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Sample records for ray current-driven instability

  1. Current driven instability in collisional dusty plasmas

    NASA Astrophysics Data System (ADS)

    Pandey, B. P.; Vladimirov, S. V.; Samarian, A.

    2009-11-01

    The current driven electromagnetic instability in a collisional, magnetized, dusty medium is considered in the present work. It is shown that in the presence of the magnetic field aligned current, the low-frequency waves in the medium can become unstable if the ratio of the current to the ambient field is larger than the light speed times the wave number. The growth rate of the instability depends upon the ratio of the Alfvén to the dust cyclotron frequency as well as on the ratio of the current density J to the dust charge density Zend, where Z is the number of electronic charge on the grain, e is the electron charge, and nd is the dust number density. The typical growth rate of this instability is on the order of Alfvén frequency which compares favorably with the electrostatic, cross-field current driven, Farley-Buneman instability and thus could play an important role in the Earth's ionosphere.

  2. Gyrokinetic simulation of current-driven instabilities

    NASA Astrophysics Data System (ADS)

    McClenaghan, Joseph

    The gyrokinetic toroidal code(GTC) capability has been extended for simulating current-driven instabilities in magnetized plasmas such as kink and resistive tearing modes with kinetic effects. This new gyrokinetic capability enables first-principles, integrated simulations of macroscopic magnetohydrodynamic(MHD) modes, which limit the performance of burning plasmas and threaten the integrity of fusion devices. The excitation and evolution of macroscopic MHD modes often depend on the kinetic effects at microscopic scales and the nonlinear coupling of multiple physical processes. GTC simulation in the fluid limit of the internal kink modes in cylindrical geometry has been verified by benchmarking with an MHD eigenvalue code. The global simulation domain covers the magnetic axis which is necessary for simulating the macroscopic MHD modes. Gyrokinetic simulations of the internal kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface. This new GTC capability for current-driven instability has now been extended to simulate fishbone instabilities excited by energetic particles and resistive tearing modes. GTC has also been applied to study the internal kink modes in astrophysical jets that are formed around supermassive black holes. Linear simulations find that the internal kink modes in astrophysical jets are unstable with a broad eigenmode. Nonlinear saturation amplitude of these kink modes is observed to be small, suggesting that the jets can remain collimated even in the presence of the internal kink modes. Generation of a mean parallel electric field by the nonlinear dynamics of internal kink modes and the potential implication of this field on particle acceleration in jets has been examined.

  3. Current-Driven Filament Instabilities in Relativistic Plasmas. Final report

    SciTech Connect

    Ren, Chuang

    2013-02-13

    This grant has supported a study of some fundamental problems in current- and flow-driven instabilities in plasmas and their applications in inertial confinement fusion (ICF) and astrophysics. It addressed current-driven instabilities and their roles in fast ignition, and flow-driven instabilities and their applications in astrophysics.

  4. Current driven electrostatic and electromagnetic ion cyclotron instabilities

    NASA Technical Reports Server (NTRS)

    Forslund, D. W.; Kennel, C. F.; Kindel, J. M.

    1971-01-01

    Growth rates and parameter dependences are calculated for the current driven instabilities of electrostatic (with finite-beta corrections) and electromagnetic ion cyclotron waves. For 0.25 (T sub e)/(T sub i) 2.5, ion cyclotron waves have large growth rates, while ion acoustic waves are still stable. In fusion devices, where electrostatic waves may be stable, electromagnetic ion cyclotron waves are unstable for beta sub i 0.001.

  5. Current-Driven Kink Instability in Relativistic Jets

    NASA Astrophysics Data System (ADS)

    Mizuno, Yosuke; Hardee, Philip E.; Lyubarsky, Yuri; Nishikawa, Ken-Ichi

    We have investigated the development of current-driven (CD) kink instability in relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depend moderately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.

  6. Current-Driven Kink Instability in Relativistic Jets

    NASA Astrophysics Data System (ADS)

    Mizuno, Yosuke; Hardee, Philip E.; Lyubarsky, Yuri; Nishikawa, Ken-Ici

    2011-06-01

    We have investigated the development of current-driven (CD) kink instability in relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic field configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends moderately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.

  7. Current driven instabilities of an electromagnetically accelerated plasma

    NASA Technical Reports Server (NTRS)

    Chouetri, E. Y.; Kelly, A. J.; Jahn, R. G.

    1988-01-01

    A plasma instability that strongly influences the efficiency and lifetime of electromagnetic plasma accelerators was quantitatively measured. Experimental measurements of dispersion relations (wave phase velocities), spatial growth rates, and stability boundaries are reported. The measured critical wave parameters are in excellent agreement with theoretical instability boundary predictions. The instability is current driven and affects a wide spectrum of longitudinal (electrostatic) oscillations. Current driven instabilities, which are intrinsic to the high-current-carrying magnetized plasma of the magnetoplasmadynmic (MPD) accelerator, were investigated with a kinetic theoretical model based on first principles. Analytical limits of the appropriate dispersion relation yield unstable ion acoustic waves for T(i)/T(e) much less than 1 and electron acoustic waves for T(i)/T(e) much greater than 1. The resulting set of nonlinear equations for the case of T(i)/T(e) = 1, of most interest to the MPD thruster Plasma Wave Experiment, was numerically solved to yield a multiparameter set of stability boundaries. Under certain conditions, marginally stable waves traveling almost perpendicular to the magnetic field would travel at a velocity equal to that of the electron current. Such waves were termed current waves. Unstable current waves near the upper stability boundary were observed experimentally and are in accordance with theoretical predictions. This provides unambiguous proof of the existence of such instabilites in electromagnetic plasma accelerators.

  8. 3D Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. 1; Instability of a Static Column

    NASA Technical Reports Server (NTRS)

    Mizuno, Yosuke; Lyubarsky, Yuri; ishikawa, Ken-Ichi; Hardee, Philip E.

    2010-01-01

    We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the non-linear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the non-linear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the non-linear regime nearly ceases for increasing magnetic pitch.

  9. Filamentation instability of nonextensive current-driven plasma in the ion acoustic frequency range

    SciTech Connect

    Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.

    2014-12-15

    The filamentation and ion acoustic instabilities of nonextensive current-driven plasma in the ion acoustic frequency range have been studied using the Lorentz transformation formulas. Based on the kinetic theory, the possibility of filamentation instability and its growth rate as well as the ion acoustic instability have been investigated. The results of the research show that the possibility and growth rate of these instabilities are significantly dependent on the electron nonextensive parameter and drift velocity. Besides, the increase of electrons nonextensive parameter and drift velocity lead to the increase of the growth rates of both instabilities. In addition, the wavelength region in which the filamentation instability occurs is more stretched in the presence of higher values of drift velocity and nonextensive parameter. Finally, the results of filamentation and ion acoustic instabilities have been compared and the conditions for filamentation instability to be dominant mode of instability have been presented.

  10. THREE-DIMENSIONAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF CURRENT-DRIVEN INSTABILITY. III. ROTATING RELATIVISTIC JETS

    SciTech Connect

    Mizuno, Yosuke; Lyubarsky, Yuri; Nishikawa, Ken-Ichi; Hardee, Philip E.

    2012-09-20

    We have investigated the influence of jet rotation and differential motion on the linear and nonlinear development of the current-driven (CD) kink instability of force-free helical magnetic equilibria via three-dimensional relativistic magnetohydrodynamic simulations. In this study, we follow the temporal development within a periodic computational box. Displacement of the initial helical magnetic field leads to the growth of the CD kink instability. We find that, in accordance with the linear stability theory, the development of the instability depends on the lateral distribution of the poloidal magnetic field. If the poloidal field significantly decreases outward from the axis, then the initial small perturbations grow strongly, and if multiple wavelengths are excited, then nonlinear interaction eventually disrupts the initial cylindrical configuration. When the profile of the poloidal field is shallow, the instability develops slowly and eventually saturates. We briefly discuss implications of our findings for Poynting-dominated jets.

  11. Current-driven magnetohydrodynamic thermal instabilities in sheared fields. [of solar corona

    NASA Technical Reports Server (NTRS)

    Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.

    1987-01-01

    Approximate analytic solutions are sought for the dispersion relation for the MHD stability of magnetized medium in current-driven filamentation modes such as those observed in the solar atmosphere. The magnetic field is assumed to have a self-consistent sheared equilibrium structure. The analysis is carried out in the small wavenumber regime, where shear length is similar to the mode wavelength. Instability is found to depend on the ratio between the thermal and magnetic diffusivities, i.e., the Prandtl number, which identifies the unstable transverse wavenumbers. The instability conditions are expressed in an algebraic equation amenable to numerical solution. Results are provided from use of the model to determine the maximum growth rate and typical scale lengths of instabilities in a precoronal atmosphere and the lower transition region.

  12. Nonlinear development of strong current-driven instabilities and selective acceleration of ^3He ions

    NASA Astrophysics Data System (ADS)

    Toida, Mieko; Okumura, Hayato

    2003-10-01

    In some solar flares, the abundance of high-energy ^3He ions is extremely increased. As a mechanism for these ^3He rich events, current-driven instabilities are believed to be important. Nonlinear development of the strong current-driven instabilities and associated energy transfer to ^3He ions are studied theoretically and numerically [1]. First, by means of a two-dimensional, electrostatic, particle simulation code, it is demonstrated that ^3He ions are selectively accelerated by fundamental H cyclotron waves with frequencies ω ≃ 2Ω_3He (Ω_3He is the cyclotron frequency of ^3He). Then, from the analysis of the dispersion relation of these waves, it is found that the ω ≃ 2 Ω_ 3He waves have the greatest growth rate, if Te > 10 T_H. Energies of the ^3He ions are also discussed. Theoretical expression for the maximum ^3He energy is presented, which is in good agreement with the simulation results. Based on this theory, it is shown that when the initial electron drift energy is of the order of 10 keV, many ^3He ions can be accelerated to energies of the order of MeV/n. [1] M. Toida and H. Okumura, J. Phys. Soc. Jpn. 72,1098 (2003)

  13. The Current-driven Kink Instability of the Poynting Flux Dominated Jets

    NASA Astrophysics Data System (ADS)

    Nakamura, Masanori; Meier, David L.

    2004-11-01

    The spatial stability properties are one of the most important problem in astrophysical jets dynamics. The non-relativistic 3-D MHD simulations of Poynting flux dominated (PFD) jets are presented. Our study focuses on the propagation of strongly magnetized hypersonic, but sub-Alfvénic flow and on the subsequent development of a current-driven (CD) kink instability. This instability may be responsible for the ``wiggled'' structures seen in sub-parsec scale (VLBI) AGN jets and pulsar jets. Our numerical results show that the PFD jets can develop CD distortions in the trans-Alfvénic flow case. An internal non axisymmetric body mode grows on time scales of order of the Alfvén crossing time and distorts the structure and magnetic configuration of the jet. The kink (m=1) mode of the CD instability, driven by the asymmetrically distribution of hoop-stress, grows faster than other higher order modes (m>1). This could be caused by a sudden loss of kinetic angular momentum to the magnetic field via the reverse slow-mode MHD shock wave. In the jet frame the mode grows locally and expands radially at each axial position where the jet is unstable: the instability, therefore, does not propagate as a wave along the jet length. The wiggled structures saturate and advect with the bulk flow and then, the local plasma flow follows a helical path along the kinked magnetic field backbone. M.N. is supported by a NRC RRA award.

  14. Nonlocal effects on the convective properties of the electrostatic current-driven ion-cyclotron instability

    NASA Technical Reports Server (NTRS)

    Ganguli, G.; Bakshi, P.; Palmadesso, P.

    1984-01-01

    The convective behavior of the current-driven ion-cyclotron instability (CDICI) in the presence of nonlocal magnetic-shear and current-channel-width effects is investigated theoretically using the analytical approach of Bakshi et al. (1983). The results are presented in graphs and discussed. Three different CDICI regimes defined by the ratio of the channel width to the shear length are obtained: a purely nonlocal regime with reduced temporal growth rate and group velocity in the z direction going to zero (ratios greater than about 0.1); a regime corresponding to the results of local theory (ratios less than 0.01); and a regime characterized by decreasing temporal growth rate and by z and y group velocities which become negative when the channel width becomes less than the mean ion Larmor radius (ratios 0.001 or less).

  15. The current-driven kink instability in magnetically dominated relativistic jets

    NASA Astrophysics Data System (ADS)

    Mizuno, Yosuke; Lyubarsky, Yuri; Nishikawa, Ken-Ichi; Hardee, Philip E.

    2012-04-01

    We have investigated the development of current-driven (CD) kink instability in relativistic jets, via 3D relativistic magnetohydrodynamic simulations. For this purpose, a static force-free equilibrium helical magnetic configuration is considered in order to study its influence on the linear and nonlinear stages of the instability. We found that this configuration is strongly distorted but not disrupted by the CD kink instability. Both the linear growth and the nonlinear evolution of this in-stability depend moderately on the radial density profile but are strongly sensitive to the magnetic pitch profile. For decreasing magnetic pitch, kink amplitude growth leads, in the nonlinear regime, to a slender helically twisted column wrapped by magnetic field. Differently, for increasing magnetic pitch, the kink amplitude nearly saturates in the nonlinear regime. We have also investigated the influence of velocity shear on the linear and non-linear development of the instability. We found that helically distorted density structures propagate along the jet with a speed and a flow structure that are dependent on the location of the velocity shear relative to the characteristic radius of the helically twisted force-free magnetic field. At small radius, the plasma flows through the kink. The kink propagation speed increases with the velocity shear radius, and the kink becomes more em-bedded in the plasma flow. Larger velocity shear radius leads to slower linear growth, with a later transition to the nonlinear stage and a larger maximum amplitude than in the case of a static plasma column. However, when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field, linear and non-linear developments become more similar to those of a static plasma column.

  16. Spatial growth of the current-driven instability in relativistic jets

    SciTech Connect

    Mizuno, Yosuke; Hardee, Philip E.; Nishikawa, Ken-Ichi

    2014-04-01

    We investigated the influence of velocity shear and a radial density profile on the spatial development of the current-driven (CD) kink instability along helically magnetized relativistic jets via three-dimensional relativistic magnetohydrodynamic simulations. In this study, we use a nonperiodic computational box, the jet flow is initially established across the computational grid, and a precessional perturbation at the inlet triggers growth of the kink instability. If the velocity shear radius is located inside the characteristic radius of the helical magnetic field, a static nonpropagating CD kink is excited as the perturbation propagates down the jet. Temporal growth disrupts the initial flow across the computational grid not too far from the inlet. On the other hand, if the velocity shear radius is outside the characteristic radius of the helical magnetic field, the kink is advected with the flow and grows spatially down the jet. In this case, flow is maintained to much larger distances from the inlet. The effect of different radial density profiles is more subtle. When the density increases with radius, the kink appears to saturate by the end of the simulation without apparent disruption of the helical twist. This behavior suggests that relativistic jets consisting of a tenuous spine surrounded by a denser medium with a velocity shear radius outside the radius of the maximum toroidal magnetic field have a relatively stable configuration.

  17. Three-Dimensional Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. I. Instability of a Static Column

    NASA Astrophysics Data System (ADS)

    Mizuno, Yosuke; Lyubarsky, Yuri; Nishikawa, Ken-Ichi; Hardee, Philip E.

    2009-07-01

    We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic magnetohydrodynamic simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the nonlinear regime, the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depend moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and reaches the nonlinear regime at a later time than the case with constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the nonlinear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.

  18. Spatial Growth of Current-driven Instability in Relativistic Rotating Jets and the Search for Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Singh, Chandra B.; Mizuno, Yosuke; de Gouveia Dal Pino, Elisabete M.

    2016-06-01

    Using the three-dimensional relativistic magnetohydrodynamic code RAISHIN, we investigated the influence of the radial density profile on the spatial development of the current-driven kink instability along magnetized rotating, relativistic jets. For the purposes of our study, we used a nonperiodic computational box, the jet flow is initially established across the computational grid, and a precessional perturbation at the inlet triggers the growth of the kink instability. We studied light and heavy jets with respect to the environment depending on the density profile. Different angular velocity amplitudes have been also tested. The results show the propagation of a helically kinked structure along the jet and a relatively stable configuration for the lighter jets. The jets appear to be collimated by the magnetic field, and the flow is accelerated owing to conversion of electromagnetic into kinetic energy. We also identify regions of high current density in filamentary current sheets, indicative of magnetic reconnection, which are associated with the kink-unstable regions and correlated with the decrease of the sigma parameter of the flow. We discuss the implications of our findings for Poynting-flux-dominated jets in connection with magnetic reconnection processes. We find that fast magnetic reconnection may be driven by the kink-instability turbulence and govern the transformation of magnetic into kinetic energy, thus providing an efficient way to power and accelerate particles in active galactic nucleus and gamma-ray-burst relativistic jets.

  19. A hybrid Rayleigh-Taylor-current-driven coupled instability in a magnetohydrodynamically collimated cylindrical plasma with lateral gravity

    NASA Astrophysics Data System (ADS)

    Zhai, Xiang; Bellan, Paul M.

    2016-03-01

    We present an MHD theory of Rayleigh-Taylor instability on the surface of a magnetically confined cylindrical plasma flux rope in a lateral external gravity field. The Rayleigh-Taylor instability is found to couple to the classic current-driven instability, resulting in a new type of hybrid instability that cannot be described by either of the two instabilities alone. The lateral gravity breaks the axisymmetry of the system and couples all azimuthal modes together. The coupled instability, produced by combination of helical magnetic field, curvature of the cylindrical geometry, and lateral gravity, is fundamentally different from the classic magnetic Rayleigh-Taylor instability occurring at a two-dimensional planar interface. The theory successfully explains the lateral Rayleigh-Taylor instability observed in the Caltech plasma jet experiment [Moser and Bellan, Nature 482, 379 (2012)]. Potential applications of the theory include magnetic controlled fusion, solar emerging flux, solar prominences, coronal mass ejections, and other space and astrophysical plasma processes.

  20. Dielectric permittivity tensor and low frequency instabilities of a magnetoactive current-driven plasma with nonextensive distribution

    SciTech Connect

    Niknam, A. R.; Rastbood, E.; Khorashadizadeh, S. M.

    2015-12-15

    The dielectric permittivity tensor of a magnetoactive current-driven plasma is obtained by employing the kinetic theory based on the Vlasov equation and Lorentz transformation formulas with an emphasize on the q-nonextensive statistics. By deriving the q-generalized dispersion relation of the low frequency modes in this plasma system, the possibility and properties of filamentation and ion acoustic instabilities are then studied. It is shown that the occurrence and the growth rate of these instabilities depend strongly on the nonextensive parameters, external magnetic field strength, and drift velocity. It is observed that the growth rate of ion acoustic instability is affected by the magnetic field strength much more than that of the filamentation instability in the low frequency range. The external magnetic field facilitates the development of the ion-acoustic instability. It is also shown that the filamentation is the dominant instability only for the high value of drift velocity.

  1. Nonlinear dynamics of filamentation instability and current filament merging in a high density current-driven plasma

    NASA Astrophysics Data System (ADS)

    Khorashadizadeh, S. M.; Taghadosi, M. R.; Niknam, A. R.

    2015-12-01

    The magnetic field generation due to the filamentation instability (FI) of a high density current-driven plasma is studied through a new nonlinear diffusion equation. This equation is obtained on the basis of quantum hydrodynamic model and numerically solved by applying the Crank-Nicolson method. The spatiotemporal evolution of the magnetic field and the electron density distribution exhibits the current filament merging as a nonlinear phase of the FI which is responsible for the strong magnetic fields in the current-driven plasmas. It is found that the general behaviour of the FI is the same as that of the classical case but the instability growth rate, its magnitude, and the saturation time are affected by the quantum effects. It is eventually concluded that the quantum effects can play a stabilizing role in such situation.

  2. Coupling of the Okuda-Dawson model with a shear current-driven wave and the associated instability

    NASA Astrophysics Data System (ADS)

    Masood, W.; Saleem, H.; Saleem

    2013-12-01

    It is pointed out that the Okuda-Dawson mode can couple with the newly proposed current-driven wave. It is also shown that the Shukla-Varma mode can couple with these waves if the density inhomogeneity is taken into account in a plasma containing stationary dust particles. A comparison of several low-frequency electrostatic waves and instabilities driven by shear current and shear plasma flow in an electron-ion plasma with and without stationary dust is also presented.

  3. Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. I. Internal kink mode

    SciTech Connect

    McClenaghan, J.; Lin, Z.; Holod, I.; Deng, W.; Wang, Z.

    2014-12-15

    The gyrokinetic toroidal code (GTC) capability has been extended for simulating internal kink instability with kinetic effects in toroidal geometry. The global simulation domain covers the magnetic axis, which is necessary for simulating current-driven instabilities. GTC simulation in the fluid limit of the kink modes in cylindrical geometry is verified by benchmarking with a magnetohydrodynamic eigenvalue code. Gyrokinetic simulations of the kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface.

  4. Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. I. Internal kink mode

    NASA Astrophysics Data System (ADS)

    McClenaghan, J.; Lin, Z.; Holod, I.; Deng, W.; Wang, Z.

    2014-12-01

    The gyrokinetic toroidal code (GTC) capability has been extended for simulating internal kink instability with kinetic effects in toroidal geometry. The global simulation domain covers the magnetic axis, which is necessary for simulating current-driven instabilities. GTC simulation in the fluid limit of the kink modes in cylindrical geometry is verified by benchmarking with a magnetohydrodynamic eigenvalue code. Gyrokinetic simulations of the kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface.

  5. Kinetic theory of the filamentation instability in a collisional current-driven plasma with nonextensive distribution

    SciTech Connect

    Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.

    2015-07-15

    The evolution of filamentation instability in a weakly ionized current-carrying plasma with nonextensive distribution was studied in the diffusion frequency region, taking into account the effects of electron-neutral collisions. Using the kinetic theory, Lorentz transformation formulas, and Bhatnagar-Gross-Krook collision model, the generalized dielectric permittivity functions of this plasma system were achieved. By obtaining the dispersion relation of low-frequency waves, the possibility of filamentation instability and its growth rate were investigated. It was shown that collisions can increase the maximum growth rate of instability. The analysis of temporal evolution of filamentation instability revealed that the growth rate of instability increased by increasing the q-parameter and electron drift velocity. Finally, the results of Maxwellian and q-nonextensive velocity distributions were compared and discussed.

  6. Particle in cell simulations of Buneman instability of a current-driven plasma with q-nonextensive electron velocity distribution

    SciTech Connect

    Niknam, A. R. Roozbahani, H.; Komaizi, D.; Hashemzadeh, M.

    2014-09-15

    The nonlinear evolution of low frequency Buneman instability in an unmagnetized current-driven plasma with q-nonextensive electron velocity distribution is investigated using particle in cell simulation. Simulation results show that the generation of electron phase space holes and the counter-streaming current induced in the plasma strongly depend on the q-parameter. It is found that by increasing the nonextensive parameter, the distribution of electron density becomes highly peaked. This density steepening or grating-like pattern occurs at the saturation time. In addition, a generalized dispersion relation is obtained using the kinetic theory. Analysis of the dispersion relation and the temporal evolution of the electric field energy density reveal that the growth rate of instability increases by increasing the q-parameter. Finally, the results of Maxwellian and q-nonextensive velocity distributions have been compared and discussed.

  7. Current-driven plasmonic boom instability in three-dimensional gated periodic ballistic nanostructures

    NASA Astrophysics Data System (ADS)

    Aizin, G. R.; Mikalopas, J.; Shur, M.

    2016-05-01

    An alternative approach of using a distributed transmission line analogy for solving transport equations for ballistic nanostructures is applied for solving the three-dimensional problem of electron transport in gated ballistic nanostructures with periodically changing width. The structures with varying width allow for modulation of the electron drift velocity while keeping the plasma velocity constant. We predict that in such structures biased by a constant current, a periodic modulation of the electron drift velocity due to the varying width results in the instability of the plasma waves if the electron drift velocity to plasma wave velocity ratio changes from below to above unity. The physics of such instability is similar to that of the sonic boom, but, in the periodically modulated structures, this analog of the sonic boom is repeated many times leading to a larger increment of the instability. The constant plasma velocity in the sections of different width leads to resonant excitation of the unstable plasma modes with varying bias current. This effect (that we refer to as the superplasmonic boom condition) results in a strong enhancement of the instability. The predicted instability involves the oscillating dipole charge carried by the plasma waves. The plasmons can be efficiently coupled to the terahertz electromagnetic radiation due to the periodic geometry of the gated structure. Our estimates show that the analyzed instability should enable powerful tunable terahertz electronic sources.

  8. Subcritical excitation of the current-driven Tayler instability by super-rotation

    NASA Astrophysics Data System (ADS)

    Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.

    2016-01-01

    It is known that in a hydrodynamic Taylor-Couette system, uniform rotation or a rotation law with positive shear ("super-rotation") is linearly stable. It is also known that a conducting fluid under the presence of a sufficiently strong axial electric-current becomes unstable against nonaxisymmetric disturbances. It is thus suggestive that a cylindrical pinch formed by a homogeneous axial electric-current is stabilized by rotation laws with dΩ/dR ≥ 0. For magnetic Prandtl number Pm ≠ 1 and for slow rotation, however, rigid rotation and super-rotation support the instability by lowering the critical Hartmann numbers. This double-diffusive instability of super-rotation even exists for toroidal magnetic fields with rather arbitrary radial profiles, the current-free profile Bϕ ∝ 1/R included. The sign of the azimuthal drift of the nonaxisymmetric hydromagnetic instability pattern strongly depends on the magnetic Prandtl number. The pattern counterrotates with the flow for Pm ≪ 1 and it corotates for Pm ≫ 1 while for rotation laws with negative shear, the instability pattern migrates in the direction of the basic rotation for all Pm. An axial electric-current of minimal 3.6 kA flowing inside or outside the inner cylinder suffices to realize the double-diffusive instability for super-rotation in experiments using liquid sodium as the conducting fluid between the rotating cylinders. The limit is 11 kA if a gallium alloy is used.

  9. Finite-width currents, magnetic shear, and the current-driven ion-cyclotron instability

    NASA Technical Reports Server (NTRS)

    Bakshi, P.; Ganguli, G.; Palmadesso, P.

    1983-01-01

    Our earlier results that non-local effects due to even a small magnetic shear produce a significant reduction of the growth rate of the ion cyclotron instability driven by a uniform current are now generalized to finite width currents. Externally prescribed as well as self-consistent shears are considered. If the current width Lc exceeds the shear length Ls, the previous results are recovered. Shear becomes less effective with reduction of Lc, and for typical parameters, the growth rate attains its (shearless) local value for Lc/Ls approximately less than 10 to the minus 2. Non-local effects of the finite current width itself come into play if Lc is further reduced to a few ion Larmor radii and can quench the instability. Previously announced in STAR as N83-28996

  10. Current-driven dust ion-acoustic instability in a collisional dusty plasma

    SciTech Connect

    Merlino, R.L.

    1997-02-01

    A fluid analysis of the excitation of dust ion-acoustic (DIA) waves in a collisional dusty plasma is presented. The DIA waves are excited by a relative drift of the electrons and ions produced by a steady-state electric field applied to the plasma. The DIA instability is more easily excited if the relative concentration of negatively charged dust is increased. The current interest in dusty plasmas is due to the realization of their importance in various astrophysical and geophysical environments (e.g., interstellar space, comet tails, planetary ring systems, and the polar mesosphere) as well as in industrial plasma processing devices used in semiconductor manufacturing.

  11. THREE-DIMENSIONAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF CURRENT-DRIVEN INSTABILITY WITH A SUB-ALFVENIC JET: TEMPORAL PROPERTIES

    SciTech Connect

    Mizuno, Yosuke; Nishikawa, Ken-Ichi; Hardee, Philip E.

    2011-06-10

    We have investigated the influence of a velocity shear surface on the linear and nonlinear development of the current-driven (CD) kink instability of force-free helical magnetic equilibria in three dimensions. In this study, we follow the temporal development within a periodic computational box and concentrate on flows that are sub-Alfvenic on the cylindrical jet's axis. Displacement of the initial force-free helical magnetic field leads to the growth of CD kink instability. We find that helically distorted density structure propagates along the jet with speed and flow structure dependent on the radius of the velocity shear surface relative to the characteristic radius of the helically twisted force-free magnetic field. At small velocity shear surface radius, the plasma flows through the kink with minimal kink propagation speed. The kink propagation speed increases as the velocity shear radius increases and the kink becomes more embedded in the plasma flow. A decreasing magnetic pitch profile and faster flow enhance the influence of velocity shear. Simulations show continuous transverse growth in the nonlinear phase of the instability. The growth rate of the CD kink instability and the nonlinear behavior also depend on the velocity shear surface radius and flow speed, and the magnetic pitch radial profile. Larger velocity shear radius leads to slower linear growth, makes a later transition to the nonlinear stage, and with larger maximum amplitude than that occuring for a static plasma column. However, when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field, linear and nonlinear development can be similar to the development of a static plasma column.

  12. Microphysics of Cosmic Ray Driven Plasma Instabilities

    NASA Astrophysics Data System (ADS)

    Bykov, A. M.; Brandenburg, A.; Malkov, M. A.; Osipov, S. M.

    2013-10-01

    Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

  13. Microphysics of Cosmic Ray Driven Plasma Instabilities

    NASA Astrophysics Data System (ADS)

    Bykov, A. M.; Brandenburg, A.; Malkov, M. A.; Osipov, S. M.

    Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

  14. COSMIC-RAY CURRENT-DRIVEN TURBULENCE AND MEAN-FIELD DYNAMO EFFECT

    SciTech Connect

    Rogachevskii, Igor; Kleeorin, Nathan; Brandenburg, Axel; Eichler, David

    2012-07-01

    We show that an {alpha} effect is driven by the cosmic-ray (CR) Bell instability exciting left-right asymmetric turbulence. Alfven waves of a preferred polarization have maximally helical motion, because the transverse motion of each mode is parallel to its curl. We show how large-scale Alfven modes, when rendered unstable by CR streaming, can create new net flux over any finite region, in the direction of the original large-scale field. We perform direct numerical simulations (DNSs) of a magnetohydrodynamic fluid with a forced CR current and use the test-field method to determine the {alpha} effect and the turbulent magnetic diffusivity. As follows from DNS, the dynamics of the instability has the following stages: (1) in the early stage, the small-scale Bell instability that results in the production of small-scale turbulence is excited; (2) in the intermediate stage, there is formation of larger-scale magnetic structures; (3) finally, quasi-stationary large-scale turbulence is formed at a growth rate that is comparable to that expected from the dynamo instability, but its amplitude over much longer timescales remains unclear. The results of DNS are in good agreement with the theoretical estimates. It is suggested that this dynamo is what gives weakly magnetized relativistic shocks such as those from gamma-ray bursts (GRBs) a macroscopic correlation length. It may also be important for large-scale magnetic field amplification associated with CR production and diffusive shock acceleration in supernova remnants (SNRs) and blast waves from GRBs. Magnetic field amplification by Bell turbulence in SNRs is found to be significant, but it is limited owing to the finite time available to the super-Alfvenicly expanding remnant. The effectiveness of the mechanisms is shown to be dependent on the shock velocity. Limits on magnetic field growth in longer-lived systems, such as the Galaxy and unconfined intergalactic CRs, are also discussed.

  15. Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

    SciTech Connect

    Trushnikov, D. N.; Mladenov, G. M. Koleva, E. G.; Belenkiy, V. Ya. Varushkin, S. V.

    2014-04-15

    Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distance between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 10{sup 16} m{sup −3}, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A·m{sup −2}, i.e. 8 mA for a 3–10 cm{sup 2} collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole.

  16. Ion temperature anisotropy effects on the dispersion relation and threshold conditions of a sheared current-driven electrostatic ion-acoustic instability with applications to the collisional high-latitude F-region

    NASA Astrophysics Data System (ADS)

    Perron, Patrick J. G.; Noël, J.-M.; St-Maurice, J.-P.; Kabin, K.

    2015-01-01

    Plasma instabilities play a important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. Ion temperature anisotropies with enhanced perpendicular temperature often exist in the high-latitude F-region. In addition to temperature anisotropies, ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). We investigated whether ion temperature anisotropy lowers the threshold conditions required for the onset of sheared CDEIA instabilities. We generalised a dispersion relation to include ion thermal anisotropy, finite Larmor radius corrections and collisions. We derived new fluid-like analytical expressions for the threshold conditions required for instability that depend explicitly on ion temperature anisotropy. We studied how the instability threshold conditions vary as a function of the wave vector direction in both fluid and kinetic regimes. We found that, despite the dampening effect of collisions on ion-acoustic waves, ion temperature anisotropy lowers in some cases the threshold drift requirements for a large range of oblique wave vector angles. More importantly, realistic ion temperature anisotropies contribute to reducing the instability threshold velocity shears that are associated with small drift thresholds, for modes propagating almost perpendicularly to the geomagnetic field. Small shear thresholds that seem to be sustainable in the ionospheric F-region are obtained for low-frequency waves. Such instabilities could play a role in the direct generation of field-aligned irregularities in the collisional F-region that could be observed with the Super Dual Auroral Radar Network (SuperDARN) array of high-frequency radars. These modes would be very sensitive to the radar probing direction since they are restricted to very narrow

  17. Alternating current driven instability in magnetic junctions.

    PubMed

    Epshtein, E M; Zilberman, P E

    2009-04-01

    An effect is considered of alternating (high-frequency) current on the spin-valve-type magnetic junction configuration. The stability with respect to small fluctuations is investigated in the macrospin approximation. When the current frequency is close to the eigenfrequency (precession frequency) of the free layer, parametric resonance occurs. Both collinear configurations, antiparallel and parallel, can become unstable under resonance conditions. The antiparallel configuration can also become unstable under non-resonant conditions. The threshold current density amplitude is of the order of the dc current density for switching of the magnetic junction. PMID:21825350

  18. A cosmic ray driven instability

    NASA Technical Reports Server (NTRS)

    Dorfi, E. A.; Drury, L. O.

    1985-01-01

    The interaction between energetic charged particles and thermal plasma which forms the basis of diffusive shock acceleration leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homogeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves.

  19. Current-driven plasma acceleration versus current-driven energy dissipation. I - Wave stability theory

    NASA Technical Reports Server (NTRS)

    Kelly, A. J.; Jahn, R. G.; Choueiri, E. Y.

    1990-01-01

    The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are investigated. The study is the first part of a three-phase program aimed at characterizing the current-driven turbulent dissipation degrading the efficiency of Lorentz force plasma accelerators such as the MPD thruster. The analysis uses a kinetic theory that includes magnetic and thermal effects as well as those of an electron current transverse to the magnetic field and collisions, thus combining all the features of previous models. Analytical and numerical solutions allow a detailed description of threshold criteria, finite growth behavior, destabilization mechanisms and maximized-growth characteristics of the dominant unstable modes. The lower hybrid current-driven instability is implicated as dominant and was found to preserve its character in the collisional plasma regime.

  20. Plasma Instabilities in Gamma-Ray Bursts

    SciTech Connect

    Tautz, Robert C.

    2008-12-24

    Magnetic fields are important in a variety of astrophysical scenarios, ranging from possible creation mechanisms of cosmological magnetic fields through relativistic jets such as that from Active Galactic Nuclei and gamma-ray bursts to local phenomena in the solar system. Here, the outstanding importance of plasma instabilities to astrophysics is illustrated by applying the so-called neutral point method to gamma-ray bursts (GRBs), which are assumed to have a homogeneous background magnetic field. It is shown how magnetic turbulence, which is a prerequisite for the creation of dissipation and, subsequently, radiation, is created by the highly relativistic particles in the GRB jet. Using the fact that different particle compositions lead to different instability conditions, conclusions can be drawn about the particle composition of the jet, showing that it is more likely of baryonic nature.

  1. Testing accretion disk instabilities in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Bagińska, Patrycja; Różańska, Agata; Janiuk, Agnieszka; Czerny, Bożena

    2014-12-01

    We study disk instabilities in black hole binaries in which X-ray novae outbursts were observed. Typically, one outburst occurs in each light curve, with total duration from 30 up to 400 days. The shape of an outburst can be very regular fast rise exponential decay (FRED) characteristic for ionisation instability mechanism that occurs in accretion disks, or irregular suggesting that, beside FRED, additional flickering occurs. We use the model which predicts time dependent evolution of ionisation instability in an accretion disk around black hole, assuming viscosity parameter to be proportional to the total pressure. We test it in detail for two objects: GX 339-4 and XTE J1818-245. The modelled light curves agree with the collected RXTE light curves, indicating that disk instability works in those objects.

  2. Current-Driven Nanowire Formation on Crystalline Conducting Substrate Surfaces

    NASA Astrophysics Data System (ADS)

    Dasgupta, Dwaipayan; Kumar, Ashish; Maroudas, Dimitrios

    Using a simulation study, we demonstrate a new, driven-assembly-based approach to single-layer nanowire formation on fcc crystalline substrate surfaces. In this approach, we manipulate individual epitaxial islands using an external electric field to drive the formation of single nanowires or arrays of them. We have developed and validated a fully nonlinear model of current-driven island evolution mediated by diffusional mass transport along the island edge and accounting for edge diffusional anisotropy and island coalescence and breakup. Using a linear stability theory, we analyze the morphological stability of islands with equilibrium shapes and predict the occurrence of morphological instability for islands larger than a critical size under the action of an electric field along the slowest edge diffusion direction on { 110 } , { 100 } , and { 111 } substrate surfaces. Consistent with the theoretical prediction, dynamical simulations show that large-size islands undergo a fingering instability which, following finger growth and, depending on the substrate orientation, necking instability, leads to formation of single or multiple nanowires. We find that the nanowires have constant widths, on the order of tens of nanometers, and explain analytically the nanowire dimensions.

  3. COSMIC-RAY-INDUCED FILAMENTATION INSTABILITY IN COLLISIONLESS SHOCKS

    SciTech Connect

    Caprioli, D.; Spitkovsky, A.

    2013-03-01

    We used unprecedentedly large two-dimensional and three-dimensional hybrid (kinetic ions-fluid electrons) simulations of non-relativistic collisionless strong shocks in order to investigate the effects of self-consistently accelerated ions on the overall shock dynamics. The current driven by suprathermal particles streaming ahead of the shock excites modes transverse to the background magnetic field. The Lorentz force induced by these self-amplified fields tends to excavate tubular, underdense, magnetic-field-depleted cavities that are advected with the fluid and perturb the shock surface, triggering downstream turbulent motions. These motions further amplify the magnetic field, up to factors of 50-100 in knot-like structures. Once downstream, the cavities tend to be filled by hot plasma plumes that compress and stretch the magnetic fields in elongated filaments; this effect is particularly evident if the shock propagates parallel to the background field. Highly magnetized knots and filaments may provide explanations for the rapid X-ray variability observed in RX J1713.7-3946 and for the regular pattern of X-ray bright stripes detected in Tycho's supernova remnant.

  4. Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

    SciTech Connect

    Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William

    2010-08-31

    CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, MIT Participation in the Center for Multiscale Plasma Dynamics, which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department,. Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009). In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a spontaneous reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as electron phase-space holes, a class of

  5. Anomalous resistivity and heating in current-driven plasma thrusters

    NASA Astrophysics Data System (ADS)

    Choueiri, E. Y.

    1999-05-01

    A theory is presented of anomalous resistivity and particle heating in current-driven plasma accelerators such as the magnetoplasmadynamic thruster (MPDT). An electromagnetic dielectric tensor is used for a current-carrying, collisional and finite-beta plasma and it is found that an instability akin to the generalized lower hybrid drift instability (GLHDI) exists for electromagnetic modes (i.e., with finite polarization). Weak turbulence theory is then used to develop a second-order description of the heating rates of particles by the waves and the electron-wave momentum exchange rate that controls the anomalous resistivity effect. It is found that the electron Hall parameter strongly scales the level of anomalous dissipation for the case of the MPDT plasma. This scaling has recently been confirmed experimentally [Phys. Plasmas 5, 3581 (1997)]. Polynomial expressions of the relevant transport coefficients cast solely in terms of macroscopic parameters are also obtained for including microturbulence effects in numerical plasma fluid models used for thruster flow simulation.

  6. Current driven asymmetric domain wall propagation

    NASA Astrophysics Data System (ADS)

    Garg, Chirag; Pushp, Aakash; Phung, Timothy; Yang, See-Hun; Hughes, Brian P.; Rettner, Charles; Parkin, Stuart S. P.

    In ultrathin magnetic heterostructures, the presence of spin-orbit coupling gives rise to chiral Neel walls which are stabilized by the Dzyaloshinskii-Moriya Interaction (DMI), and also to a highly efficient chiral spin torque mechanism. In straight nanowires, the current-driven propagation of alternating Néel DWs without the presence of an in-plane field is equivalent, leading to the lock-step motion of several DWs in a nanowire. Here, we show that by engineering the structure in which the domain walls propagate, which in our case is in the shape of a Y-shaped junction, the DW propagation process becomes selective to the polarity of the DWs even in the absence of any externally applied magnetic fields. We remarkably find that after splitting at the Y-shaped junction, the DW velocity in one branch remains largely unaffected compared to its initial velocity whereas simultaneously the DW velocity in the other branch decreases by as much as 10-90%. We show that this large change in the DW velocity in a particular branch depends on the relative angle between the local magnetization of the DW and the spin current emanating from the underlying heavy-metal layer in these nanowires.

  7. COSMIC RAY TRANSPORT THROUGH GYRORESONANCE INSTABILITY IN COMPRESSIBLE TURBULENCE

    SciTech Connect

    Yan Huirong; Lazarian, A. E-mail: alazarian@wisc.edu

    2011-04-10

    We study the nonlinear growth of kinetic gyroresonance instability of cosmic rays (CRs) induced by large-scale compressible turbulence. This feedback of CRs on turbulence was shown to induce an important scattering mechanism in addition to direct interaction with the compressible turbulence. The linear growth is bound to saturate due to the wave-particle interactions. By balancing the increase of CR anisotropy via the large-scale compression and its decrease via the wave-particle scattering, we find the steady-state solutions. The nonlinear suppression due to the wave-particle scattering limits the energy range of CRs that can excite the instabilities and be scattered by the induced slab waves. The direct interaction with large-scale compressible modes still appears to be the dominant mechanism for isotropization of high-energy CRs (>100 GeV).

  8. Magnetic field amplification in nonlinear diffusive shock acceleration including resonant and non-resonant cosmic-ray driven instabilities

    SciTech Connect

    Bykov, Andrei M.; Osipov, Sergei M.; Ellison, Donald C.; Vladimirov, Andrey E. E-mail: osm2004@mail.ru E-mail: avenovo@gmail.com

    2014-07-10

    We present a nonlinear Monte Carlo model of efficient diffusive shock acceleration where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming instability, together with non-resonant short- and long-wavelength CR-current-driven instabilities. We include the backpressure from CRs interacting with the strongly amplified magnetic turbulence which decelerates and heats the super-Alfvénic flow in the extended shock precursor. Uniquely, in our plane-parallel, steady-state, multi-scale model, the full range of particles, from thermal (∼eV) injected at the viscous subshock to the escape of the highest energy CRs (∼PeV) from the shock precursor, are calculated consistently with the shock structure, precursor heating, magnetic field amplification, and scattering center drift relative to the background plasma. In addition, we show how the cascade of turbulence to shorter wavelengths influences the total shock compression, the downstream proton temperature, the magnetic fluctuation spectra, and accelerated particle spectra. A parameter survey is included where we vary shock parameters, the mode of magnetic turbulence generation, and turbulence cascading. From our survey results, we obtain scaling relations for the maximum particle momentum and amplified magnetic field as functions of shock speed, ambient density, and shock size.

  9. Influence of the backreaction of streaming cosmic rays on magnetic field generation and thermal instability

    SciTech Connect

    Nekrasov, Anatoly K.; Shadmehri, Mohsen E-mail: nekrasov.anatoly@gmail.com

    2014-06-10

    Using a multifluid approach, we investigate streaming and thermal instabilities of the electron-ion plasma with homogeneous cold cosmic rays propagating perpendicular to the background magnetic field. Perturbations are also considered to be across the magnetic field. The backreaction of cosmic rays resulting in strong streaming instabilities is taken into account. It is shown that, for sufficiently short wavelength perturbations, the growth rates can exceed the growth rate of cosmic-ray streaming instability along the magnetic field, found by Nekrasov and Shadmehri, which is in turn considerably larger than the growth rate of the Bell instability. The thermal instability is shown not to be subject to the action of cosmic rays in the model under consideration. The dispersion relation for the thermal instability has been derived, which includes sound velocities of plasma and cosmic rays and Alfvén and cosmic-ray streaming velocities. The relation between these parameters determines the kind of thermal instability ranging from the Parker to the Field instabilities. The results obtained can be useful for a more detailed investigation of electron-ion astrophysical objects, such as supernova remnant shocks, galaxy clusters, and others, including the dynamics of streaming cosmic rays.

  10. The effect of beam-driven return current instability on solar hard X-ray bursts

    NASA Technical Reports Server (NTRS)

    Cromwell, D.; Mcquillan, P.; Brown, J. C.

    1986-01-01

    The problem of electrostatic wave generation by a return current driven by a small area electron beam during solar hard X-ray bursts is discussed. The marginal stability method is used to solve numerically the electron and ion heating equations for a prescribed beam current evolution. When ion-acoustic waves are considered, the method appears satisfactory and, following an initial phase of Coulomb resistivity in which T sub e/T sub i rise, predicts a rapid heating of substantial plasma volumes by anomalous ohmic dissipation. This hot plasma emits so much thermal bremsstrahlung that, contrary to previous expectations, the unstable beam-plasma system actually emits more hard X-rays than does the beam in the purely collisional thick target regime relevant to larger injection areas. Inclusion of ion-cyclotron waves results in ion-acoustic wave onset at lower T sub e/T sub i and a marginal stability treatment yields unphysical results.

  11. STREAMING COLD COSMIC-RAY BACK-REACTION AND THERMAL INSTABILITIES ALONG THE BACKGROUND MAGNETIC FIELD

    SciTech Connect

    Nekrasov, Anatoly K.; Shadmehri, Mohsen E-mail: nekrasov.anatoly@gmail.com

    2012-09-01

    Using a multi-fluid approach, we investigate the streaming and thermal instabilities of electron-ion-cosmic-ray astrophysical objects in which homogeneous cold cosmic rays have a drift velocity perpendicular to the background magnetic field. One-dimensional perturbations along the magnetic field are considered. The induced return current of the background plasma and back-reaction of cosmic rays are taken into account. It is shown that the cosmic-ray back-reaction results in a streaming instability with considerably higher growth rates than that due to the return current of the background plasma. This increase is by a factor of the square root of the ratio of the background plasma mass density to the cosmic-ray mass density. The maximal growth rate and the corresponding wavenumber are then found. Thermal instability is shown to be not subject to the action of cosmic rays in the model under consideration. The dispersion relation for thermal instability includes ion inertia. In the limit of a fast thermal energy exchange between electrons and ions, the isobaric and isochoric growth rates are obtained. The results can be useful for the investigation of electron-ion astrophysical objects such as galaxy clusters, including the dynamics of streaming cosmic rays.

  12. Current-driven vortex formation in a magnetic multilayer ring

    NASA Astrophysics Data System (ADS)

    Nam, Chunghee; Ng, B. G.; Castaño, F. J.; Mascaro, M. D.; Ross, C. A.

    2009-02-01

    Current-driven domain wall (DW) motion has been studied in the NiFe layer of a Co/Cu/NiFe thin film ring using giant-magnetoresistance measurements in a four-point contact geometry. The NiFe layer is initially in an onion state configuration with two 180° DWs. An electric current drives the walls around the ring so that they annihilate and the NiFe layer forms a DW-free vortex state. The direction of motion of the two DWs is determined by the current polarity, enabling the vortex chirality to be selected.

  13. Angular dependence of current-driven chiral walls

    NASA Astrophysics Data System (ADS)

    Martinez, Eduardo; Alejos, Oscar; Auxiliadora Hernandez, Maria; Raposo, Victor; Sanchez-Tejerina, Luis; Moretti, Simone

    2016-06-01

    The current-driven dynamics of chiral domain walls is theoretically studied by means of realistic micromagnetic simulations. Trains of current pulses flowing through the heavy metal underneath the ferromagnetic layer are injected with different directions with respect to the ferromagnetic strip axis. The wall displacement is highly sensitive to the wall configuration and to the angle between the current and the longitudinal axis of the strip. These simulations can account for the experimental behavior at large currents, but preliminary results at lower current density point towards incompatibilities between the model and the experiment that need further experimental and theoretical efforts.

  14. Evidence of Branching Phenomena in Current-Driven Ionization Waves

    NASA Astrophysics Data System (ADS)

    Loebner, Keith T. K.; Underwood, Thomas C.; Cappelli, Mark A.

    2015-10-01

    This Letter reports the first fully consistent experimental observations of current-driven ionization waves conforming to the magnetohydrodynamic Rankine-Hugoniot model for hydromagnetic shocks. Detailed measurements of the thermodynamic and electrodynamic plasma state variables across the ionization region confirm the existence of two types of waves, corresponding to the upper and lower solution branches of the Hugoniot curve. These waves are generated by pulsed currents in a coaxial gas-fed plasma accelerator. The coupling between the state variables of this complex, transient, three-dimensional system shows a remarkable quantitative agreement of less than 8% deviation from the quasisteady, one-dimensional theoretical model.

  15. Linear growth of the Kelvin-Helmholtz instability with an adiabatic cosmic-ray gas

    SciTech Connect

    Suzuki, Akihiro; Takahashi, Hiroyuki R.; Kudoh, Takahiro

    2014-06-01

    We investigate effects of cosmic rays on the linear growth of the Kelvin-Helmholtz instability. Cosmic rays are treated as an adiabatic gas and allowed to diffuse along magnetic field lines. We calculated the dispersion relation of the instability for various sets of two free parameters, the ratio of the cosmic-ray pressure to the thermal gas pressure, and the diffusion coefficient. Including cosmic-ray effects, a shear layer is more destabilized and the growth rates can be enhanced in comparison with the ideal magnetohydrodynamical case. Whether the growth rate is effectively enhanced or not depends on the diffusion coefficient of cosmic rays. We obtain the criterion for effective enhancement by comparing the growing timescale of the instability with the diffusion timescale of cosmic rays. These results can be applied to various astrophysical phenomena where a velocity shear is present, such as outflows from star-forming galaxies, active galactic nucleus jet, channel flows resulting from the nonlinear development of the magnetorotational instability, and galactic disks.

  16. Anomalous resistivity of current-driven isothermal plasmas due to phase space structuring

    SciTech Connect

    Buechner, Joerg; Elkina, Nina

    2006-08-15

    The anomalous electric resistivity of collisionless plasmas is an important issue in the physics of hot plasmas, e.g., in the context of auroral particle acceleration and of reconnection in the solar corona. The linear stability theory of isothermal current driven space plasmas predicts an ion-acoustic instability if the relative drift velocity of the current carrying particles exceeds a certain threshold, which, generally, depends on the plasma parameters. The spectrum of waves, excited by a marginal instability, is very narrow. Hence, the wave power at saturation and the corresponding electric resistivity due to wave-particle interaction cannot be obtained by means of a quasilinear, weak turbulence approach and the nonlinear single mode theory provides too small saturation amplitudes. To solve the nonlinear problem a newly developed unsplit conservative Eulerian Vlasov code is applied to simulate a strongly magnetized current driven plasma, which can be considered in 1D1V (one spatial, one velocity space direction). Instead of periodic boundary conditions, usually used as they are simpler to treat, open boundaries are implemented which allow to maintain a constant current flow. Simulated is a typical almost isothermal (T{sub e}=2T{sub i}) hot ({kappa}T{sub i}=1 keV) space plasma for the real mass ratio m{sub i}/m{sub e}=1836. The initial spontaneous instability is followed by a three-stage nonlinear evolution: First electron trapping leads to the formation of electron phase space holes. Due to a steepening of the leading edges of the potential wells the electron phase space holes gradually become asymmetric, they grow in size and deepen. The phase space holes accelerate until they move much faster than the initial ion-acoustic waves. The interaction of the current carriers with the asymmetric potential wells and causes a nonvanishing net momentum transfer between the particles and the self-generated electric field. After a few ion plasma periods ion trapping

  17. Current-driven resistive ballooning modes in axially bounded solar flare plasmas

    NASA Technical Reports Server (NTRS)

    Otani, Niels F.; Strauss, H. R.

    1988-01-01

    The most unstable current-driven resistive modes of an axially bounded coronal loop are found in computer simulations to exhibit the spatial structure of ballooning modes. The observed modes are not confined to mode rational surfaces, but instead have broad radial extent. A theory assuming ballooning mode spatial structure predicts that a minimum current should be required for linear instability, and that, when the mode is unstable, the linear growth rate scales linearly with the resistivity eta below a critical resistivity, and scales as cu root of eta for larger resistivities. Both predictions are borne out by simulation results. Both theory and simulation analyses of the mode suggest that the strong radial structure of the mode near the ends of the system is the primary contributing factor to the instability of the mode. A helical current sheet is formed in the nonlinear evolution of the mode near the edge of the current channel and is accompanied by a strong radial gradient in the current and partial current reversal.

  18. The CD Kink Instability in Magnetically Dominated Relativistic Jets

    NASA Astrophysics Data System (ADS)

    Hardee, Philip E.; Mizuno, Y.; Lyubarsky, Y.; Nishikawa, K.

    2010-03-01

    The relativistic jets associated with blazar emission from radio through TeV gamma-rays are thought to be accelerated and collimated by strong helically twisted magnetic fields with footpoints threading the black hole ergosphere and the surrounding accretion disk. The resulting magnetically dominated jet is current-driven (CD) unstable. In a resistive system instability may lead to magnetic reconnection, particle acceleration to the high energies required by the observed emission, and also to the observed kinetically dominated jets far from the central engine. We have investigated the temporal development of current-driven kink instability in magnetically dominated relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We find that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends moderately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch. We also present preliminary results showing the effect of velocity shear on the spatial and temporal development of the CD kink instability.

  19. The CD Kink Instability in Magnetically Dominated Relativistic Jets

    NASA Astrophysics Data System (ADS)

    Nishikawa, Ken-Ichi; Mizuno, Yosuke; Lyubarsky, Yuri; Hardee, Phil

    The relativistic jets associated with blazar emission from radio through TeV gamma-rays are thought to be accelerated and collimated by strong helically twisted magnetic fields with foot-points threading the black hole ergosphere and/or the surrounding accretion disk. The resulting magnetically dominated jet is current-driven (CD) unstable. In a resistive system instability may lead to magnetic reconnection, particle acceleration to the high energies required by the observed emission, and also to the observed kinetically dominated jets far from the central engine. We have investigated the temporal development of current-driven kink instability in magnetically dominated relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We find that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends mod-erately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch. We also present preliminary results showing the effect of velocity shear on the spatial and temporal development of the CD kink instability.

  20. Nonconservative current-driven dynamics: beyond the nanoscale.

    PubMed

    Cunningham, Brian; Todorov, Tchavdar N; Dundas, Daniel

    2015-01-01

    Long metallic nanowires combine crucial factors for nonconservative current-driven atomic motion. These systems have degenerate vibrational frequencies, clustered about a Kohn anomaly in the dispersion relation, that can couple under current to form nonequilibrium modes of motion growing exponentially in time. Such motion is made possible by nonconservative current-induced forces on atoms, and we refer to it generically as the waterwheel effect. Here the connection between the waterwheel effect and the stimulated directional emission of phonons propagating along the electron flow is discussed in an intuitive manner. Nonadiabatic molecular dynamics show that waterwheel modes self-regulate by reducing the current and by populating modes in nearby frequency, leading to a dynamical steady state in which nonconservative forces are counter-balanced by the electronic friction. The waterwheel effect can be described by an appropriate effective nonequilibrium dynamical response matrix. We show that the current-induced parts of this matrix in metallic systems are long-ranged, especially at low bias. This nonlocality is essential for the characterisation of nonconservative atomic dynamics under current beyond the nanoscale. PMID:26665086

  1. Novel current driven domain wall dynamics in synthetic antiferromagnets

    NASA Astrophysics Data System (ADS)

    Yang, See-Hun

    It was reported that the domain walls in nanowires can be moved efficiently by electrical currents by a new type of torque, chiral spin torque (CST), the combination of spin Hall effect and Dzyaloshinskii-Moriya interaction. Recently we domonstrated that ns-long current pulses can move domain walls at extraordinarily high speeds (up to ~750 m s -1) in synthetic antiferromagnetic (SAF) nanowires that have almost zero net magnetization, which is much more efficient compared with similar nanowires in which the sub-layers are coupled ferromagnetically (SF). This high speed is found to be due to a new type of powerful torque, exchange coupling torque (ECT) that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers, showing that the ECT is effective only in SAF not in SF. Moreover, it is found that the dependence of the wall velocity on the magnetic field applied along the nanowire is non-monotonic. Most recently we predict an Walker-breakdown-like domain wall precession in SAF nanowires in the presence of in-plane field based on the model we develop, and this extraordinary precession has been observed. In this talk I will discuss this in details by showing a unique characteristics of SAF sublayers' DW boost-and-drag mechanism along with CST and ECT. Novel current driven domain wall dynamics in synthetic antiferromagnets.

  2. Nonconservative current-driven dynamics: beyond the nanoscale

    PubMed Central

    Todorov, Tchavdar N; Dundas, Daniel

    2015-01-01

    Summary Long metallic nanowires combine crucial factors for nonconservative current-driven atomic motion. These systems have degenerate vibrational frequencies, clustered about a Kohn anomaly in the dispersion relation, that can couple under current to form nonequilibrium modes of motion growing exponentially in time. Such motion is made possible by nonconservative current-induced forces on atoms, and we refer to it generically as the waterwheel effect. Here the connection between the waterwheel effect and the stimulated directional emission of phonons propagating along the electron flow is discussed in an intuitive manner. Nonadiabatic molecular dynamics show that waterwheel modes self-regulate by reducing the current and by populating modes in nearby frequency, leading to a dynamical steady state in which nonconservative forces are counter-balanced by the electronic friction. The waterwheel effect can be described by an appropriate effective nonequilibrium dynamical response matrix. We show that the current-induced parts of this matrix in metallic systems are long-ranged, especially at low bias. This nonlocality is essential for the characterisation of nonconservative atomic dynamics under current beyond the nanoscale. PMID:26665086

  3. Magnetic Field Amplification by Cosmic Rays in Supernova Remnant Shocks

    NASA Astrophysics Data System (ADS)

    Riquelme, Mario A.; Spitkovsky, A.

    2010-02-01

    Cosmic rays (CRs) accelerated in supernova remnant (SNR) shocks are though to produce significant magnetic field amplification (a factor of 100 in their downstream medium). This amplification is believed to be caused by plasma instabilities driven by CRs as they stream in front of the shocks. Using particle-in-cell plasma simulations, we investigate possible instabilities, considering arbitrary angles between the CR streaming and the magnetic field. In the limit of quasi-parallel propagation, we recover Bell's cosmic ray current-driven (CRCD) instability. In the quasi-perpendicular case we find a new instability, the perpendicular current-driven (PCD) instability, and elucidate its physical nature. The PCD instability is driven by CRs protruding into regions of pre-amplified transverse field, which is likely to occur near the shocks. We study the expected saturation mechanisms of these instabilities for the case of SNR shocks. We find that the maximum amplification factor of the PCD instability is 50 in the upstream medium of the shocks, which is 5 times larger than the one corresponding to the CRCD instability. This result shows that CR-driven instabilities would play an essential role in the magnetic amplification inferred from SNR shock observations.

  4. Doppler velocimetry of a current driven spin helix

    NASA Astrophysics Data System (ADS)

    Yang, Luyi

    2012-02-01

    We present direct observation of the translational motion of spin helices in GaAs quantum wells under the influence of applied electric fields. Previously, the lifetime of such helices was observed by time-resolving the amplitude of light diffracted from the periodic spin polarization [1]. This technique cannot be applied to tracking the motion of current-driven spin helices because diffraction amplitude is insensitive to translation of the center of mass of a periodic structure. In this talk, we describe a new experimental technique, Doppler spin velocimetry, capable of resolving displacements of spin polarization at the level of 1 nm on a picosecond time scale [2]. This is accomplished through the use of heterodyne detection to measure the optical phase of the diffracted light. We discuss experiments in which this technique is used to measure the motion of spin helices as a function of temperature, in-plane electric field, and photoinduced spin polarization amplitude. Several striking observations will be reported -- for example, the spin helix velocity changes sign as a function of wavevector and is zero at the wavevector that yields the largest spin lifetime. Another important observation is that the velocity of spin polarization packets becomes equal to the drift velocity of the high-mobility electron gas in the limit of small spin helix amplitude. Finally, we show that spin helices continue propagate at the same speed as the Fermi sea even when the electron drift velocity exceeds the Fermi velocity of 10^7 cm-s-1. In collaboration with J. D. Koralek and J. Orenstein, UC Berkeley and LBNL, D. R. Tibbetts, J. L. Reno, and M. P. Lilly, SNL. Supported by DOE under Contract No. DE-AC02-05CH11231 and DE-AC04-94AL85000. [4pt] [1] J. D. Koralek et al., ``Emergency of the persistent spin helix in semiconductor quantum wells,'' Nature 458, 610-613 (2009). [0pt] [2] L. Yang et al, ``Doppler velocimetry of spin propagation in a two-dimensional electron gas,'' to appear

  5. Current-driven non-linear magnetodynamics in exchange-biased spin valves

    SciTech Connect

    Seinige, Heidi; Wang, Cheng; Tsoi, Maxim

    2015-05-07

    This work investigates the excitation of parametric resonance in exchange-biased spin valves (EBSVs). Using a mechanical point contact, high density dc and microwave currents were injected into the EBSV sample. Observing the reflected microwave power and the small rectification voltage that develops across the contact allows detecting the current-driven magnetodynamics not only in the bulk sample but originating exclusively from the small contact region. In addition to ferromagnetic resonance (FMR), parametric resonance at twice the natural FMR frequency was observed. In contrast to FMR, this non-linear resonance was excited only in the vicinity of the point contact where current densities are high. Power-dependent measurements displayed a typical threshold-like behavior of parametric resonance and a broadening of the instability region with increasing power. Parametric resonance showed a linear shift as a function of applied dc bias which is consistent with the field-like spin-transfer torque induced by current on magnetic moments in EBSV.

  6. COULD COSMIC RAYS AFFECT INSTABILITIES IN THE TRANSITION LAYER OF NONRELATIVISTIC COLLISIONLESS SHOCKS?

    SciTech Connect

    Stroman, Thomas; Pohl, Martin; Niemiec, Jacek; Bret, Antoine

    2012-02-10

    There is an observational correlation between astrophysical shocks and nonthermal particle distributions extending to high energies. As a first step toward investigating the possible feedback of these particles on the shock at the microscopic level, we perform particle-in-cell (PIC) simulations of a simplified environment consisting of uniform, interpenetrating plasmas, both with and without an additional population of cosmic rays. We vary the relative density of the counterstreaming plasmas, the strength of a homogeneous parallel magnetic field, and the energy density in cosmic rays. We compare the early development of the unstable spectrum for selected configurations without cosmic rays to the growth rates predicted from linear theory, for assurance that the system is well represented by the PIC technique. Within the parameter space explored, we do not detect an unambiguous signature of any cosmic-ray-induced effects on the microscopic instabilities that govern the formation of a shock. We demonstrate that an overly coarse distribution of energetic particles can artificially alter the statistical noise that produces the perturbative seeds of instabilities, and that such effects can be mitigated by increasing the density of computational particles.

  7. Synchrotron x-ray study of the smectic layer directional instability

    PubMed

    Dierking; Glusen; Lagerwall; Ober

    2000-02-01

    We have investigated the phenomenon of field-induced smectic layer instability, as monitored by synchrotron x-ray scattering. This instability means that, upon application of time-asymmetric electric fields to chiral smectics, the layer direction seems to "rotate" locally around an axis given by the direction of the applied field. For moderate values of field amplitude and asymmetry, domains with a favored layer inclination grow at the expense of unfavored ones, while larger fields and asymmetries generally lead to a chaotic flow behavior. At moderate amplitudes, we have followed the process of the horizontal layer folding (or horizontal chevron domain formation) and the smectic C* layer reorientation of ferroelectric liquid crystals by applying symmetric and asymmetric wave forms, respectively, and performing time resolved x-ray measurements. The studies unambiguously show the formation of a horizontal (in-plane, i.e., in a plane parallel to the cell substrates) chevron domain structure from a nonoriented sample by application of a symmetric electric field of sufficient amplitude. It is then demonstrated that a transition from the horizontal chevron domain structure to an in-plane uniform smectic layer direction takes place on application of asymmetric electric wave forms. Reversal of the field asymmetry reverses the inclination direction and selects the other layer normal direction as the uniform end state. The in-plane smectic layer reorientation process is followed here as it evolves, and analyzed directly by means of x-ray scattering. PMID:11046442

  8. Instabilities in decelerating supersonic flows with applications to cosmic ray shocks

    NASA Technical Reports Server (NTRS)

    Zank, A. P.; Mckenzie, J. F.

    1985-01-01

    The nature of instabilities in cosmic ray shocks is investigated by using two distinct models for the shock wave. For wavelengths which are short relative to the thickness of the shock wave, the shock is treated as a smoothly decelerating low, and an appropriate JWKB type expansion is used to describe the perturbations to the flow. In this, the short wavelength regime, the presence of squeezing and an effective g renders strong cosmic ray shocks unstable in a way which is similar to instabilities in other supersonic flows, such as in de Laval nozzle flow or a heat conduction dominated shock wave. In the long wavelength limit, where the shock is treated as a discontinuous transition, a stability function is derived which, if negative, corresponds to unstable disturbances growing exponentially in time. In this case, it was found that if the cosmic ray fluid is relativistic (gamma sub c = 4/3) and the background plasma ideal (gamma = 5/3), then strong shocks are unstable.

  9. On different types of instabilities in black hole accretion discs: implications for X-ray binaries and active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Janiuk, Agnieszka; Czerny, Bożena

    2011-07-01

    We discuss two important instability mechanisms that may lead to the limit-cycle oscillations of the luminosity of the accretion discs around compact objects: ionization instability and radiation pressure instability. Ionization instability is well established as a mechanism of X-ray novae eruptions in black hole binary systems, but its applicability to active galactic nuclei (AGN) is still problematic. Radiation pressure theory has still a very weak observational background in any of these sources. In this paper, we attempt to confront the parameter space of these instabilities with the observational data. At the basis of this simple survey of sources properties, we argue that the radiation pressure instability is likely to be present in several Galactic sources with the Eddington ratios being above 0.15 and in AGN with the Eddington ratio above 0.025. Our results favour the parametrization of the viscosity through the geometrical mean of the radiation and gas pressure in both Galactic sources and AGN. More examples of the quasi-regular outbursts in the time-scales of 100 s in Galactic sources and hundreds of years in AGN are needed to formulate firm conclusions. We also show that the disc sizes in the X-ray novae are consistent with the ionization instability. This instability may also considerably influence the lifetime cycle and overall complexity in the supermassive black hole environment.

  10. Simulations of Edge Current Driven Kink Modes with BOUT + + code

    NASA Astrophysics Data System (ADS)

    Li, G. Q.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Xia, T. Y.; Ma, C. H.; Xi, P. W.

    2013-10-01

    Edge kink modes (or peeling modes) play a key role in the ELMs. The edge kink modes are driven by peak edge current, which comes from the bootstrap current. We calculated sequences of equilibria with different edge current using CORSICA by keeping total current and pressure profile fixed. Based on these equilibria, with the 3-field BOUT + + code, we calculated the MHD instabilities driven by edge current. For linear low-n ideal MHD modes, BOUT + + results agree with GATO results. With the edge current increasing, the dominant modes are changed from high-n ballooning modes to low-n kink modes. The edge current provides also stabilizing effects on high-n ballooning modes. Furthermore, for edge current scan without keeping total current fixed, the increasing edge current can stabilize the high-n ballooning modes and cannot drive kink modes. The diamagnetic effect can stabilize the high-n ballooning modes, but has no effect on the low-n kink modes. Also, the nonlinear behavior of kink modes is analyzed. Work supported by China MOST grant 2013GB111000 and by China NSF grant 10975161. Also performed for USDOE by LLNL under DE-AC52-07NA27344.

  11. Disk instability and the time-dependent X-ray emission from the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Yi, Insu; Kim, Soon-Wook; Vishniac, Ethan T.; Wheeler, J. C.

    1992-01-01

    The correlation between the disk instability model for the 1981-1989 optical outbursts of the intermediate polar GK Per and the accompanying X-ray emission is examined, and the self-consistency of the combined optical-X-ray model is investigated. Special attention is given to the nature of the transition in the X-ray emission due to the time-dependent accretion rates in the simple column accretion model. The large variation in the efficiency of hard X-ray production is explained.

  12. TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF THE NONRESONANT, COSMIC-RAY-DRIVEN INSTABILITY IN SUPERNOVA REMNANT SHOCKS

    SciTech Connect

    Ohira, Yutaka; Takahara, Fumio; Reville, Brian; Kirk, John G.

    2009-06-10

    In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the 'knee' at 10{sup 15.5} eV. A nonresonant instability driven by the cosmic ray current is thought to be responsible for this effect. We perform two-dimensional, particle-in-cell simulations of this instability. We observe an initial growth of circularly polarized nonpropagating magnetic waves as predicted in linear theory. It is demonstrated that in some cases the magnetic energy density in the growing waves can grow to at least 10 times its initial value. We find no evidence of competing modes, nor of significant modification by thermal effects. At late times, we observe saturation of the instability in the simulation, but the mechanism responsible is an artifact of the periodic boundary conditions and has no counterpart in the supernova-shock scenario.

  13. Ataxia telangiectasia derived iPS cells show preserved x-ray sensitivity and decreased chromosomal instability.

    PubMed

    Fukawatase, Yoshihiro; Toyoda, Masashi; Okamura, Kohji; Nakamura, Ken-ichi; Nakabayashi, Kazuhiko; Takada, Shuji; Yamazaki-Inoue, Mayu; Masuda, Akira; Nasu, Michiyo; Hata, Kenichiro; Hanaoka, Kazunori; Higuchi, Akon; Takubo, Kaiyo; Umezawa, Akihiro

    2014-01-01

    Ataxia telangiectasia is a neurodegenerative inherited disease with chromosomal instability and hypersensitivity to ionizing radiation. iPS cells lacking ATM (AT-iPS cells) exhibited hypersensitivity to X-ray irradiation, one of the characteristics of the disease. While parental ataxia telangiectasia cells exhibited significant chromosomal abnormalities, AT-iPS cells did not show any chromosomal instability in vitro for at least 80 passages (560 days). Whole exome analysis also showed a comparable nucleotide substitution rate in AT-iPS cells. Taken together, these data show that ATM is involved in protection from irradiation-induced cell death. PMID:24970375

  14. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets.

    PubMed

    Woo, Seonghoon; Litzius, Kai; Krüger, Benjamin; Im, Mi-Young; Caretta, Lucas; Richter, Kornel; Mann, Maxwell; Krone, Andrea; Reeve, Robert M; Weigand, Markus; Agrawal, Parnika; Lemesh, Ivan; Mawass, Mohamad-Assaad; Fischer, Peter; Kläui, Mathias; Beach, Geoffrey S D

    2016-05-01

    Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s(-1) as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures. PMID:26928640

  15. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Woo, Seonghoon; Litzius, Kai; Krüger, Benjamin; Im, Mi-Young; Caretta, Lucas; Richter, Kornel; Mann, Maxwell; Krone, Andrea; Reeve, Robert M.; Weigand, Markus; Agrawal, Parnika; Lemesh, Ivan; Mawass, Mohamad-Assaad; Fischer, Peter; Kläui, Mathias; Beach, Geoffrey S. D.

    2016-05-01

    Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s-1 as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures.

  16. Z-pinch diagnostics, plasma and liner instabilities and new x-ray techniques

    SciTech Connect

    Oona, H.; Anderson, B.; Benage, J.

    1996-09-01

    Pulse power experiments of the last several decades have contributed greatly to the understanding of high temperature and high density plasmas and, more recently, to the study of hydrodynamic effects in thick imploding cylinders. Common to all these experiments is the application of a large current pulse to a cylindrically symmetric load, with the resulting Lorenz force compressing the load to produce hydrodynamic motion and/or high temperature, high density plasma. In Los Alamos, Pulsed power experiments are carried out at two facilities. Experiments at low current (from several million to ten million Amperes) are conducted on the Pegasus II capacitor bank. Experiments with higher currents (10`s to 100`s MA range) are performed in Ancho Canyon with the explosively driven Procyon and MAGO magnetic flux compression generator systems. In this paper, the authors present a survey of diagnostic capabilities and results from several sets of experiments. First, they discuss the initiation and growth of instabilities in plasmas generated from the implosion of hollow z-pinches in the pegasus and Procyon experiments. Next they discuss spectroscopic data from the plasmas produced by the MAGO system. They also show time resolved imaging data from thick ({approximately} .4 mm) liner implosions. Finally, the authors discuss improvements to x-ray and visible light imaging and spectrographic diagnostic techniques. The emphasis of this paper is not so much a detailed discussion of the experiments, but a presentation of imaging and spectroscopic results and the implications of these observations to the experiments.

  17. ANALYSIS OF MAGNETOROTATIONAL INSTABILITY WITH THE EFFECT OF COSMIC-RAY DIFFUSION

    SciTech Connect

    Kuwabara, Takuhito; Ko, Chung-Ming E-mail: cmko@astro.ncu.edu.tw

    2015-01-10

    We present the results obtained from the linear stability analysis and 2.5 dimensional magnetohydrodynamic (MHD) simulations of magnetorotational instability (MRI), including the effects of cosmic rays (CRs). We took into account the CR diffusion along the magnetic field but neglected the cross-field-line diffusion. Two models are considered in this paper: the shearing box model and differentially rotating cylinder model. We studied how MRI is affected by the initial CR pressure (i.e., energy) distribution. In the shearing box model, the initial state is uniform distribution. Linear analysis shows that the growth rate of MRI does not depend on the value of the CR diffusion coefficient. In the differentially rotating cylinder model, the initial state is a constant angular momentum polytropic disk threaded by a weak uniform vertical magnetic field. Linear analysis shows that the growth rate of MRI becomes larger if the CR diffusion coefficient is larger. Both results are confirmed by MHD simulations. The MHD simulation results show that the outward movement of matter by the growth of MRI is not impeded by the CR pressure gradient, and the centrifugal force that acts on the concentrated matter becomes larger. Consequently, the growth rate of MRI is increased. On the other hand, if the initial CR pressure is uniform, then the growth rate of the MRI barely depends on the value of the CR diffusion coefficient.

  18. Tomographic analysis of the nonthermal x-ray bursts during disruption instability in the T-10 tokamak

    NASA Astrophysics Data System (ADS)

    Savrukhin, P. V.; Ermolaeva, A. I.; Shestakov, E. A.; Khramenkov, A. V.

    2014-10-01

    Non-thermal x-ray radiation (Eγ up to 150 keV) is measured in the T-10 tokamaks during disruption instability using two sets of CdTe detectors (10 vertical and 7 horizontal view detectors). Special narrow cupper tubes collimators with lead screening and CdTe detectors integrated with amplifiers inside metallic containers provides enhanced spatial resolution of the system (r ˜ 3 cm) and assures protection from the parasitic hard x-ray (Eγ up to 1.5 MeV) and electromagnetic loads during disruption. Spatial localization of the nonthermal x-ray emissivity is reconstructed using tomographic Cormack technique with SVD matrix inversion. Analysis indicated appearance of an intensive non-thermal x-ray bursts during initial stage of the disruptions at high density. The bursts are characterized by repetitive spikes (2-3 kHz) of the x-ray emissivity from the plasma core area. Analysis indicated that the spikes can be connected with acceleration of the non-thermal electrons in enhanced longitudinal electric fields induced during energy quench at the disruption instability.

  19. Tomographic analysis of the nonthermal x-ray bursts during disruption instability in the T-10 tokamak

    SciTech Connect

    Savrukhin, P. V.; Ermolaeva, A. I.; Shestakov, E. A.; Khramenkov, A. V.

    2014-10-01

    Non-thermal x-ray radiation (E{sub γ} up to 150 keV) is measured in the T-10 tokamaks during disruption instability using two sets of CdTe detectors (10 vertical and 7 horizontal view detectors). Special narrow cupper tubes collimators with lead screening and CdTe detectors integrated with amplifiers inside metallic containers provides enhanced spatial resolution of the system (r ~ 3 cm) and assures protection from the parasitic hard x-ray (E{sub γ} up to 1.5 MeV) and electromagnetic loads during disruption. Spatial localization of the nonthermal x-ray emissivity is reconstructed using tomographic Cormack technique with SVD matrix inversion. Analysis indicated appearance of an intensive non-thermal x-ray bursts during initial stage of the disruptions at high density. The bursts are characterized by repetitive spikes (2–3 kHz) of the x-ray emissivity from the plasma core area. Analysis indicated that the spikes can be connected with acceleration of the non-thermal electrons in enhanced longitudinal electric fields induced during energy quench at the disruption instability.

  20. Tomographic analysis of the nonthermal x-ray bursts during disruption instability in the T-10 tokamak.

    PubMed

    Savrukhin, P V; Ermolaeva, A I; Shestakov, E A; Khramenkov, A V

    2014-10-01

    Non-thermal x-ray radiation (Eγ up to 150 keV) is measured in the T-10 tokamaks during disruption instability using two sets of CdTe detectors (10 vertical and 7 horizontal view detectors). Special narrow cupper tubes collimators with lead screening and CdTe detectors integrated with amplifiers inside metallic containers provides enhanced spatial resolution of the system (r ∼ 3 cm) and assures protection from the parasitic hard x-ray (Eγ up to 1.5 MeV) and electromagnetic loads during disruption. Spatial localization of the nonthermal x-ray emissivity is reconstructed using tomographic Cormack technique with SVD matrix inversion. Analysis indicated appearance of an intensive non-thermal x-ray bursts during initial stage of the disruptions at high density. The bursts are characterized by repetitive spikes (2-3 kHz) of the x-ray emissivity from the plasma core area. Analysis indicated that the spikes can be connected with acceleration of the non-thermal electrons in enhanced longitudinal electric fields induced during energy quench at the disruption instability. PMID:25362394

  1. Disc instability models for X-ray transients: evidence for evaporation and low α-viscosity?

    NASA Astrophysics Data System (ADS)

    Menou, Kristen; Hameury, Jean-Marie; Lasota, Jean-Pierre; Narayan, Ramesh

    2000-05-01

    We construct time-dependent models of accretion discs around black holes and neutron stars. We investigate the effect that evaporation of the inner disc regions during quiescence has upon the predictions of the disc instability model (DIM) for these systems. We do not include irradiation of the disc in the models. Removing the inner, most unstable, parts of the accretion disc increases the predicted recurrence times. However, DIMs with values of the viscosity parameter αhot~0.1 and αcold~0.02 (values typically used in applications of the DIM to standard dwarf nova outbursts) fail to reproduce the long recurrence times of soft X-ray transients (unless we resort to fine-tuning the parameters), independent of the evaporation strength. We show that models in which evaporation is included and a smaller value of αcold (~0.005) used do reproduce the long recurrence times and the accretion rates at the level of the Eddington rate observed in outburst. The large difference between the values of αhot and αcold, if confirmed once disc irradiation is included, suggests that several viscosity mechanisms operate in these accretion discs. For some parameter sets our models predict re-flares during the decline from outburst. The re-flares are a physical property of the model and result from the formation of a heating front in the wake of an initial cooling front, and subsequent multiple front reflections. The re-flares disappear in low-α models where front reflection cannot occur.

  2. A CORONAL MASS EJECTION AND HARD X-RAY EMISSIONS ASSOCIATED WITH THE KINK INSTABILITY

    SciTech Connect

    Cho, Kyung-Suk; Bong, Su-Chan; Kim, Yeon-Han; Park, Young-Deuk; Lee, Jeongwoo; Joshi, Bhuwan

    2009-09-20

    We present a morphological study of the 2004 August 18 solar eruption that occurred in the active region NOAA 10656 near the west limb using extreme-ultraviolet (EUV) data from the Transition Region and Coronal Explorer (TRACE), Halpha filtergram of Big Bear Solar Observatory, white light images of Mauna Loa Solar Observatory (MLSO), hard X-ray (HXR) data of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and microwave data of the Owens Valley Solar Array. In this event, we have an excellent set of observations for tracing the early evolution of the coronal mass ejection (CME) from a flux rope emergence to its propagation into space as a well-connected series of events thanks to the coronameter's field of view (FOV) down to 1.1 solar radius in an overlap with that of the TRACE. This data set reveals continuously evolving EUV, Halpha, and WL features that suggest the rise of a small, low-lying loop, its writhing motion, break of the kinked loop at its crossing point, and transformation of the ejecta to the CME. The HXR and microwave sources are found in varying locations with a complicated temporal dependence, which, we interpret, is due to two successive flares in the event. The first flare appears to be associated with the rise of the small loop, which then triggers the second flare. During the second flare a HXR coronal source is detected at the crossing point of the kinked loop, and more intriguingly, the kinked loop apparently breaks at the crossing point of the two legs, which indicates a magnetic reconnection at the X-point configuration. After the break of the kinked UV loop, a CME structure shows up in the MLSO FOV, and propagates away from the Sun. It is concluded that this CME occurred due to the kink instability.

  3. Current-driven Langmuir oscillations and amplitude modulations—Another view on electron beam-plasma interaction

    NASA Astrophysics Data System (ADS)

    Sauer, K.; Sydora, R. D.

    2015-01-01

    origin of Langmuir amplitude modulations and harmonic waves observed in the solar wind and in planetary foreshock regions is investigated in beam plasmas where the saturation process of the beam instability is accompanied with the formation of a plateau distribution. This saturated state represents a current which is shown to drive homogeneous electric field oscillations at the plasma frequency. This simple mechanism has been ignored in most numerical studies based on Vlasov or particle-in-cell simulations because of the use of the Poisson equation which is not suitable to describe the mechanism of current drive in plasmas with immobile ions; instead, Ampere's law must be used. A simple fluid description of stable plateau plasmas, coupled with Ampere's law, is applied to illustrate the basic elements of current-driven Langmuir oscillations. If beam-generated Langmuir/electron-acoustic waves with frequencies above or below the plasma frequency are simultaneously present, beating of both wave modes leads to Langmuir amplitude modulations, thus providing an alternative to parametric decay. Furthermore, very important implications of our studies (presented separately) concern the electrostatic and electromagnetic second harmonic generation by nonlinear interaction of Langmuir oscillations with finite wave number modes which are driven by the plateau current as well.

  4. Current-Driven Drift Wave Turbulence and Electron Thermal Transport in Tokamaks

    NASA Astrophysics Data System (ADS)

    Lee, C.; Diamond, P. H.; Porkolab, M.

    2009-11-01

    Recent analyses (Y. Lin, M. Porkolab; 2009) have indicated that the ``usual suspects'' for the mechanism of electron thermal transport, such as ITG, ETG, CTEM modes, etc, cannot explain results from modest density, Te>Ti plasmas, in either OH or ECH heating regimes. Interestingly, such plasmas exhibit very large toroidal current drift parameters vd/cs, thus naturally suggesting a re-visitation of current driven drift waves. In this paper, we discuss the linear, quasilinear and non-linear theory of current driven drift waves in tokamaks. Parallel electron velocity scattering, a critical effect beyond the capacity of most, gyrokinetic codes is a major focus of investigations. The coupled transport of current density and heat are considered. Work is ongoing and results will be presented.

  5. Rayleigh-Taylor instabilities in Type Ia supernova remnants undergoing cosmic ray particle acceleration - low adiabatic index solutions

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Yueh

    2011-07-01

    This study investigates the evolution of Rayleigh-Taylor (R-T) instabilities in Type Ia supernova remnants that are associated with a low adiabatic index γ, where γ < 5/3, which reflects the expected change in the supernova shock structure as a result of cosmic ray particle acceleration. Extreme cases, such as the case with the maximum compression ratio that corresponds to γ= 1.1, are examined. As γ decreases, the shock compression ratio rises, and an increasingly narrow intershock region with a more pronounced initial mixture of R-T unstable gas is produced. Consequently, the remnant outline may be perturbed by small-amplitude, small-wavelength bumps. However, as the instability decays over time, the extent of convective mixing in terms of the ratio of the radius of the R-T fingers to the blast wave does not strongly depend on the value of γ for γ≥ 1.2. As a result of the age of the remnant, the unstable gas cannot extend sufficiently far to form metal-enriched filaments of ejecta material close to the periphery of Tycho's supernova remnant. The consistency of the dynamic properties of Tycho's remnant with the adiabatic model γ= 5/3 reveals that the injection of cosmic rays is too weak to alter the shock structure. Even with very efficient acceleration of cosmic rays at the shock, significantly enhanced mixing is not expected in Type Ia supernova remnants.

  6. Current-driven antivortex core resonance measured by the rectifying effect

    NASA Astrophysics Data System (ADS)

    Goto, Minori; Nozaki, Yukio

    2016-02-01

    We demonstrate the current-driven resonance of a single antivortex core confined in a cross-shaped Ni81Fe19 wire. The antivortex core dynamics can be excited purely by spin transfer torque; therefore, it is significant to understand the current-induced magnetization dynamics. The antivortex core resonance can be measured from the frequency dependence of a rectified voltage generated by an alternating current application. We found that the resonance frequency and peak amplitude greatly depend on the external magnetic field. This result is in good agreement with micromagnetic simulation.

  7. Implications of plasma beam instabilities for the statistics of the Fermi hard gamma-ray blazars and the origin of the extragalactic gamma-ray background

    SciTech Connect

    Broderick, Avery E.; Pfrommer, Christoph; Puchwein, Ewald; Chang, Philip

    2014-08-01

    Fermi has been instrumental in constraining the luminosity function and redshift evolution of gamma-ray bright BL Lac objects, a subpopulation of blazars with almost featureless optical spectra. This includes limits on the spectrum and anisotropy of the extragalactic gamma-ray background (EGRB), redshift distribution of nearby Fermi active galactic nuclei (AGNs), and the construction of a logN-log S relation. Based on these, it has been argued that the evolution of the gamma-ray bright BL Lac population must be much less dramatic than that of other AGNs. However, critical to such claims is the assumption that inverse Compton cascades reprocess emission above a TeV into the Fermi energy range, substantially enhancing the strength of the observed limits. Here we demonstrate that in the absence of such a process, due, e.g., to the presence of virulent plasma beam instabilities that preempt the cascade, a population of TeV-bright BL Lac objects that evolve similarly to quasars is consistent with the population of hard gamma-ray BL Lac objects observed by Fermi. Specifically, we show that a simple model for the properties and luminosity function is simultaneously able to reproduce their logN-log S relation, local redshift distribution, and contribution to the EGRB and its anisotropy without any free parameters. Insofar as the naturalness of a picture in which the hard gamma-ray BL Lac population exhibits the strong redshift evolution observed in other tracers of the cosmological history of accretion onto halos is desirable, this lends support for the absence of the inverse Compton cascades and the existence of the beam plasma instabilities.

  8. Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. III. Collisionless tearing mode

    NASA Astrophysics Data System (ADS)

    Liu, Dongjian; Bao, Jian; Han, Tao; Wang, Jiaqi; Lin, Zhihong

    2016-02-01

    A finite-mass electron fluid model for low frequency electromagnetic fluctuations, particularly the collisionless tearing mode, has been implemented in the gyrokinetic toroidal code. Using this fluid model, linear properties of the collisionless tearing mode have been verified. Simulations verify that the linear growth rate of the single collisionless tearing mode is proportional to De2, where De is the electron skin depth. On the other hand, the growth rate of a double tearing mode is proportional to De in the parameter regime of fusion plasmas.

  9. Induction of Genomic Instability In Vivo by Low Doses of 137Cs gamma rays

    SciTech Connect

    Rithidech, Kanokporn; Simon, Sanford, R.; Whorton, Elbert, B.

    2006-01-06

    The overall goal of this project is to determine if low doses (below or equal to the level traditionally requiring human radiation protection, i.e. less than or equal to 10 cGy) of low LET radiation can induce genomic instability. The magnitude of genomic instability was measured as delayed chromosome instability in bone marrow cells of exposed mice with different levels of endogenous DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity, i.e. high (C57BL/6J mice), intermediate (BALB/cJ mice), and extremely low (Scid mice). In addition, at early time points (1 and 4 hrs) following irradiation, levels of activation of nuclear factor-kappa B (NF-{kappa}B), a transcription factor known to be involved in regulating the expression of genes responsible for cell protection following stimuli, were measured in these cells. Bone marrow cells were collected at different times following irradiation, i.e. 1 hr, 4 hrs, 1 month, and 6 months. A total of five mice per dose per strain were sacrificed at each time point for sample collection. As a result, a total of 80 mice from each strain were used. The frequency and the type of metaphase chromosome aberrations in bone marrow cells collected from exposed mice at different times following irradiation were used as markers for radiation-induced genomic instability. A three-color fluorescence in situ hybridization (FISH) protocol for mouse chromosomes 1, 2, and 3 was used for the analysis of delayed stable chromosomal aberrations in metaphase cells. All other visible chromatid-type aberrations and gross structural abnormalities involving non-painted chromosomes were also evaluated on the same metaphase cells used for scoring the stable chromosomal aberrations of painted chromosomes. Levels of nuclear factor-kappa B (NF-{kappa}B) activation were also determined in cells at 1 and 4 hrs following irradiation (indicative of early responses).

  10. High Efficiency Alternating Current Driven Organic Light Emitting Devices Employing Active Semiconducting Gate Layers

    NASA Astrophysics Data System (ADS)

    Smith, Gregory; Xu, Junwei; Carroll, David

    2015-03-01

    In this work, we describe the role of semiconductor-polymer interfaces in alternating current (AC) driven organic electroluminescent (EL) devices. We implement inorganic semiconducting materials between the external contact and the active layers in organic light EL devices. Precise control of capacitance and charge injection is required to realize bright and efficient large area AC driven devices. We show how this architecture results in active gating to the polymer layers, resulting in the novel ability to control the capacitance and charge injection characteristics. We propose a model based on band bending at the semiconductor-polymer interface. Furthermore, we elucidate the influence of the semiconductor-polymer interface on the internally coupled magnetic field generated in an alternating current driven organic light emitting device configuration. Magnetic fields can alter the ratios of singlet and triplet populations, and we show that internal generation of a magnetic field can dramatically alter the efficiency of light emission in organic EL devices.

  11. Numerical Simulation of Non-Inductive Current Driven Scenario in EAST Using Neutral Beam Injection

    NASA Astrophysics Data System (ADS)

    Li, Hao; Wu, Bin; Wang, Jinfang; Wang, Ji; Hu, Chundong

    2015-01-01

    For achieving the scientific mission of long pulse and high performance operation, experimental advanced superconducting tokamak (EAST) applies fully superconducting magnet technology and is equiped with high power auxiliary heating system. Besides RF (Radio Frequency) wave heating, neutral beam injection (NBI) is an effective heating and current drive method in fusion research. NBCD (Neutral Beam Current Drive) as a viable non-inductive current drive source plays an important role in quasi-steady state operating scenario for tokamak. The non-inductive current driven scenario in EAST only by NBI is predicted using the TSC/NUBEAM code. At the condition of low plasma current and moderate plasma density, neutral beam injection heats the plasma effectively and NBCD plus bootstrap current accounts for a large proportion among the total plasma current for the flattop time.

  12. Chromosome instability and X-ray hypersensitivity in a microcephalic and growth-retarded child

    SciTech Connect

    Barbi, G.; Scheres, J.M.; Schindler, D.; Taalman, R.D.; Rodens, K.; Mehnert, K.; Mueller, M.S.; Seyschab, H. )

    1991-07-01

    The authors report on a microcephalic, growth-retarded newborn girl without major anomalies who has chromosome instability in lymphocytes and fibroblasts. Frequent involvement of bands 7p13, 7q34, 14q11, and 14q32 suggested the diagnosis of ataxia telangiectasia (AT) or a related disorder. Supportive evidence was radioresistant DNA synthesis in fibroblasts and radiation hypersensitivity of short-term lymphocyte cultures. Follow-up for nearly 4 years showed largely normal development, and no signs of telangiectasia, ataxia, or immunodeficiency. Serum AFP levels turned from elevated at age 5 months to normal at age 2 years. They propose that their patient belongs to the expanding category of AT-related genetic disorders, probably to the Nijmegen breakage syndrome.

  13. Current-driven vortex domain wall motion in wire-tube nanostructures

    NASA Astrophysics Data System (ADS)

    Espejo, A. P.; Vidal-Silva, N.; López-López, J. A.; Goerlitz, D.; Nielsch, K.; Escrig, J.

    2015-03-01

    We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.

  14. Current-driven vortex domain wall motion in wire-tube nanostructures

    SciTech Connect

    Espejo, A. P.; Vidal-Silva, N.; López-López, J. A.; Goerlitz, D.; Nielsch, K.; Escrig, J.

    2015-03-30

    We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.

  15. Magnetic Amplification by Magnetized Cosmic Rays in Supernova Remnant Shocks

    NASA Astrophysics Data System (ADS)

    Riquelme, Mario A.; Spitkovsky, Anatoly

    2010-07-01

    X-ray observations of synchrotron rims in supernova remnant (SNR) shocks show evidence of efficient electron acceleration and strong magnetic field amplification (a factor of ~100 between the upstream and downstream medium). This amplification may be due to plasma instabilities driven by shock-accelerated particles or cosmic rays (CRs), as they propagate ahead of the shocks. One candidate process is the cosmic ray current-driven (CRCD) instability caused by the electric current of "unmagnetized" CRs (i.e., CRs whose Larmor radii are much larger than the length scale of the CRCD modes) propagating parallel to the upstream magnetic field. Particle-in-cell (PIC) simulations have shown that the back-reaction of the amplified field on CRs would limit the amplification factor of this instability to less than ~10 in galactic SNRs (not including the additional field compression at the shock). In this paper, we study the possibility of further amplification driven near shocks by "magnetized" CRs, whose Larmor radii are smaller than the length scale of the field that was previously amplified by the CRCD instability. We find that additional amplification can occur due to a new instability, driven by the CR current perpendicular to the field, which we term the perpendicular current-driven instability (PCDI). We derive the growth rate of this instability and, using PIC simulations, study its non-linear evolution. We show that the maximum amplification of PCDI is determined by the disruption of CR current, which happens when CR Larmor radii in the amplified field become comparable to the length scale of the instability. We find that, in regions close to the shock, PCDI grows on scales smaller than the scales of the CRCD instability, and, therefore, it results in larger amplification of the field (amplification factor up to ~45). One possible observational signature of PCDI is the characteristic dependence of the amplified field on the shock velocity, B 2 vprop v 2 sh, which

  16. MAGNETIC AMPLIFICATION BY MAGNETIZED COSMIC RAYS IN SUPERNOVA REMNANT SHOCKS

    SciTech Connect

    Riquelme, Mario A.; Spitkovsky, Anatoly E-mail: anatoly@astro.princeton.ed

    2010-07-10

    X-ray observations of synchrotron rims in supernova remnant (SNR) shocks show evidence of efficient electron acceleration and strong magnetic field amplification (a factor of {approx}100 between the upstream and downstream medium). This amplification may be due to plasma instabilities driven by shock-accelerated particles or cosmic rays (CRs), as they propagate ahead of the shocks. One candidate process is the cosmic ray current-driven (CRCD) instability caused by the electric current of 'unmagnetized' CRs (i.e., CRs whose Larmor radii are much larger than the length scale of the CRCD modes) propagating parallel to the upstream magnetic field. Particle-in-cell (PIC) simulations have shown that the back-reaction of the amplified field on CRs would limit the amplification factor of this instability to less than {approx}10 in galactic SNRs (not including the additional field compression at the shock). In this paper, we study the possibility of further amplification driven near shocks by 'magnetized' CRs, whose Larmor radii are smaller than the length scale of the field that was previously amplified by the CRCD instability. We find that additional amplification can occur due to a new instability, driven by the CR current perpendicular to the field, which we term the perpendicular current-driven instability (PCDI). We derive the growth rate of this instability and, using PIC simulations, study its non-linear evolution. We show that the maximum amplification of PCDI is determined by the disruption of CR current, which happens when CR Larmor radii in the amplified field become comparable to the length scale of the instability. We find that, in regions close to the shock, PCDI grows on scales smaller than the scales of the CRCD instability, and, therefore, it results in larger amplification of the field (amplification factor up to {approx}45). One possible observational signature of PCDI is the characteristic dependence of the amplified field on the shock velocity, B {sup

  17. Hydrodynamic instability growth of three-dimensional, "native-roughness" modulations in x-ray driven, spherical implosions at the National Ignition Facility

    NASA Astrophysics Data System (ADS)

    Smalyuk, V. A.; Weber, S. V.; Casey, D. T.; Clark, D. S.; Field, J. E.; Haan, S. W.; Hammel, B. A.; Hamza, A. V.; Hoover, D. E.; Landen, O. L.; Nikroo, A.; Robey, H. F.; Weber, C. R.

    2015-07-01

    Hydrodynamic instability growth experiments with three-dimensional (3-D) surface-roughness modulations were performed on plastic (CH) shell spherical implosions at the National Ignition Facility (NIF) [E. M. Campbell, R. Cauble, and B. A. Remington, AIP Conf. Proc. 429, 3 (1998)]. The initial capsule outer-surface roughness was similar to the standard specifications ("native roughness") used in a majority of implosions on NIF. The experiments included instability growth measurements of the perturbations seeded by the thin membranes (or tents) used to hold the capsules inside the hohlraums. In addition, initial modulations included two divots used as spatial fiducials to determine the convergence in the experiments and to check the accuracy of 3D simulations in calculating growth of known initial perturbations. The instability growth measurements were performed using x-ray, through-foil radiography of one side of the imploding shell, based on time-resolved pinhole imaging. Averaging over 30 similar images significantly increases the signal-to-noise ratio, making possible a comparison with 3-D simulations. At a convergence ratio of ˜3, the measured tent and divot modulations were close to those predicted by 3-D simulations (within ˜15%-20%), while measured 3-D, broadband modulations were ˜3-4 times larger than those simulated based on the growth of the known imposed initial surface modulations. In addition, some of the measured 3-D features in x-ray radiographs did not resemble those characterized on the outer capsule surface before the experiments. One of the hypotheses to explain the results is based on the increased instability amplitudes due to modulations of the oxygen content in the bulk of the capsule. As the target assembly and handling procedures involve exposure to UV light, this can increase the uptake of the oxygen into the capsule, with irregularities in the oxygen seeding hydrodynamic instabilities. These new experimental results have prompted

  18. Hydrodynamic instability growth of three-dimensional, “native-roughness” modulations in x-ray driven, spherical implosions at the National Ignition Facility

    SciTech Connect

    Smalyuk, V. A.; Weber, S. V.; Casey, D. T.; Clark, D. S.; Field, J. E.; Haan, S. W.; Hammel, B. A.; Hamza, A. V.; Landen, O. L.; Robey, H. F.; Weber, C. R.; Hoover, D. E.; Nikroo, A.

    2015-07-15

    Hydrodynamic instability growth experiments with three-dimensional (3-D) surface-roughness modulations were performed on plastic (CH) shell spherical implosions at the National Ignition Facility (NIF) [E. M. Campbell, R. Cauble, and B. A. Remington, AIP Conf. Proc. 429, 3 (1998)]. The initial capsule outer-surface roughness was similar to the standard specifications (“native roughness”) used in a majority of implosions on NIF. The experiments included instability growth measurements of the perturbations seeded by the thin membranes (or tents) used to hold the capsules inside the hohlraums. In addition, initial modulations included two divots used as spatial fiducials to determine the convergence in the experiments and to check the accuracy of 3D simulations in calculating growth of known initial perturbations. The instability growth measurements were performed using x-ray, through-foil radiography of one side of the imploding shell, based on time-resolved pinhole imaging. Averaging over 30 similar images significantly increases the signal-to-noise ratio, making possible a comparison with 3-D simulations. At a convergence ratio of ∼3, the measured tent and divot modulations were close to those predicted by 3-D simulations (within ∼15%–20%), while measured 3-D, broadband modulations were ∼3–4 times larger than those simulated based on the growth of the known imposed initial surface modulations. In addition, some of the measured 3-D features in x-ray radiographs did not resemble those characterized on the outer capsule surface before the experiments. One of the hypotheses to explain the results is based on the increased instability amplitudes due to modulations of the oxygen content in the bulk of the capsule. As the target assembly and handling procedures involve exposure to UV light, this can increase the uptake of the oxygen into the capsule, with irregularities in the oxygen seeding hydrodynamic instabilities. These new experimental results have

  19. Current-driven nanowire formation on surfaces of crystalline conducting substrates

    NASA Astrophysics Data System (ADS)

    Kumar, Ashish; Dasgupta, Dwaipayan; Dimitrakopoulos, Christos; Maroudas, Dimitrios

    2016-05-01

    The formation and precise manipulation of nanoscale features by controlling macroscopic forces is essential to advancing nanotechnology. Toward this end, we report here a theoretical study on formation of nanowires with precisely controlled widths, starting from single-layer conducting islands on crystalline conducting substrates under the controlled action of macroscopic forcing provided by an externally applied electric field that drives island edge electromigration. Numerical simulations based on an experimentally validated model and supported by linear stability theory show that large-size islands undergo a current-induced fingering instability, leading to nanowire formation after finger growth. Depending on the substrate surface crystallographic orientation, necking instabilities after fingering lead to the formation of multiple parallel nanowires per island. In all cases, the axis of the formed nanowires is aligned with the direction of the externally applied electric field. The nanowires have constant widths, on the order of 10 nm, which can be tuned by controlling the externally applied electric field strength. Our findings have important implications for developing future lithography-free nanofabrication and nanoelectronic patterning techniques.

  20. Investigation of domain wall motion in RE-TM magnetic wire towards a current driven memory and logic

    NASA Astrophysics Data System (ADS)

    Awano, Hiroyuki

    2015-06-01

    Current driven magnetic domain wall (DW) motions of ferri-magnetic TbFeCo wires have been investigated. In the case of a Si substrate, the critical current density (Jc) of DW motion was successfully reduced to 3×106 A/cm2. Moreover, by using a polycarbonate (PC) substrate with a molding groove of 600 nm width, the Jc was decreased to 6×105 A/cm2. In order to fabricate a logic in memory, a current driven spin logics (AND, OR, NOT) have been proposed and successfully demonstrated under the condition of low Jc. These results indicate that TbFeCo nanowire is an excellent candidate for next generation power saving memory and logic.

  1. Current-driven dynamics of skyrmions stabilized in MnSi nanowires revealed by topological Hall effect

    PubMed Central

    Liang, Dong; DeGrave, John P.; Stolt, Matthew J.; Tokura, Yoshinori; Jin, Song

    2015-01-01

    Skyrmions hold promise for next-generation magnetic storage as their nanoscale dimensions may enable high information storage density and their low threshold for current-driven motion may enable ultra-low energy consumption. Skyrmion-hosting nanowires not only serve as a natural platform for magnetic racetrack memory devices but also stabilize skyrmions. Here we use the topological Hall effect (THE) to study phase stability and current-driven dynamics of skyrmions in MnSi nanowires. THE is observed in an extended magnetic field-temperature window (15–30 K), suggesting stabilization of skyrmions in nanowires compared with the bulk. Furthermore, we show in nanowires that under the high current density of 108–109 A m−2, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field in the extended skyrmion phase region. These results open up the exploration of skyrmions in nanowires for fundamental physics and magnetic storage technologies. PMID:26400204

  2. Current-driven dynamics of skyrmions stabilized in MnSi nanowires revealed by topological Hall effect

    NASA Astrophysics Data System (ADS)

    Liang, Dong; Degrave, John P.; Stolt, Matthew J.; Tokura, Yoshinori; Jin, Song

    2015-09-01

    Skyrmions hold promise for next-generation magnetic storage as their nanoscale dimensions may enable high information storage density and their low threshold for current-driven motion may enable ultra-low energy consumption. Skyrmion-hosting nanowires not only serve as a natural platform for magnetic racetrack memory devices but also stabilize skyrmions. Here we use the topological Hall effect (THE) to study phase stability and current-driven dynamics of skyrmions in MnSi nanowires. THE is observed in an extended magnetic field-temperature window (15-30 K), suggesting stabilization of skyrmions in nanowires compared with the bulk. Furthermore, we show in nanowires that under the high current density of 108-109 A m-2, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field in the extended skyrmion phase region. These results open up the exploration of skyrmions in nanowires for fundamental physics and magnetic storage technologies.

  3. Linear calculations of edge current driven kink modes with BOUT++ code

    SciTech Connect

    Li, G. Q. Xia, T. Y.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Ma, C. H.; Xi, P. W.

    2014-10-15

    This work extends previous BOUT++ work to systematically study the impact of edge current density on edge localized modes, and to benchmark with the GATO and ELITE codes. Using the CORSICA code, a set of equilibria was generated with different edge current densities by keeping total current and pressure profile fixed. Based on these equilibria, the effects of the edge current density on the MHD instabilities were studied with the 3-field BOUT++ code. For the linear calculations, with increasing edge current density, the dominant modes are changed from intermediate-n and high-n ballooning modes to low-n kink modes, and the linear growth rate becomes smaller. The edge current provides stabilizing effects on ballooning modes due to the increase of local shear at the outer mid-plane with the edge current. For edge kink modes, however, the edge current does not always provide a destabilizing effect; with increasing edge current, the linear growth rate first increases, and then decreases. In benchmark calculations for BOUT++ against the linear results with the GATO and ELITE codes, the vacuum model has important effects on the edge kink mode calculations. By setting a realistic density profile and Spitzer resistivity profile in the vacuum region, the resistivity was found to have a destabilizing effect on both the kink mode and on the ballooning mode. With diamagnetic effects included, the intermediate-n and high-n ballooning modes can be totally stabilized for finite edge current density.

  4. Linear calculations of edge current driven kink modes with BOUT++ code

    NASA Astrophysics Data System (ADS)

    Li, G. Q.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Xia, T. Y.; Ma, C. H.; Xi, P. W.

    2014-10-01

    This work extends previous BOUT++ work to systematically study the impact of edge current density on edge localized modes, and to benchmark with the GATO and ELITE codes. Using the CORSICA code, a set of equilibria was generated with different edge current densities by keeping total current and pressure profile fixed. Based on these equilibria, the effects of the edge current density on the MHD instabilities were studied with the 3-field BOUT++ code. For the linear calculations, with increasing edge current density, the dominant modes are changed from intermediate-n and high-n ballooning modes to low-n kink modes, and the linear growth rate becomes smaller. The edge current provides stabilizing effects on ballooning modes due to the increase of local shear at the outer mid-plane with the edge current. For edge kink modes, however, the edge current does not always provide a destabilizing effect; with increasing edge current, the linear growth rate first increases, and then decreases. In benchmark calculations for BOUT++ against the linear results with the GATO and ELITE codes, the vacuum model has important effects on the edge kink mode calculations. By setting a realistic density profile and Spitzer resistivity profile in the vacuum region, the resistivity was found to have a destabilizing effect on both the kink mode and on the ballooning mode. With diamagnetic effects included, the intermediate-n and high-n ballooning modes can be totally stabilized for finite edge current density.

  5. The Cosmological Impact of Luminous TeV Blazars. I. Implications of Plasma Instabilities for the Intergalactic Magnetic Field and Extragalactic Gamma-Ray Background

    NASA Astrophysics Data System (ADS)

    Broderick, Avery E.; Chang, Philip; Pfrommer, Christoph

    2012-06-01

    Inverse Compton cascades (ICCs) initiated by energetic gamma rays (E >~ 100 GeV) enhance the GeV emission from bright, extragalactic TeV sources. The absence of this emission from bright TeV blazars has been used to constrain the intergalactic magnetic field (IGMF), and the stringent limits placed on the unresolved extragalactic gamma-ray background (EGRB) by Fermi have been used to argue against a large number of such objects at high redshifts. However, these are predicated on the assumption that inverse Compton scattering is the primary energy-loss mechanism for the ultrarelativistic pairs produced by the annihilation of the energetic gamma rays on extragalactic background light photons. Here, we show that for sufficiently bright TeV sources (isotropic-equivalent luminosities >~ 1042 erg s-1) plasma beam instabilities, specifically the "oblique" instability, present a plausible mechanism by which the energy of these pairs can be dissipated locally, heating the intergalactic medium. Since these instabilities typically grow on timescales short in comparison to the inverse Compton cooling rate, they necessarily suppress the ICCs. As a consequence, this places a severe constraint on efforts to limit the IGMF from the lack of a discernible GeV bump in TeV sources. Similarly, it considerably weakens the Fermi limits on the evolution of blazar populations. Specifically, we construct a TeV-blazar luminosity function from those objects currently observed and find that it is very well described by the quasar luminosity function at z ~ 0.1, shifted to lower luminosities and number densities, suggesting that both classes of sources are regulated by similar processes. Extending this relationship to higher redshifts, we show that the magnitude and shape of the EGRB above ~10 GeV are naturally reproduced with this particular example of a rapidly evolving TeV-blazar luminosity function.

  6. Current-Driven Dynamics of Skyrmions Stabilized in MnSi Nanowires Revealed by Topological Hall Effect

    NASA Astrophysics Data System (ADS)

    Liang, Dong; Degrave, John; Stolt, Matthew; Tokura, Yoshinori; Jin, Song

    2015-03-01

    Skyrmions, novel topologically stable spin vortices, hold promise for next-generation high-density magnetic storage technologies due to their nanoscale domains and ultralow energy consumption. One-dimensional (1D) nanowires are ideal hosts for skyrmions since they not only serve as a natural platform for magnetic racetrack memory devices but also can potentially stabilize skyrmions. We use the topological Hall effect (THE) to study the phase stability and current-driven dynamics of the skyrmions in MnSi nanowires. The THE was observed in an extended magnetic field-temperature window (15 to 30 K), suggesting stabilization of skyrmion phase in nanowires compared with the bulk (27 to 29.5 K). Furthermore, we study skyrmion dynamics in this extended skyrmion phase region and found that under the high current-density of 108-109Am-2 enabled by nanowire geometry, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field. These results open up the exploration of nanowires as an attractive platform for investigating skyrmion physics in 1D systems and exploiting skyrmions in magnetic storage concepts. This work is supported by US National Science Foundation (ECCS-1231916) and JSPS Grant-in-Aid for Scientific Research No. 24224009.

  7. Shear-flow-driven ion cyclotron and ion sound-drift instabilities of cylindrical inhomogeneous plasma

    SciTech Connect

    Mikhailenko, V. S.; Chibisov, D. V.

    2007-08-15

    The effects of the shear flow along the magnetic field on the development of the ion cyclotron, ion sound, and drift instabilities in the radially inhomogeneous cylindrical plasma are studied on the ground of a kinetic approach. It is shown that flow shear not only modifies the frequencies and growth rates of known current driven electrostatic ion cyclotron, ion sound, and drift instabilities, but is the source of the development of specific shear-flow-driven ion cyclotron, ion sound, and drift instabilities. These instabilities are excited at the levels of current along the ambient magnetic field which is below the critical value for the development of the modified by flow shear current driven ion cyclotron, ion sound, and drift instabilities.

  8. Magnetic dipole discharges. III. Instabilities

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.; Ionita, C.; Schrittwieser, R.

    2013-08-15

    Instabilities in a cross-field discharge around a permanent magnet have been investigated. The permanent magnet serves as a cold cathode and the chamber wall as an anode. The magnet is biased strongly negative and emits secondary electrons due to impact of energetic ions. The electrons outside the sheath are confined by the strong dipolar magnetic field and by the ion-rich sheath surrounding the magnet. The electron energy peaks in the equatorial plane where most ionization occurs and the ions are trapped in a negative potential well. The discharge mechanism is the same as that of cylindrical and planar magnetrons, but here extended to a 3-D cathode geometry using a single dipole magnet. While the basic properties of the discharge are presented in a companion paper, the present focus is on various observed instabilities. The first is an ion sheath instability which oscillates the plasma potential outside the sheath below the ion plasma frequency. It arises in ion-rich sheaths with low electron supply, which is the case for low secondary emission yields. Sheath oscillations modulate the discharge current creating oscillating magnetic fields. The second instability is current-driven ion sound turbulence due to counter-streaming electrons and ions. The fluctuations have a broad spectrum and short correlation lengths in all directions. The third type of fluctuations is spiky potential and current oscillations in high density discharges. These appear to be due to unstable emission properties of the magnetron cathode.

  9. Resistance switching of Cu/SiO2 memory cells studied under voltage and current-driven modes

    NASA Astrophysics Data System (ADS)

    Bernard, Y.; Gonon, P.; Jousseaume, V.

    2010-05-01

    Resistance switching in Cu/SiO2-based conductive-bridging random access memories is studied under voltage and current-driven modes. These two modes are used to study memory cycling and time-dependent switching. Voltage-current (V-I) cycles (logarithmic current ramp) are compared to I-V cycles (linear voltage ramp). The Off-On transition in V-I cycles is governed by device capacitance. The Off-On switching time (in the 10-1-103 s range) was studied under constant voltage and constant current stresses. The switching time varies as exp(V0/V) and as 1/I. Switching kinetics is discussed considering a Fowler-Nordheim tunneling injection law and a field-induced nucleation theory.

  10. Shoulder Instability

    MedlinePlus

    ... Risk Factors Is shoulder instability the same as shoulder dislocation? No. The signs of dislocation and instability might ... the same to you--weakness and pain. However, dislocation occurs when your shoulder goes completely out of place. The shoulder ligaments ...

  11. Effect of a RF Wave on Ion Cyclotron Instability in Size Distributed Impurities Containing Plasmas

    SciTech Connect

    Sharma, A. K.; Tripathi, V. K.; Annou, R.

    2008-09-07

    The effect of a large amplitude lower hybrid wave on current driven ion cyclotron waves in a dusty plasma where dust grains are size distributed is examined. The influence of the lower hybrid wave on the stabilization of the instability is studied. The efficacy of rf is dust density dependent.

  12. Hip instability.

    PubMed

    Smith, Matthew V; Sekiya, Jon K

    2010-06-01

    Hip instability is becoming a more commonly recognized source of pain and disability in patients. Traumatic causes of hip instability are often clear. Appropriate treatment includes immediate reduction, early surgery for acetabular rim fractures greater than 25% or incarcerated fragments in the joint, and close follow-up to monitor for avascular necrosis. Late surgical intervention may be necessary for residual symptomatic hip instability. Atraumatic causes of hip instability include repetitive external rotation with axial loading, generalized ligamentous laxity, and collagen disorders like Ehlers-Danlos. Symptoms caused by atraumatic hip instability often have an insidious onset. Patients may have a wide array of hip symptoms while demonstrating only subtle findings suggestive of capsular laxity. Traction views of the affected hip can be helpful in diagnosing hip instability. Open and arthroscopic techniques can be used to treat capsular laxity. We describe an arthroscopic anterior hip capsular plication using a suture technique. PMID:20473129

  13. Collective instabilities

    SciTech Connect

    K.Y. Ng

    2003-08-25

    The lecture covers mainly Sections 2.VIII and 3.VII of the book ''Accelerator Physics'' by S.Y. Lee, plus mode-coupling instabilities and chromaticity-driven head-tail instability. Besides giving more detailed derivation of many equations, simple interpretations of many collective instabilities are included with the intention that the phenomena can be understood more easily without going into too much mathematics. The notations of Lee's book as well as the e{sup jwt} convention are followed.

  14. Radio-protective effect of cinnamic acid, a phenolic phytochemical, on genomic instability induced by X-rays in human blood lymphocytes in vitro.

    PubMed

    Cinkilic, Nilufer; Tüzün, Ece; Çetintaş, Sibel Kahraman; Vatan, Özgür; Yılmaz, Dilek; Çavaş, Tolga; Tunç, Sema; Özkan, Lütfi; Bilaloğlu, Rahmi

    2014-08-01

    The present study was designed to determine the protective activity of cinnamic acid against induction by X-rays of genomic instability in normal human blood lymphocytes. This radio-protective activity was assessed by use of the cytokinesis-block micronucleus test and the alkaline comet assay, with human blood lymphocytes isolated from two healthy donors. A Siemens Mevatron MD2 (Siemens AG, USA, 1994) linear accelerator was used for the irradiation with 1 or 2 Gy. Treatment of the lymphocytes with cinnamic acid prior to irradiation reduced the number of micronuclei when compared with that in control samples. Treatment with cinnamic acid without irradiation did not increase the number of micronuclei and did not show a cytostatic effect in the lymphocytes. The results of the alkaline comet assay revealed that cinnamic acid reduces the DNA damage induced by X-rays, showing a significant radio-protective effect. Cinnamic acid decreased the frequency of irradiation-induced micronuclei by 16-55% and reduced DNA breakage by 17-50%, as determined by the alkaline comet assay. Cinnamic acid may thus act as a radio-protective compound, and future studies may focus on elucidating the mechanism by which cinnamic acid offers radioprotection. PMID:25344167

  15. Was the soft X-ray flare in NGC 3599 due to an AGN disc instability or a delayed tidal disruption event?

    NASA Astrophysics Data System (ADS)

    Saxton, R. D.; Motta, S. E.; Komossa, S.; Read, A. M.

    2015-12-01

    We present unpublished data from a tidal disruption candidate in NGC 3599 which show that the galaxy was already X-ray bright 18 months before the measurement which led to its classification. This removes the possibility that the flare was caused by a classical, fast-rising, short-peaked, tidal disruption event. Recent relativistic simulations indicate that the majority of disruptions will actually take months or years to rise to a peak, which will then be maintained for longer than previously thought. NGC 3599 could be one of the first identified examples of such an event. The optical spectra of NGC 3599 indicate that it is a low-luminosity Seyfert/low-ionization nuclear emission-line region (LINER) with Lbol ˜ 1040 erg s-1. The flare may alternatively be explained by a thermal instability in the accretion disc, which propagates through the inner region at the sound speed, causing an increase of the disc scaleheight and local accretion rate. This can explain the ≤9 yr rise time of the flare. If this mechanism is correct then the flare may repeat on a time-scale of several decades as the inner disc is emptied and refilled.

  16. Soft x-ray detector array for the study of magnetohydrodynamics instabilities in the compact helical system heliotron/torsatron

    NASA Astrophysics Data System (ADS)

    Takagi, S.; Toi, K.

    2001-01-01

    A 20 channel PIN-photodiode array is installed on the compact helical system (CHS) heliotron/torsatron to measure the radial profiles of soft x-ray (SXR) emission and fluctuations. In neutral beam injection (NBI) heated plasma on CHS, sawtooth oscillations are often observed in the SXR signals. The sawtooth has a characteristic feature of the off-axis sawtooth crash that takes place first near the 1/q=1/2 rational surface located at the normalized minor radius ρ≈0.4-0.6, where q is the safety factor. In most of cases high frequency precursor and low frequency postcursor oscillations having m/n=2/1 mode structure (m, n: the poloidal and toroidal mode numbers) appear before and after the crash. The total plasma beta derived from the measurement of SXR emission-peak position is slightly but clearly decreased by the sawtooth crash. This reduction suggests rapid transport of energetic beam ions from the core region toward the plasma edge region.

  17. ELM phenomenon as an interaction between bootstrap-current driven peeling modes and pressure-driven ballooning modes

    NASA Astrophysics Data System (ADS)

    Saarelma, S.; Günter, S.; Kurki-Suonio, T.; Zehrfeld, H.-P.

    2000-05-01

    An ELMy ASDEX Upgrade plasma equilibrium is reconstructed taking into account the bootstrap current. The peeling mode stability of the equilibrium is numerically analysed using the GATO [1] code, and it is found that the bootstrap current can drive the plasma peeling mode unstable. A high-n ballooning mode stability analysis of the equilibria revealed that, while destabilizing the peeling modes, the bootstrap current has a stabilizing effect on the ballooning modes. A combination of these two instabilities is a possible explanation for the type I ELM phenomenon. A triangularity scan showed that increasing triangularity stabilizes the peeling modes and can produce ELM-free periods observed in the experiments.

  18. Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation

    NASA Astrophysics Data System (ADS)

    Bromberg, Omer; Tchekhovskoy, Alexander

    2016-02-01

    Relativistic jets are associated with extreme astrophysical phenomena, like the core collapse of massive stars in gamma-ray bursts (GRBs) and the accretion on to supermassive black holes in active galactic nuclei. It is generally accepted that these jets are powered electromagnetically, by the magnetized rotation of a central compact object (black hole or neutron star). However, how the jets produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of relativistic, Poynting-flux-dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetized central object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a global, external kink mode that grows on long time-scales. It bodily twists the jet, reducing its propagation velocity. We show analytically that in flat density profiles, like the ones associated with galactic cores, the external mode grows and may stall the jet. In the steep profiles of stellar envelopes the external kink weakens as the jet propagates outward. (ii) a local, internal kink mode that grows over short time-scales and causes small-angle magnetic reconnection and conversion of about half of the jet electromagnetic energy flux into heat. We suggest that internal kink instability is the main dissipation mechanism responsible for powering GRB prompt emission.

  19. The Role of Macroscopic and Microscopic Jet Instabilities

    NASA Astrophysics Data System (ADS)

    Hardee, Philip E.

    2013-12-01

    Relativistic jets, be they Poynting flux or kinetic flux dominated, are current driven (CD) and/or Kelvin-Helmholtz (KH) velocity shear driven unstable. These macroscopic MHD instabilities may be responsible for some of the observed larger scale twisted jet structures and typically do not disrupt jets on less than kiloparsec scales. Here I review our understanding of the jet properties that will lead to the observed relative stability of astrophysical jets. In addition, I review the progress made on the microscopic scale plasma instabilities in shocks and velocity shears that may lead to magnetic field generation and that does lead to the particle acceleration required to produce the observed emission from radio wavelengths to TeV energies. Finally, I discuss these instabilities in the context of the jet in M87.

  20. Hybrid rocket instability

    NASA Technical Reports Server (NTRS)

    Greiner, B.; Frederick, R. A., Jr.

    1993-01-01

    The paper provides a brief review of theoretical and experimental studies concerned with hybrid rocket instability. The instabilities discussed include atomization and mixing instabilities, chuffing instabilities, pressure coupled combustion instabilities, and vortex shedding. It is emphasized that the future use of hybrid motor systems as viable design alternatives will depend on a better understanding of hybrid instability.

  1. Hybrid rocket instability

    NASA Astrophysics Data System (ADS)

    Greiner, B.; Frederick, R. A., Jr.

    1993-06-01

    The paper provides a brief review of theoretical and experimental studies concerned with hybrid rocket instability. The instabilities discussed include atomization and mixing instabilities, chuffing instabilities, pressure coupled combustion instabilities, and vortex shedding. It is emphasized that the future use of hybrid motor systems as viable design alternatives will depend on a better understanding of hybrid instability.

  2. Current driven vortex-antivortex pair breaking and vortex explosion in the Bi2Te3/FeTe interfacial superconductor

    NASA Astrophysics Data System (ADS)

    Dean, C. L.; Kunchur, M. N.; He, Q. L.; Liu, H.; Wang, J.; Lortz, R.; Sou, I. K.

    2016-08-01

    We investigated the dissipative regime of the Bi2Te3/FeTe topological insulator-chalcogenide interface superconductor at temperatures well below the Berezinski-Kosterlitz-Thouless transition. We observe a transition in the current-resistance and temperature-resistance curves that quantitatively agrees with the Likharev vortex-explosion phenomenon. In the limit of low temperatures and high current densities, we were able to demonstrate the regime of complete vortex-antivortex dissociation arising from current driven vortex-antivortex pair breaking.

  3. Magnetohydrodynamic instability

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson, R. S.

    1986-01-01

    There have been major advances in the theory of magnetic reconnection and of magnetic instability, with important implications for the observations, as follows: (1) Fast and slow magnetic shock waves are produced by the magnetohydrodynamics of reconnection and are potential particle accelerators. (2) The impulsive bursty regime of reconnection gives a rapid release of magnetic energy in a series of bursts. (3) The radiative tearing mode creates cool filamentary structures in the reconnection process. (4) The stability analyses imply that an arcade can become unstable when either its height or twist of plasma pressure become too great.

  4. Magnetohydrodynamic thermal instabilities in cool inhomogeneous atmospheres

    NASA Technical Reports Server (NTRS)

    Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.; Vaiana, G. S.

    1985-01-01

    The stability of magnetic loops to current-driven filamentation instabilities is investigated. The unperturbed atmosphere is assumed to be composed of an (upper) isothermal optically thin low-density portion and a (lower) higher-density portion which is in radiative equilibrium; in both cases, the atmosphere is in hydrostatic equilibrium, so that gravitational stratification is taken into account. In order to provide specific equilibrium conditions for evaluation of the dispersion relation, conditions appropriate for the surface of a solar-type star are adopted; i.e., a fairly low temperature (T = 5000 K) appropriate for a 'precoronal' state associated, for example, with magnetic flux emerging from photospheric levels under the action of magnetic buoyancy. A linear stability analysis is performed, and numerical results show that physically plausible current densities, which would be generated by typical loop-footpoint motions, are effective in driving MHD instabilities in such a plasma. The instability growth rates are strongly dependent on the assumed current density distribution and on the density scale height.

  5. No Evidence for the In Vivo Induction of Genomic Instability by Low Doses of 137CS Gamma Rays in Bone Marrow Cells of BALB/CJ and C57BL/6J Mice

    PubMed Central

    Rithidech, Kanokporn Noy; Udomtanakunchai, Chatchanok; Honikel, Louise M.; Whorton, Elbert B.

    2011-01-01

    In spite of extensive research, assessment of potential health risks associated with exposure to low-dose (≤ 0.1 Gy) radiation is still challenging. We evaluated the in vivo induction of genomic instability, expressed as late-occurring chromosome aberrations, in bone-marrow cells of two strains of mouse with different genetic background, i.e. the radiosensitive BALB/cJ and the radioresistant C57BL/6J strains following a whole-body exposure to varying doses of 137Cs gamma rays (0, 0.05, 0.1, and 1.0 Gy). A total of five mice per dose per strain were sacrificed at various times post-irradiation up to 6 months for sample collections. Three-color fluorescence in situ hybridization for mouse chromosomes 1, 2, and 3 was used for the analysis of stable-aberrations in metaphase-cells. All other visible gross structural-abnormalities involving non-painted-chromosomes were also evaluated on the same metaphase-cells used for scoring the stable-aberrations of painted-chromosomes. Our new data demonstrated in bone-marrow cells from both strains that low doses of low LET-radiation (as low as 0.05 Gy) are incapable of inducing genomic instability but are capable of reducing specific aberration-types below the spontaneous rate with time post-irradiation. However, the results showed the induction of genomic instability by 1.0 Gy of 137Cs gamma rays in the radiosensitive strain only. PMID:22423226

  6. Dependence of synergy current driven by lower hybrid wave and electron cyclotron wave on the frequency and parallel refractive index of electron cyclotron wave for Tokamaks

    SciTech Connect

    Huang, J.; Chen, S. Y. Tang, C. J.

    2014-01-15

    The physical mechanism of the synergy current driven by lower hybrid wave (LHW) and electron cyclotron wave (ECW) in tokamaks is investigated using theoretical analysis and simulation methods in the present paper. Research shows that the synergy relationship between the two waves in velocity space strongly depends on the frequency ω and parallel refractive index N{sub //} of ECW. For a given spectrum of LHW, the parameter range of ECW, in which the synergy current exists, can be predicted by theoretical analysis, and these results are consistent with the simulation results. It is shown that the synergy effect is mainly caused by the electrons accelerated by both ECW and LHW, and the acceleration of these electrons requires that there is overlap of the resonance regions of the two waves in velocity space.

  7. Experiments on current-driven three-dimensional ion sound turbulence. I - Return-current limited electron beam injection. II - Wave dynamics

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.

    1978-01-01

    Pulsed electron beam injection into a weakly collisional magnetized background plasma is investigated experimentally; properties of the electron beam and background plasma, as well as the low-frequency instabilities and wave dynamics, are discussed. The current of the injected beam closes via a field-aligned return current of background electrons. Through study of the frequency and wavenumber distribution, together with the electron distribution function, the low-frequency instabilities associated with the pulsed injection are identified as ion acoustic waves driven unstable by the return current. The frequency cut-off of the instabilities predicted from renormalized plasma turbulence theory, has been verified experimentally.

  8. Validating the Supernova Remnant Hypothesis of the Cosmic Ray Origin

    NASA Astrophysics Data System (ADS)

    Malkov, Mikhail

    The century-old problem of the origin and acceleration of cosmic rays (CR) could soon be resolved. However, as it is impossible to trace CR back to their accelerators because of orbit scrambling in the galactic magnetic field, the solution will not be easy. Also the direct observations of a secondary gamma emission from supernova remnant (SNR) shocks, long suspected to be the main source of galactic CRs, are complicated by the contaminating electron emission. Therefore, the SNR hypothesis of the CR origin can be proven beyond a reasonable doubt only if the acceleration theory is fully consistent with the observations. However, the complexity of plasma dynamics in SNR shocks makes the validation of the SNR hypothesis very difficult. A study of the crucial plasma processes in SNR shocks is proposed. It will determine the three-way partitioning of the shock energy between accelerated particles (protons and electrons), turbulent magnetic fields and thermal plasma. The project includes a comparative analysis of three instabilities, arguably crucial to the diffusive shock acceleration (DSA) mechanism: i.) the cyclotron resonance CR instability, ii.) the non- resonant CR-current driven (kink-type) instability and iii.) the acoustic CR-pressure gradient driven instability. By identifying the dominant instability depending on the local SNR environment, the spectra of different species of accelerated particles, their losses, and the broadband radiation will be calculated and compared to both direct observations of the secondary emission from major SNRs and to the measurements of the background CRs. The comparison will show whether the DSA mechanism production of CR in SNR is consistent with the observed emission. The remnants most visible in gamma rays expand into weakly ionized, dense gases. The physics of the CR production in such environments based on the three instabilities will be studied. The proposer's previous work has shown that the propagation of CRs in a dense SNR

  9. Delayed chromosomal instability induced by DNA damage.

    PubMed Central

    Marder, B A; Morgan, W F

    1993-01-01

    DNA damage induced by ionizing radiation can result in gene mutation, gene amplification, chromosome rearrangements, cellular transformation, and cell death. Although many of these changes may be induced directly by the radiation, there is accumulating evidence for delayed genomic instability following X-ray exposure. We have investigated this phenomenon by studying delayed chromosomal instability in a hamster-human hybrid cell line by means of fluorescence in situ hybridization. We examined populations of metaphase cells several generations after expanding single-cell colonies that had survived 5 or 10 Gy of X rays. Delayed chromosomal instability, manifested as multiple rearrangements of human chromosome 4 in a background of hamster chromosomes, was observed in 29% of colonies surviving 5 Gy and in 62% of colonies surviving 10 Gy. A correlation of delayed chromosomal instability with delayed reproductive cell death, manifested as reduced plating efficiency in surviving clones, suggests a role for chromosome rearrangements in cytotoxicity. There were small differences in chromosome destabilization and plating efficiencies between cells irradiated with 5 or 10 Gy of X rays after a previous exposure to 10 Gy and cells irradiated only once. Cell clones showing delayed chromosomal instability had normal frequencies of sister chromatid exchange formation, indicating that at this cytogenetic endpoint the chromosomal instability was not apparent. The types of chromosomal rearrangements observed suggest that chromosome fusion, followed by bridge breakage and refusion, contributes to the observed delayed chromosomal instability. Images PMID:8413263

  10. Current-driven atomic waterwheels

    NASA Astrophysics Data System (ADS)

    Dundas, Daniel; McEniry, Eunan J.; Todorov, Tchavdar N.

    2009-02-01

    A current induces forces on atoms inside the conductor that carries it. It is now possible to compute these forces from scratch, and to perform dynamical simulations of the atomic motion under current. One reason for this interest is that current can be a destructive force-it can cause atoms to migrate, resulting in damage and in the eventual failure of the conductor. But one can also ask, can current be made to do useful work on atoms? In particular, can an atomic-scale motor be driven by electrical current, as it can be by other mechanisms? For this to be possible, the current-induced forces on a suitable rotor must be non-conservative, so that net work can be done per revolution. Here we show that current-induced forces in atomic wires are not conservative and that they can be used, in principle, to drive an atomic-scale waterwheel.

  11. Current-driven atomic waterwheels.

    PubMed

    Dundas, Daniel; McEniry, Eunan J; Todorov, Tchavdar N

    2009-02-01

    A current induces forces on atoms inside the conductor that carries it. It is now possible to compute these forces from scratch, and to perform dynamical simulations of the atomic motion under current. One reason for this interest is that current can be a destructive force--it can cause atoms to migrate, resulting in damage and in the eventual failure of the conductor. But one can also ask, can current be made to do useful work on atoms? In particular, can an atomic-scale motor be driven by electrical current, as it can be by other mechanisms? For this to be possible, the current-induced forces on a suitable rotor must be non-conservative, so that net work can be done per revolution. Here we show that current-induced forces in atomic wires are not conservative and that they can be used, in principle, to drive an atomic-scale waterwheel. PMID:19197311

  12. Modeling the Parker instability in a rotating plasma screw pinch

    NASA Astrophysics Data System (ADS)

    Khalzov, I. V.; Brown, B. P.; Katz, N.; Forest, C. B.

    2012-02-01

    We analytically and numerically study the analogue of the Parker (magnetic buoyancy) instability in a uniformly rotating plasma screw pinch confined in a cylinder. Uniform plasma rotation is imposed to create a centrifugal acceleration, which mimics the gravity required for the classical Parker instability. The goal of this study is to determine how the Parker instability could be unambiguously identified in a weakly magnetized, rapidly rotating screw pinch, in which the rotation provides an effective gravity and a radially varying azimuthal field is controlled to give conditions for which the plasma is magnetically buoyant to inward motion. We show that an axial magnetic field is also required to circumvent conventional current driven magnetohydrodynamic (MHD) instabilities such as the sausage and kink modes that would obscure the Parker instability. These conditions can be realized in the Madison plasma Couette experiment (MPCX). Simulations are performed using the extended MHD code NIMROD for an isothermal compressible plasma model. Both linear and nonlinear regimes of the instability are studied, and the results obtained for the linear regime are compared with analytical results from a slab geometry. Based on this comparison, it is found that in a cylindrical pinch, the magnetic buoyancy mechanism dominates at relatively large Mach numbers (M > 5), while at low Mach numbers (M < 1), the instability is due to the curvature of magnetic field lines. At intermediate values of Mach number (1 < M < 5), the Coriolis force has a strong stabilizing effect on the plasma. A possible scenario for experimental demonstration of the Parker instability in MPCX is discussed.

  13. Three-dimensional magnetic reconnection under coupling of tearing and lower-hybrid-drift instabilities

    NASA Astrophysics Data System (ADS)

    Hoshino, Masahiro

    2016-07-01

    Understanding of the particle acceleration and plasma heating in a current sheet is an important problem in space and astrophysical plasmas. So far the inertia resistivity associated with tearing instability and the current driven instability such as the lower hybrid drift instability (LHDI) have been discussed as possible candidates for the origin of microscopic process of magnetic energy dissipation. It is known that the inertia resistivity effectively works at the neutral sheet, while the LHDI is mainly excited in the plasma sheet boundary. Then it is commonly understood that the role of the LHDI to the magnetic field dissipation is less important than that of the inertia resistivity. However, the heated electrons together with the activity of lower hybrid drift waves are often observed in the plasma sheet boundary by modern satellite observations, and their impact on the magnetic field dissipation at the neutral sheet might not be necessarily neglected. In addition, the nonlinear coupling between them is not theoretically understood yet. In this talk, we study the coupling of the collisionless reconnection and the LHDI by using a three-dimensional PIC simulation, and discuss that the current driven instabilities dynamically play an important role on magnetic reconnection.

  14. Radiative heat transport instability in a laser produced inhomogeneous plasma

    SciTech Connect

    Bychenkov, V. Yu.; Rozmus, W.

    2015-08-15

    A laser produced high-Z plasma in which an energy balance is achieved due to radiation emission and radiative heat transfer supports ion acoustic instability. A linear dispersion relation is derived, and instability is compared to the radiation cooling instability [R. G. Evans, Plasma Phys. Controlled Fusion 27, 751 (1985)]. Under conditions of indirect drive fusion experiments, the driving term for the instability is the radiative heat flux and, in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered. This instability may lead to plasma jet formation and anisotropic x-ray generation, thus affecting inertial confinement fusion related experiments.

  15. Dynamic coupling-decoupling crossover in the current-driven vortex-state in Tl[sub 2]Ba[sub 2]CaCu[sub 2]O[sub 8]studied using terahertz time-domain spectroscopy

    SciTech Connect

    Thorsmølle, V. K.; Averitt, R. D.; Aranson, I. S.; Maley, M. P.; Bulaevskiĭ, L. N.; Taylor, Antoinette J.,

    2004-01-01

    Employing terahertz time-domain spectroscopy in transmission, they have measured the Josephson plasma resonance in Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} high-T{sub c} thin films, and studied the current-driven coupling-decoupling crossover in the driven vortex lattice.

  16. Turbine instabilities: Case histories

    NASA Technical Reports Server (NTRS)

    Laws, C. W.

    1985-01-01

    Several possible causes of turbine rotor instability are discussed and the related design features of a wide range of turbomachinery types and sizes are considered. The instrumentation options available for detecting rotor instability and assessing its severity are also discussed.

  17. TRANSVERSE INSTABILITIES IN RHIC.

    SciTech Connect

    Blaskiewicz, M; Cameron, P; Catalan-Lasheras, N; Dawson, C; Degen, C; Drees, K; Fischer, W; Koropsak, E; Michnoff, R; Montag, C; Roser, T

    2003-05-12

    The beam quality in RHIC can be significantly impacted by a transverse instability which can occur just after transition [1]. Data characterizing the instability are presented and analyzed. Techniques for ameliorating the situation are considered.

  18. Instability of a current-carrying finite-beta collisional plasma.

    PubMed

    Choueiri, E Y

    2001-12-01

    The microinstability of a cross-field current-carrying plasma in which the electron collisions are important on the time scale of the oscillations and can be modeled with a Bhatnagar-Gross-Krook operator is studied using linearized kinetic theory under conditions of finite electron beta. The finiteness of beta allows for coupling between electrostatic and electromagnetic modes and necessitates dealing with the entire dispersion tensor. Fundamental features of the resulting instability are identified and contrasted with those found in previous studies of the lower hybrid current-driven instability in which either collisions or finite-beta effects were neglected. As beta increases, collisions play a more important role in destabilization, alter the character and extent of electromagnetic coupling, shift the instability to more perpendicular modes, and lead to a recapturing of some of the fluidlike properties the modes have in the electrostatic limit in contrast with their highly kinetic character in the collisionless limit. PMID:11736288

  19. Radiative heat transport instability in ICF plasmas

    NASA Astrophysics Data System (ADS)

    Rozmus, W.; Bychenkov, V. Yu.

    2015-11-01

    A laser produced high-Z plasma in which an energy balance is achieved due to radiation losses and radiative heat transfer supports ion acoustic wave instability. A linear dispersion relation is derived and instability is compared to the radiation cooling instability. This instability develops in the wide range of angles and wavenumbers with the typical growth rate on the order of cs/LT (cs is the sound speed, LT is the temperature scale length). In addition to radiation dominated systems, a similar thermal transport driven ion acoustic instability was found before in plasmas where the thermal transport coefficient depends on electron density. However, under conditions of indirect drive ICF experiments the driving term for the instability is the radiative heat flux and in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered corresponding to a thermal conductivity coefficient that is inversely proportional to the square of local particle density. In the nonlinear regime this instability may lead to plasma jet formation and anisotropic x-ray generation.

  20. The modified two stream instability at nonmagnetic planets

    SciTech Connect

    Bingham, R.; Kellett, B. J.; Shapiro, V. D.; Uecer, D.; Quest, K. B.

    2010-12-14

    We describe the role the modified two stream instability plays in the interaction of the solar wind with non-magnetized planets. The instability leads to the production of energetic electrons that can be responsible for the observed x-ray emission.

  1. Joint Instability and Osteoarthritis

    PubMed Central

    Blalock, Darryl; Miller, Andrew; Tilley, Michael; Wang, Jinxi

    2015-01-01

    Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA). Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA. PMID:25741184

  2. Joint instability and osteoarthritis.

    PubMed

    Blalock, Darryl; Miller, Andrew; Tilley, Michael; Wang, Jinxi

    2015-01-01

    Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA). Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA. PMID:25741184

  3. Instability in Rotating Machinery

    NASA Technical Reports Server (NTRS)

    1985-01-01

    The proceedings contain 45 papers on a wide range of subjects including flow generated instabilities in fluid flow machines, cracked shaft detection, case histories of instability phenomena in compressors, turbines, and pumps, vibration control in turbomachinery (including antiswirl techniques), and the simulation and estimation of destabilizing forces in rotating machines. The symposium was held to serve as an update on the understanding and control of rotating machinery instability problems.

  4. Nonlocal magnetorotational instability

    SciTech Connect

    Mikhailovskii, A. B.; Erokhin, N. N.; Lominadze, J. G.; Galvao, R. M. O.; Churikov, A. P.; Kharshiladze, O. A.; Amador, C. H. S.

    2008-05-15

    An analytical theory of the nonlocal magnetorotational instability (MRI) is developed for the simplest astrophysical plasma model. It is assumed that the rotation frequency profile has a steplike character, so that there are two regions in which it has constant different values, separated by a narrow transition layer. The surface wave approach is employed to investigate the MRI in this configuration. It is shown that the main regularities of the nonlocal MRI are similar to those of the local instability and that driving the nonaxisymmetric MRI is less effective than the axisymmetric one, also for the case of the nonlocal instability. The existence of nonlocal instabilities in nonmagnetized plasma is predicted.

  5. Absolute instability from linear conversion of counter-propagating positive and negative energy waves

    SciTech Connect

    Kaufman, A.N.; Brizard, A.J.; Morehead, J.J.; Tracy, E.R.

    1997-12-31

    The resonant interaction of a negative-energy wave with a positive-energy wave gives rise to a linear instability. Whereas a single crossing of rays in a nonuniform medium leads to a convectively saturated instability, we show that a double crossing can yield an absolute instability.

  6. Theory of local thermal instability in spherical systems

    NASA Technical Reports Server (NTRS)

    Balbus, Steven A.; Soker, Noam

    1989-01-01

    The gasdynamical properties of local thermal instability in optically thin astrophysical plasmas as it occurs in spherical accretion and winds is investigated. In a medium characterized by both thermal and hydrostatic equilibrium, if the cooling function is not an explicit function of position and does not display isentropic thermal instability, then isobaric thermal instability by the Field criterion is present if and only if convective instability is present by the Schwarzschild criterion. In this case, thermal overstability cannot occur. Convective instability by the Schwarzschild criterion will also occur in accretion flows locally dominated by external heating or in marginally unbound, radiatively cooling outflows. A very general Lagrangian equation for the development of nonradial thermal instability in flows with spherical symmetry is derived and is solved analytically in certain regimes. The results are applied to cluster X-ray cooling flows.

  7. The Parker Instability in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Rodrigues, L. F. S.; Sarson, G. R.; Shukurov, A.; Bushby, P. J.; Fletcher, A.

    2016-01-01

    We examine the evolution of the Parker instability in galactic disks using 3D numerical simulations. We consider a local Cartesian box section of a galactic disk, where gas, magnetic fields, and cosmic rays are all initially in a magnetohydrostatic equilibrium. This is done for different choices of initial cosmic-ray density and magnetic field. The growth rates and characteristic scales obtained from the models, as well as their dependences on the density of cosmic rays and magnetic fields, are in broad agreement with previous (linearized, ideal) analytical work. However, this nonideal instability develops a multimodal 3D structure, which cannot be quantitatively predicted from the earlier linearized studies. This 3D signature of the instability will be of importance in interpreting observations. As a preliminary step toward such interpretations, we calculate synthetic polarized intensity and Faraday rotation measure (RM) maps, and the associated structure functions of the latter, from our simulations; these suggest that the correlation scales inferred from RM maps are a possible probe for the cosmic-ray content of a given galaxy. Our calculations highlight the importance of cosmic rays in these measures, making them an essential ingredient of realistic models of the interstellar medium.

  8. Magnetic field-related heating instabilities in the surface layers of the sun and stars

    NASA Technical Reports Server (NTRS)

    Ferrari, A.; Rosner, R.; Vaiana, G. S.

    1982-01-01

    The stability of a magnetized low-density plasma to current-driven filamentation instabilities is investigated and the results are applied to the surface layers of stars. Unlike previous studies, the initial (i.e., precoronal) state of the stellar surface atmosphere is taken to be a low-density, optically thin magnetized plasma in radiative equilibrium. The linear analysis shows that the surface layers of main-sequence stars (including the sun) which are threaded by magnetic fields are unstable; the instabilities considered lead to structuring perpendicular to the ambient magnetic fields. These results suggest that relatively modest surface motions, in conjunction with the presence of magnetic fields, suffice to account for the presence of inhomogeneous chromospheric and coronal plasma overlying a star's surface.

  9. Nonlinear instabilities driven by coherent phase-space structures

    NASA Astrophysics Data System (ADS)

    Lesur, Maxime

    2012-10-01

    Coherent phase-space (PS) structures are an important feature of plasma turbulence. They can drive nonlinear instabilities [1], intermittency in drift-wave turbulence [2], and transport [3]. We aim at a comprehensive understanding of turbulence, not just as an ensemble of waves, as quasilinear theory implies, but as a mixture of coupled waves and localized structures. This work, which focuses on isolated PS structures, is a fundamental advance in this direction. We analyze the effects of self-binding negative fluctuations (PS holes) on stability, intermittency and anomalous resistivity, both analytically and numerically. We present a new theory which describes the growth of a hole or clump [4]. We find that PS holes grow nonlinearly, independently of linear stability. Numerical simulations clarify the physics of nonlinear instabilities in both subcritical and supercritical conditions. When many resonances are unstable, several holes can coalesce into one main macro-scale structure, which survives much longer than a quasilinear diffusion time, suggesting that it may be crucial to resolve phase-space turbulence in analytical and numerical studies of transport. These findings are applied to two fundamental paradigms of plasma physics: bump-on-tail instabilities in 1D electronic plasma and current-driven ion-acoustic instabilities electron-ion plasma. Our results expose important limits of routinely-used linear and quasilinear theories.[4pt] [1] T.H. Dupree, Phys. Fluids 15, 334 (1972); R.H. Berman et al., Phys. Rev. Lett. 48, 1249 (1982).[0pt] [2] P.W. Terry, P.H. Diamond, and T.S. Hahm, Phys. Fluids B 2, 2048 (1990).[0pt] [3] H. Biglari et al., Phys. Fluids 31, 2644 (1988); Y. Kosuga et al., Phys. Plasmas 18, 122305 (2011).[0pt] [4] M. Lesur, P.H. Diamond, submitted to Phys. Rev. Lett.

  10. Bacterial Genome Instability

    PubMed Central

    Darmon, Elise

    2014-01-01

    SUMMARY Bacterial genomes are remarkably stable from one generation to the next but are plastic on an evolutionary time scale, substantially shaped by horizontal gene transfer, genome rearrangement, and the activities of mobile DNA elements. This implies the existence of a delicate balance between the maintenance of genome stability and the tolerance of genome instability. In this review, we describe the specialized genetic elements and the endogenous processes that contribute to genome instability. We then discuss the consequences of genome instability at the physiological level, where cells have harnessed instability to mediate phase and antigenic variation, and at the evolutionary level, where horizontal gene transfer has played an important role. Indeed, this ability to share DNA sequences has played a major part in the evolution of life on Earth. The evolutionary plasticity of bacterial genomes, coupled with the vast numbers of bacteria on the planet, substantially limits our ability to control disease. PMID:24600039

  11. Rotor internal friction instability

    NASA Technical Reports Server (NTRS)

    Bently, D. E.; Muszynska, A.

    1985-01-01

    Two aspects of internal friction affecting stability of rotating machines are discussed. The first role of internal friction consists of decreasing the level of effective damping during rotor subsynchronous and backward precessional vibrations caused by some other instability mechanisms. The second role of internal frication consists of creating rotor instability, i.e., causing self-excited subsynchronous vibrations. Experimental test results document both of these aspects.

  12. Chiral plasma instabilities.

    PubMed

    Akamatsu, Yukinao; Yamamoto, Naoki

    2013-08-01

    We study the collective modes in relativistic electromagnetic or quark-gluon plasmas with an asymmetry between left- and right-handed chiral fermions, based on the recently formulated kinetic theory with Berry curvature corrections. We find that there exists an unstable mode, signaling the presence of a plasma instability. We argue the fate of this "chiral plasma instability" including the effect of collisions, and briefly discuss its relevance in heavy ion collisions and compact stars. PMID:23952387

  13. Equilibrium Electroconvective Instability

    NASA Astrophysics Data System (ADS)

    Rubinstein, I.; Zaltzman, B.

    2015-03-01

    Since its prediction 15 years ago, hydrodynamic instability in concentration polarization at a charge-selective interface has been attributed to nonequilibrium electro-osmosis related to the extended space charge which develops at the limiting current. This attribution had a double basis. On the one hand, it has been recognized that neither equilibrium electro-osmosis nor bulk electroconvection can yield instability for a perfectly charge-selective solid. On the other hand, it has been shown that nonequilibrium electro-osmosis can. The first theoretical studies in which electro-osmotic instability was predicted and analyzed employed the assumption of perfect charge selectivity for the sake of simplicity and so did the subsequent studies of various time-dependent and nonlinear features of electro-osmotic instability. In this Letter, we show that relaxing the assumption of perfect charge selectivity (tantamount to fixing the electrochemical potential of counterions in the solid) allows for the equilibrium electroconvective instability. In addition, we suggest a simple experimental test for determining the true, either equilibrium or nonequilibrium, origin of instability in concentration polarization.

  14. Measurements of the momentum and current transport from tearing instability in the Madison Symmetric Torus reversed-field pinch

    SciTech Connect

    Kuritsyn, A.; Fiksel, G.; Almagri, A. F.; Miller, M. C.; Mirnov, V. V.; Prager, S. C.; Sarff, J. S.; Brower, D. L.; Ding, W. X.

    2009-05-15

    In this paper measurements of momentum and current transport caused by current driven tearing instability are reported. The measurements are done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] in a regime with repetitive bursts of tearing instability causing magnetic field reconnection. It is established that the plasma parallel momentum profile flattens during these reconnection events: The flow decreases in the core and increases at the edge. The momentum relaxation phenomenon is similar in nature to the well established relaxation of the parallel electrical current and could be a general feature of self-organized systems. The measured fluctuation-induced Maxwell and Reynolds stresses, which govern the dynamics of plasma flow, are large and almost balance each other such that their difference is approximately equal to the rate of change of plasma momentum. The Hall dynamo, which is directly related to the Maxwell stress, drives the parallel current profile relaxation at resonant surfaces at the reconnection events. These results qualitatively agree with analytical calculations and numerical simulations. It is plausible that current-driven instabilities can be responsible for momentum transport in other laboratory and astrophysical plasmas.

  15. Measurements of the momentum and current transport from tearing instability in the Madison Symmetric Torus reversed-field pincha)

    NASA Astrophysics Data System (ADS)

    Kuritsyn, A.; Fiksel, G.; Almagri, A. F.; Brower, D. L.; Ding, W. X.; Miller, M. C.; Mirnov, V. V.; Prager, S. C.; Sarff, J. S.

    2009-05-01

    In this paper measurements of momentum and current transport caused by current driven tearing instability are reported. The measurements are done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] in a regime with repetitive bursts of tearing instability causing magnetic field reconnection. It is established that the plasma parallel momentum profile flattens during these reconnection events: The flow decreases in the core and increases at the edge. The momentum relaxation phenomenon is similar in nature to the well established relaxation of the parallel electrical current and could be a general feature of self-organized systems. The measured fluctuation-induced Maxwell and Reynolds stresses, which govern the dynamics of plasma flow, are large and almost balance each other such that their difference is approximately equal to the rate of change of plasma momentum. The Hall dynamo, which is directly related to the Maxwell stress, drives the parallel current profile relaxation at resonant surfaces at the reconnection events. These results qualitatively agree with analytical calculations and numerical simulations. It is plausible that current-driven instabilities can be responsible for momentum transport in other laboratory and astrophysical plasmas.

  16. Parametric instabilities in picosecond time scales

    SciTech Connect

    Baldis, H.A.; Rozmus, W.; Labaune, C.; Mounaix, Ph.; Pesme, D.; Baton, S.; Tikhonchuk, V.T.

    1993-03-01

    The coupling of intense laser light with plasmas is a rich field of plasma physics, with many applications. Among these are inertial confinement fusion (ICF), x-ray lasers, particle acceleration, and x-ray sources. Parametric instabilities have been studied for many years because of their importance to ICF; with laser pulses with duration of approximately a nanosecond, and laser intensities in the range 10{sup 14}--10{sup 15}W/cm{sup 2} these instabilities are of crucial concern because of a number of detrimental effects. Although the laser pulse duration of interest for these studies are relatively long, it has been evident in the past years that to reach an understanding of these instabilities requires their characterization and analysis in picosecond time scales. At the laser intensities of interest, the growth rate for stimulated Brillouin scattering (SBS) is of the order of picoseconds, and of an order of magnitude shorter for stimulated Raman scattering (SRS). In this paper the authors discuss SBS and SRS in the context of their evolution in picosecond time scales. They describe the fundamental concepts associated with their growth and saturation, and recent work on the nonlinear treatment required for the modeling of these instabilities at high laser intensities.

  17. On magnetohydrodynamic thermal instabilities in magnetic flux tubes. [in plane parallel stellar atmosphere in LTE and hydrostatic equilibrium

    NASA Technical Reports Server (NTRS)

    Massaglia, S.; Ferrari, A.; Bodo, G.; Kalkofen, W.; Rosner, R.

    1985-01-01

    The stability of current-driven filamentary modes in magnetic flux tubes embedded in a plane-parallel atmosphere in LTE and in hydrostatic equilibrium is discussed. Within the tube, energy transport by radiation only is considered. The dominant contribution to the opacity is due to H- ions and H atoms (in the Paschen continuum). A region in the parameter space of the equilibrium configuration in which the instability is effective is delimited, and the relevance of this process for the formation of structured coronae in late-type stars and accretion disks is discussed.

  18. Laboratory blast wave driven instabilities

    NASA Astrophysics Data System (ADS)

    Kuranz, Carolyn

    2008-04-01

    This presentation discusses experiments well-scaled to the blast wave driven instabilities during the explosion phase of SN1987A. Blast waves occur following a sudden, finite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 μm plastic layer that is followed by a low density foam layer. A blast wave structure similar to those in supernovae, is created in the plastic layer. The blast wave crosses a perturbed interface, which produces nonlinear, unstable growth dominated by the Rayleigh-Taylor (RT) instability. Recent experiments have been performed using complex initial conditions featuring a three-dimensional interface structure with a wavelength of 71 μm in two orthogonal directions, at times supplemented by an additional sinusoidal mode of 212 μm or 424 μm. We have detected the interface structure under these conditions, using dual orthogonal radiographs on some shots, and will show some of the resulting data. Recent advancements in our x-ray backlighting techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed. Current simulations do not show this phenomenon. This presentation will discuss the amount of mass in these spike extensions as well as the error analysis of this calculation. Future experiments will also be discussed. They will be focusing on realistic initial conditions based on 3D stellar evolution models. This research was sponsored by the Stewardship Science Academic Alliances Program through DOE Research Grants DE-FG52-07NA28058, DE-FG52-04NA00064, and other grants and contracts.

  19. Electrokinetic instability in microchannels

    NASA Astrophysics Data System (ADS)

    Schiffbauer, Jarrod; Demekhin, Evgeny A.; Ganchenko, Georgy

    2012-05-01

    The effect of geometric confinement on electroconvective instability due to nonequilibrium electro-osmotic slip at the interface of an electrolytic fluid and charge-selective solid is studied. It is shown that the topology of the marginal stability curves and the behavior of the critical parameters depend strongly on both channel geometry and dimensionless Debye length at low voltages for sufficiently deep channels, corresponding to the Rubinstein-Zaltzman instability mechanism, but that stability is governed almost entirely by channel depth for narrow channels at higher voltages. For shallow channels, it is shown that above a transition threshold, determined by both channel depth and Debye length, the low-voltage instability is completely suppressed.

  20. Buckling instability in arteries.

    PubMed

    Vandiver, Rebecca M

    2015-04-21

    Arteries can become tortuous in response to abnormal growth stimuli, genetic defects and aging. It is suggested that a buckling instability is a mechanism that might lead to artery tortuosity. Here, the buckling instability in arteries is studied by examining asymmetric modes of bifurcation of two-layer cylindrical structures that are residually stressed. These structures are loaded by an axial force, internal pressure and have nonlinear, anisotropic, hyperelastic responses to stresses. Strain-softening and reduced opening angle are shown to lower the critical internal pressure leading to buckling. In addition, the ratio of the media thickness to the adventitia thickness is shown to have a dramatic impact on arterial instability. PMID:25661070

  1. Instability of the heliopause driven by charge exchange interactions

    SciTech Connect

    Avinash, K.; Zank, G. P.; Dasgupta, B.; Bhadoria, Shikha

    2014-08-20

    The stability of the heliopause that separates the tenuous hot magnetized heliosheath plasma from the dense cool local interstellar magnetized plasma is examined using a fully general model that includes all the essential physical processes. Charge exchange coupling between plasma protons and primary interstellar neutral atoms provides an effective gravity that drives Rayleigh-Taylor (RT)-like instabilities. The velocity difference or shear between the heliosheath and interstellar flows, when coupled to energetic neutral atoms (ENAs), drives a Kelvin-Helmholtz (KH)-like instability on the heliopause. The shoulder region of the heliopause is unstable to a new instability that has characteristics of a mixed RT-KH-like mode. The instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath (OHS). ENAs play an essential role in driving the KH-like instability, which is fully stabilized in their absence by magnetic fields. The nonlinear phase of these instabilities is briefly discussed. We also discuss the possibility that RT-like or mixed KH-RT-like instabilities drag outer heliosheath/very local interstellar medium (OHS/VLISM) magnetic field lines into the inner heliosheath (IHS) with the VLISM flow, and the possibility that IHS and VLISM magnetic field lines experience reconnection. Such reconnection may (1) greatly enhance the mixing of plasmas across the heliopause and (2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and corresponding easy loss of anomalous cosmic rays from the heliosphere.

  2. Dislocation motion and instability

    NASA Astrophysics Data System (ADS)

    Zhu, Yichao; Chapman, Stephen Jonathan; Acharya, Amit

    2013-08-01

    The Peach-Koehler expression for the stress generated by a single (non-planar) curvilinear dislocation is evaluated to calculate the dislocation self stress. This is combined with a law of motion to give the self-induced motion of a general dislocation curve. A stability analysis of a rectilinear, uniformly translating dislocation is then performed. The dislocation is found to be susceptible to a helical instability, with the maximum growth rate occurring when the dislocation is almost, but not exactly, pure screw. The non-linear evolution of the instability is determined numerically, and implications for slip band formation and non-Schmid behavior in yielding are discussed.

  3. Varus Posteromedial Instability.

    PubMed

    Ramirez, Miguel A; Stein, Jason A; Murthi, Anand M

    2015-11-01

    Varus posteromedial instability of the elbow is a result of traumatic injury to the medial facet of the coronoid and usually the lateral collateral ligament. Treatment of these fractures is usually surgical; poor outcomes have been described with nonoperative treatment. Surgical management consists of coronoid fracture fixation with plates, screws, or sutures and radial collateral ligament repair. Outcomes of these injuries are mixed, but most series report fair to good objective scores. The purpose of this article is to describe the pathophysiology of varus posteromedial instability, discuss the management of this injury, and report the outcomes of treatment. PMID:26498545

  4. Ringed Accretion Disks: Instabilities

    NASA Astrophysics Data System (ADS)

    Pugliese, D.; Stuchlík, Z.

    2016-04-01

    We analyze the possibility that several instability points may be formed, due to the Paczyński mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.

  5. Electrostatic heat flux instabilities

    NASA Technical Reports Server (NTRS)

    Morrison, P. J.; Ionson, J. A.

    1980-01-01

    The electrostatic cyclotron and ion acoustic instabilities in a plasma driven by a combined heat flux and current were investigated. The minimum critical heat conduction speed (above which the plasma is unstable) is given as a function of the ratio of electron to ion temperatures.

  6. INSTABILITIES IN THE SNS.

    SciTech Connect

    BLASKIEWICZ,M.

    1999-03-29

    The 2MW Spallation Neutron Source (SNS) will have a D.C. beam current of 40 A at extraction, making it one of the worlds most intense accelerators. Coherent instabilities are a major concern and efforts to predict beam behavior are described.

  7. Two-fluid instability

    SciTech Connect

    Stewart, H.B.

    1984-01-01

    The ability of interpenetrating flow models to represent multidimensional instabilities is probed by numerical experiments with an L-shaped two-fluid jet. Periodic and nonperiodic oscillations of various types are observed, and a partial phase portrait is constructed. The numerical experiments suggest new approaches to verifying transient interpenetrating flow models. 18 references.

  8. Global Linear Instability

    NASA Astrophysics Data System (ADS)

    Theofilis, Vassilios

    2011-01-01

    This article reviews linear instability analysis of flows over or through complex two-dimensional (2D) and 3D geometries. In the three decades since it first appeared in the literature, global instability analysis, based on the solution of the multidimensional eigenvalue and/or initial value problem, is continuously broadening both in scope and in depth. To date it has dealt successfully with a wide range of applications arising in aerospace engineering, physiological flows, food processing, and nuclear-reactor safety. In recent years, nonmodal analysis has complemented the more traditional modal approach and increased knowledge of flow instability physics. Recent highlights delivered by the application of either modal or nonmodal global analysis are briefly discussed. A conscious effort is made to demystify both the tools currently utilized and the jargon employed to describe them, demonstrating the simplicity of the analysis. Hopefully this will provide new impulses for the creation of next-generation algorithms capable of coping with the main open research areas in which step-change progress can be expected by the application of the theory: instability analysis of fully inhomogeneous, 3D flows and control thereof.

  9. Tracking Code for Microwave Instability

    SciTech Connect

    Heifets, S.; /SLAC

    2006-09-21

    To study microwave instability the tracking code is developed. For bench marking, results are compared with Oide-Yokoya results [1] for broad-band Q = 1 impedance. Results hint to two possible mechanisms determining the threshold of instability.

  10. Ion-cyclotron instability in current-carrying Lorentzian (kappa) and Maxwellian plasmas with anisotropic temperatures: A comparative study

    SciTech Connect

    Basu, B.; Grossbard, N. J.

    2011-09-15

    Current-driven electrostatic ion-cyclotron instability has so far been studied for Maxwellian plasma with isotropic and anisotropic temperatures. Since satellite-measured particle velocity distributions in space are often better modeled by the generalized Lorentzian (kappa) distributions and since temperature anisotropy is quite common in space plasmas, theoretical analysis of the current-driven, electrostatic ion-cyclotron instability is carried out in this paper for electron-proton plasma with anisotropic temperatures, where the particle parallel velocity distributions are modeled by kappa distributions and the perpendicular velocity distributions are modeled by Maxwellian distributions. Stability properties of the excited ion cyclotron modes and, in particular, their dependence on electron to ion temperature ratio and ion temperature anisotropy are presented in more detail. For comparison, the corresponding results for bi-Maxwellian plasma are also presented. Although the stability properties of the ion cyclotron modes in the two types of plasmas are qualitatively similar, significant quantitative differences can arise depending on the values of {kappa}{sub e} and {kappa}{sub i}. The comparative study is based on the numerical solutions of the respective linear dispersion relations. Quasilinear estimates of the resonant ion heating rates due to ion-cyclotron turbulence in the two types of plasma are also presented for comparison.

  11. Genomic Instability and Cancer

    PubMed Central

    Yao, Yixin; Dai, Wei

    2014-01-01

    Genomic instability is a characteristic of most cancer cells. It is an increased tendency of genome alteration during cell division. Cancer frequently results from damage to multiple genes controlling cell division and tumor suppressors. It is known that genomic integrity is closely monitored by several surveillance mechanisms, DNA damage checkpoint, DNA repair machinery and mitotic checkpoint. A defect in the regulation of any of these mechanisms often results in genomic instability, which predisposes the cell to malignant transformation. Posttranslational modifications of the histone tails are closely associated with regulation of the cell cycle as well as chromatin structure. Nevertheless, DNA methylation status is also related to genomic integrity. We attempt to summarize recent developments in this field and discuss the debate of driving force of tumor initiation and progression. PMID:25541596

  12. Open field lines instabilities

    SciTech Connect

    Pozzoli, R. |

    1995-09-01

    The results of some recent theoretical papers dealing with flute-like instabilities in the scrape-off layer of a tokamak with limiter configuration, where the magnetic field intersects conducting walls, are briefly recalled. Attention is then paid to the instability driven by the electron temperature gradient across the field in conjunction with the formation of the Debye sheath at the boundary, and to the effects due to the inclination of the end walls with respect to the magnetic field. When a divertor configuration is considered, important modifications are found owing to the strong deformations of the flux tubes passing near the {ital x}-point, which contrast the onset of flute-like perturbations, and to the stochasticity of field lines that can be excited by magnetic field perturbations. {copyright} {ital 1995 American Institute of Physics.}

  13. Beam-beam instability

    SciTech Connect

    Chao, A.W.

    1983-08-01

    The subject of beam-beam instability has been studied since the invention of the colliding beam storage rings. Today, with several colliding beam storage rings in operation, it is not yet fully understood and remains an outstanding problem for the storage ring designers. No doubt that good progress has been made over the years, but what we have at present is still rather primitive. It is perhaps possible to divide the beam-beam subject into two areas: one on luminosity optimization and another on the dynamics of the beam-beam interaction. The former area concerns mostly the design and operational features of a colliding beam storage ring, while the later concentrates on the experimental and theoretical aspects of the beam-beam interaction. Although both areas are of interest, our emphasis is on the second area only. In particular, we are most interested in the various possible mechanisms that cause the beam-beam instability.

  14. Whistler modulational instability.

    NASA Technical Reports Server (NTRS)

    Brinca, A. L.

    1973-01-01

    Derivation of the modulational instability characteristics of whistlers in cold and hot plasmas. The cold-plasma analysis considers both ion motion and relativistic effects; the unstable band, with a growth rate proportional to (B/B sub zero)squared, is contiguous to Omega sub e/4 and, depending on the plasma density, lies above or below that frequency (Omega sub e is the electron cyclotron frequency of the static magnetic field; B and B sub zero are the whistler and static magnetic fields). In hot plasmas, stability occurs between Omega sub e/4 and Omega prime (less than Omega sub e), with Omega prime depending mainly on the mean energy and anisotropy of the energetic electron population; the complementary unstable band has a growth rate proportional to (B/B sub zero) to the 1/2 power. The relevance of the instability to whistlers in the magnetosphere is discussed.

  15. Robust dynamic mitigation of instabilities

    SciTech Connect

    Kawata, S.; Karino, T.

    2015-04-15

    A dynamic mitigation mechanism for instability growth was proposed and discussed in the paper [S. Kawata, Phys. Plasmas 19, 024503 (2012)]. In the present paper, the robustness of the dynamic instability mitigation mechanism is discussed further. The results presented here show that the mechanism of the dynamic instability mitigation is rather robust against changes in the phase, the amplitude, and the wavelength of the wobbling perturbation applied. Generally, instability would emerge from the perturbation of the physical quantity. Normally, the perturbation phase is unknown so that the instability growth rate is discussed. However, if the perturbation phase is known, the instability growth can be controlled by a superposition of perturbations imposed actively: If the perturbation is induced by, for example, a driving beam axis oscillation or wobbling, the perturbation phase could be controlled, and the instability growth is mitigated by the superposition of the growing perturbations.

  16. Combustion instability analysis

    NASA Technical Reports Server (NTRS)

    Chung, T. J.

    1990-01-01

    A theory and computer program for combustion instability analysis are presented. The basic theoretical foundation resides in the concept of entropy-controlled energy growth or decay. Third order perturbation expansion is performed on the entropy-controlled acoustic energy equation to obtain the first order integrodifferential equation for the energy growth factor in terms of the linear, second, and third order energy growth parameters. These parameters are calculated from Navier-Stokes solutions with time averages performed on as many Navier-Stokes time steps as required to cover at least one peak wave period. Applications are made for a 1-D Navier-Stokes solution for the Space Shuttle Main Engine (SSME) thrust chamber with cross section area variations taken into account. It is shown that instability occurs when the mean pressure is set at 2000 psi with 30 percent disturbances. Instability also arises when the mean pressure is set at 2935 psi with 20 percent disturbances. The system with mean pressures and disturbances more adverse that these cases were shown to be unstable.

  17. Chromosomal instability induced by heavy ion irradiation

    NASA Technical Reports Server (NTRS)

    Limoli, C. L.; Ponnaiya, B.; Corcoran, J. J.; Giedzinski, E.; Morgan, W. F.

    2000-01-01

    PURPOSE: To establish the dose-response relationship for the induction of chromosomal instability in GM10115 cells exposed to high-energy iron ions (1 GeV/nucleon, mean LET 146 keV/microm) and gold ions (11 GeV/nucleon, mean LET 1450 keV/microm). Past work has established that sparsely ionizing X-rays can induce a long-lived destabilization of chromosomes in a dose-dependent manner at an incidence of approximately 3% per gray. The present investigation assesses the capacity of High-Z and High-energy (HZE) particles to elicit this same endpoint. MATERIALS AND METHODS: Clonal populations derived from single progenitor cells surviving heavy-ion irradiation were analyzed cytogenetically to identify those clones showing a persistent destablization of chromosomes. RESULTS: Dose-response data, with a particular emphasis at low dose (< 1.0 Gy), indicate a frequency of approximately 4% per gray for the induction of chromosomal instability in clones derived from single progenitor cells surviving exposure to iron ions. The induction of chromosomal instability by gold ions was, however, less responsive to applied dose, as the observed incidence of this phenotype varied from 0 to 10% over 1-8 Gy. Both iron and gold ions gave dose-dependent increases in the yield of chromosomal aberrations (both chromosome- and chromatid-type) measured at the first mitosis following irradiation, as well as shoulderless survival curves having D0=0.87 and 1.1 Gy respectively. CONCLUSIONS: Based on the present dose-response data, the relative biological effectiveness of iron ions is 1.3 for the induction of chromosomal instability, and this indicates that heavy ions are only slightly more efficient than X-rays at eliciting this delayed phenotype.

  18. Hydrodynamic instabilities in supernova remnants - Self-similar driven waves

    NASA Technical Reports Server (NTRS)

    Chevalier, Roger A.; Blondin, John M.; Emmering, Robert T.

    1992-01-01

    An initial study aimed at elucidating the multidimensional aspects of the hydrodynamic instabilities in supernova remnants is presented. Self-similar solutions are found to exist for the interaction of a steep power-law density profile expanding into a relatively flat stationary power-law density profile. Consideration of the pressure and entropy profiles in the shocked 1D flows shows that the flows are subject to convective instability, by a local criterion. The growth rate for the instability becomes very large near the contact discontinuity between the two shocked regions. A linear analysis of the complete self-similar solutions shows that the solutions are unstable above a critical wavenumber and that the growth rate is greatest at the position of the contact discontinuity. The X-ray image of the remnant of SN 1572 (Tycho) shows emission from clumps of supernova ejecta, which is good evidence for instabilities in this remnant.

  19. A current-driven nanometer water pump.

    PubMed

    Su, Jiaye; Yang, Keda

    2016-03-01

    The design of a water pump, which has huge potential for applications in nanotechnology and daily life, is the dream of many scientists. In this paper, we successfully design a nanometer water pump by using molecular dynamics simulations. Ions of either sodium or chlorine in a narrow channel will generate electric current under electric fields, which then drives the water through a wider channel, similar to recent experimental setups. Considerable water flux is achieved within small field strengths that are accessible by experimentation. Of particular interest, is that for sodium the water flux increases almost linearly with field strengths; while for chlorine there exists a critical field strength, the water flux exhibits a plateau before the critical value and increases linearly after it. This result follows the behavior of ion velocity, which is related to friction behavior. We also estimate the power and energy consumption for such a pump, and compare it to the macroscopic mechanical pumps. A further comparison suggests that different ions will have different pumping abilities. This study not only provides new, significant results with possible connection to existing research, but has tremendous potential application in the design of nanofluidic devices. PMID:26822782

  20. A current-driven nanometer water pump

    NASA Astrophysics Data System (ADS)

    Su, Jiaye; Yang, Keda

    2016-03-01

    The design of a water pump, which has huge potential for applications in nanotechnology and daily life, is the dream of many scientists. In this paper, we successfully design a nanometer water pump by using molecular dynamics simulations. Ions of either sodium or chlorine in a narrow channel will generate electric current under electric fields, which then drives the water through a wider channel, similar to recent experimental setups. Considerable water flux is achieved within small field strengths that are accessible by experimentation. Of particular interest, is that for sodium the water flux increases almost linearly with field strengths; while for chlorine there exists a critical field strength, the water flux exhibits a plateau before the critical value and increases linearly after it. This result follows the behavior of ion velocity, which is related to friction behavior. We also estimate the power and energy consumption for such a pump, and compare it to the macroscopic mechanical pumps. A further comparison suggests that different ions will have different pumping abilities. This study not only provides new, significant results with possible connection to existing research, but has tremendous potential application in the design of nanofluidic devices.

  1. Radiation Induced Genomic Instability

    SciTech Connect

    Morgan, William F.

    2011-03-01

    Radiation induced genomic instability can be observed in the progeny of irradiated cells multiple generations after irradiation of parental cells. The phenotype is well established both in vivo (Morgan 2003) and in vitro (Morgan 2003), and may be critical in radiation carcinogenesis (Little 2000, Huang et al. 2003). Instability can be induced by both the deposition of energy in irradiated cells as well as by signals transmitted by irradiated (targeted) cells to non-irradiated (non-targeted) cells (Kadhim et al. 1992, Lorimore et al. 1998). Thus both targeted and non-targeted cells can pass on the legacy of radiation to their progeny. However the radiation induced events and cellular processes that respond to both targeted and non-targeted radiation effects that lead to the unstable phenotype remain elusive. The cell system we have used to study radiation induced genomic instability utilizes human hamster GM10115 cells. These cells have a single copy of human chromosome 4 in a background of hamster chromosomes. Instability is evaluated in the clonal progeny of irradiated cells and a clone is considered unstable if it contains three or more metaphase sub-populations involving unique rearrangements of the human chromosome (Marder and Morgan 1993). Many of these unstable clones have been maintained in culture for many years and have been extensively characterized. As initially described by Clutton et al., (Clutton et al. 1996) many of our unstable clones exhibit persistently elevated levels of reactive oxygen species (Limoli et al. 2003), which appear to be due dysfunctional mitochondria (Kim et al. 2006, Kim et al. 2006). Interestingly, but perhaps not surprisingly, our unstable clones do not demonstrate a “mutator phenotype” (Limoli et al. 1997), but they do continue to rearrange their genomes for many years. The limiting factor with this system is the target – the human chromosome. While some clones demonstrate amplification of this chromosome and thus lend

  2. Genome instability and aging.

    PubMed

    Vijg, Jan; Suh, Yousin

    2013-01-01

    Genome instability has long been implicated as the main causal factor in aging. Somatic cells are continuously exposed to various sources of DNA damage, from reactive oxygen species to UV radiation to environmental mutagens. To cope with the tens of thousands of chemical lesions introduced into the genome of a typical cell each day, a complex network of genome maintenance systems acts to remove damage and restore the correct base pair sequence. Occasionally, however, repair is erroneous, and such errors, as well as the occasional failure to correctly replicate the genome during cell division, are the basis for mutations and epimutations. There is now ample evidence that mutations accumulate in various organs and tissues of higher animals, including humans, mice, and flies. What is not known, however, is whether the frequency of these random changes is sufficient to cause the phenotypic effects generally associated with aging. The exception is cancer, an age-related disease caused by the accumulation of mutations and epimutations. Here, we first review current concepts regarding the relationship between DNA damage, repair, and mutation, as well as the data regarding genome alterations as a function of age. We then describe a model for how randomly induced DNA sequence and epigenomic variants in the somatic genomes of animals can result in functional decline and disease in old age. Finally, we discuss the genetics of genome instability in relation to longevity to address the importance of alterations in the somatic genome as a causal factor in aging and to underscore the opportunities provided by genetic approaches to develop interventions that attenuate genome instability, reduce disease risk, and increase life span. PMID:23398157

  3. Gas turbine combustion instability

    SciTech Connect

    Richards, G.A.; Lee, G.T.

    1996-09-01

    Combustion oscillations are a common problem in development of LPM (lean premix) combustors. Unlike earlier, diffusion style combustors, LPM combustors are especially susceptible to oscillations because acoustic losses are smaller and operation near lean blowoff produces a greater combustion response to disturbances in reactant supply, mixing, etc. In ongoing tests at METC, five instability mechanisms have been identified in subscale and commercial scale nozzle tests. Changes to fuel nozzle geometry showed that it is possible to stabilize combustion by altering the timing of the feedback between acoustic waves and the variation in heat release.

  4. Surface instabilities and nuclear multifragmentation

    SciTech Connect

    Moretto, L.G.; Tso, K.; Colonna, N.; Wozniak, G.J.

    1992-03-01

    Central heavy-ion collisions, as described by a Boltzman-Nordheim-Vlasov calculation, form nuclear disks that break up into several fragments due to surface instabilities of the Rayleigh-Taylor kind. We demonstrate that a sheet of liquid, nuclear or otherwise, stable in the limit of infinitely sharp surfaces, becomes unstable due to surface-surface interactions. The onset of this instability is determined analytically. The relevance of these instabilities to nuclear multifragmentation is discussed.

  5. Sausage Instabilities on top of Kinking Lengthening Current-Carrying Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    von der Linden, Jens; You, Setthivoine

    2015-11-01

    Observations indicate that the dynamics of magnetic flux tubes in our cosmos and terrestrial experiments involve fast topological change beyond MHD reconnection. Recent experiments suggest that hierarchies of instabilities coupling disparate plasma scales could be responsible for this fast topological change by accessing two-fluid and kinetic scales. This study will explore the possibility of sausage instabilities developing on top of a kink instability in lengthening current-carrying magnetic flux tubes. Current driven flux tubes evolve over a wide range of aspect ratios k and current to magnetic flux ratios λ . An analytical stability criterion and numerical investigations, based on applying Newcomb's variational approach to idealized magnetic flux tubes with core and skin currents, indicate a dependence of the stability boundaries on current profiles and overlapping kink and sausage unstable regions in the k - λ trajectory of the flux tubes. A triple electrode planar plasma gun (Mochi.LabJet) is designed to generate flux tubes with discrete core and skin currents. Measurements from a fast-framing camera and a high resolution magnetic probe are being assembled into stability maps of the k - λ space of flux tubes. This work was sponsored in part by the US DOE Grant DE-SC0010340.

  6. Study of cavitating inducer instabilities

    NASA Technical Reports Server (NTRS)

    Young, W. E.; Murphy, R.; Reddecliff, J. M.

    1972-01-01

    An analytic and experimental investigation into the causes and mechanisms of cavitating inducer instabilities was conducted. Hydrofoil cascade tests were performed, during which cavity sizes were measured. The measured data were used, along with inducer data and potential flow predictions, to refine an analysis for the prediction of inducer blade suction surface cavitation cavity volume. Cavity volume predictions were incorporated into a linearized system model, and instability predictions for an inducer water test loop were generated. Inducer tests were conducted and instability predictions correlated favorably with measured instability data.

  7. Editorial Commentary: Multidirectional Shoulder Instability.

    PubMed

    Lubowitz, James H

    2015-12-01

    Multidirectional shoulder instability responds to physical therapy and rehabilitation. For patients who fail rehabilitation, arthroscopic capsular plication seems the treatment of choice. PMID:26652151

  8. PARTIAL TORUS INSTABILITY

    SciTech Connect

    Olmedo, Oscar; Zhang Jie

    2010-07-20

    Flux ropes are now generally accepted to be the magnetic configuration of coronal mass ejections (CMEs), which may be formed prior to or during solar eruptions. In this study, we model the flux rope as a current-carrying partial torus loop with its two footpoints anchored in the photosphere, and investigate its stability in the context of the torus instability (TI). Previous studies on TI have focused on the configuration of a circular torus and revealed the existence of a critical decay index of the overlying constraining magnetic field. Our study reveals that the critical index is a function of the fractional number of the partial torus, defined by the ratio between the arc length of the partial torus above the photosphere and the circumference of a circular torus of equal radius. We refer to this finding as the partial torus instability (PTI). It is found that a partial torus with a smaller fractional number has a smaller critical index, thus requiring a more gradually decreasing magnetic field to stabilize the flux rope. On the other hand, a partial torus with a larger fractional number has a larger critical index. In the limit of a circular torus when the fractional number approaches 1, the critical index goes to a maximum value. We demonstrate that the PTI helps us to understand the confinement, growth, and eventual eruption of a flux-rope CME.

  9. Instability vaccination: A structural design to reduce Rayleigh Taylor instability

    NASA Astrophysics Data System (ADS)

    Esmaeili, Amin

    2013-10-01

    Instability vaccination can be defined as designing a structure to stimulate the system in order to develop immunity against its instability. In this work we have tried to do this stabilization by a new technique. Previously some suppression of R-M instability was done by insertion of magnetic field, but in this work we have tried to do this suppression by proposing a configuration similar to the shape of instability, we call it instability vaccination. This design will reduce the rotations (mostly rotations of Rayleigh Taylor instability) in the fluids that cause more mixing and instabilities. In this paper, we consider the evolution of the interface between two ideal semi-infinite fluid surfaces, using two-dimensional Riemann solver, to solve the Euler equations. First, we performed evolution of a rectangular disorder between the 2 surfaces using two-dimensional Riemann problem for the equations of Euler. Next, the interface was replaced with a perturbation that was part rectangular and part semi-circular (like a mushroom). The simulation was continued till some time steps using the HLL method. We have seen that the rotations of Rayleigh Taylor (R-T) instability were decreased in the second case. Email: amin@cavelab.cs.tsukuba.ac.jp

  10. Instability characteristics of fluidelastic instability of tube rows in crossflow

    SciTech Connect

    Chen, S.S.; Jendrzejczyk, J.A.

    1986-04-01

    An experimental study is reported to investigate the jump phenomenon in critical flow velocities for tube rows with different pitch-to-diameter ratios and the excited and intrinsic instabilities for a tube row with a pitch-to-diameter ratio of 1.75. The experimental data provide additional insights into the instability phenomena of tube arrays in crossflow. 9 refs., 10 figs.

  11. Weibel Instability Driven by Spatially Anisotropic Density Structures

    NASA Astrophysics Data System (ADS)

    Tomita, Sara; Ohira, Yutaka

    2016-07-01

    Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron–positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.

  12. Research on aviation fuel instability

    NASA Technical Reports Server (NTRS)

    Baker, C. E.; Bittker, D. A.; Cohen, S. M.; Seng, G. T.

    1983-01-01

    The underlying causes of fuel thermal degradation are discussed. Topics covered include: nature of fuel instability and its temperature dependence, methods of measuring the instability, chemical mechanisms involved in deposit formation, and instrumental methods for characterizing fuel deposits. Finally, some preliminary thoughts on design approaches for minimizing the effects of lowered thermal stability are briefly discussed.

  13. Cohabitation and Children's Family Instability

    ERIC Educational Resources Information Center

    Kelly Raley, R.; Wildsmith, Elizabeth

    2004-01-01

    This study estimates how much children's family instability is missed when we do not count transitions into and out of cohabitation, and examines early life course trajectories of children to see whether children who experience maternal cohabitation face more family instability than children who do not. Using data from the 1995 National Survey of…

  14. Instability of liquid crystal elastomers

    NASA Astrophysics Data System (ADS)

    An, Ning; Li, Meie; Zhou, Jinxiong

    2016-01-01

    Nematic liquid crystal elastomers (LCEs) contract in the director direction but expand in other directions, perpendicular to the director, when heated. If the expansion of an LCE is constrained, compressive stress builds up in the LCE, and it wrinkles or buckles to release the stored elastic energy. Although the instability of soft materials is ubiquitous, the mechanism and programmable modulation of LCE instability has not yet been fully explored. We describe a finite element method (FEM) scheme to model the inhomogeneous deformation and instability of LCEs. A constrained LCE beam working as a valve for microfluidic flow, and a piece of LCE laminated with a nanoscale poly(styrene) (PS) film are analyzed in detail. The former uses the buckling of the LCE beam to occlude the microfluidic channel, while the latter utilizes wrinkling or buckling to measure the mechanical properties of hard film or to realize self-folding. Through rigorous instability analysis, we predict the critical conditions for the onset of instability, the wavelength and amplitude evolution of instability, and the instability patterns. The FEM results are found to correlate well with analytical results and reported experiments. These efforts shed light on the understanding and exploitation of the instabilities of LCEs.

  15. Liquid propellant rocket combustion instability

    NASA Technical Reports Server (NTRS)

    Harrje, D. T.

    1972-01-01

    The solution of problems of combustion instability for more effective communication between the various workers in this field is considered. The extent of combustion instability problems in liquid propellant rocket engines and recommendations for their solution are discussed. The most significant developments, both theoretical and experimental, are presented, with emphasis on fundamental principles and relationships between alternative approaches.

  16. Neurocardiovascular Instability and Cognition

    PubMed Central

    O’Callaghan, Susan; Kenny, Rose Anne

    2016-01-01

    Neurocardiovascular instability (NCVI) refers to abnormal neural control of the cardiovascular system affecting blood pressure and heart rate behavior. Autonomic dysfunction and impaired cerebral autoregulation in aging contribute to this phenomenon characterized by hypotension and bradyarrhythmia. Ultimately, this increases the risk of falls and syncope in older people. NCVI is common in patients with neurodegenerative disorders including dementia. This review discusses the various syndromes that characterize NCVI icluding hypotension, carotid sinus hypersensitivity, postprandial hypotension and vasovagal syncope and how they may contribute to the aetiology of cognitive decline. Conversely, they may also be a consequence of a common neurodegenerative process. Regardless, recognition of their association is paramount in optimizing management of these patients. PMID:27505017

  17. Plateau Rayleigh instability simulation.

    PubMed

    Mead-Hunter, Ryan; King, Andrew J C; Mullins, Benjamin J

    2012-05-01

    The well-known phenomena of Plateau-Rayleigh instability has been simulated using computational fluid dynamics (CFD). The breakup of a liquid film into an array of droplets on a cylindrical element was simulated using a volume-of-fluid (VOF) solver and compared to experimental observations and existing theory. It is demonstrated that the VOF method can correctly predict the breakup of thins films into an array of either axisymmetric droplets or clam-shell droplets, depending on the surface energy. The existence of unrealistically large films is precluded. Droplet spacing was found to show reasonable agreement with theory. Droplet motion and displacement under fluid flow was also examined and compared to that in previous studies. It was found that the presence of air flow around the droplet does not influence the stable film thickness; however, it reduces the time required for droplet formation. Novel relationships for droplet displacement were derived from the results. PMID:22512475

  18. Combustion Instabilities Modeled

    NASA Technical Reports Server (NTRS)

    Paxson, Daniel E.

    1999-01-01

    NASA Lewis Research Center's Advanced Controls and Dynamics Technology Branch is investigating active control strategies to mitigate or eliminate the combustion instabilities prevalent in lean-burning, low-emission combustors. These instabilities result from coupling between the heat-release mechanisms of the burning process and the acoustic flow field of the combustor. Control design and implementation require a simulation capability that is both fast and accurate. It must capture the essential physics of the system, yet be as simple as possible. A quasi-one-dimensional, computational fluid dynamics (CFD) based simulation has been developed which may meet these requirements. The Euler equations of mass, momentum, and energy have been used, along with a single reactive species transport equation to simulate coupled thermoacoustic oscillations. A very simple numerical integration scheme was chosen to reduce computing time. Robust boundary condition procedures were incorporated to simulate various flow conditions (e.g., valves, open ends, and choked inflow) as well as to accommodate flow reversals that may arise during large flow-field oscillations. The accompanying figure shows a sample simulation result. A combustor with an open inlet, a choked outlet, and a large constriction approximately two thirds of the way down the length is shown. The middle plot shows normalized, time-averaged distributions of the relevant flow quantities, and the bottom plot illustrates the acoustic mode shape of the resulting thermoacoustic oscillation. For this simulation, the limit cycle peak-to-peak pressure fluctuations were 13 percent of the mean. The simulation used 100 numerical cells. The total normalized simulation time was 50 units (approximately 15 oscillations), which took 26 sec on a Sun Ultra2.

  19. Internal rotor friction instability

    NASA Technical Reports Server (NTRS)

    Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

    1990-01-01

    The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.

  20. Instability saturation by the oscillating two-stream instability in a weakly relativistic plasma

    SciTech Connect

    Pal, Barnali; Poria, Swarup; Sahu, Biswajit

    2015-04-15

    The two-stream instability has wide range of astrophysical applications starting from gamma-ray bursts and pulsar glitches to cosmology. We consider one dimensional weakly relativistic Zakharov equations and describe nonlinear saturation of the oscillating two-stream instability using a three dimensional dynamical system resulting form a truncation of the nonlinear Schrodinger equation to three modes. The equilibrium points of the model are determined and their stability natures are discussed. Using the tools of nonlinear dynamics such as the bifurcation diagram, Poincaré maps, and Lyapunav exponents, existence of periodic, quasi-periodic, and chaotic solutions are established in the dynamical system. Interestingly, we observe the multistable behavior in this plasma model. The system has multiple attractors depending on the initial conditions. We also notice that the relativistic parameter plays the role of control parameter in the model. The theoretical results presented in this paper may be helpful for better understanding of space and astrophysical plasmas.

  1. The nucleus is the target for radiation-induced chromosomal instability

    NASA Technical Reports Server (NTRS)

    Kaplan, M. I.; Morgan, W. F.

    1998-01-01

    We have previously described chromosomal instability in cells of a human-hamster hybrid cell line after exposure to X rays. Chromosomal instability in these cells is characterized by the appearance of novel chromosomal rearrangements multiple generations after exposure to ionizing radiation. To identify the cellular target(s) for radiation-induced chromosomal instability, cells were treated with 125I-labeled compounds and frozen. Radioactive decays from 125I cause damage to the cell primarily at the site of their decay, and freezing the cells allows damage to accumulate in the absence of other cellular processes. We found that the decay of 125I-iododeoxyuridine, which is incorporated into the DNA, caused chromosomal instability. While cell killing and first-division chromosomal rearrangements increased with increasing numbers of 125I decays, the frequency of chromosomal instability was independent of dose. Chromosomal instability could also be induced from incorporation of 125I-iododeoxyuridine without freezing the cells for accumulation of decays. This indicates that DNA double-strand breaks in frozen cells resulting from 125I decays failed to lead to instability. Incorporation of an 125I-labeled protein (125I-succinyl-concanavalin A), which was internalized into the cell and/or bound to the plasma membrane, neither caused chromosomal instability nor potentiated chromosomal instability induced by 125I-iododeoxyuridine. These results show that the target for radiation-induced chromosomal instability in these cells is the nucleus.

  2. Temperature anisotropy and beam type whistler instabilities

    NASA Technical Reports Server (NTRS)

    Hashimoto, K.; Matsumoto, H.

    1976-01-01

    Whistler instabilities have been investigated for two different types; i.e., a temperature-anisotropy type instability and a beam-type instability. A comparison between the two types of whistler instabilities is made within the framework of linear theory. A transition from one type to the other is also discussed, which is an extension of the work on electrostatic beam and Landau instabilities performed by O'Neil and Malmberg (1968) for electromagnetic whistler instabilities. It is clarified that the essential source of the whistler instability is not beam kinetic energy but a temperature anisotropy, even for the beam-type whistler instability.

  3. ROTATIONAL INSTABILITIES AND CENTRIFUGAL HANGUP

    SciTech Connect

    K. NEW; J. CENTRELLA

    2000-12-01

    One interesting class of gravitational radiation sources includes rapidly rotating astrophysical objects that encounter dynamical instabilities. We have carried out a set of simulations of rotationally induced instabilities in differentially rotating polytropes. An n=1.5 polytrope with the Maclaurin rotation law will encounter the m=2 bar instability at T/{vert_bar}W{vert_bar} {ge} 0.27. Our results indicate that the remnant of this in-stability is a persistent bar-like structure that emits a long-lived gravitational radiation signal. Furthermore, dynamical instability is shown to occur in n=3.33 polytropes with the j-constant rotation law at T/{vert_bar}W{vert_bar} {ge} 0:14. In this case, the dominant mode of instability is m=1. Such instability may allow a centrifugally-hung core to begin collapsing to neutron star densities on a dynamical timescale. If it occurs in a supermassive star, it may produce gravitational radiation detectable by LISA.

  4. Yet another instability in glasma

    NASA Astrophysics Data System (ADS)

    Tsutsui, Shoichiro; Iida, Hideaki; Kunihiro, Teiji; Ohnishi, Akira

    2014-09-01

    In relativistic heavy ion collisions (HIC), hydrodynamic models can describe many experimental data and suggest that the quark-gluon plasma formed at RHIC and LHC is almost perfect fluid. We need very short thermalization time and far-from-equilibrium dynamics may be important in thermalization processes of HIC. In the earliest stages of HIC, classical gluon dynamics is dominant and many types of instabilities emerge there. These instabilities may strongly affect the later stages of dynamics; realization of chaoticity and field-particle conversions. We investigate instabilities of classical gluon fields under the homogeneous, but time dependent background color magnetic fields. The background field become periodic function of time and we can analyze the stability of fluctuations based on the Floquet theory which consists the basis of the Bloch theory. As a result, we get the complete structure of instability bands for physical degrees of freedom appearing from parametric resonance. We also find that the parametric instabilities considered here have different natures from the several known instabilities; Weibel and Nielsen-Olesen instabilities. We also discuss some implications of parametric resonance to the particle productions in HIC.

  5. Shock-induced crystalline instabilities

    NASA Astrophysics Data System (ADS)

    Ravelo, Ramon; Holian, Brad Lee; Germann, Timothy C.

    2007-03-01

    Uniaxial deformations of single crystals such as those produced under planar shock loading can produce structural instabilities which compete with defect nucleation mechanisms. In fcc single crystals under (110) shock loading, the resulting body-centered orthorhombic crystal structure develops a long-wavelength dynamical instability associated with tetragonal shear distortions, which occurs at lower strains (pressures) than those predicted by the vanishing of the elastic constants at finite pressure (stiffness coefficients). The criterion for these instabilities is derived and verified by equilibrium and non-equilibrium molecular dynamics simulations [2]J. Wang, S. Yip, S.R. Phillpot, D. Wolf, Phys. Rev. Lett. 71, 4182 (1993)

  6. New instability of Saturn's ring

    SciTech Connect

    Goertz, C.K.; Morfill, G.

    1988-05-01

    Perturbations in the Saturn ring's mass density are noted to be prone to instabilities through the sporadic elevation of submicron-size dust particles above the rings, which furnishes an effective angular momentum exchange between the rings and Saturn. The dust thus elevated from the ring settles back onto it at a different radial distance. The range of wavelength instability is determinable in light of the dust charge, the average radial displacement of the dust, and the fluctuation of these quantities. It is suggested that at least some of the B-ring's ringlets may arise from the instability.

  7. Microbunching Instability in Velocity Bunching

    SciTech Connect

    Xiang, D; Wu, J.; /SLAC

    2009-05-26

    Microbunching instability is one of the most challenging threats to FEL performances. The most effective ways to cure the microbunching instability include suppression of the density modulation sources and suppression of the amplification process. In this paper we study the microbunching instability in velocity bunching. Our simulations show that the initial current and energy modulations are suppressed in velocity bunching process, which may be attributed to the strong plasma oscillation and Landau damping from the relatively low beam energy and large relative slice energy spread. A heating effect that may be present in a long solenoid is also preliminarily analyzed.

  8. Collisionless shock experiments with lasers and observation of Weibel instabilities

    DOE PAGESBeta

    Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; et al

    2015-05-13

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagneticmore » in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.« less

  9. Suppression of microbunching instability via a transverse gradient undulator

    NASA Astrophysics Data System (ADS)

    Feng, Chao; Huang, Dazhang; Deng, Haixiao; Gu, Qiang; Zhao, Zhentang

    2015-07-01

    The microbunching instability in the linear accelerator (linac) of a free-electron laser facility has always been a problem that degrades the electron beam quality. In this paper, a quite simple and inexpensive technique is proposed to smooth the electron beam current profile to suppress the instability. By directly adding a short undulator with a transverse gradient field right after the injector to couple the transverse spread into the longitudinal direction, additional density mixing in the electron beam is introduced to smooth the current profile, which results in the reduction of the gain of the microbunching instability. The magnitude of the density mixing can be easily controlled by varying the strength of the undulator magnetic field. Theoretical analysis and numerical simulations demonstrate the capability of the proposed technique in the accelerator of an x-ray free-electron laser.

  10. Collisionless shock experiments with lasers and observation of Weibel instabilities

    SciTech Connect

    Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R. D.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H. G.; Rosenberg, M.; Ross, J. S.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Turnbull, D. P.; Tzeferacos, P.; Weber, S. V.; Zylstra, A. B.

    2015-05-13

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  11. Instabilities in the aether

    SciTech Connect

    Carroll, Sean M.; Dulaney, Timothy R.; Gresham, Moira I.; Tam, Heywood

    2009-03-15

    We investigate the stability of theories in which Lorentz invariance is spontaneously broken by fixed-norm vector 'aether' fields. Models with generic kinetic terms are plagued either by ghosts or by tachyons, and are therefore physically unacceptable. There are precisely three kinetic terms that are not manifestly unstable: a sigma model ({partial_derivative}{sub {mu}}A{sub {nu}}){sup 2}, the Maxwell Lagrangian F{sub {mu}}{sub {nu}}F{sup {mu}}{sup {nu}}, and a scalar Lagrangian ({partial_derivative}{sub {mu}}A{sup {mu}}){sup 2}. The timelike sigma-model case is well defined and stable when the vector norm is fixed by a constraint; however, when it is determined by minimizing a potential there is necessarily a tachyonic ghost, and therefore an instability. In the Maxwell and scalar cases, the Hamiltonian is unbounded below, but at the level of perturbation theory there are fewer degrees of freedom and the models are stable. However, in these two theories there are obstacles to smooth evolution for certain choices of initial data.

  12. Resistive instabilities in tokamaks

    SciTech Connect

    Rutherford, P.H.

    1985-10-01

    Low-m tearing modes constitute the dominant instability problem in present-day tokamaks. In this lecture, the stability criteria for representative current profiles with q(0)-values slightly less than unit are reviewed; ''sawtooth'' reconnection to q(0)-values just at, or slightly exceeding, unity is generally destabilizing to the m = 2, n = 1 and m = 3, n = 2 modes, and severely limits the range of stable profile shapes. Feedback stabilization of m greater than or equal to 2 modes by rf heating or current drive, applied locally at the magnetic islands, appears feasible; feedback by island current drive is much more efficient, in terms of the radio-frequency power required, then feedback by island heating. Feedback stabilization of the m = 1 mode - although yielding particularly beneficial effects for resistive-tearing and high-beta stability by allowing q(0)-values substantially below unity - is more problematical, unless the m = 1 ideal-MHD mode can be made positively stable by strong triangular shaping of the central flux surfaces. Feedback techniques require a detectable, rotating MHD-like signal; the slowing of mode rotation - or the excitation of non-rotating modes - by an imperfectly conducting wall is also discussed.

  13. Sheared Electroconvective Instability

    NASA Astrophysics Data System (ADS)

    Kwak, Rhokyun; Pham, Van Sang; Lim, Kiang Meng; Han, Jongyoon

    2012-11-01

    Recently, ion concentration polarization (ICP) and related phenomena draw attention from physicists, due to its importance in understanding electrochemical systems. Researchers have been actively studying, but the complexity of this multiscale, multiphysics phenomenon has been limitation for gaining a detailed picture. Here, we consider electroconvective(EC) instability initiated by ICP under pressure-driven flow, a scenario often found in electrochemical desalinations. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of sheared EC: unidirectional vortex structures, its size selection and vortex propagation. Selected by balancing the external pressure gradient and the electric body force, which generates Hagen-Poiseuille(HP) flow and vortical EC, the dimensionless EC thickness scales as (φ2 /UHP)1/3. The pressure-driven flow(or shear) suppresses unfavorably-directed vortices, and simultaneously pushes favorably-directed vortices with constant speed, which is linearly proportional to the total shear of HP flow. This is the first systematic characterization of sheared EC, which has significant implications on the optimization of electrodialysis and other electrochemical systems.

  14. The TP53 dependence of radiation-induced chromosome instability in human lymphoblastoid cells

    NASA Technical Reports Server (NTRS)

    Schwartz, Jeffrey L.; Jordan, Robert; Evans, Helen H.; Lenarczyk, Marek; Liber, Howard

    2003-01-01

    The dose and TP53 dependence for the induction of chromosome instability were examined in cells of three human lymphoblastoid cell lines derived from WIL2 cells: TK6, a TP53-normal cell line, NH32, a TP53-knockout created from TK6, and WTK1, a WIL2-derived cell line that spontaneously developed a TP53 mutation. Cells of each cell line were exposed to (137)Cs gamma rays, and then surviving clones were isolated and expanded in culture for approximately 35 generations before the frequency and characteristics of the instability were analyzed. The presence of dicentric chromosomes, formed by end-to-end fusions, served as a marker of chromosomal instability. Unexposed TK6 cells had low levels of chromosomal instability (0.002 +/- 0.001 dicentrics/cell). Exposure of TK6 cells to doses as low as 5 cGy gamma rays increased chromosome instability levels nearly 10-fold to 0.019 +/- 0.008 dicentrics/cell. There was no further increase in instability levels beyond 5 cGy. In contrast to TK6 cells, unexposed cultures of WTK1 and NH32 cells had much higher levels of chromosome instability of 0.034 +/- 0.007 and 0.041 +/- 0.009, respectively, but showed little if any effect of radiation on levels of chromosome instability. The results suggest that radiation exposure alters the normal TP53-dependent cell cycle checkpoint controls that recognize alterations in telomere structure and activate apoptosis.

  15. Microwave instability near transition energy

    SciTech Connect

    Wei, J.; Lee, S.Y.

    1989-01-01

    Monte Carlo simulation for the microwave instability agrees with analytic calculation solving the Vlasov equation, provided that bunch shape distortion due to coupling is taken into account. 9 refs., 2 figs.

  16. Instability mechanisms in swirling flows

    NASA Astrophysics Data System (ADS)

    Gallaire, F.; Chomaz, J.-M.

    2003-09-01

    We investigate the stability of the screened Rankine vortex with added plug flow where the azimuthal velocity decreases abruptly outside the core of the vortex. The jump in circulation is known to induce centrifugal and azimuthal Kelvin-Helmholtz instabilities. Their effect on the stability of the different azimuthal wave number m is discussed using physical considerations associated with asymptotic expansions and numerical computations of the dispersion relation. It is shown that the axial shear and centrifugal instability are active for all m, and that modes with |m|⩾2 are also destabilized by azimuthal shear. In contrast, the bending modes m=±1 are stabilized by a coupling with Kelvin waves in the core. Effects of rotation on the absolute/convective transition are also discussed. The absolute instability of positive helical modes is seen to be promoted by centrifugal instability and azimuthal shear.

  17. Aerodynamic instability: A case history

    NASA Technical Reports Server (NTRS)

    Eisenmann, R. C.

    1985-01-01

    The identification, diagnosis, and final correction of complex machinery malfunctions typically require the correlation of many parameters such as mechanical construction, process influence, maintenance history, and vibration response characteristics. The progression is reviewed of field testing, diagnosis, and final correction of a specific machinery instability problem. The case history presented addresses a unique low frequency instability problem on a high pressure barrel compressor. The malfunction was eventually diagnosed as a fluidic mechanism that manifested as an aerodynamic disturbance to the rotor assembly.

  18. Waves and instabilities in plasmas

    SciTech Connect

    Chen, L.

    1987-01-01

    The contents of this book are: Plasma as a Dielectric Medium; Nyquist Technique; Absolute and Convective Instabilities; Landau Damping and Phase Mixing; Particle Trapping and Breakdown of Linear Theory; Solution of Viasov Equation via Guilding-Center Transformation; Kinetic Theory of Magnetohydrodynamic Waves; Geometric Optics; Wave-Kinetic Equation; Cutoff and Resonance; Resonant Absorption; Mode Conversion; Gyrokinetic Equation; Drift Waves; Quasi-Linear Theory; Ponderomotive Force; Parametric Instabilities; Problem Sets for Homework, Midterm and Final Examinations.

  19. Material Instabilities in Particulate Systems

    NASA Technical Reports Server (NTRS)

    Goddard, J. D.

    1999-01-01

    Following is a brief summary of a theoretical investigation of material (or constitutive) instability associated with shear induced particle migration in dense particulate suspensions or granular media. It is shown that one can obtain a fairly general linear-stability analysis, including the effects of shear-induced anisotropy in the base flow as well as Reynolds dilatancy. A criterion is presented here for simple shearing instability in the absence of inertia and dilatancy.

  20. Flare instability and driving mechanism

    NASA Astrophysics Data System (ADS)

    Raychaudhuri, Probhas

    A mechanism is described for the generation of solar flares in which a Buneman instability is produced by electrons moving faster than thermal speed. A trapped population of particles accelerates in the magnetic field of active solar regions causing a streaming of ions relative to electrons which moves and heats the electrons. The theoretical argument also concludes that instability at the inner solar core directly bears on solar activities at the outer heliosphere.

  1. Stability and instability in evolution.

    PubMed

    Benci, V; Galleni, L

    1998-10-21

    In this paper we propose a mechanism which tries to explain the presence of periods of stability and instability which occur during the evolution of living forms. According to the Gaia hypothesis there are feedback mechanisms which stabilise the biosphere. Adding the presence of parameters which are out of control of the biosphere and of different time-scales, we propose a model which might explain the periods of instability. PMID:9790828

  2. Shoulder instability surgery in Norway

    PubMed Central

    2012-01-01

    Background and purpose In January 2008, we established the Norwegian Register for Shoulder Instability Surgery. We report on the establishment, the baseline data, and the results at 1-year follow-up. Methods Primary and revision shoulder stabilization is reported by the surgeon on a 1-page paper form containing the patient's history of shoulder injury, clinical findings, and perioperative findings. The WOSI questionnaire for self-assessment of shoulder function is completed at baseline and at follow-up after 1, 2, and 5 years. To evaluate the completeness of registration, we compared our data with those in the Norwegian Patient Registry (NPR). Results The NPR reported 39 hospitals performing shoulder stabilizations. 20 of these started to report to our register during 2009, and 464 procedures (404 primary, 59 revisions) were included up to December 31, 2009, which represented 54% of the procedures reported to NPR. Of the 404 primary procedures, 83% were operations due to anterior instability, 10% were operations due to posterior instability, and 7% were operations due to multidirectional instability. Arthroscopic soft tissue techniques were used in 88% of the patients treated for primary anterior instability and open coracoid transfer was used in 10% of such patients. At 1-year follow-up of 213 patients, we found a statistically significantly improved WOSI score in all types of instability. 10% of the patients treated with arthroscopic anterior labral repair and 16% treated with arthroscopic posterior labral repair reported recurrent instability. No statistically significant difference in functional improvement or rate of recurrence was found between these groups. Interpretation The functional results are in accordance with those in previous studies. However, the incidence of recurrent instability 1 year after arthroscopic labral repair is higher than expected. PMID:22112155

  3. Astrophysical Weibel instability in counterstreaming laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Fox, William; Fiksel, Gennady; Bhattacharjee, Amitava; Change, Po-Yu; Germaschewski, Kai; Hu, Suxing; Nilson, Philip

    2014-06-01

    Astrophysical shock waves play diverse roles, including energizing cosmic rays in the blast waves of astrophysical explosions, and generating primordial magnetic fields during the formation of galaxies and clusters. These shocks are typically collisionless and require collective electromagnetic fields to couple the upstream and downstream plasmas. The Weibel instability has been proposed to provide the requisite interaction mechanism for shock formation in weakly-magnetized shocks by generating turbulent electric and magnetic fields in the shock front. This work presents the first laboratory identification of this Weibel instability between counterstreaming supersonic plasma flows and confirms its basic features, a significant step towards understanding these shocks. In the experiments, conducted on the OMEGA EP laser facility at the University of Rochester, a pair of plasmas plumes are generated by irradiating of a pair of opposing parallel plastic (CH) targets. The ion-ion interaction between the two plumes is collisionless, so as the plumes interpenetrate, supersonic, counterstreaming ion flow conditions are obtained. Electromagnetic fields formed in the interaction of the two plumes were probed with an ultrafast laser-driven proton beam, and we observed the growth of a highly striated, transverse instability with extended filaments parallel to the flows. The instability is identified as an ion-driven Weibel instability through agreement with analytic theory and particle-in-cell simulations, paving the way for further detailed laboratory study of this instability and its consequences for particle energization and shock formation.[1] W. Fox, G. Fiksel, A. Bhattacharjee, P. Y. Chang, K. Germaschewski, S. X. Hu, and P. M. Nilson, “Filamentation instability of counterstreaming laser-driven plasmas,” Phys. Rev. Lett. 111, 225002 (2013).

  4. Vertical Instability at IPNS RCS.

    SciTech Connect

    Wang, S.; Brumwell, F. R.; Dooling, J. C.; Harkay, K. C.; Kustom, R.; McMichael, G. E.; Middendorf, M. E.; Nassiri, A.; Accelerator Systems Division

    2008-01-01

    The rapid cycling synchrotron (RCS) of the intense pulsed neutron source (IPNS) at ANL accelerates > 3.0 times 10{sup 12} protons from 50 MeV to 450 MeV with 30-Hz repetition frequency. During the acceleration cycle, the rf frequency varies from 2.21 MHz to 5.14 MHz. Presently, the beam current is limited by a vertical instability. By analyzing turn-by-turn beam position monitor (BPM) data, large- amplitude mode 0 and mode 1 vertical beam centroid oscillations were observed in the later part of the acceleration cycle. The oscillations start in the tail of the bunch, build up, and remain localized in the tail half of the bunch. This vertical instability was compared with a head-tail instability that was intentionally induced in the RCS by adjusting the trim sextupoles. It appears that our vertical instability is not a classical head-tail instability [1]. More data analysis and experiments were performed to characterize the instability.

  5. Pattern Formation in Convective Instabilities

    NASA Astrophysics Data System (ADS)

    Friedrich, R.; Bestehorn, M.; Haken, H.

    The present article reviews recent progress in the study of pattern formation in convective instabilities. After a brief discussion of the relevant basic hydrodynamic equations as well as a short outline of the mathematical treatment of pattern formation in complex systems the self-organization of spatial and spatio-temporal structures due to convective instabilities is considered. The formation of various forms of convective patterns arising in the Bénard experiment, i.e. in a horizontal fluid layer heated from below, is discussed. Then the review considers pattern formation in the Bénard instability in spherical geometries. In that case it can be demonstrated how the interaction among several convective cells may lead to time dependent as well as chaotic evolution of the spatial structures. Finally, the convective instability in a binary fluid mixture is discussed. In contrast to the instability in a single component fluid the instability may be oscillatory. In that case convection sets in in the form of travelling wave patterns which in addition to a complicated and chaotic temporal behaviour exhibit more or less spatial irregularity already close to threshold.

  6. Elastic instabilities in rubber

    NASA Astrophysics Data System (ADS)

    Gent, Alan

    2009-03-01

    Materials that undergo large elastic deformations can exhibit novel instabilities. Several examples are described: development of an aneurysm on inflating a rubber tube; non-uniform stretching on inflating a spherical balloon; formation of internal cracks in rubber blocks at a critical level of triaxial tension or when supersaturated with a dissolved gas; surface wrinkling of a block at a critical amount of compression; debonding or fracture of constrained films on swelling, and formation of ``knots'' on twisting stretched cylindrical rods. These various deformations are analyzed in terms of a simple strain energy function, using Rivlin's theory of large elastic deformations, and the results are compared with experimental measurements of the onset of unstable states. Such comparisons provide new tests of Rivlin's theory and, at least in principle, critical tests of proposed strain energy functions for rubber. Moreover the onset of highly non-uniform deformations has serious implications for the fatigue life and fracture resistance of rubber components. [4pt] References: [0pt] R. S. Rivlin, Philos. Trans. Roy. Soc. Lond. Ser. A241 (1948) 379--397. [0pt] A. Mallock, Proc. Roy. Soc. Lond. 49 (1890--1891) 458--463. [0pt] M. A. Biot, ``Mechanics of Incremental Deformations'', Wiley, New York, 1965. [0pt] A. N. Gent and P. B. Lindley, Proc. Roy. Soc. Lond. A 249 (1958) 195--205. [0pt] A. N. Gent, W. J. Hung and M. F. Tse, Rubb. Chem. Technol. 74 (2001) 89--99. [0pt] A. N. Gent, Internatl. J. Non-Linear Mech. 40 (2005) 165--175.

  7. Instability of enclosed horizons

    NASA Astrophysics Data System (ADS)

    Kay, Bernard S.

    2015-03-01

    We point out that there are solutions to the scalar wave equation on dimensional Minkowski space with finite energy tails which, if they reflect off a uniformly accelerated mirror due to (say) Dirichlet boundary conditions on it, develop an infinite stress-energy tensor on the mirror's Rindler horizon. We also show that, in the presence of an image mirror in the opposite Rindler wedge, suitable compactly supported arbitrarily small initial data on a suitable initial surface will develop an arbitrarily large stress-energy scalar near where the two horizons cross. Also, while there is a regular Hartle-Hawking-Israel-like state for the quantum theory between these two mirrors, there are coherent states built on it for which there are similar singularities in the expectation value of the renormalized stress-energy tensor. We conjecture that in other situations with analogous enclosed horizons such as a (maximally extended) Schwarzschild black hole in equilibrium in a (stationary spherical) box or the (maximally extended) Schwarzschild-AdS spacetime, there will be similar stress-energy singularities and almost-singularities—leading to instability of the horizons when gravity is switched on and matter and gravity perturbations are allowed for. All this suggests it is incorrect to picture a black hole in equilibrium in a box or a Schwarzschild-AdS black hole as extending beyond the past and future horizons of a single Schwarzschild (/Schwarzschild-AdS) wedge. It would thus provide new evidence for 't Hooft's brick wall model while seeming to invalidate the picture in Maldacena's ` Eternal black holes in AdS'. It would thereby also support the validity of the author's matter-gravity entanglement hypothesis and of the paper ` Brick walls and AdS/CFT' by the author and Ortíz.

  8. An analytical description of hydrodynamic instabilities

    NASA Astrophysics Data System (ADS)

    Bulanov, S. V.; Sasorov, P. V.

    The proper approach to the investigation of the nonlinear stage of hydrodynamic instabilities in a plasma has been discussed. Both the Buneman instability and the beam instability have been considered. A similarity between the nonlinear stage of the beam plasma instability and the process of self-modulation and self-focusing of nonlinear waves is revealed.

  9. Analytical and numerical treatment of drift-tearing and resistive drift instabilities in plasma slab

    NASA Astrophysics Data System (ADS)

    Mirnov, V. V.; Hegna, C. C.; Sauppe, J. P.; Sovinec, C. R.

    2015-11-01

    We consider modification to linear resistive MHD instability theory in a slab due to two categories of non-MHD effects: (1) electron and ion diamagnetic flows caused by equilibrium pressure gradients and (2) electron and ion decoupling on short scales associated with kinetic Alfven and whistler waves. The relationship between the expected stabilizing response due to the effects (1) and the destabilizing contribution caused by the dispersive waves (2) is investigated. An analytic solution combining the effect of diamagnetic flows and the ion-sound gyroradius contribution is derived using a perturbative approach. Linear numerical simulations using the NIMROD code are performed with cold ions and hot electrons in plasma slab with a doubly periodic box bounded by two perfectly conducting walls. Configurations with magnetic shear are unstable to current-driven drift-tearing instability. A second linearly unstable resistive drift type mode with largely electrostatic perturbations is also observed in simulations. The resistive-drift mode is suppressed by magnetic shear in unbounded domains but can remain unstable in the simulations with finite slab thickness and perfectly conducting wall. Additionally, the growth rate is sensitive to the magnetic shear length. We analyze whether these modes can be unstable in cylindrical configurations with magnetic shear typical for reversed field pinches. The material is based on work supported by the U.S. DOE and NSF.

  10. [Surgical treatment of craniocervical instability. Review paper].

    PubMed

    Alpizar-Aguirre, Armando; Lara Cano, Jorge Giovanni; Rosales, Luis; Míramontes, Victor; Reyes-Sánchez, Alejandro Antonio

    2007-01-01

    The concept of spinal instability is still controversial. Anatomical, biomechanical, clinical and radiographic variants are involved and make the definition complicated. There are solid diagnostic bases in cases of fractures and degenerative disorders; however, pure spinal instability is still under study. The latter may be defined as increased mobility that goes beyond the physiological limits of one vertebra over another in at least one of the three spinal planes of motion. In the case of the craniocervical region, its understanding becomes even more challenging, since its anatomy and physiology are more complex and it is more mobile. Surgical treatment is possible with either an anterior or a posterior approach. Best results are obtained with occipitocervical or atlantoaxial stabilization through a posterior approach, since the anterior one has its limitations. For example, a transoral approach with a bone graft provides compression strength but does not enable immediate appropriate fixation and involves the risk of infection. The choice of the surgical approach must consider the patient's medical status, the specific spine levels involved, the extent of neurological compromise, the X-ray abnormalities and the individual pathology. The goals of surgery are achieved through an appropriate anatomical alignment, assuring the protection of the neural elements and achieving proper spine stabilization with as much preservation of the mobile vertebral segments as possible. PMID:17970561

  11. Beta-limiting Instabilities and Global Mode Stabilization in NSTX

    NASA Astrophysics Data System (ADS)

    Sabbagh, Steven

    2001-10-01

    Low aspect ratio and high edge q theoretically alter the plasma stability and mode structure compared to standard tokamak configurations. Below the no-wall limit, stability calculations with PEST, GATO, and DCON show the perturbed radial field is maximized near the center column and DCON and VALEN calculations show that mode stability is not greatly improved by a nearby conducting wall due to the short poloidal wavelength in this region. In contrast, as beta reaches and exceeds the no-wall limit, the mode becomes strongly ballooning with long poloidal wavelength at large major radius and is highly wall stabilized. In this way, wall stabilization is more effective at higher beta in low aspect ratio geometry. Research on the stability of spherical torus plasmas at and above the no-wall beta limit is being addressed on NSTX, which has produced low aspect ratio plasmas, R/a = 1.27 at plasma current up to 1.4 MA with high energy confinement (TauE/TauE-ITER89P = 2). Toroidal and normalized beta have reached 22%, and 4.3, respectively in q = 7 plasmas. The beta limit is observed to increase with increasing plasma internal inductance, li, and the stability factor betaN/li has reached 5.8, limited by sudden beta collapses at low li that was achieved by use of high-harmonic fast wave heating (HHFW). DCON stability analysis of equilibria reconstructed with EFIT using external magnetics show that the plasmas are below or at the no-wall beta limit for the n = 1 mode, which has characteristics of a current-driven kink. With more peaked current profiles (li greater than 0.7), core MHD instabilities are observed which saturate or slowly degrade beta. Sawteeth with large inversion radii can also cause substantial beta collapses, although current profile modification using HHFW, altered plasma growth, and increased toroidal field have each been successful in mitigating this effect.

  12. Ab initio determination of the instability growth rate of warm dense beryllium-deuterium interface

    SciTech Connect

    Wang, Cong; Zhang, Ping; Li, Zi; Li, DaFang

    2015-10-15

    Accurate knowledge about the interfacial unstable growth is of great importance in inertial confinement fusion. During implosions, the deuterium-tritium capsule is driven by laser beams or X-rays to access the strongly coupled and partially degenerated warm dense matter regime. At this stage, the effects of dissipative processes, such as diffusion and viscosity, have significant impact on the instability growth rates. Here, we present ab initio molecular dynamics simulations to determine the equations of state and the transport coefficients. Several models are used to estimate the reduction in the growth rate dispersion curves of Rayleigh-Taylor and Richtmyer-Meshkov instabilities with considering the presence of these dissipative effects. We show that these instability growth rates are effectively reduced when considering diffusion. The findings provide significant insights into the microscopic mechanism of the instability growth at the ablator-fuel interface and will refine the models used in the laser-driven hydrodynamic instability experiments.

  13. Ab initio determination of the instability growth rate of warm dense beryllium-deuterium interface

    NASA Astrophysics Data System (ADS)

    Wang, Cong; Li, Zi; Li, DaFang; Zhang, Ping

    2015-10-01

    Accurate knowledge about the interfacial unstable growth is of great importance in inertial confinement fusion. During implosions, the deuterium-tritium capsule is driven by laser beams or X-rays to access the strongly coupled and partially degenerated warm dense matter regime. At this stage, the effects of dissipative processes, such as diffusion and viscosity, have significant impact on the instability growth rates. Here, we present ab initio molecular dynamics simulations to determine the equations of state and the transport coefficients. Several models are used to estimate the reduction in the growth rate dispersion curves of Rayleigh-Taylor and Richtmyer-Meshkov instabilities with considering the presence of these dissipative effects. We show that these instability growth rates are effectively reduced when considering diffusion. The findings provide significant insights into the microscopic mechanism of the instability growth at the ablator-fuel interface and will refine the models used in the laser-driven hydrodynamic instability experiments.

  14. Nebular spectra of pair-instability supernovae

    NASA Astrophysics Data System (ADS)

    Jerkstrand, A.; Smartt, S. J.; Heger, A.

    2016-01-01

    If very massive stars (M ≳ 100 M⊙) can form and avoid too strong mass-loss during their evolution, they are predicted to explode as pair-instability supernovae (PISNe). One critical test for candidate events is whether their nucleosynthesis yields and internal ejecta structure, being revealed through nebular-phase spectra at t ≳ 1 yr, match those of model predictions. Here, we compute theoretical spectra based on model PISN ejecta at 1-3 yr post-explosion to allow quantitative comparison with observations. The high column densities of PISNe lead to complete gamma-ray trapping for t ≳ 2 yr which, combined with fulfilled conditions of steady state, leads to bolometric supernova luminosities matching the 56Co decay. Most of the gamma-rays are absorbed by the deep-lying iron and silicon/sulphur layers. The ionization balance shows a predominantly neutral gas state, which leads to emission lines of Fe I, Si I, and S I. For low-mass PISNe, the metal core expands slowly enough to produce a forest of distinct lines, whereas high-mass PISNe expand faster and produce more featureless spectra. Line blocking is complete below ˜5000 Å for several years, and the model spectra are red. The strongest line is typically [Ca II] λλ7291, 7323, one of few lines from ionized species. We compare our models with proposed PISN candidates SN 2007bi and PTF12dam, finding discrepancies for several key observables and thus no support for a PISN interpretation. We discuss distinct spectral features predicted by the models, and the possibility of detecting pair-instability explosions among non-superluminous supernovae.

  15. Fermi liquids near Pomeranchuk instabilities

    NASA Astrophysics Data System (ADS)

    Reidy, Kelly Elizabeth

    We explore features of a Fermi liquid near generalized Pomeranchuk instabilities (PIs) starting from both ordered and disordered phases. These PIs can be viewed as quantum critical points in parameter space, and thus provide an alternate viewpoint on quantum criticality. We employ the tractable crossing symmetric equation method, which is a non-perturbative diagrammatic many-particle method used to calculate the Fermi liquid interaction functions and scattering amplitudes. We consider both repulsive and attractive underlying interactions of arbitrary strength. Starting from a ferromagnetically ordered ground state, we find that upon approach to an s-wave instability in one critical channel, the system simultaneously approaches instabilities in non-critical channels. We study origins and implications of this "quantum multicriticality". We also find that a nematic (non-s-wave) instability precedes and is driven by Pomeranchuk instabilities in both the s-wave spin and density channels. Finally, we discuss potential applications of our results to physical systems, such as ferromagnetic superconductors.

  16. The Energetics of Centrifugal Instability

    NASA Astrophysics Data System (ADS)

    Dewar, W. K.; Jiao, Y.

    2014-12-01

    A recent study has argued that the California Undercurrent, and poleward eastern boundary currents in general, generate mixing events through centrifugal instability (CI). Conditions favorable for CI are created by the strong horizontal shears developed in turbulent bottom layers of currents flowing in the direction of topographic waves. At points of abrupt topographic change, like promontories and capes, the coastal current separates from the boundary and injects gravitationally stable but dynamically unstable flow into the interior. The resulting finite amplitude development of the instability involves overturnings and diabatic mixing. The purpose of this study is to examine the energetics of CI in order to characterize it as has been done for other instabilities and develop a framework in which to estimate its regional and global impacts. We argue that CI is roughly twice as efficient at mixing as is Kelvin-Helmholtz instability, and that roughly 10% of the initial energy in a CUC-like current is lost to either local mixing or the generation of unbalanced flows. The latter probably leads to non-local mixing. Thus centrifugal instability is an effective process by which energy is lost from the balanced flow and spent in mixing neighboring water masses. We argue the importance of the mixing is regional in nature, but of less importance to the global budgets given its regional specificity.

  17. Rayleigh-Taylor instability experiments in cryogenic deuterium

    NASA Astrophysics Data System (ADS)

    Hansen, J. F.; Smalyuk, V. A.

    2005-10-01

    We report on experiments under way at the Omega laser, using cryogenic deuterium to study Rayleigh-Taylor instabilities in laser targets. These instabilities are important in astrophysical situations (e.g., mixing of the different shells during a supernova explosion) and in inertial fusion (during the compression stage of a fusion target). They can be studied in small (˜1 mm) shock tubes filled with one heavy and one light material, with an interface between the two materials that is machined to seed the instability. A high-energy laser (˜5 kJ) drives a shock from the heavy to the light material. The evolution of the interface is studied using gated x-ray cameras, where x-ray illumination is obtained from additional laser beams focused on metal backlighter foils. Traditionally the heavy material is CH (1 g/cm^3) doped with I or Br for improved contrast, while the light material is a low-density (˜0.1 g/cm^3) C foam. The goal of the current experiments is to determine if contrast can be improved even further by replacing the foam with cryogenic deuterium, which has a density similar to the foam, but a lower x-ray opacity allowing clearer images, including images taken at late times in the evolution. Work performed under the auspices of the Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.

  18. Chondral Injury in Patellofemoral Instability

    PubMed Central

    Lustig, Sébastien; Servien, Elvire; Neyret, Philippe

    2014-01-01

    Objective: Patellofemoral instability is common and affects a predominantly young age group. Chondral injury occurs in up to 95%, and includes osteochondral fractures and loose bodies acutely and secondary degenerative changes in recurrent cases. Biomechanical abnormalities, such as trochlear dysplasia, patella alta, and increased tibial tuberosity-trochlear groove distance, predispose to both recurrent dislocations and patellofemoral arthrosis. Design: In this article, we review the mechanisms of chondral injury in patellofemoral instability, diagnostic modalities, the distribution of lesions seen in acute and episodic dislocation, and treatments for articular cartilage lesions of the patellofemoral joint. Results: Little specific evidence exists for cartilage treatments in patellofemoral instability. In general, the results of reparative and restorative procedures in the patellofemoral joint are inferior to those observed in other compartments of the knee. Conclusion: Given the increased severity of chondral lesions and progression to osteoarthritis seen with recurrent dislocations, careful consideration should be given to early stabilisation in patients with predisposing factors. PMID:26069693

  19. SURGICAL TREATMENT OF PATELLOFEMORAL INSTABILITY

    PubMed Central

    de Andrade, Marco Antônio Percope; de Abreu e Silva, Guilherme Moreira; Freire, Marcelo Machado; Teixeira, Luiz Eduardo Moreira

    2015-01-01

    Objective: To describe functional outcomes following surgical treatment of patients with patellofemoral instability submitted to patellar realignment. Methods: This was a retrospective study evaluating 34 operated knees for patellofemoral instability between 1989 and 2004. The patients were evaluated in the late postoperative period when a functional questionnaire was applied. Results: After a mean follow-up time of 6 years and 5 months, the mean score was 82.94 in the surgical group (p=0.00037). The results of this investigation showed pain relief in 97.05% and low rate of recurrent dislocation (5.88%), although lower scores were seen in intense articular activities (squatting, running and jumping). No patient developed osteoarthritis while being followed up. Conclusion: The procedure for joint described in this paper was shown to be effective for treating patients with recurrent patellofemoral instability. PMID:27077065

  20. A Plasma, Magnetorotational Instability Experiment

    NASA Astrophysics Data System (ADS)

    Collins, C.; Forest, C. B.; Kendrick, R.; Seltzman, A.

    2007-11-01

    A new experiment is underway at the University of Wisconsin to investigate the magnetorotational instability in a plasma. Magnetorotational instability (MRI) is a likely mechanism that could account for the observed accretion rates in astrophysical objects. The instability occurs when a weak magnetic field is present, so that tension in perturbed field lines transfers angular momentum outward while mass moves towards the center. In the Plasma Dynamo Experiment Prototype, a cylindrical, axisymmetric, ring cusp confinement geometry is used to produce a large unmagnetized plasma, confined by a highly localized magnetic field at the plasma boundary. The plasma is stirred by a novel axisymmetric electrode set that can control the rotation (angular momentum profile). The feasibility of observing the MRI will be discussed and initial results from a protoype experiment will be presented.

  1. Longitudinal instability in HIF beams

    SciTech Connect

    Smith, L.

    1991-04-01

    In contrast to an electron induction accelerator, in which the particle velocity is virtually constant, the resistive and inductive components of accelerating module impedances can cause instability for an intense non-relativistic heavy ion beam accelerated in a similar structure. Since focusing requirements at the fusion pellet imply a momentum spread {approx lt}3 {times} 10{sup {minus}4} at the end of the accelerator, it is essential to understand and suppress this instability. There is also an economic issue involved for this application; selection of parameters to control the instability must not unduly affect the efficiency and cost of the accelerator. This paper will present the results of analytic and computational work on module impedances, growth rates and feed back (forward) systems. 2 refs., 3 figs.

  2. Hydrodynamick instabilities on ICF capsules

    SciTech Connect

    Haan, S.W.

    1991-06-07

    This article summarizes our current understanding of hydrodynamic instabilities as relevant to ICF. First we discuss classical, single mode Rayleigh-Taylor instability, and nonlinear effects in the evolution of a single mode. Then we discuss multimode systems, considering: (1) the onset of nonlinearity; (2) a second order mode coupling theory for weakly nonlinear effects, and (3) the fully nonlinear regime. Two stabilization mechanisms relevant to ICF are described next: gradient scale length and convective stabilization. Then we describe a model which is meant to estimate the weakly nonlinear evolution of multi-mode systems as relevant to ICF, given the short-wavelength stabilization. Finally, we discuss the relevant code simulation capability, and experiments. At this time we are quite optimistic about our ability to estimate instability growth on ICF capsules, but further experiments and simulations are needed to verify the modeling. 52 refs.

  3. Interfacial Instability during Granular Erosion

    NASA Astrophysics Data System (ADS)

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-01

    The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results.

  4. Interfacial instabilities and Kapitsa pendula

    NASA Astrophysics Data System (ADS)

    Krieger, Madison

    2015-11-01

    Determining the critera for onset and amplitude growth of instabilities is one of the central problems of fluid mechanics. We develop a parallel between the Kapitsa effect, in which a pendulum subject to high-frequency low-amplitude vibrations becomes stable in the inverted position, and interfaces separating fluids of different density. It has long been known that such interfaces can be stabilized by vibrations, even when the denser fluid is on top. We demonstrate that the stability diagram for these fluid interfaces is identical to the stability diagram for an appopriate Kapitsa pendulum. We expand the robust, ``dictionary''-type relationship between Kapitsa pendula and interfacial instabilities by considering the classical Rayleigh-Taylor, Kelvin-Helmholtz and Plateau instabilities, as well as less-canonical examples ranging in scale from the micron to the width of a galaxy.

  5. Interfacial Instability during Granular Erosion.

    PubMed

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-12

    The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results. PMID:26919014

  6. Instability of EDS maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.

    1993-09-01

    Instabilities of an EDS maglev suspension system with 3 D.O.F. and 5 D.O.F. vehicles traveling on a double L-shaped set of guideway conductors have been investigated with various experimentally measured magnetical force data incorporated into the theoretical models. Divergence and flutter are obtained from both analytical and numerical solutions for coupled vibration of the 3 D.O.F. maglev vehicle model. Instabilities of five direction motions (heave, slip, rill, pitch and yaw) are observed for the 4 D.O.F. vehicle model. It demonstrates that system parameters, such as, system damping, vehicle geometry and coupling effects among five different motions play very important roles in the occurrence of dynamic instabilities of maglev vehicles.

  7. Faraday instability in deformable domains

    NASA Astrophysics Data System (ADS)

    Pucci, Giuseppe; Ben Amar, Martine; Couder, Yves

    2014-11-01

    We investigate the Faraday instability in floating liquid lenses, as an example of hydrodynamic instability that develops in a domain with flexible boundaries. We show that a mutual adaptation of the instability pattern and the domain shape occurs, as a result of the competition between the wave radiation pressure and the capillary response of the lens border. Two archetypes of behaviour are observed. In the first, stable shapes are obtained experimentally and predicted theoretically as the exact solutions of a Riccati equation, and they result from the equilibrium between wave radiation pressure and capillarity. In the second, the radiation pressure exceeds the capillary response of the lens border and leads to non-equilibrium behaviours, with breaking into smaller domains that have a complex dynamics including spontaneous propagation. The authors are grateful to Université Franco-Italienne (UFI) for financial support.

  8. Performance through Deformation and Instability

    NASA Astrophysics Data System (ADS)

    Bertoldi, Katia

    2015-03-01

    Materials capable of undergoing large deformations like elastomers and gels are ubiquitous in daily life and nature. An exciting field of engineering is emerging that uses these compliant materials to design active devices, such as actuators, adaptive optical systems and self-regulating fluidics. Compliant structures may significantly change their architecture in response to diverse stimuli. When excessive deformation is applied, they may eventually become unstable. Traditionally, mechanical instabilities have been viewed as an inconvenience, with research focusing on how to avoid them. Here, I will demonstrate that these instabilities can be exploited to design materials with novel, switchable functionalities. The abrupt changes introduced into the architecture of soft materials by instabilities will be used to change their shape in a sudden, but controlled manner. Possible and exciting applications include materials with unusual properties such negative Poisson's ratio, phononic crystals with tunable low-frequency acoustic band gaps and reversible encapsulation systems.

  9. Microsatellite instability in bladder cancer.

    PubMed

    Gonzalez-Zulueta, M; Ruppert, J M; Tokino, K; Tsai, Y C; Spruck, C H; Miyao, N; Nichols, P W; Hermann, G G; Horn, T; Steven, K

    1993-12-01

    Somatic instability at microsatellite repeats was detected in 6 of 200 transitional cell carcinomas of the bladder. Instabilities were apparent as changes in (GT)n repeat lengths on human chromosome 9 for four tumors and as alterations in a (CAG)n repeat in the androgen receptor gene on the X chromosome for three tumors. Single locus alterations were detected in three tumors, while three other tumors revealed changes in two or more loci. In one tumor we found microsatellite instability in all five loci analyzed on chromosome 9. The alterations detected were either minor 2-base pair changes or larger (> 2 base pairs) alterations in repeat length. All six tumors were low stage (Ta-T1), suggesting that these alterations can occur early in bladder tumorigenesis. PMID:8242615

  10. Stellar explosions, instabilities, and turbulence

    SciTech Connect

    Drake, R. P.; Kuranz, C. C.; Miles, A. R.; Muthsam, H. J.; Plewa, T.

    2009-04-15

    It has become very clear that the evolution of structure during supernovae is centrally dependent on the pre-existing structure in the star. Modeling of the pre-existing structure has advanced significantly, leading to improved understanding and to a physically based assessment of the structure that will be present when a star explodes. It remains an open question whether low-mode asymmetries in the explosion process can produce the observed effects or whether the explosion mechanism somehow produces jets of material. In any event, the workhorse processes that produce structure in an exploding star are blast-wave driven instabilities. Laboratory experiments have explored these blast-wave-driven instabilities and specifically their dependence on initial conditions. Theoretical work has shown that the relative importance of Richtmyer-Meshkov and Rayleigh-Taylor instabilities varies with the initial conditions and does so in ways that can make sense of a range of astrophysical observations.