In the framework of the compact STorage ring for Accelerator Research and Technology (cSTART) project, which will be realized at Karlsruhe Institute of Technology (KIT), a Very Large Acceptance compact Storage Ring (VLA-cSR) is planned to study the injection and the storage of 50 MeV, ultra-short (sub-ps) electron bunches from a laser plasma accelerator (LPA) and the linac-based test facility FLUTE. For such a storage ring, where a single bunch with a relatively wide range of bunch charge (1 pC - 1000 pC ) and energy spread (10’4 - 10’2) will circulate at a relatively high revolution frequency (7 MHz), the choice of beam diagnostics is very delicate. In this paper, we would like to discuss several beam diagnostics options for the storage ring and to briefly report on several tests that have been or are planned to be realized in our existing facilities

Bründermann, E.

Khechen, D. El

Mochihashi, A.

Müller, A-S.

Noll, M.-D.

Papash, A. I.

Ruprecht, R.

Schreiber, P.

Schuh, M.

Steinmann, J. L.

English

KITopen

BEAM DIAGNOSTICS FOR THE STORAGE RING OF THE cSTARTPROJECT AT KITD. El Khechen∗, E. Bründermann, A. Mochihashi, M.-D Noll, A. Papash, R. Ruprecht,M. Schuh, P. Schreiber, J.L. Steinmann and A.-S. Müller,Karlsruhe Institute of Technology, Karlsruhe, GermanyAbstractIn the framework of the compact STorage ring for Accel-erator Research and Technology (cSTART) project, whichwill be realized at Karlsruhe Institute of Technology (KIT),a Very Large Acceptance compact Storage Ring (VLA-cSR)is planned to study the injection and the storage of 50 MeV,ultra-short (sub-ps) electron bunches from a laser plasma ac-celerator (LPA) and the linac-based test facility FLUTE. Forsuch a storage ring, where a single bunch with a relativelywide range of bunch charge (1 pC - 1000 pC) and energyspread (10−4 - 10−2) will circulate at a relatively high revo-lution frequency (7 MHz), the choice of beam diagnostics isvery delicate. In this paper, we would like to discuss severalbeam diagnostics options for the storage ring and to brieflyreport on several tests that have been or are planned to berealized in our existing facilities.INTRODUCTIONA lot of R&D studies nowadays are being conducted onnew ideas and technologies for future light sources. In thiscontext, KIT plans to build a large acceptance storage ringto demonstrate the injection and storage of ultra-short andLPA-like electron bunches. The research and studies on thisproject will be exploited for the development of the infras-tructure and technology for compact LPA-based future lightsources.The cSTART project (see Fig. 1) employs two different injec-tors, which will provide ultra-short bunches: the KIT photo-injector FLUTE [1] and an LPA injector [2]. The electronbunches will be transported from the two different electronsources to the storage ring at 3 m height via a transfer line[3]. The storage ring consists of four double-bend-achromat(DBA) arcs with 45° bending magnets [4], separated by fourstraight sections, amongst which two have space availablefor one RF station per section, one section will be dedicatedfor the injection and the other one for beam diagnostics. Themagnetic elements in the arc are very close to each otherand might be realised e.g. as solid blocks (adopting theMAX-IV magnetic design [5]), leaving nearly no space forbeam diagnostics in the arcs. This along with other bunchparameters, e.g. bunch charge, bunch length, repetition rate(see Table 1), bring some challenges when choosing the typeand the design of diagnostic tools in the arc, and imposehigh-standard requirements on dynamic ranges and electron-ics. In this paper, we will give an overview of the mostimportant beam diagnostics planned for the cSTART storage∗ dima.khechen@kit.eduring and highlight the challenges of some existing designs.Furthermore, we will point out few experimental tests whichare and will be taking place at our KIT facilities to test someof these diagnostics.Figure 1: A 3D artistic view of the whole cSTART project:sextupoles and octupoles and the LPA injector are not in-cluded, courtesy to J. SchäferTable 1: Important Beam Parameters of the cSTART StorageRingParameter ValueOperation mode single bunchEnergy 50 MeVRevolution frequency 7 MHzBunch charge 1 pC to 1000 pCBunch length 10 fs to 1000 fsMomentum acceptance ± 5.5%SR losses/turn < 1 eVEnergy spread 0.01% - 1%Lifetime from 100 ms to 10 sA DESCRIPTION OF THE DIFFERENTDIAGNOSTICS TOOLSIn the very first stages of running a new machine, manyunknowns will be encountered. The very important role ofthe beam diagnostics tools is to unmask the conditions ofthe machine and to help improve the operation efficiency.Within the project, we aim to perform turn-by-turn, as wellas bunch-by-bunch, measurements of the beam parameters.In this section, we will discuss mainly the most importantbeam diagnostics tools for early stage commissioning andwe will comment on the challenges of their application anddesign.13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT026MOPOPT026ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI300MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationBeam Position MonitorsWith beam position monitors (BPMs) we aim to measurethe beam position with a precision better than 100 µm tobe able to store LPA-like electron beams. Different BPMtools are available on the market but not all of them fit tothe cSTART requirements. In the following, we discuss ahybrid BPM system based on striplines and button BPMsfor the storage ring. Concerning cavity BPMs, althoughthey acquire the best position sensitivity and resolution, weexcluded them for two reasons:• They cannot fit between magnetic elements in the arc sec-tions as they need a space of at least 30 cm• Given in a storage ring, they might induce wakefield is-sues/problems and subsequently undesired bunch instabili-ties.Stripline Pickups At cSTART, the incoherent syn-chrotron radiation (SR) is negligible given the low beamenergy of about 50 MeV. This allows the possibility of inte-grating stripline pickups inside quadrupole magnets withoutcaring about heat load from SR on the strips. In this context,we plan to install at least ten striplines inside quadrupoles inthe arc sections. The length of the striplines will be equal tothat of the quadrupoles, in the order of 8 cm. The design ofthe striplines will be adopted from that of the FLASH Linacat DESY[6], where strips will be hidden between the poles ofthe quadrupoles. It is very important not to reduce the phys-ical aperture of the beam pipe in order to store as much aspossible of the large emittance beams (𝜖𝑥 = 10 nm · mrad).Furthermore, the bellows (6 cm length) at the adjacent sidesof the stripline in the FLASH design cannot be realised inthe case of cSTART given the lack of space. These bel-lows are important to align the stripline and the quadrupoleand to compensate for thermal expansion and contractionof the whole beampipe (for example during the bake-outprocedure), thus controlling the mechanical stress on thestriplines. In this case, we plan bellows somewhere else inthe arcs to control the mechanical stress on all the compo-nents relying on non-drifting stripline-quad offsets througha solid mechanical design.Button BPMs The space between the magnetic ele-ments in the arc, when exists, will be exploited for the inser-tion of bellows and vacuum components, this won´t allowthe installation of any button BPM. Two to four button BPMswill then be installed in every straight section. The buttonBPMs developed for the European XFEL [7][8] provide aresolution ≤ 50 µm at a bunch charge of 20 pC with repetitionrates of 4.5 MHz. This makes them potential candidates inaddition to their adequate mechanical design, which allowsfitting them in the very narrow space in the arcs.Current MonitorsBunch charge measurements are very important especiallyduring the commissioning phase. For this reason, we planto install fast current monitors in the straight sections. Theturbo-ICTs along with their BCM-RF readout electronics,from Bergoz Instrumentation [9], are very sensitive (opti-mised for very low bunch charge > 50 fC) with a very goodresolution down to 1% of the single bunch charge. How-ever, the existing version of the system only provides singlebunch charge measurements at repetition rates ≤ 2 MHz.This means, using the existing turbo-ICT design, we willnot be able to resolve bunch charge every turn but we canintegrate it over three turns. Further R&D on the readoutelectronics is needed to be able to resolve the bunch chargeevery turn. The time resolution of the charge measurementcan be improved by utilizing the BPM sum signals.Beam Loss SystemFor beam loss measurements, we have thought of scintilla-tion detectors as they are very sensitive. We are consideringscintillator materials connected to photomultiplier tubes(PMT) or scintillation fiber optics routed around the ring.Hereby, we need to consider their different positioning,sensitivity and feasibility.Scintillator with PMT The compact design and ade-quate dimensions of this system makes the scintillation de-tector a good candidate for a beam loss monitor at cSTART.These detectors are readout with Libera-BLM electronicunits [10] and are able to detect fast losses (injectionlosses, etc.), and slow losses (Touschek scattering, beam-gasbremsstrahlung, etc.), in addition to many other interestingand useful features (postmortem buffers, ADC mask, etc.).These scintillators with PMT will be distributed at placeswith high dispersion functions (mainly next to bending mag-nets and sextupoles) where high losses are expected. In thearc sections, the detectors could be placed inside or out-side the solid block of magnets, while being outside mightrisk the absorption of all the electromagnetic shower fromthe lost electrons in the block material (simulations are inprogress). One concern about this system is its calibration,which should be done with either a radioactive source (seeFig. 2) or an LED, and should take the cable length intoaccount.Scintillating Fiber Optics The scintillating fiber opticswere used as a multi-purpose beam diagnostics tool (beamprofile measurements [11], beam loss, etc.) and they haveproven their reliability. These fibers could be stacked inbunches to increase the sensitive area and then attached to thebeam pipe directly, covering all the ring if necessary. Thisbrings a great advantage when unpredictable losses happenin unforeseen positions (obstacles, orbit bumps, etc.). In ourcase, simulations using FLUKA are taking place to studythe beam loss signal in such fibers. After that, a decisionon the number of fibers needed along with the scintillatingmaterial and its thickness can thus be taken.13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT026MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationMOPOPT026301ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIFigure 2: A scintillator detector (without the lead shield)being calibrated with 137Ce radioactive source at the KARAstorage ringLongitudinal Profile MeasurementsSo far, we plan an electro-optical spectral decoding(EOSD) system for longitudinal profile measurements. Thiscould be a near-field EOSD [12, 13] or a far-field EOSD[14] setup, similar to what we use at the Karlsruhe ResearchAccelerator (KARA). This system so far provides temporalresolution in the range of tens of fs and R&D is going on toimprove the resolution down to few fs [15]. At the cSTARTstorage ring, both setups for longitudinal profile measure-ment could be used. The far-field setup can be placed atone of the planned optical beamlines next to the bendingmagnets in the arcs and the near-field setup will be placedin the diagnostics straight section.Screen MonitorsSeveral screen monitors will be distributed around thering, mainly in the straight sections (where space allows)close to the entrance and exit of the arc sections. Theseconsist of motorized mechanical arms holding a standardfluorescence screen, a mirror and a CCD camera. The screenmonitors help in case of difficulties storing the beam, to knowat which stage/position in the storage ring the beam is lost.In addition, they help define the beam transverse profile as astep to optimising it by tuning the magnets in the arc.EXPERIMENTAL TESTS AT THE KARAACCELERATORAn upgrade of the beam diagnostics system in the boostersynchrotron and the KARA storage ring of the KIT LightSource takes place. This will be exploited, especially inthe booster where the beam energy and revolution time iscomparable to the storage ring of the cSTART project, totest if features of the diagnostics tools are consistent withthe requirements. In this sense, development of bunch-by-bunch and turn-by-turn readout electronics for bunch chargeand beam position in the booster is taking place, using thesum signal of a button BPM and a stripline. Furthermore,a new beam loss system based on Hamamatsu scintillatorswith PMTs is being installed, calibrated and tested in KARA.Furthermore, a near-field and a far-field (at the IR2 beam-line) EOSD setup are in operation and in commissioning,respectively, at KARA. In addition, an upgrade of the boosterdiagnostics including the installation of a bunch-by-bunch(BBB) feedback system, a transverse and longitudinal beamprofile measurement setup [16], will reveal beam dynamicsin the booster that will be used to predict expected behavioursin the cSTART storage ring.SUMMARYThe choices and challenges of choosing a beam diagnos-tics system for the unique parameters of the cSTART storagering have been discussed. The design of some already ex-isting tools will be adopted. In addition, further measureswill be taken to adapt it to the requirements of the storagering in the cSTART project, e.g. for the repetition rate in theMHz range. The ongoing and planned experimental testswith the upgraded beam diagnostics systems at the KIT ac-celerators will deliver results on the expected behaviour ofbeam diagnostics tools suitable within the cSTART project.Furthermore, studies and simulations are in progress to un-derstand and decide on the beam diagnostics tool set for theKIT-project cSTART.ACKNOWLEDGMENTSWe would like to thank all members of the cSTART teamfor their support and input which helped to realise these diag-nostics choices. As well, we would like to thank A. Ferrari,A. Lyapin, D. Lipka, P. Evtushenko, M. Wendt, S. Vilcins,T. Lensch and many others for the very interactive and usefuldiscussions.REFERENCES[1] M. Nasse et al., “Flute: A versatile linac-based thz source,”Review of Scientific Instruments, vol. 84, no. 2, p. 022 705,2013, doi:10.1063/1.4790431[2] E. Panofski et al., “Developing a 50 MeV LPA-Based In-jector at ATHENA for a Compact Storage Ring,” in Proc.IPAC’21, Campinas, Brazil, May 2021, pp. 1765–1768, doi:10.18429/JACoW-IPAC2021-TUPAB163[3] B. Härer et al., “Non-Linear Features of the cSTARTProject,” in Proc. IPAC’19, Melbourne, Australia, May2019, pp. 1437–1440, doi:10.18429/JACoW-IPAC2019-TUPGW020[4] A. I. Papash et al., “Modified Lattice of the Compact Stor-age Ring in the cSTART Project at Karlsruhe Institute ofTechnology,” in Proc. IPAC’21, Campinas, Brazil, May2021, pp. 159–162, doi:10.18429/JACoW-IPAC2021-MOPAB035[5] M. Magnuson, M. Fahlman, R. Uhrberg, L. Johansson, et al.,MAX IV conceptual design report (CDR), 2006.[6] D. Noelle, G. Priebe, M. Wendt, and M. Werner, “Bpms withprecise alignment for ttf2,” in AIP Conference Proceedings,American Institute of Physics, vol. 732, 2004, pp. 166–173,doi:10.1063/1.183114413th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT026MOPOPT026ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI302MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and Instrumentation[7] D. Lipka, B. Lorbeer, D. Noelle, M. Siemens, and S. Vil-cins, “Button BPM Development for the European XFEL,” inProc. DIPAC’11, Hamburg, Germany, May 2011, pp. 83–85,https://jacow.org/DIPAC2011/papers/MOPD19.pdf[8] D. M. Treyer et al., “Design and Beam Test Results of But-ton BPMs for the European XFEL,” in Proc. IBIC’13, Ox-ford, UK, Sep. 2013, pp. 723–726, https://jacow.org/IBIC2013/papers/WEPC21.pdf[9] Bergoz instrumentations, https://www.bergoz.com/.[10] I-tech instrumentation, https://www.i-tech.si/products/libera-blm/.[11] I. O. Ruiz, J. Spanggaard, G. Tranquille, A. Bay, andG. J. Haefeli, “A Scintillating Fibre Beam Profile Monitorfor the Experimental Areas of the SPS at CERN,” in Proc.IBIC’16, Barcelona, Spain, Sep. 2016, pp. 261–264, doi:10.18429/JACoW-IBIC2016-MOPG76[12] G. Niehues et al., “Electro-Optical Diagnostics at KARAand FLUTE - Results and Prospects,” in Proc. IPAC’21,Campinas, Brazil, May 2021, pp. 927–930, doi:10.18429/JACoW-IPAC2021-MOPAB293[13] S. Funkner et al., “High throughput data streaming of in-dividual longitudinal electron bunch profiles,” Phys. Rev.Accel. Beams, vol. 22, p. 022 801, 2 2019, doi:10.1103/PhysRevAccelBeams.22.022801[14] C. Widmann et al., “Implementing Electro-Optical Diagnos-tics for Measuring the CSR Far-Field at KARA,” in Proc.IPAC’21, Campinas, Brazil, May 2021, pp. 931–934, doi:10.18429/JACoW-IPAC2021-MOPAB294[15] H. Dinter et al., “Prototype of the Improved Electro-OpticalUnit for the Bunch Arrival Time Monitors at FLASH andthe European XFEL,” in Proc. FEL’15, Daejeon, Korea,Aug. 2015, pp. 478–482, doi:10.18429/JACoW-FEL2015-TUP049[16] D. E. Khechen et al., “Transverse and longitudinal profilemeasurements at the KARA booster synchrotron,” Bangkok,Thailand, Jun. 2022, presented at IPAC’22, Bangkok, Thai-land, Jun. 2022, paper MOPOPT027, unpublished.13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT026MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationMOPOPT026303ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI

Beam Diagnostics for the Storage Ring of the cSTART Project at KIT

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Beam Diagnostics for the Storage Ring of the cSTART Project at KIT

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