Subscribe free to our newsletters via your
  Energy News  

Subscribe free to our newsletters via your

A disappearing feast: Mean flows remain slim after eating eddies
by Staff Writers
Kyoto, Japan (SPX) Oct 28, 2016

Plasma physics experiment shows that the reduction in turbulence energy can't be explained by the increase in the mean flow energy, ruling out the predator-prey model in magnetic confinement fusion machines. Image courtesy Princeton Plasma Physics Laboratory. For a larger version of this image please go here.

Magnetic confinement fusion holds the promise of almost limitless amounts of energy, available on demand and producing zero carbon dioxide. But in order to harness that energy, we must trap plasma- an ionized gas- hotter than the center of the sun inside a donut-shaped magnetic facility called a tokamak that measures just a few yards across. As you might guess, the confined plasma becomes turbulent, and that turbulence leaks energy out from the ultra-hot core to the room-temperature wall.

But a slight increase in heating power can reduce the turbulence near the edge of the tokamak and cause the energy to leak much less. This new state of high confinement, known technically as "H-mode" and discovered in Germany in 1982, opened a promising new avenue towards the production of fusion energy.

Yet there is still no conclusive explanation for the disappearing turbulence. One popular contender, the "predator-prey" model, posits that the turbulence spontaneously dumps all of its energy into a benign spinning of the plasma called "mean flow" that does not transport heat.

According to this model, the spinning acts as a predator that feeds on eddies (prey) in the turbulence. If the predator is too successful, the population of eddies plummets and the mean flows (predators) grow accordingly. The predator-prey model suggests that the energy in the mean flows must increase by roughly the same amount that the energy in the turbulence drops. But does this really happen?

At the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL), researchers have found that it does not. They used a gas puff imaging (GPI) diagnostic that let them directly see turbulent plasma fluctuations in the edge region of PPPL's National Spherical Torus Experiment (NSTX), the laboratory's flagship fusion facility, which has since been upgraded.

Pumping small amounts of neutral gas into the plasma caused the neutrals to interact with the plasma and glow. A fast camera recorded movies of that glow and revealed how the turbulence evolved in space and time.

Researchers were also able to infer the velocity of the plasma. This enabled evaluation of both the energy in the turbulent fluctuations and in the mean flows, providing a direct check on whether the evolution of these conditions satisfies the expectations of the predator-prey model.

Surprisingly, the answer was a resounding "no." By carefully evaluating the energy in the flows and turbulence, keeping all the important terms, they found that on NSTX the energy in the mean flows was never- even in H-mode- bigger than about 1 percent of the energy in the turbulence before the transition (Figure 1) to H-mode. This clearly showed that the reduction in turbulence energy couldn't be explained by the increase in the mean flow energy, ruling out the predator-prey model.

With this result, the mystery of the H-mode deepens again. However, by ruling out one explanation, the results from NSTX may refocus efforts on other contenders, raising the chances of identifying the physics behind the mysterious "H-mode" and facilitating the ability to employ it for the success of future fusion reactors.

Abstracts: GO6.00010 Energy Exchange Dynamics across L-H transitions in NSTX - NP10.00024 Parallel Electron Force Balance and the L-H Transition

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only


Related Links
American Physical Society
Powering The World in the 21st Century at

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Previous Report
Launching fusion reactions without a central magnet, or solenoid
Washington DC (SPX) Oct 28, 2016
The tokamak is an experimental chamber that holds a gas of energetic charged particles, plasma, for developing energy production from nuclear fusion. Most large tokamaks create the plasma with solenoids - large magnetic coils that wind down the center of the vessels and inject the current that starts the plasma and completes the magnetic field that holds the superhot gas in place. But future tok ... read more

Australian consortium buys power grid after Chinese bid blocked

UNESCO urges Bangladesh to scrap Sundarbans plant

NREL releases new cost and performance data for electricity generation

Strong at the coast, weak in the cities - the German energy-transition patchwork

General atomics breakthrough enables greater control of fusion energy

Fusion reactor designs with 'long legs' show promise

From Germany comes a new twist for fusion research

High-storage sodium ion batteries

Cuomo announces major progress in offshore wind development

OX2 signs 148 MW wind power deal with Aquila Capital and Google

Prysmian Secures Contract for Offshore Wind Farm Inter-Array Submarine Cables Supply in Belgium

Wind turbines killing more than just local birds

CPP, SolarCity Deal Keeps Colton, Calif., Community Affordable and Sustainable

Schools in oil-rich Alberta to get solar panels

Renewable energy on the rise, IEA finds

Researchers discover ways to expand temperature stability range of solar cells

Rosatom Considers No Restrictions on Commercial Supplies of Uranium to US

A new method to help solve the problem of nuclear waste

Greenland uranium mining opponents join government

Bulgaria to pay Russia 600 mn euros for dropped nuclear plant

State partnerships can promote increased bio-energy production, reduce emissions

Biomass heating could get a 'green' boost with the help of fungi

Algae discovery offers potential for sustainable biofuels

The road to green hydrogen runs through mazes in algal proteins

China to enhance space capabilities with launch of Shenzhou-11

Ambitious space satellite projects set for liftoff

China's permanent station plans ride on mission

China to enhance space capabilities with launch of Shenzhou-11

Atmospheric CO2 concentration at Syowa Station in Antarctica exceeds 400 ppm

What the ancient CO2 record may mean for future climate change

Atom-by-atom growth chart for shells helps decode past climate

Concentration of CO2 in atmosphere hits new high: UN

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement