Speaker: Sofia Kostoglou (BE-ABP-HSI)

Impact of noise and modulation effects at the LHC and its High-lumi upgrade

In order to optimize the performance of a collider such as the LHC and its high-luminosity upgrade (HL-LHC), a thorough understanding of all the phenomena that can act as a luminosity degradation mechanism is required. A major concern for the transverse single-particle beam dynamics is the presence of noise, a mechanism that can impact the long term stability of the circulating particles. From the plethora of noise sources that are present in the accelerator, this seminar investigates the impact of a modulation in the strengths of the dipole and quadrupole magnets of the lattice due to power converter noise. In the presence of non-linearities, depending on the spectral components of the noise and the nature of the source, such a mechanism can increase the diffusion of the particles in the distribution through the excitation of additional resonances in the vicinity of the ones driven by the lattice non-linearities. As this effect can have severe implications on the beam performance, it is important to understand and control the noise mechanisms that have been observed in the LHC and that are anticipated in the HL-LHC era. To this end, this seminar presents the studies concerning the 50 Hz harmonics that have been observed in the beam spectrum since the beginning of the LHC operation. An overview of the most recent observations is included, which clearly indicate that the harmonics are the result of a real beam excitation rather than an instrumental feature. Based on these findings, potential sources of the perturbation are discussed and their impact on the beam performance is computed with simulations. For the HL-LHC, due to the reduction of the beam size in the interaction points of the high luminosity experiments, an increased sensitivity to noise effects is expected in the quadrupoles of the inner triplet. The modulation that may arise from the power supply ripples will be combined with the tune modulation that intrinsically emerges from the coupling of the transverse and longitudinal plane through chromaticity. The aim of this study is to determine whether tune modulation effect will pose a limitation in the luminosity production of HL-LHC.

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