Featured Research

from universities, journals, and other organizations

Putting a new spin on tokamak disruptions

Date:
November 12, 2013
Source:
American Physical Society
Summary:
Scientists at Alcator C-Mod and DIII-D investigating plasma disruptions have discovered that injecting gases heavier than the background hydrogen fuel (such as argon or neon) just before an impending disruption will spread the resulting energy around the vessel.

The tiled walls inside the Alcator C-Mod tokamak might say they've been scarred by sudden disruptions in the hydrogen fuel that periodically impacts them. MIT researchers are discovering ways to spread out the focused energy from these disruptions so that the vessel walls are not damaged.
Credit: M. Garrett

In the quest for fusion energy on earth, researchers use magnetic fields to insulate hot plasma from the walls of the chamber to maintain the reaction and prevent damage to interior surfaces. In the tokamak, a leading contender to achieve a sustained fusion burn, electrical currents flowing in the plasma inside the doughnut-shaped vacuum chamber can become unstable if the plasma current or pressure gets too high or the control system breaks, leading to a sudden termination of the discharge. This sudden termination, called a disruption, can produce concentrated heating and mechanical forces on a section of the interior surface, forcing the plant to shut down for repairs.

Researchers at MIT's Plasma Science and Fusion Center (PSFC), General Atomics, Oak Ridge National Laboratory, University of Washington, and the University of California, San Diego, believe that if the intense energy of these disruptions could be uniformly spread out around the interior of the vessel, the plasma could be prevented from melting the wall -- a necessity for the next-step fusion device, ITER, under construction in Cadarache, France. Several groundbreaking experiments at the Alcator CMod tokamak at MIT and the DIII-D tokamak in San Diego are guiding the way towards better protection for the vessel walls during disruptions.

Scientists at Alcator C-Mod and DIII-D investigating plasma disruptions have discovered that injecting gases heavier than the background hydrogen fuel (such as argon or neon) just before an impending disruption will spread the resulting energy around the vessel.

However, the Alcator C-Mod team found that the argon or neon does not uniformly spread out quite enough to prevent damage. Sometimes the heat load is still asymmetric, concentrated in one sector of the device. Even using multiple injection sites around the vessel does not necessarily improve the asymmetry, and sometimes heightens it (Olynyk, 2012 APS DPP). To explain this unexpected result, computer models (Izzo, 2012 APS DPP) indicated that internal instabilities within the plasma should determine the radiation asymmetry rather than the distribution of gas injectors.

The DIII-D team has for the first time tested the theory that internal plasma instabilities determine the radiation asymmetry. The team used 3D magnetic fields to "lock" the plasma instability in one direction or another. They found that by varying the direction in which the instability locked, they could reproducibly change the amount of energy deposited at a given location within the vessel, as expected from the computer. Moreover, no indication of the expected localized heating around the gas injector itself was found. The DIII-D results show that simply increasing the number of gas injectors does not alleviate radiation asymmetry during disruption mitigation. The results do, however, suggest that rotating the instability could spread the heat more evenly.

Using rotation to lower the heat load to the walls is exactly what was discovered at the Alcator C-Mod tokamak. The Alcator C-Mod team has discovered that the plasma can spontaneously rotate rapidly during a portion of the disruption known as the "quench." The rotation appears to be driven by smaller-scale instabilities, and the rotation ends up moving the radiating regions around the vessel quickly and thus lowering the average heat load. Future research will determine if we can control or encourage this spontaneous rotation, and thus distribute the heat more uniformly to the wall.


Story Source:

The above story is based on materials provided by American Physical Society. Note: Materials may be edited for content and length.


Cite This Page:

American Physical Society. "Putting a new spin on tokamak disruptions." ScienceDaily. ScienceDaily, 12 November 2013. <www.sciencedaily.com/releases/2013/11/131112200823.htm>.
American Physical Society. (2013, November 12). Putting a new spin on tokamak disruptions. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2013/11/131112200823.htm
American Physical Society. "Putting a new spin on tokamak disruptions." ScienceDaily. www.sciencedaily.com/releases/2013/11/131112200823.htm (accessed October 21, 2014).

Share This



More Matter & Energy News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Newsy (Oct. 21, 2014) — If you've ever watched "Back to the Future Part II" and wanted to get your hands on a hoverboard, well, you might soon be in luck. Video provided by Newsy
Powered by NewsLook.com
Robots to Fly Planes Where Humans Can't

Robots to Fly Planes Where Humans Can't

Reuters - Innovations Video Online (Oct. 21, 2014) — Researchers in South Korea are developing a robotic pilot that could potentially replace humans in the cockpit. Unlike drones and autopilot programs which are configured for specific aircraft, the robots' humanoid design will allow it to fly any type of plane with no additional sensors. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
Graphene Paint Offers Rust-Free Future

Graphene Paint Offers Rust-Free Future

Reuters - Innovations Video Online (Oct. 21, 2014) — British scientists have developed a prototype graphene paint that can make coatings which are resistant to liquids, gases, and chemicals. The team says the paint could have a variety of uses, from stopping ships rusting to keeping food fresher for longer. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Massive Air Bag Recall Affects More Than 4.5 Million Vehicles

Massive Air Bag Recall Affects More Than 4.5 Million Vehicles

Reuters - US Online Video (Oct. 21, 2014) — Major automakers are recalling millions of vehicles due to potentially defective front passenger air bag inflators that can rupture and spray metal shrapnel. Linda So reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins