Geant4  10.01.p02
G4Mag_SpinEqRhs.cc
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27 // $Id: G4Mag_SpinEqRhs.cc 78728 2014-01-20 12:57:20Z gcosmo $
28 //
29 // This is the standard right-hand side for equation of motion.
30 // This version of the right-hand side includes the three components
31 // of the particle's spin.
32 //
33 // J. Apostolakis, February 8th, 1999
34 // P. Gumplinger, February 8th, 1999
35 // D. Cote-Ahern, P. Gumplinger, April 11th, 2001
36 //
37 // --------------------------------------------------------------------
38 
39 #include "G4Mag_SpinEqRhs.hh"
40 #include "G4PhysicalConstants.hh"
41 #include "G4SystemOfUnits.hh"
42 #include "G4MagneticField.hh"
43 #include "G4ThreeVector.hh"
44 
46  : G4Mag_EqRhs( MagField ), charge(0.), mass(0.), magMoment(0.),
47  spin(0.), omegac(0.), anomaly(0.0011659208), beta(0.), gamma(0.)
48 {
49 }
50 
52 {
53 }
54 
55 void
57  G4double MomentumXc,
58  G4double particleMass)
59 {
60  G4Mag_EqRhs::SetChargeMomentumMass( particleCharge, MomentumXc, mass);
61 
62  charge = particleCharge.GetCharge();
63  mass = particleMass;
64  magMoment = particleCharge.GetMagneticDipoleMoment();
65  spin = particleCharge.GetSpin();
66 
67  omegac = (eplus/mass)*c_light;
68 
69  G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared);
70 
71  G4double g_BMT;
72  if ( spin != 0. ) g_BMT = (magMoment/muB)/spin;
73  else g_BMT = 2.;
74 
75  anomaly = (g_BMT - 2.)/2.;
76 
77  G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass));
78  beta = MomentumXc/E;
79  gamma = E/mass;
80 }
81 
82 void
84  const G4double B[3],
85  G4double dydx[] ) const
86 {
87  G4double momentum_mag_square = sqr(y[3]) + sqr(y[4]) + sqr(y[5]);
88  G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
89  G4double cof = FCof()*inv_momentum_magnitude;
90 
91  dydx[0] = y[3] * inv_momentum_magnitude; // (d/ds)x = Vx/V
92  dydx[1] = y[4] * inv_momentum_magnitude; // (d/ds)y = Vy/V
93  dydx[2] = y[5] * inv_momentum_magnitude; // (d/ds)z = Vz/V
94 
95  if (charge == 0.) {
96  dydx[3] = 0.;
97  dydx[4] = 0.;
98  dydx[5] = 0.;
99  } else {
100  dydx[3] = cof*(y[4]*B[2] - y[5]*B[1]) ; // Ax = a*(Vy*Bz - Vz*By)
101  dydx[4] = cof*(y[5]*B[0] - y[3]*B[2]) ; // Ay = a*(Vz*Bx - Vx*Bz)
102  dydx[5] = cof*(y[3]*B[1] - y[4]*B[0]) ; // Az = a*(Vx*By - Vy*Bx)
103  }
104 
105  G4ThreeVector u(y[3], y[4], y[5]);
106  u *= inv_momentum_magnitude;
107 
108  G4ThreeVector BField(B[0],B[1],B[2]);
109 
110  G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
111  G4double ucb = (anomaly+1./gamma)/beta;
112 
113  // Initialise the values of dydx that we do not update.
114  dydx[6] = dydx[7] = dydx[8] = 0.0;
115 
116  G4ThreeVector Spin(y[9],y[10],y[11]);
117 
118  G4double pcharge;
119  if (charge == 0.) pcharge = 1.;
120  else pcharge = charge;
121 
122  G4ThreeVector dSpin(0.,0.,0.);
123  if (Spin.mag2() != 0.) {
124  dSpin = pcharge*omegac*(ucb*(Spin.cross(BField))-udb*(Spin.cross(u)));
125  }
126 
127  dydx[ 9] = dSpin.x();
128  dydx[10] = dSpin.y();
129  dydx[11] = dSpin.z();
130 
131  return ;
132 }
void SetChargeMomentumMass(G4ChargeState particleCharge, G4double MomentumXc, G4double mass)
G4double GetCharge() const
CLHEP::Hep3Vector G4ThreeVector
G4double FCof() const
Definition: G4Mag_EqRhs.hh:84
virtual void SetChargeMomentumMass(G4ChargeState particleCharge, G4double MomentumXc, G4double mass)
Definition: G4Mag_EqRhs.cc:56
G4double GetSpin() const
G4double GetMagneticDipoleMoment() const
G4Mag_SpinEqRhs(G4MagneticField *MagField)
T sqr(const T &x)
Definition: templates.hh:145
double G4double
Definition: G4Types.hh:76
static const double eplus
Definition: G4SIunits.hh:178
void EvaluateRhsGivenB(const G4double y[], const G4double B[3], G4double dydx[]) const