Magnetic Mirror
A magnetic confinement configuration where converging magnetic field lines reflect charged particles back toward regions of weaker magnetic field.
Governing formula
Sin²(θ_loss) = B_min / B_max (Loss Cone Angle)
SI unit
Dimensionless Mirror Ratio B_max / B_min
In depth
As a charged particle moves into a stronger magnetic field region, conservation of magnetic moment μ = ½ m v_⊥² / B increases perpendicular velocity v_⊥ while decreasing parallel velocity v_∥ until v_∥ = 0, reflecting the particle unless its pitch angle lies inside the unconfined loss cone.
Examples in the real world
Earth's Van Allen radiation belts trapping high-energy protons and electrons between polar magnetic mirrors.