Abstract

Modern colliders bring into collision a large number of bunches to achieve a high luminosity. The long-range beam-beam effects arising from parasitic encounters at such colliders are mitigated by introducing a crossing angle. Under these conditions, crab cavities (CC) can be used to restore effective head-on collisions and thereby to increase the geometric luminosity. Such crab cavities have been proposed for both linear and circular colliders. The crab cavities are rf cavities operated in a transverse dipole mode, which imparts on the beam particles a transverse kick that varies with the longitudinal position along the bunch. The use of crab cavities in the Large Hadron Collider (LHC) may not only raise the luminosity, but it could also complicate the beam dynamics, e.g., crab cavities might not only cancel synchrobetatron resonances excited by the crossing angle but they could also excite new ones, they could reduce the dynamic aperture for off-momentum particles, they could influence the aperture and orbit, also degrade the collimation cleaning efficiency, and so on. In this paper, we explore the principal feasibility of LHC crab cavities from a beam dynamics point of view. The implications of the crab cavities for the LHC optics, analytical and numerical luminosity studies, dynamic aperture, aperture and beta beating, emittance growth, beam-beam tune shift, long-range collisions, and synchrobetatron resonances, crab dispersion, and collimation efficiency will be discussed.

Highlights

  • The Large Hadron Collider (LHC) has a design luminosity of 1034 cmÀ2 sÀ1 at the two high-luminosity protonproton experiments ATLAS and CMS, with a center-of-mass energy of 14 TeV [1]

  • For the ES and full crab crossing (FCC) approaches, crab cavities are an essential ingredient of the upgrade [3]

  • We study the crab-cavity beam dynamics issues for two LHC optics, the nominal LHC collision optics and the so-called ‘‘lowbetamax’’ upgrade optics [9]

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Summary

INTRODUCTION

The Large Hadron Collider (LHC) has a design luminosity of 1034 cmÀ2 sÀ1 at the two high-luminosity protonproton experiments ATLAS (located at interaction point 1, or ‘‘IP1’’) and CMS (located at IP5), with a center-of-mass energy of 14 TeV [1]. Studies aimed to further raise the LHC luminosity have been carried out since 2001, from 2004 onwards jointly by the European CARE-HHH network and by US-LARP These studies developed a roadmap for increasing the luminosity of LHC by a factor of 10 above its design value, to 1035 cmÀ2 sÀ1 in the second half of the decade. Three upgrade scenarios have crystallized from various considerations These three scenarios are called the early-separation (ES) scheme, the full crab crossing (FCC) scheme, and the large-Piwinski angle (LPA) scheme [2]. The crab cavities will render the effective Piwinski angle Piw 1⁄4 =2 Á z=xÃ

LOCAL AND GLOBAL SCHEME
OPTICS AND SCENARIOS
Local scenario
DYNAMIC APERTURE
18 LCC 800MHz
APERTURE AND BETA BEATING
GUINEA-PIG simulation
Design
Analytical treatment and comparison
EMITTANCE GROWTH
VIII. CRAB DISPERSION
COLLIMATION
CRAB CROSSING TUNE SHIFT AND SYNCHROBETATRON RESONANCES
LONG-RANGE EFFECTS
Findings
CONCLUSIONS
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