Scripts used for beam-reference measurements to benchmark the impedance model at the CERN-SPS
- 📁 SPS Headtail Mode 0: Studies with PyHeadtail to compute the growthrates of the HeadTail mode 0 instability for different negative chromaticities.
- 📁 SPS Tune Shifts: [TODO] Studies with PyHeadtail to compute the tune-shift with intensity for different positive chromaticities
The Head-Tail mode 0 instability growth rate is related to the real part of the transverse beam coupling impedance. The SPS transverse impedance model, which includes the major impedance contributions in the machine, can be benchmarked through measurements of growth rate as function of chromaticity. This paper summarizes the new methodology established to explore a wider range of chromatic frequency shift, and presents the measurements performed after the LHC Injectors Upgrade (LIU) for two sets of machine optics: nominal low gamma transition optics (Q20) and the former standard (Q26) optics. The measurements are compared with the current impedance model to further study its degree of accuracy
The SPS transverse impedance model, which includes the major impedance contributions in the machine, can be benchmarked through measurements of the Head-Tail mode zero instability. Since the SPS works above transition energy, the head tail mode zero is unstable for negative values of chromaticity. The measured instability growth rate is proportional to the real part of the transverse impedance. Studies performed after the LHC Injectors Upgrade (LIU) showed a relevant impedance around 2 GHz with high-gamma transition optics (Q26). This paper presents the follow-up studies to probe the behavior of this beam coupling impedance contribution.