PICMI: ionizer added despite not being initialized

[PrometheusPi]

In PICMI, ionizers like BSI and ADK can be defined and need to be added to the picongpu_interaction.
If I create ionizers, but avoid adding them (see commented-out line below), they are still added in speciesDefinition.param .
This seems to be a bug.

The following code reproduces the behavior.

# /// script
# requires-python = ">=3.11,<3.14"
# dependencies = ["picongpu @ git+https://github.com/ComputationalRadiationPhysics/picongpu@dev#subdirectory=lib/python"]
# ///

from pathlib import Path
import numpy as np
import datetime

from picongpu import picmi
from picongpu.picmi import Simulation, ElectromagneticSolver, Cartesian3DGrid


######################################
# setup parameters - please change

N_sims = 1 # number of simulations 
N_interations = 1000 # iterations for each simulation
GPU_distribution = [1, 8, 2] # GPU layout for each simulation

#######################################
# sim setup

def create_sim():
    """
    This is a warm plasma simulation
    """

    #############
    # solver

    numberCells = np.array([192, 2048, 192])
    cellSize = np.array([0.8e-6 / 128.] * 3)  # unit: meter

    solver=ElectromagneticSolver(
        method = "Yee",
        cfl = 0.95,
        grid = Cartesian3DGrid(
            picongpu_n_gpus=GPU_distribution,
            number_of_cells = numberCells.tolist(),
            lower_bound = [0,0,0],
            upper_bound = (numberCells * cellSize).tolist(),
            lower_boundary_conditions = ["periodic"] * 3,
            upper_boundary_conditions = ["periodic"] * 3,
        )
    )


    #############
    # particles

    n_c = 1.11485e27 / 0.8 / 0.8
    n_e = 448. * n_c;

    gaussianDensityProfile = picmi.distribution.GaussianDistribution(
        density=n_e,
        center_front=5.0e-6,
        sigma_front=1.0e-6,
        center_rear=10.0e-6,
        sigma_rear=1.0e-6,
        factor=-1.0,
        power=2.0,
        vacuum_front=50 * cellSize[1],
        rms_velocity=[1.0e-3 * picmi.constants.c] * 3,
    )
    

    random_layout_rods = picmi.PseudoRandomLayout(n_macroparticles_per_cell=10)

    electrons = picmi.Species(
        particle_type="electron",
        name="e",
        initial_distribution=gaussianDensityProfile,
        density_scale = 1.0,
        )

    silicon = picmi.Species(
        particle_type="Si",
        name="si",
        charge_state=2,
        initial_distribution=gaussianDensityProfile,
        density_scale = 0.5,
        )

    adk_ionization_model = picmi.ADK(
        ADK_variant=picmi.ADKVariant.LinearPolarization,
        ion_species=silicon,
        ionization_electron_species=electrons,
        ionization_current=None,
        )

    bsi_effectiveZ_ionization_model = picmi.BSI(
        BSI_extensions=[picmi.BSIExtension.EffectiveZ],
        ion_species=silicon,
        ionization_electron_species=electrons,
        ionization_current=None,
        )

    interaction = [adk_ionization_model,
                   bsi_effectiveZ_ionization_model]
    

    ##############
    # sim setup

    sim = Simulation(
        picongpu_walltime=datetime.timedelta(minutes=10.0),
        max_steps = N_interations,
        solver = solver,
        picongpu_species = [electrons, silicon],
        picongpu_particle_layout = random_layout_rods,
        #picongpu_interaction = interaction        
    )
    
    
    ###############
    # plugin output
    
    sim.diagnostics = []
    sim.diagnostics.append(picmi.diagnostics.MacroParticleCount(
            species=electrons,
            period=picmi.diagnostics.TimeStepSpec[::10],
        ))
    
    return sim

#######################################

#######################################
# create and build all PIConGPU simulations

all_picongpu_calls = []

for i in range(N_sims):
    sim = create_sim() # call picmi simulation creater
    sim_path = Path(f"./test/sim_{i:04d}") # location of simulation
    sim.run(setup_dir = sim_path / "setup",
            run_dir = sim_path / "run") # create setup, build and empty tbg
    all_picongpu_calls.append(f"{sim_path.resolve()}") # add to list of simulations

#######################################

[BrianMarre]

That is not a bug, but rather a side effect of the recent Species Translation refactor by @chillenzer.

PICMI species now follow RAII(Resource Aquisition is Initialization), meaning that the creation of an PICMI Ionizer already adds the interaction to the ion species, see here.
Adding the Ionizer to the simulation is therefore not strictly necessary anymore and only an artefact of the picmi standard.

Admittedly, that is still unexpected behaviour for a user, but I actually prefer the new method. The PICMI standard interface should just be updated to make the new behaviour clearer.

[PrometheusPi]

Thanks a lit @BrianMarre for pointing this out. I agree in both points: the new feature is definitely useful, but with the "old" picmi interface it's definitely confusing.

[chillenzer]

Thanks for spotting, @BrianMarre!