WarpX
UpdateMomentumBoris.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_BORIS_H_
9 #define WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_BORIS_H_
10 
11 #include <AMReX_REAL.H>
12 
17  amrex::ParticleReal& ux, amrex::ParticleReal& uy, amrex::ParticleReal& uz,
18  const amrex::ParticleReal Ex, const amrex::ParticleReal Ey, const amrex::ParticleReal Ez,
19  const amrex::ParticleReal Bx, const amrex::ParticleReal By, const amrex::ParticleReal Bz,
20  const amrex::ParticleReal q, const amrex::ParticleReal m, const amrex::Real dt )
21 {
22  using namespace amrex::literals;
23 
24  const amrex::ParticleReal econst = 0.5_prt*q*dt/m;
25 
26  // First half-push for E
27  ux += econst*Ex;
28  uy += econst*Ey;
29  uz += econst*Ez;
30  // Compute temporary gamma factor
31  constexpr amrex::ParticleReal inv_c2 = 1._prt/(PhysConst::c*PhysConst::c);
32  const amrex::ParticleReal inv_gamma = 1._prt/std::sqrt(1._prt + (ux*ux + uy*uy + uz*uz)*inv_c2);
33  // Magnetic rotation
34  // - Compute temporary variables
35  const amrex::ParticleReal tx = econst*inv_gamma*Bx;
36  const amrex::ParticleReal ty = econst*inv_gamma*By;
37  const amrex::ParticleReal tz = econst*inv_gamma*Bz;
38  const amrex::ParticleReal tsqi = 2._prt/(1._prt + tx*tx + ty*ty + tz*tz);
39  const amrex::ParticleReal sx = tx*tsqi;
40  const amrex::ParticleReal sy = ty*tsqi;
41  const amrex::ParticleReal sz = tz*tsqi;
42  const amrex::ParticleReal ux_p = ux + uy*tz - uz*ty;
43  const amrex::ParticleReal uy_p = uy + uz*tx - ux*tz;
44  const amrex::ParticleReal uz_p = uz + ux*ty - uy*tx;
45  // - Update momentum
46  ux += uy_p*sz - uz_p*sy;
47  uy += uz_p*sx - ux_p*sz;
48  uz += ux_p*sy - uy_p*sx;
49  // Second half-push for E
50  ux += econst*Ex;
51  uy += econst*Ey;
52  uz += econst*Ez;
53 }
54 
55 #endif // WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_BORIS_H_
#define AMREX_INLINE
#define AMREX_GPU_HOST_DEVICE
AMREX_GPU_HOST_DEVICE AMREX_INLINE void UpdateMomentumBoris(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: UpdateMomentumBoris.H:16
static constexpr auto c
vacuum speed of light [m/s]
Definition: constant.H:44
float dt
Definition: stencil.py:442