The implementation of the new Multi-Turn Extraction (MTE) at the CERN Proton Synchrotron required major hardware changes for the nearly 50-year old accelerator. The installation of new Pulse Forming Networks (PFN) and refurbished kicker magnets for the extraction, new sextupole and octupole magnets, new power converters, together with an in-depth review of the machine aperture leading to the design of new vacuum chambers was required. As a result, a heavy programme of interventions had to be scheduled during the winter shut-down 2007-8. The newly installed hardware and its commissioning is presented and discussed in details

Allard, D

Barnes, M

Berrig, O

Beuret, A

Bodart, D

Bourquin, P

Brown, R

Caccioppoli, M

Caspers, Friedhelm

Cravero, JM

De Almeida Martins, C

Dehavay, C

Dobers, T

Dupont, M

Favre, G

Fowler, T

Franchi, A

Gilardoni, S

Giovannozzi, M

Hansen, J

Karppinen, M

Lacroix, C

Mahner, E

Mertens, V

Monteiro, JL

Noulibos, R

Page, E

Principe, R

Rossi, C

Sermeus, L

Steerenberg, R

Vandoni, G

Villiger, G

Zickler, T

CERN Document Server

INSTALLATION AND HARDWARE COMMISSIONING OF THEMULTI-TURN EXTRACTION AT THE CERN PROTON SYNCHROTRONS. S. Gilardoni, D. Allard, M. J. Barnes, O. E. Berrig, A. Beuret, D. Bodart, P. Bourquin,R. Brown, M. Caccioppoli, F. Caspers, J.-M. Cravero, C. De Almeida Martins, C. Dehavay, T. Dobers,M. Dupont, G. Favre, T. Fowler, A. Franchi, M. Giovannozzi, J. Hansen, M. Karppinen, C. Lacroix,E. Mahner, V. Mertens, J.- L. Monteiro, R. Noulibos, E. Page, R. Principe, C. Rossi, L. Sermeus,R. R. Steerenberg, G. Vandoni, G. Villiger, Th. Zickler, CERN, Geneva, SwitzerlandAbstractThe implementation of the new Multi-Turn Extraction(MTE) at the CERN Proton Synchrotron required majorhardware changes for the nearly 50-year old accelerator.The installation of new Pulse Forming Networks (PFN)and refurbished kicker magnets for the extraction, new sex-tupole and octupole magnets, new power converters, to-gether with an in-depth review of the machine apertureleading to the design of new vacuum chambers was re-quired. As a result, a heavy programme of interventionshad to be scheduled during the winter shut-down 2007-8.The newly installed hardware and its commissioning is pre-sented and discussed in details.INTRODUCTIONEarly in 2001, a new scheme was proposed to extractbeam from the CERN Proton Synchrotron (PS) [1]. Themethod consists of splitting the beam in the horizontalplane in stable islands, creating five beamlets and extract-ing them over five consecutive turns. The capture is reali-sed by crossing the 1/4 horizontal resonance excited by aseries of sextupoles and octupoles. Once the beamlet se-paration is sufficient, the beam is pushed by a slow bumptowards the extraction septum blade. Fast kickers then acton five turns to extract each of the beamlets. The commis-sioning of the new extraction is reported in [3].An important hardware renovation campaign was done inthe PS to implement this new type of extraction. The PS iscomposed of 100 combined function dipoles (Main Units,MU) interleaved by 100 Straight Sections (SS) in whichauxiliary magnets are installed. The control of the lin-ear and non-linear working point is performed by power-ing four extra coils mounted on top of each MU poles andone supplementary winding of the main coil. The auxil-iary magnets used to create extraction bumps or to excitehigh order resonances are installed in the SS, typically inodd numbered SS where the horizontal betatron functionreaches the maximum.The implementation of MTE [2], described in the followingsections, required different interventions: a) design, pro-duction and installation of new octupoles; b) constructionof new power converters for the new extraction bump; c)enlargment of the extraction region aperture; d) construc-tion of new extraction kickers and their Pulse Forming Net-work (PFN). A large fraction of the PS circumference has0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100Magnet Unit or Straight SectionKicker installationAuxiliary Magnet install/removalMU vacuum chamber inter.SS vacuum chamber inter.Figure 1: Summary of the hardware interventions relatedto the MTE installation.been affected by those interventions, summarized in Fig. 1,and they were done over two consecutive winter shutdownperiods, the peak of activities occurring during 2007-2008.NEW NON-LINEAR MAGNETSThe creation of stable islands is possible by setting cor-rectly the linear and non-linear chromaticity, i.e. by power-ing the extra circuits of the main magnets mentioned beforeplus four sextupoles and two octupoles specific for MTEoperation. Whereas the four sextupoles were already exist-ing, three new octupoles, two operative magnets plus onespare, have been constructed and tested. The octupolar gra-dient difference between the three magnets is well belowthe 0.3%, as shown in Fig. 2, where also the octupolar gra-dients versus current are presented. The magnet saturationoccurs at about 500 A, whereas the operative currents isbelow 200 A, depending on the choice of the second or-der chromaticity. Two octupoles have been installed, onein SS39 and the other SS55, in a tightly packed installationtogether with two sextupoles, shown in Fig. 3.OPTIMISATION OF PS APERTUREThe standard PS vacuum pipe is elliptical with a ver-tical maximum aperture of 70 mm and horizontal of 140mm. The mechanical aperture is quite variable around theProceedings of PAC09, Vancouver, BC, Canada TU6RFP023Accelerator Technology - SubsystemsT12 - Beam Injection/Extraction and Transport 1581100 200 300 400 500 600 700Current (A)01000200030004000500060007000 d^3B/dr^3dL (Tm/m^3)0.000.100.200.300.400.50Spread %MO #1MO #2MO #3LinearSpreadFigure 2: Measured gradient of the three octupoles avail-able for installation.Figure 3: Picture of the SS39. The two yellow sextupolesare interleaved by the violet octupole.machine circumference, as presented in Fig. 4 that com-pares the horizontal aperture before and after the interven-tions for MTE. The horizontal aperture is enlarged with re-spect to the standard one in correspondance of: a) the ex-traction region to the Super Proton Synchrotron (SPS), be-tween SS14 and SS22; b) the ion injection region, betweenSS25 and SS30; c) the proton injection region, betweenSS40 and SS45; d) the slow extraction region, betweenSS57 and SS65. The study of the MTE island trajectories atextraction proved that the existing PS mechanical apertureavailable in the extraction region was critical, in particu-lar in the horizontal plane in correspondance of the MUs14,15,16,18,19 and the SS in between. The beamlets arepushed radially at the limit of the aperture at the maximumof the slow extraction bump and are pushed even furtherduring the last five turns. A redesign of the area, with theresult shown in Fig. 5 together with the beamlet envelopes,turned out to be necessary during extraction. Whereas forMU 18 and 19 a standard enlarged vacuum chamber couldbe installed, for the other units new INCONEL chambershave been designed and built as for the SS. Fig. 6 shows thedesign of the new extraction vacuum chamber of the MU16compared to the old one. The Y-shaped vacuum chamberhosts the circulating beam and the first part of the extrac-tion line. Other beams produced by the PS could profit bythe enlargement of the aperture, in particular on the MU16where the enlarged part has been prolonged basically upto the half of the MU, before the bifurcation towards theextraction line.100 200 300 400 500 60010050501001 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100mmm100 200 300 400 500 600m1005050100mm1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100Figure 4: PS horizontal mechanical aperture in 2006, be-fore the MTE installation (top), and in 2008, after the MTErenovation (bottom). The MU number (from 1 to 100) isindicated by the boxes every 5 MUs.Figure 5: Horizontal PS aperture in the extraction regionafter the MTE-related work together with the five beamletenvelopes during the first extraction turn. The MU numberis indicated on top of the picture. The extraction septum isinstalled just upstream of MU16.Figure 6: Old (top) and new (bottom) MU16 extraction va-cuum chamber design.SLOW BUMP POWER CONVERTERSExisting PS extractions used four dipole magnets con-nected in two parallel circuits of two magnets fed by aTU6RFP023 Proceedings of PAC09, Vancouver, BC, Canada1582Accelerator Technology - SubsystemsT12 - Beam Injection/Extraction and Transportunique converter to create a slow extraction bump 15 mslong. The trajectories of the beamlets at extraction requireinstead 6 bumpers individually powered to optimise thebump shape and maximize the aperture. Existing powerconverter capacitor banks had been re-arranged and theelectronic crate regulation cards have to be adjusted ac-cordingly to generate a shorter 12 ms long pulse. Four newDCCTs had to be ordered on account of the increase of thedischarge current. Furthermore the power converter of oneof dipoles must allow polarity reversal of its output current.A new system, with thyristors and appropriate electroniccontrol, had to be implemented on this converter and itsspare device.NEW MTE KICKERSThe extraction of the beamlet is done by firing fast kick-ers during the last five turns (1 PS turn is ≈2.1 µs long atextraction), creating a closed fast bump around the extrac-tion septum SMH16. In total, five kickers (KFA) are usedto extract the beam: those located in SS13, SS21 and SS9,deflect the beam constantly for five turns, whereas thosein SS4 and SS71 are used in addition to the others to ex-tract the remaining central island during the last turn. Theinstallation layout of the kickers in the ring is shown inFig. 7, together with the two supplementary fast dipoles,the DFA242 and 243 installed in the PS-SPS transfer lineused to correct the extracted beamlet trajectories, as de-scribed in [4]. The extracted beamlets, in fact, have differ-ent contours and centroids due to the closure of the extrac-tion bumps only for the central core. This in turn generatesslice-dependent horizontal oscillations in the transfer lineand, if not corrected, they would induce transverse oscilla-tions in the SPS with consequent emittance blow up afterlamentation. The optimisation of this correction lead to thedisplacement of the original DFA243 22 m downstream inthe PS-SPS transfer line.The KFA13, KFA21 and KFA4 have been implementedFigure 7: Kickers used for MTE extraction.by re-using and modifying existing hardware from thelepton operation, no more in use now, and from the oldmulti-pulsing extraction system. The main modificationsconsisted in the installation of transition contacts piecesbetween magnets and their vacuum tank to reduce theimpedance seen by the beam. High voltage connectionboxes filled with SF6, vacuum feedthroughs and high cur-rent contact fingers have also been upgraded to cope withthe more severe pulsed power conditions. The 12 µs pulsesexciting KFA13 and 21 are generated by new 80 kV pulseforming networks operated in short-circuit mode. The ren-ovation included also new vacuum equipments like new ionpumps, Ti sublimation pumps and gauges. The KFA71-KFA79 system is used for the PS fast extraction, with theKFA79 used for MTE as backup in case of unavailability ofKFA71 module(s). KFA9 is an existing magnet, presentlyused for the continuous transfer scheme, which will be re-used in the MTE scheme. The coil of the original two turnDFA242 magnet has been reduced to one turn to improvemagnet rise time. Both DFA magnets are equipped withnew connection boxes featuring a series inductor adjustedto have magnet rise time close to 350 ns and are now identi-cal. The parameters of the kickers are summarized in Table1. The kicker rise time is a fundamental parameter to re-duce beam losses at extraction. As the beam is debunchedat top energy, during the kicker rise time a fraction of thebeam intercepts the extraction septum. The losses relatedto this process are estimated to about 1-2% of the circu-lating intensity. These values have been confirmed duringthe MTE commissioning and, together with measurementdirectly on the kicker, verifies the expected rise times.Table 1: Required Kicker Strength and Rise Time Values(10% and 90%). The strengths are computed for a beamrigidity of 46.68 Tm.Turn BFA9 KFA13 KFA21 KFA71 KFA41 -0.114 1.839 1.887 0 02 -0.114 1.839 1.887 0 03 -0.114 1.839 1.887 0 04 -0.114 1.839 1.887 0 05 -0.114 1.839 1.887 -1.834 -0.400Rise time 340 350 350 70 80Max kV 35 80 80 9x80 80ACKNOWLEDGMENTSThe members of the MTE project are grateful to theCERN various groups participating in the installation ofthe MTE related hardware, for their precious support andefficiency.REFERENCES[1] R. Cappi et al., Phys. Rev. Lett. 88 (2002) 104801.[2] M. Giovannozzi (editor) et al., “The CERN PS multi-turn ex-traction based on beam splitting in stable islands of transversephase space”, Design Report, CERN2006011 .[3] S. Gilardoni et al., TU6RFP022, these proceedings.[4] A. Franchi et al.,“Trajectory Correction in the Transfer LineTT2-TT10 for the Continuous Transfer (CT)”, CERN-AB-Note-2008-005.Proceedings of PAC09, Vancouver, BC, Canada TU6RFP023Accelerator Technology - SubsystemsT12 - Beam Injection/Extraction and Transport 1583

Installation and Hardware commissioning of the Multi-Turn extraction at the CERN proton synchrotron

Installation and Hardware commissioning of the Multi-Turn extraction at the CERN proton synchrotron

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