X-band Traveling Wave Deflecting Structure For Ultra-short Bunch Length Measurement

X-ray Free Electron Laser (XFEL), is the advanced light source ofelectron linear accelerator, with the characteristics of high intensity,ultra short temporal pulse and spatial coherence. These advancefeatures make the application of XFEL extensively on many fields,including biology and medicine, material science, and environmentalscience. For the development of FEL facility, the research emphasishave transferred to the cost performance, which means develop highperformance facility with enough resource as much as possible. Atpresent, it s a big challenge for the diagnostic of ultra-short bunchlength with low emittance. To meet the requirement of compaction andultra-short bunch length on measurement, an X-band traveling wavedeflecting structure, with high deflecting gradient is the optimizedscheme.Bunch length measurement with a deflecting cavity is a highefficiency, reliable, and high resolution method among the bunch lengthdiagnostic methods.the principle of the deflecting structure is togenerate a fast changing transverse deflection field at the positionpf the bunch, which is acting on the bunch. So that the longidudinaltime structure is transformed into a transverse size on a screen atthe downstream of deflector. The operating mode in deflecting cavityis HEM11mode, due to the characteristic of polarization degeneracy,the most important question is separate the frequency of the differentdegeneracy modes.In this thesis, the research and design on x-band traveling wavedeflecting structure are discussed in detail, with computer simulationtechnologies, the simulations of deflecting structure, includingregular cavity and coupler are completed, and the optimizations oncavity parameters are listed.The main work on cavity includingoptimization of the dimensions, cells cold test, and tuning of thewhole structure. Finally, an x-band deflecting structure have beendesigned and fabricated of high deflection gradient. So far, the firstx-band deflecting structure has been completed. Over the wholedevelopment process of x-band deflecting structure, lots of experiencesare accumulated, as the base of researching and fabrication of highgradient structure. Secondly, based on the non-resonant perturbing theory’s applicationon accelerating structure, we developed the non-resonant perturbingtechnique for tuning multi-cell traveling wave deflecting structures.A new type which called cage perturbing object was made and scalingof the cage completed, which was used on the field distributionmeasurement and cavity tuning of s-band deflecting structure. Themeasurement results proved that the measurement is a reliable method.Then, another new and smaller cage type perturbing object was made,and used on the measurement and tuning of x-band deflecting structure,the results show good agreement with the theory.Finally, the new completed x-band deflecting structure will be usedon the bunch length measurement of SXFEL. Further more, we proposed anew concept of two mode operation traveling wave deflecting structure.With the multi function of bunch diagnostic and beam control, it hasa great prospect of application.