CERN, Geneva
Nominal beam parameters at 7TeV/c will only be reached after some years of operation, with each proton beam having a stored energy of 360MJ. However, a small fraction of this energy is sufficient to damage accelerator equipment or experiments in case of uncontrolled beam loss. The correct functioning of the machine protection systems is vital during the different operational phases already for initial operation. When operating the complex magnet system, with and without beam, safe operation relies on the protection and interlock systems for the superconducting circuits. For safe injection and transfer of beam from SPS to LHC, transfer line parameters are monitored, beam absorbers must be in the correct position and the LHC must be ready to accept beam. At the end of a fill and in case of failures beams must be properly extracted onto the dump blocks, for some failures within less than few hundred microseconds. Safe operation requires many systems: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. We describe the commissioning of the LHC machine protection system and the experience during the initial operation.
CERN, Geneva
The LHC beam dump system was commissioned with beam in 2009. This paper describes the operational experience with the kicker systems and the tests and measurements to qualify them for operation. The kicker performance was characterized with beam by measurements of the kicker waveforms using bunches extracted at different times along the kicker sweep. The kicker performance was also continuously monitored for each pulse with measurement and analysis of each kick pulse, allowing diagnostic of errors and of long-term drifts. The results are described and compared to the expectations.
CERN, Geneva
The commissioning of the beam transfer systems for LHC included detailed aperture measurements in the injection regions and for the beam dump systems. The measurements, mainly single pass, were made using systematic scans of different oscillation phases and amplitudes, and the results compared with the expectations from the physical aperture model of the LHC. In this paper the measurements and results are presented and compared with the specified apertures in these critical areas.
CERN, Geneva
The proposed Compact Linear Collider (CLIC) is based on a two-beam acceleration scheme. The energy of high intensity, low energy drive beams is extracted and transferred to low intensity, high energy main beams. Direct ionization loss by the beam particles is the principal damage mechanism. The total charge gives a single drive beam-train a damage potential that is two orders of magnitude above the level causing structural damage in copper. For the main beam, it is the extreme charge density due to the microscopic beam size that gives it a damage potential of four orders of magnitude above the safe level. The machine protection system has to cope with a wide variety of failures, from real time failures (RF breakdowns, kickers misfiring), to slow equipment failures, to beam instabilities (caused by e.g. temperature drifts, slow ground motions). This paper discusses the baseline for the CLIC machine protection system which is based on passive, active and permit based protection. As the permit based protection depends on the measured performance of the previous pulse, the bootstrap procedure with safe beams and stepwise increase in beam intensities, is also discussed.
CERN, Geneva
SLAC, Menlo Park, California
Fermilab, Batavia
Unbunched beam is a potentially serious issue in the LHC as it may quench the superconducting magnets during a beam abort. Unbunched particles, either not captured by the RF system at injection or leaking out of the RF bucket, will be removed by using the existing damper kickers to excite resonantly the particles in the abort gap. Following beam simulations, a strategy for cleaning the abort gap at different energies was proposed. The plans for the commissioning of the beam abort gap cleaning are described, and the first results from the beam commissioning are presented.
CERN, Geneva
Proton and ion beams will be injected into LHC at 450 GeV by two kicker magnet systems, producing magnetic field pulses of up to 7.8 μs flat top duration with rise and fall times of not more than 900 ns and 3 μs, respectively. Both systems are composed of four traveling wave kicker magnets, powered by pulse forming networks. One of the stringent design requirements of these systems is a field flat top and post pulse ripple of less than ±0.5 %. A carefully matched high bandwidth system is required to obtain the stringent pulse response. Screen conductors are placed in the aperture of the kicker magnet to provide a path for the image current of the, high intensity, LHC beam and screen the ferrite against Wake fields: these conductors affect the field pulse response. Recent injection tests provided the opportunity to directly measure the shape of the kick field pulse with high accuracy using a pilot beam. This paper details the measurements and compares the results with predictions and laboratory measurements.
CERN, Geneva
The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity (1034 - 1035 cm2/s) and a nominal centre-of-mass energy of 3 TeV: CLIC would complement LHC physics in the multi-TeV range. The CLIC design relies on the presence of Pre-Damping Rings (PDR) and Damping Rings (DR) to achieve the very low emittance, through synchrotron radiation, needed for the luminosity requirements of CLIC. In order to limit the beam emittance blow-up due to oscillations the combined flat-top ripple and droop of the field pulse, for the DR extraction kickers, must be less than 0.015%. In addition, the allowed beam coupling impedance for the kicker systems is also very low: a few Ohms longitudinally and a few MΩ/m transversally. This paper discusses initial ideas for achieving the extremely demanding requirements for the PDR and DR kickers.
CERN, Geneva
UMAN, Manchester
Uppsala University, Uppsala
The 1.5TeV CLIC beams, with a total power of 14MW per beam, are disrupted at the interaction point due to the very strong beam-beam effect. As a result, some 3.5MW reach the main dump in form of beamstrahlung photons. About 0.5MW of e+e- pairs with a very broad energy spectrum need to be disposed along the post-collision line. The conceptual design of this beam line will be presented. Emphasis will be on the optimization studies of the CLIC post-collision line design with respect to the energy deposition in windows, dumps and scrapers, on the design of the luminosity monitoring for a fast feedback to the beam steering and on the background conditions for the luminosity monitoring equipment.
CERN, Geneva
Within the scope of the LHC injector upgrade, it is proposed to replace the present injector chain by new accelerators, Linac4, SPL and PS2, for which new beam transfer lines are required. The beam properties and requirements for each of the lines are summarized. The original design of the beam lines has been fully reconsidered due to the very demanding constraints on the beam line layouts at the PS2 injection / extraction regions and a new straight section of the PS2 which led to a much improved beam line geometry. The relevant modifications and optics designs are described and a preliminary specification of the beam line equipment is also given.