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#ifndef WARPX_PARTICLES_GATHER_GETEXTERNALFIELDS_H_
#define WARPX_PARTICLES_GATHER_GETEXTERNALFIELDS_H_
#include "Particles/Pusher/GetAndSetPosition.H"
#include "Particles/WarpXParticleContainer_fwd.H"
#include "Utils/WarpXConst.H"
#include "AcceleratorLattice/LatticeElementFinder.H"
#include <AMReX.H>
#include <AMReX_Array.H>
#include <AMReX_Extension.H>
#include <AMReX_GpuQualifiers.H>
#include <AMReX_Parser.H>
#include <AMReX_REAL.H>
#include <optional>
/** \brief Functor class that assigns external
* field values (E and B) to particles.
*/
struct GetExternalEBField
{
enum ExternalFieldInitType { None, Constant, Parser, RepeatedPlasmaLens, Unknown };
GetExternalEBField () = default;
GetExternalEBField (const WarpXParIter& a_pti, int a_offset = 0) noexcept;
ExternalFieldInitType m_Etype;
ExternalFieldInitType m_Btype;
amrex::ParticleReal m_gamma_boost;
amrex::ParticleReal m_uz_boost;
amrex::GpuArray<amrex::ParticleReal, 3> m_Efield_value;
amrex::GpuArray<amrex::ParticleReal, 3> m_Bfield_value;
amrex::ParserExecutor<4> m_Exfield_partparser;
amrex::ParserExecutor<4> m_Eyfield_partparser;
amrex::ParserExecutor<4> m_Ezfield_partparser;
amrex::ParserExecutor<4> m_Bxfield_partparser;
amrex::ParserExecutor<4> m_Byfield_partparser;
amrex::ParserExecutor<4> m_Bzfield_partparser;
GetParticlePosition m_get_position;
amrex::Real m_time;
amrex::ParticleReal m_repeated_plasma_lens_period;
const amrex::ParticleReal* AMREX_RESTRICT m_repeated_plasma_lens_starts = nullptr;
const amrex::ParticleReal* AMREX_RESTRICT m_repeated_plasma_lens_lengths = nullptr;
const amrex::ParticleReal* AMREX_RESTRICT m_repeated_plasma_lens_strengths_E = nullptr;
const amrex::ParticleReal* AMREX_RESTRICT m_repeated_plasma_lens_strengths_B = nullptr;
int m_n_lenses;
amrex::Real m_dt;
const amrex::ParticleReal* AMREX_RESTRICT m_ux = nullptr;
const amrex::ParticleReal* AMREX_RESTRICT m_uy = nullptr;
const amrex::ParticleReal* AMREX_RESTRICT m_uz = nullptr;
std::optional<LatticeElementFinderDevice> d_lattice_element_finder;
AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
bool isNoOp () const { return (m_Etype == None && m_Btype == None && !d_lattice_element_finder.has_value()); }
AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
void operator () (long i,
amrex::ParticleReal& field_Ex,
amrex::ParticleReal& field_Ey,
amrex::ParticleReal& field_Ez,
amrex::ParticleReal& field_Bx,
amrex::ParticleReal& field_By,
amrex::ParticleReal& field_Bz) const noexcept
{
using namespace amrex::literals;
if (d_lattice_element_finder) {
// Note that the "*" is needed since d_lattice_element_finder is optional
(*d_lattice_element_finder)(i, field_Ex, field_Ey, field_Ez,
field_Bx, field_By, field_Bz);
}
if (m_Etype == None && m_Btype == None) return;
amrex::ParticleReal Ex = 0._prt;
amrex::ParticleReal Ey = 0._prt;
amrex::ParticleReal Ez = 0._prt;
amrex::ParticleReal Bx = 0._prt;
amrex::ParticleReal By = 0._prt;
amrex::ParticleReal Bz = 0._prt;
constexpr amrex::ParticleReal inv_c2 = 1._prt/(PhysConst::c*PhysConst::c);
if (m_Etype == Constant)
{
Ex = m_Efield_value[0];
Ey = m_Efield_value[1];
Ez = m_Efield_value[2];
}
else if (m_Etype == ExternalFieldInitType::Parser)
{
amrex::ParticleReal x, y, z;
m_get_position(i, x, y, z);
amrex::Real lab_time = m_time;
if (m_gamma_boost > 1._prt) {
lab_time = m_gamma_boost*m_time + m_uz_boost*z*inv_c2;
z = m_gamma_boost*z + m_uz_boost*m_time;
}
Ex = m_Exfield_partparser((amrex::ParticleReal) x, (amrex::ParticleReal) y, (amrex::ParticleReal) z, lab_time);
Ey = m_Eyfield_partparser((amrex::ParticleReal) x, (amrex::ParticleReal) y, (amrex::ParticleReal) z, lab_time);
Ez = m_Ezfield_partparser((amrex::ParticleReal) x, (amrex::ParticleReal) y, (amrex::ParticleReal) z, lab_time);
}
if (m_Btype == Constant)
{
Bx = m_Bfield_value[0];
By = m_Bfield_value[1];
Bz = m_Bfield_value[2];
}
else if (m_Btype == ExternalFieldInitType::Parser)
{
amrex::ParticleReal x, y, z;
m_get_position(i, x, y, z);
amrex::Real lab_time = m_time;
if (m_gamma_boost > 1._prt) {
lab_time = m_gamma_boost*m_time + m_uz_boost*z*inv_c2;
z = m_gamma_boost*z + m_uz_boost*m_time;
}
Bx = m_Bxfield_partparser(x, y, z, lab_time);
By = m_Byfield_partparser(x, y, z, lab_time);
Bz = m_Bzfield_partparser(x, y, z, lab_time);
}
if (m_Etype == RepeatedPlasmaLens ||
m_Btype == RepeatedPlasmaLens)
{
amrex::ParticleReal x, y, z;
m_get_position(i, x, y, z);
const amrex::ParticleReal uxp = m_ux[i];
const amrex::ParticleReal uyp = m_uy[i];
const amrex::ParticleReal uzp = m_uz[i];
const amrex::ParticleReal gamma = std::sqrt(1._prt + (uxp*uxp + uyp*uyp + uzp*uzp)*inv_c2);
const amrex::ParticleReal vzp = uzp/gamma;
// the current slice in z between now and the next time step
amrex::ParticleReal zl = z;
amrex::ParticleReal zr = z + vzp*m_dt;
if (m_gamma_boost > 1._prt) {
zl = m_gamma_boost*zl + m_uz_boost*m_time;
zr = m_gamma_boost*zr + m_uz_boost*(m_time + m_dt);
}
// the plasma lens periods do not start before z=0
if (zl > 0) {
// find which is the next lens
int i_lens = static_cast<int>(std::floor(zl/m_repeated_plasma_lens_period));
if (i_lens < m_n_lenses) {
amrex::ParticleReal const lens_start = m_repeated_plasma_lens_starts[i_lens] + i_lens*m_repeated_plasma_lens_period;
amrex::ParticleReal const lens_end = lens_start + m_repeated_plasma_lens_lengths[i_lens];
// Calculate the residence correction
// frac will be 1 if the step is completely inside the lens, between 0 and 1
// when entering or leaving the lens, and otherwise 0.
// This accounts for the case when particles step over the element without landing in it.
// This assumes that vzp > 0.
amrex::ParticleReal const zl_bounded = std::min(std::max(zl, lens_start), lens_end);
amrex::ParticleReal const zr_bounded = std::min(std::max(zr, lens_start), lens_end);
amrex::ParticleReal const frac = ((zr - zl) == 0._rt ? 1._rt : (zr_bounded - zl_bounded)/(zr - zl));
// Note that "+=" is used since the fields may have been set above
// if a different E or Btype was specified.
Ex += x*frac*m_repeated_plasma_lens_strengths_E[i_lens];
Ey += y*frac*m_repeated_plasma_lens_strengths_E[i_lens];
Bx += +y*frac*m_repeated_plasma_lens_strengths_B[i_lens];
By += -x*frac*m_repeated_plasma_lens_strengths_B[i_lens];
}
}
}
if (m_gamma_boost > 1._prt) {
// Transform the fields to the boosted frame
const amrex::ParticleReal Ex_boost = m_gamma_boost*Ex - m_uz_boost*By;
const amrex::ParticleReal Ey_boost = m_gamma_boost*Ey + m_uz_boost*Bx;
const amrex::ParticleReal Bx_boost = m_gamma_boost*Bx + m_uz_boost*Ey*inv_c2;
const amrex::ParticleReal By_boost = m_gamma_boost*By - m_uz_boost*Ex*inv_c2;
Ex = Ex_boost;
Ey = Ey_boost;
Bx = Bx_boost;
By = By_boost;
}
field_Ex += Ex;
field_Ey += Ey;
field_Ez += Ez;
field_Bx += Bx;
field_By += By;
field_Bz += Bz;
}
};
#endif
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