Studies of the LHC impedance at injection energy

The goal of this MD was to study the longitudinal impedance of the LHC at injection energy through measurements of synchronous phase and incoherent synchrotron frequency for bunches of different intensity and length. The length of injected bunches was varied by applying controlled emittance blow-up during the SPS ramp and intensity was changed by transverse scraping at the end of the ramp in the SPS. During this MD there were three fills, all without acceleration in the LHC. In the first fill each ring was filled with 8 bunches of varying intensity and large longitudinal emittance. During the second and the third fills 8 bunches had a smaller longitudinal emittance. During the 3rd fill the phase loop in the LHC was switched off. Measurements of phase error and bunch length evolution, as well as data extracted from the Peak Detected Schottky spectra, are presented in this Note together with the data obtained in the transverse plane (tunes and emittances). An effect of different positions (”in” and ”out”) of the two movable devices such as BSRT and TDI on beam coupling impedance was also recorded via the change in bunch characteristics.