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Amplitude reduction of nonuniformities induced by magnetic Rayleigh–Taylor instabilities in Z-pinch dynamic hohlraums
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Schematic of the ZPDH as implemented in capsule implosion experiments. The diameter radiation exit hole (REH) in the top electrode provides diagnostic access. The capsule (central filled in circle) is included for illustration purposes. It is omitted in this work, but the ZPDH is identical. The implosion is depicted at a time when the wire arrays have merged to form a single liner, and collided with the convertor. (b) Plots of the measured drive current vs time, with the end-on (axial) and side-on (radial) radiation power superimposed. Measurements are shifted in time so that peak side-on power occurs at . Peak end-on and side-on powers are 7.3 and 101.5 TW, respectively.

Image of FIG. 2.
FIG. 2.

(Color). Time resolved x-ray images recorded in experiment Z672. The time of each image relative to the peak side on x-ray power is given in nanoseconds. The brightness of each image has been adjusted to optimize the image clarity. The green circle is the approximate location of the diameter diagnostic aperture.

Image of FIG. 3.
FIG. 3.

(Color). (a) Measured end-on, x-ray intensity image. The green lines represent the locations of the ten lineouts taken for each image. (b) A representative lineout across the image in (a). The shock features are defined as the emission above the thermal radiation level ahead of the shock. A shock trajectory is obtained by tracking the location of the peak intensity in time.

Image of FIG. 4.
FIG. 4.

(Color). Shock characteristics measured in experiment Z672.

Image of FIG. 5.
FIG. 5.

(Color). Shock trajectory measured in three similar Z experiments (distinguished by shot number in the legend). The radius corresponds to one half the diameter obtained by averaging the ten lineouts at each time, with an uncertainty determined by the standard deviation. The timing uncertainty of between experiments is not shown.

Image of FIG. 6.
FIG. 6.

DH configuration used in simulations. The geometry is rotated 90° clockwise relative to Fig. 1(a). In experiments the interior walls of the hohlraum are coated with Au. The Au electrodes are delineated by thick solid lines. Current density is represented by .

Image of FIG. 7.
FIG. 7.

Snapshots of filled in density contours corresponding to the W plasma from simulations with random density perturbations of (a) 0%, (b) 0.25%, and (c) 0.5%. The plots are for the same time, , and illustrate the wide range of density modulation produced by the stated perturbations. The left- and right-hand sides of the Z-pinch acquire a concave up shape through an interaction with ablating Au, which produces an effective drag on the edges. The shape of the W plasma at the REH has significant influence on external observations of the ZPDH.

Image of FIG. 8.
FIG. 8.

(Color). (a) Color plot of filled in density contours at , with the surface of peak x-ray intensity superimposed (solid white line). The latter approximately marks the location of the shock front. The entire implosion is inside of the REH, and can be observed by a virtual, end-on diagnostic. The corresponding synthetic x-ray image is shown in (b), which is similar to the measured image at in Fig. 2. The white circle with delineates the location of the REH. (a) and (b) represent internal and external views of the ZPDH.

Image of FIG. 9.
FIG. 9.

Radial profile of the synthetic intensity image in Fig. 8(b) (solid line). Superimposed on the plot is the intensity profile that results when Au electrodes are not included in the simulation (dashed line). Comparison with Fig. 3(b) shows that the intensity profile with Au electrodes included agrees best with the measurement.

Image of FIG. 10.
FIG. 10.

(Color). (a) Comparison of intensity profiles corresponding to measured and synthetic x-ray images at times and before peak side-on power. (b) Comparison of simulated and measured shock trajectories (solid black and dashed red lines, respectively) for the case with 0.25% random density perturbation. The peak of the measured, normalized side-on power (solid green curve) marks the zero of time. Aligning the simulated and measured shock trajectories provides a time shift that is used to map simulation results to the time frame of the experiment.

Image of FIG. 11.
FIG. 11.

Comparison of shock trajectories (a) and intensity profiles (b) from simulations with random density perturbations of 0%, 0.25%, and 1.0%. Evidently, neither are affected significantly by the amplitude of MRT modulations in the imploding W plasma.

Image of FIG. 12.
FIG. 12.

(Color). Plots of filled in density contours at (a) and (b) prior to peak side-on power from the simulation with 0.5% random density perturbation. Superimposed on each plot are (1) the interface (solid white line), (2) the surface of maximum current density (solid magenta line), and (3) the surface of peak emission intensity (solid blue line).

Image of FIG. 13.
FIG. 13.

(Color). Plots of the interface (black line), the surface of maximum current density (magenta line), and the surface of peak emission intensity (blue line), which represents the shock front, for perturbation levels of 0.25% (a, b), 0.5% (c, d), and 0.7% (e, f) at times (a, c, and e) and (b, d, and f) prior to peak side-on power.

Image of FIG. 14.
FIG. 14.

Plots of density and integrated intensity vs at for times corresponding to the density snapshots in Fig. 12, (a) and (b) . The interface is labeled, and an arrow points to its location. In both plots, the region of increasing intensity approximately marks the location of the shock front. The local density maximum at in (a) is the result of an ablatively driven shock in the foam, which does not cause sufficient emission to show up in synthetic x-ray images. In (a) the region of maximum intensity occurs in foam accreted at the inner surface of the tungsten liner, and the peak intensity coincides with the interface.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Amplitude reduction of nonuniformities induced by magnetic Rayleigh–Taylor instabilities in Z-pinch dynamic hohlraums