Space-Charge Effects Near A Cathode

RF photocathode guns are excellent sources of high brightness electron bunches. To mitigate space charge effects downstream of the gun it is often desirable to produce electron bunches with a uniform density distribution. Our goal is to understand how the longitudinal bunch profile is determined by the emission dictated by the laser pulse intensity and the effects of the self-field dynamics near the cathode. The particle-in-cell simulation XOOPIC is used to simulate beam dynamics near the cathode and the results are compared to those obtained from linear theory. Studies are focused on flat-top and Gaussian bunch profiles.