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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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15 | // * use. Please see the license in the file LICENSE and URL above * |
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17 | // * * |
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18 | // * This code implementation is the result of the scientific and * |
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19 | // * technical work of the GEANT4 collaboration. * |
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24 | // ******************************************************************** |
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25 | // |
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26 | // |
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27 | // $Id: G4EqEMFieldWithSpin.cc,v 1.9 2010/07/14 10:00:36 gcosmo Exp $ |
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28 | // GEANT4 tag $Name: field-V09-03-03 $ |
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29 | // |
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30 | // |
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31 | // This is the standard right-hand side for equation of motion. |
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32 | // |
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33 | // 30.08.2007 Chris Gong, Peter Gumplinger |
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34 | // 14.02.2009 Kevin Lynch |
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35 | // 06.11.2009 Hiromi Iinuma |
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36 | // |
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37 | // ------------------------------------------------------------------- |
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38 | |
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39 | #include "G4EqEMFieldWithSpin.hh" |
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40 | #include "G4ElectroMagneticField.hh" |
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41 | #include "G4ThreeVector.hh" |
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42 | #include "globals.hh" |
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43 | |
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44 | G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4ElectroMagneticField *emField ) |
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45 | : G4EquationOfMotion( emField ), fElectroMagCof(0.), fMassCof(0.), |
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46 | omegac(0.), anomaly(0.0011659208), pcharge(0.), E(0.), gamma(0.), beta(0.) |
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47 | { |
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48 | } |
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49 | |
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50 | G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() |
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51 | { |
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52 | } |
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53 | |
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54 | void |
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55 | G4EqEMFieldWithSpin::SetChargeMomentumMass(G4double particleCharge, // e+ units |
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56 | G4double MomentumXc, |
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57 | G4double particleMass) |
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58 | { |
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59 | fElectroMagCof = eplus*particleCharge*c_light ; |
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60 | fMassCof = particleMass*particleMass ; |
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61 | |
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62 | omegac = 0.105658387*GeV/particleMass * 2.837374841e-3*(rad/cm/kilogauss); |
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63 | |
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64 | pcharge = particleCharge; |
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65 | |
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66 | E = std::sqrt(sqr(MomentumXc)+sqr(particleMass)); |
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67 | beta = MomentumXc/E; |
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68 | gamma = E/particleMass; |
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69 | |
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70 | } |
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71 | |
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72 | void |
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73 | G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G4double y[], |
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74 | const G4double Field[], |
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75 | G4double dydx[] ) const |
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76 | { |
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77 | |
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78 | // Components of y: |
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79 | // 0-2 dr/ds, |
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80 | // 3-5 dp/ds - momentum derivatives |
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81 | // 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives |
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82 | |
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83 | // The BMT equation, following J.D.Jackson, Classical |
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84 | // Electrodynamics, Second Edition, |
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85 | // dS/dt = (e/mc) S \cross |
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86 | // [ (g/2-1 +1/\gamma) B |
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87 | // -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta |
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88 | // -(g/2-\gamma/(\gamma+1) \beta \cross E ] |
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89 | // where |
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90 | // S = \vec{s}, where S^2 = 1 |
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91 | // B = \vec{B} |
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92 | // \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1 |
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93 | // E = \vec{E} |
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94 | |
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95 | G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ; |
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96 | |
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97 | G4double Energy = std::sqrt( pSquared + fMassCof ); |
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98 | G4double cof2 = Energy/c_light ; |
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99 | |
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100 | G4double pModuleInverse = 1.0/std::sqrt(pSquared) ; |
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101 | |
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102 | G4double inverse_velocity = Energy * pModuleInverse / c_light; |
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103 | |
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104 | G4double cof1 = fElectroMagCof*pModuleInverse ; |
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105 | |
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106 | dydx[0] = y[3]*pModuleInverse ; |
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107 | dydx[1] = y[4]*pModuleInverse ; |
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108 | dydx[2] = y[5]*pModuleInverse ; |
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109 | |
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110 | dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ; |
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111 | |
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112 | dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ; |
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113 | |
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114 | dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ; |
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115 | |
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116 | dydx[6] = dydx[8] = 0.;//not used |
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117 | |
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118 | // Lab Time of flight |
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119 | dydx[7] = inverse_velocity; |
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120 | |
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121 | G4ThreeVector BField(Field[0],Field[1],Field[2]); |
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122 | G4ThreeVector EField(Field[3],Field[4],Field[5]); |
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123 | |
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124 | EField /= c_light; |
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125 | |
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126 | G4ThreeVector u(y[3], y[4], y[5]); |
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127 | u *= pModuleInverse; |
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128 | |
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129 | G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u); |
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130 | G4double ucb = (anomaly+1./gamma)/beta; |
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131 | G4double uce = anomaly + 1./(gamma+1.); |
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132 | |
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133 | G4ThreeVector Spin(y[9],y[10],y[11]); |
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134 | |
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135 | G4ThreeVector dSpin |
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136 | = pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u)) |
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137 | // from Jackson |
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138 | // -uce*Spin.cross(u.cross(EField)) ); |
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139 | // but this form has one less operation |
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140 | - uce*(u*(Spin*EField) - EField*(Spin*u)) ); |
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141 | |
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142 | dydx[ 9] = dSpin.x(); |
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143 | dydx[10] = dSpin.y(); |
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144 | dydx[11] = dSpin.z(); |
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145 | |
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146 | return ; |
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147 | } |
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