Black-box Parametric Estimation Methods for Longitudinal Beam Transfer Function Measurements

In the CERN PS Booster (PSB), longitudinal Beam Transfer Function (BTF) measurements are used to determine the energy spectrum of the linac beam injected and coasting on an extended flat bottom of the magnet cycle. The short duration (about 10 ms) of the measurement and coherent signals from density structure of the injected beam yielded strongly fluctuating results, and the system fell into disuse for a while. BTF measurements can be degraded by different kinds of noise, which together with small excitations to avoid alteration of the beam, give a big variance of the results. Particularly in the PSB, this is seen as a base-line offset (BLO) of the energy distribution, whose variance is due to the noise and is not to be improved by longer data records. Different signal processing techniques are investigated to reduce the variance, where black-box parametric estimation methods are shown to have significantly lower BLO than other methods applied in the field.