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Information about HB2004

Published on June 19, 2007

Author: Mahugani

Source: authorstream.com

Multiturn Extraction Based on Trapping in Stable Islands:  Multiturn Extraction Based on Trapping in Stable Islands Introduction Continuous Transfer Novel Extraction Experimental results until 2003 Latest experimental results Summary and outlook M. Giovannozzi and R. Cappi, S. Gilardoni, M. Martini, E. Métral, P. Scaramuzzi, R. Steerenberg, CERN A.-S. Müller, ISS, Forschungszentrum Karlsruhe Introduction - I:  Introduction - I Three approaches are normally used to extract beam from a circular machine: Fast Extraction (one turn) A kicker (fast dipole) displaces the beam from nominal closed orbit. A septum magnet deflects displaced beam towards transfer line. This extraction can be used both to transfer beam towards a ring or an experimental area. Slow Extraction (millions turns) The separatix of the third-order resonance increases particles’ amplitude until they jump beyond the septum. The tune is changed to shrink the stable region, thus pushing the particles towards larger amplitudes. This extraction is used to transfer beam towards an experimental area. Introduction - II:  Introduction - II 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. 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. 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? Present Continuous Transfer – I:  Present Continuous Transfer – I 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) CSPS = 11 CPS PS PS SPS circumference Present Continuous Transfer – II:  Present Continuous Transfer – II Length Kicker strength Four turns Fifth turn X X’ 1 3 5 2 4 Electrostatic septum blade Slow bump Slow bump Electrostatic septum (beam shaving) Extraction septum Kickers magnets used to generate a closed orbit bump around electrostatic septum Extraction line Present Continuous Transfer –III:  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. Novel multiturn extraction – I:  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. Novel multiturn extraction – II:  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. Novel multiturn extraction – III:  Novel multiturn extraction – III Position of extraction septum after capture Final stage after 20000 turns (about 42 ms for CERN PS) Simulation parameters: Third-order polynomial map representing a FODO cell with sextupole and octupole Novel multiturn extraction - IV:  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. The same approach can be applied for multiturn injection (time-reversal property of the physics involved). Novel multiturn extraction with other resonances - I:  Novel multiturn extraction with other resonances - I Simulation parameters: Third-order polynomial map representing a FODO cell with sextupole and octupole The third-order resonance is used, thus giving a three-turn extraction Phase space portrait Tune variation Novel multiturn extraction with other resonances - II:  Novel multiturn extraction with other resonances - II The fifth-order resonance is used, thus giving a six-turn extraction The second-order resonance is used, thus giving a two-turn extraction Novel multiturn extraction with multiple extractions - I :  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. Novel multiturn extraction with multiple extractions - II:  Novel multiturn extraction with multiple extractions - II Novel multiturn injection: new application!:  Novel multiturn 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. Experimental results until 2003 - I:  Experimental results until 2003 - 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. Experimental results until 2003 - II:  Experimental results until 2003 - II Key elements for experimental tests. Phase space reconstruction is based on fast digitiser applied to closed orbit pick-ups. Experimental results until 2003 - III:  Experimental results until 2003 - 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. Experimental results until 2003 - IV:  Experimental results until 2003 - IV Capture established for nominal intensity required for CNGS upgrade. Capture established without losses for the low-intensity beam. Capture achieved with high-intensity beam. However, losses effects the end of the capture process and islands separation. No solution was found for the losses (about 15-20 % of the beam intensity). Low- and high intensity beams have same horizontal emittance (sieve is used for the low-intensity beam), but the vertical emittance is larger (about 2.5 times) than that of the low-intensity beam. Furthermore, octupoles are located in a large bV section (due to an aperture limitation of standard PS octupoles). Programme of the 2004 studies:  Programme of the 2004 studies Measurement of the phase space topology generated by the new hardware. Completed. It was performed using a single-bunch, low-intensity, pencil beam. Capture with low-intensity beam. Completed. Virtually loss-less capture obtained (as in the past years). Scans of various parameters (octupole strength, Dp/p, reversibility, horizontal emittance, kicker) performed. Capture with high-intensity beam. In progress. Virtually loss-less capture obtained (unlike previous years). Scans of various parameters (octupole strength, Dp/p, reversibility, horizontal emittance, kicker) performed. Extraction with high-intensity beam. In progress. Very likely it will not be possible to extract the beam with present hardware. Data analysis and beam parameters:  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 Thanks to PSB specialists (M. Benedikt, M. Chanel)! Intensity e*H(s)/e*V(s) Low-intensity pencil beam 5×1011 2.3/ 1.3 Low-intensity large H emittance 5×1011 6×1012 6.2/ 1.6 High intensity beam 9.4/ 6.4 Reversibility:  Reversibility Before After Fast crossing: Dt 5 ms. Trapped particles Trapped particles Slow crossing: Dt 90 ms. Before After Large Gaussian tails No difference observed if Dt andgt; 20-40 ms. Influence of momentum spread:  Influence of momentum spread Dp/p(2s) =0.9×10-3 Dp/p(2s)= 1.4 ×10-3 Q’H ~ 1.9 xH ~ 0.3 Fraction of particles trapped in the islands is almost independent on momentum spread. Beamlets’ position does not depend on momentum spread. Beamlets’ width depends on momentum spread. Influence of octupole strength:  Influence of octupole strength Octupole action Island size. Detuning with amplitude. Problems with the fit Influence of injected horizontal emittance:  Influence of injected horizontal emittance Fraction of trapped particles increases by increasing injected emittance. Beamlets’ position does not depend on the value of the injected emittance. Beamlets’ width depends on the injected emittance. Influence of extraction kicker:  Influence of extraction kicker Red: 80 kV single-kick Blue: 100 kV single-kick Core becomes wider! Crucial part: high-intensity beam – I:  Crucial part: high-intensity beam – I Summary 2003: 15-20 % losses after beamlets separation. No cure found for this. 2004: 5-10 % losses after beamlets separation: effect of new location of octupole. andlt; 1% losses after beamlets separation: beamlets separation is obtained by tune variation and by changing the octupole strength. final touch: longitudinal setting-up. Thanks to rf specialist (S. Hancock)! Crucial part: high-intensity beam - II:  Crucial part: high-intensity beam - II Reduction of octupole strength to move the beamlets outwards 14 GeV/c flat-top 1.4 GeV flat-bottom Tune sweep After optimisation of transverse and longitudinal parameters:  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 The evolution of beam distribution and other developments:  The evolution of beam distribution and other developments A series of horizontal profiles have been taken during the capture process with high-intensity beam. Dependence on external parameters is essentially the same as for the low-intensity beam Example of tomographic reconstruction using beam profiles measured by two horizontal wire scanners. Fast-extraction tests in TT2:  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 mm). Beamlets projected onto x-axis Fast-extraction of a single beamlet performed successfully! Summary and Outlook:  Summary and Outlook Since a few years, a novel multiturn extraction is under study. 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 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

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