Observations of anomalous x-ray emission at early stages of hot-spot formation in deuterium-tritium cryogenic implosions

In deuterium-tritium cryogenic implosions, hot-spot x-ray self-emission is observed to begin at a larger shell radius than is predicted by a one-dimensional radiation-hydrodynamic implosion model. Laser-imprint is shown to explain the observation for a low-adiabat implosion. For more-stable implosions the data are not described by the imprint model and suggest there are additional sources of decompression of the dense fuel.

Figure 1

(a) Observed soft x-ray self-emission at the onset of hot-spot core emission a cryogenic implosions experiment. The lower sector indicated by dotted white lines can include emission related to stalk mounting and is excluded from analysis. (b) Angle-averaged radial profile from the experimental image is shown by the solid black curve. The result from 1D modeling at matched position of the ablation front is shown with the dotted black curve. The dashed cyan curve shows the 1D result obtained $\sim 70$ ps later at which time the center emission reaches the prominence observed in the data.

Figure 2

3D aster results. (a) Density for uniform (left) and imprint simulations (right). (b) Angle average of mass density (uniform, solid black curve; imprint, red dashed curve). (c) Self-emission images and (d) angle-averaged emission profiles [same formatting as in (c)]. The dotted blue curve excludes carbon emission interior to radial values less than 200 $\mu \mathrm{m}$.

Figure 3

Central emission versus inferred ablation front radius for (a) $S$ = 21.8, $\alpha$ = 1.7, and (b) $S=7.9, \alpha =2.8$ implosions. Data are indicated by solid circles with cyan line showing fit. Results from uniform aster are indicated by dotted black line for all three cases. High-resolution aster with laser imprinting is shown by dashed red line.

Figure 4

Survey of six implosions of Table 1 showing difference in measured onset of hot-spot emission as compared to models ($\mathrm{\Delta }{R}_{\mathrm{emis}}$) versus instability parameter ($S$). The comparison relative to 1D lilac is indicated by black circles and relative to 3D aster with imprint by the red squares (two available cases only).