| 1 | $Id: README,v 1.3 2007/01/18 09:07:20 hbu Exp $ |
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| 2 | ------------------------------------------------------------------- |
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| 3 | |
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| 4 | ========================================================= |
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| 5 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
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| 6 | ========================================================= |
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| 7 | |
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| 8 | TestEm16 |
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| 9 | -------- |
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| 10 | Simulate synchrotron radiation |
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| 11 | |
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| 12 | 1- GEOMETRY DEFINITION |
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| 13 | |
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| 14 | The geometry consists of a single block of a homogenous material. |
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| 15 | |
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| 16 | Two parameters define the geometry : |
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| 17 | - the material of the box, |
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| 18 | - the (full) size of the box. |
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| 19 | The default is 500 m of vacuum. |
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| 20 | |
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| 21 | A transverse uniform magnetic field can be applied. |
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| 22 | |
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| 23 | The default geometry is constructed in DetectorConstruction class, |
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| 24 | but all of the above parameters can be changed interactively via |
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| 25 | the commands defined in the DetectorMessenger class. |
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| 26 | |
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| 27 | 2- PHYSICS LIST |
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| 28 | |
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| 29 | The particle list is the one of novice/exampleN03 and TestEm6 |
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| 30 | with in addition synchrotron radiation. |
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| 31 | To make the synchrotron radiation easily visible, a very low |
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| 32 | pressure "vaccuum" and a magnetic field of by default 1 Tesla |
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| 33 | in z-direction is used. |
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| 34 | |
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| 35 | 3- AN EVENT : THE PRIMARY GENERATOR |
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| 36 | |
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| 37 | The primary kinematic consists of a single particle which hits the |
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| 38 | block perpendicular to the input face. The type of the particle |
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| 39 | and its energy are set in the PrimaryGeneratorAction class, and can |
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| 40 | changed via the G4 build-in commands of ParticleGun class (see |
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| 41 | the macros provided with this example). |
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| 42 | The default is an positron of 10 GeV. |
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| 43 | |
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| 44 | In addition one can choose randomly the impact point of the incident |
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| 45 | particle. The corresponding interactive command is built in |
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| 46 | PrimaryGeneratorMessenger class. |
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| 47 | |
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| 48 | A RUN is a set of events. |
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| 49 | |
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| 50 | |
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| 51 | 4- VISUALIZATION |
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| 52 | |
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| 53 | The Visualization Manager is set in the main(). |
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| 54 | The initialisation of the drawing is done via the command |
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| 55 | > /control/execute vis.mac |
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| 56 | > /run/beamOn 1 |
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| 57 | |
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| 58 | The detector has a default view which is a longitudinal view of the box. |
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| 59 | |
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| 60 | The tracks are drawn at the end of event, and erased at the end of run. |
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| 61 | Optionaly one can choose to draw all particles, only the charged one, |
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| 62 | or none. This command is defined in EventActionMessenger class. |
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| 63 | |
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| 64 | 5- PHYSICS DEMO |
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| 65 | |
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| 66 | The particle's type and the physic processes which will be available |
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| 67 | in this example are set in PhysicsList class. |
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| 68 | |
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| 69 | In addition a build-in interactive command (/process/inactivate proname) |
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| 70 | allows to activate/inactivate the processes one by one. |
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| 71 | |
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| 72 | The threshold for producing secondaries can be changed. |
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| 73 | eg: /run/particle/setCut 100 micrometer |
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| 74 | /run/initialize |
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| 75 | |
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| 76 | To visualize the Synchrotron radiation : |
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| 77 | /control/execute vis.mac |
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| 78 | |
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| 79 | 6- HOW TO START ? |
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| 80 | |
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| 81 | - compile and link to generate an executable |
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| 82 | % cd geant4/examples/extended/electromagnetic/TestEm16 |
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| 83 | % make |
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| 84 | |
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| 85 | - execute Test in 'batch' mode from macro files |
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| 86 | % TestEm16 run01.mac |
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| 87 | |
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| 88 | - execute Test in 'interactive mode' with visualization |
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| 89 | % TestEm16 |
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| 90 | .... |
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| 91 | Idle> type your commands |
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| 92 | .... |
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| 93 | Idle> exit |
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| 94 | |
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| 95 | 7 - TRACKING : stepMax and setMaxStepLength |
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| 96 | |
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| 97 | In order to control the accuracy of the deposition, the user can limit |
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| 98 | 'by hand' the maximum step size stepMax of charged particles. |
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| 99 | |
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| 100 | The maximum tracking step length for computing of magnetic field lines |
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| 101 | is by default set to 1 km. |
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| 102 | Synchrotron radiation in very weak magnetic fields of the order of 1 Gauss |
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| 103 | may require longer pathlength. |
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| 104 | This can be achieved with using setMaxStepLength like |
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| 105 | /testem/tracking/setMaxStepLength 100 km |
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| 106 | |
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| 107 | 8- HISTOGRAMS |
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| 108 | |
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| 109 | TestEm16 produces 3 histograms which illustrate synchrotron radiation. |
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| 110 | The photon energy spectrum (photons / energy bin) and the power spectrum |
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| 111 | (photon spectrum weighted with the photon energy) and a histogram |
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| 112 | of the path length between photon radiation is produced. |
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| 113 | |
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| 114 | By default the histograms are not activated. To activate histograms |
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| 115 | the environment variable G4ANALYSIS_USE should be defined. For instance |
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| 116 | uncomment the flag G4ANALYSIS_USE in GNUmakefile. |
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| 117 | |
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| 118 | Before compilation of the example it is optimal to clean up old files: |
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| 119 | make histclean |
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| 120 | make |
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| 121 | |
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| 122 | By default the histograms are saved as testem16.hbook |
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| 123 | It is possible to choose the format of the histogram file (hbook, root, XML) |
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| 124 | and the binning using /testem/histo/ command, see run01.mac |
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