The HiLumi LHC Design Study (a sub-system of HL-LHC) is co-funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement Fermi Research Alliance, LLC operates Fermilab under Contract DE-AC02-07CH11359 with the US Department of Energy. This work was partially supported by the US LHC Accelerator Research Program (LARP). BBLR compensation for HL-LHC A.Valishev (Fermilab/US LARP), S.Fartoukh (CERN), D.Shatilov (BINP) 4 th Joint HiLumi LHC – 23rd LARP Collaboration Meeting November 18, 2014

18 Nov 2014 A.Valishev, HL-LHC BBLR2Acknowledgments C.Milardi, M.Zobov (LNF/INFN) C.Milardi, M.Zobov (LNF/INFN) Y.Papaphilippou, H.Schmickler (CERN) Y.Papaphilippou, H.Schmickler (CERN) G.Stancari (FNAL) G.Stancari (FNAL)

18 Nov 2014 A.Valishev, HL-LHC BBLR3 Long-Range Compensation J.P. Koutchouk, LHC Project Note 223 (2000) J.P. Koutchouk, LHC Project Note 223 (2000) This note shows that the long-range beam-beam interactions, presently considered as the most drastic limitation of LHC performance, can be rather accurately corrected for both their linear and non-linear perturbations. The principle of the corrector is simple though departing from classical multipolar lenses. It requires a conductor running parallel to the beam and carrying a current of about 60 A over 2 m or 600 A over 20 cm. Ideally 8 such correctors would be needed, grouped in 4 boxes on either side of IP1 and IP5, placed at about 40 m from the exit face of D2 towards D1. This note shows that the long-range beam-beam interactions, presently considered as the most drastic limitation of LHC performance, can be rather accurately corrected for both their linear and non-linear perturbations. The principle of the corrector is simple though departing from classical multipolar lenses. It requires a conductor running parallel to the beam and carrying a current of about 60 A over 2 m or 600 A over 20 cm. Ideally 8 such correctors would be needed, grouped in 4 boxes on either side of IP1 and IP5, placed at about 40 m from the exit face of D2 towards D1. See more in Y. Papaphilippou’s talk

18 Nov 2014 A.Valishev, HL-LHC BBLR4 Motivation for BBLR in HL-LHC 1.Flat optics + wires (S. Fartoukh, 5th HL-LHC coordination meeting, 2013) HL-LHC Plan B without crab cavities Implication of flat optics – no mutual compensation of long-range collisions at IP1,5 requires large crossing angle to create  separation. Current wires can be used to allow reducing crossing angle and recover geometrical luminosity loss.

18 Nov 2014 A.Valishev, HL-LHC BBLR5 Motivation for BBLR in HL-LHC 2.V-V crossing scheme (S. Fartoukh, F.Cerutti – WP10) allows strong mitigation of the heat load from the debris produced at the IP and arriving in D2/Q4 Same as 1 – no mutual compensation of long-range collisions at IP1,5 requires large crossing angle to create  separation. Current wires can be used to allow reducing crossing angle and preserve the crab cavity voltage. For full flexibility, do we then need to foresee 8 wires per IR (one in each transverse plane, per beam, and per IP side)?

18 Nov 2014 A.Valishev, HL-LHC BBLR6 Motivation for BBLR in HL-LHC 3.Flexible tool for overcoming intensity limitations (S. Fartoukh) wires allow to restore full freedom in the choice of octupole polarity minimize the octupole strength and preserve the DA which otherwise may be limited in the ATS (M.Fitterer, 19 Nov.).

18 Nov 2014 A.Valishev, HL-LHC BBLR7 Motivation for BBLR in HL-LHC 4.Crab-Kissing scheme (S. Fartoukh, Phys. Rev. ST Accel. Beams 17, , 2014) Together with crab cavities and flat optics, wires are a key ingredient allowing to reduce the pile-up. CK requires crab cavities in two planes.

18 Nov 2014 A.Valishev, HL-LHC BBLR8 BBLR Campaign and Collaboration Strategy Use computer simulations and modeling to evaluate the scenarios and predict performance plan beam studies formulate requirements to implementation, observables, instrumentation Perform tests in the LHC (talk by Y. Papaphilippou) Develop instrumentation (talk by R. Jones)

18 Nov 2014 A.Valishev, HL-LHC BBLR9 Motivation for BBLR in HL-LHC – Example #1 Flat optics  *=30/7.5 cm, assuming leveling with  *  =2.5  m,  z =10cm, N p =1.1×10 11 (end-of-fill) intergation ?!

Flat optics  *=30/7.5 cm, assuming leveling with  *  =2.5  m,  z =10cm, N p =1.1×10 11 (end-of-fill)  =320  rad 18 Nov 2014 A.Valishev, HL-LHC BBLR10 Motivation for BBLR in HL-LHC – Example #1

18 Nov 2014 A.Valishev, HL-LHC BBLR11 Wire configuration for Example #1 Flat optics  *=30/7.5 cm Distance from IR 150 m (replaces CC ) Distance to beam 9.3 , and current 320 A×m Adjusted to mitigate the most important resonances BBLR

Flat optics  *=30/7.5 cm, assuming leveling with  *  =2.5  m,  z =10cm, N p =1.1×10 11 (end-of-fill)  =320  rad 18 Nov 2014 A.Valishev, HL-LHC BBLR12 Effect of BBLR in HL-LHC – Example #1

Flat optics  *=30/7.5 cm, assuming leveling with  *  =2.5  m,  z =10cm, N p =1.1×10 11 (end-of-fill)  =320  rad 18 Nov 2014 A.Valishev, HL-LHC BBLR13 Effect of BBLR in HL-LHC – Example #1 N.B. no working point optimization – further improvement possible

18 Nov 2014 A.Valishev, HL-LHC BBLR14 BBLR in HL-LHC – Example #2 Flat optics 40/10 cm,  z =10cm Flat optics 40/10 cm,  z =10cm L/L 0  =340  rad (11.7  separation)  z =7.5cm – compare to 0.34 in nominal L/L 0  =340  rad (11.7  separation)  z =7.5cm – compare to 0.34 in nominal  =340  rad  z =10cm  =340  rad  z =10cm

18 Nov 2014 A.Valishev, HL-LHC BBLR15 Wire configuration for Example #2 Flat optics  *=40/10 cm Distance from IR 90 m Distance to beam ~10 , and current 420 A×m Adjusted to mitigate the most important resonances BBLR

18 Nov 2014 A.Valishev, HL-LHC BBLR16 BBLR in HL-LHC – Example #2 results bbw=off cc=off bbw=off cc=on bbw=on cc=offbbw=on cc=on  x=0.02  y=0.02 L=9.6E34  x=0.03  y=0.031 L=15.4E34 x-angle 340  rad, 11.7  sep.,  z=10cm, Np=2.2E11

18 Nov 2014 A.Valishev, HL-LHC BBLR17 BBLR in HL-LHC – Example #2 results Can operate without Crab Cavities but the pileup density is at the same level as in baseline scheme Can operate without Crab Cavities but the pileup density is at the same level as in baseline scheme

18 Nov 2014 A.Valishev, HL-LHC BBLR18 Crab-Kissing results: DA Not shown – multiparticle simulations of luminosity evolution

18 Nov 2014 A.Valishev, HL-LHC BBLR19 Computer code validation DAFNE experiments are a natural choice In 2005, simulations with Lifetrac were used to justify the wire installation and predict performance We used the latest version with the full account of machine detail and the latest simulation tools to reproduce the experimental data

18 Nov 2014 A.Valishev, HL-LHC BBLR20 DAFNE Lifetime Optimization with BBLR C. Milardi, D. Alesini, M.A. Preger, P. Raimondi, M. Zobov, D. Shatilov, (2008) C. Milardi, D. Alesini, M.A. Preger, P. Raimondi, M. Zobov, D. Shatilov, (2008) … During the operation for the KLOE experiment two such wires have been installed at both ends of the interaction region. They produced a relevant improvement in the lifetime of the weak beam (positrons) at the maximum current of the strong one (electrons) without luminosity loss, in agreement with the numerical predictions. … During the operation for the KLOE experiment two such wires have been installed at both ends of the interaction region. They produced a relevant improvement in the lifetime of the weak beam (positrons) at the maximum current of the strong one (electrons) without luminosity loss, in agreement with the numerical predictions. The only demonstration of long-range compensation with wires in collider operations.

DA  NE Lepton collider Wiggler dominated rings Experimental solenoid field is integral part of the lattice All magnetic elements are independently powered Flat beams (  x * = 2mm  y * = 20   z * = 20 mm) colliding with horizontal crossing angle Bunch separation 2.7 ns, shortest among the existing factories and colliders Working point close to the integer Beam lifetime dominated by the Toushek effect FINUDA KLOE Slide courtesy C.Milardi

Parasitic Crossings in the DA  NE IR1 In the DA F NE IRs the beams experience 24 Long Range Beam Beam interactions IP1 Slide courtesy C.Milardi

Numerical simulations show that BBLR interactions can be compensated by current windings (WIRES) The weak-strong Lifetrack code was used to simulate the equilibrium distribution of the positron (weak) beam The wires were simulated as additional PCs (‘wire-PC’) because the  x,y functions at the wire locations (  x =16.5 m,  y = 4 m) are:  much larger than both the bunch and wire lengths  rather small to have a large separation in units of the transverse beam size (≈20), so the actual ‘shape of wire’ does not matter and it works like a simple 1/r lens. Simulation results have shown:  the computed tails growth due to PCs for a ‘weak’ e + beam colliding against a ‘strong’ e - beam (I - bunch = 10 mA) is quite relevant  switching on the wires with the proper polarity the tails shrink  powering the wires with the wrong polarity, the tails blow-up becomes even stronger. The PCs compensation with a single wire on each side of the IR is not perfect since distances between the beams at PC locations are different in terms of the horizontal sigma and phase advances between PCs and wires are not completely compensated. Numerical simulations did not show improvements in luminosity the only positive effect is the tails reduction leading to a longer lifetime and to a larger integrated luminosity. Slide courtesy C.Milardi

Systematic study (March 2006) WIRES ONWIRES ON WIRES OFFWIRES OFF L I t Have shown that is possible to improve the lifetime t + of the ‘weak’ positron beam in collision. Slide courtesy C.Milardi  =1800 s  BB ~ 4500 s  =1100 s  BB ~ 1700 s  Touschek ~ 3000 s  Lumi ~ 3E5 s

18 Nov 2014 A.Valishev, HL-LHC BBLR Lifetrac Simulation Full DAFNE-2005 mad-x lattice with experimental solenoid, sextupoles, etc. Simulated Equilibrium distribution – tail growth, luminosity, beam life time Frequency Maps Dynamic Aperture Observables available for benchmarking: 1. Specific luminosity 2. Beam lifetime

18 Nov 2014 A.Valishev, HL-LHC BBLR Lifetrac Simulation – Equilibrium Distribution BBLR=offBBLR=on Computed specific luminosity is the same in both cases and matches the experiment within 15% Beam lifetime is times better with wires=on  BB=2.5E4 s  BB=2.5E8 s Constant density lines in invariant amplitude space

18 Nov 2014 A.Valishev, HL-LHC BBLR Lifetrac Simulation – FMA BBLR=offBBLR=on Stochastic layer facilitating the diffusion of particles to large vertical amplitudes starts at smaller amplitudes with bblr=off

18 Nov 2014 A.Valishev, HL-LHC BBLR Lifetrac Simulation – DA (2×10 5 turns) DA simulations are not very relevant for a machine with synchrotron radiation damping

18 Nov 2014 A.Valishev, HL-LHC BBLR Lifetrac Simulation Summary The general conclusions of campaign have been reproduced Full machine detail does not change the results in particular strong coupling in the IR due to experimental solenoid sextupoles No effect on specific luminosity from BBLR good quantitative agreement with experiment Lifetime effect reproduced qualitatively quantitative analysis requires aperture model

18 Nov 2014 A.Valishev, HL-LHC BBLR30 Characterizing LHC Tests (Ongoing) Goals: Reproduce previous work Come up with a MD scenario / observables

18 Nov 2014 A.Valishev, HL-LHC BBLR31 Nominal LHC with BBLR  *=55 cm, N p =1.2×10 11, e=2  m, wires at 9  between D1 and D2 DA improves by 1  No effect on beam life time

18 Nov 2014 A.Valishev, HL-LHC BBLR32 Integration Issues All work so far has been done with the requirement of BBLR being in the shadow of collimators > 9-10 . All work so far has been done with the requirement of BBLR being in the shadow of collimators > 9-10 . Simulations suggest that large gains could be made at smaller separation. Simulations suggest that large gains could be made at smaller separation. Can we come closer? – E-Lens, see next slide. Can we come closer? – E-Lens, see next slide. Integration may be an issue for E-Lens due to radiation load Integration may be an issue for E-Lens due to radiation load For H crossing the wires should be put in between the two beams For H crossing the wires should be put in between the two beams integration impossible if too close to D1 integration impossible if too close to D1 very challenging in general between D1 and D2 very challenging in general between D1 and D2 favoring a slot in between Q4 or Q5 favoring a slot in between Q4 or Q5 Smaller  – when does the wire size begin to matter? Smaller  – when does the wire size begin to matter?

18 Nov 2014 A.Valishev, HL-LHC BBLR33 Electron Lens as BBW R. Steinhagen, 3rd Joint HiLumi LHC-LARP Annual Meeting, Daresbury 2013 No limit on the distance from circulating beam No limit on the distance from circulating beam Easy position adjustment, no mechanical moving parts Easy position adjustment, no mechanical moving parts A.Valishev and G.Stancari, In the simplest case wire must compensate the kick of N LR collision points In the simplest case wire must compensate the kick of N LR collision points Current wire produces kick through magnetic field Current wire produces kick through magnetic field Electron Lens produces kick through electrical and magnetic field: gain factor 6 in current! Electron Lens produces kick through electrical and magnetic field: gain factor 6 in current! L EL =63 A m

18 Nov 2014 A.Valishev, HL-LHC BBLR34Summary Preliminary results for application of BBLR compensators in HL-LHC with flat optics to reduce the necessary crossing angle are very encouraging Preliminary results for application of BBLR compensators in HL-LHC with flat optics to reduce the necessary crossing angle are very encouraging For two considered cases, BBLR compensators allow to reduce the crossing angle by ~50%, or allow for ~ factor of 2 increase of the bunch intensity/luminosity For two considered cases, BBLR compensators allow to reduce the crossing angle by ~50%, or allow for ~ factor of 2 increase of the bunch intensity/luminosity Computer simulation successfully validated against the 2005 DAFNE BBLR experiments Computer simulation successfully validated against the 2005 DAFNE BBLR experiments Work on the simulation of upcoming LHC tests is ongoing Work on the simulation of upcoming LHC tests is ongoing

18 Nov 2014 A.Valishev, HL-LHC BBLR35 Backup slides

18 Nov 2014 A.Valishev, HL-LHC BBLR36 Other Work SPS BBLR Tests SPS BBLR Tests U. Dorda et al., EPAC08 (2008) U. Dorda et al., EPAC08 (2008) F. Zimmermann et al., PAC05 (2005) F. Zimmermann et al., PAC05 (2005) J.-P. Koutchouk et al., EPAC04 (2004) J.-P. Koutchouk et al., EPAC04 (2004) RHIC BBLR Tests RHIC BBLR Tests R. Calaga et al., PRST-AB, 14, (2011) R. Calaga et al., PRST-AB, 14, (2011) Simulations of BBLR Simulations of BBLR H.J. Kim et al., PRST-AB, 12, (2009) H.J. Kim et al., PRST-AB, 12, (2009) U. Dorda et al., PAC07 (2007) U. Dorda et al., PAC07 (2007) T.L. Rijoff et al., IPAC12 (2012) T.L. Rijoff et al., IPAC12 (2012)