Hydrodynamic instability growth of three-dimensional modulations in radiation-driven implosions with “low-foot” and “high-foot” drives at the National Ignition Facility
Hydrodynamic instability growth has been studied using three-dimensional (3-D) broadband modulations by comparing “high-foot” and “low-foot” spherical plastic (CH) capsule implosions at the National Ignition Facility (NIF) [E. M. Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. The initial perturbat...
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Veröffentlicht in: | Physics of plasmas 2017-04, Vol.24 (4) |
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Zusammenfassung: | Hydrodynamic
instability growth
has been studied using three-dimensional (3-D) broadband modulations by comparing “high-foot” and
“low-foot” spherical plastic (CH) capsule implosions at the National Ignition Facility
(NIF) [E. M. Campbell et al., AIP Conf. Proc. 429, 3
(1998)]. The initial perturbations included capsule outer-surface roughness and
capsule-mounting membranes (“tents”) that were similar to those used in a majority of
implosions on NIF. The tents with thicknesses of 31-nm, 46-nm, and 109-nm were used in the
experiments. The outer-surface roughness in the “low-foot” experiment was similar to the
standard specification, while it was increased by ∼4 times in the “high-foot” experiment
to compensate for the reduced growth. The ablation-front instability growth was
measured using a
Hydrodynamic
Growth Radiography
platform at a convergence ratio of ∼3. The dominant capsule perturbations, generated by
the tent mountings, had measured perturbation amplitudes comparable to the capsule thickness
with the “low-foot” drive. These tent perturbations were reduced by ∼3 to 10 times in
implosions with the “high-foot” drive. Unexpectedly, the measured perturbations with
initially thinner tents were either larger or similar to the measured perturbations with
thicker tents for both “high-foot” and “low-foot” drives. While the measured
instability growth
of 3-D broadband
perturbations was also significantly reduced by ∼5 to 10 times with the “high-foot” drive,
compared to the “low-foot” drive, the growth mitigation was stronger than expected based
on previous “growth-factor” results measured with two-dimensional modulations [D. T. Casey
et al., Phys. Rev. E 90, 011102 (2014)]. One of the
hypotheses to explain the results is based on the 3-D modulations of the oxygen
content in the bulk of the capsule having a stronger effect on the overall growth of
capsule perturbations than the outer-surface capsule roughness. |
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ISSN: | 1070-664X 1089-7674 |
DOI: | 10.1063/1.4980002 |