A novel method of noise suppression in beam transfer function measurements

Beam transfer functions (BTF), giving the frequency domain response of the beam to an external excitation, are widely used to measure the impedance of the beam environment, to analyse stability conditions and to determine the true momentum distribution in spite of strong signal shielding in dense, cooled beams. A problem encountered in low-intensity (antiproton and rare ion) storage rings is the unwanted noise on the BTF signal. We have developed a method of noise suppression which may be viewed as gating in time domain: Transforming (by software) the BTF into time domain, cutting off the tail after the response decayed and going back into frequency space we obtain a significantly cleaner signal. The tail of the time response contains information on beam and system noise which can be treated separately. Results obtained on the low energy antiproton ring LEAR are discussed