Total energy of beam (left) and tail (middle) electrons, both normalized to the initial beam energy E ₀, and the average energy of a tail electron (right), all evaluated at t = 100τ _ql, against the parameter R = τ _D /τ _ql, which gives a measure of the degree of inhomogeneity. Beam and plasma parameters, and ranges for and v ₀ are as given in the text. The asterisks mark the three levels of inhomogeneity shown in Figure 1. The dashed lines are polynomial fits to the data to illustrate its general trends.