Nonlinear absorption of high-power microwave pulses in a plasma filled waveguide

We observe complete absorption of an ∼1.2 GW, 0.5 ns, 25.6 GHz high power microwave pulse propagating in a plasma-filled waveguide when the plasma density dependent waveguide cutoff frequency is close to the pulse frequency. Some of the plasma electrons are ejected to the walls, leaving in the waveguide an uncompensated ion charge which forms a potential well where the remaining electrons oscillate in the pulse field. Due to the decreased group velocity of the wave, these trapped electrons have sufficient time to collide with ions, while their regular oscillatory motion becomes chaotic and thermal. Almost all the energy of the electromagnetic pulse is transferred to the kinetic energy of the electrons. This mechanism of absorption is absent when the pulse power is low, and a potential well does not form in the waveguide.