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25 // 25 //
26 // G4EqEMFieldWithSpin implementation 26 // G4EqEMFieldWithSpin implementation
27 // 27 //
28 // Created: Chris Gong & Peter Gumplinger, 30. 28 // Created: Chris Gong & Peter Gumplinger, 30.08.2007
29 // ------------------------------------------- 29 // -------------------------------------------------------------------
30 30
31 #include "G4EqEMFieldWithSpin.hh" 31 #include "G4EqEMFieldWithSpin.hh"
32 #include "G4ElectroMagneticField.hh" 32 #include "G4ElectroMagneticField.hh"
33 #include "G4ThreeVector.hh" 33 #include "G4ThreeVector.hh"
34 #include "globals.hh" 34 #include "globals.hh"
35 #include "G4PhysicalConstants.hh" 35 #include "G4PhysicalConstants.hh"
36 #include "G4SystemOfUnits.hh" 36 #include "G4SystemOfUnits.hh"
37 37
38 G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4Ele 38 G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4ElectroMagneticField *emField )
39 : G4EquationOfMotion( emField ) 39 : G4EquationOfMotion( emField )
40 { 40 {
41 } 41 }
42 42
43 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() = 43 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() = default;
44 44
45 void 45 void
46 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4C 46 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4ChargeState particleCharge,
47 G4d 47 G4double MomentumXc,
48 G4d 48 G4double particleMass)
49 { 49 {
50 charge = particleCharge.GetCharge(); 50 charge = particleCharge.GetCharge();
51 mass = particleMass; 51 mass = particleMass;
52 magMoment = particleCharge.GetMagneticDipol 52 magMoment = particleCharge.GetMagneticDipoleMoment();
53 spin = particleCharge.GetSpin(); 53 spin = particleCharge.GetSpin();
54 54
55 fElectroMagCof = eplus*charge*c_light ; 55 fElectroMagCof = eplus*charge*c_light ;
56 fMassCof = mass*mass; 56 fMassCof = mass*mass;
57 57
58 omegac = (eplus/mass)*c_light; 58 omegac = (eplus/mass)*c_light;
59 59
60 G4double muB = 0.5*eplus*hbar_Planck/(mass/ 60 G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared);
61 61
62 G4double g_BMT; 62 G4double g_BMT;
63 if ( spin != 0. ) 63 if ( spin != 0. )
64 { 64 {
65 g_BMT = (std::abs(magMoment)/muB)/spin; 65 g_BMT = (std::abs(magMoment)/muB)/spin;
66 } 66 }
67 else 67 else
68 { 68 {
69 g_BMT = 2.; 69 g_BMT = 2.;
70 } 70 }
71 71
72 anomaly = (g_BMT - 2.)/2.; 72 anomaly = (g_BMT - 2.)/2.;
73 73
74 G4double E = std::sqrt(sqr(MomentumXc)+sqr( 74 G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass));
75 beta = MomentumXc/E; 75 beta = MomentumXc/E;
76 gamma = E/mass; 76 gamma = E/mass;
77 } 77 }
78 78
79 void 79 void
80 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G 80 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G4double y[],
81 const G 81 const G4double Field[],
82 G 82 G4double dydx[] ) const
83 { 83 {
84 84
85 // Components of y: 85 // Components of y:
86 // 0-2 dr/ds, 86 // 0-2 dr/ds,
87 // 3-5 dp/ds - momentum derivatives 87 // 3-5 dp/ds - momentum derivatives
88 // 9-11 dSpin/ds = (1/beta) dSpin/dt - s 88 // 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives
89 89
90 // The BMT equation, following J.D.Jackson, 90 // The BMT equation, following J.D.Jackson, Classical
91 // Electrodynamics, Second Edition, 91 // Electrodynamics, Second Edition,
92 // dS/dt = (e/mc) S \cross 92 // dS/dt = (e/mc) S \cross
93 // [ (g/2-1 +1/\gamma) B 93 // [ (g/2-1 +1/\gamma) B
94 // -(g/2-1)\gamma/(\gamma+1) 94 // -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta
95 // -(g/2-\gamma/(\gamma+1) \b 95 // -(g/2-\gamma/(\gamma+1) \beta \cross E ]
96 // where 96 // where
97 // S = \vec{s}, where S^2 = 1 97 // S = \vec{s}, where S^2 = 1
98 // B = \vec{B} 98 // B = \vec{B}
99 // \beta = \vec{\beta} = \beta \vec{u} with 99 // \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1
100 // E = \vec{E} 100 // E = \vec{E}
101 101
102 G4double pSquared = y[3]*y[3] + y[4]*y[4] + 102 G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;
103 103
104 G4double Energy = std::sqrt( pSquared + f 104 G4double Energy = std::sqrt( pSquared + fMassCof );
105 G4double cof2 = Energy/c_light ; 105 G4double cof2 = Energy/c_light ;
106 106
107 G4double pModuleInverse = 1.0/std::sqrt(pS 107 G4double pModuleInverse = 1.0/std::sqrt(pSquared) ;
108 108
109 G4double inverse_velocity = Energy * pModul 109 G4double inverse_velocity = Energy * pModuleInverse / c_light;
110 110
111 G4double cof1 = fElectroMagCof*pModuleInver 111 G4double cof1 = fElectroMagCof*pModuleInverse ;
112 112
113 dydx[0] = y[3]*pModuleInverse ; 113 dydx[0] = y[3]*pModuleInverse ;
114 dydx[1] = y[4]*pModuleInverse ; 114 dydx[1] = y[4]*pModuleInverse ;
115 dydx[2] = y[5]*pModuleInverse ; 115 dydx[2] = y[5]*pModuleInverse ;
116 116
117 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field 117 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ;
118 118
119 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field 119 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ;
120 120
121 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field 121 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ;
122 122
123 dydx[6] = dydx[8] = 0.;//not used 123 dydx[6] = dydx[8] = 0.;//not used
124 124
125 // Lab Time of flight 125 // Lab Time of flight
126 dydx[7] = inverse_velocity; 126 dydx[7] = inverse_velocity;
127 127
128 G4ThreeVector BField(Field[0],Field[1],Fiel 128 G4ThreeVector BField(Field[0],Field[1],Field[2]);
129 G4ThreeVector EField(Field[3],Field[4],Fiel 129 G4ThreeVector EField(Field[3],Field[4],Field[5]);
130 130
131 EField /= c_light; 131 EField /= c_light;
132 132
133 G4ThreeVector u(y[3], y[4], y[5]); 133 G4ThreeVector u(y[3], y[4], y[5]);
134 u *= pModuleInverse; 134 u *= pModuleInverse;
135 135
136 G4double udb = anomaly*beta*gamma/(1.+gamma 136 G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
137 G4double ucb = (anomaly+1./gamma)/beta; 137 G4double ucb = (anomaly+1./gamma)/beta;
138 G4double uce = anomaly + 1./(gamma+1.); 138 G4double uce = anomaly + 1./(gamma+1.);
139 139
140 G4ThreeVector Spin(y[9],y[10],y[11]); 140 G4ThreeVector Spin(y[9],y[10],y[11]);
141 141
142 G4double pcharge; 142 G4double pcharge;
143 if (charge == 0.) 143 if (charge == 0.)
144 { 144 {
145 pcharge = 1.; 145 pcharge = 1.;
146 } 146 }
147 else 147 else
148 { 148 {
149 pcharge = charge; 149 pcharge = charge;
150 } 150 }
151 151
152 G4ThreeVector dSpin(0.,0.,0.); 152 G4ThreeVector dSpin(0.,0.,0.);
153 if (Spin.mag2() != 0.) 153 if (Spin.mag2() != 0.)
154 { 154 {
155 dSpin = pcharge*omegac*( ucb*(Spin.cross 155 dSpin = pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u))
156 // from Jackson 156 // from Jackson
157 // -uce*Spin.cross( 157 // -uce*Spin.cross(u.cross(EField)) );
158 // but this form ha 158 // but this form has one less operation
159 - uce*(u*(Spin*EField) - 159 - uce*(u*(Spin*EField) - EField*(Spin*u)) );
160 } 160 }
161 161
162 dydx[ 9] = dSpin.x(); 162 dydx[ 9] = dSpin.x();
163 dydx[10] = dSpin.y(); 163 dydx[10] = dSpin.y();
164 dydx[11] = dSpin.z(); 164 dydx[11] = dSpin.z();
165 165
166 return; 166 return;
167 } 167 }
168 168