Possible Quadrupole-first Options with beta* <= 0.25 m 20/03/2000 Possible Quadrupole-first Options with beta* <= 0.25 m J-P Koutchouk , CERN 5/11/2019 CARE-HHH-LHC LUMI 2005

Outline Requirements and objectives Overview of the anticipated advantages and drawbacks of the quad-first solution Hints from the LHC design The yield from a reduced beta* The internal wheels of the simplified scaling model used Comparison of a range of solutions Conclusions of this exercise 5/11/2019 CARE-HHH-LHC LUMI 2005

Some sources F. Ruggiero et al., Possible scenarios for an LHC upgrade, HHH2004, CERN-2005-006. J. Strait et al., Overview of possible LHC IR Upgrade Layouts, HHH2004, CERN-2005-006. + several other contributions in the same workshop F. Ruggiero et al., Performance limits and IR design for an LHC upgrade, EPAC2004. R. Ostojic et al., Low-beta quad designs for the LHC upgrade, PAC2005 J. Strait, Very high gradient quads, PAC2001. P. McIntyre et al., Towards an optimization of the LHC IR using new Magnet technology, PAC2005. T. Sen et al., Beam physics issues for the IR upgrade. T. Sen et al. PAC2001. 5/11/2019 CARE-HHH-LHC LUMI 2005

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 A clear view of the performance objective Make up for a beam current that does not reach nominal value Contribute in a significant way to the factor 10 in lumi increase. The ideal being a lego system that allows both. Be ready for installation in 2012/2015 Robust design to cope for unknowns if a new technology is to be used. Maximize the probability for an efficient take-off Depending on the objective, the behavior versus the energy deposition and radiation lifetime are obviously major issues. 5/11/2019 CARE-HHH-LHC LUMI 2005

General Advantages and Drawbacks Minimization of βmax, 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 5/11/2019 CARE-HHH-LHC LUMI 2005

Hints from the LHC Design The arc sextupoles are specified for the chromatic correction (first and second order) of 4 low-beta insertions (l*=23/21 m) tuned at 25 cm (LHC PN38) for a 90 degree phase advance (version 4). The 2nd order Chrom. can as well be minimized by adjusting the betatron phase shift between IP’s (LHC PN103) The structure of the LHC optics allows reducing β* to 25 cm. An optics solution must include a well behaved un-squeeze to the injection optics: can be difficult and time-consuming. The difficulty increases rapidly with *. 5/11/2019 CARE-HHH-LHC LUMI 2005

The yield from a reduced beta* Luminosity increase vs beta*: no Xing angle, nominal Xing and bunch length, BBLR?, 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. 5/11/2019 CARE-HHH-LHC LUMI 2005

A simple-minded exploration of the triplet parameter space Goal: Investigate solutions based on a scaled LHC triplet vs distance to the IP, β* Beam intensity Xing strategy and beam-beam compensation Quadrupole length Quadrupole technology “oversize” factor for the inner coil diameter Model output: 5/11/2019 CARE-HHH-LHC LUMI 2005

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Discussion of the options (1) Ingredients, scaling laws and recipes: Xing strategy: small angle: HV, HH, HH+BBLR Triplet layout: same as LHC with same relative quad. lengths. LHC inter-quad space kept unscaled. Gradient: All triplet quads have the same gradient; scaled from nominal by followed by “matching” consisting in getting “reasonable” β’s and α’s at Q4 by small trims the gradient. <lQ>: average quad length. 5/11/2019 CARE-HHH-LHC LUMI 2005

Discussion of the options (2) Ingredients, scaling laws and recipes: Maximum beam extent: βmax, σ, a_disp, beam sep. are all taken in the middle of Q2 (thick lens transport), nominal ε. Beam extent due to dispersion: usual momentum range (0.86 E-3) in presence of spurious dispersion (0.4m in the arcs) and the vertical dispersion excited by the HV Xing scheme. LR: Long-range interaction length: IP + triplet+2 5/11/2019 CARE-HHH-LHC LUMI 2005

Discussion of the options (3) Ingredients, scaling laws and recipes: Xing angle: BBLR suppresses intensity dependence Beam separation: effect of the Xing angle transported to the mid-Q2: gives about 9.5 sigma. Beam aperture: 5/11/2019 CARE-HHH-LHC LUMI 2005

Discussion of the options (4) Ingredients, scaling laws and recipes: K2: Relative excitation of the lattice sextupoles scaled from version 4 (LHCPN38) +20% inefficiency due to phase advance. Geometric aberrations: 5/11/2019 CARE-HHH-LHC LUMI 2005

Discussion of the options (5) Ingredients, scaling laws and recipes: Innercoil diameter: Margins and efficiencies: For NbTi and NbTiTa, ultimate performance is taken at 66% of critical field (13T, 14T), i.e. 8.6T and 9.2T. For Nb3Sn, this is taken to 57% of 23T, i.e. 13T. The efficiency measures how this ultimate performance is approached. I understand a margin of 20% is usually wanted. 5/11/2019 CARE-HHH-LHC LUMI 2005

Discussion of the options (6) Ingredients, scaling laws and recipes: Power deposition in the coil: First attempt, based on few readings Nominal taken to be 0.4 mW/g; 5σ chosen to fit a doubling of the power deposition as calculated by A. Mokhov. 5/11/2019 CARE-HHH-LHC LUMI 2005

Case Studies (1) Strategy: Scenario where the beam intensity cannot exceed nominal/2. Do nothing Squeeze to aperture Move the triplet towards the IP Complement each MQX with a MQY Upgrade based on NbTi technology: Test some former proposals Optimize at l*=23m Investigate triplet closer to IP 5/11/2019 CARE-HHH-LHC LUMI 2005

Case Studies (2) Strategy: Upgrade based on Nb3Sn technology: Investigate at l*=23m Investigate at l*=19m Investigate at l*=16m Investigate at l*=12m 5/11/2019 CARE-HHH-LHC LUMI 2005

Nominal LHC 5/11/2019 CARE-HHH-LHC LUMI 2005

Intensity=nominal/2 5/11/2019 CARE-HHH-LHC LUMI 2005

Intensity=nominal/2; squeeze to aperture 5/11/2019 CARE-HHH-LHC LUMI 2005

Intensity=nominal/2; squeeze to aperture + HH Xing 5/11/2019 CARE-HHH-LHC LUMI 2005

Intensity=nominal/2; triplet pushed by 4m towards IP 5/11/2019 CARE-HHH-LHC LUMI 2005

Intensity=nominal/2; add a MQY to each MQX 5/11/2019 CARE-HHH-LHC LUMI 2005

Intensity=nominal/2; new NbTiTa insertion 5/11/2019 CARE-HHH-LHC LUMI 2005

Partial conclusion on making up for a too small beam intensity As is, the baseline triplet offers a very limited potential for compensating a beam current lower than anticipated (+20% to +30% in ). Pushing the triplet by 4m towards the IP yields an increase of 50% in  . The peak field reaches 7.5T but the power deposition is 2 times lower than nominal. To double the luminosity, NbTiTa is necessary but the solution appears stretched (need to start at 19m from IP, small margin, high chromatic and geometric aberrations) 5/11/2019 CARE-HHH-LHC LUMI 2005

Epac2004 solution 5/11/2019 CARE-HHH-LHC LUMI 2005

Pac2005 Cern solution 5/11/2019 CARE-HHH-LHC LUMI 2005

Very long and large weak quadrupoles 5/11/2019 CARE-HHH-LHC LUMI 2005

Optimization at l*=23m 5/11/2019 CARE-HHH-LHC LUMI 2005

Optimization at l*=23m 5/11/2019 CARE-HHH-LHC LUMI 2005

Partial conclusion on an upgrade using NbTi or NbTiTa technology According to the model, the EPAC2004 solution is too demanding. This is traced to the extra aperture required by a 9.5 σ separation and the Dy due to the HV Xing. The Ostojic et al. solution (l*=23m) works if the coil diameter is enlarged to 110 or better 120 mm and the technology NbTiTa used.  increases by 40%. Very long (16m) and large (212mm) weak (5.5T) quads appear to give a modest luminosity increase (25%) and large geometric aberrations but have some advantages (losses). 5/11/2019 CARE-HHH-LHC LUMI 2005

Partial conclusion on an upgrade using NbTi or NbTiTa technology(2) The same  increase is more easily obtained (diameter 105 mm) by pushing the triplet towards the IP (l*=18m). It seems the only possibility for the NbTi technology. 5/11/2019 CARE-HHH-LHC LUMI 2005

Nb3Sn: Optimization at l*=23m 5/11/2019 CARE-HHH-LHC LUMI 2005

Nb3Sn: Optimization at l*=23m, high intensity 5/11/2019 CARE-HHH-LHC LUMI 2005

Nb3Sn: Optimization at l*=23m, high intensity, BBLR 5/11/2019 CARE-HHH-LHC LUMI 2005

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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 (Ib×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: 5/11/2019 CARE-HHH-LHC LUMI 2005

Partial conclusion on an upgrade using Nb3Sn technology (2) 5/11/2019 CARE-HHH-LHC LUMI 2005

Back to the Xing angle issue 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? Orbit corrector Q1 Q3 Q2 5/11/2019 CARE-HHH-LHC LUMI 2005

Nb3Sn: Optimization at l*=19m, Xing/2 at IP 5/11/2019 CARE-HHH-LHC LUMI 2005

Beyond triplets? The ideal solution would be a two-stage system: Performance booster made of a doublet or triplet pushed inside the detector, optimized for its environment, i.e. with large margins, transparency, could accept some technological or planning risk… Followed by a triplet/dipole or dipole/triplet with more conservative design, margins,…that could provide a performance increase even in the absence of the booster (some resemblance with the LEP solution with a warm back-up of the sc low-beta doublet). Investigations to be done this fall. 5/11/2019 CARE-HHH-LHC LUMI 2005

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. 5/11/2019 CARE-HHH-LHC LUMI 2005

Conclusions What about separating the beams as early as possible with an orbit corrector? Investigations are planned on a two-stage system with the goal of mitigating the technological challenges. 5/11/2019 CARE-HHH-LHC LUMI 2005

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