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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 ), charge(0.), mass(0.), magMoment(0.),
>> 40 spin(0.), fElectroMagCof(0.), fMassCof(0.), omegac(0.),
>> 41 anomaly(0.0011659208), beta(0.), gamma(0.)
40 { 42 {
41 } 43 }
42 44
43 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() = << 45 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin()
>> 46 {
>> 47 }
44 48
45 void 49 void
46 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4C 50 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4ChargeState particleCharge,
47 G4d 51 G4double MomentumXc,
48 G4d 52 G4double particleMass)
49 { 53 {
50 charge = particleCharge.GetCharge(); 54 charge = particleCharge.GetCharge();
51 mass = particleMass; 55 mass = particleMass;
52 magMoment = particleCharge.GetMagneticDipol 56 magMoment = particleCharge.GetMagneticDipoleMoment();
53 spin = particleCharge.GetSpin(); 57 spin = particleCharge.GetSpin();
54 58
55 fElectroMagCof = eplus*charge*c_light ; 59 fElectroMagCof = eplus*charge*c_light ;
56 fMassCof = mass*mass; 60 fMassCof = mass*mass;
57 61
58 omegac = (eplus/mass)*c_light; 62 omegac = (eplus/mass)*c_light;
59 63
60 G4double muB = 0.5*eplus*hbar_Planck/(mass/ 64 G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared);
61 65
62 G4double g_BMT; 66 G4double g_BMT;
63 if ( spin != 0. ) << 67 if ( spin != 0. ) g_BMT = (std::abs(magMoment)/muB)/spin;
64 { << 68 else g_BMT = 2.;
65 g_BMT = (std::abs(magMoment)/muB)/spin; <<
66 } <<
67 else <<
68 { <<
69 g_BMT = 2.; <<
70 } <<
71 69
72 anomaly = (g_BMT - 2.)/2.; 70 anomaly = (g_BMT - 2.)/2.;
73 71
74 G4double E = std::sqrt(sqr(MomentumXc)+sqr( 72 G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass));
75 beta = MomentumXc/E; 73 beta = MomentumXc/E;
76 gamma = E/mass; 74 gamma = E/mass;
77 } 75 }
78 76
79 void 77 void
80 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G 78 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G4double y[],
81 const G 79 const G4double Field[],
82 G 80 G4double dydx[] ) const
83 { 81 {
84 82
85 // Components of y: 83 // Components of y:
86 // 0-2 dr/ds, 84 // 0-2 dr/ds,
87 // 3-5 dp/ds - momentum derivatives 85 // 3-5 dp/ds - momentum derivatives
88 // 9-11 dSpin/ds = (1/beta) dSpin/dt - s 86 // 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives
89 87
90 // The BMT equation, following J.D.Jackson, 88 // The BMT equation, following J.D.Jackson, Classical
91 // Electrodynamics, Second Edition, 89 // Electrodynamics, Second Edition,
92 // dS/dt = (e/mc) S \cross 90 // dS/dt = (e/mc) S \cross
93 // [ (g/2-1 +1/\gamma) B 91 // [ (g/2-1 +1/\gamma) B
94 // -(g/2-1)\gamma/(\gamma+1) 92 // -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta
95 // -(g/2-\gamma/(\gamma+1) \b 93 // -(g/2-\gamma/(\gamma+1) \beta \cross E ]
96 // where 94 // where
97 // S = \vec{s}, where S^2 = 1 95 // S = \vec{s}, where S^2 = 1
98 // B = \vec{B} 96 // B = \vec{B}
99 // \beta = \vec{\beta} = \beta \vec{u} with 97 // \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1
100 // E = \vec{E} 98 // E = \vec{E}
101 99
102 G4double pSquared = y[3]*y[3] + y[4]*y[4] + 100 G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;
103 101
104 G4double Energy = std::sqrt( pSquared + f 102 G4double Energy = std::sqrt( pSquared + fMassCof );
105 G4double cof2 = Energy/c_light ; 103 G4double cof2 = Energy/c_light ;
106 104
107 G4double pModuleInverse = 1.0/std::sqrt(pS 105 G4double pModuleInverse = 1.0/std::sqrt(pSquared) ;
108 106
109 G4double inverse_velocity = Energy * pModul 107 G4double inverse_velocity = Energy * pModuleInverse / c_light;
110 108
111 G4double cof1 = fElectroMagCof*pModuleInver 109 G4double cof1 = fElectroMagCof*pModuleInverse ;
112 110
113 dydx[0] = y[3]*pModuleInverse ; 111 dydx[0] = y[3]*pModuleInverse ;
114 dydx[1] = y[4]*pModuleInverse ; 112 dydx[1] = y[4]*pModuleInverse ;
115 dydx[2] = y[5]*pModuleInverse ; 113 dydx[2] = y[5]*pModuleInverse ;
116 114
117 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field 115 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ;
118 116
119 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field 117 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ;
120 118
121 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field 119 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ;
122 120
123 dydx[6] = dydx[8] = 0.;//not used 121 dydx[6] = dydx[8] = 0.;//not used
124 122
125 // Lab Time of flight 123 // Lab Time of flight
126 dydx[7] = inverse_velocity; 124 dydx[7] = inverse_velocity;
127 125
128 G4ThreeVector BField(Field[0],Field[1],Fiel 126 G4ThreeVector BField(Field[0],Field[1],Field[2]);
129 G4ThreeVector EField(Field[3],Field[4],Fiel 127 G4ThreeVector EField(Field[3],Field[4],Field[5]);
130 128
131 EField /= c_light; 129 EField /= c_light;
132 130
133 G4ThreeVector u(y[3], y[4], y[5]); 131 G4ThreeVector u(y[3], y[4], y[5]);
134 u *= pModuleInverse; 132 u *= pModuleInverse;
135 133
136 G4double udb = anomaly*beta*gamma/(1.+gamma 134 G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
137 G4double ucb = (anomaly+1./gamma)/beta; 135 G4double ucb = (anomaly+1./gamma)/beta;
138 G4double uce = anomaly + 1./(gamma+1.); 136 G4double uce = anomaly + 1./(gamma+1.);
139 137
140 G4ThreeVector Spin(y[9],y[10],y[11]); 138 G4ThreeVector Spin(y[9],y[10],y[11]);
141 139
142 G4double pcharge; 140 G4double pcharge;
143 if (charge == 0.) 141 if (charge == 0.)
144 { 142 {
145 pcharge = 1.; 143 pcharge = 1.;
146 } 144 }
147 else 145 else
148 { 146 {
149 pcharge = charge; 147 pcharge = charge;
150 } 148 }
151 149
152 G4ThreeVector dSpin(0.,0.,0.); 150 G4ThreeVector dSpin(0.,0.,0.);
153 if (Spin.mag2() != 0.) 151 if (Spin.mag2() != 0.)
154 { 152 {
155 dSpin = pcharge*omegac*( ucb*(Spin.cross 153 dSpin = pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u))
156 // from Jackson 154 // from Jackson
157 // -uce*Spin.cross( 155 // -uce*Spin.cross(u.cross(EField)) );
158 // but this form ha 156 // but this form has one less operation
159 - uce*(u*(Spin*EField) - 157 - uce*(u*(Spin*EField) - EField*(Spin*u)) );
160 } 158 }
161 159
162 dydx[ 9] = dSpin.x(); 160 dydx[ 9] = dSpin.x();
163 dydx[10] = dSpin.y(); 161 dydx[10] = dSpin.y();
164 dydx[11] = dSpin.z(); 162 dydx[11] = dSpin.z();
165 163
166 return; 164 return;
167 } 165 }
168 166