Steffen Hain

Beam generated ablation pressure

Abstract The theoretical basis of ablative pressure generation is presented and discussed for laser, ion and X-ray beams. With lasers a comparison is made with experimental results and an excellent agreement was found without fitting any free parameters. It results that heat flow into the corona and ponderomotive profile steepening effects are thereby essential. At superhigh intensities the plasma pressure still plays an important role and cannot be omitted in favour of the radiation pressure. In the lower Mbar pressure domain ion beams may compete with the laser and are expected to offer some net advantages.

Fast ignitor: Fluid dynamics of channel formation and laser beam propagation

The concept of fast ignitor is intimately connected with the fundamental phenomenon of ultra-intense light beam propagation through dense matter in which kinetic effects combine with radiation pressure dominated hydrodynamics to form a complex scenario of extremely non-linear physics. In this paper, the fluid dynamic aspect of channel formation in a highly over-dense plasma is studied and possible attenuation mechanisms of the propagating pulse are evaluated in one dimension. Under the assumption that mass ablation reaches a quasistationary state, the radiation-assisted ablation pressure, the speed of the bow shock, and the density steepening around the critical point are determined self-consistently from the ID fluid conservation relations and the electromagnetic wave equation. Due to ponderomotive profile steepening, the ablation pressure is reduced by 40% in the subsonic region and is dominated by the radiation pressure in the supersonic domain. Channel lengths are calculated for various intensities and pellet compression ratios. Likewise, the nonlinear propagation of a superintense electromagnetic wave in an underdense plasma channel is investigated for the ID case with the help of a relativistic fluid model.

Fast coronal ignition and the problem of energy transport

An alternative scheme of fast ignition is proposed and the key issue of dense matter heating, common to all fast ignition schemes, is discussed.

Ultraintense laser-solid interaction phenomena

In the variety of processes occurring in matter under the action of superstrong laser fields rapid field ionization and ponderomotive effects play a dominant role. We investigate field ionization by solving the time-dependent Schrodinger equation numerically and compare the results with classical calculations. We obtain the ionization rates of hydrogen-like ions, the ejection energy spectrum of the electrons, and we show the transition to classical behavior at high energies. In addition, we are able to give a physical explanation of non-sequential ionization. Our ionization rates differ by more than an order of magnitude from the standard expressions. A model is presented which allows to calculate the back action of field ionization on the laser beam. Finally, we present the most general relativistic derivation of ponderomotive forces on single particles and present their transformation properties. Ponderomotive forces are of non-Newtonian character.