Linac structure design for high brightness beams for free electron lasers

Several issues in the design of linear accelerator structures are examined in the context of producing electron beams for free electron lasers. Among the issues discussed are: accelerator structure requirements of harmonic acceleration; advantages of short, high gradient, low impedance, superconducting structures; interactions of an electron beam with structure modes, with particular attention given to anomalously trapped modes and regenerative beam breakup; and finally, acceleration gradient limitations in the proposed structures. Results and analysis of tests of two prototype structures are also presented.; The major findings of this dissertation are: (1) harmonic acceleration of relativistic electrons can produce a superior beam when the fundamental and harmonic fields are spatially separated rather than superimposed; (2) single or double cell, low impedance, superconducting structures have definite advantages over traditional accelerator structures in dealing with higher order structure modes; (3) electron multipacting may be effectively eliminated with appropriate design of the accelerator cell geometry; and (4) superconducting structures of the type described herein may be expected to consistently reach 8 MV/m acceleration gradients, limited by electron field emission, if high thermal conductivity niobium is used in construction.