Glossary

The beta value of a fusion plasma is defined as the ratio of the thermal plasma pressure p to the magnetic field pressure B² / 2 µ₀ that has to be externally applied (µ₀ beeing the vacuum permeability). It is expressed as beta = 2 µ₀ p / B². Since for fusion the plasma pressure has to be kept as high as possible and for cost reasons the external magnetic field B should be as small as possible, a high beta value is desirable.