Classical diffusion

The classical diffusion of plasma confined by the magnetic field refers to the collision dominated transport that follows the 1/B² scaling, where B is the magnetic field strength.

Diffusion is a random walk process that can be quantified by the two key parameters: Δx, the step size, and Δt, the time interval when the walker takes a different step. Thus, the diffusion coefficient is defined as D≡(Δx)²/(Δt).

In a uniform magnetic field, a particle undergoes random walk across the field lines by the step size of gyroradius ρ≡v_th/Ω, where v_th denotes the thermal velocity, and Ω≡qB/mc, the gyrofrequency. The steps are randomized by the collisions to lose the coherence. Thus, the time step, or the decoherence time, is inverse of the collisional frequency ν_c. The rate of diffusion is given by ν_cρ², with the rather favorable B⁻² scaling law.

See also

• Bohm diffusion
• Hsu diffusion
• Plasma diffusion