Nav: Home

New feedback system could allow greater control over fusion plasma

March 20, 2017

Like a potter shaping clay as it spins on a wheel, physicists use magnetic fields and powerful particle beams to control and shape the plasma as it twists and turns through a fusion device. Now a physicist has created a new system that will let scientists control the energy and rotation of plasma in real time in a doughnut-shaped machine known as a tokamak.

"When designing fusion machines, it's becoming more and more important to use control systems and modeling techniques taken from the world of aeronautics engineering," said Imène Goumiri, the scientist who led the work. "What's new is that these tools have now been applied to plasma physics problems; that's what makes this research unique." Goumiri was a Princeton University doctoral graduate student who conducted research at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and now is a physicist at the University of Wisconsin-Madison.

Goumiri's system, known as a feedback controller, includes sensors within the tokamak that are linked to a computer algorithm that interprets the data the sensors gather. The algorithm actuates six beams of neutral particles that heat and spin the plasma inside the tokamak and actuates six rectangular magnetic coils situated around the machine's exterior. "This is the first time these two actuators have been used together to control the plasma rotation profile," said Steven Sabbagh, a senior research scientist and adjunct professor of applied physics at Columbia University who has collaborated with PPPL for 27 years and was one of the paper's co-authors.

By controlling rotation, physicists can prevent instabilities from degrading the magnetic field and allowing the plasma to dissipate, shutting down the fusion reactions.

Researchers designed the algorithm for the National Spherical Torus Experiment-Upgrade (NSTX-U), which has an enhanced neutral beam system that affects the plasma rotation by colliding with the plasma's charged particles and transferring momentum. The system has two emitters with three neutral beam sources each. One emitter targets the core of the plasma while the other targets the edge to exert leverage over the plasma as a whole. A flexible magnet system allows physicists to further control the plasma rotation distribution. In general, the algorithm uses the magnetic coils and the neutral beam emitters in different combinations to change how different regions of the plasma rotate.

The algorithm also balances the effects of the magnets and the neutral beams to make sure the overall plasma doesn't lurch roughly from one speed to another. The aim is to achieve a particular amount of plasma heat, or stored energy, along with the desired plasma rotation -- an innovation that an earlier version of the algorithm lacked.

Goumiri and the team tested the new controller algorithm on a simulated tokamak created by the computer code TRANSP, a PPPL-designed program used in magnetic fusion research around the world. The test showed that the algorithm could successfully modify both the plasma's rotation profile and stored energy in ways that would increase the plasma's stability.

In the future, Goumiri hopes to test her controller algorithm on NSTX-U. Once in operation, the lessons physicists learn from using the algorithm could influence the design of future fusion reactors. Such reactors will have more than one algorithm to control plasma rotation, electric current, and the shape of the plasma. Future research will need to focus on how all the controllers operate together and to design a global system that will allow the controllers to operate harmoniously.

This research was published in February 2017 in the online version of Physics of Plasmas and was funded by the DOE's Office of Science (Fusion Energy Sciences).
-end-
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.

DOE/Princeton Plasma Physics Laboratory

Related Plasma Articles:

Table top plasma gets wind of solar turbulence
Scientists from India and Portugal recreate solar turbulence on a table top using a high intensity ultrashort laser pulse to excite a hot, dense plasma and followed the evolution of the giant magnetic field generated by the plasma dynamics.
Getting the biggest bang out of plasma jets
Capillary discharge plasma jets are created by a large current that passes through a low-density gas in what is called a capillary chamber.
Neptune: Neutralizer-free plasma propulsion
Plasma propulsion concepts are gridded-ion thrusters that accelerate and emit more positively charged particles than negatively charged ones.
UCLA researchers discover a new cause of high plasma triglycerides
People with hypertriglyceridemia often are told to change their diet and lose weight.
Where does laser energy go after being fired into plasma?
An outstanding conundrum on what happens to the laser energy after beams are fired into plasma has been solved in newly-published research at the University of Strathclyde.
More Plasma News and Plasma 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

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
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...