1

Introduction

The desirability of fusion power is undeniable. There is, after all, sufficient fusion fuel to supply the entire world’s energy needs for millions of years.1 Furthermore, fusion power plants would have negligible environmental impact since they would produce no greenhouse gases and, if appropriately designed, no long-lived radioactive waste.2 However, achieving fusion at the cost and scale needed for energy generation is still a major challenge.3 To initiate fusion, the deuterium and tritium fuel must be heated to over 50 million degrees and held together for long enough for the reactions to take place (see Appendix A). The two main approaches to fusion achieve these conditions differently: In magnetic confinement fusion, the low-density fuel is held indefinitely in a magnetic field while it reacts; in inertial confinement fusion (ICF), a small capsule of fuel (the “target”) is compressed and heated so that it reacts rapidly before it disassembles (see Figure 1.1). In this study, the committee assesses the prospects and challenges for generating power using ICF.

The current U.S. fleet of inertial fusion facilities offers a unique opportunity to experiment at “fusion scale,” where fusion conditions are accessible for the first

__________________________

1 Tritium (superheavy hydrogen) and deuterium (heavy hydrogen) are the fuels for the easiest fusion reaction. Tritium must be made by being “bred” from lithium. One liter of sea water contains enough lithium and deuterium to make roughly 1 kWh of fusion energy. See Appendix A.

2 S.W. White and G.L. Kulcinski, 2000, Birth to death analysis of the energy payback ratio and CO2gas emission rates from coal, fission, wind, and DT-fusion electrical power plants, Fusion Engineering and Design 48: 473-481.

3 To initiate fusion, the deuterium and tritium fuel must be heated to over 50 million degrees and held together long enough for the reactions to take place (see Appendix A).



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1 Introduction The desirability of fusion power is undeniable. There is, after all, sufficient fusion fuel to supply the entire world’s energy needs for millions of years.1 Further­ more, fusion power plants would have negligible environmental impact since they would produce no greenhouse gases and, if appropriately designed, no long-lived radioactive waste.2 However, achieving fusion at the cost and scale needed for energy generation is still a major challenge.3 To initiate fusion, the deuterium and tritium fuel must be heated to over 50 million degrees and held together for long enough for the reactions to take place (see Appendix A). The two main approaches to fusion achieve these conditions differently: In magnetic confinement fusion, the low-density fuel is held indefinitely in a magnetic field while it reacts; in inertial confinement fusion (ICF), a small capsule of fuel (the “target”) is compressed and heated so that it reacts rapidly before it disassembles (see Figure 1.1). In this study, the committee assesses the prospects and challenges for generating power using ICF. The current U.S. fleet of inertial fusion facilities offers a unique opportunity to experiment at “fusion scale,” where fusion conditions are accessible for the first 1  Tritium (superheavy hydrogen) and deuterium (heavy hydrogen) are the fuels for the easiest fusion reaction. Tritium must be made by being “bred” from lithium. One liter of sea water contains enough lithium and deuterium to make roughly 1 kWh of fusion energy. See Appendix A. 2  S.W. White and G.L. Kulcinski, 2000, Birth to death analysis of the energy payback ratio and CO 2 gas emission rates from coal, fission, wind, and DT-fusion electrical power plants, Fusion Engineering and Design 48: 473-481. 3  To initiate fusion, the deuterium and tritium fuel must be heated to over 50 million degrees and held together long enough for the reactions to take place (see Appendix A). 12

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Introduction 13 FIGURE 1.1  Simple schematic of the four stages of inertial confinement fusion via hot spot ignition. Stage 1: Energy is delivered to the surface of a tiny hollow sphere a few millimeters in diameter containing fusion fuel (the “target”). The blue arrows represent the “driver energy” delivered to the target—this is the laser light, X-rays, or particle beams that heat the outer yellow shell. Stage 2: Orange arrows indicate the ablation of the outer shell that pushes the inner shell toward the center. The compression of the fusion fuel to very high density increases the potential fusion reaction rate. Stage 3: The central low-density region, comprising a small percentage of the fuel, is heated to fusion temperatures. The light blue arrows represent the energy transported to the center to heat the hot spot. This initiates the fusion burn. Stage 4: An outwardly propagating fusion burn wave triggers the fusion of a significant fraction of the remaining fuel during the brief period before the pellet explodes/ disassembles. Steady power production is achieved through rapid, repetitive fusion microexplosions of this kind. (A more detailed primer on the physics is given in Appendix A.) time. Indeed, significant fusion burn is expected on the National Ignition Facility (NIF) in this decade (see Box 1.1). A key aim of this study is to determine how best to exploit the opportunity offered by the NIF to advance the science and technol- ogy of inertial fusion energy (IFE).The committee judges that the potential benefits of IFE justify its inclusion as part of the long-term U.S. energy R&D portfolio, recognizing that the practical realization of fusion energy remains decades away. Conclusion 1-1: The potential benefits of energy from inertial confinement fusion (abundant fuel, minimal greenhouse gas emissions, and limited high- level radioactive waste requiring long-term disposal) also provide a com- pelling rationale for including inertial fusion energy R&D as part of the long-term R&D portfolio for U.S. energy. A portfolio strategy hedges against uncertainties in the future availability of alternatives, such as those that arise from unforeseen circumstances. While the IFE concept is simple, the practical implementation and the high- energy-density target physics are not. If the compression of the target is insuf- ficient, the fusion reaction rate is too slow and the target disassembles before the reactions take place. Delivering the driver energy and compressing the target

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14 An Assessment of the Prospects for Inertial Fusion Energy BOX 1.1 Recent Results from the National Ignition Facility The National Ignition Campaign (NIC) formally ended on September 30, 2012, but the e ­ ffort to achieve thermonuclear ignition on the NIF is expected to continue, albeit at a somewhat reduced level. While the initial expectations of LLNL scientists for a speedy success in achiev- ing ignition were dashed, much progress was made toward the goal of demonstrating thermo- nuclear ignition in the laboratory for the first time. The NIC experimental plan for cryogenic deuterium-tritium (DT) layered target implosions and diagnostics is described in the reference given in the footnote.1 The latest results on the implosion performance are provided in S.H. Glenzer et al.2 Future directions for experimental and theoretical investigations are described in the proceedings of the workshop on the science of ignition.3 Experts in high-energy-density science and ICF convened in San Ramon, California, between May 22 and 24, 2012, for the international workshop Science of Fusion Ignition on NIF to review the results of the NIC experiments, so as to identify major science issues and propose priorities for future research to enhance the understanding of ignition in ICF. Subpanels of specialists ana- lyzed results in all of the areas relevant to the implosion physics, from laser-plasma interaction and radiation transport, to implosion hydrodynamics, and burn physics. In their final report, the group of experts recognizes the need for an improved predictive capability to better guide ignition experiments. They recommend specific experiments to validate models and codes, and to improve basic understanding of the complex physics phenomena occurring in a laser-driven implosion. In their most recent review, on May 31, 2012, a team appointed by the NNSA also concluded that “better understanding through detailed measurements and model adjustments informed by rigorous quantifications of uncertainties are needed both to better approach the ignition process and to benefit the stockpile stewardship program.”4 Another review panel, the NIC Technical Review Committee, concluded that “the NIF is operating in a stable, reli- able, predictable, and controllable manner” and that “there is sufficient body of knowledge regarding nuclear fusion and plasma physics to conclude that it should be possible to achieve controlled thermonuclear fusion on a laboratory scale.”5 NNSA recently released a report that lays out a 3-year plan for NNSA’s ICF program, stating that “the emphasis going forward will be to illuminate the physics and to improve models and codes used in the ICF program until agreement with experimental data is achieved. Once the codes and models are improved to the point at which agreement is reached, NNSA will be able to determine whether and by what approach ignition can be achieved at the NIF.”6 An overall performance parameter used by the LLNL group is the experimental ignition threshold factor (ITFx).7 The ITFx has been derived by fitting the results of hundreds of computer simulations of ignition targets to find a measurable parameter indicative of the performance with respect to ignition. An implosion with ITFx = 1 has a 50 percent probability of ignition. To date, the highest value of the ITFx achieved in DT layered implosion experiments on NIF is about 0.1.8 To improve the implosion performance and raise the ITFx the LLNL group is tak- ing several steps to reduce the ablator-fuel mix. Further reducing target surface roughness9 is an obvious remedy. Other available options range from a thicker ablator, a thicker ice layer, and higher entropy implosions. All of these options come with a laser energy penalty. To drive thicker ice or thicker ablator targets will require more laser energy to reach the required implosion velocity. Higher entropy implosions will be more hydrodynamically stable, but high entropy degrades the areal density thus reducing both the one-dimensional margin for ignition and the energy gain in the event of ignition. Another possible cause of performance degrada- tion is the growth of long wavelength spatial nonuniformities induced by asymmetries in the x-ray drive (or other sources).10 Attempts to mitigate ablator-fuel mix and to measure drive ­ symmetries are currently under way at LLNL.11 Other strategies to improve the performance a include using different ­ blators other than plastic (CH). For instance, studies involving high- a density carbon or beryllium ablators are under way.

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Introduction 15 Improving the ignition threshold factor by an order of magnitude will be challenging, but several options are available to improve implosion performance. The continuing experimental campaign at the NIF will explore these options and develop a more fundamental understanding of the key physics issues that are currently preventing the achievement of ignition. While the committee considers the achievement of ignition as an essential prerequisite for initiating a national, coordinated, broad-based IFE program, the committee does not believe that the fact that NIF did not achieve ignition by the end of the NIC on September 30, 2012, lessens the long-term technical prospects for inertial fusion energy. It is important to note that none of the expert committees12 that reviewed NIF’s target performance concluded that ignition would not be achievable at the facility. Furthermore, as the ICF Target Physics Panel concluded, “So far as target physics is concerned, it is a modest step from NIF scale to IFE scale.”13 A better understanding of the physics of indirect-drive implosions is needed, as well as improved capa- bilities for simulating them. In addition, alternative implosion modes (laser direct drive, shock ignition, heavy-ion drive, and pulsed power drive) have yet to be adequately explored. It will therefore be critical that the unique capabilities of the NIF be used to determine the viability of ignition at the million joule energy scale. NOTE: Appendix I provides a technical discussion of the recent results from the NIF. 1  M.J. Edwards et al., 2011, The experimental plan for cryogenic layered target implosions on the National Ignition Facility—The inertial confinement approach to fusion, Physics of Plasmas 18: 051003. 2  S.H. Glenzer et al., 2012, Cryogenic thermonuclear fuel implosions on the National Ignition Facility, Physics of Plasmas 19: 056318. 3  LLNL, 2012, Science of Fusion Ignition on NIF, Report from the Workshop on the Science of Fusion Ignition on NIF held on May 22-24, Document LLNL-TR-570412; available at http:// tinyurl.com/8p879e6. 4  DOE, 2012, Memo by D.H. Crandall to D.L. Cook, “External Review of the National Igni- tion Campaign,” July 19. 5  NIC Technical Review Committee, “The National Ignition Campaign Technical Review Committee Report, For the Meeting Held on May 30 through June 1, 2012.” 6  NNSA, 2012, NNSA’s Path Forward to Achieving Ignition in the Inertial Confinement Fusion Program: Report to Congress, December. 7  B.K. Spears et al., 2012, Performance metrics for inertial confinement fusion implosions: Aspects of the technical framework for measuring progress in the National Ignition Campaign, Physics of Plasmas 19: 056316. 8  S.H. Glenzer et al., 2012, Cryogenic thermonuclear fuel implosions on the National Ignition Facility, Physics of Plasmas 19: 056318; and R. Betti, 2012, “Theory of Ignition and Hydroequivalence for Inertial Confinement Fusion, Overview Presentation,” OV5-3, 24th IAEA Fusion Energy Conference, October 7-12, San Diego, Calif. 9  NIC Technical Review Committee, “The National Ignition Campaign Technical Review Committee Report, For the Meeting Held on May 30 through June 1, 2012.” 10  Ibid. 11  Ibid. 12  DOE, Memo by D.H. Crandall to D.L. Cook, “External Review of the National Ignition Campaign,” July 19, 2012; NIC Technical Review Committee, “The National Ignition Campaign Technical Review Committee Report, For the Meeting Held on May 30 through June 1, 2012”; National Research Council, “Assessment of Inertial Confinement Fusion Targets,” The National Academies Press, Washington, D.C., 2012. 13  See Overarching Conclusion 1 from the Panel report, Assessment of Inertial Confinement Fusion Targets, released as a prepublication in early 2013.

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16 An Assessment of the Prospects for Inertial Fusion Energy uniformly without exciting instabilities that compromise the compression requires high precision in space and timing. Large capsules/targets are in many ways easier since they disassemble more slowly and therefore require less compression. They can also deliver greater gain (“gain” is fusion energy out divided by the driver energy delivered to compress and heat the capsule). However, the fusion energy per explosion—and therefore the size of the capsule—is limited by the need to contain and utilize the energy released. Thus capsules with yields of approximately 100 MJ to 10 GJ (the latter is equivalent to the explosive power of 2.5 tons of TNT) have been proposed as candidates for energy production. The issues that influence the technology choices are explored in subsequent chapters. High fusion gain with limited yield is a prerequisite for practical IFE. An IFE power plant must do much more than simply ignite a high-gain tar- get. Commercial power production requires many integrated systems, each with technological challenges. It must make the targets, ignite targets repetitively, extract the heat, breed tritium from lithium (see Appendix A), and generate electricity. Furthermore it must do this reliably and economically. The fully integrated system (see Figure 1.2) consists of (1) a target factory to produce about 107 to 109 low- cost targets per year, (2) a driver to heat and compress the targets to ignition, (3) a fusion chamber to recover the fusion energy pulses from the targets and breed the FIGURE 1.2  Schematic of the four major components of an IFE power plant. SOURCE: Opportunities in the Fusion Energy Sciences Program, 1999, http://www.ofes.fusion.doe.gov/more_html/FESAC/ FES_all.pdf.

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Introduction 17 FIGURE 1.3  Schematic energy flow in an inertial fusion power plant. Note that Q E = 1/f. The numbers beside the arrows indicate the proportionality of the energy flows. Tritium breeding (discussed in Chapter 3) is excluded from this diagram for simplicity. tritium, and (4) a steam plant to convert fusion heat into electricity.4 A key goal for exploring the engineering feasibility of IFE will be to achieve reproducible gain at the required repetition rate. OVERALL POWER PLANT EFFICIENCY Although target gain can be used to validate the target physics, a new parameter ­ is required for assessing the viability of a fusion energy system. The so-called “engineering Q,” or “QE,” is often used as a figure of merit for a power plant. It represents the ratio of the total electrical power produced to the (recirculating) power required to run the plant—that is, the input to the driver and other aux- iliary systems. QE = 1/f, where f is the recycling power fraction (see Figure 1.3). Typically, QE ≥ 10 is required for a viable electrical power plant. For a power plant with a driver wall-plug efficiency ηD, target gain G, thermal-to-electrical conver- sion efficiency ηth, and blanket amplification AB,5 QE = ηthηDABG (see Figure 1.3). Achievable values of the blanket amplifications and thermal efficiency might be AB ~ 1.1 and ηth ~ 0.4 and should be largely independent of the driver. Therefore, 4  W. Meier, F. Najmabadi, J. Schmidt, and J. Sheffield, “Role of Fusion Energy in a Sustainable Global Energy Strategy,” 18th World Energy Congress, Buenos Aires, Argentina, March 7, 2001. Available at http://tinyurl.com/ck84fao. 5  Amplification, A , is the energy multiplier—a dimensionless number—on the total energy of B 14.1 MeV neutrons entering the blanket via nuclear reactions with the structural, coolant, and breeding material.

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18 An Assessment of the Prospects for Inertial Fusion Energy the required target gain is inversely proportional to the driver efficiency. For a power plant with a large recirculating power f = 20 percent (QE = 5), the required target gain is G = 75 for a 15 percent efficient driver, and G = 160 for a 7 percent efficient driver. There will likely be some shot-to-shot variation in target gain resulting from imperfect fabrication, variations in driver pulses, and fluctuations in beam align- ment. A power plant must even allow for the possibility of some complete duds. An important goal of the program will be to achieve very good reproducibility and to increase the average target gain as close as possible to the best achievable value (see Table 1.1). In this report, the gain values in various tables and milestones are understood to be average reproducible values. For example, where the report lists modest gain as a milestone, the intended meaning is average, reproducible modest gain. Similarly, the ignition milestone includes the requirement of some reproduc- ibility. Ignition on every shot is not likely, particularly initially, but to achieve the ignition milestone, ignition must be demonstrated in multiple cases. DRIVERS The driver is required to deliver megajoules of energy in a few nanoseconds— typically, a significant fraction of a petawatt of power. This energy must be delivered with an electrical efficiency ηD of around 10 percent or more. Four main systems are being studied as potential drivers of inertial fusion plants: diode-pumped, solid- state lasers (DPSSLs), krypton fluoride (KrF) gas lasers, heavy-ion beams from accelerators, and pulsed (electric) power drivers that are connected directly to a load that contains the target. See Chapter 2 for a full description of these options. TABLE 1.1  Some Reference Examples of Driver, Target, and Chamber Wall Options Electrical Efficiency Energy (MJ)/ Target Gain Chamber Driver ηD (%) Repetition Rate (Hz) Target Type G Wall DPSS laser 16 1.8-2.2/16 Indirect 60-90 Solid KrF laser 7 0.5-2.0/10 Direct 100-250 Solid Heavy ion 25-45 1.8-3.3/5 Indirect 90-130 Liquid Pulsed power 20-50 33/0.1 Magnetic direct ~300 Liquid NOTE: Many other examples are possible; their validation will require confirmation from the NIF or other experimental facilities. These figures represent values that are hoped to be achievable. It has not yet been demonstrated that these driver energies are sufficient to achieve ignition and the indicated gain with cur- rent implosion parameters. These examples used computations of different levels of sophistication. SOURCE: Presentations to the committee and their supporting papers.

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Introduction 19 TARGETS Current inertial confinement fusion (ICF) targets are made by hand, which is time consuming and expensive. For commercial viability, these high-precision targets must be mass-produced cheaply. Proposed targets vary, depending on the driver, from yields of ~100 MJ to 10 GJ, and the price required for commercial viability depends on many factors. To set the typical scale, consider a plant with a repetition rate of 10 targets per second and 1 GW electrical output; with typical thermal efficiencies, this would mean a target yield of approximately 250 MJ. The cost of targets will depend on many factors, including their materials, complexity, and yield. It is estimated that the fraction of the cost of electricity from an IFE power plant that the manufacturing of targets contributes will range from about 6 percent for the relatively simpler direct-drive laser targets to more than 30 per- cent for the more complex indirect-drive laser targets, with heavy-ion fusion and pulsed-power targets falling between these two.6,7,8 IFE target masses are small (usually less than 1 g) and the cost of materials is minimal unless gold or other expensive elements are used. Therefore, the challenge for IFE is the development of manufacturing techniques that can achieve the required cost and precision (see Chapter 3).9 For laser-driven fusion, targets come in two main categories: direct-drive targets, in which the driver energy is coupled directly into the target; and indirect- drive targets, in which the driver energy is used to make X-rays inside a cavity called a hohlraum that couple to the target (see Figure 1.4). For heavy-ion and pulsed-power fusion, the distinction between direct and indirect drive is not as clear, as discussed in more detail in Chapter 2. To provide the energy that heats the hot spot to initiate fusion burn, several variants—for example, fast ignition or shock ignition on the scheme depicted in Figure 1.1 have been proposed that may yield higher gain (see further discussion in Chapter 2). For pulsed-power fusion schemes, tens of millions of amperes of electrical current are pulsed through an assembly around the target. The magnetic pressure ­created by these currents compresses the target and drives the fusion (see Chapter 2). 6  This percentage includes the fusion fuel (target materials and fabrication costs), the tritium plant, and target injection and tracking. Most of the contribution comes from the target materials and fabrication. 7  T. Anklam, Lawrence Livermore National Laboratory, “LIFE Economics and Delivery Pathway,” Presentation to the committee on January 29, 2011. 8  D. Goodin, General Atomics, “Target Fabrication and Injection Challenges in Developing an IFE Reactor,” Presentation to the committee on January 29, 2011. 9  W. Meier, F. Najmabadi, J. Schmidt, and J. Sheffield, “Role of Fusion Energy in a Sustainable Global Energy Strategy,” 18th World Energy Congress, Buenos Aires, Argentina, March 7, 2001. Available at http://tinyurl.com/ck84fao.

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20 An Assessment of the Prospects for Inertial Fusion Energy FIGURE 1.4 Direct- and indirect-drive targets. Top: Direct-drive target: laser or ion beam shines directly onto the target. Bottom left: Ion beam indirect-drive target: ion beams shine on radiation convertor; X-rays (squiggly lines) from radiation convertors fill the inside of the hohlraum and heat the capsule. Bottom right: Laser beam indirect-drive target: laser beams shine on the inside of the hohlraum, creating X-rays (squiggly lines) inside the hohlraum that heat the capsule. SOURCE: DOE, Fusion Energy ­ ciences Committee, “Summary of Opportunities in the Fusion Energy Sciences S P ­ rogram, June 1999.” Available at http://tinyurl.com/c4yvffw. Some of the physics processes involved in ICF for energy applications have parallels with the processes that take place inside thermonuclear weapons, and for this reason most of the research into ICF in the United States has been funded by weapons programs. In modern thermonuclear weapons, a boosted fission device consisting of a plutonium shell containing deuterium and tritium is imploded by conventional explosives. The X-rays produced by the resulting reactions are used to compress a second component. This second component, the “secondary,” contains lithium deuteride. The neutrons produced by the reaction D + D are captured in the lithium, producing tritium. The equivalent of up to 60 million tons of high explosives has been released by this process. The IFE effort seeks to release this fusion energy by compression and heating of a small spherical target contain- ing fusion fuel, without the need for a fission trigger. Because of the parallels between ICF for energy applications and for weapons applications, concerns have been raised about whether pursuit of IFE around the world might facilitate the proliferation of nuclear weapons and expertise. This

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Introduction 21 important issue is discussed in the report of the Panel on the Assessment of Inertial Confinement Fusion (ICF) Targets (see Appendix H for that report’s Summary). CHAMBERS The fusion reaction yields kinetic energy, one-fifth of which is invested in a helium nucleus (alpha particle) and four-fifths in a neutron (see Appendix A). The alpha particle heats the fuel and supports the burn. Ultimately, however, the alpha energy is emitted as fast-charged particles and X-rays from the exploding capsule. The neutrons barely interact with the capsule and therefore deposit their energy in the chamber wall. Tritium will be bred by the capture of fusion neutrons in lithium—either in a flowing liquid wall of lithium, lithium-lead, or a lithium salt, or in a blanket that contains lithium as a liquid or solid. The energy of the neutrons, the lithium reactions, and the charged particles must all be collected in the chamber walls and used to power a turbine. The tritium must also be collected for use in new capsules. Making a reliable, long-lived chamber is challenging since the charged particles, target debris, and X-rays will erode the wall surface and the neutrons will embrittle and weaken the solid materials. Many concepts for chamber components have been considered in design studies, including (1) chambers with thick layers of liquid or granules, which protect the structural wall from neutrons, X-rays, charged particles and target debris; (2) first walls that are protected from X-rays and target debris by a thin liquid layer; and (3) dry wall chambers, which are filled with low-pressure gas to protect the first wall from X-rays and target debris. The last two types have structural first walls that must withstand the neutron flux.10 Although the specific issues for any particular chamber depend on the choice of driver and target, as well as the choice of wall protection concept, there is a set of challenges that is generic to all concepts: (1) wall protection; (2) chamber dynamics ­ and achievable clearing rate following capsule ignition and burn; (3) injection of targets into the chamber environment; (4) propagation of beams to the target; (5) entry of driver beams into the chamber and protection of the driver from dam- age; (6) coolant chemistry, corrosion, wetting, and tritium recovery; (7) neutron damage to solid materials; and (8) safety and environmental impacts of first wall, hohlraum, and coolant choices.11,12 10  C.Baker, University of California at San Diego, “Advances in Fusion Technology,” January 2000, Document UCSD-ENG-077. Available at http://aries.ucsd.edu/LIB/REPORT/UCSD-ENG/UCSD- ENG-077.pdf. 11  Ibid. 12  Items (4) and (5) do not apply to pulsed-power IFE.

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22 An Assessment of the Prospects for Inertial Fusion Energy Many of the issues for inertial fusion regarding materials, the technology of heat exchange, blankets, and tritium recovery are shared with magnetic confine- ment fusion. Indeed ITER13 will test breeding blanket modules for the first time. The ­balance-of-plant (see Chapter 3) will likely be similar to that of existing fission reactors. MAJOR CONCLUSIONS OF PREVIOUS STUDIES14 Over the past 25 years, several prominent studies have reported favorably on scientific progress toward ICF ignition and the prospects for IFE15 and have recom- mended that a modest, coordinated program should be initiated that is devoted to energy applications with some level of research on all of the components of an IFE system.16 The current designs for IFE plants have used best-guess cost estimates for com- ponents and targets.17 These estimates have provided cost numbers that could be competitive with other future energy sources if there are no major surprises in the physics and technology performance of IFE systems. Chapter 3 provides further discussion of these studies and the economic challenges associated with making IFE a practical energy source. 13  ITER is an international project to build an experimental magnetic confinement fusion reactor in the south of France. It is based on the tokamak concept. 14  See bibliography in Appendix E. 15  See, for example, Fusion Policy Advisory Committee (FPAC), 1990, Final Report, September; FEAC, Report of the Inertial Fusion Energy Review Panel: July 1996, Journal of Fusion Energy 18 (4) 1999; FESAC, 2004, A Plan for the Development of Fusion Energy, March. 16  FEAC, 1994, Panel 7 report on inertial fusion energy, Journal of Fusion Energy 13 (2/3); FESAC, 2004, Review of the Inertial Fusion Energy Research Program, March. 17  Examples of such estimates are contained in the following: T.M. Anklam, M. Dunne, W.R. Meier, S. Powers, and A.J. Simon, 2011, LIFE: The case for early commercialization of fusion energy, Fusion Science and Technology 60: 66; W.R. Meier, 2008, Systems modeling for a laser-driven IFE power plant using direct conversion, Journal of Physics Conference Series 112: 032036; S.S. Yu, W.R. Meier, R.P. Abbott, J.J. Barnard, T. Brown, D.A. Callahan, C. Debonnel, P. Heitzenroeder, J.F. Latkowski, B.G. Logan, S.J. Pemberton, P.F. Peterson, D.V. Rose, G-L. Sabbi, W.M. Sharp, and D.R. Welch, 2003, An updated point design for heavy ion fusion, Fusion Science and Technology 44: 266-273; W.R. Meier, 2006, Systems modeling for Z-IFE power plants, Fusion Engineering and Design 81: 1661; W.R. Meier, 1994, Osiris and SOMBRERO inertial fusion power plant designs—Summary, Conclusions and Recommendations, Fusion Engineering and Design 25: 145-157; L.M. Waganer, 1994, Innovation leads the way to attractive inertial fusion energy reactors—Prometheus-L and Prometheus-H, Fusion Engineering and Design 25: 125-143.

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Introduction 23 MAJOR U.S. RESEARCH PROGRAMS Inertial fusion energy research gained impetus in the United States following the end of underground nuclear weapons testing in the early 1990s. As a result, major research facilities were constructed to test the physics of target implosion in the laboratory. The work in ICF is funded by the National Nuclear Secu- rity Administration (NNSA) and involves the weapons laboratories—Lawrence L ­ ivermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL) and Sandia National Laboratories (SNL)—along with the Naval Research Labo- ratory (NRL) and a number of universities, notably the Laboratory for Laser Energetics (LLE) at the University of Rochester. The major facilities are the lasers NIF at LLNL, OMEGA at LLE, and NIKE at NRL, and the pulsed power system Z at SNL (Box 1.2). The weapons laboratories and a number of universities house smaller facilities. The heavy-ion fusion (HIF) program is undertaken by a Virtual National Laboratory consisting of Lawrence Berkeley National Laboratory (LBNL), LLNL, and the Princeton Plasma Physics Laboratory (PPPL); its present work is focused on high-energy-density physics. The magnetized target fusion approach (see Chapter 2) is studied by LANL and the Air Force. Sources of funding for IFE R&D have been diverse. They have included Labora- tory Directed Research and Development (LDRD) funds at NNSA laboratories—for example, Laser Inertial Fusion Energy (LIFE) and pulsed power approaches—direct funding through the Office of Fusion Energy Sciences—for example, heavy ion fusion, fast ignition, and magnetized target fusion—and congressionally mandated funding. Beginning in FY1999, Congress directed the initiation of the High Aver- age Power Laser (HAPL) program, to be sponsored by NNSA. The HAPL program was an integrated program to develop the science and technology for fusion energy using laser direct drive. Initially focused on the development of solid-state and KrF laser drivers, the program then expanded to address all of the key components of an IFE system, including target fabrication, target injection and engagement, chamber technologies and final optics, and tritium processing. The HAPL program was terminated after FY2009. MAJOR FOREIGN PROGRAMS A brief summary of the main foreign IFE programs is given below. A more detailed description can be found in Appendix F. • China. The present program is focused on the development of diode- pumped, solid-state lasers and fast ignition. The near-term goal is fusion ignition and plasma burning, to be achieved around 2020. China is also investigating the use of KrF lasers.

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24 An Assessment of the Prospects for Inertial Fusion Energy BOX 1.2 Major Inertial Confinement Fusion Facilities in the United States (A) Cutaway illustration of the NIF at LLNL. SOURCE: LLNL, Preparing for the X games of ­science, Science & Technology Review. Available at http://tinyurl.com/7d57jha. (B) Cutaway illustration of the OMEGA laser facility at the LLE at the University of Rochester. Available at http://tinyurl.com/d57ruq2. (C) The Z Pulsed Power Facility at SNL. Available at http://www.sandia.gov/z-machine/.

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Introduction 25 (D) The NIKE laser target chamber at the NRL. SOURCE: S. Obenschain, NRL, Presentation to the committee on January 29, 2011. (E) The Neutralized Drift Compression Experiment II (NDCX-II) at LBNL. SOURCE: Roy Kaltschmidt, LBNL. Available at http://tinyurl.com/8xz9kfw.

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26 An Assessment of the Prospects for Inertial Fusion Energy • Europe. The main European Union laser fusion research facilities are in France (the Laser Megajoule (LMJ), the Laboratoire pour l’Utilization des Lasers Intenses (Luli), and Petula); the Czech Republic (Prague Asterix Laser System (PALS)); and the United Kingdom (ORION, Vulcan). The high power laser energy research facility (HiPER) is a power plant study involving 12 countries, including Russia, and is led by the United Kingdom. Its goal is to develop a strategic route to laser fusion power production for Europe. Defining features of HiPER include the high repetition rate; the fact that it is system driven rather than physics driven; and the international, collaborative approach. The present design study envisages using DPSSLs, polar drive, shock ignition (possible test in LMJ at one-third of its maxi- mum energy delivery), and a dry wall with some protection. The start of reactor design is planned for 2026 and operation for 2036. Much of the design of European approaches to IFE is being done using DUED,18 a code developed in Italy, and MULTI,19 a code developed in Spain. • Germany. German laboratories are involved in HiPER. Heavy-ion fusion is studied at GSI-Darmstadt using RF-accelerators. • Japan. The main program is focused on DPSSLs and fast ignition with the facility FIREX-1 in operation and FIREX-2 in design. The main goal is for demonstration to begin in 2029. There is collaboration with European programs. A more modest heavy-ion fusion program is undertaken in universities. • Russia. Russia collaborates closely with Germany. The Institute for Theoret- ical and Experimental Physics’ terawatt accumulator (ITEP-TWAC) project will be the main test bed and is now under construction. Russia has recently announced a project to build a 2.8 MJ laser for ICF and weapons research. The Research Institute of Experimental Physics will develop the concept. STATEMENT OF TASK Recent scientific and technological progress in ICF, together with the campaign for achieving the important milestone of ignition on the NIF, motivated the DOE’s Office of the Under Secretary for Science to request that the National Research Council (NRC) undertake a study that assesses the prospects for IFE, and provides advice on the preparation of an R&D roadmap leading to an IFE demonstration 18  S. Atzeni, A. Schiavi, F. Califano, F. Cattani, F. Cornolti, D. Del Sarto, T.V. Liseykina, A. Macchi, and F. Pegoraro, 2005, Fluid and kinetic simulation of inertial confinement fusion plasmas, Proceedings of the Europhysics Conference on Computational Physics 2004 169: 153-159. 19 R. Ramis, R. Schmalz, and J. Meyer-ter-Vehn, 1988, MULTI—A computer code for one-dimensional multigroup radiation hydrodynamics, Computer Physics Communications 49 (3): 475-505.

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Introduction 27 plant. In response to this request, the NRC established the Committee on the P ­ rospects for Inertial Confinement Fusion Energy Systems; the committee mem- bership is provided in the front matter of this report. The statement of task for the study is as follows: The Committee will prepare a report that will: • Assess the prospects for generating power using inertial confinement fusion; • Identify scientific and engineering challenges, cost targets, and R&D objectives associ- ated with developing an IFE demonstration plant; and • Advise the U.S. Department of Energy on its development of an R&D roadmap aimed at creating a conceptual design for an inertial fusion energy demonstration plant. The Committee will also prepare an interim report to inform future year planning by the federal government. SCOPE AND COMMITTEE APPROACH The study committee, consisting of 22 members from many fields, published its interim report in 2012.20 Although the committee carried out its work in an unclassified environment, it was recognized that some of the research relevant to the prospects for IFE systems has been conducted under the auspices of the nation’s nuclear weapons program and has been classified. Therefore, the NRC established a separate Panel on the Assessment of Inertial Confinement Fusion (ICF) Targets to explore the extent to which past and ongoing classified research affects the prospects for practical inertial fusion energy systems. The panel was also tasked with the analysis of the nuclear proliferation risks associated with IFE. The panel’s statement of task is given in Appendix B. The panel on targets exchanged unclassified information informally with the committee in the course of the study process, and the committee was aware of its evolving conclusions. The unclassified version of the Summary from the panel’s report is included as Appendix H. The analysis in this report is based on the following: • Reviewing many past studies on inertial fusion energy systems (see Appen- dix E); • Receiving briefings on ongoing research related to IFE systems in the United States and around the world; 20  NRC, 2012, Interim Report—Status of the Study “Assessment of the Prospects for Inertial Fusion Energy,” The National Academies Press: Washington, D.C.

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28 An Assessment of the Prospects for Inertial Fusion Energy • Conducting site visits to major inertial confinement fusion facilities in the United States; and • Exploiting the expertise of its membership in key areas relating to inertial confinement fusion. The committee held seven meetings and four site visits at which presentations were invited from key researchers (both national and international) in the field, skeptics who question the current approaches, and independent experts in areas relevant to the commercialization of new technologies. At each meeting, there was also opportunity for public comment. Meeting agendas are given in Appendix C. During the course of the study, the committee consulted with most of the key individuals and laboratories at the forefront of IFE-related research. STRUCTURE OF THE REPORT Chapter 2 describes the status of the main approaches to driving the implo- sion of IFE targets as well as specific challenges that must be met in the near term, medium term, and far term to make the various drivers suitable for use in com- mercial IFE plants. The status and R&D challenges of the targets themselves, as well as those of the other components of an IFE plant, are discussed in Chapter 3, which also includes a discussion of economic considerations associated with the commercialization of IFE. Finally, Chapter 4 describes the committee’s proposed R&D roadmaps for various driver-target combinations in the form of branching decision trees leading to an IFE demonstration plant, as required in its statement of task. For each technological approach, the committee identifies a series of critical R&D objectives that must be met for that approach to be viable. If these objectives cannot be met, then other approaches will need to be considered.