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 H. Braun

Heat load in IR7 dispersion suppressor,  =12 min H. Braun

Interaction cross sections at LHC collision energy Cross-section for Pb totally dominated by electromagnetic processes

Electromagnetic Interactions of Heavy ions (Numerous other changes of ion charge and mass state happen at smaller rates.)

Pb 81+ footprint in a dipole From LHC design report To interaction point Pb 81+ beam separated from the Pb 82+ beam Pb 81+ beam parameters Energy: 2.75 TeV/u  x about few mm  s = 55 cm Incident angle = 0.5 mrad Expected intensity ~ 2.5e5 Pb 81+ /s Energy deposition in dipole simulated using FLUKA to evaluate the quenching risk

Dipole geometry model and magnetic field map Thanks to Fluka collaborators. ¼ of the magnet Field at nominal collision value of 8.33 TThe simulation of a single Pb ion at 2.75 TeV/u in this geometry and without biasing takes about 10 hours

Energy deposition in a LHC dipole z(cm) 10 m phi(rad) x(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/cm 3 or W/cm 3. 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? From A. Siemko, Chamonix ‘05 More precise conversion of the energy deposition into temperature understand the binning choice understand the quench level FOR IONS 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

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 ( ): 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 RHIC RHIC run V : Cu-Cu 100 GeV/u (Cu Z=29) nb -1 (01/03/05) delivered so far ( Possibility to observe BFPP due to larger momentum deviation than for Au-Au run

Experimental RHIC Pin-diode detectors located outside the dipole cryostats Most probable locations of losses computed by J. Jowett Experiment status: first data yesterday Photos from Jowett’s visit two weeks ago Pin-diode Aims: first attempt to measure BFPP cross section cross check of Monte Carlo simulation of ion transport in matter

Impact point determination Calculation from J. Jowett Circular Beam pipe Collision point Predicted impact ~ 137 m

First data from RHIC BFCC experiment Luminosity measurement Nice correlation between diode at 141 m and luminosity. Discrepancy with m due likely to particle shower development Preliminary Received: 02/03/05

Conclusions/Summary Pb 81+ 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