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7Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2019
TRACKING HOT ELECTRONS IN MATTER BY SPHERICAL
CRYSTAL IMAGERS
D. Batani12
1CELIA, University of Bordeaux, Talence, France
2
Department of Plasma Physics, National Research Nuclear University MEPhI, Moscow, Russia
e-mail: dimitri.batani@u-bordeaux.fr
Spherically bent crystal is a diagnostic tool which has been introduced in physics research by Anatoly Faenov and his collaborators. This techniquecoupled Bragg reflection from the crystal atomic planes to the focusing properties of spherical mirrors, well-known in geometrical optics. In particular, therefore, spherically bent crystals allow obtaining monochromatic images of objects emitting X-rays or illuminated by X-rays.
In recent years,spherically bent crystals have found a huge application to study the generation of hot electrons in laser-plasma interaction experiments and the propagation of such electrons in matter. Usually in this kind of experiments, a tracer layer is embedded in the target. Hot electrons produced at the critical density by the interaction of the laser beam with the front side of the target reach the tracer layer and induce inner-shell ionization which is followed by recombination and the emission of K-a photons which are characteristics of each material. Spherically bent crystals have therefore allowed to image the K-a source at the tracer layer and measure its size. The variation of the size with the embedding depth of the tracer layer allowed to measure the divergence of the hot electron beam. The "shape" of the image allowed to conclude on whether the propagation was uniform or was characterized by filamentation of the hot electron beam. Finally, by integrating over the source size one can obtain the total K-a yield and, from the variation of K-a yield vs. depth, one can measure the propagation depth of hot electrons and therefore infer the hot electron "temperature".
This diagnostics technique has found very many applications in the study of hot electrons in the context of inertial confinement fusion (fast ignition and shock ignition) and of laser-driven secondary sources.
