Local transit-time dissipation and Landau damping

A generalization of local transit-time dissipation theory to coherent electrostatic wave packets with nonzero mean wave number is presented. The connection between Landau damping and transit time damping is derived in a concise, 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 wave number or asymmetric incident particle distributions, the nonresonant damping can dominate over Landaudamping. In the opposite extreme of infinitely large, constant-amplitude wave packets, the nonresonant part of transit time dissipation vanishes, and only Landau damping remains. All the analytical results presented are verified independently by numerical test-particle calculations.