Guiding center

The Alfvénsche approximation ( by Hannes Alfvén, also drift approximation) allowed in plasma physics is a simplified description of the motion of particles in a magnetic field.

Under appropriate conditions, this movement can be decomposed into a whirling ( gyration ) and an average effective (drift ) fraction.

Condition

The approximation is then well applicable when the magnetic field is homogeneous to the order of the radius of curvature of the web, so

The radius of curvature and the amount of magnetic field strength. As a weak temporal change of the field is required.

Approximation

Accordance with the condition is Gyrationsbewegung "small" and fast compared to the other scales of the system, " magnetic particles ", which allows the motion of the particle over a Gyrationsperiode to transmit and so as to obtain an effective (drift ) movement.

The drift velocity is dependent on the inhomogeneity of the magnetic field (more precisely, the gradient of the magnetic field strength ), the curvature of the magnetic field lines, and additionally acting forces.

The radius of the Gyrationsbewegung is in the approximation of the Larmor radius, the corresponding frequency is the cyclotron frequency.

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