Berkeley Engineering alumni help achieve decades-long quest for nuclear fusion
Annie Kritcher (M.S.’07, Ph.D.’09 NE) and Brian Spears (Ph.D.’04 ME) share their thoughts on the future of fusion research and how their time at Berkeley shaped their careers
On Dec. 5, scientists at Lawrence Livermore National Laboratory’s National Ignition Facility (NIF) achieved fusion ignition for the first time in history. This major breakthrough — in which a controlled fusion reaction produced more energy than was required to start it — was decades in the making. In the experiment, researchers directed powerful lasers emitting 2.05 megajoules (MJ) of energy at a specially designed capsule containing hydrogen atoms, causing them to fuse together and release 3.15 MJ of energy. This achievement provides vastly improved capabilities for maintaining the nation’s nuclear weapons stockpile and brings us closer to the promise of clean energy.
Berkeley Engineering alumni Annie Kritcher (M.S.’07, Ph.D.’09 NE) and Brian Spears (Ph.D.’04 ME) played an integral role in the work leading up to this milestone. In a recent conversation, they shared their thoughts on the future of fusion research and reflected on how their time at Berkeley helped shape their careers.
This type of research involves very large teams. Could you tell us about your role in this latest breakthrough?
Annie: I was the lead, or principal, designer. My job is to define the input conditions to the experiment, so [for example] the target dimensions, geometries, materials we want to shoot and details about the laser pulse. I’m trying to design the target and laser conditions so that we can create the extreme plasma conditions that are required for ignition.
Brian: Our team is about 1,000 people, across all kinds of disciplines. It’s my privilege to lead the modeling half of the inertial confinement fusion program’s science and physics team. We’re roughly in two pieces — modeling and experiment — and I help drive and guide the modeling side.
Nuclear fusion research has been going on for decades. What was the difference this time?
Annie: We’ve been doing different designs basically for a decade, and where we started is very different from where we ended up. This particular experiment was part of a campaign called Hybrid-E that started making progress back in 2020, during COVID, [and] was actually an a-ha moment at that time.
We spent years trying to optimize different aspects of the experiment, but then we made the capsule that holds the fusion fuel 50 microns smaller — about the width of a hair — and that was enough to let us re-optimize every other aspect of the implosion. That gave us our first big bump in yield in a long time. Since then, we’ve been working to try to optimize various aspects of the implosion in steps.
Brian: We also created a more spherically symmetrical implosion than in past experiments. [That] made a huge difference.
It’s taken decades of research and billions of dollars to reach this point. Has there ever been a time when you felt discouraged? How do you stay focused on the end goal?
Annie: There’s a good chance that any one experiment will be a failure. I have been really discouraged at times. But the good news is those feelings go away fast. I have a quote by Winston Churchill that I keep on my desk: “If you’re going through hell, just keep going.” And [the quote by Josh Shipp] “Perseverance is stubbornness with a purpose.” That’s exactly how it’s felt for me.
Brian: For me, it’s like having to learn a complicated skill, like doing a back handspring in gymnastics. You fail the first time, the sixth time and maybe the 15th time. And you are never happy about failing, but you know that the only way to achieve what you want to do is to try again. So our team has tried again and again, making progress, until we accomplished what we did on Dec. 5.
With this breakthrough, people have high hopes about clean energy, lab-based testing of nuclear arms and an accelerated timeline for nuclear fusion reactors. What do you see as some of the most significant implications?
Annie: I think the scientific breakthrough is an essential accomplishment. It demonstrates that power generation with fusion is possible in the laboratory. It’s going to instigate a lot more support than we’ve had in the past, and that will help things happen at a more rapid pace. I do think it’s moved up the timeline for fusion energy. It’s not a question of if, but when. It is going to be hard and a challenge — and we shouldn’t expect something in a few years or even 10 years.
Brian: Our principal mission at [NIF] is to steward the nuclear stockpile. The United States has not done underground nuclear testing since 1992, which means that we’re certifying a nuclear stockpile without experimental validation in the sense of underground tests. Moving forward, we can use a combination of simulations, AI and machine learning capabilities, and the data from lab-based nuclear fusion tests to model performance. That capability to make strong, quantifiable predictions about intense phenomenon has enormous value for the stockpile as a deterrent.
The computing that has grown out of this, so we can do the prediction, underpins so many things. I’m very hopeful about what ignition means for our central NNSA [National Nuclear Security Administration] mission, for energy and for applications that go far beyond fusion.
After this breakthrough, what’s next? What are your hopes or thoughts when looking ahead?
Brian: We now know how to take our computational technologies and predict what’s going to happen in a laboratory situation, like we did with the ignition shot. We can use our simulation codes and capabilities, wrapped in AI and machine learning, to compare with diagnostic data, and make a decision about the next experiment to do. All of that [can be done] in the computer with only 100 milliseconds between the last experiment and the next one. These capabilities can position us to do very rapid discovery, so things like we’ve done at the NIF, instead of taking months or years or decades to do, we can do them on a seconds, minutes or days timescale.
Annie: I can speak to more of the near term. The enhanced laser capability, which enabled the design changes we made for this last experiment, was actually the first step. By the end of the year, they are going to increase that laser capability even further. The idea is to burn up more of the fusion fuel. The last experiment burned up twice as much as the one before it. This laser upgrade, together with some design changes, enables you to essentially hold the implosion together longer, so you can burn more of the fuel.
How would you say your experience at Berkeley prepared you for this work?
Annie: I would not be here if I didn’t go to UC Berkeley and [wasn’t part of] the nuclear engineering department because I actually did my thesis work with Siegfried Glenzer, a scientist at [LLNL]. I spent most of my Berkeley time learning and doing real hands-on plasma physics experimental work at the lab. It 100% prepared me for the type of work that I’m doing now.
Brian: It did two things: It taught me to think and to learn for myself. And it allowed me to engage not just with the best thinkers but with some of the best teachers. Three Berkeley faculty made a huge difference in my life: Andrew Szeri, my Ph.D. advisor, and Panos Papadopoulos and Oliver O’Reilly. They changed the way that I think and the way that I work — and taught me how to treat people.
Berkeley, as a publicly funded institution, also played a huge role in my education. Every bit of my education was government funded. I had a National Defense Science and Engineering Graduate Fellowship that paid for my graduate education, and I moved into doing work in the public sector at an FFRDC [Federally Funded Research and Development Center] here at Livermore. And Berkeley and its public mission are central to having set me up for that.
What advice do you have for students considering this field?
Annie: It’s the best time to come and join the field. It’s not going to be us who will bring fusion energy to the world. It’s probably going to be a new generation, and we need people. Come and spend a summer here.
Brian: Our lab motto is making the impossible possible. I would encourage people to take a look at what we’ve done and see themselves in those achievements, see where there are chances to lean in and use the skills they’re learning at Berkeley to do something transformational.