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Enhancing Electron Beam Radiative Energy Extraction Efficiency in Free-Electron Laser Oscillators Through Beam Energy Ramping

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<mark>Journal publication date</mark>1/11/2017
<mark>Journal</mark>IEEE Transactions on Microwave Theory and Techniques
Issue number11
Volume65
Number of pages7
Pages (from-to)4218-4224
Publication StatusPublished
Early online date19/05/17
<mark>Original language</mark>English

Abstract

Free-electron lasers are used to generate laser radiation using an accelerated electron beam. In this paper, an electrostatic accelerator was used with a thermionic cathode. Lasing pulses of the order of tens of microseconds were generated by passing the current pulses through a wiggler and resonator combination. The change in lasing power as a result of postsaturation variation of the energy of the electron beam during the lasing period is presented in this paper in the form of experimental measurements and simulations. In the experiments, the initial electron beam energy was similar to 1.4 MeV and the current was 1.13 A, whilst the lasing frequency was always close to 102 GHz. It is shown that postsaturation, positively ramping the beam energy increases the radiation extraction efficiency by around 50%. Whilst a falling beam energy results in a reduction in extraction efficiency.