Pulsed Micro-Undulator for Terahertz and X-Ray Free-Electron Lasers

We propose and test experimentally the design of a planar micro-undulator, which allows ensuring a simple profile of the undulator parameter with a value of about unity at a period of 1 mm, as well as the possibility to operate in a regime with a repetition frequency of tens of hertz. Along with small-size sources of high-density beams of accelerated electrons, such as the photo-injection accelerator or the plasma wakefield accelerator, this micro-undulator can be used to make small-size sources of the terahertz and X-ray radiation. It is shown that the Joule heating inhibits the further decrease in the period value. Analytical estimates of the undulator parameter agree well with both the results of numerical simulations and the results of experimental tests.