Generation of powerful subnanosecond microwave pulses by intense electron bunches moving in a periodic backward wave structure in the superradiative regime

Abstract

Experimental results of the observation of coherent stimulated radiation from subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating wave are presented. The subnanosecond microwave pulses in Ka and W bands were generated with repetition frequencies of up to 25 Hz. The mechanism of microwave pulse generation was associated with self-bunching, and the mutual influence of different parts of the electron pulse due to slippage of the wave with respect to the electrons; this can be interpreted as superradiance. The illumination of a panel of neon bulbs resulted in a finely structured pattern corresponding to the excitation of the TM01 mode. Observation of rf breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the absolute peak power as high as 60 MW for the 300-ps pulses at 38 GHz. These results are compared with numerical simulations. The initial observation of 75-GHz, 10-15-MW radiation pulses with a duration of less than 150 ps is also reported.

Generation of high-power ultrashort electromagnetic pulses on the basis of effects of superradiance of electron bunches

“…In this respect, in Sec. 2 we present a brief theoretical analysis of SR effects based on various mechanisms of stimulated radiation, as well as results of the first experimental observations of these effects [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. In those experiments, SR pulses with maximum peak power and uniquely short duration (less than 300 ps) were obtained during theČerenkov interaction of a rectilinearly moving electron bunch with a slow spatial harmonic of the counterpropagating electromagnetic wave in a periodic slow-wave system.…”

Generation of Super-Radiance rf Pulses in a Sectioned Backward-Wave Oscillator

“…An effective method for generation of powerful pulses of coherent microwave electromagnetic radiation is the use of the so-called super-radiance (SR) regime of operation of a Cherenkov backward-wave oscillator (BWO) [1][2][3][4][5][6][7][8][9]. It is well-known that if the length of the electron-wave interaction region of a BWO significantly exceeds the starting threshold, then the transient process of excitation of the oscillator includes excitation of a short powerful rf pulse [1].…”

Absolute-instability growth rates and eigenmode structures in the electron-beam—backward-wave system with large excesses over the generation threshold

“…6. The found growth rates (19) and structures (17) of the eigenmodes can be applied to the studies of the ultashort-pulse generation in the pulsed electronbeam -backward electromagnetic wave system [1][2][3]. Actually, in these processes, the mode with the longitudinal structure described by Eq.…”

“…Analysis of the nonlinear stage of interaction shows that the field pulse generated at the initial linear stage begins to shift upstream of the electron beam with group velocity as the amplitude increases. As a result of this process, a short pulse, which is interpreted as a superradiance pulse in [1][2][3], is emitted from the system. It should be mentioned that the formation of a short pulse with large excesses over the generation threshold also takes place for an M-type BWO [4].…”

“…The studies of the superradiance effects of short electron bunches [1][2][3] has recently generated interest in analysis of the nonstationary processes in the electron-beam -backward-wave system for large reduced lengths of the interaction space. It was noted in the numerical simulation that the field distribution at the initial linear stage of interaction has a characteristic maximum near the collector end of the system.…”