society and International War.
van Bottenburg, Maarten
2001-01-01
Why is soccer the sport of choice in South America, while baseball has soared to popularity in the Carribean? How did cricket become India's national sport, while China is a stronghold of table tennis? In Global Games, Maarten van Bottenburg asserts that it is the 'hidden competition' of social and
Auroral vortex street formed by the magnetosphere-ionosphere coupling instability
Hiraki, Yasutaka
2014-01-01
By performing three-dimensional nonlinear MHD simulations including Alfven eigenmode perturbations most unstable to the ionospheric feedback effects, we reproduced the auroral vortex street that often appears just before substorm onset. We found that an initially placed arc splits, intensifies, and rapidly deforms into a vortex street. We also found that there is a critical convection electric field for growth of the Alfven eigenmodes. The vortex street is shown to be a consequence of coupling between the magnetospheric Alfven waves carrying field-aligned currents and the ionospheric density waves driven by Pedersen/Hall currents.
Manners, Ian
2010-01-01
The mythology of the European Union (EU) in world politics can be told and untold in many different ways. This article focuses on the lore or stories of who did what to whom, the ideological projection of the past onto the present and the escapist pleasure of story telling in looking at the mytho......The mythology of the European Union (EU) in world politics can be told and untold in many different ways. This article focuses on the lore or stories of who did what to whom, the ideological projection of the past onto the present and the escapist pleasure of story telling in looking...... at the mythology of ‘global Europa' - the EU in the world. It concludes with a reflection on the way in which the many diverse myths of global Europa compete for daily attention, whether as lore, ideology, or pleasure. In this respect the mythology of global Europa is part of our everyday existence, part of the EU...
Global Noise and Global Englishes
Alastair Pennycook
2013-09-01
Full Text Available Global Noise: Rap and Hip-Hop Outside the USA, alluding to Tricia Rose’s US rap-music book, Black Noise, aims to do much more than merely extend the reach of the study of rap and hip-hop beyond the USA, as its subtitle might suggest. While acknowledging the importance of the work of both Rose and Potter, this collection’s editor, Tony Mitchell, contests their respective views that rap and hip-hop are essentially expressions of African-American culture, and that all forms of rap and hip-hop derive from these origins. He argues that these forms have become ‘a vehicle for global youth affiliations and a tool for reworking local iden- tity all over the world’.
Global climate experiment; Globales Klimaexperiment
Quasching, V. [Deutsche Zentrum fuer Luft- und Raumfahrt e.V., Plataforma Solar de Almeria (Spain)
2003-07-01
Continued greenhouse gas emissions are part of one of our today's largest scientific experiments. Most scientists agree that anthropogenic influences are responsible for already observed climatic changes. Others demand further investigations and justify continued unlimited use of fossil energy sources. This paper describes generally accepted facts on greenhouse gas emissions and climatic change with focus on part and influence of the global energy industry. [German] Mit dem fortgesetzten Ausstoss von Treibhausgasen wird zurzeit ein globales naturwissenschaftliches Experiment betrieben. Viele Wissenschaftler sind sich einig, dass bereits beobachtete Klimaveraenderungen auf den Einfluss des Menschen zurueckzufuehren sind. Andere fordern hingegen weitere Untersuchungen und halten bis dahin eine weitere uneingeschraenkte Verwendung fossiler Energietraeger fuer gerechtfertigt. Dieser Beitrag fasst weitgehend anerkannte Fakten ueber Treibhausgasemissionen und Klimaveraenderungen zusammen und beschreibt die Rolle und den Einfluss der Energiewirtschaft.
Krishnamoorthy, Sriram; Daily, Jeffrey A.; Vishnu, Abhinav; Palmer, Bruce J.
2015-11-01
Global Arrays (GA) is a distributed-memory programming model that allows for shared-memory-style programming combined with one-sided communication, to create a set of tools that combine high performance with ease-of-use. GA exposes a relatively straightforward programming abstraction, while supporting fully-distributed data structures, locality of reference, and high-performance communication. GA was originally formulated in the early 1990’s to provide a communication layer for the Northwest Chemistry (NWChem) suite of chemistry modeling codes that was being developed concurrently.
Global instabilities and transient growth in Blasius boundary-layer flow over a compliant panel
K Tsigklifis; A D Lucey
2015-05-01
We develop a hybrid of computational and theoretical approaches suited to study the fluid–structure interaction (FSI) of a compliant panel, flush between rigid upstream and downstream wall sections, with a Blasius boundary-layer flow. The ensuing linear-stability analysis is focused upon global instability and transient growth of disturbances. The flow solution is developed using a combination of vortex and source boundary-element sheets on a computational grid while the dynamics of a plate-spring compliant wall are couched in finite-difference form. The fully coupled FSI system is then written as an eigenvalue problem and the eigenvalues of the various flow- and wall-based instabilities are analysed. It is shown that coalescence or resonance of a structural eigenmode with either a flow-based Tollmien–Schlichting Wave (TSW) or wall-based travelling-wave flutter (TWF) modes can occur. This can render the nature of these well-known convective instabilities to become global for a finite compliant wall giving temporal growth of system disturbances. Finally, a non-modal analysis based on the linear superposition of the extracted temporal modes is presented. This reveals a high level of transient growth when the flow interacts with a compliant panel that has structural properties which render the FSI system prone to global instability. Thus, to design stable finite compliant panels for applications such as boundary-layer transition postponement, both global instabilities and transient growth must be taken into account.
Global simulations of galactic winds including cosmic ray streaming
Ruszkowski, Mateusz; Zweibel, Ellen
2016-01-01
Galactic outflows play an important role in galactic evolution. Despite their importance, a detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. In an effort to gain more insight into the nature of these flows, we perform global three-dimensional magneto-hydrodynamical simulations of an isolated Milky Way-size starburst galaxy. We focus on the dynamical role of cosmic rays injected by supernovae, and specifically on the impact of the streaming and anisotropic diffusion of cosmic rays along the magnetic fields. We find that these microphysical effects can have a significant effect on the wind launching and mass loading factors depending on the details of the plasma physics. Due to the cosmic ray streaming instability, cosmic rays propagating in the interstellar medium scatter on self-excited Alfven waves and couple to the gas. When the wave growth due to the streaming instability is inhibited by some damping process, such as the turbulent damping, the cosmic ...
Global environmental policy; Globale Umweltpolitik
Varwick, J. (ed.)
2008-07-01
For some years, the interest in global environmental problems and global environmental policy increased substantially. In order to prevent a sustainable and irreversible damage of the global ecological systems, it requires an ecological restructuring of the economy of the industrial nations and a environmental compatible development in the developing countries. Under this aspect, the book under consideration dedicates itself to this problem by means of five scientific contributions: (a) The principle sustainability (Felix Ekardt); (b) Climate change as a world problem (Andreas Rechkemmer); (c) The role of the pioneer of the European Union in the international climate policy: Successes and challenges (Sebastian Oberthuer); (d) Cause for conflict water (Tobias Lindenberg); (e) Environmental political instruments in theory and practice (Johanna Reichenbach/Till Requate). Instruction practice also is concerned with a cross section topic consisting of environmental and European politics: Competent instructions concerning to the European Union - an instruction series for the secondary school I (George Wiesseno, Valentin Eck). Two forum contributions go beyond the topic: (a) Against rigid (society-)political borders in the science (Tim Engartner); (b) Elections in Hamburg - Schwarz-Gruen as new coalition model for the federation? In the column 'the current topic' Gotthard Breit reports on the protests against China on the occasion of the Olympic Games 2008. The author focuses some strangenesses in the debate and pleads for a sober view of the topic. With a report on 'the Beutelsbacher discussions' at 18th to 20th February, 2008, Timo Web finishes this book.
Global teaching of global seismology
Stein, S.; Wysession, M.
2005-12-01
Our recent textbook, Introduction to Seismology, Earthquakes, & Earth Structure (Blackwell, 2003) is used in many countries. Part of the reason for this may be our deliberate attempt to write the book for an international audience. This effort appears in several ways. We stress seismology's long tradition of global data interchange. Our brief discussions of the science's history illustrate the contributions of scientists around the world. Perhaps most importantly, our discussions of earthquakes, tectonics, and seismic hazards take a global view. Many examples are from North America, whereas others are from other areas. Our view is that non-North American students should be exposed to North American examples that are type examples, and that North American students should be similarly exposed to examples elsewhere. For example, we illustrate how the Euler vector geometry changes a plate boundary from spreading, to strike-slip, to convergence using both the Pacific-North America boundary from the Gulf of California to Alaska and the Eurasia-Africa boundary from the Azores to the Mediterranean. We illustrate diffuse plate boundary zones using western North America, the Andes, the Himalayas, the Mediterranean, and the East Africa Rift. The subduction zone discussions examine Japan, Tonga, and Chile. We discuss significant earthquakes both in the U.S. and elsewhere, and explore hazard mitigation issues in different contexts. Both comments from foreign colleagues and our experience lecturing overseas indicate that this approach works well. Beyond the specifics of our text, we believe that such a global approach is facilitated by the international traditions of the earth sciences and the world youth culture that gives students worldwide common culture. For example, a video of the scene in New Madrid, Missouri that arose from a nonsensical earthquake prediction in 1990 elicits similar responses from American and European students.
Effect of Be disc evolution on global one-armed oscillations
Oktariani, F.; Okazaki, A. T.; Kunjaya, C.; Aprilia
2016-07-01
We study the effect of density distribution evolution on the global one-armed oscillation modes in low-viscosity discs around isolated and binary Be stars. Observations show that some Be stars exhibit evidence of formation and dissipation of the equatorial disc. In this paper, we first calculate the density evolution in discs around isolated Be stars. To model the formation stage of the disc, we inject mass at a radius just outside the star at a constant rate for 30-50 yr. As the disc develops, the density distribution approaches the form of the steady disc solution. Then, we turn-off the mass injection to model the disc dissipation stage. The innermost part of the disc starts accretion, and a gap forms between the star and the disc. Next, we calculate the one-armed modes at several epochs. We neglect the effect of viscosity because the time-scale of oscillations is much shorter than the disc evolution time-scale for low viscosity. In the disc formation stage, the eigenfrequency increases with time towards the value for the steady state disc. On the other hand, one-armed eigenmodes in dissipating Be discs have significantly higher eigenfrequencies and narrower propagation regions. Observationally, such a change of mode characteristics can be taken as an evidence for gap opening around the star. In binary Be stars, the characteristics of the disc evolution and the eigenmodes are qualitatively the same as in isolated Be stars, but quantitatively, they have shorter evolution time-scales and higher eigenfrequencies, which is in agreement with the observed trend.
Electromagnetic microinstabilities in tokamak plasmas using a global spectral approach
Falchetto, G. L
2002-03-01
Electromagnetic microinstabilities in tokamak plasmas are studied by means of a linear global eigenvalue numerical code. The code is the electromagnetic extension of an existing electrostatic global gyrokinetic spectral toroidal code, called GLOGYSTO. Ion dynamics is described by the gyrokinetic equation, so that ion finite Larmor radius effects are taken into account to all orders. Non adiabatic electrons are included in the model, with passing particles described by the drift-kinetic equation and trapped particles through the bounce averaged drift-kinetic equation. A low frequency electromagnetic perturbation is applied to a low -but finite- {beta}plasma (where the parameter {beta} identifies the ratio of plasma pressure to magnetic pressure); thus, the parallel perturbations of the magnetic field are neglected. The system is closed by the quasi-neutrality equation and the parallel component of Ampere's law. The formulation is applied to a large aspect ratio toroidal configuration, with circular shifted surfaces. Such a simple configuration enables one to derive analytically the gyrocenter trajectories. The system is solved in Fourier space, taking advantage of a decomposition adapted to the toroidal geometry. The major contributions of this thesis are as follows. The electromagnetic effects on toroidal Ion Temperature Gradient driven (ITG) modes are studied. The stabilization of these modes with increasing {beta}, as predicted in previous work, is confirmed. The inclusion of trapped electron dynamics enables the study of its coupling to the ITG modes and of Trapped Electron Modes (TEM) .The effects of finite {beta} are considered together with those of different magnetic shear profiles and of the Shafranov shift. The threshold for the destabilization of an electromagnetic mode is identified. Moreover, the global formulation yields for the first time the radial structure of this so-called Alfvenic Ion Temperature Gradient (AITG) mode. The stability of the
MacMillan, Ian C; van Putten, Alexander B; McGrath, Rita Gunther
2003-05-01
Competition among multinationals these days is likely to be a three-dimensional game of global chess: The moves an organization makes in one market are designed to achieve goals in another in ways that aren't immediately apparent to its rivals. The authors--all management professors-call this approach "competing under strategic interdependence," or CSI. And where this interdependence exists, the complexity of the situation can quickly overwhelm ordinary analysis. Indeed, most business strategists are terrible at anticipating the consequences of interdependent choices, and they're even worse at using interdependency to their advantage. In this article, the authors offer a process for mapping the competitive landscape and anticipating how your company's moves in one market can influence its competitive interactions in others. They outline the six types of CSI campaigns--onslaughts, contests, guerrilla campaigns, feints, gambits, and harvesting--available to any multiproduct or multimarket corporation that wants to compete skillfully. They cite real-world examples such as the U.S. pricing battle Philip Morris waged with R.J. Reynolds--not to gain market share in the domestic cigarette market but to divert R.J. Reynolds's resources and attention from the opportunities Philip Morris was pursuing in Eastern Europe. And, using data they collected from their studies of consumer-products companies Procter & Gamble and Unilever, the authors describe how to create CSI tables and bubble charts that present a graphical look at the competitive landscape and that may uncover previously hidden opportunities. The CSI mapping process isn't just for global corporations, the authors explain. Smaller organizations that compete with a portfolio of products in just one national or regional market may find it just as useful for planning their next business moves.
Houghton, John
2005-06-01
'Global warming' is a phrase that refers to the effect on the climate of human activities, in particular the burning of fossil fuels (coal, oil and gas) and large-scale deforestation, which cause emissions to the atmosphere of large amounts of 'greenhouse gases', of which the most important is carbon dioxide. Such gases absorb infrared radiation emitted by the Earth's surface and act as blankets over the surface keeping it warmer than it would otherwise be. Associated with this warming are changes of climate. The basic science of the 'greenhouse effect' that leads to the warming is well understood. More detailed understanding relies on numerical models of the climate that integrate the basic dynamical and physical equations describing the complete climate system. Many of the likely characteristics of the resulting changes in climate (such as more frequent heat waves, increases in rainfall, increase in frequency and intensity of many extreme climate events) can be identified. Substantial uncertainties remain in knowledge of some of the feedbacks within the climate system (that affect the overall magnitude of change) and in much of the detail of likely regional change. Because of its negative impacts on human communities (including for instance substantial sea-level rise) and on ecosystems, global warming is the most important environmental problem the world faces. Adaptation to the inevitable impacts and mitigation to reduce their magnitude are both necessary. International action is being taken by the world's scientific and political communities. Because of the need for urgent action, the greatest challenge is to move rapidly to much increased energy efficiency and to non-fossil-fuel energy sources.
Nielsen, Rikke Kristine
2017-01-01
This paper addresses the call for identification of organizational contingencies related to global mindset, exploration of different forms of global mindset and their relationship with global strategies (Osland, Bird, Mendenhall & Osland, 2006). To this end, this paper explores global mindset...
B. Alonso
2006-01-01
Full Text Available Un avance significativo dentro del área de la ecología sólo se podrá lograr con la adopción generalizada de un sistema basado en el uso compartido de los datos entre científicos. Esta práctica, apoyada por el desarrollo de metadatos precisos que acompañen a los propios datos, conseguirá aumentar la escala temporal y espacial de los objetos de estudio, ventajas evidentes en un área en la que cuestiones de carácter global como el estudio de los efectos del cambio climático van adquiriendo cada vez mayor importancia. En la actualidad existen numerosos grupos de científicos que trabajan voluntariamente en el desarrollo de herramientas que faciliten a los científicos la documentación y el almacenaje de sus datos. Asimismo, Internet está demostrando ser un potente instrumento para compartirlos. Aprovechar estos recursos es decisión nuestra.
Making Globalization Work: Towards Global Economic Justice
Khan, Haider
2008-01-01
Globalization as a corporate-led process has come under much justifiable criticism. This paper attempts to give the term analytic content distinct from its more ideological formulations.. It then focuses on a normative analysis of globalization from the capabilities perspective. A freedom-centered perspective such as the capabilities approach emphasizes policies and institutions that can enhance freedom globally and locally. A global governance structure based on transparent principles of bo...
Mills, Melinda
2009-01-01
Globalization is increasingly linked to inequality, but with often divergent and polarized findings. Some researchers show that globalization accentuates inequality both within and between countries. Others maintain that these claims are patently incorrect, arguing that globalization has disintegrat
Globalization and economic cooperation
Javier Divar
2006-12-01
Full Text Available Economic globalization is nothing, really, that the universality of capitalism. Not globalized culture, and economic participation, and human rights, ... has only globalized market. We must react by substituting those materialistic values with cooperative economy.
Turcan, Romeo V.
2016-01-01
The purpose of this viewpoint paper is to motivate a program of research on late globalization, a program that could eventually lead to one or more significant theories of late globalization. The paper explores the phenomenon of late globalization as well as the idea of “late” by drawing on sparse...... literature on late globalization from sociocultural and economic perspectives. It illustrates in a vignette the character and features of late globalization observable in the withdrawal from foreign locations or deinternationalization of universities, as late globalizing entitis. The paper discusses...... the range of constructs around the core idea of late globalization, generating questions for future work in a late globalization research program....
MHD Field Line Resonances and Global Modes in Three-Dimensional Magnetic Fields
C.Z. Cheng
2002-05-30
By assuming a general isotropic pressure distribution P = P (y,a), where y and a are three-dimensional scalar functions labeling the field lines with B = -y x -a, we have derived a set of MHD eigenmode equations for both global MHD modes and field line resonances (FLR). Past MHD theories are restricted to isotropic pressures with P = P (y only). The present formulation also allows the plasma mass density to vary along the field line. The linearized ideal-MHD equations are cast into a set of global differential equations from which the field line resonance equations of the shear Alfvin waves and slow magnetosonic modes are naturally obtained for general three-dimensional magnetic field geometries with flux surfaces. Several new terms associated with the partial derivative of P with respect to alpha are obtained. In the FLR equations, a new term is found in the shear Alfvin FLR equation due to the geodesic curvature and the pressure gradient in the poloidal flux surface. The coupling between the shear Alfvin waves and the magnetosonic waves is through the combined effects of geodesic magnetic field curvature and plasma pressure as previously derived. The properties of the FLR eigenfunctions at the resonance field lines are investigated, and the behavior of the FLR wave solutions near the FLR surface are derived. Numerical solutions of the FLR equations for three-dimensional magnetospheric fields in equilibrium with high plasma pressure will be presented in a future publication.
Global cities: Global parks: Globalizing of digital leisure networks.
P.A. Arora (Payal)
2013-01-01
textabstractThis paper proposes to understand the globalizing of online Social Network Sites (SNS) through the spatial metaphor of global parks. It builds upon a commonly accepted ideation of the city as socially-constructed and that which has been harnessed to understand the spatiality of the Inte
GLOBALIZATION AND BUSINESS ETHICS
Khadartseva, L.; Agnaeva, L.
2014-01-01
It is assumed that local conditions of markets may be different, but some global markets, ethics and social responsibility principles should be applicable to all markets. As markets globalize and an increasing proportion of business activity transcends national borders, institutions need to help manage, regulate, and police the global marketplace, and to promote the establishment of multinational treaties to govern the global business system
Wang Zaibang
2007-01-01
To enhance global governance has become more urgent with rapid development of globalization in the post-Cold War years. China has benefited from the process of globalization and hence should make greater contribution to the global governance in the future.
Globalization challenges in a globalized world
Dr.Sc. Gjon Boriçi
2016-01-01
Full Text Available Globalization is an ongoing phenomenon trying to redefine the economic, social, cultural and political dynamics of contemporary societies. The communication among countries and not only them, has been increased expanding political ties, making possible greater economic integration and wider cultural relations combined with augmented global wealth across the world. But, the process of globalization is in wider terms considered a beneficial one, but also viewed by some countries as a menace to national sovereignty and national culture. This paper tries to explain the obstacles to the process of globalization and its attendant benefits. Although globalization has arisen as a result of a more stable world, the factors that had contributed to its rise also help the factions interested to bring destabilization. In an academic approach in this article, between the research and comparative methods, I have been trying to get the maxims between economy, politics and diplomacy in their efforts of affecting the global era.
Global health and the global economic crisis.
Benatar, Solomon R; Gill, Stephen; Bakker, Isabella
2011-04-01
Although the resources and knowledge for achieving improved global health exist, a new, critical paradigm on health as an aspect of human development, human security, and human rights is needed. Such a shift is required to sufficiently modify and credibly reduce the present dominance of perverse market forces on global health. New scientific discoveries can make wide-ranging contributions to improved health; however, improved global health depends on achieving greater social justice, economic redistribution, and enhanced democratization of production, caring social institutions for essential health care, education, and other public goods. As with the quest for an HIV vaccine, the challenge of improved global health requires an ambitious multidisciplinary research program.
Theorising Global Business Spaces
Jones, A
2009-01-01
Over the last decade, geographers have paid a great deal of attention to transnational firms (TNCs) and global production networks (GPNs) in the global economy, to the emergence of a mobile transnational business class and also to the development of global or globalizing cities. All three literatures have made important contributions to understanding the spatiality of global economic activity, but each adopts a fairly discreet theoretical and empirical focus. This article aims to outline a nu...
Globalization and human cooperation.
Buchan, Nancy R; Grimalda, Gianluca; Wilson, Rick; Brewer, Marilynn; Fatas, Enrique; Foddy, Margaret
2009-03-17
Globalization magnifies the problems that affect all people and that require large-scale human cooperation, for example, the overharvesting of natural resources and human-induced global warming. However, what does globalization imply for the cooperation needed to address such global social dilemmas? Two competing hypotheses are offered. One hypothesis is that globalization prompts reactionary movements that reinforce parochial distinctions among people. Large-scale cooperation then focuses on favoring one's own ethnic, racial, or language group. The alternative hypothesis suggests that globalization strengthens cosmopolitan attitudes by weakening the relevance of ethnicity, locality, or nationhood as sources of identification. In essence, globalization, the increasing interconnectedness of people worldwide, broadens the group boundaries within which individuals perceive they belong. We test these hypotheses by measuring globalization at both the country and individual levels and analyzing the relationship between globalization and individual cooperation with distal others in multilevel sequential cooperation experiments in which players can contribute to individual, local, and/or global accounts. Our samples were drawn from the general populations of the United States, Italy, Russia, Argentina, South Africa, and Iran. We find that as country and individual levels of globalization increase, so too does individual cooperation at the global level vis-à-vis the local level. In essence, "globalized" individuals draw broader group boundaries than others, eschewing parochial motivations in favor of cosmopolitan ones. Globalization may thus be fundamental in shaping contemporary large-scale cooperation and may be a positive force toward the provision of global public goods.
Global health research needs global networking
Ignaciuk, A.; Leemans, R.
2012-01-01
To meet the challenges arising from global environmental change on human health, co-developing common approaches and new alliances of science and society are necessary. The first steps towards defining cross-cutting, health-environment issues were developed by the Global Environmental Change and Hum
Tanev, Stoyan
2012-01-01
This article provides insights from recent research on firms that are "born global". A born-global firm is a venture launched to exploit a global niche from the first day of its operations. The insights in this article are relevant to technology entrepreneurs and top management teams of new...... technology firms. After discussing various definitions for the term "born global" and identifying the main characteristics of born-global firms, this article lists a few salient characteristics of firms that are born global in the technology sector. The article concludes by identifying opportunities...
Rask, Morten
insight from the literature about business models, international product policy, international entry modes and globalization into a conceptual model of relevant design elements of global business models, enabling global business model innovation to deal with differences in a downstream perspective...... regarding the customer interface and in an upstream perspective regarding the supply infrastructure. The paper offers a coherent conceptual dynamic meta-model of global business model innovation. Students, scholars and managers within the field of international business can use this conceptualization...... to understand, to study, and to create global business model innovation. Managerial and research implications draw on the developed ideal type of global business model innovation....
DEEPAK NAYYAR
2015-09-01
Full Text Available ABSTRACTThe gathering momentum of globalization in the world economy has coincided with the spread of political democracy across countries. Economies have become global. But politics remains national. This essay explores the relationship between globalization and democracy, which is neither linear nor characterized by structural rigidities. It seeks to analyze how globalization might constrain degrees of freedom for nation states and space for democratic politics, and how political democracy within countries might exercise some checks and balances on markets and globalization. The essential argument is that the relationship between globalization and democracy is dialectical and does not conform to ideological caricatures.
Unified Description of Tokamak Ideal MHD Instabilities（I）
石秉仁
2002-01-01
By using a coordinate system associated with magnetic surfaces,a unified eigenmode equation for describing the tokamak ideal MHD instabilities is derived in the shear-Alfven approximation.Based on this equation having a general operator form,the eigen-mode equation governing the large-scale perturbation (such as the kink mode,the low-n ballooning mode and the Alfven mode) and small-scale perturbation(such as the high-n ballooning mode,the local mode) can be further deduced.In the first part of the present study,the small-scale perturbation is discussed in detail.
COMPETING CONCEPTIONS OF GLOBALIZATION
Leslie Sklair
2015-08-01
Full Text Available Globalization is a relatively new idea in the social sciences, although people who work in and write about the mass media, transnational corporations and international business have been using it for some time. The purpose of this paper is to critically review the ways in which sociologists and other social scientists use ideas of globalization and to evaluate the fruitfulness of these competing conceptions. The central feature of the idea of globalization is that many contemporary problems cannot be adequately studied at the level of nation-states, that is, in terms of each country and its inter-national relations. Instead, they need to be conceptualized in terms of global processes. Some have even gone so far as to predict that global forces, by which they usually mean transnational corporations and other global economic institutions, global culture or globalizing belief systems/ideologies of various types, or a combination of all of these, are becoming so powerful that the continuing existence of the nation-state is in serious doubt. This is not a necessary consequence of most theories of globalization. The argument of this paper is that much of the globalization literature is confused because not all those who use the term distinguish it clearly enough from internation-alization, and some writers appear to use the two terms interchangeably. I argue that a clear distinction must be drawn between the inter-national and the global. The hyphen in inter-national is to distinguish (inadequate conceptions of the global' founded on the existing even if changing system of nation-states, from (genuine conceptions of the global based on the emergence of global processes and a global system of social relations not founded on national characteristics or nation-states. This global system theory is the framework for my own research. Globalization studies can be categorized on the basis of four research clusters:1. The world-systems approach; 2. The global
Global solidarity, migration and global health inequity.
Eckenwiler, Lisa; Straehle, Christine; Chung, Ryoa
2012-09-01
The grounds for global solidarity have been theorized and conceptualized in recent years, and many have argued that we need a global concept of solidarity. But the question remains: what can motivate efforts of the international community and nation-states? Our focus is the grounding of solidarity with respect to global inequities in health. We explore what considerations could motivate acts of global solidarity in the specific context of health migration, and sketch briefly what form this kind of solidarity could take. First, we argue that the only plausible conceptualization of persons highlights their interdependence. We draw upon a conception of persons as 'ecological subjects' and from there illustrate what such a conception implies with the example of nurses migrating from low and middle-income countries to more affluent ones. Next, we address potential critics who might counter any such understanding of current international politics with a reference to real-politik and the insights of realist international political theory. We argue that national governments--while not always or even often motivated by moral reasons alone--may nevertheless be motivated to acts of global solidarity by prudential arguments. Solidarity then need not be, as many argue, a function of charitable inclination, or emergent from an acknowledgment of injustice suffered, but may in fact serve national and transnational interests. We conclude on a positive note: global solidarity may be conceptualized to helpfully address global health inequity, to the extent that personal and transnational interdependence are enough to motivate national governments into action.
Global Governance of Migration
2011-01-01
The aim of this thesis is to analyze the recently formed global governance of migration, which has got an unprecedented trans-boundary nature due to the impacts og globalization in the post Cold War era.
Information Global Marketing Management
Aleksandar Grubor
2010-01-01
Global marketing management needs to be implemented based on valid, i.e. reliable, timely, verifiable and high-quality marketing information, which will enable valid decision-making in global business operations...
Roesgaard, Marie Højlund
2016-01-01
Global citizenship as an idea has become an increasingly important issue on the educational agenda since the late 1970’s. The importance allotted to this issue is clear in the attention given to it by for example UNESCO where global citizenship education (GCED) is an area of strategic focus....... Increasingly schools all over the world are attempting to or expected to educate the global citizen, but how exactly do you educate the global citizen? What does this global citizenship consist of? While surely the type of training and education needed to train a global citizen will vary greatly depending......, that it is possible to develop a feeling of global citizenship in a society. However, it is very important to keep in mind that global citizenship education as treated in the literature so far has been quite Eurocentric (this includes North America). A survey of research on GCED found that two thirds of the research...
Global Health Observatory (GHO)
... Data repository Reports Country statistics Map gallery Standards Global Health Observatory (GHO) data Monitoring health for the ... Health financing Health workforce 3.d National and global health risks International Health Regulations (2005) Monitoring Framework ...
... Issue Past Issues From the NIH Director: A Global Health System Past Issues / Spring 2008 Table of ... officials the issues of world health and NIH's global outreach. He spoke with MedlinePlus ' Christopher Klose on ...
Democratic Support and Globalization
Thomas, K
2016-01-01
This chapter explores the impact of globalization on satisfaction with democracy in a comparative perspective. It explicitly tests whether globalization fosters or constrains support for democracy and if its potential negative effects vanish once countries compensate for the potential negative effects of globalization. The analyses rely on survey data collected by the Comparative Study of Electoral Systems to indicate citizens’ support for democracy. Globalization is captured by the KOF Index...
Adrian-Gabriel DINESCU
2017-05-01
Full Text Available Once humanity had made the necessary technological leaps for promoting fast and easy travel, the acceleration of human endeavors was inevitable. This acceleration has made possible the integration and globalization of national economies, a global economy emerging. Globalization has become a force impossibile to resist and impossible to deny. Globalization has both advantages and disadvantages. The issue that humanity must understand is it cannot be reversed, just its disadvantages reduced or made bearable.
Sørensen, Olav Jull
The conference paper aims to develop the global value chain concept by including corporate internal value adding activities and competition to the basic framework in order to turn the global value chain into a strategic management tool......The conference paper aims to develop the global value chain concept by including corporate internal value adding activities and competition to the basic framework in order to turn the global value chain into a strategic management tool...
Sørensen, Olav Jull
The conference paper aims to develop the global value chain concept by including corporate internal value adding activities and competition to the basic framework in order to turn the global value chain into a strategic management tool......The conference paper aims to develop the global value chain concept by including corporate internal value adding activities and competition to the basic framework in order to turn the global value chain into a strategic management tool...
Toft, Kristian Høyer
2012-01-01
claims to justice. This article investigates how GMOs might generate claims to global justice and what type of justice is involved. The paper argues that the debate on GMOs and global justice can be categorized into three views, i.e., the cosmopolitan, the pluralist, and the sceptic. The cosmopolitan...... on the premise that global cooperation on GMO production provides the relevant basis for assessing the use of GMOs by the standard of global distributive justice....
Global Governance, Educational Change
Mundy, Karen
2007-01-01
In the last half decade, a rising literature has focused on the idea that processes of economic, political and social globalization require analysis in terms of governance at the global level. It is argued in this article that emerging forms of global governance have produced significant challenges to conventional conceptions of international…
Security Components of Globalization
Florin Iftode
2015-05-01
Full Text Available The objective of this paper is our intention to present what are the main connections between globalization and international security. In terms of global security we can perceive the globalization as a process by which global state is represented by the UN, with a single world system, represented by major security organizations and with global effects. We will present from the beginning the main theoretical aspects that define the phenomenon of globalization, and then our contribution in assessing the implications of this phenomenon on the regional and global security. The results of our research are materialized in the last part of the paper. They emphasize the personal assessments on how the phenomenon of globalization has direct effect on global security. When talking about government, we think of norms, rules and decisionmaking procedures in the management of international life. The value that we add to the new scientific interpretation of the definition of globalization is represented, primarily, by the valuable bibliographic used resources and the original approach on the concept that refers to the links between globalization and security. This article may be, at any time, a starting point in an interesting research direction in the field of global security.
Global Cancer Humanitarian Award
Pat Garcia-Gonzalez of the Max Foundation accepted the first annual NCI Global Cancer Medicine Humanitarian Award for her work in chronic myeloid leukemia at the NCI, Center for Global Health Symposium for Global Cancer Research, held in Boston on March 25, 2015.
Peter J. Ince; Joseph Buongiorno
2007-01-01
This chapter discusses economic globalization and world trade in relation to forest sector modeling for the US/North American region. It discusses drivers of economic globalization and related structural changes in US forest product markets, including currency exchange rates and differences in manufacturing costs that have contributed to the displacement of global...
2017-09-21
Dr. Jordan Tappero, a CDC senior advisor on global health, discusses the state of global health security. Created: 9/21/2017 by National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Center for Global Health (CGH). Date Released: 9/21/2017.
Developing Successful Global Leaders
Training, 2011
2011-01-01
Everyone seems to agree the world desperately needs strong leaders who can manage a global workforce and all the inherent challenges that go with it. That's a big part of the raison d'etre for global leadership development programs. But are today's organizations fully utilizing these programs to develop global leaders, and, if so, are they…