First polar direct-drive exploding-pusher target experiments on the ShenGuang laser facility*

Abstract

Low density and low convergence implosion occurs in the exploding-pusher target experiment, and generates neutrons isotropically to develop a high yield platform. In order to validate the performance of ShenGuang (SG) laser facility and test nuclear diagnostics, all 48-beam lasers with an on-target energy of 48 kJ were firstly used to drive room-temperature, DT gas-filled glass targets. The optimization has been carried out and optimal drive uniformity was obtained by the combination of beam repointing and target. The final irradiation uniformity of less than 5% on polar direct-drive capsules of 540 μ m in diameter was achieved, and the highest thermonuclear yield of the polar direct-drive DT fuel implosion at the SG was 1.04×1013. The experiment results show neutron yields severely depend on the irradiation uniformity and laser timing, and decrease with the increase of the diameter and fuel pressure of the target. The thin CH ablator does not impact the implosion performance, but the laser drive uniformity is important. The simulated results validate that the cos γ distribution laser design is reasonable and can achieve a symmetric pressure distribution. Further optimization will focus on measuring the symmetry of the hot spot by self-emission imaging, increasing the diameter, and decreasing the fuel pressure.

A simple analytical model of laser direct-drive thin shell target implosion

“…The implosion bang time was measured by the neutron fusion reaction rate diagnostic system [27] on the 100 kJ laser facility, and less than 700 ps. [22] The measurement error was more than 200 ps in 2015 and decreases to 50 ps after 2018. The Omega bang time was diagnosed by neutrons and gammas, and more than 1.4 ns.…”

“…In order to validate the analytical model of thin shell target implosion, the DD and DT experimental data at Shenguang-III prototype laser facility, 100 kJ laser facility, Omega and NIF are compared with the analytical model. The target diameters on the Shenguang-III prototype laser facility and 100 kJ laser facility [22] were ∼ 540 µm and ∼ 720 µm, the glass wall thickness were ∼ 2.6 µm and ∼ 2 µm, the plastic wall thickness were ∼ 1 µm, and the DT or DD gas was 10-45 atm. The capsule diameters were ∼ 1100 µm used on the Omega [23] and ∼ 1500 µm used on the NIF, [24][25][26] the glass wall was more thicker and the same with ∼ 4.5 µm, and the DT or DD gas was 5-10 atm.…”

“…For the Φ540 µm target on the 100 kJ laser facility, the final irradiation uniformity is less than 4%. [22] The irradiation uniformity on the Omega is better than 1% [28] because of the laser arrange of the direct drive. The experimental results in Figs.…”