Nav: Home

Fast action: Novel device may rapidly control plasma disruptions in a fusion facility

January 24, 2019

Scientists seeking to capture and control on Earth fusion energy, the process that powers the sun and stars, face the risk of disruptions -- sudden events that can halt fusion reactions and damage facilities called tokamaks that house them. Researchers at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL), and the University of Washington have developed a novel prototype for rapidly controlling disruptions before they can take full effect.

The device, called an "electromagnetic particle injector" (EPI), is a type of railgun that fires a high-velocity projectile from a pair of electrified rails into a plasma on the verge of disruption. The projectile, called a "sabot," releases a payload of material into the center of the plasma that radiates, or spreads out, the energy stored in the plasma, reducing its impact on the interior of the tokamak.

Deeply penetrating payloads

This process may prove faster and may allow payloads to penetrate more deeply into the plasma than today's most developed techniques. Current systems release pressurized gas or gas-propelled shattered pellets using a gas valve into the plasma, but with velocity limited by the mass of the gas particles. "The primary advantage of the EPI concept over gas-propelled systems is its potential to meet short-warning time scales," said Roger Raman, a University of Washington physicist on long-term assignment to PPPL and lead author of a Nuclear Fusion paper that describes the new system.

The risk of disruptions is particularly great for ITER, the large international tokamak under construction in France to demonstrate the feasibility of fusion power. ITER's dense, high-power discharges of plasma, the state of matter that fuels fusion reactions, will make it difficult for current gas-propelled methods of mitigation to penetrate deeply enough into the highly energetic ITER plasma to take good effect.

On ITER, mitigation is desired in less than 20 milliseconds, or thousands of a second, from the warning of a disruption, with 10 milliseconds as ideal. Tests of the EPI prototype show that it can deliver a payload of correctly sized particles in fewer than 10 milliseconds, compared with 30 milliseconds for gas-propelled systems.

The prototype, built at the University of Washington, harkens back to a fusion reactor fueling system that Raman worked on years ago. That system injected plasmoids, football shaped plasmas with their own magnetic fields, that were injected into a fusion plasma at high velocity. Raman adapted some features of the system to allow much more mass to be injected in a simpler configuration, as would be required for a long standby mode of operation, to develop the EPI.

Electrically conducting rails

The prototype houses the sabot between two electrically conducting rails located some 2-to-3 centimeters apart and connected to a capacitor bank that holds an electrical charge. Discharging the bank produces electromagnetic forces that accelerate the sabot, enabling release of the payload in just 2 milliseconds. The material, consisting of light-metal granules or pellets, would radiate the energy of a disruption from the center of the plasma to the edge, spreading out the energy and weakening its impact on the tokamak walls.

Further development of the EPI system has been proposed to be conducted at PPPL. Plans call for construction of second-and third-generation prototypes with increasingly strong magnetic fields over a three-year period, followed by deployment on a tokamak in the fourth year. Results so far, as reported in Nuclear Fusion, provide a degree of confidence that an effective EPI system can be developed to mitigate powerful disruptions on ITER.

Joining Raman in this research publication are Jonathan Menard and Masa Ono of PPPL, and Wei-Siang Lay and Thomas Jarboe of the University of Washington. Support for this work comes from the DOE Office of Science.

PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas -- ultra-hot, charged gases -- and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energy's Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
-end-


DOE/Princeton Plasma Physics Laboratory

Related Magnetic Fields Articles:

Visualizing strong magnetic fields with neutrons
Researchers at the Paul Scherrer Institute PSI have developed a new method with which strong magnetic fields can be precisely measured.
Scientists deepen understanding of magnetic fields surrounding Earth and other planets
Now, a team of scientists has completed research into waves that travel through the magnetosphere, deepening understanding of the region and its interaction with our own planet, and opening up new ways to study other planets across the galaxy.
Technique pulls interstellar magnetic fields within easy reach
A new, more accessible and much cheaper approach to surveying the topology and strength of interstellar magnetic fields -- which weave through space in our galaxy and beyond, representing one of the most potent forces in nature -- has been developed by researchers at the University of Wisconsin-Madison.
A bubbly new way to detect the magnetic fields of nanometer-scale particles
The method provides manufacturers with a practical way to measure and improve their control of the properties of magnetic nanoparticles for a host of medical and environmental applications.
Quantum sensing method measures minuscule magnetic fields
A new technique developed at MIT uses quantum sensors to enable precise measurements of magnetic fields in different directions.
More Magnetic Fields News and Magnetic Fields Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...