Testing Of A Photo-cathode RF Gun And Research Of Drive Laser Shaping Technology

The free electron lasers (FEL) with short wavelength require short, high-brightness electron bunches that are typically obtained from a photoinjector. The minimum wave-length of a FEL,which is driven by a linac, scales in inverse proportion to reciprocal normalized transverse emittance. To increase the power gain and reduce the saturation length of FEL, the transverse emittance and peak current of electron bunch should also be improved.In this paper, we first introduced the development of FEL and Photocathode RF Gun, demonstrated the electron beam dynamics in RF Gun, analyzed the contribution factors of the growth of the transverse emittance and introduced the method and prin-ciple of emittance compensation technology.The system of Photocathode RF Gun in HeFei Light Source were introduced. The parameters of drive laser system, which is the key part of the whole system, were mea-sured by the numbers. A maintenance process of the drive system was summarized during the daily operation. The synchronization system was tested, and high precision was achieved. The high power testing of the Photocathode RF Gun was carried out, the performance of gun and quality of the electron beam were presented in this paper. Besides, problems arisen in the experience were also discussed.For the BNL type gun with drive laser blaze at the photocathode obliquely, the disadvantageous effects induced by oblique incidence were analyzed particularly. A simple adjustable way (wavefront shaping of drive laser) to eliminate these effects were introduced, and the accordant experiment and simulation results were also presented. From the simulation research, what was pointed out is that the elliptical spot with ap-propriate ellipticity is more favorable to generate electron beam with high quality.To reduce the transverse emittance caused by nonlinear space charge effect, spatial and temporal shaping of picoseconds drive laser were carried out, and ideal shaping results of laser pulse were acquired. An uniform ellipsoidal beam with only linear space charge force can get further improvement of transverse emittance, scheme of quasi-ellipsoidal shaping was proposed. The elevation of critical parameters were studied by simulation, and laser beam size was chosen carefully.Finally, the expectation was pointed out. In-situ cleaning technology of photocath-ode was discussed in this paper, which is favorable to improve the quantum efficiency, and a scheme of laser cleaning was proposed. Improvement technologies of photocath-ode were also discussed in this part.