1. Beam loss mechanisms in relativistic heavy-ion colliders
PhD thesis, Lund University 2009
Roderik Bruce
CERN - BE/ABP, Geneva, Switzerland
MAX-lab, Lund University, Sweden
Supervisors:
John M. Jowett, CERN
Simone Gilardoni, CERN
Erik Wallén, MAX-lab

2. accelerating RF system R. Bruce - PAC11 Awards Session
Large Hadron Collider
Designed to collide 7 TeV protons and 7 Z TeV Pb82+ ions (now 3.5 Z TeV = 1.38 A TeV)
Will operate about 1 month per year with ions
Superconducting magnets: most operating at 1.9K
Nominal stored beam energy: 362 MJ for protons, 3.81 MJ for ions
accelerating RF system
Beam extraction
collimators
collimators
Injection
beam 1
Injection
beam 2
=> Machine protection crucial design parameter!
Losses must be controlled!
transfer line
transfer line
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Ion beam losses
During operation with ions, loss mechanisms not present with protons exist
Creation of ions with charge-to-mass ratio different from the main beam:
Interactions at IP (fragmentation, electron capture, electromagnetic dissociation)
Interactions in collimator (fragmentation, electromagnetic dissociation)
Follow dispersion, lost in localized spot
Example: Bound-Free pair production between colliding beams
Example: BFPP at IP2
Interaction point
Secondary Pb81+ beam emerging from IP and impinging on beam screen
Beam screen
Main Pb82+ beam
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4. Dispersive orbits from ALICE
Acceptance: ||< (=fractional deviation in magnetic rigidity)
Bound-free pair production (=0.012, =281 barn)
1-neutron electromagnetic dissociation (= , = 96 barn)
2-neutron electromagnetic dissociation (= , = 29 barn)
Compare: hadr= 8 barn
All these processes create beam losses
Decreasing lifetime
Potentially quenching magnets
Beam direction
Nom.
BFPP
EMD1
EMD2
collimators
Earlier work: J.M. Jowett et al. in EPAC 2004
S.R. Klein, Nucl. Inst. & Methods A 459, 51 (2001)
Meier et al. Phys. Rev. A, 63, (2001)
Pshenichnov et al. Phys. Rev. C 64, (2001)
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5. 3-step simulation, BFPP at IP2
Particle tracking gives impact coordinates in SC dipole
Simulation of the particle-matter interaction to estimate the power load with Monte Carlo program FLUKA
Thermal network simulation of heat flow by D. Bocian gives resulting temperature profile in magnet
Ptot = BFPP L Eparticle
Beam impact
P (mW/cm3)
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Simulation results
Simulation uncertainty dominated by FLUKA (factor ~3)
Different optical configurations simulated
Simulated heat load around 40% above quench limit in nominal configuration
Alleviation: extra collimators or redistributing losses by optics manipulations
R. Bruce, D. Bocian, S. Gilardoni, J.M. Jowett. Phys. Rev. STAB 12, (2009)
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BFPP at RHIC
Measurements of losses from BFPP with Cu29+ beams in RHIC during Run-5 in collaboration with colleagues at BNL
Optical tracking + FLUKA simulations of the shower
Van der Meer scan in Phenix
Localized losses observed at expected location and well correlated with luminosity
R. Bruce, A. Drees, W. Fischer, S. Gilardoni, J.M. Jowett, S.R Klein, and S. Tepikian. Phys. Rev. Lett. 99, (2007).
Expected BLM signal agrees with FLUKA simulation within a factor 2 Later: contributions from other collisional losses play a role
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8. Ion collimation studies at SPS
Fragmentation of ions in primary collimator makes collimation less efficient than for protons
Collimation measurements in CERN SPS of ions and protons confirms simulation models
Further topic: Models of time evolution of luminosity and bunch parameters during colliding beams (RHIC and LHC)
106.4 A GeV Pb82+ IONS
R. Bruce, R.W. Assmann, G. Bellodi, C. Bracco, H.H. Braun, S. Gilardoni, E.B. Holzer, J.M. Jowett, S. Redaelli, and T. Weiler. Phys. Rev. STAB 12, (2009).
270 GeV PROTONS
R. Bruce, M. Blaskiewicz, W. Fischer and J.M. Jowett. Phys. Rev. STAB 13, (2010).
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9. LHC ion losses in 2010, 1.38 A TeV No quenches predicted.
Momentum collimation: 208Pb82+ (IBS)
207Pb82+ (EMD1)
208Pb81+(BFPP at ATLAS)
Betatron collimation:
many nuclides from hadronic fragmentation and EMD in TCPs
208Pb81+ BFPP at CMS
Possibly: 206Pb82+ (EMD2 at IPs), other nuclides from collimation ??
208Pb81+(BFPP at ALICE)
No quenches predicted.
Generally according to predictions, detailed analysis under way.
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Summary
Beam-loss mechanisms, not present with protons, exist in relativistic heavy-ion colliders
Electron capture or nuclear fragmentation create dispersive secondary beams and very localized losses
Bound-free pair production (electron capture at the IP) most serious
Observations at RHIC in agreement with expectations
Predicted through 3-step simulation to limit nominal LHC performance with ions
2010 LHC ion run confirms predictions qualitatively. Quantitative analysis under way
For details, see thesis or publications
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Acknowledgements
thanks to the following people for valuable help and advise:
Supervision: J.M. Jowett, S. Gilardoni and E. Wallén
Other collaborators and people I want to thank: G. Arduini, R. Assmann, S. Aumon, M. Blaskiewicz, G. Bellodi, C. Bracco, H.H. Braun, D. Bocian, B. Dehning, R. DeMaria, A. Drees, M. Eriksson, A. Ferrari, W. Fischer, M. Giovannozzi, B. Goddard, M. Gresham, B. Holzer, J-B. Jeanneret, S.R. Klein, M. Magistris, L. Ponce, S. Redaelli, G. Robert-Demolaize, T. Roser, B. Schröder, G.I. Smirnov, M. Stockner, S. Tepikian, V. Vlachoudis, T. Weiler, S. White, C. Zamanzas, F. Zimmermann
Thank you for your attention
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