Linear and nonlinear theory of cyclotron autoresonance masers with multiple waveguide modes

Abstract

The interaction of multiple waveguide modes with a relativistic electron beam in an overmoded, single-frequency, cyclotron autoresonance maser amplifier is analyzed using a nonlinear self-consistent model and kinetic theory. It is shown analytically, and confirmed by simulation, that all of the coupled waveguide modes grow at the spatial growth rate of the dominant unstable mode, but suffer different launching losses which depend upon detuning. The phases of coupled modes are locked in the exponential gain regime, and remain approximately locked for some finite interaction length beyond saturation. The saturated power in each mode is found to be insensitive to the input modal rf power distribution, but sensitive to detuning. Simulations indicate that the saturated fractional rf power in a given mode reaches a maximum at its resonant magnetic field, and then decreases rapidly off resonance. Good agreement is found between the simulations and the kinetic theory in the linear regime.

Experimental and theoretical investigation of high gradient acceleration

“…The code can model a single TE or TM mode, Multiple TE and/or TM modes, cyclotron harmonics, magnetic field tapering, momentum and energy spread, waveguide losses, and various beam loading options. It has been benchmarked against a linear kinetic theory [i9], [20], and has been found in good agreement with recent CARM amplifier experiments [21]. Space-charge terms have also been included in the CSPOT simulation and it being used to study the 17GHz CARM amplifier.…”

“…As summarized previously, a three-dimensional, multimode, self-consistent code, CSPOT [19], [20], [23] has been developed for the simulation of CARM amplifiers and CRL accelerators. The code can model a single TE or TM mode, Multiple TE and/or TM modes, cyclotron harmonics, magnetic field tapering, momentum and energy spread, waveguide losses, and various beam loading options.…”

“…Design modelling of a high-current CRL accelerator in the microwave regime [11] is being performed using a three-dimensional self-consistent simulation code (CSPOT [20], [23]). The code takes into account the self-consistent evolution of the amplitude and phase of the driving wave due to the inverse cyclotron resonance interaction.…”

Proposed research on advanced accelerator concepts

“…Self-consistent modelling of a 33.3 GHz high-current, high-efficiency CRL accelerator A detailed design modelling of a high-current CRL accelerator has been conducted in the microwave regime [6], using a three-dimensional self-consistent simulation code CSPOT [15], [18]. The code takes into account the self-consistent evolution of the amplitude and phase of the driving wave due to the cyclotron resonance interaction in the high-current regime.…”

The CARM beam-wave interaction and cavity design

“…In parallel to the development of the full numerical analysis, we have undertaken the cavity design by the use of "home-made" 1D/3D code, based on the selfconsistent procedure discussed by several authors [3][4][5] and on the "universal" scaling formulae that describe the CARM performances including inhomogeneous broadening effects and the beam current, as it happens in the case of Undulator FEL [6]. An effective analysis tool in term of analytical formulae and computer simulation has been accordingly obtained.…”