A new wide band time normaliser circuit for bunch position measurements with high bandwidth and wide dynamic range

Trajectory and closed orbit measurements are vital for commissioning and operation of accelerators. With the push for high luminosities at modern colliders, the azimuthal bunch distribution becomes very complex, so that various phenomena (beam-beam forces, wake fields) strongly affect the orbits of individual bunches. Hence a system with high bandwidth capable of measuring the transverse position of any bunch is desirable. With the current techniques a bandwidth above 100 MHz can only be achieved by individual integration and digitisation of the pick-up signals. The drawback of such an approach is the limited dynamic range of typically 30 dB. In the context of the development of an orbit system for the LHC at CERN a high bandwidth could be achieved by extending the principle of phase normalisation to a wide band time normalisation of the position monitor signals. The circuit described in this paper (Wide band time normalizer) combines the signals of two pick-up electrodes with different delays and converts the beam position information into a pulse width modulation of the digital output signal. This way a bandwidth of more than 40 MHz and a dynamic range of about 50 dB could be achieved. The paper introduces the requirements for the LHC orbit system, compares various technical solutions and finally explains the working principle of the wide band time normalizer including some laboratory tests results.