Diagnosing laser-driven, shock-heated foam target with Al absorption spectroscopy on OMEGA EP

Abstract

Results on diagnoses of laser-driven, shock-heated foam plasma with time-resolved Al 1s-2p absorption spectroscopy are reported. Experiments were carried out to produce a platform for the study of relativistic electron transport. In cone-guided Fast Ignition (FI), relativistic electrons generated by a high-intensity, short-pulse igniter beam must be transported through a cone tip to an imploded core. Transport of the energetic electrons could be significantly affected by the temperature-dependent resistivity of background plasmas. The experiment was conducted using four UV beams of the OMEGA EP laser at the Laboratory For Laser Energetics. One UV beam (1.2kJ, 3.5ns square) was used to launch a shock wave into a foam package target, consisting of 200mg/cm3 CH foam with aluminum dopant and a solid plastic container surrounding the foam layer. The other three UV beams with the total energy of 3.2kJ in 2.5ns pulse duration were tightly focused onto a Sm dot target to produce a point X-ray source in the energy range of 1.4–1.6keV. The quasi-continuous X ray signal was transmitted through the shock-heated Al-doped, foam layer and recorded with an X-ray streak camera. The measured 1s-2p Al absorption features were analyzed using an atomic physics code FLYCHK. Electron temperature of 40eV inferred from the spectral analysis is consistent with 2-D DRACO Radiation-hydrodynamic simulations.