C. Widmann

Development of a Superconducting Transverse-Gradient Undulator for Laser-Wakefield Accelerators

Relativistic electrons with small energy spread propagating through undulators produce monochromatic radiation with high spectral intensity. The working principle of undulators requires a small energy spread of the electron beam in the order of ΔE/E ~ 0.1%. Laser-wakefield accelerators can produce electron bunches with an energy of several 100 MeV within a few millimeters acceleration length, but with a relatively large energy spread (ΔE/E ~ 1-10%). In order to produce monochromatic undulator radiation with these electrons, a novel scheme involving transverse-gradient superconducting undulators was proposed in an earlier work. This paper reports on the design-optimization and construction of an iron-free cylindrical superconducting undulator tailored to the particular beam properties of the laser-wakefield electron accelerator at the University of Jena, Germany.

Progress on experiments towards LWFA-driven transverse gradient undulator-based FELs

Abstract Free Electron Lasers (FEL) are commonly regarded as the potential key application of laser wakefield accelerators (LWFA). It has been found that electron bunches exiting from state-of-the-art LWFAs exhibit a normalized 6-dimensional beam brightness comparable to those in conventional linear accelerators. Effectively exploiting this beneficial beam property for LWFA-based FELs is challenging due to the extreme initial conditions particularly in terms of beam divergence and energy spread. Several different approaches for capturing, reshaping and matching LWFA beams to suited undulators, such as bunch decompression or transverse-gradient undulator schemes, are currently being explored. In this article the transverse gradient undulator concept will be discussed with a focus on recent experimental achievements.

Detailed Analysis of a Linear Beam Transport Line from a Laser Wakefield Accelerator to a Transverse-Gradient Undulator

A linear beam transport system, experimentally tested at the Laser Wakefield Accelerator in Jena, Germany, has been carefully analyzed in order to gain a deeper understanding of the experimental results and to develop experimental strategies for the future. This analysis encompassed a detailed characterization of the focusing magnets and an investigation of the effects of source parameters as well as magnet and alignment errors on the observables accessible in the experiment. A dedicated tracking tool was developed for these investigations. In this contribution we review the main results of these studies.