Beam dynamics in spreaders for future X-ray free electron laser facilities

• Main Author: Angal-Kalinin, Deepa
• Published: University of Liverpool 2017
• Subjects: 539.7
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.724514

This thesis describes various design options for beam spreaders to allow the inclusion of multiple beam lines as an integral part of X-ray Free Electron Laser (FEL) facilities. The accelerator configuration driving an X-ray FEL follows a linear geometry so as to maintain the ultra-bright properties of the electron beam generated at the injector. Bending the beam is typically restricted only to the bunch compressor chicane in order to avoid an increase in transverse emittance due to the emission of coherent synchrotron radiation. Unlike storage ring based light sources, X-ray FELs serve either one experiment at a time or a number of experiments (quasi-simultaneously) by splitting the radiation from a single FEL line; the radiation pulse repetition rate is set by the injector and the technology used for acceleration. Multiple beam lines provide flexibility in experiments and provide access for a greater number of users. However, in providing multiple beam lines, bending the electron beam is unavoidable and its high quality (i.e. low emittance, low energy spread and high peak current) must be ensured by very careful design of the beam spreader. Two main aspects of the beam spreader design (namely, the options for switching and the lattice design) have been studied and are presented here in detail. Two lattice design concepts, one based on a Triple Bend Achromat magnetic lattice and the other based on a Double Bend Achromat magnetic lattice, are discussed. The relative merits, advantages and disadvantages of these design options are detailed, including mitigation of the effects from coherent synchrotron radiation which include increases in both the beam emittance and energy spread. Experimental studies related to the Triple Bend Achromat arc on the ALICE facility are used to recommend beam diagnostics and instrumentation in different spreader design concepts. The results presented in this thesis will be central to the design of an optimised beam spreader for any future UK X-FEL facility.