beta

Beta (β) in plasma physics is the ratio of plasma pressure to magnetic pressure.

     P      nkBT
β = ———— = ————————
    Pmag   B²/(2μ0)

• P - pressure (within the plasma).
• P_mag - magnetic pressure.
• n - electron density.
• k_B - Boltzmann constant.
• T - temperature.
• B - magnitude of magnetic flux density.
• μ₀ - vacuum magnetic permeability.

Beta is used when discussing the interaction of plasma in space with different magnetic fields, such as the interaction of the solar wind with the magnetic fields of the Sun or the Earth.

The term beta naturally has many other uses in astrophysics and planetary science, such as in beta drift and beta decay.