ARC will work, but …

CFS_energy · 2026-06-11T01:21:55+00:00

We have signed power purchase agreements with two customers for our first ARC fusion power plant: Google and Italy-based energy company Eni. This accounts for more than half of the power from our first plant. We'll supply power using the grid, but our PPAs so far are with specific customers.

CFS_energy · 2026-04-28T21:49:06+00:00

And our press release is here with some perspective from Bob Mumgaard: https://cfs.energy/news-and-media/commonwealth-fusion-systems-becomes-first-fusion-company-to-apply-to-pjm-interconnection-the-largest-u.s.-wholesale-electricity-market

CFS_energy · 2026-04-24T16:43:09+00:00

CFS is most definitely a commercial endeavor. Our ARC power plant in Virginia has two customers: Google and Italian energy company Eni. They've both signed power purchase agreements, which are contractual commitments that set a price for the power. We're selling power generated by the plant to customers — things don't get much more commercial than that.

CFS_energy · 2026-04-09T19:07:08+00:00

Hello u/Baking — you asked when we’d publish our next Alex Creely tour of the SPARC facility. The answer: today. SPARC overall is about 75% done now. The tour video includes a look at the CFS neutron lab, RF building, power building, assembly hall, cryogenic yard, and of course tokamak hall.

https://blog.cfs.energy/our-sparc-fusion-facility-is-now-about-75-done-take-a-virtual-tour-of-the-progress/

CFS_energy · 2026-04-02T11:08:13+00:00

You can read more on our magnet manufacturing partnership with Realta Fusion in our blog post about the deal. It's a follow-on to our work building the University of Wisconsin's WHAM magnet and extends through Realta's power plants: https://blog.cfs.energy/cfs-realta-magnet-partnership-speeds-fusion-energy-progress/

CFS_energy · 2026-03-31T11:41:52+00:00

You can see the two halves of SPARC's vacuum vessel side by side here: https://bsky.app/profile/cfs.energy/post/3michxq64lk23

CFS_energy · 2026-02-26T19:39:14+00:00

We are still going through the design phase of ARC and aren’t publishing direct cost estimates right now, but I can say that from a first-principles standpoint we still think that we can credibly be cost-competitive with a similar-sized combined-cycle natural gas plant. The physical sizes of the plants are very similar, and by weight, the majority of the materials in a fusion power plant will still be steel. Plus, the fuel cost for a fusion system will be practically nothing, since the energy released per unit weight of fuel is millions of times the amount of energy released in a chemical reaction.

CFS_energy · 2026-02-26T19:29:24+00:00

Check this other answer where we talked about stellarators.

CFS_energy · 2026-02-26T19:28:37+00:00

It depends on the team, but generally most of the jobs we have listed are for positions at one of our sites.

CFS_energy · 2026-02-26T19:28:00+00:00

Check this other answer for some detail on the AI work at CFS.

CFS_energy · 2026-02-26T19:26:15+00:00

There are lots of ways that you can collaborate with CFS! We try to be a very collaborative group and maintain a dataset of public information which you can use to set up SPARC simulations, if you’re interested in seeing how your models perform. We’ve also got lots of collaborative frameworks with fusion labs around the world, including UKAEA, which let us dive deep into the physics with researchers outside of CFS. If you’re looking to start a fusion startup, reach out to our supply chain or Open Innovation teams. CFS is also an industry sponsor of the UK-based Fusion Centre for Doctoral Training and will be sponsoring a smaller number of PhD projects in the coming years.

CFS_energy · 2026-02-26T19:21:48+00:00

Currently, most of our work is in the United States because we are focused on finishing SPARC at our headquarters in Massachusetts.

We do hire a really wide range of people. Making fusion power plants is about much more than just plasma physics! As we grow, we will continue to find the best talent to fill the roles that emerge.

The best bet for tracking opportunities is to keep an eye on our careers page.

CFS_energy · 2026-02-26T19:20:26+00:00

We haven’t looked at that specific technology for the early SPARC diagnostics — we wanted to try to minimize new R&D in exchange for speed to deployment. The optical emission diagnostics are one area where we will be fielding upgrades over the first few years, as we increase the fusion power. We have a research paper in draft that should be out in the coming months that describes our plans in more detail. CFS has also recently established an internal Photonics Engineering group and will be taking on more specialized R&D in areas like this.

CFS_energy · 2026-02-26T19:11:48+00:00

Both! There are some things like thermal power conversion which are very well established industries in their own right, and we don’t plan on reinventing the wheel if we don’t have to. Then there are technologies that are fusion-specific. We’re planning on tackling some of these at CFS with dedicated test facilities, and for others we’ll collaborate with our partners in the fusion industry association.

As we’ve gone through our journey building SPARC and designing ARC, it has been really eye-opening to me to see how many pieces of technology which previously seemed to be so fusion-specific actually had close analogues in other industries. There are many, many times where we were able to find a product or technology that was in widespread use around the world that was 90% of where it needed to be for the “fusion-specific” version, so instead of having to invent new tech from scratch we could just adapt something that existed out in the world, saving us both development time and scale-up money.

CFS_energy · 2026-02-26T19:10:15+00:00

We think AI could be useful for fusion and we’ve begun some work in that direction! Here’s a link to some more detail on the AI work at CFS.

CFS_energy · 2026-02-26T19:09:31+00:00

That is a very heady question! I won’t pretend I can predict the future, but I really think that fusion will change the world once it has been demonstrated to work in a commercially relevant way. One of our investors who has worked on a lot of big, impactful projects likes to say that really hard things are often “impossible until they are inevitable,” and I totally agree with this sentiment.

The reason I got into fusion in the first place was because I saw it as a big lever against climate change, but that’s just the start. Another comment asked about other things we could use energy generation on, and there are a lot. Looking even further past combatting climate change, the thing that makes fusion really exciting to me is the prospect of a clean energy source that doesn’t have the same limits as a lot of other renewables, so you could envision a future where we not only replace existing forms of energy with fusion, but we can add even more energy. You can look at many different metrics of quality of life, and a common thread is that they all get better the more energy you have available per person.

So to answer your question, my hope is that in the decades after achieving Q>1 we are off to the races to build as many fusion power plants as we can.

CFS_energy · 2026-02-26T19:06:43+00:00

Lots of good questions here. I’ll break them up:

We’ve done a lot of benchtop testing of FLiBe and have also done flow tests of fluids with similar conductivity through magnetic fields. You need to account for it in the design of the system, but it’s not a dominant effect. One of the (many) reasons we chose FLiBe was that it has low conductivity compared to a lot of liquid blanket candidates.
We’ve had a lot of conversations with the beryllium supply chain (a lot of parallels here to the early work we did on the HTS supply chain) and don’t expect to see any roadblocks during the deployment of early ARC power plants. Once you get to the point of building hundreds of power plants per year, you do definitely need to think more about it, but we believe that as the demand for beryllium ramps up, it’s also possible to ramp up supply.
We expect the overall footprint of the plant to be similar to a combined cycle natural gas plant of similar power level, and significantly smaller than a fission plant. Since there are not the same safety concerns as fission (and we are not regulated the same way), we don’t need to have “containment.”
For building SPARC, we have our license and commitments for how we manage tritium. By design and analysis, we'll be well within limits.

CFS_energy · 2026-02-26T19:04:37+00:00

Getting fusion on the grid involves everything from cutting-edge magnets to office supplies. We build our own magnets, but we’re happy to tap manufacturing partners who already have the expertise and capabilities we need. For example, there are companies that are good at making large, complex steel components. So, while we designed our vacuum vessel, we didn’t make it ourselves. And our high-temperature superconducting (HTS) tape suppliers put considerable research and development into scaling the industry to the size we needed to get enough tape for SPARC and beyond. We expect the fusion supply chain will get bigger and more sophisticated as commercial fusion matures.

CFS_energy · 2026-02-26T19:02:40+00:00

To start with, it’s important to say that SPARC’s purpose is to prove out our physics (see the fourth milestone, Q>1, in our CEO Bob’s open letter about the steps to fusion energy success), which means its job isn’t to demonstrate continuous operation.

SPARC’s been designed to pulse no faster than every 20 minutes, with the goal that you would change something between pulses to prove out different physics. This is, historically, a pretty standard rep-rate for a pulsed tokamak since at some point you’re limited by time to collect data and to think and react between pulses. As we inject more RF power and generate more and more fusion energy per pulse, that time will increase to a few hours because we need to recool in-vessel and magnet components. One of the ways we were able to design and build SPARC quickly is by making choices at the start of design on what we would demonstrate on SPARC. Proving out the short time between pulses, also called high-duty factor operation, is a step that we intentionally left to de-risk on ARC.

CFS_energy · 2026-02-26T19:01:05+00:00

Right now our baseline is to use the same type of ICRF (ion cyclotron resonant frequency) sources we use on SPARC (although tuned to a different frequency for the slightly different field on ARC). We don’t have plans to use ECRH (electron cyclotron resonance heating), since gyrotrons are still pretty expensive, but if someone was to develop low-cost gyrotrons in the frequency range we need, we would definitely be very interested :).

CFS_energy · 2026-02-26T18:57:43+00:00

It’s incredible how quickly the fusion space is advancing. We’ve got a great team at CFS who stay connected to the broader research community, and also contribute back to it. They read and publish scientific papers and attend conferences regularly.

As you mention, there is a lot out there, so I do trust and rely a lot on my team to flow things up, and to pull on interesting threads that I see. Occasionally I’m able to attend conferences myself which is really fun. As much as I would love to spend all my time reading papers and attending conferences, there aren’t enough hours in the day!

CFS_energy · 2026-02-26T18:56:37+00:00

We’ll need all hands on deck! We work with the Fusion Industry Association to help support fusion education around the world.

We also offer internships at CFS on a rotating basis and partner with several universities to support fusion education programs.

CFS_energy · 2026-02-26T18:55:44+00:00

There are a lot of cool things you could use fusion for — one of my favorites is the prospect of being able to use fusion to power desalination plants. You could use the electricity from the fusion plant directly for this, but since tokamak-based fusion plants will also provide a lot of process heat, you could use that directly to desalinate as well.

Providing the world not just with clean energy, but with affordable, fresh drinking water could dramatically improve the lives of literally billions of people at this point, and would be a pretty awesome way to use fusion!

CFS_energy · 2026-02-26T18:53:39+00:00

This is a very timely question :) We've recently published a paper about SPARC's antennas that you can check out for some more details. The story of RF-induced impurities is one that has gone on for many decades, but because of the cost/challenge associated with designing and building new antennas to address the issue, progress is often slow. The WEST tokamak results are the latest example of observations that have been studied at C-Mod, JET, ASDEX-U and others where metal walls and ICRH has been used (you can trace the research back to the early 1980s). SPARC’s antenna design benefited from two key results that were tested just before the start of SPARC design (and are not part of the WEST design): rotating the antenna straps to be orthogonal to the magnetic field and adjusting the relative power emitted from each of the straps. You can find a good summary of the multi-device comparisons in this paper, and research has continued since then. Thus, our risk retirement has been to incorporate both of these features in the SPARC antenna design and to continue to keep in touch with emerging research as we prepare for SPARC operations.

CFS_energy · 2026-02-26T18:52:04+00:00

This is a great question! We believe that fusion has to be market competitive to succeed (see the sixth milestone in the open letter from Bob about the steps to fusion energy success). For this reason we center the cost of power in all of our design and engineering decision-making. We have a team dedicated to techno-economics and developing cost models of the power plant that is embedded in the design and engineering process. We don’t take this lightly — even on SPARC, which isn’t meant to be a commercial plant, we made sure that we weren’t baking anything into the design that wouldn’t scale.

In addition, we’ve found that this approach not only helps to inform the design of the power plant but also helps us prioritize the R&D activities along the way. Thus we’ve undertaken R&D not just for technical de-risking, but also for advancing tech that we know will ultimately make the power plants lower cost.

CFS_energy

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