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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.
Depending on for what sort of problem BDSIM is used, different sorts of physics processes 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. Some physics lists allow biasing and re-weighting for some processes e.g. muon production. To set the amount of biasing see option. Further details of the QGSP, FTFP and BERT hadronic physics lists can be found in 5.
standard | transportation of primary particles only
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em_standard | transportation of primary particles, ionization, bremsstrahlung, Cerenkov, multiple scattering
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em_low | the same but using low energy electromagnetic models
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em_muon | em_standard plus muon production processes with biased muon cross-sections
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lw | list for laser wire simulation - standard electromagnetic
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| physics and "laser wire" physics which is Compton Scattering with total cross-section renormalized to 1.
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merlin | transportation of primary particles, and the following processes for electrons: multiple scattering, ionisation, and bremsstrahlung
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hadronic_standard | em_standard plus fission, neutron capture, neutron and proton elastic and inelastic scattering
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hadronic_muon | hadronic_standard plus muon production processes with biased muon cross-sections
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hadronic_QGSP_BERT | em_standard plus hadron physics using the quark gluon string plasma (QGSP) model and the Bertini cascade model (BERT)
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hadronic_QGSP_BERT_muon | hadron_QGSP_BERT plus muon production processes with biased muon cross-sections
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hadronic_QGSP_BERT_HP_muon | hadron_QGSP_BERT_muon with high precision neutron tracking
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hadronic_FTFP_BERT | em_standard plus hadron physics using the Fritiof model followed by Reggion cascade and Precompound and evaporation models for the nucleus de-excitation (FTFP) model and the Bertini cascade model (BERT)
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hadronic_FTFP_BERT_muon | hadronic_FTFP_BERT plus muon production processes with biased muon cross-sections
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By default the standard physics List is used
The transportation follows the scheme: the step length is selected which 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. Then the particle is pushed to the new position and secondaries are generated if necessary. Each volume has an associated transportation algorithm. For an on-energy particle travelling close to the optical axis of a quadrupole, dipole or a drift, standard matrix transportation algorithms are used 4. For multipoles of higher orders and for off-axis/energy particles Runge-Kutta methods are used.
The following options influence the tracking accuracy
chordStepMinimum | minimum chord length for the step
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deltaIntersection | determines the precision of locating the point of intersection
of the particle trajectory with the boundary and hence the error in the path length in each
volume. This may influence the results especially in the case when EM fields are present.
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deltaChord |
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lengthSafety | all volumes will have an additional overlap of this length
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thresholdCutCharged | energy below which charged particles are not tracked
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thresholdCutPhotons | energy below which photons are not tracked
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