Multipole.H

Go to the documentation of this file.

/* Copyright 2022-2023 The Regents of the University of California, through Lawrence
 *           Berkeley National Laboratory (subject to receipt of any required
 *           approvals from the U.S. Dept. of Energy). All rights reserved.
 *
 * This file is part of ImpactX.
 *
 * Authors: Chad Mitchell, Axel Huebl
 * License: BSD-3-Clause-LBNL
 */
#ifndef IMPACTX_MULTIPOLE_H
#define IMPACTX_MULTIPOLE_H
 
#include "particles/ImpactXParticleContainer.H"
#include "mixin/alignment.H"
#include "mixin/beamoptic.H"
#include "mixin/thin.H"
#include "mixin/lineartransport.H"
#include "mixin/named.H"
#include "mixin/nofinalize.H"
 
#include <AMReX_Extension.H>
#include <AMReX_GpuComplex.H>
#include <AMReX_REAL.H>
#include <AMReX_SIMD.H>
 
#include <cmath>
#include <stdexcept>
 
 
namespace impactx::elements
{
    struct Multipole
    : public mixin::Named,
      public mixin::BeamOptic<Multipole>,
      public mixin::LinearTransport<Multipole>,
      public mixin::Thin,
      public mixin::Alignment,
      public mixin::NoFinalize
#ifndef _WIN32
      // https://github.com/AMReX-Codes/amrex/issues/4609
      , public amrex::simd::Vectorized<amrex::simd::native_simd_size_particlereal>
#endif
    {
        static constexpr auto type = "Multipole";
        using PType = ImpactXParticleContainer::ParticleType;

        void
        compute_factorial ()
        {
            int const m = m_multipole - 1;
            m_mfactorial = 1;
            for( int n = 1; n < m + 1; n = n + 1 ) {
                m_mfactorial *= n;
            }
        }

        Multipole (
            int multipole,
            amrex::ParticleReal K_normal,
            amrex::ParticleReal K_skew,
            amrex::ParticleReal dx = 0,
            amrex::ParticleReal dy = 0,
            amrex::ParticleReal rotation_degree = 0,
            std::optional<std::string> name = std::nullopt
        )
        : Named(std::move(name)),
          Alignment(dx, dy, rotation_degree),
          m_multipole(multipole), m_Kn(K_normal), m_Ks(K_skew)
        {
            compute_factorial();
        }

        using BeamOptic::operator();

        void compute_constants (RefPart const & refpart)
        {
            using namespace amrex::literals; // for _rt and _prt
 
            Alignment::compute_constants(refpart);
 
            // assign complex position and complex multipole strength
            m_alpha = {m_Kn, m_Ks};
 
            m_inv_factorial = 1.0_prt / static_cast<amrex::ParticleReal>(m_mfactorial);
        }

        template<typename T_Real=amrex::ParticleReal, typename T_IdCpu=uint64_t>
        AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
        void operator() (
            T_Real & AMREX_RESTRICT x,
            T_Real & AMREX_RESTRICT y,
            [[maybe_unused]] T_Real & AMREX_RESTRICT t,
            T_Real & AMREX_RESTRICT px,
            T_Real & AMREX_RESTRICT py,
            T_Real & AMREX_RESTRICT pt,
            [[maybe_unused]] T_IdCpu & AMREX_RESTRICT idcpu,
            [[maybe_unused]] RefPart const & AMREX_RESTRICT refpart
        ) const
        {
            using namespace amrex::literals; // for _rt and _prt
 
            // shift due to alignment errors of the element
            shift_in(x, y, px, py);
 
            // a complex type with two T_Real
            using Complex = amrex::GpuComplex<T_Real>;
 
            // access reference particle values to find (beta*gamma)^2
            //amrex::ParticleReal const pt_ref = refpart.pt;
            //amrex::ParticleReal const betgam2 = powi<2>(pt_ref) - 1.0_prt;
 
            // initialize output values
            T_Real xout = x;
            T_Real yout = y;
            T_Real tout = t;
            T_Real pxout = px;
            T_Real pyout = py;
            T_Real ptout = pt;
 
            // assign complex position and complex multipole strength
            Complex const zeta(x, y);
 
            // compute complex momentum kick
            int const m = m_multipole - 1;
            Complex const kick = amrex::pow(zeta, m) * m_alpha;
            T_Real const dpx = -1.0_prt * kick.m_real * m_inv_factorial;
            T_Real const dpy = kick.m_imag * m_inv_factorial;
 
            // advance position and momentum
            // xout = x;
            pxout = px + dpx;
 
            // yout = y;
            pyout = py + dpy;
 
            // tout = t;
            ptout = pt;
 
            // assign updated values
            x = xout;
            y = yout;
            t = tout;
            px = pxout;
            py = pyout;
            pt = ptout;
 
            // undo shift due to alignment errors of the element
            shift_out(x, y, px, py);
        }

        using Thin::operator();

        using LinearTransport::operator();

        AMREX_GPU_HOST AMREX_FORCE_INLINE
        Map6x6
        transport_map ([[maybe_unused]] RefPart const & AMREX_RESTRICT refpart) const
        {
            throw std::runtime_error(std::string(type) + ": Envelope tracking is not yet implemented!");
            return Map6x6::Identity();
        }
 
        int m_multipole; 
        amrex::ParticleReal m_Kn; 
        amrex::ParticleReal m_Ks; 
 
      private:
        // constants that are independent of the individually tracked particle
        // see: compute_factorial() to refresh
        int m_mfactorial;  
        // see: compute_constants() to refresh
        amrex::GpuComplex<amrex::ParticleReal> m_alpha;
        amrex::ParticleReal m_inv_factorial;
    };
 
} // namespace impactx
 
#endif // IMPACTX_MULTIPOLE_H