The achievement of high gains in inertial fusion confinement ICF devices is strongly determined by the stability of the imploding targets. Non-uniformities of irradiation during the early phase of laser absorption and plasma formation can act as seeds for instabilities, which would finally degrade the fuel mixing and the core plasma temperature. The use of structured materials as volume absorbers for laser radiation can be beneficial in redistributing the laser energy before it finally reaches the underlying target surface [1,2]. On the other hand, it is important that the absorber does not limit the overall energy efficiency of the process. Experiments aimed to characterize the efficiency of energy transmission through porous absorbers have been performed in the ABC laser facility in Frascati [3,4]: beam energy and intensity were about 50 J and 1013-14 W/cm2 respectively; pulse duration was 3 ns at the basic wavelength 1054 nm of Nd-glass laser. The laser spot size was 500 μm using ISI plates as flux density profile smoothers. In this experimental campaign the absorbers were polystyrene foams of different density (10-40 mg/cm3) and thickness (200-800 μm) in contact with metal substrates (Al, Sn). During the interaction process the laser energy is initially stored in the foam and finally released to the metal substrate by the resulting shock wave. The melting of the substrate produced by the shock wave leaves an imprint in the metal in the shape of a small crater. Measurements of the crater physical properties are shown as a function of foam thickness and interaction parameters. To characterize a foam absorber plasma interferometry, ion-collectors and soft X-ray measurements  have been performed as well. Copyright © (2013) by the European Physical Society (EPS).
|Titolo:||Experiments on laser-driven energy transfer to solid target through a foam on the ABC laser|
|Data di pubblicazione:||2013|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|