Neil F. Cramer

Nonlinear perpendicular propagation of ordinary mode electromagnetic wave packets in pair plasmas and electron-positron-ion plasmas

The nonlinear amplitude modulation of electromagnetic waves propagating in pair plasmas, e.g., electron-positron or fullerene pair-ion plasmas, as well as three-component pair plasmas, e.g., electron-positron-ion plasmas or doped (dusty) fullerene pair-ion plasmas, assuming wave propagation in a direction perpendicular to the ambient magnetic field, obeying the ordinary (O-) mode dispersion characteristics. Adopting a multiple scales (reductive perturbation) technique, a nonlinear Schrodinger-type equation is shown to govern the modulated amplitude of the magnetic field (perturbation). The conditions for modulation instability are investigated, in terms of relevant parameters. It is shown that localized envelope modes (envelope solitons) occur, of the bright- (dark-) type envelope solitons, i.e., envelope pulses (holes, respectively), for frequencies below (above) an explicit threshold. Long wavelength waves with frequency near the effective pair plasma frequency are therefore unstable, and may evolve int...

Simulation of a Collision between Shock Waves and a Magnetic Flux Tube: Excitation of Surface Alfvén Waves and Body Alfvén Waves

To explain the observed dynamics of the small-scale magnetic flux tubes in the quiet photospheric network, Furusawa & Sakai presented simulation results on the collision of two flux tubes. They found that shock waves appear during the collision of two magnetic flux tubes, when two magnetic flux tubes with weak electric current collide with each other. The shock waves so generated can subsequently collide with another flux tube, and we investigate here the interaction process of the shock with the flux tube. It is found that during the collision of a shock wave with a magnetic flux tube with weak electric current, surface Alfven waves can be generated and propagate along the flux tube. However, when the shock wave collides with a magnetic flux tube with strong current, body Alfven waves can be generated and propagate along the flux tube. It is also shown that, when we take into account the effect of a background density inhomogeneity due to gravity, there occurs a strong upward plasma jet along the flux tube, as well as surface Alfven waves. The energy conversion rate from the shock wave energy to the upward MHD waves, as well as upward plasma flows, is about 40% and thus is very efficient. We apply our results to the problem of solar coronal heating.

Alfvén surface waves in a magnetized dusty plasma

Surface wave propagation in a dusty magnetized plasma at frequencies below and of the order of the ion‐cyclotron frequency, but well above the dust cyclotron frequency, is considered. The dust grains are assumed to be stationary, but to carry a proportion of the negative charge of the plasma. The dispersion relation for surface waves propagating on an interface between a dusty plasma and a vacuum is derived and discussed. The damping of the waves due to Alfven resonance absorption in a narrow but non‐zero width interface is derived.

Nonlinear Torsional and Compressional Waves in a Magnetic Flux Tube with Electric Current near the Quiet Solar Photospheric Network

Recent high-resolution observations from photospheric magnetograms made with the SOHO/Michelson Doppler Imager instrument and the Swedish Vacuum Solar Telescope on La Palma showed that magnetic flux tubes in the quiet photospheric network of the solar photosphere are highly dynamic objects with small-scale substructures. We investigate nonlinear waves propagating along a magnetic flux tube in weakly ionized plasmas with high plasma beta (β 1) by using three-dimensional neutral MHD equations. Recently Sakai et al. investigated nonlinear wave propagation along a magnetic flux tube with a weak current for the two cases of uniform density along the flux tube and density inhomogeneity due to solar gravity. They showed that shear Alfven waves are excited by localized, predominantly rotational perturbations and that excited waves with a strong upflow of wave energy can propagate only upward along the flux tube when density inhomogeneity due to gravity is taken into account. In this paper we extend this work by investigating nonlinear torsional and compressional waves in a magnetic flux tube with a strong electric current, i.e., a twisted magnetic field, near the quiet solar photospheric network. If gravity is neglected, the torsional waves are found to propagate in a direction such as to decrease the twist of the magnetic field, while the compressional waves propagate symmetrically. We have found that solar gravity results in the important effect that wave energies excited by both torsional and compressional disturbances can be transferred upward in both untwisted and highly twisted flux tubes and eventually contribute to coronal heating.

Simulation of Nonlinear Waves in a Magnetic Flux Tube near the Quiet Solar Photospheric Network

Recent high-resolution observations from photospheric magnetograms made with the SOHO/Michelson Doppler Imager instrument and Swedish Vacuum Solar Telescope on La Palma showed that magnetic flux tubes in the quiet photospheric network of the solar photosphere are highly dynamic objects with small-scale substructures. We investigate nonlinear waves propagating along a magnetic flux tube in weakly ionized plasmas with high plasma beta ( β 1) by using three-dimensional neutral-MHD equations. We investigate the wave propagation along a magnetic flux tube with weak current for the two cases of uniform density along the flux tube and density inhomogeneity due to solar gravity. It is shown that shear Alfven waves are excited due to localized predominantly rotational perturbations, which might be induced in the quiet photospheric network boundaries. Excited waves with strong upflow of wave energy can propagate only upward along the flux tube when the density inhomogeneity due to the gravity is taken into account. We apply the simulation results to the problem of coronal heating from the quiet photospheric network of the solar photosphere.

Low-frequency modes in the dust-plasma crystal

It is shown that there are low-frequency modes associated with vertical oscillations in the Coulomb crystal of dust grains arranged in horizontal chains in a sheath region of a low-temperature gas discharge plasma. The dispersion relations and characteristic frequencies of the modes are found.

NONLINEAR WAVEPACKETS IN PAIR-ION AND ELECTRON-POSITRON-ION PLASMAS

The occurrence of amplitude-modulated electrostatic and electromagnetic wavepackets in pair plasmas is investigated. A static additional charged background species is considered, accounting for dust defects or for heavy ion presence in the background. Relying on a two-fluid description, a nonlinear Schrodinger type evolution equation is obtained and analyzed, in terms of the slow dynamics of the wave amplitude. Exact envelope excitations are obtained, modelling envelope pulses or holes, and their characteristics are discussed.