Studies on high brightness electron beams for short pulses and free electron laser

Abstract: Accelerator based lightsources are one of the most powerful tools today for producing high intensity radiation at very short wavelengths. While synchrotron storage rings provide a high average brilliance in a wide wavelength range, the next generation of lightsources aim towards producing ultra-short pulses in the X-ray regime. A very promising technique implemented or proposed at many accelerator laboratories around the world is the free electron laser (FEL). In an FEL a high brightness electron beam interacts with an electric field in an undulator to produce coherent radiation at short wavelengths. The FEL puts very high demands on the quality of the electron beam, such as low energy spread, low emittance and high peak current. In another method, spontaneous, incoherent X-ray pulses are produced in an undulator or wiggler. In these sources focus is put on achieving ultra-short pulses at very short wavelengths and the demands on the high brightness electron beam are high when it comes to bunch length, and bunch shape. In this thesis I discuss some design concepts for producing the high brightness electron beams needed in an accelerator based short-pulse X-ray source. I present results from beam dynamics studies and start-to-end simulations of some future and present lightsources, including beam linearisation, bunch compression and collective effects. The thesis also contains a description of the FEL test facility constructed at MAX-lab where the concepts of seeding and harmonic generation are tested. Full start-to-end simulations of the facility, from the production of electrons at the gun cathode, through acceleration and bunch compression to the harmonic generation of coherent photons, have been performed. Progress of commissioning and results from experiments are presented, including characterisation of a photoinjector and bunch compression measurements.

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