WP2: Accelerator Physics

Objectives

Task 2.1. Coordination and Communication

  • Coordinate and schedule work package tasks 

  • Monitor work progress and inform the project management and work package participants 

  • Manage the WP budget and use of resources 

  • Prepare internal and deliverable reports

Task 2.2. Optics and Layout

  • Identify layout options for the Interaction Region (IR) upgrades. 

  • Identify optics solutions for the LHC upgrade.

Task 2.3. Particle Simulations

  • Determine field quality tolerances for new magnetic elements for the LHC upgrade. 

  • Specify tolerances of the correction circuit settings. 

  • Evaluate the dynamic aperture.

Task 2.4. Intensity Limitations

  • Specify limits for maximum acceptable impedance of new components, and evaluate intensity limitations due to the machine impedance. 

  • Estimate impact of electron cloud effects. 

  • Estimate emittance growth rates from intrabeam scattering.

Task 2.5. Beam-Beam Effects

  • Evaluate beam-beam effects for the LHC upgrade and identify minimum requirements for the beam separations in the Interaction Regions. 

  • Evaluate the limitations imposed by beam-beam interactions.

Task 2.6. Beam Parameter and Luminosity Optimization

  • Identify relevant experience from LHC commissioning and operation. 

  • Determine optimum sets of machine and beam parameters based on the outcomes of Tasks 2.2, 2.3, 2.4 and 2.5, and the operational experience of the LHC.

Description of work

Task 2.1. Coordination and Communication

The activities of this task are for the work package coordinators [CERN, UNILIV] to oversee and co-ordinate the work of all other work package tasks, to ensure the consistency of the work according to the project plan and to coordinate the WP technical and scientific tasks with tasks carried out by the other work packages when relevant. The coordination duties also include the organization of WP internal steering meetings, the setting up of proper reviewing, the reporting to the project management and the distribution of the information within the WP as well as to the other work packages running in parallel.

The task also covers the organization of and support to the annual meetings dedicated to the WP activity review and possible activity workshops or specialized working sessions, implying the attendance of invited participants from inside and outside the consortium.

Task 2.2. Optics and Layout

The goal of this task is to prepare reference lattice and optics files for various configurations that can be used for further beam dynamic studies (e.g. particle loss and heat deposition studies in the IRs and preparation of new configurations for the LHC cleaning insertions), to explore the performance limitations in terms of the optics design (e.g. chromatic aberrations, number of long-range beam-beam encounters, required minimum collimator apertures) and to generate critical magnet parameters (magnet length, gradient, and aperture) for the various scenarios for all linear magnet systems including the orbit correctors for generating the crossing angle generation and the skew quadrupole correction system. The generation of optics files implies the preparation of complete injection and collision optics files that feature continues transitions of the magnet gradients (squeeze). The optics studies should also provide estimates for the maximum acceptable linear optic errors, specify alignment and orbit tolerances for the machine and discuss correction strategies for these effects during operation.

This task is linked to task 2.3 and to WP5, in addition the lattice and optics files generated by task 2.2 for the different configurations under consideration for HL-LHC will be made available to all partner laboratories and collaborators in a central project database. Task 2.2 therefore provides direct input into WP1 of the HiLumi LHC project.

The task will involve the following: 
• IR4 optics design with room for a global Crab cavity installation. CERN and INFN will generate lattice and optics files for the full LHC machine using the new IR4 solution and the design configurations in the remaining insertions. 
• Study options for correcting chromatic aberrations from the optics focal system near the experiments. This will be carried out by CERN and EPFL. 
• Generate optics and lattice files for different magnet solutions: Optics and Layout Design for Nb-Ti and Nb3Sn solutions with and without local crab cavities, β* < 0.5m and optics design for round and flat beams featuring single bore triplet magnets and lattice and optics files for the full LHC machine (CERN, CEA, BINP, CSIC, UNILIV, UNIMAN). The flat beam option should include estimates of the maximum acceptable coupling and strategies for its correction. These are built to a large extent on the existing Phase 1 upgrade study. The solutions under investigation are as follows: 
o a single bore Nb-Ti magnet solution with * < 0.5m (CERN, CSIC) 
o as above but with local Crab Cavities (CERN, UNILIV and UNIMAN) 
o a 2-in-1 Nb-Ti magnet solution with * < 0.5m (CERN, BINP) 
o a single bore Nb3Sn magnet solution with * < 0.5m (CERN) 
o as above but with local Crab Cavities (CERN, UNILIV and UNIMAN) 
o 2-in-1 Nb3Sn magnet solution with * < 0.5m (CERN, BINP)

Task 2.3 Particle Simulations

This task aims at studying the dependence of the Dynamic Aperture of the machine on the field quality of the magnetic focusing system and the separation-recombination dipole magnets next to the experiments for a selection of optics configuration from Task 1.

Studies of other Work Packages of the HiLumi LHC project, such as WP3 ‘Magnet design’ and WP5 ‘Collimation and cleaning efficiency studies’ require detailed information on the likely working configuration of the LHC.

The work of Task 2.3 consist in the generation of magnet field quality specifications, specification of required correction circuits and proposals for potential working points for operation. All information will be made available to all partner laboratories and collaborators in a central project database. Task 2.3 therefore provides direct input into all work packages of the HiLumi LHC project.

This task involves the following: 
• Monte Carlo tracking studies: CERN, INFN, CSIC, UNIMAN, BNL and SLAC will perform single particle Monte Carlo (different realizations for machine imperfections) tracking studies for selected configurations of Task 2.2 with the aim of defining the required field quality of the magnets and designing magnetic correction systems. 
• Preparation of simulation tools: CERN and KEK will prepare simulation tools for studying the effect of beam-beam interactions and non-linear fields on the single particle dynamics for operation with large crossing angles, flat beams and variation of the longitudinal bunch orientation along the machine with Crab cavities. The currently used programmes for particle simulation studies such as MADX and Sixtrack do not yet offer all required tools and modules for the study of beam-beam interactions with large crossing angles, hour-glass effect and Crab cavity implementations. 
• Specification of required correction circuits: CERN, UNILIV and UNIMAN will specify the required non-linear correction systems for the new insertions 
• Study of optimum working points (tunes) for the upgrade: CERN will evaluate synchro-betatron resonances and perform single particle tracking with the aim of identifying the optimum working point (tune values) for the two LHC beams. 
• Radiation and heat deposition studies: FNAL and BINP will quantify the expected radiation and heat deposition values for selected elements (e.g. triplet magnets, TAS and TAN (radiation absorbers placed in the triplet region), magnets in the collimation regions etc).

Task 2.4 Intensity Limitations

This task will look after performance limitations arising from the interaction of the beam with itself and its surrounding. The goal of this task is to define key parameters such as maximum acceptable impedance values and to identify optimum beam configurations (e.g. required chromaticity control and landau damping octupole settings) for the different scenarios of Task 2.2.

This task will provide critical input for estimates the potential performance reach of the upgraded LHC and therefore feed directly into WP1 and other tasks of WP2 of the HiLumi LHC project. It will involve the following: 
• DESY and INFN will estimate the impedance of new components of the upgrade options. 
• SLAC will estimate the required corrector circuit settings (chromaticity and Landau damping octupoles). 
• STFC and INFN will provide estimates for the Intra Beam Scattering (IBS) growth rates for different beam parameters. 
• DESY will evaluate electron cloud effects.

Task 2.5 Beam-Beam Effects

This task will evaluate performance limitations arising from the interaction between the two beams. The goal of this task is to define key parameters such as minimum required beam separation and maximum acceptable beam brightness values and to identify optimum beam configurations (e.g. flat beam versus round beam IR design) for the different scenarios of Task 2.2.

This task will provide critical input for estimates of the potential performance reach of the upgraded LHC and will therefore feed directly into WP1 and other tasks of WP2 of the HiLumi LHC project. It will consist of: 
• Calculations by CERN, INFN and BNL of bunch-by-bunch orbit variations due to self-consistent treatment of the beam-beam interactions. 
• Evaluations by CERN, LBNL and FNAL of compensation schemes for the long-range beam-beam interactions (e.g. DC and pulsed wire installations). 
• Evaluations by CERN, EPFL and BINP of compensation schemes for the head-on beam-beam interactions (correction of the linear and non-linear effect) (e.g. electron lens installation). 
• Studies by CERN, KEK and STFC of crab cavity beam-beam compensation scheme.

Task 2.6 Beam Parameter and Luminosity Optimization

This task will evaluate the experience from the first years of LHC operation and determine the optimum choice for the beam parameters (e.g. minimum achievable emittances, optimum bunch length and minimum acceptable bunch spacing).

This task will provide optimized beam parameters and optics configurations for various scenarios of Task 2.1 based on the operational experience from the first years of LHC operation. It feeds directly into WP1, WP5, WP6 and other tasks of WP2 of the HiLumi LHC project. It consists of: 
• Evaluation by STFC of the geometric luminosity reduction factor for various configurations of Task 2.2 and look into options for luminosity levelling (e.g. via Crab cavities or crossing angle variations or dynamic optic changes). 
• Evaluation by LBNL of options for optimizing the luminosity production by variation of beam parameters during a fill (e.g. tune, beam separation, emittance [radiation damping] etc.). 
• Determination of STFC of the optimum beam parameter values (e.g. initial emittance, beam brightness, bunch length and bunch separation) for different scenarios of Task 2.2.

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