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Progress of the Nonlinear Collimation System

Progress of the Nonlinear Collimation System. T. Asaka A. Faus-Golfe J. Resta López D. Schulte F. Zimmermann. Outline. The CS of a LC Nonlinear CS for LC Basic scheme State of the art Scheme using 2+1 skew sextupoles A Nonlinear CS for CLIC

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Progress of the Nonlinear Collimation System

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  1. Progress of the Nonlinear Collimation System T. Asaka A. Faus-Golfe J. Resta López D. Schulte F. Zimmermann

  2. Outline • The CS of a LC • Nonlinear CS for LC • Basic scheme • State of the art • Scheme using 2+1 skew sextupoles • A Nonlinear CS for CLIC • Previous design: Energy-Betatron Collimation • New designs: Energy Collimation A. Faus-Golfe

  3. The Collimation System of a LC Final doublet collimator • reduce the background in the detector by removing particles at large betatron amplitudes or energy offsets, which otherwise would be lost generating muons near the IP or emit synchrotron radiation photons in the final doublet • withstand the impact of a full bunch train in case of machine failure • not produce intolerable wake fields that might degrade the orbit stability or dilute the emittance The CS for a LC must fulfill: A. Faus-Golfe

  4. The Collimation System of a LC only linear elements: Standard Linear System: quads and bends Energy Betatron A. Faus-Golfe

  5. increase beam size at the spoiler cancel aberrations NonLinear CS for LC: Basic Scheme Deflection at the nonlinear element A. Faus-Golfe

  6. Nonlinear CS for LC:Basic Scheme • Nonlinear elements used are: skew sextupoles or octupoles • Higher-order multipoles(decapoles, dodecapoles, …) are not useful because they do not penetrate to the small distances needed [N. Merminga et al., SLAC-PUB-5165Rev. May 1994] A. Faus-Golfe

  7. Nonlinear CS for LC: State of the art • Scheme with skew-sextupole pairs for nonlinear collimation only in the vertical plane [N.Merminga, J. Irwin, R. Helm and R. Ruth, SLAC PUB 5165 Rev. (1994)] • “Tail folding” octupoles in the NLC final focus system [R. Brinkmann, P. Raimondi and A. Seryi, PAC2001, PAC 2001 Chicago] • A Magnetic Energy Spoiler (MES) for the TESLA post-linac collimation system [R. Brinkmann, N. J. Walker and G. Blair, DESY TESLA-01-12 (2001)] • Scheme with (2+1) skew sextupoles for CLIC [A. Faus-Golfe and F. Zimmermann, EPAC 2002, Paris] A. Faus-Golfe

  8. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles Energy and Betatron collimation Optics design: Increase sx,yat spoiler Orthogonal IP phase collimation Cancellation of geometric aberrations A. Faus-Golfe

  9. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles The Hamiltonian: The deflection: A. Faus-Golfe

  10. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles Position at the downstream spoiler: Position at the downstream spoiler w/o skew sextupole: A. Faus-Golfe

  11. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles Beam size at the spoiler: Gaussian momentum distribution: Uniform flat momentum distribution: New Formulas! average momentum offset A. Faus-Golfe

  12. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles Beam size at the spoiler for Gaussian: Beam size at the spoiler for Uniform flat: A. Faus-Golfe

  13. minimum beam size [S. Fartoukh et al.,”Heat Deposition by Transient Beam Passage in the Spoilers” CERN SL 2001 012 AP (2001)] Nonlinear CS for LC:Scheme using 2+1 skew sextupoles For spoiler survival: A. Faus-Golfe

  14. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles The achievable value of Dxsis limited by the emittance growth Δ(γεx) due to SR in the dipole magnets: 7% 1.0 x 10-19 m f: fraction of the initial emittance I5: radiation integral A. Faus-Golfe

  15. Energy collimation depth (units of d) Nonlinear CS for LC:Scheme using 2+1 skew sextupoles In addition to energy collimation the sextupolar deflection also yields a collimation for horizontal or vertical amplitudes at collimation depth (units of s) of: Alternatively we can collimate (in the other betatron phase) using the linear optics: A. Faus-Golfe

  16. Nonlinear CS for LC:Scheme using 2+1 skew sextupoles By combining these equations we could collimate in both betatron phases and in energy using a single spoiler. Alternatively, we could choose either linear or nonlinear collimation in one phase. If we opt for nonlinear betatron collimation, the other phase could also be collimated by installing a “pre” skew sextupole with a phase advance of p/2 in front of the first skew sextupole in a non dipersive location. A. Faus-Golfe

  17. FFS 1 1 2 2 A Nonlinear CS forPrevious design: Energy-Betatron Collimation Normal sextupoles for chromaticity correction Tracking studies show: strong residual aberration A. Faus-Golfe

  18. A Nonlinear CS forEnergy Collimation Main changes compared to previous CLIC design: • collimation only in energy • linear energy collimation in horizontal plane • 1st skew sextupole is only to increase vertical spot size at the spoiler • increase the overall fraction of the system occupied by bends, decrease bending angle until SR effect is reasonably small • keep b-functions as regular as possible to avoid need of chromatic correction A. Faus-Golfe

  19. Sk Sk Sp A Nonlinear CS forEnergy Collimation 1st optics solution: No bends between the skews A. Faus-Golfe

  20. A Nonlinear CS forEnergy Collimation Beam, optics and collimation parameters A. Faus-Golfe

  21. A Nonlinear CS forEnergy Collimation There is however a problem: • collimation system is not that short (2.8 km) To make further progress….. • fill as many of the cells with weak bends • increase the dispersion at the spoiler • increase the bending angle (I5 < 1.0 x 10-19) • increase the cell length … A. Faus-Golfe

  22. Sk Sk Sp A Nonlinear CS forEnergy Collimation 2nd optics solution: Bends between the skews A. Faus-Golfe

  23. A Nonlinear CS forEnergy Collimation Beam, optics and collimation parameters A. Faus-Golfe

  24. A Nonlinear CS forEnergy Collimation Goal: Compare the performance and collimation efficiency of the nonlinear system with those of alternative linear designs for CLIC A. Faus-Golfe

  25. A Nonlinear CS forEnergy Collimation See J. Resta López talk Ongoing work: • Collimation survival • install perfect spoiler & perform simulations with MAD and PLACET [T.Asaka, J. Resta López “Characterization and Performance of the CLIC BDS with MAD, SAD and PLACET” ELAN (2005)] • consider real spoiler with scattering, install absorbers, optimize absorber locations, run BDSIM or SIXTRACK or MARS simulations (linear system already contains spoilers and absorbers) [Drozhdin et al, “Comparison of the TESLA, NLC and Beam Collimation system performance” CLIC Note 555 (2003)] • Chromatic properties & Luminosity performance & Beam size at the spoiler vs sextupole strength & average momentun off-set A. Faus-Golfe

  26. A Nonlinear CS forEnergy Collimation • Outlook: • Optics with bends between the skews shows better performance from the collimation efficiency point of view but there is no complete cancellation of the geometric aberration and the luminosity is very poor • Further work: • New optics with no bends between the skews to avoid the luminosity degradation keeping good collimation efficiency A. Faus-Golfe

  27. A Nonlinear CS for Energy-Betatron Collimation Optics design: [A. Faus-Golfe and F. Zimmermann, EPAC 2002, Paris] A. Faus-Golfe

  28. A Nonlinear CS for Energy-Betatron Collimation A weak pre-skew sextupole 1st skew sextupole Single spoiler 2nd skew sextupole Δμ=π/2 Δμ=π/2 Does not include chromatic correction ! Δμ=π/2 A. Faus-Golfe

  29. A Nonlinear CS for Energy-Betatron Collimation Old Formulas ! Beam, optics and collimation parameters A. Faus-Golfe

  30. FFS 1 1 2 2 A Nonlinear CS forEnergy-Betatron Collimation Normal sextupoles for chromaticity correction Tracking studies show:strong residual aberration A. Faus-Golfe

  31. A Nonlinear CS for Betatron Collimation Optics design • The LHC momentum spreadis 2 orders of magnitude smaller than in CLIC, cannot be exploited for widening the beam during collimation • Emittance growthfrom SR is insignificant, not constrain in the design of the collimation system • The geometric vertical emittanceis about 3 orders of magnitude larger than in CLIC A. Faus-Golfe

  32. A Nonlinear CS for Betatron collimation Multiparticle tracking shows encouraging results LHC Collimation group A. Faus-Golfe

  33. A Nonlinear CS for Betatron collimation Beam, optics and collimation parameters A. Faus-Golfe

  34. A Nonlinear CS for Betatron collimation Further work: • include spoiler between two skew sextupoles • optimize the collimator’s gap to reduce impedance budget A. Faus-Golfe

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