G4MonopoleEquation.cc

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// $Id: G4MonopoleEquation.cc,v 1.2 2010/12/12 18:02:24 sunanda Exp $
// GEANT4 tag $Name: CMSSW_6_2_0 $
//
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
//
//
// class G4MonopoleEquation
//
// Class description:
//
//
//  This is the standard right-hand side for equation of motion.
//
//  The only case another is required is when using a moving reference
//  frame ... or extending the class to include additional Forces,
//  eg an electric field
//
//  10.11.98   V.Grichine
//
//  30.04.10   S.Burdin (modified to use for the monopole trajectories).
//
//  15.06.10   B.Bozsogi (replaced the hardcoded magnetic charge with
//                        the one passed by G4MonopoleTransportation)
//                       +workaround to pass the electric charge.
// 
//  12.07.10  S.Burdin (added equations for the electric charges)
// -------------------------------------------------------------------

#include "SimG4Core/MagneticField/interface/G4MonopoleEquation.hh"
#include "globals.hh"
#include <iomanip>

G4MonopoleEquation::G4MonopoleEquation(G4ElectroMagneticField *emField )
      : G4EquationOfMotion( emField ) {
}

void  
G4MonopoleEquation::SetChargeMomentumMass(G4double particleMagneticCharge, // e+ units
                                          G4double particleElectricCharge,
                                          G4double particleMass)
{
  //   fElCharge = particleElectricCharge;
   fElCharge =eplus* particleElectricCharge*c_light;
   
   
   fMagCharge =  eplus*particleMagneticCharge*c_light ;

//    G4cout << " G4MonopoleEquation: ElectricCharge=" << particleElectricCharge
//    << "; MagneticCharge=" << particleMagneticCharge
//    << G4endl;

   
   fMassCof = particleMass*particleMass ; 
}

void
G4MonopoleEquation::EvaluateRhsGivenB(const G4double y[],
                            const G4double Field[],
                              G4double dydx[] ) const
{
  
   // Components of y:
   //    0-2 dr/ds, 
   //    3-5 dp/ds - momentum derivatives 

   G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;

   G4double Energy   = std::sqrt( pSquared + fMassCof );
   
   //   G4double pModuleInverse  = (pSquared <= 0.0) ? 0.0 : 1.0/std::sqrt(pSquared);
   G4double pModuleInverse  = 1.0/std::sqrt(pSquared);

   G4double inverse_velocity = Energy * pModuleInverse / c_light;

   G4double cofEl     = fElCharge * pModuleInverse ;
   G4double cofMag = fMagCharge * Energy * pModuleInverse; 


   dydx[0] = y[3]*pModuleInverse ;                         
   dydx[1] = y[4]*pModuleInverse ;                         
   dydx[2] = y[5]*pModuleInverse ;                    
     
   // G4double magCharge = twopi * hbar_Planck / (eplus * mu0);    
   // magnetic charge in SI units A*m convention
   //  see http://en.wikipedia.org/wiki/Magnetic_monopole   
   //   G4cout  << "Magnetic charge:  " << magCharge << G4endl;
   
   // dp/ds = dp/dt * dt/ds = dp/dt / v = Force / velocity
   
   //     dydx[3] = fMagCharge * Field[0]  * inverse_velocity  * c_light;    // multiplied by c_light to convert to MeV/mm
   //     dydx[4] = fMagCharge * Field[1]  * inverse_velocity  * c_light; 
   //     dydx[5] = fMagCharge * Field[2]  * inverse_velocity  * c_light; 
   
   dydx[3] = cofMag * Field[0] + cofEl * (y[4]*Field[2] - y[5]*Field[1]);   
   dydx[4] = cofMag * Field[1] + cofEl * (y[5]*Field[0] - y[3]*Field[2]); 
   dydx[5] = cofMag * Field[2] + cofEl * (y[3]*Field[1] - y[4]*Field[0]); 
   
//        G4cout << std::setprecision(5)<< "E=" << Energy
//        << "; p="<< 1/pModuleInverse
//        << "; mC="<< magCharge
//        <<"; x=" << y[0]
//        <<"; y=" << y[1]
//        <<"; z=" << y[2]
//        <<"; dydx[3]=" << dydx[3]
//        <<"; dydx[4]=" << dydx[4]
//        <<"; dydx[5]=" << dydx[5]
//        << G4endl;

   dydx[6] = 0.;//not used

   
   // Lab Time of flight
   dydx[7] = inverse_velocity;
   return ;
}