r/fusion • u/Cruisin4Fusion • 6h ago
r/fusion • u/CFS_energy • 28d ago
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!

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 • u/steven9973 • 15h ago
Is fusion power here at last? The imagined energy of the future is becoming very real right now (with Holland+Mumgaard)
Interesting podcast with Andrew Holland/FIA and Bob Mumgaard/CFS regarding all important topics for it.
r/fusion • u/steven9973 • 15h ago
The power exhaust constrained SPARC separatrix operational space
r/fusion • u/steven9973 • 16h ago
FIA Outlines EU Financing Pathway for Fusion - Fusion Industry Association
Fallout Pipboy technology Irl
Cortical Labs.
Miniature fusion..
The Future of biohacking?
Now whose working on a central line pic display port?
Dr ....
Hey cortical labs... how small could you make fusion?
Fuzors.net
r/fusion • u/steven9973 • 1d ago
Max-Planck-Institut für Plasmaphysik (IPP) (@plasmaphysik.bsky.social) BlueSky: meeting in Greifswald with digiLab to discuss AI strategy for W7-X
r/fusion • u/steven9973 • 1d ago
News Analysis BlueSky (@newsanalysis.com): BBC on fusion propulsion by Pulsar Fusion, Avalanche and Princeton Satellite Systems
r/fusion • u/FourQFusion • 1d ago
Sense checking claims about the cost of electricity from fusion (spoiler: it's gonna be expensive!)
Intuitively, you might expect that the 'holy grail' of energy will be expensive. Yet, government labs, academics, and private fusion companies promise that cheap green electricity is just around the corner.
Billions of dollars of public and private money have been invested in fusion, and earlier this month General Fusion listed publicly with a promise to deliver carbon free electricity to the grid in the 2030's, and that ultimately the electricity would become cost competitive.
The problem? New research published in the Journal of Fusion Energy shows that some of those promises are fallacious.
About the study
The study puts questions and debate about technology and timelines to one side, and assumes that the tech delivers as promised, today.
Rather than taking the conventional approach of estimating the costs of each yet-to-be-designed component and adding them up, the study works backwards from a claimed cost. By methodically removing the known costs (such as financing, steam turbines, cooling systems, and so on) the implied costs of fusion hardware are revealed.
It is shown that in some cases, such as the General Fusion investor information filed with the Securities and Exchange Commission, the fusion hardware would have to be produced for free to make the sums work. This is nonsense.
Why it matters
We are being asked to invest, either directly by purchasing shares, or indirectly through our taxes. Indeed, billions of dollars of taxpayer money and private investment have already been spent on fusion research. Yet, it can easily be shown that even if the technology worked today, and we could build a powerplant overnight, then the electricity would not be affordable.1
There's an opportunity cost to the pursuit of uneconomic fusion schemes. For one, money is being diverted from other 'better' (cheaper, greener, more economical, ...) technologies to pursue something that, even if it worked, appears doomed to be uneconomical.
Despite the hype, fusion schemes such as the one proposed by General Fusion have clear and obvious shortcomings that even a high school level analysis can identify. Why are policy makers and investors blind to this?
Judge for yourself
Have a read of the paper here:
http://dx.doi.org/10.1007/s10894-026-00592-w
1 Note that the study specifically pertains to fusion thermal powerplants (tokamaks, stellarators, MTF, ...). It says nothing about schemes that rely on direct energy conversion.
r/fusion • u/steven9973 • 2d ago
From miniTRUST to TRUST (Tokamak)Project: building fusion engineering one step at a time. Every complex scientific facility begins with a reliable engineering platform. | Giuseppe Calabrò - Italy/China
r/fusion • u/steven9973 • 3d ago
Non-inductive start of spherical tokamak LATE - overcome pulsed solenoid approach
iopscience.iop.orgr/fusion • u/Corealist • 4d ago
Thea Helios reactor. What is the probability for it to work.
while looking at the differences between tokamaks and stellarators, I found the following ( unpublished) article about the Thea Helios reactor. (https://thea.energy/wp-content/uploads/2025/12/20251210_FPP_Helios_overview_paper.pdf).
To me this seems to be a well thought out reactor design with realistic design goals, but I am not an expert. The only thing that seems problematic is the size, which in my opinion would probably make the reactor too expensive to build.
I would be interested in the opinion of people with fusion expertise on this reactor.
r/fusion • u/steven9973 • 4d ago
A comparison of cusp and mirror topologies for beta -> I onmagnetic confinement | Journal of Plasma Physics | Cambridge Core - commercial consider Mimi loop
cambridge.orgr/fusion • u/Queasy-Chain-2886 • 5d ago
electrical engineer to fusion tech
so im a elctrical engineer im really intrested in fusion tech but confused how to get into it im currently in my 1st year
r/fusion • u/Mountain_Bluebird150 • 4d ago
Acrylic bell jar for a demo fusor?
Will it melt, will it implode, or is it fine to use?
r/fusion • u/steven9973 • 5d ago
Pacific Fusion Says Pulsed-Power Prototype Hits Milestone at National Lab (3000 shots)
r/fusion • u/Ok-Supermarket-4431 • 4d ago
American Fusion Update
American Fusion Inc. (OTC: AMFN) (“American Fusion” or the “Company”), developer of the proprietary Texatron™ Fusion Engine™, announced that it has received a Certificate for Industrial Radiation Machines from the Texas Department of State Health Services (“DSHS”), representing a significant regulatory and operational milestone as the Company continues executing its engineering, testing, and validation program.
r/fusion • u/steven9973 • 5d ago
A world-first lens brings neutrons into sharper focus (another possible use for fusion born neutrons, Focused Energy is already involved in neutron imaging)
r/fusion • u/steven9973 • 5d ago
Kyoto Fusioneering and NGK Announce Strategic Partnership to Develop Molten Salt FLiBe (blanket)Technology for Fusion Power Plants | NEWS | Kyoto Fusioneering
r/fusion • u/steven9973 • 5d ago
Optimized finite-β tokamak-stellarator hybrid configurations achieved by planar dipole-field coils
List of Fusion Demonstration and Pilot Plants proposed locations
Commonwealth Fusion Systems
- Demonstration: SPARC - Devens, MA 75% complete
- Pilot (eventually commercial) 400MW: ARC - Chesterfield Co, VA Groundbreaking 2027
Helion Energy
- Demonstration: Polaris - Everett, WA Operational 2025
- Pilot 50MW: Orion - Malaga, WA Groundbreaking April 2026
Type One Energy
- Demonstration: Infinity One - Claxton, TN inside Bull Run Turbine Hall(North)
- Pilot 350MW: Infinity Two - Claxton, TN at Bull Run site TBD
Proxima Fusion
- Demonstration: Alpha - Garching at Max Planck IPP
- Pilot 1GW: Stellaris - Gundremmingen at former NPP
Realta Fusion
- Demonstration: Hammir - Madison, WI (OM Depot) "The Forge"
- Pilot 200MW: Hammir-DT location TBD
Thea Energy
- Demonstration: Eos location TBD (2026?)
- Pilot 390MW: Helios location TBD
Xcimer Energy
- Laser-only Prototypes: Phoenix 1-2kJ (June 2026) and Anvil 200kJ (2028) - Denver, CO
- Demonstration: Vulcan 4MJ-12MJ (2031) location TBD
- Pilot 400MW: Athena (2035) location TBD
TAE Technologies
- Demonstration: Copernicus - Irvine, CA (cancelled)
- Pilot 50MW: Da Vinci location TBD (2026? AL, TX, OH, or GA)
Pacific Fusion
- Demonstration: DS (Demonstration System) - Albuquerque, NM (Mesa Del Sol)
UKAEA
- Pilot 100MW: STEP - West Burton Power Station, Nottinghamshire, UK (2040)
Focused Energy
- Demonstration: LightHouse - Biblis at former NPP
- Pilot: at Biblis former NPP (2037)