CYCLOTRON ECHOES IN PLASMAS.

Experimental observations of cyclotron echo phenomena in rare-gas and nitrogen afterglow plasmas in the presence of a slightly inhomogeneous magnetic field are presented. The formation of cyclotron echoes is treated theoretically, and specialized to the case of a velocity-dependent collision frequency mechanism, which seems to best explain our experimental observations. Detailed calculations for this case, including such factors as echo amplitude, echo lifetime, and the form of echo decay envelopes, are made and related to the present experimental results. Comparison is made with other mechanisms of cyclotron echo formation. In addition, a detailed discussion of the effects on two-pulse and three-pulse echo amplitude due to electron diffusion into regions of inhomogeneous magnetic field is included.