When a steady-state cylindrical plasma discharge is centrally fuelled, the collisionless radial electron flux is canonically coupled to an axial current. The identification and analysis of this transport driven current, previously reported in collisionless simulations [W. J. Nunan and J. M. Dawson, Phys. Rev. Lett. $\mathbf{73}$, 1628 (1994)], is addressed analytically and extended to the collisional regime by means of first-principles kinetic models. Collisionless radial transport is described with the standard quasilinear model and collisional velocity anisotropy relaxation with the Landau kinetic equation. When trapped particles corrections are taken into account, the solution of this kinetic model provides the analytical expression for the transport driven current in a centrally fuelled steady-state tokamak as a function of the thermonuclear power and discharge parameters. For ITER type discharges, with central fuelling, a current of about one mega-ampere is predicted by this first-principles analytical kinetic model.

We have studied plasma-induced smoothing due to stimulated Brillouin scattering (SBS) under the aspect of the extremal statistics of smoothed laser beams. As pointed out in the work by Rose and DuBois (1994 Phys. Rev. Lett. 72 2883), scattered light can be subject to uncontrolled (or even 'explosive') behaviour, associated with a critical gain value for SBS. In this work we show how this critical behaviour can be predicted on the basis of the order statistics of laser speckle fields, and we analyse the transition to uncontrolled behaviour of the laser beam due to the dominance of high intensity speckles.

We present an overview of the interpretation of laser plasma interaction (LPI) experiments carried out on the LIL facility. These multikilojoule experiments have been done using underdense foam targets at 0.351 μm laser light leading to high temperature and large plasmas. We discuss the interpretation using our different numerical tools: hydrodynamics simulations carried out with the code FCI2 to characterize the plasma, linear gain estimates with the postprocessor Piranah and paraxial simulations with the code HERA.

Using ultrafast x-ray probing, we experimentally observed a progressive loss of ordering within solid-density aluminum as the temperature raises from 300 K to >10{4} K. The Al sample was isochorically heated by a short ( approximately ps), laser-accelerated proton beam and probed by a short broadband x-ray source around the Al K edge. The loss of short-range ordering is detected through the progressive smoothing of the time-resolved x-ray absorption near-edge spectroscopy (XANES) structure. The results are compared with two different theoretical models of warm dense matter and allow us to put an upper bound on the onset of ion lattice disorder within the heated solid-density medium of approximately 10 ps.

An acceleration process based on the interaction between an ion, a tapered periodic magnetic structure, and a circularly polarized oscillating electric field is identified and analyzed, and its potential is evaluated. A Hamiltonian analysis is developed in order to describe the interplay between the cyclotron motion, the electric acceleration, and the magnetic modulation. The parameters of this universal class of magnetic modulation leading to continuous acceleration without Larmor radius increase are expressed analytically. Thus, this study provides the basic scaling of what appears as a compact unfolded cyclotron accelerator.

The collisional dynamics of a relativistic electron jet in a magnetized plasma are investigated within the framework of kinetic theory. The relativistic Fokker-Planck equation describing slowing down, pitch angle scattering, and cyclotron rotation is derived and solved. Based on the solution of this Fokker-Planck equation, an analytical formula for the root mean square spot size transverse to the magnetic field is derived and this result predicts a reduction in radial transport. Some comparisons with particle-in-cell simulation are made and confirm striking agreement between the theory and the simulation. For fast electron with 1 MeV typical kinetic energy interacting with a solid density hydrogen plasma, the energy deposition density in the transverse direction increases by a factor 2 for magnetic field of the order of 1 T. Along the magnetic field, the energy deposition profile is unaltered compared with the field-free case. c 2010 American Institute of Physics. [doi: 10.1063/1.3356066]

A study of isochoric heating of Al foil by laser-accelerated proton beam is presented, coupling self-consistent hydrodynamic simulations (including proton stopping) with experimental measurements. The proton source that induces the heating has been characterized experimentally and the induced heating has been inferred through critical density expansion velocity measurement. The low-energy part of the proton spectrum that plays the dominant part in the heating process has been studied in detail. The experimental results are compared with the results of 1-dimensional hydrodynamic simulations that use as input the measured proton source and good agreement between the two is found using the SESAME EOS.

The acceleration of protons, induced by electrons generated by a short-pulse laser, is experimentally investigated when varying the density of the plasma target the laser is interacting with. The experimental results are compared with particle-in-cell (PIC) simulations for which the target conditions are inferred from hydrodynamic simulations. High-energy protons are observed only for the two extreme configurations, namely solid-density foils and near-critical-density plasmas having large gradients. Cold solid foils, however, yield the highest energy protons and best proton beam profiles. As suggested by simulations, near-critical-density plasmas could be optimized to further increase the proton energy.

A relativistic effect that occurs in a magnetized plasma irradiated by a circularly polarized wave is identified and analyzed: the usual plasma frequency associated with longitudinal oscillations splits into two new frequencies. We set up a Hamiltonian description of the plasma dynamic in order to identify this effect that results from the coupling between the plasma oscillation and the transverse circular motion driven by both the magnetic and wave fields. Within the small oscillations approximation, we compute for right- and left-handed polarization the two characteristics frequencies of the electron oscillations as functions of the field and wave parameters. We also describe the electron trajectories in the wave, magnetic, and restoring plasma fields. This new class of oscillations is rotational and therefore radiate suggesting a method for the diagnostics of strong static magnetic field in laser-plasma experiments.

dense regime J. Robiche, J. Fuchs, A. Mancic, P. Antici, P. Audebert, P. Combis, P. Renaudin, G. Maynard and J. Vassaux Laboratoire pour l’Utilisation des Lasers Intenses, Ecole Polytechnique, route de Saclay 91 128 Palaiseau Cedex, France Departement de Physique Theorique et Appliquee, CEA/DAM Ile-de-France BP12-F, 91 680, Bruyeres-Le-Châtel, France 3 Laboratoire de Physique des Gaz et des Plasmas, Universite Paris-Sud, 91405 Orsay Cedex

A new isotope separation process based on selective cyclotron resonant interaction between ions and a tapered helicoidal magnetic structure is identified, analyzed, and evaluated. On the basis of a Hamiltonian analysis, the existence of a class of tapered magnetic modulation that provide a full conversion of linear momentum into angular momentum is discovered. The characteristics and parameters of this field configuration are analyzed and described. The dynamic of the nonresonant isotope is investigated in order to set up a separation criterion. This autoresonant ion cyclotron isotope separation mechanism provides an efficient alternative to other niches of enrichment process.

An original computational method for solving the two-dimensional problem of the scattering of an axisymmetric laser beam by an arbitrary-shaped inhomogeneous body of revolution is presented. This method relies on a domain decomposition of the scattering zone into concentric spherical radially homogeneous subdomains and on an expansion of the angular dependence of the fields on the Legendre functions. Numerical results for the fields obtained for various scatterer geometries are presented and analyzed.

The collisional dynamics of a relativistic electron population in a Lorentzian plasma are investigated and analyzed within the framework of kinetic theory. The relativistic Fokker-Planck equation describing both slowing down and pitch angle scattering is derived, analyzed, and solved. The analytical Green function is used to express the electron range, the range straggling, and the mean radial dispersion as a function of the plasma parameters. Compared to standard slowing down theories, the inclusion of the pitch angle scattering without any Gaussian approximation appears to be essential to calculate these quantities.

The nonlinearity of the plasma sheath in dual frequency capacitively coupled reactors is investigated for frequencies well above the ion plasma frequency. This work focuses on the behaviour of the voltage and the sheath width with respect to the driving current source and the collisionality regime. For typical plasma processing applications, the gas pressure ranges from a few milliTorrs to hundreds of milliTorrs, and the ion dynamics span different collisional regimes. To describe these different ion dynamics, we have used a collisionless model and a variable mobility model. The sheath widths and the voltages obtained from these two models have then been compared.

Relativistic second-harmonic generation with ultrahigh intensity laser pulses in a weakly magnetized plasma is analyzed. Both ordinary mode conversion to second-harmonic extraordinary mode and extraordinary mode conversion to second-harmonic extraordinary mode are considered. Extraordinary mode conversion turns out to be more efficient, and a new frequency doubling scheme based on a tapered magnetic wiggler is identified, described, and analyzed. The important issues of phase matching, pump depletion, and relativistic tapering are addressed and solved. Both permanent magnet and laser-driven wigglers are considered. The interaction of multi-terawatt laser pulses with a magnetized plasma appears to provide an efficient scheme to generate short wavelengths.

The relativistic stochastic kinetic equations describing noninductive current generation in the presence of generic low frequency electric and magnetic turbulent fields is analyzed. The limitations of previous phenomenological models based on local diffusion are discussed. The difference between electric and magnetic current profile broadening is analyzed. The width of the noninductive current channel is calculated as a function of the electric and magnetic fields autocorrelations functions.