Effects of random density fluctuations on the growth of Langmuir waves that lead to electromagnetic emission. (a) Temporal evolution of the Langmuir wave intensity , in units of electron beam energy W_b, is shown as a function of density fluctuation level. The time of growth of the Langmuir wave until the maximum amplitude x is denoted as t_r. (b) The time of growth of Langmuir wave energy (t_r, panel a) during the beam relaxation, in units of inverse growth rate for homogeneous plasma t_r[1/γ_homog], is presented as a function of density fluctuations Δn/n_o. Three different electron beam speeds (V_b in units of the thermal speed V_T; where V_T is 0.01c) are considered. (c) Cartoon representation of an electron beam propagating through diverging magnetic field lines interacting with density blobs of different scales at different frequencies. The frequency levels are marked based on Fig. 5 and they roughly correspond to the different regions where the striae and envelope are observed. The enhanced growth of Langmuir waves is shown in different blobs with the wavy orange markers. Panels (a) and (b) were adapted from Tkachenko et al. (2021).