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3 Plasma Physics at High Energy Density
Pages 75-114

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From page 75...
... Small-laboratory HED plasmas include the nanometer-sized clusters irradiated by very high intensity lasers, and the ~1 µm, 10 million K, near-solid-density plasmas produced when dense plasma columns  The committee has chosen 1010 J/m3 as a reasonable lower limit of HED matter, even though it is an order of magnitude lower than the value chosen in the NRC report Frontiers in High Energy Density Physics: The X-Games of Contemporary Science (Washington, D.C.: The National Academies Press, 2003) , in order to include solid-density material at 1 eV.
From page 76...
... At temperatures above a few thousand kelvin, any mate rial becomes at least partially ionized, so HED physics is necessarily HED plasma physics. Such "warm dense matter" lies at the intersection of plasma science and condensed matter/materials science.
From page 77...
... Some of the highest power facilities used for HED experiments in the United States are listed in Table 3.1. The widespread laboratory study of HED plasmas enabled by these facilities exemplifies the point made in Chapter 1 -- namely, that new plasma regimes have become the subject of plasma physics research in the past decade.
From page 78...
... 78 Plasma Science TABLE 3.1  Selected HED Facilities Peak Type of Energy Power/ Energy Repetition Facility Machine Delivered Current Delivery Rate Location Status Large-scale National Laser 1.8 MJ 500 TW Ultraviolet ~1 shot/ Lawrence To be Ignition photons 3 hr Livermore completed in Facility National 2009 Laboratory ZR Pulsed 3.5 MJ 350 TW/ Electric ~1 shot/ Sandia National To be power 26 MA; current; day Laboratories completed in 4 Mbar magnetic 2007 pressure Omega/ Lasers ~30 kJ 30 TW/ IR/ ~1 shot/ Laboratory Operational/EP Omega EP long pulse ultraviolet 3 hr for Laser to be completed 3 kJ short EP 1 PW photons Energetics, in 2008 pulse Rochester Linac X-ray free- 1 mJ 10 GW X-ray 120 Hz Stanford Linear To be Coherent electron photons Accelerator completed in Light laser Center 2009 Source Mid-scale Titan Laser 200 J 400 TW Infrared ~1 shot/hr Lawrence Operational photons Livermore National Laboratory Z-Beamlet/ Laser 1 kJ + 500 1 TW/1 Optical/IR ~1 shot/ Sandia National Operational/1 PW Z-Petawatt J short PW photons 3 hr Laboratories to be completed pulse in 2007 Texas Laser 250 J 1 PW Infrared ~1 shot/hr University of To be Petawatt photons Texas completed in 2007 L'Oasis Laser 4J 100 TW Infrared ~1 Hz Lawrence Under upgrade photons Berkeley National Laboratory Hercules Laser 20 J 800 TW Infrared ~1 shot/ University of To be photons min Michigan completed in 2008 Cobra Pulsed ~100 kJ 1 TW/1 MA Electric ~3 shots/ Cornell Operational power current day University Nevada Pulsed 100 kJ 2 TW/1 MA Electric 1 shot/day University of Operational; Terawatt power and 35 J laser +100 TW current + Nevada laser under laser laser IR photons construction NOTE: Not included in this table are several important 10- to 100-TW lasers in use and under development at university and national laboratory facilities -- for example, the 100-TW Diocles laser facility at the University of Nebraska at Lincoln. ZR, Z refurbishment; EP, extended pulse; IR, infrared.
From page 79...
... Although that report is more comprehensive than this committee can be in its discussion of HED science opportunities, this committee will take advantage of the fact that this is a fast-moving field. Just since 2003, there has been great progress in several areas of HED plasma studies, including stockpile stewardship, ICF, and plasma wake field accelerators, as well as in basic HED science, some of which will be highlighted in this chapter.
From page 80...
... • Plasma accelerators.  Can we generate, using intense, short pulse lasers or electron beams interacting with plasmas, multigigavolt per centimeter electric fields in a configuration suitable for accelerating charged particles to energies far beyond the present limits of standard accelerators? • Laboratory plasma astrophysics.  Can we better understand some aspects of observed high-energy astrophysical phenomena, such as supernova explo sions or galactic jets, by carrying out appropriately scaled experiments to study the underlying physical processes and thereby benchmark the com puter codes used to simulate both?
From page 81...
... Until perhaps 20 years ago, when high-power laser facilities became available, essential parts of that research had to be carried out using underground nuclear tests; there was no alternative method to address such physics issues as radiation transport and the physical properties of hot dense matter. In addition, an understanding of the effects of a nuclear explosion on nearby weapons and on both civilian and military electronics was achieved partially by testing components and subsystems of the weapons using high fluxes of x rays produced by pulsed power machines and partially by testing underground.
From page 82...
... Intellectual Importance The coupling of HED plasma physics to several other subdisciplines of physics serves to broaden its intellectual impact well beyond its national security and ICF energy base. To summarize, • Studying the properties of warm dense matter brings together plasma re search and condensed matter and materials research.
From page 83...
... • Condensed matter physics and materials science.  Studies of "warm dense matter" straddle the boundary between condensed matter and plasma physics. The kinds of equations of state and dynamic properties of mate rials questions being addressed by experiments on warm, dense, partially ionized matter at high pressure connect to the questions being addressed by materials science studies.
From page 84...
... Recent Progress and Future Opportunities This subsection begins with the main drivers of HED plasma physics research that were introduced in the last section. However, fundamental HED research is also driven by the access to new states of matter provided by pulsed-power machines and increasingly powerful short-pulse lasers.
From page 85...
... -- such as an intense laser, a high current particle beam, or a HED imploding plasma from a pulsed power machine -- is converted into x rays inside an enclosure, called a hohlraum, to assure symmetric irradiation of the fuel capsule contained within the hohlraum. That x-ray bath then causes an ablation-driven spherically symmetric implosion of the fuel capsule.
From page 86...
... Advances in the ability to carry out large-scale two- and three-dimensional computer simulations on ICF target designs, together with technology developments and high-quality experiments carried out using the largest available laser and pulsed power systems, OMEGA and Z, have all contributed to the forward momentum of the ICF effort during the last 10 years. The development of exquisite diagnostics enabling mean ingful comparison of experiments with simulations has been key to this progress.
From page 87...
... The simplicity of the required target (only a fuel capsule is necessary) could be a substantial benefit for inertial fusion energy.
From page 88...
... . State-of-the-art computer simulations of the latest hohlraum-plus-fuel-capsule designs imply that if the experiments go as predicted, as little as 50 percent of the NIF laser design energy will be needed to achieve ignition (ignition is defined as the ratio of fusion energy released to laser energy absorbed in the hohlraum)
From page 89...
... More fuel is predicted to undergo fusion reactions for a given driver energy, and the total laser energy that must be delivered to a fuel capsule to achieve the high gain needed for inertial fusion energy is predicted to be an order of magnitude less for fast ignition than for hot-spot ignition. The coupling of laser energy into the compressed fuel depends on the generation and control of extremely large currents (~109 A)
From page 90...
... . Inertial Fusion Energy Achieving fusion ignition in a single fuel capsule at the NIF is both the first step for SSP applications and the proof-of-principle step for the development of ICF as a practical path to the inexhaustible energy source that many believe fusion a b FIGURE 3.4  Comparison of a computer simulation and an experiment addressing fast ignition.
From page 91...
... This intellectual milestone will then have to be followed by major developments in high-repetitionrate drivers, large-scale fuel capsule manufacturing, and other technologies that are required for practical fusion energy based on ICF. Issues such as developing materials that can tolerate the high neutron flux of a fusion reactor and tritium handling are common to both ICF and magnetic confinement fusion.
From page 92...
... First, with the heavy reli ance of ICF target design on computer simulation capability, the achievement of fusion ignition in an ICF fuel capsule will be a major integrated test of the predic tive capability of multidimensional computer simulation codes that model self consistently the many physical processes relevant to nuclear weapon explosions. In addition, achieving ignition of an ICF fuel capsule will greatly extend the range of temperatures, densities, shock strengths, etc.
From page 93...
... Properties of Warm Dense Matter and Hot Dense Matter An important aspect of HED plasma research is the study of the fundamental properties of dense matter subject to extremes of pressure and temperature. How compressible is it?
From page 94...
... . In the past decade, many advances have been made toward understanding the properties of warm and hot dense matter, examples of which follow: • Equation of state (EOS)
From page 95...
... • Radiative properties.  Much progress has been made in computational methods for determining the radiative and opacity properties of dense plasmas. Experiments have been important in validating these calculations, as was illustrated in a pioneering Z-machine experiment on the opacity of iron, which is important for understanding the structure of the Sun.
From page 96...
... Hutchinson, "Supersonic ionization wave driven by radiation transport in a short pulse laser produced plasma," Physical Review Letters 77: 498 (1996)
From page 97...
... Thus studies of the strongly coupled plasma physics of warm dense matter between 0.1 and 1 eV can be carried out even with relatively low energy beams that are made available in the inertial fusion energy program by uniformly heating thin foil targets. The experimental advances strongly suggest that interesting WDM plasmas can be studied with ion-beam drivers in the next few years.
From page 98...
... Radiative Properties in Extreme Magnetic Fields While great progress has been made in the study of the radiative properties of dense plasmas without embedded magnetic fields, much less is known about hot dense matter with very strong magnetic fields. Such information would help us to understand some astrophysical phenomena, laser–target interaction experiments, and z-pinch implosions.
From page 99...
... accelerator technology. Highlights Based on research carried out since the late 1970s and spurred on by recent developments in laser technology and multidimensional computer simulation capability, laser-based wake field accelerator experiments in 2004 by three independent groups achieved accelerated beams of electrons at the ~100 MeV energy level.
From page 100...
... 100 Plasma Science FIGURE 3.7  (a) Laser wake field accelerator experiments demonstrated production of low-energy spread electron beams using plasma channels to extend the interaction distance beyond the diffraction distance.
From page 101...
... Understanding the interplay among the nonlinear physical processes in plasma wake field accelerators requires numerical simulations. Particle-based models, such as fully explicit particle-in-cell (PIC)
From page 102...
... The NRC report Connecting Quarks with the Cosmos says that the goal of laboratory plasma astrophysics is to discern the physical principles that govern extreme astrophysical environments through the laboratory study of HED physics. The challenge here is to develop physically credible scaling relationships that enable, through the intermediary of a computer code, laboratory experiments on the scale of centimeters or meters to illuminate physical processes taking in a distant part of the universe over enormous length scales (see, for ex ample, Figure 1.14)
From page 103...
... The use of HED laboratory experiments to investigate physical processes thought to be operative in astrophysical phenomena is a relatively new and controversial endeavor. It is generally believed that laboratory experiments cannot directly simulate an astrophysical situation even if some of the relevant dimensionless parameters are on the same side of some critical value, whatever that might be, in both the laboratory and the cosmos.
From page 104...
... Research in many of these areas is of importance not only for intellectual reasons but also because the projects train students who ultimately become the leaders in the large projects that address national priorities. Advanced Computer Simulation of HED Plasmas Advances in predictive capability made possible by computer simulations are revolutionizing all areas of HED plasma research.
From page 105...
... These new diagnostics coupled with a detailed understanding of atomic physics in dense plasmas will lead to new ways of measuring and studying HED plasmas in the coming decade, including igniting ICF cores.
From page 106...
... (c) Experimental radiograph on strong shock-driven experiments done at the OMEGA laser.
From page 107...
... Nonlinear optical phenomena attributable to the relativistic mass change of the electrons in the laser field lead to self-focusing and -channeling of the laser, or the generation of high-order harmonics in the laser field. The physics of how laser pulses interact with underdense plasma is critical in ICF and wake field accelerator research.
From page 108...
... largely reserved for mission-oriented re search. However, there are synergies between mission-oriented SSP science and fundamental HED science, and there are benefits to the cross-fertilization that occurs when university–national laboratory collaborations are developed.
From page 109...
... . Notice the short wavelength structure in the plasmas around each exploding wire.
From page 110...
... experiments that involve collaborations be tween university and national laboratory scientists, in which both parties benefit, the former by acquiring publishable data together and the latter by advancing stockpile stewardship science, and • Outside user programs on all major NNSA facilities, similar to the program at the National Laser User Facility (the OMEGA laser) at the University of Rochester, which sets aside perhaps 10-15 percent of the run time for investigator-driven research.
From page 111...
... Conclusion:  The exciting research opportunities in high energy density (HED) plasma science extend far beyond the inertial confinement fusion, stockpile stewardship, and advanced accelerator missions of the National Nuclear Security Administration and the Department of Energy's Office of High Energy Physics.
From page 112...
... The U.S. fusion program includes inertial fusion energy as a potential alter native path to practical fusion energy in parallel with the magnetic confinement fusion approach.
From page 113...
... As declared in that report and in the current report, the field is developing rapidly. In particular, science topics such as laser–plasma interactions and warm dense matter could be explored at intermediate-scale facilities.
From page 114...
... The DOE Office of Science should provide a framework for plasma science as a whole and play a role in managing a robust user program for broader science experiments at NNSA's largest facilities.


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