| Geant4 Cross Reference |
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 // G4EqEMFieldWithEDM implementation
27 //
28 // This is the standard right-hand side for equation of motion.
29 //
30 // Created: Kevin Lynch, 19.02.2009 - Based on G4EqEMFieldWithSpin
31 // Modified: Hiromi Iinuma, 06.11.2009 - see:
32 // http://hypernews.slac.stanford.edu/HyperNews/geant4/get/emfields/161.html
33 // -------------------------------------------------------------------
34
35 #include "G4EqEMFieldWithEDM.hh"
36 #include "G4ElectroMagneticField.hh"
37 #include "G4ThreeVector.hh"
38 #include "globals.hh"
39 #include "G4PhysicalConstants.hh"
40 #include "G4SystemOfUnits.hh"
41
42 G4EqEMFieldWithEDM::G4EqEMFieldWithEDM(G4ElectroMagneticField* emField )
43 : G4EquationOfMotion( emField )
44 {
45 }
46
47 G4EqEMFieldWithEDM::~G4EqEMFieldWithEDM() = default;
48
49 void
50 G4EqEMFieldWithEDM::SetChargeMomentumMass(G4ChargeState particleCharge,
51 G4double MomentumXc,
52 G4double particleMass)
53 {
54 charge = particleCharge.GetCharge();
55 mass = particleMass;
56 magMoment = particleCharge.GetMagneticDipoleMoment();
57 spin = particleCharge.GetSpin();
58
59 fElectroMagCof = eplus*charge*c_light;
60 fMassCof = mass*mass;
61
62 omegac = (eplus/mass)*c_light;
63
64 G4double muB = 0.5*eplus*hbar_Planck/(mass/c_squared);
65
66 G4double g_BMT;
67 if ( spin != 0. )
68 {
69 g_BMT = (std::abs(magMoment)/muB)/spin;
70 }
71 else
72 {
73 g_BMT = 2.;
74 }
75
76 anomaly = (g_BMT - 2.)/2.;
77
78 G4double E = std::sqrt(sqr(MomentumXc)+sqr(mass));
79 beta = MomentumXc/E;
80 gamma = E/mass;
81 }
82
83 void
84 G4EqEMFieldWithEDM::EvaluateRhsGivenB(const G4double y[],
85 const G4double Field[],
86 G4double dydx[] ) const
87 {
88
89 // Components of y:
90 // 0-2 dr/ds,
91 // 3-5 dp/ds - momentum derivatives
92 // 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives
93
94 // The BMT equation, following J.D.Jackson, Classical
95 // Electrodynamics, Second Edition, with additions for EDM
96 // evolution from
97 // M.Nowakowski, et.al. Eur.J.Phys.26, pp 545-560, (2005)
98 // or
99 // Silenko, Phys.Rev.ST Accel.Beams 9:034003, (2006)
100
101 // dS/dt = (e/m) S \cross
102 // MDM: [ (g/2-1 +1/\gamma) B
103 // -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta
104 // -(g/2-\gamma/(\gamma+1) \beta \cross E
105 //
106 // EDM: eta/2( E - gamma/(gamma+1) \beta (\beta \cdot E)
107 // + \beta \cross B ) ]
108 //
109 // where
110 // S = \vec{s}, where S^2 = 1
111 // B = \vec{B}
112 // \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1
113 // E = \vec{E}
114
115 G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;
116
117 G4double Energy = std::sqrt( pSquared + fMassCof );
118 G4double cof2 = Energy/c_light ;
119
120 G4double pModuleInverse = 1.0/std::sqrt(pSquared) ;
121
122 G4double inverse_velocity = Energy * pModuleInverse / c_light;
123
124 G4double cof1 = fElectroMagCof*pModuleInverse ;
125
126 dydx[0] = y[3]*pModuleInverse ;
127 dydx[1] = y[4]*pModuleInverse ;
128 dydx[2] = y[5]*pModuleInverse ;
129
130 dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ;
131
132 dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ;
133
134 dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ;
135
136 dydx[6] = dydx[8] = 0.;//not used
137
138 // Lab Time of flight
139 dydx[7] = inverse_velocity;
140
141 G4ThreeVector BField(Field[0],Field[1],Field[2]);
142 G4ThreeVector EField(Field[3],Field[4],Field[5]);
143
144 EField /= c_light;
145
146 G4ThreeVector u(y[3], y[4], y[5]);
147 u *= pModuleInverse;
148
149 G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
150 G4double ucb = (anomaly+1./gamma)/beta;
151 G4double uce = anomaly + 1./(gamma+1.);
152 G4double ude = beta*gamma/(1.+gamma)*(EField*u);
153
154 G4ThreeVector Spin(y[9],y[10],y[11]);
155
156 G4double pcharge;
157 if (charge == 0.)
158 {
159 pcharge = 1.;
160 }
161 else
162 {
163 pcharge = charge;
164 }
165
166 G4ThreeVector dSpin(0.,0.,0.);
167 if (Spin.mag2() != 0.)
168 {
169 dSpin = pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u))
170 // from Jackson
171 // -uce*Spin.cross(u.cross(EField)) )
172 // but this form has one less operation
173 - uce*(u*(Spin*EField) - EField*(Spin*u))
174 + eta/2.*(Spin.cross(EField) - ude*(Spin.cross(u))
175 // +Spin.cross(u.cross(Bfield))
176 + (u*(Spin*BField) - BField*(Spin*u)) ) );
177 }
178
179 dydx[ 9] = dSpin.x();
180 dydx[10] = dSpin.y();
181 dydx[11] = dSpin.z();
182
183 return;
184 }
185