Nav: Home

PPPL physicist conducts experiments indicating efficiency of fusion start-up technique

May 31, 2016

Physicist Fatima Ebrahimi at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University has for the first time performed computer simulations indicating the efficiency of a start-up technique for doughnut-shaped fusion machines known as tokamaks. The simulations show that the technique, known as coaxial helicity injection (CHI), could also benefit tokamaks that use superconducting magnets. The research was published in March 2016, in Nuclear Fusion, and was supported by the DOE's Office of Science.

Physicists are interested in CHI because it could produce part of the complex web of magnetic fields that controls the superhot plasma within tokamaks. One component of that web is produced by large "D"-shaped magnets that surround the tokamak and pass through the hole in its center. The other component is produced by a central electromagnet known as a solenoid, which induces a current inside the plasma that creates another set of magnetic fields. These fields combine with the fields produced by the "D"-shaped magnets to form a twisting vortex that prevents the plasma from touching the tokamak's walls.

Future tokamaks -- especially compact spherical tokamaks like NSTX-U -- might not have enough room for solenoids, though. CHI could be ideal for those tokamaks because it doesn't require solenoids at all. During CHI, magnetic field lines, or loops, are inserted into the tokamak's vacuum vessel through openings in the vessel's floor. The field lines then expand to fill the vessel space, like a balloon inflating with air, until the loops undergo a process known as magnetic reconnection and snap closed. (Think of tying off that inflated balloon.) The newly formed closed field lines then induce current in the plasma.

By performing simulations, Ebrahimi found that narrowing the part of the magnetic loop that extends up into the tokamak through the floor could cause 70 percent of the field lines to close, compared with 20 to 30 percent without such narrowing. "For the first time, we see a large volume of closure during computer simulations," she said. The number of field lines that close is important because the more field lines that close, the greater the current flowing through the plasma, and the stronger the magnetic fields holding the plasma in place.

"The findings help us figure out how we can get maximum start-up current in NSTX-U," said Ebrahimi. "That is a direct application of the research. But now we also have insight into some basic physical phenomena: what are the physics behind the process of reconnection? How do the lines actually close?"

The simulations also provide a boost to the advancement of fusion energy. "Can we create and sustain a big-enough magnetic bubble in a tokamak to support a strong electric current without a solenoid?" asks Ebrahimi. "The findings indicate that 'yes, we can do it.'"

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. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. 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

DOE/Princeton Plasma Physics Laboratory

Related Magnetic Fields Articles:

Are gamma-ray bursts powered by a star's collapsing magnetic fields?
In its final moments of life, a distant massive star releases an intense burst of high-energy gamma radiation - a Gamma Ray Burst (GRB) - the brightest sources of energy in the universe, detectable to humans through powerful telescopes.
Not everything is ferromagnetic in high magnetic fields
High magnetic fields have a potential to modify the microscopic arrangement of magnetic moments because they overcome interactions existing in zero field.
Ultracold gases in time-dependent magnetic fields
Zk Noor Nabi from Zhejiang University, China and co-workers from the Indian Institute of Technology studied the phase transition between the Mott insulating (MI) and superfluid (SF) states of an ultracold gas in a time-dependent magnetic field.
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.
The FASEB Journal: Magnetic fields enhance bone remodeling
Since the creation of 3D-printed (3DP) porous titanium scaffolds in 2016, the scientific community has been exploring ways to improve their ability to stimulate osteogenesis, or bone remodeling.
Tangled magnetic fields power cosmic particle accelerators
Magnetic field lines tangled like spaghetti in a bowl might be behind the most powerful particle accelerators in the universe.
More Magnetic Fields News and Magnetic Fields Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at