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25 // 25 //
26 // G4EqEMFieldWithSpin implementation <<
27 // 26 //
28 // Created: Chris Gong & Peter Gumplinger, 30. << 27 // $Id: G4EqEMFieldWithSpin.cc 95822 2016-02-26 08:04:51Z gcosmo $
>> 28 //
>> 29 //
>> 30 // This is the standard right-hand side for equation of motion.
>> 31 //
>> 32 // 30.08.2007 Chris Gong, Peter Gumplinger
>> 33 // 14.02.2009 Kevin Lynch
>> 34 // 06.11.2009 Hiromi Iinuma
>> 35 //
29 // ------------------------------------------- 36 // -------------------------------------------------------------------
30 37
31 #include "G4EqEMFieldWithSpin.hh" 38 #include "G4EqEMFieldWithSpin.hh"
32 #include "G4ElectroMagneticField.hh" 39 #include "G4ElectroMagneticField.hh"
33 #include "G4ThreeVector.hh" 40 #include "G4ThreeVector.hh"
34 #include "globals.hh" 41 #include "globals.hh"
35 #include "G4PhysicalConstants.hh" 42 #include "G4PhysicalConstants.hh"
36 #include "G4SystemOfUnits.hh" 43 #include "G4SystemOfUnits.hh"
37 44
38 G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4Ele 45 G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4ElectroMagneticField *emField )
39 : G4EquationOfMotion( emField ) << 46 : G4EquationOfMotion( emField ), charge(0.), mass(0.), magMoment(0.),
>> 47 spin(0.), fElectroMagCof(0.), fMassCof(0.), omegac(0.),
>> 48 anomaly(0.0011659208), beta(0.), gamma(0.)
40 { 49 {
41 } 50 }
42 51
43 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() = << 52 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin()
>> 53 {
>> 54 }
44 55
45 void 56 void
46 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4C 57 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4ChargeState particleCharge,
47 G4d << 58 G4double MomentumXc,
48 G4d << 59 G4double particleMass)
49 { 60 {
50 charge = particleCharge.GetCharge(); 61 charge = particleCharge.GetCharge();
51 mass = particleMass; 62 mass = particleMass;
52 magMoment = particleCharge.GetMagneticDipol 63 magMoment = particleCharge.GetMagneticDipoleMoment();
53 spin = particleCharge.GetSpin(); 64 spin = particleCharge.GetSpin();
54 65
55 fElectroMagCof = eplus*charge*c_light ; 66 fElectroMagCof = eplus*charge*c_light ;
56 fMassCof = mass*mass; 67 fMassCof = mass*mass;
57 68
58 omegac = (eplus/mass)*c_light; 69 omegac = (eplus/mass)*c_light;
59 70
60 G4double muB = 0.5*eplus*hbar_Planck/(mass/ 71 G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared);
61 72
62 G4double g_BMT; 73 G4double g_BMT;
63 if ( spin != 0. ) << 74 if ( spin != 0. ) g_BMT = (std::abs(magMoment)/muB)/spin;
64 { << 75 else g_BMT = 2.;
65 g_BMT = (std::abs(magMoment)/muB)/spin; <<
66 } <<
67 else <<
68 { <<
69 g_BMT = 2.; <<
70 } <<
71 76
72 anomaly = (g_BMT - 2.)/2.; 77 anomaly = (g_BMT - 2.)/2.;
73 78
74 G4double E = std::sqrt(sqr(MomentumXc)+sqr( 79 G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass));
75 beta = MomentumXc/E; 80 beta = MomentumXc/E;
76 gamma = E/mass; 81 gamma = E/mass;
77 } 82 }
78 83
79 void 84 void
80 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G 85 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G4double y[],
81 const G 86 const G4double Field[],
82 G 87 G4double dydx[] ) const
83 { 88 {
84 89
85 // Components of y: 90 // Components of y:
86 // 0-2 dr/ds, 91 // 0-2 dr/ds,
87 // 3-5 dp/ds - momentum derivatives 92 // 3-5 dp/ds - momentum derivatives
88 // 9-11 dSpin/ds = (1/beta) dSpin/dt - s 93 // 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives
89 94
90 // The BMT equation, following J.D.Jackson, 95 // The BMT equation, following J.D.Jackson, Classical
91 // Electrodynamics, Second Edition, 96 // Electrodynamics, Second Edition,
92 // dS/dt = (e/mc) S \cross 97 // dS/dt = (e/mc) S \cross
93 // [ (g/2-1 +1/\gamma) B 98 // [ (g/2-1 +1/\gamma) B
94 // -(g/2-1)\gamma/(\gamma+1) 99 // -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta
95 // -(g/2-\gamma/(\gamma+1) \b 100 // -(g/2-\gamma/(\gamma+1) \beta \cross E ]
96 // where 101 // where
97 // S = \vec{s}, where S^2 = 1 102 // S = \vec{s}, where S^2 = 1
98 // B = \vec{B} 103 // B = \vec{B}
99 // \beta = \vec{\beta} = \beta \vec{u} with 104 // \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1
100 // E = \vec{E} 105 // E = \vec{E}
101 106
102 G4double pSquared = y[3]*y[3] + y[4]*y[4] + 107 G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;
103 108
104 G4double Energy = std::sqrt( pSquared + f 109 G4double Energy = std::sqrt( pSquared + fMassCof );
105 G4double cof2 = Energy/c_light ; 110 G4double cof2 = Energy/c_light ;
106 111
107 G4double pModuleInverse = 1.0/std::sqrt(pS 112 G4double pModuleInverse = 1.0/std::sqrt(pSquared) ;
108 113
109 G4double inverse_velocity = Energy * pModul 114 G4double inverse_velocity = Energy * pModuleInverse / c_light;
110 115
111 G4double cof1 = fElectroMagCof*pModuleInver << 116 G4double cof1 = fElectroMagCof*pModuleInverse ;
112 117
113 dydx[0] = y[3]*pModuleInverse ; 118 dydx[0] = y[3]*pModuleInverse ;
114 dydx[1] = y[4]*pModuleInverse ; 119 dydx[1] = y[4]*pModuleInverse ;
115 dydx[2] = y[5]*pModuleInverse ; 120 dydx[2] = y[5]*pModuleInverse ;
116 121
117 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field 122 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ;
118 123
119 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field 124 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ;
120 125
121 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field 126 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ;
122 127
123 dydx[6] = dydx[8] = 0.;//not used 128 dydx[6] = dydx[8] = 0.;//not used
124 129
125 // Lab Time of flight 130 // Lab Time of flight
126 dydx[7] = inverse_velocity; 131 dydx[7] = inverse_velocity;
127 132
128 G4ThreeVector BField(Field[0],Field[1],Fiel 133 G4ThreeVector BField(Field[0],Field[1],Field[2]);
129 G4ThreeVector EField(Field[3],Field[4],Fiel 134 G4ThreeVector EField(Field[3],Field[4],Field[5]);
130 135
131 EField /= c_light; 136 EField /= c_light;
132 137
133 G4ThreeVector u(y[3], y[4], y[5]); 138 G4ThreeVector u(y[3], y[4], y[5]);
134 u *= pModuleInverse; 139 u *= pModuleInverse;
135 140
136 G4double udb = anomaly*beta*gamma/(1.+gamma 141 G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
137 G4double ucb = (anomaly+1./gamma)/beta; 142 G4double ucb = (anomaly+1./gamma)/beta;
138 G4double uce = anomaly + 1./(gamma+1.); 143 G4double uce = anomaly + 1./(gamma+1.);
139 144
140 G4ThreeVector Spin(y[9],y[10],y[11]); 145 G4ThreeVector Spin(y[9],y[10],y[11]);
141 146
142 G4double pcharge; 147 G4double pcharge;
143 if (charge == 0.) << 148 if (charge == 0.) pcharge = 1.;
144 { << 149 else pcharge = charge;
145 pcharge = 1.; <<
146 } <<
147 else <<
148 { <<
149 pcharge = charge; <<
150 } <<
151 150
152 G4ThreeVector dSpin(0.,0.,0.); 151 G4ThreeVector dSpin(0.,0.,0.);
153 if (Spin.mag2() != 0.) << 152 if (Spin.mag2() != 0.) {
154 { << 153 dSpin =
155 dSpin = pcharge*omegac*( ucb*(Spin.cross << 154 pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u))
156 // from Jackson 155 // from Jackson
157 // -uce*Spin.cross( 156 // -uce*Spin.cross(u.cross(EField)) );
158 // but this form ha 157 // but this form has one less operation
159 - uce*(u*(Spin*EField) - 158 - uce*(u*(Spin*EField) - EField*(Spin*u)) );
160 } 159 }
161 160
162 dydx[ 9] = dSpin.x(); 161 dydx[ 9] = dSpin.x();
163 dydx[10] = dSpin.y(); 162 dydx[10] = dSpin.y();
164 dydx[11] = dSpin.z(); 163 dydx[11] = dSpin.z();
165 164
166 return; << 165 return ;
167 } 166 }
168 167