Abstract
Simulations of coherent spontaneous undulator radiation in a waveguide demonstrate that the use of negative mass instability (NMI) for retaining longitudinal sizes of dense electron bunches, which are formed in laser-driven photoinjectors, allows one to increase power capabilities of a terahertz radiation source by many times. The NMI is realized in an undulator with combined helical and over-resonance uniform longitudinal magnetic fields due to nonisochronous longitudinal oscillations of electrons, whose frequencies increase/decrease with increasing/decreasing particle energy. In such conditions, an effective longitudinal size of the bunches can be preserved at long distance even at an extremely high electron density. Correspondingly, an energy extraction efficiency of more than 20% is revealed at a narrow frequency radiation spectrum, suggesting realization of a compact and powerful THz source.
Highlights
Terahertz electromagnetic radiation is currently of increasing interest for basic science and many promising applications
Simulations of coherent spontaneous undulator radiation in a waveguide demonstrate that the use of negative mass instability (NMI) for retaining longitudinal sizes of dense electron bunches, which are formed in laser-driven photoinjectors, allows one to increase power capabilities of a terahertz radiation source by many times
The NMI is realized in an undulator with combined helical and over-resonance uniform longitudinal magnetic fields due to nonisochronous longitudinal oscillations of electrons, whose frequencies increase/decrease with increasing/decreasing particle energy
Summary
Terahertz electromagnetic radiation is currently of increasing interest for basic science and many promising applications. A powerful coherent Doppler-frequency-up-shifted radiation from preformed short ultrarelativistic electron bunches in undulators, which was proposed many years ago by Ginzburg [1] and Motz [2], is still fairly attractive. This method was very popular in the 1950s and later, its frequency possibilities were essentially limited because of the problems with formation of dense electron bunches, whose effective longitudinal sizes should be smaller than the radiation wavelength. IV we discuss the capabilities of an advanced THz source, which could be realized on the basis of a laser-driven photocathode gun in Ariel University
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