Magnetic mirror

Under an (ideal) magnetic bottle refers to a rotationally symmetric magnetic field configuration, which is a unique axis and at the ends - having high magnetic field strength - compared with the center. In such a configuration, charged particles can be permanently enclosed.

The magnetic field of a magnetic bottle must not be ideal rotationally symmetric. This is only an assumption makes it possible to find an analytical solution for the trajectories of charged particles. An example of a magnetic bottle with non- rotationally symmetrical magnetic field, the Earth's magnetic field, which is deformed by the solar wind (see also Van Allen belts ). The bottleneck created here by the fact that the strength of the magnetic field increases toward the geomagnetic poles.

In the laboratory magnetic bottles are also referred to as mirror machines, they serve the confinement of plasmas (see fusion by magnetic confinement ).

Principle

Charged particles moving perpendicular to a uniform magnetic field, a circular motion, because of the Lorentz force in the plane perpendicular to the magnetic field. The radius of the circular motion is called Larmor radius, it is great for weak magnetic fields and small for strong magnetic fields.

The particles additionally have a component of velocity in the direction of the magnetic field, it is apparent from the superposition of circular motion (perpendicular to the magnetic field ), and the drift of movement (in the direction of the magnetic field ), a helical movement around the magnetic field lines.

Increases in the course of movement of the drift, the strength of the magnetic field gradually, the Larmor radius is small, and the particles results in an increasingly close coil movements. Simultaneously, the magnetic field lines to no longer parallel to the direction of drift, but to each other. The Lorentz force, so that no longer acts perpendicular to the drift direction, but it is replaced by a component that is directed against the direction of drift. The particle is thus accelerated toward the drift direction. As a result, the drift motion is slowed down, it can - depending on the kinetic energy of the particle and the magnetic field strength - brought to a standstill and eventually even reversed: the particle is ' reflected ' in the neck of the magnetic bottle. This is also referred to as a magnetic mirror.

A magnetic bottle formed by the combination of two magnetic mirrors. Charged particles are reflected by the magnetic mirrors at the ends of the magnetic cylinder and can therefore be permanently included.