Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Putting a new spin on tokamak disruptions

13.11.2013
Rapid plasma rotation may be the key to softening the blow of powerful plasma disruptions

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.


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 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.

Research Contacts:

Robert Granetz, MIT, (617)-253-8634, granetz@mit.edu

N.W. Eidietis, General Atomics, (858)-455-2459, eidietis@fusion.gat.com

N. Commaux, Oak Ridge National Laboratory, (858)-455-2073

V.A Izzo, University of California, San Diego, (858)-455-4144, izzo@fusion.gat.com

Abstracts:

CO4.00009 Effects of Magnetic Shear on Toroidal Rotation in C-Mod Plasmas with LHCD
Session CO4: C-Mod Tokamak
2:00 PM–5:00 PM, Monday, November 11, 2013
Room: Plaza D
GO4.00002 Overview of DIII-D Disruption Mitigation Experimental Results
Session GO4: DIII-D Tokamak
9:30 AM–12:30 PM, Tuesday, November 12, 2013
Room: Plaza D

James Riordon | EurekAlert!
Further information:
http://www.aps.org

More articles from Physics and Astronomy:

nachricht Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>