BreitWheelerEngineWrapper.H

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/* Copyright 2019 Luca Fedeli
 *
 * This file is part of WarpX.
 *
 * License: BSD-3-Clause-LBNL
 */
#ifndef WARPX_breit_wheeler_engine_wrapper_h_
#define WARPX_breit_wheeler_engine_wrapper_h_

#include "QedWrapperCommons.H"
#include "QedChiFunctions.H"
#include "Utils/WarpXConst.H"

#include <AMReX_Array.H>
#include <AMReX_Vector.H>
#include <AMReX_Gpu.H>

#include <physics/breit_wheeler/breit_wheeler_engine_tables.hpp>
#include <physics/breit_wheeler/breit_wheeler_engine_core.hpp>

#include <string>
#include <vector>

// Aliases =============================
using BW_dndt_table_params =
    picsar::multi_physics::phys::breit_wheeler::
    dndt_lookup_table_params<amrex::Real>;

using BW_dndt_table =
    picsar::multi_physics::phys::breit_wheeler::
    dndt_lookup_table<
    amrex::Real,
    amrex::Gpu::DeviceVector<amrex::Real>>;

using BW_dndt_table_view = BW_dndt_table::view_type;

using BW_pair_prod_table_params =
    picsar::multi_physics::phys::breit_wheeler::
    pair_prod_lookup_table_params<amrex::Real>;

using BW_pair_prod_table =
    picsar::multi_physics::phys::breit_wheeler::
    pair_prod_lookup_table<
    amrex::Real,
    amrex::Gpu::DeviceVector<amrex::Real>>;

using BW_pair_prod_table_view = BW_pair_prod_table::view_type;

struct PicsarBreitWheelerCtrl
{
    BW_dndt_table_params dndt_params;
    BW_pair_prod_table_params pair_prod_params;
};

// Functors ==================================

// These functors allow using the core elementary functions of the library.
// They are generated by a factory class (BreitWheelerEngine, see below).
// They can be included in GPU kernels.

class BreitWheelerGetOpticalDepth
{
public:
    BreitWheelerGetOpticalDepth ()
    {};

    AMREX_GPU_HOST_DEVICE
    AMREX_FORCE_INLINE
    amrex::Real operator() (amrex::RandomEngine const& engine) const noexcept
    {
        namespace pxr_bw = picsar::multi_physics::phys::breit_wheeler;

        //A random number in [0,1) should be provided as an argument.
        return pxr_bw::get_optical_depth(amrex::Random(engine));
    }
};
//____________________________________________

class BreitWheelerEvolveOpticalDepth
{
public:

    BreitWheelerEvolveOpticalDepth (){}


    BreitWheelerEvolveOpticalDepth (
        const BW_dndt_table_view table_view,
        const amrex::ParticleReal bw_minimum_chi_phot):
        m_table_view{table_view}, m_bw_minimum_chi_phot{bw_minimum_chi_phot}{};

    AMREX_GPU_DEVICE
    AMREX_FORCE_INLINE
    int operator()(
        const amrex::Real ux, const amrex::Real uy, const amrex::Real uz,
        const amrex::Real ex, const amrex::Real ey, const amrex::Real ez,
        const amrex::Real bx, const amrex::Real by, const amrex::Real bz,
        const amrex::Real dt, amrex::Real& opt_depth) const noexcept
    {
        namespace pxr_m = picsar::multi_physics::math;
        namespace pxr_p = picsar::multi_physics::phys;
        namespace pxr_bw = picsar::multi_physics::phys::breit_wheeler;

        constexpr amrex::Real m_e = PhysConst::m_e;
        const auto u_norm = std::sqrt(ux*ux + uy*uy + uz*uz);
        const auto energy = u_norm*m_e*PhysConst::c;

        const auto chi_phot = QedUtils::chi_photon(
            m_e*ux, m_e*uy, m_e*uz, ex, ey, ez, bx, by, bz);

        //Optical depth is not evolved for photons having less energy than what is
        //required to generate a pair or a quantum parameter smaller than
        //m_bw_minimum_chi_phot
        const auto gamma_photon = u_norm/PhysConst::c;
        if (gamma_photon < pxr_m::two<amrex::Real> ||
            chi_phot < m_bw_minimum_chi_phot)
            return 0;

        const auto is_out = pxr_bw::evolve_optical_depth<
            amrex::Real,
            BW_dndt_table_view,
            pxr_p::unit_system::SI>(
                energy, chi_phot, dt, opt_depth, m_table_view);

        return is_out;
    }

private:
    BW_dndt_table_view m_table_view;
    amrex::ParticleReal m_bw_minimum_chi_phot;
};

class BreitWheelerGeneratePairs
{
public:

    BreitWheelerGeneratePairs (){}

    BreitWheelerGeneratePairs (const BW_pair_prod_table_view table_view):
        m_table_view{table_view}{};

    AMREX_GPU_DEVICE
    AMREX_FORCE_INLINE
    int operator()(
    const amrex::Real ux, const amrex::Real uy, const amrex::Real uz,
    const amrex::Real ex, const amrex::Real ey, const amrex::Real ez,
    const amrex::Real bx, const amrex::Real by, const amrex::Real bz,
    amrex::Real& e_ux, amrex::Real& e_uy, amrex::Real& e_uz,
    amrex::Real& p_ux, amrex::Real& p_uy, amrex::Real& p_uz) const noexcept
    {
        using namespace amrex;
        namespace pxr_m = picsar::multi_physics::math;
        namespace pxr_p = picsar::multi_physics::phys;
        namespace pxr_bw = picsar::multi_physics::phys::breit_wheeler;

        const auto rand_zero_one_minus_epsi = amrex::Random();

        constexpr ParticleReal me = PhysConst::m_e;
        constexpr ParticleReal one_over_me = 1._prt/me;

        // Particle momentum is stored as gamma * velocity.
        // Convert to m * gamma * velocity
        auto px = ux*me;
        auto py = uy*me;
        auto pz = uz*me;

        const auto chi_photon = QedUtils::chi_photon(
            px, py, pz, ex, ey, ez, bx, by, bz);

        const auto momentum_photon = pxr_m::vec3<amrex::Real>{px, py, pz};
        auto momentum_ele = pxr_m::vec3<amrex::Real>();
        auto momentum_pos = pxr_m::vec3<amrex::Real>();

        const auto is_out = pxr_bw::generate_breit_wheeler_pairs<
            amrex::Real,
            BW_pair_prod_table_view,
            pxr_p::unit_system::SI>(
                chi_photon, momentum_photon,
                rand_zero_one_minus_epsi,
                m_table_view,
                momentum_ele, momentum_pos);

        e_ux = momentum_ele[0]*one_over_me;
        e_uy = momentum_ele[1]*one_over_me;
        e_uz = momentum_ele[2]*one_over_me;
        p_ux = momentum_pos[0]*one_over_me;
        p_uy = momentum_pos[1]*one_over_me;
        p_uz = momentum_pos[2]*one_over_me;

        return is_out;
    }

private:
    BW_pair_prod_table_view m_table_view;
};

// Factory class =============================

class BreitWheelerEngine
{
public:
    BreitWheelerEngine ();

    BreitWheelerGetOpticalDepth build_optical_depth_functor () const;

    BreitWheelerEvolveOpticalDepth build_evolve_functor () const;

    BreitWheelerGeneratePairs build_pair_functor () const;

    bool are_lookup_tables_initialized () const;

    std::vector<char> export_lookup_tables_data () const;

    bool init_lookup_tables_from_raw_data (
        const std::vector<char>& raw_data,
        const amrex::Real bw_minimum_chi_phot);

    void init_builtin_tables(const amrex::Real bw_minimum_chi_phot);

    void compute_lookup_tables (const PicsarBreitWheelerCtrl ctrl,
        const amrex::Real bw_minimum_chi_phot);

    PicsarBreitWheelerCtrl get_default_ctrl() const;

    amrex::Real get_minimum_chi_phot() const;

private:
    bool m_lookup_tables_initialized = false;

    //Variables to store the minimum chi parameters to enable
    //Quantum Synchrotron process
    amrex::Real m_bw_minimum_chi_phot;

    BW_dndt_table m_dndt_table;
    BW_pair_prod_table m_pair_prod_table;

    void init_builtin_dndt_table();
    void init_builtin_pair_prod_table();


};

//============================================

#endif //WARPX_breit_wheeler_engine_wrapper_H_