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Low-mode drive asymmetries are known as significant performance degradation factors in indirect-drive inertial confinement fusion (ICF) implosions. We propose a two-dimensional (2D) dynamic model to explore the impact of time-dependent low-mode drive asymmetries on the shell asymmetries in acceleration phases of implosions. Since during acceleration, the shell areal density ( ρ R s ) asymmetries are relatively small, we can treat the shell as thin shell pieces with finite mass and infinitesimally small thicknesses, neglecting the angular flows between these pieces. The radial motion of each shell piece is dominated by Newton’s law. Through this model, the evolution of the shell radial velocity v s and the shell radius R s asymmetries of degree n can be characterized in terms of the drive temperature, time-dependent drive asymmetry of degree n and the average ρ R s , v s , R s obtained from one-dimensional (1D) simulations. The acceleration phases of typical gas-fill capsule and layered DT capsule implosions with P 2 or P 4 drive asymmetries are explored using this model and validated using both 2D radiation hydrodynamic simulations and available backlit shell distortion measurements. This model gives a useful tool for ICF design, with an advantage of simplicity and speed.

We present for the first time characterization of the time-dependent radiation drive on the capsule by measuring the localized re-emitted flux at Shenguang-III prototype laser facility. The drive flux was obtained with measured re-emitted flux from the capsule and radiation fluxes from the hohlraum wall, in combination with radiation hydrodynamic simulations. It revealed that the temporal behavior of the drive flux was quite distinguished from the radiation flux from the hohlraum wall, and the drive flux was approximately 6 eV (12 eV) lower than the measured flux at up 55° (up 30°). This technique presents a novel way for the assessment of the drive flux, both in cylindrical hohlraums and novel hohlraums with more than two laser entrance holes. Pre-processed radiation hydrodynamic simulations indicate that this technique can also be applied in integrated implosion experiments utilizing standard fusion capsule with carbon-hydrogen ablators.

A new method for measuring the time-dependent drive flux at the hohlraum center is proposed as a better alternative to conventional wall-based techniques. The drive flux here is obtained by simultaneous measurement of the reemitted flux and shock velocity from a three-layered "cakelike" sample. With these two independent observables, the influence induced by the uncertainty of the material parameters of the sample can be effectively decreased. The influence from the closure of the laser entrance hole, which was the main challenge in conventional wall-based techniques, was avoided through localized reemitted flux measurement, facilitating drive flux measurement throughout the entire time history. These studies pave a new way for probing the time-dependent drive flux, for both cylindrical hohlraums and novel hohlraums with six laser entrance holes.

The electron thermal conduction strongly affects the hot-spot formation and the hydrodynamic instability growth in inertial confinement fusion implosions. A harmonic-mean flux-limited conductivity model has been widely used in implosion simulations. In this paper, using the high foot implosion N140520 as an example, we have performed a series of one-dimensional (1D) no-alpha simulations to quantify the impact of different conductivity models including the Spitzer–Harm model, the Lee–More model, and the recently proposed coupled Gericke-Murillo-Schlanges model [Ma et al., Phys. Rev. Lett. 122, 015001 (2019)] with the flux limiter fe ranging from 0.03 to 0.15 on the performance of cryogenic implosions. It is shown that varying fe has a bigger impact on the performance than changing conductivity models. Therefore, we have only performed two-dimensional (2D) no-alpha simulations using the Lee–More model with different flux limiters [Formula: see text] to quantify the effect of the electron thermal conduction on the performance, with single-mode velocity perturbations with different mode numbers L seeded on the inner shell surface near the peak implosion velocity. We find that in both the 1D implosions and the 2D implosions with the same L, increasing fe leads to more hot-spot mass and lower hot-spot-averaged ion temperature, resulting in approximately constant hot-spot internal energy. In addition, the no-alpha yield [Formula: see text] is dominated by the neutron-averaged ion temperature Tn in these two cases. Increasing [Formula: see text] from 0.0368 to 0.184 reduces Tn by ∼15% in 1D and by ∼20% for the 2D implosions with the same L, both leading to a ∼20% reduction in [Formula: see text].

Understanding and controlling time-dependent implosion asymmetry are essential requirements to achieve ignition. In a recent symmetry tuning experiment at the 100 kJ laser facility, an effective time-dependent symmetry control was demonstrated by modifying the ratio of the inner beam power to the outer beam power. The hohlraum radiation and the P2 drive asymmetry of a shot used to measure backlit shell asymmetry have been analyzed, and the sensitivity of the P2 shell asymmetry to the drive asymmetry has been illustrated by using the two-dimensional code LARED. The variation in the shell P2 distortion, resulting from the variation in the P2 drive asymmetry due to the three-dimensional perturbing effects introduced to the hohlraum by the diagnostic windows (DWs) and the eight removed beams, has been assessed quantitatively using a three-dimensional postprocessor. It is found that the DWs and the four removed inner beams do not vary the P2 drive asymmetry, while the four removed outer beams cause a ∼−1% variation in the P2 drive asymmetry, resulting in a more prolate implosion.

To achieve ignition with high gain in inertial confinement fusion, precise symmetry control is one of the key issues to guarantee the PdV work converting into the inner energy efficiently and maximize the pressure of the hot spot. The shaped pulse is used to maintain a low adiabat of the shell. A longer pulse and more compressible shell require more rigorous symmetry control, especially the driven symmetry during the picket pulse and main pulse. A surrogate capsule with high Z materials is usually used for the early-time symmetry tuning. The passive diagnosis of the re-emission spheres gives the time-resolved measurement of the first 2 ns, and the precision is mainly affected by the weak signals due to the low radiation temperature of the hohlraum. To compare with the re-emission technique with high Z surrogate capsule, we demonstrated the early-time symmetry tuning for picket pulse by using thin-shell capsule radiography technique. Combined with 1D hydrodynamics simulation and backlit imaging simulation, the driven asymmetry was quantified. A view factor assessment was also carried out by IRAD3D and coincided with the experimental consequences.

Implosion asymmetry is a crucial problem quenching ignition in the field of inertial confinement fusion. A forward-calculation method based on 1D and 2D hydrodynamic simulations has been developed to generate and to study the x-ray images of hot-spot self-emission, indicating asymmetry integrated over the entire drive pulse. It is shown that the x-ray imaging photon energy should be higher to avoid the influence of remaining shell. The contour level (percentage of the maximum emission intensity) and spatial resolution should be as low as possible, optimally less than 20% and 3 microns, for characterization of higher-mode signatures such as P8 to P12 by x-ray self-emission images. On the contrary, signatures of lower-mode such as P2 remain clear at all contour levels and spatial resolutions. These key results can help determine the optimal diagnostics, laser and target parameters for implosion experiments. Recent typical hot-spot asymmetry measurements and applications on Shenguang 100kJ-class laser facility are also reported.

The first implosion tuning experiment with a shaped pulse driven was performed on the SGIII laser facility by using 2D X-ray radiography. Under the careful design, we obtained the driven symmetry both in the picket and peak. The experimental results show that the P2/P0 asymmetry can be tuned by varying the fraction energy in the inner cone both in the picket and peak. The radiation symmetry at the peak is consistent with our simulation. However, the radiation symmetry in first 0.5 ns (picket) had an unexpected negative P2/P0, which is different from the simulation; it may be caused by inner cone absorption in the tent which supported the capsule.

The first 0.1 MJ scale shaped pulse implosion experiment was performed at the Shenguang-III laser facility in 2016. The hohlraum radiation of three representative shots with troughs of 1.0 ns, 1.5 ns, and 2.5 ns is analysed using the two-dimensional code LARED with the multi-group radiation transfer model. It is found that the simulated multi-angle radiation temperatures are generally in good agreement with the measurements within ∼3%. However, our simulations underestimate the peak radiation temperature at 64° by ∼6% for the shot with the 2.5 ns trough, due to the much smaller laser entrance hole in our calculations. In addition, we simulate the time-integrated M-band (2–4 keV) x-ray image at the view angle of 20° for the shot with the 1.0 ns trough. The simulated laser spot positions are consistent with the measurement. But the relative brightness between the inner beams and the outer beams is larger than the experimental result, which may be caused by the overestimation of the plasma density at the edge of the bubbles in our simulation. With the bubble contribution approximately removed, the simulated relative brightness between the inner beams and the outer beams approaches the experimental result.

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.

Achieving ignition via inertial confinement approach is of strong application value and important science significance. It is also a project of large scale that depends on the national strength. Involving theory, target fabrication, diagnostics, and laser facilities, integrated implosion experiment plays an important role in the research of ICF. Since the first successful neutron production with directly driven implosion in the 80’s, the quasi one-dimensional implosion performance dominated by shock compression was demonstrated in the period of 1990–2010, and the quasi one-dimensional implosion performance dominated by inertial compression was achieved in recent years. All of these facts definitely show the progress on improving the performance of integrated implosion. With the completion of SG-III laser facility, and in the situation of facing frustration in the US ignition program, there is grand opportunity and challenge when we are exploring toward the ignition parameter space with higher convergence ratio and lower adiabat.

The cylindrical vacuum hohlraum energy at the SGIII laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007) and W. Zheng et al., High Power Laser Sci. Eng. 4, e21 (2016)] is investigated for the first time. The hohlraum size and the laser energy are intermediate between the Nova and NIF typical hohlraum experiments. It is found that the SGIII hohlraum exhibits an x-ray conversion efficiency of about 85%, which is more close to that of the NIF hohlraum. The LARED simulations of the SGIII hohlraum underestimate about 15% of the radiation flux measured from the laser entrance hole, while the capsule radiation drive inferred from the x-ray bangtime is roughly consistent with the experiments. The underestimation of the SGIII hohlraum radiation flux is mainly caused by the more enclosed laser entrance hole in the LARED simulation. The comparison between the SGIII and NIF hohlraum simulations by LARED indicates that the LARED generally underestimates the measured radiation flux by 15% for the hi...