ChrDrift.H

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/* 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_CHRDRIFT_H
#define IMPACTX_CHRDRIFT_H
 
#include "particles/ImpactXParticleContainer.H"
#include "mixin/alignment.H"
#include "mixin/pipeaperture.H"
#include "mixin/beamoptic.H"
#include "mixin/thick.H"
#include "mixin/lineartransport.H"
#include "mixin/named.H"
#include "mixin/nofinalize.H"
 
#include <AMReX_Extension.H>
#include <AMReX_Math.H>
#include <AMReX_REAL.H>
#include <AMReX_SIMD.H>
 
#include <cmath>
#include <stdexcept>
 
 
namespace impactx::elements
{
    struct ChrDrift
    : public mixin::Named,
      public mixin::BeamOptic<ChrDrift>,
      public mixin::LinearTransport<ChrDrift>,
      public mixin::Thick,
      public mixin::Alignment,
      public mixin::PipeAperture,
      public mixin::NoFinalize,
      public amrex::simd::Vectorized<amrex::simd::native_simd_size_particlereal>
    {
        static constexpr auto type = "ChrDrift";
        using PType = ImpactXParticleContainer::ParticleType;

        ChrDrift (
            amrex::ParticleReal ds,
            amrex::ParticleReal dx = 0,
            amrex::ParticleReal dy = 0,
            amrex::ParticleReal rotation_degree = 0,
            amrex::ParticleReal aperture_x = 0,
            amrex::ParticleReal aperture_y = 0,
            int nslice = 1,
            std::optional<std::string> name = std::nullopt
        )
        : Named(std::move(name)),
          Thick(ds, nslice),
          Alignment(dx, dy, rotation_degree),
          PipeAperture(aperture_x, aperture_y)
        {
        }

        using BeamOptic::operator();

        void compute_constants (RefPart const & refpart)
        {
            using namespace amrex::literals; // for _rt and _prt
            using amrex::Math::powi;
 
            Alignment::compute_constants(refpart);
 
            // length of the current slice
            m_slice_ds = m_ds / nslice();
 
            // access reference particle values to find beta, gamma
            m_beta = refpart.beta();
            m_gamma = refpart.gamma();
 
            m_const1 = 1_prt / (2_prt * powi<3>(m_beta) * powi<2>(m_gamma));
        }

        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,
            T_Real & AMREX_RESTRICT t,
            T_Real & AMREX_RESTRICT px,
            T_Real & AMREX_RESTRICT py,
            T_Real & AMREX_RESTRICT pt,
            T_IdCpu & AMREX_RESTRICT idcpu,
            [[maybe_unused]] RefPart const & AMREX_RESTRICT refpart
        ) const
        {
            using namespace amrex::literals; // for _rt and _prt
            using amrex::Math::powi;
            using namespace std; // for cmath(float)
 
            // shift due to alignment errors of the element
            shift_in(x, y, px, py);
 
            // access position data
            T_Real const xout = x;
            T_Real const yout = y;
            T_Real const tout = t;
 
            // initialize output values of momenta
            T_Real const pxout = px;
            T_Real const pyout = py;
            T_Real const ptout = pt;
 
            // compute particle momentum deviation delta + 1
            T_Real const idelta1 = 1_prt / sqrt(1_prt - 2_prt*pt/m_beta + powi<2>(pt));
 
            // advance transverse position and momentum (drift)
            x = xout + m_slice_ds * px * idelta1;
            // pxout = px;
            y = yout + m_slice_ds * py * idelta1;
            // pyout = py;
 
            // the corresponding symplectic update to t
            T_Real term = 2_prt * powi<2>(pt) + powi<2>(px) + powi<2>(py);
            term = 2_prt - 4_prt*m_beta*pt + powi<2>(m_beta)*term;
            term = -2_prt + powi<2>(m_gamma)*term;
            term = (-1_prt+m_beta*pt)*term;
            term = term * m_const1;
            t = tout - m_slice_ds * (1_prt / m_beta + term * powi<3>(idelta1));
            // ptout = pt;
 
            // assign updated momenta
            px = pxout;
            py = pyout;
            pt = ptout;
 
            // apply transverse aperture
            apply_aperture(x, y, idcpu);
 
            // undo shift due to alignment errors of the element
            shift_out(x, y, px, py);
        }

        AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
        void operator() (RefPart & AMREX_RESTRICT refpart) const
        {
            using namespace amrex::literals; // for _rt and _prt
            using amrex::Math::powi;
 
            // assign input reference particle values
            amrex::ParticleReal const x = refpart.x;
            amrex::ParticleReal const px = refpart.px;
            amrex::ParticleReal const y = refpart.y;
            amrex::ParticleReal const py = refpart.py;
            amrex::ParticleReal const z = refpart.z;
            amrex::ParticleReal const pz = refpart.pz;
            amrex::ParticleReal const t = refpart.t;
            amrex::ParticleReal const pt = refpart.pt;
            amrex::ParticleReal const s = refpart.s;
 
            // length of the current slice
            amrex::ParticleReal const slice_ds = m_ds / nslice();
 
            // assign intermediate parameter
            amrex::ParticleReal const step = slice_ds /std::sqrt(powi<2>(pt)-1.0_prt);
 
            // advance position and momentum (drift)
            refpart.x = x + step*px;
            refpart.y = y + step*py;
            refpart.z = z + step*pz;
            refpart.t = t - step*pt;
 
            // advance integrated path length
            refpart.s = s + slice_ds;
        }

        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();
        }
 
      private:
        // constants that are independent of the individually tracked particle,
        // see: compute_constants() to refresh
        amrex::ParticleReal m_slice_ds;  
        amrex::ParticleReal m_beta;
        amrex::ParticleReal m_gamma;
        amrex::ParticleReal m_const1;
    };
 
} // namespace impactx
 
#endif // IMPACTX_CHRDRIFT_H