G. Maynard

Ion beam-plasma interaction: A standard model approach

Abstract The interaction of energetic multicharged ion beams with separately produced target plasmas is investigated within a projectile-ion-target-electron bin

Density effect and charge dependent stopping theories for heavy ions in the intermediate velocity regime

Abstract The density effect for swift heavy ions in carbon target is analyzed from a stopping power theory point of view. This is done using our recently derived charge dependent stopping model of partially ionized heavy ions. We show that high order correction terms and partial screening by the projectile electrons reduce the charge state dependence of the stopping power. These effects are more in favor of the Bohr and Lindhard (BL) descriptions of the density effect rather than this of Betz and Grodzins (BG).

Mean excitation energies for ions in gases and plasmas

A variational approach yields accurate upper and lower bounds for mean excitation energies and other related parameters describing the stopping of nonrelativistic point charges by isolated species and ions embedded in dense and hot matter of relevance to particle‐driven inertial fusion. The resulting I compares nicely with previous ones by Hartree–Fock–Slater and with experimental data when available. An efficient pseudo‐analytic formula based on the Thomas–Fermi method is obtained, together with a cubic spline interpolation variationally improved. It is shown that in high temperature plasmas (kBT≥10 eV) mean excitation energies are significantly smaller than their cold homologue.

Aberration-free laser beam in the soft x-ray range.

By seeding an optical-field-ionized population-inverted plasma amplifier with the 25th harmonic of an IR laser, we have achieved what we believe to be the first aberration-free laser beam in the soft x-ray spectral range. This laser emits within a cone of 1.34 mrad(1/e(2)) at a repetition rate of 10 Hz at a central wavelength of 32.8 nm. The beam exhibits a circular profile and wavefront distortions as low as lambda/17. A theoretical analysis of these results shows that this high beam quality is due to spatial filtering of the seed beam by the plasma amplifier aperture.

The charge state dependence of desorption. A way to study the energy transfer to the surface

Abstract Various experiments on the charge state dependence of secondary ion emission from insulators have been performed recently using the heavy ion accelerators in Orsay and Darmstadt. A survey of the results is presented with the intention of exhibiting phenomenological trends over a wide range of beam parameters. The yields of certain small fragment ions ejected from organic samples depend strongly on the initial charge of the incident ions but not on their atomic number. Large molecule-specific ions show a different behaviour. Their yields increase considerably with the atomic number when the initial charge state is kept constant. This phenomenon is interpreted in terms of a depth contribution to desorption. By means of an averaging procedure, we calculated a mean interaction depth, from which contributions to desorption reach the surface. For a coronen target, this mean interaction depth ranges from 12 to 160 A, when the target is irradiated by 1.16 MeV/n beams of Ne, Ar, and Kr having charge states from 5+ to 24+. The interaction depth, as defined in this work, increases linearly with the specific energy loss. An attempt was made to introduce the depth effect into the ion track model. The range of interaction predicted by these model calculations can not, however, reproduce the experimental observations.

Theory and simulation of short intense laser pulse propagation in capillary tubes with wall ablation

The theory and simulations of short intense laser pulses propagating in capillary tubes, whose properties are changed in time and space under the action of the laser field, are presented. A hybrid approach has been used in which the dynamics of fields inside the capillary tube is described analytically, whereas the ionization, heating, and expansion of the plasma created at the inner wall of the tube under the action of the transverse energy flux are calculated by numerical simulation. This hybrid method has allowed to determine the behavior of high laser fluxes guided over large distances. The threshold value for the incident intensity at which plasma creation plays a significant role has been estimated analytically and confirmed by numerical results. For intensities above the threshold, the transmission becomes highly sensitive to the energy of the laser pulse, being minimum at the intensity level for which the electron temperature of the capillary wall slightly exceeds the Fermi level and the electron collision frequency has a maximum.

A 3D trajectory numerical simulation of the transport of energetic light ion beams in plasma targets

We present in this paper a theoretical modeling and a numerical simulation devoted to the problem of transport and energy deposition profile of high current light ion beams interacting with dense matter. A numerical code, named MBC-ITFIP, is used to follow the trajectories of light atomic or molecular ions inside plasma targets with non-uniform density, temperature and composition profiles. MBC-ITFIPhas been more specifically optimized for application of ion beams generated by the new high intensity laser sources, such as radiography and isochoric heating of dense plasmas.

Nonlinear effects in stopping of partially ionized swift heavy ions

Abstract We present stopping power calculations for swift heavy ions in a hydrogen gas target. The point-like model is reviewed and compared to a new theory which includes the projectile elastic form factor. It is shown that, even for highly ionized ions, the projectile form factor yields a substantial modification over the standard stopping results.

Thomas–Fermi‐like and average atom models for dense and hot matter

All the Thomas–Fermi approaches to the thermodynamics and atomic physics properties of dense and ionized matter consisting of a single element are systematically derived and compared within a density‐functional theoretical framework. The corresponding results are contrasted to those of the average atom model by using similar approximations for exchange, correlation, and gradient corrections. Emphasis is led on equations of state, ionization, level shifts, and radial moments. The same numerical algorithms are used to unravel similar trends or identify specific ones, in terms of density and temperature variations. The most sophisticated Thomas–Fermi–Dirac–Weizacker method yields the closest results to the hybrid average atom model using quantized bound states. Parameters ranges of potential interest for inertially confined thermonuclear fusion stress out density in the 0.1–10 times the solid, and temperature up to 10 keV.

Fourier-limited seeded soft x-ray laser pulse

We present what we believe to be the first measurement of the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam. Using an interferometric method, the spectral profile of a seeded Ni-like krypton soft x-ray laser (32.8 nm) generated by optical field ionization has been experimentally determined, and the shortest possible pulse duration has been deduced. The source exhibits a Voigt spectral profile with an FWHM of 3.1+/-0.3 mA, leading to a Fourier-transform pulse duration of 4.7 ps. This value is comparable with the upper limit of the soft x-ray pulse duration determined by experimentally investigating the gain dynamics, from which we conclude that the source has reached the Fourier limit. The measured bandwidth is in good agreement with the predictions of a radiative transfer code, including gain line narrowing and saturation rebroadening.