Analysis and measurements of emittance dilution from vacuum windows in the Fermilab Recycler transfer lines

Round-trip beam transfers between the Fermilab Main Injector and Recycler (antiproton accumulator) have been plagued by an emittance dilution of about a factor of 2 with corresponding beam loss. The source of the large dilution was traced to two Ti vacuum windows, one installed in each of the two transfer lines that connect the machines for beam injection/extraction. The dilution can be accounted for by calculating the increase in beam divergence due to multiple scattering in the windows followed by an amplitude mismatch that serves to further enhance the instantaneous dilution immediately downstream of the window. This work presents the analytical basis for the phase-space, or emittance, dilution due to the window, the subsequent optics mismatch, and then presents an analysis of beamline measurements that evidences the effect and validates the analytical argument. The data showed a strong skew quadrupole component in the transfer line optics that initially complicated the analysis, but was effectively eliminated in some of the data samples acquired under specific beam conditions.