Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why solar wind is rhombic-shaped

15.11.2011
Temperature and energy equipartition in cosmic plasmas explained / RUB researchers report in Physical Review Letters

Why the temperatures in the solar wind are almost the same in certain directions, and why different energy densities are practically identical, was until now not clear. With a new approach to calculating instability criteria for plasmas, Bochum researchers lead by Prof. Dr. Reinhard Schlickeiser (Chair for Theoretical Physics IV) have solved both problems at once.


Solar wind data: The plasma beta represents the ratio of kinetic to magnetic pressure in the cosmic plasma. The anisotropy is the ratio of the perpendicular and parallel temperatures to the magnetic field lines. The number of measured values is shown in colour (red corresponds to many values, blue to few values). Why the measurements take on the characteristic rhombic shape is explained by a new model by Bochum’s physicists. Source: Physical Review Letters © American Physical Society

They were the first to incorporate the effects of collisions of the solar wind particles in their model. This explains experimental data significantly better than previous calculations and can also be transferred to cosmic plasmas outside our solar system. The scientists report on their findings in Physical Review Letters.

Temperatures and pressures in the cosmic plasma

The solar wind consists of charged particles and is permeated by a magnetic field. In the analysis of this plasma, researchers investigate two types of pressure: the magnetic pressure describes the tendency of the magnetic field lines to repel each other, the kinetic pressure results from the momentum of the particles. The ratio of kinetic to magnetic pressure is called plasma beta and is a measure of whether more energy per volume is stored in magnetic fields or in particle motion. In many cosmic sources, the plasma beta is around the value one, which is the same as energy equipartition. Moreover, in cosmic plasmas near temperature isotropy prevails, i.e. the temperature parallel and perpendicular to the magnetic field lines of the plasma is the same.

Explaining satellite data

For over a decade, the instruments of the near-earth WIND satellite have gathered various solar wind data. When the plasma beta measured is plotted against the temperature anisotropy (the ratio of the perpendicular to the parallel temperature), the data points form a rhombic area around the value one. “If the values move out of the rhombic configuration, the plasma is unstable and the temperature anisotropy and the plasma beta quickly return to the stable region within the rhombus” says Prof. Schlickeiser. However, a specific, detailed explanation of this rhombic shape has, until now, been lacking, especially for low plasma beta.

Collisions in the solar wind

In previous models it was assumed that, due to the low density, the solar wind particles do not directly collide, but only interact via electromagnetic fields. “Such assumptions are, however, no longer justified for small plasma beta, since the damping due to particle collisions needs to be taken into account” explains Dipl.-Phys. Michal Michno. Prof. Schlickeiser’s group included this additional damping in their model, which led to new rhombic thresholds i.e. new stability conditions. The Bochum model explains the solar wind data measured significantly better than previous theories.

Universally valid solution

The new model can be applied to other dilute cosmic plasmas which have densities, temperatures and magnetic field strengths similar to the solar wind. Even if the diagram of temperature anisotropy and plasma beta does not have exactly the rhombic shape that the researchers found for the solar wind, the newly discovered mechanism predicts that the values are always close to one. In this way, the theory also makes an important contribution to the explanation of the energy equipartition in cosmic plasmas outside of our solar system.

Further information

Prof. Dr. Reinhard Schlickeiser, Chair for Theoretical Physics IV, Faculty of Physics and Astronomy at the Ruhr-Universität, 44780 Bochum, Tel.: 0234/32-22032

rsch@tp4.ruhr-uni-bochum.de

Michal Michno, Chair for Theoretical Physics IV, Faculty of Physics and Astronomy at the Ruhr-Universität, 44780 Bochum, Tel.: 0234/32-22051

mjm@tp4.ruhr-uni-bochum.de

Bibliographic record

R. Schlickeiser, M. J. Michno, D. Ibscher, M. Lazar, T. Skoda (2011): Modified temperature-anisotropy instability thresholds in the solar wind, Physical Review Letters, 107, 201102, doi: 10.1103/PhysRevLett.107.201102

Editor
Dr. Julia Weiler

Dr. Josef König | idw
Further information:
http://www.ruhr-uni-bochum.de

More articles from Physics and Astronomy:

nachricht Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

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: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Predicting unpredictability: Information theory offers new way to read ice cores

07.12.2016 | Earth Sciences

Sea ice hit record lows in November

07.12.2016 | Earth Sciences

New material could lead to erasable and rewriteable optical chips

07.12.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>