Magnetic Mirroring and the Loss Cone
Posted On 2007-10-05
by Dr. Zee
A particle's pitch angle increases as it moves into a region of stronger magnetic field and decreases as it moves into a region of weaker field.
In a simple magnetic mirror geometry the magnetic field reaches a minimum value at the center of the geometry and a maximum value at the end. Particles within such a geometry can follow a range of trajectories, as described below.
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cannot move into a region of stronger magnetic field, so a particle with 
(at the center of the magnetic mirror, where B = Bmin) cannot move away from the center of the mirror.
is free to move anywhere and readily travels out of the magnetic mirror.
are said to be in the loss cone and can escape the magnetic mirror.