Experimental investigation of mode build-up and mode competition process in a prebunched free-electron maser oscillator

A unique experimental set up at Tel-Aviv University (TAU) enables the study, observation and quantitative measurements of the mode competition process in a Free-Electron Maser (FEM) oscillator. The experimental results provide data on the mode build-up from noise level to steady-state saturation and on mode competition. The experimental results are recorded with the aid of a fast digital oscilloscope and are analyzed to obtain the Fourier components by use of a computer program, which we developed. The Fourier analysis shows clearly the build-up and competition of the longitudinal modes (eigenfrequencies) excited in the oscillator. We studied mode competition for two cases (1) free-running oscillator (no beam prebunching) (2) oscillator with prebunching of the e-beam. We also compared the experimental results with the results of the multi frequency simulation code MALT1D3, and found good agreement. ( 1998 Elsevier Science B.V. All rights reserved.