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Possible Quadrupole-first Options with beta* <= 0.25 m

This document explores the advantages and drawbacks of quadrupole-first options with beta* values of less than or equal to 0.25 m for an IR upgrade design. It discusses requirements, objectives, insights from the LHC design, and yields from reduced beta*. It also presents a simple-minded exploration of the triplet parameter space and discusses the options based on scaling laws, recipes, and various ingredients.

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Possible Quadrupole-first Options with beta* <= 0.25 m

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  1. Possible Quadrupole-first Options with beta* <= 0.25 m J-P Koutchouk , CERN CARE-HHH-LHC LUMI 2005

  2. 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 CARE-HHH-LHC LUMI 2005

  3. 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. CARE-HHH-LHC LUMI 2005

  4. 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. CARE-HHH-LHC LUMI 2005

  5. General Advantages and Drawbacks CARE-HHH-LHC LUMI 2005

  6. 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 *. CARE-HHH-LHC LUMI 2005

  7. 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. CARE-HHH-LHC LUMI 2005

  8. 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: CARE-HHH-LHC LUMI 2005

  9. CARE-HHH-LHC LUMI 2005

  10. 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. CARE-HHH-LHC LUMI 2005

  11. 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 CARE-HHH-LHC LUMI 2005

  12. 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: CARE-HHH-LHC LUMI 2005

  13. 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: CARE-HHH-LHC LUMI 2005

  14. 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. CARE-HHH-LHC LUMI 2005

  15. 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. CARE-HHH-LHC LUMI 2005

  16. 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 CARE-HHH-LHC LUMI 2005

  17. 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 CARE-HHH-LHC LUMI 2005

  18. Nominal LHC CARE-HHH-LHC LUMI 2005

  19. Intensity=nominal/2 CARE-HHH-LHC LUMI 2005

  20. Intensity=nominal/2; squeeze to aperture CARE-HHH-LHC LUMI 2005

  21. Intensity=nominal/2; squeeze to aperture + HH Xing CARE-HHH-LHC LUMI 2005

  22. Intensity=nominal/2; triplet pushed by 4m towards IP CARE-HHH-LHC LUMI 2005

  23. Intensity=nominal/2; add a MQY to each MQX CARE-HHH-LHC LUMI 2005

  24. Intensity=nominal/2; new NbTiTa insertion CARE-HHH-LHC LUMI 2005

  25. 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) CARE-HHH-LHC LUMI 2005

  26. Epac2004 solution CARE-HHH-LHC LUMI 2005

  27. Pac2005 Cern solution CARE-HHH-LHC LUMI 2005

  28. Very long and large weak quadrupoles CARE-HHH-LHC LUMI 2005

  29. Optimization at l*=23m CARE-HHH-LHC LUMI 2005

  30. Optimization at l*=23m CARE-HHH-LHC LUMI 2005

  31. 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). CARE-HHH-LHC LUMI 2005

  32. 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. CARE-HHH-LHC LUMI 2005

  33. Nb3Sn: Optimization at l*=23m CARE-HHH-LHC LUMI 2005

  34. Nb3Sn: Optimization at l*=23m, high intensity CARE-HHH-LHC LUMI 2005

  35. Nb3Sn: Optimization at l*=23m, high intensity, BBLR CARE-HHH-LHC LUMI 2005

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