261 / 2023-04-22 23:45:58

Laser plasma instability in large-energy, high-power multi-beam cluster

inertial confinement fusion,laser plasma instability

The goal of laser plasma instability (LPI) study in the indirect-drive ICF is to minimize its uncertainty during the coupling of laser energy to capsule. Because the quantitative interpretation of LPI reflectivity has always been a major challenge, continuous experimental efforts on laser-plasma couplings are conducted in different irradiation and plasma condition on Shenguang laser facilities. Large-energy and high-power laser facilities are experiencing the development trend from single beam to multi-beam, and then to multi-cluster. The cluster laser is a configuration of bundling multiple laser beams together to form an effective beam, which is an important way to produce megajoule laser. The cluster laser has the unique characteristics of small angle overlap over a long distance of multiple laser beams, large F number of single sub-beam, which produce new phenomena different from traditional single beam and large angle multi-beam LPI, greatly promotes the extremity and complexity of LPI, and makes the cluster laser at great risk of beam smoothing inhibition failure .



A new experimental platform Octuplet has been developed to scale the LPI from the present SG-180kJ facility to those on the next facility. Octuplet is a bundle of eight beams injected though one single port, which has a laser configuration close to the future. Gas-filled hohlraums between 3 and 7 mm length have been heated from one side by overlapping the focal spot of the eight beams from one octuplet operated at 351nm with a total energy of 30kJ, creating unique conditions for the LPI study at scale length not previously accessible on Shenguang. Laser propagation and backscattering are measured to study the effects of several laser parameters (single beam’s F#, multi-color, etc.), in order to solve several challenging problems such as “it behaves like one single beam or eight individual beams ?” or “it can collectively excite LPI that coupled to a common plasma or scattered wave ?”