Direct Laser-Driven Quasi-Isentropic Compression on HEAVEN-I Laser

Ultraviolet ultra-short pulse laser has incomparable advantages in strong field physics and fast ignition of inertial confinement nuclear fusion. In addition to the short wavelength and strong focusing ability, UV laser has a larger critical density and is closer to the over-dense fuel target region, thus simplifies all the process relates to the energy transport. Based on the I-λ 2 scaling law, ultraviolet laser is enough to produce hot electrons with the temperature required for fast ignition. Meanwhile, excimer laser has unique advantages in amplifying ultra-short pulses. In order to increase the laser energy irradiating on the target, the amplifier with larger energy cross section and higher energy extraction capacity are required. In this paper, a method of beam combination amplification of ultraviolet ultrashort pulse laser in a discharge-pumped excimer laser amplifier has been explored by conjugated polarization, and the feasibility of applying this technique to excimer laser is verified.

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Equation-of-state measurements for polystyrene under high presure driven by HEAVEN-I laser facility

Bao-Xian¹,

Wang²,

Feng-Ming³

et al. 2021

Acta Phys. Sin.

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The equation of state (EOS) for CH material used as an ablator layer at high pressure is important in the study of implosion dynamics and target design for inertial confinement fusion (ICF). At present, most of EOS data are on the Hugoniot line under shock compression. The EOS data below Hugoniot line need further studying for low-entropy pre- compression. In the present article, the EOS of polystyrene is established under quasi-isentropic compression driven by HEAVEN-I KrF laser facility with a long rising edge (~20 ns). The shock dynamic behaviors of three kinds of CH targets are simulated, which are 100 μm CH planar target, Al-coated CH planar target (10 μm Al, 50 or 150 μm CH), and flyer-impact target composed of flyer (Al-coated CH), 100 μm vacuum layer, and 100 μm CH layer. The planar targets and flyer-impact targets with different thickness are irradiated by six-focused laser beams with total energy of 50–100J, and the free surface velocity and wave average transit velocity are measured by side-on shadowgraph technique. The simulation results indicate that the initial loading process is quasi-isentropic compression process, and then evolves into a weak shock compression process for the CH planar target in the rising edge stage. Comparing with the CH planar target, the reflected rarefaction waves from the Al-CH interface of Al-coated CH target can suppress the enhancement of compression wave, and delay the formation of shock wave when laser directly irradiates the Al layer. The shock pressure of the CH target layer (the third layer) is significantly higher than those of the former two targets in the flyer-impact target. However, the chasing rarefaction wave can unload the compression state incompletely and reduce the pressure when the CH target layer is much thicker than Al layer. The final pressure is about 15 GPa in the CH planar target, while the final pressure is about 30 GPa in flyer-impact target: both of them are less than the pressure threshold of opacity change for the transparent polystyrene. The quasi-isentropic dynamical process is difficult to measure by the velocity interferometer system for any reflector technique. The experimental results show that the average wave transit velocity is significantly less than the final shock velocity derived from the free surface velocities in the CH and Al-coated CH planar target side-on shadow experiments. They indicate that the compression wave enhancement and quasi-isentropic compression process occur in the propagation of wave front. The shock pressure is about 12 GPa in the CH planar target, and about 34 GPa under shock load in the flyer-impact target. The experimental data and shock dynamic processes are basically consistent with the simulation results.

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Direct Laser-Driven Quasi-Isentropic Compression on HEAVEN-I Laser

Cited by 3 publications

References 14 publications

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Equation-of-state measurements for polystyrene under high presure driven by HEAVEN-I laser facility

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