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.
@article{arxiv.1801.05312,
title = {Helical Undulator Based on Partial Redistribution of Uniform Magnetic Field},
author = {N. Balal and I. V. Bandurkin and V. L. Bratman and A. E. Fedotov},
journal= {arXiv preprint arXiv:1801.05312},
year = {2018}
}