The MAX IV facility presently under construction will include two storage rings for the production of synchrotron radiation. The 3 GeV ring will house insertion devices for the production of x-rays while the 1.5 GeV ring will serve UV and IR users. Both rings will be operated at a constant 500 mA of stored current with top-up shots supplied by the 3.5 GeV MAX IV linac acting as a full-energy injector. So far, injection into both storage rings has been designed us- ing a conventional approach: a closed four-kicker injection bump brings the stored beam to the septum blade where the injected bunches are captured in a single turn. Recently, studies have been carried out to investigate the feasibility of using a pulsed multipole for injection into the storage rings. Pulsed multipole injection does not require an injec- tion bump and has the potential to make top-up injection transparent to users. This paper reports on these studies and summarizes requirements for the pulsed sextupole magnet to be installed for injection into the MAX IV storage rings

Leemann, Simon

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LUND UNIVERSITYPO Box 117221 00 Lund+46 46-222 00 00Pulsed Multipole Injection for the MAX IV Storage RingsLeemann, SimonPublished in:PAC 2011 Proceedings2011Link to publicationCitation for published version (APA):Leemann, S. (2011). Pulsed Multipole Injection for the MAX IV Storage Rings. In PAC 2011 Proceedings (pp.2522-2524). IEEE - Institute of Electrical and Electronics Engineers Inc..http://accelconf.web.cern.ch/AccelConf/PAC2011/papers/thp214.pdfTotal number of authors:1General rightsUnless other specific re-use rights are stated the following general rights apply:Copyright and moral rights for the publications made accessible in the public portal are retained by the authorsand/or other copyright owners and it is a condition of accessing publications that users recognise and abide by thelegal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private studyor research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portalRead more about Creative commons licenses: https://creativecommons.org/licenses/Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will removeaccess to the work immediately and investigate your claim.PULSED MULTIPOLE INJECTION FOR THE MAX IV STORAGE RINGSS.C. Leemann∗, MAX-lab, Lund University, SE-22100 Lund, SwedenAbstractThe MAX IV facility presently under construction willinclude two storage rings for the production of synchrotronradiation. The 3 GeV ring will house insertion devices forthe production of x-rays while the 1.5 GeV ring will serveUV and IR users. Both rings will be operated at a constant500 mA of stored current with top-up shots supplied by the3.5 GeV MAX IV linac acting as a full-energy injector. Sofar, injection into both storage rings has been designed us-ing a conventional approach: a closed four-kicker injectionbump brings the stored beam to the septum blade where theinjected bunches are captured in a single turn. Recently,studies have been carried out to investigate the feasibilityof using a pulsed multipole for injection into the storagerings. Pulsed multipole injection does not require an injec-tion bump and has the potential to make top-up injectiontransparent to users. This paper reports on these studies andsummarizes requirements for the pulsed sextupole magnetto be installed for injection into the MAX IV storage rings.INTRODUCTIONBoth the 3 GeV [1] and the 1.5 GeV storage rings [2] ofthe MAX IV facility [3] will operate at 500 mA stored cur-rent in top-up mode. The 3.5 GeV MAX IV linac [4] willbe used as a full-energy injector delivering low-emittanceshots with 300 pC at up to 10 Hz to either ring via twotransfer lines. At the end of the transfer lines, a verticalLambertson septum bends the injected bunch into the hori-zontal plane. The septum blade is at −10 mm (−15.5 mm)from the position of the unperturbed stored beam in the3 GeV ring (1.5 GeV ring). The horizontal acceptance ofthe storage ring is 10.6 mm mrad (40.5 mm mrad). Pre-viously, a local four-kicker injection bump (FKIB) wasforeseen in order to bring the stored beam to −8 mm(−12 mm), that is, within 5.5 mm (7 mm) of the injectedbunch (cf. Fig. 1). After the injection bump, the injectedbunch is within the acceptance of the storage ring and pro-ceeds to damp down while it oscillates around the storedbeam. With a transverse damping time of roughly 15 ms(6 ms), there is ample time for the injected bunch to dampdown before the next shot is injected. Because of the hori-zontal tune of 42.20 (11.22), the injection bump needs to beclosed within less than 4–5 revolution periods, i.e. 8.8 μs(1.5 μs).Since continuous top-up injection is foreseen, an impor-tant criterium for the choice of injection scheme is that top-up shots should be as transparent to users as possible. In∗ simon.leemann@maxlab.lu.seMatching CellSeptumMatching CellShort Str. Long Straight Short Str.K4K3K2K1xySeptum Blade5º SeptumInjection Bump–8 mmInjected BunchStored Beam5.5 mmFigure 1: Conventional injection with a local bump in theMAX IV 3 GeV storage ring. Injection is displayed as seenfrom above (top) and in the transverse plane (bottom).light of this aspect, the conventional FKIB scheme has sev-eral disadvantages:• Four dipole kickers and their pulsers need to be per-fectly matched, synchronized, and aligned so thebump reaches its design amplitude and is properlyclosed.• If the local injection bump is not fully closed, a coher-ent betatron oscillation of the stored beam is excited.This leads to fluctuations of the electron beam positionand intensity in the insertion device (ID) thus degrad-ing the photon beam at the experiments (the positionalstability requirement for the electron beam in the userstraights of the 3 GeV ring is 200 nm).• Much space is required to house four strong dipolekickers and the septum. If more space is required thanavailable in the injection straight, injection elementsmay take up space otherwise reserved for IDs.• If sextupoles and/or octupoles are contained withinthe injection bump, the bump cannot be perfectlyclosed for all particles within the stored beam.The first two points underline the complexity introducedby a FKIB. Although this injection scheme is commonin third generation light sources, operational experienceshows that despite vigorous correction and optimizationefforts, top-up injection with a FKIB cannot be made en-tirely transparent to users [5]. As stability criteria becometougher in newer storage ring designs, this method of in-jection becomes less favorable. Therefore, several labshave started investigating alternative injection schemes,e.g. [6, 7, 8, 9, 10].For the storage rings in the MAX IV facility, especiallythe two last points present a problem. In the 3 GeV ring,THP214 Proceedings of 2011 Particle Accelerator Conference, New York, NY, USA2522Copyrightc ○2011byPAC’11OC/IEEE—ccCreativeCommonsAttribution3.0(CCBY3.0)Light Sources and FELsTech 12: Injection, Extraction, and Transportstrong sextupoles and octupoles are used to optimize chro-matic and amplitude-dependent tune shifts [11]. Therefore,nonlinear behavior for particles at large amplitudes (such asthe injected bunch) is very pronounced (cf. Fig. 3).In the 1.5 GeV ring there is only a single 3.5 m longstraight between each of the 12 achromats. Because ofthe space required for all elements in the FKIB, the bumpwould have to span at least two achromats (containingstrong sextupoles and significant dispersion). In addition,the length available for installation of IDs in the upstreamand downstream straights is limited by two of the four thekickers. Therefore, alternative injection schemes for theMAX IV storage rings are being investigated. A promisingcandidate is pulsed multipole injection (PMI) where a sin-gle multipole magnet is used to capture injected buncheswithout perturbing the stored beam.PULSED MULTIPOLE INJECTIONIn PMI capture is achieved without bumping the orbit ofthe stored beam. Instead, the injected bunch is kicked intothe storage ring acceptance by a pulsed multipole magnet.Since the stored beam passes the multipole magnet throughthe magnetic center, it sees approximately zero field. Theonly synchronization required is between the pulser and thepassage of the injected bunch. Alignment also becomeseasier than in conventional FKIB: the stored beam has topass the magnetic center of only a single pulsed magnet.This can be achieved either by the orbit correction systemor beam-based alignment of the pulsed magnet. The pulsecan last up to several revolution periods depending on thefractional tune. In most cases the exact pulse shape is notcrucial as long as fall time is sufficiently fast. Since besidesthe septum, only a single magnet is required for capture,PMI requires substantially less space than a conventionalFKIB scheme.The most basic setup uses a pulsed quadrupole magnet(PQM). Such an injection scheme has been successfully de-signed and commissioned at the PF-AR at KEK [6]. How-ever, there are advantages to using higher-order multipolemagnets, for example a pulsed sextupole magnet (PSM).Around the magnet center, the PSM field is symmetric andflat so that stored beam particles receive a much lower kickfrom the PSM compared to the PQM. In fact, since the idealmagnet for PMI has a large field component at the ampli-tude of the injected bunch and zero field elsewhere, evenhigher-order multipoles or irregular multipole magnets canbe considered [5].Injection with a PSM was demonstrated recently at thePF at KEK [10]. First experience with PSM top-up injec-tion has been very positive with unprecedented levels ofbeam stability observed during injection [12]. The MAXIV facility will use PSM injection in both storage rings.Its feasibility has been demonstrated and it is regarded asa reasonable compromise between expected performanceand required development effort. In fact, the MAX IV stor-age rings will be the first light sources designed from thestart to use PSM injection. A conventional FKIB will notbe implemented at all.PULSED SEXTUPOLE INJECTION FORTHE MAX IV STORAGE RINGSStarting with the coordinates of the injected bunch at theinjection point (IP), i.e. at the end of the septum, and tak-ing into account the storage ring’s acceptance, an optimumlocation for a PSM can be derived. Assuming linear be-tatron motion, a location within available drift spaces canbe chosen where the minimum injection invariant using aPSM of minimum strength can be achieved [10]. In gen-eral however, betatron motion is nonlinear (especially forthe large amplitudes of the injected bunch) and the actualPSM injection scheme has to be derived from tracking.3 GeV Storage Ring InjectionAt the IP in the 3 GeV ring, the injected bunch is atxinj = −13.5 mm. The PSM is at the end of the sec-ond long straight. With b3l = 54 m−2 the PSM kicksthe injected bunch to the minimum injection invariant of2.3 mm mrad (cf. Fig. 2), well within the storage ring ac-ceptance and substantially below what was achieved usinga conventional FKIB scheme.-15-10-5 0 5 10 15 0  10  20  30  40  50  60  70x [mm]s [m]PSMPSM onPSM offFigure 2: Tracy-3 tracking results for injection and capturewith the PSM in the 3 GeV ring (only first three achromatsshown).In order to relax pulser requirements (and potentiallyalso PSM strength) it is of interest to investigate multi-turnPSM injection, where the PSM is excited by a half-sinepulse with a base length longer than two revolution peri-ods so the injected bunch sees the PSM kick on its first andsecond passage. An example is shown in Fig. 3 where amaximum PSM strength of only b3l = 27.5 m−2 is deliv-ered at the first passage. At the second passage the avail-able strength is reduced by a factor sin(3π/4). In this way,the base length of the half-sine PSM excitation can be in-creased to 7 μs (four times the revolution period). Despiteincreased pulse length and reduced PSM strength, a finalinjection invariant of 3.1 mm mrad is achieved.Proceedings of 2011 Particle Accelerator Conference, New York, NY, USA THP214Light Sources and FELsTech 12: Injection, Extraction, and Transport 2523 Copyrightc ○2011byPAC’11OC/IEEE—ccCreativeCommonsAttribution3.0(CCBY3.0)-2-1.5-1-0.5 0 0.5 1 1.5 2-15 -10 -5  0  5  10  15x’ [mrad]x [mm]Acceptance1st turn2nd turn3rd4th5thFigure 3: Tracy-3 tracking results at the 3 GeV PSM (two-turn injection). The + show 100 turns without PSM kicksor aperture limitations. The × show actual coordinates ofthe injected bunch during capture.1.5 GeV Storage Ring InjectionThe injected bunch is at xinj = −19 mm at the 1.5 GeVring IP. It reaches the PSM in the third straight whereb3l = 47 m−2 kicks it down to a minimum injection in-variant of 8.8 mm mrad well within the storage ring ac-ceptance. The negligible perturbation of the stored beamby the PSM is displayed in Fig. 4. A difficulty with PSMinjection in the 1.5 GeV ring is the pulse length (the revo-lution period is only 0.32 μs). In order to facilitate pulserdesign, a two-turn injection scheme has been designed sothe required base length for the half-sine pulser excitationcan be increased to 1.3 μs. At the same b3l, the resultinginjection invariant is increased by only 3.5%. Alternatively,a reduced b3l = 32 m−2 still allows capture in two turns.-0.1-0.05 0 0.05 0.1 0.15-0.6 -0.4 -0.2  0  0.2  0.4  0.6x’ [mrad]x [mm]Before 1st turnAfter 5 turnsFigure 4: DIMAD tracking results at the 1.5 GeV IP show-ing the effect of the PSM in single-turn injection mode onthe stored beam (εx = 6 nm rad, σδ = 7.5 × 10−4, Gaus-sian distribution with cut-off at 3σ).SUMMARY AND OUTLOOKInjection schemes using PSMs have been designed forboth storage rings in the MAX IV facility. Preliminarymagnet and ceramic chamber designs have been completedand specifications for the pulsers have been compiled. Therequired field strengths and pulse durations are consideredfeasible so that a call for bids is being prepared.Studies have been carried out to investigate sensitivityto optics mismatches and misalignments. The MAX IVlinac injects low-emittance bunches with low energy spreadwhich can easily be fitted into the storage ring acceptancedespite optics mismatches at injection, thus rendering a ro-bust injection with high efficiency. Tracking studies revealthat the effect of the PSM on the stored beam is indeed verylow, however exact (beam-based) alignment of the PSMwill be necessary to reduce perturbations to the stored beamto the very low levels required for fully transparent top-upinjection.ACKNOWLEDGMENTSThe author would like to express his gratitude toLes Dallin (CLS) for many interesting discussions andcross-checking of tracking results.REFERENCES[1] S.C. Leemann et al., Phys. Rev. ST Accel. Beams, 12,120701 (2009).[2] S.C. Leemann et al., “Status of the MAX IV Storage Rings”,IPAC10, Kyoto, Japan, May 2010, WEPEA058, p. 2618.[3] M. Eriksson et al., “Challenge of MAX IV Towards a Mul-tipurpose Highly Brilliant Light Source”, this conference,TUOBS4.[4] S. Thorin et al., “Design of the MAX IV Ring Injector andSPF/FEL Driver”, this conference, THP178.[5] P. Kuske, “Novel Injection Schemes”, presentation at theTop-Up Workshop, Melbourne, Australia, October 2009.[6] K. Harada et al., Phys. Rev. ST Accel. Beams 10, 123501,(2007).[7] P. Kuske et al., “Preparations of BESSY for Top-Up Op-eration”, EPAC08, Genoa, Italy, June 2008, WEPC037,p. 2067.[8] T. Shaftan et al., “Alternative Designs of the NSLS-II In-jection Straight Section”, PAC09, Vancouver, BC, Canada,May 2009, TU5RFP012, p. 1114.[9] C. Sun et al., “Pulsed Multipole Injection for the ALS Up-grade”, IPAC10, Kyoto, Japan, May 2010, WEPEA068,p. 2642.[10] H. Takaki et al., Phys. Rev. ST Accel. Beams 13, 020705,(2010).[11] S.C. Leemann, A. Streun, Phys. Rev. ST Accel. Beams, 14,030701 (2011).[12] H. Takaki et al., “Stored Beam Stability During PulsedSextupole Injection at the Photon Factory Storage Ring”,PAC09, Vancouver, BC, Canada, May 2009, TU6RFP045,p. 1647.THP214 Proceedings of 2011 Particle Accelerator Conference, New York, NY, USA2524Copyrightc ○2011byPAC’11OC/IEEE—ccCreativeCommonsAttribution3.0(CCBY3.0)Light Sources and FELsTech 12: Injection, Extraction, and Transport

Pulsed Multipole Injection for the MAX IV Storage Rings

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Pulsed Multipole Injection for the MAX IV Storage Rings

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