Abstract
Effects caused by misalignment of undulator segments on the gain of a free electron laser (FEL) based on the process of self-amplified spontaneous emission are theoretically studied. The well-known FEL equations are solved analytically and numerically with boundary conditions describing the misalignment effect in order to obtain the amplification gain as a function of the distance from the undulator entrance. The two worst cases of alignment are considered. One is that the phase slip over the drift section between the adjacent segments is $\ensuremath{\pi}$, and the other is that the radiation is cut off at the drift section. Calculations show that if the undulator segment is several times as long as the gain length, the radiation power is close to that of no segmentation in both cases.
Highlights
In x-ray free electron laser (FEL) projects based on the process of self-amplified spontaneous emission (SASE), e.g., Linac Coherent Light Source [1], TESLA [2], and SPring-8 Compact SASE Source [3], a long undulator is to be installed
Let us consider the practical case of misalignment
Possible sources of the transverse misalignment are error magnetic fields of the undulator and misalignment of the focusing magnets placed in the drift section
Summary
In x-ray free electron laser (FEL) projects based on the process of self-amplified spontaneous emission (SASE), e.g., Linac Coherent Light Source [1], TESLA [2], and SPring-8 Compact SASE Source [3], a long undulator (typically longer than 20 m) is to be installed. In such a case, the undulator is usually divided into several segments to provide drift sections for installation of focusing magnets and beam-diagnostics instruments. By means of these technologies, it is possible to construct one undulator segment close to an ideal device with low phase errors and electronorbit deviations
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