Beam Loss and Collimation at LHC

Azhgirei, I.L.; Aßmann, Ralph; Baishev, I.; Jeanneret, J.B.; Wróblewski, A.; Kurtyka, T.; Kalchev, D.

doi:10.1063/1.1522622

Cited by 8 publications

(15 citation statements)

References 4 publications

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“…To calculate A 1 at a given β Ã , the so-called n 1 method [48,49] was used in 2010, as well as during the LHC design phase. It is a theoretical calculation, where the worst-case value of A 1 is determined using the combination of several error sources.…”

Section: Calculation Of Triplet Aperturementioning

confidence: 99%

Calculations of safe collimator settings andβ*at the CERN Large Hadron Collider

Bruce

Assmann

Redaelli

2015

Phys. Rev. ST Accel. Beams

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The first run of the Large Hadron Collider (LHC) at CERN was very successful and resulted in important physics discoveries. One way of increasing the luminosity in a collider, which gave a very significant contribution to the LHC performance in the first run and can be used even if the beam intensity cannot be increased, is to decrease the transverse beam size at the interaction points by reducing the optical function β Ã . However, when doing so, the beam becomes larger in the final focusing system, which could expose its aperture to beam losses. For the LHC, which is designed to store beams with a total energy of 362 MJ, this is critical, since the loss of even a small fraction of the beam could cause a magnet quench or even damage. Therefore, the machine aperture has to be protected by the collimation system. The settings of the collimators constrain the maximum beam size that can be tolerated and therefore impose a lower limit on β Ã . In this paper, we present calculations to determine safe collimator settings and the resulting limit on β Ã , based on available aperture and operational stability of the machine. Our model was used to determine the LHC configurations in 2011 and 2012 and it was found that β Ã could be decreased significantly compared to the conservative model used in 2010. The gain in luminosity resulting from the decreased margins between collimators was more than a factor 2, and a further contribution from the use of realistic aperture estimates based on measurements was almost as large. This has played an essential role in the rapid and successful accumulation of experimental data in the LHC.

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Section: Calculation Of Triplet Aperturementioning

confidence: 99%

Calculations of safe collimator settings andβ*at the CERN Large Hadron Collider

Bruce

Assmann

Redaelli

2015

Phys. Rev. ST Accel. Beams

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“…For this study, taking account of the cylindrical symmetry of the problem, the representative volume is a sector with a radial dimension of 1.5 cm corresponding to the thickness of one of the superconducting coils, a length of 5 cm and azimuthal angle of 4 degrees. The maximum energy deposition is then evaluated to be about 7.2 mW/cm 3 , exceeding the quench limit of 4.5 mW/cm 3 given in [8] by about 60%. However this comparison is biased by two assumptions: First, the heating and cooling conditions in which the 4.5 mW/cm 3 limit was determined are different for the case of either proton or ion losses in the operating accelerator.…”

Section: Simulation Resultsmentioning

confidence: 75%

“…The possibility of quenching the MB with protons has already been considered in [8] for short losses, basically following the same philosophy. However, for this specific case, losses induced by ions in a well-defined location, a different volume binning may be appropriate.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…Ions tend to lose energy more rapidly than protons because of their high charge state; hence most of the initial energy deposited in matter is produced by electromagnetic interactions and more localized. This would suggest a reduction of the volume used for the proton case, in particular for the direction parallel to the shower development, reducing the 10 cm proposed in [8] to 5 cm.…”

Section: Simulation Resultsmentioning

confidence: 99%

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Luminosity Limit from Bound-Free Pair Production in the LHC

Jowett

Bruce²,

Gilardoni³

Proceedings of the 2005 Particle Accelerator Conference

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The luminosity of the LHC as a lead-ion collider is known to be limited by the large cross-sections for electromagnetic processes in ultra-peripheral collisions. In particular, the process of bound-free e -e + pair production creates secondary beams of Pb 81+ ions emerging from the collision points and impinging on the vacuum envelope inside superconducting magnets. New Monte-Carlo simulations, exploiting recent implementations of the physics of ion interactions with matter, are helping us to quantify the relationships among luminosity, energy deposition in the magnet coils a view to predicting and alleviating the quench limit on luminosity. AbstractThe luminosity of the LHC as a lead-ion collider is known to be limited by the large cross-sections for electromagnetic processes in ultra-peripheral collisions. In particular, the process of bound-free e -e + pair production creates secondary beams of Pb 81+ ions emerging from the collision points and impinging on the vacuum envelope inside superconducting magnets. New Monte-Carlo simulations, exploiting recent implementations of the physics of ion interactions with matter, are helping us to quantify the relationships among luminosity and energy deposition in the magnet coils a view to predicting and alleviating the quench limit on luminosity.

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“…The absorber (TDI) has to protect the machine and experiments in case of misfiring. This requires the vertical phase advance from MKI to TDI to exceed 70 [5]. This condition can be satisfied if the Q4 quadrupole is defocusing; Q5 then enhances the efficiency of the kicker magnet.…”

Section: Experimental Insertionsmentioning

confidence: 99%

A more robust and flexible lattice for LHC

Faus‐Golfe

Grote²,

Koutchouk³

et al.

Proceedings of the 1997 Particle Accelerator Conference (Cat. No.97CH36167)

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Faus-Golfe, A.; Grote, H. ; Koutchouk, J.-P. ; Risselada, T. ; Verdier, A ; Weisz, S.To correct more efficiently the arc dispersion, the exact antisymmetry of the LHC optics is now broken, except in the low-β triplets common to the two rings. A new quadrupole is added between the experimental insertions and the dispersion suppressors and several arc quadrupoles are complemented by a small trim quadrupole. The larger number of parameters gives flexibility to the lattice and allows a partial separation of the optical functions, with a decrease of the total number of quadrupole units. It is possible to change rather freely the phase advances of the arc cells. The nominal tunes are split by 4 units to reduce coupling. The β* tuning range in the experimental low-β is significantly increased, allowing e.g. a larger beam separation at injection. The super-periodicity of LHC remains 1. We plan to study whether it can be increased within the LHC hardware constraints AbstractTo correct more efficiently the arc dispersion , the exact antisymmetry of the LHC optics is now broken, except in the low-triplets common to the two rings. A new quadrupole is added between the experimental insertions and the dispersion suppressors and several arc quadrupoles are complemented by a small trim quadrupole. The larger number of parameters gives flexibility to the lattice and allows a partial separation of the optical functions, with a decrease of the total number of quadrupole units. It is possible to change rather freely the phase advances of the arc cells. The nominal tunes are split by 4 units to reduce coupling.The tuning range in the experimental low-is significantly increased, allowing e.g. a larger beam separation at injection. The super-periodicity of LHC remains 1. We plan to study whether it can be increased within the LHC hardware constraints.

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Beam Loss and Collimation at LHC

Cited by 8 publications

References 4 publications

Calculations of safe collimator settings andβ*at the CERN Large Hadron Collider

Calculations of safe collimator settings andβ*at the CERN Large Hadron Collider

Luminosity Limit from Bound-Free Pair Production in the LHC

A more robust and flexible lattice for LHC

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