path: root/Source/Particles/ElementaryProcess/QEDInternals/QuantumSyncEngineWrapper.H

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

#include "BreitWheelerEngineWrapper_fwd.H"

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

#include <AMReX_Extension.H>
#include <AMReX_GpuQualifiers.H>
#include <AMReX_REAL.H>
#include <AMReX_Random.H>

#include <picsar_qed/containers/picsar_array.hpp>
#include <picsar_qed/math/cmath_overloads.hpp>
#include <picsar_qed/math/vec_functions.hpp>
#include <picsar_qed/physics/phys_constants.h>
#include <picsar_qed/physics/quantum_sync/quantum_sync_engine_core.hpp>
#include <picsar_qed/physics/quantum_sync/quantum_sync_engine_tables.hpp>
#include <picsar_qed/physics/unit_conversion.hpp>

#include <cmath>
#include <vector>

namespace amrex { struct RandomEngine; }

// Aliases =============================
using QS_dndt_table_params =
    picsar::multi_physics::phys::quantum_sync::
    dndt_lookup_table_params<amrex::ParticleReal>;

using QS_dndt_table =
    picsar::multi_physics::phys::quantum_sync::
    dndt_lookup_table<
    amrex::ParticleReal,
    PicsarQedVector<amrex::ParticleReal>>;

using QS_dndt_table_view = QS_dndt_table::view_type;

using QS_phot_em_table_params =
    picsar::multi_physics::phys::quantum_sync::
    photon_emission_lookup_table_params<amrex::ParticleReal>;

using QS_phot_em_table =
    picsar::multi_physics::phys::quantum_sync::
    photon_emission_lookup_table<
    amrex::ParticleReal,
    PicsarQedVector<amrex::ParticleReal>>;

using QS_phot_em_table_view = QS_phot_em_table::view_type;

struct PicsarQuantumSyncCtrl
{
    QS_dndt_table_params dndt_params;
    QS_phot_em_table_params phot_em_params;
};

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

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

/**
*  Functor to initialize the optical depth of leptons for the
*  Quantum Synchrotron process
*/
class QuantumSynchrotronGetOpticalDepth
{
public:
    /**
     * Constructor does nothing because optical depth initialization
     * does not require control parameters or lookup tables.
     */
    QuantumSynchrotronGetOpticalDepth () = default;

    /**
     * () operator is just a thin wrapper around a very simple function to
     * generate the optical depth. It can be used on GPU.
     */
    AMREX_GPU_HOST_DEVICE
    AMREX_FORCE_INLINE
    amrex::ParticleReal operator() (amrex::RandomEngine const& engine) const noexcept
    {
        namespace pxr_qs = picsar::multi_physics::phys::quantum_sync;

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

/**
 * Functor to evolve the optical depth of leptons due to the
 * Quantum Synchrotron process
 */
class QuantumSynchrotronEvolveOpticalDepth
{
public:

    /**
     * Default constructor: it leaves the functor in a non-initialized state.
     */
    QuantumSynchrotronEvolveOpticalDepth () = default;

    /**
     * Constructor to be used to initialize the functor.
     *
     * @param[in] table_view a view of a QS_dndt_table lookup table
     * @param[in] qs_minimum_chi_part the minimum quantum parameter to evolve the optical depth
     */
    QuantumSynchrotronEvolveOpticalDepth (
        const QS_dndt_table_view table_view,
        const amrex::ParticleReal qs_minimum_chi_part):
        m_table_view{table_view}, m_qs_minimum_chi_part{qs_minimum_chi_part}{}

    /**
     * Evolves the optical depth. It can be used on GPU.
     * If the  quantum parameter parameter of the particle is
     * < qs_minimum_chi_part, the method returns immediately.
     *
     * @param[in] ux,uy,uz gamma*v components of the lepton.
     * @param[in] ex,ey,ez electric field components (SI units)
     * @param[in] bx,by,bz magnetic field components (SI units)
     * @param[in] dt timestep (SI units)
     * @param[in,out] opt_depth optical depth of the particle.
     * @return a flag which is 1 if chi_part was out of table.
     */
    AMREX_GPU_DEVICE
    AMREX_FORCE_INLINE
    int operator()(
        const amrex::ParticleReal ux, const amrex::ParticleReal uy, const amrex::ParticleReal uz,
        const amrex::ParticleReal ex, const amrex::ParticleReal ey, const amrex::ParticleReal ez,
        const amrex::ParticleReal bx, const amrex::ParticleReal by, const amrex::ParticleReal bz,
        const amrex::Real dt, amrex::ParticleReal& opt_depth) const noexcept
    {
        using namespace amrex::literals;
        namespace pxr_p = picsar::multi_physics::phys;
        namespace pxr_qs = picsar::multi_physics::phys::quantum_sync;

        constexpr amrex::ParticleReal m_e = PhysConst::m_e;
        constexpr amrex::ParticleReal inv_c2 = 1._rt/(PhysConst::c*PhysConst::c);
        const amrex::ParticleReal gamma = std::sqrt(1._rt + (ux*ux + uy*uy + uz*uz)*inv_c2);
        const auto energy = gamma*m_e*PhysConst::c*PhysConst::c;

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

        if (chi_part < m_qs_minimum_chi_part)
            return 0;

        const auto is_out = pxr_qs::evolve_optical_depth<
            amrex::ParticleReal,
            QS_dndt_table_view,
            pxr_p::unit_system::SI>(
                energy, chi_part, dt, opt_depth, m_table_view);

        return is_out;
    }

private:
    QS_dndt_table_view m_table_view;
    amrex::ParticleReal m_qs_minimum_chi_part;
};

/**
 * Functor to generate a photon via the Quantum Synchrotron process
 * and to update momentum accordingly
 */
class QuantumSynchrotronPhotonEmission
{
public:

    /**
     * Default constructor: it leaves the functor in a non-initialized state.
     */
    QuantumSynchrotronPhotonEmission () = default;

    /**
     * Constructor acquires pointers to control parameters and
     * lookup tables data.
     * lookup_table uses non-owning vectors under the hood. So no new data
     * allocations should be triggered on GPU
     *
     * @param[in] table_view a view of a QS_phot_em_table lookup table
     */
    QuantumSynchrotronPhotonEmission (
        const QS_phot_em_table_view table_view):
        m_table_view{table_view}{}

    /**
     * Generates photons according to Quantum Synchrotron process.
     * It can be used on GPU.
     *
     * @param[in,out] ux,uy,uz gamma*v components of the lepton. They are modified (SI units)
     * @param[in] ex,ey,ez electric field components (SI units)
     * @param[in] bx,by,bz magnetic field components (SI units)
     * @param[out] g_ux,g_uy,g_uz gamma*v components of the generated photon (SI units)
     * @param[in] engine random number generator engine
     * @return a flag which is 1 if chi_photon was out of table
     */
    AMREX_GPU_DEVICE
    AMREX_FORCE_INLINE
    bool operator()(
    amrex::ParticleReal& ux, amrex::ParticleReal& uy,
    amrex::ParticleReal& uz,
    const amrex::ParticleReal ex, const amrex::ParticleReal ey,
    const amrex::ParticleReal ez, const amrex::ParticleReal bx,
    const amrex::ParticleReal by, const amrex::ParticleReal bz,
    amrex::ParticleReal& g_ux, amrex::ParticleReal& g_uy,
    amrex::ParticleReal& g_uz, amrex::RandomEngine const& engine) const noexcept
    {
        using namespace amrex;
        namespace pxr_m = picsar::multi_physics::math;
        namespace pxr_p = picsar::multi_physics::phys;
        namespace pxr_qs = picsar::multi_physics::phys::quantum_sync;

        const auto rand_zero_one_minus_epsi = amrex::Random(engine);

        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_particle = QedUtils::chi_ele_pos(
            px, py, pz, ex, ey, ez, bx, by, bz);

        auto momentum_particle = pxr_m::vec3<amrex::ParticleReal>{px, py, pz};
        auto momentum_photon = pxr_m::vec3<amrex::ParticleReal>();

        const auto is_out = pxr_qs::generate_photon_update_momentum<
            amrex::ParticleReal,
            QS_phot_em_table_view,
            pxr_p::unit_system::SI>(
                chi_particle, momentum_particle,
                rand_zero_one_minus_epsi,
                m_table_view,
                momentum_photon);

        ux = momentum_particle[0]*one_over_me;
        uy = momentum_particle[1]*one_over_me;
        uz = momentum_particle[2]*one_over_me;
        g_ux = momentum_photon[0]*one_over_me;
        g_uy = momentum_photon[1]*one_over_me;
        g_uz = momentum_photon[2]*one_over_me;

        return is_out;
    }

private:
    QS_phot_em_table_view m_table_view;

};

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

/**
 * Wrapper for the Quantum Synchrotron engine of the PICSAR library
 */
class QuantumSynchrotronEngine
{
public:
    /**
     * Constructor requires no arguments.
     */
    QuantumSynchrotronEngine () = default;

    /**
     * Builds the functor to initialize the optical depth
     */
    QuantumSynchrotronGetOpticalDepth build_optical_depth_functor ();

    /**
     * Builds the functor to evolve the optical depth
     */
    QuantumSynchrotronEvolveOpticalDepth build_evolve_functor ();

    /**
     * Builds the functor to generate photons
     */
    QuantumSynchrotronPhotonEmission build_phot_em_functor ();

    /**
     * Checks if the optical tables are properly initialized
     */
    bool are_lookup_tables_initialized () const;

    /**
     * Export lookup tables data into a raw binary Vector
     *
     * @return the data in binary format. The Vector is empty if tables were
     * not previously initialized.
     */
    std::vector<char> export_lookup_tables_data () const;

    /**
     * Init lookup tables from raw binary data.
     *
     * @param[in] raw_data a vector of char
     * @param[in] qs_minimum_chi_part minimum chi parameter to evolve the optical depth of a particle.
     * @return true if it succeeds, false if it cannot parse raw_data
     */
    bool init_lookup_tables_from_raw_data (const std::vector<char>& raw_data,
        amrex::ParticleReal qs_minimum_chi_part);

    /**
     * Init lookup tables using built-in (low resolution) tables
     *
     * @param[in] qs_minimum_chi_part minimum chi parameter to evolve the optical depth of a particle.
     */
    void init_builtin_tables(amrex::ParticleReal qs_minimum_chi_part);

    /**
     * Computes the lookup tables. It does nothing unless WarpX is compiled with QED_TABLE_GEN=TRUE
     *
     * @param[in] ctrl control params to generate the tables
     * @param[in] qs_minimum_chi_part minimum chi parameter to evolve the optical depth of a particle.
     */
    void compute_lookup_tables (PicsarQuantumSyncCtrl ctrl,
        amrex::ParticleReal qs_minimum_chi_part);

    /**
     * gets default values for the control parameters
     *
     * @return default control params to generate the tables
     */
    PicsarQuantumSyncCtrl get_default_ctrl() const;

    amrex::ParticleReal get_minimum_chi_part() const;

private:
    bool m_lookup_tables_initialized = false;

    //Variables to store the minimum chi parameters to enable
    //Quantum Synchrotron process
    amrex::ParticleReal m_qs_minimum_chi_part;

    QS_dndt_table m_dndt_table;
    QS_phot_em_table m_phot_em_table;

    void init_builtin_dndt_table();
    void init_builtin_phot_em_table();
};

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

#endif //WARPX_quantum_sync_engine_wrapper_h_