geant4/examples/extended/field/field04/include/F04GlobalField.hh

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/// \file F04GlobalField.hh
/// \brief Definition of the F04GlobalField class

#ifndef F04GlobalField_h
#define F04GlobalField_h 1

#include "F04DetectorConstruction.hh"
#include "F04ElementField.hh"
#include "F04FieldMessenger.hh"

#include "G4ChordFinder.hh"
#include "G4ElectroMagneticField.hh"
#include "G4EqEMFieldWithSpin.hh"
#include "G4EqMagElectricField.hh"
#include "G4FieldManager.hh"
#include "G4MagIntegratorStepper.hh"
#include "G4Mag_EqRhs.hh"
#include "G4Mag_SpinEqRhs.hh"
#include "G4MagneticField.hh"
#include "G4PropagatorInField.hh"

#include <vector>

//  F04GlobalField - handles the global ElectroMagnetic field
//
//  There is a single G04GlobalField object.
//
//  The field from each individual beamline element is given by a
//  ElementField object. Any number of overlapping ElementField
//  objects can be added to the global field. Any element that
//  represents an element with an EM field must add the appropriate
//  ElementField to the global GlobalField object.

using FieldList = std::vector<F04ElementField*>;

class F04GlobalField : public G4ElectroMagneticField
{
    // class F04GlobalField : public G4MagneticField {

  private:
    F04GlobalField(F04DetectorConstruction* const);
    F04GlobalField(const F04GlobalField&);

    F04GlobalField& operator=(const F04GlobalField&);

    void SetupArray();

  public:
    ~F04GlobalField() override;

    /// GetObject() returns the single F04GlobalField object.
    /// It is constructed, if necessary.
    static F04GlobalField* GetObject(F04DetectorConstruction* const);
    static F04GlobalField* GetObject();

    /// GetFieldValue() returns the field value at a given point[].
    /// field is really field[6]: Bx,By,Bz,Ex,Ey,Ez.
    /// point[] is in global coordinates: x,y,z,t.
    void GetFieldValue(const G4double* point, G4double* field) const override;

    /// DoesFieldChangeEnergy() returns true.
    G4bool DoesFieldChangeEnergy() const override { return true; }

    /// AddElementField() adds the ElementField object for a single
    /// element to the global field.
    void AddElementField(F04ElementField* f)
    {
      if (fFields) fFields->push_back(f);
    }

    /// Clear() removes all ElementField-s from the global object,
    /// and destroys them. Used before the geometry is completely
    /// re-created.
    void Clear();

    /// constructs all field tracking objects
    void ConstructField();

    /// Set the Stepper types
    void SetStepperType(G4int i) { fStepperType = i; }

    /// Set the Stepper
    void SetStepper();

    /// Set the minimum step length
    void SetMinStep(G4double stp) { fMinStep = stp; }

    /// Set the delta chord length
    void SetDeltaChord(G4double dcr) { fDeltaChord = dcr; }

    /// Set the delta one step length
    void SetDeltaOneStep(G4double stp) { fDeltaOneStep = stp; }

    /// Set the delta intersection length
    void SetDeltaIntersection(G4double its) { fDeltaIntersection = its; }

    /// Set the minimum eps length
    void SetEpsMin(G4double eps) { fEpsMin = eps; }

    /// Set the maximum eps length
    void SetEpsMax(G4double eps) { fEpsMax = eps; }

    /// Return the list of Element Fields
    FieldList* GetFields() { return fFields; }

  protected:
    /// Get the global field manager
    G4FieldManager* GetGlobalFieldManager();

  private:
    static G4ThreadLocal F04GlobalField* fObject;

    G4int fNfp = 0;
    G4bool fFirst = true;

    FieldList* fFields = nullptr;

    const F04ElementField** fFp = nullptr;

  private:
    // A. INVARIANTS:
    // --------------
    // INVARIANT: an integer to indicate the type of RK integration method ('stepper') used
    G4int fStepperType = 4;  // ClassicalRK4 is default stepper;

    // INVARIANTS: Accuracy parameters of field propagation (and the integration it uses.)
    // 1. These values are lengths - initialised in src
    G4double fMinStep = 0.01 * CLHEP::mm;
    G4double fDeltaChord = 3.0 * CLHEP::mm;
    G4double fDeltaOneStep = 0.01 * CLHEP::mm;
    G4double fDeltaIntersection = 0.1 * CLHEP::mm;
    // 2. Dimensionless numbers - can initialise here
    G4double fEpsMin = 2.5e-7;  // Relative accuracy of integration (minimum)
    G4double fEpsMax = 0.001;  // Relative accuracy of integration (maximum)

    // B. STATE: objects which carry out the propagation and are modified during tracking
    // --------
    //  G4Mag_EqRhs*            fEquation;
    //  G4Mag_SpinEqRhs*        fEquation;

    //  G4EqMagElectricField*   fEquation;
    G4EqEMFieldWithSpin* fEquation = nullptr;

    G4FieldManager* fFieldManager = nullptr;
    G4PropagatorInField* fFieldPropagator = nullptr;
    G4MagIntegratorStepper* fStepper = nullptr;
    G4ChordFinder* fChordFinder = nullptr;

    // INVARIANTS during tracking: Auxiliary class & information - used for setup
    F04FieldMessenger* fFieldMessenger;
    F04DetectorConstruction* fDetectorConstruction = nullptr;
};

#endif