Add class for field ionization (#75)

* Add class for field ionization

* Make interactions more generic

* Update init file

* Use numpy style formatting in docstring

Examples/laser_acceleration/laser_acceleration_PICMI.py

@@ -103,9 +103,10 @@
 # Set the ionization for the species number 1 (Argon)
 # and place the created electrons into the species number 2 (electron)
 if picmi.codename != 'warpx':
-    plasma['Argon'].activate_field_ionization(
-        model           = "ADK", # Ammosov-Delone-Krainov model
-        product_species = plasma['e-'])
+    argon_ionization = picmi.FieldIonization(
+                model           = "ADK", # Ammosov-Delone-Krainov model
+                ionized_species = plasma['Argon'],
+                product_species = plasma['e-'])
 
 # --- electron bunch
 beam_dist = picmi.GaussianBunchDistribution(
@@ -191,6 +192,9 @@
 sim.add_species(species=beam, layout=beam_layout,
                 initialize_self_field=initialize_self_field)
 
+if picmi.codename != 'warpx':
+    sim.add_interaction(argon_ionization)
+
 # Add the diagnostics
 sim.add_diagnostic(field_diag)
 sim.add_diagnostic(part_diag)

PICMI_Python/__init__.py

@@ -2,6 +2,7 @@
 from .diagnostics import *
 from .fields import *
 from .applied_fields import *
+from .interactions import *
 from .lasers import *
 from .particles import *
 from .simulation import *

PICMI_Python/interactions.py

@@ -0,0 +1,29 @@
+"""Classes following the PICMI standard
+These should be the base classes for Python implementation of the PICMI standard
+The classes in this file are related to interactions (e.g. field ionization, collisions, QED)
+"""
+
+from .base import _ClassWithInit
+
+class PICMI_FieldIonization(_ClassWithInit):
+    """
+    Field ionization on an ion species
+
+    Parameters
+    ----------
+    model: string
+        Ionization model, e.g. "ADK"
+
+    ionized_species: species instance
+        Species that is ionized
+
+    product_species: species instance
+        Species in which ionized electrons are stored.
+    """
+    def __init__(self, model, ionized_species, product_species, **kw):
+        self.model = model
+        self.ionized_species = ionized_species
+        self.product_species = product_species
+
+        self.handle_init(kw)
+

PICMI_Python/particles.py

@@ -84,12 +84,6 @@ def __init__(self, particle_type=None, name=None, charge_state=None, charge=None
 
         self.handle_init(kw)
 
-    def activate_field_ionization(self, model, product_species):
-        # --- TODO: One way of handling interactions is to add a class for each type
-        # ---       of interaction. Instances would be added to the interactions list
-        # ---       instead of the list of parameters.
-        self.interactions.append(['ionization', model, product_species])
-
 
 class PICMI_MultiSpecies(_ClassWithInit):
     """

PICMI_Python/simulation.py

@@ -67,6 +67,8 @@ def __init__(self, solver=None, time_step_size=None, max_steps=None, max_time=No
 
         self.diagnostics = []
 
+        self.interactions = []
+
         self.cpu_split = cpu_split
         self.load_balancing = load_balancing
 
@@ -177,6 +179,17 @@ def add_diagnostic(self, diagnostic):
         """
         self.diagnostics.append(diagnostic)
 
+    def add_interaction(self, interaction):
+        """
+        Add an interaction
+
+        Parameters
+        ----------
+        interaction: interaction instance
+            One of the interaction objects.
+        """
+        self.interactions.append(interaction)
+
     def set_max_step(self, max_steps):
         """
         Set the default number of steps for the simulation (i.e. the number