fix functionality

src/python/impactx/dashboard/simulation.py

@@ -83,14 +83,19 @@ def run_simulation():
     )
 
     distribution = distribution_parameters()
-    sim.add_particles(bunch_charge_C, distribution, npart)
 
     lattice_configuration = lattice_elements()
     sim.lattice.extend(lattice_configuration)
 
     tracking_modes = {
-        "Particle Tracking": sim.track_particles,
-        "Envelope Tracking": sim.track_envelope,
+        "Particle Tracking": lambda: (
+            sim.add_particles(bunch_charge_C, distribution, npart),
+            sim.track_particles(),
+        ),
+        "Envelope Tracking": lambda: (
+            sim.init_envelope(ref, distribution),
+            sim.track_envelope(),
+        ),
         "Reference Tracking": sim.track_reference,
     }
 
@@ -100,11 +105,12 @@ def run_simulation():
     fig = adjusted_settings_plot(pc)
     ctrl.matplotlib_figure_update(fig)
 
-    fig_original = pc.plot_phasespace()
+    if state.tracking_mode == "Particle Tracking":
+        fig_original = pc.plot_phasespace()
 
-    if fig_original is not None:
-        image_base64 = fig_to_base64(fig_original)
-        state.phase_space_png = f"data:image/png;base64, {image_base64}"
+        if fig_original is not None:
+            image_base64 = fig_to_base64(fig_original)
+            state.phase_space_png = f"data:image/png;base64, {image_base64}"
 
     sim.finalize()