FES Research: Sustain a Burning Plasma
To produce energy from fusion, fusion devices must be able to achieve and sustain a burning plasma. Plasmas are extraordinarily hot gases in which electrons have broken free from their associated atomic nuclei. A burning plasma occurs when heat generated by the fusion process is higher than the heat supplied from external sources.
To generate power from this process, three critical conditions related to the plasma must be met: sufficient density, temperature, and confinement. The two main fusion approaches achieve these conditions in distinct ways:
- Magnetic confinement: Uses powerful magnetic fields to contain the high-temperature plasma.
- Inertial Confinement: Involves rapidly compressing and heating a small pellet of fusion fuel using lasers or other drivers.
FES supports a variety of approaches to confining plasmas in fusion energy systems. These include advanced tokamaks, spherical tokamaks, high-field tokamaks, stellarators, pulsed magnetic fusion, and laser inertial fusion.
Tokamaks
A tokamak is a type of fusion device that confines a plasma into a donut shape using magnetic fields. These magnetic fields allow scientists to control the plasma and create the conditions needed for fusion.
There are two major strategies for designing tokamaks – conventional and spherical. These devices offer complementary strategies for improving confinement while also remaining compact. Spherical tokamaks use enhanced plasma physics properties while high-field conventional tokamaks rely on high-field magnets.
The DIII-D Office of Science User Facility at General Atomics in San Diego, California, is a conventional tokamak. It is also the largest magnetic fusion research experiment in the U.S. Recently, an international team of researchers at DIII-D developed an innovative tokamak operation method. They inverted the shape of the plasma boundary. This approach avoids harmful spikes of heat exhaust that increase the erosion of materials. At the same time, this approach distributed the steady-state exhaust over a larger area of the tokamak’s first wall. This change could potentially extend the lifespan of critical internal components such as the tokamak divertor.
The SPARC tokamak under construction by Commonwealth Fusion Systems – a project supported by FES – has similar conventional aspect ratios. However, it will be operated at even higher toroidal magnetic fields.
The NSTX-U Office of Science User Facility at DOE’s Princeton Plasma Physics Laboratory is designed to explore the physics of plasmas confined in a spherical torus configuration. Instead of a donut shape, spherical tokamaks have more of a cored apple shape. The NSTX-U has a much higher ratio of plasma pressure to the pressure of the confining magnetic field than other tokamaks in the world. This characteristic allows scientists to study plasmas in this unique.
Other tokamak facilities used by researchers supported by FES include JT-60SA in Japan. ITER – which is currently under construction in France – will be a tokamak that is an industrial-scale burning plasma experimental facility.
Stellarators
Stellarators also use magnetic fields to confine plasma, but in a different shape. Stellarators generate twisting magnetic fields that wrap the long way around the donut shape.
Compared to tokamaks, stellarators are less likely to have transient events that cause harmful disruptions. The 3D shaping of plasma also provides more flexibility compared to the 2D design of tokamaks. They also require less injected power and could be simpler to control.
However, the stellarator design is much more complex, especially the magnetic field coils. Conventional stellarators lack symmetry along their axes. This lack of symmetry reduces the confinement of energetic ions. As these ions must be confined to heat the plasma, improving this issue would greatly increase efficiency.
FES’s stellarator research focuses on improving this concept through quasi-symmetric shaping. This concept was invented in the U.S. and could provide a path forward for developing stable, well-confined, steady-state stellarator plasma confinement.
One stellarator device is the Wendelstein 7-X (W7-X) in Germany, which the U.S. is a formal research partner on. Accordingly, the U.S. is participating fully in W7-X research and access to data. The U.S. collaboration on this machine focuses on developing and assessing 3D divertor configurations for long-pulse, high-performance stellarators. U.S. researchers develop control schemes to maintain plasmas with stable boundaries for operation. They also address challenges related to controlling the superconducting coils and managing the relationship between diagnostics and controls. U.S. researchers also play key roles in developing the operational scenarios and hardware configuration for this device.
Inertial Fusion Energy
In inertial fusion energy devices, lasers, for example, fire onto a tiny capsule of fusion fuel. The heat from the lasers causes the capsule to implode, compressing and heating the fuel inside it. This process initiates fusion reactions in the fuel.
IFE has entered a groundbreaking era, marked by significant achievements at the National Ignition Facility (NIF). In 2022, NIF successfully achieved a burning plasma, a pivotal step toward harnessing fusion energy. Since this initial success, NIF has repeatedly demonstrated burning plasma conditions, with ten successful ignition experiments to date. The most recent of these experiments set a new energy yield record, delivering an impressive 8.6 MJ—more than four times the 2.08 MJ of energy input to the target.
FES’s inertial fusion energy program aims to translate ignition breakthroughs from NIF into practical fusion power for the nation. Currently, the United States is the undisputed leader in inertial confinement fusion. To maintain that leadership, the U.S. IFE ecosystem was established to connect research, innovation, and talent. It ensures that research efforts across National Laboratories, universities, and industry are coordinated with the Fusion Science & Technology Roadmap. It also leverages AI and machine learning to accelerate fusion discovery and builds a skilled workforce by providing hands-on access to advanced facilities where students, engineers, and technicians can engage directly with real experimental systems.
The FES IFE program benefits from the DOE Office of Science’s world-class User Facilities, such as the Linac Coherent Light Source, as well as leadership computing resources at the Oak Ridge Leadership Computing Facility and the National Energy Research Scientific Computing Center. It also benefits from the NNSA inertial confinement fusion program by leveraging scientific advancements at the National Ignition Facility, the Z Pulsed Power Facility, and the Omega Laser Facility. LaserNetUS, North America’s first high-intensity laser network supported by the Office of Science, is also playing an important role in advancing inertial fusion energy (IFE).
Supporting Areas
FES also supports research into developing transformative and innovative diagnostic techniques, including quantum-based systems. This research is looking for ways to apply these techniques to new, unexplored, or unfamiliar plasma regimes or scenarios.
It also runs a Future Facilities Studies activity that supports research for required facilities that are critical to the development of fusion energy and address needs of both the public and private sectors.
Learn more about research supported by the Fusion Energy Sciences program:
