WarpX
UpdateMomentumVay.H
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1 /* Copyright 2019 David Grote, Maxence Thevenet, Remi Lehe
2  * Weiqun Zhang
3  *
4  * This file is part of WarpX.
5  *
6  * License: BSD-3-Clause-LBNL
7  */
8 #ifndef WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_VAY_H_
9 #define WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_VAY_H_
10 
11 #include "Utils/WarpXConst.H"
12 
13 #include <AMReX_FArrayBox.H>
14 #include <AMReX_REAL.H>
15 
16 
21  amrex::ParticleReal& ux, amrex::ParticleReal& uy, amrex::ParticleReal& uz,
22  const amrex::ParticleReal Ex, const amrex::ParticleReal Ey, const amrex::ParticleReal Ez,
23  const amrex::ParticleReal Bx, const amrex::ParticleReal By, const amrex::ParticleReal Bz,
24  const amrex::ParticleReal q, const amrex::ParticleReal m, const amrex::Real dt )
25 {
26  using namespace amrex::literals;
27 
28  // Constants
29  const amrex::ParticleReal econst = q*dt/m;
30  const amrex::ParticleReal bconst = 0.5_prt*q*dt/m;
31  constexpr amrex::ParticleReal invclight = 1._prt/PhysConst::c;
32  constexpr amrex::ParticleReal invclightsq = 1._prt/(PhysConst::c*PhysConst::c);
33  // Compute initial gamma
34  const amrex::ParticleReal inv_gamma = 1._prt/std::sqrt(1._prt + (ux*ux + uy*uy + uz*uz)*invclightsq);
35  // Get tau
36  const amrex::ParticleReal taux = bconst*Bx;
37  const amrex::ParticleReal tauy = bconst*By;
38  const amrex::ParticleReal tauz = bconst*Bz;
39  const amrex::ParticleReal tausq = taux*taux+tauy*tauy+tauz*tauz;
40  // Get U', gamma'^2
41  const amrex::ParticleReal uxpr = ux + econst*Ex + (uy*tauz-uz*tauy)*inv_gamma;
42  const amrex::ParticleReal uypr = uy + econst*Ey + (uz*taux-ux*tauz)*inv_gamma;
43  const amrex::ParticleReal uzpr = uz + econst*Ez + (ux*tauy-uy*taux)*inv_gamma;
44  const amrex::ParticleReal gprsq = (1._prt + (uxpr*uxpr + uypr*uypr + uzpr*uzpr)*invclightsq);
45  // Get u*
46  const amrex::ParticleReal ust = (uxpr*taux + uypr*tauy + uzpr*tauz)*invclight;
47  // Get new gamma
48  const amrex::ParticleReal sigma = gprsq-tausq;
49  const amrex::ParticleReal gisq = 2._prt/(sigma + std::sqrt(sigma*sigma + 4._prt*(tausq + ust*ust)) );
50  // Get t, s
51  const amrex::ParticleReal bg = bconst*std::sqrt(gisq);
52  const amrex::ParticleReal tx = bg*Bx;
53  const amrex::ParticleReal ty = bg*By;
54  const amrex::ParticleReal tz = bg*Bz;
55  const amrex::ParticleReal s = 1._prt/(1._prt+tausq*gisq);
56  // Get t.u'
57  const amrex::ParticleReal tu = tx*uxpr + ty*uypr + tz*uzpr;
58  // Get new U
59  ux = s*(uxpr+tx*tu+uypr*tz-uzpr*ty);
60  uy = s*(uypr+ty*tu+uzpr*tx-uxpr*tz);
61  uz = s*(uzpr+tz*tu+uxpr*ty-uypr*tx);
62 }
63 
64 #endif // WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_VAY_H_
#define AMREX_INLINE
#define AMREX_GPU_HOST_DEVICE
AMREX_GPU_HOST_DEVICE AMREX_INLINE void UpdateMomentumVay(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, const amrex::ParticleReal q, const amrex::ParticleReal m, const amrex::Real dt)
Push the particle's positions over one timestep, given the value of its momenta ux,...
Definition: UpdateMomentumVay.H:20
static constexpr auto c
vacuum speed of light [m/s]
Definition: constant.H:44
float dt
Definition: stencil.py:442