J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ LHC Operation with Heavy Ions John Jowett

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Plan of talk n Reminder of Early and Nominal Pb-Pb schemes n Differences from pp for principal systems n Plan for Commissioning LHC Rings with Lead Ions n An opportunity n Performance limits, transition to Nominal Pb-Pb

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Acknowledgements n Contributors to this talk: –Hans Braun, Roderik Bruce, Christian Carli, Alfredo Ferrari, Simone Gilardoni, Moira Gresham, Mateo Magistris, Stephan Maury, Amy Nicholson, Adriana Rossi, Karlheinz Schindl, George Smirnov, André Verdier + everybody in I-LHC project n Useful discussions and information: –Gianluigi Arduini, Roger Bailey, Philippe Baudrenghien, Tony Baltz, Oliver Brüning, Helmut Burkhardt, Paul Collier, Bernd Dehning, Claude Fischer, Kai Hencken, Noel Hilleret, Wolfgang Höfle, Barbara Holzer, Bernard Jeanneret, Spencer Klein, Daniela Macina, Andreas Morsch, Igor Pschenichnov, Rudiger Schmidt, Elena Shaposhnikova, Jörg Wenninger + many others in LHC, RHIC, ALICE, ATLAS, CMS, …

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Nominal scheme parameters (Design Report)

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Nominal scheme, lifetime parameters (Design Report) 2 experiments

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Early scheme Parameters (Design Report) Only show parameters that are different from nominal scheme 2 experiments

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Operational Parameter Space for Pb Ions I b  1.        cm 2 s  1 Visibility threshold on FBCT Nominal Visible on BCTDC Early Visibility threshold on arc BPM BFPP Quench limits ? Nominal single bunch current Visible on BCTDC Thresholds for visibility on BPMs and BCTs. Collimation limit?

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Beam Intensity at Instrumentation Thresholds (Injection) n  Pilot ion beam for setting up machine is a single bunch with % of nominal bunch intensity –Higher damage potential on surfaces than proton pilot –Should not quench a magnet

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Beam Intensity at Instrumentation Thresholds (Collision) n Work with most of design intensity from the beginning n Premium on minimising beam losses n Lifetime measurements slow (H. Schmickler’s talk) n Possible interest of “flying blind” in latter parts of long fills –Depends on turn-round time and injector availability

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Vacuum Requirements for Pb Ions n Chamonix 2004: Beam-gas cross sections ~ times proton values  Ions need much better vacuum than protons n Main gas source (cold LHC) during Pb ion operation is ion losses themselves –Desorption coefficient: 10 5 molecules/ion ( E. Mahner SPS, RHIC) n Ion losses giving max. density for 100 h beam lifetime: –2×10 6 ions/turn  beam lifetime < 2 s n Localised fast loss of 10 8 Pb ions, enough to quench one magnet = (loss rate for 500 s NOMINAL beam lifetime) ×(1 s)  pressure increase with negligible effect on beam lifetime n Vacuum not expected to be limiting factor for Pb ion beam lifetime –(Remaining uncertainties related to grazing angles … ?) A. Rossi, I-LHC Project meeting, 9/12/2004

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Optics for the Early and Nominal Ion Schemes n Same geometrical transverse beam size and emittance –Optics, dynamic aperture, mechanical acceptance, etc. similar to protons. n Injection and ramp done with exactly the same optics, orbits, corrections, etc. as for protons –Should shorten ion commissioning time considerably! n Colliding in ATLAS, CMS  same squeeze as protons n Leave IR8 in injection configuration n Main difference is that IR2 is squeezed to –May - or may not - be operationally convenient to commission the ion optics first with low-intensity protons. n Crossing angle at IP2 (1,5?) may be small (includes ALICE muon spectrometer, details in Design Report) –Aperture requirements somewhat relaxed w.r.t. protons –Operational time for polarity reversals

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Squeeze of IR2 O. Bruning, LHC Project Note 188 Ring 1, left Ring 1, right Ring 2, left Ring 2, right Needs update for V6.5 C.F talk by O. Bruning, in Session 1 Low excitations

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Alignment of IR2 Quadrupole Triplets n Procedure –K-modulation to find quadrupole centres w.r.t. BPMs –Alignment with special optics, triplet quads off n Only possible with Beam 2 –Phase advance injection kicker to TDI n May not be necessary in first year –Can be done with protons –Consider scheduling together with other IRs? New alignment optics for IR2 (+IR1, IR5) A. Verdier

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Longitudinal parameters Longitudinal emittance at injection from SPS has been reduced since we no longer have 200 MHz RF system for capture.

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ RF n Larger frequency swing than with protons, no problem n Different bunch filling schemes n RF noise to be clarified (SPS MD to test continuous use) n Needed to blow-up longitudinal emittance at collision energy (IBS) 208 Pb 82+ p

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Plan for Commissioning LHC Rings with Lead Ions (1) n Ensure that all systems know about, and do the right thing by, ions (all species!) –Software, hardware interlocks, instrumentation, etc., etc.: whenever the particle charge, mass, energy, beam energy, etc. appear! –No unnecessary “safety” impediments due to quick fixes. n Assume that protons can be collided –Injection, ramp, squeeze (where applicable) are set up n Re-commission injection and first turns with single ion “pilot” bunch –Adjust BST –Energy matching to different SPS cycle, each ring –Should go quickly (magnetic reproducibility…) –Deal with any difference of geometric beam size from protons (collimator settings, etc.) n Set up RF and capture (“few shifts”), instrumentation

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Plan for Commissioning LHC Rings with Lead Ions (2) n Re-commission ramp –Should also go quickly (magnetic reproducibility again) –Deal with any difference of geometric beam size from protons (collimator settings, etc.) n Commission squeeze of IP2 (if applicable) –Including crossing angle with ALICE spectrometer bump –(Alignment of IR2 triplet quadrupoles?) –Could take a few days (see experience with IP1 and IP5) n Collide Pb-Pb –Re-optimise collimation (how?), measurements, etc. Need to review time requirements with proton experience. Provide > 4 weeks of physics with Early Scheme for ALICE, ATLAS, CMS. Don’t forget MD time (  Nominal Scheme) with Pb ions

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Minimum Pre-requisites for switching from p-p to Pb-Pb n Pb-ion injection should be ready –S. Maury, Session 5 –Nominally in Spring 2008, but there is a fighting chance that they could be ready earlier n Injection, ramp and collisions work with protons –Squeeze is not strictly necessary –E.g. conditions of the Pilot Run …

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Beam energy (TeV)6.0, 6.5 or 7.0 Number of bunches (per beam) β* in IP 1, 2, 5, 8 (m)18,10,18,102,10,2,10 Crossing Angle (µR)000 Transverse emittance (µm)3.75 Bunch spacing (µs) Bunch Intensity Luminosity in IP 1 & 5 (cm -2 s -1 ) ~ ~ ~ Luminosity in IP 2 (cm -2 s -1 )~ ~ ~ Optical Conditions in Proton Pilot Run Initial Pilot Run conditions with Early Ion beam would give Pb-Pb luminosity of: Any reason why this would not work ? ALICE will be taking head-on collisions. Minimum change to LHC configuration.

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Base Program I (J. Schukraft, LHCC workshop 2002) – Step 1: ~ day even at very low initial Luminosity n few events => global event properties – Step 2: ~ week, still below design Lum. n some 10 6 events => most of hadronic signals – Step 3: ~ month (> 10 6 effective s), max Lum. n Integrated luminosity => rare hard signals Few  first physics results from LHC??? A Pilot Pb-Ion run would be a nice extra … but does not replace the Early Scheme run.

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Evolution during a fill n Model evolution of beam intensities and emittance evolve under the effects of: –Beam loss (nuclear scattering and EMD on residual gas) –Emittance blow-up from multiple scattering on residual gas –Luminosity lifetime: no. of experiments illuminated,  * –Intra-beam scattering (Bjorken-Mtingwa, complete optics) –Radiation damping –RF noise Much help from A. Nicholson

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Synchrotron Radiation n Bunched-beam cooling at collision energy for free! n Radiation damping for Pb is twice as fast as for protons n Many very soft photons n Critical energy in visible spectrum n Modifies evolution of transverse emittance –Counters (N b -dependent) intra-beam scattering, multiple scattering on residual gas. n Beneficial for luminosity, halo n RF noise helps to counter too much longitudinal damping (IBS) No radiation damping, D RF =0 Radiation damping, D RF >0 Example of transverse emittance evolution in a fill starting with nominal parameters

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Luminosity evolution: Nominal scheme Assuming good vacuum conditions, but including all effects. Particles per bunch Transverse emittance Luminosity Increasing number of experiments reduces beam and luminosity lifetime.

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Example: average luminosity Average luminosity with 3h turn- around time, starting from nominal initial luminosity. Average luminosity depends strongly on time taken to dump, recycle, refill, ramp and re-tune machine for collisions. Fills may be quite long in the early days …

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Luminosity evolution: Early scheme Assuming good vacuum conditions, but including all effects. Particles per bunch Transverse emittance Luminosity

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/  *-tuning Try to maximise integrated luminosity by gradually reducing  * while beams collide (advocated by A. Morsch) Try to maximise integrated luminosity by gradually reducing  * while beams collide (advocated by A. Morsch) –Stay below luminosity limit but use available intensity –Keep luminosity higher for longer –Reduce impact of additional experiments –May not be simple in real operation (tuning time …)

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Bound-free Pair Production (BFPP, formerly ECPP) n Direct limit on luminosity (see Chamonix ) n More accurate estimates of quench levels from secondary beam of Pb 81+ emerging from IPs –New heat deposition calculations (FLUKA) started recently, quantify quench level, explore possible alleviations –Continually improving the modelling of the physics of the interaction of heavy ions with matter in FLUKA n Nuclear fragmentation ~ OK n Electromagnetic disocciation, pair production in material

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Heat deposition from BFPP at IP2, Pb81+ n Dipole in dispersion suppressor –Mid-plane of 3D model n Impact point inner side of beam pipe (towards other aperture) n Other main goal of these calculations is to relate losses to signals on beam loss monitors –Also for collimation studies –Heavy computing requirements R. Bruce, S. Gilardoni, JMJ

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Heat deposition in coils of dipole magnet Inner coil Outer coil Dipole length Azimuthal angle around beam R. Bruce, S. Gilardoni, JMJ Review quench levels for magnets Impact point

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Energy Loss by High Energy Ions in Matter n Electromagnetic effects, including pair production, are important for energy deposition by lost ions and physics of collimation –Improving implementation in FLUKA G. Smirnov

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Collimation n Ion nuclear physics  collimation more complicated –Isotopes miss secondary collimators, and are lost in downstream SC magnets H. Braun

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Heat load in IR2 quads, for  =12 min H. Braun

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Heat load in IR7 dispersion suppressor,  =12 min H. Braun

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Pb-Ion Collimation Status n No solution on paper for nominal luminosity –Present collimation system acts almost like single- stage system –Many uncertainties in simulations, work going on to resolve them –Limit expected to be well above Early Scheme –Depends a lot on minimum lifetime accepted –Important to get experience with Early Scheme –Will there be any opportunity to schedule change of hardware if a solution is found ?

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Elucidation of Performance Limits n From the start of the "Early Ion Scheme“ onwards, it will be important to explore limits to ion performance: –Test simulations of BFPP n Some measurements in present Cu-Cu run at RHIC –Test simulations of losses from collimation n Hope for some tests at RHIC soon –Beam current limit from collimation scales directly with 12 min minimum lifetime: operational experience may validate a higher value. –Commission  * -tuning –Un-locked RF systems at injection, ramp (for p-Pb) n Message: Heavy Ion MD time must also be scheduled

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Evolution to nominal luminosity. n Intermediate bunch numbers –Especially if total beam current is limited by collimation –Drop pulses from ends of trains as required – pattern might become, say,

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Lower collision energy with Pb Ions n Reducing Collision energy will –Increase lowest available  * –Increase IBS. –Slow down radiation damping with E 3. –Raise quench level –Reduce peak and integrated luminosity. n Ion running possible but highest energy is preferable

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Scheduling Heavy-Ion Runs: General Considerations n Many of the potential difficulties with commissioning proton operation need not delay ion operation. n Heavy-Ion runs help to avoid problems of over-activation of PS-SPS complex and LHC by high proton intensity. n Or provide useful cool-down periods afterwards.

J.M. Jowett, LHC Project Workshop, Chamonix XIV, 17/1/ Summary n Early Ion Scheme to be scheduled –1-3 weeks setup (??), 4 weeks physics n Opportunity for additional Pilot Ion Run for very early physics results –If ion injection available at the right time n Performance limits for Nominal Scheme to be clarified with Early Scheme (MD time) –Collimation, BFPP n After Early Scheme Run, increase number of bunches towards Nominal and complete first phase of LHC ion programme (~1 nb -1 Pb-Pb)