Massimo GiovannozziPAC05, May 16th FINAL RESULTS FROM THE NOVEL MULTI-TURN EXTRACTION STUDIES AT CERN PROTON SYNCHROTRON M. Giovannozzi and R. Cappi, S. Gilardoni, M. Martini, E. Métral, R. Steerenberg, CERN A.-S. Müller, ISS, Forschungszentrum Karlsruhe Summary:  Introduction  Present multi-turn extraction  New multi-turn extraction  Measurement results  Conclusions Acknowledgments: PS-Booster specialists and PS Operations Crew

Massimo GiovannozziPAC05, May 16th Introduction: aim of multi-turn extraction The beam has to be “manipulated” to increase the effective length beyond the machine circumference. 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 would appreciate having even more (about 4.8×10 13 p in the PS). Will the present technique for multi-turn extraction be the appropriate solution also for future beams?

Massimo GiovannozziPAC05, May 16th Present multi-turn extraction – I 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)

Massimo GiovannozziPAC05, May 16th Electrostatic septum blade Present multi-turn extraction – II 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

Massimo GiovannozziPAC05, May 16th Present multi-turn extraction –III The main drawbacks of the present scheme are: Losses (about 10% 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.

Massimo GiovannozziPAC05, May 16th 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.

Massimo GiovannozziPAC05, May 16th Model Used In Numerical Simulations Standard approach: nonlinear elements represented as a single kick at the same location in the ring (Hénon-like polynomial maps). Vertical motion neglected. Normalised (adimensional co-ordinates). QuadrupolesSextupoleOctupole The linear tune is time-dependent

Massimo GiovannozziPAC05, May 16th Novel multi-turn extraction - II Tune variation Phase space portrait Simulation parameters: Hénon-like map representing a FODO cell with sextupole and octupole

Massimo GiovannozziPAC05, May 16th Novel multiturn extraction – III 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

Massimo GiovannozziPAC05, May 16th 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.

Massimo GiovannozziPAC05, May 16th 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. Extraction line Slow bump Sextupole magnets Extraction septum Octupole magnets Flying wires Kicker magnet Section 71 Section 64 Section 55 Section 16 Section 21 Section 20 Section 54

Massimo GiovannozziPAC05, May 16th 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.

Massimo GiovannozziPAC05, May 16th 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. Intensity  * H (  )/  * V (  ) Low-intensity pencil beam 5× / 1.3 Low-intensity large H emittance 5× / 1.6 High intensity beam 6× / 6.4

Massimo GiovannozziPAC05, May 16th Reversibility BeforeAfter Trapped particles Fast crossing  t 5 ms. Trapped particles BeforeAfter Large tails Large tails Slow crossing  t 90 ms. No difference observed if  t > ms.

Massimo GiovannozziPAC05, May 16th Influence of octupole strength Octupole action Island size. Island size. Detuning with amplitude. Detuning with amplitude. Problems with the fit

Massimo GiovannozziPAC05, May 16th Crucial part: high-intensity beam Reduction of octupole strength to move the beamlets outwards 14 GeV/c flat-top 1.4 GeV flat-bottom Tune sweep

Massimo GiovannozziPAC05, May 16th After optimisation of transverse and longitudinal parameters Depleted region: extraction septum blade will not intercept any particle Horizontal beam profile No losses are observed during the beam splitting

Massimo GiovannozziPAC05, May 16th A movie to show the evolution of beam distribution A series of horizontal beam profiles in section 54 have been taken during the capture process. The beam is the high-intensity one.

Massimo GiovannozziPAC05, May 16th Other studies with high-intensity beams: how to increase the fraction of trapped particles The horizontal emittance delivered by the PS-Booster was increased at its maximum value. The strength of the octupole was varied to change the island size The strength of the sextupoles was changed too (more difficult as this has an impact on chromaticity). Summary of results: The fraction of trapped particles reached about 18% (NB: the limit set by SPS on the turn-by-turn intensity variation is 20% ±5% for the last beamlet). Some losses were observed during resonance crossing (about 2-3%).

Massimo GiovannozziPAC05, May 16th Experimental conditions sextupoles and octupole scan Injection Free parameter during octupole scan Free parameter during sextupole scan Profile measurement Beginning of magnetic flat-top

Massimo GiovannozziPAC05, May 16th Best result in terms of capture Assuming that: Beamlets are observed under 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 Scintillator is on this side! 18% three rightmost beamlets Capture 16% single leftmost beamlet 18% three rightmost beamlets Capture 16% single leftmost beamlet

Massimo GiovannozziPAC05, May 16th Fast-extraction tests in TT2 The high-intensity beam is fast extracted towards the dump D3. Prior to extraction beamlets are partially merged back with central core. The OTR in TT2 allows visualising the 2D beam distribution (pixel size is 225  m). Beamlets projected onto x-axis X Y

Massimo GiovannozziPAC05, May 16th Summary and Outlook - I The novel multi-turn extraction approach allows manipulating the transverse emittance in a synchrotron! Numerical simulations on a simple model confirmed the validity of the principle. Experimental tests showed that: Capture into stable islands: successfully* obtained with both low- and high-intensity, single-bunch beam. Beamlets separation: successfully* obtained with both low- and high-intensity, single-bunch beam. Multi-turn extraction proper: attempted. Hardware limitations prevented realistic tests. Increased trapping efficiency: about 18 % of the beam can be trapped inside islands. However, some beam losses during resonance crossing where observed (2-3 %). *without measurable losses

Massimo GiovannozziPAC05, May 16th Summary and Outlook - II Next steps: Final decision should be taken late in Spring 2005 about the definition of a project to implement the proposed multi-turn extraction. Critical issue is the construction of kickers for the novel extraction layout. Exact time scale has to be defined. The implementation will be staged (two steps) First stage should be operational by 2008

Massimo GiovannozziPAC05, May 16th 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! More details in TPAT014: M. Giovannozzi, J. Morel