Dynamics of Mode Competition in the Gyrotron Backward-Wave Oscillator

Abstract

The axial modes of the gyrotron backward-wave oscillator (gyro-BWO) each exhibit a distinctive asymmetry in axial field profile. As a result, and in sharp contrast to the behavior of the familiar resonator-based gyrotron oscillator, particle simulations of the gyro-BWO reveal a radically different pattern of mode competition in which a fast-growing and well-established mode is subsequently suppressed by a later-starting mode with a more favorable field profile. This is verified in a Ka-band experiment and the interaction dynamics are elucidated with a time-frequency analysis.

Generation of Rogue Waves in Gyrotrons Operating in the Regime of Developed Turbulence

“…In this paper, we demonstrate that rogue waves can appear in gyrotrons operating in the regime of developed turbulence. It is well known that in electronic oscillators, including gyrotrons, an increase of the excess over the starting conditions leads to a complication of the radiation spectrum caused by the appearance of periodic self-modulation and then chaotic turbulent generation regimes [11][12][13][14][15][16][17]. Typically, realization of self-modulation regimes is a result of combination of a nonlinearity and delay effects [12].…”

“…One more critical factor which should be included into consideration is the change of the longitudinal momentum of electrons. This effect is not significant for a steady-state generation regime and, as a rule, is ignored in the gyrotron theory [14][15][16][17][18]. However, in the process of the formation of giant ultrashort pulses with a very steep profile, significant gradients of the electric field appear at their fronts.…”

Experimental study from linear to chaotic regimes on a terahertz-frequency gyrotron oscillator

“…These theoretical studies were made on advanced models based on the slow-time scale formulation of the selfconsistent interaction equations 1,2,7,8,15,27 or on more firstprinciple set of equations solved using a particle in cell approach. 16,17,22 Experimental studies have been carried out by Chang et al 10 and more recently on a system where delayed feedback mechanisms were introduced for accessing to chaotic regimes.…”

Effects of tapering structures on the characteristics of a coaxial-waveguide gyrotron backward-wave oscillator

“…A higher order axial mode can penetrate a tapered structure deeper than the fundamental axial mode can, so a longer effective interaction length lowers its start oscillation current. 10 Since the field of a higher order axial mode concentrates in the downstream end and differs from that of the fundamental axial mode, applying distributed losses at the down stream end of the interaction structure effectively suppresses high order axial modes. 11,12 In addition to axial mode competition, transverse mode competition may also occur.…”

“…9 Also, recent studies considered mode competition under various tuning conditions. [10][11][12][13] A gyro-BWO with a tapered structure is susceptible to the problem of axial mode competition. A higher order axial mode can penetrate a tapered structure deeper than the fundamental axial mode can, so a longer effective interaction length lowers its start oscillation current.…”