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