Add flag to disable laser evolution

docs/source/run/parameters.rst

@@ -646,6 +646,10 @@ which are valid only for certain beam types, are introduced further below under
     Whether the beam particles are pushed along the z-axis. The momentum is still fully updated.
     Note: using ``do_z_push = 0`` results in unphysical behavior.
 
+``<beam name>.accelerate`` (`bool`) optional (default `1`)
+    Whether the beam particles are accelerated. The transverse momentum is still fully updated.
+    Note: using ``accelerate = 0`` results in unphysical behavior.
+
 * ``<beam name> or beams.do_push`` (`bool`) optional (default `1`)
     When set to `0`, disables the beam particle pusher.
 
@@ -959,10 +963,11 @@ Parameters starting with ``lasers.`` apply to all laser pulses, parameters start
     the field to laser interpolation of chi. Currently, `0,1,2,3` are implemented.
 
 * ``lasers.solver_type`` (`string`) optional (default `multigrid`)
-    Type of solver for the laser envelope solver, either ``fft`` or ``multigrid``.
+    Type of solver for the laser envelope solver, either ``fft``, ``multigrid`` or ``off``.
     Currently, the approximation that the phase is evaluated on-axis only is made with both solvers.
     With the multigrid solver, we could drop this assumption.
     For now, the fft solver should be faster, more accurate and more stable, so only use the multigrid one with care.
+    If set ``off``, the laser will not evolve and remain as the initial profile through the simulation.
 
 * ``lasers.MG_tolerance_rel`` (`float`) optional (default `1e-4`)
     Relative error tolerance of the multigrid solver used for the laser pulse.

src/laser/MultiLaser.cpp

@@ -39,7 +39,8 @@ MultiLaser::ReadParameters ()
     m_linear_polarization = polarization == "linear";
     queryWithParser(pp, "use_phase", m_use_phase);
     queryWithParser(pp, "solver_type", m_solver_type);
-    AMREX_ALWAYS_ASSERT(m_solver_type == "multigrid" || m_solver_type == "fft");
+    AMREX_ALWAYS_ASSERT(m_solver_type == "multigrid" || m_solver_type == "fft" ||
+                        m_solver_type == "off");
     queryWithParser(pp, "interp_order", m_interp_order);
     AMREX_ALWAYS_ASSERT(m_interp_order <= 3 && m_interp_order >= 0);
 
@@ -463,8 +464,21 @@ MultiLaser::AdvanceSlice (const int islice, const Fields& fields, amrex::Real dt
         AdvanceSliceMG(dt, is_first_step);
     } else if (m_solver_type == "fft") {
         AdvanceSliceFFT(dt, is_first_step);
+    } else if (m_solver_type == "off") {
+        for ( amrex::MFIter mfi(m_slices, DfltMfi); mfi.isValid(); ++mfi ){
+            Array3<amrex::Real> arr = m_slices.array(mfi);
+            amrex::ParallelFor(
+                to2D(mfi.tilebox()),
+                [=] AMREX_GPU_DEVICE (int i, int j) {
+                    using namespace WhichLaserSlice;
+                    // copy current laser to slice of the next time step
+                    arr(i, j, np1j00_r) = arr(i, j, n00j00_r);
+                    arr(i, j, np1j00_i) = arr(i, j, n00j00_i);
+                }
+            );
+        }
     } else {
-        amrex::Abort("laser.solver_type must be fft or multigrid");
+        amrex::Abort("laser.solver_type must be fft, multigrid or off");
     }
 }
 

src/particles/beam/BeamParticleContainer.H

@@ -245,6 +245,7 @@ public:
     amrex::Real m_spin_anom = 0.00115965218128;
     /** ratio of beam particles that are written to the openPMD output */
     int m_output_ratio = 1;
+    bool m_acc_z = true; /**<if accelerator the beam on z */
 private:
     std::string m_name; /**< name of the species */
     /** injection type, fixed_width or fixed_ppc */

src/particles/beam/BeamParticleContainer.cpp

@@ -57,6 +57,7 @@ BeamParticleContainer::ReadParameters ()
     getWithParser(pp, "injection_type", m_injection_type);
     queryWithParser(pp, "duz_per_uz0_dzeta", m_duz_per_uz0_dzeta);
     queryWithParser(pp, "do_z_push", m_do_z_push);
+    queryWithParser(pp, "accelerate", m_acc_z);
     queryWithParserAlt(pp, "do_push", m_do_push, pp_alt);
     queryWithParserAlt(pp, "do_radiation_reaction", m_do_radiation_reaction, pp_alt);
     queryWithParserAlt(pp, "insitu_period", m_insitu_period.m_func_str, pp_alt);

src/particles/pusher/BeamParticleAdvance.cpp

@@ -25,7 +25,7 @@ AdvanceBeamParticlesSlice (
     using namespace amrex::literals;
 
     const PhysConst phys_const = get_phys_const();
-
+    const bool acc_z = beam.m_acc_z;
     const bool do_z_push = beam.m_do_z_push;
     const int n_subcycles = beam.m_n_subcycles;
     const bool radiation_reaction = beam.m_do_radiation_reaction;
@@ -200,7 +200,6 @@ AdvanceBeamParticlesSlice (
                     auto [shape_n, ncell] = shape_factor<2>(zmid, 0);
 
                     Ezp *= (1._rt - shape_p - shape_n);
-
                     // Gather Ez field on particle from grid
                     for (int iy=0; iy<=depos_order.value; iy++){
                         for (int ix=0; ix<=depos_order.value; ix++){
@@ -218,7 +217,7 @@ AdvanceBeamParticlesSlice (
                     ApplyExternalField(xp, yp, zp, time, clight, ExmByp, EypBxp, Ezp, Bxp, Byp, Bzp,
                         external_fields);
                 }
-
+                if(!acc_z) Ezp = 0;
                 ExmByp *= inv_clight;
                 EypBxp *= inv_clight;
                 Ezp *= inv_clight;