Design of an x-ray free electron laser undulator

Roger Carr
An undulator designed to be used for an x-ray free electron laser has to meet a set of stringent requirements. With no optical cavity, an x-ray FEL operates in the single pass Self Amplfied Spontaneous Emission (SASE) mode; an electron macropulse is microbunched by an undulator and the radiation it creates. The microbunched pulse emits spontaneous radiation and coherent FEL radiation, whose power may reach saturation in a sufficiently long and perfect undulator. The pulse must have low
more » ... and high current, and its trajectory in the undulator must keep the radiation and the pulse together with a very high degree of overlap. We shall consider the case of the Linear Coherent Light Source (LCLS ) FEL project at SLAC, which is intended to create 1.5 8, x-rays using an electron beam with 15 GeV energy, 1.5n mm-mrad normalized emittance, 3400 A peak current, and 280 fsec FWHM bunch duration. We find that this 65 pm rms diameter beam must overlap its radiation with a walkoff of no more than 5 w for efficient gain. This places severe limitations on the magnetic field errors and other mechanical tolerances. The following is a discussion of the undulator design, specifications, alignment, engineering, and beam position monitoring we plan to implement for the LCLS X-ray FEL.
doi:10.1063/1.54589 fatcat:ej7bnwalkvfsjl6e6pxhsqzo5e