NIF Diagnostics

Lawrence Livermore turns an event too fast, too hot, and too dense to touch into knowledge.

• 0:02Speaker 00

  December 5th, 2022, 1:27 a.m. The house is dark and quiet. Dave Schlossberg is asleep at home. Hours earlier, he'd told the scientist running the overnight experiment to call if there's anything to report. And then, the phone rings.

• 0:26Speaker 01

  Yeah. About like 2:00 in the morning, Alex calls me up and says, "Hey, Dave, I think something interesting happened."

• 0:33Speaker 00

  Dave jumps off the bed and grabs his computer, pulling up signals from instruments surrounding the target chamber at Lawrence Livermore's National Ignition Facility. And as the numbers resolve, he sees something extraordinary. Something they'd chased for 50 years.

• 0:51Speaker 01

  We started looking at the data and said, "You know, I think this is actually ignition. This is more energy out than we used to start the reaction."

• 0:58Speaker 00

  But the shot is already over. The target is gone. The chamber is dark again, and no one saw fusion ignition happen. Only the signals remain. At NIF, Lawrence Livermore's diagnostics turn an invisible instant into evidence that can shape the next experiment and strengthen confidence in the nuclear stockpile. Welcome to the Big Ideas Lab, your exploration inside Lawrence Livermore National Laboratory.

• 1:39Speaker 00

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• 2:23Speaker 00

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• 2:50Speaker 02

  Main laser operation will begin in approximately 1 minute.

• 2:59Speaker 00

  Inside Lawrence Livermore's National Ignition Facility, 192 laser beams race toward a target smaller than a peppercorn and arrive almost simultaneously. Then, in a fraction of a second, it's gone. No one can look inside while the lasers fire. The event is too fast, too hot, and too dense for anyone to observe directly. But understanding exactly what happens is essential. So NIF relies on diagnostics. Dave Schlossberg is an experimental physicist at NIF, where he leads the nuclear diagnostics team.

• 3:41Speaker 01

  People are very familiar with diagnostics in the medical field. For example, if you want to know what your temperature is, you use a thermometer. If you want to look inside your body and see if you have a broken bone, you use an X-ray machine. Those diagnostics, those instruments, look inside a very complex system to understand what's going on.

• 3:55Speaker 00

  And while the principle is familiar, the environment isn't.

• 3:59Speaker 01

  We can't just stick a thermometer in our experiment because it's 200 million degrees and hotter than the center of the sun. And we can't use an X-ray machine because it's 50 times denser than lead.

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  Whatever happened inside has to be measured from the light, radiation, and particles that escape.

• 4:16Speaker 01

  We have to develop really clever, innovative techniques that let us measure the system of interest. The longest NIF experiment is 50 billionths of a second. That's 2 million times faster than you can blink your eye. 2 million times.

• 4:30Speaker 00

  Blink once, right now. Go ahead. That blink took you about a tenth of a second. In that sliver of time, this fusion event, the one we've been describing, could happen and disappear 2 million times over. And in that sliver of time, the diagnostics have to catch everything.

• 4:52Speaker 01

  We measure temperatures, densities, shape, pressure, fusion yields, structural composition, X-ray emission, particles, electromagnetic pulses coming off the experiment. If you name it, we're trying to measure it, or we already have measured it.

• 5:06Speaker 00

  Setting up a fusion ignition experiment takes at least eight full hours.

• 5:11Speaker 01

  The whole thing is over in 100 trillionths of a second. I often sit back and reflect that when I go to work, it's an amazing opportunity to really understand a process that is like something out of science fiction.

• 5:22Speaker 00

  And the stakes of those measurements reach far beyond a single experiment.

• 5:26Speaker 01

  The United States has a stockpile of nuclear weapons that, since the early 1990s, we can't do any testing on. But we need them to be guaranteed to work.

• 5:35Speaker 00

  It's like taking care of a car you want to last for 40 years, except you can't ever turn it on to make sure it runs.

• 5:44Speaker 01

  But when you do turn it on, you need it to work every time, all the time, no questions asked.

• 5:48Speaker 00

  That's one of the problems NIF helps solve. Without underground nuclear testing, scientists need another way to study how materials and systems may behave as the stockpile ages. At NIF, they can recreate pieces of those extreme environments in the laboratory and use diagnostics to measure what happens inside them. But the stockpile isn't standing still either. The National Nuclear Security Administration is rapidly modernizing key systems, introducing new designs and materials into weapons that must still perform exactly as intended. Before any of those changes reach production, designers need proof that they will work.

• 6:31Speaker 00

  NIF gives them a place to build that proof: recreating the pressures and temperatures a new design will face and using diagnostics to measure whether it behaves the way the models predict.

• 6:42Speaker 01

  In developing new diagnostics, and even using the ones on the NIF, they come from a very long and strong family tree. The diagnostics we've developed and used have a history from actually underground testing that the US did before the 90s. Back then, they were looking at an incredibly bright, very intense source that you can't physically go and measure. So you need to develop diagnostics that are stood off and can tell you about what's going on in there. And so what we've done over the last several decades is refine and improve those measurements and customize them on the National Ignition Facility.

• 7:16Speaker 00

  That evolution continues today, with each generation of diagnostics designed to capture more information faster and under more extreme conditions. One of the newest is called Fiddle. Kara Venary is an experimental physicist at NIF. She came to Lawrence Livermore with a background in geology, studying how matter behaves deep inside planets, places humans cannot directly observe. At NIF, Fiddle allows her to watch similar transformations unfold in the laboratory, frame by frame.

• 7:52Speaker 03

  Fiddle is a time-resolved X-ray diffraction diagnostic. So it takes snapshot images that are 2 billionths of a second long. It takes four of them per NIF shot. So we're able to measure the density and understand the structure of a material on very short time scales over the course of a single experiment.

• 8:12Speaker 00

  These four snapshots create something like a stop-motion view of a material changing under pressure.

• 8:18Speaker 03

  If you compare graphite and diamond, those are both pure carbon materials, but one is extremely hard and one is extremely soft. Those two materials have the same chemical structure, but their physical structure is completely different, and that changes the properties of them really drastically. So understanding, as we apply pressure, that will change a material from one phase to another, like graphite to diamond.

• 8:42Speaker 00

  Under enough pressure, those atoms can rearrange, transforming one material into something with entirely different properties.

• 8:50Speaker 03

  We understand roughly what pressure and temperature materials should change from one phase to another, but we don't really understand how the kinetics affect that phase transition, how long it will actually take all the atoms to rearrange and generate a new structure.

• 9:06Speaker 00

  That transition is the missing piece. Under extreme conditions, the way a material transforms can be just as important as the state it ultimately reaches.

• 9:16Speaker 03

  We're using that as a test to develop the diagnostic for future applications that can be for discovery science or stockpile modernization.

• 9:24Speaker 00

  To produce that atomic transformation in the laboratory, scientists need an extraordinary amount of pressure, measured in gigapascals, or GPA.

• 9:33Speaker 03

  At ambient pressure, like on the surface of the Earth, we're at 0 GPA, 1 atmosphere. The experiments that I'm working on are compressing lead. We understand what structures it can exist at, at high pressures and high temperatures. We are basically compressing that sample from 0 to 110 GPA over about 15 nanoseconds.

• 9:54Speaker 00

  110 gigapascals is roughly equivalent to the weight of 500,000 elephants pressing down on a single city manhole cover. And the instrument trying to capture what happens sits just centimeters from the target.

• 10:09Speaker 03

  The closest part of the target to the closest part of Fiddle is 2.5 centimeters away.

• 10:14Speaker 00

  That proximity gives Fiddle the view it needs, but it also places its sensitive electronics directly in the path of everything the experiment throws off, kind of like needing to shield your eyes from the headlights of an oncoming car or the sun on the horizon.

• 10:30Speaker 03

  We have this problem where we generate a plasma, and a plasma is basically a gas with electrons pulled off of it. Those hot electrons fly around, and I've called them the poltergeists of NIF because they hit everything. And then unfortunately, when they hit stuff, they make it start glowing in X-rays. Basically, when an electron hits a material, it excites the electrons inside it, lets on more light. Unfortunately, that process happens in our experiments, and those X-rays that get generated increase the background crazy amounts on our sensors. So there's a lot of work to understand how to control the secondary X-rays that are generated during the experiment.

• 11:08Speaker 00

  So the team redesigned part of Fiddle target's shielding, hoping they solved the problem.

• 11:14Speaker 03

  We were like, oh, we're going to be so smart. We'll just put plastic on it, and then we won't get any background.

• 11:18Speaker 00

  This plastic shielding created a barrier intended to stop the X-rays created by hot electrons before they could reach the instrument's sensitive detectors. They installed the new component on the target, positioned Fiddle close to the target, and prepared for another experiment. Then the warning lights came on. The target chamber closed, the laser fired.

• 11:43Speaker 03

  And it was, I would say, a catastrophe.

• 11:52Speaker 00

  Lawrence Livermore National Laboratory is hiring. If you're passionate about tackling real-world challenges in science, engineering, business, or skilled trades, there's a place for you at the lab. Right now, positions are open for a Senior Guidance, Navigation, and Controls Engineer and a Senior Business Operations Specialist. These are just a few of the more than 100 exciting roles available. At Lawrence Livermore, you'll work on projects that matter, from national security to cutting-edge scientific advancements. Join a team that

• 12:28Speaker 00

  values innovation, collaboration, and professional growth. Explore opportunities at llnl.gov/careers, where your next career move could make history.

• 12:49Speaker 00

  At NIF, building something new often means learning first from the version that doesn't work. The team had hoped the plastic shielding would block the unwanted background. Instead, the failed shot revealed something different.

• 13:03Speaker 03

  It was as if we had nothing on there, and we realized that the problem actually was that we were generating maybe lower-energy X-rays, but the transparency of that material to those X-rays was much lower than the metal was. So they were making X-rays and then had a complete line of sight to our sensors.

• 13:20Speaker 00

  The change didn't remove the unwanted signal. It gave it a clearer path in. They needed a different type of shielding.

• 13:29Speaker 01

  You can beat yourself up for being wrong and not making the correct prediction, or you can really view it as an opportunity to learn and say, hey, here's something that we don't quite understand, and we can really dive in and try to figure out what's going on.

• 13:42Speaker 00

  In experimental science, an unexpected result isn't the end of the work. It's new information. And the build, test, learn, and redesign cycle is how NIF's diagnostics continue to evolve.

• 13:58Speaker 01

  Diagnostics are both the scoreboard and the map. They're the scoreboard for ignition to say how much fusion came out, how symmetric was the implosion, what was the performance like. And they're also the map to tell us, how do we move forward next? What's the impact of the changes that we made, and what should we change next?

• 14:16Speaker 00

  At NIF, that feedback not only shapes the next shot, it can shape the next diagnostic.

• 14:22Speaker 01

  We're constantly refining and evaluating and upgrading and even conceptualizing new diagnostics. It's a really nice feedback loop of, here's what we measured, here's what we think we understand about it, but we still don't understand this process, so let's build something else to actually tell us what we need to know. And if it's really difficult to measure, it makes it even more fun.

• 14:42Speaker 00

  Fiddle itself grew out of that progression.

• 14:45Speaker 03

  There was a predecessor diagnostic called G3D, and that was a testing diagnostic to see if the sensors that we wanted to use in Fiddle would survive the extreme conditions that are inside of NIF. And then, once that proved possible with these HCMOS sensors, then we built Fiddle, which has more of the sensors and can cover more of the diffraction angles that are required for these kinds of experiments.

• 15:10Speaker 00

  Now, the team is developing the next generation of that diagnostic.

• 15:14Speaker 03

  We will be building a new diagnostic called Falcon in the next few years that will have eight sensors, and will have a different type of sensor that will be able to get, instead of just four snapshots, six snapshots during an experiment.

• 15:26Speaker 00

  More snapshots create a richer record of the experiment. The next challenge is turning that record into a measurement scientists can understand.

• 15:35Speaker 01

  There's a couple of things we do with the data that gets collected. The first thing is we take raw signals that we collect, like voltage and time and light, and we convert them into something that's physically meaningful. And the way we do that is we apply calibrations and corrections, and we compare the data with backgrounds. It's not just you get a voltage and you know, aha, that's what the temperature is. There's a whole slew of supplemental and background work that needs to happen in order to understand what that signal is telling you.

• 16:03Speaker 00

  That means removing the background noise and examining the X-ray diffraction peaks left behind by the material.

• 16:11Speaker 03

  For any one-shot, we get many different diagnostics, and we want to understand every aspect of it. We subtract the raw shot, which is any background that could be contributed by just the sensor being turned on. And then, we analyze the peaks using Labeye Fitz, which is a standard X-ray diffraction technique. So we know what structure the material should be in. We can generate a synthetic X-ray diffraction pattern, and then we can pull out the density that we measured during the experiments.

• 16:39Speaker 00

  Each diagnostic preserves a different piece of the same event. Scientists also compare those pieces, looking for independent measurements that tell a consistent story.

• 16:50Speaker 01

  Another thing we do with the data that we collect is we compare it with different diagnostics. For example, if one system tells us the fusion yield is some value, and then another diagnostic that's independent confirms that value, then it gives us more confidence in that measurement. On the NIF, we do have some diagnostics that measure the same quantity, and that's by design so that we understand, yes, this is a value that we can have high confidence in.

• 17:12Speaker 00

  Scientists also compare those measurements with what computer models predicted before the shot: how the pressure should rise, how the material should respond, and what the diagnostics should see.

• 17:24Speaker 01

  We run the experiment and collect data, and that data either confirms the model's predictions or says, hey, nature doesn't quite behave like you think it does. You need to update your model and change your understanding of things. And so, one thing we do with the data is we compare it to these models and use it to refine our understanding.

• 17:41Speaker 00

  That understanding can then travel beyond the experiment itself, informing new designs and even bringing knowledge to related fields, like the quest to make fusion energy practical. There's synergy between NIF diagnostics and research and the needs of future fusion energy plants.

• 17:59Speaker 01

  In terms of fusion energy, there's a laboratory institute called LIF, Livermore Institute for Fusion Technology, and that is geared towards taking some of the understanding that we've developed and saying, how do we leverage that to move towards fusion energy? It's a great organization that interfaces between public-private partnerships, as well as trying to push forwards the entire field.

• 18:21Speaker 00

  The shot may be over in an instant, but scientists and engineers can return to its data for hours, days, and years, reconstructing what happened, testing new explanations, and designing better experiments.

• 18:35Speaker 01

  The shot on NIF itself is gone almost instantly, but the data remains for hours, days, years after that. And so, what we can do is we can have hundreds of scientists and engineers reconstruct what happened over time, test hypotheses, and build better experiments for the next round of operations. So the real product of diagnostics is not just the numbers that get produced, but the understanding of what's going on in these physical processes.

• 19:00Speaker 00

  At NIF, the most important part of the experiment is also the part no one can see directly. The target compresses, materials transform, fusion reactions unfold, and within a fraction of a second, the event is gone. But the diagnostics do more than explain a single experiment.

• 19:21Speaker 01

  I think what is so unique and fulfilling about the work that the National Institution Facility and Lawrence Livermore National Laboratory do is that it's built in with purpose. The work I do is really relevant for stockpile modernization, it's really relevant for national security, it's really relevant for fusion and fusion energy.

• 19:39Speaker 00

  The instruments make hidden physics visible. What scientists do with that view is what turns an experiment into something the country can use.

• 20:02Speaker 00

  Looking for a career that challenges and inspires? Lawrence Livermore National Laboratory is hiring for a Power Grid Dynamics Engineer and a Transmission Grid Engineer, along with many other roles in science, technology, engineering, and beyond. At the lab, every role contributes to groundbreaking projects in national security, advanced computing, and scientific research, all within a collaborative, mission-driven environment. Discover open positions at llnl.gov/careers, where big ideas come to life.

• 20:47Speaker 00

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