Collisionality

In Plasma Physics, collisionality is a dimensionless parameter proportional to the ion-ion collision frequency

Definition

The plasma collisionality $\nu^*$ is defined as^[1]:
$\nu^* = \nu_{ii}\sqrt{\frac{m_i}{k_B T_i}}\epsilon^{-3/2}qR$
where $\nu_{ii}$ denotes the ion-ion collision frequency, $R$ is the plasma major radius, $\epsilon$ is the inverse aspect-ratio, and $q$ is the safety factor.
The plasma parameters $m_i$ and $T_i$ denote, respectively, the ion mass and ion temperature, and $k_B$ is the Boltzmann constant.

References

^ Nucl. Fusion, Vol. 39, No. 12 (1999)