Beam loss mechanisms in relativistic heavy-ion colliders

1. Beam loss mechanisms inrelativistic 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. 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 R. Bruce - PAC11 Awards Session

3. During operation with ions, loss mechanisms not present with protons exist Creation of ions with charge-to-mass ratiodifferent 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 Example: BFPP at IP2 Interaction point Secondary Pb81+ beam emerging from IP and impinging on beam screen Beam screen Main Pb82+ beam R. Bruce - PAC11 Awards Session 2

4. Dispersive orbits from ALICE Nom. • 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 BFPP EMD1 Beam direction 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, 032713 (2001) Pshenichnov et al. Phys. Rev. C 64, 024903 (2001) R. Bruce - PAC11 Awards Session 3

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 = BFPPL Eparticle Beam impact P (mW/cm3) R. Bruce - PAC11 Awards Session 4

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 manipulations • R. Bruce, D. Bocian, S. Gilardoni, J.M. Jowett. Phys. Rev. STAB 12, 071002 (2009) 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 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, 144801 (2007). Expected BLM signal agrees with FLUKA simulation within a factor 2Later: contributions from other collisional losses play a role R. Bruce - PAC11 Awards Session

8. Ion collimation studies at SPS 106.4 A GeV Pb82+ IONS • 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 • R. Bruce, M. Blaskiewicz, W. Fischer and J.M. Jowett. Phys. Rev. STAB 13, 091001 (2010). R. Bruce - PAC11 Awards Session

9. LHC ion losses in 2010, 1.38 A TeV 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. R. Bruce - PAC11 Awards Session

10. 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 Summary http://cdsweb.cern.ch/record/1246025/files/CERN-THESIS-2010-030.pdf R. Bruce - PAC11 Awards Session 9

11. Acknowledgements R. Bruce - PAC11 Awards Session 10 • 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