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Diffstat (limited to 'Source/Particles/Pusher/UpdateMomentumBoris.H')
-rw-r--r-- | Source/Particles/Pusher/UpdateMomentumBoris.H | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/Source/Particles/Pusher/UpdateMomentumBoris.H b/Source/Particles/Pusher/UpdateMomentumBoris.H new file mode 100644 index 000000000..71e9a8ed1 --- /dev/null +++ b/Source/Particles/Pusher/UpdateMomentumBoris.H @@ -0,0 +1,47 @@ +#ifndef WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_BORIS_H_ +#define WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_BORIS_H_ + +#include <AMReX_REAL.H> + +/* \brief Push the particle's positions over one timestep, + * given the value of its momenta `ux`, `uy`, `uz` */ +AMREX_GPU_HOST_DEVICE AMREX_INLINE +void UpdateMomentumBoris( + amrex::Real& ux, amrex::Real& uy, amrex::Real& uz, amrex::Real& gaminv, + const amrex::Real Ex, const amrex::Real Ey, const amrex::Real Ez, + const amrex::Real Bx, const amrex::Real By, const amrex::Real Bz, + const amrex::Real q, const amrex::Real m, const amrex::Real dt ) +{ + const amrex::Real econst = 0.5*q*dt/m; + + // First half-push for E + ux += econst*Ex; + uy += econst*Ey; + uz += econst*Ez; + // Compute temporary gamma factor + constexpr amrex::Real inv_c2 = 1./(PhysConst::c*PhysConst::c); + const amrex::Real inv_gamma = 1./std::sqrt(1. + (ux*ux + uy*uy + uz*uz)*inv_c2); + // Magnetic rotation + // - Compute temporary variables + const amrex::Real tx = econst*inv_gamma*Bx; + const amrex::Real ty = econst*inv_gamma*By; + const amrex::Real tz = econst*inv_gamma*Bz; + const amrex::Real tsqi = 2./(1. + tx*tx + ty*ty + tz*tz); + const amrex::Real sx = tx*tsqi; + const amrex::Real sy = ty*tsqi; + const amrex::Real sz = tz*tsqi; + const amrex::Real ux_p = ux + uy*tz - uz*ty; + const amrex::Real uy_p = uy + uz*tx - ux*tz; + const amrex::Real uz_p = uz + ux*ty - uy*tx; + // - Update momentum + ux += uy_p*sz - uz_p*sy; + uy += uz_p*sx - ux_p*sz; + uz += ux_p*sy - uy_p*sx; + // Second half-push for E + ux += econst*Ex; + uy += econst*Ey; + uz += econst*Ez; + gaminv = 1./std::sqrt(1. + (ux*ux + uy*uy + uz*uz)*inv_c2); +} + +#endif // WARPX_PARTICLES_PUSHER_UPDATEMOMENTUM_BORIS_H_ |