Fig. 1

Variation of \(V_{\text{g}}\), \(V_{\text{p}}\), and \(V_{\text{R}}\). Group velocity \(V_{\text{g}}\) in black solid line, phase velocity \(V_{\text{p}}\) in magenta, and resonance velocities \(V_{\text{R}}\) in dashed line for different energies K = 10 keV (black), 100 keV (blue), 500 keV (green), and 2 MeV (red) as functions of frequency \(\omega\) with the plasma frequency \(\omega _{\text{pe}} = 4 \Omega _{\text{e}}\)