Abstract
A new type of helical undulator based on redistribution of magnetic field of a solenoid by ferromagnetic helix has been proposed and studied both in theory and experiment. Such undulators are very simple and efficient for promising sources of coherent spontaneous THz undulator radiation from dense electron bunches formed in laser-driven photo-injectors.
Highlights
Advanced laser-driven photo-injectors make possible formation of very dense picosecond and sub-picosecond electron bunches with charge of the order of 1 nC and moderate energy of 3–6 MeV [1,2,3,4,5]
One of the recently proposed efficient methods for stabilization of the electron bunches length and for corresponding increase of their spontaneous Doppler-up-shifted terahertz undulator radiation energy [12,13] is based on development of the so-called negative-mass instability (NMI) [14,15,16,17] in the bunches moving in undulators
We demonstrate that in such a system, the undulator field can be created by redistributing the strong uniform field by a periodic ferromagnetic helix
Summary
Advanced laser-driven photo-injectors make possible formation of very dense picosecond and sub-picosecond electron bunches with charge of the order of 1 nC and moderate energy of 3–6 MeV [1,2,3,4,5]. Such bunches can be attractive for production of power THz electromagnetic pulses [6,7,8,9,10,11,12,13], if very strong mutual Coulomb longitudinal repulsion of bunch particles is prevented or mitigated. Realization of the NMI-based terahertz source amplitude of this component can be readily obtained
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