Meet the Director: David Hill, DIII-D
This is part of a continuing profile series on directors of the Department of Energy (DOE) Office of Science user facilities. These scientists lead institutions that provide researchers with the most advanced tools of modern science including accelerators, colliders, supercomputers, light sources, and neutron sources, as well as facilities for studying the nano world, genomics, the environment, and the atmosphere.
Meet the Director:
To eight-year-old David Hill, the UFO-like top and spindly legs of the Space Needle looked like the future. Outside his suburban Seattle home, he'd climb trees to watch workers as they built the Space Needle in preparation for the 1962 World's Fair. When he saw the Needle finally completed, he felt like he was experiencing "tomorrow" right in the present day.
"That really motivated me," he said. "I think having big, audacious goals changes the world."
Inspired in part by that taste of technology, 14 years later Hill graduated from college as a physics major. Although his PhD at the University of California, Irvine focused on space plasmas, Hill's interests took a turn after graduation.
"I hadn't really thought about fusion," he said, "but it came time to get a job." With more jobs available in fusion energy research than space plasma physics, practicality won out.
It was the perfect shift. When he started interviewing at fusion research facilities, including the Department of Energy's (DOE) national laboratories, he discovered a new passion.
"Fusion, to me, was a perfect melding," he said, referring to the right combination of scientific research and societal impact.
Now, Hill gets to pursue that vision as the director of the largest magnetic fusion facility in the U.S., the DIII-D National Fusion Facility. DIII-D is a DOE Office of Science user facility hosted by technology company General Atomics. As director, Hill leads a team of more than 600 researchers working together to achieve one of science's boldest goals: fusion energy for the future.
The Director's Background:
Fusion brought Hill's space plasma physics background down to Earth.
Plasma — gas made up of charged particles — occurs throughout space and across our planet. Our sun, which is made of plasma, is so hot that hydrogen atoms fuse together to create heavier elements and massive amounts of energy. A fusion power plant would harness this process to create energy. It could potentially provide reliable power, produce no greenhouse gases, and result in no long-lasting radioactive waste.
With these benefits in mind, Hill took a position at DOE's Lawrence Livermore National Laboratory. Arriving at the height of the arms race during the Cold War, he saw collaborations in fusion energy that didn't seem to mirror any of the worldwide conflicts of the time.
"It was amazing that there were all of these exchanges across all of these different political boundaries that you wouldn't imagine were happening," he said. "That I found very motivating and encouraging."
Funding for his program at Livermore ended after three years. But General Atomics — which had just finished building DIII-D — saw promise in a diagnostic tool he had developed.
As a Livermore employee, Hill moved to General Atomics with the intention of staying there a year or two — just enough time to gather his data. But he ended up staying more than a decade longer than expected.
"It felt like a really dynamic group that provided exciting opportunities for anyone to contribute. And we were making big gains towards fusion energy," Hill said. "Frankly, I think we were outdoing everybody."
In his time at DIII-D, he took on an increasing role in leading a research team.
"It was as fun or more fun, and more satisfying, to actually work with a team of people," he said. "If somehow I could help the team function better, that to me was very rewarding."
After a stint managing a small experiment back at Livermore, Hill returned to DIII-D in 2006. He became DIII-D director in 2015.
The heart of DIII-D is a tokamak, a device scientists use to research fusion energy. It consists of a hollow metal donut-shaped chamber surrounded by two sets of magnetic field coils. These coils create magnetic fields 40,000 times stronger than Earth's own magnetic field. The chamber holds hydrogen gas; the machine heats the gas and turns it into plasma using large electrical currents, microwaves, and particle beams. The magnetic fields control the donut-like shape of the plasma. That shape keeps it as hot and stable as possible.
To produce energy from fusion, scientists will need to get the plasma hot and dense enough to have a self-sustaining reaction. They will also need to keep it burning for long periods of time.
Creating and controlling the same reaction that occurs inside the Sun is incredibly hard. Some of the biggest challenges are keeping the plasma's core hot enough, controlling instabilities that can cool down the plasma, and managing the heat and particles the plasma releases.
Researchers must dig into the science of every step of plasma production and management. To understand what's going on inside the tokamak, DIII-D has more than 80 different diagnostic systems, which are operated by General Atomics, universities, and DOE national labs.
"It's arguably the best-diagnosed fusion experiment in the world," said Raffi Nazikian, who leads a research department at DOE's Princeton Plasma Physics Laboratory that includes the lab's collaboration on DIII-D.
This knowledge also feeds into running the largest fusion facility ever planned: ITER. Currently under construction in France, ITER plans to create its first plasma in 2025. Also, research at DIII-D will inform the next generation of fusion devices after ITER. As Nazikian said, "DIII-D may not be the world's biggest [fusion] machine, but we may be the world's most productive one."
In addition to working with the ITER team to inform its design, GA is building what will become the largest pulsed superconducting magnet in the world. This magnet will drive 15 million amps of electric current into ITER's plasma. The DIII-D team is also helping to build a number of ITER's diagnostic tools.
While DIII-D's technology is impressive, it's the people who make it run. DIII-D works with researchers who come from more than 100 institutions around the world to use the facility.
"It's just a great sense of teamwork and camaraderie," said Nazikian. "It's this sense of community and it goes beyond institutional affiliations."
Much of Hill's job is making sure his team gets the best and most essential data out of each experiment. As scientists come up with plans, he provides feedback and helps them find the right resources.
"He wants people to think through and argue very effectively for their perspective," said Nazikian. "I'm always impressed by his questions."
Once the plan and resources are in place, it's go-time. The DIII-D tokamak runs experiments 14 to 25 weeks out of the year. On experiment days, about 30 people assemble in the control room while another 50 to 60 are operating the tokamak.
"All of these experiments are highly collaborative," said Hill.
First, the team powers up the massive magnets and the heating systems that control and create the plasma. The plasma lasts for just five seconds. Displays on the walls of the control room trace the plasma's progress.
"Everyone watches and can tell in real time what's going on. Everyone feverishly looks at the data and decides, ‘Did the plasma do what we wanted?'" said Hill.
Ten minutes later, it's time to start the whole process over again.
Right now, Hill and his team are facing a different set of challenges. DIII-D is just finishing up a planned year-long upgrade. They are adding a new device that heats the plasma's electrons more effectively, upgrading a beam that heats the plasma, and strengthening the facility's microwave generators. The upgrades are designed to allow DIII-D to mimic ITER's conditions even more accurately and point the way to next-generation tokamaks.
"We want to make sure the work we're doing is cutting-edge," Hill said.
One of DIII-D's focus areas is preventing disruptions from shortening the lifetime of a tokamak fusion reactor. During a disruption, the plasma turns off abruptly and can generate very high-energy electrons. While DIII-D is quite robust, disruptions could cause damage to more powerful fusion facilities in the future, interrupting their regular operation.
Scientists are investigating how to avoid disruptions by using precisely aimed beams of high-power microwaves. They use these microwaves to suppress instabilities in the plasma before the instabilities grow too large. In addition to precision aiming, scientists can also vary the microwave power in time to damp down the instabilities as they pass through the beam. Both techniques require precise control of the microwave beams.
By testing various combinations of timing, aiming, and power, the researchers at DIII-D are determining their best options for reliably avoiding disruptions in the future.
Advice for a Future Director:
"Stay focused on the fusion energy goal. Prioritize the science with the highest leverage for that goal. Stay engaged with the researchers. Stay engaged with the people who operate the tokamak and the team that keeps it going and keeps it operating safely. Pay attention to what the rest of the world is doing," Hill said. "Remember, it's not about you."
In Fiscal Year 2018, DIII-D and the other user facilities welcomed more than 36,000 researchers — from academic, industry, and government laboratories in all 50 states and the District of Columbia — to perform new scientific research. For details on the DOE Office of Science user facilities, go to https://science.energy.gov/user-facilities/.
This article originally appeared on the DOE Office of Science news: https://science.energy.gov/news/featured-articles/2019/04-02-19/