Beam Based Nonlinear Corrections in Storage Rings: Review and Applications for the LHC Commissioning

After summarising the required correction circuits in the LHC we will give a short summary of potential tools for measuring non-linear resonances and error distributions in a storage ring. The aim is to identify the limits and strength for each method and to identify how they can be used for adjusting the different correction circuits in the LHC

An Impedance Data Base Program for LEP2 and the LHC

The development of an impedance data base program was motivated by the changing impedance budgets in the LEP and LHC machines and the resulting need to recalculate the instability thresholds for different parameters. For LEP, the changes are implied by the LEP2 upgrade and for the LHC, the impedance data for most items is still being calculated and continues to change as the geometries of the impedance components converge to a final design. In both cases, feedback from the impedance calculations is desirable. A central data base that allows a semi-automatic recalculation of the impedance data once the geometry of an item changes facilitates such a feedback. The development of the program was guided by four goals. First, the data base program should collect the impedance information in a central place and in a standard format allowing easy access. Second, it should provide procedures for estimating the impact of the impedance on the beam dynamics. Third, the program should provide a user friendly graphical interface to the data base and all external programs that are used for calculating the impedance data. Fourth, it should store he input files for the external programs allowing a semi-automatic recalculation of the impedance data once the geometry of an item changes

Numerical Simulations for the Beam-Induced Electron Cloud in the LHC Beam Screen

The following work summarises simulation results obtained at CERN for the beam-induced electron cloud and looks at possible cures for the heat load in the LHC beam screen. The synchrotron radiation in the LHC creates a continuous flow of photoelectrons. These electrons are accelerated by the electric field of the bunch and hit the vacuum chamber on the opposite side of the beam pipe where they crea te secondary electrons which are again accelerated by the next bunch. For a large secondary emission yield the above mechanism leads to an exponential growth of the electron cloud which is limited by space charge forces. The simulations use a two-dimensional mesh for the space charge calculations and include the effect of image charges on the vacuum chamber wall. Depending on the quantum yield for the production of photoelectrons, the secondary emission yield and the reflectivity, the heat load can vary from 0.1 W/m to more than 15 W/m

Optics Solutions for the Combined Experimental and Injection Regions in the LHC

The geometrical acceptance in the interaction regions of the LHC must be large enough to accommodate both beams in the common part of the ring with a beam separation of 10 $\sigma$ at injection. In ad dition, the acceptance of the combined experimental and injection insertions at IP2 and IP8 is further restricted by the injection kicker and septum. The following paper summarises the resulting const raints and presents optics solutions for these two interaction regions

ZBASE User's Guide Version 1.1: an Impedance Data Base Program

The development of an impedance data base program was motivated by the changing impedance budgets in the LEP and LHC machines and the resulting need to recalculate the instability thresholds for different parameters. For LEP, the changes are implied by the LEP-II upgrade and for the LHC, the impedance data for most items is still being calculated and continues to change as the geometries of the impedance components converge to a final design. The development of the {\bf ZBASE} program was guided by four goals. First, the data base program should collect the impedance information in a central place and in a standard format which allows easy access. Second, it should include information required for estimating the impact of the impedance on the beam dynamics. Third, the program should provide a user friendly graphical interface and fourth, it should provide an interface to the programs that are used for calculating the impedance data. Collecting not only the impedance data but also the input files for the programs that were used for calculating it and all data necessary for calculating stability threshold currents, greatly facilitates the recalculation of the threshold currents if the parameters change. For LEP-II, for example, the transverse mode coupling instability is expected to limit the maximum current in the machine. As the number of installed impedance components and the optics functions in the machine will change during the upgrade of LEP from 1996 to 1998 it is desirable to provide all the information required for estimating the instability threshold current in the data base and to provide an estimate for any stage of the upgrade. For the LHC, most of the impedance items are still in the design process and feedback from impedance calculations is desirable at this stage. A central data base that allows a semi-automatic recalculation of the impedance data once the geometry of an item changes will facilitate such a feedback

LHC Progress and Commissioning Plans

The LHC at CERN is in its final installation phase and hardware commissioning has started in 2006. The commissioning of the machine with beam is planned for summer 2007. The paper summarizes the current status of the LHC installation, outlines the expected performance limitations for the commissioning and summarizes the main milestones and phases for the commissioning and their potential performance levels

Field Quality vs Beam Based Corrections in Large Hadron Colliders

After summarising the main types of field errors in superconducting magnets the paper discusses limits for correcting the magnet field quality via dedicated correction circuits in a collider storage ring and the possibility of adjusting the powering of such correction circuits via beam based measurements