Abstract
Since the beginning of the Large Hadron Collider (LHC) commissioning, spectral components at harmonics of the mains frequency (50 Hz) have been observed in the transverse beam spectrum. This paper presents an overview of the most important observations, collected during the latest physics operation of the LHC in 2018, which clearly indicates 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 a correlation with power supply ripple originating from the magnets' power supplies is presented.
Highlights
In particle accelerators, studies of the beam spectrum can reveal important information concerning the existence of external noise sources that perturb the motion of the particles
This paper focuses on the investigation of such a mechanism that has been observed in the transverse beam spectrum of the Large Hadron Collider (LHC) [5], which is contaminated by harmonics of 50 Hz [6,7,8,9]
The purpose of the current study was to investigate the origin of the 50 Hz harmonics, an effect that has been observed in the beam signal since the start of the LHC operation
Summary
Studies of the beam spectrum can reveal important information concerning the existence of external noise sources that perturb the motion of the particles. Noise effects such as power supply ripple, ground motion, and the noise induced by the transverse feedback system are an important issue for the single-particle beam dynamics in past, present, and future accelerators. The source of the perturbation was identified as the main dipoles by injecting an external sinusoidal ripple on their power supply. A similar observation of 50 Hz high-order harmonics perturbing the beam spectrum in the form of dipolar excitations is systematically made in the LHC. Supply ripple and the tracking simulations aiming to determine whether the observed power supply ripple leads to a degradation of the beam performance are treated in a second paper [21]
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