The BDSIM Toolkit - RHUL Physics Department TWiki
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1. x10 x10 Soya amp 0 2 0 4 F E 0 0 05 0 2 0 4 OF E 0 6 0 05 0 8 E 1 i 0 1 if ae j Peere ee e e a 0 1 0 05 0 0 05 0 1 1 2 1500 1000 500 0 500 1000 1500 x0 x 5 2 3 sbend In sector wedge and rectangular bending magnets the transportation is according to the formula 0 5Fh 8 To 1 Ap p y Mx Yo y Yo 0 Ap Apo 0 P P where cos F 4sin F 0 0 4 1 cos F fsin F cos F 0 0 sin F M 0 0 1 L 0 0 0 0 1 0 0 0 0 0 1 18 p is the bending radius of the central trajectory F kh k 1 1n p n dB dx p B 5 2 4 sextupole and octupole For tracking in sextupoles and octupoles the track is approximated by a chord with curvature determined by the local magnetic field The step size h is determined by the required precision 5 2 5 other elements In all other elements 4th order Runge Kutta method is used for tracking in electromag netic fields and interaction with material is standard 5 3 Electromagnetic Physics Following electromagnetic processes are available e Multiple Scattering Ionization Bremsstrahlung Positron annihilation e Gamma conversion Compton Scattering Planck Scattering Photoelectric effect Synchrotron radiation Muon production and transport For most of the studies the physics list em_standard is sufficient which includes multiple scattering ionization and bremsstrahlung 5 4 Hadronic Physics Following2. 3 1 Program structure A GMAD program consists of a sequence of element definitions and control commands For example tracking a 1 GeV electron beam through a FODO cell will require a file like this qf quadrupole 1 0 5 m k1 0 1 qd quadrupole 1 0 5 m k1 0 1 d drift 1 0 5 m fodo line qf d qd d use period fodo beam particle e energy 1 GeV Generally the user has to define a sequence of elements with drift quadrupole line etc then select the beamline with the use command and specify beam parameters and other options with beam and option commands The sample command controls what sort of information will be recorded during the execution The parser is case sensitive However for convenience of porting lattice descriptions from MAD the keywords can be both lower and upper case The GMAD language is discussed in more detail below 3 2 Arithmetical expressions Throughout the program a standard set of arithmetical expressions is available Every expression is ended with a semicolon For example x 1 y 2 5 x z sin x log y 8e 5 The variables then could be used along with numerical constants The if else clause is also available for example z 1 if z lt 2 y 2 5 x else y 15 3 3 Physical elements and Entities GMAD implements almost all the standard MAD elements but also allows to define arbitrary geometric entities and magnetic field configurations The geometry descrip tion ca
3. eV I gt KeV 1076 MeV 107 TeV 103 m 1 mm 4 cm Je rad 1 mrad J clight 2 99792458e 8 3 3 6 sbend sbend defines a sector bending magnet Attributes e length m default 0 e angle bending angle rad default 0 e B magnetic field T e aper aperture m default same as beampipe radius The meaning of B and angle is the same as for rbend Example rbi rbend 1 0 5 m angle 0 01 3 3 7 quadrupole quadrupole defines a quadrupole Attributes e length m default 0 e k1 normal quadrupole coefficient k1 1 Bp dB dx m Positive k1 means horizontal focusing of positively charged particles default 0 e ks1 skew quadrupole coefficient ks1 1 Bp dB dx m where x y is now a coordinate system rotated by 45 degrees around s with respect to the normal one default 0 e tilt rad roll angle about the longitudinal axis clockwise e aper aperture m default same as beampipe radius Example qf quadrupole 1 0 5 m kl 0 5 tilt 0 01 3 3 8 sextupole sextupole defines a sextupole Attributes e 1 length m default 0 e k2 normal sextupole coefficient k2 1 Bp d B dx m gt e ks2 skew sextupole coefficient ks2 1 Bp d B dx m where x y is now a coordinate system rotated by 30 degrees around s with respect to the normal one default 0 e tilt rad roll angle about the longitudinal axis clockwise e aper aperture m d
4. constants are concerned 3 3 3 marker marker has no effect but allows one to identify a position in the beam line say where a sampler will be placed It has no attributes Example mi marker Table 1 Units Length angle quadrupole coefficient multipole coefficient electric voltage electric field strength particle energy particle mass particle momentum beam current particle charge emittances 3 3 4 drift m metres rad radians m 2n poles m MV Megavolts MV m GeV GeV c GeV c A Amperes e elementary charges 7 m mrad drift defines a straight drift space Attributes e length m default 0 e aper aperture m default same as beampipe radius Example di3 drift 1 0 5 m 3 3 5 rbend rbend defines a rectangular bending magnet Attributes e length m default 0 e angle bending angle rad default 0 e B magnetic field T e aper aperture m default same as beampipe radius when B is set this defines a magnet with appropriate field strength and angle is not taken into account Otherwise the B that corresponds to the bending angle angle for a particle in use defined by the beam command with appropriate energy and rest mass is calculated and used in the simulations Example rbi rbend 1 0 5 m angle 0 01 Table 2 predefined numerical constants pi 3 14159265358979 me electron rest mass mp proton rest mass GeV 1
5. used ngenerate number of primery particles fires when in batch mode nperfile number of events recorded per file 3 4 2 beam The parameters related to the beam are given by the beam command beam name value The available parameters are particle particle name e et gamma proton etc energy particle energy distrType type of distribution distrFile input bunch file beam particle et energy 100 MeV distrType gauss 13 3 4 3 sample To record the tracking results one uses the sample command sample range lt name gt puts a plane sampler before element lt name gt csample range lt range gt 1 lt l gt r lt r gt puts a cylindrical sampler of length and radius r around element lt name gt Example d drift 1l 1 m sample range d csample range d 3 4 4 use use command selects the beam line for study test line sb d d qf use period test 4 Visualization When BDSIM is invoked in interactive mode the run is controlled by the Geant4 shell A visualization macro should be then provided A simple visualization macro is listed below Invoke the OGLSX driver Create a scene handler and a viewer for the OGLSX driver vis open OGLIX Create an empty scene vis scene create Add detector geometry to the current scene vis scene add volume Attach the current scene handler to the current scene omittable vis sceneHandler attach Add trajectorie
6. ATH variable to point to the parser directory and to the directory containing libbdsim so BDSIM is invoked by the command bdsim lt option gt where the options are file lt filename gt specify the lattice file output lt fmt gt output format rootlascii default ascii outfile lt file gt output file name Will be appended with _N where N 0 1 2 3 etc vis_mac lt file gt visualization macro script default vis mac help display this message verbose display general parameters before run verbose_event display information for every event verbose_step N display tracking information after each step verbose_event_num display tracking information for event number N batch batch mode no graphics BDSIM is supported on Linux and MacOS with gcc compiler To run bdsim one first has to define the beamline geometry in a file which is then passed to bdsim via the file command line option for example bdsim file line gmad output root batch The next section describes how to do this in more detail 3 Lattice description The beamline beam properties and physics processes are specified in the input file written in the GMAD 5 language which is a variation of MAD 4 language extended to handle sophisticated geometry and parameters relevant to radiation transport GMAD is described in this section Examples of input files can be found in the BDSIM distribution in the examples directory
7. EUROTeV Report 2006 014 1 The BDSIM Toolkit I Agapov G Blair J Carter O Dadount March 1 2006 Abstract This report is a description of the BDSIM toolkit based on the User s Manual for the v0 1 version Royal Holloway University London UK LAL Orsay France 1 Introduction BDSIM is a Geant4 3 extension toolkit for simulation of particle transport in accelerator beamlines It provides a collection of classes representing typical accelerator components a collection of physics processes for fast tracking procedures of on the fly geometry construction and interfacing to ROOT analysis 2 Obtaining installing and running BDSIM can be downloaded from http flc pp rhul ac uk bdsim html This site also contains some information on planned releases and other issues Alternatively a development version is accessible under http cvs pp rhul ac uk Download the tarball and extract the source code Make sure Geant4 is installed and appropriate environment variables defined Then go through the configuration procedure by running the configure script configure It will create a Makefile from the template defined in Makefile in Then start the com pilation by typing make If the compilation is successful an executable called bdsim should be created in the current directory or in the directory to which the GZWORKDIR environment variable points if this variable is defined Next set up the LD_LIBRARY_P
8. F EXISTS DATABASE_NAME CREATE DATABASE DATABASE_NAME USE DATABASE_NAME A table must be created to allow for the insertion of the geometry descriptions A table is created using the following MySQL compliant commands CREATE TABLE TABLE NAME_GEOMETRY TYPE TABLE PARAMETER VARIABLE TYPE TABLE PARAMETER VARIABLE TYPE TABLE PARAMETER VARIABLE TYPE 24 Once a table has been created values must be entered into it in order to define the solids and position them The insertion command must appear after the table creation and must the MySQL compliant table insertion command INSERT INTO TABLE NAME_GEOMETRY TYPE VALUES value1 value2 char value The values must be inserted in the same order as their corresponding parameter types are described in the table creation Note that ALL length types must be specified in mm and that ALL angles must be in radians An example of two simple boxes with no visual attributes set is shown below The first box is a simple vacuum cube whilst the second is an iron box with length 10mm length_y 150mm length_z 50mm positioned at x 1m y 0 z 0 5m and with zero rotation CREATE TABLE mytable_BOX NAME VARCHAR 32 MATERIAL VARCHAR 32 LENGTHX DOUBLE 10 3 LENGTHY DOUBLE 10 3 LENGTHZ DOUBLE 10 3 POSX DOUBLE 10 3 POSY DOUBLE 10 3 POSZ DOUBLE 10 3 ROTPSI DOUBLE 10 3 ROTTHETA DOUBLE 10 3 ROTPHI DOUBLE 10 3 INSERT INTO mytable_BOX VALUES a_b
9. YPE set to QUAD then a quadrupole field with this K1 value will be set up within the object Default it set to zero K2 Variable type DOUBLE 10 3 This is an optional parameter If set to a value other than zero in conjuction with MAGTYPE set to SEXT then a sextupole field with this K2 value will be set up within the object Default it set to zero POSX Variable type DOUBLE 10 3 This is a required parameter This is the X position in mm used to place the object in the component volume It is defined with respect to the center of the component volume and with respect to the component volume s rotation POSY Variable type DOUBLE 10 3 This is a required parameter This is the Y position in mm used to place the object in the component volume It is defined with respect to the center of the component volume and with respect to the component volume s rotation POSZ Variable type DOUBLE 10 3 27 This is a required parameter This is the Z position in mm used to place the object in the component volume It is defined with respect to the start of the component volume and with respect to the component volume s rotation ROTPSI Variable type DOUBLE 10 3 This is an optional parameter This is the psi Euler angle in radians used to rotate the object before it is placed The default is set to zero ROTTHETA Variable type DOUBLE 10 3 This is an optional parameter This is the theta Euler angle in radians use
10. ame in order to make use of the G4Cons solid type The following table parameters are specific to the polycone solid e NZPLANES Variable type INTEGER 11 This is a required parameter This value will be used to specify the number of z planes to be used in the polycone This value must be set to greater than 1 e PLANEPOS1 PLANEPOS2 PLANEPOSN Variable type DOUBLE 10 3 These are required parameters These values will be used to specify the z position of the corresponding z plane of the polycone There should be asmany PLANEPOS parameters set as the number of z planes For example 3 z planes will require that PLANEPOS1 PLANEPOS2 and PLANEPOS3 are all set up o RINNER1 RINNER2 RINNERN Variable type DOUBLE 10 3 These are required parameters These values will be used to specify the inner radius of the corresponding z plane of the polycone There should be as many RINNER parameters set as the number of z planes For example 3 z planes will require that RINNER1 RINNER2 and RINNER3 are all set up e ROUTER1 ROUTER2 ROUTERN Variable type DOUBLE 10 3 These are required parameters These values will be used to specify the outer radius of the corresponding z plane of the polycone There should be as many ROUTER parameters set as the number of z planes For example 3 z planes will require that ROUTER1 ROUTER2 and ROUTERS are all set up 31 e STARTPHI Variable type DOUBLE 10 3 This is an optional paramete
11. d to rotate the obejct before it is placed The default is set to zero ROTPHI Variable type DOUBLE 10 3 This is an optional parameter This is the phi Euler angle in radians used to rotate the obejct before it is placed The default is set to zero RED Variable type DOUBLE 10 3 This is an optional parameter This is the red component of the RGB colour assigned to the object and should be a value between 0 and 1 The default is set to zero BLUE Variable type DOUBLE 10 3 This is an optional parameter This is the blue component of the RGB colour assigned to the object and should be a value between 0 and 1 The default is set to zero GREEN Variable type DOUBLE 10 3 This is an optional parameter This is the green component of the RGB colour assigned to the object and should be a value between 0 and 1 The default is set to zero VISATT Variable type VARCHAR 32 This is an optional parameter This is the visual state setting for the object Setting this to W results in a wireframe displayment of the object S produces a shaded solid and I leaves the object invisible The default is set to be wireframe 28 A 2 3 Box Solid Types Append BOX to the table name in order to make use of the G4Box solid type The following table parameters are specific to the box solid e LENGTHX Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the x extent of the b
12. e distrType guineapig_bunch distrFile distr dat The formats currently supported are listed below guineapig_bunch E GeV x micrometer ylmicrometer zl micrometer x microrad y microrad guineapig_slac E GeV z nanometer x nanometer y micrometer x rad y rad guineapig_pairs E GeV x rad y rad z rad x manometer y nanometer z nanometer here a particle with E gt 0 is assumed to be an electron and with E lt 0 a positron The following distribution types can be generated Gaussian beam distrType gauss sigmaX lt sx gt soigmaXp lt sxp gt yP g gm gmap P sigmaY lt sy gt sigmaYp lt syp gt sigmaE lt se gt Elliptic shell generated a thin elliptic shell in z x and y y with given semi axes beam distrType eshell x lt x gt xp lt xp gt y lt y gt yp lt yp gt Acknowledgement Work supported by the Commission of European Communities under the 6t Framework Programme Structuring the European Research Area contract number RIDS 011899 33 References 1 G Blair Simulation of the CLIC Beam Delivery System using BDSIM CLIC Note 509 2001 ROOT User s guide http root cern ch root doc RootDoc html Geant4 User s guide http wwwasd web cern ch wwwasd geant4 MAD X User s Guide http mad home cern ch mad uguide html I Agapov GMAD accelerator description language EUROTeV Memo 2006 002 1 http www lcsi
13. e of the cone The default value is zero e DELTAPHI Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the delta angle of the cone The default value is 2 PI A 2 5 Torus Solid Types Append _TORUS to the table name in order to make use of the G4Torus solid type The following table parameters are specific to the torus solid e RINNER Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the inner radius of the torus tube The default value is zero e ROUTER Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the outer radius of the torus tube e RSWEPT Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the swept radius of the torus It is defined as being the distance from the center of the torus ring to the center of the torus tube For this reason this value should not be set to less than ROUTER 30 e STARTPHI Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the starting angle of the torus The default value is zero e DELTAPHI Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the delta swept angle of the torus The default value is 2 PI A 2 6 Polycone Solid Types Append _POLYCONE to the table n
14. efault same as beampipe radius Example sf sextupole 1 0 5 m k2 0 5 tilt 0 01 3 3 9 octupole octupole defines an octupole Attributes e 1 length m default 0 e k2 normal sextupole coefficient k3 1 Bp d B dx m Positive k1 means horizontal focusing of positively charged particles default 0 e ks3 skew sextupole coefficient ks3 1 Bp d B dx m where x y is now a coordinate system rotated by 30 degrees around s with respect to the normal one default 0 e tilt rad roll angle about the longitudinal axis clockwise Example octp octupole 1 0 5 m k3 0 5 tilt 0 01 3 3 10 multipole will be implemented starting from v0 2 3 3 11 rcol rcol defines a rectangular collimator Attributes e length m default 0 e xsize horizontal aperture m e xsize vertical aperture m e material material Example coli rcol 1 0 4 m xsize 2 mm ysize 1 mm material W The longitudinal collimator structure is not taken into account To do this the user has to describe the collimator with the generic type element 3 3 12 ecol ecol defines an elliptical collimator Attributes e length m default 0 e xsize horizontal aperture m e xsize vertical aperture m e material material Example col2 ecol 1 0 4 m xsize 2 mm ysize 1 mm material W Here the longitudinal collimator structure is also not taken into account 3 3 13 solen
15. hadronic processes are available e neutron and proton elastic and inelastic scattering e neutron capture e fission e radioactive decay 19 Figure 4 Calculations with EM physics Energy of Reflected Photons at the IP Mean 0 34 MeV 0 01 0 1 1 10 100 Energy MeV 6 Output Analysis During the execution the following things are recorded Energy deposition along the beamline Sampler hits If the output format is ASCII i e if BDSIM was invoked with the output ascii option then the output file output txt containing the hits will be written which has rows like hits PDGtype p GeV c x micron y micron z m x microrad y microrad 11 250 4 72907 5 86656 5 00001e 06 0 0 11 250 8 17576 4 99729 796 001 0 320334 0 126792 if ROOT output is used then the root files output_O root output_1l root etc will be created with each file containing the number of events given by nperfile option The file contains the energy loss histogram and a tree for every sampler in the line with self explanatory branch names 20 Figure 5 An example of root analysis Applications Places Desktop SOA SAG a gt Mon Feb 27 11 01PMQ Fd ROOT Object Browser SEE Eile View Options Help amp sampler_phys 1 al 2af ESEA lt l s lel S Option gt all Folders Contents of ROOT Files output_O root sampler_phys_1 Groot PROOF Sessions E homedliasdevelopment BDSIM ROOT File
16. jects with visibility flag set to false will not be dr ex awn vi vis viewer set culling global false to Draw such objects Also see other vis viewer set commands Idle gt vis viewer pan 0 1 E Y Idle gt vis viewer pan 0 1 Idle gt J Ne em y rerem rren e r ege eree erare p reee peeo e aee EEN GO zl E Find echo QO Find Next Find Previous Highlight _ Match case Done B ilia ancp24s BDSIM parser 1 ilia dhep245 O gmad h emacs O manual texi em viewer 0 Open ECHO 5 1 physicsList option Depending on for what sort of problem BDSIM is used different sorts of physics pro cesses should be turned on This processes are grouped into so called physics lists The physics list is specified by the physicsList option in the input file e g option physicsList em_standard Several predefined physics lists are available standard transportation of primary particles only em_standard transporation of primary particles ionization bremsstrahlung multiple scattering 16 em_low the same but using low energy electromagnetic models er electromagnetic physics and synchrotron radiation generation lw list for laser wire simulation standard electromagnetic physics and laser wire physics which is Compton Scattering with the event probability renormalized to 1 standard_hadronic standard electromagnetic fission neutron capture neutron a
17. lse POSZ will be defined with respect to the center of the parent object e ALIGNIN Variable type INTEGER 11 This is an optional parameter If set to 1 then the placement of components will be rotated and translated such that the incoming beamline will pass through the z axis of this object The default is set to 0 e ALIGNOUT Variable type INTEGER 11 This is an optional parameter If set to 1 then the placement of the next beamline component will be rotated and translated such that the outgoing beamline will pass through the z axis of this object The default is set to 0 26 SETSENSITIVE Variable type INTEGER 11 This is an optional parameter If set to 1 then the object will be set up to register energy depositions made within it and to also record the z position at which this deposition occurs This information will be saved in the ELoss Histogram if using ROOT output The default is set to 0 MAGTYPE Variable type VARCHAR 32 This is an optional parameter If supplied then the object will be set up to produce the appropriate magnetic field using the supplied K1 or K2 table parameter values Two magnet types are available QUAD and SEXT The default is set to no magnet type Note that if MAGTYPE is set to a value whilst K1 or K2 are not set then no magnetic field will be implemented K1 Variable type DOUBLE 10 3 This is an optional parameter If set to a value other than zero in conjuction with MAGT
18. m org software Icdd 34
19. me with the Geant4 distribution Some additional physics processes are implemented BD SLaserWirePhysics MounPhysics etc The interface to the output an analysis is in the BDSOutput class The primary particle generator is implemented in the BDSBunch class 21 Figure 6 Chart of BDSIM architecture Mokka Geometry Drivers T GMAD parser GDML Element Classes Physics Processes BDSQuad l eBremsstrahlung uadrupole pen A BDSCollimator Transportation Steppe Steppers i A Geometry description formats The element with user defined physical geometry is defined by lt element_name gt element geometry format filename attributes for example colli element geometry gmad colli geo A 1 gmad format gmad is a simple format used as G4geometry wrapper It can be used for specifying more or less simple geometries like collimators Available shapes are Box x0 x_origin y0 y_origin z0 z_origin x xsize y ysize Z zZsize material MaterialName temperature T Tubs x0 x_origin y0 y_origin z0 z_origin x xsize y ysize Z zsize material MaterialName temperature T For example Cons x0 0 y0 0 z0 0 rmini 5 rmax1 500 rmin2 5 rmax2 500 z 250 material Graphite phi0 0 dphi 360 temperature 1 A file can contain several objects which will be placed consequently into the volume A user has to make sure that there i
20. nd proton elastic and inelastic scattering By default the standard physics list is used 5 2 Transportation The transportation follows the scheme the step length is defined either by the distance of the particle to the boundary of the logical volume it is currently in which could be e g field boundary material boundary or boundary between two adjacent elements or by the mean free path of the activated processes The step size can also be limited for precision considerations Then the particle is transported to the new position and secondaries are generated if necessary Each volume has an associated transportation algorithm 5 2 1 drift The particles are translated along straight lines inside drift spaces x 1h O 0 Xo x 10100 i gA ia o i ah Ne y 00 04 yf If the trajectory reaches the boundary of the beam pipe then multiple scattering and other activated atomic and nuclear processes determine the random transport 5 2 2 quadrupole A similar procedure applies to quadrupoles with transport matrices inside the beampipe x Xo x ze a yY Yo y Yo where for a focusing quadrupole 17 cos hy k z sin hv k 0 0 M Vksin hVk cos hvk 0 0 f 0 0 ch hvk sh hvk 0 0 vVksh hvk ch hvk and for a defocusing one ch hv k sh hvk 0 0 m VEsh hvk ch hvk 0 nes 0 0 cos hv k z sin hvk 0 0 vVksin hvk cos hvk Figure 3 An example of distribution tracked through a beamline
21. oid will be implemented starting from v0 2 3 3 14 hkicker and vkicker hkicker and vkicker are equivalent to an rbend and an rbend rotated by 90 degrees respectively 3 3 15 transform3d An arbitrary 3 dimensional transformation of the coordinate system is done by placing a transform3d element in the beamline The next element after it will be placed with respected to the new coordinates The attributes are e x x offset y y offset z z offset phi phi Euler angle e theta theta Euler angle e psi psi Euler angle Example d drift 1l 1 m rot transform3d psi pi 2 test line d rot sb Here the sector bend will act in the vertical plane 3 3 16 element All the elements are in principle examples of a general type element which can represent an arbitrary geometric entity with arbitrary field maps Its attributes are e geometry geometry_description e bmap bmap description Descriptions are of the form format filename where filename is the path to the file with the geometry description and format defines the geometry description format and Example qq element geometry mokka qq geom bmap mokka qq bmap Possible formats are specific to each geometry driver and described in Appendix A 10 Figure 1 An example of a cryomodule described as element 3 3 17 line elements are grouped into sequences by the line command line_name line element_1 element_2 whe
22. ox vacuum 50 0 50 0 50 0 0 0 0 0 0 0 0 0 0 0 0 0 25 INSERT INTO mytable_BOX VALUES another_box iron 10 0 150 0 50 0 1000 0 0 0 500 0 0 0 0 0 0 0 Further examples of the Mokka geometry implementation can be found in the exam ples Mokka General directory See the common table parameters and solid type sections below for more information on the table parameters available for use A 2 2 Common Table Parameters The following is a list of table parameters that are common to all solid types either as an optional or mandatory parameter e NAME Variable type VARCHAR 32 This is an optional parameter If supplied then the Geant4 LogicalVolume asso ciated with the solid will be labelled with this name The default is set to be the table s name plus an automatically assigned volume number e MATERIAL Variable type VARCHAR 32 This is an optional parameter If supplied then the volume will be created with this material type note that the material must be given as a character string inside double quotation marks The default material is set as Vacuum e PARENTNAME Variable type VARCHAR 32 This is an optional parameter If supplied then the volume will be placed as a daughter volume to the object with ID equal to PARENTNAME The default parent is set to be the Component Volume Note that if PARENTID is set to the Component Volume then POSZ will be defined with respect to the start of the object E
23. ox s dimensions e LENGTHY Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the y extent of the box s dimensions e LENGTHZ Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the z extent of the box s dimensions A 2 4 Cone Solid Types Append CONE to the table name in order to make use of the G4Cons solid type The following table parameters are specific to the cone solid e LENGTH Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the z extent of the cone s dimensions e RINNERSTART Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the inner radius of the start of the cone The default value is zero e RINNEREND Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the inner radius of the end of the cone The default value is zero 29 e ROUTERSTART Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the outer radius of the start of the cone e ROUTEREND Variable type DOUBLE 10 3 This is a required parameter This value will be used to specify the outer radius of the end of the cone e STARTPHI Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the starting angl
24. pabilities are extended by using drivers to other geometry description formats which makes interfacing and standardization easier The syntax of a physical element declaration is element_name element_type attributes for example qd quadrupole 1 0 1 0 1 k1 0 01 element _type can be of basic type or inherited Allowed basic types are e marker e drift e sbend e rbend e quadrupole e sextupole e octupole e multipole e vkicker e hkicker e rcol e ecol e laser e transform3d e element All elements except element are by default modeled by an iron box given by the box Size option with the vacuum filled beampipe defined by beampipeRadius option An already defined element can be used as a new element type The child element will have the attributes of the parent one as default q quadrupole l 1 m k1 0 1 qq q k1 0 2 3 3 1 Coordinate system A standard coordinate system used in accelerator studies is assumed The horizontal coordinates are x and x vertical coordinates are y and y and the longitudinal coordi nates are the distance along the nominal orbit z and the momentum z is influenced by every component of nonzero length and x and y coordinates by bending magnets and coordinate transformations transform3d 3 3 2 Units In GMAD the SI units are used see Table 1 There are some predefined numerical values see Table 2 For example one can write either 100 or 0 1 KeV when energy
25. r If set then this value will be used to specify the starting angle of the polycone The default value is zero e DELTAPHI Variable type DOUBLE 10 3 This is an optional parameter If set then this value will be used to specify the delta angle of the polycone The default value is 2 PI A 2 7 Creating a geometry list A geometry list is a simple file consisting of a list of filenames that contain geometry descriptions This is the file that should be passed to the GMAD file when defining the mokka element An example of a geometry list containing boxes sql and cones sql would be symbols can be used for commenting out an entire line directory boxes sql directory cones sql A 2 8 Defining a Mokka element in the gmad file The Mokka element can be defined by the following command lt element_name gt element geometry format filename attributes where format must be set to mokka and filename must point to a file that contains a list of files that have the geometry descriptions for example collimator element geometry mokka coll_geomlist sql 32 A 3 GDML GDML is a XML schema for detector description 6 GDML will be fully supported as an external format starting from next release B Bunch description formats For compatibility with other simulation codes several bunch formats can be read For example to use the file distr dat as input the beam definition should look like beam particle
26. re element_n can be any element or another line For example a sequence of FODO cells can be defines as qf quadrupole 1 0 5 k1 0 1 qd quadrupole 1 0 5 ki 0 1 d drift 1 0 5 fodo line qf d qd d section line fodo fodo fodo beamline line section section section 3 3 18 laser laser defines a drift section with a laser beam inside 11 lt laser_name gt laser position lt x gt lt y gt lt z gt direction lt dx gt lt dy gt lt dz gt wavelen lt val gt spotsize lt val gt intensity lt val gt Attributes e length of the drift section e position position of an arbitrary point on the beam axis relative to the center of the drift section e direction vector pointing in the beam direction e wavelen laser wave length m e spotsize spot size sigma m e intensity W the laser is considered to be the intersection of the laser beam with the volume of the drift section For example laser1 laser 1 10 cm position 0 0 0 direction 1 0 0 wavelen 532e 9 m spotsize le 6 m intensity 10e6 3 3 19 Element number when several elements with the same name are present in the beamline they can be accessed by their number in the sequence In the next example the sampler is put before the second drift bl line d d d sample rang d 2 3 3 20 Element attributes Elements attributes such as length multipole coefficients etc can be accessed by putting
27. s amp Qoutput_o roat sampler phy BREO Benev Akparti weight FRx E E o vy ETI Per Ryo Ryd e R20 File Edit Run Options Help Command Option Histogram htemp Current Folder X x0 EO empty Byp eH o empty SRE 2Z empty EC gt empty Ree S empty x0 Jk weight amp Scan box xp0 kert Eo empty 0 Penev EO empty ypo EO empty E0 Eo empty 20 lt gt empty E x Ec gt empty p Eo empty y ist otist conte slo laf Z Reser wl 30 Obiects E iia localhost deve O BDSMaterials cc e Fi ROOT Object Browser O TreeViewer e a o m ae 7 Implementation Notes In this section the architecture of BDSIM is briefly described for someone wishing to use it as a class library see Figure 6 The GMAD parser is written in flex bison and is in the parser directory of the dis tribution The interface is defined in gmad h The output of the parser is a list of elements This list is passed to the BDSDetectorConstruction class which does the ge ometry construction The geometrical entities are instances of classes BDSDrift BDSS bend BDSElement etc Every element has an associated stepper class BDSSectStep per BDSQuadStepper etc which is responsible for the transportation BDSPhysicsList class is responsible for defining physics processes Most of the physics processes co
28. s no overlap between them 23 A 2 mokka As well as using the gmad format to describe user defined physical geometry it is also possible to use a Mokka style format This format is currently in the form of a dumped MySQL database format although future versions of BDSIM will also support online querying of MySQL databases Note that throughout any of the Mokka files a 4 may be used to represent a commented line There are three key stages which are detailed in the following sections that are required to setting up the Mokka geometry e Describing the geometry e Creating a geometry list e Defining a Mokka Element to load geometry descriptions from a list A 2 1 Describing the geometry An object must be described by creating a MySQL file containing commands that would typically be used for uploading creating a database and a corresponding new table into a MySQL database BDSIM supports only a few such commands specifically the CREATE TABLE and INSERT INTO commands When writing a table to describe a solid there are some parameters that are common to all solid types such as NAME and MATERIAL and some that are more specific such as those relating to radii for cone objects A full list of the standard and specific table parameters as well as some basic examples are given below with each solid type All files containing geometry descriptions must have the following database creation commands at the top of the file DROP DATABASE I
29. s to the current scene 14 Note This command is not necessary in exampleN0O3 since the C method DrawTrajectory is described in the event action vis viewer set viewpointThetaPhi 90 90 vis drawVolume vis scene add trajectories tracking storeTrajectory 0 vis viewer zoom tracking storeTrajectory 1 for BDS vis viewer zoom 300 vis viewer set viewpointThetaPhi 3 45 By default the macro is read from the file named vis mac The name of the file with the macro can also be passed via the vis_mac switch bdsim file line gmad vis_mac my_macro mac In interactive mode all the Geant4 interactive commands are available For instance to fire 100 particles type run beamOn 100 runs the simulation with 100 particles and to end the session type exit To display help menu help For more details see 3 5 Physics BDSIM can exploit all physics processes that come with Geant4 In addition fast tracking inside multipole magnets is provided More detailed description of the physics is given below 15 Figure 2 A screenshot with an example BDSIM visualization Applications Places Desktop 2QaSe9 B GBr D Thu Feb 23 7 10 PM Q Oo manual texi emacs dhcp245 pp rhul ac uk lolx a x O viewer 0 OpenGLStoredX x x blopment BDSIM docs SoG oc ex ilia dhcp245 development BDSIM examples 3d File Edit View Terminal Tabs Help df WARNING ob
30. square brackets after the element name for example d drift 1 0 5 m x d 1 3 3 21 Material table There is a set of predefined materials for use in elements such as collimators e g Al W Iron Copper Graphite etc Note that each geometry driver such as Mokka has its own set of materials 12 3 4 Run control and output The execution control is performed in the GMAD input file through option and sample commands How the results are recorded is controlled by the sample command When the visualization is turned on it is also controlled through Geant4 command prompt 3 4 1 option Most of the options in BDSIM are set up by the command option name value The following options influence the geometry beampipeRadius default beampipe radius m beampipeThickness default beampipe thickness m tunnelRadius tunnel Radius m boxsize default accelerator component size m The following options influence the tracking and output deltaChord chord finder precision deltaIntersection boundary intersection precision chordsStepMinimum minumum step size lengthSafety element overlap safety thresholdCutCharged charged particle cutoff energy thresholdCutPhotons photon cutoff energy randomSeed seed for the random number generator stopTracks if set tracks are terminated after interaction with material and energy deposit recorded physicsList determines the set of physics processes
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