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25 //
26 // G4EqGravityField implementation
27 //
28 // This is the right-hand side for equation of motion for a
29 // massive particle in a gravitational field.
30 //
31 // Created: P.Gumplinger, 14.06.11 - Adopted from G4EqMagElectricField
32 // Thanks to P.Fierlinger (PSI) and A.Capra and A.Fontana (INFN Pavia)
33 // -------------------------------------------------------------------
34
35 #include "G4EqGravityField.hh"
36 #include "globals.hh"
37 #include "G4PhysicalConstants.hh"
38
39 G4EqGravityField::G4EqGravityField(G4UniformGravityField* gField)
40 : G4EquationOfMotion( gField )
41 {
42 }
43
44 G4EqGravityField::~G4EqGravityField() = default;
45
46 void
47 G4EqGravityField::SetChargeMomentumMass(G4ChargeState,
48 G4double,
49 G4double particleMass )
50 {
51 fMass = particleMass;
52 }
53
54 void
55 G4EqGravityField::EvaluateRhsGivenB(const G4double y[],
56 const G4double G[],
57 G4double dydx[] ) const
58 {
59
60 // Components of y:
61 // 0-2 dr/ds,
62 // 3-5 dp/ds - momentum derivatives
63
64 G4double momentum_mag_square = y[3]*y[3] + y[4]*y[4] + y[5]*y[5];
65 G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
66
67 G4double Energy = std::sqrt(momentum_mag_square + fMass*fMass);
68 G4double cof2 = Energy/c_light;
69 G4double cof1 = inv_momentum_magnitude*fMass;
70 G4double inverse_velocity = Energy*inv_momentum_magnitude/c_light;
71
72 dydx[0] = y[3]*inv_momentum_magnitude; // (d/ds)x = Vx/V
73 dydx[1] = y[4]*inv_momentum_magnitude; // (d/ds)y = Vy/V
74 dydx[2] = y[5]*inv_momentum_magnitude; // (d/ds)z = Vz/V
75
76 dydx[3] = G[0]*cof1*cof2/c_light;
77 dydx[4] = G[1]*cof1*cof2/c_light; // m*g
78 dydx[5] = G[2]*cof1*cof2/c_light;
79
80 // Lab Time of flight
81 //
82 dydx[7] = inverse_velocity;
83
84 return;
85 }
86