Electron cyclotron echoes from plasma

The observed response of a low-density magnetoplasma column to a pair of RF pulses near the cyclotron frequency is a series of pulses known as two-pulse echoes. A similar three-pulse echo train may be obtained by applying a third pulse. This behaviour involves some type of non-linearity, and for a low-density plasma the most promising mechanism appears to be velocity-dependent electron-neutral collisions. This gives velocity-dependent decay to induced currents, and velocity-dependent diffusion. The latter may be important in three-pulse echo formation. In this paper computations from these theories are compared with experimental data with these findings: (1) diffusion is not primarily responsible for three-pulse echoes; (2) the predictions of the collisional current decay theory are in reasonable agreement with the experimental results.