Multiturn extraction and injection using stable resonances M
Multiturn extraction and injection using stable resonances M. Giovannozzi and R. Cappi, S. Gilardoni, M. Martini, E. Métral, J. Morel, P. Scaramuzzi, R. Steerenberg, CERN A. -S. Müller, ISS, Forschungszentrum Karlsruhe • • • Introduction Continuous Transfer Novel Extraction Experimental results Other developments Summary and outlook 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 1
Introduction Three approaches are normally used to extract beam from a circular machine: Fast Extraction (one turn) Slow Extraction turns) (millions Multiturn extraction (2 -10 turns, 5 is the relevant case for CERN application) The beam has to be “manipulated” to increase its effective length and to reduce transverse emittance. AT CERN this mode is used to transfer the proton beam between PS and SPS. These beams are high-intensity (~3× 1013 p in PS). Even higher intensities are required (~4. 8× 1013 p in PS, with eight bunches injected from PS-Booster of ~6× 1012 p each). Will the present technique for multiturn extraction be the appropriate solution also for future beams? 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 2
Present Continuous Transfer – I 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) 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 3
Slow bump Electrostatic septum (beam shaving) Kickers magnets used to generate a closed orbit bump around electrostatic septum Slow bump Extraction line 10/11/2004 Extraction septum Kicker strength Present Continuous Transfer – II Fifth turn Four turns Length X’ 3 2 5 4 1 X Electrostatic septum blade M. Giovannozzi - First CARE-HHH-APD Workshop 4
Present Continuous Transfer –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. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 5
Novel multiturn 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. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 6
Novel multiturn extraction – II 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. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 7
Novel multiturn extraction – III Simulation parameters: Third-order polynomial map representing a FODO cell with sextupole and octupole Final stage after 20000 turns (about 42 ms for CERN PS) Position of extraction septum after capture 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 8
Novel multiturn extraction – IV The original goal of this study was to find a replacement to the present Continuous Transfer used at CERN for the high-intensity proton beams. However the novel technique proved to be useful also in different context (according to numerical simulations), e. g. Multiturn extraction over a different number of turns can be designed, provided the appropriate resonance is used. Multiple multiturn extractions could be considered, e. g. to extract the beam remaining in the central part of phase space. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 9
Novel multiturn extraction with other resonances - I Simulation parameters: Tune variation Phase space portrait 10/11/2004 Third-order polynomial map representing a FODO cell with sextupole and octupole The thirdorder resonance is used, thus giving a threeturn extraction M. Giovannozzi - First CARE-HHH-APD Workshop 10
Novel multiturn extraction with other resonances - II The second-order resonance is used, thus giving a two-turn extraction The fifth-order resonance is used, thus giving a six-turn extraction 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 11
Novel multiturn extraction with multiple extractions - I The beam left around the origin (in case of stable resonance) can be extracted Using a kicker, i. e. in a single turn. Repeating the splitting using the resonance: The tune is put back to the initial value. Relative position beam/islands is adapted to the new beam size, i. e. nonlinearities increased or beam blown-up. The resonance is crossed again. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 12
Novel multiturn extraction with multiple extractions - II 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 13
Experimental results - I Experimental tests were undertaken since 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 highintensity 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. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 14
Experimental results - II Key elements for experimental tests. Phase space reconstruction is based on fast digitiser applied to closed orbit pick-ups. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 15
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 e*H(s)/e*V(s) Low-intensity pencil beam 5× 1011 2. 3/ 1. 3 Low-intensity large H emittance 5× 1011 6. 2/ 1. 6 High intensity beam 6× 1012 9. 4/ 6. 4 10/11/2004 Thanks to PSB specialists (M. Benedikt, M. Chanel)! M. Giovannozzi - First CARE-HHH-APD Workshop 16
Reversibility Slow crossing: Dt 90 ms. Fast crossing: Dt 5 ms. Large Gaussian tails Before After Trapped particles No difference observed if Dt > 20 -40 ms. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 17
Influence of octupole strength Octupole action Island size. Detuning with amplitude. Problems with the fit 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 18
High-intensity beam - I 14 Ge. V/c flat-top 1. 4 Ge. V flat-bottom Reduction of octupole strength to move the beamlets outwards Tune sweep 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 19
High-intensity beam - II A series of horizontal profiles was taken during the capture process. Capture losses reduced to zero… 10/11/2004 Horizontal beam profile are Depleted extraction blade will intercept any M. Giovannozzi - First CARE-HHH-APD Workshop region: septum not particle 20
Fast-extraction tests in TT 2 The high-intensity beam is fast extracted towards the dump D 3. Prior to extraction beamlets are partially merged back with central core. Beamlets projected onto x-axis The OTR in TT 2 allows visualising the 2 D beam distribution (pixel size is 225 mm). Fast-extraction of a single beamlet performed successfully! 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 21
Other developments - I The successful results of the studies for a novel multiturn extraction open up a series of new applications: The transverse beam emittance can be manipulated! Hence, in an injectors’ chain it does not need to be kept constant to the value required by the final machine (see longitudinal gymnastic in the PS machine for the LHC). The trapping process can be reversed so to have injection into stable islands. This turns out to be an efficient technique to generate hollow bunches. Hence, it could be useful in space charge dominate machines. 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 22
Other developments - II Simulation parameters: Third-order polynomial map representing a FODO cell with sextupole and octupole Tune variation The fourth-order resonance is used for a four-turn injection Phase space portrait By injecting some beam in the centre it is possible to shape the final beam distribution. 10/11/2004 Study in progress… M. Giovannozzi - First CARE-HHH-APD Workshop 23
Summary and Outlook A novel multiturn extraction is under study since a few years This 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. Multiturn extraction proper: attempted. Hardware limitations might prevent realistic tests. No difference between low- and high-intensity case (a factor of 12 in intensity) found: space charge effects seem to be negligible. The same principle can be used for injection. Transverse shaping is possible, i. e. generation of hollow bunches. *without measurable losses 10/11/2004 M. Giovannozzi - First CARE-HHH-APD Workshop 24
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