First integrated implosion experiments on the SG-III laser facility

Abstract

We present the first integrated implosion experiments which were carried out on the SG-III Laser facility in 2015. Vacuum hohlraums and squared laser pulses were used in the experiments. The purpose of the experiments was to demonstrate the one-dimensional implosion performance at low-convergence ratios. To characterize the implosion performance, the hohlraum energetics, the implosion dynamics and the nuclear products were measured. In particular, the radiation flux was diagnosed through laser entrance hole at different angles by an array of flat response detectors, and the energy and the spectrum of the back-scattered lasers were monitored for 8 laser beams which correspond to 2 beams in each cone at the lower hemisphere. Moreover, the hotspot shape was imaged using KB microscopes of high spatial resolution simultaneously from the equator and polar views. Taking advantage of the high resolution, some detailed structures in the hotspots were noticed. For the best implosion performances, the neutron yields over 1D calculation reached 50% at the convergence-ratios of 15.

Three-dimensional reconstruction of integrated implosion targets from simulated small-angle pinhole images

“…Based on the experimental results in Ref. [11], two cases were considered: one is that only four pinhole images of a single LEH were used; the other is that four pinhole images of a single LEH and four pinhole images of the diagnostic hole were used in calculation. The maximum projection angle of these pinhole images was 10° to the central axis of the hole.…”

“…The model parameter setting is based on the physical parameter of the experimental device of 100-kJ-level laser facility in China [11], and vacuum hohlraums were used in the experiments. A total of 48 lasers were simultaneously injected into vacuum hohlraums of 4400 μm in length and 2200 μm in diameter from two LEHs.…”

“…According to the time-integral imaging of the central plasma core from the polar and equatorial directions of the experiments in Ref. [11], we assumed that the radiation distribution of the core is a sphere that is symmetrical in the X and Y directions, but asymmetrical in the Z direction. As there was a certain radiation distribution on the vacuum hohlraum wall due to re-emission, we set it to a fixed value for simplicity.…”

“…From the experimental results in Ref. [11], the central self-radiation area of the hohlraum was essentially a flat ellipsoid, and its diameter at the axial direction was smaller than that at the horizontal direction, which ensured that the estimated central self-radiation area contained the original central self-radiation area of the hohlraum. The space-constrained area was finally selected as the portion from the inside of the hohlraum wall to the outside of the central self-radiation area.…”

“…However, the direct 3D measurement of implosion targets is still difficult to achieve in limited conditions. In 2015, the first integrated implosion experiments in vacuum hohlraums were conducted at the 100-kJ-level laser facility in China [11]. To evaluate the asymmetry of radiation driving, pinhole cameras and a multichannel KB microscope were used to obtain the high spatial resolution shape information of the hotspots from the polar and equatorial directions.…”