On the Laser-Fusion Milestone | Daniel Jassby | Inference
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Short Notes
Vol. 7, NO. 3
December 2022
Daniel Jassby
Letters to the Editors
In response to “On the Laser-Fusion Milestone”
The milestone achieved at the NIF (National Ignition Facility) on December 5 involved the third of three fusion pulses, or shots, that together comprise the most important episode in the seven-decade history of controlled fusion research.1 For the first time, researchers have demonstrated definitively the scientific feasibility of at least one approach to controlled fusion energy. This new result also serves to reinforce many of the points I made in an essay for Inference published earlier this year.2 Especially the observation that inertial confinement fusion (ICF) has established a clear lead over magnetic confinement fusion (MCF) in attaining reactor-relevant fusion conditions.
When my essay appeared at the end of the May, the NIF at Livermore had already produced the first of these so-called supershots. Achieved on August 8, 2021, that initial result was heralded as reaching the “threshold of fusion ignition,”3 where heating from the fusion reaction itself exceeded energy losses from the hot deuterium-tritium (D-T) plasma. After a year of less spectacular results, the first supershot was essentially replicated on September 19, 2022.4 By contrast, the December 5 record shot generated more than twice the fusion output of the earlier supershots and indicated both definitive achievement of thermonuclear ignition in the D-T core and substantial propagation of a thermonuclear burn into the surrounding D-T fuel.
The NIF’s latest success has only accentuated the disparity described in my essay between the recent advances of ICF and the quarter-century stagnation of MCF. Other approaches lag even further behind. The promoters of different fusion concepts have conflated the NIF results with their own systems, claiming that the NIF success shows that their approach will work as well. But the NIF results say nothing about the feasibility of any other proposed method for controlled fusion. All other current fusion concepts have performance parameters that fall drastically short of any similar demonstration, and most—perhaps all—will never make the grade.
With these latest results in mind, an obvious question is whether an ICF facility similar to NIF could form the basis for a power-producing reactor in the near future. There is no chance whatsoever that such a power plant will appear any time soon because a host of barely existent technologies must first be developed—or in some cases invented—before a fusion reactor that produces net electric power can be realized. In the following comments, the acronym IFE denotes Inertial Fusion Energy, which commonly refers to the application of ICF plasmas for power production.
Consider the following characteristics of the current NIF system:
The neodymium-glass laser system has an electrical efficiency of about 0.5% and can only fire a full-energy pulse once or twice each day.
The tiny and intricate target assemblies comprising the hohlraum and fuel capsule cost more than US$10,000 each, require several weeks to fabricate, and hours of careful adjustments to position precisely in the target chamber.
No attempt is made to capture the fusion output or to replenish the burned tritium fuel.
By comparison, the basic requirements for a fully-realized power-producing IFE system are as follows:
The implosion driver must deliver 5MJ with an overall electrical efficiency of at least 10% and be capable of firing several times per second.
A half-million identical fuel targets must be fabricated daily at a cost of no more than 20 cents each.
After each shot, all debris must be removed and the next target inserted and precisely positioned in a fraction of a second—a process that will be repeated a half-million times each day.
The survival of exposed optical and target-tracking components must be ensured.
The target must be surrounded by a liquid metal falls—analogous to a waterfall—to absorb the explosive fusion...