Variation of relativistic BWO generation mode considering the features of pulsed guiding magnetic field

The goal of investigations was a variation of relativistic Ka-band BWO generation mode (desirably from quasi-stationary to non-stationary) from pulse to pulse, when slow-wave structure (SWS), cathode diameter, current and accelerating voltage of e-beam were unchanged. This is imperative for the tasks when duration and power of multi-megawatt microwave pulses should be varied rapidly. For conservative current of the beam, BWO generation mode depends on the device starting current [1]. The field of synchronous harmonics of the wave (this is TM<;sub>01<;/sub>, in our case) descends exponentially along the radii from the SWS wall. Therefore, with the beam approaching to the wall, the "beam-to wave" coupling rises, and starting current drops. To do that, one should increase the diameter of tubular e-beam throughout SWS section. This can be attained practically by application of two-sectional dc solenoid with independent feeding of the windings [2]. We suggested alternative method which applicable for a single-winding pulsed solenoids. Its background is that the shell of e-beam diode (Section 1) is made of non-magnetic steel, while 1-mm-thick copper is the material of the SWS wall (Section 2). Due to pronounced skin-effect and finite time of B-field diffusion through the copper wall, magnetic field inside SWS is weakened and delayed. If B-field envelope in the Section1 represents a half-period of the function B₁(t)~B₀₁sin(co₁t), then in the Section 2: B₂(t)~B₀₂sin(co₂t), where B₀₂ <; B₀₁; ω₀₂ <; ω₀₁. Radial displacement of the beam trajectory is available with the change of ratio (B₂(t*)/B₁(t*)) and easily attainable with synchronization instant (t*) variation. There is distinguished point (intersection of B1(t) and B₂(t)), where the character of B-field distribution along both Section 1 and Section 2 does not differ from static distribution except of decreased field amplitude. This is the only synchronization point where experiment could be compared with simulation correctly, as long as B-field profile used in PIC models of BWOs is generally static. In the report we suggest examples of experiments on the BWO generation electronic readjustment in the band from 2 ns to a tenth of nanosecond with the peak power from tens to hundreds of megawatts, respectively.