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Massimo GiovannozziHB2006 - May 29 - June 2 20061 DESIGN AND TESTS OF A LOW- LOSS MULTI-TURN EJECTION FOR THE CERN PS M. Giovannozzi For PS Multi-Turn.

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Presentation on theme: "Massimo GiovannozziHB2006 - May 29 - June 2 20061 DESIGN AND TESTS OF A LOW- LOSS MULTI-TURN EJECTION FOR THE CERN PS M. Giovannozzi For PS Multi-Turn."— Presentation transcript:

1 Massimo GiovannozziHB May 29 - June 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

2 Massimo GiovannozziHB May 29 - June 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 between PS 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 3×10 13 p in the PS). CNGS requested to receive even more beam (about 4.8×10 13 p in the PS).

3 Massimo GiovannozziHB May 29 - June Electrostatic septum blade Present multi-turn extraction – I Length Kicker strength Four turns Fifth turn X X’ Slow bump Electrostatic septum (beam shaving) Extraction septum Kicker magnets used to generate a closed orbit bump around electrostatic septum Extraction line E field =0 E field ≠0

4 Massimo GiovannozziHB May 29 - June Present multi-turn extraction – II First PS batch Second PS batch Gap for kicker C SPS = 11 C PS PSPS SPS circumference Beam current transformer in the PS/SPS transfer line (total spill duration ms) (total spill duration ms)

5 Massimo GiovannozziHB May 29 - June 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. emittance blow-up. The slices have different emittances and optical parameters.

6 Massimo GiovannozziHB May 29 - June 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 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: 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.

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

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

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

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

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

12 Massimo GiovannozziHB May 29 - June Experimental results - III The pencil beam is kicked into the islands producing a strong coherent signal (filamentation is suppressed). Initial wiggles represent beam oscillations around the islands’ centre. Measured detuning inside an island compared to numerical simulations.

13 Massimo GiovannozziHB May 29 - June 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 Intensity  * H (  )/  * V (  ) Low-intensity pencil beam 5× / 1.3 Low-intensity large H emittance 5× / 1.6 High intensity beam 6× / 6.4

14 Massimo GiovannozziHB May 29 - June Influence of octupole strength Octupole action Island size. Island size. Detuning with amplitude. Detuning with amplitude. Problems with the fit

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

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

17 Massimo GiovannozziHB May 29 - June A movie to show the evolution of beam distribution 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

18 Massimo GiovannozziHB May 29 - June 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). Fit constraint: same integral Capture 18% three rightmost beamlets 16% single leftmost beamlet Scintillator is on this side!

19 Massimo GiovannozziHB May 29 - June 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 2  ) of two sextupoles one octupole will be used

20 Massimo GiovannozziHB May 29 - June 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.

21 Massimo GiovannozziHB May 29 - June 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)

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

23 Massimo GiovannozziHB May 29 - June Critical issues: available mechanical aperture - I

24 Massimo GiovannozziHB May 29 - June Critical issues: available mechanical aperture - II

25 Massimo GiovannozziHB May 29 - June Time scale of changes Install slow extraction sextupoles in SS03, keeping those in SS19. Replace magnets of slow bump 16 with type 205 magnets. 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

26 Massimo GiovannozziHB May 29 - June Kick amplitude (s) Kick amplitude (s) 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 t (  s)

27 Massimo GiovannozziHB May 29 - June Losses estimates: CT - II Normalised Jacobian of Loss function

28 Massimo GiovannozziHB May 29 - June Losses estimates: MTE Losses (%) -> Continuous Bunched (h=16) Bunched (h=8) Nominal scheme (recuperated kickers, slow rise time) Total (capture+extraction) Upgrade (improved kickers, faster rise time) < 0.1 Total (capture+extraction) Upgrade (reduced thickness of magnetic septum) Total (capture+extraction) 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). 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).

29 Massimo GiovannozziHB May 29 - June 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

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

31 Massimo GiovannozziHB May 29 - June 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 Tune variation Phase space portrait Efficient method to generate hollow beams! Study in progress with the contribution by J. Morel.


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