Power Plant and Fusion Chamber Considerations for Fast Ignition
A large number of inertial fusion energy (IFE) chamber concepts have been proposed and analyzed to various levels of detail [1, 2]. A smaller number of detailed power plant design studies (i.e., studies considering self-consistent integration of targets, drivers and chambers) have also been completed for both direct-drive and indirect-drive, central ignition (CI) targets [3-5]. There have not been any comparable studies of fusion chambers or integrated power plants for fast-ignition (FI) based IFE. Some specific aspects (advantages and issues) have been previously describe [6, 7], but not to the level of detail of the large integrated design studies. In this paper, we review current understanding of chamber design and power plant features for fast-ignition. We approach this topic by asking what chamber and power plant issues and features will be different for fast ignition compared to central ignition. In this article, we consider first wall and final optics design issues for various chamber concepts with direct and indirect drive FI targets, while target manufacture and injection issues are considered in another paper in this special issue [8]. If it is found that the ignitor beams can efficiently penetrate the plasma that is blown off the fuel capsule surface during the compression phase, the FI targets may look much like CI targets. In this case the fusion chamber and final optics issues are likely to be very similar to those for CI targets, except for the final optics of the ignitor beams. It is more likely that the efficiency of transferring ignitor beam energy through the blow-off plasma to the ignition spot fuel will be so low that whatever advantage fast ignition has in reducing required compression driver energy will be more than offset by the size and, therefore, cost of the ignitor lasers themselves. Therefore, it has been proposed to use a cone of high-Z material [9] to shield the ignitor beam line-of-sight from the blow-off plasma and possibly help focus the short pulse ignitor beams onto the dense fuel. Figure 1 illustrates what these cone focus targets might look like for laser direct-drive, laser indirect-drive and heavy ion indirect-drive concepts. The Tabak article in this special issue describes the operation and performance of these targets [10]. The cones must be relatively heavy and thick to avoid breaking up during the implosion of the fuel. In the direct-drive case, the cone must also be long enough that ablated material from the fuel capsule does not go around the end and into the ignitor beam line of sight. It has been suggested that the cone length may have to be up to four times the initial radius of the fuel capsule [7]. For hohlraum targets, the cones need not be as long because the hohlraum wall itself retards the expanding plasma. The presence of the massive high-Z cone in close proximity to the high density fuel will affect the energy partition of the burning capsule output and its x-ray and debris spectra. It can also affect the aerodynamics of the target during injection. Finally, if the capsule fails to ignite, the consequences of the dud may be different for cone targets than for central ignition targets. All these potential differences will be examined in this article. In Section 2, we discuss the power plant benefits of FI cone-focus targets with emphasis on the economic advantages of high target gain at low driver energy. Section 3 shows how the energy partition and spectra of cone focus targets compares with central ignition targets. Section 4 covers possible chamber concepts that are compatible with indirect-drive fast ignition. Section 5 reviews two special issues for FI power plants: Section 5.1 describes the survival of final optics, especially for the extremely intense ignitor beams, while Section 5.2 discusses the consequences of duds, which may occur more frequently for FI targets. Section 6 lists recommended near-term future work for FI power plant issues discussed in this article, and Section 7 gives our conclusions.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 897987
- Report Number(s):
- UCRL-JRNL-210570; TRN: US200706%%175
- Journal Information:
- Fusion Science and Technology, vol. 49, N/A, April 1, 2006, pp. 532-541, Journal Name: Fusion Science and Technology, vol. 49, N/A, April 1, 2006, pp. 532-541
- Country of Publication:
- United States
- Language:
- English
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