In the booster synchrotron of the Karlsruhe Research Accelerator (KARA), the beam is injected from the microtron at 53 MeV and ramped up to 500 MeV. Though the injected beam current from the microtron to the booster seems good, the injection efficiency into the booster is currently low due to various effects. Consequently, an upgrade of the whole beam diagnostics system is taking place in the booster, in order to improve the injection efficiency through understanding the loss mechanisms and the behavior of bunches. Among these diagnostics tools are beam loss monitors, a transverse profile monitor and a longitudinal profile monitor. In this paper, we will describe the setups used for bunch profile measurements in both transverse and longitudinal planes and report on first data analysis results

Blomley, E.

Bründermann, E.

Huttel, E.

Khechen, D. El

Mochihashi, A.

Müller, A-S.

Noll, M.-D.

Ruprecht, R.

Schreiber, P.

Schuh, M.

Steinmann, J. L.

Widmann, C.

English

KITopen

TRANSVERSE AND LONGITUDINAL PROFILE MEASUREMENTSAT THE KARA BOOSTER SYNCHROTROND. El Khechen∗, E. Blomley, E. Bründermann, E. Huttel, A. Mochihashi, M.-D. Noll, R. Ruprecht,M. Schuh, P. Schreiber, J.L. Steinmann, C. Widmann and A.-S. Müller,Karlsruhe Institute of Technology, Karlsruhe, GermanyAbstractIn the booster synchrotron of the Karlsruhe Research Ac-celerator (KARA), the beam is injected from the microtronat 53 MeV and ramped up to 500 MeV. Though the injectedbeam current from the microtron to the booster seems good,the injection efficiency into the booster is currently low dueto various effects. Consequently, an upgrade of the wholebeam diagnostics system is taking place in the booster, in or-der to improve the injection efficiency through understandingthe loss mechanisms and the behavior of bunches. Amongthese diagnostics tools are beam loss monitors, a transverseprofile monitor and a longitudinal profile monitor. In thispaper, we will describe the setups used for bunch profilemeasurements in both transverse and longitudinal planesand report on first data analysis results.INTRODUCTIONThe injection complex of KARA [1](see Fig. 1) consistsof a thermal DC electron gun (CW and pulsed mode), whichgenerates a 90 keV electron beam, a racetrack microtron,which increases the beam energy to 53 MeV, and an injec-tion line, which transports the beam to the booster where itis injected off-axis on a multi-turn scheme. The booster thenramps up the beam energy from 53 MeV up to 500 MeV ina cycle of 1 s. The booster parameters are summarized inTable 1. Recently, an upgrade of the booster’s diagnosticssystem took place. This includes the installation of a newbeam position monitor (BPM) readout electronics based onLibera Spark [2], a Dimtel Bunch-By-Bunch feedback sys-tem [3] in both horizontal and vertical planes, four Liberabeam loss scintillators [2] near the injection and extractionsepta, a CCD camera for transverse profile measurementsand the preparation of infrastructure and equipment for lon-gitudinal profile measurements. Moreover, various measure-ments and beam diagnostics tests are planned in the boosterto predict the expected behaviour of some diagnostic toolsin cSTART [4], a KIT project. In the following, we willdescribe the experimental setups for transverse and longi-tudinal profile measurements and report on recent results.TRANSVERSE PROFILEMEASUREMENTSTwo synchrotron light ports (vacuumed) exist in thebooster on two bending magnets, one after the injectionpoint and one after the extraction point. For our transverse∗ dima.khechen@kit.edu0 1 2 mExtraktionInjektionMikrotronBooster53 MeV - 500 MeVFigure 1: The schematic of the injection complex of KARAstorage ring. Courtesy of U. Herberger, KIT.Table 1: Important Parameters of the KARA Booster Syn-chrotronParameter KARA boosterFilling pattern CW or single bunchEnergy 53 MeV to 500 MeVCircumference 26.4 mRevolution frequency 11.36 MHzRF frequency 499.74 MHzHarmonic number 44Beam current 5 mAprofile measurements we used the optical window near tothe injection point, on which we mounted directly a prismand a CCD camera at 90° (see Fig. 2). The CCD camerais powered with a power-over-ethernet (PoE) scheme andsynchronized to the injection trigger. We used two types offilters, a neutral-density (ND) filter and a broadband filter(model: FB500-40 [5]) for the transmission of green lightin the range of 480 nm to 530 nm. It is worth mentioningthat these filters needed to be removed when taking dataat the fixed energy of 53 MeV, as due to the lower criticalfrequency of the SR radiation at injection energy the inten-sity of the radiation in the spectral range of the camera wastoo low with the filters. Furthermore, to avoid saturation13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT027MOPOPT027ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI304MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and Instrumentationin the camera, we set appropriate exposure times for differ-ent measurement conditions (dominantly beam energy andbeam current). We assume that the source of the synchrotronlight is the center of the bending magnet (740 mm from theaperture of the port/prism) and the distance from the prismto the camera is 83 mm. The calibration of the camera tookplace with a 5 mm square paper, where we placed the paperat 1.2 m (740 mm + 83 mm) from the camera and convertedthe pixels to mm. The calibration curve is presented in Fig. 3and the calibration value is given by the slope of the fit whichis 21 pixel/mm in this case.Figure 2: The experimental setup of the CCD camera in thebooster.Figure 3: The calibration plot of the CCD camera´s lens.To have an idea of the expected beam size values in thebooster, we estimated the beam sizes at 500 MeV (𝜎𝑥 =0.63 mm and 𝜎𝑦 = 0.12 mm) from the design values ofthe emittances (𝜖𝑥=150 nm · rad and 𝜖𝑦=2.3 nm · rad [1])and the 𝛽-functions at the center of the bending magnet(𝛽𝑥=2.7 m and 𝛽𝑦= 7.2 m). Measurements were taken be-fore the latest accelerator shutdown in May. The results areshown in Fig. 4. The double core image seen just after in-jection at 53 MeV is mainly due to the fact of injecting on amulti-turn scheme with a kicker on the opposite side of theinjection point. During ramping the two cores merge to asingle core and we can clearly notice the beam size shrinkingin both planes. Results of the beam size measurements andfits are summarized in Table 2. Measurements at differenttime stamps and thus different beam energies were achievedby delaying the trigger on the CCD camera by a few ms to afew hundred ms. The beam energies are derived from theramping profile of the booster magnets. The data is thus in-tegrated over all bunches and over several revolution periods(the number of revolution periods depends directly on theexposure time of the camera).Figure 4: The synchrotron light image from the CCD camerain the booster before the shutdown, directly after injectionat 53 MeV (left) and at the end of the ramping at 500 MeV(right).Table 2: Measured Beam Sizes in the Booster Before theShutdown in MayBeam energy (MeV) 𝜎𝑥 (mm) 𝜎𝑦 (mm)53 2.2 0.85100 2.1 0.93150 1.75 0.95200 1.43 0.93250 1.18 0.8300 0.93 0.7350 0.8 0.63400 0.7 0.55450 0.68 0.48500 0.75 0.4After the shutdown, we observed a vertical blowup athigher energies in the booster (from around 350 MeV) (seeFig. 5), which is not yet understood. A few tests are plannedto investigate the origin of such a blow-up.Figure 5: The synchrotron light image from the CCD cam-era at different beam energies after the shutdown, where avertical blowup appears starting at about 350 MeV.This observation already highlights the importance ofperforming transverse profile measurements to understand13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT027MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationMOPOPT027305ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIthe beam dynamics in the booster as a step to improve theinjection efficiency.LONGITUDINAL PROFILEMEASUREMENTSTo provide an insight on the longitudinal profile mea-surements in the booster, we combined the signal from thefour pickups of a button BPM using a power combinerand we transported the signal to an experimental hutchoutside of the booster radiation shielding wall via a 35 mcoaxial cable. On the way, the sum signal is amplified withthree pre-amplifiers of around 14 dB amplification each andreadout with an oscilloscope. We triggered the oscilloscopeto acquire one data-set every 231 turns of the booster forone injection resulting in about 30 000 measurement pointsper cycle. In each data set we acquired 200 ns of datacorresponding to one and a half booster turns. The injectedbeam from the microtron to the booster is expected to havethe temporal length in the order of 1.6 µs [1]. Given themismatch in the RF frequencies between the microtron(3 GHz) and the booster (500 MHz), a re-bunching of thelong beam arriving from the microtron takes place alongwith significant beam losses. After re-bunching is finishedand by the start of ramping in the booster, the bunchlength is expected to get shorter with energy. A plot ofthe measured bunch shape at 0.15 s, 0.5 s and 0.7 s afterinjection is presented in Fig. 6, where the bunch is verybroad (with a non-defined shape) in the beginning of thebooster cycle and gets more defined and shorter until theend of the ramping cycle. To get the bunch length overthe energy ramp, we fitted all the bunches of each dataset with a Gaussian fit individually. We then calculatedthe mean and standard deviation (std) of the 2 · 𝜎 of theGaussian fit, i.e. the rms bunch length, over all the bunchesin the data set. Figure 7 shows a moving average over themean values of the bunch lengths and their std as a measurefor the statistical error (± one std) over a window of 1 ms(corresponding to 50 data sets).−1 −0.5 0 0.5 1−0.100.000.10Time (ns)Voltage(V)t=0.15 s t=0.5 s t=0.7 sFigure 6: The bunch shape at three different time delaysafter the injection in the booster. Note: the signals have anegative polarity.At the KARA storage ring (500 MeV to 2.5 GeV), we per-form longitudinal profile measurements with a streak cam-era [6] placed at the optical light port. We plan to use thesame streak camera for longitudinal profile measurements100 200 300 400 50000.51Electron Energy (MeV)BunchLength(ns)Figure 7: The fitted bunch length in the booster as a functionof energy (blue line) along with errors (light blue band).in the booster by transporting the synchrotron light fromthe booster to the optical light port via fiber optics, whilea fiber optics adapter for the streak camera will be used. Aphoto-diode with a digitizer allows to measure the longitu-dinal profile, which will be used too. This will enable usto compare different methods of profile measurements andcheck the reliability of each at different bunch and boosterconditions.SUMMARYA substantial effort has been put to upgrade the diagnosticssystem of KARA´s booster synchrotron aiming to improvethe bunch conditions and the injection efficiency. Few pre-liminary tests and measurements of the transverse profileusing a setup with a CCD camera, and of the longitudinalprofile through reading the sum signal from a button BPMwith a real-time oscilloscope, have been achieved. Expectedbehaviours of the transverse and longitudinal profiles as afunction of the beam energy have been observed. However,a vertical blowup at higher energies in the booster after theshutdown in May was seen, which is still not clear and underinvestigation. Such measurements are very useful to clearlyunderstand the beam dynamics in the booster as a step toimprove it. For this reason, the combined view from theBPMs, the profile and the tune measurements along withthe BBB feedback system can bring improvements of thebooster synchrotron operation.REFERENCES[1] L. Præstegaard, “Investigation of the ANKA Injector: Lattice,Beam Properties, and Performance,” Ph.D. thesis, DanfysikA/S and University of Aarhus, Denmark, 2001.[2] i-Tech Instrumentation, https://www.i-tech.si/.[3] Dimtel, Inc., https://www.dimtel.com/.[4] D. E. Khechen et al., “Beam Diagnostics for the StorageRing of the cSTART Project at KIT,” presented at IPAC’22,Bangkok, Thailand, Jun. 2022, paper MOPOPT026, this con-ference.[5] Thorlabs, https://www.thorlabs.com/thorproduct.cfm?partnumber=FB500-40[6] B. Kehrer et al., “Visible Light Diagnostics at the ANKA Stor-age Ring”, in Proc. IPAC’15, Richmond, VA, USA, May 2015,pp. 866–868. doi:10.18429/JACoW-IPAC2015-MOPHA03713th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT027MOPOPT027ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI306MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and Instrumentation

Transverse and Longitudinal Profile Measurements at the KARA Booster Synchrotron

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Transverse and Longitudinal Profile Measurements at the KARA Booster Synchrotron

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