CERN, Geneva
The very demanding LHC beam parameters put very strict requirements on the beam quality along the SPS-to-LHC transfer. In particular, the budget for the emittance increase is very tight. During the LHC commissioning, the emittances have been measured in the SPS, the two SPS-to-LHC transfer lines and in the LHC. Preliminary results show the importance of a very well controlled beam steering in the transfer lines together with the need of a robust trajectory correction strategy in order to guarantee long-term reproducibility. Another source of emittance comes from the tilt mis¬match be¬tween the LHC and its trans¬fer lines which generates cou¬pling at in¬jec-tion into the LHC and in turn will contribute to emittance increase. Preliminary results are also discussed.
CERN, Geneva
EPFL, Lausanne
The energy ramp and the betatron squeeze at the CERN Large Hadron Collider (LHC) are particularly critical operational phases that involve the manipulation of beams well above the safe limit for damage of accelerator components. In particular, the squeeze is carried out at top energy with reduced quench limit of superconducting magnets and reduced aperture in the triplet quadrupoles. In 2010, the commissioning of the ramp from 450 GeV to 3.5 TeV and the squeeze to 2 m in all the LHC experiments has been achieved and smoothly became operational. In this paper, the operational challenges associated to these phases are discussed, the commissioning experience with single- and multi-bunch operation is reviewed and the performance during standard operation is presented.
CERN, Geneva
The energy stored in the nominal LHC beams surpasses previous accelerators by roughly two orders of magnitude. The LHC relies on a complex machine protection system to prevent damage to accelerator components induced by uncontrolled beam loss. Around 20'000 signals feed directly or in-directly into the machine protection system. Major hardware sub-systems involved in machine protection include beam and powering interlock systems, beam loss and beam excursion monitors, collimators and the beam dumping system. Since the LHC startup in December 2009 the machine protection system components have been progressively commissioned with beam. Besides the usual individual component tests, global machine protection tests have been performed by triggering failures with low intensity beams to validate the protection systems. This presentation will outline the major commissioning steps and present the operational experience with beam of the LHC machine protection system.
CERN, Geneva
The LHC transfer lines, injection and beam dump systems are equipped with a series of active and passive protection systems. These are designed to prevent as many failures as possible, for example through surveillance and interlocking, or to absorb any beam which is mis-kicked or mis-steered on passive absorbers. The commissioning, validation tests and performance of the different systems are described, and the implications for the protection of the LHC against different failures during beam transfer are discussed.
CERN, Geneva
Uni HH, Hamburg
The 7 km long CERN Super Proton Synchrotron (SPS) is, apart from the LHC, the accelerator with the largest stored beam energy worldwide of up to 3 MJ. In 2008, an equipment failure led to a fast tune shift towards an integer resonance and an uncontrolled loss of a high intensity beam, which resulted in major damage of the accelerator. Distinct experimental studies and simulations provide clear understanding of the beam dynamics and the beam loss pattern at different SPS tune resonances. Diverging closed orbit oscillations, a resonant dispersion and increased beta beating are the driving effects that lead to a complete beam loss in as little as 3 turns (69μs). At the moment, the commissioning of a new turn-by-turn position interlock system which will counteract the vulnerability of the SPS is ongoing.