Gabriele Cosmo
190 lines
7.3 KiB
C++
190 lines
7.3 KiB
C++
// ********************************************************************
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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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// G4BorisScheme implementation
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//
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// Author: Divyansh Tiwari, Google Summer of Code 2022
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// Supervision: John Apostolakis,Renee Fatemi, Soon Yung Jun
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// --------------------------------------------------------------------
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#include "G4BorisScheme.hh"
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#include "G4FieldUtils.hh"
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#include"G4SystemOfUnits.hh"
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#include "globals.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4EquationOfMotion.hh"
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//#include "G4EqMagElectricField.hh"
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using namespace field_utils;
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G4BorisScheme::G4BorisScheme( G4EquationOfMotion* equation,
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G4int nvar )
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: fEquation(equation), fnvar(nvar)
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{
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if (nvar <= 0)
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{
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G4Exception("G4BorisScheme::G4BorisScheme()",
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"GeomField0002", FatalException,
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"Invalid number of variables; must be greater than zero!");
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}
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}
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void G4BorisScheme::DoStep(const G4double restMass,const G4double charge, const G4double yIn[],
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G4double yOut[], G4double hstep) const
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{
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G4double yOut1Temp[G4FieldTrack::ncompSVEC];
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G4double yOut2Temp[G4FieldTrack::ncompSVEC];
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// Used the scheme described in the following paper:https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/153167/eth-5175-01.pdf?sequence=1
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UpdatePosition(restMass, charge, yIn, yOut1Temp, hstep/2);
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UpdateVelocity(restMass, charge, yOut1Temp, yOut2Temp, hstep);
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UpdatePosition(restMass, charge, yOut2Temp, yOut, hstep/2);
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}
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void G4BorisScheme::UpdatePosition(const G4double restMass, const G4double /*charge*/, const G4double yIn[],
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G4double yOut[], G4double hstep) const
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{
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// Particle information
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copy(yOut, yIn);
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// Obtaining velocity
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G4ThreeVector momentum_vec =G4ThreeVector(yIn[3],yIn[4],yIn[5]);
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G4double momentum_mag = momentum_vec.mag();
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G4ThreeVector momentum_dir =(1.0/momentum_mag)*momentum_vec;
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G4double velocity_mag = momentum_mag*(c_l)/(std::sqrt(sqr(momentum_mag) +sqr(restMass)));
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G4ThreeVector velocity = momentum_dir*velocity_mag;
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//Obtaining the time step from the length step
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hstep /= velocity_mag*CLHEP::m;
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// Updating the Position
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for(G4int i = 0; i <3; i++ )
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{
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G4double pos = yIn[i]/CLHEP::m;
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pos += hstep*velocity[i];
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yOut[i] = pos*CLHEP::m;
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}
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}
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void G4BorisScheme::UpdateVelocity(const G4double restMass, const G4double charge, const G4double yIn[],
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G4double yOut[], G4double hstep) const
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{
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//Particle information
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G4ThreeVector momentum_vec =G4ThreeVector(yIn[3],yIn[4],yIn[5]);
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G4double momentum_mag = momentum_vec.mag();
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G4ThreeVector momentum_dir =(1.0/momentum_mag)*momentum_vec;
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G4double gamma = std::sqrt(sqr(momentum_mag) + sqr(restMass))/restMass;
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G4double mass = (restMass/c_squared)/CLHEP::kg;
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//Obtaining velocity
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G4double velocity_mag = momentum_mag*(c_l)/(std::sqrt(sqr(momentum_mag) +sqr(restMass)));
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G4ThreeVector velocity = momentum_dir*velocity_mag;
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////Obtaining the time step from the length step
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hstep /= velocity_mag*CLHEP::m;
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// Obtaining the field values
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G4double dydx[G4FieldTrack::ncompSVEC];
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G4double fieldValue[6] ={0,0,0,0,0,0};
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fEquation->EvaluateRhsReturnB(yIn, dydx, fieldValue);
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//Initializing Vectors
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G4ThreeVector B;
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G4ThreeVector E;
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copy(yOut, yIn);
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for( G4int i = 0; i < 3; i++)
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{
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E[i] = fieldValue[i+3]/CLHEP::volt*CLHEP::meter;// FIXME - Check Units
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B[i] = fieldValue[i]/CLHEP::tesla;
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}
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//Boris Algorithm
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G4double qd = hstep*(charge/(2*mass*gamma));
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G4ThreeVector h = qd*B;
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G4ThreeVector u = velocity + qd*E;
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G4double h_l = h[0]*h[0] + h[1]*h[1] + h[2]*h[2];
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G4ThreeVector s_1 = (2*h)/(1 + h_l);
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G4ThreeVector ud = u + (u + u.cross(h)).cross(s_1);
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G4ThreeVector v_fi = ud +qd*E;
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G4double v_mag = std::sqrt(v_fi.mag2());
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G4ThreeVector v_dir = v_fi/v_mag;
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G4double momen_mag = (restMass*v_mag)/(std::sqrt(c_l*c_l - v_mag*v_mag));
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G4ThreeVector momen = momen_mag*v_dir;
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// Storing the updated momentum
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for(int i = 3; i < 6; i++)
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{
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yOut[i] = momen[i-3];
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}
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}
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// ----------------------------------------------------------------------------------
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void G4BorisScheme::copy(G4double dst[], const G4double src[]) const
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{
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std::memcpy(dst, src, sizeof(G4double) * fnvar);
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}
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// ----------------------------------------------------------------------------------
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// - Methods using the Boris Scheme Stepping to estimate integration error
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// ----------------------------------------------------------------------------------
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void G4BorisScheme::
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StepWithErrorEstimate(const G4double yIn[], G4double restMass, G4double charge, G4double hstep,
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G4double yOut[], G4double yErr[]) const
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{
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// Use two half-steps (comparing to a full step) to obtain output and error estimate
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G4double yMid[G4FieldTrack::ncompSVEC];
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StepWithMidAndErrorEstimate(yIn, restMass, charge, hstep, yMid, yOut, yErr);
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}
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// ----------------------------------------------------------------------------------
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void G4BorisScheme::
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StepWithMidAndErrorEstimate(const G4double yIn[], G4double restMass, G4double charge, G4double hstep,
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G4double yMid[], G4double yOut[], G4double yErr[]
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) const
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{
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G4double halfStep= 0.5*hstep;
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G4double yOutAlt[G4FieldTrack::ncompSVEC];
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// In a single step
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DoStep(restMass, charge, yIn, yOutAlt, hstep );
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// Same, and also return mid-point evaluation
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DoStep(restMass, charge, yIn, yMid, halfStep );
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DoStep(restMass, charge, yMid, yOut, halfStep );
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for( G4int i= 0; i<fnvar; i++ )
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{
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yErr[i] = yOutAlt[i] - yOut[i];
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}
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}
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