IMPLEMENTATION OF LUMINOSITY LEVELING BY BETATRON FUNCTION ADJUSTMENT AT THE LHC INTERACTION POINTS

Abstract Growing expectations for integrated luminosity during upcoming LHC runs introduce new challenges for LHC beam operation in the scope of online luminosity control. Because some LHC experiments are limited in the maximum event rates, their luminosity is leveled to a constant value. Various techniques may be used for luminosity leveling, changing the betatron function at the interaction point is one of them. This paper explains the main operational requirements of a betatron function leveling scheme for the upcoming LHC run. Issues concerning the beam optics, orbits and collimator settings are discussed. The proposed architecture for control system integration will be discussed. A few operational scenarios with different beam configurations foreseen for the next LHC run will be presented. LUMINOSITY An important parameter that affects the quality of the recorded luminosity at the LHC is the event pile-up, the number of simultaneous particle interactions during one bunch crossing. A high event pile-up complicates the physics analysis and degrades the data quality for certain types of physics channels. The event pile-up µ is directly proportional to the luminosity per bunch crossing L bb , µ = L bb × σ P , where σ P is the total cross section for pp interactions at the LHC, σ P = 70 − 85 mbarn. The total luminosity L p is given by L p = k L bb where k is the number of bunch crossings per turn. The bunch pair luminosity for round beams at an interaction point can be written as where N stands for number of particles in the bunch, ε N for the normalized emittance and β * for the betatron function at the interaction point. f is the revolution frequency and γ the relativistic factor. F is a correction factor for the crossing angle. For round beams ε N and β * are identical for both transverse planes. d is the transverse offset (separation) between the colliding beams. The transverse separation d and the betatron function β* can be seen as a way for control luminosity. LHC RUN 2 BEAM PROJECTIONS After the long shutdown the LHC will restart beam operation in 2015 at an energy of 6.5 TeV. The LHC has two high luminosity experiments ATLAS and CMS that are installed at interaction points 1 and 5 (IR1 and IR5). Those experiments can cope with a maximum average pile-up of 50 and a time-averaged pile-up of 30 to 40. The LHCb experiment in IR8 on the other hand will operate at a maximum pile-up of µ = 1.6. Luminosity leveling is required for the LHCb experiment for all scenarios, while for the high luminosity experiments only the 50 ns scenario definitely requires leveling. With 25 ns some leveling is required in IR1 and IR5 only for the brightest beams. For the LHC luminosity upgrade HL-LHC (from 2023) [1] luminosity leveling by β* is part of the operational baseline

MODELLING AND LONG TERM DYNAMICS OF CRAB CAVITIES IN THE LHC

Abstract The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) aims to achieve an integrated luminosity of 250-300 fb −1 per year. This upgrade includes the use of crab cavities to mitigate the geometric loss of luminosity arising from the beam crossing angle. The tight space constraints at the location of the cavities leads to cavity designs which are axially non-symmetric and have a potentially significant effect on the long term dynamics and dynamic aperture of the LHC. In this paper we present the current status of advanced modelling of crab cavities

CONDITIONS ON THE GRAZING FUNCTION g FOR EFFICIENT

Abstract The grazing function g is introduced -a synchrobetatron optical quantity that parametrizes the rate of change of total angle with respect to synchrotron amplitude for particles grazing a collimator or aperture. The grazing function is particularly important for crystal collimators, which have limited acceptance angles. The implications for RHIC, SPS, Tevatron and LHC crystal implementations are discussed. An analytic approximation is derived for the maximum value of g in a matched FODO cell, and is shown to be in good agreement with a realistic numerical example. The grazing function scales linearly with FODO cell bend angle, but to is independent of FODO cell length

Transverse beam transfer functions of colliding beams in RHIC DISCLAIMER TRANSVERSE BEAM TRANSFER FUNCTIONS OF COLLIDING BEAMS IN RHIC*

Abstract We use transverse beam transfer functions to measure tune distributions of colliding beams in RHIC. The tune has a distribution due to the beam-beam interaction, nonlinear magnetic fields --particularly in the interaction region magnets, and non-zero chromaticity in conjunction with momentum spread. The measured tune distributions are compared with calculations

SIMULATION STUDIES OF MACROPARTICLES FALLING INTO THE LHC PROTON BEAM

Abstract We report updated simulations on the interaction of macroparticles falling from the top of the vacuum chamber into the circulating LHC proton beam. The path and charge state of micron size micro-particles are computed together with the resulting beam losses, which -if high enough -can lead to the local quench of superconducting (SC) magnets. The simulated time evolution of the beam loss is compared with observations in order to constrain some macroparticle parameters. We also discuss the possibility of a "multiple crossing" by the same macroparticle, the effect of a strong dipole field, and the dependence of peak loss rate and loss duration on beam current and on beam size