51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009;
Atlanta, Georgia
Session NI2: ICF Capsules and Rayleigh-Taylor Instability
9:30 AM–12:30 PM,
Wednesday, November 4, 2009
Room: Centennial I
Chair: David Meyerhofer, University of Rochester
Abstract ID: BAPS.2009.DPP.NI2.6
Abstract: NI2.00006 : Investigations into the Seeding of Instabilities due to X-ray Preheat in Beryllium-Based Inertial Confinement Fusion Targets
12:00 PM–12:30 PM
Preview Abstract
Abstract
Author:
Eric Loomis
(Los Alamos National Laboratory)
The geometry of inertial confinement fusion (ICF) capsules makes
them susceptible to various types of hydrodynamic instabilities
at different stages during an ICF implosion. From the beginnings
of ICF research, it has been known that grain-level anisotropy
and defects could be a primary source of instability seeding in
solid capsules. This has steered ICF designs to include amorphous
materials such as plastic; however, the benefits of low-Z
metallic materials, i.e. beryllium, has kept these materials the
focus of much research. Recently, experiments were conducted at
the Trident laser facility to measure dynamic surface roughening
from hard x-ray preheat. M-band emission from laser produced gold
plasma was used to heat beryllium targets with different amounts
of copper doping to temperatures comparable to National Ignition
Facility (NIF) preheat levels. Temporal and spectral x-ray
diagnostics were used to estimate the target heating, which was
also predicted by multi-dimensional radiation hydrodynamics
calculations. Wave profiles of varying complexity due to
differences in copper doping were
observed with free surface line imaging velocity interferometry.
Dynamic roughening measurements were made on the surface away
from the plasma at discrete times up to 8 ns after the beginning
of the drive pulse using a surface displacement interferometer
with nanometer scale sensitivity. Undoped, large-grained targets
were measured to roughen between 15 and 50 nm rms depending on
variations in x-ray absorption through the target thickness.
Fine-grained, copper-doped targets were observed to roughen near
the sensitivity limit of the interferometer and approached the
Rev2 NIC design point of 0.9 nm. The results of this combined
experimental and modeling effort have shed light on the effects
of high-Z doping and microstructural refinement on the dynamics
of differential thermal expansion and have shown that current NIF
capsule designs using beryllium are very effective in reducing
preheat related roughening ahead of the first shock.
These experiments have raised additional questions, however, such
as the possibility of spallation from intense thermal expansion,
which will also be discussed.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DPP.NI2.6