On damped Bernstein modes in a weakly relativistic pair plasma

Relativistic Bernstein modes are not totally undamped, but have a small, negative definite imaginary frequency component which peaks where the frequency is closest to the rest cyclotron harmonic

Automatic recognition and characterisation of supergranular cells from photospheric velocity fields

We have developed an exceptionally noise resistant method for accurate and automatic identification of supergranular cell boundaries from velocity measurements. Due to its high noise tolerance the algorithm can produce reliable cell patterns with only very small amounts of smoothing of the source data in comparison to conventional methods. In this paper we describe the method and test it with simulated data. We then apply it to the analysis of velocity fields derived from high-resolution continuum data from MDI (Michelson Doppler Imager) on SOHO. From this, we can identify certain basic properties of supergranulation cells, such as their characteristic sizes, the flow speeds within cells and their dependence on cell areas at high resolution. The effect of the noise and smoothing on the derived cell boundaries is investigated and quantified using simulated data. We show in detail the evolution of supergranular cells over their lifetime, including observations of emerging, splitting, and coalescing cells. A key result of our analysis of cell internal velocities is that there is a simple linear relation between cell size and cell internal velocity, rather than the power law usually suggested

Ionization fronts in coupled MHD-gas simulations

Partially ionized plasmas are ubiquitous in both nature and the laboratory, and their behaviour is best described by models which take into account the interactions between the neutral and charged species. We present a new non-linear, 3-dimensional, finite difference Gas-MHD Interactions Code designed to solve simultaneously the time evolution of fluid equations of both species in the conservation form as well as collisional interactions between them via appropriate choices of source term; in particular, we present results from this code in simulating Alfvén ionization in a partially ionized plasma. In this fashion, larger changes in the ionization fraction than were addressable in the linear limit are possible. Alfvén ionization is shown to impart plasmas with an inherent resistance to rapid recombination, where the recombination itself is significant enough to drive relative motion between the ionised and neutral species at speeds in excess of the critical velocity

Pulsar magnetospheres: numerical simulations of large amplitude electron-positron oscillations

The numerical simulation of non-linear electron-positron oscillations is reported, showing the evolution of the electric field and the plasma number density for large amplitude disturbances. Sharp density gradients and changes in the oscillation frequency are demonstrated, and a new analytical framework is presented to illustrate these phenomena, particularly in the context of pulsar plasmas

Modelling nonlinear electrostatic oscillations in plasmas

The nonlinear 1-D plasma electrostatic oscillation is formulated in an analytic framework that allows closed-form analytic solutions along the characteristics, and solved numerically in configuration space. Additionally, a novel iterative analytical form for the finite-amplitude oscillation solution is derived, which compares favourably with the other two techniques. A fresh insight into the evolution of the oscillation is gained, including defining the least achievable density in the nonlinear oscillation as half of the equilibrium value, and relating the associated maximum density achievable in terms of that minimum

Bernstein modes in a weakly relativistic electron-positron plasma

The kinetic theory of weakly relativistic electron-positron plasmas, producing dispersion relations for the electrostatic Bernstein modes was addressed. The treatment presented preserves the full momentum dependence of the cyclotron frequency, albeit with a relaxation on the true relativistic form of the distribution function. The implications of this new treatment were confined largely to astrophysical plasmas, where relativistic electronpositron plasmas occur naturally

Plasma Decontamination of Sealed Packages

We have developed an unusual plasma source that allows the generation of plasma exclusively within a sealed container or bag, from an entirely external electrode system. This device is unique in that it can be applied to standard sealed packaging and does not subject the package contents to any significant electric fields. This system can be used to modify the atmosphere inside the package by generating active species such as free radicals and ozone from the gas within it. This allows, for example, sterilisation or decontamination of the contents of a presealed container without the risks associated with handling ozone in open atmosphere. We present results showing the efficacy of this system in reducing the contamination of foodstuffs with pathogens such as Campylobacter and E.coli

Precision charging of microparticles in plasma via the Rayleigh instability for evaporating charged liquid droplets

In this paper we describe a novel method for delivering a precise, known amount of electric charge to a micron-sized solid target. Aerosolised microparticles passed through a plasma discharge will acquire significant electric charge. The fluid stability under evaporative stress is a key aspect that is core to the research. Initially stable charged aerosols subject to evaporation (i.e. a continually changing radius) may encounter the Rayleigh stability limit. This limit arises from the electrostatic and surface tension forces and determines the maximum charge a stable droplet can retain, as a function of radius. We demonstrate that even if the droplet charge is initially much less than the Rayleigh limit, the stability limit will be encountered as the droplet evaporates. The instability emission mechanism is strongly linked to the final charge deposited on the target, providing a mechanism that can be used to ensure a predictable charge deposit on a known encapsulated microparticle

A Plasma Formulary for Physics, Technology, and Astrophysics

Counter Plasma physics has matured rapidly as a discipline, and now touches on many different research areas, including manufacturing processes. This collection of fundamental formulae and definitions in plasma physics is vital to anyone with an interest in plasmas or ionized gases, whether in physics, astronomy or engineering. Both theorists and experimentalists will find this book useful, as it incorporates the latest results and findings. The text treats astrophysical plasmas, fusion plasmas, industrial plasmas and low temperature plasmas as aspects of the same discipline - a unique approach made possible by the abbreviated nature of a formulary

Similarity theory of nonlinear cold pair-plasma dynamics

In this article the waves and dynamics of an inhomogeneous cold magnetized electron-positron plasma are investigated using similarity methods to study particular classes of plasma wave behavior. A cold two-fluid plasma model in a cylindrical geometry (ρ,θ,z) and time t is assumed, but attention is restricted to (ρ,t) variations only. The application of similarity procedures reduces the set of partial differential equations which describe the spatial and temporal evolution of the plasma to a set of ordinary differential equations. This model has particular relevance to the description of the evolution of the electron-positron component of pulsar magnetospheres. Some typical solutions of these similarity equations are presented which characteristically have the property of blow-up phenomena