Review of Emittance Diagnostics for Space Charge Dominated Beams for AWAKE e⁻ Injector

For a low energy, high intensity beam, total beam emittance is dominated by defocusing space charge force. This is most commonly observed in photo-injectors. In this low energy regime, emittance measurement techniques such as quadrupole scans fail as they consider the beam size only depends on optical functions. The pepper-pot method is used for 2D emittance measurements in a single shot manner. In order to measure the beam emittance in space charge dominated regime by quadrupole scans, space charge term should be carefully incorporated into the transfer matrices. On the other hand, methods such as divergence interferometry via optical transition radiation (OTRI), phase space tomography using 1D projections of quadrupole scans can be suitably applied for such conditions. In this paper, the design of a versatile pepper-pot system for AWAKE experiment at CERN is presented for a wide range of bunch charges from 0.1 to 1nC where the space charge force increases significantly. In addition, other aforementioned methods and respective algorithms are introduced as alternative methods.