Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Unexpected connection: Rotation reversal tied to energy confinement saturation

11.11.2011
News from the 53rd Annual Meeting of the APS Division of Plasma Physics

Research on the Alcator C-Mod experiment at MIT has made an unexpected connection between two seemingly unrelated but important phenomena observed in tokamak plasmas: spontaneous plasma rotation and the global energy confinement of the plasma.


Plasma fluctuations, that accompany the low density, low confinement regime and disappear promptly at the rotation reversal may provide the link between these two seemingly disparate phenomena. Credit: John Rice, MIT

Self-generated flows, the spontaneous plasma rotation which arises even when there is no external momentum input, can have a strong beneficial effect on plasma transport and stability. But in a fusion reactor, unlike most current experiments, there will be little or no external rotation drive—thus it is crucial to understand and be able to predict plasma rotation under these conditions. In the discharges studied at Alcator C-Mod, the flows can reverse direction at a very precise transition point, depending on plasma density and current.

This flow reversal turns out to be tightly connected to the global energy confinement of the plasma. Since the early days of tokamak research (1970s), it was known that the energy confinement time (the ratio of the energy content of the plasma and the total input power) increased as the density of the plasma increased. This generated a great deal of excitement since one of the goals of fusion research was to operate at high density with good confinement, so this improvement was a bonus. At high enough density, however, the energy confinement stopped increasing.

The results of these experiments suggest that energy confinement and rotation reversal are closely related. At low density, where the energy confinement time increases with the density, the plasma rotates in one direction at roughly +5 km/s. Then at the critical density, the rotation direction reverses direction to values around -20 km/s and the energy confinement saturates. The critical density depends on plasma conditions, increasing with plasma current and decreasing with machine size.

These observations reveal the fundamental connection between the two phenomena and how they both depend on the nature of the underlying plasma turbulence. One hypothesis is that at low density, the turbulence is driven by trapped electron modes, which strongly degrade the confinement and which propagate in a particular direction. As the density is raised, these modes are suppressed, and turbulence driven by ion temperature gradients dominates. These modes at higher density regulate the confinement and propagate in the opposite direction. Evidence for this explanation is emerging from careful measurements of plasma fluctuations.

Abstract:

NI2.00006 Rotation Reversal and Energy Confinement Saturation in Alcator C-Mod Ohmic L-mode Plasmas: A Novel Transport Bifurcation
Session NI2: Transport of Momentum and Particles,
Ballroom BD, Wednesday, November 16, 2011, 12:00PM:30PM

Saralyn Stewart | 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 >>>