Abstract
Harmonics of the mains frequency (50 Hz) have been systematically observed in the transverse beam spectrum of the Large Hadron Collider (LHC) since the start of its operation in the form of dipolar excitations. In the presence of strong non-linearities such as beam-beam interactions, as many of these power supply ripple tones reside in the vicinity of the betatron tune they can increase the tune diffusion of the particles in the distribution, leading to proton losses and eventually to a significant reduction of the beam lifetime. The aim of this paper is to determine whether the 50~Hz harmonics have an impact on the beam performance of the LHC. A quantitative characterization of the ripple spectrum present in the operation of the accelerator, together with an understanding of its source is an essential ingredient to also evaluate the impact of the 50~Hz harmonics on the future upgrade of the LHC, the High Luminosity LHC (HL-LHC). To this end, simulations with the single-particle tracking code, SixTrack, are employed including a realistic ripple spectrum as extracted from experimental observations to quantify the impact of such effects in terms of tune diffusion, Dynamic Aperture and beam lifetime. The methods and results of the tracking studies are reported and discussed in this paper.
Highlights
Power supply ripple at harmonics of the mains power frequency (50 Hz) has been systematically observed in the transverse beam spectrum of the Large Hadron Collider (LHC) since the start of its operation
Two regimes of interest have been identified in the transverse beam spectrum: a series of 50 Hz harmonics extending up to approximately 3.6 kHz, referred to as the low-frequency cluster, and a cluster of 50 Hz harmonics centered around the alias of the betatron frequency, i.e., frev − fx, where frev 1⁄4 11.245 kHz is the LHC revolution
The purpose of the current paper was to determine whether the 50 Hz harmonics perturbation is a mechanism that can impact the beam performance during the LHC operation
Summary
Power supply ripple at harmonics of the mains power frequency (50 Hz) has been systematically observed in the transverse beam spectrum of the Large Hadron Collider (LHC) since the start of its operation. Power supply ripple can impact the beam performance by introducing resonances in addition to the ones excited due to the nonlinearities of the lattice These resonances can increase the tune diffusion of the particles in the distribution, which may lead to the reduction of the beam lifetime. Throughout the present paper the term power supply ripple refers to the 50 Hz harmonics observed in the transverse beam spectrum in the form of dipolar excitations. The impact of the harmonics on the beam performance in terms of tune diffusion, DA and lifetime is discussed in Sec. III by including in the simulations a power supply ripple spectrum with the most important 50 Hz harmonics as acquired from experimental observations. IV, which provides a tool for the validation of the DA simulations in the presence of power supply ripple
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