[831] | 1 | // |
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| 2 | // ******************************************************************** |
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| 3 | // * License and Disclaimer * |
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| 4 | // * * |
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| 5 | // * The Geant4 software is copyright of the Copyright Holders of * |
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| 6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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| 7 | // * conditions of the Geant4 Software License, included in the file * |
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| 8 | // * LICENSE and available at http://cern.ch/geant4/license . These * |
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| 9 | // * include a list of copyright holders. * |
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| 10 | // * * |
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| 11 | // * Neither the authors of this software system, nor their employing * |
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| 12 | // * institutes,nor the agencies providing financial support for this * |
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| 13 | // * work make any representation or warranty, express or implied, * |
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| 14 | // * regarding this software system or assume any liability for its * |
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| 15 | // * use. Please see the license in the file LICENSE and URL above * |
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| 16 | // * for the full disclaimer and the limitation of liability. * |
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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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| 20 | // * By using, copying, modifying or distributing the software (or * |
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| 21 | // * any work based on the software) you agree to acknowledge its * |
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| 22 | // * use in resulting scientific publications, and indicate your * |
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| 23 | // * acceptance of all terms of the Geant4 Software license. * |
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| 24 | // ******************************************************************** |
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| 25 | // |
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| 26 | // |
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[1340] | 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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[831] | 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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[1231] | 34 | // 14.02.2009 Kevin Lynch |
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[1340] | 35 | // 06.11.2009 Hiromi Iinuma |
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[831] | 36 | // |
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| 37 | // ------------------------------------------------------------------- |
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| 38 | |
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| 39 | #include "G4EqEMFieldWithSpin.hh" |
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[921] | 40 | #include "G4ElectroMagneticField.hh" |
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[831] | 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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[1340] | 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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[1231] | 47 | { |
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[921] | 48 | } |
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[831] | 49 | |
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[921] | 50 | G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin() |
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| 51 | { |
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| 52 | } |
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| 53 | |
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[831] | 54 | void |
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| 55 | G4EqEMFieldWithSpin::SetChargeMomentumMass(G4double particleCharge, // e+ units |
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[921] | 56 | G4double MomentumXc, |
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[831] | 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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[1340] | 64 | pcharge = particleCharge; |
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[831] | 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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[921] | 69 | |
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[831] | 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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[921] | 74 | const G4double Field[], |
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| 75 | G4double dydx[] ) const |
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[831] | 76 | { |
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| 77 | |
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| 78 | // Components of y: |
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[1231] | 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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[831] | 82 | |
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[1231] | 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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[831] | 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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[1231] | 122 | G4ThreeVector EField(Field[3],Field[4],Field[5]); |
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[831] | 123 | |
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[1231] | 124 | EField /= c_light; |
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| 125 | |
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[831] | 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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[1231] | 131 | G4double uce = anomaly + 1./(gamma+1.); |
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[831] | 132 | |
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| 133 | G4ThreeVector Spin(y[9],y[10],y[11]); |
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[921] | 134 | |
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[1231] | 135 | G4ThreeVector dSpin |
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[1340] | 136 | = pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u)) |
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[1231] | 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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[1340] | 140 | - uce*(u*(Spin*EField) - EField*(Spin*u)) ); |
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[921] | 141 | |
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[831] | 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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