Observations of plasma jet braking by Cluster

4 July 2011

Artist's impression of the Cluster quartet. (c) ESA

Most of the matter in the universe is in a plasma state - a hot gas in which the electrons are stripped from the atomic nuclei. High speed plasma flows, or jets, are seen throughout the universe, from solar flares to emissions from black holes. A recent study by the Swedish Institute of Space Physics, Uppsala, and Mullard Space Science Laboratory, University College London has provided new insights into the mechanisms that control these plasma jets.

The charged particles that make up a plasma can be strongly influenced by magnetic fields. In the Earth's outer magnetosphere, the plasma is so sparse that the particles motion is controlled by the magnetic field. This magnetic field is constantly changing, with the most dramatic changes caused by the process of magnetic reconnection. This process accelerates the plasma along the magnetic field and ultimately causes the aurora.

ESA's Cluster mission is a quartet of spacecraft designed to study the plasma in and around Earth's magnetosphere. On 3 September 2006, they observed a jet of plasma caused by magnetic reconnection in the magnetosphere. Just prior to these observations, Cluster observed in increase in the magnetic field strength and so-called Whistler Mode waves. The presence of these waves and the magnetic field pile-up show that the plasma in the jet was not only accelerated by the reconnection process, but further accelerated by a betatron process, similar to that used in early particle accelerators.

These new and unique observations were made possible from the high time-resolution data from the Cluster spacecraft. Their implications go beyond processes at Earth, revealing how plasma can be energised far from the original site.

For further information, see:

Yu. V. Khotyaintsev, C. M. Cully, A. Vaivads, M. André, and C. J. Owen, Plasma Jet Braking: Energy Dissipation and Nonadiabatic Electrons, Physical Review Letters, vol. 106, 165001, 2011, DOI:10.1103/PhysRevLett.106.165001

News stories also available on the ESA Cluster Website and CERN Courier

UCL-MSSL contact:

Prof. Chris Owen
Email: cfo [a t] mssl.ucl.ac.uk
Tel: +44 1483 204281

Page last modified on 07 sep 11 16:42