Frontiers in High Energy Density Physics The X-Games of Contemporary Science (2003) / Chapter Skim
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3. High Energy Density Laboratory Plasmas
3. High Energy Density Laboratory Plasmas
Pages 71-119
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From page 71... ...
Not surprisingly, this study of extreme science has considerable overlap with astrophysics and nuclear weapons physics, es well as inertial confinement fusion research.This chapter gives a broad survey of laboratory HED physics, starting in the next section with a list of important scientific questions that could potentially be addressed on 71
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From page 72... ...
72 Frontiers in High Energy Density Physics T time Time 1 ~ FIGURE 3.1 X-ray pinhole camera "movie" of a directly driven inertial confinement fusion implosion on the OMEGA laser system, from the laser irradiating the shell at early times, to the formation of a hot spot.
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From page 73... ...
Can thermonuclear ignition be achieved in the laboratory? Can high-yield inertial confinement fusion implosion experiments contribute to our understanding of aspects of thermonuclear supernova explosions?
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From page 74... ...
Can nuclear reactions under highly screened conditions in dense plasmas relevantto the cores of massive stars be studied in the laboratory? Can macroscopic assemblies of relativistically degenerate matter (Fermi temperature, Fermi > mec2)
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From page 75... ...
TABLE 3.1 Three Currently Operating High Energy Density Facilities That Provide the Highest Energy Densities to Experimental Targets OMEGA Atlas (University of (Los Alamos Rochester National Laboratory; Laboratory of Z-machine To Be Moved to Existing Laser Energetics) (Sandia National Laboratories)
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From page 76... ...
All three of these facilities were built primarily for high energy density plasma studies relevant to nuclear weapons science, including inertial confinement fusion, but the National , ,
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From page 77... ...
Nuclear Security Administration, which operates them, makes a portion of their time available for fundamental high energy density physics research. Table 3.2 shows other existing HED facilities.
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From page 78... ...
that is currently under construction at Lawrence Livermore National Laboratory, showing the location of various components and support facilities. When completed, the NIF will be the nation's highest-power MJ-class high energy density physics facility, built primarily for weapons-relevant high energy density physics research, including inertial confinement fusion.
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From page 79... ...
A key distinguishing feature of the HED facilities is that macroscopic volumes of matter can be placed in these extreme conditions for laboratory study. High Energy Density Materials Properties When an object (solid, liquid, or gas)
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From page 80... ...
Modern HED drivers are also capable of delivering shaped pressure pulses that enable isentropic compression experiments, or other off-Hugoniot conditions. High energy density facilities are particularly well suited for EOS studies at high compression, because of the very high pressures possible.
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From page 81... ...
As mentioned in Chapter 2, new results could significantly impact models of planetary structure and possibly planetary formation models, and they could also affect the modeling of inertial confinement fusion implosions. It should also be noted that in measurements relevant to planetary interiors, the experimental results should be directly applicable, without any scaling (see Figure 1 .1 in Chapter 1)
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From page 82... ...
In this case, matter was impulsively heated at the surface with a ~70-fs laser pulse from a high-repetition-rate (1 kHz) Ti:sapphire laser, and probed with bursts of 10 keV x rays from the Advanced Photon Source.
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From page 83... ...
Q.8 O A 7 0.6 O.5 0~4 O.3 O.2 0.1 FIGURE 3.4 Time-resolved x-ray diffraction from an InSb crystal that is irradiated with a 70-fs laser pulse from a 1-kHz repetition rate Ti:sapphire laser, synchronized with a burst of collimated 1 0-keV x rays from the Advanced Photon Source (APS)
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From page 84... ...
Partially or Fully Degenerate Matter Cool dense matter corresponds to conditions where kT/OF << 1, and = e2/akT >> 1, where ELF iS the Fermi temperature and ~ is the plasma coupling constant, that is, the ratio of the interparticle coulomb energy (for typical interparticle spacing, a) to the particle thermal energy, kT.
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From page 85... ...
One way to access warm dense matter states is through the use of ultrafast laser systems to heat matter on a time scale that is short compared to its hydrodynamic response time. This allows solid-state density materials to be heated to temperatures in the high energy density regime (e.g., densities, temperatures, and energy densities of 1024 cm-3, a few electronvolts, and ~1012 ergs/cm3 = 1011 J/m3, respectively)
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From page 86... ...
In the context of future HED experiments FIGURE3.5 Shear-layer scalarfield. Blue: pure high-speedfluid.
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From page 87... ...
The Mach number then expresses the ratio of kinetic energy per unit mass, K = U2 / 2, to thermal energy per unit mass in the flow, h, since Ma = [2K/~y- 1)
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From page 88... ...
At sufficiently high temperature and density, the photon "fluid" carries a significant fraction of the energy density. If the scale of the photon mean free path is long compared to characteristic spatial scales of the flow, then radiative cooling can remove thermal energy, lowering the temperature and pressure and increasing the compressibility and Mach number of the flow.
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From page 89... ...
HED facilities, in particular, excel in this respect because they can focus macroscopic energies into microscopic volumes in nanosecond time intervals. Fundamental issues abound, such as what the effect of strong shocks passing through a turbulent medium is, and how radiative emissions and magnetic fields couple to the dynamics.
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From page 90... ...
with images of strong-shock laboratory experiments that reproduce aspects of the same supernova dynamics, (c)
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From page 91... ...
Radiative Hydrodynamics Very strong shocks and very high Mach number flows invariably enter the regime of coupled radiative hydrodynamics. Indeed, perhaps one of the defining features of HED facilities is their ability to create and probe a wide variety of radiative-hydrodynamic conditions.
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From page 92... ...
It may also be possible to experimentally create conditions of radiation-dominated hydrodynamics and turbulence relevant to the vicinities of accreting neutron stars and black holes. This potential is only starting to be explored, but the extraordinary ability to focus macroscopic amounts of energy into microscopic volumes in nanosecond and even picosecond time intervals make this possibility fertile for consideration.
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From page 93... ...
an Mjet ~ 30 jet explosively driven from a conical liner of Cu; (c) laser light converted to an x-ray drive that "imploded" a solid cylindrical pin of Al; the free end of the Al pin was mounted flush against a reservoir of plastic; (d)
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From page 94... ...
The absorbing layers become hot and vaporize, in response to which a strong-shock compression wave is launched into the sample. This is the fundamental dynamics of inertial confinement fusion, where millimeter-scale capsules are imploded by this ablation pressure at the capsule surface (see Figure 3.11.
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From page 95... ...
The capsules had preimposed ripples imposed on their outer surfaces, to study the hydrodynamic instabilities relevant to ICE capsule implosions in convergent geometry. SOURCES: Images (a)
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From page 96... ...
Inertial confinement fusion relies on inertia to confine fusionable material, usually a mixture of deuterium and tritium (DT) , for a time long enough for a significant number of fusion reactions to occur.
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From page 97... ...
The ignition beam will then be generated from high-intensity, collimated electrons or ions that result from petawatt laser-matter i Interaction. Th us, the fast ign itor concept reduces the requ i rements on the compression phase of an inertial confinement target.
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From page 98... ...
For laboratory systems that produce a few hundred megajoules or more of nuclear energy per shot, this means successful ICF implosions at ~1-Hz repetition rates for several years without substantial plant maintenance. A number of requirements devolve from this highest-level specification: inexpensive mass production of well-characterized targets; high-repetition-rate drivers; a target chamber that will survive years of intense implosions/explosions and also produce reliable useful heat from the ICF-uenerated neutrons; a sufficiently tJ J accurate target injection system; and some way to deal with radioactive by-products and waste.
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From page 99... ...
However, at ~0.1 Mbar with little evidence of collective effects, extreme ultraviolet lithography is very much at the low end of the high energy density plasma spectrum. This technology has huge market potential and could prove to be the most significant potential commercial application of high energy density plasmas.
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From page 100... ...
Conditions relevant to nuclear weapons research, inertial confinement fusion, the center of Earth, the core of Jupiter, the interior of stars, and possibly even the vicinity of black holes can be recreated in the laboratory. The time intervals over which such extreme conditions can be maintained are necessarily brief, typically being measured in billionths of seconds (10-9 s)
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From page 101... ...
The high energy density facilities are quite unique in their ability to create high-Reynoldsnumber flows, over a time span covering their transition to turbulence. Radiation-Dominated Hydrodynamics It seems plausible that dynamically evolving flows, and even turbulent flows, could be created on HED facilities such as ZR (the proposed refurbished version of the Z-machine at Sandia National Laboratories)
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From page 102... ...
Also, in a system with a mixture of H and He gases that is compressed until the H becomes metallic, one may be able to determine whether He comes out of solution, a phenomena that is of critical importance to planetary interior models. Nuclear Burn If the inertial confinement fusion programs succeed in generating a standard ignition capsule testbed, controlled tests of quantities that affect the nuclear burn wave will become possible.
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From page 103... ...
The time scale for specific phase transitions can also be measured. The time scale for specific phase transitions, which can vary from subpicosecond to tens of nanoseconds or longer, can also be measured.
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From page 104... ...
This research includes inertial confinement fusion (as described above) in both direct- and indirect-drive modes, strongly shocked materials, the evolution of hydrodynamic instabilities relevant to both laboratory and astrophysical plasmas, material opacities under extreme conditions, and generation of intense x-ray radiation sources.
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From page 105... ...
These lasers can be coupled to other technologies, such as electron beams, to generate short bursts of Compton scattered x rays, or to a high energy density system (laser or pulsed power) to study the fast ignition approach to inertial confinement fusion, or to a target for ultrafast x-ray radiography.
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From page 106... ...
The energy can be directly deposited in a plasma; it can be used to compress a preexisting plasma; it can be converted into extremely large fluxes of x rays that subsequently are coupled to a target material; or the magnetic energy can be used directly to launch shock waves in materials or to launch flyer plates that create high energy density conditions in a target. The largest pulsed-power systems can deliver energies orders of magnitude larger than the energy in current laser systems (though NIF will be comparable)
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From page 107... ...
This process is known as radiative collapse. Single-wire Z-pinches can, in fact, form micropinches, that is, very small spots at random locations along the wire length where intense kiloelectronvolt x-ray emission occurs, most likely a result of the "sausage instability." The final radius and density reached in those micropinches may be determined at least in part by radiative cooling of the imploding plasma until it becomes optically thick to its own emission.
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From page 108... ...
In addition, the X-pinch can be used for x-ray radiography. A large number of wires in the form of a cylindrical wire-array is necessary to drive a hohiraum to a radiation temperature of interest for inertial confinement fusion or other high energy density science applications requiring megajoules of x rays.
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From page 109... ...
It is expected to be possible to produce beams at 1 to 10 GeV and 1 04 A for ~1 0 ns and to focus them to ~1 04 5 W/cm2, as is required for inertial confinement fusion, but the proof-of-principle experiments for this are still in the planning stage (as discussed earlier in this chapter)
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From page 110... ...
In a heavy ion beam entering an inertial confinement fusion target chamber, the kinetic energy of the individual ions may be high enough that charge neutrality is not a necessity for propagation. In that case, the kinetic energy density and the energy densities in the electric and magnetic fields are large.
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From page 111... ...
The main advantages of these x-ray lasers are their scalability to shorter wavelengths with higher output energy that would allow them to be developed as unique diagnostic tools for picosecond interferometry of other high energy density conditions such as those that the NIF will generate. Gas Guns and Diamond Anvils A fundamental goal of geophysics is a basic understanding of the structure and dynamics of Earth's interior in general and of the generation of Earth's magnetic field in particular.
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From page 112... ...
When combined with a bright source of x rays in the kiloelectronvolt energy range, such as that supplied by a synchrotron light source, this setup is an extremely powerful tool for determining the phases of materials. Experiments on diamond anvil cells are static, with strain rates of <10-6 so.
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From page 113... ...
Diagnosis of nuclear reaction products includes detailed spectral and temporal measurements of neutron and charged particle spectra from primary, secondary, and tertiary reactions. For laser and pulsed-power facilities to be attractive to users for high energy density plasma physics experiments, or for secondary experiments using the high energy density plasmas as drivers, the facilities must have excellent diagnostic systems providing information about the plasma conditions as a function of time.
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From page 114... ...
Diagnostic imaging of perturbed, high-density targets allows the evolution of these instabilities to be measured and compared with numerical simulations and theoretical predictions. Constraints are many and varied, with a goal of simultaneously resolving the space and time evolution of the perturbations with time windows, spatial amplitudes, and perturbation wavelengths that are as small as possible.
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From page 115... ...
The higher nuclear reaction yields associated with current and future ICF implosions lead to the opportunity to measure astrophysically relevant nuclear reaction rates under conditions that are close to those in astrophysical objects. Nuclear reaction cross-sections are typically measured in beam-target experiments with beam energies of hundreds of kiloelectronvolts or megaelectronvolts.
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From page 116... ...
Beam propagation in a gas or plasma introduces similar problems for direct measurements because, for example, the resulting reverse current induced in the plasma or gas after breakdown can partially or completely eliminate the selfmagnetic field of the beam current. Therefore, alternate diagnostic methods must be used to monitor beam properties, such as the intensity of x rays induced in a thin foil as the beam passes through it, for electrons, and nuclear reactions that yield an easily observed reaction product, for ions.
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From page 117... ...
The flexibility engendered by high energy density systems has led to even more complicated targets, some that lack any symmetry, others that might be designed to enable multiple backlighting sources, and all requiring extreme precision throughout the manufacturing process. An important future goal of high energy density physics requiring advances in target fabrication is the production of energy from inertial fusion.
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From page 118... ...
capabilities developed for inertial fusion energy would also be beneficial for many high energy density experiments. High-Performance Computing Computational capabilities have been revolutionized in recent years, bringing physical phenomena within the scope of numerical simulation that were out of reach only a few years ago.
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From page 119... ...
Furthermore, some of these codes model the intense electromagnetic wave/particle interaction of high-intensity beams, from plasma coronal nascence through high-density heating. While no codes include all of these effects simultaneously, relevant parts of high energy density physics problems can be simulated, yielding results with predictive value.
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