Fix neutral particle got pushed (#4643)

* Update PushSelector.H

add the pointer of the array of ion_lev to the pusher function, and use this pointer to determine whether to change the charge instead of the value of ion_lev

* Update PhysicalParticleContainer.cpp

Change the variable in the targeted function

* Alternative approach

---------

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

Author: GivenChen

Source/Particles/PhysicalParticleContainer.cpp

@@ -2880,7 +2880,7 @@ PhysicalParticleContainer::PushPX (WarpXParIter& pti,
 
             doParticleMomentumPush<0>(ux[ip], uy[ip], uz[ip],
                                       Exp, Eyp, Ezp, Bxp, Byp, Bzp,
-                                      ion_lev ? ion_lev[ip] : 0,
+                                      ion_lev ? ion_lev[ip] : 1,
                                       m, q, pusher_algo, do_crr,
 #ifdef WARPX_QED
                                       t_chi_max,
@@ -2900,7 +2900,7 @@ PhysicalParticleContainer::PushPX (WarpXParIter& pti,
 
                 doParticleMomentumPush<1>(ux[ip], uy[ip], uz[ip],
                                           Exp, Eyp, Ezp, Bxp, Byp, Bzp,
-                                          ion_lev ? ion_lev[ip] : 0,
+                                          ion_lev ? ion_lev[ip] : 1,
                                           m, q, pusher_algo, do_crr,
                                           t_chi_max,
                                           dt);
@@ -3140,7 +3140,7 @@ PhysicalParticleContainer::ImplicitPushXP (WarpXParIter& pti,
         {
             doParticleMomentumPush<0>(ux[ip], uy[ip], uz[ip],
                                       Exp, Eyp, Ezp, Bxp, Byp, Bzp,
-                                      ion_lev ? ion_lev[ip] : 0,
+                                      ion_lev ? ion_lev[ip] : 1,
                                       m, q, pusher_algo, do_crr,
 #ifdef WARPX_QED
                                       t_chi_max,
@@ -3152,7 +3152,7 @@ PhysicalParticleContainer::ImplicitPushXP (WarpXParIter& pti,
             if constexpr (qed_control == has_qed) {
                 doParticleMomentumPush<1>(ux[ip], uy[ip], uz[ip],
                                           Exp, Eyp, Ezp, Bxp, Byp, Bzp,
-                                          ion_lev ? ion_lev[ip] : 0,
+                                          ion_lev ? ion_lev[ip] : 1,
                                           m, q, pusher_algo, do_crr,
                                           t_chi_max,
                                           dt);

Source/Particles/Pusher/PushSelector.H

@@ -57,7 +57,7 @@ void doParticleMomentumPush(amrex::ParticleReal& ux,
                             const amrex::Real dt)
 {
     amrex::ParticleReal qp = a_q;
-    if (ion_lev) { qp *= ion_lev; }
+    qp *= ion_lev;
 
     if (do_crr) {
 #ifdef WARPX_QED