For the minimum and maximum wavenumbers included in
the turbulence generator, the following considerations apply: (i)
the resonance condition states that there has to be a wavenumber
k so that RLk ≈ 1, where RL denotes the particle’s Larmor radius
so that scattering predominantly occurs when a particle can interact
with a wave mode over a full gyration cycle; (ii) the scaling
condition requires that RLΩrelt < Lmax, where Ωrel = qB/(γmc)
is the relativistic gyrofrequency and where Lmax ∝ 1/kmin is the
maximum extension of the system, which is given by the lowest
wavenumber (for which one has kmin = 2π/λmax, thereby proving
the argument). In practice, the second condition determines
Ω t
μ(t)
R = 10−1
Fig. 1. Pitch-angle cosine, μ = v/v as a function of the normalized time,
τ = Ωt for a relative slab turbulence strength δB/B0 = 10−2. Four particles
with initial pitch angles in the range 0.1 μ0 0.8 are highlighted
to guide the eye. (This figure is available in color in electronic form)