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Ion operation and beam losses H. Braun, R. Bruce, S. Gilardoni, J.Jowett CERN - AB/ABP Lead ion nominal scheme parameters Some operation issues are the same as for protons, however others are related to the fact that an ion is an ensemble of nucleons and charges. Collimation Issues Electromagnetic Interaction Ion losses Possible magnet quench Collimation • Ion nuclear physics collimation more complicated – Isotopes miss secondary collimators, and are lost in downstream SC magnets • Basically an ion lost can became a source of ions Electromagnetic Dissociation cross sections for 208Pb on 12C 300 300 250 250 200 200 (mbarn) (mbarn) Hadronic Fragmentation cross sections for 208Pb on 12C 150 100 150 100 50 50 0 0 185 185 Ma 190 ss Nu 195 mb er A 190 Ma s sN 200 205 74 76 78 80 N mic o t A Z er b um 82 H. Braun 195 um be r 200 A 205 74 76 78 N mic o t A 82 Z ber m u 80 Heat load in IR7 dispersion suppressor, t=12 min Fractional heat load in dispersion suppressor, t =12min Pb208 20 Pb207 Pb206 Pb205 Pb204 15 Pb203 Tl204 Tl203 10 Tl201 Tl200 Tl199 Tl198 Hg201 Hg200 5 Hg199 570 580 590 600 distance from TCP.D6L7.B1 (m) 610 620 H. Braun MQTLI.11R7.B1 MQ.11R7.B1 MB.B11R7.B1 MB.A11R7.B1 MQTLI.10R7.B1 0 MQ.10R7.B1 ' P (W/m) Tl202 Maximum for continous loss, corresponds to local collimation inefficiency of 1.61 10-3m-1 630 Interaction cross sections at LHC collision energy Cross-section for Pb totally dominated by electromagnetic processes 400 200 barn Total cross - section for ion removal from beam tot ECP P EMD H H He O Ar Kr In Pb0 tot H EMD ECPP H Hydrogen Helium Oxygen Argon Krypton Indium Lead 0.105 0.35 1.5 3.1 4.5 5.5 8 EMD 0 0.002 0.13 1.7 15.5 44.5 225. ECPP 4.25 10 1. 10 8 0.00016 0.04 3. 18.5 280.756 tot 11 0.105 0.352 1.63016 4.84 23. 68.5 513.756 Electromagnetic Interactions of Heavy ions QED effects in the peripheral collisions of heavy ions Rutherford scattering: Free pair production: Electron capture by pair production (ECPP) Electromagnetic Dissociation (EMD) 208 Pb82 208 Pb82 208 Copious but harmless 208 Pb82 208 Pb82 208 Pb82 208 Pb82 e e Pb82 208 Pb82 208 Pb82 208 Pb82 Pb82 208 Pb81 e Electron can be captured to a number of bound states, not only 1s. 208 208 Pb82 208 Pb82 208 Pb82 ( 208 Pb82 ) * 207 82 Pb n Copious but harmless Secondary beam out of IP, effectively off-momentum” p Secondary beam out of IP, effectively off-momentum: p (Numerous other changes of ion charge and mass state happen at smaller rates.) 208 Pb 82 208 Pb 82 208 1 0.012 for Pb Z 1 Pb82 208 Pb81 e 1 4.8 10 3 for Pb A 1 Pb81+ footprint in a dipole Pb81+ beam separated from the Pb82+ beam Pb81+ beam parameters Energy: 2.75 TeV/u x about few mm s = 55 cm Incident angle = 0.5 mrad Expected intensity ~ 2.5e5 Pb81+/s From LHC design report Energy deposition in dipole simulated using FLUKA to evaluate the quenching risk Dipole geometry model and magnetic field map ¼ of the magnet The simulation of a single Pb ion at Field at nominal collision value of 8.33 T 2.75 TeV/u in this geometry and without biasing takes about 10 hours Thanks to Fluka collaborators. Energy deposition in a LHC dipole x(cm) phi(rad) z(cm) 10 m 10 m z(cm) Impact point Energy deposition vs. z Beam direction Quench limit as quoted in LHC design report Energy deposition vs. angle Quench limit as quoted in LHC design report Mesh chosen for FLUKA calculation Energy deposition or power losses quoted in GeV/cm3 or W/cm3. Important to choose the right dimension for the representative volume Assumptions: • z binning should be a fraction of the electromagnetic interaction length of the wire materials and comparable to the wire winding length, both about 15 cm • r, compared to the typical distance to embrace a volume which behave as a single thermal body z = 5 cm r = 1.55 cm = 4 What is missing? FLUKA results can be dominated by a “not too clever” choice of the binning: • cyan and blue line dominated by statistical fluctuation well above the quench limit More precise conversion of the energy deposition into temperature • understand the binning choice • understand the quench level FOR IONS From A. Siemko, Chamonix ‘05 How to validate the Monte-Carlo results • Compare FLUKA results with other codes – GEANT4 high energy ions hadronic interaction under development (Thanks to H.P. Wellisch from PH/SFT group) – preliminary results for thin targets with Pb at 100 GeV/u show no major discrepancies between FLUKA and G4 • Check the approach with past experience in other proton machines – Fermilab – Extrapolation to ion case not easy – Simulations pretty old (1980-1990): Monte-Carlo simulation improved consistently • Investigate existing machine – RHIC experiment Comparison with Tevatron dipole geometry Is the model used for the geometry precise enough to be predictive? Technical design of FNAL dipole Geometry implemented for simulation From FERMILAB-PUB-87/113 Comparisons between data and Monte-Carlo not completely satisfactory but due to hadronic cascade modelling. It was in 1987 and the Cascade Calculation evolved a lot. BFPP experiment @ RHIC RHIC run V : Cu-Cu collisions @ 100 GeV/u (Cu Z=29) 13.32 nb-1 (01/03/05) delivered so far (http://www.agsrhichome.bnl.gov/AP/RHIC2005/) Possibility to observe BFPP due to larger momentum deviation than for Au-Au run Experimental setup @ RHIC •Pin-diode detectors located outside the dipole cryostats Pin-diode •Most probable locations of losses computed by J. Jowett •Experiment status: first data yesterday Photos from Jowett’s visit two weeks ago Aims: •first attempt to measure BFPP cross section •cross check of Monte Carlo simulation of ion transport in matter Impact point determination Collision point Predicted impact point @ ~ 137 m Circular Beam pipe Calculation from J. Jowett First data from RHIC BFCC experiment Luminosity measurement Nice correlation between diode at 141 m and luminosity. Discrepancy with prediction @137 m due likely to particle shower development Conclusions/Summary • Pb81+ ions losses may lead to magnet quenching – Possible solution under investigation: • optics steering to decrease, for example, the beam density • FLUKA simulation still under way – Validation of results obtained with other codes • GEANT4 and MARS – Checking that the optics solution really help on the energy deposition – However would be better to integrate Monte-Carlo calculation with thermodynamic simulation to understand the quench limit in the specific case • From RHIC data – Check the BFPP cross section – Simulation of RHIC dipole also to validate simulation chain Thanks to... • A. Ferrari, G. Smirnov, M. Magistris and all the FLUKA team. • B. Jeanneret, A. Siemko, M. Giovannozzi for the fruitful discussions • H.P. Wellisch and V. Grichine for the GEANT4 support • Angelika Drees, Wolfram Fischer, Spencer Klein and all the RHIC team