24.1 PlasmaState

The PlasmaState unit was introduced in FLASH4.4 as a place to implement auxiliary routines that have knowledge of the behavior of plasmas. Currently, the PlasmaState unit contains routines for calculating the plasma parameter (Coulomb logarithm) $\ln \Lambda$ (PlasmaState_logLambda), the collision time $\tau$ (PlasmaState_tau), and the electron-ion equilibration time $\tau_{ei}$ (PlasmaState_ieEquilTime). The Coulomb logarithm and collision time subroutines have options for computing the quantity for electron-electron, electron-ion, or ion-ion collisions. The value of $\tau$ for electron-ion collisions is shown in (Eqn:CollisionTime).

$$\tau = \frac{3 \sqrt{m_\mathrm{ele}} (k_B T_\mathrm{ele})^{3/2}}{4 \sqrt{2 \pi} e^4 {\bar z}^2 n_\mathrm{ion} \ln \Lambda_{ei} }.$$ (24.1)

where:

• $k_B$ is the Boltzmann constant
• $e$ is the electron charge
• $m_\mathrm{ele}$ is the mass of an electron
• $\bar z$ is the average ionization as computed by the EOS and subject to a floor value of 1.0
• $n_\mathrm{ion}$ is the ion number density in the plasma
• $\ln \Lambda_{ei}$ is the Coulomb Logarithm associated with electron-ion collision, further description below.

Additional details on the electron-ion equilibration time and Coulomb logarithm can be found in Sec. 18.5.

These PlasmaState subroutines are used by various materialProperties units in calculating transport coefficients, by the Heatexchange unit, and in some cases by the Hydro unit. The PlasmaState unit may eventually include routines to compute other quantities of interest such as plasma frequencies, Hall parameters, etc.

There is also a routine named PlasmaState_getComposition, for computing the elemantal composition of the mixture of materials in a cell (expressed as number fractions of elements). It is intended to be used with the Multispecies unit. Note that to get correct results, a simulation has to define the elemental compositions of the different species (materials) that may be present.