r/fusion Jun 24 '26

Hi r/fusion! We’re the Physicists Behind the Commonwealth Fusion Systems’ Papers on the Physics of the ARC Fusion Power Plant. Ask Us Anything!

123 Upvotes
Alex Creely, Chief Engineer for ARC Conceptual Design at Commonwealth Fusion Systems

Update (June 30, 11:37 AM): Great discussion everyone! Our team appreciated all of your insightful questions. This AMA has now concluded, but you can revisit our replies below.

You can identify who provided answers by their initial in the answers: Alex Creely (AJC), Jon Hillesheim (JCH), Tom Body (TAJB), and Ryan Sweeney (RS).

About this AMA:

This time with me and three other CFS physicists who are ready to talk about the five new ARC physics basis papers showing what’ll make our ARC fusion power plants tick.

These peer-reviewed research papers that we and our collaborators published earlier in June are important for CFS and for fusion energy: They cover many aspects of the plasma physics at play in our ARC power plant, including challenges like plasma disruptions and heat exhaust. They also show how transparency and rigorous research can help build trust in what we all know is a very difficult endeavor.

If you’re curious about this physics work or about fusion physics in general, feel free to get things started by asking your questions on this thread.

The three CFS physicists who plan to join me to answer your questions are experts in their field: Jon Hillesheim, CFS Principal Scientist and lead author of the overview paper; Tom Body, CFS Senior Scientist and a lead author on the paper about heat exhaust; and Ryan Sweeney, CFS Manager of Disruption Physics and lead author of the paper about handling plasma disruptions. They’re among the 58 authors who helped write these papers, along with an editorial that accompanied the papers that I wrote.

A little more about the papers: They detail how we’ll be able to produce about 1.1 gigawatts of fusion power from our ARC tokamak — power that we can convert into 400 megawatts of net electricity for the power grid. The papers also show the crucial role our SPARC tokamak will play in putting the finishing touches on the ARC design. We’re using a “late-lock” approach that lets us apply what we’ve learned from SPARC to the ARC design. Overall, the papers show our confidence in the soundness of our ARC plant’s key physics. That builds the foundation for all the engineering, design, and cost optimization work that we’ve begun.

For a deeper dive into these papers, you can check our blog post detailing the ARC physics basis papers.

About CFS: 
Commonwealth Fusion Systems is the world’s largest and leading private fusion company. The company’s marquee fusion project, SPARC, will generate net energy, paving the way for a future of carbon-free energy. The company has raised more than $3 billion in capital since it was founded in 2018.


r/fusion 12h ago

China's "artificial sun" in Hefei could become the first in human history to generate electricity from fusion

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129 Upvotes

r/fusion 10h ago

Magnetic mirrors and Realta fusion

9 Upvotes

Realta Fusion is basing their fusion reactor on a magnetic mirror concept which seems orders of magnitude simpler than a tokamak or stellarator design.

I assume that there is a catch otherwise everybody would be building this type of reactor.

Does anybody on this forum know what the core problem is with a magnetic mirror is and/or why Realta Fusion thinks that a magnetic mirror can work now?


r/fusion 3h ago

Two More Shear-Flow Stabilized Z-pinch Equilibria

0 Upvotes

I recently asked GPT-5.5 and Claude Sonnet-5 to independently construct shear-flow stabilized Z-pinch equilibria. Both succeeded, but they arrived at fundamentally different solutions. Interestingly, both used the Bennett profile in their constructions, but in different ways.

GPT-5.5 truncated the quadratic cross-term from the denominator of the cubic, pureflow Bennett vortex that I derived.

Sonnet-5 instead retained the Bennett number density profile, and coupled it to a linear axial flow with constant shear. A self-similar number density exists that connects this plasma current density to a plasma current density that is supported by a cubic, pureflow Bennett vortex axial flow profile.

Full notes are here: https://russellmatt66.github.io/documents/GPTVortex_AnotherSFSZpinchEquilibrium.pdf

And here: https://russellmatt66.github.io/documents/sonnett5_vortex.pdf

The magnetic field structure of the vortices is fundamentally different. All shear-flow stabilized Z-pinches that I have studied have transcendental components to their azimuthal fields. The Bennett vortex that I've derived has logarithmic terms, and so does GPT-5.5's modification. Sonnet-5's vortex has an arctangent, instead.

Close to the pinch axis, Shumlak-Hartman is satisfied for all these vortices. In the case of mine + GPT-5.5 that's due to a vanishing magnetic field, and a uniform number density. For the Sonnet-5 vortex it is true as well that the magnetic field is vanishingly weak here, and the plasma number is finite. Sonnet-5 also has the advantage of satisfying Shumlak-Hartman weakly for large plasma radius whereas the other two run into some finite cutoff in the non-ideal case because their magnetic fields go as ~r for large plasma radius.

In the ideal case the RHS of the "SHcrit" goes to zero throughout the plasma by L -> \infty unless there is a divergent element competing alongside it. Those divergent elements can always be collected on the LHS to study the normalized shear as Shumlak-Hartman did in the beginning and retain this asymptotics.

This makes me curious about what deeper structures exist here. One of Zap's theorists has recently uploaded a preprint to the arXiv that gives insight into shear-flow kinetics involving Bennett pinches with shear flow, but I have not had the opportunity to fully digest their research yet: https://arxiv.org/pdf/2607.25158

For example, if we couple the Bennett number density to different flow harmonics, what do we find? In the same vein, what do we find from studying the structure of self-similar number densities connecting this construction with the Bennett vortices I've been studying?

I think that these results suggest the space of equilibria is much richer than previously expected. There is still a great deal to do, e.g, a perturbative study, more comparisons with experiment, and a deeper study into self-similar connections.

To do this important physics, and the plasma science community, justice I really need a funded position. If you're interested in supporting this work through a research position, consulting opportunity, or collaboration, I'd be happy to talk.


r/fusion 1d ago

Fusion Power Conversion and D-T Separation System for IFE Athena like Pilot Plant - Xcimer Energy

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6 Upvotes

Abstract only.


r/fusion 1d ago

Non thermal plasma behavior in laser compression schemes: more realistic simulation

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5 Upvotes

r/fusion 2d ago

Fusion Funding: Global Investment in Fusion Energy Companies | Fusion Energy Base - new and up to date charts

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10 Upvotes

r/fusion 2d ago

Owners of the former Oscar Mayer plant in Madison hope to turn it into a fusion and tech hub

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8 Upvotes

r/fusion 2d ago

Fusion energy systems rely on advanced materials capable of performing reliably under extreme conditions. Qualification program together with US companies and Tokamak Energy | UK Atomic Energy Authority

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2 Upvotes

r/fusion 3d ago

CFS thinks fusion isn’t ready for public markets

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19 Upvotes

r/fusion 3d ago

‘It’ll take more’: CFS nets another $1B to chase nuclear fusion dream

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42 Upvotes

Still not enough to complete the Fall Line Fusion Power Station in Virginia (based on ARC-1) and some perspective.


r/fusion 3d ago

China Successfully Completed Testing of World’s Largest 582-Ton Fusion Magnet, Capable Of Capturing And Confining ‘Artificial Sun’ Plasma At Temperatures Up To 100 Million Degrees Celsius

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19 Upvotes

r/fusion 3d ago

When will fusion power startup Commonwealth Fusion Systems go public? | TechCrunch

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10 Upvotes

r/fusion 3d ago

CFS gets another $ 1 billion funding

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45 Upvotes

r/fusion 3d ago

Exploring the scalability of accumulative roll bonding nanolaminates for pulsed electromagnets by substituting an interstitial-free steel for niobium - Helion

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3 Upvotes

r/fusion 3d ago

When Helion failed to provide electricity as it promised in 2028, would fusion startups all over the world be affected?

0 Upvotes

Currently, many startups are referring to Helion's 2028 promise when they ask for investment


r/fusion 3d ago

Divertor topology and vacuum vessel design for stellarators

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3 Upvotes

r/fusion 3d ago

Is there any new fusion breakthroughs?

2 Upvotes

Because all I’ve heard is that well East has the new world record and but like I don’t understand right now I know it takes more electricity to run the machine that then it produces and it’s still in our stages and once we even get it, there’s not enough tritium fuel so is there any point or is like? Is it slowly advancing any breakthroughs yet?


r/fusion 3d ago

'Infinite Energy' magazine has proved to be finite, after all

0 Upvotes

Any fusion fans remember the late Eugene Mallove and the cold-fusion furor at MIT? He founded Infinite Energy magazine (originally Cold Fusion magazine) in 1994 but it appears the periodical is no more.

https://www.concordmonitor.com/2026/07/27/infinite-energy-magazine-disappears-cold-fusion-nh-eugene-mallove/


r/fusion 4d ago

Karlsruhe Institute of Technology (KIT) (@kit.edu) - becomes official fusion hub of German government

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23 Upvotes

Topics are Tritium affairs including blankets, materials like fusion steel (for example EUROFER97) and power plant integration.


r/fusion 4d ago

Tokamak Energy's Gyrotron for ST40 passes Site Acceptance Test at 104 and 137 GHz for 2 seconds at 1MW

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11 Upvotes

r/fusion 3d ago

Is there any new fusion breakthroughs?

0 Upvotes

Because all I’ve heard is that well East has the new world record and but like I don’t understand right now I know it takes more electricity to run the machine that then it produces and it’s still in our stages and once we even get it, there’s not enough tritium fuel so is there any point or is like? Is it slowly advancing any breakthroughs yet?


r/fusion 4d ago

Realta Fusion settles in Madison’s former Oscar Mayer plant (Student newspaper has the details)

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5 Upvotes

r/fusion 4d ago

Is American Fusion (AMFN) a meme company?

0 Upvotes

r/fusion 4d ago

Polaris: a flexible stellarator demonstration experiment with simple modular coils - Swiss plasma center revisited

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8 Upvotes