Summary of Session 1: Optics and Layout P. Raimondi

US-LARP Progress on IR Upgrades Tanaji Sen FNAL

Topics IR optics designs Energy deposition calculations Magnet designs Beam-beam experiment at RHIC Strong-strong beam-beam simulations Future plans

IR designs Quadrupoles first – extension of baseline Dipoles first – triplet focusing Dipoles first – doublet focusing (appealing but a new world for the beam-beam) All solutions in principle duable in terms of quads gradients and stay clear Energy deposition more tricky

Energy Deposition in Quads First Energy deposition and radiation are major issues for new IRs. In quad-first IR, Edep increases with L and decreases with quad aperture. – Emax > 4 mW/g, (P/L)max > 120 W/m, Ptriplet >1.6 kW at L = cm -2 s -1. –Radiation lifetime for G11CR < 6 months at hottest spots. More radiation hard material required. A. Zlobin et al, EPAC 2002 N, Mokhov

Energy deposition in dipoles Problem is even more severe for dipole-first IR. Cosine theta dipole On-axis field sprays particles horizontally power deposition is concentrated in the mid-plane L = cm -2 s -1 E max on mid-plane (Cu spacers) ~ 50 mW/g; E max in coils ~ 13 mW/g Quench limit ~ 1.6 mW/g Power deposited ~3.5 kW Power deposition at the non-IP end of D1 N. Mokhov et al, PAC 2003

Open mid-plane dipole Open mid-plane => showers originate outside the coils; peak power density in coils is reasonable. Tungsten rods at LN temperature absorb significant radiation. Magnet design challenges addressed Good field quality Minimizing peak field in coils Dealing with large Lorentz forces w/o a structure between coils Minimizing heat deposition Designing a support structure R. Gupta et al, PAC 2005

RHIC – Wire compensator Possible location of wire Parasitic interaction Phase advance from parasitic to wire = 6 o IP6 RHIC provides unique environment to study experimentally long-range beam-beam effects akin to LHC Proposal: Install wire compensator In summer of 2006, downstream of Q3 in IR6 Proposed Task  Design and construct a wire compensator  Install wire compensator on movable stand in a ring  First study with 1 proton bunch in each ring with 1 parasitic at flat top. Compensate losses for each separation with wire  Test robustness of compensation w.r.t current ripple, non-round beams, alignment errors, … New LARP Task for FY06

RHIC – Wire compensator Possible location of wire Parasitic interaction Phase advance from parasitic to wire = 6 o IP6 RHIC provides unique environment to study experimentally long-range beam-beam effects akin to LHC Proposal: Install wire compensator In summer of 2006, downstream of Q3 in IR6 Proposed Task  Design and construct a wire compensator  Install wire compensator on movable stand in a ring  First study with 1 proton bunch in each ring with 1 parasitic at flat top. Compensate losses for each separation with wire  Test robustness of compensation w.r.t current ripple, non-round beams, alignment errors, … New LARP Task for FY06

Possible Dipole First Options and Challenges - early beam separation  less long range interactions - no crossing-angle bump inside triplet magnets motivation and advantages: - reduced radiation inside the triplet magnets LHC LUMI 2005; ; ArcidossoOliver Brüning 10 - alternative solution to nominal layout  pro & cons  requires less aperture inside triplet magnets (assuming equal  -function values)  no feed-down errors & simpler correction options  local field error correction per triplet assembly  relaxed magnet design and more aperture

Possible Dipole First Options and Challenges -large radiation levels for dipole magnets  magnetic TAS (spectrometer dipole & absorber) dis-advantages & challenges: LHC LUMI 2005; ; ArcidossoOliver Brüning 11 - increased quadrupole distance from IP  larger  max  is it a valid assumption that large aperture, high field dipole magnets are easier to design compared to large aperture, high gradient quadrupoles?  requires larger aperture inside triplet magnets  implies larger chromatic aberrations  transfers design challenges for triplet quadrupole to D1 dipole design

Long Range Beam-Beam Interactions beam separation: LHC LUMI 2005; ; ArcidossoOliver Brüning 12 -the nominal IR layout features 32 long range beam-beam interactions for a bunch spacing of 25ns: D1 Q3 Q2 Q1Q1 Q2 Q3 D1 IP 2 x 23 m 35 m 13 long range interactions ca. 10 long range interactions  all layout options benefit from reduced L  !  changing the sequence of D1 and triplet magnets cuts the number of long range interaction in half! 24 m

Options For a Dipole First Layout LHC LUMI 2005; ; ArcidossoOliver Brüning 13 1) Simple swap of D1 and triplet magnets Q3 Q2 Q1 D1 D1 Q1 Q2 Q3 IP 2 x 23 m 13 long range interactions separated beams  changing the sequence of D1 and triplet magnets cuts the number of long range interaction in half!  Increased L* increases beam size in triplet magnets

Aperture Requirements single bore design requires aperture for beam separation: LHC LUMI 2005; ; ArcidossoOliver Brüning 14  -10  beam envelope -10  beam separation -20% beta beat -closed orbit error (4 mm) -alignment errors + beam screen (3mm) d(triplet) > 33  + 7 mm with  D   

Aperture Requirements 2-in-1 magnet design requires no aperture for beam separation: LHC LUMI 2005; ; ArcidossoOliver Brüning  beam envelope -20% beta beat -closed orbit error (4 mm) -alignment errors + beam screen 3mm? (economic use of space  flat beam screen) d(triplet) > 22  + 7 mm with  D    

Summary LHC LUMI 2005; ; ArcidossoOliver Brüning 16 dipole first layout options:  four options have been identified so far but only one is being studied in detail radiation:  any luminosity upgrade requires a TAS upgrade  a dipole first layout provides efficient magnetic TAS  a dipole first layout requires 2-in-1 magnets with central whole for neutron flux! beam-beam interaction:  dipole first layout reduces number of long range beam-beam interactions

Summary LHC LUMI 2005; ; ArcidossoOliver Brüning 17 optics:  chromaticity increases with  -funtion inside triplet magnets  dipole first layout implies larger chromatic aberrations aspects related to field error corrections:  2-in-1 magnet design provides efficient field error correction aspects related to crossing angle generation:  2-in-1 magnet design allows large crossing angles (v-xing?) aperture:  all IR upgrade options benefit from smaller L*  dipole first layout does not require larger magnet aperture and allows an efficient implementation of beam screens

J-P Koutchouk, CERN Possible Quadrupole-first Options with beta* <= 0.25 m

Requirements and objectives The IR upgrade design cannot be split in slices, as before. All requirements must be incorporated from the start and the technology is leading the dance. →Need for a global model 1.A clear view of the performance objective a)Make up for a beam current that does not reach nominal value b)Contribute in a significant way to the factor 10 in lumi increase. c)The ideal being a lego system that allows both. 2.Be ready for installation in 2012/ Robust design to cope for unknowns if a new technology is to be used. 4.Maximize the probability for an efficient take-off 5.Depending on the objective, the behavior versus the energy deposition and radiation lifetime are obviously major issues.

General Advantages and Drawbacks AdvantagesDrawbacks Minimization of β max, optical aberrations and sensitivity: most robust optics solution. Larger potential for beta* reduction Strong coupling to other upgrade options thru Xing angle and aperture: goal must be well defined The magnet most exposed to debris is as well the less sensitive (sweeps less) A priori, long-range beam- beam stronger Builds on the operational experience of 1rst generation: potential gain in ∫  dt The two LHC rings remain coupled: operations more involved but large experience

The yield from a reduced beta* Luminosity increase vs beta*: 1. no Xing angle, 2. nominal Xing and bunch length, 3.BBLR?, 4.Bunch length/2 For both options and even more for the Q first, pushing the low-beta makes sense if simultaneously the impact of the Lumi. geometrical factor is acted upon.

Partial conclusion on an upgrade using Nb3Sn technology (1) A solution very similar to the baseline triplet exists with coil diameter of 95 mm, dipole length of 5.5 m with a 1.5 increase in . For the full upgrade (I b ×2), the diameter and length required increase to 121mm and 6.7m. With BBLR/HH Xing, this increase is not needed and  increases further. Luminosity and feasibility both increase when pushing the triplet towards the IP:

Back to the Xing angle issue Q1 Q2 Q3 Orbit corrector An “easy” way to reduce or cancel the Xing angle at the IP and gain 20% to 50% in luminosity. Is it possible for the detectors?

Conclusions (1) The baseline triplet or “small” variations around it offer a very modest potential for luminosity improvement. The NbTi(Ta) technology can offer an improvement in luminosity of the order of 40% but requires some 120 mm diameter at 23m from the IP. At 18m, this is reduced to 105 mm. This option does not seem compatible with an increase of the beam intensity. These limits are removed by the Nb3Sn technology. A significant improvement in the performance and feasibility is observed with BBLR and when moving the triplet toward the IP.

Several solutions are presented each with its own sets of benefits The more appealing cases require intense R&D (e.g. Nb3Sn quads or crab cavities) R&D required in almost all the cases to cope with the increased heat load Symulations of all the crytical issues (optics, background etc) very detailed and useful to understand where to go Critical choices for the more ambitious improvement strongly linked to R&D results and LHC experience Probably still to early to reduce the number of options to one (or even two)

Optical requirements for the magnetic lattice of the high energy injectors (SSPS in the SPS tunnel) G. Arduini – CERN-AB/ABP

Outline Constraints from SPS tunnel Expected functionalities Arc aperture SPS to SSPS transfer Slow extraction in the SSPS Fast extraction Other issues

Constraints for SSPS in the SPS tunnel RF BI – TAIL CLEANING INJ. – BEAM DUMP

Constraints for SSPS in the SPS tunnel

Required functionalities 1.Injection 2.Acceleration 3.Fast extraction 1 to LHC (LSS4 if we want to use the TI8 tunnel) 4.Fast extraction 2 to LHC (LSS6 if we want to use the TI2 tunnel) 5.Slow resonant extraction (LSS2 if we want to use the TT20 tunnel to North area) 6.Beam dump 7.Betatron collimation 8.Momentum collimation Need to combine 2 functions in at least 2 LSSs

Arc aperture Peak dispersion 4.5 to 3 m  Required half- aperture in the arcs: 46 / 82 (H) × 27 (V) mm (10 % gain in the aperture at injection) Useful if together with increased  H at ES  proper insertions with independent powering of the quadrupoles in the dispersion suppressor, in the straight section and possibly in 1 arc cell might be required.

SPS to SSPS transfer Cohabitation with the SPS in the SPS tunnel will imply hosting the SPS fast extraction to the SSPS and the injection in the SSPS in the same straight section In order to gain space might need to install the SPS fast extraction kickers in the missing dipole section providing an H kick towards a Lambertson magnet in the following dispersion free section bending the beam vertically The Injection in the SSPS could be “symmetric” to the SPS extraction. This solution might be incompatible with a reduction of the cell length.

Tentative summary Only a few issues have been sketched Constraint on the length of the straight sections and increased energy impose to design dedicated insertions (no simple FODO lattice) Slow-extraction and dispersion drive and/or contribute significantly to the aperture in the arcs  proper matching and insertion design Cohabitation of different functionalities in the same straight section is necessary and implications need to be studied