Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists further understanding of a process that causes heat loss in fusion devices

07.04.2017

Everyone knows that the game of billiards involves balls careening off the sides of a pool table -- but few people may know that the same principle applies to fusion reactions. How charged particles like electrons and atomic nuclei that make up plasma interact with the walls of doughnut-shaped devices known as tokamaks helps determine how efficiently fusion reactions occur. Specifically, in a phenomenon known as secondary electron emission (SEE), electrons strike the surface of the wall, causing other electrons to be emitted. Those secondary electrons cool the plasma's edge and dampen the plasma's overall performance.

Scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have been studying SEE for decades, and in the past year have made important advances that further their understanding.


Physicist Angela Capece working with an ultrahigh vacuum chamber in PPPL's Surface Science and Technology Lab.

Credit: Elle Starkman

Most recently, two of the physicists -- Marlene Patino, a graduate student at the University of California, Los Angeles, and Angela Capece, a professor at the College of New Jersey -- have focused their efforts on researching how SEE is affected by different wall materials and structures.

Understanding SEE is crucial because the behavior of the secondary electrons could affect the performance of future fusion machines. "When heat losses become large, the fusion machine is less able to produce power," Capece said.

In her SEE research, Capece studied how electrons interacted with lithium, a wall material that could improve the ability of tokamaks to confine plasma. Other scientists interested in lithium have created computer models that simulate how lithium interacts with electrons from the plasma, but those models have not taken into account how easily lithium bonds with other trace elements in the plasma, like oxygen, to form new molecules like lithium oxide. Those new molecules interact with electrons differently than pure lithium would.

Specifically, when electrons strike lithium oxide on a tokamak wall, many more secondary electrons are released into the plasma than for non-lithium wall materials like tungsten and carbon. If a tokamak has a lining made of graphite, one electron striking it with a particular amount of energy may produce one secondary electron. On the other hand, if an electron with the same energy strikes a lining made of lithium oxide, from one to three secondary electrons could result.

This discrepancy is crucial. "When incorporating SEE into models of fusion devices, it is important to account for the reactivity of lithium and that it will form lithium oxide in a tokamak environment," Capece said.

Capece ultimately found that, in general, it becomes easier for an electron to release a secondary electron when the oxygen content in lithium linings rises. Her research quantified exactly how the amount of oxygen bound to the lithium in the wall changes the amount of secondary electrons that can enter the plasma. While an increased SEE yield could drive up heat loss, many variables at the edge of the plasma could modify the impact.

Patino studied SEE from a different perspective. She researched tiny structures, known as "fuzz," that form on tungsten linings when they have been bombarded by helium nuclei. She observed that in comparison to smooth tungsten, tungsten with fuzz can reduce SEE by 40 percent to 60 percent. These findings were significant because past researchers' studies involved manufactured microstructures, while in this study the tungsten fuzz grew by itself.

Moreover, unlike with manufactured structures, the reduction of SEE does not depend on the angle at which the electrons approach the wall, both because the secondary electrons are trapped by the fuzz and the fibers in the fuzz are distributed randomly. "This lack of dependence on incident angle is important for walls in plasma machines since the electrons will impact the walls at large oblique angles," Patino said.

Her work was published in the November 2016 issue of Applied Physics Letters. Capece's was published in the July 2016 issue of the same journal. Their research was funded by the DOE's Office of Science (Fusion Energy Sciences). Patino's work also received funding from the Air Force Office of Scientific Research (AFOSR).

SEE first attracted the attention of PPPL scientists through both experimentation and theoretical research into plasma thrusters, devices that could one day propel spacecraft to distant cosmic objects. "PPPL researchers came up with the idea of using surface-architectured materials such as carbon velvet to suppress SEE and thereby improve the performance and longevity of the plasma thrusters," said Yevgeny Raitses, a principal research physicist at PPPL and principal investigator on both Patino's and Capece's projects.

###

Previous SEE research at PPPL has involved a number of collaborators. These include PPPL principal investigators Raitses and Igor Kaganovich, together with Dr. Dmytro Sydorenko of the University of Alberta; Professor Andrei Smolyakov of the University of Saskatchewan; Professors Bruce Koel and Nat Fisch of Princeton University; and Professors Richard Wirz and Nasr Ghoniem of the University of California-Los Angeles. Their research has been funded by the AFOSR and the DOE's Office of Science (Fusion Energy Sciences).

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

Media Contact

Raphael Rosen
rrosen@pppl.gov

 @PPPLab

http://www.pppl.gov 

Raphael Rosen | EurekAlert!

More articles from Physics and Astronomy:

nachricht When fluid flows almost as fast as light -- with quantum rotation
22.06.2018 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

nachricht Thermal Radiation from Tiny Particles
22.06.2018 | Universität Greifswald

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: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Towards universal influenza vaccines – is Neuraminidase underrated?

22.06.2018 | Life Sciences

Thermal Radiation from Tiny Particles

22.06.2018 | Physics and Astronomy

Polar ice may be softer than we thought

22.06.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>