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Plasma Beta

The fundamental measure of a magnetic field's effect on a plasma is the magnetization parameter, $ \delta$ . The fundamental measure of the inverse effect is called $ \beta$ , and is defined as the ratio of the thermal energy density, $ n\,T$ , to the magnetic energy density, $ B^{\,2}/(2\,\mu_0)$ . It is conventional to identify the plasma energy density with the pressure,

$\displaystyle p \equiv n\,T,$ (1.34)

as in an ideal gas, and to define a separate $ \beta_s$ for each plasma species. Thus,

$\displaystyle \beta_s = \frac{2\,\mu_0\,p_s}{B^{\,2}}.$ (1.35)

The total $ \beta$ is written

$\displaystyle \beta = \sum_s \beta_s.$ (1.36)

Richard Fitzpatrick 2016-01-23