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Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains. To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional (1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However, double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.
Experimental investigations of heavy-ion-generated shock waves in
solid, multilayered targets were performed by applying a Schlieren and
a laser-deflection technique. Shock velocity and the corresponding
pressures, temporal and spatial density profiles inside the material
compressed by multiple shock waves, and details of the shock dynamics
were determined. Important for equation-of-state and phase transition
studies, such experiments extend their relevance to inertial
confinement fusion and astrophysical fundamental research.
By the interaction of intense (1010
particles/500 ns) relativistic (∼300
MeV/amu) heavy ion beams with solid targets, large volumes
(several cubic millimeters) of strongly coupled plasmas are
produced at solid-state densities and temperatures of up to
1 eV, with relevance for equation-of-state (EOS) studies of
matter at high energy density and heavy ion-beam-driven inertial
confinement fusion (ICF). The time and space profile of the
ion beams, focused by the plasma lens to diameters of a minimum
of 0.5 mm in order to obtain specific energy depositions of
up to about 4 kJ/g, were measured to calculate the energy
deposition in the target. In the present work, the plasmas created
by ion beam interaction with cryogenic gas crystals and metallic
targets are studied, among other methods, by backlighting
shadowgraphy and electrical conductivity measurements. The
experiments are coupled with two-dimensional hydrodynamic simulations.
At the Gesellschaft für Schwerionenforschung (GSI, Darmstadt)
intense beams of energetic heavy ions have been used to generate
high-energy-density (HED) state in matter by impact on solid
targets. Recently, we have developed a new method by which we
use the same heavy ion beam that heats the target to provide
information about the physical state of the interior of the
target (Varentsov et al., 2001). This is accomplished
by measuring the energy loss dynamics (ELD) of the
beam emerging from the back surface of the target. For this
purpose, a new time-resolving energy loss spectrometer
(scintillating Bragg-peak (SBP) spectrometer) has been developed.
In our experiments we have measured energy loss dynamics of
intense beams of 238U, 86Kr, 40Ar,
and 18O ions during the interaction with solid rare-gas
targets, such as solid Ne and solid Xe. We observed continuous
reduction in the energy loss during the interaction time due
to rapid hydrodynamic response of the ion-beam-heated target
matter. These are the first measurements of this kind.
Two-dimensional hydrodynamic simulations were carried out using
the beam and target parameters of the experiments. The conducted
research has established that the ELD measurement technique
is an excellent diagnostic method for HED matter. It specifically
allows for direct and quantitative comparison with the results
of hydrodynamic simulations, providing experimental data for
verification of computer codes and underlying theoretical models.
The ELD measurements will be used as a standard diagnostics
in the future experiments on investigation of the HED matter
induced by intense heavy ion beams, such as the HI-HEX (Heavy
Ion Heating and EXpansion) EOS studies (Hoffmann et al.,
The X-ray spectral distribution of swift heavy Ti and Ni ions
(11 MeV/u) observed inside aerogels (ρ = 0.1
g/cm3) and dense solids (quartz, ρ = 2.23
g/cm3) indicates a strong presence of simultaneous
3–5 charge states with one K-hole. We show that the
theoretical analysis can be split into two tasks: first, the
treatment of complex autoionizing states together with the
originating spectral distribution, and, second, a charge-state
distribution model. Involving the generalized line profile function
theory, we discuss attempts to couple charge-state distributions.
The dynamics of low entropy weak shock waves induced by heavy
ion beams in solid targets was investigated by means of a schlieren
technique. The targets consist of a metallic absorber for the
beam energy deposition followed by a plexiglass block for optical
observations. Multiple waves propagating with supersonic velocities
at 15 kbar pressures were observed in the plexiglass, for pressures
of up to 70 kbar numerically calculated in the absorbers. Pressures
in the megabar ranges are predicted for a near future beam upgrade,
enabling studies of phase transition to metallic states of H,
Kr, and Xe.
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