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DESIGN AND TESTS OF A LOW-LOSS MULTI-TURN EJECTION FOR THE CERN PS

DESIGN AND TESTS OF A LOW-LOSS MULTI-TURN EJECTION FOR THE CERN PS. M. Giovannozzi For PS Multi-Turn Extraction Study Group. Summary: Introduction Present multi-turn extraction New multi-turn extraction (MTE). Measurement results Implementation of MTE Losses estimates. Introduction.

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DESIGN AND TESTS OF A LOW-LOSS MULTI-TURN EJECTION FOR THE CERN PS

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  1. DESIGN AND TESTS OF A LOW-LOSS MULTI-TURN EJECTION FOR THE CERN PS M. Giovannozzi For PS Multi-Turn Extraction Study Group Summary: • Introduction • Present multi-turn extraction • New multi-turn extraction (MTE) • Measurement results • Implementation of MTE • Losses estimates HB2006 - May 29 - June 2 2006

  2. Introduction Multi-turn extraction • The beam has to be “manipulated” to increase the effective length beyond the machine circumference. • This extraction mode is used to transfer beam between circular machines. • AT CERN this mode is used to transfer the proton beam betweenPS and SPS. In the SPS the beam is used for • Fixed Target physics (broad sense) • Neutrino experiments (until 1998) • CERN Neutrino to Gran Sasso (CNGS) (from 2006) • These beams are high-intensity (about 3×1013 p in the PS). CNGS requested to receive even more beam (about 4.8×1013 p in the PS). HB2006 - May 29 - June 2 2006

  3. Electrostatic septum (beam shaving) Fifth turn Four turns Kicker strength Slow bump Kicker magnets used to generate a closed orbit bump around electrostatic septum Length Slow bump Extraction line Extraction septum Present multi-turn extraction – I Efield=0 X’ Efield≠0 2 3 5 1 X 4 Electrostatic septum blade HB2006 - May 29 - June 2 2006

  4. CSPS = 11 CPS PS PS SPS circumference First PS batch Second PS batch Gap for kicker Beam current transformer in the PS/SPS transfer line 1 2 3 4 5 (total spill duration 0.010 ms) Present multi-turn extraction – II HB2006 - May 29 - June 2 2006

  5. Present multi-turn extraction –III The main drawbacks of the present scheme are: • Losses (about 15% of total intensity) are unavoidable due to the presence of the electrostatic septum used to slice the beam. • The electrostatic septum is irradiated. This poses problems for hands-on maintenance. • The phase space matching is not optimal (the various slices have “fancy shapes”), thus inducing betatronic mismatch in the receiving machine, i.e. emittanceblow-up. • The slices have different emittances and optical parameters. HB2006 - May 29 - June 2 2006

  6. Novel multi-turn extraction – I The main ingredients of the novel extraction: • The beam splitting is not performed using a mechanical device, thus avoiding losses. Indeed, the beam is separated in the transverse phase space using • Nonlinear magnetic elements (sextupoles ad octupoles) to create stable islands. • Slow (adiabatic) tune-variation to cross an appropriate resonance. • This approach has the following beneficial effects: • Losses are reduced (virtually to zero). • The phase space matching is improved with respect to the present situation. • The beamlets have the same emittance and optical parameters. HB2006 - May 29 - June 2 2006

  7. Left: initial phase space topology. No islands. Right: intermediate phase space topology. Islands are created near the centre. Bottom: final phase space topology. Islands are separated to allow extraction. Novel multi-turn extraction – II HB2006 - May 29 - June 2 2006

  8. Tune variation Phase space portrait Novel multi-turn extraction - III Simulation parameters: Hénon-like map (i.e. 2D polynomial – degree 3 - mapping) representing a FODO cell with sextupole and octupole HB2006 - May 29 - June 2 2006

  9. Novel multi-turn extraction – IV Final stage after 20000 turns (about 42 ms for CERN PS) At the septum location Slow (few thousand turns) bump first (closed distortion of the periodic orbit) Bfield = 0 Bfield≠ 0 Fast (less than one turn) bump afterwards (closed distortion of periodic orbit) About 6 cm in physical space HB2006 - May 29 - June 2 2006

  10. Experimental results - I • Experimental tests were undertaken since 2002. • 2002 run: proof-of-principle of the capture process using a low intensity beam. • 2003 run: detailed study of capture process with low-intensity beam and first tests with high-intensity proton beam. • 2004 run: main focus on high-intensity beam to solve problems observed in 2003. • Overall strategy: • Phase space reconstruction using low-intensity, pencil beam. • Capture with low-intensity, large horizontal emittance beam. • Capture with high-intensity beam. HB2006 - May 29 - June 2 2006

  11. Experimental results - II Key elements for experimental tests. Phase space reconstruction is based on fast digitiser applied to closed orbit pick-ups. HB2006 - May 29 - June 2 2006

  12. Experimental results - III The pencil beam iskicked intothe islands producing astrong coherent signal(filamentation is suppressed). Initialwigglesrepresentbeam oscillationsaround theislands’ centre. Measured detuning inside an island compared to numerical simulations. HB2006 - May 29 - June 2 2006

  13. Data analysis and beam parameters • The wire scanner is the key instrument for these studies. • Raw data are stored for off-line analysis. • Five Gaussians are fitted to the measured profiles to estimate beam parameters of five beamlets. Beam parameters HB2006 - May 29 - June 2 2006

  14. Influence of octupole strength Octupole action • Island size. • Detuning with amplitude. Problems with the fit HB2006 - May 29 - June 2 2006

  15. Crucial part: high-intensity beam - I 14 GeV/c flat-top 1.4 GeV flat-bottom Reduction of octupole strength to move the beamlets outwards Tune sweep HB2006 - May 29 - June 2 2006

  16. After optimisation of transverse and longitudinal parameters Horizontal beam profile Capture losses are reduced to zero… Depleted region: extraction septum blade will not intercept any particle HB2006 - May 29 - June 2 2006

  17. The high-intensity beam is fast extracted towards the dump D3. Prior to extraction beamlets are partially merged back with central core. Beamlets projected onto x-axis A movie to show the evolution of beam distribution HB2006 - May 29 - June 2 2006

  18. 18%three rightmost beamlets 16%single leftmost beamlet Capture Best result in terms of capture Assuming that: • Beamlets are affected by a different solid angle • Beamlets are fitted using five gaussians. Instead of imposing the same integral for the four beamlets (physical arguments), only three have such a constraint (solid angle consideration). Scintillator is on this side! Fit constraint: same integral HB2006 - May 29 - June 2 2006

  19. Implementation of MTE - I • Three main items: • Generation of stable islands • Extraction proper: • Slow bump to approach the septum • Fast bump to jump septum • Generation of stable islands • two pairs (spaced by 2p) of • two sextupoles • one octupole • will be used HB2006 - May 29 - June 2 2006

  20. Implementation of MTE - II • Extraction proper: slow bump • Six dipoles, independently powered, are foreseen. • Large number of magnets -> optimal bump shape. • Present slow bump: four dipoles powered with a series/parallel circuit. HB2006 - May 29 - June 2 2006

  21. Implementation of MTE - III • Extraction proper: fast bump • Five kicker systems in the PS ring. • Two kickers to correct the extraction trajectories in the transfer line. • Maximum kick about 1.8 mrad at 14 GeV/c. Fast bump for extracting the fifth turn (centre core) HB2006 - May 29 - June 2 2006

  22. Summary of changes in the PS ring SS39 SS35 SS55 SS22 SS21 Legend: • SS -> Straight Section. • MU -> Magnet Unit. • Red circle -> “heavy” intervention: mechanical design, vacuum intervention. • Orange circle -> “light” intervention: auxiliary magnet exchange. SS60 SS20 Sextupoles and octupoles MU19 SS68 SS19 Extraction region MU18 SS74 SS18 MU16 MU15 SS02 SS15 SS03 MU14 SS13 SS04 SS08 SS12 HB2006 - May 29 - June 2 2006

  23. Critical issues: available mechanical aperture - I HB2006 - May 29 - June 2 2006

  24. Critical issues: available mechanical aperture - II HB2006 - May 29 - June 2 2006

  25. Time scale of changes • Install slow extraction sextupoles inSS03, keeping those inSS19. • Replace magnets of slow bump16with type205magnets. • General clean-up of the machine. • Remove slow extraction sextupoles in SS19. • Install new power converters for bump 16. • Install kickers. • Install modified vacuum chambers (straight sections and magnets). • Install sextupoles and new octupoles. • Move cavity. • Install new wire scanner. 05/06 06/07 07/08 HB2006 - May 29 - June 2 2006

  26. Losses estimates: CT - I Assumptions for analytical estimates • Gaussian distribution (transverse). • Parabolic distribution (longitudinal). • Kickers rise time (5%-95%): 820 ns Machine circumference Measured values of • Septum thickness • Septum angle • Beam emittance Kick amplitude (s) t (ms) HB2006 - May 29 - June 2 2006

  27. Normalised Jacobian of Loss function Losses estimates: CT - II HB2006 - May 29 - June 2 2006

  28. Losses estimates: MTE • No more slicing -> capture losses • Overall extraction losses -> interplay between • kicker rise time • bunch structure • septum thickness For the nominal MTE scheme the losses are reduced by a factor 3-4 with respect to CT! Even higher reduction could be expected (capture losses). HB2006 - May 29 - June 2 2006

  29. The members of the PS Multi-Turn Extraction Study Group M. J. Barnes*, O. E. Berrig, A. Beuret, J. Borburgh, P. Bourquin, R. Brown, J.-P. Burnet, F. Caspers, J.-M. Cravero, T. Dobers, T. Fowler, S. Gilardoni, M. Giovannozzi (Study Group Leader), M. Hourican, W. Kalbreier, T. Kroyer, F. di Maio, M. Martini, E. Métral, V. Mertens, K. D. Metzmacher, C. Rossi, J.-P. Royer, L. Sermeus, R. Steerenberg, G. Villiger, T. Zickler. *On leave from TRIUMF – CA HB2006 - May 29 - June 2 2006

  30. The second-order resonance is used, thus giving a two-turn extraction The fifth-order resonance is used, thus giving a six-turn extraction Novel multi-turn extraction with other resonances HB2006 - May 29 - June 2 2006

  31. Tune variation Phase space portrait Novel multi-turn injection: new application! Simulation parameters: Third-order polynomial map representing a FODO cell with sextupole and octupole The fourth-order resonance is used for a four-turn injection Efficient method to generate hollow beams! Study in progress with the contribution by J. Morel. HB2006 - May 29 - June 2 2006

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