sublime fusion

The sublimes of specious fusion concepts

sublime /səˈblaɪm/ adjective

tending to inspire awe usually because of elevated quality

specious /ˈspiːʃəs/ adjective

having a false look of truth or genuineness; having deceptive attraction or allure

Bent Flyvbjerg, an academic expert on megaprojects, wrote about the four sublimes that explain the common story arcs of megaprojects and “seduce decision makers to underestimate hidden risks, and to overestimate benefits”:

The “technological sublime” describes the excitement engineers and technologists get in pushing the envelope for what is possible in “longest-tallest-fastest” types of projects.

The “political sublime” describes the tendency politicians have for constructing monumental infrastructure to benefit themselves and their causes.

The “economic sublime” describes the delight business people and trade unions get from making lots of money and jobs from megaprojects.

Finally, the “aesthetic sublime” is the pleasure designers and people who appreciate good design derive from building and using iconic and beautiful megaprojects.

In reviewing fusion companies and reactor concepts, I have found a similar pattern. There is a set of common sublimes that arise again and again: ideas that seem so attractive they can make other hard problems all but disappear.

The compactness sublime

A compact fusion device sounds like the clean answer to the giant fusion projects typified by ITER, NIF, and others. Make it smaller and it will cost less. Make it simple and the timelines shrink. Make it look like a product instead of infrastructure.

No one is building a fusion device bigger than it needs to be for their purposes. The problem is that fusion has fundamental limits to scale. Neutrons need a meter or two of shielding, even for aneutronic fuels. Thermal plasmas need distance for insulation. Materials have limits to power density, stresses, etc.

The non-thermal sublime

There are some who believe the laws of nature are like the laws of man, that they can pick which ones to follow and choose not to follow the laws of thermodynamics. They want to play Maxwell’s demon. They think they can reduce energy losses from ions to electrons. They think they can keep ions non-thermal with minimal recirculating power.

But physics sets the house rules and the house always wins. The Rider Thesis is the boogeyman to Maxwell’s demon in fusion.

The aneutronic sublime

Aneutronic fusion is the clean-fusion dream: no tritium, fewer neutrons, less activation, simpler licensing, and direct energy conversion. Some even go so far as to falsely claim it has zero radiation production.

It is easy to see the appeal. Tritium breeding is hard. Neutron damage is hard. Remote maintenance is hard.

But an aneutronic fuel does not make the system easier. Aneutronic fuels come with much harder plasma requirements: higher temperatures, better confinement, and stringent impurity control. These fuels always produce high energy radiation via secondary reactions which make truly aneutronic fusion reactors a fiction.

The direct-conversion sublime

Fusion is an advanced technology; why shouldn’t it have an advanced energy conversion system, one that is more efficient than just boiling water?

Much of the energy is released in charged particles, which can then be converted by electric and/or magnetic fields directly into electricity.

The problem is that it is hardly as simple as the cartoon picture. Real particles scatter energy. Real plasmas radiate photons. Real collectors need to survive harsh environments. While direct conversion could increase the conversion efficiency of fusion energy to electricity, the realities of physics and engineering constraints greatly reduce the benefits from what is purported.

The simulation sublime

The plots are beautiful. The fields look clean. The particles stay confined. Net energy is one experiment away.

All too often, simplistic models are used to demonstrate that a clever new fusion concept is the next ideal confinement device. In the compromises to build a solvable model, important physics is thrown out. The device never performs nearly as well as the initial models indicated.

All models are wrong. Some are useful. The least useful model is the one that works because it excludes the physics that would kill the concept.

The founder sublime

Investors are vulnerable to a good founder story. They love the outsider genius, the person who sees what the establishment missed.

Fusion is one of the most complex endeavors humanity has undertaken. There is not a single person on Earth who has a complete picture of how fusion energy will turn out. The romantic idea of an outsider displacing the field is unlikely; they all come in missing some of the important fundamentals, many of which are summarized in other sublimes here.

The useful question is whether the concept survives review after the founder leaves the room.

The secrecy sublime

A company says the key breakthrough is proprietary. They cannot share the information with reviewers, even under NDA. They are scared that it will be stolen.

Fusion companies should protect real intellectual property. But if the central physics claim cannot be checked under NDA by competent reviewers, secrecy is no longer protection; it is insulation from reality.

The incumbent-failure sublime

Tokamaks are too big. ITER is too slow. NIF is not a power plant. Stellarators are too complex. Magnets are expensive. Lasers are inefficient.

A critique of the incumbent is not validation of the alternative. The alternative still has to close on its own merits.

The single-bottleneck sublime

The magnets are the issue. The laser is the issue. The fuel is the issue. The materials are the issue.

Fusion is a coupled system. Higher field helps confinement but increases stress and shielding challenges. Smaller size reduces capital cost but increases wall loading.

There are no isolated issues or miracles in fusion.

The cheap-option sublime

Some concepts survive because the next experiment is cheap enough to fund.

For an investor, that may be reasonable. A $10M experiment can be a cheap way to buy optionality on a huge outcome. It is also a form of Pascal’s wager, a bet on a low-probability, high-impact outcome.

While “expensive to test” does mean “less likely to become a power plant,” the converse of “cheap to test” does not mean “more likely to become a power plant.” It means cheap to test.

The conclusion

Every specious fusion concept has its own selection of sublimes. The machine is small. The ions are non-thermal. The fuel is clean. The conversion is direct. The simulation works. The founder saw what others missed. The details are secret. The next experiment is cheap.

All too often, these sublimes seduce investors into funding concepts that will fail. The sublimes cannot replace the integrated and complicated physics and engineering needed to make fusion work. Fusion is hard. That is why the field needs discipline.

Ultimately, fusion energy is its own sublime. Once realized, it will be one of the great achievements of humanity. Fusion should inspire awe; but don’t let its aura blind you into making a financial decision based on one of these sublimes without understanding the whole picture.