Plasma Zoo: Gyroresonant Scattering
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- Visualizations by:
- Tom Bridgman
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- Written by:
- Mara Johnson-Groh
- View full credits
In regions like planetary magnetospheres, a number of more complex interactions can occur between charged particles, fields, and electromagnetic waves. One of these processes is called gyroresonant scattering or alternatively pitch-angle scattering.
In gyroresonant scattering, a charged particle undergoing gyromotion in a background magnetic field interacts with the electric field of a circularly-polarized electromagnetic wave. To the moving particle, the wave appears Doppler-shifted, and if this Doppler-shifted wave frequency is close to the gyro-frequency, the rotating electric field of the wave and add or remove energy from the particle. In the case of a uniform background magnetic field this 'pumping' of energy into and out of the particle can occur all along the particle trajectory. However, if the background magnetic field varies along the particle trajectory, the wave may get only one opportunity to inject or remove energy from the particle.
When this process acts on a collection of particles of different energies and pitch-angles, the process can alter the distribution of energy and pitch angles. This process may be responsible for the 'flushing' of electrons out of some regions of the radiation belts by VLF radio waves, and 'bunching' of other particles.

As the upper electron begins to interact with the wave, the electric field of wave is initially oriented in a way that removes energy from the particle, slowing its speed perpendicular to the magnetic field, which makes the pitch angle (the angle between the particle velocity vector and the magnetic field vector) and gyro-radius smaller.

As the wave field decelerates the electron, its gyro-frequency gets closer matched to the electromagnetic wave. If the electric field is directed radially with the gyromotion, the particle is no longer accelerated by the electric field and the particle 'surfs' the wave, the energy no longer changing (and the particle trail is white).

The increasing magnetic field gradient moves the particle gyrofrequency well past the resonance condition. Then the particle oscillates between losing small amounts of energy (blue trail) and gaining small amounts of energy (red trail), with little changes to total energy as it propagates in the wave.
For More Information
See NASA.gov
Credits
Please give credit for this item to:
NASA's Scientific Visualization Studio
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Data visualizer
- Tom Bridgman (Global Science and Technology, Inc.) [Lead]
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Writer
- Mara Johnson-Groh (Wyle Information Systems) [Lead]
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Scientists
- Alex Boyd (New Mexico Consortium)
- Geoff Reeves (New Mexico Consortium & Los Alamos National Laboratory)
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Project support
- Ian Jones (ADNET Systems, Inc.)
- Laurence Schuler (ADNET Systems, Inc.)
Series
This visualization can be found in the following series:Papers used in this visualization
Datasets used in this visualization
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ParticleSimulator
ID: 846
Note: While we identify the data sets used in these visualizations, we do not store any further details, nor the data sets themselves on our site.