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In this chapter we address the low-density and high-temperature regime of high-energy-density physics identified in Chap. 1. While phenomena produced in this regime often connect with those discussed in the previous chapters, there are real differences in the underlying physics. A high-energy-density, thermal, relativistic plasma would have a minimum temperature of 511 keV and a density exceeding 1018 cm-3. At the turn of the century, such plasmas did not exist in the laboratory. Producing them can be taken as a challenge for the early 21st century. [ABSTRACT FROM AUTHOR]

Thus far we have examined primarily systems that are purely hydrodynamic. In so doing, we have ignored a major aspect of many high-energy-density systems: radiation. It is easy to see why radiation often matters. At any given pressure, the temperature increases as density decreases, and there is some density below which radiative fluxes will exceed material fluxes. [ABSTRACT FROM AUTHOR]

Chapter 8 represented a turning point in our discussion. The earlier chapters were focused on the physical fundamentals of high-energy-density physics. Chapter 8 showed how we could create such conditions, which in turn makes possible the application of high-energy-density systems to the pursuit of various goals. This and the next chapter are much more focused on these goals. The goal that has been and remains dominant in high-energy-density research is the development of inertial confinement fusion, or ICF. This is our topic in the present chapter. [ABSTRACT FROM AUTHOR]

Nature often creates high-energy-density conditions. At root, the cause is always gravity. At the center of the Earth, for example, the pressure is 3.6 Mbars, almost entirely due to gravity. Jupiter is similar, with a pressure of ~40 Mbars at its core. In stars, the gravitational assembly of the stellar mass leads to heating by nuclear fusion, which produces much larger pressures - the pressure at the core of the Sun is roughly 0.2 terabars. Once fusion creates conditions that lead to supernova explosions, even larger pressures occur. For example, some supernovae produce neutron stars, and the magnetic field at the surface of a typical neutron star is near 1 teraGauss. The pressure of such a magnetic field is about 40 petabars. [ABSTRACT FROM AUTHOR]

It is fair to say that we never directly experience radiation hydrodynamic phenomena - that is, phenomena in which the radiation directly participates in the hydrodynamic evolution of a system. We do experience consequences of radiative heat transport, as for example when heating by solar irradiation produces wisps of fog above a wet road. And we are aware of some systems, such as solar sails, in which radiation directly causes material motion. But as we shall see, radiation hydrodynamic phenomena require temperatures of millions of degrees, more or less, so they are outside the realm of our direct experience. [ABSTRACT FROM AUTHOR]

In Chap. 1 we looked forward to potential connections between high-energydensity physics and astrophysics. Some of these connections arise because one can produce in the laboratory circumstances that actually exist in astrophysics and can measure the propertiesof these systems. We have seen examples of this in the areas of equations of state, in Chap. 3, and opacities, in Chap. 6. Other connections arise because high-energy-density experiments can produce hydrodynamic or radiation hydrodynamic behavior under conditions that are relevant to astrophysical systems. [ABSTRACT FROM AUTHOR]

Our discussion of the previous chapter focused on one-dimensional phenomena, in which a physical system was structured as a function of linear or radial distance, but by assumption was not structured in the other two dimensions. Common experience tells us that this will rarely be a good assumption. We see turbulent clouds and whirlwinds in the air and complex eddies in water. We know of three-dimensional turbulent motions within the Earth and within the Sun. For that matter, if we focus our attention, we can see amazing hydrodynamic phenomena every day in the bathroom sink. We know that one can save fuel in cars and in airplanes by careful design that reduces the energy delivered to turbulence in the air. In fact, our experiences and common knowledge would lead us to conclude that hydrodynamic fluids are more often than not unstable and turbulent in some sense. [ABSTRACT FROM AUTHOR]

The discussion of energy in Sect. 2.1 was entirely based on the notion of a polytropic gas. The speed of sound waves, which we found by examining fluctuations in density and velocity, was found to depend upon the variation of pressure with density. These observations reveal the tip of an iceberg, and the iceberg is known as the closure problem. The fluid equations can be derived by taking moments of the velocity distribution of the particles, as is done for example in graduate courses in plasma physics. Here we designate particle velocities by v and fluid velocities by u. Thus the continuity equation is the moment taken with v0, the momentum equation is the moment with v, the energy equation is the moment with v2, the heat transport equation is the moment with v3, and one can keep going. The closure problem arises because every moment equation contains terms involving the next higher moment. Equation (2.1) involves the momentum (ρu), (2.2) involves the energy density (as p), and (2.3) would involve the heat flux had we not assumed it to be zero. Because we assumed the heat flux to be zero, (2.1) to (2.3) form a closed system of equations. In general, one obtains a closed system of fluid equations by assuming that some moment of the velocity distribution is either zero or a known function of lower moments. As another example, sometimes the energy equation is expressed as an equation for temperature and the heat flux is written as —κth∇T, which also produces a closed system of three equations. [ABSTRACT FROM AUTHOR]

Not long ago, one could say that 99% of the known universe is plasma. The recent discovery of dark matter and dark energy imply that this may no longer be true, but it will remain the case that 99% of the readily observed universe is plasma. The interstellar medium, stars, and more exotic compact objects are all composed of or surrounded by ionized matter. Without understanding something about plasmas, one cannot hope to understand the universe. [ABSTRACT FROM AUTHOR]

The word "shock" is used very widely in common experience. One is shocked by an unexpected event; a wounded victim goes into shock; and one shocks a material by suddenly cooling it. A "shock wave" is a sudden transition in the properties of a fluid medium, involving a difference in flow velocity across a narrow (ideally, abrupt) transition. In high-energy-density physics, nearly any experiment involves at least one shock wave. Such shock waves may be produced by applying pressure to a surface or by creating a collision between two materials. In astrophysics, nearly every sudden event produces a shock wave. Yet in common experience one encounters very few shock waves. We hear thunder after lightning, which is a long-term consequence of the shock wave produced by the lightning channel, but as we shall see below one would hope never to directly experience this shock wave. Most of us hear sonic booms infrequently, but they are the only shock wave of human origin we typically encounter. [ABSTRACT FROM AUTHOR]

This book concerns itself with the physics of systems having high-energydensity. By high-energy-density systems, we refer to those having a pressure above one million atmospheres. The units of this pressure can be designated by 1 Mbar, 1011 Pascals, 1011 J/m3, 1012 dynes/cm2, or 1012 ergs/cm3. We will tend to express the pressure in Mbars, as this is the most common of these units found in the relevant literature. This characterization was developed in a report of the National Academy of Sciences in the U.S., entitled Frontiers in High-Energy-Density Physics: the X-games of Contemporary Science. It reflects several observations. For example, one learned in school that solids and liquids are "incompressible", but this is not strictly true. If one applies a pressure exceedin ~1 Mbar to ordinary solid matter, it compresses. Another way to make this point is to say that the internal energy of a hydrogen molecule is ~1 Mbar. [ABSTRACT FROM AUTHOR]

We present here the results from an extensive scintillation study of twenty pulsars in the dispersion measure (DM) range 3 - 35 pc cm−3 carried out using the Ooty Radio Telescope, to investigate the distribution of ionized material in the local interstellar medium (LISM). Our analysis reveals several anomalies in the scattering strength, which suggest that the distribution of scattering material in the solar neighborhood is not uniform. Our model suggests the presence of a low density bubble surrounded by a shell of much higher density fluctuations. We are able to put some constraints on geometrical and scattering properties of such a structure, and find it to be morphologically similar to the local bubble known from other studies. [ABSTRACT FROM AUTHOR]