Helmut Burkhardt

BEAM LOSS SCENARIOS AND STRATEGIES FOR MACHINE PROTECTION AT THE LHC

At the Large Hadron Collider (LHC) with nominal parameters at 7 TeV, each proton beam has an energy of more than 330 MJ threatening to damage accelerator equipment in case of uncontrolled beam loss. To prevent such damage, kickers are fired in case of failure deflecting the beams into dump blocks. The dump blocks are the only elements that can safely absorb the beams without damage. The time constant for particle losses depends on the specific failure and ranges from microseconds to several seconds. Starting with some typical failure scenarios, the strategy for the protection during LHC beam operation is illustrated. The systems designed to ensure safe operation, such as beam dump, beam instruments, collimators / absorbers and interlocks are discussed.

Designing and building a collimation system for the high-intensity LHC beam

The Large Hadron Collider (LHC) will collide proton beams at 14 TeV c.m. with unprecedented stored intensities. The transverse energy density in the beam will be about three orders of magnitude larger than previously handled in the Tevatron or in HERA, if compared at the locations of the betatron collimators. In particular, the population in the beam halo is much above the quench level of the superconducting magnets. Two LHC insertions are dedicated to collimation with the design goals of preventing magnet quenches in regular operation and preventing damage to accelerator components in case of irregular beam loss. We discuss the challenges for designing and building a collimation system that withstands the high power LHC beam and provides the required high cleaning efficiency. Plans for future work are outlined.

Comparison of Different Tracking Codes for Beam Delivery Systems of Linear Colliders

The vertical RMS spot sizes at the interaction point of linear colliders are in the 1 nm to 5 nm range at beam energies from 0.25 TeV to 1.5 TeV. Numerical tracking of particles through the magnetic focusing systems is used for the design and the performance prediction of the magnetic systems. In view of the small spot sizes and the high beam energies, it is important that the numerical codes include a careful treatment of the chromatic magnet properties and an accurate modelling of synchrotron radiation. Significant differences in the results of various codes have been observed and some fixes have been applied. In order to establish a basis for future simulations, the results of various tracking and modelling codes are compared for identical input.

Photon photon and electron photon colliders with energies below a TeV

We investigate the potential for detecting and studying Higgs bosons in {gamma}{gamma} and e{gamma} collisions at future linear colliders with energies below a TeV. Our study incorporates realistic {gamma}{gamma} spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: (a) a SM-like Higgs boson based on a devoted low energy machine with {radical}(s{sub ee}) {le} 200 GeV; (b) the heavy MSSM Higgs bosons; and (c) charged Higgs bosons in e{gamma} collisions.

Expected Emittance Growth and Beam Tail Repopulation-From Errors at Injection into the LHC

The preservation of the transverse emittance of the proton beam at injection into the LHC is crucial for luminosity performance. The population of the beam tails is also important for beam losses and collimation. The transfer and injection process is particularly critical in this respect, and several effects can contribute to the expected emittance increase and tail repopulation, like optical and geometrical mismatch, injection offsets and coupling, etc. The various effects are described, together with the tolerance limits on the parameters, and the expected contributions evaluated analytically where possible. The emittance growth and tail distributions are also simulated numerically using realistic errors. The implications for the tolerances on the matching of the transfer lines are discussed.

Simulation of Machine Induced Background in the LHCb Experiment: Methodology and Implementation

Numerical analyses of Machine Induced Background in the LHCb experiment have been performed for early and nominal operation of the LHC. In order to have a comprehensive view of the Machine Background in the experiment all of its sources, ranging from collimators cleaning inefficiency to distant and local beam-gas interactions need to be estimated; particles showering from the losses are then to be transported all the way to the experimental setup and the response of the detector evaluated. Each step in the chain is simulated with software specific to the task and provides input to the subsequent step. We will describe the methodology used for the studies and give some examples of the results obtained. Further, we will discuss in detail the various steps in the chain together with the advantages such a modular method allows in evaluating operational conditions where scaling of the initial sources can be applied.

Simulation of Machine Induced Background in the LHCb experiment: Methodology and implementation

Numerical analyses of machine induced background at the LHC are needed to evaluate the complete running environment of an experiment. In order to have a comprehensive view of the machine background in an experiment all of its sources, ranging from collimators cleaning inefficiency to distant and local beam-gas interactions need to be estimated; particles showering from the losses are then to be transported all the way to the experimental setup and the response of the detector evaluated. In this paper we describe a novel methodology implemented for the LHCb experiment to achieve this. Each step in the chain is simulated with software specific to the task and provides input to the subsequent step through a well-defined and clear interface. Further, we will discuss in detail the various steps in the chain together with the advantages such a modular method allows in evaluating operational conditions where scaling of the initial sources can be applied. We will also give some examples of the results obtained.

Special Collimation System Configuration for the LHC High-Beta Runs

H. Garcia-Morales∗, Royal Holloway University of London, UK, CERN, Geneva, Switzerland R. Bruce, H. Burkhardt, M. Deile, S. Jakobsen, A. Mereghetti, S. Redaelli, CERN, Geneva, Switzerland Abstract Special LHC high-β∗ optics is required for the forward physics program of TOTEM and ATLAS-ALFA. In this configuration, the beam is de-squeezed (the β-function at the collision point is increased) in order to minimize the divergence for measurements at very small scattering angles. In these low beam intensity runs, it is important to place the Roman Pots (RPs) as close as possible to the beam, which demands special collimator settings. During Run I, a significant amount of background was observed in the forward detectors due to particles outscattered from the primary collimator. During Run II, a different collimation configuration was used where a tungsten collimator was used as primary collimator instead of the usual one made of carbon. Using this configuration, a significant reduction of the background at the RPs was observed. In this paper we present a description of the new collimator configuration and the results obtained during the high-β∗ run carried out in 2016.

5 Interactions of Beams With Surroundings

With the exceptions of Synchrotron Radiation sources, beams of accelerated particles are generally designed to interact either with one another (in the case of colliders) or with a specific target (for the operation of Fixed Target experiments, the production of secondary beams and for medical applications). However, in addition to the desired interactions there are unwanted interactions of the high energy particles which can produce undesirable side effects. These interactions can arise from the unavoidable presence of residual gas in the accelerator vacuum chamber, or from the impact of particles lost from the beam on aperture limits around the accelerator, as well as the final beam dump. The wanted collisions of the beams in a collider to produce potentially interesting High Energy Physics events also reduces the density of the circulating beam and can produce high fluxes of secondary particles.