Measurement of preheat due to fast electrons in laser implosions

Abstract

Fast electrons due to the two-plasmon decay instability have been shown to be generated in laser interaction experiments. The purpose of the present experiment is to determine the preheat level due to these electrons, using the Kα emission from a two-layer, Ti–V, planar target. The target is designed to separate the contributions of fast electrons and radiation to the observed Kα intensity. About 0.3% of the incident laser energy is found to be deposited as preheat due to fast electrons. It is shown that the preheat level can alternatively be determined directly from the hard x-ray continuum without the need to know the electron dynamics; the only required parameters are the total energy in hard x rays and the temperature of the fast electrons.

Stopping of directed energetic electrons in high-temperature hydrogenic plasmas

“…In another important context in ICF, workers addressed the issue of fuel pre-heat due to energetic electrons (~50-300 keV) [5,18,19], the consequence of which is to elevate the fuel adiabat to levels that would prohibit ignition. Herein we show that scattering effects could be significant for quantitative evaluations of preheat.…”

Experiment on the Mass Stripping of an Interstellar Cloud Following Shock Passage

“…Even so, we find that the observed expansion in Figure 3 is consistent with our CALE simulation, which has a $3.7 m density gradient on the equator and $1.5 m on the back side. Since CALE does not include hot electrons, we therefore conclude that hot electrons, as expected from the findings of Yaakobi et al (2000), play a much smaller role than radiative preheat in our experiment.…”

“…The front side of the sphere (the hemisphere facing the ablation front) will be heated more than the back side of the sphere; the ''equator'' between the two hemispheres is heated to an intermediate value. Hot electrons will heat both the CRF and the Al sphere volumetrically, but likely to much lower temperatures than the radiative preheat; radiative preheat tends to mask preheat due to electrons in ultraviolet ( UV ) laser experiments ( Yaakobi et al 2000). Since the Al sphere has a higher density than the surrounding CRF, and since it also tends to absorb more preheat and thus become hotter, the sphere will expand due to preheat, creating a density gradient of Al plasma.…”

Evolution of surface structure in laser-preheated perturbed materials

“…This preheat can cause instability-like growth of structure at interfaces present in the system, which in turn alters the initial conditions and therefore complicates the analysis of processes that depend upon those initial conditions. Existing studies of preheat typically focus either on quantifying the amount of energy deposited [4][5][6][7] and/or the transport mechanism [3,8] involved. Studies considering the subsequent interface dynamics themselves have either been computational [9][10][11] or have involved complex structure tailored to a specific application [12].…”