ALICE tomography section: measurements and analysis

The ALICE tomography section at Daresbury is a diagnostic setup in the injection line of EMMA, the world's first non-scaling FFAG accelerator. We present our measurements and analysis of the transverse emittance, Twiss parameters and phase space distribution of the electron beam that is injected into EMMA. The measurements are carried out at 12 MeV, for bunch charges from 20 to 80 pC. Quadrupole scans and tomography are used. The results show that space charge effect does not change the beam emittance significantly over the length of the tomography section. Starting from projections of the beam images, the quadrupole scan technique can be applied to give the emittance and Twiss parameters. The same projections can be processed using tomography to give the phase space distribution. A careful treatment of the background noise is required to produce consistent emittances between quadrupole scans at different locations. Extending this in a natural way to tomography, we are also able to remove most of the the streaking artefacts from reconstructions obtained using the Filtered Back Projection technique.