Plasma Beta
The ratio of kinetic thermal plasma pressure to magnetic field pressure in a magnetized plasma.
Governing formula
β = p_kinetic / p_magnetic = (n k_B T) / (B² / (2 μ₀))
SI unit
Dimensionless Ratio
In depth
Measures magnetic field confinement efficiency. High-beta plasmas (β ~ 1) require smaller magnetic fields to confine thermal pressure but are prone to pressure-driven MHD instabilities. Tokamaks operate at low-to-moderate beta (β ~ 0.02–0.08).
Examples in the real world
Optimizing plasma beta in spherical tokamaks and magnetic fusion reactor designs.