Z. Zinamon

Energy deposition by fast protons in pellet fusion targets

The energy loss of energetic protons in heavy metal targets is calculated at temperatures and densities of interest for pellet fusion. The contributions of bound and free electrons to the stopping power are considered. It is found that in the temperature range of interest the increase in the number of free electrons in the target plasma causes range shortening with increasing temperatures and specific volumes. In order to study this effect on the ablation process, a one‐dimensional calculation of the hydrodynamic flow with energy deposition was carried out.

Intraband and interband absorption of femtosecond laser pulses in copper

We investigated the optical properties of pure copper irradiated by a femtosecond laser pulse. Self-absorption of 50-fs laser pulses at 800 nm and 400 nm wavelengths (below and above the interband absorption threshold, respectively) is studied for peak laser intensities up to 10 15 W/cm 2 . Theoretical description of laser interaction with copper target is developed, solving numerically the energy balance equations for electron and ion subsystems together with Maxwell equations for laser radiation field inside the target. The theory accounts for both intraband and interband absorption mechanisms. We treated in detail the changes in electron structure and distribution function with an increase in electron temperature, as well as the ensuing changes in thermodynamic properties, collision frequencies, optical and transport coefficients. Experimental work on self-absorption of femtosecond laser pulses in copper targets at 800 nm and 400 nm wavelengths is ongoing. Results for 800 nm wavelength are reported. Theory and experiment are in good agreement.

Plasma effects in the interaction of intense light ion beams with light targets

It is shown that with present‐day ion beam intensities, plasma effects on the range are important in light targets. It is suggested to use the strong dependence of Kα emission on particle energy in order to observe this effect in layered targets. Neutron diagnostics in the case of deuteron beam CD2 target interaction are also considered.

The interaction of large fast carbon clusters with plasma

The energy loss and disintegration dynamics of large carbon clusters (C 60 molecules) in hot plasmas is calculated. The calculation self-consistently includes the cluster disintegration, the evolution of the charge of the fragment ions, the screened Coulomb forces among them, and the effects of interference between neighboring ions on the energy loss. A range of projectile energies and plasma parameters is considered. A large enhancement factor in the energy deposition due to the interference is found at the early stage of the interaction.

High‐current‐density relativistic electron beams in conical diodes

Current densities of 20 MA/cm2 are obtained in the focus of a modest (450 kV, 60 kA) beam in a conical ’’parapotential’’ diode. The electron flow in the diode is studied using pinhole photography and bremsstrahlung angular distribution measurements.

Electron flow in the pinch region of a relativistic electron‐beam diode

The flow of electrons produced in the pinch region of a relativistic electron beam (REB) diode is studied by means of the time‐dependent Kα emission from a double‐layered anode. The anode materials were Cu and Ni foils of various thicknesses. The experimental data were analyzed using detailed Monte‐Carlo simulation. Results indicate that no anomalous deposition processes seem to occur, and that the angular distribution at the anode can be fairly well represented by an axially symmetric angular distribution with an angle of incidence of 60° to the normal.

Energy content of target and electron flow in femtosecond laser target interactions

The heating of the titanium foil in a recent femtosecond laser plasma experiment is investigated theoretically in two different ways. In the first, the energy content and thus the heating efficiency of the central volume of the foil is derived by integrating the transverse temperature profiles obtained in this experiment, using specific heats based on the average atom model. In the second approach target heating by the fast electrons, both by direct energy deposition and by resistive heating is investigated. The latter approach makes use of a specially devised electron flow model which includes a simplified quantitative treatment of multi-refluxing as a crucial component. In all, the calculated results of electron beam heating are consistent with experiment within the limitations of the modeling. Finally, a prediction for the temporal dependence of the Kα pulse from the central volume of the foil based on our electron flow model is given.

Pinch dynamics in thin foil relativistic electron beam diodes

Time‐resolved Kα emission from targets struck by relativistic electrons is used as a diagnostic of the electron flow in pinch relativistic electron beam diodes. Pinch dynamics in thin foil anode diodes are studied. A transition from a regime of reflexing pinch to a regime of flow dominated by ion emission from the anode is observed. Current fluctuations in the pinch region are also detected.

K α emission and secondary electrons in femtosecond laser target interactions

This paper deals with the contribution of secondary electron emission, produced during the slowing down of fast electrons, on the intensity and temporal shape of the generated K α pulse. The problem is treated in a general manner emphasizing laser–plasma interactions, where it was suggested in the literature that these electrons could play an important role on the temporal duration. Here, we make use of a hybrid model which includes secondary emission in conjunction with the continuous slowing down approximation (CSDA). The results are compared with those obtained from a simple CSDA calculation, with no detailed accounting of secondary emission and without straggling. Secondary electrons were calculated to contribute up to an additional 20% to the total K α yield and in the case of monoenergetic electron beams in thick targets also to influence the temporal shape. The pulse duration is not affected in a significant manner by the secondary electrons.

Electron flow in a relativistic electron beam pinched diode collective acceleration system

Investigations of the electron component of the composite collectively accelerated ion and electron beam produced in a relativistic electron beam pinch diode are reported. The experiments consisted of examining the Kα x‐ray signal induced by the propagating electron beam and comparing this with the Kα signal produced in the anode. The measurements dealt with propagation velocity, beam front current density as a function of distance from the anode, and the temporal structure of the beam front as a function of distance. Time dependent structure consisting of several peaks was observed. The velocity of the beam front was seen to increase with the addition of CH2 to the anode.