Diocotron wave echoes in a pure electron plasma

Abstract—Experimental images illustrate spatial Landau damping of an externally launched diocotron mode, and the re-sulting echo from a second externally launched wave. Filaments at the resonance layer exhibit spiral wind-up during the collisionless damping process, and “unwind ” during the echo formation. Index Terms—Diocotron, echo phenomenon, electron plasmas, Kelvin waves, spatial Landau damping, two-dimensional vortex dynamics. THE ECHO phenomenon beautifully exemplifies the re-versal of the microscopic phase evolution of a system by a macroscopic operation. Here, the phase evolution is a result of spatial Landau damping. The external excitation of a second wave reverses the phase evolution of this damping, resulting in an echo. Echoes have been previously observed in longitudinal electron plasma waves [1], but no diocotron wave echoes hav