Benchmarking of 3D space charge codes using direct phase space   measurements from photoemission high voltage DC gun
  We present a comparison between space charge calculations and direct measurements of the transverse phase space for space charge dominated electron bunches after a high voltage photoemission DC gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit setup for a set of parameters such as charge per bunch and the solenoid current. The data is compared with detailed simulations using 3D space charge codes GPT and Parmela3D with initial particle distributions created from the measured transverse and temporal laser profiles. Beam brightness as a function of beam fraction is calculated for the measured phase space maps and found to approach the theoretical maximum set by the thermal energy and accelerating field at the photocathode. 
Ivan V. Bazarov, Bruce M. Dunham, Colwyn Gulliford, Yulin Li,   Xianghong Liu, Charles K. Sinclair, Ken Soong, and Fay Hannon