MULTITURN EXTRACTION BASED ON TRAPPING IN STABLE ISLANDS AT CERN PS: RECENT MEASUREMENT ADVANCES

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1 MULTITURN EXTRACTION BASED ON TRAPPING IN STABLE ISLANDS AT CERN PS: RECENT MEASUREMENT ADVANCES M. Giovannozzi and R. Cappi, S. Gilardoni, M. Martini, E. Métral, M A. Sakumi, R. Steerenberg, CERN A.-S. Müller, M ISS, Forschungszentrum Karlsruhe Present multiturn extraction New multiturn extraction Measurements: phase space reconstruction Summary: Measurements: trapping low- intensity beam Measurements: trapping high- intensity beam Massimo Giovannozzi EPAC04, July

2 Introduction: why multiturn extraction? The beam has to be manipulated 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 intensity (about p in the PS). An intensity upgrade for CNGS is under consideration (about p in the PS, corresponding to 8 bunches of p each ). Massimo Giovannozzi EPAC04, July

3 Present multiturn extraction I C SPS SPS = 11 C PS PS PS SPS circumference First PS batch Second PS batch Gap for kicker Beam current transformer in the PS/SPS transfer line (total spill duration ms) Massimo Giovannozzi EPAC04, July

4 Present multiturn extraction II Slow bump Extraction line Electrostatic septum (beam shaving) Slow bump Kickers magnets used to generate a closed orbit bump around electrostatic septum Extraction septum Kicker strength Fifth turn Four turns X Length X Electrostatic septum blade Massimo Giovannozzi EPAC04, July

5 Present multiturn 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 up. The slices have different emittances and optical parameters. Massimo Giovannozzi EPAC04, July

6 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( 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. Massimo Giovannozzi EPAC04, July

7 Novel multiturn extraction II 1 X (a) -1-1 X 1 Left: initial phase space topology. No islands. Right: intermediate phase space topology. Islands are created near the centre. 1 (c) 1 X (b) -1-1 X 1 X -1-1 X 1 Bottom: final phase space topology. Islands are separated to allow extraction. Massimo Giovannozzi EPAC04, July

8 Novel multiturn extraction - III Tune variation 2D polynomial mapping representing a FODO cell with sextupole and octupole Phase space portrait Simulation results Massimo Giovannozzi EPAC04, July

9 Measurement Campaign Efforts were devoted to the experimental proof of the proposed extraction: 2002: : proof of principle using a single-bunch bunch, low- intensity beam. 2003: : proof of splitting in realistic conditions, i.e. using a single-bunch bunch, high-intensity intensity beam. Type of measurements: Phase space reconstruction to ensure the presence of islands: based on turn-by by-turn beam position acquisition. Beam profile measurement to visualise splitting: based on wire scanners. Massimo Giovannozzi EPAC04, July

10 Sextupoles installed for the year 2003 campaign Used to generate stable islands Extraction line Instrumentation and hardware Sextupole magnets Octupole magnets Slow bump Flying wire Kicker magnet Extraction septum Beam profile measurement Phase space measurement Magnets used in the year 2002 campaign Massimo Giovannozzi EPAC04, July

11 Phase space reconstruction The pencil beam is kicked into the islands: this produces a strong coherent signal (filamentation is completely suppressed). H Signal PU1: blue - PU2: red Turn 15 5 Normalized Coordinates Initial wiggles represent beam oscillations around the islands centre (damped by filamentation). -5 DETAILED ANALYSIS IN IN POSTER WEPLT X 5 15 Massimo Giovannozzi EPAC04, July

12 Trapping low-intensity beam The horizontal emittance of the low-intensity beam (5 10( 11 is artificially increased to simulate the high-intensity intensity beam Left/right asymmetry is is unphysical! It It is is due to to the scintillator acceptance. 11 p) measurement results! Same Same behaviour found found in in Massimo Giovannozzi EPAC04, July

13 Trapping high-intensity intensity beam - I Tests with high-intensity intensity (about ) beam started in second half of Losses were observed by the end of the capture process (15( %).% 0.4 extraction 3 Hint for losses: intensity the octupoles are 0.3 profile measurement located in a 2 large-β octupoles V section D quads due to hardware 0.2 limitations, thus sextupoles 1 enhancing H/V 0.1 coupling. Intensity (a.u.) F quads 0.0 res. sweep Time (s) high-int. NB: ε high-int. int. V ~ 2 ε low-int. V Massimo Giovannozzi EPAC04, July

14 Capture of high-intensity intensity beam - II x10 12 protons 6.05x10 12 protons x(mm) Massimo Giovannozzi EPAC04, July

15 How to increase capture efficiency - I Two approaches are possible to capture more beam in the islands. Increase islands size.. This requires increasing nonlinearities (sextupoles and octupoles). It is a delicate procedure (chromaticity has to be corrected difficult in CERN PS machine). Change beam distribution,, e.g. induce core- emittance blow-up. It is much easier than playing with islands size. No need to increase the strength of nonlinearities (always delicate!). The kicker of the q-metre was used. Massimo Giovannozzi EPAC04, July

16 How to increase capture efficiency -II q-meter off q-meter on x(mm) The influence of the q-metre is clearly visible for a high- intensity bunch More islands. Less core. beam in the beam in the The beneficial effect depends of the direction of resonance crossing. Massimo Giovannozzi EPAC04, July

17 Adiabaticity tests with low- intensity beam - I A number of tests were performed by crossing twice the resonance and measuring the profile before and after. A symmetric tune curve is used Only t is varied Very mild dependence on t.. As long as t t > few ms no more changes in the final profile Time Measurement results indicate that the process is not reversible! Massimo Giovannozzi EPAC04, July Q h Q h =6.25 t 180 ms Profile measurements

18 Adiabaticity tests with low- intensity beam - II before crossing after crossing The horizontal beam profile after crossing Looks like a superposition of two distributions The wider distribution features non- gaussian tails x(mm) Massimo Giovannozzi EPAC04, July

19 Adiabaticity tests with low- intensity beam - III Horizontal beam profile t (ms) Open markers: before crossing Solid markers: after double crossing Halo parameter rms central peak rms (mm) Massimo Giovannozzi EPAC04, July

20 Conclusions and Outlook Experimental verification of the proposed approach started in 2002 and continued in Final results: Capture established for a bunch of up to 6.25X10 12 protons. Clean capture,, i.e. without losses, obtained for the low- intensity beam. Losses still present at the end of capture, i.e. when islands are separated for the high-intensity intensity beam. These losses might be induced by H/V coupling due to location of octupoles at large β V. In the shutdown 2003/2004 octupoles were installed in a small β V section. The year 2004 is crucial for drawing conclusions on the feasibility of this scheme for the CNGS Project (nominal and upgraded intensity). Massimo Giovannozzi EPAC04, July

21 Tune variation Phase space portrait The novel multiturn extraction works also with other resonances Simulation results results 2D polynomial mapping representing a FODO cell with sextupole and octupole The third- order resonance is used, thus giving a three-turn turn extraction Massimo Giovannozzi EPAC04, July

22 Novel multiturn extraction IV Final stage after turns (about 42 ms for CERN PS) Position of extraction septum after capture Three beamlets are superimposed in the projections Projected beam distr ^ One units in X correponds to about 6 cm ^ X Massimo Giovannozzi EPAC04, July

23 Qy Q v How to increase capture efficiency - III Example from low-energy space charge studies Direction of crossing Qy Q v Direction of crossing Coherent tune Tail particles Coherent tune Core particles Courtesy E. Métral Q h Qx Courtesy E. Métral Q h Qx Massimo Giovannozzi EPAC04, July