Nuclear
Science using
High Energy Density Plasmas - A new field of research
Johan
Frenje
Plasma Science and
Fusion Center, Massachusetts Institute
of Technology, USA
Thermonuclear
reaction
rates and nuclear processes have been explored traditionally by
means
of conventional accelerator experiments, which are difficult,
and at times even
impossible, to execute at energies and conditions relevant to
stellar
nucleosynthesis. Thus,
nuclear reactions
at stellar energies are often studied through extrapolations
from higher energy
data, or in low-background experiments such as those at the LUNA
underground
laboratory. Even
when measurements are
possible using accelerators, thermonuclear reaction rates in
burning plasmas of
stars are inherently different from those in accelerator
experiments. The
fusing nuclei are surrounded by bound
electrons in accelerator experiments, whereas electrons occupy
mainly continuum
states in a stellar environment. In
accelerator
experiments, extrapolations from higher energies and
electron-screening corrections are also based on theoretical
models that have
not been checked experimentally. Nuclear
physics
research will therefore benefit from an enlarged toolkit for
studies of
various fundamental nuclear reactions. In this presentation, we
report on the first
use of laser-driven Inertial Confinement Fusion (ICF)
experiments for studies
of basic nuclear physics. These
experiments
were carried out at the OMEGA laser facility and the National
Ignition Facility (NIF), in which spherical capsules were
spherically
irradiated with powerful lasers to compress and heat the fuel to
high enough
temperatures and densities for significant nuclear reactions to
occur. Three
experiments using ICF plasmas will be
highlighted in this presentation. In the first experiment, the
differential
cross sections for the elastic neutron-triton (n-3H)
and
neutron-deuteron (n-2H) scattering at 14.1 MeV were
measured with
significantly higher accuracy than achieved in previous
accelerator
experiments. In the
second experiment,
the 3H(3H,2n)4He reaction,
which is an
important mirror reaction to the 3He(3He,2p)4He
reaction
that plays an important role in the proton-proton chain that
transforms hydrogen into ordinary 4He in stars like
our Sun, was
studied at center-mass energies in the range 15-40 keV, and in
the third
experiment, ICF plasmas were uniquely used to directly study the
3He+3He
solar fusion reaction. As
the conditions
in these ICF implosions better mimic the burning core in stars
than the
conditions in accelerator experiments, these types of studies
open up new areas
of research fundamental to both stellar nucleosynthesis and
basic nuclear
physics. We call
this field of research
plasma nuclear science. The work described here was supported in
part by NLUF
(DOE award No. DE-NA0000877), FSC (Rochester Sub award PO No.
415023-G, UR
Acct. No. 5-24431), US
DOE (Grant No. DE
FG03-03SF22691), LLE (No. 412160-001G), and LLNL (No. B504974),
and GA under
DOE (DE-AC52-06NA27279).