AbstractThe particle and energy balance equations in the scrape‐off layer (SOL) plasma are solved analytically in a rectangular domain. The parallel flow is supposed to be convective, whereas the cross field flow is assumed diffusive, with modifications due to a radial E field. When the energy balance equation is neglected we get a quadratic equation for λ, the e‐folding density scale length. The normalized e‐folding scale length λ/λ0 (λ0 = λ for E = 0) is a function of single parameter α (= eEλ0/2kT, where T is the plasma temperature, e the elementary charge and k is Boltzmann's constant), and monotonically increases with α. Taking the energy balance equation into account and neglecting R1 (the ionization rate), the quadratic equation is further simplified, and λ/λ0 again depends on a single parameter, determined by Q (the input power flux), D (the cross field diffusion coefficient), γ (the sheath transmission coefficient for energy) and np (the plate density). Now λ/λ0 decreases with Q and increases linearly with D, γ and np. The variation of λ/λ0 with E is estimated for TdeV and ITER. We find that, by a proper choice of parameters, biasing may be a very valuable tool to modify the SOL properties at modest E fields, provided the heat load on the divertor plate is not excessively large.