# MCC collisions
cross_sec_direc = '../../../../warpx-data/MCC_cross_sections/He/'
mcc_electrons = picmi.MCCCollisions(
name='coll_elec',
species=electrons,
background_density=N_INERT,
background_temperature=T_INERT,
background_mass=ions.mass,
scattering_processes={
'elastic' : {
'cross_section' : cross_sec_direc+'electron_scattering.dat'
},
'excitation1' : {
'cross_section': cross_sec_direc+'excitation_1.dat',
'energy' : 19.82
},
'excitation2' : {
'cross_section': cross_sec_direc+'excitation_2.dat',
'energy' : 20.61
},
'ionization' : {
'cross_section' : cross_sec_direc+'ionization.dat',
'energy' : 24.55,
'species' : ions
},
}
)
mcc_ions = picmi.MCCCollisions(
name='coll_ion',
def __init__(self,
electron_species,
ion_species,
T_INERT,
P_INERT=None,
N_INERT=None,
scraper=None,
**kwargs):
"""Initialize MCC parameters.
Arguments:
electron_species (picmi.Species): Species that will be producing the
ions via impact ionization. This will normally be electrons.
ion_species (picmi.Species): Ion species generated from ionization
events. Charge state should be specified during Species
construction. Also used to obtain the neutral mass.
T_INERT (float): Temperature for injected ions in
Kelvin.
P_INERT (float): Pressure of the neutral "target" for
impact ionization, in Torr. Assumed to be such that the density
is much larger than both the electron and ion densities, so that
the neutral dynamics can be ignored. Cannot be specified if
N_INERT is specified.
N_INERT (float): Neutral gas density in m^-3. Cannot be specified
if P_INERT is specified.
scraper (pywarpx.ParticleScraper): The particle scraper is
instructed to save pid's for number of MCC events.
**kwargs that can be included:
exclude_collisions (list): A list of collision types to exclude.
"""
self.electron_species = electron_species
self.ion_species = ion_species
self.T_INERT = T_INERT
self.N_INERT = N_INERT
self.P_INERT = P_INERT
self.name = kwargs.get(
'name',
f"mcc_{self.electron_species.name}_{self.ion_species.name}")
self.exclude_collisions = kwargs.get("exclude_collisions", None)
if self.exclude_collisions is None:
self.exclude_collisions = []
if self.N_INERT is not None:
# N and P cannot both be specified
if self.P_INERT is not None:
raise ValueError("Must specify N_INERT or P_INERT, not both")
# if N is not None and P is None, everything is all good
# N and P cannot both be unspecified
elif self.P_INERT is None:
raise ValueError("Must specify one of N_INERT or P_INERT")
# set N using ideal gas law if only P is specified
else:
self.N_INERT = (mwxutil.ideal_gas_density(self.P_INERT,
self.T_INERT))
self.scraper = scraper
# Use environment variable if possible, otherwise look one
# directory up from warpx
path_name = os.environ.get(
"MCC_CROSS_SECTIONS_DIR",
os.path.join(mwxutil.mewarpx_dir,
"../../../warpx-data/MCC_cross_sections"))
path_name = os.path.join(path_name, self.ion_species.particle_type)
# include all collision processes that match species
file_paths = glob.glob(os.path.join(path_name, "*.dat"))
elec_collision_types = {
"electron_scattering": "elastic",
"excitation_1": "excitation1",
"excitation_2": "excitation2",
"ionization": "ionization",
}
ion_collision_types = {
"ion_scattering": "elastic",
"ion_back_scatter": "back",
"charge_exchange": "charge_exchange"
}
required_energy = {
"He": {
"excitation_1": 19.82,
"excitation_2": 20.61,
"ionization": 24.55
},
"Ar": {
"excitation_1": 11.5,
"ionization": 15.7596112
},
"Xe": {
"excitation_1": 8.315,
"ionization": 12.1298431
}
}
# build scattering process dictionaries
elec_scattering_processes = {}
ion_scattering_processes = {}
for path in file_paths:
file_name = os.path.basename(path)
coll_key = file_name.split('.dat')[0]
# exclude collision type if specified
if coll_key in self.exclude_collisions:
continue
# if electron process
if coll_key in elec_collision_types:
coll_type = elec_collision_types[coll_key]
scatter_dict = {"cross_section": path}
# add energy if needed
ion = self.ion_species.particle_type
if coll_key in required_energy[ion]:
scatter_dict["energy"] = required_energy[ion][coll_key]
# specify species for ionization
if coll_key == "ionization":
scatter_dict["species"] = self.ion_species
elec_scattering_processes[coll_type] = scatter_dict
# if ion process
elif coll_key in ion_collision_types:
coll_type = ion_collision_types[coll_key]
scatter_dict = {"cross_section": path}
ion_scattering_processes[coll_type] = scatter_dict
else:
raise ValueError(
f"{path}: filename not recognized as an MCC cross-section "
"file. Please move outside this folder or end with "
"something other than .dat if it is not a cross-section "
"file.")
# raise an error if no scattering processes exist
if (not elec_scattering_processes) and (not ion_scattering_processes):
raise ValueError(
"No scattering processes for electron or ion species.")
if mwxrun.simulation.collisions is None:
mwxrun.simulation.collisions = []
if elec_scattering_processes:
self.electron_mcc = picmi.MCCCollisions(
name=f'coll_{self.electron_species.name}',
species=self.electron_species,
background_density=self.N_INERT,
background_temperature=self.T_INERT,
background_mass=self.ion_species.mass,
scattering_processes=elec_scattering_processes)
mwxrun.simulation.collisions.append(self.electron_mcc)
if ion_scattering_processes:
self.ion_mcc = picmi.MCCCollisions(
name=f'coll_{self.ion_species.name}',
species=self.ion_species,
background_density=self.N_INERT,
background_temperature=self.T_INERT,
scattering_processes=ion_scattering_processes)
mwxrun.simulation.collisions.append(self.ion_mcc)
# add E_total PID to both species
self.electron_species.add_pid("E_total")
self.ion_species.add_pid("E_total")
callbacks.installbeforecollisions(self._get_particle_data_before)
callbacks.installaftercollisions(self._get_particle_data_after)
def setup_run(self):
"""Setup simulation components."""
#######################################################################
# Set geometry and boundary conditions #
#######################################################################
self.grid = picmi.Cartesian1DGrid(
number_of_cells=[self.nz],
warpx_max_grid_size=128,
lower_bound=[0],
upper_bound=[self.gap],
lower_boundary_conditions=['dirichlet'],
upper_boundary_conditions=['dirichlet'],
lower_boundary_conditions_particles=['absorbing'],
upper_boundary_conditions_particles=['absorbing'],
warpx_potential_hi_z=self.voltage,
)
#######################################################################
# Field solver #
#######################################################################
self.solver = picmi.ElectrostaticSolver(grid=self.grid,
method='Multigrid',
required_precision=1e-12,
warpx_self_fields_verbosity=0)
#######################################################################
# Particle types setup #
#######################################################################
self.electrons = picmi.Species(
particle_type='electron',
name='electrons',
initial_distribution=picmi.UniformDistribution(
density=self.plasma_density,
rms_velocity=[
np.sqrt(constants.kb * self.elec_temp / constants.m_e)
] * 3,
))
self.ions = picmi.Species(
particle_type='He',
name='he_ions',
charge='q_e',
mass=self.m_ion,
initial_distribution=picmi.UniformDistribution(
density=self.plasma_density,
rms_velocity=[
np.sqrt(constants.kb * self.gas_temp / self.m_ion)
] * 3,
))
#######################################################################
# Collision initialization #
#######################################################################
cross_sec_direc = '../../../../warpx-data/MCC_cross_sections/He/'
mcc_electrons = picmi.MCCCollisions(
name='coll_elec',
species=self.electrons,
background_density=self.gas_density,
background_temperature=self.gas_temp,
background_mass=self.ions.mass,
scattering_processes={
'elastic': {
'cross_section':
cross_sec_direc + 'electron_scattering.dat'
},
'excitation1': {
'cross_section': cross_sec_direc + 'excitation_1.dat',
'energy': 19.82
},
'excitation2': {
'cross_section': cross_sec_direc + 'excitation_2.dat',
'energy': 20.61
},
'ionization': {
'cross_section': cross_sec_direc + 'ionization.dat',
'energy': 24.55,
'species': self.ions
},
})
mcc_ions = picmi.MCCCollisions(
name='coll_ion',
species=self.ions,
background_density=self.gas_density,
background_temperature=self.gas_temp,
scattering_processes={
'elastic': {
'cross_section': cross_sec_direc + 'ion_scattering.dat'
},
'back': {
'cross_section': cross_sec_direc + 'ion_back_scatter.dat'
},
# 'charge_exchange' : {
# 'cross_section' : cross_sec_direc+'charge_exchange.dat'
# }
})
#######################################################################
# Initialize simulation #
#######################################################################
self.sim = picmi.Simulation(
solver=self.solver,
time_step_size=self.dt,
max_steps=self.max_steps,
warpx_collisions=[mcc_electrons, mcc_ions],
warpx_load_balance_intervals=self.max_steps // 5000,
verbose=self.test)
self.sim.add_species(self.electrons,
layout=picmi.GriddedLayout(
n_macroparticle_per_cell=[self.seed_nppc],
grid=self.grid))
self.sim.add_species(self.ions,
layout=picmi.GriddedLayout(
n_macroparticle_per_cell=[self.seed_nppc],
grid=self.grid))
#######################################################################
# Add diagnostics for the CI test to be happy #
#######################################################################
field_diag = picmi.FieldDiagnostic(
name='diag1',
grid=self.grid,
period=0,
data_list=['rho_electrons', 'rho_he_ions'],
write_dir='.',
warpx_file_prefix='Python_background_mcc_1d_plt')
self.sim.add_diagnostic(field_diag)