Feedbacks on Tune and Chromaticity

Feedbacks on tune, coupling and chromaticity are becoming an integral part of safe and reliable accelerator operation. Tight tolerances on beam parameters typically constrain the allowed oscillation amplitudes to the micrometre range, leaving only a small margin for the transverse beam and momentum excitations required for tune and chromaticity measurements. This contribution presents an overview of these beam-based feedback systems, their architecture and design choices involved. It discusses performance limitations due to cross constraints, non-linearities, the coupling between multiple nested loops, and the interdependence of beam parameters

Real-timefeedback on beam parameters

Traditionally, tight beam parameter stability requirements were most pronounced for light sources and lepton colliders but have now become increasingly important for present and future hadron accelerator operation, not only for performance but also for reasons of machine protection, as recent improvements have led to significantly increased stored beam energies. In the latest generation machines, performance depends critically on the stability of the beam. In order to counteract disturbances due to magnetic imperfections, misalignments, ground motion, temperature changes and other dynamic effects, fully automated control of the key beam parameters â orbit, tune, coupling, chromaticity and energy â becomes an increasingly important aspect of accelerator operation. This contribution presents an overview of beam-based feedback systems, their architecture, performance limitations and design choices involved

LHC Beam Stability and Feedback Control - Orbit and Energy -

This report presents the stability and control of the Large Hadron Collider's (LHC) two beam orbits and their particle momenta using beam-based feedback systems. The LHC, presently being built at CERN, will store, accelerate and provide particle collisions with a maximum particle momentum of 7TeV/c and a nominal luminosity of L = 10^34 cm^â2s^â1. The presence of two beams, with both high intensity as well as high particle energies, requires excellent control of particle losses inside a superconducting environment, which will be provided by the LHC Cleaning and Machine Protection System. The performance and function of this and other systems depends critically on the stability of the beam and may eventually limit the LHC performance. Environmental and accelerator-inherent sources as well as failure of magnets and their power converters may perturb and reduce beam stability and may consequently lead to an increase of particle loss inside the cryogenic mass. In order to counteract these disturbances, control of the key beam parameters â orbit, tune, energy, coupling and chromaticity â will be an integral part of LHC operation. Since manual correction of these parameters may reach its limit with respect to required precision and expected time-scales, the LHC is the first proton collider that requires automatic feedback control systems for safe and reliable machine operation. The aim of this report is to help and contribute towards these efforts

The alignment of the LHC

The Large Hadron Collider (LHC) has been aligned using both classical and non-standard techniques. The results of these alignments were seen on September 10th, 2008 when the beam made several turns in the machine with very few correctors activated. This paper will present the different steps of the alignment as well the techniques used to obtain the alignment accuracy required for beam operation. The correlation of these results with the position recorded by the beam position monitors (BPM) will be presented

LHC Beam Stability and Feedback Control - Orbit and Energy -

This report presents the stability and control of the Large Hadron Collider's (LHC) two beam orbits and their particle momenta using beam-based feedback systems. The LHC, presently being built at CERN, will store, accelerate and provide particle collisions with a maximum particle momentum of 7TeV/c and a nominal luminosity of L = 10^34 cm^â2s^â1. The presence of two beams, with both high intensity as well as high particle energies, requires excellent control of particle losses inside a superconducting environment, which will be provided by the LHC Cleaning and Machine Protection System. The performance and function of this and other systems depends critically on the stability of the beam and may eventually limit the LHC performance. Environmental and accelerator-inherent sources as well as failure of magnets and their power converters may perturb and reduce beam stability and may consequently lead to an increase of particle loss inside the cryogenic mass. In order to counteract these disturbances, control of the key beam parameters â orbit, tune, energy, coupling and chromaticity â will be an integral part of LHC operation. Since manual correction of these parameters may reach its limit with respect to required precision and expected time-scales, the LHC is the first proton collider that requires automatic feedback control systems for safe and reliable machine operation. The aim of this report is to help and contribute towards these efforts

The FPGA-based Continious FFT Tune Measurement System for the LHC and its test at the CERN SPS

A base band tune (BBQ) measurement system has been developed at CERN. This system is based on a high-sensitivity direct-diode detection technique followed by a high resolution FFT algorithm implemented in an FPGA. The system allows acquisition of continuous real-time spectra with 32-bit resolution, while a digital frequency synthesiser (DFS) can provide an acquisition synchronised chirp excitation. All the implemented algorithms support dynamic reconfiguration of processing and excitation parameters. Results from both laboratory measurements and tests performed with beam at the CERN SPS are presented

On the Continuous Measurement of the LHC Beta-Function - Prototype Studies at the SPS

Until now, the continuous monitoring of the LHC lattice has been considered impractical due to tight constraints on the maximum allowed beam excitations and acquisition time usually required for betatron function measurements. As a further exploitation of the Base-Band-Tune (BBQ) detection principle, already widely used for tune diagnostics, a real-time beta-beat measurement prototype has been successfully tested at the CERN SPS and is based on the continuous measurement of the cell-to-cell betatron phase advance. Tests show that the phase resolution is better than a degree corresponding to a peak-to-peak beta-beat resolution of better than a percent. Due to the system’s high sensitivity, it required only micrometre-range excitation, making it compatible with nominal LHC operation. This contribution discusses results, measurement systematics and exploitation possibilities that may be used to improve the nominal LHC performance

Closed orbit correction at synchrotrons for symmetric and near-symmetric lattices

This contribution compiles the benefits of lattice symmetry in the context of closed orbit correction. A symmetric arrangement of BPMs and correctors results in structured orbit response matrices of Circulant or block Circulant type. These forms of matrices provide favorable properties in terms of computational complexity, information compression and interpretation of mathematical vector spaces of BPMs and correctors. For broken symmetries, a nearest-Circulant approximation is introduced and the practical advantages of symmetry exploitation are demonstrated with the help of simulations and experiments in the context of FAIR synchrotrons

Tune shift induced by nonlinear resistive wall wake field of flat collimator

We present formulae for the coherent and incoherent tune shifts due to the nonlinear resistive wall wake field for a single beam traveling between two parallel plates. In particular, we demonstrate that the nonlinear terms of the resistive-wall wake field become important if the gap between the plates is comparable to the transverse rms beam size. We also compare the theoretically predicted tune shift as a function of gap size with measurements for an LHC prototype graphite collimator in the CERN SPS and with simulations