Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Identifying New Sources of Turbulence in Spherical Tokamaks

30.11.2015

For fusion reactions to take place efficiently, the atomic nuclei that fuse together in plasma must be kept sufficiently hot. But turbulence in the plasma that flows in facilities called tokamaks can cause heat to leak from the core of the plasma to its outer edge, causing reactions to fizzle out.

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have for the first time modeled previously unsuspected sources of turbulence in spherical tokamaks, an alternative design for producing fusion energy. The findings, published online in October in Physics of Plasmas, could influence the development of future fusion facilities. This work was supported by the DOE Office of Science.


Eliot Feibush

Computer simulation of turbulence in a model of the NSTX-U.

Spherical tokamaks, like the recently completed National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL, are shaped like cored apples compared with the mushroom-like design of conventional tokamaks that are more widely used. The cored-apple shape provides some distinct characteristics for the behavior of the plasma inside.

The paper, with principal research physicist Weixing Wang as lead author, identifies two important new sources of turbulence based on data from experiments on the National Spherical Torus Experiment prior to its upgrade. The discoveries were made by using state-of-the-art large-scale computer simulations. These sources are:

• Instabilities caused by plasma that flows faster in the center of the fusion facility than toward the edge when rotating strongly in L-mode — or low confinement — regimes. These instabilities, called “Kelvin-Helmholtz modes” after physicists Baron Kelvin and Hermann von Helmholtz, act like wind that stirs up waves as it blows over water and are for the first time found to be relevant for realistic fusion experiments.

Such non-uniform plasma flows have been known to play favorable roles in fusion plasmas in conventional and spherical tokamaks. The new results from this study suggest that we may need to keep these flows within an optimized level in spherical tokamaks.

• Trapped electrons that bounce between two points in a section of the tokamak instead of swirling all the way around the facility. These electrons were shown to cause significant leakage of heat in H-mode — or high-confinement — regimes by driving a specific instability when they collide frequently. This type of instability is believed to play little role in conventional tokamaks but can provide a robust source of plasma turbulence in spherical tokamaks.

Most interestingly, the model predicts a range of trapped electron collisions in spherical tokamaks that can be turbulence-free, thus improving the plasma confinement. Such favorable plasmas could possibly be achieved by future advanced spherical tokamaks operating at high temperature.

Findings of the new model can be tested on the NSTX-U and will help guide experiments to identify non-traditional sources of turbulence in the spherical facility. Results of this research can shed light on the physics behind key obstacles to plasma confinement in spherical facilities and on ways to overcome them in future machines.

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 http://www.science.energy.gov.

Contact Information
John Greenwald
Science Editor
jgreenwa@pppl.gov
Phone: 609-243-2672

http://www.pppl.gov

John Greenwald | newswise

More articles from Physics and Astronomy:

nachricht Innovative LED High Power Light Source for UV
22.06.2017 | Omicron - Laserage Laserprodukte GmbH

nachricht Spin liquids − back to the roots
22.06.2017 | Universität Augsburg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

Im Focus: Optoelectronic Inline Measurement – Accurate to the Nanometer

Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.

New Manufacturing Technologies for New Products

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

A new technique isolates neuronal activity during memory consolidation

22.06.2017 | Life Sciences

Plant inspiration could lead to flexible electronics

22.06.2017 | Materials Sciences

A rhodium-based catalyst for making organosilicon using less precious metal

22.06.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>