The tracking code Placet has recently undergone several improvements. A redesign of its internal data structures and a new user interface based on the mathematical toolbox Octave considerably expanded its simulation capabilities. Several new lattice elements, optimization algorithms and physics processes were added to allow for more complete start-to-end simulations. Finally, the use of the AML language and the Universal Parser Library have extended its interfacing capability. A review of these new features is presented in this paper

Adli, E

Burkhardt, H

Latina, A

Renier, Y

Rumolo, G

Schulte, D

Tomás, R

CERN Document Server

CERN-AB-2008-017RECENT IMPROVEMENTS IN THE TRACKING CODE PLACET*The tracking code Placet has recently undergone several improvements. A redesign of its internal datastructures and a new user interface based on the mathematical toolbox Octave considerably expanded itssimulation capabilities. Several new lattice elements, optimization algorithms and physics processes wereadded to allow for more complete start-to-end simulations. Finally, the use of the AML language and theUniversal Parser Library have extended its interfacing capability. A review of these new features ispresented in this paper.EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHCERN   -   AB DepartmentGeneva, SwitzerlandAugust 2008AbstractCERN-AB-2008-017CLIC-Note -759EUROTeV-Report-2008-0431) LAL, Paris, France*Work supported by the Commission of the European Communities under the 6th Framework Programme“Structuring the European Research Area”, contract number RIDS-011899.A. Latina, E. Adli, H. Burkhardt, Y. Renier1), G. Rumolo, D. Schulte, R. TomasCERN, Geneva, SwitzerlandPresented atEPAC'08, 11th European Particle Accelerator Conference, Genoa, Italy - June 23-27, 2008RECENT IMPROVEMENTS IN THE TRACKING CODE PLACET∗A. Latina, E. Adli, H. Burkhardt, G. Rumolo, D. Schulte, R. Tomas, CERN, Geneva, SwitzerlandY. Renier, LAL, Paris, FranceAbstractThe tracking code Placet has recently undergone severalimprovements. A redesign of its internal data structuresand a new user interface based on the mathematical tool-box Octave considerably expanded its simulation capabili-ties. Several new lattice elements, optimization algorithmsand physics processes were added to allow for more com-plete start-to-end simulations. Finally, the use of the AMLlanguage and the Universal Parser Library have extendedits interfacing capability. A review of these new features ispresented in this paper.EMBEDDING OF OCTAVEThe tracking code Placet has been recently extendedto embed the Octave’s interpreter [1]. Octave is a high-level interactive language for numerical computations thatis mostly compatible with MatLab c©. Octave can do arith-metic for real and complex scalars and matrices, solve setsof nonlinear algebraic equations, integrate functions andhas a large set of tool-boxes and optimization routines.The version of the code that includes Octave is calledPlacet-Octave. Placet-Octave is based on the originalTcl/Tk core but embeds the Octave’s command line in-terpreter and can run scripts where both Tcl/Tk and Oc-tave’s instructions are present. The two interpreters sharethe same data structures in memory, so there is no overheaddue to data exchange when passing from one environmentto the other.Placet-Octave offers to the user all Octave’s commands,libraries and tool-boxes that are available for the stand-alone version of Octave, plus several commands that havebeen specifically created to run the Placet simulations.Some of these commands are built-in the code, as fast C++routines, others are written as Placet-Octave’s scripts them-selves. This is transparent to the user. Placet-Octave’scommands can be divided into two categories: commandsthat allow the user to inquire and modify the status of abeamline and commands that allow to run specific Placet-actions, such as tracking the bunches, or minimizing thefinal emittance in presence of imperfections.The user can access Placet-Octave’s functions from a Tclscript using the keyword Octave. This keyword has twoways of operation:• Octave(without any argument) interrupt the script execution∗Work supported by the Commission of the European Communitiesunder the 6th Framework Programme “Structuring the European ResearchArea”, contract number RIDS-011899.and open an interactive Octave command line inter-face• Octave { here some octave code }execute a batch of Octave’s commands and continuethe execution of the scriptHere is an example of a Placet-Octave call in Tcl:Octave {# calculate the response matrixR0 = placet_get_response_matrix("beamline", BI, CI);# track a bunch through a misaligned beamlineplacet_test_no_correction("beamline","beam","misalign");# read the bpms, calculate the correction and correctBpm = placet_get_bpm_readings("beamline", BI);Corr = R0 \ Bpm;placet_vary_corrector("beamline", CI, Corr);}Here, BI and CI are vectors containing the list of bpmsand correctors, respectively; this code performs a one-to-one correction. A full list of Placet-Octave’s commands isavailable in the Placet’s manual [2].NEW COMMANDSSeveral new keywords have enriched the Placet’s set ofcommands.New Lattice ElementsCrabCavity. It simulates a crab cavity taking into ac-count wakefield effects. Input parameters are voltage, fre-quency and phase of the cavity, plus a set of wakefieldmodes. For an example, see Fig. 1 and [3].DynamicElement. Through a specific application pro-gramming interface, based on the C language, this com-mand allows to use an external shared library as an elementtype to be inserted in the lattice.New CommandsTestRfAlignment. This new alignment routine reducesthe emittance growth due to wakefield effects in the ac-celerating cavities by moving the supports of the girderswhere the cavities are placed on. Girders are moved in or-der to minimize the sum of the squared positions read inthe cavity position monitors. Fig. 2BeamlineSaveAML. It saves the beamline in AcceleratorMarkup Language (AML) file format. AML is a speci-fication of the XML language designed to be used withFigure 1: Removal of spurious vertical bunch rotations atthe IP, caused by tilted crab cavities. Upper plot showsthe Y − Z phase space at the IP of the ILC when the crabcavity has a 10 mrad roll misalignment. Lower plot showsthe phase space profile after the anti-crab cavity correction.the Universal Accelerator Parser (UAP) [4]. The UAP isa project of the Cornell University to simplify the data ex-change among the most diffused codes (XSIF and MADdeck files are supported, for instance).LinkElements. This command links two elements of thelattice so that they are rigidly integral with each other; thatis, any misalignment applied to one of the two will bepropagated to its partner as if they lied on the same sup-port. This command is useful when converting compositeelements, such as QUADBPMs, from MAD files, becausesuch elements are usually divided in three parts during theconversion:QUADBPM = 1/2 QUAD + BPM + 1/2 QUAD︸ ︷︷ ︸elements to be linkedGetTransferMatrix. It returns the transfer matrix of abeamline (or a part of it). 0 0.5 1 1.5 2 2.5 3 0  500  1000  1500  2000  2500ε y [nm]quadrupole [#]NO CORRECTION1-TO-1 CORRECTIONGIRDER ALIGNMENTFigure 2: Successful example of girder alignment in theCLIC main linac. The red line shows the emittance growthdue to cavity vertical misalignment (threfore purely due towakefields effects) without correction. Emittance is recov-ered after a 1-to-1 correction (green line) and a girder align-ment (blue line) as described in the text.New optimization routinesPlacet-Octave allowed to access all optimization routinesavailable for Octave. Making use of the Octave’s func-tion fmins(), that finds the minimum of a function of sev-eral variables using the Nelder&Mead Simplex algorithm,a new commands has been created:placet_optimize("beamline","merit_function","correctors","leverages", ["constraints"]);This routine minimizes an arbitrary merit function pro-vided by the user, changing arbitrary attributes (leverages)of a set of correctors. This optimization routine has beenused for• sophisticated Twiss parameters matching with emit-tance growth reduction (see the case of the CLICinjector linac, where the large energy spread of thebunch caused a considerable emittance growth, whenapplying the standard matching procedures; [5] andFig. 3).• non linear alignment techniques (see the algorithmproposed for the static alignment of the CLIC beamdelivery system in [6]) 0 1 2 3 4 5 6 7 8 0  20  40  60  80  100  120  140  160  180  200Δε/ε [%]s [m]horizontalvertical 0 0.5 1 1.5 2 2.5 3 0  50  100  150  200  250Δε/ε [%]s [m]horizontalverticalFigure 3: Twiss parameters matching using the newPlacet’s optimization functions. Upper plot shows the emit-tance growth when using a lattice uniquely matched us-ing MAD. Lower plot shows the emittance growth aftera re-matching that takes into account the emittance, usingPlacet.NEW PHYSICAL PROCESSESCoherent Synchrotron Radiation EmissionA module for the simulation of Coherent SynchrotronRadiation emission (CSR) has been implemented. Themethodology follows closely the implementation of Ele-gant [7], which is based on the the work of [8]. Thismethodology uses a 1D CSR model and does not take intoaccount shielding, but it has the advantage that it correctlycalculates the transient build-up of the CSR in a bend. ThePlacet model has currently implemented CSR in the bend-ing magnets, plus a simple field exponential decay modelfor the drift spaces(update to better models is planned inthe near future). The module is very easy to use, as CSRis enabled simply by setting a parameters for the SBendelement. A throughout benchmarking of the code againstElegant was performed (with F. Stulle, PSI). The resultsshowed excellent agreement between Placet and Elegantfor CSR in bends and at high energies (for energies be-low ∼ 100 MeV, the results differs substantially due to thev = c assumption of Placet). See Fig. 4.INTERFACING PLACETPlacet has also been extended in its interfacing capabil-ities. Its interface toward the the halo and tail generationpackage HTGEN [9] has recently been streamlined anddoes no longer require external libraries.Reading AML Deck FilesBesides the new command BeamlineSaveAML, thatwrites the beamline on disk in AML format, a tool to readAML deck files into Placet has also been created. Thisopens the possibility to exchange beamline informationwith any code making use of AML. Tools converting fromMAD, XSIF and BMAD into AML already exist.Placet-BDSIMIn order to simulate the impact of halo particles on thebeam pipe walls, under the effect of kicks due to the col-limator wakefields or other imperfections, Placet has beeninterfaced to BDSIM [10]. BDSIM is a code designed totrack single particles and their secondaries deriving fromthe interactions with the materials, based on Geant4.Combining the abilities of BDSIM and Placet allows toachieve an accurate simulation of the secondary particlesgeneration in the collimators and their tracking. The in-terface is based on the following schema: tracking is per-formed in parallel by both codes. BDSIM tracks the haloparticles and simulates the emission of secondary particlesin the collimators, while Placet tracks core and halo, in-cluding secondary particles. At each collimator’s entranceand exit, the two codes synchronize each others knowledgeof the beam. A first application of this combo can be foundin [11].Figure 4: PLACET calculations of CSR in the PSI bench-mark chicane.CONCLUSIONSThe tracking code Placet is reaching its maturity: theuser interface has been improved to support Octave’s in-structions, simplifying the writing of even more complexsimulation scripts, new elements and new physical effectshave been added, allowing to perform more complete startto end simulations. For instance, Placet can now take intoaccount Coherent Synchrotron Radiation emission, thatmight be relevant in the sections of the accelerator wherethe energy is low, such as the RTML; as well as it can prop-erly simulate and track the secondary particles emitted inthe collimation system of the beam delivery of a future lin-ear collider. Its interfacing capabilities have also been ex-panded, opening for further, future, extensions.REFERENCES[1] J.W. Eaton et al., http://www.octave.org[2] D. Schulte et al.,http://savannah.cern.ch/projects/placet[3] G.Burt et al., “Anti-Crab Cavities for the Removal of Spu-rious Vertical Bunch Rotations Caused by Crab Cavities”;submitted for publication on PRST-AB[4] D. Sagan et al., “The Accelerator Markup Language and theUniversal Accelerator Parser”, Proceedings EPAC 2006, Ed-inburgh, Scotland (2006);http://www.lns.cornell.edu/ dcs/aml[5] A. Ferrari et al., “Beam Dynamics Studies in the CLIC In-jector Linac”; CERN-AB-2007-071; CLIC-Note-723[6] R: Tomas, et al., “Alignment of the CLIC BDS”; these pro-ceedings[7] M. Borland; Argonne National Laboratory Advanced; Pho-ton Source Report No. LS-287, 2000.[8] E. L. Saldin et al., “On the coherent radiation of an electronbunch moving in an arc of a circle”; NIM A 398 (1997) 392[9] H. Burkhardt et al.,http://hbu.home.cern.ch/hbu/HTGEN.html[10] G. Blair et al., “The BDSIM Toolkit”, 2006, EUROTeV-Report-2006-014[11] S. Malton et al., “Full Simulation of CLIC and ILC Colli-mation System”; these proceedings

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