ASTeC and the University of Liverpool have completed the first tomographic reconstructions of the VELA transverse phase space, allowing characterisation of the full 4-dimensional beam distribution.
The images below show the normalised phase space determined from data collected on 23 June (the first attempt!), with 4.5 MeV/c beam momentum and 10 pC bunch charge. A beam perfectly matched to the lattice would give a circular distribution; the distortion shows the beam is not perfectly matched. The black and white ellipses show different measures of the emittance and lattice functions, demonstrating a sub-micron normalised emittance on VELA.
For the vertical phase space, the beam distribution is well characterised by a 2D Gaussian: the black and white ellipses are similar. In the horizontal phase space, there is significant distortion from a 2D Gaussian, leading to a larger discrepancy between the black and white ellipses. This nicely illustrates how the tomography analysis gives a much more detailed characterisation of the beam than could be obtained from standard measurements.
Work is now in progress to develop further the phase space tomography technique so that it can be applied to higher bunch charges, where space-charge effects are more significant, and to cases where there is strong coupling between the transverse degrees of freedom.
Horizontal Phase Space Reconstruction Vertical Phase Space Reconstruction