Gabriele Cosmo
125 lines
4.6 KiB
C++
125 lines
4.6 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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// $Id: G4Mag_SpinEqRhs.cc,v 1.16 2010-07-14 10:00:36 gcosmo Exp $
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// GEANT4 tag $Name: not supported by cvs2svn $
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//
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// This is the standard right-hand side for equation of motion.
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// This version of the right-hand side includes the three components
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// of the particle's spin.
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//
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// J. Apostolakis, February 8th, 1999
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// P. Gumplinger, February 8th, 1999
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// D. Cote-Ahern, P. Gumplinger, April 11th, 2001
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//
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// --------------------------------------------------------------------
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#include "G4Mag_SpinEqRhs.hh"
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#include "G4MagneticField.hh"
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#include "G4ThreeVector.hh"
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G4Mag_SpinEqRhs::G4Mag_SpinEqRhs( G4MagneticField* MagField )
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: G4Mag_EqRhs( MagField ), omegac(0.), anomaly(0.0011659208),
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pcharge(0.), E(0.), gamma(0.), beta(0.)
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{
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}
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G4Mag_SpinEqRhs::~G4Mag_SpinEqRhs()
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{
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}
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void
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G4Mag_SpinEqRhs::SetChargeMomentumMass(G4double particleCharge, // in e+ units
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G4double MomentumXc,
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G4double particleMass)
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{
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// To set fCof_val
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G4Mag_EqRhs::SetChargeMomentumMass(particleCharge, MomentumXc, particleMass);
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omegac = (eplus/particleMass)*c_light;
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pcharge = particleCharge;
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E = std::sqrt(sqr(MomentumXc)+sqr(particleMass));
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beta = MomentumXc/E;
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gamma = E/particleMass;
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G4double neutronAnomaly = -2.913042725;
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if (pcharge==0.) SetAnomaly(neutronAnomaly);
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}
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void
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G4Mag_SpinEqRhs::EvaluateRhsGivenB( const G4double y[],
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const G4double B[3],
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G4double dydx[] ) const
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{
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G4double momentum_mag_square = sqr(y[3]) + sqr(y[4]) + sqr(y[5]);
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G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
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G4double cof = FCof()*inv_momentum_magnitude;
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dydx[0] = y[3] * inv_momentum_magnitude; // (d/ds)x = Vx/V
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dydx[1] = y[4] * inv_momentum_magnitude; // (d/ds)y = Vy/V
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dydx[2] = y[5] * inv_momentum_magnitude; // (d/ds)z = Vz/V
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if (pcharge == 0.) {
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dydx[3] = 0.;
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dydx[4] = 0.;
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dydx[5] = 0.;
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} else {
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dydx[3] = cof*(y[4]*B[2] - y[5]*B[1]) ; // Ax = a*(Vy*Bz - Vz*By)
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dydx[4] = cof*(y[5]*B[0] - y[3]*B[2]) ; // Ay = a*(Vz*Bx - Vx*Bz)
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dydx[5] = cof*(y[3]*B[1] - y[4]*B[0]) ; // Az = a*(Vx*By - Vy*Bx)
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}
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G4ThreeVector u(y[3], y[4], y[5]);
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u *= inv_momentum_magnitude;
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G4ThreeVector BField(B[0],B[1],B[2]);
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G4double udb = anomaly*beta*gamma/(1.+gamma) * (BField * u);
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G4double ucb = (anomaly+1./gamma)/beta;
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// Initialise the values of dydx that we do not update.
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dydx[6] = dydx[7] = dydx[8] = 0.0;
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G4ThreeVector Spin(y[9],y[10],y[11]);
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G4ThreeVector dSpin;
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if (pcharge == 0.) {
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// dSpin = (3.8260837/2.)*omegac*(Spin.cross(BField));
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dSpin = omegac*(ucb*(Spin.cross(BField))-udb*(Spin.cross(u)));
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} else {
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dSpin = pcharge*omegac*(ucb*(Spin.cross(BField))-udb*(Spin.cross(u)));
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}
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dydx[ 9] = dSpin.x();
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dydx[10] = dSpin.y();
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dydx[11] = dSpin.z();
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return ;
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}
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