All quantities are in Gaussian (cgs) units except energy and temperature which are in electronvolts. For the sake of simplicity, a single ionic species is assumed. The ion mass is expressed in units of the proton mass, μ μ = m i / m p and the ion charge in units of the elementary charge e , Z = q i / e (in the case of a fully ionized atom, Z equals to the respective atomic number). The other physical quantities used are the Boltzmann constant ( k ), speed of light ( c ), and the Coulomb logarithm ( ln ⁡ ⁡ Λ Λ ).