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1 // 2 // ******************************************************************** 3 // * License and Disclaimer * 4 // * * 5 // * The Geant4 software is copyright of the Copyright Holders of * 6 // * the Geant4 Collaboration. It is provided under the terms and * 7 // * conditions of the Geant4 Software License, included in the file * 8 // * LICENSE and available at http://cern.ch/geant4/license . These * 9 // * include a list of copyright holders. * 10 // * * 11 // * Neither the authors of this software system, nor their employing * 12 // * institutes,nor the agencies providing financial support for this * 13 // * work make any representation or warranty, express or implied, * 14 // * regarding this software system or assume any liability for its * 15 // * use. Please see the license in the file LICENSE and URL above * 16 // * for the full disclaimer and the limitation of liability. * 17 // * * 18 // * This code implementation is the result of the scientific and * 19 // * technical work of the GEANT4 collaboration. * 20 // * By using, copying, modifying or distributing the software (or * 21 // * any work based on the software) you agree to acknowledge its * 22 // * use in resulting scientific publications, and indicate your * 23 // * acceptance of all terms of the Geant4 Software license. * 24 // ******************************************************************** 25 // 26 // G4Mag_SpinEqRhs implementation 27 // 28 // Created: J.Apostolakis, P.Gumplinger - 08.02.1999 29 // -------------------------------------------------------------------- 30 31 #include "G4Mag_SpinEqRhs.hh" 32 #include "G4PhysicalConstants.hh" 33 #include "G4SystemOfUnits.hh" 34 #include "G4MagneticField.hh" 35 #include "G4ThreeVector.hh" 36 37 G4Mag_SpinEqRhs::G4Mag_SpinEqRhs( G4MagneticField* MagField ) 38 : G4Mag_EqRhs( MagField ) 39 { 40 } 41 42 G4Mag_SpinEqRhs::~G4Mag_SpinEqRhs() = default; 43 44 void 45 G4Mag_SpinEqRhs::SetChargeMomentumMass(G4ChargeState particleCharge, 46 G4double MomentumXc, 47 G4double particleMass) 48 { 49 G4Mag_EqRhs::SetChargeMomentumMass( particleCharge, MomentumXc, mass); 50 51 charge = particleCharge.GetCharge(); 52 mass = particleMass; 53 magMoment = particleCharge.GetMagneticDipoleMoment(); 54 spin = particleCharge.GetSpin(); 55 56 omegac = (eplus/mass)*c_light; 57 58 G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared); 59 60 G4double g_BMT; 61 if ( spin != 0. ) 62 { 63 g_BMT = (std::abs(magMoment)/muB)/spin; 64 } 65 else 66 { 67 g_BMT = 2.; 68 } 69 70 anomaly = (g_BMT - 2.)/2.; 71 72 G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass)); 73 beta = MomentumXc/E; 74 gamma = E/mass; 75 } 76 77 void 78 G4Mag_SpinEqRhs::EvaluateRhsGivenB( const G4double y[], 79 const G4double B[3], 80 G4double dydx[] ) const 81 { 82 G4double momentum_mag_square = sqr(y[3]) + sqr(y[4]) + sqr(y[5]); 83 G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square ); 84 G4double cof = FCof()*inv_momentum_magnitude; 85 86 dydx[0] = y[3] * inv_momentum_magnitude; // (d/ds)x = Vx/V 87 dydx[1] = y[4] * inv_momentum_magnitude; // (d/ds)y = Vy/V 88 dydx[2] = y[5] * inv_momentum_magnitude; // (d/ds)z = Vz/V 89 90 if (charge == 0.) 91 { 92 dydx[3] = 0.; 93 dydx[4] = 0.; 94 dydx[5] = 0.; 95 } 96 else 97 { 98 dydx[3] = cof*(y[4]*B[2] - y[5]*B[1]) ; // Ax = a*(Vy*Bz - Vz*By) 99 dydx[4] = cof*(y[5]*B[0] - y[3]*B[2]) ; // Ay = a*(Vz*Bx - Vx*Bz) 100 dydx[5] = cof*(y[3]*B[1] - y[4]*B[0]) ; // Az = a*(Vx*By - Vy*Bx) 101 } 102 103 G4ThreeVector u(y[3], y[4], y[5]); 104 u *= inv_momentum_magnitude; 105 106 G4ThreeVector BField(B[0],B[1],B[2]); 107 108 G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u); 109 G4double ucb = (anomaly+1./gamma)/beta; 110 111 // Initialise the values of dydx that we do not update. 112 dydx[6] = dydx[7] = dydx[8] = 0.0; 113 114 G4ThreeVector Spin(y[9],y[10],y[11]); 115 116 G4double pcharge; 117 if (charge == 0.) 118 { 119 pcharge = 1.; 120 } 121 else 122 { 123 pcharge = charge; 124 } 125 126 G4ThreeVector dSpin(0.,0.,0.); 127 if (Spin.mag2() != 0.) 128 { 129 dSpin = pcharge*omegac*(ucb*(Spin.cross(BField))-udb*(Spin.cross(u))); 130 } 131 132 dydx[9] = dSpin.x(); 133 dydx[10] = dSpin.y(); 134 dydx[11] = dSpin.z(); 135 136 return; 137 } 138