beam loss mechanisms in relativistic heavy-ion colliders
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Beam loss mechanisms inBeam loss mechanisms inrelativistic heavy-ion relativistic heavy-ion
colliderscolliders
Roderik Bruce
CERN - BE/ABP, Geneva, SwitzerlandMAX-lab, Lund University, Sweden
Supervisors:John M. Jowett, CERN
Simone Gilardoni, CERNErik Wallén, MAX-lab
PhD thesis, Lund University 2009
2011.03.31 R. Bruce - PAC11 Awards Session 2
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
transfer line
Injectionbeam 1
transfer line
Injection beam 2
collimators
accelerating RF system
Beam extraction
collimators
=> Machine protection crucial design parameter!
Losses must be controlled!
2011.03.31 R. Bruce - PAC11 Awards Session 3
• 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
Ion beam losses
3
Example: BFPP at IP2Example: BFPP at IP2
Secondary Pb81+ beam emerging from IP and impinging on beam
screen
Secondary Pb81+ beam emerging from IP and impinging on beam
screen
Main Pb82+ beamMain Pb82+ beam
Interaction point
Interaction point
Beam
screen
Beam
screen
2011.03.31 R. Bruce - PAC11 Awards Session 4
Dispersive orbits from ALICEDispersive orbits from ALICE
4
Nom.BFPPEMD1EMD2
Beam direction
• Acceptance: ||<0.006 (=fractional deviation in magnetic rigidity)
•Bound-free pair production (=0.012, =281 barn)•1-neutron electromagnetic dissociation (=-0.0048, = 96 barn)•2-neutron electromagnetic dissociation (=-0.0096, = 29 barn)
•Compare: hadr= 8 barn
•All these processes create beam losses– Decreasing lifetime– Potentially quenching magnets
collimators
Meier et al. Phys. Rev. A, 63, 032713 (2001)Pshenichnov et al. Phys. Rev. C 64, 024903 (2001)
Earlier work: J.M. Jowett et al. in EPAC 2004S.R. Klein, Nucl. Inst. & Methods A 459, 51 (2001)
2011.03.31 R. Bruce - PAC11 Awards Session 55
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
10 5 10 4 10 3 10 2 10 1 100 101 P mW cm 3
Beam impactBeam impact
Ptot = BFPP L EparticlePtot = BFPP L Eparticle
P (mW/cm3)
2011.03.31 R. Bruce - PAC11 Awards Session 6
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 manipulationsR. Bruce, D. Bocian, S. Gilardoni, J.M. Jowett. Phys. Rev. STAB 12,
071002 (2009)
2011.03.31 R. Bruce - PAC11 Awards Session 7
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
R. Bruce, A. Drees, W. Fischer, S. Gilardoni, J.M. Jowett, S.R Klein, and S.
Tepikian. Phys. Rev. Lett. 99, 144801 (2007).
Localized losses observed at expected location and well correlated with luminosity
Expected BLM signal agrees with FLUKA simulation within a factor 2Later: contributions from other collisional losses play a role
Van der Meer scan in Phenix
2011.03.31 R. Bruce - PAC11 Awards Session 8
Ion collimation studies at SPS• Ion collimation
– 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)
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, 011001 (2009). 270 GeV PROTONS
106.4 A GeV Pb82+ IONS
R. Bruce, M. Blaskiewicz, W. Fischer and J.M. Jowett. Phys. Rev. STAB 13, 091001 (2010).
2011.03.31 R. Bruce - PAC11 Awards Session 9
208Pb81+
(BFPP at ATLAS)
208Pb81+(BFPP at ALICE)
208Pb81+ BFPP at
CMS
Momentum collimation:
208Pb82+ (IBS)207Pb82+
(EMD1)Betatron
collimation:many nuclides from
hadronic fragmentation and
EMD in TCPs
Possibly: 206Pb82+
(EMD2 at IPs), other nuclides
from collimatio
n ??
No quenches predicted.
Generally according to predictions,
detailed analysis under way.
LHC ion losses in 2010, 1.38 A TeVLHC ion losses in 2010, 1.38 A TeV
2011.03.31 R. Bruce - PAC11 Awards Session 1010
• 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
SummarySummary
http://cdsweb.cern.ch/record/1246025/files/CERN-THESIS-2010-030.pdf
2011.03.31 R. Bruce - PAC11 Awards Session 1111
AcknowledgementsAcknowledgements
• 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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