Transverse Emittance Measurements and Optimization for a Superconducting RF Photon Injector

As one of the most promising continuous wave (CW) injectors for high brightness electron beams, ELBE superconducting radio-frequency (SRF) gun has been developed and optimized. This gun can provide beams with good quality for the ELBE user facility. One important aspect is to measure the transverse emittance accurately and efficiently. This thesis contributes to the progress in this field and focuses on measuring and optimizing the transverse emittance for ELBE SRF gun. The slit-scan, quadrupole scan, and an advanced thermal emittance measurement method, called single shot cathode transverse momentum imaging, have been studied and applied at this SRF gun. A fast slit-scan emittance measurement system consisting of a continuously moving slit and a yttrium aluminium garnet (YAG) screen has been developed. During the beamlet image processing, the machine learning (ML) algorithms have been integrated in order to improve the signal-to-noise ratio effectively. This is the first time to successfully apply the ML in such diagnostic methods. The measurement speed is improved about ten times and accuracy is also better than before. The errors of slit-scan emittance measurement, arising from slit position, beamlet intensity, center position and root mean square (RMS) width uncertainties, have been analyzed. The quadrupole scan emittance measurement method has been studied too. The influence of the space charge effect on quadrupole scan results has been revealed. The error of the quadrupole scan measurement has also been analyzed. To compensate the transverse emittance due to space charge effect, a superconducting (SC) solenoid is placed as close as possible to the exit of the SRF cavity. Another important part in this thesis is the investigation and optimization of the SC solenoid. The spherical aberration of the SC solenoid has been analyzed. In order to decrease it, a new yoke geometry of SC solenoid for the next generation SRF gun has been designed. The multipole transverse