Beta (plasma physics)

The beta of a plasma, symbolized by β, is the ratio of the plasma pressure (p = n k_B T) to the magnetic pressure (pmag = B²/2μ₀). Beta is a parameter indicating the relative importance of kinetic to electromagnetic phenomena. In fusion power applications, beta can be thought of as an economic figure of merit. The magnetic field in a fusion device has technological limits such as the critical field of practical superconductors. The fusion power density, which determines the power output of a reactor, scales with the square of the plasma pressure. Therefore the output of a reactor can be said to scale with the square of the average beta. In a tokamak, for example, there is a fairly firm limit on the value beta can have before destructive instabilities occur.
See more at Wikipedia.org...