Mapping Particle Injections in Earth's Magnetosphere

Electrons gyrating along the lines of Earth's magnetic field make another orbit around Earth and strike the Van Allen Probe A AGAIN! Opening view of radiation belts and the orbits of the Van Allen probes. A view of the Van Allen Probe orbits and the radiation belts sliced open for a cross-section view. A pulse of electrons is injected into the radiation belts by impact of a passing coronal mass ejection (CME). The electrons gyrate around the magnetic field lines, mirroring at high and low latitudes. Once the pulse of accelerated electrons are injected into the radiation belts, the magnetic gradient drift guides them around Earth where they serendipitiously strike the particle detectors of Van Allen Probe A. On March 17, 2016, Van Allen Probe A detected a pulse of high energy electrons in the radiation belts, generated by the impact of a recent coronal mass ejection striking Earth's magnetosphere. The gradient drift speed of the electron pulse was high enough, that it propagated completely around Earth and was detected by the spacecraft again as the pulse spread out in the radiation belt. Because the particles have a range of energies, the pulse spread out as it moved around Earth, generating a weaker signal the next time it hit the spacecraft. Related pages

Visualization from two camera positions of simple gyro-motion of charged particles in a changing magnetic field. Motions of charged particles in electromagnetic fields are important in understanding the behaviors of plasmas in space. In Plasma Zoo, we present visualizations of particle motions in simple electromagnetic field configurations.One of the more fundamental motions of charged particles in a magnetic field is gyro-motion, or cyclotron motion. If a charged particle is moving in a magnetic field, the particle experiences a force perpendicular to the direction of the charge motion and the field. This direction is determined by the Right-Hand Rule (Wikipedia). The resulting force directs the motion in a curve such that if we view along the direction the magnetic field is pointing, we will see the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise.Consider a magnetic field which fills a region of space with uniform intensity and direction. Here we represent that magnetic field (designated with the letter 'B') as a cyan (light green) arrow, its direction representing the direction of the field vector. In examples Plasma Zoo: Gyromotion in Two Dimensions and Plasma Zoo: Gyromotion in Three Dimensions, we looked at cases where the magnetic field has a constant magnitude and direction through the region of space. But what happens if the magnetic field intensity varies in the region where the particles are moving? Such changes in intensity with position are called gradients. When a road is sloping, such as on a hillside, we describe the angle of the slope as the grade of the road, which is a term derived from the similar concept.In this example, the magnetic field is constant in one direction, but is stronger further away from the observer (represented by the longer cyan arrow) and weaker closer to the observer (represented by the shorter cyan arrow).So what happens with the particle motion?In regions where the magnetic field is stronger the gyro-radius is smaller - the particle wants to move in a tighter circle. In regions where the field is weaker, the gyro-radius is larger - the particle wants to move in a wider circle.The net effect of the gyro-radius changing as the particle moves is these differing gyro-radii add up to make the particle slowly drift in one direction. Note that the particles drift in opposite directions depending on their electric charge is positive ('+') or negative ('-').While the positive charge is moving away from the observer, and a negative charge is moving towards the observer, these two motions contribute to a net positive charge away from the observer. This motion in a magnetic gradient drives the ring current (Wikipedia) in Earth's magnetosphere.Important Note: The example here shows particles with the same speed and mass. If the masses are different (for example, a positive proton has about 1836 times more mass than an electron), the radius of the gyromotion will be proportionally larger for the same speed. Related pages

Visualization of the radiation belts with confined charged particles (blue & yellow) and plasmapause boundary (blue-green surface) Earth surrounded by plasmapause (blue-green surface) and radiation belts (multi-color). View as above but now radiation belts sliced open to reveal plasmapause surface, particle trajectories trapped by magnetic field. View as above, but now plasmapause sliced open to reveal inner radiation belt. View as above, more particle motion. View as above, even more particle motion. The near-Earth space enviroment is a complex interaction between Earth's magnetic field, cool plasma moving up from Earth's ionosphere, and hotter plasma coming in from the solar wind. This interactions combine to maintain the radiation belts around Earth.Plasma interactions can generate sharply delineated regions in these belts. In addition to the inner and outer radiation belts, the cooler plasma of the plasmasphere interacts so that it keeps out the higher-energy electrons from outside its boundary (called the plasmapause).In this visualization, the radiation belts (rainbow-color) and plasmapause (blue-green surface) surround Earth, its structure largely determined by Earth's dipole magnetic field (represented by cyan curved lines). The radiation belt is sliced open, simultaneously revealing representative confined charged particles spiraling around the magnetic field structure. Yellow particles represent negative-charged electrons, blue particles represent positive-charged ions. However, if realistically scaled for particle mass and energies, the spiral motion would not be visible at this distance so particle masses and size scales are adjusted to make them visible.The inner blue-green plasmapause boundary is then sliced open to reveal more of the inner structure of the radiation belts, including the innermost belt. For More InformationSee [NASA.gov](http://www.nasa.gov/content/goddard/van-allen-probes-spot-impenetrable-barrier-in-space/) Related pages