In the context of Inertial Confinement Fusion, Shock Ignition (SI) is a promising approach to reach the ignition and burning of a thermonuclear fuel pellet. It consists of a two-steps scheme, where ignition is achieved by a strong converging shock wave launched by a laser spike at an intensity I?2 >1016 W cm-2 ?m2 at the end of the compression phase. Its attractiveness relies mainly in the high potential gains leading to a lower laser energy needed for the fuel ignition. In this intensity regime, however, laser -plasma interaction is strongly affected by the growth of a variety of parametric instabilities, including stimulated Raman scattering (SRS), Brillouin scattering (SBS) and Two Plasmon Decay (TPD), leading to the waste of a considerable amount of laser energy and to the generation of fast electrons, which could produce a detrimental preheating of the compressed fuel. To investigate laser-plasma coupling in the SI regime, several measurement campaigns have been carried out at the Prague Asterix Laser Facility (PALS). A strong shock has been produced by focusing a laser spike at intensities 1015-1016 Wcm-2 (250 ps, 438 nm and 1315 nm) on an extended plasma corona, which was created by a previous laser pulse at intensity I~7·1013 Wcm-2 (250 ps, 1315 nm). The pre-plasma temperature and density were inferred by x-ray spectroscopy, ion diagnostics and interferometry. Parametric instabilities were investigated by calorimetry and spectroscopy of the backscattered radiation in the full angular range; the emission peaks at (3/2)?, ? and ?/2 emission provided information on TPD, SBS and SRS, respectively. K? spectroscopy was utilized to investigate fast electron generation. Finally, the shock pressure produced by the laser spike was derived by shock breakout chronometry and by the morphology of craters formed in massive targets. The main results of these experimental campaigns, with a particular emphasis to the relevance of parametric instabilities, are here presented [1-3]. The obtained results are critically discussed in the perspective of SI and future directions of investigation are suggested.
Experimental investigation on laser-plasma coupling in the shock ignition regime at PALS
G Cristoforetti;F Baffigi;P Koester;L Labate;L A Gizzi;
2014
Abstract
In the context of Inertial Confinement Fusion, Shock Ignition (SI) is a promising approach to reach the ignition and burning of a thermonuclear fuel pellet. It consists of a two-steps scheme, where ignition is achieved by a strong converging shock wave launched by a laser spike at an intensity I?2 >1016 W cm-2 ?m2 at the end of the compression phase. Its attractiveness relies mainly in the high potential gains leading to a lower laser energy needed for the fuel ignition. In this intensity regime, however, laser -plasma interaction is strongly affected by the growth of a variety of parametric instabilities, including stimulated Raman scattering (SRS), Brillouin scattering (SBS) and Two Plasmon Decay (TPD), leading to the waste of a considerable amount of laser energy and to the generation of fast electrons, which could produce a detrimental preheating of the compressed fuel. To investigate laser-plasma coupling in the SI regime, several measurement campaigns have been carried out at the Prague Asterix Laser Facility (PALS). A strong shock has been produced by focusing a laser spike at intensities 1015-1016 Wcm-2 (250 ps, 438 nm and 1315 nm) on an extended plasma corona, which was created by a previous laser pulse at intensity I~7·1013 Wcm-2 (250 ps, 1315 nm). The pre-plasma temperature and density were inferred by x-ray spectroscopy, ion diagnostics and interferometry. Parametric instabilities were investigated by calorimetry and spectroscopy of the backscattered radiation in the full angular range; the emission peaks at (3/2)?, ? and ?/2 emission provided information on TPD, SBS and SRS, respectively. K? spectroscopy was utilized to investigate fast electron generation. Finally, the shock pressure produced by the laser spike was derived by shock breakout chronometry and by the morphology of craters formed in massive targets. The main results of these experimental campaigns, with a particular emphasis to the relevance of parametric instabilities, are here presented [1-3]. The obtained results are critically discussed in the perspective of SI and future directions of investigation are suggested.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
