Kinetic simulation of the O-X conversion process in dense magnetized plasmas

The ordinary-extraordinary-Bernstein (O-X-B) double conversion is considered and simulated with a kinetic particle model vs full wave model for parameters of the TJ-II stellarator. This simulation has been done with the particle-in-cell code, XOOPIC (X11-based object-oriented particle-incell). XOOPIC is able to model the non-monotonic density and magnetic profile of TJ-II. The first step of conversion, O-X conversion, is observed clearly. By applying some optimizations such as increasing the number of computational particles in the region of the X-B conversion, the simulation of the second step is also possible. By considering the electric and magnetic components of launched and reflected waves, the O-mode wave and the X-mode wave can be easily detected. Via considering the power of launched O-mode wave and converted X-mode wave, the efficiency of O-X conversion for the best theoretical launch angle is obtained, which is in good agreement with previous computed efficiencies via full-wave simulations. For the optimum angle of 47? between the wave-vector of the incident O-mode wave and the external magnetic field, the conversion efficiency is 66%

Regional mechanics and energetics of stunned myocardium in vivo

There is still some controversy about the definition of ischemia. a tenn originally derived from ischo hairna (to restrain blood). In this thesis. I would like to follow the defInition of Robert Kloner: "Myocardial ischemia is that state in which blood flow (oxygen and substrate delivery) to the myocardium has been reduced to the point where myocardial metabolism shifts from aerobic to anaerobic and the products of anoxic metabolism accumulate in the tissue. The reduction in blood flow may be absolute, as occurs with a total coronary artery occlusion or relative, as occurs when there is an increase in oxygen demand that outweighs oxygen supply (as in the case of a coronary stenosis in the setting of exercise or rapid pacing)". The reason to choose this definition lies in the fact that an absolute reduction in blood flow is not necessary for ischemia. and that it clearly defInes when blood flow is inadequate. Apart from myocardial stunning, which is defined below. several other ischemic syndromes have been described. In this section I will concisely discuss ischemic preconditioning, myocardial hibernation, and silent ischemia

Introduction to plasma accelerators : the basics

In this article, we concentrate on the basic physics of relativistic plasma wave accelerators. The generation of relativistic plasma waves by intense lasers or electron beams in low-density plasmas is important in the quest for producing ultra-high acceleration gradients for accelerators. A number of methods are being pursued vigorously to achieve ultra-high acceleration gradients using various plasma wave drivers; these include wakefield accelerators driven by photon, electron, and ion beams. We describe the basic equations and show how intense beams can generate a large-amplitude relativistic plasma wave capable of accelerating particles to high energies. We also demonstrate how these same relativistic electron waves can accelerate photons in plasmas

Peak intensity measurement of relativistic lasers via nonlinear Thomson scattering

The measurement of peak laser intensities exceeding 10^{20} \text{W/cm^2} is in general a very challenging task. We suggest a simple method to accurately measure such high intensities up to about 10^{23} \text{W/cm^2}, by colliding a beam of ultrarelativistic electrons with the laser pulse. The method exploits the high directionality of the radiation emitted by ultrarelativistic electrons via nonlinear Thomson scattering. Initial electron energies well within the reach of laser wake-field accelerators are required, allowing in principle for an all-optical setup. Accuracies of the order of 10% are theoretically envisaged.Comment: 4 pages, 2 figure

Weak collisionless shocks in laser-plasmas

We obtain a theory describing laminar shock-like structures in a collisionless plasma and examine the parameter limits, in terms of the ion sound Mach number and the electron/ion temperature ratio, within which these structures exist. The essential feature is the inclusion of finite ion temperature with the result that some ions are reflected from a potential ramp. This destroys the symmetry between upstream and downstream regions that would otherwise give the well-known ion solitary wave solution. We have shown earlier (Cairns et al 2014 Phys. Plasmas 21 022112) that such structures may be relevant to problems such as the existence of strong, localized electric fields observed in laser compressed pellets and laser acceleration of ions. Here we present results on the way in which these structures may produce species separation in fusion targets and suggest that it may be possible to use shock ion acceleration for fast ignition.PostprintPeer reviewe

Interpreting Ulysses data using inverse scattering theory: Oblique Alfv\'en waves

Solitary wave structures observed by the Ulysses spacecraft in the solar wind were analyzed using both inverse scattering theory as well as direct numerical integration of the derivative nonlinear Schr\"odinger (DNLS) equation. Several of these structures were found to be consistent with soliton solutions of the DNLS equation. Such solitary structures have been commonly observed in the space plasma environment and may, in fact, be long-lived solitons. While the generation of these solitons may be due to an instability mechanism, e.g., the mirror instability, they may be observable far from the source region due to their coherent nature.Comment: 20 pages, 3 figures, accepted by Journal of Geophysical Research: Space Physics; typographical errors fixe

Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering

Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterised by doughnut shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high gradient positron acceleration. The production of ultrahigh intensity twisted laser pulses could then also have a broad influence on relativistic laser-matter interactions. Here we show theoretically and with ab-initio three-dimensional particle-in-cell simulations, that stimulated Raman backscattering can generate and amplify twisted lasers to Petawatt intensities in plasmas. This work may open new research directions in non-linear optics and high energy density science, compact plasma based accelerators and light sources.Comment: 18 pages, 4 figures, 1 tabl