ESA Science & Technology30-Jun-2005 16:31:37
 

Background Science

Energetic Charged Particles

Space scientists use the term "energetic charged particles" to describe ions and electrons that have gained enough energy to move through space at a reasonable fraction of the speed of light. Because they carry an electrical charge, energetic charged particles are constrained to move along the lines of force of the magnetic fields in space. In the Earth's magnetosphere, energetic particles trapped in the Earth's magnetic field form the radiation belts. In the heliosphere, the majority of energetic particles are accelerated near the Sun in solar flares or at shock waves driven by CMEs. These are often called Solar Energetic Particles, and can have energies as high as 1 billion electron volts (1 GeV). For comparison, electrons in a TV tube are accelerated to 30 thousand electron volts.

The highest energy charged particles are Galactic Cosmic Rays, completely ionized atomic nuclei originating outside the heliosphere. Representing a true sample of extra solar-system material, GCRs are thought to be accelerated to very high energies in explosions of distant stars. By studying the composition of cosmic ray nuclei, we can learn a great deal about the way our galaxy and stars like the Sun have evolved.

Instruments

Four instruments on Ulysses make measurements of energetic charged particles:  

  • HI-SCALE (Heliosphere Instrument for Spectra, Composition and Anisotropies at Low Energies)  
  • EPAC (Energetic Particle Composition experiment)  
  • COSPIN (Cosmic Ray and Solar Particle Investigation)  
  • URAP (Unified Radio and Plasma Wave experiment)

HI-SCALE (Heliosphere Instrument for Spectra, Composition and Anisotropies at Low Energies)
HI-SCALE measures the composition and arrival directions of low-energy electrons and ions using five separate sensor heads to cover all viewing directions.

EPAC (Energetic PArticle Composition experiment)
EPAC measures the composition and arrival directions of low-energy ions using four separate sensor heads to cover all viewing directions.

COSPIN (COsmic Ray and Solar Particle INvestigation)
COSPIN measures solar energetic particle and cosmic ray electrons and ions over a wide range of energies, using five separate sensors. One of these, the High Energy Telescope (HET), is making the most precise determination to date of cosmic ray isotopic composition.

URAP (Unified Radio And Plasma Wave experiment)
Although not a particle detector in the traditional sense, URAP can provide data on energetic electrons emitted from solar flares by sensing the radio emission they generate while streaming away from the Sun along the heliospheric magnetic field lines.

Image of a supernova made by the
Hubble Space Telescope. Supernova
explosions are thought to be the sites
of cosmic ray acceleration.



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