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 JT3: Tutorial: The Physics of Ignition Scale Hohlraums and ICF Implosions: When does size matter?
2:00 PM–3:00 PM,
Tuesday, November 15, 2011
Room: Ballroom AC
Chair: Robert Kirkwood, Lawrence Livermore National Laboratory
Abstract ID: BAPS.2011.DPP.JT3.1
Abstract: JT3.00001 : The Physics of Ignition Scale Hohlraums and ICF Implosions: When does size matter?*
2:00 PM–3:00 PM
Preview Abstract
Author:
Mordecai Rosen
(Lawrence Livermore National Laboratory)
Ignition scale, high drive, hohlraums with ICF ignition capsules
are four times larger than any laser-illuminated targets
attempted previously. In addition, the precision in symmetry and
pulse-shape / shock timing required for achieving ignition is
quite stringent. This tutorial deals with the challenges
presented by these issues. They are now subject to experimental
study, facilitated by the capability of the National Ignition
Facility (NIF) to deliver, with great precision, the very large
laser energy and power needed for ignition. Given this large
excursion in scale size, we disentangle here the following: What
elements of our previous understanding, based on smaller scale
laser experiments, might carry over smoothly to this regime,
because they are scale independent? On the other hand, which
might need to be refined, because small-scale experimental
results were not sufficiently sensitive to issues that may become
more important at NIF scale? For example, we explain how hohlraum
x-ray drive has an additional component due to the large scale
size, allowing Au coronal emission to play
a role. Yet at the same time, we explain, on firm theoretical
grounds, why certain changes/improvements in hohlraum design,
based on previous results on smaller scale lasers, can be made
with confidence: Size doesn't always matter. Similarly, we show
how large scale-lengths may bring laser-plasma-instabilities
(LPI) into more prominence. Equally important, however, is our
understanding of how LPI is affected by the basic plasma
conditions (T$_{e}$, n$_{e})$. A valuable knowledge base of these
basics was obtained via experiments on smaller facilities. A
third such example of the interplay between scale dependent and
independent phenomena involves the soft-x-ray transport in the CH
capsule ablator, in the presence of the higher Z dopants. These
dopants are, by design, placed in the ablator in order to control
higher frequency x-ray preheat. We present a computational model,
(the ``High Flux Model'') which uses our most modern tools, that
has helped explore some of these issues, and describe how it
continues to be refined. We also explain why, due to the
stringent precision required for ignition, we depend on our
models as general guideposts to the path to
ignition, and not as infallible oracles. We demonstrate how an
experimental campaign, guided by those models, can, in principle,
achieve the precision in implosion velocity, symmetry, shock
timing and hydrodynamic instability needed for ignition.
*Work performed for the U.S. DoE by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-490359.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.JT3.1