Local transit-time dissipation and Landau damping

A generalization of local transit-time dissipation theory to coherent elect rostatic wave packets with nonzero mean wave number is presented. The conne ction between Landau damping and transit time damping is derived in a conci se, mathematically rigorous manner, settling a longstanding controversy. It is shown that transit time dissipation involves both Landau-type resonant damping and nonresonant damping. For small wave packets with nonzero mean w ave number or asymmetric incident particle distributions, the nonresonant d amping can dominate over Landaudamping. In the opposite extreme of infinite ly large, constant-amplitude wave packets, the nonresonant part of transit time dissipation vanishes, and only Landau damping remains. All the analyti cal results presented are verified independently by numerical test-particle calculations. (C) 1999 American Institute of Physics. [S1070-664X(99)00709 -0].