As part of the R\&D for the 50 MeV ThomX Compton source project, we have
studied the effect of several beam dynamics processes on the evolution of the
beam in the ring. The processes studied include among others Compton
scattering, intrabeam scattering, coherent synchrotron radiation. We have
performed extensive simulations of a full injection/extraction cycle (400000
turns). We show how each of these processes degrades the flux of photons
produced and how a feedback system contributes to recovering most of the flux.Comment: Submitted to IPAC'14, WEPRO00

Bruni, C.

Chaikovska, I

Delerue, N.

Drebot, I.

Jacquet, M.

Loulergue, A.

Variola, A.

Zomer, F.

English

arXiv

WEPRO001 - This work is supported by the French "Agence Nationale de la Recherche" as part of the program "investing in the future" under reference ANR-10-EQPX-51. This work was also supported by grants from Région Ile-de-France. http://accelconf.web.cern.ch/AccelConf/IPAC2014/papers/wepro001.pdfInternational audienceAs part of the R&D for the 50 MeV ThomX Compton source project, we have studied the effect of several beam dynamics processes on the evolution of the beam in the ring. The processes studied include among others Compton scattering, intrabeam scattering, coherent synchrotron radiation. We have performed extensive simulations of a full injection/ extraction cycle (400000 turns). We show how each of these processes degrades the flux of photons produced and how a feedback system contributes to recovering most of the flux

Chaikovska, I.

HAL-IN2P3

EFFECT OF BEAM DYNAMICS PROCESSES IN THE LOW ENERGYRING THOMX∗N. Delerue†, C. Bruni, I Chaikovska, I. Drebot‡, M. Jacquet, A. Variola, F. ZomerLaboratoire de l’Accélérateur Linéaire (LAL), Université Paris-Sud XI, F-91898 Orsay, FranceA. Loulergue, Synchrotron SOLEIL, St Aubin, FranceAbstractAs part of the R&D for the 50 MeV ThomX Comptonsource project, we have studied the effect of several beamdynamics processes on the evolution of the beam in the ring.The processes studied include among others Compton scat-tering, intrabeam scattering, coherent synchrotron radiation.We have performed extensive simulations of a full injec-tion/extraction cycle (400000 turns). We show how each ofthese processes degrades the flux of photons produced andhow a feedback system contributes to recovering most of theflux.BEAM DYNAMICS AT THOMXThomX [1] will be a 50 MeV compact accelerator usedto produce X-rays by Compton scattering between electronsand a laser. It will be made of a linac and a ring in which thebeam will be stored for 20 ms. A more detailed descriptionof the project is available elsewhere in these proceedings [2]and in the projet’s TDR [3]. Given the very short storagetime, the short bending radius and the low energy of theelectrons, several beam dynamics effect will have a strongeffect on the expected flux.An extensive study of the beam dynamics at ThomX hasbeen performed, including among others the effects of Comp-ton backscattering (CBS), intrabeam scattering (IBS) and co-herent synchrotron radiation (CSR). This study is describedin [4] and we present here its main results.SIMULATION CODEThe simulation code we have used is based on Matlab. Itis written as a shell in which several beam dynamics effectsare implemented with macro-particles beings passed fromthe simulation of one effect to the other as arrays. The codehas also the flexibility of calling external program such asCAIN [5]. The properties of the macro-particles can beexported after each turn although it is advised to do it lessoften to minimize the disk space used. The structure of thecode is shown on figure 1.The possibility of exporting all macro-particles proper-ties also allows to break the execution of the simulation inseveral jobs to be executed serially on a computer farm. The∗ This work is supported by the French "Agence Nationale de la Recherche"as part of the program "investing in the future" under reference ANR-10-EQPX-51. This work was also supported by grants from RégionIle-de-France.† delerue@lal.in2p3.fr‡ illya.drebot@mi.infn.it now at INFN-Milan, ItalyFigure 1: Structure of the simulation code. Top: overallstructure. Bottom: Simulation loop.duration of the simulation will depend on the number ofmacro-particles chosen. For 105 macro-particle a simula-Proceedings of IPAC2014, Dresden, Germany WEPRO00102 Synchrotron Light Sources and FELsA16 Advanced ConceptsISBN 978-3-95450-132-81933 Copyright©2014CC-BY-3.0andbytherespectiveauthorsFigure 2: Evolution of the bunch in the longitudinal phase space (energy spread versus longitudinal position) as function ofturn number (indicate above each image). The color of the dots indicate the particles intensity at that location red beingmore intense than green and green more intense than blue.tion of the full injection/extraction cycle will take severalweek although, as we will see below, this can be significantlyshortened if one is mostly interested in what happen duringthe initial transient period.INITIAL INSTABILITIES DUE TOMISMATCHINGUsing the code with have made a full simulation of theevolution of the longitudinal phase space as function of time.As expected and as shown on figure 2 just after injection thebeam enters in a turbulent regime. This is due to the shapeof the injected beam being mismatched with the shaped ofthe bucket. During this turbulent regime a fraction of thecharge may be lost.EFFECT OF COHERENT SYNCHROTRONRADIATIONAt high charge the most disruptive effect is CSR. Whileperforming our simulations we saw that sometimes CSR cansplit the bunch in two or more parts leading to a significantfraction of the charge to be ejected from the bunch. Thisresult in a lower X-ray yield. Examples of simulations ofthe longitudinal phase space with and without such beambreak-up are shown on figure 3: for the same initial beam pa-rameters but for different random distributions of the macroparticles one case leads to a relatively stable beam whereasthe other case leads to the bunch been split in two partswithin less than 10 000 turns and one of the two parts is thenlost shortly after leave only 56% of the macro particules inthe bunch.This beam break-up means that there is a threshold abovewhich adding charge at injection will in fact decrease theFigure 3: Longitudinal phase space of the bunch (energyspread versus longitudinal position), at injection (top), after10 000 turns (middle) and after 70 000 turns (bottom) in twocases with the same beam parameters (but different initialrandom distributions of the macro particles). On the left thebunch is relatively stable and only 2% of the macro particlesare lost whereas on the right the bunch is unstable and it issplit in less than 10 000 turns, leading to the loss of 44%of the charge. The color of the dots indicate the particlesintensity at that location red being more intense than greenand green more intense than blue.charge that can actually be stored and therefore decrease theX-ray yield. This is shown on figure 4 where one can seethat the average flux produced for an initial charge of 1nC ishigher than the flux produced for an initial charge of 1.1nC.WEPRO001 Proceedings of IPAC2014, Dresden, GermanyISBN 978-3-95450-132-81934Copyright©2014CC-BY-3.0andbytherespectiveauthors02 Synchrotron Light Sources and FELsA16 Advanced ConceptsFigure 4: Average photon flux produced for 10 simulationsof 1500 000 turns each for 5 different initial charges. At 1nCand above during some simulations the beam get partiallylost leading to a lower photon yield.OVERALL FLUXUsing the simulation code it is possible to simulate a fullstorage and predict the spectrum obtained. Figure 5 shows anexample of photons spectrum where the intensity is plottedagainst the energy (vertical axis) and the scattering angle(horizontal axis).Figure 5: Distribution of the scattered photons as functionof their energy and scattering angle. The color indicate thephoton intensity at a given coordinate point from blue (lessintense) to red (more intense).It is also possible to investigate the effect of each beamdynamics effect on the final flux. For that we made severalsimulations where we turned on or off some effect selectivelyto see how doing this changed the flux. The result of thesesimulations is shown on figure 6. Although in reality it willnot be possible to turn off effects, understanding what iscausing the losses will help us in designing the best possiblemitigation strategy.0 5 10 15 2000.511.522.5x 1010Time (ms)Flux [photons/ms]  IBS 0 FB 0 EnOf 0 LSC 0 RW 0 CSR 0; Flux=3.9e+11IBS 1 FB 0 EnOf 0 LSC 0 RW 0 CSR 0; Flux=3.9e+11IBS 0 FB 0 EnOf 0 LSC 1 RW 1 CSR 0; Flux=3.4e+11IBS 0 FB 0 EnOf 0 LSC 1 RW 1 CSR 1; Flux=2.7e+11IBS 1 FB 0 EnOf 0 LSC 1 RW 1 CSR 0; Flux=3.3e+11IBS 1 FB 0 EnOf 0 LSC 1 RW 1 CSR 1; Flux=2.7e+11IBS 1 FB 1 EnOf 1 LSC 1 RW 1 CSR 1; Flux=3.9e+11Figure 6: Photon flux as function of the turn number withvarious effects turned on or off. In the caption, IBS stands forIntrabeam Scattering, FB for longitudinal feedback, EnOffor Energy Offset (to compensate beam mismatch), LSCfor longitudinal space charge, RW for resistive wall effect,CSR for Coherent Synchrotron Radiation. When an effect isfollowed by a 0 it means that it is turned off. If it is followedby a one, it means that it is turned on in the simulations. Theflux in the caption is given in number of photons (integratedover the duration of the simulation).OUTLOOKWe have written a simulation code to study the beamdynamics at the ThomX Compact Light Source. This allowsus to better understand how beam dynamics will affect thephoton flux with the aim of designing a mitigation strategy.We see that CSR is the effect that will the most significantlydecrease the flux and the main reduction in flux will occurduring the first 5 ms of the cycle.REFERENCES[1] Variola, et al., The ThomX project  [2] Variola, et al., The ThomX project status[3] Variola, et al., ThomX TDR3269, (2014).[4] I. Drebot, Electron beam dynamics with and without comptonback scattering , Doctoral Thesis, (2013).[5] K. Yokoya, T. Tauchi, P. Chen Cain , 41(29),WEOAA01, IPAC 2011, San Sebastian, Spain, (2011).,IPAC 2014, Dresden, Germany, (2014).,(1993)., Part. Acc., LAL/RT 14-21 SOLEIL/SOU-RA-,Université Paris-SudProceedings of IPAC2014, Dresden, Germany WEPRO00102 Synchrotron Light Sources and FELsA16 Advanced ConceptsISBN 978-3-95450-132-81935 Copyright©2014CC-BY-3.0andbytherespectiveauthors

Effect of beam dynamics processes in the low energy ring ThomX

Effect of Beam Dynamics Processes in the Low Energy Ring ThomX

Effect of Beam Dynamics Processes in the Low Energy Ring ThomX

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