53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011;
Salt Lake City, Utah
Session YI3: ICF Physics; Postdeadline Invited
9:30 AM–12:30 PM,
Friday, November 18, 2011
Room: Ballroom AC
Chair: Craig Sangster, University of Rochester
Abstract ID: BAPS.2011.DPP.YI3.1
Abstract: YI3.00001 : Crossed-Beam Energy Transfer in Direct-Drive Implosions
9:30 AM–10:00 AM
Preview Abstract
Abstract
Author:
I.V. Igumenshchev
(Laboratory for Laser Energetics, U. of Rochester)
Direct-drive-implosion experiments on OMEGA have revealed the
importance of
crossed-beam energy transfer\footnote{I. V. Igumenshchev\textit{
et al.}, Phys. Plasmas
\textbf{17}, 122708 (2010).} (CBET), which is caused by
stimulated Brillouin
scattering. The CBET reduces the laser absorption in a target
corona by
$\sim $10{\%} to 20{\%} and, therefore, decreases the implosion
performance.
The signature of CBET is observed in time-resolved,
reflected-light spectra
as a suppression of red-shifted light during the main laser pulse.
Simulations without CBET typically predict an earlier bang time and
overestimate the laser absorption in high-compression, low-adiabat
implosions. Simulations using a CBET model and a nonlocal
heat-transport
model\footnote{V. N. Goncharov\textit{ et al.}, Phys. Plasmas
\textbf{15}, 056310 (2008).}
explain well the scattered-light and bang-timing measurements.
This talk
will summarize the possible mitigation strategies for CBET
required for
robust ignition designs. CBET most effectively scatters incoming
light that
interacts with outgoing light originated from laser beam edges.
This makes
it possible to mitigate CBET by reducing the beam diameter with
respect to
the target diameter. Implosion experiments using large
1400-\textit{$\mu $}m-diam plastic
shells and in-focus and defocus laser beams have demonstrated the
reduction
of CBET in implosions with a smaller ratio of the beam-to-target
diameters.
Simulations predict the optimum range of this ratio to be 0.7 to
0.8.
Another mitigation strategy involves splitting the incident light
into two
or more colors. This reduces CBET by shifting and suppressing the
coupling
resonances. The reduction in scattered light caused by CBET is
predicted to
be up to a factor of 2 when incident light colors are separated
by \textit{$\delta \lambda $} $>$ 6
{\AA}. This work was supported by the U.S. Department of Energy
Office of
Inertial Confinement Fusion under Cooperative Agreement No.
DE-FC52-08NA28302.
\\[4pt]
In collaboration with W. Seka, D. H. Edgell, D. H. Froula, V. N.
Goncharov, R. S. Craxton, R. L. McCrory, A. V. Maximov, D. D.
Meyerhofer, J. F. Myatt, T. C. Sangster, A. Shvydky, S. Skupsky,
and C. Stoeckl.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.YI3.1