Phase stabilization of a relativistic backward wave oscillator by controlling the cathode characteristics for a slowly rising voltage pulse

Abstract

We found that the start time in microwave generation of a relativistic backward wave oscillator (RBWO) for a slowly rising voltage pulse demonstrates a large jitter, which can be explained by the spread of explosive electron emission thresholds and plasma formation rates of the explosive emission cathode, and this large jitter is reduced greatly by a weak external RF signal. So, the effects of the emission threshold and plasma formation rate on the oscillation start time of a single RBWO and on the phase synchronization in two parallel RBWOs are investigated using particle-in-cell simulations. The 2D simulations show that a larger emission threshold and a faster plasma formation rate lead to a shorter start time due to the stronger shock excitation provided by the sharper beam current leading edge. For some special emission thresholds, the start time is abnormally long, which is due to the generation of other frequencies because of the shock excitation. The 3D simulations illustrate that with a larger emission threshold and a faster plasma formation rate, phase synchronization can be obtained in two parallel RBWOs even for a large voltage rise time. Therefore, we expect that by choosing the appropriate cathode emission threshold and plasma formation rate, it is possible to realize phase stabilization of an RBWO for a slowly rising voltage pulse even without an external RF signal.

Emission Features and Structure of an Electron Beam versus Gas Pressure and Magnetic Field in a Cold-Cathode Coaxial Diode

“…Currently, in the field of high-power microwave (HPM) generation (see, e.g., Refs. [1,2], and citations therein), research on the phase-stable excitation of high-current electron generators is ongoing [3][4][5][6][7][8][9][10][11]. Along with the use of external radiation sources [12][13][14][15], this mode is possible when a seed electromagnetic (EM) signal appears at a stable front of the beam, and has the required power and spectral range [16,17].…”

Numerical Analysis of High-Power X-Band Sources, at Low Magnetic Confinement, for Use in a Multisource Array

“…The Backward-Wave Oscillator (BWO) has proven suitable for use in such an array [11]- [17], where each individual BWO may be considered an independent radiative element. Efficient operation requires active control of the timing of the different outputs to ensure constructive, coherent, far-field interference, with peak operation obtained when the constituent BWOs are effectively phase-synchronous, or phase-locked.…”