Early-time symmetry quantifying with thin-shell capsule radiography for pulse shaped implosion

Abstract

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.

A 2D dynamic model for the impact of time-dependent low-mode drive asymmetries on the shell asymmetries during acceleration phases of ICF implosions

“…2 /P 0 drive asymmetry in the 2D capsule-only simulation and the model, we compare the percent R s P 2 /P 0 asymmetries vs the average R s extracted from the measured backlit images (Exp) in our previous backlit shell distortion experiment [18], the 2D simulated result (Simu_2D), and the model, as shown in figure 7. The estimated error of the experimental data includes both the accuracy of the measurement and the statistical uncertainty in the fitting process of the shell distortion [19]. It is found that the model result is in good agreement with both the experimental and the 2D simulated results.…”

“…In this section, we apply the dynamic model to the acceleration phases of typical gas-fill capsule and layered DT capsule implosions with P 2 or P 4 drive asymmetries, and compare the P n mode amplitudes of v s and R s derived from the model, the 2D capsule-only radiation hydrodynamic simulations and available backlit shell distortion measurements. The angleaveraged ρR s (t), v s (t), and R s (t) in equations ( 13), ( 14), (18), and (19) were obtained from 1D multi-group radiation transfer (MGRT) code RDMG [31]. The 2D capsule-only simulations were performed using the 2D MGRT code LARED [32][33][34].…”

“…is the P n mode amplitude of R s in our model. The term t − t 2 in equation (19) indicates that the R s asymmetry gradually accumulates with time. Meanwhile, the Green's function W R (t, t 2 ) for the R s asymmetry of degree n is given through equation (18) as…”

“…Finally, the P n mode amplitudes of v s and R s during acceleration can be extracted from equations ( 13), ( 14), (18), and (19), in which v s , R s , and ρR s are obtained from 1D implosion simulations and defined as…”

“…Over the past few decades, the ICF community has performed a lot of experiments to measure implosion asymmetries and explore the impact of low-mode drive asymmetries on the implosion performances [11][12][13][14][15][16][17][18][19]. Meanwhile, significant efforts have been dedicated to theoretical investigations on the sensitivity of the implosion performances to low-mode drive asymmetries.…”