Collisionality

Plasma parameters define various characteristics of a plasma, an electrically conductive collection of charged particles that responds collectively to electromagnetic forces. Plasma typically takes the form of neutral gas-like clouds or charged ion beams, but may also include dust and grains. The behaviour of such particle systems can be studied statistically. Plasma parameters define various characteristics of a plasma, an electrically conductive collection of charged particles that responds collectively to electromagnetic forces. Plasma typically takes the form of neutral gas-like clouds or charged ion beams, but may also include dust and grains. The behaviour of such particle systems can be studied statistically. All quantities are in Gaussian (cgs) units except energy and temperature expressed in eV and ion mass expressed in units of the proton mass μ = m i / m p {displaystyle mu =m_{i}/m_{p}} ; Z {displaystyle Z} is charge state; k {displaystyle k} is Boltzmann's constant; K {displaystyle K} is wavenumber; ln ⁡ Λ {displaystyle ln Lambda } is the Coulomb logarithm. In the study of tokamaks, collisionality is a dimensionless parameter which expresses the ratio of the electron-ion collision frequency to the banana orbit frequency. The plasma collisionality ν ∗ {displaystyle u ^{*}} is defined as where ν e i {displaystyle u _{mathrm {ei} }} denotes the electron-ion collision frequency, R {displaystyle R} is the major radius of the plasma, ϵ {displaystyle epsilon } is the inverse aspect-ratio, and q {displaystyle q} is the safety factor.The plasma parameters m i {displaystyle m_{mathrm {i} }} and T i {displaystyle T_{mathrm {i} }} denote, respectively, the mass and temperature of the ions, and k B {displaystyle k_{mathrm {B} }} is the Boltzmann constant.