G4Mag_SpinEqRhs Class Reference

G4Mag_SpinEqRhs defines the equation of motion for a particle with spin in a pure magnetic field. The three components of the particle's spin are treated utilising BMT equation. More...

#include <G4Mag_SpinEqRhs.hh>

Inheritance diagram for G4Mag_SpinEqRhs:

Public Member Functions
	G4Mag_SpinEqRhs (G4MagneticField *MagField)
	~G4Mag_SpinEqRhs () override=default
void	SetChargeMomentumMass (G4ChargeState particleCharge, G4double MomentumXc, G4double mass) override
void	EvaluateRhsGivenB (const G4double y[], const G4double B[3], G4double dydx[]) const override
void	SetAnomaly (G4double a)
G4double	GetAnomaly () const
G4EquationType	GetEquationType () const override
Public Member Functions inherited from G4Mag_EqRhs
	G4Mag_EqRhs (G4MagneticField *magField)
	~G4Mag_EqRhs () override=default
G4double	FCof () const
Public Member Functions inherited from G4EquationOfMotion
	G4EquationOfMotion (G4Field *Field)
virtual	~G4EquationOfMotion ()=default
void	RightHandSide (const G4double y[], G4double dydx[]) const
void	EvaluateRhsReturnB (const G4double y[], G4double dydx[], G4double Field[]) const
void	GetFieldValue (const G4double Point[4], G4double Field[]) const
const G4Field *	GetFieldObj () const
G4Field *	GetFieldObj ()
void	SetFieldObj (G4Field *pField)

Detailed Description

G4Mag_SpinEqRhs defines the equation of motion for a particle with spin in a pure magnetic field. The three components of the particle's spin are treated utilising BMT equation.

Definition at line 51 of file G4Mag_SpinEqRhs.hh.

Constructor & Destructor Documentation

G4Mag_SpinEqRhs()

G4Mag_SpinEqRhs::G4Mag_SpinEqRhs

(

G4MagneticField *

MagField

)

Constructor for G4Mag_SpinEqRhs.

Parameters

[in]

MagField

Pointer to the associated magnetic field.

Definition at line 37 of file G4Mag_SpinEqRhs.cc.

  : G4Mag_EqRhs( MagField )
{
}

~G4Mag_SpinEqRhs()

G4Mag_SpinEqRhs::~G4Mag_SpinEqRhs ( )

overridedefault

Default Destructor.

Member Function Documentation

EvaluateRhsGivenB()

void G4Mag_SpinEqRhs::EvaluateRhsGivenB ( const G4double y[], const G4double B[3], G4double dydx[] ) const

overridevirtual

Calculates the value of the derivative, given the value of the field.

Parameters

[in]	y	Coefficients array.
[in]	B	Field value.
[out]	dydx	Derivatives array.

Implements G4Mag_EqRhs.

Definition at line 76 of file G4Mag_SpinEqRhs.cc.

{
   G4double momentum_mag_square = sqr(y[3]) + sqr(y[4]) + sqr(y[5]);
   G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
   G4double cof = FCof()*inv_momentum_magnitude;
 
   dydx[0] = y[3] * inv_momentum_magnitude;       //  (d/ds)x = Vx/V
   dydx[1] = y[4] * inv_momentum_magnitude;       //  (d/ds)y = Vy/V
   dydx[2] = y[5] * inv_momentum_magnitude;       //  (d/ds)z = Vz/V
 
   if (charge == 0.)
   {
      dydx[3] = 0.;
      dydx[4] = 0.;
      dydx[5] = 0.;
   }
   else
   {
      dydx[3] = cof*(y[4]*B[2] - y[5]*B[1]) ;   // Ax = a*(Vy*Bz - Vz*By)
      dydx[4] = cof*(y[5]*B[0] - y[3]*B[2]) ;   // Ay = a*(Vz*Bx - Vx*Bz)
      dydx[5] = cof*(y[3]*B[1] - y[4]*B[0]) ;   // Az = a*(Vx*By - Vy*Bx)
   }
 
   G4ThreeVector u(y[3], y[4], y[5]);
   u *= inv_momentum_magnitude; 
 
   G4ThreeVector BField(B[0],B[1],B[2]);
 
   G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u); 
   G4double ucb = (anomaly+1./gamma)/beta;
 
   // Initialise the values of dydx that we do not update.
   dydx[6] = dydx[7] = dydx[8] = 0.0;
 
   G4ThreeVector Spin(y[9],y[10],y[11]);
 
   G4double pcharge;
   if (charge == 0.)
   {
     pcharge = 1.;
   }
   else
   {
     pcharge = charge;
   }
 
   G4ThreeVector dSpin(0.,0.,0.);
   if (Spin.mag2() != 0.)
   {
     dSpin = pcharge*omegac*(ucb*(Spin.cross(BField))-udb*(Spin.cross(u)));
   }
 
   dydx[9] = dSpin.x();
   dydx[10] = dSpin.y();
   dydx[11] = dSpin.z();
 
   return;
}

GetAnomaly()

G4double G4Mag_SpinEqRhs::GetAnomaly ( ) const

inline

Definition at line 87 of file G4Mag_SpinEqRhs.hh.

{ return anomaly; }

GetEquationType()

G4EquationType G4Mag_SpinEqRhs::GetEquationType ( ) const

inlineoverridevirtual

Returns the equation of motion type ID, i.e. "kEqMagneticWithSpin".

Reimplemented from G4EquationOfMotion.

Definition at line 92 of file G4Mag_SpinEqRhs.hh.

{ return kEqMagneticWithSpin; }

SetAnomaly()

void G4Mag_SpinEqRhs::SetAnomaly ( G4double a )

inline

Setter and getter for the magnetic anomaly.

Definition at line 86 of file G4Mag_SpinEqRhs.hh.

{ anomaly = a; }

SetChargeMomentumMass()

void G4Mag_SpinEqRhs::SetChargeMomentumMass ( G4ChargeState particleCharge, G4double MomentumXc, G4double mass )

overridevirtual

Sets the charge momentum mass value.

Reimplemented from G4Mag_EqRhs.

Definition at line 43 of file G4Mag_SpinEqRhs.cc.

{
   G4Mag_EqRhs::SetChargeMomentumMass( particleCharge, MomentumXc, mass);
 
   charge = particleCharge.GetCharge();
   mass      = particleMass;
   magMoment = particleCharge.GetMagneticDipoleMoment();
   spin      = particleCharge.GetSpin();
 
   omegac = (eplus/mass)*c_light;
 
   G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared);
 
   G4double g_BMT;
   if ( spin != 0. )
   {
     g_BMT = (std::abs(magMoment)/muB)/spin;
   }
   else
   {
     g_BMT = 2.;
   }
 
   anomaly = (g_BMT - 2.)/2.;
 
   G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass));
   beta  = MomentumXc/E;
   gamma = E/mass;
}

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The documentation for this class was generated from the following files:

• G4Mag_SpinEqRhs.hh
• G4Mag_SpinEqRhs.cc