Spatial Collapse of Beam-Driven Plasma Waves

Electron-plasma waves driven unstable by an electron beam are observed to be backscattered by stationary density perturbations to form standing waves. Above a certain threshold these standing waves develop into sharply localized ($\sim 10{\lambda }_{\mathrm{D}}$) intense fields, $\frac{{E_{max}}^2}{4\pi n_0\kappa T_e}\approx 1$. Significant fractions of beam electrons are scattered in velocity space by these stationary spikes of high-frequency field.