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parameters.md

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Parameter Files

ATTPCROOT uses FairRoot's parameter system to manage experiment-specific detector configuration. The main container class is AtDigiPar, defined in AtParameter/AtDigiPar.h.

Loading Parameters in a Macro

FairRuntimeDb *rtdb = run->GetRuntimeDb();
FairParAsciiFileIo *parIo = new FairParAsciiFileIo();
parIo->open("parameters/ATTPC.myexperiment.par", "in");
rtdb->setFirstInput(parIo);
rtdb->getContainer("AtDigiPar");

Parameter files live in parameters/. Each file typically contains an [AtDigiPar] section followed by key-value pairs. Pick the file that matches the experiment or create a new one by copying a current experiment file such as parameters/ATTPC.e20020.par.

AtDigiPar Parameters

AtDigiPar::getParams() requires the following keys:

Electromagnetic Fields

Parameter Type Unit Description
EField Double_t V/m Longitudinal drift electric field
BField Double_t T Longitudinal magnetic field

Detector Geometry

Parameter Type Unit Description
TBEntrance Int_t time buckets Beam entrance position at detector entrance
ZPadPlane Double_t mm Position of the micromegas pad plane (detector length)

Gas Physics

Parameter Type Unit Description
DriftVelocity Double_t cm/µs Electron drift velocity
EIonize Double_t eV Effective ionization energy of the fill gas
Fano Double_t — Fano factor of the fill gas
CoefL Double_t cm²/µs Longitudinal diffusion coefficient
CoefT Double_t cm²/µs Transverse diffusion coefficient
GasPressure Double_t torr Gas pressure
Density Double_t kg/m³ Gas density

Electronics

Parameter Type Unit Description
SamplingRate Int_t MHz GET electronics sampling frequency
GETGain Double_t fC Gain from GET electronics
PeakingTime Int_t ns Electronic response peaking time
Gain Double_t — Average micromegas amplification factor

Accessing Parameters in Code

Tasks retrieve AtDigiPar from FairRuntimeDb in their Init():

auto *rtdb = FairRuntimeDb::instance();
fPar = dynamic_cast<AtDigiPar *>(rtdb->getContainer("AtDigiPar"));

Then in Exec():

double driftVel = fPar->GetDriftVelocity(); // cm/µs
double bField   = fPar->GetBField();         // T

Example AtDigiPar Block

[AtDigiPar]
BField:Double_t         2.0
EField:Double_t         5000
TBEntrance:Int_t        445
ZPadPlane:Double_t      1000.0
EIonize:Double_t        15.603
Fano:Double_t           0.24
CoefL:Double_t          0.0003
CoefT:Double_t          0.0003
GasPressure:Double_t    600
Density:Double_t        0.197
DriftVelocity:Double_t  0.87
Gain:Double_t           1000
SamplingRate:Int_t      3
GETGain:Double_t        1000
PeakingTime:Int_t       720

Copy a complete file from parameters/ and edit the values for the target experiment.