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25 // 25 //
26 // G4EqEMFieldWithSpin implementation <<
27 // 26 //
28 // Created: Chris Gong & Peter Gumplinger, 30. << 27 // $Id: G4EqEMFieldWithSpin.cc,v 1.8.2.1 2010/09/08 14:25:35 gcosmo Exp $
>> 28 // GEANT4 tag $Name: geant4-09-03-patch-02 $
>> 29 //
>> 30 //
>> 31 // This is the standard right-hand side for equation of motion.
>> 32 //
>> 33 // 30.08.2007 Chris Gong, Peter Gumplinger
>> 34 // 14.02.2009 Kevin Lynch
>> 35 // 06.11.2009 Hiromi Iinuma
>> 36 //
29 // ------------------------------------------- 37 // -------------------------------------------------------------------
30 38
31 #include "G4EqEMFieldWithSpin.hh" 39 #include "G4EqEMFieldWithSpin.hh"
32 #include "G4ElectroMagneticField.hh" 40 #include "G4ElectroMagneticField.hh"
33 #include "G4ThreeVector.hh" 41 #include "G4ThreeVector.hh"
34 #include "globals.hh" 42 #include "globals.hh"
35 #include "G4PhysicalConstants.hh" <<
36 #include "G4SystemOfUnits.hh" <<
37 43
38 G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4Ele 44 G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4ElectroMagneticField *emField )
39 : G4EquationOfMotion( emField ) << 45 : G4EquationOfMotion( emField ), fElectroMagCof(0.), fMassCof(0.),
>> 46 omegac(0.), anomaly(0.0011659208), pcharge(0.), E(0.), gamma(0.), beta(0.)
40 { 47 {
41 } 48 }
42 49
43 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() = << 50 G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin()
>> 51 {
>> 52 }
44 53
45 void 54 void
46 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4C << 55 G4EqEMFieldWithSpin::SetChargeMomentumMass(G4double particleCharge, // e+ units
47 G4d << 56 G4double MomentumXc,
48 G4d << 57 G4double particleMass)
49 { 58 {
50 charge = particleCharge.GetCharge(); << 59 fElectroMagCof = eplus*particleCharge*c_light ;
51 mass = particleMass; << 60 fMassCof = particleMass*particleMass ;
52 magMoment = particleCharge.GetMagneticDipol << 61
53 spin = particleCharge.GetSpin(); << 62 omegac = 0.105658387*GeV/particleMass * 2.837374841e-3*(rad/cm/kilogauss);
54 <<
55 fElectroMagCof = eplus*charge*c_light ; <<
56 fMassCof = mass*mass; <<
57 <<
58 omegac = (eplus/mass)*c_light; <<
59 <<
60 G4double muB = 0.5*eplus*hbar_Planck/(mass/ <<
61 <<
62 G4double g_BMT; <<
63 if ( spin != 0. ) <<
64 { <<
65 g_BMT = (std::abs(magMoment)/muB)/spin; <<
66 } <<
67 else <<
68 { <<
69 g_BMT = 2.; <<
70 } <<
71 63
72 anomaly = (g_BMT - 2.)/2.; << 64 pcharge = particleCharge;
73 65
74 G4double E = std::sqrt(sqr(MomentumXc)+sqr( << 66 E = std::sqrt(sqr(MomentumXc)+sqr(particleMass));
75 beta = MomentumXc/E; 67 beta = MomentumXc/E;
76 gamma = E/mass; << 68 gamma = E/particleMass;
>> 69
77 } 70 }
78 71
79 void 72 void
80 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G 73 G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G4double y[],
81 const G 74 const G4double Field[],
82 G 75 G4double dydx[] ) const
83 { 76 {
84 77
85 // Components of y: 78 // Components of y:
86 // 0-2 dr/ds, 79 // 0-2 dr/ds,
87 // 3-5 dp/ds - momentum derivatives 80 // 3-5 dp/ds - momentum derivatives
88 // 9-11 dSpin/ds = (1/beta) dSpin/dt - s 81 // 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives
89 82
90 // The BMT equation, following J.D.Jackson, 83 // The BMT equation, following J.D.Jackson, Classical
91 // Electrodynamics, Second Edition, 84 // Electrodynamics, Second Edition,
92 // dS/dt = (e/mc) S \cross 85 // dS/dt = (e/mc) S \cross
93 // [ (g/2-1 +1/\gamma) B 86 // [ (g/2-1 +1/\gamma) B
94 // -(g/2-1)\gamma/(\gamma+1) 87 // -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta
95 // -(g/2-\gamma/(\gamma+1) \b 88 // -(g/2-\gamma/(\gamma+1) \beta \cross E ]
96 // where 89 // where
97 // S = \vec{s}, where S^2 = 1 90 // S = \vec{s}, where S^2 = 1
98 // B = \vec{B} 91 // B = \vec{B}
99 // \beta = \vec{\beta} = \beta \vec{u} with 92 // \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1
100 // E = \vec{E} 93 // E = \vec{E}
101 94
102 G4double pSquared = y[3]*y[3] + y[4]*y[4] + 95 G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;
103 96
104 G4double Energy = std::sqrt( pSquared + f 97 G4double Energy = std::sqrt( pSquared + fMassCof );
105 G4double cof2 = Energy/c_light ; 98 G4double cof2 = Energy/c_light ;
106 99
107 G4double pModuleInverse = 1.0/std::sqrt(pS 100 G4double pModuleInverse = 1.0/std::sqrt(pSquared) ;
108 101
109 G4double inverse_velocity = Energy * pModul 102 G4double inverse_velocity = Energy * pModuleInverse / c_light;
110 103
111 G4double cof1 = fElectroMagCof*pModuleInver << 104 G4double cof1 = fElectroMagCof*pModuleInverse ;
112 105
113 dydx[0] = y[3]*pModuleInverse ; 106 dydx[0] = y[3]*pModuleInverse ;
114 dydx[1] = y[4]*pModuleInverse ; 107 dydx[1] = y[4]*pModuleInverse ;
115 dydx[2] = y[5]*pModuleInverse ; 108 dydx[2] = y[5]*pModuleInverse ;
116 109
117 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field 110 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ;
118 111
119 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field 112 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ;
120 113
121 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field 114 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ;
122 115
123 dydx[6] = dydx[8] = 0.;//not used 116 dydx[6] = dydx[8] = 0.;//not used
124 117
125 // Lab Time of flight 118 // Lab Time of flight
126 dydx[7] = inverse_velocity; 119 dydx[7] = inverse_velocity;
127 120
128 G4ThreeVector BField(Field[0],Field[1],Fiel 121 G4ThreeVector BField(Field[0],Field[1],Field[2]);
129 G4ThreeVector EField(Field[3],Field[4],Fiel 122 G4ThreeVector EField(Field[3],Field[4],Field[5]);
130 123
131 EField /= c_light; 124 EField /= c_light;
132 125
133 G4ThreeVector u(y[3], y[4], y[5]); 126 G4ThreeVector u(y[3], y[4], y[5]);
134 u *= pModuleInverse; 127 u *= pModuleInverse;
135 128
136 G4double udb = anomaly*beta*gamma/(1.+gamma 129 G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
137 G4double ucb = (anomaly+1./gamma)/beta; 130 G4double ucb = (anomaly+1./gamma)/beta;
138 G4double uce = anomaly + 1./(gamma+1.); 131 G4double uce = anomaly + 1./(gamma+1.);
139 132
140 G4ThreeVector Spin(y[9],y[10],y[11]); 133 G4ThreeVector Spin(y[9],y[10],y[11]);
141 134
142 G4double pcharge; << 135 G4ThreeVector dSpin
143 if (charge == 0.) << 136 = pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u))
144 { << 137 // from Jackson
145 pcharge = 1.; << 138 // -uce*Spin.cross(u.cross(EField)) );
146 } << 139 // but this form has one less operation
147 else << 140 - uce*(u*(Spin*EField) - EField*(Spin*u)) );
148 { <<
149 pcharge = charge; <<
150 } <<
151 <<
152 G4ThreeVector dSpin(0.,0.,0.); <<
153 if (Spin.mag2() != 0.) <<
154 { <<
155 dSpin = pcharge*omegac*( ucb*(Spin.cross <<
156 // from Jackson <<
157 // -uce*Spin.cross( <<
158 // but this form ha <<
159 - uce*(u*(Spin*EField) - <<
160 } <<
161 141
162 dydx[ 9] = dSpin.x(); 142 dydx[ 9] = dSpin.x();
163 dydx[10] = dSpin.y(); 143 dydx[10] = dSpin.y();
164 dydx[11] = dSpin.z(); 144 dydx[11] = dSpin.z();
165 145
166 return; << 146 return ;
167 } 147 }
168 148