“When you said ‘no showstoppers’, you were referring to heavy ions?” — Tom Cochran (Natural Resources Defense Council), DOE Energy Research Advisory Board, 1979 IntroductionBy 1979, the design “parts bin” and” tool-kit”for HIF drivers had been established. Over its illustrious history, a major aspect of high-energy accelerator development has been the serial inventions that permit high-energy physics research to achieve the outstanding scientific feats it is famous for. “Colliders” were invented to increase the count rate by focusing (in time as well as space) two beams to hit head on in what has been called “needle on needle”, to characterize the precision involved. Realization that this technology is able to produce beams carrying the necessary megajoules total energy and focusing to the spot size needed for ICF came with success of the Intersecting Storage Rings (ISR) at CERN in 1975. HIF’s need was to repeat these numbers with heavy ions. The ultimate importance of FPC’s proprietary advantage is that it defines a comprehensive fusion power system for which every question has an answer. The history of ICF from the early 1960s through the 1970s and 1980s made clear that the magnitude of the ignition challenge required exceeding—not just meeting—the official ignition requirements, which were minimal requirements fit to the limitations of evolving laser technology. Although the capabilities of HIF’s first conceptual designs captured the enthusiasm of the world community, pushing the capabilities into the realm of confidence that is reached via design margin would need more than accelerator techniques that stressed lowest possible cost for research. In the research environment, beam intensity, although important, is secondary. For ICF, intensity is everything. To more fully exploit the potential that heavy ion acceleration offers, our Chief Technology Officer proposed (1978) telescoping beams of different heavy ion isotopes. In 1976, the heavy ion driver had completed conceptually the fusion power concept envisioned by our CTO in 1973. While leading the HIF group at the Argonne National Laboratory in the 1970s, our CTO formed an industrial collaboration to take HIF to power production. By 1979, Argonne’s HIF program, with essential contributions from the partner Hughes Research Laboratories, had answered the most basic question: source beam brightness. In the slowed rate of development post-1979, international vetting of telescoping beams took until the European HIF study of 1994-97, HIDIF. This development induced a review of HIF’s status, leading to the complete baseline concept on which FPC is founded. Still an issue in the HIDIF concept was the second of the two basic questions. Electrostatic repulsion between beam ions requires HIF ignition pulse generators to work with heavy ions in a low charge state (small number of electrons removed from the neutral atom , e.g., the +1 charge state). Whereas machines built for research using protons or “highly stripped” (multiply ionized) heavy ions can reduce cost by taking seconds (even hours) for beam accumulation because of the low probability of beam-beam collisions leading to loss of the beam, HIF’s need to use +1 heavy ions requires generating each ignition pulse in a few milliseconds to avoid excessive beam loss as a result of collisions that change the charge state. Collisions between HIF’s lightly charged heavy ions and background gas atoms would remove one or more additional electrons from beam ions, kicking them onto trajectories that hit the vacuum pipe wall. Although conceptually soluble, this posed a programmatic dilemma. The only way to prove the workability of HIF systems that accumulate beam in storage rings would be to build one at nearly full size. As this is seen as a risk element, the effort is concentrated at the Helmholtz GSI lab in Germany, where the accelerators for the demonstrations are, again, being built primarily for basic research. Compounding the programmatic dilemma was that the accomplishments of storage rings had been foundational for HIF, and the intense effort required to work out a new HIF configuration needed an impetus that was lacking. In the event, the 10-year process of defining FPC’s reconfigured accelerator driver not only met the need to generate the ignition beams in milliseconds but discovered that the reconfiguration made the beams much more potent. In a “look what I found!” moment, the unanticipated development at a stroke secured HIF’s ability to achieve fast ignition and to increase the total energy in the ignition pulse to the point that the requirements can be met with design margin. Unique in the 70-year history of the quest for civilian fusion power, having design margin brings the risk down to a level that is manageable. Proprietary advantage in the arena of fusion power is almost a curious notion. Its essential significance, aside from the contributions to practical fusion power, is to provide a platform for FPC to argue that the private sector can assume the leadership role. Engagement of major industrial and financial interests, in concert with the government, is essential. FPC’s key protected IP provides armor for the Company to venture into this high powered environment. 
As well as being of the highest importance, this unique set of attributes also is remarkable for being self-consistent. The chamber uses thick layers of lithium for protection from the neutrons, as planned by FPC’s Chief Technology Officer when he introduced the concept in 1973. The use of lithium “thick liquid walls” for ICF chambers has since become mainstream. However, use of this means of neutron protection in other concepts, where the fusion pulses are small and rapidly repeating, runs into issues regarding the pulse-to-pulse stability of the lithium jets. In contrast, as originally planned, FPC’s chamber pulses roughly once per second, producing very hot lithium gas. The hot gas expands toward the chamber ends, while being isolated from the walls by lithium flows, and enters the heat exchangers. Fresh lithium restores the vacuum needed to admit the ion beam for the next pulse. The incoming lithium cools the chamber materials to about 200oC, where its vapor pressure is less than 1e-7 Torr. |
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