294 / 2023-04-25 21:58:38

Improving symmetry tuning with I-raum in indirect-drive implosions

indirect-drive,implosion,symmetry tuning,I-raum

惯性约束聚变物理学 > 内爆和不稳定性-海报

Indirect-drive inertial confinement fusion implosions were performed at the 100kJ laser facility. In the original design with 2-step shaped laser pulses, 24 laser beams at each end, which were divided into inner and outer cones, respectively, entered into a gas-filled cylindrical hohlraum. The intense laser energy was converted into thermal x-ray radiation with gold wall, which ablated a capsule filled with deuterium fuel and drove a spherical implosion. When a new design with 3-step shaped laser pulses was employed, late-time propagation of the inner laser beams was impeded by the expansion of gold plasma "bubbles", which were initiated from the outer laser spots. As a result, the lack of x-ray drive at the equator of the capsule generated an unacceptable oblate implosion. In an I-raum modified from the cylindrical hohlraum, the outer laser spots were displaced radially outward and axially inward to the equator, with a small recessed cylindrical pocket at each half cylinder, which made compensation and mitigation for the weaker drive at the equator. Contrast experiments with two kinds of hohlraums were performed with different shaped laser pulses, respectively. X-ray emission from hohlraum and hotspot were observed for investigation of bubble expansion, x-ray radiation and implosion asymmetry, respectively. In addition, numerical simulation with post-shot laser parameters provided reference for evaluation of the experimental variations. Results from both simulations and experiments show that, the I-raum can be used to significantly reduce the impact of expanding gold bubbles, which helps to tune the drive symmetry, and to improve overall implosion performance.