Foam Au driven by 4ω–2ω ignition laser pulse for inertial confinement fusion

• Published in: Physics of plasmas Vol. 24; no. 5
• Main Authors: Lan, Ke, Song, Peng
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.05.2017
• Subjects: Conversion; Efficiency; Ignition; Inertial confinement fusion; Laser fusion; Lasers; Plasma physics; Pulse shape; X ray spectra
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4983329

Green light (2ω) has the potential to drive ignition target for laser fusion with significantly more energy than blue light (3ω) and a relatively higher damage threshold for the optic components in the final optic assembly, but it has issues of a relatively low laser to x-ray conversion efficiency and a hard x-ray spectrum as compared to 3ω. In this paper, we propose to drive a foam hohlraum wall with an ignition laser pulse by taking a 4ω laser at the pre-pulse and a 2ω laser at the main-pulse, called as 4ω–2ω ignition pulse. This novel design has the following advantages: (1) benefiting from 2ω of its relatively high energy output and low damage threshold during main-pulse; (2) benefiting from foam in its relatively high laser to x-ray conversion efficiency and relatively low M-band fraction in re-emission; (3) benefiting from 4ω of its low LPI and low M-band fraction during pre-pulse. From our one-dimensional simulations with the Au material, the laser to x-ray conversion in a foam driven by 4ω–2ω pulse has an increase of 28% as compared to a solid target driven by 3ω with the same pulse shape. The relatively thin optical depth of foam is one of the main reasons for the increase of laser to x-ray conversion efficiency inside a foam target.