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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,
p \equiv n\,T,
\end{displaymath} (33)

as in an ideal gas, and to define a separate $\beta_s$ for each plasma species. Thus,
\beta_s = \frac{2\,\mu_0\,p_s}{B^2}.
\end{displaymath} (34)

The total $\beta$ is written
\beta = \sum_s \beta_s.
\end{displaymath} (35)

Richard Fitzpatrick 2011-03-31