Magnetic bottle
An (ideal) magnetic bottle is understood to be a rotationally symmetrical magnetic field configuration that lies around a marked axis and has a high magnetic field strength at the ends compared to the center . In such a configuration, charged particles can be permanently trapped.
The magnetic field of a magnetic bottle does not have to be ideally rotationally symmetrical. This is just an assumption that makes it possible to find an analytical solution for the charged particle trajectories . An example of a magnetic bottle with a non-rotationally symmetrical magnetic field is the earth's magnetic field , which is deformed by the solar wind (see also Van Allen Belt ). The bottleneck arises here because the strength of the magnetic field increases in the direction of the geomagnetic poles .
In the laboratory, magnetic bottles are also known as mirror machines , they are used to contain plasmas (see fusion by means of magnetic containment ).
principle
Charged particles that move perpendicular to a homogeneous magnetic field perform a circular movement in the plane perpendicular to the magnetic field due to the Lorentz force . The radius of the circular motion is called the Larmor radius . It is large for weak magnetic fields and small for strong magnetic fields.
If the particles also have a speed component in the direction of the magnetic field, the superposition of circular movement (perpendicular to the magnetic field) and drift movement (in the direction of the magnetic field) results in a helical movement around the magnetic field lines.
If the strength of the magnetic field increases gradually in the course of the drift movement, the Larmor radius becomes smaller and the particle executes increasingly narrow screw movements. At the same time, the magnetic field lines no longer run parallel to the drift direction, but towards one another. This means that the Lorentz force no longer acts perpendicular to the drift direction, but receives a component that is directed against the drift direction. The particle is accelerated against the drift direction . As a result, the drift movement is slowed down, it can - depending on the kinetic energy of the particle and the strength of the magnetic field - be brought to a standstill and finally even reversed: the particle is 'reflected' in the neck of the magnetic bottle. This is also known as a magnetic mirror .
A magnetic bottle is created by combining two magnetic mirrors. Charged particles are reflected on the magnetic mirrors at the ends of the magnetic bottle and can thus be permanently trapped.
Individual evidence
- ↑ Heino Henke: Electromagnetic Fields: Theory and Application , Gabler Wissenschaftsverlage, 2011, ISBN 3642197450 , p. 233 ff, limited preview in Google book search, limited preview in Google book search