Thermal ion effects on kinetic beta-induced Alfven eigenmodes excited by energetic ions
Energy Technology Data Exchange (ETDEWEB)
Qi Longyu; Sheng, Z. M. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Dong, J. Q. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Southwestern Institute of Physics, Chengdu 610041 (China); Bierwage, A. [Aomori Research and Development Center, Japan Atomic Energy Agency, Rokkasho, Aomori 039-3212 (Japan); Lu Gaimin [Southwestern Institute of Physics, Chengdu 610041 (China)
2013-03-15
Kinetic beta-induced Alfven eigenmodes (KBAEs) driven by energetic ions are numerically investigated using revised AWECS code. The thermal ion density and temperature gradients are taken into account. It is found that the growth rate of the KBAEs increases with the thermal ion pressure gradient, and the contributions from the density gradient and temperature gradient of the thermal ions to the enhancement of the instability are comparable. The damping effect of thermal ion dynamics on the modes is also observed.
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.
Energy Technology Data Exchange (ETDEWEB)
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.
Magneto-Hydrodynamic Activity and Energetic Particles - Application to Beta Alfven Eigenmodes
International Nuclear Information System (INIS)
The goal of magnetic fusion research is to extract the power released by fusion reactions and carried by the product of these reactions, liberated at energies of the order of a few MeV. The feasibility of fusion energy production relies on our ability to confine these energetic particles, while keeping the thermonuclear plasma in safe operating conditions. For that purpose, it is necessary to understand and find ways to control the interaction between energetic particles and the thermonuclear plasma. Reaching these two goals is the general motivation for this work. More specifically, our focus is on one type of instability, the Beta Alfven Eigenmode (BAE), which can be driven by energetic particles and impact on the confinement of both energetic and thermal particles. In this work, we study the characteristics of BAEs analytically and derive its dispersion relation and structure. Next, we analyze the linear stability of the mode in the presence of energetic particles. First, a purely linear description is used, which makes possible to get an analytical linear criterion for BAE destabilization in the presence of energetic particles. This criterion is compared with experiments conducted in the Tore-Supra tokamak. Secondly, because the linear analysis reveals some features of the BAE stability which are subject to a strong nonlinear modification, the question is raised of the possibility of a sub-critical activity of the mode. We propose a simple scenario which makes possible the existence of meta-stable modes, verified analytically and numerically. Such a scenario is found to be relevant to the physics and scales characterizing BAEs. (author)
Beta-induced Alfven-acousti Eigenmodes in NSTX and DIII-D Driven by Beam Ions
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N. N.; Van Zeeland, M. A.; Berk, H. L.; Crocker, N. A.; Darrow, D.; Fredrickson, E.; Fu, G. Y.; Heidbrink, W. W.; Menard, J.; Nazikian, R.
2009-03-06
Kinetic theory and experimental observations of a special class of energetic particle driven instabilities called here Beta-induced Alfven-Acoustic Eigenmodes (BAAE) are reported confirming previous results [N.N. Gorelenkov H.L. Berk, N.A. Crocker et. al. Plasma Phys. Control. Fusion 49 B371 (2007)] The kinetic theory is based on the ballooning dispersion relation where the drift frequency effects are retained. BAAE gaps are recovered in kinetic theory. It is shown that the observed certain low-frequency instabilities on DIII-D [J.L. Luxon, Nucl. Fusion 42 614 (2002)] and National Spherical Torus Experiment [M. Ono, S.M. Kaye, Y.-K M. Peng et. al., Nucl. Fusion 40 3Y 557 (2000)] are consistent with their identification as BAAEs. BAAEs deteriorated the fast ion confinement in DIII-D and can have a similar effect in next-step fusion plasmas, especially if excited together with multiple global Toroidicity-induced shear Alfven Eigenmode (TAE) instabilities. BAAEs can also be used to diagnose safety factor profiles, a technique known as magnetohydrodynamic spectroscopy.
Phenomenology of Compressional Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
E.D. Fredrickson; N.N. Gorelenkov; J. Menard
2004-05-13
Coherent oscillations with frequency 0.3 {le} {omega}/{omega}{sub ci} {le} 1, are seen in the National Spherical Torus Experiment [M. Ono, S.M. Kaye, Y-K.M. Peng, et al., Nucl. Fusion 40, 557 (2000)]. This paper presents new data and analysis comparing characteristics of the observed modes to the model of compressional Alfven eigenmodes (CAE). The toroidal mode number has been measured and is typically between 7 < n < 9. The polarization of the modes, measured using an array of four Mirnov coils, is found to be compressional. The frequency scaling of the modes agrees with the predictions of a numerical 2-D code, but the detailed structure of the spectrum is not captured with the simple model. The fast ion distribution function, as calculated with the beam deposition code in TRANSP [R.V. Budny, Nucl. Fusion 34, 1247 (1994)], is shown to be qualitatively consistent with the constraints of the Doppler-shifted cyclotron resonance drive model. This model also predicts the observed scaling of the low frequency limit for CAE.
Phenomenology of Compressional Alfven Eigenmodes
International Nuclear Information System (INIS)
Coherent oscillations with frequency 0.3 (le) ω/ωci (le) 1, are seen in the National Spherical Torus Experiment [M. Ono, S.M. Kaye, Y-K.M. Peng, (and others), Nucl. Fusion 40, 557 (2000)]. This paper presents new data and analysis comparing characteristics of the observed modes to the model of compressional Alfven eigenmodes (CAE). The toroidal mode number has been measured and is typically between 7 < n < 9. The polarization of the modes, measured using an array of four Mirnov coils, is found to be compressional. The frequency scaling of the modes agrees with the predictions of a numerical 2-D code, but the detailed structure of the spectrum is not captured with the simple model. The fast ion distribution function, as calculated with the beam deposition code in TRANSP [R.V. Budny, Nucl. Fusion 34, 1247 (1994)], is shown to be qualitatively consistent with the constraints of the Doppler-shifted cyclotron resonance drive model. This model also predicts the observed scaling of the low frequency limit for CAE
Kinetic Damping of Toroidal Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
G.Y. Fu; H.L. Berk; A. Pletzer
2005-05-03
The damping of Toroidal Alfven Eigenmodes in JET plasmas is investigated by using a reduced kinetic model. Typically no significant damping is found to occur near the center of the plasma due to mode conversion to kinetic Alfven waves. In contrast, continuum damping from resonance near the plasma edge may be significant, and when it is, it gives rise to damping rates that are compatible with the experimental observations.
Characteristics of Short Wavelength Compressional Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
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.
Alfven eigenmodes and their impact on plasma characteristics in JT-60U
International Nuclear Information System (INIS)
In weak or reversed magnetic shear plasmas of JT-60U, the excitation and the stabilization of Alfven eigenmodes and their impact on energetic ion confinement were investigated with the negative-ion-based neutral beam injection at 330-360 keV. Toroidicity-induced Alfven eigenmodes (TAEs) were observed in weak shear plasmas with h>≥0.1% and 0.4≤vbparallel/vA≤1. The stability of TAEs is consistent with the predictions by the NOVA-K code. New burst modes and chirping modes were observed at a higher beta regime of h>≥0.2%. The effect of TAEs, burst modes and chirping modes on the fast ion confinement is small so far. The strongly-reversed shear plasma with the internal transport barrier suppresses Alfven eigenmodes. (author)
Alpha particle destabilization of the toroidicity-induced Alfven eigenmodes
International Nuclear Information System (INIS)
The high frequency, low mode number toroidicity-induced Alfven eigenmodes (TAE) are shown to be driven unstable by the circulating and/or trapped α-particles through the wave-particle resonances. Satisfying the resonance condition requires that the α-particle birth speed vα ≥ vA/2|m-nq|, where vA is the Alfven speed, m is the poloidal model number, and n is the toroidal mode number. To destabilize the TAE modes, the inverse Landau damping associated with the α-particle pressure gradient free energy must overcome the velocity space Landau damping due to both the α-particles and the core electrons and ions. The growth rate was studied analytically with a perturbative formula derived from the quadratic dispersion relation, and numerically with the aid of the NOVA-K code. Stability criteria in terms of the α-particle beta βα, α-particle pressure gradient parameter (ω*/ωA) (ω* is the α-particle diamagnetic drift frequency), and (vα/vA) parameters will be presented for TFTR, CIT, and ITER tokamaks. The volume averaged α-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume averaged α-particle beta threshold is in the order of 10-4. Typical growth rates of the n=1 TAE mode can be in the order of 10-2ωA, where ωA=vA/qR. Other types of global Alfven waves are stable in D-T tokamaks due to toroidal coupling effects
Excitation of global Alfven Eigenmodes by RF heating in JET
Energy Technology Data Exchange (ETDEWEB)
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.
Alfven Eigenmode Stability with Beams in ITER-like Plasma
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov; H.L. Berk; R.V. Budny
2004-07-16
Toroidicity Alfven Eigenmodes (TAE) in ITER can be driven unstable by two groups of energetic particles, the 3.5 MeV {alpha}-particle fusion products and the tangentially injected 1MeV beam ions. Stability conditions are established using the perturbative NOVA/NOVA-K codes. A quasi-linear diffusion model is then used to assess the induced redistribution of energetic particles.
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
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.
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
International Nuclear Information System (INIS)
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.
Non-linear modulation of short wavelength compressional Alfven eigenmodes
Energy Technology Data Exchange (ETDEWEB)
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.
Reversed shear Alfven eigenmode stabilization by localized electron cyclotron heating
Energy Technology Data Exchange (ETDEWEB)
Van Zeeland, M A; Hyatt, A W; Lohr, J; Petty, C C [General Atomics, PO Box 85608 San Diego, CA 92186-5608 (United States); Heidbrink, W W [University of California-Irvine, Irvine, CA 92697 (United States); Nazikian, R; Solomon, W M; Gorelenkov, N N; Kramer, G J [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Austin, M E [University of Texas-Austin, Austin, TX 78712 (United States); Berk, H L [Institute for Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States); Holcomb, C T; Makowski, M A [Lawrence Livermore National Laboratory, Livermore, CA (United States); McKee, G R [University of Wisconsin-Madison, Madison, WI 53726 (United States); Sharapov, S E [Euratom/UKAEA Fusion Association, Culham, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Rhodes, T L [University of California-Los Angeles, Los Angeles, California, 90095 (United States)], E-mail: vanzeeland@fusion.gat.com
2008-03-15
Reversed shear Alfven eigenmode (RSAE) activity in DIII-D is stabilized by electron cyclotron heating (ECH) applied near the minimum of the magnetic safety factor (q{sub min}) in neutral beam heated discharges with reversed-magnetic shear. The degree of RSAE stabilization, fast ion density and the volume averaged neutron production (S{sub n}) are highly dependent on ECH deposition location relative to q{sub min}. While discharges with ECH stabilization of RSAEs have higher S{sub n} and more peaked fast ion profiles than discharges with significant RSAE activity, neutron production remains strongly reduced (up to 60% relative to TRANSP predictions assuming classical fast ion transport) even when RSAEs are stabilized.
Evolution of toroidal Alfven eigenmode instability in TFTR
Energy Technology Data Exchange (ETDEWEB)
Wong, K.L.; Majeski, R.; Petrov, M. [Princeton Univ., NJ (United States). Plasma Physics Lab.] [and others
1996-07-01
The nonlinear behavior of the Toroidal Alfven Eigenmode (TAE) driven unstable by energetic ions in TFTR is studied. The evolution of instabilities can take on several scenarios: a single mode or several modes can be driven unstable at the same time, the spectrum can be steady or pulsating and there can be negligible or anomalous loss associated with the instability. This paper presents a comparison between experimental results and recently developed nonlinear theory. The authors find many features observed in experiment are compatible with the consequences of the nonlinear theory. Examples include the structure of the saturated pulse that emerges from the onset of instability of a single mode and the decrease but persistence of TAE signals when the applied rf power is reduced or shut off.
Observation of compressional Alfven eigenmodes (CAE) in a conventional tokamak
International Nuclear Information System (INIS)
Fast-ion instabilities with frequencies somewhat below the ion cyclotron frequency occur frequently in spherical tokamaks such as the National Spherical Torus Experiment (NSTX). NSTX and the DIII-D tokamak are nearly ideal for fast-ion similarity experiments, having similar neutral beams, fast-ion to Alfven speed vf/vA, fast-ion pressure, and shape of the plasma but with a factor of two difference in major radius. When DIII-D is operated at low field (0.6 T), compressional Alfven eigenmode (CAE) instabilities appear that closely resemble the NSTX instabilities. In particular, the mode frequencies, polarization and beam-energy threshold are nearly identical to NSTX. CAE in high-field discharges and emission at cyclotron harmonics are also observed. As on NSTX, the basic stability properties are consistent with the idea that the instability is driven by anisotropy in the fast-ion velocity distribution and is damped predominantly by Landau damping of electrons. The results suggest that these modes might be excited in ITER
Destabilization of Alfven eigenmodes by fast particles in W7-AS
Energy Technology Data Exchange (ETDEWEB)
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
Energy Technology Data Exchange (ETDEWEB)
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
Simulation study of energetic ion transport due to Alfven eigenmodes in LHD plasma
International Nuclear Information System (INIS)
The creation of holes and clumps in an energetic ion energy spectrum associated with Alfven eigenmodes was examined using the neutral particle analyzer (NPA) on the LHD shot no.47645. The difference in slowing-down times between the holes and clumps suggested that the energetic ions were transported over 10% of the plasma minor radius. The spatial profile and frequency of the Alfven eigenmodes were analyzed with the AE3D code. The phase space structures of the energetic ions on the NPA line-of-sight were investigated with Poincare plots, where an oscillating Alfven eigenmode was employed for earth plot. The phase space regions trapped by the Alfven eigenmodes appeared as islands in the Poincare plots. The radial width of the islands corresponded to the transport distance of the energetic ions. Since island width depends on Alfven eigenmode amplitude, it was found that Alfven eigenmodes with amplitude δBr/B - 10-3 transported energetic ions over 10% of the minor radius. (author)
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
Energy Technology Data Exchange (ETDEWEB)
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.
Beam Anisotropy Effect on Alfven Eigenmode Stability in ITER-like Plasma
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov; H.L. Berk; R.V. Budny
2004-08-18
This work studies the stability of the toroidicity-induced Alfven Eigenmodes (TAE) in the proposed ITER burning plasma experiment, which can be driven unstable by two groups of energetic particles, the 3.5-MeV {alpha}-particle fusion products and the tangentially injected 1-MeV beam ions. Both species are super-Alfvenic but they have different pitch-angle distributions and the drive for the same pressure gradients is typically stronger from co-injected beam ions as compared with the isotropically distributed {alpha}-particles. This study includes the effect of anisotropy of the beam-ion distribution function on TAE growth rate directly via the additional velocity space drive and indirectly in terms of the enhanced effect of the resonant particle phase space density. For near parallel injection, TAEs are marginally unstable if the injection aims at the plasma center where the ion Landau damping is strong, whereas with the off-axis neutral-beam injection the instability is stronger with the growth rate near 0.5% of TAE mode frequency. In contrast, for perpendicular beam injection TAEs are predicted to be stabilized in nominal ITER discharges. In addition, the effect of TAEs on the fast-ion beta profiles is evaluated on the bases of a quasi-linear diffusion model which makes use of analytic expressions for the local growth and damping rates. These results illustrate the parameter window that is available for plasma burn when TAE modes are excited.
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
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.
Subcyclotron Instability of Alfven Eigenmodes due to Energetic Ions in Low Aspect Ratio Plasmas
International Nuclear Information System (INIS)
High-frequency modes with frequencies below the fundamental cyclotron frequency of thermal ions were observed in the National Spherical Torus Experiment (NSTX). Based on the measured spectrum of high-frequency modes they are identified as Compressional Alfven Eigenmodes (CAEs) and Global Alfven Eigenmodes (GAEs). CAEs have similar time evolution as plasma parameters change, while GAEs may intersect due to q-profile relaxation. A theory has been developed to study the properties of these modes. Both types of instabilities are driven by the tangential neutral-beam injection in NSTX. Beam ions excite CAEs/GAEs through the Doppler-shifted cyclotron resonance. The main source for the drive is the velocity space anisotropy of the beam ion distribution function. Simulations of the effect CAEs/GAEs may have on plasma ions indicate that these modes may provide a channel for efficient energy transfer from fast ions directly to thermal ions
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.
Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging
Energy Technology Data Exchange (ETDEWEB)
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.
Predictions and observations of global beta-induced Alfven-acoustic modes in JET and NSTX
Energy Technology Data Exchange (ETDEWEB)
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.
Predications and Observations of Global Beta-induced Alfven-acoustic Modes in JET and NSTX
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov, et. al.
2008-10-21
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.
Perturbative Study of Energetic Particle Redistribution by Alfven Eigenmodes in ITER
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
The National Spherical Torus Experiment (NSTX, (M. Ono et al., Nucl. Fusion 40, 557 (2000))) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfvenic, with velocities 1 fast/vAlfven < 5. This provides a strong drive for toroidicity-induced Alfven eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (∼<30%) fast ion losses over ∼ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
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.
Stochastic Orbit Loss of Neutral Beam Ions From NSTX Due to Toroidal Alfven Eigenmode Avalanches
Energy Technology Data Exchange (ETDEWEB)
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.
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
International Nuclear Information System (INIS)
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 βα(0) required for instability. No TAE activity was observed when the central alpha particle βα 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
International Nuclear Information System (INIS)
The spectrum of Compressional Alfven Eigenmodes (CAE) driven by phase space gradient measured in NSTX and DIII-D plasmas is analyzed numerically for the first time. Advanced diagnostic capabilities made it possible to measure single mode polarization and toroidal mode numbers, which unambiguously identifies studied modes to be of compressional branch. CAE modes form the discrete spectrum with each mode having three (quantum) mode numbers (M, S, n), where M, S, and n are poloidal, radial and toroidal mode numbers, respectively. CAE mode frequency splitting corresponding to change of each of these mode numbers seem to be observed in experiments and is consistent with our numerical analysis. CAE mode structure is computed to be localized in both radial and poloidal directions and is shown to be consistent with the internal reflectometer diagnostic data. (author)
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...
Alfven eigenmode stability and fast ion loss in DIII-D and ITER reversed magnetic shear plasmas
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
The stability of the Global Alfven Eigenmodes is investigated in the presence of super-Alfvenic energetic particles, such as the fusion-product alpha particles in an ignited deuterium-tritium tokamak plasma. Alpha particles tend to destabilize these modes when ω*α > ωA, where ωA is the shear-Alfven modal frequency and ω*α is the alpha particle diamagnetic drift frequency. This destabilization due to alpha particles is found to be significantly enhanced when the alpha particles are modeled with a slowing-down distribution function rather than with a Maxwellian. However, previously neglected electron damping due to the magnetic curvature drift is found to be comparable in magnitude to the destabilizing alpha particle term. Furthermore, the effects of toroidicity are also found to be stabilizing, since the intrinsic toroidicity induces poloidal mode coupling, which enhances the parallel electron damping from the sideband shear-Alfven Landau resonance. In particular, for the parameters of the proposed Compact Ignition Tokamak, the Global Alfven Eigenmodes are found to be completely stabilized by either the electron damping that enters through the magnetic curvature drift or the damping introduced by finite toroidicity. 29 refs., 8 figs., 1 tab
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...
Sears, Stephanie; Anderson, Jay; Capecchi, William; Bonofiglo, Phillip; Kim, Jungha
2015-11-01
Alfven wave dissipation is an important mechanism behind anomalous ion heating, both in astrophysical and reversed-field pinch (RFP) plasma systems. Additionally, the damping rate has implications for the stability of energetic particle driven modes (EPMs) and their associated nonlinear dynamics and fast ion transport, which are crucial topics for any burning plasma reactor. With a 1 MW neutral beam injector on the MST RFP, a controlled set of EPMs and Alfvenic eigenmodes can be driven in this never-before-probed region of strong magnetic shear and weak externally applied magnetic field. The decay time of the average of 100s of reproducible bursts is computed for different equilibrium profiles. In this work, we report initial measurements of Alfvenic damping rates with varied RFP equilibria (including magnetic shear and flow shear) and the effects on fast ion transport. This research is supported by DOE and NSF.
Wang, Ge; Berk, H. L.
2011-10-01
The frequency chirping signal arising from spontaneous a toroidial Alfven eigenmode (TAE) excited by energetic particles is studied for both numerical and analytic models. The time-dependent numerical model is based on the 1D Vlasov equation. We use a sophisticated tracking method to lock onto the resonant structure to enable the chirping frequency to be nearly constant in the calculation frame. The accuracy of the adiabatic approximation is tested during the simulation which justifies the appropriateness of our analytic model. The analytic model uses the adiabatic approximation which allows us to solve the wave evolution equation in frequency space. Then, the resonant interactions between energetic particles and TAE yield predictions for the chirping rate, wave frequency and amplitudes vs. time. Here, an adiabatic invariant J is defined on the separatrix of a chirping mode to determine the region of confinement of the wave trapped distribution function. We examine the asymptotic behavior of the chirping signal for its long time evolution and find agreement in essential features with the results of the simulation. Work supported by Department of Energy contract DE-FC02-08ER54988.
Alfven eigenmode observations on DIII-D via two-colour CO{sub 2} interferometry
Energy Technology Data Exchange (ETDEWEB)
Zeeland, M A van [ORISE, PO Box 117, Oak Ridge, TN 37831-0117 (United States); Kramer, G J [Princeton Plasma Physics Lab., PO Box 451, Princeton, NJ 08543 (United States); Nazikian, R [Princeton Plasma Physics Lab., PO Box 451, Princeton, NJ 08543 (United States); Berk, H L [Institute of Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States); Carlstrom, T N [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Solomon, W M [Princeton Plasma Physics Lab., PO Box 451, Princeton, NJ 08543 (United States)
2005-09-01
Measurements are presented of toroidicity-induced (TAEs) and reverse shear (RSAEs) Alfven eigenmodes made using the standard two-colour CO{sub 2} interferometer on DIII-D modified for increased bandwidth. Typical values of the effective line-integrated density perturbation in DIII-D are found to be d(nL)/nL {approx} 10{sup -3}, and comparisons are made with NOVA calculations as well as magnetic measurements. There is a strong difference in the measured power spectrum between vertical and radial chords through the plasma. On average, vertical views are characterized by a larger line-integrated density perturbation due to TAEs than radial chords. Radial chords, however, can be used much more reliably than vertical chords to identify the presence of RSAEs in the plasma-a result found to be due to the radially localized nature of these modes. In general, the apparent amplitude of the observed modes for both TAE and RSAE is found to be highly dependent on viewing location. (letter to the editor)
Energy Technology Data Exchange (ETDEWEB)
Podesta, M; Crocker, N A; Fredrickson, E D; Gorelenkov, N N; Heidbrink, W W; Kubota, S; LeBlanc, B P
2011-04-26
The National Spherical Torus Experiment (NSTX, [M. Ono et al., Nucl. Fusion 40, 557 (2000)]) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfv enic, with velocities 1 < vfast=vAlfven < 5. This provides a strong drive for toroidicity-induced Alfv en eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (≤ 30%) fast ion losses over ~ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
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.
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...
Energy Technology Data Exchange (ETDEWEB)
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.
1.5D quasilinear model and its application on beams interacting with Alfven eigenmodes in DIII-D
Energy Technology Data Exchange (ETDEWEB)
Ghantous, K.; Gorelenkov, N. N. [Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543-0451 (United States); Berk, H. L. [Institute for Fusion Studies, University of Texas, 2100 San Jacinto Blvd., Austin, Texas 78712-1047 (United States); Heidbrink, W. W. [Department of Physics and Astronomy, University of California Irvine, Irvine, California 92697 (United States); Van Zeeland, M. A. [General Atomics, PO Box 85608, San Diego, California 92186-560 (United States)
2012-09-15
We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges no. 142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and no. 127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.
Energy Technology Data Exchange (ETDEWEB)
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.
Toroidal Alfven wave stability in ignited tokamaks
Energy Technology Data Exchange (ETDEWEB)
Cheng, C.Z.; Fu, G.Y.; Van Dam, J.W.
1989-01-01
The effects of fusion-product alpha particles on the stability of global-type shear Alfven waves in an ignited tokamak plasma are investigated in toroidal geometry. Finite toroidicity can lead to stabilization of the global Alfven eigenmodes, but it induces a new global shear Alfven eigenmodes, which is strongly destabilized via transit resonance with alpha particles. 8 refs., 2 figs.
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N. N.; Berk, H. L.; Fredrickson, E.; Sharapov, S. E.
2007-07-02
New global MHD eigenmode solutions arising in gaps in the low frequency Alfvén -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 Alfvén-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfvén-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 Alfvén 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.
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.
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.
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.
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...
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.
Low-n shear Alfven spectra in axisymmetric toroidal plasmas
International Nuclear Information System (INIS)
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
Nonlinearly Driven Second Harmonics of Alfven Cascades
International Nuclear Information System (INIS)
In recent experiments on Alcator C-Mod, measurements of density fluctuations with Phase Contrast Imaging through the plasma core show a second harmonic of the basic Alfven Cascade (AC) signal. The present work describes the perturbation at the second harmonic as a nonlinear sideband produced by the Alfven Cascade eigenmode via quadratic terms in the MHD equations. (author)
Alfven wave heating and stability
International Nuclear Information System (INIS)
Alfven waves in fusion plasmas play an important role in a number of situations. First, in Alfven Wave Heating (AWH) schemes. Second, both theory and experiment have demonstrated the existence of Global Alfven Eigenmodes (GAEs). GAEs have been observed in different tokamaks (PRETEXT, TCA, TEXTOR, etc.) and, more recently, in a stellarator (Wendelstein 7-AS) where they were shown to become unstable under intense Neutral Beam injection. Third, the existence and possible destabilization by fast ions of Toroidicity induced Alfven Eigenmodes (TAEs) has been evidenced both theoretically and experimentally. This destabilization could hamper the operation of a magnetically confined fusion reactor by setting a limit on the number of fusion alpha particles in the plasma. It is therefore crucial to understand the mechanisms leading to the occurrence of the instability and also those that can stabilize the TAEs by increasing the strength of the damping. The aim is to be able to devise possible ways to avoid the instability of Alfven eigenmodes in a region of parameter space that is compatible with the functioning of a fusion reactor. A global perturbative approach is presented to tackle the problem of the linear stability of TAEs. Our model computes the overall wave particle power transfers to the different species and thus could also be applied to the study of alpha power extraction in the presence of Alfven waves. We indicate also how to go beyond the perturbative approach. (author) 15 figs., 38 refs
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
Spectrum of compressional Alfven waves
International Nuclear Information System (INIS)
The spectrum of compressional Alfven eigenmodes localized in the potential well created by a combination of the variation in plasma density and the wave number k/sub perpendicular to/ = m/r, is obtained, and its importance for ratio frequency current drive is discussed. It is found that modes with small parallel wave numbers and frequencies below the ion cyclotron frequency are attractive for current drive
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 ...
International Nuclear Information System (INIS)
Seven chapters are included. Chapters 1 and 2 introduce the Alfven wave and describe its linear properties in a homogeneous medium. Chapters 3 and 4 cover the effects of inhomogeneities on these linear properties. Particular emphasis is placed on the appearance of a continuum spectrum and the associated absorption of the Alfven wave which arise due to the inhomogeneity. The explanation of the physical origin of absorption is given using kinetic theory. Chapter 5 is devoted to the associated plasma instabilities. Nonlinear effects discussed in Chapter 6 include quasilinear diffusion, decay, a solitary wave, and a modulational instability. The principles of Alfven wave heating, a design example and present-day experimental results are described in Chapter 7
International Nuclear Information System (INIS)
This paper discusses experiments on linear high beta helical axis stellarators. Experiments considered are: formation of linear high beta heliac plasma configurations; Alfven wave heating in a straight tube and in a linear high beat stellarator; shifted hardcore heliac studies; a system for measuring the timing of high-current switches in a pulsed high voltage fusion experiment; HBQM general refurbishment; and proposed experiment on excitation of the m = 1 tilt mode in field-reversed configurations
Adiabatic trapping in coupled kinetic Alfven-acoustic waves
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
This paper discusses induced axial current studies in a hardcore Theta-Pinch; nonaxisymmetric RF heating of a high-Beta plasma column; formation of Axisymmetric hardcore theta pinches with notched hardcore current; and externally driven till made experiments on the high-beta Q machine field reversed configuration
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.
International Nuclear Information System (INIS)
The first direct observation of the internal structure of driven global Alfven eigenmodes in a tokamak plasma is presented. A carbon dioxide laser scattering/interferometer has been designed, built, and installed on the PRETEXT tokamak. By using this diagnostic system in the interferometer configuration, we have for the first time, thoroughly investigated the resonance conditions required for, and the spatial wave field structure of, driven plasma eigenmodes at frequencies below the ion cyclotron frequency in a confined, high temperature, tokamak plasma
Kinetic Alfven wave turbulence in space plasmas
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
The physics of Alfven-wave heating is particularly sensitive to the character of the linear mode conversion which occurs at the Alfven resonance layer. Parameter changes can profoundly affect both the location within the plasma and the mechanism for the power absorption. Under optimal conditions the heating power may be absorbed by electron Landau damping and by electron transit-time magnetic pumping in the plasma interior, or by the same processes acting near the resonance layer on the mode-converted kinetic Alfven wave. The method is outlined for computing the coefficients for reflection, transmission and absorption at the resonance layer and some representative results are offered
Institute of Scientific and Technical Information of China (English)
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.
Energy Technology Data Exchange (ETDEWEB)
Weng, C. J. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Lee, L. C. [Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Institute of Earth Science, Academia Sinica, Nankang 115, Taiwan (China); Kuo, C. L. [Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Wang, C. B. [CAS Key Laboratory of Geospace Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei (China)
2013-03-15
Alfven waves are low-frequency transverse waves propagating in a magnetized plasma. We define the Alfven frequency {omega}{sub 0} as {omega}{sub 0}=kV{sub A}cos{theta}, where k is the wave number, V{sub A} is the Alfven speed, and {theta} is the angle between the wave vector and the ambient magnetic field. There are partially ionized plasmas in laboratory, space, and astrophysical plasma systems, such as in the solar chromosphere, interstellar clouds, and the earth ionosphere. The presence of neutral particles may modify the wave frequency and cause damping of Alfven waves. The effects on Alfven waves depend on two parameters: (1) {alpha}=n{sub n}/n{sub i}, the ratio of neutral density (n{sub n}), and ion density (n{sub i}); (2) {beta}={nu}{sub ni}/{omega}{sub 0}, the ratio of neutral collisional frequency by ions {nu}{sub ni} to the Alfven frequency {omega}{sub 0}. Most of the previous studies examined only the limiting case with a relatively large neutral collisional frequency or {beta} Much-Greater-Than 1. In the present paper, the dispersion relation for Alfven waves is solved for all values of {alpha} and {beta}. Approximate solutions in the limit {beta} Much-Greater-Than 1 as well as {beta} Much-Less-Than 1 are obtained. It is found for the first time that there is a 'forbidden zone (FZ)' in the {alpha}-{beta} parameter space, where the real frequency of Alfven waves becomes zero. We also solve the wavenumber k from the dispersion equation for a fixed frequency and find the existence of a 'heavy damping zone (HDZ).' We then examine the presence of FZ and HDZ for Alfven waves in the ionosphere and in the solar chromosphere.
Simulation of the interaction between Alfven waves and fast particles
International Nuclear Information System (INIS)
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
Alfven solitons in the solar wind
Ovenden, C.; Schwartz, S. J.
1983-01-01
A nonlinear Alfven soliton solution of the MHD equations is presented. This solution represents the final state of modulationally unstable Alfven waves. A model of the expected turbulent spectrum due to a collection of such solitons is briefly described.
International Nuclear Information System (INIS)
Kinetic effects of Alfven wave spatial resonances near the plasma edge are investigated numerically and analytically in a cylindrical tokamak model. In Part 1, cold plasma surface Alfven eigenmodes (SAE's) in a pure plasma are examined. Numerical calculations of antenna-driven waves exhibiting absorption resonances at certain discrete frequencies are first reviewed. From a simplified kinetic equation, an analytical dispersion relation is then obtained with the antenna current set equal to zero. The real and imaginary parts of its roots, which are the complex eigenfrequencies, agree with the central frequencies and widths, respectively, of the numerical antenna-driven resonances. These results serve as an introduction to the companion paper, in which it is shown that, in the presence of a minority species, certain SAE's, instead of heating the plasma exterior, can dissipate substantial energy in the two-ion hybrid layer near the plasma center. 11 refs., 8 figs., 1 tab
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.
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.
Rogue waves in Alfvenic turbulence
International Nuclear Information System (INIS)
Rogue waves, in the form of giant breathers, are shown to develop in the Alfven wave (AW) turbulence regime described by the randomly driven derivative nonlinear Schroedinger equation in the presence of a weak dissipation. The distribution of the instantaneous global maxima of the AW intensity fluctuations is seen to be accurately fitted by power laws, which contrasts with the integrable regime (absence of dissipation and forcing) where the behavior is rather exponential. As the dissipation is reduced, freak waves form less frequently but reach larger amplitudes. -- Highlights: → Rogue wave formation in long-wavelength Alfvenic turbulence. → Huge waves form by quasi-collapse of breathers in presence of weak dissipation. → Amplitude distribution of rogue waves is fitted by power laws. → Possible relation with SLAMS pulses observed near the Earth bow shock.
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...
On Nonlinear Alfv\\'en Waves Generated by Cosmic Ray Streaming Instability
Zirakashvili, V N; Völk, H J
2001-01-01
Nonlinear damping of parallel propagating Alfv\\'en waves in high-$\\beta$ plasma is considered. Trapping of thermal ions and Coulomb collisions are taken into account. Saturated damping rate is calculated. Applications are made for cosmic ray propagation in the Galaxy.
Electromagnetic transport components and sheared flows in drift-Alfven turbulence
DEFF Research Database (Denmark)
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...
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...
Three-dimensional numerical simulations of fast-to-Alfven conversion in sunspots
Felipe, T
2012-01-01
The conversion of fast waves to the Alfven mode in a realistic sunspot atmosphere is studied through three-dimensional numerical simulations. An upward propagating fast acoustic wave is excited in the high-beta region of the model. The new wave modes generated at the conversion layer are analyzed from the projections of the velocity and magnetic field in their characteristic directions, and the computation of their wave energy and fluxes. The analysis reveals that the maximum efficiency of the conversion to the slow mode is obtained for inclinations of 25 degrees and low azimuths, while the Alfven wave conversions peaks at high inclinations and azimuths between 50 and 120 degrees. Downward propagating Alfven waves appear at the regions of the sunspot where the orientation of the magnetic field is in the direction opposite to the wave propagation, since at these locations the Alfven wave couples better with the downgoing fast magnetic wave which are reflected due to the gradients of the Alfven speed. The simul...
Alfven fluctuations in an inhomogeneous nonequilibrium plasma
Energy Technology Data Exchange (ETDEWEB)
Timofeev, A.V.; Meitlis, V.P.; Chulkov, G.N.
1978-09-01
The injection of fast ions into a tokamak plasma can cause Alfven waves to grow. If the Alfven velocity varies monotonically in the direction across the magnetic field, there are no unstable resonant waves, and the initial perturbations grow for only a finite time. Then the finite plasma conductivity leads to a damping of these waves. The fluctuations in the electron microcurrents caused by collisions with ions represent an unavoidable source of initial perturbations. Associated with these perturbations is some steady-state level of the fluctuating Alfven waves. This level is determined, and the energy lost by the fast ions due to wave excitation is calculated.
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...
Polyakov loop fluctuations in Dirac eigenmode expansion
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-01-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal non-twisted periodic boundary condition for the link-variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phase by numerical simulations in SU(3) quenched QCD. Thes...
Alfven wave. DOE Critical Review Series
Energy Technology Data Exchange (ETDEWEB)
Hasegawa, A.; Uberoi, C.
1982-01-01
This monograph deals with the properties of Alfven waves and with their application to fusion. The book is divided into 7 chapters dealing with linear properties in homogeneous and inhomogeneous plasmas. Absorption is treated by means of kinetic theory. Instabilities and nonlinear processes are treated in Chapters 1 to 6, and the closing chapter is devoted to theory and experiments in plasma heating by Alfven waves. (MOW)
MIMO Identical Eigenmode Transmission System (IETS) - a Channel Decomposition Perspective
Shakir, Muhammad Zeeshan; Durrani, Tariq
2007-01-01
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 dat...
Alfvenic waves in solar spicules
Ebadi, Hossein
2016-07-01
We analyzed O VI (1031.93 A) and O VI (1037.61 A line profiles from the time series of SOHO/SUMER data. The wavelet analysis is used to determine the fundamental mode and its first harmonic periods and their ratio. The period ratio, P_1/P_2 is obtained as 2.1 based on our calculations. To model the spicule oscillations, we consider an equilibrium configuration in the form of an expanding straight magnetic flux tube with varying density along tube. We used cylindrical coordinates r, phi, and z with the z-axis along tube axis. Standing Alfvenic waves with steady flows are studied. More realistic background magnetic field, plasma density, and spicule radios inferred from the actual magnetoseismology of observations are used. It is found that the oscillation periods and their ratio are shifted because of the steady flows. The observational values are reached in P_1/P_2, when the steady flows are 0.2-0.3, the values which are reported for classical spicules.
Nonlinear Energetic Particle Transport in the Presence of Multiple Alfvenic Waves in ITER
Schneller, Mirjam; Briguglio, Sergio
2015-01-01
This work presents the results of a multi mode ITER study on Toroidal Alfven Eigenmodes, using the nonlinear hybrid HAGIS-LIGKA model. It is found that main conclusions from earlier studies of ASDEX Upgrade discharges can be transferred to the ITER scenario: global, nonlinear effects are crucial for the evolution of the multi mode scenario. This work focuses on the ITER 15 MA baseline scenario with with a safety factor at the magnetic axis of $q_0 =$ 0.986. The least damped eigenmodes of the system are identified with the gyrokinetic, non-perturbative LIGKA solver, concerning mode structure, frequency and damping. Taking into account all weakly damped modes that can be identified linearly, nonlinear simulations with HAGIS reveal strong multi mode behavior: while in some parameter range, quasi-linear estimates turn out to be reasonable approximations for the nonlinearly relaxed energetic particle profile, under certain conditions low-n TAE branches can be excited. As a consequence, not only grow amplitudes of ...
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.
Polyakov loop fluctuations in Dirac eigenmode expansion
Doi, Takahiro M; Sasaki, Chihiro; Suganuma, Hideo
2015-01-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal non-twisted periodic boundary condition for the link-variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phase by numerical simulations in quenched QCD. These results indicate that there is no direct, one-to-one correspondence between confinement and chiral symmetry breaking in QCD in the context of different properties of the Polyakov loop fluctuation ratios.
Effect of Rossby and Alfv\\'{e}n waves on the dynamics of the tachocline
Leprovost, Nicolas; Kim, Eun-Jin
2006-01-01
To understand magnetic diffusion, momentum transport, and mixing in the interior of the sun, we consider an idealized model of the tachocline, namely magnetohydrodynamics (MHD) turbulence on a $\\beta$ plane subject to a large scale shear (provided by the latitudinal differential rotation). This model enables us to self-consistently derive the influence of shear, Rossby and Alfv\\'{e}n waves on the transport properties of turbulence. In the strong magnetic field regime, we find that the turbule...
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.
Ultra-high Q even eigenmode resonance in terahertz metamaterials
Energy Technology Data Exchange (ETDEWEB)
Al-Naib, Ibraheem, E-mail: ibraheemalnaib@gmail.com; Dignam, Marc M. [Department of Physics, Engineering Physics and Astronomy, Queen' s University, Kingston, Ontario K7L 3N6 (Canada); Yang, Yuping; Zhang, Weili [School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078 (United States); Singh, Ranjan, E-mail: ranjans@ntu.edu.sg [Centre for Disruptive Photonic Technologies, Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore 637371 (Singapore)
2015-01-05
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.
Calibration of higher eigenmodes of cantilevers
Labuda, Aleksander; Kocun, Marta; Lysy, Martin; Walsh, Tim; Meinhold, Jieh; Proksch, Tania; Meinhold, Waiman; Anderson, Caleb; Proksch, Roger
2016-07-01
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.
Roles of Fast-Cyclotron and Alfven-Cyclotron Waves for the Multi-Ion Solar Wind
Xiong, Ming; Li, Xing
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 s...
Alfven wave heating of a theta pinch
International Nuclear Information System (INIS)
The process of shear Alfven wave resonant absorption for plasma heating has been applied to a theta pinch. The m=1 mode is excited by means of a helical launching structure with a given wavelength, at a number of different frequencies. When the frequency lies in the continuous Alfven spectrum the kink energy is transferred to the Alfven wave and then is rapidly thermalized. The heating power is measured by a diamagnetic probe. It is shown that the probe signal can be treated as a thermodynamic variable permitting an exact energy balance to be deduced. The measured resonance curve of the heating power is in agreement with the predicted behaviour. A 50% efficiency is achieved and the coupling between the plasma and the external circuit is strong, in spite of the high compression ratio. (author)
Alfvenic Heating of Protostellar Accretion Disks
Vasconcelos, M. J.; Jatenco-Pereira, V.; R. Opher
1999-01-01
We investigate the effects of heating generated by damping of Alfven waves on protostellar accretion disks. Two mechanisms of damping are investigated, nonlinear and turbulent, which were previously studied in stellar winds (Jatenco-Pereira & Opher 1989a, b). For the nominal values studied, f=delta v/v_{A}=0.002 and F=varpi/Omega_{i}=0.1, where delta v, v_{A} and varpi are the amplitude, velocity and average frequency of the Alfven wave, respectively, and Omega_{i} is the ion cyclotron freque...
The nonlinear compressional Alfven wave equation
International Nuclear Information System (INIS)
The nonlinear wave equation of the compressional Alfven mode is derived in Lagrangian fluid coordinate. The nonlinearity attributes unequal weight to the terms of temporal and spatial derivatives. Two specific solutions relevant to transit-time magnetic pumping plasma heating and theta-pinch implosions are given. (Author)
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...
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.
An improved perfectly matched layer for the eigenmode expansion technique
DEFF Research Database (Denmark)
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...
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.
Alfven waves: a journey between space and fusion plasmas
International Nuclear Information System (INIS)
Alfven waves discovered by Hannes Alfven (1942 Nature 150 405) are fundamental electromagnetic oscillations in magnetized plasmas existing in the nature and laboratories. Alfven waves play important roles in the heating, stability and transport of plasmas. The anisotropic nearly incompressible shear Alfven wave is particularly interesting since, in realistic non-uniform plasmas, its wave spectra consist of both the regular discrete and the singular continuous components. In this Alfven lecture, I will discuss these spectral properties and examine their significant linear and nonlinear physics implications. These discussions will be based on perspectives from my own research in both space and laboratory fusion plasmas, and will demonstrate the positive feedback and cross-fertilization between these two important sub-disciplines of plasma physics research. Some open issues of nonlinear Alfven wave physics in burning fusion as well as magnetospheric space plasmas will also be explored.
Stationary nonlinear Alfven waves and solitons
Hada, T.; Kennel, C. F.; Buti, B.
1989-01-01
Stationary solutions of the derivative nonlinear Schroedinger equation are discussed and classified by using a pseudopotential formulation. The solutions consist of a rich family of nonlinear Alfven waves and solitons with parallel and oblique propagation directions. Expressions for the envelope and the phase of nonlinear waves with periodic envelope modulation, and 'hyperbolic' and 'algebraic' solitons are given. The propagation angle for the slightly modulated elliptic, periodic waves and for oblique solitons is evaluated.
Excitation of Alfven Waves and Pulsar Radio Emission
Lyutikov, Maxim
1999-01-01
We analyze mechanisms of the excitation of Alfv\\'{e}n wave in pulsar magnetospheres as a possible source of pulsar radio emission generation. We find that Cherenkov excitation of obliquely propagating Alfv\\'{e}n waves is inefficient, while excitation at the anomalous cyclotron resonance by the particles from the primary beam and from the tail of the bulk distribution function may have a considerable growth rate. The cyclotron instability on Alfv\\'{e}n waves occurs in the kinetic regime still ...
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.
Alfven wave studies on a tokamak
International Nuclear Information System (INIS)
The continuum modes of the shear Alfven resonance are studied on the Tokapole II device, a small tokamak operated in a four node poloidal divertor configuration. A variety of antenna designs and the efficiency with which they deliver energy to the resonant layer are discussed. The spatial structure of the driven waves is studied by means of magnetic probes inserted into the current channel. In an attempt to optimize the coupling of energy in to the resonant layer, the angle of antenna currents with respect to the equilibrium field, antenna size, and plasma-to-antenna distance are varied. The usefulness of Faraday shields, particle shields, and local limiters are investigated. Antennas should be well shielded, either a dense Faraday shield or particle shield being satisfactory. The antenna should be large and very near to the plasma. The wave magnetic fields measured show a spatial resonance, the position of which varies with the value of the equilibrium field and mass density. They are polarized perpendicular to the equilibrium field. A wave propagates radially in to the resonant surface where it is converted to the shear Alfven wave. The signal has a short risetime and does not propagate far toroidally. These points are all consistent with a strongly damped shear Alfven wave. Comparisons of this work to theoretical predictions and results from other tokamaks are made
The eigenmode perspective of NMR spin relaxation in proteins
Energy Technology Data Exchange (ETDEWEB)
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
Dissipation of non-linear circularly polarized Alfven waves
Turkmani, R
2001-01-01
We study propagating Alfven waves by solving the time-dependent equations of magnetohydrodynamics (MHD) in one dimension numerically. In a homogeneous medium the circularly polarized Alfven wave is an exact solution of the ideal MHD equations, and therefore it does not suffer from any dissipation. A high-amplitude linearly polarized Alfven wave, on the other hand, steepens and form current sheets, in which the Poynting flux is lost. In a stratified medium, however, a high-amplitude circularly polarized Alfven wave can also lose a significant fraction of its Poynting flux.
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...
International Nuclear Information System (INIS)
With the first injection of neutral beams into the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40, 557 (2000)], a broad spectrum of fluctuations consisting of nearly equally spaced peaks in the frequency range from about 0.2 to 1.2 times the ion cyclotron frequency was observed. The frequencies scale with toroidal field and plasma density consistently with Alfven waves. From these and other observations, the modes have been identified as compressional Alfven eigenmodes (CAE). It has also recently been found that the ratio of the measured ion and electron temperatures in NSTX during neutral beam heating is anomalously high [Bell, Bull. Am. Phys. Soc. 46, 206 (2001)]. To explain the anomaly in the ratio of ion to electron temperature, it has been suggested that the CAE, driven by the beam ions, stochastically heat the thermal ions [Gates et al., Phys. Rev. Lett. 87, 205003 (2001)]. In this paper it is shown through studies of the power balance that stochastic heating of the thermal ions by the observed CAE alone is not solely responsible for the anomaly in the ion to electron temperature ratio
Nonlinear propagation of short wavelength drift-Alfven waves
DEFF Research Database (Denmark)
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...
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...
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...
Eigenmode Splitting in all Hydrogenated Amorphous Silicon Nitride Coupled Microcavity
Institute of Scientific and Technical Information of China (English)
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.
Nonlinear standing Alfven wave current system at Io: Theory
International Nuclear Information System (INIS)
We present a nonlinear analytical model of the Alfven current tubes continuing the currents through Io (or rather its ionosphere) generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma. We thereby extend the linear work by Drell et al. (1965) to the fully nonlinear, sub-Alfvenic situation also including flow which is not perpendicular to the background magnetic field. The following principal results have been obtained: (1) The portion of the currents feeding Io is aligned with the Alfven characteristics at an angle theta/sub A/ is the Alfven Mach number. (2) The Alfven tubes act like an external conductance Σ/sub A/=1/(μ0V/sub A/(1+M/sub A/2+2M/sub A/ sin theta)/sup 1/2/ where V/sub A/ is the Alfven wave propagation. Hence the Jovian ionospheric conductivity is not necessary for current closure. (3) In addition, the Alfven tubes may be reflected from either the torus boundary or the Jovian ionosphere. The efficiency of the resulting interaction with these boundaries varies with Io position. The interaction is particularly strong at extreme magnetic latitudes, thereby suggesting a mechanism for the Io control of decametric emissions. (4) The reflected Alfven waves may heat both the torus plasma and the Jovian ionosphere as well as produce increased diffusion of high-energy particles in the torus. (5) From the point of view of the electrodynamic interaction, Io is unique among the Jovian satellites for several reasons: these include its ionosphere arising from ionized volcanic gases, a high external Alfvenic conductance Σ/sub A/, and a high corotational voltage in addition to the interaction phenomenon with a boundary. (6) We find that Amalthea is probably strongly coupled to Jupiter's ionosphere while the outer Galilean satellites may occasionally experience super-Alfvenic conditions
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
DEFF Research Database (Denmark)
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...
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.
Intermittency of Energy Dissipation in Alfvenic Turbulence
Zhdankin, Vladimir; Chen, Christopher H K
2015-01-01
We investigate the intermittency of energy dissipation in Alfvenic turbulence by considering the statistics of the coarse-grained energy dissipation rate, using direct measurements from numerical simulations of magnetohydrodynamic turbulence and surrogate measurements from the solar wind. We compare the results to the predictions of the log-normal and log-Poisson random cascade models. We find that, to a very good approximation, the log-normal model describes the probability density function for the energy dissipation over a broad range of scales, but does not accurately describe the scaling exponents of the moments. The log-Poisson model better describes the scaling exponents of the moments, while the comparison with the probability density function is not straightforward.
The Source of Alfven Waves That Heat the Solar Corona
Ruzmaikin, A.; Berger, M. A.
1998-01-01
We suggest a source for high-frequency Alfven waves invoked in coronal heating and acceleration of the solar wind. The source is associated with small-scale magnetic loops in the chromospheric network.
Development of Alfven wave antenna system for TCABR Tokamak
International Nuclear Information System (INIS)
The advanced antenna system for Alfven wave plasma heating and current drive in TCABR tokamak is presented. The antenna system is capable of exciting the travelling waves M=- 1, N=-4, -6 with single helicity and provides the possibility to improve Alfven wave plasma heating efficiency and to increase RF power input up 1 MW, without an uncontrolled density rise. The basic features of the antenna design and the results of preliminary tests are analyzed. (author)
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.
Embedded monopoles in quark eigenmodes in quenched SU(2) QCD
Chernodub, M N
2006-01-01
We study the embedded QCD monopoles (``quark monopoles'') using low-lying eigenmodes of the overlap Dirac operator in zero- and finite-temperature quenched SU(2) gauge theory on the lattice. These monopoles correspond to gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles were suggested to be agents of the chiral symmetry restoration since their cores should suppress the chiral condensate. We study numerically the scalar, axial and chirally invariant definitions of the embedded monopoles and show that the monopole densities are in fact globally anti-correlated with the density of the Dirac eigenmodes. We observe, that the embedded monopoles corresponding to low-lying Dirac eigenvalues are dense in the chirally invariant (high temperature) phase and dilute in the chirally broken (low temperature) phase. We find that the scaling of the scalar and axial monopole densities towards the continuum limit is similar to the scaling of the string-like objects while the chirally invariant monopole...
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.
Nonlinear Hybridization of the Fundamental Eigenmodes of Microscopic Ferromagnetic Ellipses
Demidov, V. E.; Buchmeier, M.; Rott, Karsten; Krzysteczko, Patryk; Münchenberger, Jana; Reiss, Günter; Demokritov, S. O.
2010-01-01
We have studied experimentally with high spatial resolution the nonlinear eigenmodes of microscopic Permalloy elliptical elements. We show that the nonlinearity affects the frequencies of the edge and the center modes in an essentially different way. This leads to repulsion of corresponding resonances and to nonlinear mode hybridization resulting in qualitative modifications of the spatial characteristics of the modes. We find that the nonlinear counterparts of the edge and the center modes s...
Nonlinear hybridization of the fundamental eigenmodes of microscopic ferromagnetic ellipses.
Demidov, V E; Buchmeier, M; Rott, K; Krzysteczko, P; Münchenberger, J; Reiss, G; Demokritov, S O
2010-05-28
We have studied experimentally with high spatial resolution the nonlinear eigenmodes of microscopic Permalloy elliptical elements. We show that the nonlinearity affects the frequencies of the edge and the center modes in an essentially different way. This leads to repulsion of corresponding resonances and to nonlinear mode hybridization resulting in qualitative modifications of the spatial characteristics of the modes. We find that the nonlinear counterparts of the edge and the center modes simultaneously exhibit features specific for both their linear analogues. PMID:20867132
Polyakov loop fluctuations in the Dirac eigenmode expansion
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-01-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal nontwisted periodic boundary condition for the link variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phases by numerical simulations in SU(3) quenched QCD. Thes...
International Nuclear Information System (INIS)
Stationary transonic super-Alfven, subsonic super-Alfven, supersonic sub-Alfven, and Alfven magnetohydrodynamic flows, obtained by numerical modeling of their build-up processes, in coaxial canals in the presence of longitudinal magnetic field have been considered
Reflection of Alfven waves in the solar wind
Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Nerney, S. F.; Moore, R. L.
1994-01-01
We have revisited the problem of propagation of toroidal and linear Alfven waves formulated by Heinemann and Olbert (1980) to compare Wentzel-Kramers-Brillouin (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 in WKB waves. There are several recently published papers that 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 purposse 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 Heinimann and Olbert, namely, calculate the efficieny of Alfven wave reflection by using the reflection coefficient and identfy the region of strongest wave reflection in different wind models. To achieve these goals, we investigate the influence of temperature, electron desity distribution, wind velocity, and magnetic field strength on te 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)/cu cm. 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
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
Low-frequency waves in a high-beta collisionless plasma Polarization, compressibility and helicity
Gary, S. P.
1986-01-01
This paper considers the linear theory of waves near and below the ion cyclotron frequency in an isothermal electron-ion Vlasov plasma which is isotropic, homogeneous and magnetized. Numerical solutions of the full dispersion equation for the magnetosonic/whistler and Alfven/ion cyclotron modes at beta(i) = 1.0 are presented, and the polarizations, compressibilities, helicities, ion Alfven ratios and ion cross-helicities are exhibited and compared. At sufficiently large beta(i) and theta, the angle of propagation with respect to the magnetic field, the real part of the polarization of the Alfven/ion cyclotron wave changes sign, so that, for such parameters, this mode is no longer left-hand polarized. The Alfven/ion cyclotron mode becomes more compressive as the wavenumber increases, whereas the magnetosonic/whistler becomes more compressive with increasing theta.
Multi-frequency tapping-mode atomic force microscopy beyond three eigenmodes in ambient air
Directory of Open Access Journals (Sweden)
Santiago D. Solares
2014-09-01
Full Text Available We present an exploratory study of multimodal tapping-mode atomic force microscopy driving more than three cantilever eigenmodes. We present tetramodal (4-eigenmode imaging experiments conducted on a thin polytetrafluoroethylene (PTFE film and computational simulations of pentamodal (5-eigenmode cantilever dynamics and spectroscopy, focusing on the case of large amplitude ratios between the fundamental eigenmode and the higher eigenmodes. We discuss the dynamic complexities of the tip response in time and frequency space, as well as the average amplitude and phase response. We also illustrate typical images and spectroscopy curves and provide a very brief description of the observed contrast. Overall, our findings are promising in that they help to open the door to increasing sophistication and greater versatility in multi-frequency AFM through the incorporation of a larger number of driven eigenmodes, and in highlighting specific future research opportunities.
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...
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. ...
Localized eigenmodes of the overlap operator and their impact on the eigenvalue distribution
Energy Technology Data Exchange (ETDEWEB)
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.)
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.
Moore, R. L.; Hammer, R.; Musielak, Z. E.; Suess, S. T.; An, C.-H.
1992-01-01
In our recent analysis of Alfven wave reflection in solar coronal holes, we found evidence that coronal holes are heated by reflected Alfven waves. This result suggests that the reflection is inherent to the process that dissipates these Alfven waves into heat. We propose a novel dissipation process that is driven by the reflection, and that plausibly dominates the heating in coronal holes.
Alfven QPOs in magnetars in the anelastic approximation
Cerdá-Durán, Pablo; Font, José A
2009-01-01
We perform two-dimensional simulations of Alfven oscillations in magnetars, modeled as relativistic stars with a dipolar magnetic field. We use the anelastic approximation to general relativistic magnetohydrodynamics, which allows for an effective suppression of fluid modes and an accurate description of Alfven waves. In addition, we compute Alfven oscillation frequencies along individual magnetic field lines with a semi-analytic approach, employing a short-wavelength approximation. Our main findings are as follows: a) we confirm the existence of two families of quasi-periodic oscillations (QPOs), with harmonics at integer multiples of the fundamental frequency, as was found in the linear study of Sotani, Kokkotas & Stergioulas (2008); b) the QPOs appearing near the magnetic axis are split into two groups, depending on their symmetry across the equatorial plane. The antisymmetric QPOs have only odd integer-multiple harmonics; c) the continuum obtained with our semi-analytic approach agrees remarkably well...
Stable Alfven wave dynamo action in the reversed field pinch
International Nuclear Information System (INIS)
Recent advances in linear resistive MHD stability analysis are used to calculate the quasi-linear dynamo mean electromotive force of Alfven waves. This emf is incorporated into a one-dimensional transport and mean-field evolution code. The changing equilibrium is then fed back to the stability code to complete a computational framework that self-consistently evaluates a dynamic plasma dynamo. Static quasi-linear Alfven wave calculations have shown that dynamo emfs on the order of eta vector J are possible. This suggested a possible explanation of RFP behavior and a new (externally driven) mechanism for extending operation and controlling field profiles (possibly reducing plasma transport). This thesis demonstrates that the dynamo emf can quickly induce plasma currents whose emf cancels the dynamo effect. This thesis also contains extensive studies of resistive Alfven wave properties. This includes behavior versus spectral location, magnetic Reynolds number and wave number
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...
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.
Free-boundary toroidal Alfvén eigenmodes
Chen, Eugene Y.; Berk, H. L.; Breizman, B.; Zheng, L. J.
2011-05-01
A numerical study is presented for the n = 1 free-boundary toroidal Alfvén eigenmodes (TAE) in tokamaks, which shows that there is considerable sensitivity of n = 1 modes to the position of the conducting wall. An additional branch of the TAE is shown to emerge from the upper continuum as the ratio of conducting wall radius to plasma radius increases. Such phenomena arise in plasma equilibria with both circular and shaped cross sections, where the shaped profile studied here is similar to that found in Alcator C-Mod.
Optical Control of Fluorescence through Plasmonic Eigenmode Extinction
Xu, Xiaoying; Lin, Shih-Che; Li, Quanshui; Zhang, Zhili; Ivanov, Ilia N.; Li, Yuan; Wang, Wenbin; Gu, Baohua; Zhang, Zhenyu; Hsueh, Chun-Hway; Snijders, Paul C.; Seal, Katyayani
2015-04-01
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.
Polyakov loop fluctuations in the Dirac eigenmode expansion
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-11-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal nontwisted periodic boundary condition for the link variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phases by numerical simulations in SU(3) quenched QCD. These results indicate that there is no direct, one-to-one correspondence between confinement and chiral symmetry breaking in QCD in the context of different properties of the Polyakov loop fluctuation ratios.
Resonant Alfven wave instabilities driven by streaming fast particles
International Nuclear Information System (INIS)
A plasma simulation code is used to study the resonant interactions between streaming ions and Alfven waves. The medium which supports the Alfven waves is treated as a single, one-dimensional, ideal MHD fluid, while the ions are treated as kinetic particles. The code is used to study three ion distributions: a cold beam; a monoenergetic shell; and a drifting distribution with a power-law dependence on momentum. These distributions represent: the field-aligned beams upstream of the earth's bow shock; the diffuse ions upstream of the bow shock; and the cosmic ray distribution function near a supernova remnant shock. 92 refs., 31 figs., 12 tabs
KINETIC ALFVEN WAVES EXCITED BY OBLIQUE MAGNETOHYDRODYNAMIC ALFVEN WAVES IN CORONAL HOLES
International Nuclear Information System (INIS)
Kinetic Alfven waves (KAWs) are small-scale dispersive AWs that can play an important role in particle heating and acceleration of space and solar plasmas. An excitation mechanism for KAWs created by the coupling between large-scale oblique AWs and small-scale KAWs is presented in this paper. Taking into account both the collisional and Landau damping dissipations, the results show that the net growth rate of the excited KAWs increases with their perpendicular wavenumber kperpendicular and reaches maximum at λe kperpendicular ∼ 0.3, where λe is the electron inertial length. However, for KAWs with shorter perpendicular wavelengths, the net growth rate decreases rapidly due to dissipative effects. The evaluation of the threshold amplitude of the AW implies that for KAWs with λe kperpendicular e kperpendicular < 0.3 can be not only efficiently excited in the interplume region but also strongly dissipated in the dense plume due to the Landau damping.
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
Interacting Eigenmodes of a plasma diode with a density gradient
International Nuclear Information System (INIS)
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
Interacting Eigenmodes of a plasma diode with a density gradient
Energy Technology Data Exchange (ETDEWEB)
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. PMID:25353549
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...
ALFVEN WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA
Energy Technology Data Exchange (ETDEWEB)
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.
Three-fluid solar wind model with Alfven waves
Esser, Ruth; Habbal, Shadia R.; Hu, You Q.
1995-01-01
We present a study of a three-fluid solar wind model. with continuity, momentum and separate energy equations for protons. alpha particles and electrons. Allowing separate coronal heat sources for all three species, we study the flow properties of the solar wind as a function of heat input, Alfven wave energy input, and alpha particle abundance.
Quantum effects on compressional Alfven waves in compensated semiconductors
Energy Technology Data Exchange (ETDEWEB)
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.
Nonlinear Alfven waves and solitons in cold plasma
International Nuclear Information System (INIS)
A finite-zone sector for the derivative nonlinear Schroedinger equation, which describes nonlinear small-amplitude. Alfven waves in the long-wave approximation, is investigated. The formulas for periodic one-phase and one-soliton solutions and the general formula for an n-soliton solution envelope are obtained
Variational analysis of eigenmodes of integrated optical waveguides and applications
Institute of Scientific and Technical Information of China (English)
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.
Eigenmodes of quasi-static magnetic islands in current sheet
International Nuclear Information System (INIS)
As observation have shown, magnetic islands often appear before and/or after the onset of magnetic reconnections in the current sheets, and they also appear in the current sheets in the solar corona, Earth's magnetotail, and Earth's magnetopause. Thus, the existence of magnetic islands can affect the initial conditions in magnetic reconnection. In this paper, we propose a model of quasi-static magnetic island eigenmodes in the current sheet. This model analytically describes the magnetic field structures in the quasi-static case, which will provide a possible approach to reconstructing the magnetic structures in the current sheet via observation data. This model is self-consistent in the kinetic theory. Also, the distribution function of charged particles in the magnetic island can be calculated.
Analysis of topological structure of the QCD vacuum with overlap-Dirac operator eigenmode
Iritani, Takumi; Hashimoto, Shoji
2013-01-01
Using the eigenmodes of the overlap-Dirac operator, we study the topological structure of the QCD vacuum. We investigate the space-time profile of the low-lying eigenmodes and their contribution to the vacuum action density and chiral condensate under the existence of static color sources. We demonstrate that the low-lying Dirac eigenmode shows the flux-tube structure, which suggests the relevance to confinement. We also analyze the chiral condensate in the flux-tube. Chiral symmetry is partially restored inside the flux, and the reduction of the condensate is about 20% at the center of the tube.
1.5D quasilinear model and its application on beams interacting with Alfvén eigenmodes in DIII-D
Ghantous, K.; Gorelenkov, N. N.; Berk, H. L.; Heidbrink, W. W.; Van Zeeland, M. A.
2012-09-01
We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges #142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and #127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.
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.
Refined Critical Balance in Strong Alfv\\'enic Turbulence
Mallet, A; Chandran, B D G
2014-01-01
We present numerical evidence that in strong Alfv\\'enic turbulence, the critical balance principle---equality of the nonlinear decorrelation and linear propagation times---is scale invariant, in the sense that the probability distribution of the ratio of these times is independent of scale. This result only holds if the local alignment of the Elsasser fields is taken into account in calculating the nonlinear time. At any given scale, the degree of alignment is found to increase with fluctuation amplitude, supporting the idea that the cause of alignment is mutual dynamical shearing of Elsasser fields. The scale-invariance of critical balance (while all other quantities of interest are strongly intermittent, i.e., have scale-dependent distributions) suggests that it is the most robust of the scaling principles used to describe Alfv\\'enic turbulence.
Alfv\\'en waves in simulations of solar photospheric vortices
Shelyag, S; Reid, A; Mathioudakis, M
2013-01-01
Using advanced numerical magneto-hydrodynamic simulations of the magnetised solar photosphere, including non-grey radiative transport and a non-ideal equation of state, we analyse plasma motions in photospheric magnetic vortices. We demonstrate that apparent vortex-like motions in photospheric magnetic field concentrations do not exhibit "tornado"-like behaviour or a "bath-tub" effect. While at each time instance the velocity field lines in the upper layers of the solar photosphere show swirls, the test particles moving with the time-dependent velocity field do not demonstrate such structures. Instead, they move in a wave-like fashion with rapidly changing and oscillating velocity field, determined mainly by magnetic tension in the magnetised intergranular downflows. Using time-distance diagrams, we identify horizontal motions in the magnetic flux tubes as torsional Alfv\\'en perturbations propagating along the nearly vertical magnetic field lines with local Alfv\\'en speed.
Hammer, 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
Hammer, 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
Fligsen, T; Van Rienen, U
2014-01-01
The computation of eigenmodes for complex accelerating structures is a challenging and important task for the design and operation of particle accelerators. Discretizing long and complex structures to determine its eigenmodes leads to demanding computations typically performed on super computers. This contribution presents an application example of a method to compute eigenmodes and other parameters derived from these eigenmodes for long and complex structures using standard workstation computers. This is accomplished by the decomposition of the complex structure into several single segments. In a next step, the electromagnetic properties of the segments are described in terms of a compact state-space model. Subsequently, the state-space models of the single structures are concatenated to the full structure. The results of direct calculations are compared with results obtained by the concatenation scheme in terms of computational time and accuracy.
Attractors of magnetohydrodynamic flows in an Alfvenic state
Energy Technology Data Exchange (ETDEWEB)
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)
Experimental observation of the shear Alfven resonance in a tokamak
International Nuclear Information System (INIS)
Experiments in Tokapole II have demonstrated the shear Alfven resonance in a tokamak by direct probe measurement of the wave magnetic field within the plasma. The resonance is driven by external antennas and is identified as radially localized enhancements of the poloidal wave magnetic field. The radial location agrees with calculations which include toroidicity and noncircularity of the plasma cross-section. Other properties such as polarization, radial width, risetime, and wave enhancement also agree with MHD theory
The Alf'ven Effect and Conformal Field Theory
Tabar, M. R. Rahimi; Rouhani, S
1995-01-01
Noting that two-dimensional magnetohydrodynamics can be modeled by conformal field theory, we argue that when the Alf'ven effect is also taken into account one is naturally lead to consider conformal field theories, which have logarithmic terms in their correlation functions. We discuss the implications of such logarithmic terms in the context of magnetohydrodynamics, and derive a relationship between conformal dimensions of the velocity stream function, the magnetic flux function and the Rey...
Looking for Cosmological Alfven Waves in WMAP Data
Chen, Gang; Mukherjee, Pia; Kahniashvili, Tina; Ratra, Bharat; Wang, Yun
2004-01-01
A primordial cosmological magnetic field induces and supports vorticity or Alfven waves, which in turn generate cosmic microwave background (CMB) anisotropies. A homogeneous primordial magnetic field with fixed direction induces correlations between the $a_{l-1,m}$ and $a_{l+1,m}$ multipole coefficients of the CMB temperature anisotropy field. We discuss the constraints that can be placed on the strength of such a primordial magnetic field using CMB anisotropy data from the WMAP experiment. W...
Enhanced phase mixing of Alfv\\'en waves propagating in stratified and divergent coronal structures
Smith, P. D.; Tsiklauri, D.; Ruderman, M. S.
2007-01-01
Corrected analytical solutions describing the enhanced phase mixing of Alfven waves propagating in divergent stratified coronal structures are presented. These show that the enhanced phase mixing mechanism can dissipate Alfven waves at heights less than half that is predicted by the previous analytical solutions. The enhanced phase mixing of 0.1 Hz harmonic Alfven waves propagating in strongly divergent, H_b=5 Mm, stratified coronal structures, H_rho=50 Mm, can fulfill 100% of an active regio...
Inductive Eigenmodes of a resistive toroidal surface in vacuum
Energy Technology Data Exchange (ETDEWEB)
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
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 the Solar Wind, Magnetosheath, and Outer Magnetosphere
Sibeck, D. G.
2007-01-01
Alfven waves Propagating outward from the Sun are ubiquitous in the solar wind and play a major role in the solar wind-magnetosphere interaction. The passage of the waves generally occurs in the form of a series of discrete steepened discontinuities, each of which results in an abrupt change in the interplanetary magnetic field direction. Some orientations of the magnetic field permit particles energized at the Earth's bow shock to gain access to the foreshock region immediately upstream from the Earth's bow shock. The thermal pressure associated with these particles can greatly perturb solar wind plasma and magnetic field parameters shortly prior to their interaction with the Earth's bow shock and magnetosphere. The corresponding dynamic pressure variations batter the magnetosphere, driving magnetopause motion and transient compressions of the magnetospheric magnetic field. Alfven waves transmit information concerning the dynamic pressure variations applied to the magnetosphere to the ionosphere, where they generate the traveling convection vortices (TCVs) seen in high-latitude ground magnetograms. Finally, the sense of Alfvenic perturbations transmitted into the magnetosheath reverses across local noon because magnetosheath magnetic field lines drape against the magnetopause. The corresponding change in velocity perturbations must apply a weak torque to the Earth's magnetosphere.
Multiple regimes of operation in bimodal AFM: understanding the energy of cantilever eigenmodes
Daniel Kiracofe; Arvind Raman; Dalia Yablon
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...
Theory and calculation of finite beta drift wave turbulence
International Nuclear Information System (INIS)
Using numerical techniques, we calculate eigenmodes of the nonlinear universal mode with finite beta in order to determine the scaling of the saturation level of the instability with beta. We use two different renormalizations in the calculations and find that using the appropriate renormalization, we are able to recover Alcator density scaling, as originally found in analytic work by Molvig and Hirshman. We also find that the universal mode should be stable in ohmically heated tokamaks above a critical beta on the order of 0.02
Shear Alfven wave excitation by direct antenna coupling and fast wave resonant mode conversion
International Nuclear Information System (INIS)
Antenna coupling to the shear Alfven wave by both direct excitation and fast wave resonant mode conversion is modelled analytically for a plasma with a one dimensional linear density gradient. We demonstrate the existence of a shear Alfven mode excited directly by the antenna. For localised antennas, this mode propagates as a guided beam along the steady magnetic field lines intersecting the antenna. Shear Alfven wave excitation by resonant mode conversion of a fast wave near the Alfven resonance layer is also demonstrated and we prove that energy is conserved in this process. We compare the efficiency of these two mechanisms of shear Alfven wave excitation and present a simple analytical formula giving the ratio of the coupled powers. Finally, we discuss the interpretation of some experimental results. 45 refs., 7 figs
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.
Nonlinear absorption of Alfven wave in dissipative plasma
Energy Technology Data Exchange (ETDEWEB)
Taiurskii, A. A., E-mail: tayurskiy2001@mail.ru; Gavrikov, M. B., E-mail: nadya-p@cognitive.ru [Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 4 Miusskaya sq. Moscow 125047 (Russian Federation)
2015-10-28
We propose a method for studying absorption of Alfven wave propagation in a homogeneous non-isothermal plasma along a constant magnetic field, and relaxation of electron and ion temperatures in the A-wave. The absorption of a A-wave by the plasma arises due to dissipative effects - magnetic and hydrodynamic viscosities of electrons and ions and their elastic interaction. The method is based on the exact solution of two-fluid electromagnetic hydrodynamics of the plasma, which for A-wave, as shown in the work, are reduced to a nonlinear system of ordinary differential equations.
Theoretical Studies of Drift-Alfven and Energetic Particle Physics
Energy Technology Data Exchange (ETDEWEB)
CHEN, L.
2014-05-14
The research program supported by this DOE grant has been rather successful and productive in terms of both scientific investigations as well as human resources development; as demonstrated by the large number (60) of journal articles, 6 doctoral degrees, and 3 postdocs. This PI is particularly grateful to the generous support and flexible management of the DOE–SC-OFES Program. He has received three award/prize (APS Excellence in Plasma Physics Research Award, 2004; EPS Alfven Prize, 2008; APS Maxwell Prize, 2012) as the results of research accomplishments supported by this grant.
Density Limit in TCABR Plasmas With Alfven Wave Heating
International Nuclear Information System (INIS)
Alfven Waves (AW) were launched in tokamak (TCABR) density limit plasmas for the first time. Experimental evidence of plasma heating is backed up by calculations from an 1-D numerical cylindrical code, based on the toroidal electric field diffusion. Simultaneously, increase in the density limit and plasma pressure with negligible impurities level launched by the AW antennas were also observed, without major appearance of a resistive disruption. The increase in the density limit and the heating might be related to the expected edge and off-axis AW power deposition, respectively, in agreement with the calculation performed by an 1-D numerical code linked to ASTRA
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...
Ion temperature anisotropy limitation in high beta plasmas
Energy Technology Data Exchange (ETDEWEB)
Scime, Earl E. [West Virginia University, Morgantown, West Virginia 26506 (United States); Keiter, Paul A. [West Virginia University, Morgantown, West Virginia 26506 (United States); Balkey, Matthew M. [West Virginia University, Morgantown, West Virginia 26506 (United States); Boivin, Robert F. [West Virginia University, Morgantown, West Virginia 26506 (United States); Kline, John L. [West Virginia University, Morgantown, West Virginia 26506 (United States); Blackburn, Melanie [West Virginia University, Morgantown, West Virginia 26506 (United States); Gary, S. Peter [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States)
2000-05-01
Measurements of parallel and perpendicular ion temperatures in the Large Experiment on Instabilities and Anisotropies (LEIA) space simulation chamber display an inverse correlation between the upper bound on the ion temperature anisotropy and the parallel ion beta ({beta}=8{pi}nkT/B{sup 2}). Fluctuation measurements indicate the presence of low frequency, transverse, electromagnetic waves with wave numbers and frequencies that are consistent with predictions for Alfven Ion Cyclotron instabilities. These observations are also consistent with in situ spacecraft measurements in the Earth's magnetosheath and with a theoretical/computational model that predicts that such an upper bound on the ion temperature anisotropy is imposed by scattering from enhanced fluctuations due to growth of the Alfven ion cyclotron instability. (c) 2000 American Institute of Physics.
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.
Dispersion relation and energy allotment of eigenmode of layer-by-layer photonic crystal
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The photonic crystal of layer-by-layer(LBL) structure is discussed in this paper.The structure of LBL photonic crystal is body-centered tetragonal (b.c.t)rather than face-centered tetragonal(f.c.t.)For the LBL photonic crystal of f.e.c or b.c.c lattice,to obtain the fulll information on its Brillouin zone,the calculation of three restricted volumes is needed and our calculation result agrees well with the experiment.The allotments of optical fields of eigenmodes in a dielectric material are also calculated.In the dielectric material,for the eigenmode at the bottom of the forbidden gap,electric field takes a larger fraction of the whole energy than magnetic field,while for the eigenmode at the top of the forbidden gap,allotment of energy is just the other way round.
Eigenfrequencies and eigenmodes of a beam with periodically continuously varying spatial properties
DEFF Research Database (Denmark)
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...
Cossu, Guido; Hashimoto, Shoji
2016-06-01
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 Möbius 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 ˜ 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.
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.
Emission of Alfven Waves by Planets in Close Orbits
MacGregor, Keith B.; Pinsonneault, M. H.
2011-01-01
We examine the electrodynamics of a conducting planet orbiting within a magnetized wind that emanates from its parent star. When the orbital motion differs from corotation with the star, an electric field exists in the rest frame of the planet, inducing a charge separation in its ionosphere. Because the planet is immersed in a plasma, this charge can flow away from it along the stellar magnetic field lines it successively contacts in its orbit. For sufficiently rapid orbital motion, a current system can be formed that is closed by Alfvenic disturbances that propagate along field lines away from the planet. Using a simple model for the wind from a Sun-like star, we survey the conditions under which Alfven wave emission can occur, and estimate the power radiated in the form of linear waves for a range of stellar, planetary, and wind properties. For a Jupiter-like planet in a close (a type star, the emitted wave power can be as large as 1027 erg/s. While only a small influence on the planet's orbit, a wave power of this magnitude may have consequences for wind dynamics and localized heating of the stellar atmosphere. NCAR is sponsored by the NSF.
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...
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
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.
New non-axisymmetric eigenmodes associated with an edge plasma layer
International Nuclear Information System (INIS)
Effects of a rarefied plasma layer surrounding a cylindrical main plasma on Alfven waves are investigated. The plasma is approximated with a two-step density profile and is assumed to be surrounded with a conducting wall. When the Alfven resonance exists inside the rarefied plasma layer, two new modes are generated. One has its maximum of the wave intensity at the wall, is thus similar to a surface wave and the other is a short of a coaxial mode. These results are re-examined in a diffuse boundary plasma and the presence of these modes is confirmed. (author)
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.
Preliminary results on Alfven wave system in the TCABR tokamak
International Nuclear Information System (INIS)
A brief review of the Alfven Wave Excitation System (AWES) designed for the TCABR tokamak and the first experimental results on RF plasma heating are presented. One of four antenna modules has been completely installed in the vacuum chamber and the initial experiments were carried out in the low power regime using the four-phase RF generator. The main objectives were the antenna tuning according to the typical plasma parameters of TCABR and the evaluation of the antenna parasitic loading, as well as the calibration of the RF diagnostic tools in real discharge conditions. The first results have been obtained with standard diagnostics and with the RF signals measured using high sampling rate digital oscilloscopes. They showed that daily antenna cleaning and correct wave helicity excitation reduce significantly the parasitic loading and are crucial for efficient plasma coupling
Maruta, Kazuki; Iwakuni, Tatsuhiko; Ohta, Atsushi; Arai, Takuto; Shirato, Yushi; Kurosaki, Satoshi; Iizuka, Masataka
2016-01-01
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.
Nature of sub-band gap luminescent eigenmodes in a ZnO nanowire
Rühle, S.; van Vugt, L.K.; Li, H.-Y.; Keizer, N.A.; Kuipers, L.; Vanmaekelbergh, D.A.M.
2008-01-01
The emission spectrum of individual high-quality ZnO nanowires consists of a series of Fabry-Pérot-like eigenmodes that extend far below the band gap of ZnO. Spatially resolved luminescence spectroscopy shows that light is emitted predominantly at both wire ends, with identical spectra reflecting st
Spiral eigenmodes triggered by grooves in the phase space of disc galaxies
De Rijcke, Sven
2015-01-01
We use linear perturbation theory to investigate how a groove in the phase space of a disc galaxy changes the stellar disc's stability properties. Such a groove is a narrow trough around a fixed angular momentum from which most stars have been removed, rendering part of the disc unresponsive to spiral waves. We find that a groove can dramatically alter a disc's eigenmode spectrum by giving rise to a set of vigorously growing eigenmodes. These eigenmodes are particular to the grooved disc and are absent from the original ungrooved disc's mode spectrum. We discuss the properties and possible origin of the different families of new modes. By the very nature of our technique, we prove that a narrow phase-space groove can be a source of rapidly growing spiral patterns that are true eigenmodes of the grooved disc and that no non-linear processes need to be invoked to explain their presence in N-body simulations of disc galaxies. Our results lend support to the idea that spiral structure can be a recurrent phenomeno...
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.
Directory of Open Access Journals (Sweden)
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.
Maruta, Kazuki; Iwakuni, Tatsuhiko; Ohta, Atsushi; Arai, Takuto; Shirato, Yushi; Kurosaki, Satoshi; Iizuka, Masataka
2016-01-01
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. PMID:27399715
Internal Kink Mode Dynamics in High-beta NSTX Plasmas
Energy Technology Data Exchange (ETDEWEB)
J.E. Menard; R.E. Bell; E.D. Fredrickson; D.A. Gates; S.M. Kaye; B.P. LeBlanc; S.S. Medley; W. Park; S.A. Sabbagh; A. Sontag; D. Stutman; K. Tritz; W. Zhu; the NSTX Research Team
2004-12-22
Saturated internal kink modes have been observed in many of the highest toroidal {beta} discharges of the National Spherical Torus Experiment (NSTX). These modes often cause rotation flattening in the plasma core, can degrade energy confinement, and in some cases contribute to the complete loss of plasma angular momentum and stored energy. Characteristics of the modes are measured using soft X-ray, kinetic profile, and magnetic diagnostics. Toroidal flows approaching Alfvenic speeds, island pressure peaking, and enhanced viscous and diamagnetic effects associated with high-{beta} may contribute to mode nonlinear stabilization. These saturation mechanisms are investigated for NSTX parameters and compared to experimental data.
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.
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.
Alfven Waves in a Plasma Sheet Boundary Layer Associated with Near-Tail Magnetic Reconnection
Institute of Scientific and Technical Information of China (English)
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.
Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited
Burkhart, Blakesley; A. Lazarian; 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 ...
Shao, X.; Karavaev, A. V.; Gumerov, N.; Sharma, A. S.; Papadopoulos, K.; Gekelman, W. N.; Wang, Y.; Vincena, S. T.; Pribyl, P.
2010-12-01
Recent experiments conducted in the Large Plasma Device (LAPD) located at UCLA demonstrated efficient excitation of whistler and shear Alfven waves by a Rotating Magnetic Field (RMF) source. We present analytical theory, computational modeling and experimental results of the shear Alfven wave excitation by RMF source created by a phased orthogonal two-loop antenna in a plasma. An analytical theory and simulations using a three-dimensional cold two-fluid model of Alfven wave excitation were developed and compared with experiments. These comparisons show good agreement on linear shear Alfven wave properties, namely, spatio-temporal wave structure, dispersion relation, and the dependence of wave magnitude on the wave frequency. From the simulations it was found that the energy of the Alfven wave generated by the rotating magnetic field source is distributed among the kinetic energies of ions and electrons and the electromagnetic energy of the wave. The wave magnetic field power calculated from the experimental data and using a fluid model agrees within 1 percent. The RMF source is thus very efficient in generating shear Alfven waves. Work supported by ONR MURI grant.
Borysov, Stanislav S; Balatsky, Alexander V; Haviland, David B
2014-01-01
We present a theoretical framework for the dynamic calibration of the higher eigenmode parameters (stiffness and optical lever responsivity) of a cantilever. The method is based on the tip-surface force reconstruction technique and does not require any prior knowledge of the eigenmode shape or the particular form of the tip-surface interaction. The calibration method proposed requires a single-point force measurement using a multimodal drive and its accuracy is independent of the unknown physical amplitude of a higher eigenmode.
A Unique Self-Sensing, Self-Actuating AFM Probe at Higher Eigenmodes
Wu, Zhichao; Guo, Tong; Tao, Ran; Liu, Leihua; Chen, Jinping; Fu, Xing; Hu, Xiaotang
2015-01-01
With its unique structure, the Akiyama probe is a type of tuning fork atomic force microscope probe. The long, soft cantilever makes it possible to measure soft samples in tapping mode. In this article, some characteristics of the probe at its second eigenmode are revealed by use of finite element analysis (FEA) and experiments in a standard atmosphere. Although the signal-to-noise ratio in this environment is not good enough, the 2 nm resolution and 0.09 Hz/nm sensitivity prove that the Akiyama probe can be used at its second eigenmode under FM non-contact mode or low amplitude FM tapping mode, which means that it is easy to change the measuring method from normal tapping to small amplitude tapping or non-contact mode with the same probe and equipment. PMID:26580619
A Unique Self-Sensing, Self-Actuating AFM Probe at Higher Eigenmodes
Directory of Open Access Journals (Sweden)
Zhichao Wu
2015-11-01
Full Text Available With its unique structure, the Akiyama probe is a type of tuning fork atomic force microscope probe. The long, soft cantilever makes it possible to measure soft samples in tapping mode. In this article, some characteristics of the probe at its second eigenmode are revealed by use of finite element analysis (FEA and experiments in a standard atmosphere. Although the signal-to-noise ratio in this environment is not good enough, the 2 nm resolution and 0.09 Hz/nm sensitivity prove that the Akiyama probe can be used at its second eigenmode under FM non-contact mode or low amplitude FM tapping mode, which means that it is easy to change the measuring method from normal tapping to small amplitude tapping or non-contact mode with the same probe and equipment.
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.
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.
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.
Eigenmodes of superconducting cavities calculated on an APE-100 supercomputer (SIMD)
Neugebauer, F
1999-01-01
The construction of modern accelerators is usually supported by the numerical determination of eigenmodes in the accelerating cavities. Often the rotational symmetry of the cavity is used to simplify the numerical simulation. However, in cases where the cavity lacks rotational symmetry resp. where attached components like couplers have to be taken into account, a fully three dimensional treatment of the Maxwell equations is necessary. This requires more computer power than is available on a normal high end workstation. Therefore, in the present approach a parallel SIMD super computer (APE-100) is used to compute the eigenmodes of accelerating cavities. As an example parts of the superconducting TESLA structure are investigated. The geometry input is parsed by MAFIA which transfers the resulting system matrix, incorporating geometry and material information, to the APE-100. The result of the diagonalization procedure is then read back to the MAFIA host where further data analysis and visualization can be done....
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...
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.
Recent Results of Alfven Wave Studies in TCABR
International Nuclear Information System (INIS)
The results on comparative studies of Alfven wave plasma heating by two different antenna types in TCABR are presented. Emphasis is placed on the excited wave spectra and parasitic coupling with the edge plasma. The antenna modules have two groups of RF current-carrying straps separated by a toroidal angle of approximately 22 deg. In type I antenna, each group consists of two circular loops that are cut in two half-turn windings. The feeders of each loop pair are rotated 90 deg. in the poloidal direction with respect to each other, to decrease the mutual coupling between them and make it possible to excite single helicity plasma modes (M=+1 or M=-1). In type II antenna, each group consists of two poloidal straps located at the low-magnetic-field side of the vacuum chamber. The poloidal extension of each strap is around 90 deg. and the angle between straps is also of the same value. In both antenna types, the straps have side protectors of boron nitride. Initial experiments indicate that the parasitic interaction with the edge plasma is quite different for the two antennae. Also the first type has larger self-inductance, making it more difficult to deliver high currents to the antenna without increasing the dynamic polarization voltage up to breakdown limits. Results on the excited spectrum and floating potential at the plasma edge are presented
Shear-Alfven dynamics of toroidally confined plasmas. Part A
International Nuclear Information System (INIS)
Recent developments in the stability theory of toroidally confined plasmas are reviewed, with the intention of providing a picture comprehensible to non-specialists. The review considers a class of low-frequency, electromagnetic disturbances that seem especially pertinent to modern high-temperature confinement experiments. It is shown that such disturbances are best unified and understood through consideration of a single, exact fluid moment: the shear-Alfven law. Appropriate versions of this law and its corresponding closure relations are derived - essentially from first principles - and applied in a variety of mostly, but not exclusively, linear contexts. Among the specific topics considered are: flux coordinates (including Hamada coordinates), the Newcomb solubility condition. Shafranov geometry, magnetic island evolution, reduced MHD and its generalizations, drift-kinetic electron response, classical tearing, twisting, and kink instabilities, pressure-modified tearing instability (Δ-critical), collisionless and semi-collisional tearing modes, the ballooning representation in general geometry, ideal ballooning instability, Mercier criterion, near-axis expansions, the second stability region, and resistive and kinetic ballooning modes. The fundamental importance of toroidal topology and curvature is stressed
Institute of Scientific and Technical Information of China (English)
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.
Omega3P: A Parallel Finite-Element Eigenmode Analysis Code for Accelerator Cavities
Energy Technology Data Exchange (ETDEWEB)
Lee, Lie-Quan; Li, Zenghai; Ng, Cho; Ko, Kwok; /SLAC
2009-03-04
Omega3P is a parallel eigenmode calculation code for accelerator cavities in frequency domain analysis using finite-element methods. In this report, we will present detailed finite-element formulations and resulting eigenvalue problems for lossless cavities, cavities with lossy materials, cavities with imperfectly conducting surfaces, and cavities with waveguide coupling. We will discuss the parallel algorithms for solving those eigenvalue problems and demonstrate modeling of accelerator cavities through different examples.
Identification of an Island-induced Alfvén Eigenmode in MST plasmas
Anderson, J. K.; Cook, C. R.; Hegna, C. C.; Boguski, J.; Feng, R.; McCollam, K. M.; Sears, S. H.; Spong, D. A.; Hirshman, S. P.
2015-11-01
Recent theoretical work analytically computes the effect of a magnetic island on the shear Alfvén continuum and may explain unresolved Alfvénic activity observed in neutral beam-heated MST plasmas. Consideration of the previously-ignored core-localized n=5 island leads to theoretical Alfvén continua that provide a gap in which the observed n=4 Alfvénic bursts reside. Numerical simulations using the STELLGAP/AE3D codes, as well as a new code called SIESTAlfvén have identified the bursts as the first observation of an Island-induced Alfvén Eigenmode (IAE). The IAE arises from a helical coupling of mode numbers, similar to the helicity-induced Alfvén eigenmode, but occurs in the core of an island. The observed frequency of bursting n=4 Alfvénic modes fall within the island-induced gap over a wide range of MST operating parameters. Characteristics such as mode frequency, width and damping rate are measured as a function of experimentally-varied magnetic island width. Coincident bursts with toroidal mode number n=1 may exhibit frequency scaling of an Alfvénic eigenmode; the possibility of an island induced extremum mode is explored as an explanation. Work supported by US DoE under grants DE-FG02-99ER54546, DE-SC0006103 and DE-FC02-05ER54814.
Production and maintenance of high poloidal beta tokamak plasmas by means of rf current drive
Energy Technology Data Exchange (ETDEWEB)
Luckhardt, S.C.; Chen, K.; Coda, S.; Kesner, J.; Kirkwood, R.; Lane, B.; Porkolab, M.; Squire, J.
1989-03-27
It is shown that in tokamak plasmas sustained by rf current drive, the contribution of the suprathermal rf-driven electron population to the poloidal beta (..beta../sub p/) can be substantial if the total current is comparable to the Alfven critical current, I/sub A/ = (4..pi..mcv/..mu../sub 0/ec)..gamma... Equilibria with values of epsilon..beta../sub p/ up to approximately 1.3 were obtained, and no equilibrium or gross stability limits were observed.
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...
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...
On the origin of solar wind. Alfven waves induced jump of coronal temperature
Mishonov, T M; Maneva, Y G
2007-01-01
Absorbtion of Alfven waves is considered as the main mechanism of heating of solar corona. It is concluded that the sharp increase of the plasma temperature by two orders of magnitude is related to a self-induced opacity with respect to Alfven waves. The maximal frequency for propagation of Alfven waves is determined by the strongly temperature dependent kinematic viscosity. In such a way the temperature jump is due to absorption of high frequency Alfven waves in a narrow layer above the solar surface. There is calculated the dissipated in this layer power, which blows up the plasma and gives birth to the solar wind. A model short wave-length (WKB) evaluation takes into account the 1/f^2 frequency dependance of the transversal magnetic field and velocity spectral densities. Such spectral densities agree with an old magnetometer's data taken by Voyager 1 and recent theoretical calculations in the framework of Langevin-Burgers MHD. The present theory predicts existence of intensive high frequency Alfven waves i...
Alfven wave. [Book on linear and nonlinear properties for fusion applications
Energy Technology Data Exchange (ETDEWEB)
Hasegawa, A.; Uberoi, C.
1978-11-01
Seven chapters are included. Chapters 1 and 2 introduce the Alfven wave and describe its linear properties in a homogeneous medium. Chapters 3 and 4 cover the effects of inhomogeneities on these linear properties. Particular emphasis is placed on the appearance of a continuum spectrum and the associated absorption of the Alfven wave which arise due to the inhomogeneity. The explanation of the physical origin of absorption is given using kinetic theory. Chapter 5 is devoted to the associated plasma instabilities. Nonlinear effects discussed in Chapter 6 include quasilinear diffusion, decay, a solitary wave, and a modulational instability. The principles of Alfven wave heating, a design example and present-day experimental results are described in Chapter 7.
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.
Magnetohydrodynamics in the Early Universe and the Damping of Non-linear Alfven Waves
Subramanian, K; Subramanian, Kandaswamy; Barrow, John D.
1998-01-01
The evolution and viscous damping of cosmic magnetic fields in the early universe, is analysed. Using the fact that the fluid, electromagnetic, and shear viscous energy-momentum tensors are all conformally invariant, the evolution is transformed from the expanding universe setting into that in flat spacetime. Particular attention is paid to the evolution of nonlinear Alfven modes. For a small enough magnetic field, which satisfies our observational constraints, these wave modes either oscillate negligibly or, when they do oscillate, become overdamped. Hence they do not suffer Silk damping on galactic and subgalactic scales. The smallest scale which survives damping depends on the field strength and is of order a dimensionless Alfven velocity times the usual baryon-photon Silk damping scale. After recombination, nonlinear effects can convert the Alfven mode into compressional, gravitationally unstable waves and seed cosmic structures if the cosmic magnetic field is sufficiently strong.
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...
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.
Benchmarking Fast-to-Alfven Mode Conversion in a Cold MHD Plasma
Cally, Paul S.; Hansen, Shelley C.
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 conver...
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.
Alfven-wave particle interaction in finite-dimensional self-consistent field model
International Nuclear Information System (INIS)
A low-dimensional Hamiltonian model is derived for the acceleration of ions in finite amplitude Alfven waves in a finite pressure plasma sheet. The reduced low-dimensional wave-particle Hamiltonian is useful for describing the reaction of the accelerated ions on the wave amplitudes and phases through the self-consistent fields within the envelope approximation. As an example, the authors show for a single Alfven wave in the central plasma sheet of the Earth's geotail, modeled by the linear pinch geometry called the Harris sheet, the time variation of the wave amplitude during the acceleration of fast protons
Energy Technology Data Exchange (ETDEWEB)
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.
Experimental study of high beta toroidal plasmas
International Nuclear Information System (INIS)
Experiments on the Wisconsin Levitated Toroidal Octupole have produced a wide range of stable high β plasmas with β significantly above single fluid MHD theory predictions. A stable β approx. 8% plasma, twice the fluid limit, is obtained with 5 rho/sub i/ approx. L/sub n/ and tau/sub β/ approx. = 6000 tau/sub Alfven/ = 600 μsec. The enhanced stability is explained with a kinetic treatment that includes the effect of finite ion gyroradius which couples the ballooning mode to an ion drift wave. In a more collisional, large gyroradius (2 rho/sub i/ approx. L/sub n/) regime, a stable β approx. 35% plasma is obtained with a decay time of 1000 Alfven times. Measurement of the equilibrium magnetic field in this regime indicates that the diamagnetic current density is five times smaller than predicted by ideal MHD, probably due to ion gyroviscosity. Particle transport is anomalous and ranges from agreement with the classical diffusion rate at the highest beta, lowest field plasma (B/sub P/ = 200 G), to thirteen times the classical rate in a β=11%, high field plasma (B/sub P/ = 860 G) where the level of enhancement increase with magnetic field. Fluctuations in density, electrostatic potential, and magnetic field have been studied in plasmas with β from 0.1% to 40%
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
Energy Technology Data Exchange (ETDEWEB)
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.
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
International Nuclear Information System (INIS)
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
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
Bowden, G. W.; Hole, M. J.; Könies, A.
2015-09-01
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.
Signal-to-noise eigenmode analysis of the two-year cobe maps
Bond, J R
1994-01-01
To test a theory of cosmic microwave background fluctuations, it is natural to expand an anisotropy map in an uncorrelated basis of linear combinations of pixel amplitudes --- statistically-independent for both the noise and the signal. These S/N-eigenmodes are indispensible for rapid Bayesian analyses of anisotropy experiments, applied here to the recently-released two-year COBE {\\it dmr} maps and the {\\it firs} map. A 2-parameter model with an overall band-power and a spectral tilt \
Ying, Guanwen; Kouzaev, Guennadi
2016-10-01
We present the eigenmodal analysis techniques enhanced towards calculations of optical and non-interacting Bose-Einstein condensate (BEC) modes formed by random potentials and localized by Anderson effect. The results are compared with the published measurements and verified additionally by the convergence criterion. In 2-D BECs captured in circular areas, the randomness shows edge localization of the high-order Tamm-modes. To avoid strong diffusive effect, which is typical for BECs trapped by speckle potentials, a 3-D-lattice potential with increased step magnitudes is proposed, and the BECs in these lattices are simulated and plotted.
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 ...
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. ...
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 ...
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...
Configurational Effects on Alfvenic modes and Confinement in the H-1NF Heliac
Blackwell, B D; Howard, J; Nazikian, R; Kumar, S T A; Oliver, D; Byrne, D; Harris, J H; Nuhrenberg, C A; McGann, M; Dewar, R L; Detering, F; Hegland, M; Potter, G I; Read, J W
2009-01-01
The flexible Heliac coil set of helical axis stellarator H-1 (R=1m, ~0.15-0.2 m) permits access to a wide range of magnetic configurations. Surprisingly, in the absence of any obvious population of energetic particles, Alfven modes normally associated with energetic populations in larger fusion experiments are observed. Using H-1's unique combination of flexibility and advanced diagnostics, RF-generated plasma in H-1 is shown to have a very complex dependence on configuration of both the electron density and fluctuations in the MHD Alfven range. Magnetic fluctuations range from highly coherent, often multi-frequency, to approaching broad-band (df/f ~ 0.02-0.5), in the range 1-200 kHz. Application of datamining techniques to a wide range of configurations classifies these fluctuations and extracts poloidal and toroidal mode numbers, revealing that a significant class of fluctuations exhibit scaling which is i) Alfvenic with electron density (within a constant factor) and ii) shear Alfvenic in rotational transf...
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...
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.
Global kink and ballooning modes in high-beta systems and stability of toroidal drift modes
International Nuclear Information System (INIS)
A numerical code (HBT) has been developed which solves for the equilibrium, global stability and high-n stability of plasmas with arbitrary cross-section. Various plasmas are analysed for their stability to these modes in the high-beta limit. Screw-pinch equilibria are stable to high-n ballooning modes up to betas of 18%. The eigenmode equation for drift waves is analysed numerically. The toroidal branch is shown to be destabilized by the non-adiabatic response of trapped and circulating particles. (author)
From micro- to nanomagnetic dots: evolution of the eigenmode spectrum on reducing the lateral size
Carlotti, G.; Gubbiotti, G.; Madami, M.; Tacchi, S.; Hartmann, F.; Emmerling, M.; Kamp, M.; Worschech, L.
2014-07-01
Brillouin light scattering experiments and micromagnetic simulations have been exploited to investigate the spectrum of thermally excited magnetic eigenmodes in 10 nm-thick elliptical Permalloy dots, when the longer axis D is scaled down from about 1000 to 100 nm. It is shown that for D larger than about 200 nm the characteristics of the spin-wave eigenmodes are dominated by dipolar energy, while for D in the range of about 100 to 200 nm exchange energy effects cause qualitative and quantitative differences in the spin-wave spectrum. In this ‘mesoscopic’ regime, the usual classification scheme, involving one fundamental mode with large average magnetization and many other modes collected in families with specific symmetries, no longer holds. Rather, one finds the simultaneous presence of two modes with ‘fundamental’ character, i.e. with a significant and comparable value of the average dynamical magnetization: the former is at larger frequency and has its maximum amplitude at the dot's centre, while the latter occurs at lower frequency and is localized at the dot's edges. Interestingly, the maximum intensity swaps from the higher frequency mode to the lower frequency one, just when the dot size is reduced from about 200 to 100 nm. This is relevant in view of the exploitation of nanodots for the design of nanomagnetic devices with lateral dimensions in the above interval, such as memory cells, logic gates, reading heads and spin-torque oscillators.
Holographic modal analysis for the separation of narrow-spaced eigenmodes
Klingele, Hermann; Steinbichler, Hans; Freymann, Raymond; Honsberg, Wolfram; Haberstok, Carsten
1996-08-01
The automotive industry has particular interest in obtaining modal models of panel-like structures in the higher frequency range where the accuracy of FE-models normally is not longer sufficient to predict the dynamic response of a car body structure to a given operational excitation. Experimental modal analysis can fill this gap. However, the sensors which are currently used for the acquisition of vibrational data (accelerometers, laser vibrometer) are limited in spatial resolution and therefore higher-order panel modes are hard to be investigated. Holographic interferometry is widely used for qualitative and quantitative measurements of the mode shapes of dynamic systems, where its high spatial resolution outperforms any other kind of vibrational dynamic sensor. The limitations of holography with respect to the sampling rate can be overcome in the context of modal analysis by using stepped sine testing. A large number of holograms is then automatically recorded and evaluated. First results on a test structure which exhibits narrow-spaced eigenmodes are shown using this kind of measurement setup with a high frequency resolution. The dense vibration data enables the modal analysis software to separate the eigenmodes.
Energy Technology Data Exchange (ETDEWEB)
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.
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.
Spin wave eigenmodes in single and coupled sub-150 nm rectangular permalloy dots
Energy Technology Data Exchange (ETDEWEB)
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.
Nonlinear magnetohydrodynamic effects on Alfvén eigenmode evolution and zonal flow generation
Todo, Y.; Berk, H. L.; Breizman, B. N.
2010-08-01
Nonlinear magnetohydrodynamic (MHD) effects on Alfvén eigenmode evolution were investigated via hybrid simulations of an MHD fluid interacting with energetic particles. The investigation focused on the evolution of an n = 4 toroidal Alfvén eigenmode (TAE) which is destabilized by energetic particles in a tokamak. In addition to fully nonlinear code, a linear-MHD code was used for comparison. The only nonlinearity in that linear code is from the energetic-particle dynamics. No significant difference was found in the results of the two codes for low saturation levels, δB/B ~ 10-3. In contrast, when the TAE saturation level predicted by the linear code is δB/B ~ 10-2, the saturation amplitude in the fully nonlinear simulation was reduced by a factor of 2 due to the generation of zonal (n = 0) and higher-n (n >= 8) modes. This reduction is attributed to the increased dissipation arising from the nonlinearly generated modes. The fully nonlinear simulations also show that geodesic acoustic mode is excited by the MHD nonlinearity after the TAE mode saturation.
Non-linear modulation of short wavelength compressional Alfvén eigenmodes
International Nuclear Information System (INIS)
Most Alfvénic activity in the frequency range between toroidal Alfvén 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 ≈1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfvén 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.
Cally, P S
2007-01-01
The efficacy of fast/slow MHD mode conversion in the surface layers of sunspots has been demonstrated over recent years using a number of modelling techniques, including ray theory, perturbation theory, differential eigensystem analysis, and direct numerical simulation. These show that significant energy may be transferred between the fast and slow modes in the neighbourhood of the equipartition layer where the Alfven and sound speeds coincide. However, most of the models so far have been two dimensional. In three dimensions the Alfven wave may couple to the magneto-acoustic waves with important implications for energy loss from helioseismic modes and for oscillations in the atmosphere above the spot. In this paper, we carry out a numerical ``scattering experiment'', placing an acoustic driver 4 Mm below the solar surface and monitoring the acoustic and Alfvenic wave energy flux high in an isothermal atmosphere placed above it. These calculations indeed show that energy conversion to upward travelling Alfven ...
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
Nonlinear coupling of O- and X-mode radio emission and Alfven waves in the solar corona
International Nuclear Information System (INIS)
The nonlinear coupling of extraordinary and ordinary waves via kinetic Alfven waves (KAWs) is investigated on the basis of two fluid magnetohydrodynamics. The equation governing the time dependence of electric field of excited O-mode is found. We estimate the time of effective coupling between modes and corresponding interaction distance in solar corona. Our theoretical results show that the X- and O-mode couplings via Alfven waves can be efficient depolarization mechanism for the coronal radioemission
Todo, Y.; Berk, H. L.; Breizman, B. N.
2012-03-01
A hybrid simulation code for nonlinear magnetohydrodynamics (MHD) and energetic-particle dynamics has been extended to simulate recurrent bursts of Alfvén eigenmodes by implementing the energetic-particle source, collisions and losses. The Alfvén eigenmode bursts with synchronization of multiple modes and beam ion losses at each burst are successfully simulated with nonlinear MHD effects for the physics condition similar to a reduced simulation for a TFTR experiment (Wong et al 1991 Phys. Rev. Lett. 66 1874, Todo et al 2003 Phys. Plasmas 10 2888). It is demonstrated with a comparison between nonlinear MHD and linear MHD simulation results that the nonlinear MHD effects significantly reduce both the saturation amplitude of the Alfvén eigenmodes and the beam ion losses. Two types of time evolution are found depending on the MHD dissipation coefficients, namely viscosity, resistivity and diffusivity. The Alfvén eigenmode bursts take place for higher dissipation coefficients with roughly 10% drop in stored beam energy and the maximum amplitude of the dominant magnetic fluctuation harmonic δBm/n/B ~ 5 × 10-3 at the mode peak location inside the plasma. Quadratic dependence of beam ion loss rate on magnetic fluctuation amplitude is found for the bursting evolution in the nonlinear MHD simulation. For lower dissipation coefficients, the amplitude of the Alfvén eigenmodes is at steady levels δBm/n/B ~ 2 × 10-3 and the beam ion losses take place continuously. The beam ion pressure profiles are similar among the different dissipation coefficients, and the stored beam energy is higher for higher dissipation coefficients.
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.
International Nuclear Information System (INIS)
Overlap fermions, which preserve exact chiral symmetry on the lattice, provide a powerful tool for investigating the topological structure of the vacuum. Applying this formulation to zerotemperature quenched SU(3) configurations generated by means of the Luescher-Weisz action, we define the topological charge density with and without UV filtering and study its properties by looking at the density profile and the two-point correlation function. We observe that the density possesses global sign coherent structures, which get increasingly tangled as more and more modes are included. This change of the structure is also detected by the increasing negative tail of the two-point function. We also study the inverse participation ratio of the eigenmodes and discuss their dimensionality. (orig.)
Low frequency eigenmodes of thin anisotropic current sheets and Cluster observations
Directory of Open Access Journals (Sweden)
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.
Parallel equilibrium current effect on existence of reversed shear Alfvén eigenmodes
International Nuclear Information System (INIS)
A new fast global eigenvalue code, where the terms are segregated according to their physics contents, is developed to study Alfvén modes in tokamak plasmas, particularly, the reversed shear Alfvén eigenmode (RSAE). Numerical calculations show that the parallel equilibrium current corresponding to the kink term is strongly unfavorable for the existence of the RSAE. An improved criterion for the RSAE existence is given for with and without the parallel equilibrium current. In the limits of ideal magnetohydrodynamics (MHD) and zero-pressure, the toroidicity effect is the main possible favorable factor for the existence of the RSAE, which is however usually small. This suggests that it is necessary to include additional physics such as kinetic term in the MHD model to overcome the strong unfavorable effect of the parallel current in order to enable the existence of RSAE
A singular finite element technique for calculating continuum damping of Alfvén eigenmodes
International Nuclear Information System (INIS)
Damping due to continuum resonances can be calculated using dissipation-less ideal magnetohydrodynamics provided that the poles due to these resonances are properly treated. We describe a singular finite element technique for calculating the continuum damping of Alfvén waves. A Frobenius expansion is used to determine appropriate finite element basis functions on an inner region surrounding a pole due to the continuum resonance. The location of the pole due to the continuum resonance and mode frequency is calculated iteratively using a Galerkin method. This method is used to find the complex frequency and mode structure of a toroidicity-induced Alfvén eigenmode in a large aspect ratio circular tokamak and is shown to agree closely with a complex contour technique
Distortional eigenmodes and homogeneous solutions for semi-discretized thin-walled beams
DEFF Research Database (Denmark)
Jönsson, Jeppe; Andreassen, Michael Joachim
2011-01-01
as part of a semi-discretization process. In this process the cross-section is discretized into finite cross-section elements and the axial variation of the displacement functions are solutions to the established coupled fourth order differential equations of GBT. We use a novel finite-element...... solution is given as well as transformations between different degree of freedom spaces. This new approach is a considerable theoretical improvement, since the obtained GBT equations found by discretization of the cross-section are now solved analytically and the formulation is valid without special...... attention also for closed single or multi cell cross-sections. Further more the found eigenvalues have clear mechanical meaning, since they represent the attenuation of the distortional eigenmodes and may be used in the automatic meshing of approximate distortional beam elements. The magnitude...
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.
Reappraising Transition Region Line Widths in light of Recent Alfv\\'{e}n Wave Discoveries
McIntosh, Scott W; Tarbell, Theodore D
2008-01-01
We provide a new interpretation of ultraviolet transition region emission line widths observed by the SUMER instrument on the Solar and Heliospheric Observatory (SOHO). This investigation is prompted by observations of the chromosphere at unprecedented spatial and temporal resolution from the Solar Optical Telescope (SOT) on Hinode revealing that all chromospheric structures above the limb display significant transverse (Alfvenic) perturbations. We demonstrate that the magnitude, network sensitivity and apparent center-to-limb isotropy of the measured line widths (formed below 250,000K) can be explained by an observationally constrained forward-model in which the line width is caused by the line-of-sight superposition of longitudinal and Alfvenic motions on the small-scale (spicular) structures that dominate the chromosphere and low transition region.
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.
Alfven wave spectrum control in the heating and current drive experiments
International Nuclear Information System (INIS)
In this report we present the diagnostic system that has been developed for wave field spectrum analysis and control during Alfven wave heating and current drive experiments in the TCABR tokamak The system permits to register simultaneously the phase and the amplitude of the toroidal Β-tilde φ and poloidal Β-tildeθ magnetic field components of the waves with M ±1, N = ±, N = ±(2+6) in the frequency range ∫ = 2-8 MHz and RF pulse duration τ = 20-50 ms and to generate a feedback signal for plasma parameters control. The wave mode and frequency selectivity are ensured by the adjustment of the magnetic probe position and by utilization of specially designed 'lock-in' amplifiers that use 'sin' and 'cos' reference signals produced on the basis of the Alfven antenna feeding current. (author)
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).
Transient evolution of eigenmodes in dynamic cavities and time-varying media
Gradoni, Gabriele; Arnaut, Luk R.
2015-12-01
In this paper, we investigate the perturbation of natural eigenmodes of dynamic cavities with boundaries moving at quasi-static speeds relative to the wave velocity. For an arbitrarily shaped source-free cavity, the amplitude of the irrotational mode is modeled as a damped harmonic oscillator with time-varying eigenfrequency, i.e., a parametric oscillator. It is found that the effect of the pure Doppler shift of the resonance frequencies of the eigenmodes is small at nonrelativistic speeds. However, it is known that any spectrum of eigenenergies that is perturbed by a space- and/or time-fluctuating medium can develop frequency shifts of arbitrary magnitude. By using a linear dynamic (time-dependent) shift for the cavity broad resonances, we find that Doppler-like large shifts result in a mere frequency modulation of the total (resultant) field amplitude, while nonuniform red or blue shift can create a hybrid amplitude and frequency modulation. Interestingly, the combined action of red and blue shifts of uniform magnitude can also create a hybrid modulation. If the angle between modal wave vector and stirrer speed is accounted for in the static (time-independent) shift, the resulting red and blue shifts lead to irregular hybrid modulations. This can occur even for regular perturbations in regular cavities. In addition, owing to the stochastic nature of mode-stirred cavities, the effect of random Doppler-like shifts is also investigated, leading to a Fokker-Planck equation whose diffusion coefficient shows quadratic dependence on the mode amplitude. Thus, the analysis of random perturbations offers an effective framework for observed instantaneous Doppler effects in closed electromagnetic environments. The mathematical framework obtained in terms of stochastic differential equations is useful to predict the nonstationary response of dynamic cavities with complicated or unknown boundary geometry.
Study of Nonlinear Interaction and Turbulence of Alfven Waves in LAPD Experiments
Energy Technology Data Exchange (ETDEWEB)
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
Magnetosphere--Ionosphere Coupling: Effects of Plasma Alfven Wave Relative Motion
Christiansen, P. J.; Dum, C. T.
1989-06-01
The introduction of relative perpendicular motion between a flux-tube supporting shear Alfven wave activity and the background plasma is studied in the context of the coupling of a wave generating region with a distant ionosphere. The results of a representative simulation, using an extended version of the code developed by Lysak & Dum (J. geophys. Res. 88, 365 (1983)), are used as a basis for interpreting some aspects of recent satellite observations.
Magnetohydrodynamics in the Early Universe and the Damping of Non-linear Alfven Waves
Subramanian, Kandaswamy; Barrow, John D.
1997-01-01
The evolution and viscous damping of cosmic magnetic fields in the early universe, is analysed. Using the fact that the fluid, electromagnetic, and shear viscous energy-momentum tensors are all conformally invariant, the evolution is transformed from the expanding universe setting into that in flat spacetime. Particular attention is paid to the evolution of nonlinear Alfven modes. For a small enough magnetic field, which satisfies our observational constraints, these wave modes either oscilla...
Mallet, A.; Schekochihin, A. A.
2016-01-01
We propose a simple statistical model of three-dimensionally anisotropic, intermittent, strong Alfv\\'enic turbulence, incorporating both critical balance and dynamic alignment. Our model is based on log-Poisson statistics for Elsasser-field increments {\\em along} the magnetic field. We predict the scalings of Elsasser-field conditional two-point structure functions with point separations in all three directions in a coordinate system locally aligned with the direction of the magnetic field an...
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).
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.
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 $10~\\mathrm{Mm...
Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets V: Alfv\\'{e}n Ionization
Stark, Craig R; Diver, Declan A; Rimmer, Paul B
2013-01-01
Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbour localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfv\\'{e}n ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization ($\\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...
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...
Alfven Wave Reflection Model of Field-Aligned Currents at Mercury
Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James
2010-01-01
An Alfven Wave Reflection (AWR) model is proposed that provides closure for strong field-aligned currents (FACs) driven by the magnetopause reconnection in the magnetospheres of planets having no significant ionospheric and surface electrical conductance. The model is based on properties of the Alfven waves, generated at high altitudes and reflected from the low-conductivity surface of the planet. When magnetospheric convection is very slow, the incident and reflected Alfven waves propagate along approximately the same path. In this case, the net field-aligned currents will be small. However, as the convection speed increases. the reflected wave is displaced relatively to the incident wave so that the incident and reflected waves no longer compensate each other. In this case, the net field-aligned current may be large despite the lack of significant ionospheric and surface conductivity. Our estimate shows that for typical solar wind conditions at Mercury, the magnitude of Region 1-type FACs in Mercury's magnetosphere may reach hundreds of kilo-Amperes. This AWR model of field-aligned currents may provide a solution to the long-standing problem of the closure of FACs in the Mercury's magnetosphere. c2009 Elsevier Inc. All rights reserved.
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.
Effects of heavy ion temperature on low-frequency kinetic Alfven waves
International Nuclear Information System (INIS)
Heavy ion-electron (or proton) temperature ratio varies in a wide range in the solar and space environment. In this paper, proton and heavy ion temperatures are included in a three-fluid plasma model. For the specified parameters, low-frequency (<< heavy ion gyrofrequency) kinetic Alfven waves (KAWs) with sub- and super-Alfvenic speeds are found to coexist in the same plasma environment. Our results show that the temperature ratio of heavy ions to electrons can considerably affect the dispersion, propagation, and electromagnetic polarizations of the KAWs. In particular, the temperature ratio can increase the ratio of parallel to perpendicular electric fields and the normalized electric to magnetic field ratio, the variations of which are greatly different in regions with a high heavy ion temperature and with a low one. The results may help to understand the physical mechanism of some energization processes of heavy ions in the solar and space plasma environment. Effects of the ratio of electron thermal to Alfven speeds and the heavy ion abundance on these parameters are also discussed.
Influence of Ion Nonlinear Polarization Drift and Warm Ions on Solitary Kinetic Alfven Wave
Institute of Scientific and Technical Information of China (English)
DUANSu-Ping; LIZhong-Yuan
2003-01-01
Considering the effects of ion nonlinear polarization drift and warm ions, we adopt two-fluid model to investigate the character of low-frequency Solitary Kinetic Alfven Wave (SKAW hereafter) in a magnetic plasma. The results derived in this paper indicate that dip SKAW and hump SKAW both exist in a wide range in magnetosphere (for the pressure parameter β-10-5 -0.01, where β is the ratio of thermal pressure to magnetic pressure, i.e.β=2μonT/B02 ). These two kinds of SKAWs propagate at either Super-Alfvenic velocity or Sub-Alfvenic velocity. In the inertial region β>β>>me/mi. These results are different from previous ones. That indicates that the effects of ion nonlinear polarization drift and warm ions are important and they cannot be neglected. The SKAW has an electric field parallel to the ambient magnetic field, which makes the SKAW take an important role in the acceleration and energization of field-aligned charged particles in magnetic plasmas. And the SKAW is also important for the heating of a local plasma.So it makes a novel physical mechanism of energy transmission possible.
Solar off-limb line widths: Alfven waves, ion-cyclotron waves, and preferential heating
Dolla, L
2008-01-01
Alfven waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper corona (UVCS/SOHO remote-sensing results). We propose a method to constrain both the Alfven wave amplitude and the preferential heating induced by ion-cyclotron resonance, above a partially developed polar coronal hole observed with the SUMER/SOHO spectrometer. The instrumental stray light contribution is first substracted from the spectra. By supposing that the non-thermal velocity is related to the Alfven wave amplitude, it is constrained through a density diagnostic and the gradient of the width of the Mg X 625 A line. The temperatures of several coronal ions, as functions of the distance above the limb, are then determined by substracting the non-thermal component to the observed line widths. The effect of st...
The Modulation of Ionospheric Alfven Resonator on Heating HF Waves and the Doppler Effect
Institute of Scientific and Technical Information of China (English)
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.
Supergranulation-driven Alfven waves in the solar chromosphere and related phenomena.
Hollweg, J. V.
1972-01-01
It has recently been recognized that Alfven waves frequently dominate the microstructure of the solar wind at the orbit of the earth. We seek a solar source for these waves, and consider here their excitation by the supergranular motions. The wave equation is solved in a horizontally stratified, bi-exponential solar atmosphere. The interaction of Alfven wave motions associated with adjacent supergranules is discussed qualitatively. The Alfven wave effectively conveys the supergranular motions to great heights in the chromosphere. These motions are oppositely directed above intersupergranule boundaries, and compress the magnetic field there. A naive calculation of the compression, based on balancing dynamic and magnetic pressures, leads to adequate agreement with observations of the chromospheric network. We find that the magnetic field is appreciably compressed only below about 1500 km, and on this basis we reject theories of spicule formation which require large vertical magnetic fields at the heights reached by spicules. We advance a theory for spicule formation, in which spicules form as a result of matter being squeezed upward, out of the compression region between adjacent supergranules.
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...
k-space Imaging of the Eigenmodes of Sharp Gold Tapers for Scanning Near-Field Optical Microscopy
Esmann, Martin; da Cunha, Bernard B; Brauer, Jens H; Vogelgesang, Ralf; Gross, Petra; Lienau, Christoph
2013-01-01
We investigate the radiation patterns of sharp conical gold tapers, designed as adiabatic nanofocusing probes for scanning near-field optical microscopy (SNOM). Field calculations show that only the lowest order eigenmode of such a taper can reach the very apex and thus induce the generation of strongly enhanced near-field signals. Higher order modes are coupled into the far field at finite distances from the apex. Here, we demonstrate experimentally how to distinguish and separate between the lowest and higher order eigenmodes of such a metallic taper by filtering in the spatial frequency domain. Our approach has the potential to considerably improve the signal-to-background ratio in spectroscopic experiments on the nanoscale.
Perez, Jean C
2013-01-01
We present direct numerical simulations of inhomogeneous reduced magnetohydrodynamic (RMHD) turbulence between the Sun and the Alfv\\'en critical point. These are the first such simulations that take into account the solar-wind outflow velocity and the radial inhomogeneity of the background solar wind without approximating the nonlinear terms in the governing equations. RMHD turbulence is driven by outward-propagating Alfv\\'en waves ($z^+$ fluctuations) launched from the Sun, which undergo partial non-WKB reflection to produce sunward-propagating Alfv\\'en waves ($z^-$ fluctuations). We present ten simulations with different values of the correlation time $\\tau_{\\rm c\\,\\sun}^+$ and perpendicular correlation length $L_{\\perp \\sun}$ of outward-propagating Alfv\\'en waves (AWs) at the coronal base. We find that between 15\\% and 33\\% of the $z^+$ energy launched into the corona dissipates between the coronal base and Alfv\\'en critical point. Between 33\\% and 40\\% of this input energy goes into work on the solar-wind...
Lazarian, A
2016-01-01
This paper considers turbulent damping of Alfven waves in magnetized plasmas. We identify two cases of damping, one related to damping of cosmic rays streaming instability, the other related to damping of Alfven waves emitted by a macroscopic wave source, e.g. stellar atmosphere. The physical difference between the two cases is that in the former case the generated waves are emitted in respect to the local direction of magnetic field, in the latter in respect to the mean field. The scaling of damping is different in the two cases. We the regimes of turbulence ranging from subAlfvenic to superAlfvenic we obtain analytical expressions for the damping rates and define the ranges of applicability of these expressions. Describing the damping of the streaming instability, we find that for subAlfvenic turbulence the range of cosmic ray energies influenced by weak turbulence is unproportionally large compared to the range of scales that the weak turbulence is present. On the contrary, the range of cosmic ray energies...
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.
Global marginal stability of TAEs in the presence of fast ions
International Nuclear Information System (INIS)
The global stability of toroidicity-induced Alfven eigenmodes (TAEs) in the presence of fast ions in realistic tokamak fusion-grade plasmas is analyzed with a global, perturbative approach. Volume averaged fast particle betas for marginal stability are obtained and analyzed for a wide range of plasma parameters such as the fast ion radial density profile width, the ratio of birth velocity to the Alfven velocity on axis and the bulk plasma beta. The different stability behaviour of two types of TAEs ('internal' or 'external') is evidenced. (author) 19 figs., 22 refs
Saturation of a toroidal Alfvén eigenmode due to enhanced damping of nonlinear sidebands
Todo, Y.; Berk, H. L.; Breizman, B. N.
2012-09-01
This paper examines nonlinear magneto-hydrodynamic effects on the energetic particle driven toroidal Alfvén eigenmode (TAE) for lower dissipation coefficients and with higher numerical resolution than in the previous simulations (Todo et al 2010 Nucl. Fusion 50 084016). The investigation is focused on a TAE mode with toroidal mode number n = 4. It is demonstrated that the mechanism of mode saturation involves generation of zonal (n = 0) and higher-n (n ⩾ 8) sidebands, and that the sidebands effectively increase the mode damping rate via continuum damping. The n = 0 sideband includes the zonal flow peaks at the TAE gap locations. It is also found that the n = 0 poloidal flow represents a balance between the nonlinear driving force from the n = 4 components and the equilibrium plasma response to the n = 0 fluctuations. The spatial profile of the n = 8 sideband peaks at the n = 8 Alfvén continuum, indicating enhanced dissipation due to continuum damping.
Analytical formulae of the Polyakov and Wilson loops with Dirac eigenmodes in lattice QCD
International Nuclear Information System (INIS)
We derive an analytical gauge-invariant formula between the Polyakov loop LP and the Dirac eigenvalues λn in QCD, i.e., LP∝∑nλnNt−1〈n|U-^4|n〉, in ordinary periodic square lattice QCD with odd-number temporal size Nt. Here, |n〉 denotes the Dirac eigenstate, and U-^4 the temporal link-variable operator. This formula is a Dirac spectral representation of the Polyakov loop in terms of Dirac eigenmodes |n〉. Because of the factor λnNt−1 in the Dirac spectral sum, this formula indicates a negligibly small contribution of low-lying Dirac modes to the Polyakov loop in both confinement and deconfinement phases, while these modes are essential for chiral symmetry breaking. Next, we find a similar formula between the Wilson loop and Dirac modes on arbitrary square lattices, without restriction of odd-number size. This formula suggests a small contribution of low-lying Dirac modes to the string tension σ, or the confining force. These findings support no crucial role of low-lying Dirac modes for confinement, i.e., no direct one-to-one correspondence between confinement and chiral symmetry breaking in QCD, which seems to be natural because heavy quarks are also confined even without light quarks or the chiral symmetry
Eigenmode expansion methods for simulation of optical propagation in photonics: pros and cons
Gallagher, Dominic F. G.; Felici, Thomas P.
2003-06-01
With the rapid growth of the telecommunications industry over the last 5 to 10 years has come the need to solve ever more complex electromagnetic problems and to solve them more precisely than ever before. The basic EME (EigenMode Expansion) technique is a powerful method for calculation of electromagnetic propagation which has been well known amongst academic environments and also in microwave fields, representing the electromagnetic fields everywhere in terms of a basis set of local modes. It is at the same time a rigorous solution of Maxwell's Equations and is able to deal with very long structures. We discuss here progress that the authors and others have made recently in applying and extending it to integrated, fibre, and diffractive optics - including development of efficient ways of modelling tapers and other smoothly varying structures, new more efficient boundary conditions and improved mode finders. We outline the advantages it has over other techniques and also its limitations. We illustrate its application with a variety of real life examples, including diffractive elements, directional couplers, tapers, MMI's, bend modelling, periodic structures and others.
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.
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.
Flow shear suppression of turbulence using externally driven ion Bernstein and Alfven waves
International Nuclear Information System (INIS)
The utilization of externally-launched radio-frequency waves as a means of active confinement control through the generation of sheared poloidal flows is explored. For low-frequency waves, kinetic Alfven waves are proposed, and are shown to drive sheared E x B flows as a result of the radial variation in the electromagnetic Reynolds stress. In the high frequency regime, ion Bernstein waves are considered, and shown to generate sheared poloidal rotation through the ponderomotive force. In either case, it is shown that modest amounts of absorbed power (∼ few 100 kW) are required to suppress turbulence in a region of several cm radial width. 9 refs
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
Energy Technology Data Exchange (ETDEWEB)
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}.
International Nuclear Information System (INIS)
The results of the initial experimental studies of the Alfven wave antenna module, which is destined to be a part of the advanced antenna system of TCABR tokamak, are presented. The tests were carried out in a specially constructed vacuum chamber and included the measurement of antenna electrical parameters and testing of the power diagnostic tools. The complex impedances and inductive mutual coupling of antenna loops were measured and results were compared with theoretical calculations. The tests have shown that the parameters of the antenna module have values according to the design. (author)
Zonal Flows Driven by Small-Scale Drift-Alfven Modes
Institute of Scientific and Technical Information of China (English)
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.
Design of the RF system for Alfven wave heating and current drive in a TCA/BR tokamak
International Nuclear Information System (INIS)
The advanced RF system for Alfven wave plasma heating and current drive in TCA/BR tokamak is presented. The antenna system is capable of exciting the standing and travelling wave M = -1,N = 1,N =-4,-6 with single helicity and thus provides the possibility to improve Alfven wave plasma heating efficiency in TCA/BR tokamak and to increase input power level up to P ≅ 1 MW, without the uncontrolled density rise which was encountered in previous TCA (Switzerland) experiments. (author). 4 refs., 3 figs
International Nuclear Information System (INIS)
This report discusses the following topics: Nonaxisymmetric radio- frequency heating in an l = 1 stellarator and in a linear plasma column; measurement of induced current in a hardcore theta pinch; externally driven tilt mode study on an FRC; elimination of induced plasma current in a hardcore theta pinch; and simulated toroidicity studies
Beta-dependent upper bound on ion temperature anisotropy in a laboratory plasma
Energy Technology Data Exchange (ETDEWEB)
Keiter, Paul A. [West Virginia University, Morgantown, West Virginia 26506 (United States); Scime, Earl E. [West Virginia University, Morgantown, West Virginia 26506 (United States); Balkey, Matthew M. [West Virginia University, Morgantown, West Virginia 26506 (United States); Boivin, Robert [West Virginia University, Morgantown, West Virginia 26506 (United States); Kline, John L. [West Virginia University, Morgantown, West Virginia 26506 (United States); Gary, S. Peter [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States)
2000-03-01
Laser induced fluorescence measurements of ion temperatures, parallel and perpendicular to the local magnetic field, in the Large Experiment on Instabilities and Anisotropies space simulation chamber (a steady-state, high beta, argon plasma) display an inverse correlation between the upper bound on the ion temperature anisotropy and the parallel ion beta ({beta}=8{pi}nkT/B{sup 2}). These observations are consistent with in situ spacecraft measurements in the Earth's magnetosheath and with a theoretical/computational model that predicts that such an upper bound is imposed by scattering from enhanced fluctuations due to growth of the ion cyclotron anisotropy instability (the Alfven ion cyclotron instability). (c) 2000 American Institute of Physics.
Identification of Local Alfven Wave Resonances with Reflectometry as a Diagnostic Tool in Tokamaks
Elfimov, A; Ruchko, L; Manso, M E; Elfimov, Artur; Galvao, Ricardo; Ruchko, Leonid; Manso, Maria Emilia
2004-01-01
Local Alfven wave (LAW) resonances are excited in tokamak plasmas by an externally driven electro-magnetic field, with the frequency below the ion cyclotron frequency, where using of the Alfven waves is assumed. Recently, wave driven density fluctuations at the LAW resonance m=+/-1, N=+/-2 with few kW power deposition and 4 MHz frequency were detected in TCABR (Bt =1.1T, q0 =1.1, n0=1.4-2.0 10^{19}/ m^3) using a fixed frequency (32.4GHz) O-mode reflectometer. Here, we show that combination of small power deposition in LAW resonances, swept by plasma density variation or scanned with generator frequencies, in combination with detection of the density fluctuations in the LAW resonances by reflectometry can serve as diagnostic tool for identification of the effective ion mass number Aef and q-profile in tokamaks. The idea is based on the simultaneous detection of the position of m=+/-1 local AW resonances, which are excited by M/N=+/-1/+/-2 antenna modes, and m=0 generated by poloidal mode coupling effect in tok...
Alfven waves, alpha particles, and pickup ions in the solar wind
Goldstein, B. E.; Neugebauer, M.; Smith, E. J.
1995-01-01
Past studies of the properties of Alfven waves in the solar wind have indicated that (1) the amplitude of the velocity fluctuations is almost always smaller than expected on the basis of the amplitude of the field fluctuations, even when the anisotropy of the plasma is taken into account, and (2) the alpha particles do not participate in the wave motions because they 'surf' on the waves carried by the proton fluid. Ulysses data are used to demonstrate that (1) the discrepancy between the velocity and field fluctuations is greater at high heliographic latitudes than in the ecliptic plane, and (2) the alphas do participate in the waves, being either in phase or out of phase with the proton motions depending on whether the differential flow speed between the alphas and protons is greater than or less than the 'observed' wave speed, B(sub o)(delta v squared / delta B squared)exp 1/2, as determined from the ratio of the amplitudes of the velocity and magnetic fluctuations. It is proposed that the modification of Alfven wave propagation speed is due to pressure anisotropies resulting from asymmetric distributions of interstellar pickup ions. If the proposed explanation is correct, it indicates that scattering of pickup ions onto a (bi)spherical shell may not be as complete as generally supposed.
Integrated campaign to study the stationary inertial Alfven wave in the laboratory and space regimes
International Nuclear Information System (INIS)
A small, off-axis mesh-anode electrode at one plasma-column end is used to create a paraxial channel of electron current and depleted density in the large plasma device upgrade at UCLA. We show that the on-axis, larger, surrounding-plasma column rotates about its cylindrical axis because a radial electric field is imposed by a multiple-segmented-disc termination electrode on the same end as the mesh-anode electrode. The radial profile of azimuthal velocity is shown to be consistent with predictions of rigid-body rotation. Launched inertial Alfven waves are shown to concentrate in the off-axis channel of electron current and depleted plasma density. In the absence of launched waves, time varying boundary conditions, or spatially structured boundary conditions, a non-fluctuating, non-traveling pattern in the plasma density is shown to arise spontaneously in the channel, but only in the combined presence of electron current, density depletion, and spontaneously in the channel, cross-field convection (i.e. rotation). These results may be relevant to the stationary Alfven wave in the inertial regime in space and laboratory plasmas
Observation of fast-ion Doppler-shifted cyclotron resonance with shear Alfven waves
International Nuclear Information System (INIS)
The Doppler-shifted cyclotron resonance (ω-kzvz=Ωf) between fast ions and shear Alfven waves is experimentally investigated (ω, wave frequency; kz, axial wavenumber; vz, fast-ion axial speed; Ωf, fast-ion cyclotron frequency). A test particle beam of fast ions is launched by a Li+ source in the helium plasma of the LArge Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)], with shear Alfven waves (SAW) (amplitude δ B/B up to 1%) launched by a loop antenna. A collimated fast-ion energy analyzer measures the nonclassical spreading of the beam, which is proportional to the resonance with the wave. A resonance spectrum is observed by launching SAWs at 0.3-0.8ωci. Both the magnitude and frequency dependence of the beam-spreading are in agreement with the theoretical prediction using a Monte Carlo Lorentz code that launches fast ions with an initial spread in real/velocity space and random phases relative to the wave. Measured wave magnetic field data are used in the simulation.
Search for Alfv\\'en waves in a bright network element observed in Halpha
Koza, J; Gömöry, P; Rybák, J; Kucera, A
2013-01-01
Alfven waves are considered as potential transporters of energy heating the solar corona. We seek spectroscopic signatures of the Alfven waves in the chromosphere occupied by a bright network element, investigating temporal variations of the spectral width, intensity, Dopplershift, and the asymmetry of the core of the Halpha spectral line observed by the tunable Lyot filter installed on the Dutch Open Telescope. The spectral characteristics are derived through the fitting of five intensity samples, separated from each other by 0.35 A, by a 4th-order polynomial. The bright network element displays the most pronounced variations of the Dopplershift varying from 0 to 4 km/s about the average of 1.5 km/s. This fact implies a persistent redshift of the Halpha core with a redward asymmetry of about 0.5 km/s, suggesting an inverse-C bisector. The variations of the core intensity up to +-10% and the core width up to +-5% about the respective averages are much less pronounced, but still detectable. The core intensity ...
Alfven waves and current relaxation: attenuation at high frequencies and large resistivity
International Nuclear Information System (INIS)
The dispersion relations of Alfven waves propagating in a resistive plasma are explored by assuming a finite relaxation time for the current density. It is shown that the proposed approach is consistent with the hydromagnetic approximation. An extension for the equation governing the space and time evolution of Alfven waves is provided. New results are found at high values of the wave frequency ω: for a small resistivity, the wavelength increases as the cube of the equilibrium magnetic field but decreases with the cube of ω; for a large resistivity, the wave attenuation does not depend on ω, saturating to a finite value which is fully determined by the relaxation time of the current density. A transition frequency, ωt, between two sharply distinct regimes of the perturbation is identified: for ω t, the disturbance propagates in the resistive plasma as an attenuated oscillation; for ω > ωt the wave ceases very rapidly to oscillate (in space), its amplitude saturating to a finite value. The results presented here may be relevant for investigations of some transient phenomena in plasma physics such as the reconnection of magnetic field lines.
Advanced antenna system for Alfven wave plasma heating and current drive in TCABR tokamak
International Nuclear Information System (INIS)
An advanced antenna system that has been developed for investigation of Alfven wave plasma heating and current drive in the TCABR tokamak is described. The main goal was the development of such a system that could insure the excitation of travelling single helicity modes with predefined wave mode numbers M and N. The system consists of four similar modules with poloidal windings. The required spatial spectrum is formed by proper phasing of the RF feeding currents. The impedance matching of the antenna with the four-phase oscillator is accomplished by resonant circuits which form one assembly unit with the RF feeders. The characteristics of the antenna system design with respect to the antenna-plasma coupling and plasma wave excitation, for different phasing of the feeding currents, are summarised. The antenna complex impedance Z=ZR+ZI is calculated taking into account both the plasma response to resonant excitation of fast Alfven waves and the nonresonant excitation of vacuum magnetic fields in conducting shell. The matching of the RF generator with the antenna system during plasma heating is simulated numerically, modelling the plasma response with mutually coupled effective inductances with corresponding active ZR and reactive ZI impedances. The results of the numerical simulation of the RF system performance, including both the RF magnetic field spectrum analysis and the modeling of the RF generator operation with plasma load, are presented. (orig.)
Alfvenic Turbulence from the Sun to 65 Solar Radii: Numerical predictions.
Perez, J. C.; Chandran, B. D. G.
2015-12-01
The upcoming NASA Solar Probe Plus (SPP) mission will fly to within 9 solar radii from the solar surface, about 7 times closer to the Sun than any previous spacecraft has ever reached. This historic mission will gather unprecedented remote-sensing data and the first in-situ measurements of the plasma in the solar atmosphere, which will revolutionize our knowledge and understanding of turbulence and other processes that heat the solar corona and accelerate the solar wind. This close to the Sun the background solar-wind properties are highly inhomogeneous. As a result, outward-propagating Alfven waves (AWs) arising from the random motions of the photospheric magnetic-field footpoints undergo strong non-WKB reflections and trigger a vigorous turbulent cascade. In this talk I will discuss recent progress in the understanding of reflection-driven Alfven turbulence in this scenario by means of high-resolution numerical simulations, with the goal of predicting the detailed nature of the velocity and magnetic field fluctuations that the SPP mission will measure. In particular, I will place special emphasis on relating the simulations to relevant physical mechanisms that might govern the radial evolution of the turbulence spectra of outward/inward-propagating fluctuations and discuss the conditions that lead to universal power-laws.
The Spatial and Temporal Dependence of Coronal Heating by Alfven Wave Turbulence
Asgari-Targhi, M; Cranmer, S R; DeLuca, E E
2013-01-01
The solar atmosphere may be heated by Alfven waves that propagate up from the convection zone and dissipate their energy in the chromosphere and corona. To further test this theory, we consider wave heating in an active region observed on 2012 March 7. A potential field model of the region is constructed, and 22 field lines representing observed coronal loops are traced through the model. Using a three-dimensional (3D) reduced magneto-hydrodynamics (MHD) code, we simulate the dynamics of Alfven waves in and near the observed loops. The results for different loops are combined into a single formula describing the average heating rate Q as function of position within the observed active region. We suggest this expression may be approximately valid also for other active regions, and therefore may be used to construct 3D, time-dependent models of the coronal plasma. Such models are needed to understand the role of thermal non-equilibrium in the structuring and dynamics of the Sun's corona.
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...
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.
Control of the higher eigenmodes of a microcantilever: Applications in atomic force microscopy
Energy Technology Data Exchange (ETDEWEB)
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.
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\\...
Energy Technology Data Exchange (ETDEWEB)
Carter, T A
2006-11-16
Final report for DOE Plasma Physics Junior Faculty Development award DOE-FG02-02ER54688. Reports on research undertaken from 8/1/2002 until 5/15/2006, investigating nonlinear interactions between Alfven waves in a laboratory experiment.
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 ...
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.
Kretov, D A
2004-01-01
Based on the computer molecular dynamics (MD) modeling methods we have calculated the ground-state energy and eigenvalue frequencies of the adenine-thymine and guanine-cytosine nucleotide doublets and performed their geometry optimization. We have found the eigenmodes in the infrared and radio-frequency ranges. The possibility of application of the simulation results in detection of bio-structures through the spectral analysis is considered. In the quantum chemistry MD calculations we employed the \\textit{Gaussian98} code and MOLDEN package.
International Nuclear Information System (INIS)
Detailed calculations concerning the field structure and excitation of the fast magnetosonic wave are presented keeping in mind RF heating of a Tokamak near the ion cyclotron harmonic. The new contributions are - a discussion of the cylindrical problem in an inhomogeneous plasma including surface waves and the splitting of the eigenmodes by the poloidal field - a calculation of the field structure in the toroidal cavity resonator and the application to mode tracking - a formulation of the loading impedance of various coupling structures: array of coils in the low frequency limit or transmission lines in the high frequency case
BETA-S, Multi-Group Beta-Ray Spectra
International Nuclear Information System (INIS)
1 - Description of program or function: BETA-S calculates beta-decay source terms and energy spectra in multigroup format for time-dependent radionuclide inventories of actinides, fission products, and activation products. Multigroup spectra may be calculated in any arbitrary energy-group structure. The code also calculates the total beta energy release rate from the sum of the average beta-ray energies as determined from the spectral distributions. BETA-S also provides users with an option to determine principal beta-decaying radionuclides contributing to each energy group. The CCC-545/SCALE 4.3 (or SCALE4.2) code system must be installed on the computer before installing BETA-S, which requires the SCALE subroutine library and nuclide-inventory generation from the ORIGEN-S code. 2 - Methods:Well-established models for beta-energy distributions are used to explicitly represent allowed, and 1., 2. - and 3. -forbidden transition types. Forbidden non-unique transitions are assumed to have a spectral shape of allowed transitions. The multigroup energy spectra are calculated by numerically integrating the energy distribution functions using an adaptive Simpson's Rule algorithm. Nuclide inventories are obtained from a binary interface produced by the ORIGEN-S code. BETA-S calculates the spectra for all isotopes on the binary interface that have associated beta-decay transition data in the ENSDF-95 library, developed for the BETA-S code. This library was generated from ENSDF data and contains 715 materials, representing approximately 8500 individual beta transition branches. 3 - Restrictions on the complexity of the problem: The algorithms do not treat positron decay transitions or internal conversion electrons. The neglect of positron transitions in inconsequential for most applications involving aggregate fission products, since most of the decay modes are via electrons. The neglect of internal conversion electrons may impact on the accuracy of the spectrum in the low
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.
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.
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.
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 $\
Zonal Flows Driven by Small-Scale Drift-Alfven Modes
International Nuclear Information System (INIS)
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. (magnetically confined plasma)
Acceleration and heating of two-fluid solar wind by Alfven waves
Sandbaek, Ornulf; Leer, Egil
1994-01-01
Earlier model studies of solar wind driven by thermal pressure and Alfven waves have shown that wave amplitudes of 20-30 km/s at the coronal base are sufficient to accelerate the flow to the high speeds observed in quasi-steady streams emanating from large coronal holes. We focus on the energy balance in the proton gas and show that heat conduction from the region where the waves are dissipated may play an important role in determining the proton temperature at the orbit of Earth. In models with 'classical' heat conduction we find a correlation between high flow speed, high proton temperature, and low electron temperature at 1 AU. The effect of wave heating on the development of anisotropies in the solar wind proton gas pressure is also investigated in this study.
Alfven Waves and Turbulence in the Solar Atmosphere and Solar Wind
Verdini, Andrea; Velli, Marco
2007-01-01
We solve the problem of propagation and dissipation of Alfvenic turbulence in a model solar atmosphere consisting of a static photosphere and chromosphere, transition region, and open corona and solar wind using a phenomenological model for the turbulent dissipation based on wave reflection. We show that most of the dissipation for a given wave frequency spectrum occurs in the lower corona, and the overall rms amplitude of the fluctuations evolves in a way consistent with observations. The frequency spectrum for a Kolmogorov-like slope is not found to change dramatically from the photosphere to the solar wind; however, it does preserve signatures of transmission throughout the lower atmospheric layers, namely, oscillations in the spectrum at high frequencies reminiscent of the resonances found in the linear case. These may disappear once more realistic couplings for the nonlinear terms are introduced or if time-dependent variability of the lower atmospheric layer is introduced.
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 $\\tilde n = - 3.5$,...
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...
Measures of Three-Dimensional Anisotropy and Intermittency in Strong Alfv\\'enic Turbulence
Mallet, A; Chandran, B D G; Chen, C H K; Horbury, T S; Wicks, R T; Greenan, C C
2015-01-01
We measure the local anisotropy of numerically simulated strong Alfv\\'enic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. We find significant scaling anisotropy with respect to both these directions: the fluctuations are "ribbon-like" --- statistically, they are elongated along both the mean magnetic field and the fluctuating field. The latter form of anisotropy is due to scale-dependent alignment of the fluctuating fields. The intermittent scalings of the $n$th-order conditional structure functions in the direction perpendicular to both the local mean field and the fluctuations agree well with the theory of Chandran et al. 2015, while the parallel scalings are consistent with those implied by the critical-balance conjecture. We quantify the relationship between the perpendicular scalings and those in the fluctuation and parallel directions, and find that the scaling exponent of ...
Mallet, A
2016-01-01
We propose a simple statistical model of three-dimensionally anisotropic, intermittent, strong Alfv\\'enic turbulence, incorporating both critical balance and dynamic alignment. Our model is based on log-Poisson statistics for Elsasser-field increments {\\em along} the magnetic field. We predict the scalings of Elsasser-field conditional two-point structure functions with point separations in all three directions in a coordinate system locally aligned with the direction of the magnetic field and of the fluctuating fields and obtain good agreement with numerical simulations. We also derive a scaling of the parallel coherence scale of the fluctuations, $l_\\parallel \\propto \\lambda^{1/2}$, where $\\lambda$ is the perpendicular scale. This is indeed observed for the bulk of the fluctuations in numerical simulations.
Doppler-shifted cyclotron resonance of fast ions with circularly polarized shear Alfven waves
International Nuclear Information System (INIS)
The Doppler-shifted cyclotron resonance between fast ions and shear Alfven waves (SAWs) has been experimentally investigated with a test-particle fast-ion (Li+) beam launched in the helium plasma of the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. Left- or right-hand circularly polarized SAWs are launched by an antenna with four current channels. A collimated fast-ion energy analyzer characterizes the resonance by measuring the nonclassical spreading of the averaged beam signal. Left-hand circularly polarized SAWs resonate with the fast ions but right-hand circularly polarized SAWs do not. The measured fast-ion profiles are compared with simulations by a Monte Carlo Lorentz code that uses the measured wave field data.
Kinetic Alfven solitary waves in a magnetized plasma with superthermal electrons
International Nuclear Information System (INIS)
A study of the ion Larmor radius effects on the solitary kinetic Alfven waves (SKAWs) in a magnetized plasma with superthermal electrons is presented by employing the kinetic theory. The linear dispersion relation of SKAW is shown to depend on the superthermal parameter κ, ion to electron temperature ratio, and the angle of wave propagation. Using the Sagdeev potential approach, the energy balance equation has been derived to study the dynamics of SKAWs. The effects of various plasma parameters are investigated for the propagation of SKAWs. It is shown that only compressive solitons can exist and in the Maxwellian limit our results are in good agreement with previous studies. Further, the characteristics of small amplitude SKAWs are investigated. Present study could be useful for the understanding of SKAWs in a low β plasma in astrophysical environment, where particle distributions are superthermal in nature
Solitary Kinetic Alfven Waves in a Low-β Dusty Plasma
Institute of Scientific and Technical Information of China (English)
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.
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...
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 Alfven solitary waves in a magnetized plasma with superthermal electrons
Energy Technology Data Exchange (ETDEWEB)
Panwar, A., E-mail: anurajrajput@gmail.com, E-mail: ryu201@postech.ac.kr, E-mail: bainsphysics@yahoo.co.in; Ryu, C. M., E-mail: anurajrajput@gmail.com, E-mail: ryu201@postech.ac.kr, E-mail: bainsphysics@yahoo.co.in [POSTECH, Hyoja-Dong San 31, KyungBuk, Pohang 790-784 (Korea, Republic of); Bains, A. S., E-mail: anurajrajput@gmail.com, E-mail: ryu201@postech.ac.kr, E-mail: bainsphysics@yahoo.co.in [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatchewan S7N5E2 (Canada)
2015-09-15
A study of the ion Larmor radius effects on the solitary kinetic Alfven waves (SKAWs) in a magnetized plasma with superthermal electrons is presented by employing the kinetic theory. The linear dispersion relation of SKAW is shown to depend on the superthermal parameter κ, ion to electron temperature ratio, and the angle of wave propagation. Using the Sagdeev potential approach, the energy balance equation has been derived to study the dynamics of SKAWs. The effects of various plasma parameters are investigated for the propagation of SKAWs. It is shown that only compressive solitons can exist and in the Maxwellian limit our results are in good agreement with previous studies. Further, the characteristics of small amplitude SKAWs are investigated. Present study could be useful for the understanding of SKAWs in a low β plasma in astrophysical environment, where particle distributions are superthermal in nature.
The Nonlinear Coupling of Alfven and Lower Hybrid Waves in Space Plasma
Khazanov, George V.
2004-01-01
Space plasmas support a wide variety of waves, and wave-particle interactions as well as wave-wave interactions which are of crucial importance to magnetospheric and ionospheric plasma behavior. The excitation of lower hybrid waves (LHWs) in particular is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves may generate LHWs in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We present several examples of observational data which illustrate that the proposed mechanism is a plausible candidate to explain certain classes of LHW generation events in the ionosphere and magnetosphere and demonstrate electron and ion energization involving these processes. We discuss the morphology dynamics and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7 1998 storm period on the global scale. The LHWs were calculated based on a newly developed self-consistent model (Khazanov et. al. 2002) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.
Fast-ion losses induced by ACs and TAEs in the ASDEX Upgrade tokamak
Garcia-Munoz, M.; Hicks, N.; van Voornveld, R.; Classen, I.G.J.; Bilato, R.; Bobkov, V.; Brambilla, M.; Bruedgam, M.; Fahrbach, H. U.; Igochine, V.; Jaemsae, S.; Maraschek, M.; Sassenberg, K.
2010-01-01
The phase-space of convective and diffusive fast-ion losses induced by shear Alfven eigenmodes has been characterized in the ASDEX Upgrade tokamak. Time-resolved energy and pitch-angle measurements of fast-ion losses correlated in frequency and phase with toroidal Alfven eigenmodes (TAEs) and Alfven
Role of explosive instabilities in high-$\\beta$ disruptions in tokamaks
Aydemir, A Y; Lee, S G; Seol, J; Park, B H; In, Y K
2016-01-01
Intrinsically explosive growth of a ballooning finger is demonstrated in nonlinear magnetohydrodynamic calculations of high-$\\beta$ disruptions in tokamaks. The explosive finger is formed by an ideally unstable n=1 mode, dominated by an m/n=2/1 component. The quadrupole geometry of the 2/1 perturbed pressure field provides a generic mechanism for the formation of the initial ballooning finger and its subsequent transition from exponential to explosive growth, without relying on secondary processes. The explosive ejection of the hot plasma from the core and stochastization of the magnetic field occur in Alfv\\'enic time scales, accounting for the extremely fast growth of the precursor oscillations and the rapidity of the thermal quench in some high-$\\beta$ disruptions.
Zaqarashvili, T. V.; Khodachenko, M. L.; Rucker, H.O.
2011-01-01
Chromospheric and prominence plasmas contain neutral atoms, which may change the plasma dynamics through collision with ions. Most of the atoms are neutral hydrogen, but a significant amount of neutral helium may also be present in the plasma with a particular temperature. Damping of MHD waves due to ion collision with neutral hydrogen is well studied, but the effects of neutral helium are largely unknown. We aim to study the effect of neutral helium in the damping of Alfven waves in solar pa...
Wang, X.; Briguglio, S.; Chen, L.; Di Troia, C; Fogaccia, G.; Vlad, G.; Zonca, F.
2010-01-01
Adopting the theoretical framework for the generalized fishbonelike dispersion relation, an extended hybrid magnetohydrodynamics gyrokinetic simulation model has been derived analytically by taking into account both thermal ion compressibility and diamagnetic effects in addition to energetic particle kinetic behaviors. The extended model has been used for implementing an eXtended version of Hybrid Magnetohydrodynamics Gyrokinetic Code (XHMGC) to study thermal ion kinetic effects on Alfv\\'enic...
Cally, P. S.; Goossens, M.
2007-01-01
The efficacy of fast/slow MHD mode conversion in the surface layers of sunspots has been demonstrated over recent years using a number of modelling techniques, including ray theory, perturbation theory, differential eigensystem analysis, and direct numerical simulation. These show that significant energy may be transferred between the fast and slow modes in the neighbourhood of the equipartition layer where the Alfven and sound speeds coincide. However, most of the models so far have been two...
Guo, Zhifang; Hong, Minghua; Lin, Yu; Du, Aimin; Wang, Xueyi; Wu, Mingyu; Lu, Quanming
2015-02-01
In this paper, effects of a fast flow in the tail plasma sheet on the generation of kinetic Alfven waves (KAWs) in the high-latitude of the near-Earth magnetotail are investigated by performing a two-dimensional (2-D) global-scale hybrid simulation, where the plasma flow is initialized by the E ×B drift near the equatorial plane due to the existence of the dawn-dusk convection electric field. It is found that firstly, the plasma sheet becomes thinned and the dipolarization of magnetic field appears around (x ,z ) =(-10.5 RE,0.3 RE) , where RE is the radius of the Earth. Then, shear Alfven waves are excited in the plasma sheet, and the strong earthward flow is braked by the dipole-like magnetic field. These waves propagate along the magnetic field lines toward the polar regions later. Subsequently, KAWs with k⊥≫k∥ are generated in the high-latitude magnetotail due to the existence of the non-uniformity of the magnetic field and density in the polar regions. The ratio of the electric field to the magnetic field in these waves is found to obey the relation (δEz)/(δBy )˜ω/k∥ of KAWs. Our simulation provides a mechanism for the generation of the observed low-frequency shear Alfven waves in the plasma sheet and kinetic Alfven waves in the high-latitude near-Earth magnetotail, whose source is suggested to be the flow braking in the low-latitude plasma sheet.
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
Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport
Collins, C. S.; Heidbrink, W. W.; Austin, M. E.; Kramer, G. J.; Pace, D. C.; Petty, C. C.; Stagner, L.; Van Zeeland, M. A.; White, R. B.; Zhu, Y. B.
2016-03-01
Experiments in the DIII-D tokamak show that fast-ion transport suddenly becomes stiff above a critical threshold in the presence of many overlapping small-amplitude Alfvén eigenmodes (AEs). The threshold is phase-space dependent and occurs when particle orbits become stochastic due to resonances with AEs. Above threshold, equilibrium fast-ion density profiles are unchanged despite increased drive, and intermittent fast-ion losses are observed. Fast-ion D α spectroscopy indicates radially localized transport of the copassing population at radii that correspond to the location of midcore AEs. The observation of stiff fast-ion transport suggests that reduced models can be used to effectively predict alpha profiles, beam ion profiles, and losses to aid in the design of optimized scenarios for future burning plasma devices.
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.
Energy Technology Data Exchange (ETDEWEB)
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.
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.
Fernandez, Pablo
2003-01-01
We prove that in a world without leverage cost the relationship between the levered beta ( L) and the unlevered beta ( u) is the No-costs-of-leverage formula: L = u + ( u - d) D (1 - T) / E. We also analyze 6 alternative valuation theories proposed in the literature to estimate the relationship between the levered beta and the unlevered beta (Harris and Pringle (1985), Modigliani and Miller (1963), Damodaran (1994), Myers (1974), Miles and Ezzell (1980), and practitioners) and prove that all ...
DEFF Research Database (Denmark)
Hansen, Peter Reinhard; Lunde, Asger; Voev, Valeri Radkov
2014-01-01
as the beta. We apply the model to a large set of assets and find the conditional betas to be far more variable than usually found with rolling-window regressions based exclusively on daily returns. In the empirical part of the paper, we examine the cross-sectional as well as the time variation...... of the conditional beta series during the financial crises....
Oblique non-neutral solitary Alfven modes in weakly nonlinear pair plasmas
Energy Technology Data Exchange (ETDEWEB)
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.
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...
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.
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.
International Nuclear Information System (INIS)
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
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.
International Nuclear Information System (INIS)
The spectrum of JET discharges heated with new antennas is analyzed. A series of peaks in the coupling resistance are observed when the monopole phasing is used. A detailed and unambiguous identification of radial eigenmodes, which are between the ion-ion hybrid cut-off layer and the antenna, is obtained. The comparison of slab model predictions with the data analysis for the spacings of the onset of these peaks is carried out. The modelling of the peak-to-valley ratios for the coupling resistance is performed. It is shown that the variations in the coupling resistance are reduced when dipole phasing is used. Data is examined to gauge the effects of eigenmode excitation during high power ion cyclotron resonance heating
Search for alpha-driven BAE modes in TFTR
International Nuclear Information System (INIS)
A search for alpha-driven beta-induced Alfven eigenmodes (BAE modes) was conducted in low current (1.0--1.6 MA) TFTR supershots. Stable high-beta deuterium-tritium (DT) discharges were obtained with Bρ = 2.4 and central alpha beta of 0.1%. Instabilities between 75--200 kHz were observed by magnetic probes in many DT discharges, but the activity was also present in deuterium-deuterium (DD) comparison discharges, indicating that these modes are not destabilized (principally) by the alpha-particle population. Losses of fusion products are also similar in the two sets of discharges
A synopsis of collective alpha effects and implications for ITER
Energy Technology Data Exchange (ETDEWEB)
Sigmar, D.J.
1990-10-01
This paper discusses the following: Alpha Interaction with Toroidal Alfven Eigenmodes; Alpha Interaction with Ballooning Modes; Alpha Interaction with Fishbone Oscillations; and Implications for ITER.
Singh, Nagendra; Khazanov, George; Mukhter, Ali
2007-01-01
We present results here from 2.5-D particle-in-cell simulations showing that the electrostatic (ES) components of broadband extremely low frequency (BBELF) waves could possibly be generated by cross-field plasma instabilities driven by the relative drifts between the heavy and light ion species in the electromagnetic (EM) Alfvenic component of the BBELF waves in a multi-ion plasma. The ES components consist of ion cyclotron as well as lower hybrid modes. We also demonstrate that the ES wave generation is directly involved in the transverse acceleration of ions (TAI) as commonly measured with the BBELF wave events. The heating is affected by ion cyclotron resonance in the cyclotron modes and Landau resonance in the lower hybrid waves. In the simulation we drive the plasma by the transverse electric field, E(sub y), of the EM waves; the frequency of E(sub y), omega(sub d), is varied from a frequency below the heavy ion cyclotron frequency, OMEGA(sub h), to below the light ion cyclotron frequency, OMEGA(sub i). We have also performed simulations for E(sub y) having a continuous spectrum given by a power law, namely, |Ey| approx. omega(sub d) (exp -alpha), where the exponent alpha = _, 1, and 2 in three different simulations. The driving electric field generates polarization and ExB drifts of the ions and electrons. When the interspecies relative drifts are sufficiently large, they drive electrostatic waves, which cause perpendicular heating of both light and heavy ions. The transverse ion heating found here is discussed in relation to observations from Cluster, FAST and Freja.
DEFF Research Database (Denmark)
Frazzini, Andrea; Heje Pedersen, Lasse
We present a model with leverage and margin constraints that vary across investors and time. We find evidence consistent with each of the model’s five central predictions: (1) Since constrained investors bid up high-beta assets, high beta is associated with low alpha, as we find empirically for U.......S. equities, 20 international equity markets, Treasury bonds, corporate bonds, and futures; (2) A betting-against-beta (BAB) factor, which is long leveraged low beta assets and short high-beta assets, produces significant positive risk-adjusted returns; (3) When funding constraints tighten, the return...... of the BAB factor is low; (4) Increased funding liquidity risk compresses betas toward one; (5) More constrained investors hold riskier assets....
DEFF Research Database (Denmark)
Frazzini, Andrea; Heje Pedersen, Lasse
2014-01-01
We present a model with leverage and margin constraints that vary across investors and time. We find evidence consistent with each of the model's five central predictions: (1) Because constrained investors bid up high-beta assets, high beta is associated with low alpha, as we find empirically...... for US equities, 20 international equity markets, Treasury bonds, corporate bonds, and futures. (2) A betting against beta (BAB) factor, which is long leveraged low-beta assets and short high-beta assets, produces significant positive risk-adjusted returns. (3) When funding constraints tighten......, the return of the BAB factor is low. (4) Increased funding liquidity risk compresses betas toward one. (5) More constrained investors hold riskier assets....
DEFF Research Database (Denmark)
Bollerslev, Tim; Li, Sophia Zhengzi; Todorov, Viktor
Motivated by the implications from a stylized equilibrium pricing framework, we investigate empirically how individual equity prices respond to continuous, or \\smooth," and jumpy, or \\rough," market price moves, and how these different market price risks, or betas, are priced in the cross......-section of expected returns. Based on a novel highfrequency dataset of almost one-thousand individual stocks over two decades, we find that the two rough betas associated with intraday discontinuous and overnight returns entail significant risk premiums, while the intraday continuous beta is not priced in the cross......-section. An investment strategy that goes long stocks with high jump betas and short stocks with low jump betas produces significant average excess returns. These higher risk premiums for the discontinuous and overnight market betas remain significant after controlling for a long list of other firm characteristics...
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.
Crocker, N. A.; Tritz, K.; White, R. B.; Fredrickson, E. D.; Gorelenkov, N. N.; NSTX-U Team
2015-11-01
New simulation results demonstrate that high frequency compressional (CAE) and global (GAE) Alfvén eigenmodes cause radial convection of electrons, with implications for particle and energy confinement, as well as electric field formation in NSTX-U. Simulations of electron orbits in the presence of multiple experimentally determined CAEs and GAEs, using the gyro-center code ORBIT, have revealed substantial convective transport, in addition to the expected diffusion via orbit stochastization. These results advance understanding of anomalous core energy transport expected in high performance, beam-heated NSTX-U plasmas. The simulations make use of experimentally determined density perturbation (δn) amplitudes and mode structures obtained by inverting measurements from 16 a channel reflectometer array using a synthetic diagnostic. Combined with experimentally determined mode polarizations (i.e. CAE or GAE), the δn are used to estimate the ExB displacements for use in ORBIT. Preliminary comparison of the simulation results with transport modeling by TRANSP indicate that the convection is currently underestimated. Supported by US DOE Contracts DE-SC0011810, DE-FG02-99ER54527 & DE-AC02-09CH11466.
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...
Energy Technology Data Exchange (ETDEWEB)
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.
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.
He, Yue-Jing; Hung, Wei-Chih; Lai, Zhe-Ping
2016-01-01
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. PMID:26861322
Directory of Open Access Journals (Sweden)
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.
Energy Technology Data Exchange (ETDEWEB)
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.
DEFF Research Database (Denmark)
Christoffersen, Peter; Jacobs, Kris; Vainberg, Gregory
-looking. This paper introduces a radically different approach to estimating market betas. Using the tools in Bakshi and Madan (2000) and Bakshi, Kapadia and Madan (2003) we employ the information embedded in the prices of individual stock options and index options to compute our forward-looking market beta...
Tsiklauri, D
2014-01-01
Previous studies [Malara et al ApJ, 533, 523 (2000)] considered small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC) magnetic field using WKB approximation. In this work linearly polarised Alfven wave dynamics in ABC magnetic field via direct 3D MHD numerical simulation is studied for the first time. Gaussian AW pulse with length-scale much shorter than ABC domain length and harmonic AW with wavelength equal to ABC domain length are studied for four different resistivities. While it is found that AWs dissipate quickly in the ABC field, surprisingly, AW perturbation energy increases in time. In the case of the harmonic AW perturbation energy growth is transient in time, attaining peaks in both velocity and magnetic perturbation energies within timescales much smaller than resistive time. In the case of the Gaussian AW pulse velocity perturbation energy growth is still transient in time, attaining a peak within few resistive times, while magnetic perturbation energy continues to grow. It ...
Neutrinoless double beta decay
Indian Academy of Sciences (India)
Kai Zuber
2012-10-01
The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations as well as the current status of experiments are presented. Finally, an outlook towards the future, work on nuclear matrix elements and alternative processes is given.
... chemotherapy for a blood cancer called lymphoblastic leukemia. Mental performance. Some evidence suggests that taking beta-carotene ... One is water-based, and the other is oil-based. Studies show that the water-based version ...
International Nuclear Information System (INIS)
Our activities on High Beta Tokamak Research during the past 20 months of the present grant period can be divided into six areas: reconstruction and modeling of high beta equilibria in HBT; measurement and analysis of MHD instabilities observed in HBT; measurements of impurity transport; diagnostic development on HBT; numerical parameterization of the second stability regime; and conceptual design and assembly of HBT-EP. Each of these is described in some detail in the sections of this progress report
{beta} - amyloid imaging probes
Energy Technology Data Exchange (ETDEWEB)
Jeong, Jae Min [Seoul National University College of Medicine, Seoul (Korea, Republic of)
2007-04-15
Imaging distribution of {beta} - amyloid plaques in Alzheimer's disease is very important for early and accurate diagnosis. Early trial of the {beta} -amyloid plaques includes using radiolabeled peptides which can be only applied for peripheral {beta} - amyloid plaques due to limited penetration through the blood brain barrier (BBB). Congo red or Chrysamine G derivatives were labeled with Tc-99m for imaging {beta} - amyloid plaques of Alzheimer patient's brain without success due to problem with BBB penetration. Thioflavin T derivatives gave breakthrough for {beta} - amyloid imaging in vivo, and a benzothiazole derivative [C-11]6-OH-BTA-1 brought a great success. Many other benzothiazole, benzoxazole, benzofuran, imidazopyridine, and styrylbenzene derivatives have been labeled with F-18 and I-123 to improve the imaging quality. However, [C-11]6-OH-BTA-1 still remains as the best. However, short half-life of C-11 is a limitation of wide distribution of this agent. So, it is still required to develop an Tc-99m, F-18 or I-123 labeled agent for {beta} - amyloid imaging agent.
Generation of Alfven-ion cyclotron waves on auroral field lines in the presence of heavy ions
Lysak, R. L.; Temerin, M. A.
1983-01-01
Observation of electromagnetic waves in the low-altitude auroral zone at frequencies between the proton and helium gyrofrequencies suggests that Alfven-ion cyclotron waves modified by the presence of helium ions are being excited. Estimates of the growth rates for this mode indicate that the auroral electron beam can provide the free energy for the instability. The effect of the heavy ions is to decrease the group velocity of the waves, leading to larger convective growth. Theoretical wave spectra are computed in the local approximation, which assumes that the gradient scale lengths in density and magnetic field are constant over the ray paths. Narrow banded spectral peaks similar to observations may be produced when the thickness of the electron beam is small (200 m at 3000 km altitude). Narrow beams also limit growth of whistler mode waves, which compete for the free energy of the electron beam.
Slow shock formation and its structure with sub-Alfvenic shear flow in magnetic reconnection
Ma, Zhi-Wei
2011-10-01
Slow shock formation and its structures associated with magnetic reconnection are investigated in the presence of sub-Alfvénic shear flow based on compressible resistive MHD model and compressible Hall MHD model. It is found for the first time that one or two pairs of the slow shocks are formed in the inflow region away from the reconnection separatrices in the compressible resistive MHD. The distributions of the slow shocks largely depend on the plasma beta and the shear flow velocity. One pair of the slow shocks is formed for the case β = 0 . 2 and two pairs of the low shocks are generated for the case β = 1 . 0 with the shear flow velocity around the range from 0.6VA to 0.9 VA. In the case of the high plasma beta (β = 5 . 0) , there is no slow shock formed outside the reconnection separatrices. In the compressible Hall MHD, the slow shocks are gradually evolved into wave trains as increase of the ion inertial length di. This work is supported by China NSF Grant No. 10975160.
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.
DEFF Research Database (Denmark)
Løvborg, Leif; Gaffney, C. F.; Clark, P. A.;
1985-01-01
Experimental and/or theoretical estimates are presented concerning, (i) attenuation within the sample of beta and gamma radiation from the soil, (ii) the gamma dose within the sample due to its own radioactivity, and (iii) the soil gamma dose in the proximity of boundaries between regions...... of differing radioactivity. It is confirmed that removal of the outer 2 mm of sample is adequate to remove influence from soil beta dose and estimates are made of the error introduced by non-removal. Other evaluations include variation of the soil gamma dose near the ground surface and it appears...
International Nuclear Information System (INIS)
The great sensitivity of double beta decay to neutrino mass and right handed currents has motivated many new and exciting attempts to observe this elusive nuclear phenomenon directly. Experiments in operation and other coming on line in the next one or two years are expected to result in order-of-magnitude improvements in detectable half lives for both the two-neutrino and no-neutrino modes. A brief history of double beta decay experiments is presented together with a discussion of current experimental efforts, including a gas filled time projection chamber being used to study selenium-82. (author)
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.
Evaluation of neutrino masses from $m_{\\beta\\beta}$ values
Khrushchov, V V
2008-01-01
A neutrino mass matrix is considered under conditions of the CP invariance and the negligible reactor mixing $\\theta_{13}$ angle. Absolute mass values for three neutrinos are evaluated in normal and inverted hierarchy spectra on the ground of data for oscillation mixing neutrino parameters and effective neutrino mass entering into a probability of neutrinoless two beta decay $m_{\\beta\\beta}$ values.
Trichoderma .beta.-glucosidase
Dunn-Coleman, Nigel; Goedegebuur, Frits; Ward, Michael; Yao, Jian
2006-01-03
The present invention provides a novel .beta.-glucosidase nucleic acid sequence, designated bgl3, and the corresponding BGL3 amino acid sequence. The invention also provides expression vectors and host cells comprising a nucleic acid sequence encoding BGL3, recombinant BGL3 proteins and methods for producing the same.
Energy Technology Data Exchange (ETDEWEB)
Rich, B.L.
1986-01-01
Measurements of beta and/or nonpenetrating exposure results is complicated and past techniques and capabilities have resulted in significant inaccuracies in recorded results. Current developments have resulted in increased capabilities which make the results more accurate and should result in less total exposure to the work force. Continued development of works in progress should provide equivalent future improvements.
Neutrinoless Double Beta Decay
Päs, Heinrich
2015-01-01
We review the potential to probe new physics with neutrinoless double beta decay $(A,Z) \\to (A,Z+2) + 2 e^-$. Both the standard long-range light neutrino mechanism as well as short-range mechanisms mediated by heavy particles are discussed. We also stress aspects of the connection to lepton number violation at colliders and the implications for baryogenesis.
Interferon beta-1b injection is used to reduce episodes of symptoms in patients with relapsing-remitting (course ... and problems with vision, speech, and bladder control). Interferon beta-1b is in a class of medications ...
Genetics Home Reference: beta thalassemia
... for Disease Control and Prevention Centre for Genetics Education (Australia) Cold Spring Harbor Laboratory: Your Genes Your Health Disease InfoSearch: Beta Thalassemia Genomics Education Programme (UK) MalaCards: dominant beta-thalassemia Merck Manual ...
Beta emitters and radiation protection
DEFF Research Database (Denmark)
Jødal, Lars
2009-01-01
BACKGROUND. Beta emitters, such as 90Y, are increasingly being used for cancer treatment. However, beta emitters demand other precautions than gamma emitters during preparation and administration, especially concerning shielding. AIM. To discuss practical precautions for handling beta emitters...... on the outside of the primary shielding material. If suitable shielding is used and larger numbers of handlings are divided among several persons, then handling of beta emitters can be a safe procedure....
Misleading Betas: An Educational Example
Chong, James; Halcoussis, Dennis; Phillips, G. Michael
2012-01-01
The dual-beta model is a generalization of the CAPM model. In the dual-beta model, separate beta estimates are provided for up-market and down-market days. This paper uses the historical "Anscombe quartet" results which illustrated how very different datasets can produce the same regression coefficients to motivate a discussion of the…
Blaney Davidson, E.N.; Kraan, P.M. van der; Berg, W.B. van den
2007-01-01
OBJECTIVE: Cartilage damage is a major problem in osteoarthritis (OA). Growth factors like transforming growth factor-beta (TGF-beta) have great potential in cartilage repair. In this review, we will focus on the potential therapeutic intervention in OA with TGF-beta, application of the growth facto
Tsiklauri, David
2015-04-01
Previous studies (e.g., Malara et al., Astrophys. J. 533, 523 (2000)) considered small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC) magnetic field using WKB approximation. They draw a distinction between 2D AW dissipation via phase mixing and 3D AW dissipation via exponentially divergent magnetic field lines. In the former case, AW dissipation time scales as S 1/3 and in the latter as log(S) , where S is the Lundquist number. In this work [1], linearly polarised Alfven wave dynamics in ABC magnetic field via direct 3D magnetohydrodynamic (MHD) numerical simulation is studied for the first time. A Gaussian AW pulse with length-scale much shorter than ABC domain length and a harmonic AW with wavelength equal to ABC domain length are studied for four different resistivities. While it is found that AWs dissipate quickly in the ABC field, contrary to an expectation, it is found the AW perturbation energy increases in time. In the case of the harmonic AW, the perturbation energy growth is transient in time, attaining peaks in both velocity and magnetic perturbation energies within timescales much smaller than the resistive time. In the case of the Gaussian AW pulse, the velocity perturbation energy growth is still transient in time, attaining a peak within few resistive times, while magnetic perturbation energy continues to grow. It is also shown that the total magnetic energy decreases in time and this is governed by the resistive evolution of the background ABC magnetic field rather than AW damping. On contrary, when the background magnetic field is uniform, the total magnetic energy decrease is prescribed by AW damping, because there is no resistive evolution of the background. By considering runs with different amplitudes and by analysing the perturbation spectra, possible dynamo action by AW perturbation-induced peristaltic flow and inverse cascade of magnetic energy have been excluded. Therefore, the perturbation energy growth is attributed
International Nuclear Information System (INIS)
With the first injection of neutral beams into the National Spherical Torus Experiment (NSTX) [Ono, et al., Nucl. Fusion 40 (2000) 557] a broad spectrum of fluctuations consisting of nearly equally spaced peaks in the frequency range from about 0.2 to 1.2 times the ion cyclotron frequency was observed. The frequencies scale with toroidal field and plasma density consistently with Alfvin waves. From these and other observations, the modes have been identified as Compressional Alfvin Eigenmodes (CAE). It has also recently been found that the ratio of the measured ion and electron temperatures in NSTX during neutral-beam heating is anomalously high [Bell, Bull. Am. Phys. Soc. 46 (2001) 206]. To explain the anomaly in the ratio of ion to electron temperature, it has been suggested that the CAE, driven by the beam ions, stochastically heat the thermal ions [Gates, et al., Phys. Rev. Lett. 87 (2001) 205003]. In this paper, it is shown through studies of the power balance that stochastic heating of the thermal ions by the observed CAE alone is not solely responsible for the anomaly in the ion to electron temperature ratio
Galanello, Renzo; Origa, Raffaella
2010-05-21
Beta-thalassemias are a group of hereditary blood disorders characterized by anomalies in the synthesis of the beta chains of hemoglobin resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals. The total annual incidence of symptomatic individuals is estimated at 1 in 100,000 throughout the world and 1 in 10,000 people in the European Union. Three main forms have been described: thalassemia major, thalassemia intermedia and thalassemia minor. Individuals with thalassemia major usually present within the first two years of life with severe anemia, requiring regular red blood cell (RBC) transfusions. Findings in untreated or poorly transfused individuals with thalassemia major, as seen in some developing countries, are growth retardation, pallor, jaundice, poor musculature, hepatosplenomegaly, leg ulcers, development of masses from extramedullary hematopoiesis, and skeletal changes that result from expansion of the bone marrow. Regular transfusion therapy leads to iron overload-related complications including endocrine complication (growth retardation, failure of sexual maturation, diabetes mellitus, and insufficiency of the parathyroid, thyroid, pituitary, and less commonly, adrenal glands), dilated myocardiopathy, liver fibrosis and cirrhosis). Patients with thalassemia intermedia present later in life with moderate anemia and do not require regular transfusions. Main clinical features in these patients are hypertrophy of erythroid marrow with medullary and extramedullary hematopoiesis and its complications (osteoporosis, masses of erythropoietic tissue that primarily affect the spleen, liver, lymph nodes, chest and spine, and bone deformities and typical facial changes), gallstones, painful leg ulcers and increased predisposition to thrombosis. Thalassemia minor is clinically asymptomatic but some subjects may have moderate anemia. Beta-thalassemias are caused by point mutations or, more rarely, deletions in the beta
Directory of Open Access Journals (Sweden)
Origa Raffaella
2010-05-01
Full Text Available Abstract Beta-thalassemias are a group of hereditary blood disorders characterized by anomalies in the synthesis of the beta chains of hemoglobin resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals. The total annual incidence of symptomatic individuals is estimated at 1 in 100,000 throughout the world and 1 in 10,000 people in the European Union. Three main forms have been described: thalassemia major, thalassemia intermedia and thalassemia minor. Individuals with thalassemia major usually present within the first two years of life with severe anemia, requiring regular red blood cell (RBC transfusions. Findings in untreated or poorly transfused individuals with thalassemia major, as seen in some developing countries, are growth retardation, pallor, jaundice, poor musculature, hepatosplenomegaly, leg ulcers, development of masses from extramedullary hematopoiesis, and skeletal changes that result from expansion of the bone marrow. Regular transfusion therapy leads to iron overload-related complications including endocrine complication (growth retardation, failure of sexual maturation, diabetes mellitus, and insufficiency of the parathyroid, thyroid, pituitary, and less commonly, adrenal glands, dilated myocardiopathy, liver fibrosis and cirrhosis. Patients with thalassemia intermedia present later in life with moderate anemia and do not require regular transfusions. Main clinical features in these patients are hypertrophy of erythroid marrow with medullary and extramedullary hematopoiesis and its complications (osteoporosis, masses of erythropoietic tissue that primarily affect the spleen, liver, lymph nodes, chest and spine, and bone deformities and typical facial changes, gallstones, painful leg ulcers and increased predisposition to thrombosis. Thalassemia minor is clinically asymptomatic but some subjects may have moderate anemia. Beta-thalassemias are caused by point mutations or, more rarely
DEFF Research Database (Denmark)
Kristensen, Bent Bruun; Madsen, Ole Lehrmann; Møller-Pedersen, Birger;
In object-oriented programming, a program execution is viewed as a physical model of some real or imaginary part of the world. A language supporting object-oriented programming must therefore contain comprehensive facilities for modeling phenomena and concepts form the application domain. Many ap...... applications in the real world consist of objects carrying out sequential processes. Coroutines may be used for modeling objects that alternate between a number of sequential processes. The authors describe coroutines in BETA...
Lipkin, Harry Jeannot
1962-01-01
The ""pedestrian approach"" was developed to describe some essentially simple experimental results and their theoretical implications in plain language. In this graduate-level text, Harry J. Lipkin presents simply, but without oversimplification, the aspects of beta decay that can be understood without reference to the formal theory; that is, the reactions that follow directly from conservation laws and elementary quantum mechanics.The pedestrian treatment is neither a substitute for a complete treatment nor a watered-down version.
Integration of BETA with Eclipse
DEFF Research Database (Denmark)
Andersen, Peter; Madsen, Ole Lehrmann; Enevoldsen, Mads Brøgger
2004-01-01
This paper presents language interoperability issues appearing in order to implement support for the BETA language in the Java-based Eclipse integrated development environment. One of the challenges is to implement plug-ins in BETA and be able to load them in Eclipse. In order to do this, some form...... of language interoperability between Java and BETA is required. The first approach is to use the Java Native Interface and use C to bridge between Java and BETA. This results in a workable, but complicated solution. The second approach is to let the BETA compiler generate Java class files. With this approach...... it is possible to implement plug-ins in BETA and even inherit from Java classes. In the paper the two approaches are described together with part of the mapping from BETA to Java class files. http://www.sciencedirect.com/science/journal/15710661...
Regulation of beta cell replication
DEFF Research Database (Denmark)
Lee, Ying C; Nielsen, Jens Høiriis
2008-01-01
Beta cell mass, at any given time, is governed by cell differentiation, neogenesis, increased or decreased cell size (cell hypertrophy or atrophy), cell death (apoptosis), and beta cell proliferation. Nutrients, hormones and growth factors coupled with their signalling intermediates have been...... suggested to play a role in beta cell mass regulation. In addition, genetic mouse model studies have indicated that cyclins and cyclin-dependent kinases that determine cell cycle progression are involved in beta cell replication, and more recently, menin in association with cyclin-dependent kinase...... inhibitors has been demonstrated to be important in beta cell growth. In this review, we consider and highlight some aspects of cell cycle regulation in relation to beta cell replication. The role of cell cycle regulation in beta cell replication is mostly from studies in rodent models, but whether...
Beta cell adaptation in pregnancy
DEFF Research Database (Denmark)
Nielsen, Jens Høiriis
2016-01-01
Pregnancy is associated with a compensatory increase in beta cell mass. It is well established that somatolactogenic hormones contribute to the expansion both indirectly by their insulin antagonistic effects and directly by their mitogenic effects on the beta cells via receptors for prolactin...... and growth hormone expressed in rodent beta cells. However, the beta cell expansion in human pregnancy seems to occur by neogenesis of beta cells from putative progenitor cells rather than by proliferation of existing beta cells. Claes Hellerström has pioneered the research on beta cell growth for decades......, but the mechanisms involved are still not clarified. In this review the information obtained in previous studies is recapitulated together with some of the current attempts to resolve the controversy in the field: identification of the putative progenitor cells, identification of the factors involved...
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 ...
LHCb: $2\\beta_s$ measurement at LHCb
Conti, G
2009-01-01
A measurement of $2\\beta_s$, the phase of the $B_s-\\bar{B_s}$ oscillation amplitude with respect to that of the ${\\rm b} \\rightarrow {\\rm c^{+}}{\\rm W^{-}}$ tree decay amplitude, is one of the key goals of the LHCb experiment with first data. In the Standard Model (SM), $2\\beta_s$ is predicted to be $0.0360^{+0.0020}_{-0.0016} \\rm rad$. The current constraints from the Tevatron are: $2\\beta_{s}\\in[0.32 ; 2.82]$ at 68$\\%$CL from the CDF experiment and $2\\beta_{s}=0.57^{+0.24}_{-0.30}$ from the D$\\oslash$ experiment. Although the statistical uncertainties are large, these results hint at the possible contribution of New Physics in the $B_s-\\bar{B_s}$ box diagram. After one year of data taking at LHCb at an average luminosity of $\\mathcal{L}\\sim2\\cdot10^{32}\\rm cm^{-2} \\rm s^{-1}$ (integrated luminosity $\\mathcal{L}_{\\rm int}\\sim 2 \\rm fb^{-1}$), the expected statistical uncertainty on the measurement is $\\sigma(2\\beta_s)\\simeq 0.03$. This uncertainty is similar to the $2\\beta_s$ value predicted by the SM.
Xeroradiography in. beta. -thalassaemia
Energy Technology Data Exchange (ETDEWEB)
Scutellari, P.N.; Orzincolo, C.; Tamarozzi, R.
1985-01-01
Xeroradiographic investigations of the skull, hand, and elbow were performed on 27 patients with homozygous ..beta..-thalassaemia. The results were compared with plain radiographic examinations. Xeroradiography, because of its technical properties (i.e. edge contrast enhancement and wide latitude), was shown to demonstrate cortical thinning of long bones, swelling of the diploic space in the skull, and reticulated patterns in the elbow better than standard radiography. Moreover, the use of 'positive' mode imaging was shown to have advantages in the study of the skull and extremities.
Double beta decay: present status
Barabash, A. S.
2008-01-01
The present status of double beta decay experiments (including the search for $2\\beta^{+}$, EC$\\beta^{+}$ and ECEC processes) are reviewed. The results of the most sensitive experiments are discussed. Average and recommended half-life values for two-neutrino double beta decay are presented. Conservative upper limits on effective Majorana neutrino mass and the coupling constant of the Majoron to the neutrino are established as $ < 0.75$ eV and $ < 1.9 \\cdot 10^{-4}$, respectively. Proposals fo...
Simultaneous beta and gamma spectroscopy
Farsoni, Abdollah T.; Hamby, David M.
2010-03-23
A phoswich radiation detector for simultaneous spectroscopy of beta rays and gamma rays includes three scintillators with different decay time characteristics. Two of the three scintillators are used for beta detection and the third scintillator is used for gamma detection. A pulse induced by an interaction of radiation with the detector is digitally analyzed to classify the type of event as beta, gamma, or unknown. A pulse is classified as a beta event if the pulse originated from just the first scintillator alone or from just the first and the second scintillator. A pulse from just the third scintillator is recorded as gamma event. Other pulses are rejected as unknown events.
Aubert, B; Boutigny, D; Couderc, F; Gaillard, J M; Hicheur, A; Karyotakis, Yu; Lees, J P; Tisserand, V; Zghiche, A; Palano, A; Pompili, A; Chen, J C; Qi, N D; Rong, G; Wang, P; Zhu, Y S; Eigen, G; Ofte, I; Stugu, B; Abrams, G S; Borgland, A W; Breon, A B; Brown, D N; Button-Shafer, J; Cahn, R N; Charles, E; Day, C T; Gill, M S; Gritsan, A V; Groysman, Y; Jacobsen, R G; Kadel, R W; Kadyk, J; Kerth, L T; Kolomensky, Yu G; Kukartsev, G; Lynch, G; Mir, L M; Oddone, P J; Orimoto, T J; Pripstein, M; Roe, N A; Ronan, Michael T; Shelkov, V G; Wenzel, W A; Barrett, M; Ford, K E; Harrison, T J; Hart, A J; Hawkes, C M; Morgan, S E; Watson, A T; Fritsch, M; Goetzen, K; Held, T; Koch, H; Lewandowski, B; Pelizaeus, M; Steinke, M; Boyd, J T; Chevalier, N; Cottingham, W N; Kelly, M P; Latham, T E; Wilson, F F; Çuhadar-Dönszelmann, T; Hearty, C; Knecht, N S; Mattison, T S; McKenna, J A; Thiessen, D; Khan, A; Kyberd, P; Teodorescu, L; Blinov, A E; Blinov, V E; Druzhinin, V P; Golubev, V B; Ivanchenko, V N; Kravchenko, E A; Onuchin, A P; Serednyakov, S I; Skovpen, Yu I; Solodov, E P; Yushkov, A N; Best, D; Bruinsma, M; Chao, M; Eschrich, I; Kirkby, D; Lankford, A J; Mandelkern, M A; Mommsen, R K; Röthel, W; Stoker, D P; Buchanan, C; Hartfiel, B L; Foulkes, S D; Gary, J W; Shen, B C; Wang, K; Del Re, D; Hadavand, H K; Hill, E J; MacFarlane, D B; Paar, H P; Rahatlou, S; Sharma, V; Berryhill, J W; Campagnari, C; Dahmes, B; Levy, S L; Long, O; Lu, A; Mazur, M A; Richman, J D; Verkerke, W; Beck, T W; Eisner, A M; Heusch, C A; Lockman, W S; Nesom, G; Schalk, T; Schmitz, R E; Schumm, B A; Seiden, A; Spradlin, P; Williams, D C; Wilson, M G; Albert, J; Chen, E; Dubois-Felsmann, G P; Dvoretskii, A; Hitlin, D G; Narsky, I; Piatenko, T; Porter, F C; Ryd, A; Samuel, A; Yang, S; Jayatilleke, S M; Mancinelli, G; Meadows, B T; Sokoloff, M D; Abe, T; Blanc, F; Bloom, P; Chen, S; Ford, W T; Nauenberg, U; Olivas, A; Rankin, P; Smith, J G; Zhang, J; Zhang, L; Chen, A; Harton, J L; Soffer, A; Toki, W H; Wilson, R J; Zeng, Q L; Altenburg, D; Brandt, T; Brose, J; Dickopp, M; Feltresi, E; Hauke, A; Lacker, H M; Müller-Pfefferkorn, R; Nogowski, R; Otto, S; Petzold, A; Schubert, J; Schubert, Klaus R; Schwierz, R; Spaan, B; Sundermann, J E; Bernard, D; Bonneaud, G R; Brochard, F; Grenier, P; Schrenk, S; Thiebaux, C; Vasileiadis, G; Verderi, M; Bard, D J; Clark, P J; Lavin, D; Muheim, F; Playfer, S; Xie, Y; Andreotti, M; Azzolini, V; Bettoni, D; Bozzi, C; Calabrese, R; Cibinetto, G; Luppi, E; Negrini, M; Piemontese, L; Sarti, A; Treadwell, E; Baldini-Ferroli, R; Calcaterra, A; De Sangro, R; Finocchiaro, G; Patteri, P; Piccolo, M; Zallo, A; Buzzo, A; Capra, R; Contri, R; Crosetti, G; Lo Vetere, M; Macri, M; Monge, M R; Passaggio, S; Patrignani, C; Robutti, E; Santroni, A; Tosi, S; Bailey, S; Brandenburg, G; Morii, M; Won, E; Dubitzky, R S; Langenegger, U; Bhimji, W; Bowerman, D A; Dauncey, P D; Egede, U; Gaillard, J R; Morton, G W; Nash, J A; Nikolich, M B; Taylor, G P; Charles, M J; Grenier, G J; Mallik, U; Cochran, J; Crawley, H B; Lamsa, J; Meyer, W T; Prell, S; Rosenberg, E I; Yi, J; Davier, M; Grosdidier, G; Höcker, A; Laplace, S; Le Diberder, F R; Lepeltier, V; Lutz, A M; Petersen, T C; Plaszczynski, S; Schune, M H; Tantot, L; Wormser, G; Cheng, C H; Lange, D J; Simani, M C; Wright, D M; Bevan, A J; Chavez, C A; Coleman, J P; Forster, I J; Fry, J R; Gabathuler, Erwin; Gamet, R; Parry, R J; Payne, D J; Sloane, R J; Touramanis, C; Back, J J; Harrison, P F; Mohanty, G B; Cowan, G; Flack, R L; Flächer, H U; Green, M G; Jackson, P S; McMahon, T R; Ricciardi, S; Salvatore, F; Winter, M A; Brown, D; Davis, C L; Allison, J; Barlow, N R; Barlow, R J; Hodgkinson, M C; Lafferty, G D; Lyon, A J; Williams, J C; Farbin, A; Hulsbergen, W D; Jawahery, A; Kovalskyi, D; Lae, C K; Lillard, V; Roberts, D A; Blaylock, G; Dallapiccola, C; Flood, K T; Hertzbach, S S; Kofler, R; Koptchev, V B; Moore, T B; Saremi, S; Stängle, H; Willocq, S; Cowan, R; Sciolla, G; Taylor, F; Yamamoto, R K; Mangeol, D J J; Patel, P M; Robertson, S H; Lazzaro, A; Palombo, F; Bauer, J M; Cremaldi, L M; Eschenburg, V; Godang, R; Kroeger, R; Reidy, J; Sanders, D A; Summers, D J; Zhao, H W; Brunet, S; Côté, D; Taras, P; Nicholson, H; Fabozzi, F; Lista, L; Monorchio, D; Paolucci, P; Piccolo, D; Sciacca, C; Baak, M; Bulten, H; Raven, G; Snoek, H L; Wilden, L; Jessop, C P; LoSecco, J M; Gabriel, T A; Allmendinger, T; Brau, B; Gan, K K; Honscheid, K; Hufnagel, D; Kagan, H; Kass, R; Pulliam, T; Rahimi, A M; Ter-Antonian, R; Wong, Q K; Brau, J E; Frey, R; Igonkina, O; Potter, C T; Sinev, N B; Strom, D; Torrence, E; Colecchia, F; Dorigo, A; Galeazzi, F; Margoni, M; Morandin, M; Posocco, M; Rotondo, M; Simonetto, F; Stroili, R; Tiozzo, G; Voci, C; Benayoun, M; Briand, H; Chauveau, J; David, P; La Vaissière, C de; Del Buono, L; Hamon, O; John, M J J; Leruste, P; Malcles, J; Ocariz, J; Pivk, M; Roos, L; T'Jampens, S; Therin, G; Manfredi, P F; Re, V; Behera, P K; Gladney, L; Guo, Q H; Panetta, J; Anulli, F; Biasini, M; Peruzzi, I M; Pioppi, M; Angelini, C; Batignani, G; Bettarini, S; Bondioli, M; Bucci, F; Calderini, G; Carpinelli, M; Forti, F; Giorgi, M A; Lusiani, A; Marchiori, G; Martínez-Vidal, F; Neri, N; Paoloni, E; Rama, M; Rizzo, G; Sandrelli, F; Walsh, J; Haire, M; Judd, D; Paick, K; Wagoner, D E; Danielson, N; Elmer, P; Lau, Y P; Lü, C; Miftakov, V; Olsen, J; Smith, A J S; Telnov, A V; Bellini, F; Cavoto, G; Faccini, R; Ferrarotto, F; Ferroni, F; Gaspero, M; Li Gioi, L; Mazzoni, M A; Morganti, S; Pierini, M; Piredda, G; Safai-Tehrani, F; Voena, C; Christ, S; Wagner, G; Waldi, R; Adye, T; De Groot, N; Franek, B J; Geddes, N I; Gopal, G P; Olaiya, E O; Aleksan, Roy; Emery, S; Gaidot, A; Ganzhur, S F; Giraud, P F; Hamel de Monchenault, G; Kozanecki, Witold; Langer, M; Legendre, M; London, G W; Mayer, B; Schott, G; Vasseur, G; Yéche, C; Zito, M; Purohit, M V; Weidemann, A W; Wilson, J R; Yumiceva, F X; Aston, D; Bartoldus, R; Berger, N; Boyarski, A M; Buchmüller, O L; Claus, R; Convery, M R; Cristinziani, M; De Nardo, Gallieno; Dong, D; Dorfan, J; Dujmic, D; Dunwoodie, W M; Elsen, E E; Fan, S; Field, R C; Glanzman, T; Gowdy, S J; Hadig, T; Halyo, V; Hast, C; Hrynóva, T; Innes, W R; Kelsey, M H; Kim, P; Kocian, M L; Leith, D W G S; Libby, J; Luitz, S; Lüth, V; Lynch, H L; Marsiske, H; Messner, R; Müller, D R; O'Grady, C P; Ozcan, V E; Perazzo, A; Perl, M; Petrak, S; Ratcliff, B N; Roodman, A; Salnikov, A A; Schindler, R H; Schwiening, J; Simi, G; Snyder, A; Soha, A; Stelzer, J; Su, D; Sullivan, M K; Vavra, J; Wagner, S R; Weaver, M; Weinstein, A J R; Wisniewski, W J; Wittgen, M; Wright, D H; Yarritu, A K; Young, C C; Burchat, Patricia R; Edwards, A J; Meyer, T I; Petersen, B A; Roat, C; Ahmed, S; Alam, M S; Ernst, J A; Saeed, M A; Saleem, M; Wappler, F R; Bugg, W; Krishnamurthy, M; Spanier, S M; Eckmann, R; Kim, H; Ritchie, J L; Satpathy, A; Schwitters, R F; Izen, J M; Kitayama, I; Lou, X C; Ye, S; Bianchi, F; Bóna, M; Gallo, F; Gamba, D; Borean, C; Bosisio, L; Cartaro, C; Cossutti, F; Della Ricca, G; Dittongo, S; Grancagnolo, S; Lanceri, L; Poropat, P; Vuagnin, G; Panvini, R S; Banerjee, Sw; Brown, C M; Fortin, D; Jackson, P D; Kowalewski, R V; Roney, J M; Sobie, R J; Band, H R; Dasu, S; Datta, M; Eichenbaum, A M; Graham, M; Hollar, J J; Johnson, J R; Kutter, P E; Li, H; Liu, R; Mihályi, A; Mohapatra, A K; Pan, Y; Prepost, R; Rubin, A E; Sekula, S J; Tan, P; Von Wimmersperg-Töller, J H; Wu, J; Wu, S L; Yu, Z; Greene, M G; Neal, H
2004-01-01
We present results on $B\\to J/\\psi\\xspace K\\pi$ decays using $e^+e^-$ annihilation data collected with the BABAR detector at the $\\Upsilon(4S)$ resonance. The detector is located at the PEP-II asymmetric-energy storage ring facility at the Stanford Linear Accelerator Center. Using approximately 88 million $B\\bar{B}$ pairs, we measure the decay amplitudes for the flavor eigenmodes and observe strong-phase differences indicative of final-state interactions with a significance of 7.6 standard deviations. We use the interference between the $K\\pi$ $S$-wave and $P$-wave amplitudes in the region of the $K^*(892)$ to resolve the ambiguity in the determination of these strong phases. We then perform an ambiguity-free measurement of $\\cos2\\beta$ using the angular and time-dependent asymmetry in $B\\to J/\\psi\\xspace K^{*0}(K_S^0\\pi^0$) dec With $\\sin 2 \\beta$ fixed at its measured value and $\\cos 2 \\beta$ treated as an in we find $\\cos 2\\beta=2.72_{-0.79}^{+0.50}\\mathrm{(stat)} \\pm 0.27\\mathrm{(syst)}$, de sign of $\\cos...
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.
Scintillator based beta batteries
Rensing, Noa M.; Tiernan, Timothy C.; Shirwadkar, Urmila; O'Dougherty, Patrick; Freed, Sara; Hawrami, Rastgo; Squillante, Michael R.
2013-05-01
Some long-term, remote applications do not have access to conventional harvestable energy in the form of solar radiation (or other ambient light), wind, environmental vibration, or wave motion. Radiation Monitoring Devices, Inc. (RMD) is carrying out research to address the most challenging applications that need power for many months or years and which have undependable or no access to environmental energy. Radioisotopes are an attractive candidate for this energy source, as they can offer a very high energy density combined with a long lifetime. Both large scale nuclear power plants and radiothermal generators are based on converting nuclear energy to heat, but do not scale well to small sizes. Furthermore, thermo-mechanical power plants depend on moving parts, and RTG's suffer from low efficiency. To address the need for compact nuclear power devices, RMD is developing a novel beta battery, in which the beta emissions from a radioisotope are converted to visible light in a scintillator and then the visible light is converted to electrical power in a photodiode. By incorporating 90Sr into the scintillator SrI2 and coupling the material to a wavelength-matched solar cell, we will create a scalable, compact power source capable of supplying milliwatts to several watts of power over a period of up to 30 years. We will present the latest results of radiation damage studies and materials processing development efforts, and discuss how these factors interact to set the operating life and energy density of the device.
Beta section Beta: biogeographical patterns of variation and taxonomy.
Letschert, J.P.W.
1993-01-01
In Chapter 1 an account is given of the historical subdivision of the genus Beta and its sections, and the relations of the sections are discussed. Emphasis is given to the taxonomic treatment of wild section Beta by various authors. The Linnaean names B. vulgaris L. and B. maritima L. are lectotypi
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.
Beta Function and Anomalous Dimensions
DEFF Research Database (Denmark)
Pica, Claudio; Sannino, Francesco
2011-01-01
We demonstrate that it is possible to determine the coefficients of an all-order beta function linear in the anomalous dimensions using as data the two-loop coefficients together with the first one of the anomalous dimensions which are universal. The beta function allows to determine the anomalous...
L. Zou
2006-01-01
The issue of 'best-beta' arises as soon as potential errors in the Sharpe-Lintner-Black capital asset pricing model (CAPM) are acknowledged. By incorporating a target variable into the investor preferences, this study derives a best-beta CAPM (BCAPM) that maintains the CAPM's theoretical appeal and
Energy Technology Data Exchange (ETDEWEB)
Rabiti, Cristian [Idaho National Lab. (INL), Idaho Falls, ID (United States); Alfonsi, Andrea [Idaho National Lab. (INL), Idaho Falls, ID (United States); Cogliati, Joshua Joseph [Idaho National Lab. (INL), Idaho Falls, ID (United States); Mandelli, Diego [Idaho National Lab. (INL), Idaho Falls, ID (United States); Kinoshita, Robert Arthur [Idaho National Lab. (INL), Idaho Falls, ID (United States); Wang, Congjian [Idaho National Lab. (INL), Idaho Falls, ID (United States); Maljovec, Daniel Patrick [Idaho National Lab. (INL), Idaho Falls, ID (United States); Talbot, Paul William [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2016-02-01
This documents the release of the Risk Analysis Virtual Environment (RAVEN) code. A description of the RAVEN code is provided, and discussion of the release process for the M2LW-16IN0704045 milestone. The RAVEN code is a generic software framework to perform parametric and probabilistic analysis based on the response of complex system codes. RAVEN is capable of investigating the system response as well as the input space using Monte Carlo, Grid, or Latin Hyper Cube sampling schemes, but its strength is focused toward system feature discovery, such as limit surfaces, separating regions of the input space leading to system failure, using dynamic supervised learning techniques. RAVEN has now increased in maturity enough for the Beta 1.0 release.
1984-01-01
The atmospheric backscatter coefficient, beta, measured with an airborne CO Laser Doppler Velocimeter (LDV) system operating in a continuous wave, focussed model is discussed. The Single Particle Mode (SPM) algorithm, was developed from concept through analysis of an extensive amount of data obtained with the system on board a NASA aircraft. The SPM algorithm is intended to be employed in situations where one particle at a time appears in the sensitive volume of the LDV. In addition to giving the backscatter coefficient, the SPM algorithm also produces as intermediate results the aerosol density and the aerosol backscatter cross section distribution. A second method, which measures only the atmospheric backscatter coefficient, is called the Volume Mode (VM) and was simultaneously employed. The results of these two methods differed by slightly less than an order of magnitude. The measurement uncertainties or other errors in the results of the two methods are examined.
International Nuclear Information System (INIS)
This documents the release of the Risk Analysis Virtual Environment (RAVEN) code. A description of the RAVEN code is provided, and discussion of the release process for the M2LW-16IN0704045 milestone. The RAVEN code is a generic software framework to perform parametric and probabilistic analysis based on the response of complex system codes. RAVEN is capable of investigating the system response as well as the input space using Monte Carlo, Grid, or Latin Hyper Cube sampling schemes, but its strength is focused toward system feature discovery, such as limit surfaces, separating regions of the input space leading to system failure, using dynamic supervised learning techniques. RAVEN has now increased in maturity enough for the Beta 1.0 release.
Beta Beams Implementation at CERN
Hansen, Christian
2011-01-01
Beta Beam,the concept of generating a pure and intense (anti) neutrino beam by letting accelerated radioactive ions beta decay in a storage ring, called Decay Ring (DR), is the base of one of the proposed next generation neutrino oscillation facilities, necessary for a complete study of the neutrino oscillation parameter space. Sensitivities of the unknown neutrino oscillation parameters depend on the Decay Ring's ion intensity and of it's duty factor (the filled ratio of the ring). Therefore efficient ion production, stripping, bunching, acceleration and storing are crucial sub-projects under study and development within the Beta Beam collaboration. Specifically the feasibility of these tasks as parts of a Beta Beam implementation at CERN will be discussed in this report. The positive impact of the large {\\theta}13 indications from T2K on the Beta Beam performance will also be discussed.
[Serum beta 2 microglobulin (beta 2M) following renal transplantation].
Pacheco-Silva, A; Nishida, S K; Silva, M S; Ramos, O L; Azjen, H; Pereira, A B
1994-01-01
Although there was an important improvement in graft and patient survival the last 10 years, graft rejection continues to be a major barrier to the success of renal transplantation. Identification of a laboratory test that could help to diagnose graft rejection would facilitate the management of renal transplanted patients. PURPOSE--To evaluate the utility of monitoring serum beta 2M in recently transplanted patients. METHODS--We daily determined serum beta 2M levels in 20 receptors of renal grafts (10 from living related and 10 from cadaveric donors) and compared them to their clinical and laboratory evolution. RESULTS--Eight patients who presented immediate good renal function following grafting and did not have rejection had a mean serum beta 2M of 3.7 mg/L on the 4th day post transplant. The sensitivity of the test for the diagnosis of acute rejection was 87.5%, but the specificity was only 46%. Patients who presented acute tubular necrosis (ATN) without rejection had a progressive decrease in their serum levels of beta 2M, while their serum creatinine changed as they were dialyzed. In contrast, patients with ATN and concomitance of acute rejection or CSA nephrotoxicity presented elevated beta 2M and creatinine serum levels. CONCLUSION--Daily monitoring of serum beta 2M does not improve the ability to diagnose acute rejection in patients with good renal function. However, serum beta 2M levels seemed to be useful in diagnosing acute rejection or CSA nephrotoxicity in patients with ATN.
Intuitionistic Fuzzy Generalized Beta Closed Mappings
D. Jayanthi
2014-01-01
In this paper we introduce intuitionistic fuzzy generalized beta closed mappings and intuitionistic fuzzy generalized beta open mappings. We investigate some of their properties. We also introduce intuitionistic fuzzy M-generalized beta closed mappings as well as intuitionistic fuzzy M-generalized beta open mappings. We provide the relation between intuitionistic fuzzy M-generalized beta closed mappings and intuitionistic fuzzy generalized beta closed mappings.
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...
Energy Technology Data Exchange (ETDEWEB)
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.
Effect of beta blockade and beta stimulation on stage fright.
Brantigan, C O; Brantigan, T A; Joseph, N
1982-01-01
Stage fright, physiologically the "fight or flight" reaction, is a disabling condition to the professional musician. Because it is mediated by the sympathetic nervous system, we have investigated the effects of beta blockade on musical performance with propranolol in a double blind fashion and the effects of beta stimulation using terbutaline. Stage fright symptoms were evaluated in two trials, which included a total of 29 subjects, by questionnaire and by the State Trai Anxiety Inventory. Quality of musical performance was evaluated by experienced music critics. Beta blockade eliminates the physical impediments to performance caused by stage fright and even eliminates the dry mouth so frequently encountered. The quality of musical performance as judged by experienced music critics is significantly improved. This effect is achieved without tranquilization. Beta stimulating drugs increase stage fright problems, and should be used in performing musicians only after consideration of the detrimental effects which they may have on musical performance. PMID:6120650
Experiments on double beta decay
Energy Technology Data Exchange (ETDEWEB)
Busto, J. [Neuchatel Univ. (Switzerland). Inst. de Physique
1996-11-01
The Double Beta Decay, and especially ({beta}{beta}){sub 0{nu}} mode, is an excellent test of Standard Model as well as of neutrino physics. From experimental point of view, a very large number of different techniques are or have been used increasing the sensitivity of this experiments quite a lot (the factor of 10{sup 4} in the last 20 years). In future, in spite of several difficulties, the sensitivity would be increased further, keeping the interest of this very important process. (author) 4 figs., 5 tabs., 21 refs.
Dosimetry of {beta} extensive sources; Dosimetria de fuentes {beta} extensas
Energy Technology Data Exchange (ETDEWEB)
Rojas C, E.L.; Lallena R, A.M. [Departamento de Fisica Moderna, Universidad de Granada, E-18071 Granada (Spain)
2002-07-01
In this work, we have been studied, making use of the Penelope Monte Carlo simulation code, the dosimetry of {beta} extensive sources in situations of spherical geometry including interfaces. These configurations are of interest in the treatment of the called cranealfaringyomes of some synovia leisure of knee and other problems of interest in medical physics. Therefore, its application can be extended toward problems of another areas with similar geometric situation and beta sources. (Author)
Beta-gamma discriminator circuit
International Nuclear Information System (INIS)
The major difficulty encountered in the determination of beta-ray dose in field conditions is generally the presence of a relatively high gamma-ray component. Conventional dosimetry instruments use a shield on the detector to estimate the gamma-ray component in comparison with the beta-ray component. More accurate dosimetry information can be obtained from the measured beta spectrum itself. At Los Alamos, a detector and discriminator circuit suitable for use in a portable spectrometer have been developed. This instrument will discriminate between gammas and betas in a mixed field. The portable package includes a 256-channel MCA which can be programmed to give a variety of outputs, including a spectral display, and may be programmed to read dose directly
Peginterferon Beta-1a Injection
... symptoms such as headaches, bone or muscle aches, fever, chills, and tiredness during your treatment with peginterferon beta- ... not go away: headache muscle or joint pain fever chills weakness Some side effects can be serious. If ...
The period ratio P_1/P_2 of torsional Alfv\\'en waves with steady flows in spicules
Ebadi, H; Farahani, S Vasheghani
2016-01-01
The aim here is to model the standing torsional oscillations in solar spicules in the presence of density stratification, magnetic field expansion, and steady flows. By implementing cylindrical geometry, the eigenfrequencies, eigenfunctions, and the period ratio P_1/P_2 of these waves is obtained for finite plasma-beta. The shifts created by the steady flow justifies the divergence of the observed period ratio for the first and second periods from the number 2.
Synthesis of Beta Pyridyl Carbinol Tartrate
Directory of Open Access Journals (Sweden)
S. K. Shukla
1968-04-01
Full Text Available A process for the synthesis of Beta pyridine carboxylic acid ethy1 ester starting from quinoline has been developed. Beta-pyridine carboxylic acid ethy1 ester on reduction with lithium aluminium hydride gave Beta-pyridy1 carbinol which on treatment tartaric acid yielded Beta-pyridy1 carbinol tartrate, a vaso dilator known in trade as "Ronicoltartrate".
Apollo applications of beta fiber glass
Naimer, J.
1971-01-01
The physical characteristics of Beta fiber glass are discussed. The application of Beta fiber glass for fireproofing the interior of spacecraft compartments is described. Tests to determine the flammability of Beta fiber glass are presented. The application of Beta fiber glass for commercial purposes is examined.
Vasodilatory mechanisms of beta receptor blockade.
Rath, Géraldine; Balligand, Jean-Luc; Dessy, Chantal
2012-01-01
Beta-blockers are widely prescribed for the treatment of a variety of cardiovascular pathologies. Compared to traditional beta-adrenergic antagonists, beta-blockers of the new generation exhibit ancillary properties such as vasodilation through different mechanisms. This translates into a more favorable hemodynamic profile. The relative affinities of beta-adrenoreceptor antagonists towards the three beta-adrenoreceptor isotypes matter for predicting their functional impact on vasomotor contro...
Tables of double beta decay data
Energy Technology Data Exchange (ETDEWEB)
Tretyak, V.I. [AN Ukrainskoj SSR, Kiev (Ukraine)]|[Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires; Zdesenko, Y.G. [AN Ukrainskoj SSR, Kiev (Ukraine)
1995-12-31
A compilation of experimental data on double beta decay is presented. The tables contain the most stringent known experimental limits or positive results of 2{beta} transitions of 69 natural nuclides to ground and excited states of daughter nuclei for different channels (2{beta}{sup -}; 2{beta}{sup +}; {epsilon}{beta}{sup +}; 2{epsilon}) and modes (0{nu}; 2{nu}; 0{nu}M) of decay. (authors). 189 refs., 9 figs., 3 tabs.
The GERDA experiment on 0{nu}{beta}{beta} decay
Energy Technology Data Exchange (ETDEWEB)
Freund, Kai [Eberhard Karls Universitaet Tuebingen (Germany); Collaboration: GERDA-Collaboration
2012-07-01
The Gerda (Germanium Detector Array) collaboration searches for the neutrinoless double beta decay (0{nu}{beta}{beta}) of {sup 76}Ge. The existence of this decay would give rise to the assumption that the neutrino is a Majorana particle, i.e. its own antiparticle. A measured half-life could be used to determine the effective neutrino mass and hence resolve the neutrino mass hierarchy problem. Germanium diodes, isotopically enriched in {sup 76}Ge, are used as both source and detector. Due to the low rate of this decay (T{sub 1/2}>10{sup 25} y), the experimental background must be reduced to a level of 10{sup -2}counts/(kg y keV) or better in the region around Q{sub {beta}{beta}}. To minimize background from cosmogenically produced secondary particles, a low Z shielding is employed. Thus, the naked diodes are operated in a liquid argon cryostat, which is surrounded by a water tank acting as both passive shield and active muon Cherenkov veto. Gerda started the commissioning runs in 2010 and in November 2011, the first phase of data taking with enriched detectors has begun. In this talk, the first year of the experiment is summarized.
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.
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.
In-trap decay spectroscopy for {beta}{beta} decays
Energy Technology Data Exchange (ETDEWEB)
Brunner, Thomas
2011-01-18
The presented work describes the implementation of a new technique to measure electron-capture (EC) branching ratios (BRs) of intermediate nuclei in {beta}{beta} decays. This technique has been developed at TRIUMF in Vancouver, Canada. It facilitates one of TRIUMF's Ion Traps for Atomic and Nuclear science (TITAN), the Electron Beam Ion Trap (EBIT) that is used as a spectroscopy Penning trap. Radioactive ions, produced at the radioactive isotope facility ISAC, are injected and stored in the spectroscopy Penning trap while their decays are observed. A key feature of this technique is the use of a strong magnetic field, required for trapping. It radially confines electrons from {beta} decays along the trap axis while X-rays, following an EC, are emitted isotropically. This provides spatial separation of X-ray and {beta} detection with almost no {beta}-induced background at the X-ray detector, allowing weak EC branches to be measured. Furthermore, the combination of several traps allows one to isobarically clean the sample prior to the in-trap decay spectroscopy measurement. This technique has been developed to measure ECBRs of transition nuclei in {beta}{beta} decays. Detailed knowledge of these electron capture branches is crucial for a better understanding of the underlying nuclear physics in {beta}{beta} decays. These branches are typically of the order of 10{sup -5} and therefore difficult to measure. Conventional measurements suffer from isobaric contamination and a dominating {beta} background at theX-ray detector. Additionally, X-rays are attenuated by the material where the radioactive sample is implanted. To overcome these limitations, the technique of in-trap decay spectroscopy has been developed. In this work, the EBIT was connected to the TITAN beam line and has been commissioned. Using the developed beam diagnostics, ions were injected into the Penning trap and systematic studies on injection and storage optimization were performed. Furthermore, Ge
A kinetic-MHD model for low frequency phenomena
International Nuclear Information System (INIS)
A hybrid kinetic-MHD model for describing low-frequency phenomena in high beta anisotropic plasmas that consist of two components: a low energy core component and an energetic component with low density. The kinetic-MHD model treats the low energy core component by magnetohydrodynamic (MHD) description, the energetic component by kinetic approach such as the gyrokinetic equation, and the coupling between the dynamics of these two components through plasma pressure in the momentum equation. The kinetic-MHD model optimizes both the physics contents and the theoretical efforts in studying low frequency MHD waves and transport phenomena in general magnetic field geometries, and can be easily modified to include the core plasma kinetic effects if necessary. It is applicable to any magnetized collisionless plasma system where the parallel electric field effects are negligibly small. In the linearized limit two coupled eigenmode equations for describing the coupling between the transverse Alfven type and the compressional Alfven type waves are derived. The eigenmode equations are identical to those derived from the full gyrokinetic equation in the low frequency limit and were previously analyzed both analytically nd numerically to obtain the eigenmode structure of the drift mirror instability which explains successfully the multi-satellite observation of antisymmetric field-aligned structure of the compressional magnetic field of Pc 5 waves in the magnetospheric ring current plasma. Finally, a quadratic form is derived to demonstrate the stability of the low-frequency transverse and compressional Alfven type instabilities in terms of the pressure anisotropy parameter τ and the magnetic field curvature-pressure gradient parameter. A procedure for determining the stability of a marginally stable MHD wave due to wave-particle resonances is also presented
A kinetic-MHD model for low frequency phenomena
Energy Technology Data Exchange (ETDEWEB)
Cheng, C.Z.
1991-07-01
A hybrid kinetic-MHD model for describing low-frequency phenomena in high beta anisotropic plasmas that consist of two components: a low energy core component and an energetic component with low density. The kinetic-MHD model treats the low energy core component by magnetohydrodynamic (MHD) description, the energetic component by kinetic approach such as the gyrokinetic equation, and the coupling between the dynamics of these two components through plasma pressure in the momentum equation. The kinetic-MHD model optimizes both the physics contents and the theoretical efforts in studying low frequency MHD waves and transport phenomena in general magnetic field geometries, and can be easily modified to include the core plasma kinetic effects if necessary. It is applicable to any magnetized collisionless plasma system where the parallel electric field effects are negligibly small. In the linearized limit two coupled eigenmode equations for describing the coupling between the transverse Alfven type and the compressional Alfven type waves are derived. The eigenmode equations are identical to those derived from the full gyrokinetic equation in the low frequency limit and were previously analyzed both analytically nd numerically to obtain the eigenmode structure of the drift mirror instability which explains successfully the multi-satellite observation of antisymmetric field-aligned structure of the compressional magnetic field of Pc 5 waves in the magnetospheric ring current plasma. Finally, a quadratic form is derived to demonstrate the stability of the low-frequency transverse and compressional Alfven type instabilities in terms of the pressure anisotropy parameter {tau} and the magnetic field curvature-pressure gradient parameter. A procedure for determining the stability of a marginally stable MHD wave due to wave-particle resonances is also presented.
The microbial oxidation of (-)-beta-pinene by Botrytis cinerea.
Farooq, Afgan; Choudhary, M Iqbal; Tahara, Satoshi; Rahman, Atta-ur; Başer, K Hüsnü Can; Demirci, Fatih
2002-01-01
(-)-beta-pinene, a flavor and fragrance monoterpene is an important constituent of essential oils of many aromatic plants. It was oxidized by a plant-pathogenic fungus, Botrytis cinerea to afford four metabolites characterized as (-)-6a-hydroxy-beta-pinene, (-)-4beta,5beta-dihydroxy-beta-pinene, (-)-2beta,3beta-dihydroxypinane, and (-)-4beta-hydroxy-beta-pinene-6-one by detailed spectroscopic studies along with other known metabolites.
Mechanism of inactivation of alanine racemase by beta, beta, beta-trifluoroalanine
International Nuclear Information System (INIS)
The alanine racemases are a group of PLP-dependent bacterial enzymes that catalyze the racemization of alanine, providing D-alanine for cell wall synthesis. Inactivation of the alanine racemases from the Gram-negative organism Salmonella typhimurium and Gram-positive organism Bacillus stearothermophilus with beta, beta, beta-trifluoroalanine has been studied. The inactivation occurs with the same rate constant as that for formation of a broad 460-490-nm chromophore. Loss of two fluoride ions per mole of inactivated enzyme and retention of [1-14C]trifluoroalanine label accompany inhibition, suggesting a monofluoro enzyme adduct. Partial denaturation (1 M guanidine) leads to rapid return of the initial 420-nm chromophore, followed by a slower (t1/2 approximately 30 min-1 h) loss of the fluoride ion and 14CO2 release. At this point, reduction by NaB3H4 and tryptic digestion yield a single radiolabeled peptide. Purification and sequencing of the peptide reveals that lysine-38 is covalently attached to the PLP cofactor. A mechanism for enzyme inactivation by trifluoroalanine is proposed and contrasted with earlier results on monohaloalanines, in which nucleophilic attack of released aminoacrylate on the PLP aldimine leads to enzyme inactivation. For trifluoroalanine inactivation, nucleophilic attack of lysine-38 on the electrophilic beta-difluoro-alpha, beta-unsaturated imine provides an alternative mode of inhibition for these enzymes
DEFF Research Database (Denmark)
Winther, Kenneth Lillelund; Steenstrup, Søren Resen
2016-01-01
Smart beta has become the flavor of the decade in the investment world with its low fees, easy access to rewarded risk premiums, and appearance of providing good investment results relative to both traditional passive benchmarks and actively managed funds. Although we consider it well documented......-documented smart beta risk premiums and still motivate active managers to avoid value traps, too highly priced small caps, defensives, etc. By constructing the equity portfolios of active managers that resemble the most widely used risk premiums, we show that the returns and risk-adjusted returns measures...
Leenders, RGG; Damen, EWP; Bijsterveld, EJA; Scheeren, HW; Houba, PHJ; van der Meulen-Muileman, IH; Boven, E; Haisma, HJ
1999-01-01
A series of anthracycline prodrugs containing an immolative spacer was synthesized for application in selective chemotherapy. The prodrugs having the general structure anthracycline-spacer-beta-glycoside were designed to be activated by beta-glucuronidase or beta-galactosidase. Prodrugs with -chloro
Constraining neutrinoless double beta decay
International Nuclear Information System (INIS)
A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.
DEFF Research Database (Denmark)
Heller, R Scott; Madsen, Ole D; Nielsen, Jens Høiriis
2013-01-01
The very modern Kyoto International Conference Center provided the site for the 8th workshop on Beta cells on April 23-26, 2013. The preceding workshops were held in Boston, USA (1991); Kyoto, Japan (1994); Helsingør, Denmark (1997); Helsinki, Finland (2003); El Perello, Spain (2006); Peebles...
Abstraction Mechanisms in the BETA Programming Language
DEFF Research Database (Denmark)
Kristensen, Bent Bruun; Madsen, Ole Lehrmann; Møller-Pedersen, Birger;
1983-01-01
The BETA programming language is developed as part of the BETA project. The purpose of this project is to develop concepts, constructs and tools in the field of programming and programming languages. BETA has been developed from 1975 on and the various stages of the language are documented in [BETA...... a]. The application area of BETA is programming of embedded as well as distributed computing systems. For this reason a major goal has been to develop constructs that may be efficiently implemented. Furthermore the BETA language is intended to have a few number of basic but general constructs....... It is then necessary that the abstraction mechanisms are powerful in order to define more specialized constructs. BETA is an object oriented language like SIMULA 67 ([SIMULA]) and SMALLTALK ([SMALLTALK]). By this is meant that a construct like the SIMULA class/subclass mechanism is fundamental in BETA. In contrast...
Neutron Beta Decay Studies with Nab
Baeßler, S; Alonzi, L P; Balascuta, S; Barrón-Palos, L; Bowman, J D; Bychkov, M A; Byrne, J; Calarco, J R; Chupp, T; Vianciolo, T V; Crawford, C; Frlež, E; Gericke, M T; Glück, F; Greene, G L; Grzywacz, R K; Gudkov, V; Harrison, D; Hersman, F W; Ito, T; Makela, M; Martin, J; McGaughey, P L; McGovern, S; Page, S; Penttilä, S I; Počanić, D; Rykaczewski, K P; Salas-Bacci, A; Tompkins, Z; Wagner, D; Wilburn, W S; Young, A R
2012-01-01
Precision measurements in neutron beta decay serve to determine the coupling constants of beta decay and allow for several stringent tests of the standard model. This paper discusses the design and the expected performance of the Nab spectrometer.
How Do Beta Blocker Drugs Affect Exercise?
... Stroke More How do beta blocker drugs affect exercise? Updated:Aug 5,2015 Beta blockers are a ... about them: Do they affect your ability to exercise? The answer can vary a great deal, depending ...
The beta subunit of casein kinase II
DEFF Research Database (Denmark)
Boldyreff, B; Piontek, K; Schmidt-Spaniol, I;
1991-01-01
cDNAs encoding the beta subunit of pig and mouse CKII were isolated. The porcine cDNA was expressed as a fusion protein in Escherichia coli and used for the production of anti-CKII-beta subunit specific antibodies.......cDNAs encoding the beta subunit of pig and mouse CKII were isolated. The porcine cDNA was expressed as a fusion protein in Escherichia coli and used for the production of anti-CKII-beta subunit specific antibodies....
Neoclassical transport in high [beta] tokamaks
Energy Technology Data Exchange (ETDEWEB)
Cowley, S.C.
1992-12-01
Neoclassical, transport in high [beta] large aspect ratio tokamaks is calculated. The variational method introduced by Rosenbluth, et al., is used to calculate the full Onsager matrix in the banana regime. These results are part of a continuing study of the high [beta] large aspect ratio equilibria introduced in Cowley, et al. All the neoclassical coefficients are reduced from their nominal low [beta] values by a factor ([var epsilon]/q[sup 2][beta])[sup [1/2
Beta measurements at Department of Energy facilities
International Nuclear Information System (INIS)
Pacific Northwest Laboratory performed a two-step process to characterize the current beta measurement practices at DOE facilities. PNL issued a survey questionnaire on beta measurement practices to DOE facilities and reported the results. PNL measured beta doses and spectra at seven selected DOE facilities and compared selected measurement techniques in the facility environment. This report documents the results of the radiation field measurements and the comparison of measurement techniques at the seven facilities. Data collected included beta dose and spectral measurements at seven DOE facilities that had high beta-to-gamma ratios (using a silicon surface barrier spectrometer, a plastic scintillator spectrometer, and a multielement beta dosimeter). Other dosimeters and survey meters representative of those used at DOE facilities or under development were also used for comparison. Field spectra were obtained under two distinct conditions. Silicon- and scintillation-based spectrometer systems were used under laboratory conditions where high beta-to-gamma dose ratios made the beta spectra easier to observe and analyze. In the second case, beta spectrometers were taken into actual production and maintenance areas of DOE facilities. Analyses of beta and gamma spectra showed that 234Th- /sup 234m/Pa, 231Th, 137Cs, and 90Sr/90Y were the major nuclides contributing to beta doses at the facilities visited. Beta doses from other fission products and 60Co were also measured, but the potential for exposure was less significant. 21 refs., 64 figs., 18 tabs
Measurement of the beta asymmetry in neutron beta decay
International Nuclear Information System (INIS)
Neutron beta decay is the simplest semi-leptonic weak decay and described accurately by the standard model using the first CKM-matrix element and the ratio of vector and axial vector couplings, λ. With more than a dozen observables it is a sensitive probe for investigating the nature of weak interaction and to search for physics beyond the standard model. In the past, measuring the beta asymmetry A in polarized neutron decay has been the most precise way of determining λ and nowadays it allows - together with other observables - to derive limits on non-standard model interactions, such as scalar and tensor couplings. The neutron decay spectrometer Perkeo III was installed at the PF1B cold neutron beam site at the Institut Laue-Langevin to measure the beta asymmetry. By using a pulsed beam combined with an improved detector design a significant reduction of several systematic uncertainties has been achieved compared to the predecessor, Perkeo II. In this talk recent results of the measurements with Perkeo III will be presented. In particular, we show the energy distribution of the electrons together with the calibration tools for the detectors.
Beta thalassaemia mutations in Turkish Cypriots.
Sozuoz, A; Berkalp, A; A. Figus; Loi, A; Pirastu, M.; Cao, A
1988-01-01
Using oligonucleotide hybridisation or restriction endonuclease analysis, we have characterised the molecular defect in 94 patients with thalassaemia major and four with thalassaemia intermedia of Turkish Cypriot descent. We found that four mutations, namely beta+ IVS-1 nt 110, beta zero IVS-1 nt, beta+ IVS-1 nt 6, and beta+ IVS-2 nt 745 were prevalent, accounting for 69.9%, 11.7%, 8.7%, and 5.6% respectively of the beta thalassaemia chromosomes. This information may help in the organisation ...
Richardson, Thomas; Lehnert, Matt
2013-01-01
The inner profile of Dark Matter (DM) halos remains one of the central problems in small-scale cosmology. At present, the problem can not be resolved in dwarf spheroidal galaxies due to a degeneracy between the DM profile and the velocity anisotropy beta of the stellar population. We discuss a method which can break the degeneracy by exploiting 3D positions and 1D line-of-sight (LOS) velocities. With the full 3D spatial information, we can determine precisely what fraction of each stars LOS motion is in the radial and tangential direction. This enables us to infer the anisotropy parameter beta directly from the data. The method is particularly effective if the galaxy is highly anisotropic. Finally, we argue that such a test could be applied to Sagittarius and potentially other dwarfs with RR Lyrae providing the necessary depth information.
International Nuclear Information System (INIS)
The measurement of the shape of the first forbidden beta transition of 185W is interesting from the point of view of the fact that this nucleus belongs to the deformed region 150185W is carried out employing an optimized Siegbahn-Slatis beta ray spectrometer and the result is compared with the theoretical shape factor incorporating Nilsson's wavefunctions using Simms formalism. The experimental shape factor is fitted to the correction factor C(W)=k(1+aW) with α=0.0026+-0.0432. The theoretical shape factor computed following the matrix elements due to Nilsson model is in good agreement with the present experimental shape factor. The value Λ(2.358) computed in the present measurement in the light of Nilsson model matrix elements of 185W is in agreement with the predicted value (2.4) of J.J. Fujita. (author)
Review of double beta experiments
Sarazin, X.
2012-01-01
C13-10-22.1 International audience This paper gives a review of the double beta experimental techniques and projects, in the search for the Majorana neutrino. The purpose of this review is to detail, for each technique, the different origins of background, how they can be identified, and how they can be reduced. Advantages and limitations of the different techniques are discussed. 1. Introduction The neutrino is one of the most puzzling elementary particle with very unique properties. I...
Myokardinfarkt und Beta-Blocker
Directory of Open Access Journals (Sweden)
Stühlinger H-G
2003-01-01
Full Text Available Im Rahmen eines akuten koronaren Syndroms (akuter Herzinfarkt, Angina pectoris kommt es, aufgrund eines Ungleichgewichtes zwischen Angebot und Bedarf, zu einem akuten Mangel an Sauerstoff im Herzmuskel. Ursache ist eine reduzierte Sauerstoffzufuhr durch verengte bzw. verschlossene Gefäße. Bis zur Behebung der Ursache vergehen oft mehrere Stunden. In dieser Phase muß - durch Verminderung des Sauerstoffbedarfs im Herzmuskel - eine Verlangsamung der Nekroseentwicklung erreicht werden. Das Ausmaß der Nekrose wird reduziert, somit die für die Langzeitprognose wichtige Linksventrikelfunktion verbessert. Eine Verminderung des Sauerstoffbedarfs erreicht man durch kontrollierte Frequenzsenkung mittels intravenöser Beta-Blockade. In optimaler Weise wird diese Methode durch die Anwendung eines kardioselektiven Beta-Blockers mit kurzer Halbwertszeit durchgeführt. Beta-Blocker haben nicht nur auf die Nekroseentwicklung, sondern auch auf die Inzidenz von Rhythmusstörungen - besonders in der Akutphase - Auswirkungen. Vor allem die mit dieser therapeutischen Maßnahme verbundene Reduktion von Kammerflimmern ist von großer Bedeutung.
Lifescience Database Archive (English)
Full Text Available 17913496 Immunoreceptor-like signaling by beta 2 and beta 3 integrins. Jakus Z, Fod...) Show Immunoreceptor-like signaling by beta 2 and beta 3 integrins. PubmedID 17913496 Title Immunoreceptor-like signaling by beta... 2 and beta 3 integrins. Authors Jakus Z, Fodor S, Abram CL
Oran, R; van der Holst, B; Sokolov, I V; Gombosi, T I
2014-01-01
In the present work, we test the predictions of the AWSoM model, a global extended-MHD model capable of calculating the propagation and turbulent dissipation of Alfv\\'en waves in any magnetic topology, against high resolution spectra of the quiescent off-disk solar corona. Wave dissipation is the only heating mechanism assumed in this model. Combining 3D model results with the CHIANTI atomic database, we were able to create synthetic line-of-sight spectra which include the effects of emission line broadening due to both thermal and wave-related non-thermal motions. To the best of our knowledge this is the first time a global model is used to obtain synthetic non-thermal line broadening. We obtained a steady-state solution driven by a synoptic magnetogram and compared the synthetic spectra with SUMER observations of a quiescent area above the solar west limb extending between 1.04 and 1.34 solar radii at the equator. Both the predicted line widths and the total line fluxes were consistent with the observations...
Beta-dosimetry studies at LLNL
International Nuclear Information System (INIS)
This paper summarizes three beta-dosimetry studies made recently at the Lawrence Livermore National Laboratory. The first study was to determine the beta-gamma exposure rates at the Los Alamos Godiva IV Critical Assembly. The beta spectra from the assembly were evaluated using absorption curves and the beta-gamma dose-rate ratios were determined at various distances from the assembly. A comparison was made of the doses determined using two types of TLD personnel dosimeters and a film badge. The readings of an Eberline RO-7 instrument and the dose rates determined by TLDs were compared. Shielding provided by various metals, gloves, and clothing were measured. The second study was to determine the beta energy response of the Eberline RO-7 instrument based on measurements made with the PTB beta sources. This study required additional calibration points for the PTB sources which were made using extrapolation chamber measurements. The third study resulted in two techniques to determine the beta energy (E/sub max/) from the readings of this-window portable survey instruments. Both techniques are based on the readings obtained using aluminium filters. One technique is for field application, requires one filter, and provides a quick estimate of the beta energy in three energy groups: 1.5 MeV. The second technique is more complex requiring measurements with two or three filters, but gives the beta energy and the approximate shape of the beta spectrum. 9 references, 6 figures
General Description of Ideal Tokamak MHD Instability Ⅱ
Institute of Scientific and Technical Information of China (English)
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.
This chapter covers the use of wild beets in sugar beet improvement, including the basic botany of the species, its distribution; geographical locations of genetic diversity; morphology; cytology and karyotype; genome size; taxonomic position; agricultural status (model plant/weeds/invasive species/...
Alpha particle destabilization of the TAE modes
International Nuclear Information System (INIS)
The high frequency, low mode number toroidicity-induced Alfven eigenmodes (TAE) are shown to be driven unstable by the circulating and/or trapped α-particles through the wave-particle resonances. For a poloidal harmonic to satisfy the resonance condition it requires that the α-particle birth speed vα ≥ vA/(2|m-nq|), where vA is the Alfven speed, m is the poloidal mode number, and n is the toroidal mode number. To destabilize the TAE modes, the inverse Landau damping associated with the α-particle pressure gradient free energy must overcome the velocity space Landau damping due to both the slowing-down α-particle and the core Maxwellian electron and ion distributions. Stability criteria in terms of the α-particle beta βα, α-particle pressure gradient parameter (ω*/ωA) (ω* is the α-particle diamagnetic drift frequency), and (vα/vA) parameters are presented for TFTR, CIT, and ITER tokamaks. The volume averaged α-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume averaged α-particle beta threshold is in the order of 10-4 if the continuum damping effect is absent. Typical growth rates of the n = 1 TAE mode can be in the order of 10-2ωA, where ωA = vA/qR. Stability of higher n TAE modes is also studied. Other types of global Alfven waves are stable due to sideband mode continuum damping resulting from toroidal coupling effects. If the Alfven continuum gap does not exist across the whole minor radius, continuum damping exists for some poloidal harmonics. The continuum damping effect is studied by employing both a resistive MHD stability code (NOVA-R) and an analytical matching method, and the results are presented. 1 ref
Philip, A; Bostedt, L; Stigbrand, T; O'Connor-McCourt, M D
1994-04-15
Pregnancy zone protein (PZP) is quantitatively the most important pregnancy-associated plasma protein and it has strong similarity to alpha 2-macroglobulin. Since alpha 2-macroglobulin is a binding protein for transforming growth factors-beta (TGF-beta), it was of interest to test whether the related protein, PZP, also binds to these growth-regulatory proteins. Using affinity-labelling methods, we demonstrate that PZP binds both TGF-beta 1 and TGF-beta 2 and that the binding characteristics are similar to those of the TGF-beta-alpha 2-macroglobulin interaction. TGF-beta 2 and TGF-beta 1 bind to PZP in a predominantly noncovalent manner in vitro. TGF-beta 1 and TGF-beta 2 bind to both the dimeric and tetrameric forms of PZP. Our studies also indicate that PZP binds TGF-beta 2 with higher affinity than TGF-beta 1. Finally, we demonstrate that PZP inhibits the binding of TGF-beta 1 and TGF-beta 2 to their cell surface receptors. The increased level of PZP during pregnancy may affect the action of TGF-beta by regulating the distribution, clearance and/or general availability of TGF-beta. The preferential binding of TGF-beta 2 over TGF-beta 1 by PZP implies that PZP may differentially regulate the action of TGF-beta 1 and TGF-beta 2.
On gaps in Rényi $\\beta$-expansions of unity for $\\beta > 1$ an algebraic number.
Verger-Gaugry, Jean-Louis
2006-01-01
Let $\\beta> 1$ be an algebraic number. We study the strings of zeros (“gaps”) in the Rényi $\\beta$ -expansion $d_{\\beta}(1)$ of unity which controls the set $\\mathbb{Z}_{\\beta}$ of $\\beta$-integers. Using a version of Liouville's inequality which extends Mahler's and Güting's approximation theorems, the strings of zeros in $d_{\\beta}(1)$ are shown to exhibit a “gappiness” asymptotically bounded above by $log(M(\\beta ))/ log(\\beta)$, where $M(\\beta)$ is the Mahler measure of $\\beta$ . The proo...
Resistance training & beta-hydroxy-beta-methylbutyrate supplementation on hormones
Directory of Open Access Journals (Sweden)
Hamid Arazi
2015-10-01
Full Text Available RESUMOIntroduction:In recent years, there was an increased interest on the effects of beta-hydroxy-beta-methylbutyrate (HMB supplementation on skeletal muscle due to its anti-catabolic effects.Objectives:To investigate the effect of HMB supplementation on body composition, muscular strength and anabolic-catabolic hormones after resistance training.Methods:Twenty amateur male athletes were randomly assigned to supplement and control groups in a double-blind crossover design and participated in four weeks resistance training. Before and after the test period fasting blood samples were obtained to determine anabolic (the growth hormone and testosterone and catabolic (cortisol hormones, and fat mass, lean body mass (LBM and muscular strength were measured. Dependent and independent t-tests were used to analyze data.Results:After the training period, there were no significant differen-ces between the groups with respect to fat mass, LBM and anabolic-catabolic hormones. HMB supplementation resulted in a significantly greater strength gain (p≤0.05.Conclusion:Greater increase in strength for HMB group was not accompanied by body composition and basal circulating anabolic-catabolic hormonal changes. It seems that HMB supplementation may have beneficial effects on neurological adaptations of strength gain.
GSK3beta is involved in JNK2-mediated beta-catenin inhibition.
Directory of Open Access Journals (Sweden)
Dong Hu
Full Text Available BACKGROUND: We have recently reported that mitogen-activated protein kinase (MAPK JNK1 downregulates beta-catenin signaling and plays a critical role in regulating intestinal homeostasis and in suppressing tumor formation. This study was designed to determine whether JNK2, another MAPK, has similar and/or different functions in the regulation of beta-catenin signaling. METHODOLOGY AND PRINCIPAL FINDINGS: We used an in vitro system with manipulation of JNK2 and beta-catenin expression and found that activated JNK2 increased GSK3beta activity and inhibited beta-catenin expression and transcriptional activity. However, JNK2-mediated downregulation of beta-catenin was blocked by the proteasome inhibitor MG132 and GSK3beta inhibitor lithium chloride. Moreover, targeted mutations at GSK3beta phosphorylation sites (Ser33 and Ser37 of beta-catenin abrogated JNK2-mediated suppression of beta-catenin. In vivo studies further revealed that JNK2 deficiency led to upregulation of beta-catenin and increase of GSK3-beta phosphorylation in JNK2-/- mouse intestinal epithelial cells. Additionally, physical interaction and co-localization among JNK2, beta-catenin and GSK3beta were observed by immunoprecipitation, mammalian two-hybridization assay and confocal microscopy, respectively. CONCLUSION AND SIGNIFICANCE: In general, our data suggested that JNK2, like JNK1, interacts with and suppresses beta-catenin signaling in vitro and in vivo, in which GSK3beta plays a key role, although previous studies have shown distinct functions of JNK1 and JNK2. Our study also provides a novel insight into the crosstalk between Wnt/beta-catenin and MAPK JNKs signaling.
Scriver, C R; Pueschel, S; Davies, E
1966-03-24
Hyper-beta-alaninemia was found in a somnolent, convulsing infant. Hyper-beta-aminoaciduria (beta-ala, betaAIB and taurine) was also observed, varying directly with plasma beta-alanine concentration. The beta-aminoaciduria is explained by the interaction between beta-alanine and a specific cellular-transport system with preference for beta-amino compounds. Gamma-aminobutyricaciduria was also observed, its excretion being independent of beta-alanine levels. Dietary modifications, pyridoxine, pantothenic acid and antibiotic therapy were not beneficial. Post-mortem tissues had elevated levels of beta-alanine and carnosine; GABA levels in brain were probably elevated for the age of the patient. A proposed block in beta-alanine-alpha-ketoglutarate transaminase would expand the free beta-alanine pool, thus increasing tissue carnosine. beta-Alanine is a central-nervous-system depressant. Associated inhibition of GABA transaminase and displacement of GABA from central-nervous-system binding sites would produce GABAuria and convulsions. PMID:17926374
Beta-2-mikroglobulin ved medicinske sygdomme
DEFF Research Database (Denmark)
Hansen, P B; Olsen, Niels Vidiendal
1989-01-01
Beta-2-microglobulin (beta 2M) is a low-molecular protein which is filtered freely over the glomeruli. Under normal circumstances, more than 99.9% is resorbed in the proximal tubuli of the kidneys and is metabolized there. In renal disease with damage to this segment of the nephron, eg acute tubulo......-interstitial nephropathy, increased quantities of beta 2M are excreted in the urine. If the rate of glomerular filtration is reduced, serum-beta 2M is increased and this is also the case in persons with increased cell division despite normal renal function. Serum-beta 2M is, therefore, raised in numerous malignant...... diseases and reflects the size of the tumour mass. During cytostatic treatment of myelomatosis and chronic lymphatic leukaemia, the serum-beta 2M levels decrease on remission and increase on relapse. In acute leukaemia and malignant lymphoma with infiltration of the CNS, similar conditions prevail for CSF...
Hypersomnolence with beta-adrenergic blockers.
Thachil, J; Zeller, J R; Kochar, M S
1987-11-01
An elderly, mildly demented, hypertensive male patient developed hypersomnolence on administration of propranolol for treatment of hypertension; no other cause for hypersomnolence was detected. Upon replacement of propranolol with atenolol, he felt better but continued to be quite somnolent. When atenolol was discontinued, he reported to have lack of sleep. On readministration of subtherapeutic doses of the same beta-adrenergic blocking agents, he once again experienced excessive sleepiness. By discontinuing beta-blocking agents and introducing captopril, he felt much better, became pleasant and talkative, and blood pressure was well controlled. Beta antagonists are important drugs in the management of many cardiovascular problems. Propranolol, a lipophilic beta-blocking agent, and atenolol, a hydrophilic beta-blocking agent, are two of the major agents currently used clinically in the United States. Numerous neuropsychiatric side-effects of the beta-adrenergic blocking drugs have been reported, but hypersomnolence is not readily recognized as one of them. PMID:3665616
Beta blockers: A new role in chemotherapy
Nagaraja, Archana S; Sadaoui, Nouara C.; Lutgendorf, Susan K.; Ramondetta, Lois M.; Sood, Anil K
2013-01-01
Beta-blockers are a class of drugs widely used to treat cardiac, respiratory and other ailments. They act by blocking beta-adrenergic receptor–mediated signalling. Studies in various cancers have shown that patients taking a beta-blocker have higher survival and lower recurrence and metastasis rates. This is supported by several preclinical and in vitro studies showing that adrenergic activation modulates apoptosis, promotes angiogenesis and other cancer hallmarks, and these effects can be ab...
The pancreatic beta cell surface proteome
Stützer, I.; Esterházy, D.; Stoffel, M.
2012-01-01
The pancreatic beta cell is responsible for maintaining normoglycaemia by secreting an appropriate amount of insulin according to blood glucose levels. The accurate sensing of the beta cell extracellular environment is therefore crucial to this endocrine function and is transmitted via its cell surface proteome. Various surface proteins that mediate or affect beta cell endocrine function have been identified, including growth factor and cytokine receptors, transporters, ion channels and prote...
Constructions for a bivariate beta distribution
Olkin, Ingram; Trikalinos, Thomas A.
2014-01-01
The beta distribution is a basic distribution serving several purposes. It is used to model data, and also, as a more flexible version of the uniform distribution, it serves as a prior distribution for a binomial probability. The bivariate beta distribution plays a similar role for two probabilities that have a bivariate binomial distribution. We provide a new multivariate distribution with beta marginal distributions, positive probability over the unit square, and correlations over the full ...
Milk Intolerance, Beta-Casein and Lactose
Sebely Pal; Keith Woodford; Sonja Kukuljan; Suleen Ho
2015-01-01
True lactose intolerance (symptoms stemming from lactose malabsorption) is less common than is widely perceived, and should be viewed as just one potential cause of cows’ milk intolerance. There is increasing evidence that A1 beta-casein, a protein produced by a major proportion of European-origin cattle but not purebred Asian or African cattle, is also associated with cows’ milk intolerance. In humans, digestion of bovine A1 beta-casein, but not the alternative A2 beta-casein, releases beta-...
Milk Intolerance, Beta-Casein and Lactose
Directory of Open Access Journals (Sweden)
Sebely Pal
2015-08-01
Full Text Available True lactose intolerance (symptoms stemming from lactose malabsorption is less common than is widely perceived, and should be viewed as just one potential cause of cows’ milk intolerance. There is increasing evidence that A1 beta-casein, a protein produced by a major proportion of European-origin cattle but not purebred Asian or African cattle, is also associated with cows’ milk intolerance. In humans, digestion of bovine A1 beta-casein, but not the alternative A2 beta-casein, releases beta-casomorphin-7, which activates μ-opioid receptors expressed throughout the gastrointestinal tract and body. Studies in rodents show that milk containing A1 beta-casein significantly increases gastrointestinal transit time, production of dipeptidyl peptidase-4 and the inflammatory marker myeloperoxidase compared with milk containing A2 beta-casein. Co-administration of the opioid receptor antagonist naloxone blocks the myeloperoxidase and gastrointestinal motility effects, indicating opioid signaling pathway involvement. In humans, a double-blind, randomized cross-over study showed that participants consuming A1 beta-casein type cows’ milk experienced statistically significantly higher Bristol stool values compared with those receiving A2 beta-casein milk. Additionally, a statistically significant positive association between abdominal pain and stool consistency was observed when participants consumed the A1 but not the A2 diet. Further studies of the role of A1 beta-casein in milk intolerance are needed.
Energy Technology Data Exchange (ETDEWEB)
Lee, Sang Hoo; Yi, Dong Heui; Jung, Seun Ho [Konkuk University, Seoul (Korea, Republic of)
2004-02-15
{beta}-CD and CM-{beta}-CD as chiral NMR shift agents were used to resolve the enantiomers of noradrenaline (NA). The stoichiometry of each complex formed between the CDs and the enantiomers of NA was found to be 1 : 1 through the continuous variation plots. The binding constants (K) of the complexes were determined from 1H NMR titration curves. This result indicated that both {beta}-CD and CM-{beta}-CD formed the complexes with the S (+)-NA more preferentially than its R(.)-enantiomer. The K values for the complexes with {beta}-CD (KS(+) = 537 M{sup -1} and K{sub R}({sub -}) = 516 M{sup -1}) was larger than those with CM-{beta}-CD (K{sub S}({sub +}) = 435 M{sup -1} and K{sub R}({sub -}) = 313 M{sup -1}), however, enantioselectivity ({alpha}) of S({sub +})- and R(-)-NA to CM-{beta}-CD ({alpha} = 1.38) was larger than that to {beta}-CD ({alpha} = 1.04), indicating that CM-{beta}-CD was the better chiral NMR solvating agents for the recognition of the enantiomers of NA. Two dimensional rotating frame nuclear Overhauser enhancement spectroscopy (ROESY) experiments were also performed to explain the binding properties in terms of spatial fitting of the NA molecule into the macrocyclic cavities
Review of double beta experiments
Sarazin, Xavier
2012-01-01
This paper is the first part of the manuscript written in April 2012 for my academic Accreditation to supervise research. It offers a review of the double beta experimental techniques. My purpose is to detail, for each technique, the different origins of background, how they can be identified, and how they can be reduced. Advantages and limitations are discussed. This review is organized as follows. First, the question of the possible Majorana nature for the neutrino is presented and the physic of neutrinoless double beta decay is summarized. Then I begin by presenting the tracko-calo NEMO-3 and SuperNEMO experiments. I've worked on these two experiments since 15 years. So it was natural to start with them with a relatively more exhaustive description. I will then present the germanium technique. I will then review the bolometer technique. I will describe in detail the recent progress in scintillating bolometers because I think that it is one of the most promising techniques. Finally I will review the large l...
Beta attenuation transmission system (BATS)
Energy Technology Data Exchange (ETDEWEB)
Hagan, R.C.; Fullbright, H.J.
1977-01-01
The beta attenuation transmission system (BATS) is an automated radiation gauge designed for quantitative measurement of component thickness in explosive detonators. The BATS was designed and built by Group M-1, the Nondestructive Testing Group, of the Los Alamos Scientific Laboratory to measure the areal thickness, in mg/cm/sup 2/, of a cylinder of high explosive (HE) enclosed within a plastic holder. The problem is to determine the density of the HE. A /sup 90/Sr source is collimated by a 0.25 x 1.59-mm slit, and the transmitted beta-particle flux is detected by a plastic scintillator, coupled to a photomultiplier tube. The detonator is transported through the radiation beam by a leadscrew, ballnut, stepping-motor combination. Continuous analog position data are available, derived from the output from a linear-actuated potentiometer attached to the scanner. A linear electrometer amplifies the detected signal, which is then integrated for a preselected time, to obtain the desired statistical accuracy. A microprocessor (..mu..P) is used to control the scanner position and to make the data readings at the assigned positions. The data are stored, and, at the completion of the scan, are processed into the desired format. The final answer is displayed to the operator or output to a peripheral device for permanent record. The characteristics of the radiation source, the collimator, the signal detection and conditioning, and the final results are described in detail. The scanner and the microprocessor control system are briefly outlined.
Challenges in Double Beta Decay
Directory of Open Access Journals (Sweden)
Oliviero Cremonesi
2014-01-01
Full Text Available In the past ten years, neutrino oscillation experiments have provided the incontrovertible evidence that neutrinos mix and have finite masses. These results represent the strongest demonstration that the electroweak Standard Model is incomplete and that new Physics beyond it must exist. In this scenario, a unique role is played by the Neutrinoless Double Beta Decay searches which can probe lepton number conservation and investigate the Dirac/Majorana nature of the neutrinos and their absolute mass scale (hierarchy problem with unprecedented sensitivity. Today Neutrinoless Double Beta Decay faces a new era where large-scale experiments with a sensitivity approaching the so-called degenerate-hierarchy region are nearly ready to start and where the challenge for the next future is the construction of detectors characterized by a tonne-scale size and an incredibly low background. A number of new proposed projects took up this challenge. These are based either on large expansions of the present experiments or on new ideas to improve the technical performance and/or reduce the background contributions. In this paper, a review of the most relevant ongoing experiments is given. The most relevant parameters contributing to the experimental sensitivity are discussed and a critical comparison of the future projects is proposed.
Cianetti, L; Care, A; Sposi, N M; Giampaolo, A; Calandrini, M; Petrini, M.; Massa, A.; Marinucci, M.; Mavilio, F; Ceccanti, M.
1984-01-01
An Italian family in which heterocellular hereditary persistence of fetal haemoglobin (HPFH) interacts with both beta(+)- and delta beta-thalassaemia is described. The index case was an 8 year old girl who was presumed to inherit both heterocellular HPFH and beta (+)-thalassaemia from her mother and delta beta-thalassaemia from her father. She was healthy and never needed blood transfusions. The possible contribution of heterocellular HPFH to the less severe expression of the compound delta b...
The impact of beta-elemene on beta-tubulin of human hepatoma hepg2 cells
Institute of Scientific and Technical Information of China (English)
Yuqiu Mao; Liying Ban; Jielin Zhang; Li Hou; Xiaonan Cui
2014-01-01
Objective:The aim of this study was to investigate the impact of beta-elemene injection on the growth and beta-tubulin of human hepatocarcinoma HepG2 cells. Methods:cellproliferation was assessed by MTT assay. cellcycle distribution was detected by flow cytometry (FCM). The mRNA expression of beta-tubulin was measured by RT-PCR. West-ern blot analysis was used to determine protein expression of beta-tubulin and the polymerization of beta-tubulin. Results:Beta-elemene injection inhibited HepG2 cells proliferation in a dose-and time-dependent manner;FCM analysis indicated beta-elemene injection induced cellcycle arrested at S phase. RT-PCR and western-blot analysis showed that beta-elemene injection down-regulated beta-tubulin expression at both mRNA and protein levels, presenting a dose-dependent manner. Moreover, beta-elemene injection reduced the polymerization of microtubules in a dose-dependent manner. Conclusion:Beta-elemene injection can inhibit the proliferation of hepatoma HepG2 cells, the mechanism might be partly related to the down-regulation of beta-tubulin and inhibition of microtubular polymerization.
Expressions of GSK-3beta, Beta-Catenin and PPAR-Gamma in Medulloblastoma
Institute of Scientific and Technical Information of China (English)
Xiong Zhang; Lu Si; Yu Li; Can Mi
2009-01-01
Objective: To investigate the expressions of GSK-3beta, Beta-catenin and PPAR-gamma, and their relationship in medulloblastoma, and to explore their value in clinic application.Methods: Immunohistochemical staining with SP method was conducted to determine the expressions of GSK-3beta, Beta-catenin and PPAR-gamma in 48 cases of medulloblastoma and 10 normal cerebellar tissues.Results: The rate of abnormal expressions of beta-catenin and PPAR-gamma in MB was higher than that in normal. Conversely, GSK-3beta in MB was lower than that in the normal (P<0.05). Furthermore, in medulloblastoma, beta-catenin and GSK-3beta showed a negative correlation, PPAR-gamma and beta-catenin had a positive correlation.Conclusion: Abnormal expression of beta-catenin plays a crucial role in the development of medulloblastoma. Meanwhile, PPAR-gamma and GSK-3beta which are tightly related with beta-catenin are both involved in the genesis and development of medulloblastoma.
The pharmacokinetics of beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin in the rat
Frijlink, H W; Visser, J; Hefting, N R; Oosting, R; Meijer, D K; Lerk, C F
1990-01-01
Hydroxypropyl-beta-cyclodextrin was analyzed by HPLC using postcolumn complexation with phenolphthalein and negative colorimetric detection, with a detection limit of 20 micrograms/ml. The pharmacokinetics of beta-cyclodextrin and of hydroxypropyl-beta-cyclodextrin were studied after intravenous adm
Energy Technology Data Exchange (ETDEWEB)
Cataldo, Franco, E-mail: franco.cataldo@fastwebnet.i [Lupi Chemical Research, Via Casilina 1626/A, 00133 Rome (Italy); Lilla, Edo; Ursini, Ornella [Institute of Chemical Methodologies, CNR, Via Salaria Km. 29300, Monterotondo Stazione 00016, Rome (Italy)
2011-06-15
Poly-{beta}(+)-pinene (pB(+)p) was synthesized with {gamma} irradiation of the monomer {beta}(+)-pinene in bulk under vacuum at 1181 kGy. Also scalemic mixtures of {beta}(+)-pinene and {beta}(-)-pinene were irradiated at 1181 kGy to obtain synthetic copolymers of pB(+)/B(-)p. For comparison also {beta}(-)-pinene was converted into poly-{beta}(-)-pinene (pB(-)p) under the identical conditions adopted for its enantiomer. Furthermore pB(+)p and pB(-)p were also synthesized by thermal processing under the action of a chemical free radical initiator. The optical rotatory dispersion (ORD) of all pBp resins synthesized were accurately studied in the spectral range comprised between 375 and 625 nm and a curious asymmetry in the ORD of pB(+)p versus the ORD of pB(-)p is reported. Furthermore, it is shown that (+)-p-menth-1-ene and (-)-p-menth-1-ene are useful as a model compounds for the pBp resins and for the explanation of the amplification of the optical activity of the {beta}(+)-pinene and {beta}(-)-pinene after their ring-opening polymerization to pB(+)p and pB(-)p. The pBp resins were studied also by FT-IR spectroscopy and by thermal analysis (TGA and DTG).
Imperfect World of beta beta-decay Nuclear Data Sets
Energy Technology Data Exchange (ETDEWEB)
Pritychenko, B. [Brookhaven National Lab. (BNL), Upton, NY (United States). NNDC
2015-01-03
The precision of double-beta ββ-decay experimental half lives and their uncertainties is reanalyzed. The method of Benford's distributions has been applied to nuclear reaction, structure and decay data sets. First-digit distribution trend for ββ-decay T^{2v}_{1/2} is consistent with large nuclear reaction and structure data sets and provides validation of experimental half-lives. A complementary analysis of the decay uncertainties indicates deficiencies due to small size of statistical samples, and incomplete collection of experimental information. Further experimental and theoretical efforts would lead toward more precise values of-decay half-lives and nuclear matrix elements.