4

A Roadmap for Inertial Fusion Energy

The statement of task for this study charged the committee to “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.” While crucial milestones such as ignition and reactor-scale gain have yet to be achieved, the committee judges that inertial fusion energy (IFE) has made sufficient progress that a roadmap can be usefully considered as part of planning for an IFE segment of the long-term U.S. energy portfolio (see Conclusion 1-1). This chapter will consider the status of the options that are discussed in the previous chapters and will develop an approach for a composite event-based roadmap.

The committee had extensive discussions about which type of roadmap for an IFE demonstration plant would best meet the needs of the Department of Energy (DOE) and its oversight committees and agencies. The classical approach to roadmapping is to develop time-based phases and budgetary levels required to complete each phase. The main advantage of this approach is that a timeline is set and the needed resources are delineated. However, for IFE, uncertainties in the pace of scientific understanding and technology development—and the vagaries of the budgeting process—make it difficult, if not impossible, to maintain a time-based roadmap. Thus, the committee decided that a milestone-based (in other words, event-based) roadmap would be most appropriate here.

In this chapter, the committee sets out the roadmapping approach that best fits the needs of DOE; considers the status of development of the IFE options (i.e., laser-, ion beams-, pulsed power-based, etc.); lists the critical milestones that each of the options must reach in order for development of that option to continue;



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4 A Roadmap for Inertial Fusion Energy The statement of task for this study charged the committee to “advise the U.S. Department of Energy on its development of an R&D roadmap aimed at creat- ing a conceptual design for an inertial fusion energy demonstration plant.” While crucial milestones such as ignition and reactor-scale gain have yet to be achieved, the committee judges that inertial fusion energy (IFE) has made sufficient progress that a roadmap can be usefully considered as part of planning for an IFE segment of the long-term U.S. energy portfolio (see Conclusion 1-1). This chapter will consider the status of the options that are discussed in the previous chapters and will develop an approach for a composite event-based roadmap. The committee had extensive discussions about which type of roadmap for an IFE demonstration plant would best meet the needs of the Department of Energy (DOE) and its oversight committees and agencies. The classical approach to roadmapping is to develop time-based phases and budgetary levels required to complete each phase. The main advantage of this approach is that a timeline is set and the needed resources are delineated. However, for IFE, uncertainties in the pace of scientific understanding and technology development—and the vagaries of the budgeting process—make it difficult, if not impossible, to maintain a time-based roadmap. Thus, the committee decided that a milestone-based (in other words, event-based) roadmap would be most appropriate here. In this chapter, the committee sets out the roadmapping approach that best fits the needs of DOE; considers the status of development of the IFE options (i.e., laser-, ion beams-, pulsed power-based, etc.); lists the critical milestones that each of the options must reach in order for development of that option to continue; 146

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A Roadmap for Inertial Fusion Energy 147 and then constructs the first element of an event-based roadmap—that portion leading to ignition. It also lays out a conceptual path for steps leading to success: i.e., the decision to proceed with the conceptual design of a demonstration plant (DEMO). A discussion of key terminology leading to a DEMO is given in Box 4.1. The DEMO, which will test many technologies together at or near full scale for the first time, will not be expected to work flawlessly as designed or even eco- nomically in its early stages. In fact, the DEMO should be designed for ease of retrofitting, and it will have extensive monitoring capabilities, which will increase BOX 4.1 Description of Programmatic Terms Used in This Chapter The committee decided that a milestone- or event-based roadmap is most appropriate for IFE because of the current stage of technical maturity. However, before describing this road mapping approach, a few definitions are needed. • Technology Application (TA). The committee has defined a technology application as a combination of a driver-target-chamber approach that has been discussed in the previous chapters and is included in this road mapping exercise because of its po- tential for success, scientific results to date, and level of development. For simplicity, we define three TAs based on the three main driver approaches: lasers, heavy ions, and pulsed-power. • Integrated Research Experiment (IRE): An IRE tests the simultaneous operation of sev- eral aspects of a fusion reactor, but not necessarily all of them. For example, a single laser driver module would be aimed at injected surrogate targets at a rate of up to a reactor’s repetition rate to test driver quality, target launching, tracking, and intercep- tion. Such facilities might be upgraded to include a few modules, for example, for undertaking scaled implosions for speeding up the testing of targets. For pulsed power, the equivalent would be demonstrating repetitive recyclable-transmission-line replace- ment at high power without arcing. • Fusion Test Facility (FTF): The FTF is a demonstration of repetitive deuterium-tritium (DT) target shots using reactor-scale driver energy that generates high gain for the relevant TA. An FTF may be used initially for demonstrations of gain at very low fre- quency, followed by an increasing repetition rate to within an order of magnitude of the repetition rate of a commercial power plant, accumulating a total number of shots exceeding, say, 106 per year, or perhaps 105 for pulsed power fusion (since pulsed- power would operate at a lower repetition rate and higher yield/target compared to other approaches). As experience is gained with a successful TA, the FTF might be used to accumulate operating experience with longer run times. • Demonstration reactor (DEMO): A demonstration reactor has to deliver enough electric power to the grid over 5 to 10 years to enable industry to judge the potential commer- cial viability of IFE through the conduct of reliability analyses, to establish reasonable cost estimates, and to assess safety sufficiently well to ensure that commitments could be made for construction and economical operation of commercial fusion power plants that must operate for more than 25 years.

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148 An Assessment of the Prospects for Inertial Fusion Energy its capital costs. Nevertheless, the DEMO will be built when technology is at such a level that a successful DEMO could provide the confidence needed for the private sector to take on IFE as a commercial product, albeit with some design modifica- tions and some initial government assistance. There is a continuum of technology levels between a Fusion Test Facility (FTF) and a DEMO, so a sufficiently com- plete set of driver, target, and chamber data leading straight to an early DEMO, by-passing an FTF, is not precluded but is highly unlikely. In addition, assuming that progress in one or more approaches to practical IFE can be realized, the organizational structure for conducting the research must be considered as well as the potential program costs. However, since IFE research is currently funded only at a low level and in diverse ways, the rate of progress will be limited until ignition and ignition with modest gain are attained. The event- based roadmap provided in this chapter uses these two events (ignition and modest gain) as early milestones that could trigger the creation of a robust IFE program. INTRODUCTION The development of any science- or technology-based roadmap requires that guidelines and criteria be established so that options are evaluated on a common and consistent basis. The committee believes that the guidelines detailed in the DOE Technology Readiness Assessment Guide1 are useful and appropriate for the development of an IFE roadmap, so the committee uses them here. Figure 4.1 shows the integration between technology development and project management. As can be seen from the chart, a conceptual design is created at the CD-0 point (yellow box) in a project. As suggested in DOE G 413.3-4A, a useful and recommended approach to assure that the various technical components are at a stage of technical maturity suitable to initiate the next phase in the program is used—the concept of “tech- nology readiness levels” (TRLs). The TRLs of the overall system as well as its com- ponents must be advanced and evaluated over time. Table 4.1 lists the nine TRLs discussed in the Guide, which contains more detailed descriptions of the TRLs. In keeping with the Guide, the committee has assumed that all necessary tech- nology options and their components must have met the criteria of TRL 6 for DOE to initiate the conceptual design for an IFE DEMO. Development activities and test facilities, including major test facilities such as integrated test facilities (IREs) and an FTF, as defined in Box 4.1, will help to advance the TRLs of components necessary for DEMO. However, the components of an IRE and an FTF must also 1  U.S. Department of Energy, Technology Readiness Assessment Guide, DOE G 413.3-4A, October 12, 2009. Available at http://tinyurl.com/84qk6qw.

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A Roadmap for Inertial Fusion Energy 149 FIGURE 4.1  Process and performance requirements to support plant startup, commissioning, and operations. SOURCE: DOE Technology Readiness Assessment Guide. TABLE 4.1  Technology Readiness Levels Basic Technology Research   TRL 1: Basic principles observed and reported   TRL 2: Technology concept/application formulated Research to Prove Feasibility   TRL 3: Proof of concept Technology Development   TRL 4: Validation in laboratory environment   TRL 5: Integrated component validation in laboratory Technology Demonstration   TRL 6: Engineering/pilot scale validation System Commissioning   TRL 7: Prototypical system demonstration   TRL 8: System qualified through test and demonstration System Operations   TRL 9: Full range of actual system operations

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150 An Assessment of the Prospects for Inertial Fusion Energy have reached certain TRLs in order for those facilities to be built. The TRLs for each IFE option are summarized in the later section “TRLs for Inertial Fusion Energy.” TECHNOLOGY APPLICATIONS There are many possible combinations of drivers, targets and chambers that could be considered as technology applications (TAs). As mentioned above, the committee has defined three TAs based on the three main driver approaches: lasers, pulsed power, and heavy ions. These three TAs cover the main options for targets, drivers, and chambers, and simplify the task of planning an event-based roadmap. For example, the heavy-ion fusion plan would require the research needed to select between radio-frequency and induction accelerators and an approach to target design. Similarly, the laser TA would have to consider the research needed to decide between diode pumped solid state laser (DPSSL) and KrF laser drivers and between direct and indirect drive. The focus is on the research needed to make decisions and to optimize progress rather than to sustain a particular TA as long as possible. Thus, eventually, either a single TA would be taken to the DEMO stage or no TA would be judged to be both technically feasible and economically viable. For each TA, the driver is the most expensive component in the power plant. In all three cases, the driver will consist of a large number of modules. As discussed in Chapter 2, good progress has been made in developing the repetitively pulsed systems required for fusion energy. Nevertheless, there remain substantial chal- lenges in developing systems that would have the reliability, maintainability, and availability to provide between 3 × 106 and 4 × 108 shots per year, depending on the driver. As concluded in Chapter 2, it will be necessary to build and demonstrate each multikilojoule module early in the program. Recommendation 4-1: When a technical approach is chosen, high priority should be given to the design and construction of a driver module and to demonstrating that the individual driver module meets its specifications so that when aggregated into a complete system, the appropriate gain can be achieved. Institutional competition has been important in driving innovation in IFE, as it has been in many fields. At this point in time, however, the IFE community would benefit from greater cooperation and integration. A recent white paper developed by the IFE community reached the same conclusion.2 Without a coordinated 2  M. Hockaday, N. Alexander, S. Batha, M. Cuneo, M. Dunne, G. Logan, D. Meyerhofer, A. Nikroo, S. Obenshain, D. Rej, and J. Sethian, “White Paper Compilation on Inertial Fusion Energy (IFE) Development,” March 30, 2011.

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A Roadmap for Inertial Fusion Energy 151 approach to IFE, it will be difficult for the nation to make informed decisions using reliable cost estimates and confidence levels. Within heavy-ion fusion, there is almost no difference in the research programs needed for direct drive and indirect drive in the near term. The beam require- ments for the two options are sufficiently similar that it is not necessary to split the approaches into two TAs. At some point in the future, however, there is a key choice to be made between these two options. The existence of a Virtual National Laboratory for HIF has facilitated thinking about the program as a single TA. The multiple institutions involved in heavy-ion fusion research work together closely, and no institution is threatened when a major decision is made. There are enough internal advocates of various approaches to maintain innovation, but DOE should monitor this to assure that innovation remains active. In contrast, the competition between the various approaches for laser-driven, heavy-ion-driven, and pulsed-power-driven fusion is led by institutions, each of which advocates a different approach. The IFE effort would benefit greatly from a joint plan together with an approach to program governance that can make difficult decisions but is able to retain the strengths of all the institutions. Virtual laboratories could well serve the decision analysis required to advance IFE research. Two examples of such virtual laboratories are given in Box 4.2. A virtual laboratory can facilitate difficult decisions involving programmatic direction. For example, LLNL began building a small recirculating induction accel- erator while LBNL was working on the more standard linear induction accelerator. It became apparent that one could not sensibly carry out both approaches with BOX 4.2 Virtual Laboratories The Virtual Laboratory for Technology (VLT) was created in 1999 by DOE’s Office of F ­ usion Energy Sciences (OFES) to coordinate and represent all magnetic fusion technology a ­ ctivities funded by OFES. It is an on-going national activity. The scope of activities includes or has included plasma heating and fueling technologies, magnet systems, plasma facing com- ponents, fusion nuclear technologies including tritium-breeding blankets, fusion safety analysis, research on advanced materials, and fusion systems studies and analysis. A wide variety of national laboratories, universities, and industry are or have been members of the VLT. The Heavy-Ion Fusion Virtual Laboratory (HIF-VL) was created in the mid-1990s. It was created with a formal agreement among LLNL, LBNL, and the Princeton Plasma Physics Labora- tory (PPPL). The director of the HIF-VL has been from LBNL since LBNL has the largest program of the three laboratories. The two deputy directors are from LLNL and PPPL. Their meetings and seminars are frequent and are handled by teleconference. LLNL representatives have offices at LBNL, which also facilitates communication.

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152 An Assessment of the Prospects for Inertial Fusion Energy realistic budgets, so a choice between the two was necessary. The laboratories had the requisite expertise to make a technical decision, but DOE did not, so the HIF-VL took the lead and a decision was reached. An analogous situation for lasers would be a choice between the KrF and DPSSL laser, for example. If there is not enough funding to pursue both options, a choice will have to be made. A virtual laboratory can help keep the discussion of technical decisions at the technical level and avoids nontechnical considerations that can prevent optimal decisions from being reached. Conclusion 4-1: The focus of any formal inertial fusion energy program would be best served if the program were organized according to the three Technical Applications (TAs): laser systems, heavy-ion systems, and pulsed power systems. To accomplish this organization, several actions are recommended. Recommendation 4-2: The national inertial fusion energy program should be organized according to three technical applications: laser systems, heavy- ion systems, and pulsed power systems. Recommendation 4-3: The Department of Energy should consider the estab- lishment of virtual laboratories for each technical application with sufficient internal expertise for the various approaches to advance technically and maintain innovation. EVENT-BASED ROADMAPS In Chapters 2 and 3 the committee discussed the status of the driver options, including the targets and various fusion technologies, for each approach under consideration for IFE. In doing so, it came to several general conclusions that help govern the development of a composite roadmap. In Chapter 2 the committee came to some general conclusions: • There are a number of technical approaches, each involving a different combination of driver, target, and chamber, that show promise for lead- ing to a viable IFE power plant. These approaches involve three kinds of targets: indirect drive, direct drive, and magnetized target. In addition, the chamber may have a solid or a thick-liquid first wall that faces the fusion fuel explosion. • Substantial progress has been made in the last 10 years in advancing most of the elements of these approaches, despite erratic funding for some

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A Roadmap for Inertial Fusion Energy 153 programs. Nonetheless, a substantial amount of R&D will be required to show that any particular combination of driver, target, and chamber would meet the requirements for a demonstration power plant. • In all cases, the drivers may build on decades of research in their area. In all technical approaches there is the need to build a reactor-scale driver module for use in an FTF. Similarly, the committee stated three general conclusions in Chapter 3. First, it said that technology issues—e.g., chamber materials damage, target fabrication, and injection, etc.—can have major impacts on the basic feasibility and attractiveness of IFE and thus on the direction of IFE development. Next, it concluded that at this time, there appear to be no insurmountable IFE fusion technology barriers to the realization of the components of an IFE system, although knowledge gaps and large performance uncertainties remain, including for the performance of the system as a whole. And finally it determined that significant IFE technology research and engi- neering efforts are required to identify and develop solutions for critical technology issues and systems, such as: targets and target systems; reaction chambers (first wall/ blanket/shield); materials development; tritium production, recovery and manage- ment systems; environment and safety protection systems; and economics analysis. Thus, each of the three TAs, as the committee has defined it above, has to achieve certain significant milestones, or events (e.g., ignition) before it can logi- cally move on to the next step. What is needed is a scientific understanding of gain and target design for robust operation—not just gain. For example, (1) ignition, (2) reactor-scale gain, (3) reactor-scale gain with potential cost-effective targets, and (4) reactor-scale gain at high repetition rate are examples of milestone events that must be satisfactorily achieved before going on to the next step: Interval 1 Interval 2 Interval 3 Interval n Interval n + 1 ----------(event)----------(event)----------(event)--//-------(event)---------DEMO For each interval one needs to consider the following: • Significant development(s) required, • Potential scientific and technological roadblocks, • Required facilities, existing or new (if a new facility is needed, one must indicate when it needs to be started (CD-0) (see Figure 4-1), • Synergies with the magnetic fusion energy (MFE) program, and • Estimated costs to accomplish activities in each interval. The significant events that are listed above are target- and driver-centric because ignition has not yet been achieved in ICF, but target and driver concerns

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154 An Assessment of the Prospects for Inertial Fusion Energy are not the only issues facing inertial fusion. Chambers (materials) that survive and that are economical must also be found. For laser-driven systems, optics that survive and retain their optical quality for a long time in an adverse environment must exist. The drivers not only must achieve the desired repetition rate, but also must achieve durability and reliability objectives. The cost of the drivers must be acceptable. A given TA could march relatively easily through a given set of signifi- cant science-based events but still fail as a power plant because of technology and economic considerations. Each TA will require years of research and development before a DEMO can be designed in any detail. No TA has yet demonstrated fusion gain, reactor-level driver energy at repetition rate, or chamber life.3 In summary, the following criteria (events) must all be satisfied before com- mitting to a DEMO. 1. First and foremost, ignition must be demonstrated. Absent ignition, any IFE program will be severely limited in scope. 2. Modest (or adequate) gain must be demonstrated to a level relevant to the TA4 in question to ensure that the TA has a feasible technical approach to achieving high gain. 3. Target gain must be demonstrated at the relevant high level, which varies with each TA, depending on the driver efficiency. One guideline, based on basic power balance considerations, is that the product of driver efficiency times the gain should be greater than or equal to 10. Obviously, having a margin on this requirement would be an advantage. Table 4.2 contains estimates of driver efficiency—supported by component and subsystem tests—and goals for reactor-scale gain that are supported by theoretical modeling and computer simulations for the various approaches. 4. Driver life at energies corresponding to the reactor-scale gain level must be demonstrated to >107 pulses (except pulsed power, which must be demon- strated to >106 pulses) and must extend in predictable ways to 100 times greater than 107 (or 106) pulses before commitment to an FTF or DEMO. 5. Target fabrication for each TA has to be automated at a level related to the target consumption in the FTF and must extend predictably to the DEMO consumption level at costs consistent with a competitive cost of electricity. 3  Appendix J indicates the steps required for each TA to reach the starting point of the DEMO conceptual design. The specific steps are meant to be illustrative of the conditional requirements that DOE should set down in its planning process—requirements that should be regularly updated based on scientific and technological progress. 4  The relevant gain varies with each technical approach and depends on the driver’s efficiency. See Table 4.2.

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A Roadmap for Inertial Fusion Energy 155 TABLE 4.2  Driver Efficiencies and Minimum Gains That Will Be Required to Demonstrate the Viability of Reactors Based on Various Driver Technologies Estimated Driver Reactor-Scale Gain Technology Approach Efficiency ηD (%) ηD × G > 10 Solid-state lasers 16 >60 KrF lasers ~7 >140 Heavy-ion beams 25-45 20-40 Pulsed power 20-50 20-50 NOTE: The numbers in this table are only illustrative and are not meant to be definitive. 6. Chamber design, including neutron shielding, tritium breeding, and mate- rials survival, has to be sufficiently developed to generate a high probability of successful operation for multiple years. It is not possible to fully test the chamber design under fusion conditions short of executing an FTF or a DEMO. One of the strongest reasons for an FTF to precede a DEMO is to validate the chamber design. The most appropriate ordering of the milestones in a roadmap will differ for different driver/target combinations. Conclusion 4-2: Despite the significant advances in inertial confinement fusion, many of the technologies needed for an integrated inertial fusion energy system are still at an early stage of technological maturity. For all approaches to inertial fusion energy examined by the committee (diode- pumped lasers, krypton fluoride lasers, heavy-ion accelerators, pulsed power; indirect drive and direct drive), there remain critical scientific and engineering challenges associated with establishing the technical basis for an inertial fusion energy demonstration plant. It would be premature at the present time to choose a particular driver approach as the preferred option for an inertial fusion energy demonstration plant. It is clear that reactor-scale gain must be uniquely defined for each TA since the understanding of gain involves laser-plasma interaction physics, hohlraum physics (for indirect drive only), ablation physics, instabilities and mix, symmetry control, equations of state, real-world fabrication and alignment tolerances, and temperature control. Conclusion 4-3: Owing to the technical complexity, the specific definitions of modest (or adequate) and high gain should be determined independently for each technology application.

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156 An Assessment of the Prospects for Inertial Fusion Energy COMPOSITE ROADMAP AND DECISION ANALYSIS FOR THE PRE-IGNITION STAGE Given that there are many variables and options to consider before being able to proceed with the conceptual design for a DEMO plant, the committee believes it would be most useful to focus on the earliest stage—namely, pre-ignition—by add- ing a decision-tree analysis to only this first phase of the roadmap.5 The immediate future is the most clear, and it is also the most critical time for IFE as the National Nuclear Security Administration (NNSA) program strives to demonstrate igni- tion. Accordingly, the committee’s analysis was based on the effort at the National Ignition Facility (NIF) in 2011-2012 to achieve ignition under the National Igni- tion Campaign (NIC). Pre-ignition contingency planning was considered in more detail, but the details have not been included here because events and NNSA’s path forward have changed the basis for such a plan; however, the committee believes that event-based, decision-tree analysis (contingency planning) is important for a complex, multifaceted program such as IFE.6 ICF research has been driven by NNSA for stockpile stewardship requirements. The decision to build the NIF, which is designed to operate in single-shot mode and is not currently equipped to serve as a test facility for repetition-rated operation or engineering tests for IFE, was based upon those requirements. NIF conducted the NIC with the end objective being ignition by the end of FY2012, Having reached the end of the NIC campaign on September 30, 2012, without achieving ignition, NNSA decided to revise the operational program for NIF.7 Given the substantial investment already made in the NIF, from the NNSA per- spective, laser indirect-drive is the preferred approach for stockpile stewardship if ignition with sufficient yield for the desired experiments can be achieved. When one considers the application of ICF for the production of practical electric power in the 5  C.B. Chapman and S. Ward, 2003, Project Risk Management: Processes, Techniques, and Insights, 2nd ed., Hoboken, N.J.: Wiley. 6  To assist in its thinking about pre-ignition contingency planning across TAs, the committee prepared several detailed hypothetical examples. The common elements are included in the text. 7  On December 8, 2012, NNSA released its report to Congress, “NNSA’s Path Forward to Achieving Ignition in the Inertial Confinement Fusion Program” (hereinafter referred to as “NNSA Path Forward 2012 Report to Congress”). This report represents the views of the NNSA and was prepared princi- pally by program representatives from the ICF laboratories and other principal contractors through participation in various working groups. The NNSA report proposes a time-based (3-year) plan. The report describes the path forward for NIF as requiring a transition from the NIC to a facility with greater focus on the broader scientific applications of NIF and a priority on key questions regarding stockpile stewardship. For IFE pre-ignition efforts, the approach advocated by the NRC Commit- tee on the Prospects for Inertial Confinement Fusion Energy Systems is event-based (as opposed to time-based) and thus might not be limited to 3 years, and might include TAs not considered in the NNSA’s 3-year plan.

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160 An Assessment of the Prospects for Inertial Fusion Energy the next step. Again, a spherical direct drive system would not rule out continuing tests with indirect drive by using approximately two-thirds of the beams. If both the laser-indirect and laser-direct drive approaches continue to experi- ence difficulty reaching ignition over the next 5 or so years, then it would be justified to put more resources to the MagLIF and HIF approaches. Depending on the reasons for the failure of the laser-based approach—e.g., laser plasma ­instabilities—it might also be appropriate to consider alternate laser driver approaches. DOE support for reactor design studies of ideas using these drivers is important, including partici- pation by groups that are not advocates. Viable reactor designs would be required before there is a substantial ramping up of such approaches. These design studies should help guide the related decisions. Recommendation 4-6: Although ignition was not achieved at the National Ignition Facility by the end of FY2012 as planned, efforts to achieve igni- tion with indirect drive should not cease. Contingent on the availability of funds and Department of Energy priorities, these efforts should continue at least until new configurations (e.g., polar direct drive) can be tested on the National Ignition Facility, which would require at least 4 years of devel- opment. However, under this scenario, a commitment should be made to undertake pretesting of polar direct drive on the National Ignition Facility and, if the pretests are successful, prepare NIF to test polar direct drive. Even if ignition should be reached with indirect drive before polar direct drive becomes operational, the funding for direct drive will still have been well spent, for it is desirable to test polar direct drive in the hope of getting a higher gain (with the same drive energy) than may be possible with indirect drive. (A technical discussion of direct and indirect drive is given in Chapter 2.) As discussed in Chapter 2, the energy required to achieve ignition in laser- based indirect and direct drive approaches favors direct drive. Moreover, for a fixed laser energy, the calculated gain is higher for direct drive. Nevertheless, there are important uncertainties in laser-plasma physics and implosion dynamics that must be addressed for fusion-scale targets, particularly for shock ignition. The NIF is currently a unique tool for addressing these issues, some of which could be addressed with NIF in its present configuration. Others may require modifica- tions such as improvements in beam smoothness, or ultimately even a different illumination geometry. Conclusion 4-5: Each target design and each driver approach has potential advantages and uncertainties to the extent that “the best driver approach” remains an open question.

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A Roadmap for Inertial Fusion Energy 161 Recommendation 4-7: The achievement of ignition with laser-indirect drive at the National Ignition Facility should not preclude experiments to test the feasibility of laser-direct drive. Direct drive experiments should also be carried out because of their potential for achieving higher gain and/or other technological advantages. Conclusion 4-6: It is essential for the IFE program to develop reliable ­models and improve the physics understanding of the phenomena underlying experi- mental tests of the target physics. Knowledge gained through experimental tests should be used to validate and improve the models, so that there can be reasonable confidence that the predictions are not restricted to the parameter ­ space explored in the experimental tests. Models will be important for opti- mizing designs from both a technological and economic perspective. Conclusion 4-7: Achieving higher gains has the potential to provide improved technical margins and potential economic advantages for the system as a whole. If calculations are confirmed, fewer targets would be needed to pro- duce a given amount of power, or the driver repetition rate or driver energy could be reduced, thereby reducing costs. TRLs FOR INERTIAL FUSION ENERGY An important question is which facilities will need to be built to successfully reach the goals of the IFE program. Table 4.3 is based on the data provided in the discussions in Chapters 2 and 3 on the TAs respecting what has been done and what is under way in IFE, as well as what the magnetic fusion energy program provides and what needs to be done to reach the conceptual design stage of DEMO and commercial deployment of IFE. In addition to a number of smaller test facilities (i.e., IREs), it assumes that there will be an additional two major facilities: (1) a Fusion Test Facility (FTF), a staged facility with repetitively targeted deuterium- tritium (DT), high-gain capsules that would bring all aspects of the technology of IFE up to TRL 6 using a prototypical driver that would be determined by the IFE program, and (2) the end point of the IFE development program, DEMO, which would complete the TRL process. As shown in Table 4.3, NIF and FTF are absolutely critical to move the TAs and their technological components from TRLs of 4 or less to 6 for the CD-0 DEMO decision process. Note also that it has been assumed in Table 4.3 that certain tech- nologies (e.g., materials, handling) will be developed, at least in part, using existing MFE facilities, as described in Chapter 3.

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162 An Assessment of the Prospects for Inertial Fusion Energy TABLE 4.3  Facilities and Efforts Required to Advance Fusion Energy Technologies to Various Technology Readiness Levels (TRLs) TRL Area 1 2 3 4 5 6 7 8 9 Target physics Weapons, NIF FTF DEMO OMEGA, etc. Target manufacture GA work, HAPL NIF ATFF/FTF DEMO Driversa Depends on system FTF DEMO Controlb HAPL NIF FTF DEMO Diagnostics OMEGA, etc. NIF FTF DEMO Materialsc MFE IFMIF FTF DEMO Tritium breed MFE, lab tests liquids ITER FTF DEMO Tritium system JET, TFTR, TSTA ITER FTF DEMO Power handling ITER, FTF DEMO Remote handling JET ITER, FTF DEMO Reliability FTF DEMO Availability FTF DEMO Safety NIF ITER, FTF DEMO Waste handling TFTR, JET, fission facilities, ITER, FTF FTF DEMO NOTE: NIF, National Ignition Facility; FTF, Fusion Test Facility; DEMO, Demonstration Power Plant; HAPL, High Average Power Laser program; GA, General Atomics; ATFF, Automated Target Fabrication Facility; MFE, magnetic fusion energy; IFMIF, International Fusion Materials Irradiation Facility; ITER, International Thermonuclear Experimental Reactor; JET, Joint European Tokamak; TFTR, Tokamak Fusion Test Reactor; and TSTA, Tritium System Test Assembly. a The various drivers are at different TRLs in FY2012. For example: NIF single-shot laser, TRL 9; Repeti- tion rate of IFE solid state lasers, TRL 4; Heavy-ion beams: TRL 3 to TRL 6, if existing but different accel- erators are taken into account; Pulsed power, TRL 5. b Present targets are fixed. Repetitive targeting of DT targets on the fly will have to wait for FTF. c The answer depends on which type of first wall is considered—thick liquid wall, thin liquid wall, or solid wall. Conclusion 4-8: There are several technology development areas in which there is overlap and/or synergy between magnetic fusion energy (MFE) and inertial fusion energy (IFE). Recommendation 4-8: The overlap and synergies that exist between MFE and IFE technology development areas should be exploited. The Department of Energy should assure that the research program plans for IFE and MFE are coordinated and that the research results are fully shared between the two programs.

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A Roadmap for Inertial Fusion Energy 163 COST AND FUNDING CONSIDERATIONS The further one looks into the future, the more difficult it is to estimate what the appropriate budget levels should be. Not only are there variables in the budget­ng process, there are also uncertainties as to the probability of achieving i the research objectives and milestones identified in this report as well as to the length of time needed to achieve them. What makes planning particularly difficult is the fact that three competitive approaches exist, and, ultimately, only one can be selected as the TA for the DEMO. Research in ICF is currently funded largely by NNSA and involves the weapons laboratories (LLNL, LANL, SNL), NRL, and a number of university-managed labo- ratories, most notably the Laboratory for Laser Energetics (LLE) at the University of Rochester and LBNL. The major experimental facilities are the laser facilities NIF (at LLNL), OMEGA (at LLE) and NIKE (at NRL), and the pulsed power system Z at SNL. The weapons laboratories and a number of universities house smaller facilities. A Virtual National Laboratory for Heavy Ion Fusion Science consisting of LBNL, LLNL, and the Princeton Plasma Physics Laboratory undertakes the heavy- ion fusion program; its present work is focused on high-energy-density physics and heavy ion fusion science and is funded by DOE’s Office of Fusion Energy Sciences. The magnetized target fusion approach is studied by LANL and the Air Force Research Laboratory.11 Previous funding sources for IFE R&D have been diverse and have included Laboratory Directed Research and Development (LDRD) funds at the NNSA laboratories—for example, Laser Inertial Fusion Energy (LIFE) and pulsed power approaches—direct funding through the Office of Fusion Energy Sciences (e.g., heavy ion fusion, fast ignition, and magnetized target fusion), and congressionally- mandated funding. Beginning in FY1999, Congress directed the initiation of the HAPL program, to be managed 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, HAPL then expanded to address all of the key components of an IFE system, includ- ing target fabrication, target injection and engagement, chamber technologies and final optics, and tritium processing. Currently, by far the largest support for ICF comes under the NNSA Stockpile Stewardship program, which supports LLNL’s activities (including NIF), the pro- gram on the OMEGA laser at the University of Rochester, the use of KrF lasers at NRL, and Sandia’s pulsed-power efforts on the Z facility. Within this NNSA pro- gram, the main focus was the NIC at NIF. The NIC carried out a 200-shot program on the NIF managed by LLNL. The sequence of shots was focused on a stepwise 11  See Chapter 2 for more discussion on the activities at these institutions.

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164 An Assessment of the Prospects for Inertial Fusion Energy progression in driver beam power and intensity, including shock timing, optical focus, mix, and target-hohlraum geometries. The schedule called for the 200-shot NIC program to culminate in ignition by the end of FY 2012. As discussed in Box 1.2 and Appendix I, ignition was not achieved by the end of the NIC. Conclusion 4-9: While there have been diverse past and ongoing research efforts sponsored by various agencies and funding mechanisms that are rel- evant to IFE, at the present time there is no nationally coordinated research and development program in the United States aimed at the development of inertial fusion energy that incorporates the spectrum of driver approaches (diode-pumped lasers, heavy ions, krypton fluoride (KrF) lasers, pulsed power, or other concepts), the spectrum of target designs, or any of the unique technologies needed to extract energy from any of the variety of driver and target options. Conclusion 4-10: Funding for inertial confinement fusion is largely moti- vated by the U.S. nuclear weapons program, due to its relevance to steward- ship of the nuclear stockpile. The National Nuclear Security Administration (NNSA) does not have an energy mission and—in the event that ignition is achieved—the NNSA and inertial fusion energy (IFE) research efforts will continue to diverge as technologies relevant to IFE (e.g., high-repetition- rate driver modules, chamber materials, mass-producible targets) begin to receive a higher priority in the IFE program. The largest technology component of the NNSA stockpile stewardship budget deals with target physics. Based on information provided to the committee, this support appears to be around $260 million per year.12 At this stage the objectives for target physics of the NNSA’s ICF program are relevant to the inertial fusion energy program. While NNSA will continue to have an interest in target physics research after ignition is achieved, it will become less critical to meeting national security objectives, and there will be less overlap with the needs of IFE. For example, an IFE target may need to have a higher yield than NNSA would normally be interested in, and NNSA might not be interested generally in certain approaches. Accordingly, NNSA is unlikely to undertake technology research that is relevant only to fusion energy (e.g., chambers). Conclusion 4-11: If a coordinated national program in inertial fusion energy is established, one of the first orders of business will be to resolve responsibility 12 Jeffrey Quintenz, “Status of the National Ignition Campaign and Plans Post-FY 2012,” Presenta- tion to the committee on February 22, 2012.

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A Roadmap for Inertial Fusion Energy 165 and budgeting for target physics work, understanding that the needs for the inertial fusion energy program diverges from those for stockpile stewardship. While existing NNSA facilities (NIF, Z, OMEGA) are critical to the IFE effort, this report notes that, in order to reach the CD-0 stage for a DEMO plant, other facilities will need to be built, and these, in turn, must also go through the various project phases and decisions (CD-0 through CD-4). The largest and most impor- tant precursor facility for IFE is an FTF. As evident from the preceding discussion, the design of the FTF should begin at a propitious time in order to start tritium operations of the FTF in a timely manner and to have data for input to the DEMO project decision process. Conclusion 4-12: Existing facilities (NIF, Z, OMEGA, NDCX-II, HCX, NIKE, and Electra) will play critical roles in advancing the technical applications and their technological components from technical readiness levels (TRLs) of 4 or less to TRL 6 for the CD-0 demonstration plant (DEMO) decision pro- cess. In addition, to have a successful national IFE program, adequate funds are required to implement one or more integrated research experiments, at least one Fusion Test Facility, and the upfront costs for the DEMO design. Table 4.4, based on the inputs to Chapters 2 and 3 and the above considerations, provides a rough outline of the near-term programmatic funding requirements if an IFE program were to proceed in a two-step ramping process with annual budgets of at least $50 million after ignition is attained and some $90 million-$150 mil- lion after ignition plus modest gain has been demonstrated. Table 4.5 contains an order-of-­ agnitude estimate of future minimum capital cost requirements for an m IFE program. It is difficult to provide an overall programmatic cost estimate since there are several significant uncertainties that have to be resolved, such as the length of time required to reach the decision on DEMO, the ability to successfully complete milestones in a timely fashion, the extent to which each TA will be pursued, the number of IREs that will be required, and whether more than one FTF will be built. In 2003, the Fusion Energy Sciences Advisory Committee (FESAC) made a combined magnetic fusion energy and inertial fusion energy programmatic cost estimate.13 Based upon that report and the LIFE point design forecast,14 the com- mittee’s order-of-magnitude estimates for facility capital costs, subject to the DOE G 413.3-4 process, are provided in Table 4.5. 13  FESAC, Fusion Development Panel, 2003, A Plan for the Development of Fusion Energy, March. 14  T. Anklam, M. Dunne, W.R. Meier, S. Powers, A.J. Simon, LIFE: The case for early commercializa- tion of fusion energy, Fusion Science and Technology, 60: 66-71.

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166 An Assessment of the Prospects for Inertial Fusion Energy TABLE 4.4  Estimated Near-Term Inertial Fusion Energy Roadmap Development Cost Forecast, After Ignitiona Annual Budget (millions of 2012$) Technology Application Post-Ignition Post-Ignition/Modest Gain DPSSL/KrF lasersb 20-30c 40-60d,e HIF ~10 20-30 Pulsed power ~10 10-20 Technology development 10-20 20-40 Totals 50-70 90-150 a The values given are capital and development costs and do not include operating costs. b Michael Dunne, LLNL, Presentation to the committee on February 22, 2012, and subsequent communications. c Ibid. d Ibid. e This is the estimated annual cost over 3 years to build and commission the single beam line laser source for LIFE. TABLE 4.5  Estimated Inertial Fusion Energy Roadmap Facility Capital Cost Forecast (millions of dollars)a,b,c Facility Cost NIF upgrade (polar drive) 50-60d,e NIF upgrade (spherical drive)f Unknowng IRE 300-775 FTF 3,100-4,750 DEMO 6,250-9,500 a All values include a 25 percent contingency. b All numbers have been escalated from 2002$ to 2012$ using the Office of Management and Budget’s GDP (Chained) Price Index (estimate for 2012), except for the NIF upgrade (polar drive), which is given in as-spent dollars. c All costs are capital costs and are subject to the DOE G 413.3-4 process. d Cost for the procurement of unique hardware, optics, and controls systems. e LLNL, 2012, “Polar Drive Ignition Campaign Conceptual Design,” LLNL TR-553311, submitted to NNSA in April 2012 by LLNL and revised and submitted to NNSA by LLE in September 2012. f If needed to obtain high gain. Some of this cost might be covered as part of the stockpile stewardship program if sufficient gain is not obtained with indirect drive. g The committee is unaware of any detailed cost estimate for this upgrade. The cost would depend on the options chosen. For instance, if it was deemed desirable to retain both spherical and polar drive capability (by adding an equatorial beam), the committee assumes the cost would be in the hundreds of millions of dollars. On the other hand, repositioning the existing beams would presumably cost much less but would narrow the options available to researchers.

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A Roadmap for Inertial Fusion Energy 167 The reader should note that the capital cost estimates presented in Tables 4.4 and 4.5 are early-stage estimates and that such estimates for future technology facilities often prove to be underestimates. THE NEED FOR A NATIONAL INERTIAL FUSION ENERGY R&D PROGRAM In addition to target science, there are other deep science issues embedded in what is usually labeled “technology” (e.g., chambers) involving a broad range of scientific disciplines, including nuclear and atomic physics, materials and surface science, and engineering science.  In the next several years, the IFE program will probably not be involved in engineering development but rather in science and engineering research aimed at determining if feasible solutions exist to the very challenging problems. An organized program that encompasses all technology options most effec- tively determines the roadmap to an IFE DEMO plant. Only such a program will have a broad enough view to ultimately identify the most promising IFE DEMO design(s). The committee recognizes how challenging and complex the unresolved issues are and how much remains to be accomplished and understood if IFE is to become a practical energy source. Each potential driver and target combination has advan- tages and disadvantages, technologies are evolving rapidly, and scientific challenges remain. If the nation intends to establish IFE as part of its energy R&D portfolio, it is clear that both science and technology components must be addressed in an integrated and coordinated effort. The roadmap concept put forward by this committee carries forward all IFE approaches to some point at which off-ramp or continuation decisions are made. Should the NIF achieve ignition with indirect drive and the nation decide to pursue IFE, the R&D required to pursue IFE as a practical energy option would begin to diverge from the R&D that NNSA is likely to support for stockpile stewardship applications. In this case, a nationally coordinated R&D program for IFE would be needed to pursue a broad-based roadmap. Inertial fusion energy is an integrated concept whose overall probability of success depends on the success of several individual items. If one component fails a physics test or fails to be cost-effective, the system fails, regardless of whether reactor-scale ignition and gain are reached. There has been considerable discussion within the committee about the tim- ing for—and the extent of—a technology development element (chambers, target fabrication, etc.) as described in Chapter 3, as part of the early phase(s) of the IFE program. The committee recognizes that absent ignition within the physics element of the program, technology would be of limited value as part of the early phase(s) of the IFE program. There are, however, several reasons for establishing a technology element even in the earliest phases of the IFE program.

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168 An Assessment of the Prospects for Inertial Fusion Energy A program is needed that attempts to answer whether there is any TA that appears to be practical as well as economically viable. Only certain combinations of targets, drivers, and chambers seem to be possible in this sense. While the emphasis today and in the near future should be on scientific issues related to driver and target performance, working only on these problems could easily lead to solutions that are not compatible with practical commercial driver and chamber options. Such a serial approach could lead to dead ends and would also extend the timescale to the possible practical implementation of IFE. Technology R&D is not done in a vacuum, and certain answers from the technology research will be beneficial to the overall IFE program in its earlier phases. The design of a FTF and a DEMO cannot be accomplished absent critical technology developments even in the conceptual stages. If the IFE program is to continue advancing, there must be supporting technology developments all along the event pathways. And, perhaps most importantly, if there is to be a meaningful IFE program, it is vital that there be a skilled workforce to investigate the myriad of technology problems over the coming decades. These trained technical experts will not be available unless there is meaningful and challenging R&D for them to carry out early on. That will be possible only if there is a long-term sustained technology element included in the IFE program. Such a program element can be enhanced by identifying synergistic opportunities between the magnetic fusion energy and IFE programs and incorporating them in both programs. Conclusion 4-13: The appropriate time for the establishment of a national, coordinated, broad-based inertial fusion energy program within DOE is when ignition is achieved. Conclusion 4-14: There is a compelling need for a sustained, long-term engineering science and technology component in a national inertial fusion energy program. Such a program would require a sustained effort that is initially devoted pri- marily to an improved understanding of target physics, particularly the relation- ship between absorbed energy and gain. Once the target physics is understood, modest gain has been achieved, and there is confidence that reactor-scale gain can be achieved, funding would then be ramped up and devoted primarily to technol- ogy development of the three TAs, including target manufacture, driver modules, chamber design, and materials. TA (driver) down-select should occur as part of the technology development phase. The committee’s order-of-magnitude estimate for accomplishing this in a two-step approach is given in Table 4.4.

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A Roadmap for Inertial Fusion Energy 169 Recommendation 4-9: An engineering science and technology development component should be included in a national inertial fusion energy program. Conclusion 4-15: The National Ignition Facility (NIF), designed for stockpile stewardship applications, is also of great potential importance for advancing the technical basis for inertial fusion energy (IFE) research. For a national IFE program, NIF can be utilized for ignition optimization and for demonstration of reactor-scale gain and of reactor-scale gain with more cost- effective targets, as the target physics of direct drive and indirect drive advance technically. Furthermore, modification of NIF to accommodate polar direct drive would not preclude further experiments with indirect drive. This appears to be consistent with the NNSA strategy following completion of the NIC.15 Recommendation 4-10: Planning should begin for making effective use of the National Ignition Facility as one of the major program elements in an assessment of the feasibility of inertial fusion energy. With the approach described here, there needs to be a serious discussion about how such a program should be managed. Certainly it is the prerogative and responsibility of DOE to make such a decision. However, in the interests of cost- effectiveness and efficiency, the committee is of the opinion that a single program- matic office should be established. The committee recognizes that, for an extended period, some overlap will likely continue with programs needed for stockpile stewardship, but that an early effort will be required to facilitate the transition to a national IFE program and to minimize the potential for some overlap. Conclusion 4-16: At the present time, there is no single administrative home within the Department of Energy that has been invested with the respon- sibility for administering a national inertial fusion energy R&D program. Recommendation 4-11: In the event that ignition is achieved on the National Ignition Facility or another facility, and assuming that there is a federal com- mitment to establish a national inertial fusion energy R&D program, the Department of Energy should develop plans to administer such a national program (including both science and technology research) through a single program office. 15  J. Quintenz, NNSA, Presentation to the committee on February 22, 2012, and LLNL, 2012, “Polar Drive Ignition Campaign Conceptual Design,” LLNL TR-553311, submitted to NNSA in April 2012 by LLNL and revised and submitted to NNSA by LLE in September 2012.

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170 An Assessment of the Prospects for Inertial Fusion Energy It is expected that this would facilitate the management and planning of a focused, coordinated, cost-effective national program, the development of the n ­ ecessary technologies, and eventual down-selection among driver options and target designs. A single program office would also facilitate the transition of the national IFE program from a science- and technology-based R&D program in the near term to an engineering-based development program in the long term. In the interim, while IFE is being funded by several offices, it is important to utilize to the maximum extent possible existing facilities in the NNSA and Office of Fusion Energy Sciences programs to minimize costs as much as possible. This will also be true if a national IFE program is established.