fix RRcoeff to be consistent with re obtained from re_squred in FRR

RevathiJambunathan · Dec 2, 2023 · 5a9c710 · 5a9c710
1 parent 13ed05a
commit 5a9c710
Showing 1 changed file with 6 additions and 1 deletion.
diff --git a/Source/Particles/Pusher/UpdateMomentumBorisWithRadiationReaction.H b/Source/Particles/Pusher/UpdateMomentumBorisWithRadiationReaction.H
@@ -89,7 +89,12 @@ void UpdateMomentumBorisWithRadiationReaction(
 #ifdef PULSAR
     // For a scaled down system, we scale up radiation reaction drag force by upscaling re
     // re_scaled is derived by equating the drag force and accelerating force, for a set gammarad < sigma_LC
-    const amrex::ParticleReal RRcoeff = (2.0_prt/3.0_prt)*PhysConst::r_e*re_scaledratio*q_over_mc*q_over_mc;
+    //const amrex::ParticleReal RRcoeff = (2.0_prt/3.0_prt)*PhysConst::r_e*re_scaledratio*q_over_mc*q_over_mc;
+    // Since we re-write FRR as f(re*re), the coefficient is 2/3*4*pi*eps * re*re/m
+    // The division by m is because in WarpX, we update u = gamma*v
+    const amrex::ParticleReal re2 = PhysConst::re * PhysConst::re;
+    const amrex::ParticleReal re2_scaled = re2 * re_scaledratio * re_scaledratio;
+    const amrex::ParticleReal RRcoeff = (2.0_prt/3.0_prt)*4 * MathConst::pi * PhyConst::ep0 * re2_scaled/m;
 #else
     const amrex::ParticleReal RRcoeff = (2.0_prt/3.0_prt)*PhysConst::r_e*q_over_mc*q_over_mc;
 #endif