Scripts used for beam-reference measurements to benchmark the impedance model at the CERN-SPS
- 📁 SPS Headtail Mode 0 Growth rates: 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
- 📁 SPS Chromaticity from Intrabunch: Scripts to obtain the chromaticity from intrabunch headtail motion on the fly
- 📁 SPS Multi-Bunch Tune Shifts: Studies with PyHeadtail to compute the tune-shift of multi-bunch beams for different intensities
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.
After the implementation of major upgrades as part of the LHC Injector Upgrade Project (LIU), the Super Proton Synchrotron (SPS) delivers high intensity bunch trains with 25 ns bunch spacing to the Large Hadron Collider (LHC). These beams are exposed to several collective effects in the SPS, such as beam coupling impedance, space charge and electron cloud, leading to relatively large bunch-by-bunch coherent and incoherent tune shifts. Tune correction to the nominal values at injection is crucial to ensure beam stability and good beam transmission. Measurements of the bunch-by-bunch coherent tune shifts have been performed under different beam conditions. In this paper, we present the measurements of the bunch-by-bunch tune shift as function of bunch intensity for trains of 72 bunches. The experimental data are compared to multiparticle tracking simulations (including other beam variants such as 8b4e beam and hybrid beams) using the SPS impedance model.
- 🔗 https://jacow.org/hb2023/papers/wea1c1.pdf
- DOI: 10.18429/JACoW-HB2023-WEA1C1