Bob Mumgaard, Commonwealth Fusion Systems — Founder Story

DFJ Growth
DFJ Growth News
Published in
9 min readJul 20, 2022


But by the early 2000s, I realized that climate change was going to be a really, really, really big deal. I also realized that the energy transition was going to be difficult and would involve a lot of challenges. That was interesting to me. Being from Nebraska, you grow up knowing about weather and climate.

It is the ultimate clean energy source.

In a world where tech hype often reaches for the stars, that assertion might seem more of the same. Not so when we think about the potential impact of fusion power.

Scientists have known about fusion even longer than they have known about nuclear fission. The process features nuclei of light elements such as hydrogen combining to form heavier elements, releasing enormous amounts of energy.

This is the same process that powers the sun, along with all other stars. In theory, fusion could become the source of limitless clean, safe, and affordable energy and meet the world’s insatiable energy demand. But harnessing fusion to work on Earth presents technical challenges — not the least being that our globe does not possess the massive gravitational force found on the Sun needed to generate the high-pressure conditions required for fusion.

Enter Commonwealth Fusion Systems (CFS), a fusion energy startup out of Massachusetts Institute of Technology (MIT). Last fall, CFS collaborated with MIT researchers to develop a high-temperature superconducting electromagnet that generated the most powerful magnetic field of its kind ever created on Earth. That immense technical achievement removed one of the biggest obstacles preventing progress in building compact fusion power plants.

In the words of CFS Co-Founder and CEO Bob Mumgaard, this is a moment where the conversation is changing from “this is impossible” to “this will be inevitable.”

Mumgaard and his team are now hard at work to demonstrate the feasibility of fusion within the decade. We caught up with him recently to learn more about what CFS is doing to finally capture the holy grail of renewable energy.

Q: Let’s start at the beginning. You’re a native Cornhusker?

Yes. I’m originally from Nebraska. I grew up and went to school there, through undergrad.

Q: What part of the state did you grow up in?

Just outside of Omaha in a small suburb called Papillion.

There were a lot of gravel roads and I had family and friends who had farms.

Q: Given your later trajectory, I’m curious about your parents. Were they involved in the sciences?

No. My mom was in banking and then she became a florist. My dad worked as an attorney and civil servant for the city of Omaha and then the city council in the town where I’m from.

Q: I’m probably not going out on a limb by assuming you were a pretty good student. What were you interested in back then?

Yeah, I was always a pretty good student. I was big in the arts — music and plays and stuff like that, which has almost nothing to do with what I do now. I was good at math but wasn’t big in the sciences.

Q: Fusion wasn’t an early passion?

No. One of the interesting things about fusion is it’s a field where there are deeply passionate people in it who have put their entire lives into it; like they wanted to do fusion since the third grade. I was not like that.

Q: What did you decide you wanted to pursue?

I went to college to study engineering but realized I did not want to be an engineer.

Mechanical engineers in Nebraska are very talented, but they end up building things like combines and tractors and cool hardware. That wasn’t what I wanted to do. I fell in love with physics late. I applied to grad school and ended up at MIT working in fusion because I had the right skillset that they needed to advance a specific part of a project.

Q: Is it true that you thought you would become a professor?

Yes. That’s what you do when you go for your PhD. But by the early 2000s, I realized that climate change was going to be a really, really, really big deal. I also realized that the energy transition was going to be difficult and would involve a lot of challenges. That was interesting to me. Being from Nebraska, you grow up knowing about weather and climate. I also became really interested in the history of technology and while at MIT, I spent a lot of time learning about how technologies can go from nothing to something.

Q: Talk about the genesis of the idea for a fusion startup. What lit the light bulb where everything came together and you said, “Okay, this is what we need to do, and this is how I’m going to do it”?

It was not a single light bulb moment. By 2013, there was a growing interest in climate change and consideration of how fusion might evolve. I was one of the people MIT tasked to help figure that out. At the time, we didn’t know what MIT’s role would be, or what the right strategy was. But through that process, we were able to gather investors, energy consumers, academics, and environmentalists to come up with MIT’s point of view. The shared point of view was that now was the time to build a fusion industry. If we waited too long, we would miss the opportunity to have the impact needed to meet the challenge of climate change. The technology was good enough and you could envision untapped avenues to improve the technology.

Q: At the time, you were a PhD plasma scientist. Did you know much about business at that point in your life?

Yes. I had started smaller businesses before. Also, in the ecosystem around Boston, most everybody knows what a startup looks like and there is a lot of back and forth between MIT and startups in biotech, energy, robotics, etc. And I had friends who built companies or worked at startups, so stepping out of my comfort zone wasn’t an issue.

Q: There’s a punchline to an industry joke about fusion that goes — fusion is 30 years away and always will be. We’ve known about fusion since the 1940s. Why is it taking so long?

Yes, we’ve known about fusion since 1941 when Arthur Eddington, the astronomer, put all the pieces together. The stars must be doing a process that converts hydrogen to helium. And that process converts mass to energy. He didn’t call it fusion, but it was quickly recognized that this was fusion. The challenge was to create the right set of conditions to make that happen in the lab. We had to make a state of matter that had never been made in the lab before — plasma. And that state of matter has different properties than other states of matter.

Here’s a comparison. Mankind understood what flight was since the primordial days, but it took us a long time to achieve it. First, we had to understand wind tunnels. We had to understand stability. We had to understand how to build a combustion engine to harness flight, which the Wright brothers famously did. But that moment for the Wright brothers was built on a huge history of systematically exploring gliding and wind tunnels and engines and stability. That’s a normal evolution of things. That’s what electricity did. That’s what the steam engine did. They all took a long time. Fusion has been systematically getting further and further along in science and understanding to the point where it feels like we are right at the level where you can see that there’s the equivalent of gliders and there’s the equivalent of engines and there’s the equivalent of stability. Now put them together and you have the Wright brothers.

Q: There’s now a debate underway about the replacement infrastructure to move beyond fossil fuels. Fusion makes so much sense, but why has it been only recently that we’re starting to see this breakout moment?

There’s now a set of serious people at the national labs, the White House, the universities, the startups, and at large energy companies who understand this well enough to see what fusion would look like as a practical energy source.

The debate really is around when this is going to happen. Will it happen in 50 years? In 30 years? In 10 years?

Q: Speaking of breakthroughs, talk about the magnet breakthrough last year. Was that the first time you had a high temperature electromagnet ramped up?

That’s right. This was one of the things that came out of MIT’s look at where fusion was heading. The leading concept for making fusion “work” is basically from a big magnetic bottle. You build a machine that’s made from magnets and inside that machine it creates the conditions that are inside the stars. And it does that because the machine is a force field, if you will, using magnets.

That sounds weird, but I can tell you that the steam engine was weird. You’re going to take fire and steam and make it move a piston? That was weird.

What we’ve known after building over 150 of these things, and by validating the science from the ground up from Newton’s law, all the way to what we actually see in these machines at places like Princeton, MIT, the University of Wisconsin, and national labs like Los Alamos, is that if you build that magnetic bottle and the strength of the magnetic field goes up, the performance goes up — and it goes up like the fourth power of the magnetic field. That’s a huge lever.

Q: That opens the door to demonstrating fusion in a lab?

Yes. It’s exciting. All along, we said that if we want to make fusion faster, we need to rely less on discovery and more on engineering…and if we did that in the magnet, that would mean that the fusion machines were much more practical. We could harness what we already knew in a way that was much more amicable because it was smaller, and it was faster.

That’s what we built. We laid out that plan in 2014 and built the company starting in 2017. By 2021, when we had the magnet, it was “thesis validated” and now onto the next piece.

Q: I’d like to shift gears and touch on your evolution as a manager and entrepreneur .

I’ve always been entrepreneurial. I’m one of six co-founders and the other five people are all really, really, talented, smart, and capable.

MIT incubates things quite well, as does the Boston ecosystem, with fellowships and entrepreneurial programs and venture capitalists who believe in companies that are going to change the world by working on hard problems. I’ve been a beneficiary of all that.

Q: What’s been the toughest skill for you to master?

For me, it’s constantly realizing that you must go out and find people that are better than you in any given thing and give away your job to that person. At the company, we call it giving away your Legos. You have a pile of Legos in front of you and you want to build with them. But you need to realize that you’re better off if you paint a picture of what we’re all building together and to find someone who’s way better at building and give them the pieces they need. That’s been a skillset to learn. It’s also a mindset and a philosophy for someone who moved from the academic world where you want to keep it all and be the leader in this one thing that’s super specialized, and to get people who are good at those things and make them into a team.

Q: Before letting you go, the getaway questions. First, do you have a favorite book?

I read so many, but I’ll go with The Path Between The Seas: The Creation of the Panama Canal, by David McCullough.

Q: Is there a motto that you’ve incorporated into your routine which expresses your approach to life?

Give away your Legos.

Q: Last, but not least, who’s the one person you would say has had the most impact on your career?

More than one. I’d say Alan Eustace, who’s on our board and one of the earliest engineers at Google. Vinod Khosla, who’s one of our earliest investors. I always appreciate his viewpoint even when I don’t share his viewpoint, but I think there’s got to be space for that. And Dennis Whyte, who’s a co-founder of mine, and an extremely strong academic and science visionary.