Prompt Electron Acceleration in the Radiation Belts

A view from above the northern hemisphere of particle injection propagation constructed from their respective satellite detections. Distinct injections, and their detection by satellites, are represented by different colors. A view from the dusk limb of Earth, transitioning to a view above the northern hemisphere of particle injection propagation constructed from their respective satellite detections. Distinct injections, and their detection by satellites, are represented by different colors. Near-Earth space is not empty. It is filled with energetic charged particles and magnetic fields from the Sun and Earth. Some of these energetic particles make it into Earth's upper atmosphere, where they can create auroras around the north and south magnetic poles. But most of these energetic particles stay trapped by Earth's magnetic field, forming concentric belts encircling the planet, called the Van Allen Radiation Belts (Radiation Belts & Plasmapause). When energetic particles are injected into Earth's radiation belts, perhaps by a reconnection event in Earth's magnetotail, they can become trapped by the geomagnetic field. Consequently, these energetic particles will propagate around Earth as they slowly disperse. If a satellite with particle monitors lies along the particle trajectory, the satellite can detect these particles (Prompt Electron Acceleration in the Radiation Belts). With multiple satellite detections, it is possible to approximately reconstruct the origin and path of the original particle injection. These visualizations illustrate the results of this reconstruction applied to a series of particle injections detected by multiple satellites on April 7, 2016.In this visualization, we distinguish each injection with a different color, and that color is used to flash the satellite detecting that particular injection. The injections drift around Earth by a process called gradient drift (Plasma Zoo: Particle Drift in a Magnetic Gradient). Negative charged particles drift eastward (corresponding to counter-clockwise in the visualization view above the north geographic pole), while positive charged particles drift westward (corresponding to clockwise in the visualization view). For More InformationSee [NASA.gov](https://www.nasa.gov/feature/goddard/2017/all-missions-onboard-for-nasa-heliophysics-research) Related pages

This visualization opens with a full view of the radiation belt of trapped electrons circling Earth. We open a slice of the belts, to display a cross-section for clarity and move the camera to a more equatorial view. Earth rotation and solar motion have been turned off for this visualization to reduce distracting additional motions. Since their discovery at the dawn of the Space Age, Earth's radiation belts continue to reveal new complex structures and behaviors.During a particularly intense event in late June 2015, the inner edge of the region of trapped electrons moved closer to Earth. The electrons of interest had energies in excess of a million electron volts (Wikipedia). As the region retreated outward, it left behind a population of high-energy electrons forming another radiation belt inside the L=2 shell (The 'L-shell' value identifies a field line in a magnetic dipole. The numerical value corresponds to the furthest distance from Earth in Earth radii, in this case two Earth radii). This flux of high-energy electrons persisted considerably longer than expected, the relativistic electrons slowly leaking away. It took over a year for the relativistic electron flux in the belt to decline below the level of detectability for the instruments on the Van Allen Probes.The 3-dimensional radiation belt model in the visualizations above was constructed by propagating electron flux measurements, corresponding to a given time and distance from Earth measured by the Van Allen Probes, along a 3-dimensional structure of magnetic dipole field lines. 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