Paper  Title  Page 

WEPPR011  Numerical Simulation Study of the Montague Resonance at the CERN Proton Synchrotron  2958 


Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP) under Contract No. DEAC0205CH11231. The Montague resonance provides a coupling between the vertical and the horizontal dynamics of beams and can cause particle losses due to unequal aperture sizes of the accelerator. In this paper, we present a new numerical simulation study of a previous Montague resonance crossing experiment at the CERN PS including detailed threedimensional spacecharge effects and machine nonlinearity. The simulation reproduces the experimental data and suggests that the longitudinal synchrotron motion played an important role in enhancing transverse resonance coupling. 

WEPPR062  The Mode Matching Method Applied to Beam Coupling Impedance Calculations of Finite Length Devices  3069 


The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be less accurate approximation for segmented devices. This contribution presents the study of the beam coupling impedance in the case of a finite length device: a cylindrical cavity loaded with a toroidal slab of material. In order to take into account the finite length we will decompose the field in the cavity and in the beam pipe into a set of orthonormal modes and apply the mode matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations as well as applications to the impedance of short beam pipe inserts, where the longitudinal and transverse dimensions are difficult to model in numerical simulations.  
WEPPR065  Electromagnetic Simulations of the Impedance of the LHC Injection Protection Collimator  3075 


During the 2011 LHC run, significant vacuum and temperature increase were observed at the location of the LHC injection protection collimators (TDI) during the physics fills. Besides, measurements of the LHC transverse tune shift while changing the TDI gap showed that the impedance of the TDI was significantly higher than the LHC impedance model prediction based on multilayer infinite length theory. This contribution details the electromagnetic simulations performed with a full 3D model of the TDI to obtain both longitudinal and transverse impedances and their comparison with measured observables.  
WEPPR069  Measurements and Simulations of Transverse CoupledBunch Instability Rise Times in the LHC  3087 


In the current configuration of the LHC, multibunch instabilities due to the beamcoupling impedance would be in principle a critical limitation if they were not damped by the transverse feedback. For the future operation of the machine, in particular at higher bunch intensities and/or higher number of bunches, one needs to make sure the coupledbunch instability rise times are still manageable by the feedback system. Therefore, in May 2011 experiments were performed to measure those rise times and compare them with the results obtained from the LHC impedance model and the HEADTAIL wake fields simulation code. At injection energy, agreement turns out to be very good, while a larger discrepancy appears at top energy.  
WEPPR070  Beam Coupling Impedance Simulations of the LHC TCTP Collimators  3090 


As part of an upgrade to the LHC collimation system, 8 TCTP and 1 TCSG collimators are proposed to replace existing collimators in the collimation system. In an effort to review all equipment placed in the accelerator complex for potential side effects due to collective effects and beamequipment interactions, beam coupling impedance simulations are carried out in both the timedomain and frequencydomain of the full TCTP design. Particular attention is paid to trapped modes that may induce beam instabilities and beaminduced heating due to cavity modes of the device.  
WEPPR071  Evaluation of the Beam Coupling Impedance of New Beam Screen Designs for the LHC Injection Kicker Magnets  3093 


During the 2011 run of the LHC there was a measured temperature increase in the LHC Injection Kicker Magnets (LHCMKI) during operation with 50ns bunch spacing. This was suspected to be due to increased beaminduced heating of the magnet due to beam impedance. Due to concerns about future heating with the increased total intensity to nominal and ultimate luminosities a review of the impedance reduction techniques within the magnet was required. A number of new beam screen designs are proposed and their impedance evaluated. Heating estimates are also given with a particular attention paid to future intensity upgrades to ultimate and HLLHC parameters.  
WEPPR075  Monitoring the Progress of LHC ElectronCloud Scrubbing by Benchmarking Simulations and PressureRise Observations  3105 


Electron bombardment of a surface has been proven to reduce drastically the secondary electron yield of a material. This technique, known as scrubbing, is the ultimate solution to decrease the negative effects of an electron cloud buildup in any particle accelerator operating with intense beams. Its effectiveness has been already observed at the LHC. Since at the LHC no insitu secondaryyield measurements are available, it has been necessary to develop a method to infer different key beampipe surface parameters by benchmarking simulations and pressurerise observations. The method developed allows us to monitor the scrubbing process in order to decide on the most appropriate strategies for machine operation. In this paper we present the latest results of applying this method to the LHC in the fall of 2011 and early 2012, including data for the nominal bunch spacing of 25 ns.  
THYB03  Collective Effects in the LHC and its Injector Complex  3218 


Operation during 48 hours at a constant luminosity of five times the nominal one (with “leveling”) is required for the CERN HL(High Luminosity)LHC project to be able to reach integrated luminosities of ~ 250 fb1 per year and ~ 3 ab1 twelve years after the upgrade. This means that the potential peak luminosity should be at least two times larger than the leveled one, i.e. a factor more than ten compared to the nominal case is contemplated. Even though the LHC had a bold beginning, reaching one third of the nominal peak luminosity at the end of the 2011 run, a factor more than thirty remains to be gained, which will be achieved only if all the collective effects are deeply understood and mastered both in the LHC and its injectors. The observations made during the 20102011 runs are first reviewed and compared to predictions to try and identify possible bottlenecks. The lessons learned and the possible solutions and/or mitigation measures to implement in the HLLHC and the LHC Injectors Upgrade (LIU) projects are then discussed.  
Slides THYB03 [34.295 MB]  
THPPP007  ProtonBeam Emittance Growth in SPS Coasts  3737 


Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP). Protonbeam transverse emittance growth rates have been measured during SPS coasts to assess the possibility of using the SPS as a testbed for the LHC prototype crab cavities. The SPS measurements in coasts were performed at different beam energies, for varying RF voltage, beam intensity, and chromaticity. Results from these measurements are presented with potential explanations for the observed emittance growth. 
