LASER FUSION | POWER PLANT DESIGN


A slight variation of the laser driven fusion approach works a bit more like a traditional combustion engine. A two-phase laser bombardment, or “fast ignition” for short, is the favoured approach for economic viability. First, a green laser flash compresses the capsule before a subsequent laser-generated proton beam heats the dense matter to ignition temperature. It works much more efficiently thanks to separate compression and ignition phases. This approach is favoured for commercial energy production because it relaxes the stringent requirements of the lasers needed to compress the fuel, and it offers a more viable approach to the high energy gains of greater than 100 needed for electricity production.


The Focused Energy approach The Focused Energy approach builds on the tremendous progress made over the past decade, and introduces a few changes to increase the possibility for viable energy production. In addition to shifting from the compression- heating approach to fast ignition, Focused Energy will also use slightly different laser parameters and target configuration. To perform fast ignition, Focused Energy will not use perfectly spherical targets as previous experiments have employed, but will instead use capsules with a cone inserted from the side. In addition to providing the second target for ultrashort pulse lasers to produce the proton “spark plug,” this configuration allows for easier filling of the pellet with fusion fuel and makes a more robust target for injecting into the reactor. In addition, Focused Energy will compress the fusion fuel with green light instead of more traditional blue laser light used in previous experiments. The benefit of using green laser light for pellet


compression has to do, among other things, with an extended service life of the laser optics in this frequency range. In addition, the laser flashes can use the electricity from the socket more efficiently than in previous systems. These factors point to both operational and process advantages of the two-phase fast ignition solution. Focused Energy is taking this fast-ignition approach


to IFE through high-intensity lasers, using the research and experiments conducted over the past 30 years. It is inherently safe, efficient, and economically feasible and the energy produced will be “CO2


friendly”.


Industrial process technology in view In terms of next steps, it will be crucial to refine production of the fusion target pellets and capsule robotic placement within the fusion chamber. There, the high-precision placement of new pellets must be able to occur every 3 minutes. By comparison, existing laser fusion facilities flash on average only every two hours. The current conversion of laser energy to fusion energy is about 0.7, which was demonstrated by Lawrence Livermore National Laboratory’s National Ignition Facility (NIF) in August 2021. The experiment proved it’s possible to “ignite” a laser fusion pellet. The goal is an energy yield efficiency of around 150. This


is the factor by which the fusion energy obtained should exceed the laser energy irradiating the target. The target robot required for the demonstration system has been fully developed and is already in experimental use.


Above: Green laser light is used to compress the hydrogen fuel pelet in a two-stage fusion reaction process Photo credit: Focused Energy


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Another wrinkle to iron out concerns the optimisation of pellet coating. Here, the aim is to achieve the lowest possible cost of materials and simplified production processes, while at the same time improving evaporation properties in the second ignition phase of fusion. In commercial operation, a pellet must not be more expensive than 50 US cents. In addition, sufficient production capacity is needed. After all, with 24-hour reactor operation, the 10-hertz tempo in the fusion chamber requires no less than 860,000 pellets per day.


The future of energy is fusion While there are still steps to be taken, inertial fusion energy through high-power lasers is now far closer than ever before to being viable under terrestrial conditions. The advances being made point to market viability much sooner than expected – within the next 10 years. Among others,


exciting recent advances include: ● In August 2021, the NIF in California produced >1.3 MJ of fusion yield with 1.9 MJ of laser drive – a 70% conversion of laser energy to fusion energy.


● Very high efficiency in laser-driven proton sources has been experimentally observed. More than 10% of picosecond laser pulse energy has been converted to a proton burst, and new techniques for fabricating cone-in- shell proton fast ignition targets are being developed.


● Lasers with many hundreds of joules of energy operating at 10 Hz can now be constructed, and 100 J pulsed lasers operating at 10 Hz have been fielded. This is only within about a factor of 10 or 20 of what will be needed for the laser beams in an operating fusion power plant.


Commercialising fusion will have significant implications for the energy sector, provide a reliable way forward to solving climate challenges, and be a remarkable achievement in science and technology. ■


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