149 lines
5.2 KiB
C++
149 lines
5.2 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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// $Id$
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//
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//
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// This is the standard right-hand side for equation of motion.
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//
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// 30.08.2007 Chris Gong, Peter Gumplinger
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// 14.02.2009 Kevin Lynch
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// 06.11.2009 Hiromi Iinuma
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//
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// -------------------------------------------------------------------
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#include "G4EqEMFieldWithSpin.hh"
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#include "G4ElectroMagneticField.hh"
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#include "G4ThreeVector.hh"
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#include "globals.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4SystemOfUnits.hh"
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G4EqEMFieldWithSpin::G4EqEMFieldWithSpin(G4ElectroMagneticField *emField )
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: G4EquationOfMotion( emField ), fElectroMagCof(0.), fMassCof(0.),
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omegac(0.), anomaly(0.0011659208), pcharge(0.), E(0.), gamma(0.), beta(0.)
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{
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}
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G4EqEMFieldWithSpin::~G4EqEMFieldWithSpin()
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{
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}
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void
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G4EqEMFieldWithSpin::SetChargeMomentumMass(G4double particleCharge, // e+ units
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G4double MomentumXc,
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G4double particleMass)
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{
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fElectroMagCof = eplus*particleCharge*c_light ;
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fMassCof = particleMass*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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}
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void
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G4EqEMFieldWithSpin::EvaluateRhsGivenB(const G4double y[],
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const G4double Field[],
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G4double dydx[] ) const
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{
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// Components of y:
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// 0-2 dr/ds,
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// 3-5 dp/ds - momentum derivatives
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// 9-11 dSpin/ds = (1/beta) dSpin/dt - spin derivatives
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// The BMT equation, following J.D.Jackson, Classical
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// Electrodynamics, Second Edition,
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// dS/dt = (e/mc) S \cross
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// [ (g/2-1 +1/\gamma) B
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// -(g/2-1)\gamma/(\gamma+1) (\beta \cdot B)\beta
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// -(g/2-\gamma/(\gamma+1) \beta \cross E ]
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// where
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// S = \vec{s}, where S^2 = 1
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// B = \vec{B}
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// \beta = \vec{\beta} = \beta \vec{u} with u^2 = 1
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// E = \vec{E}
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G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;
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G4double Energy = std::sqrt( pSquared + fMassCof );
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G4double cof2 = Energy/c_light ;
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G4double pModuleInverse = 1.0/std::sqrt(pSquared) ;
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G4double inverse_velocity = Energy * pModuleInverse / c_light;
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G4double cof1 = fElectroMagCof*pModuleInverse ;
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dydx[0] = y[3]*pModuleInverse ;
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dydx[1] = y[4]*pModuleInverse ;
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dydx[2] = y[5]*pModuleInverse ;
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dydx[3] = cof1*(cof2*Field[3] + (y[4]*Field[2] - y[5]*Field[1])) ;
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dydx[4] = cof1*(cof2*Field[4] + (y[5]*Field[0] - y[3]*Field[2])) ;
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dydx[5] = cof1*(cof2*Field[5] + (y[3]*Field[1] - y[4]*Field[0])) ;
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dydx[6] = dydx[8] = 0.;//not used
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// Lab Time of flight
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dydx[7] = inverse_velocity;
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G4ThreeVector BField(Field[0],Field[1],Field[2]);
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G4ThreeVector EField(Field[3],Field[4],Field[5]);
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EField /= c_light;
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G4ThreeVector u(y[3], y[4], y[5]);
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u *= pModuleInverse;
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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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G4double uce = anomaly + 1./(gamma+1.);
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G4ThreeVector Spin(y[9],y[10],y[11]);
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G4ThreeVector dSpin
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= pcharge*omegac*( ucb*(Spin.cross(BField))-udb*(Spin.cross(u))
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// from Jackson
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// -uce*Spin.cross(u.cross(EField)) );
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// but this form has one less operation
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- uce*(u*(Spin*EField) - EField*(Spin*u)) );
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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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