add new option to initialize external fields on grid upto a max user…

…-defined level

Docs/source/usage/parameters.rst

@@ -1440,6 +1440,17 @@ Grid initialization
     the field solver. In particular, do not use any other boundary condition
     than periodic.
 
+* ``warpx.maxlevel_extEMfield_init`` (default is maximum number of levels in the simulation)
+    With this parameter, the externally applied electric and magnetic fields with paramters
+    ``warpx.E_ext_grid_init_style="constant"``,
+    ``warpx.B_ext_grid_init_style="constant"``,
+    ``warpx.E_ext_grid_init_style="parse_E_ext_grid_function"`` and
+    ``warpx.B_ext_grid_init_style="parse_B_ext_grid_function"`` will not be initialized with the external field
+    for levels strictly greater than ``warpx.maxlevel_extEMfield_init``. For some mesh-refinement simulations,
+    the external fields are only applied to the parent grid and not the refined patches. In such cases,
+    ``warpx.maxlevel_extEMfield_init`` can be set to 0. Note that the other levels will be initialized to
+    a default value of 0.
+
 Applied to Particles
 ^^^^^^^^^^^^^^^^^^^^
 

Source/Initialization/WarpXInitData.cpp

@@ -747,6 +747,17 @@ WarpX::InitLevelData (int lev, Real /*time*/)
                    E_ext_grid_s.begin(),
                    ::tolower);
 
+    // Externally imposed fields are only initialized until the user-defined maxlevel_extEMfield_init.
+    // The default maxlevel_extEMfield_init value is the total number of levels in the simulation
+    // Note that if the external fields are not provided, the fields, E and B, on all levels
+    // will still be initialized with the default value of 0.
+    if ( (B_ext_grid_s == "constant") || (B_ext_grid_s == "parse_b_ext_grid_function")) {
+        if (lev > maxlevel_extEMfield_init) continue;
+    }
+    if ( (E_ext_grid_s == "constant") || (E_ext_grid_s == "parse_e_ext_grid_function")) {
+        if (lev > maxlevel_extEMfield_init) continue;
+    }
+
     // if the input string is "constant", the values for the
     // external grid must be provided in the input.
     if (B_ext_grid_s == "constant")

Source/WarpX.H

@@ -159,6 +159,12 @@ public:
     //! User-defined parser to initialize z-component of the electric field on the grid
     std::unique_ptr<amrex::Parser> Ezfield_parser;
 
+    /** Maximum level upto which the externally defined electric and magnetic fields are initialized.
+     *  The default value is set to the max levels in the simulation.
+     *  if lev > maxlevel_extEMfield_init, the fields on those levels will have a default value of 0
+     */
+    int maxlevel_extEMfield_init;
+
     // Algorithms
     //! Integer that corresponds to the current deposition algorithm (Esirkepov, direct, Vay)
     static short current_deposition_algo;

Source/WarpX.cpp

@@ -734,6 +734,9 @@ WarpX::ReadParameters ()
             add_external_E_field = true;
         }
 
+        maxlevel_extEMfield_init = maxLevel();
+        pp_warpx.query("maxlevel_extEMfield_init", maxlevel_extEMfield_init);
+
         electrostatic_solver_id = GetAlgorithmInteger(pp_warpx, "do_electrostatic");
         // if an electrostatic solver is used, set the Maxwell solver to None
         if (electrostatic_solver_id != ElectrostaticSolverAlgo::None) {