A thermal plasma
(or cold plasma) is a plasma in which the particles are supposed to
be motionless in the absence of perturbation. In a non equilibrium state,
only electrons can be affected by perturbations. They can also oscillate
a characteristic frequency named plasma frequency. Waves that propagate
at frequencies at or below the local plasma frequency are called "plasma
waves".
At higher frequencies
they are called "radio waves". Plasma waves interact with
the particles via resonant instabilities. The properties of such waves
(i.e. polarization, ellipticity, wave normal directions, direction of
the Poynting vector) depend on their frequency and on the local properties
of the medium (plasma frequency, ion composition, gyrofrequencies, etc.).
Radio waves don't interact with the medium. At frequencies much larger
than the local plasma frequency, they propagate as in vacuum.
The LPC2E designs,
develops and interprets experiments that are dedicated to :
- the study of
plasma waves (electrostatic and electromagnetic) generated within
the solar wind and the magnetosphere or reaching these regions after
propagation,
- the determination
of the characteristic parameters of plasmas (electron density and
temperature).
While keeping
an activity on the analysis of data from past missions (VIKING, AUREOL-3,
INTERBALL), the LPC2E is engaged in the interpretation of data from
the CLUSTER mission and more specifically of those delivered by the
WHISPER and STAFF experiments. WHISPER is an experiment under the
responsibility of LPC2E. In its active mode, it sounds the plasma in
order to determine its thermal properties, in particular the electron
density. By sounding from 4 points in space one gets information on
the density gradients in three directions. In its passive mode, WHISPER
observes natural emissions up to 80 kHz. STAFF is an experiment under
the responsibility of the Centre d'étudesdes Environnements
Terrestre et Planétaires (CETP, Paris), which observes the
plasma waves below 4 kHz. The LPC2E is involved in the determination
of the propagation characteristics of waves and turbulence, using
this instrument.
Contact : P.
Décréau, J.L.
Pinçon, J.L. Rauch
