All solutions are world-class, but why each solution has different challenges with different events, as well as putting it all together
Last week, The Fusion Report kicked off our series entitled “The Fusion Decathlon”. Today we have part two of the series, which is why different solutions have issues with different components of the total event: putting together a commercial fusion power plant. Specifically, we’ll look at inertial fusion energy (IFE), magnetic confinement fusion (MCF), and hybrid fusion solutions to see which events are uniquely easy for them, and which events are uniquely difficult for them. The quest to achieve commercial fusion energy still takes on significant importance, especially for the US’s European and East Asian allies, even though the US-Iran conflict now has a two-week ceasefire.
The Problems That No One Has Solved Yet, Regardless of Approach…
In the 18th century, a number of inventors including James Watt, Thomas Newcomen and Richard Trevithick invented steam engine technology. The engines, which typically utilized coal to fire them (but could also use wood), turned thermal energy into rotational energy which could drive mechanical devices, or eventually (in the mid-1800s) a generator, which can change rotational energy into electricity. In essence, the Electrical Age was born.
From a very real sense, fusion has not yet entered the age of electricity. Because no one has hooked up a fusion machine to an electrical generator. While there is no doubt that this can be done given enough heat (after all, generators have been around for 175 years), that is not the biggest problem that fusion has to solve today. The one exception is Helion’s Polaris technology, which generates electricity inherently through the same coils that are used to compress the plasma to fusion temperatures and pressures, essentially using the plasma recoil of the fusion reaction’s high-energy charged particles, though this requires deuterium-helium3 (D-He3) fusion rather than the lower-energy deuterium-tritium (D-T) fusion, which produces high energy neutrons rather than charged particles.
The other big general problem which fusion has yet to solve is tritium breeding. Tritium, an ion of hydrogen, is a fairly short-lived radioactive element with a half-life of 12 years. Currently, the only method for breeding tritium is through special breeder fission reactors. The only commercially working tritium breeder reactors today are in Canada and South Korea, with sites for defense purposes (i.e., tritium for nuclear weapons) highly likely in the US (Watts Bar), Russia and China. Given that a 1 GW fusion power plant would consume nearly 55 kilograms of tritium a year, this is a problem. Currently, all of the fusion companies are planning on creating tritium breeder capabilities within their fusion machines, including ITER, but this is yet to be demonstrated. Helium-3 is even rarer on Earth (though it is relatively abundant on the Moon), and is produced by the decay of tritium; its breeding is even more complicated than that of tritium.
Inertial Fusion Energy: Brute-Force Strength and Precision
The thing that differentiates IFE than anything else is the application of highly concentrated energy to a very precise target. When you think about pointing hundreds of beams of high energy at a millimeter-sized target, it is quite a feat, whether it is laser beams in the NIF and its descendants, beams of high-voltage electrical pulses like the Sandia Z machine or Pacific Fusion’s fusion machine, or high-speed collapsing liquid metal walls in magnetized target fusion (MTF) like in General Fusion, this is an event that requires precision that can be repeated over and over. In that sense, IFE is very much like Star Trek’s impulse engines (if not exactly the same). In that sense, IFE makes several of the challenges related to fusion trivial. Unlike magnetic confinement fusion (MCF), it doesn’t need high-power magnets or anything along those lines, nor does it have the physics of incredibly difficult magnetic fields to constantly tune and manage. This is because the confinement in IFE (the process of compressing and heating the fusion fuel) actually happens through the myriad of laser beams, electricity pulses, or similar approaches.
On the other hand, every one of the lasers, electrical beams, or liquid metal compressors must do their job EXACTLY the same every time, or the unequal compression of the fuel will result in lack of fusion. Moreover, the injection of the fusion targets must also be precise; if there is any variation in positioning or timing of the target injection, the target will be unequally radiated or potentially missed completely. In essence, you have a high precision mechanical machine which must function correctly all the time for years on end; not impossible, but certainly not simple. By reference, this is a problem that NIF never had to solve; its targets were placed manually each time it was fired.
Scaling inertial fusion to power plants is mostly hard because the physics happens in tiny, violent bursts, while a power plant needs those bursts to be repeated reliably, cheaply, and efficiently thousands to millions of times over its lifetime. The main bottlenecks are target manufacturing, driver efficiency, repetition rate, and keeping every shot precise enough to ignite the fuel. In inertial fusion, a fuel pellet must be compressed extremely symmetrically; small defects can grow into hydrodynamic instabilities that ruin the implosion. That means the target itself, the laser pulse shape, and the beam uniformity all have to be controlled with very high precision
Scaling Experiments into Reality: The Path Forward For IFE
Challenge #1 of IFE is achieving the requisite efficiency required to achieve net facility gain. Lasers are notoriously inefficient; the pulsed flashlamps used by NIF (the only facility to achieve Q>1, and that was scientific gain, not facility gain) are roughly 0.5% efficient at turning electricity into laser light. By example, for every MW of electricity put into the NIF lasers, the laser output energy is only 5 kW, making a ‘big hole’ that has to be overcome to create a net facility gain.
Newer generation solid-state lasers, much like solid-state LED lighting systems, are much better and achieve at least 10% efficiency, and potentially 20% efficiency in the future. That is a 20x to 40x improvement over the NIF flashlamp lasers. In a similar manner, non-laser based IFE systems such as the Z Machine have similar or potentially better efficiencies than solid state lasers. This significantly improves the likelihood that IFE can reach the efficiency required to achieve break even or better power outputs.
Similarly, electrical beam current machines utilizing impedance-matched Marx generator (IMG) technologies like those of Pacific Fusion’s device put out high-current beams far more efficiently, and with much smaller and less exotic, capacitors than older machines such as the Z-Machine at the Sandia National Labs Z Pulsed Power Facility.
Main Engineering Hurdles of IFE Reaching Power Plant Scale
Scaling inertial fusion to power plants is mostly hard because the physics happens in tiny, violent bursts, while a power plant needs those bursts to be repeated reliably, cheaply, and efficiently thousands to millions of times over its lifetime. The main bottlenecks are target manufacturing, driver efficiency, repetition rate, and keeping every shot precise enough to ignite the fuel. A power plant also needs a much faster “shot rate” than today’s laboratory systems. Studies and reviews note that practical inertial fusion power would require firing targets several times per second or more, which is far beyond current laser capability.
Luckily, IFE has some “tricks” in the collective pockets of its various commercial companies to address at least some of these difficulties. While the collection of the thermal energy from those violent bursts is not trivial, thermal inertia does help spread out that power more evenly. Additionally, solid state lasers, driven in part by their use as industrial cutting devices, are getting better and better all the time. That leaves target fabrication, injection and beam aiming. These are areas that Inertia Fusion (among others), the newest company in IFE, is focused on solving. In a sense, electronics manufacturing (making small, inexpensive parts; part placement by robots; and adjustment of part placement to deal with variations in product geometries) is not that different from the same problems that IFE is dealing with. By employing technologies and people with capabilities and expertise in these fields as part of their teams (or to team with other companies), inertial fusion companies will be reasonably able to solve these problems over time.
Conclusion: Fusion and IFE Have Some Difficulties to Overcome…
One fusion entrepreneur once said “Fusion isn’t rocket science. If it was, it would already be done”. He was not wrong: any form of fusion has a lot of ‘moving parts’ that must be perfected to consistently generate electricity or thermal heat efficiently. In the next article in our series, we’ll look at the leading alternative to inertial fusion energy, known as magnetic confinement fusion (MCF), and the strengths and challenges that it has as a working approach for building a commercial fusion commercial power plant.
