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Generation of rogue waves in gyrotrons with high excess over the threshold
摘要： Many physical systems exhibit behavior associated with the emergence of the so-called rogue waves which represent dramatically high-amplitude events that occur with low probability but much more frequently than expected in ordinary wave statistics [1]. For example, in laser physics and optics rogue waves arise in the process of supercontinuum generation and represent pulses of ultra broadband light with extremely high peak power [2]. In this paper within the framework of the average approach and in direct 3D PIC (particle-in-cell) simulations we demonstrate that rogue waves can also appear in gyrotrons operating with high excess over the threshold. The mechanism of extreme spikes formation is related to simultaneous cyclotron interaction of a gyrating electron beam with forward and backward waves near the waveguide cutoff frequency as well as with the longitudinal deceleration of electrons. From the practical point of view, experimental observation of the rogue waves generation in gyrotrons can be interesting as a method for production of high-power millimeter-wave radiation with an ultra broadband spectrum. The required exceeding over the threshold can be achieved for routine parameters of the driving electron beams formed by the magnetron-injection guns due to operation at the lowest modes of microwave cavities.
关键词： high-power millimeter-wave radiation,rogue waves,gyrotrons,ultra broadband spectrum
更新于2025-09-10 09:29:36
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Propagation of few-cycle pulses in a nonlinear medium and an integrable generalization of the sine-Gordon equation
摘要： The generalized sine-Gordon equation is obtained under the theoretical investigation of interaction of few-cycle pulses in a nonlinear medium modeled by a set of four-level atoms. This equation is derived without the use of the slowly varying envelope approximation and is shown to be integrable in the frameworks of the inverse scattering transformation method. Its solutions describing the propagation of the solitons and breathers and their interaction are investigated. In the case of different signs of the parameters of the equation considered, it is revealed, in particular, that the collision of solitons with opposite polarities can lead to an appearance of the short-living pulse having extraordinarily large amplitude, whose dynamics is similar to that of rogue waves. Also, the solitons of “rectangular” form and the breathers with rectangular oscillations exist in the case of the same signs of the parameters.
关键词： few-cycle pulses,generalized sine-Gordon equation,rogue waves,breathers,solitons,nonlinear medium
更新于2025-09-09 09:28:46
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Incoherent Shock and Collapse Singularities in Non-Instantaneous Nonlinear Media
摘要： We study the dynamics of a partially incoherent optical pulse that propagates in a slowly responding nonlinear Kerr medium. We show that irrespective of the sign of the dispersion (either normal or anomalous), the incoherent pulse as a whole exhibits a global collective behavior characterized by a dramatic narrowing and amplification in the strongly non-linear regime. The theoretical analysis based on the Vlasov formalism and the method of the characteristics applied to a reduced hydrodynamic model reveal that such a strong amplitude-incoherent pulse originates in the existence of a concurrent shock-collapse singularity (CSCS): The envelope of the intensity of the random wave exhibits a collapse singularity, while the momentum exhibits a shock singularity. The dynamic behavior of the system after the shock-collapse singularity is characterized through the analysis of the phase-space dynamics.
关键词： non-linear waves,optical turbulence,shockwaves,partially coherent beams and pulses,Vlasov formalism,coherence,rogue waves
更新于2025-09-04 15:30:14
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Generation of Electromagnetic Rogue-Waves in Submillimeter-Band Gyrotrons
摘要： Rogue-waves in gyrotrons represent sporadically emitted ultrashort electromagnetic pulses with intensities significantly greater than the average radiation power and, in optimal conditions, higher than the power of the driving electron beams. In this paper within the framework of the average approach and direct 3D PIC (particle-in-cell) simulations, we study the possibility of rogue wave generation in submillimeter-band gyrotrons operating at high-order modes. It is demonstrated that in a 500 GHz fundamental cyclotron harmonic gyrotron excited by the 30 kV/50 A helical electron beam the peak power of generated picosecond electromagnetic spikes at TE61 mode can reach 5 MW that more than three times exceeds the power of the driving beam.
关键词： Rogue waves,Submillimeter-wave radiation,Gyrotron
更新于2025-09-04 15:30:14