1 files changed, 29 insertions, 0 deletions
diff --git a/Source/Particles/Pusher/UpdatePositionPhoton.H b/Source/Particles/Pusher/UpdatePositionPhoton.H
new file mode 100644
index 000000000..bd6e6cd21
--- /dev/null
+++ b/Source/Particles/Pusher/UpdatePositionPhoton.H
@@ -0,0 +1,29 @@
+#ifndef WARPX_PARTICLES_PUSHER_UPDATEPOSITIONPHOTON_H_
+#define WARPX_PARTICLES_PUSHER_UPDATEPOSITIONPHOTON_H_
+
+#include <WarpXConst.H>
+
+#include <AMReX_FArrayBox.H>
+#include <AMReX_REAL.H>
+
+/* \brief Push the position of a photon particle over one timestep,
+ *    given the value of its momenta `ux`, `uy`, `uz` */
+AMREX_GPU_HOST_DEVICE AMREX_INLINE
+void UpdatePositionPhoton(
+    amrex::Real& x, amrex::Real& y, amrex::Real& z,
+    const amrex::Real ux, const amrex::Real uy, const amrex::Real uz,
+    const amrex::Real dt )
+{
+    // Compute speed of light over inverse of momentum modulus
+    const amrex::Real c_over_umod = PhysConst::c/std::sqrt(ux*ux + uy*uy + uz*uz);
+
+    // Update positions over one time step
+    x += ux * c_over_umod * dt;
+#if (defined WARPX_DIM_3D) || (defined WARPX_DIM_RZ) // RZ pushes particles in 3D
+    y += uy * c_over_umod * dt;
+#endif
+    z += uz * c_over_umod * dt;
+
+}
+
+#endif // WARPX_PARTICLES_PUSHER_UPDATEPOSITION_H_