First Light Fusion Generates Neutrons

First Light used a large two-stage hyper-velocity gas gun to launch a projectile at a target, containing the fusion fuel and achieved fusion. The projectile reached a speed of 6.5 km per second before impact. First Light’s highly sophisticated target focuses this impact, with the fuel accelerated to over 70 km per second (151,000 mph) as it implodes, an increase in velocity achieved through their proprietary advanced target design, making it the fastest moving object on earth at that point.

They confirmed the production of deuterium-deuterium (DD) fusion neutrons by an inertial confinement fusion target that is driven by a one-sided impact. Experiments were performed on First Light Fusion’s 38 mm bore, two-stage light gas gun. This facility can launch a 100 g solid projectile at 6.5 km s−1. Neutron diagnostics included scintillators and moderated helium-3 proportional counters. They have demonstrated repeatable, coincident detection of particles on multiple scintillator detectors, within the expected time window.

First Light has received about $107 million in funding and they just raised a series C. They were founded in 2011.

Target Dates for First Light and Competing Fusion Projects

First Light Fusion made big promises back in 2020. The University of Oxford spin-off called First Light Fusion claimed in 2020 it would demonstrate breakeven in 2024. Breakeven has slipped to 2025-2026.

First Light is building an ICF reactor in which the “claw” consists of a metal disk-shaped projectile and a cube with a cavity filled with deuterium-tritium fuel. The projectile’s impact creates shock waves, which produce cavitation bubbles in the fuel. As the bubbles collapse, the fuel within them is compressed long enough and forcefully enough to fuse. In 2020, Hawker said First Light hopes to initiate its first fusion reaction this year in 2020. Howeveer, the first fusion reaction was in 2020. It is likely that the demonstration net energy gain has slipped from 2024 to 2026. Fusion energy doesn’t just need to be scientifically feasible but it needs to be commercially viable. Successful demonstrations should lead to a planned commercial pilot plant, which it is currently targeting in for “the early 2030s”.

US-based Helion raised US$500mln. Helion plans build its Polaris fusion electricity demonstration generator, which it aims to demonstrate net electricity from fusion in 2024 and enable its long-term goal of producing electricity with no carbon emissions for 1 cent per kilowatt-hour. Helion has 40ft-long accelerators shaped like a giant dumbbell. They heat deuterium and helium-3 fuel. Helion uses powerful magnets to confine the resulting plasma and ramp up the pressure to create a relatively stable donut-shaped ring of plasma called a Field Reversed Configuration (FRC). Two of these FRCs are then accelerated to 1 million mph from opposite ends of its accelerator. When they collide in the bulging handle of the dumbbell shaped accelerator they are further compressed by more magnets until they reach fusion temperatures of 100mln °C.

Back in 2020 in Cambridge, Mass., MIT-affiliated researchers at Commonwealth Fusion Systems say their latest reactor design is on track to exceed breakeven by 2025.

The California startup TAE Technologies had issued a breathtakingly ambitious five-year timeline for the commercialization of its fusion reactor. However, 2025 was only the target for when they would get clearly on the path to commercializaation. The current TAE Copernicus is a reactor-scale device designed to operate at about 100mln °C to simulate net energy production from its fuel cycle and so “will provide opportunities to license its technology for D-T fusion, while scaling to its ultimate goal”. TAE wants to start commercialisation of p-B11 fusion power plants “beginning by the late 2020s”. Start of commercialization is confusingly not a working commercial reactor but some nebulous kickoff to the final commercialization project.

Details of First Light Fusion

Projectile fusion is a new approach to inertial fusion that is simpler, more energy-efficient, and has lower physics risk. Inertial fusion is a pulsed process, where, like an internal combustion engine, a small amount of fuel is injected and sparked to make it burn. The main existing approach to inertial fusion uses a large laser as the “spark plug”, triggering the reaction.

Target Design is the Key First Light Technology

Projectile fusion has been considered before and the required velocity was found to be very high. First Light’s target technology is the crucial game-changer. Our targets have two aspects, an amplifier and a fuel capsule. The amplifier does two things, it boosts the pressure generated by the impact of the projectile, delivering a much higher pressure to the fuel. This amplification reduces the required projectile velocity; the fuel implodes much faster than the original impact.

The amplifier also creates convergence. Whilst the initial impact comes from only one side, the fuel is squashed from many directions. This is crucial for reaching the required final density.

The targets are the key technology in First Light’s approach to fusion and they are nearly all trade secrets. One example uses three cavities, two big and one small. The collapse of the two bigger cavities focuses the pressure onto the small one in between, which is collapsed with a higher pressure and from two sides rather than one.

Comparing First Lught target design to other fusion approaches using the triple product shows the unique space that First Light occupies. The targets achieve very high values of the density-time product and span a previously unexplored parameter space. To reach gain, they need to increase the temperature, and the principal way to do this is to increase the projectile velocity.

Inspired by Nature

First Light’s journey to a new method for fusion started in nature, with the pistol shrimp. The pistol shrimp has an oversized claw, which it can “click” shut at very high speed. The motion is so fast that it launches a shock wave into the water and stresses it so much that it rips apart and forms a bubble. The shock wave and the bubble interact and the bubble collapses just as quickly as it forms. The vapour inside is heated to tens of thousands of degrees and emits a bright flash of light.

Pulsed Reactor

The first Light inertial fusion is a pulsed process, like an internal combustion engine. Each target releases a large amount of energy; the power output is the energy per shot multiplied by the frequency. A pulsed approach gives great design flexibility, trading off energy per shot and frequency. First Light is aiming the lowest risk plant design possible. High energy per shot reduces physics risk, and slower frequency and small overall plant size reduce the engineering risk.

The target will simply be dropped into the reaction chamber from above, falling under gravity. The projectile is launched downwards on top of the target and catches it up in the centre of the chamber. The impact is focused by the target and a pulse of fusion energy* is released. That energy is absorbed by the lithium flowing inside the vessel, heating it up. Finally, a heat exchanger transfers the heat of the lithium to water, generating steam that turns a turbine and produces electricity.

This plant design avoids the three biggest engineering challenges of fusion: preventing neutron damage, producing tritium, and managing extreme heat flux. Lithium is used to produce tritium, one of the two fusion fuels. The design allows tritium self-sufficiency with pure lithium in the natural isotope balance. This is a major advantage as the only by-product is helium, and there is an established supply chain for normal lithium.

The thick liquid lithium also blocks the neutrons from reaching the vessel, meaning that it will last for the lifetime of the plant. The liquid first wall also addresses the issue of very high heat flux. Some of the lithium will be vapourised by the energy release, but it simply recondenses.

There is a large amount of existing engineering that can be reused to realise this plant design. Fast breeder reactors, a type of nuclear plant, use liquid metal as the coolant, typically sodium or sodium-potassium mixture. The engineering from these plants can be ported over to lithium. After the lithium heat exchanger, the plant is identical to many other already working facilities. Most of the cost is low risk engineering.

They are aiming for a power plant producing ~150 MW of electricity, firing once every 30 seconds, and costing less than $1 billion.

UKAEA Review

UKAEA have conducted a review of First Light Fusion Ltd’s recent (485 series) experimental campaign. The UKAEA technical team involved have had the opportunity to interact with the FLF experimental team as part of the review. The review included assessments of the experimental planning, scientific equipment used and associated diagnostics, processes to extract and analyse the data obtained from the diagnostics and analysis included within the associated experimental report.

The experimental campaign comprised 21 high velocity impact experiments (‘shots’) overall. 12 of these were reported to have used deuterium-fuelled (base-case) targets, one was a deuterium design variant shot, four were H2 null shots and a further four were test shots. UKAEA staff witnessed a sub-set of these which were two deuterium-fuelled target shots; the first was a deuterium shot on the 22nd February 2022 which yielded no detection events (reportedly due to projectile failure); the second (successful) shot on the 4th March 2022 yielded three scintillator events and a single 3He detection event within the defined time windows.

In assessing the experimental campaign as a whole the diagnostic data obtained and analyses performed from the experiments in aggregate, and with detailed consideration of terrestrial background or other potential sources of spurious signals, we support FLF’s finding that high energy particles have been detected. In the context of fusion experiments the number of events detected is small. However, the events detected and the associated temporal analysis are sufficient to indicate a link to the impact experiments using deuterium-loaded targets. The aggregated time-of-flight data comprising 29 detection events obtained using the scintillator array (each event corresponds to the detection of a single particle), together with the basic analysis performed to estimate a neutron energy range provides some evidence that neutrons have been produced which would be consistent with the energy of those produced in D-D fusion processes. The supporting 3He detection events within an expected time window following the expected fusion time are fewer, though in aggregate do provide some complementary evidence through a separate detection system to the scintillator array that neutrons are present.

25 thoughts on “First Light Fusion Generates Neutrons”

  1. Interesting, but the operation of "light gas guns" does not lend itself to rapid operations. Maybe the large cylinder could be operated pneumatically, rather than by combustion. It takes time to return the piston to starting position, refill the space between the piston, and barrel with light gas, place a new projectile, and place a cap over the barrel muzzle, and evacuate it.

    I suppose you'd need many LGGs, automated to the degree possible. I wonder how many joules per shot a production machine would release?

  2. A lot of greens don't like wind at all, with the noise and the bird-blender feature.

    A lot of people don't like the look either, but I think windmills look kind of cool myself. Admittedly, I don't have a bunch dominating the skyline every day.

  3. According to the LPPFusion's monthly update:

    "They announced that they had achieved fusion reactions for the first time with their approach, recoding a total of 50 neutrons. The energy input to the device, in the form of gunpowder to drive the gun, is 9MJ. By comparison LPPFusion’s best results have produced 5 billion times more fusion reactions from 150 times less input energy."

  4. I wonder if we'll ever see 'commercially' viable fusion? I just wish the NRC promoted cheap, modular fission reactors, preferably molten salt or some other form that cannot 'melt down'.

    A man can still dream, right?

  5. Being a mechanical engineer, I'm slightly acquainted with conservation of momentum. My point is that if you take the same energy, and dump it into 1 kg of mass, instead of 300 kg, the resulting explosion carries the same energy, but about 17 times less momentum when it hits the wall. So, in *mechanical* terms, you're actually talking about the equivalent of 17-18 kg of TNT.

    I guess it comes down to the depth of penetration of the energy being deposited. As I pointed out, lithium is molten over an unusually wide range; Melts at 180.5C, boils at 1,342C. Which means it can absorb a LOT of energy without being converted to a gas.

    But, yes, everything is happening so fast that you're probably going to generate a shockwave in the molten lithium, which you really want to reduce to heat before it reaches the outer wall of the reactor and possibly causes spalling. Probably the best way to do that would be to suspend some kind of solid particle in the lithium, with a different speed of sound.

    I'd suggest using a lead-lithium alloy, but *not* the eutectic, so that over a wide temperature range it would be kind of pasty.

  6. Momentum is conserved. A stationary stick of dynamite has zero momentum both before and after exploding. The trick is that momentum is a vector property unlike energy; distributing energy to more particles will necessarily increase the absolute sum of momentums of individual particles greatly as per your argument; but it won't necessarily go directly into harmless undirected, thermal motion.

    What I expect to happen is for the soft xrays and hot charged particles from the explosion to impinge on whatever they first encounter and ablate off the surface, causing a large recoil. I expect some of this lithium to be directly connected to the vessel so that it is not protected from the short, sharp shock.

  7. I wouldn't describe it as "peaceful". Rather, momentum scales as M*V, while energy is M*V^2/2, so this target, which will become EXTREMELY hot, will be more on the energy than the momentum side of things. A blast of heat, rather than an impact, relatively speaking.

    And divided over multiple tons of molten lithium. The molten first wall can be a good long ways away from the detonation.

    So I think making it work, assuming they can get the fusion output, is feasible.

  8. Since they state no figures of merit it should be expected that they have only been able to detect enough neutrons to distinguish it from the null hypothesis that neutrons aren't being produced.

  9. Neither does the energy in 300 kg of TNT. On average for each D-T reaction 3.5 MeV will go into He-4 which will go into heating the target and 14.1 MeV will go into neutrons; some small fraction of which will dump energy into heating the target. At least 20% ends up in the target, which goes boom. Some of that energy goes into x-rays which ablate nearby streams of metal, which goes boom. For D-D fusion, which will be present to some extent, even more of the energy ends up in charged particles.

    I don't think it's going to be nearly as peaceful as you think to release that amount of energy on a microsecond time-scale.

  10. It's not as bad as you make it out to be: While the energy content of a shot may amount to the equivalent of 300 kg of TNT, it's not delivered in the form of an explosive blast producing mechanical impact. It's a pulse of radiation which will cause bulk heating of the molten lithium wall. Depending on the mass of lithium involved, this could be manageable.

    Also, consider that the expensive part of the system is likely the accelerator. Which is firing vertically into a hollow cylinder of rotating molten lithium, to meet a free falling target. You can stack those hollow cylinders, and cycle through them by just altering the timing so that the target and projectile meet at different heights.

    Each shot produces about 1.4^9 J of thermal energy.
    Lithium has a specific heat of 3582 j/KgK, and a molten range of over a thousand degrees, so is capable of absorbing about 3^6 J/K. That works out to needing about 500kg of lithium in that rotating wall. Well, in the portion absorbing it, since it will have to be fairly thick to shield everything outside it.

    That's about a cubic meter. Honestly, while 300Kg of TNT sounds horrific, when you run the numbers, it looks feasible. You're going to have a lot of cubic meters of lithium to divide that across.

  11. They have said that their first experiment was with gunpowder as a POC, but that they will switch to something like a rail gun.

    I would hope that “something like” actually means an induction gun, not a rail gun. Because a rail gun tears itself up after just a few shots. There’s no way a commercial plant could be shooting a rail gun repeatedly for years. But an induction gun has much less acceleration, so I don’t know if it’s even possible for fusion.

  12. My impression is that they actively want to render grid based utilities economically infeasible, in order to force everyone into local energy self-sufficiency. From that perspective, the disadvantages of wind power suddenly become advantages.

  13. Definitely agree with the Greens bit. If they're against hydro, they cannot be for any realistic sort of fusion, which does generate radioactivity. In fact, it is a mystery to me why they tolerate even wind…

  14. This design has bad prospects for scaling. If it shoots only once every 5 seconds as is their target repeat rate for a demonstration plant, then getting a moderate 100 MWe /300 MWth requires explosions of the order of 300 kg TNT. That's way too much energy per shot or their target plant is small to the point of being useless.

    If they target both a reasonable power output of 100 MWe and an explosion size that is maneagable they'll get a repeat rate more like 10 times per second. But if they do this, they only get a couple of kWh per pulse and that requires targets to cost << 10 cents each.

    This is the same problem as all the other LIF and ZPinch devices that use some manufactured target.

    If the targets are plastic they up making water (not compatible with lithium metal) if there is any oxygen in it and all kinds of tar. At a high repeat rate this is really large amounts of cruft that has to be managed.

    Pulsed fusion isn't a problem if it doesn't used manufactured targets. E.g. focus fusion, if it scales, makes the plasmoids insitu; there's no complex manufacturing of targets, so a high repeat rate isn't an obstacle.

  15. I actually agree; If you really wanted practical fusion for baseline utility use, you'd go with some version of Project PACER. You could have had fusion reactors back in the 60's that way.

    The problem was, it was totally uneconomic compared to just building conventional fission reactors.

    If you make your decisions on a basis of pure engineering feasibility, you'd forget about fusion, and concentrate on improving fission plants. Fusion is unlikely to be economically viable even if the engineering problems are solved, it's just too finicky.

    At least on Earth. In space, the ultra high temperatures involved would theoretically allow for a very high Carnot efficiency compared to conventional fission plants, reducing the size of expensive radiators.

    But you could get the same gains with fission, by switching to dusty plasma reactors. If I were calling the shots, the money going into fusion would have been spent there, and we'd likely already be generating power that way on a routine basis, it's so much easier than fusion.

    Fission is simply superior to fusion, if you have the fuel available. As it is on Earth, but maybe not in the asteroid belt and outer solar system.

    My suspicion is that the Greens' tolerance for fusion is illusory, they just use it as the best to be the enemy of the good, a mirage to pretend they're not categorically opposed to all sorts of nuclear energy. The moment somebody gets it working, even starts to look like they will, they'll turn on it.

  16. So, they're currently using a light gas gun? I have to think that for a power production plant they'd need to use something more efficient, and capable of being cycled more rapidly. Maybe some sort of mass driver.

  17. It's a pity that there are no numbers available. So where are they now? one billionth of breakeven? One trillionth? Counting backwards from the number of detected neutrons, how many fusion events took place in one shot?


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