INERTIAL CONFINEMENT FUSION (ICF) ARTICLE ANNOUNCEMENT: From: physnews@aip.org (AIP listserver) PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 246 October 25, 1995 by Phillip F. Schewe and Ben Stein IN INERTIAL CONFINEMENT FUSION (ICF) a "driver" consisting of multiple laser or particle beams converge on a target. The resulting compression heats up a deuterium-tritium mixture until fusion reactions begin. Scientists studying this fusion fireball have both practical applications in mind---they aim to convert fusion energy into commercial electrical energy---and military applications---since fusion reactions are at the heart of modern nuclear weapons. In what is likely to become the ICF bible for years to come, Livermore physicist John Lindl (510-422-5430) lays out the nuts and bolts of ICF research in the November issue of the journal Physics of Plasmas. Lindl's 90-page report includes extensive discussion of research that until the past year or so was classified as secret information. Much of the declassified material has to do with target design. In the indirect-drive approach to ICF, the driver beams do not strike the fuel capsule but rather an outer casing consisting of high-atomic-weight material, which heats up and emits x rays. It is the x rays which cause the implosion of the fuel capsule. At the proposed National Ignition Facility (which, if approved, would be constructed by about 2002) scientists hope to extract 10 times as much energy from the fuel as goes in. (Journalists can obtain copies of the article from AIP Public Information at physnews@aip.org) REVIEW OF ICF ARTICLE BY CAREY SUBLETTE Review of _Development of the Indirect-Drive Approach to Inertial Confinement Fusion and the Target Physics Basis for Ignition and Gain_ by John Lindl; Physics of Plasmas Vol. 2, No. 11, November 1995; pp. 3933-4024. This is a newly published article is a review of the current state of laser- driven inertial confinement fusion (ICF) research. It's author, John Lindl of Lawrence Livermore National Laboratory (LLNL), has long been a major researcher in this field (see the brief bio on Lindl at the end of this review). Although important ICF research has and is being conducted in Japan, the world's major ICF research program has been the U.S. program funded by the Department of Energy. Much of the progress made in this program has been cloaked in secrecy due to the relationship between laboratory scale ICF, especially indirect-drive ICF, and thermonuclear weapons design, since thermonuclear weapons are essentially enormous indirect-drive ICF systems. This article unveils a substantial body of ICF research for the first time. It is also the best comprehensive survey of the physics of laser ICF in recent years and, in my opinion, the best such survey since Brueckner and Jorna 21 years ago (Review of Modern Physics 46, pg. 325, 1974). As good as it was, the Brueckner and Jorna article was basically a discussion of physical principles and concepts as no body of actual research existed at the time. In contrast, Lindl devotes most of his article to describing actual experimental techniques and results. On the other hand, in keeping with its publication in a professional physics journal, Lindl assumes familiarity with the physical principles and concepts rather than providing them so substantial background is necessary to adequately absorb the material he presents. It is thus likely to be slow going for those who have not investigated ICF physics before. The Brueckner and Jorna article is still a good reference discussing ICF specifically. I would recommend as an introduction to the basic physics (ahem) my own newly released Nuclear Weapons FAQ, Section 3: Matter, Energy, and Radiation Hydrodynamics on this web page. A very readable and authoritative reference work that I also highly recommend is _Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena_, by Yaacov B. Zel'dovich and Yuli Raizer, (ed. by W. D. Hayes and R.F. Probstein, 1966, Academic Press). This article collects and organizes material that until now, required the reader to hunt through dozens of journal articles scattered over many years. This is definitely the place to start to familiarize yourself with the state of this field. The article is divided into 14 sections: 1. ICF Overview 2. Historical Development of Indirect Drive in the U.S. ICF Program 3. Ignition Physics 4. Pulse Shaping 5. Implosion Dynamics 6. Hydrodynamic Instability 7. Capsule Gain 8. Hohlraum Coupling Efficiency 9. Hohlraum Radiation Uniformity 10. Combined Tests of Symmetry and Hydrodynamic Stability 11. Hohlraum Plasma Conditions 12. Hot Electron Preheat 13. National Ignition Facility and Ignition Targets 14. Inertial Fusion Energy Since this review is being written for the High Energy Weapons Archive, I will focus my discussion on the significance of the Lindl article with regards to nuclear weapons research and design. A rough indication of the amount of newly unclassified information in this 92 page article can be gained by observing that 57 of the 266 references cited are unpublished documents (which Lindl indicates means that they have been classified until now), principally LLNL reports. Additional classified sources my be concealed in the substantial number of "private communications" in the references. These references are concentrated in the later part of the historical overview (Section 2) which describes the overall course and progress of the U.S. program, and in the sections describing hohlraum physics and experiments. The extensive, detailed descriptions of hohlraum designs and experimental results from the late 1970s to the present day are clearly new information not available elsewhere. Lindl makes clear two direct connections between indirect-drive ICF and U.S. nuclear weapons programs. The first is that U.S. research in this field is a direct result of weapons work. John Nuckolls, who has long been the leading researcher in the field, based his important 1972 paper in Nature (Nuckolls, et al; 1972; Nature Vol. 239, pp. 129) on work he initiated in the later 1950s in creating the smallest possible fusion explosion. In a very real sense ICF is, and has been from the beginning, an attempt to shrink thermonuclear weapons physics and design to laboratory scale. The second direct link is that nuclear weapons tests have been used as experimental tools in developing ICF. By 1975 the U.S. ICF program had largely abandoned direct-drive ICF in favor of indirect-drive radiation implosion, the foundation of the Teller-Ulam fusion weapon architecture. Due the limitations of existing lasers, in 1978 the Halite/Centurion program was undertaken jointly by LLNL and Los Alamos (Halite was the LLNL portion, and Centurion the LANL part). This secret program used underground nuclear explosions at the Nevada Test Site to provide the high intensity radiation flux needed to test ICF targets ( fuel capsule/hohlraum systems). It continued until 1988. For those seeking insight into thermonuclear weapons physics from this article, I caution you to keep in mind the significant differences between laser-driven ICF and thermonuclear devices. As an example, issues connected directly to the delivery of laser energy are unlikely to be relevant for weapons design where the conversion step of optical energy to x-ray energy does not occur. The majority of Section 11 (Hohlraum Plasma Conditions), which deals with such issues as Raman and Stimulated Brillouin Scattering of laser energy is thus mostly irrelevant. The last section, which mentions heavy ion indirect drive ICF, and briefly contrasts it with the laser-driven approach, helps to sort out these issues since to some degree it highlights which ones are laser-specific. Heavy ion ICF more closely resembles the design of weapon implosion systems in a number of ways (x-rays are emitted directly into a closed hohlraum cavity for example). Lindl discusses plans for the next stage in laser-driven ICF research extensively: the proposed $1.07 billion National Ignition Facility (NIF) to be built at Livermore. Here however he fails to point out the close connection with weapons physics. The significance of this connection can be illustrated by noting trends in the scale differences between thermonuclear weapons and ICF targets. The first fusion weapon design (Ivy Mike) had a diameter of 2 meters, and as technology improved weapons became more compact until modern designs like the W-80 have a diameter of 30 cm or even less (in fact I maintain that the 20 cm diameter W- 71 neutron bomb is actually a radiation implosion device). Indirect-drive ICF targets on the other hand were initially quite small, 0.05 cm in diameter, and have increased in size so that the proposed NIF target has a diameter of 0.9 cm. While the early fusion and early ICF designs had a difference in scale of 4000:1, making comparisons of the physics involved between them somewhat suspect, the NIF target has a difference in scale with small modern weapons of only 20-30:1. This is a small enough scale ratio to show that the underlying physics must be substantially similar (note that there is an 18:1 scale difference between the early ICF targets and NIF!) This connection is actually claimed by LLNL, LANL, and the Department of Energy as a major reason for building NIF. Consider for example this excerpt from a DOE web page [http://web.fie.com/web/fed/doe/oor/]: The National Ignition Facility (NIF) would simulate, on a small but diagnosable scale, conditions of pressure, temperature, and density close to those that occur during the detonation of a nuclear weapon. With the NIF, it would be possible in the laboratory, for the first time ever, to study radiation physics in a regime close to that of secondaries. The NIF would be used to investigate hydrodynamic and mix phenomena relevant to modern nuclear weapons. The NIF would also provide a unique laboratory capability for studying thermonuclear ignition and burn of dense deuterium-tritium gas. Furthermore, by studying NIF-heated targets, we would be able to improve our ability to predict the effects of x-radiation on weapon components and weapon systems; these studies would be a valuable complement to experiments at other Department of Defense and Department of Energy facilities. Without the capabilities offered only by the NIF, uncertainties about some physics areas that affect secondary performance would go unanswered, and improvements in our predictive capabilities would suffer. Equally important, without the NIF and similar frontier-expanding facilities, the weapons laboratories would find it increasingly difficult to maintain the necessary expertise and skill bases unique to nuclear weapons and essential for science-based stockpile stewardship and management. To summarize, for anyone seriously interested in fusion energy (beneficial or otherwise) this article by John Lindl is a landmark. ***************** About John Lindl (excerpted from http://www-phys.llnl.gov/X_Div/index.html): John Lindl's theoretical and computational work has helped transform ICF. He developed the design for the first high-gain, indirect radiation drive ICF targets and showed the superiority of these targets -- compared to direct drive -- for hydrodynamic stability and implosion symmetry. He also proposed and outlined the first series of experiments to test the feasibility of laser drive radiation implosion. Lindl has had a continuous career in inertial fusion at Livermore since receiving his Ph.D. in astrophysics from Princeton in 1972. His work has spanned a wide range of topics including high-gain target designs for lasers and particle beams, hydrodynamic instabilities in ICF, implosion symmetry and hohlraum design, high-energy electron production and plasma evolution in hohlraums, and the physics of compression and ignition. Lindl served as X-Division leader from 1984_1991, led the ICF Target Physics Program from 1991-94, and was named ICF Scientific Director in 1994. Lindl was a joint recipient of the 1994 E.O. Lawrence Award.