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| MPPP004 | LHC Orbit Stablisation Tests at the SPS | feedback, ground-motion, optics, quadrupole | 886 | ||
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The LHC presently build at CERN is the first proton collider that requires a continuous orbit control for safe and reliable machine operation. A realistic test of the orbit feedback system has been performed in 2004 using already present LHC instrumentation and infrastructure on a 270 GeV coasting beam in the SPS. It has been demonstrated that the chosen feedback architecture can stabilise the beam better than 10 micrometre and is essentially limited by the noise of the beam position monitor and the bandwidth of the corrector magnets. The achieved orbit stability is comparable to those found at modern light sources and gives enough operational margin with respect to the requirements of the LHC Cleaning System (70 micrometre). Estimates for the long term drifts and achievable stability will be presented based on the experimental results.
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| TPAP003 | Exploring a Nonlinear Collimation System for the LHC | sextupole, optics, betatron, insertion | 877 | ||
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We explore the adaptation of a nonlinear collimation system, as previously considered for linear colliders, to LHC betatron cleaning. A possible nonlinear system for LHC consists of a horizontal and vertical primary collimator located in between a pair of skew sextupoles. We discuss the modified LHC optics, the need for and optimum placement of secondary absorbers, and the simulated cleaning efficiency.
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| TPAP004 | Mechanical Design for Robustness of the LHC Collimators | injection, proton, simulation, beam-losses | 913 | ||
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The functional specification of the LHC Collimators requires, for the start-up of the machine and the initial luminosity runs (Phase 1), a collimation system with maximum robustness against abnormal beam operating conditions. The most severe cases to be considered in the mechanical design are the asynchronous beam dump at 7 TeV and the 450 GeV injection error. To ensure that the collimator jaws survive such accident scenarios, low-Z materials were chosen, driving the design towards Graphite or Carbon/Carbon composites. Furthermore, in-depth thermo-mechanical simulations, both static and dynamic, were necessary.This paper presents the results of the numerical analyses performed for the 450 GeV accident case, along with the experimental results of the tests conducted on a collimator prototype in Cern TT40 transfer line, impacted by a 450 GeV beam of 3.1·1013 protons, with impact parameters from 1 to 5 mm.
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| TPAP006 | Detecting Impacts of Proton Beams on the LHC Collimators with Vibration and Sound Measurements | proton, radiation, acceleration, beam-losses | 1018 | ||
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The 350 MJ stored energy of the 7 TeV LHC beams can seriously damage the beam line elements in case of accidental beam losses. Notably, the LHC collimators, which sit at 6 to 7 σs from the beam centre (1.2-1.4 mm), might be hit and possibly damaged in case of failures, with a consequent degradation of their cleaning performance. The experience from operating machines shows that an a-posteriori identification of the damaged collimators from the observed performance degradation is extremely challenging. Collimator tests with beam at the SPS have proven that the impact of 450 GeV proton beams at intensities from 1010 to 3x1013 can be detected by measuring the collimator vibrations. This was achieved by using high-resolution, radiation hard accelerometers and a microphone to record mechanical and sound vibrations of a LHC-like prototype collimator with impacting beams at different intensities and depth. A similar system could be also used in the LHC to detect collimators damaged by the beam.
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| TPAP007 | LHC Collimation: Design and Results from Prototyping and Beam Tests | impedance, proton, insertion, beam-losses | 1078 | ||
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The problem of collimation and beam cleaning concerns one of the most challenging aspects of the LHC project. A collimation system must be designed, built, installed and commissioned with parameters that extend the present state-of-the-art by 2-3 orders of magnitude. Problems include robustness, cleaning efficiency, impedance and operational aspects. A strong design effort has been performed at CERN over the last two years. The system design has now been finalized for the two cleaning insertions. The adopted phased approach is described and the expected collimation performance is discussed. In parallel robust and precisely controllable collimators have been designed. Several LHC prototype collimators have been built and tested with the highest beam intensities that are presently available at CERN. The successful beam tests are presented, including beam-based setup procedures, a 2 MJ robustness test and measurements of the collimator-induced impedance. Finally, an outlook is presented on the challenges that are ahead in the coming years.
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| TPAP008 | Measurements of the LHC Collimator Impedance with Beam in the SPS | impedance, betatron, pick-up, vacuum | 1132 | ||
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The transverse impedance of the LHC collimators will likely dominate the overall transverse impedance in the LHC at high energies and potentially limit the maximum intensity. A prototype collimator was recently tested in the SPS. Small, but significant tune shifts depending on the collimator position have been observed using different independent high resolution tune measurement methods. In addition trapped modes predicted from numerical simulation at the ends of the collimator jaws have been identified by bench measurement techniques as well as with the beam. We present a description of the measurements and an analysis of the results.
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| TPAP009 | Collimation in the Transfer Lines to the LHC | injection, septum, optics, simulation | 1135 | ||
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Injection intensities for the LHC are over an order of magnitude above damage level. The TI 2 and TI 8 transfer lines between the SPS and LHC are each about 2.5 km long and comprise many active elements running in pulsed mode. The collimation system in the transfer lines is designed to dilute the beam energy sufficiently in case of accidental beam loss or mis-steered beam. A system using three collimator families spaced by 60 degrees in phase advance, both in the horizontal and the vertical plane has been chosen. We discuss the reasons for this choice, the layout and, the expected performance of the system in terms of maximum amplitudes and energy deposition.
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| TPAP014 | Energy Deposition Studies for the Betatron Cleaning Insertion (IR7) of LHC | insertion, simulation, proton, quadrupole | 1386 | ||
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Two insertions (IR3, IR7) of the Large Hadron Collider (LHC) are dedicated to beam cleaning with the design goals of absorbing part of the primary beam halo and of the secondary radiation. The tertiary halo which escapes the collimation system in IR7 may heat the cold magnets at unacceptable levels, if no additional absorber is used. In order to assess the energy deposition in sensitive components, extensive simulations were run with the Monte Carlo cascade code FLUKA. The straight section and the dispersion suppressors of IR7 were fully implemented. A modular approach in the geometry definition and an extensive use of user-written programs allowed the implementation of all magnets and collimators with high precision, including flanges, steel supports and magnetic field. This paper provides the number and location of additional absorbers needed to keep the energy deposition in the coils of the magnets below the quenching limit.
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| TPAP035 | Energy Deposition Issues at 8 GeV H- Beam Collimation and Injection to the Fermilab Main Injector | injection, kicker, proton, quadrupole | 2372 | ||
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The energy deposition and radiation issues at 8 GeV H- beam collimation in the beam transfer line and at stripping injection to the Fermilab Main Injector are analyzed. Detailed calculations with the STRUCT and MARS15 codes are performed on heating of collimators, stripping foils and other critical components, as well as on beam line and accelerator element radioactivation both at normal operation and accidental beam loss. Extraction of the unstripped part of the beam to the external beam dump and loss of the excited-state Ho atoms in the Main Injector are also studied.
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| TPPP023 | Simulation of PEP-II Accelerator Backgrounds Using TURTLE | scattering, background, betatron, electron | 1835 | ||
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We present studies of accelerator-induced backgrounds in the BaBar detector at the SLAC B-Factory, carried out using a modified version ofthe DECAY TURTLE simulation package. Lost-particle backgrounds in PEP-II are dominated by a combination of beam-gas bremstrahlung, beam-gas Coulomb scattering, radiative-Bhabha events and beam-beam blow-up. The radiation damage and detector occupancy caused by the associated electromagnetic shower debris can limit the usable luminosity. In order to understand and mitigate such backgrounds, we have performed a full programme of beam-gas and luminosity-background simulations, that include the effects of the detector solenoidal field, detailed modelling of limiting apertures in both collider rings, and optimization of the betatron collimation scheme in the presence of large transverse tails.
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| WPAE014 | Conceptual Design of a Longitudinal Halo Collimator for J-PARC Linac | linac, emittance, simulation, optics | 1413 | ||
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In a high-intensity proton accelerator, avoidance of excess beam loss is essentially important to enable hands-on maintenance. To reduce the uncontrolled beam loss in the following ring, we plan to install a longitudinal halo collimator system in a beam transport line after the injector linac. The collimator system is supposed to have two main roles: One is the elimination of longitudinal tail or halo particles destined to be lost in the following ring, and the other is the removal of anomalous beams which can be resulted from, for example, RF discharge of an accelerating cavity. We plan to adopt a "periodic collimation scheme" in the collimator system taking advantage of the three-fold symmetry of the arc section. The momentum aperture of the collimator system is expected to be reduced by the factor of two adopting periodic collimation. In this paper, conceptual design of the collimator system is presented together with the results of particle simulations.
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| WOAD002 | Lepton Collider Operation with Constant Currents | injection, background, luminosity, linac | 149 | ||
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Funding: Work supported by US DOE under contract DE-AC03-76SF00515 |
Traditionally, electron-positron colliders have been operating in a top-off-and-coast fashion with a cycle time depending on the beam life time, typically on the order of an hour. Each top-off involves ramping detector systems in addition to the actual filling time. The loss in accumulated luminosity is typically 20-50%. During the last year, both B-Factories have commissioned a continuous-injection mode of operation in which beam is injected without ramping the detector, thus raising luminosity integration by constant operation at peak luminosity. Constant beam currents reduce thermal drift and trips caused by change in beam loading. To achieve this level of operation, special efforts were made to reduce the injection losses and also to implement special gating procedures in the detectors, minimizing dead time. Bunch-injection control decides which bunch to inject into next while maintaining small charge variation between bunches. Beam collimation can reduce injection noise but also cause an increase in background rates. A challenge can be determining beam lifetime, important to maintain tuning of the beams. The paper will discuss the special features of continuous injection in both KEKB and PEP-II. |
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| RPAE052 | Overview of Accelerator Physics Studies and High Level Software for the Diamond Light Source | booster, storage-ring, linac, dipole | 3188 | ||
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DIAMOND is a 3 GeV synchrotron light source under construction at Rutherford Appleton Laboratory in Oxfordshire (UK). The accelerators complex consists of a 100 MeV LINAC, a full energy booster and a 3GeV storage ring with 22 straight sections available for IDs. Installation of all three accelerators has begun, and LINAC commissioning is due to start in Spring 2005. This paper will give an overview of the accelerator physics activity to produce final layouts and prepare for the commissioning of the accelerator complex. The DIAMOND facility is expected to be operational for users in 2007
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| RPAP021 | A Portable Electron Radiography System | electron, quadrupole, proton, permanent-magnet | 1715 | ||
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The technique of charged particle radiography has been developed and proven with 800 MeV protons at LANSCE and 24 GeV protons at the AGS. Recent work at Los Alamos National Laboratory in collaboration with the Idaho Accelerator Center has extended this diagnostic technique to electron radiography through the development of an inexpensive and portable electron radiography system. This system has been designed to use 30 MeV electrons to radiograph thin static and dynamic systems. The system consists of a compact 30 MeV pulsed electron linear accelerator coupled to a quadrupole lens magnifier constructed from permanent magnet quadrupoles. The design features and operational characteristics of this radiography system are presented as well as the radiographic performance parameters.
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| RPAP036 | A Compact 5 MeV S-Band Electron Linac Based X-Ray Source for Industrial Radiography | linac, electron, target, insertion | 2428 | ||
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A compact and reliable X-ray source, based on a 5 MeV, 1 kW, S-band electron linac, has been set up at the Dipartimento di Fisica, Universit\‘a di Messina. This source, coupled with a GOS scintillator screen and a CCD camera, represents an innovative transportable system for industrial radiography and X-ray tomography. Optimization of the parameters influencing the e-gamma conversion and the X-ray beam characteristics have been studied by means of the MCNP-4C2 code. The converter choice is the result of the study of the e-gamma conversion performances for different materials and materials thicknesses. Also the converter position with respect to the linac exit window was studied. The chosen converter consists in a Ta-Cu target inserted close to the linac window. The Cu layer acts as a filter both on the electrons from the source and on the low energy X-rays. The X-ray beam angular profile was studied by means of GafChromic films with and without collimation. In the final source project, a collimation system provides a 14 cm diameter X-ray spot at the sample position and first radiographyc results were obtained by inspecting different density materials and thicknesses.
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| ROPB008 | Halo Mitigation Using Nonlinear Lattices | focusing, simulation, damping, space-charge | 620 | ||
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This work shows that halos in beams with space charge effects can be controlled by combining nonlinear focusing and collimation. The study relies on Particle-in-Cell (PIC) simulations for a one dimensional, continuous focusing model. The PIC simulation results show that nonlinear focusing leads to damping of the beam oscillations thereby reducing the mismatch. It is well established that reduced mismatch leads to reduced halo formation. However, the nonlinear damping is accompanied by emittance growth causing the beam to spread in phase space. As a result, inducing nonlinear damping alone cannot help mitigate the halo. To compensate for this expansion in phase space, the beam is collimated in the simulation and further evolution of the beam shows that the halo is not regenerated. The focusing model used in the PIC is analysed using the Lie Transform perturbation theory showing that by averaging over a lattice period, one can reuduce the focusing force to a form that is identical to that used in the PIC simulation.
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| RPPP028 | Simulation of Wake Field Effects on High Energy Particle Beams | linear-collider, simulation, collider, optics | 2018 | ||
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We discuss the wake fields that are liable to arise in the Beam Delivery System of a Future Linear Collider, and we present studies made using the MERLIN simulation program of the effects such fields would have on the bunch shape and hence the luminosity of the proposed design.
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| RPPP048 | Beam Collimation and Machine-Detector Interface at the International Linear Collider | photon, radiation, synchrotron, synchrotron-radiation | 2995 | ||
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Funding: Work supported by the Universities Research Association, Inc., under contract DE-AC02-76CH03000 with the U.S. Department of Energy. |
Synchrotron radiation, spray from the dumps and extraction lines, beam-gas and beam halo interactions with collimators and other components in the ILC beam delivery system create fluxes of muons and other secondaries which can exceed the tolerable levels at a detector by a few orders of magnitude. It is shown that with a multi-stage collimation system, magnetized iron spoilers which fill the tunnel and a set of masks in the detector, one can hopefully meet the design goals. Results of modeling with the STRUCT and MARS15 codes of beam loss and energy deposition effects are presented in this paper. We concentrate on collimation system and mask design and optimization, short- and long-term survivability of the critical components (spoilers, absorbers, magnets, separators, dumps), dynamic heat loads and radiation levels in magnets and other components, machine-related backgrounds and damage in collider detectors, and environmental aspects (prompt dose, ground-water and air activation). |
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| FPAE016 | Spallation Neutron Source Ring - Design and Construction Summary | injection, SNS, power-supply, extraction | 1499 | ||
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Funding: * SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge. |
(J. Wei for the Spallation Neutron Source Collaboration) After six years, the construction of the Spallation Neutron Source (SNS) accumulator ring [1] and the transport lines is completed in March 2005. Designed to deliver 1.5 MW beam power (1.5 x 1014 protons of 1 GeV kinetic energy at a repetition rate of 60 Hz), stringent measures have been implemented in the fabrication, test, and assembly to ensure the quality of the accelerator systems. This paper summarizes the construction of the ring and transport systems with emphasis on the challenging technical issues and their solutions [2]. [1] J. Wei, et al, Phys. Rev. ST-AB, Vol. 3, 080101 (2000). [2] J. Wei, "Synchrotrons and Accumulators for High-Intensity Proton Beams", Rev. Mod. Phys., Vol. 75, 1383 – 1432 (2003). |
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| FPAT081 | A New Version of SixTrack with Collimation and Aperture Interface | simulation, proton, betatron, scattering | 4084 | ||
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Simulations of collimation and beam cleaning were so far often performed with simplified computer models. However, the increase in available CPU power has opened the possibility for far more realistic simulations. For large accelerators like LHC it is now possible to track millions of particles, element by element over hundreds of turns. The well established SixTrack code treats the full six-dimensional phase space and considers the non-linear magnet components up to very high order. This code is being used for all LHC tracking simulations and has well developed linear and non-linear error models. SixTrack was extended for tracking of large ensembles of halo particles, taking into account halo interaction with arbitrarily placed collimators. An interface to a program for aperture analysis allows obtaining beam loss maps in the machine aperture. A standardized and portable SixTrack version is now available, providing all functionality of the old SixTrack, as well as the newly added support for halo tracking, collimation and aperture loss maps.
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