The TARANIS laser : A multi-terawatt system for laser plasma physics

The Terawatt Apparatus for Relativistic And Non-linear Interdisciplinary Science (TARANIS), installed in the Centre for Plasma Physics at the Queen's University Belfast, supports a wide ranging science program, including laser-driven particle acceleration, X-ray lasers and high energy density physics experiments. We present (1) an overview of the laser facility, (2) results of preliminary investigations on proton acceleration, laser action at 13.9 nm and Kα sources and (3) speculation on future experiments using these extreme sources.

Electromagnetic envelope solitons in magnetized plasma

A multiple scales technique is employed to solve the fluid-Maxwell equations describing a weakly nonlinear circularly polarized electromagnetic pulse in magnetized plasma. A nonlinear Schrodinger-type (NLS) equation is shown to govern the amplitude of the vector potential. The conditions for modulational instability and for the existence of various types of localized envelope modes are investigated in terms of relevant parameters. Right-hand circularly polarized (RCP) waves are shown to be modulationally unstable regardless of the value of the ambient magnetic field and propagate as bright-type solitons. The same is true for left-hand circularly polarized (LCP) waves in a weakly to moderately magnetized plasma. In other parameter regions, LCP waves are stable in strongly magnetized plasmas and may propagate as dark-type solitons (electric field holes). The evolution of envelope solitons is analyzed numerically, and it is shown that solitons propagate in magnetized plasma without any essential change in amplitude and shape. (C) 2009 Elsevier B.V. All rights reserved.

Electron beam-plasma interaction and ion-acoustic solitary waves in plasmas with a superthermal electron component

The study of non-Maxwellian plasmas is crucial to the understanding of space and astrophysical plasma dynamics. In this paper, we investigate the existence of arbitrary amplitude ion-acoustic solitary waves in an unmagnetized plasma consisting of ions and excess superthermal electrons (modelled by a kappa-type distribution), which is penetrated by an electron beam. A kappa (kappa-) type distribution is assumed for the background electrons. A (Sagdeev-type) pseudopotential formalism is employed to derive an energy-balance like equation. The range of allowed values of the soliton speed (Mach number), wherein solitary waves may exist, is determined. The Mach number range (allowed soliton speed values) becomes narrower under the combined effect of the electron beam and of the superthermal electrons, and may even be reduced to nil (predicting no solitary wave existence) for high enough beam density and low enough kappa (significant superthermality). For fixed values of all other parameters (Mach number, electron beam-to-ion density ratio and electron beam velocity), both soliton amplitude and (electric potential perturbation) profile steepness increase as kappa decreases. The combined occurrence of small-amplitude negative potential structures and larger amplitude positive ones is pointed out, while the dependence of either type on the plasma parameters is investigated.

Multiphysics Simulation of Thermal Plasma Produced by Lightning Strike on Aircraft Structures

A novel numerical technique is proposed to model thermal plasma of microseconds/milliseconds time-scale effect. Modelling thermal plasma due to lightning strike will allow the estimation of electric current density, plasma pressure, and heat flux at the surface of the aircraft structure. These input data can then be used for better estimation of the mechanical/thermal induced damage on the aircraft structures for better protection systems design. Thermal plasma generated during laser cutting, electric (laser) welding and other plasma processing techniques have been the focus of many researchers. Thermal plasma is a gaseous state that consists from a mixture of electrons, ions, and natural particles. Thermal plasma can be assumed to be in local thermodynamic equilibrium, which means the electrons and the heavy species have equal temperature. Different numerical techniques have been developed using a coupled Navier Stokes – Heat transfer – Electromagnetic equations based on the assumption that the thermal plasma is a single laminar gas flow. These previous efforts focused on generating thermal plasma of time-scale in the range of seconds. Lighting strike on aircraft structures generates thermal plasma of time-scale of milliseconds/microseconds, which makes the previous physics used not applicable. The difficulty comes from the Navier-Stokes equations as the fluid is simulated under shock load, this introducing significant changes in the density and temperature of the fluid.

Direct observation of strong coupling in a dense plasma

We present differential x-ray scattering cross sections for a radiatively heated plasma showing overall consistency, in both form and absolute value, with theoretical simulations. In particular, the evolution of the plasma from a strongly coupled high density phase to a lower density weakly coupled phase is quite clearly shown in both experiment and simulation. The success of this experiment shows that x-ray scattering has the potential to become an extremely useful diagnostic technique for dense plasma physics.

Instability and dynamics of two nonlinearly coupled laser beams in a plasma

The nonlinear interaction between two laser beams in a plasma is investigated in the weakly nonlinear and relativistic regime. The evolution of the laser beams is governed by two nonlinear Schrodinger equations that are coupled with the slow plasma density response. A nonlinear dispersion relation is derived and used to study the growth rates of the Raman forward and backward scattering instabilities as well of the Brillouin and self-focusing/modulational instabilities. The nonlinear evolution of the instabilities is investigated by means of direct simulations of the time-dependent system of nonlinear equations. (c) 2006 American Institute of Physics.

Characterization of stationary and pulsed inductively coupled RF discharges for plasma sterilization

Sterilization of bio-medical materials using radio frequency (RF) excited inductively coupled plasmas (ICPs) has been investigated. A double ICP has been developed and studied for homogenous treatment of three-dimensional objects. Sterilization is achieved through a combination of ultraviolet light, ion bombardment and radical treatment. For temperature sensitive materials, the process temperature is a crucial parameter. Pulsing of the plasma reduces the time average heat strain and also provides additional control of the various sterilization mechanisms. Certain aspects of pulsed plasmas are, however, not yet fully understood. Phase resolved optical emission spectroscopy and time resolved ion energy analysis illustrate that a pulsed ICP ignites capacitively before reaching a stable inductive mode. Time resolved investigations of the post-discharge, after switching off the RF power, show that the plasma boundary sheath in front of a substrate does not fully collapse for the case of hydrogen discharges. This is explained by electron heating through super-elastic collisions with vibrationally excited hydrogen molecules.

Observation of fast hydrogen atoms formed by ion bombarding of surfaces

We report on the observation of fast hydrogen atoms in a capacitively coupled RF reactor by optical emission spectroscopy. For the analysis we use the prominent H-alpha emission line of atomic hydrogen in combination with other lines from molecular hydrogen and argon. Several chaxacteristic emission structures can be identified. One of these structures is related to fast hydrogen atoms traveling from the surface of the powered electrode to the plasma bulk. From the appearance time within the RF period we conclude that this feature originates from ion bombardment of the electrode surface. Measured pressure dependencies and a simple model for the ion dynamics support this assumption.