Scientific team

N. Dubouloz (PI), J.-J. Berthelier, M. Malingre, D. Delcourt
Yu. Galperin, T. Mularchik, D. Chugunin, L. Zinin

Technical team:

J. Covinhes, G. Gogly, F. Vivat

Instrument description

HYPERBOLOID is a plasma spectrometer aimed at the investigation of the low energy ions dynamics in the polar ionosphere and magnetosphere on the INTERBALL Auroral Probe. Scientific objectives of this experiment include studies of:
  • thermal plasma transport by magnetospheric convection and escape along high latitude magnetic field lines,
  • ion heating and acceleration by electrostatic and electromagnetic turbulence,
  • generation and propagation of magnetic field aligned small-scale structures in the auroral plasma.

The instrument is basically a multi-directional ion mass spectrometer measuring ion distribution functions over an energy range from ~0.1 to 80 eV. In normal modes of operation, the four major species H+, He+, O+, O++ can be measured simultaneously; special modes may be used to detect minor species as N+ or the molecular ions.

The ion angular and energy distribution are obtained by means of an electrostatic optics defining 2 planes with several entrance windows. In the main plane, there are 16 windows at 10 intervals with individual FOV ~ 12 and effective entrance area ~ 0.8 cm2. This plane cotains the spacecraft spin axis so that the instrument is able to sample practically the full space in a complete spin period (120 s). Depending on the number of windows simultaneously opened, the angular resolution can be varied from 10 to 40, thus providing an adjustable trade off between angular and time resolution. The second plane of measurement is almost orthogonal to the first one with 10 windows at 15 intervals, FOV ~ 5 and effective entrance area ~ 5 to 8 times less than in the main plane. Again, from 1 to 4 windows can be activated simultaneously. This second plane of measurement is meant at obtaining a better time resolution (~ 1 s) for a full distribution function when the instrument is facing the rammed plasma, thus enabling to look at fast plasma variations.

Each window is followed by a spherical electrostatic energy analyzer. In normal modes of operation the energy resolution is ~ +/- 10% for the main 16 windows and +/- 5% for the 10 secondary ones. By pre-accelerating or decelerating the ions at the entrance of the analyzer, one can vary this energy resolution by a factor between ~ 0.5 and 2.

An arrangement of 2 toroidal concentrators is used to focus ions at the entrance of a magnet (which provides the mass separation), irrespective of their direction of arrival. There are 4 identical detectors in the focal plane, one for each of the major ions, which depending on the ion flux can be operated either in digital (pulse counting) or in analogical (charge integration) mode, thus providing a total dynamic range of 1e11.

The temporal resolution of the instrument for a complete angular and energy scan depends on the telemetry rate and varies from ~ 1 to 16 s in most modes of operation.

To date, the instrument is working nominally.

Figure captions

Figure 1 (28/10/96 22:00-23:00 UT)
Ion escape processes are frequently observed by HYPERBOLOID in the auroral and polar regions. Here, H+ ion escape is most clearly visible on the time/energy spectrogram (second spectrogram from bottom) between 22:28 and 22:40, and 22:52 and 23:00 UT. The spin-averaged moments displayed in the upper panel exhibit H+ escape velocities (Vx component, anti-parallel to the local geomagnetic field, blue curve) up to 30 km/s. Flow directions can also be retrieved by comparing the time/window spectrograms (four top spectrograms) and the spectrogram displaying pitch angles as a function of time and window.

Figure 2 (22/10/96 21:00-22:00 UT)
Example of the ion acceleration processes sometimes observed in the auroral regions. Between 21:04 and 21:22 UT, the H+ ion typical energy raises from ~ 5 up to 80 eV. Simultaneously, an intense electric turbulence is observed.

Figure 3 (27/10/96 00:00-01:00 UT)
In the subauroral regions, counterstreaming ion flows (essentially H+, He+ and O+) are commonly observed along closed magnetic field lines, as evidenced here below ~ 10 eV and between 00:26 and 00:56 UT.

For more information contact:

Dr. Nicolas Dubouloz
4 avenue de Neptune
94107 Saint-Maur Cedex
Tel. +33 1 45 11 42 70
Fax +33 1 48 89 44 33
Email: Nicolas.DUBOULOZ@cetp.ipsl.fr