56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session PI1: Indirect Drive
2:00 PM–5:00 PM,
Wednesday, October 29, 2014
Room: Acadia
Chair: David Montgomery, Los Alamos National Laboratory
Abstract ID: BAPS.2014.DPP.PI1.6
Abstract: PI1.00006 : Studying shock dynamics and in-flight $\rho $R asymmetries in NIF implosions using proton spectroscopy*
4:30 PM–5:00 PM
Preview Abstract
Abstract
Author:
Alex Zylstra
(MIT)
Ignition-scale, indirect-drive implosions of CH capsules filled with
D$^{3}$He gas have been studied with proton spectroscopy at the NIF.
Spectral measurements of D$^{3}$He protons produced at the shock-bang time
provide information about the shock dynamics and in-flight characteristics
of these implosions. The observed energy downshift of the D$^{3}$He-proton
spectra are interpreted with a self-consistent 1-D model to infer $\rho $R,
shell R$_{cm}$, and yield at this time. The observed $\rho $R at shock-bang
time is substantially higher for implosions where the laser drive is on
until near the compression-bang time (``short-coast'') while longer-coasting
implosions generate lower $\rho $R at shock-bang time. This is most likely
due to a larger temporal difference between the shock- and compression-bang
time in the long-coast implosions ($\sim$800ps) than in
the short-coast implosions ($\sim$400ps). These
differences are determined from the D$^{3}$He proton spectra and in-flight
x-ray radiography data, and it is found to contradict radiation-hydrodynamic
simulations, which predict a 700 -- 800ps temporal difference independent of
coasting time. A large variation in the shock proton yield is also observed
in the dataset, which is interpreted with a Guderley shock model and found
to correspond to $\sim 2 \times$ variation in incipient hot-spot
adiabat caused by shock heating. This variation may affect the
compressibility of NIF implosions. Finally, data from multiple proton
spectrometers placed at the pole and equator reveal large $\rho $R
asymmetries, which are interpreted as mode-2 polar or azimuthal asymmetries.
At the shock-bang time (CR $\sim 3-5$), asymmetry amplitudes
$\ge $10{\%} are routinely observed. Compared to compression-bang time x-ray
self-emission symmetry, no apparent asymmetry-amplitude growth is observed,
which is in contradiction to several growth models. This is attributed to a
lack of correspondence between shell and hot-spot symmetry at peak
compression, as discussed in recent computational studies [R.H.H. Scott et
al., Phys. Rev. Lett. 110, 075001 (2013)].
*This work was performed in collaboration with the NIF team and was supported in part by the U.S. DOE, LLNL and LLE.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.PI1.6