Input File: Fluids

Relativistic Cold Fluid

The following object generates a module that computes the motion of a cold, relativistic, electron fluid. It is assumed there is an immobile background of ions. Temperature only comes into the computation of the Coulomb collision frequency. The electron temperature is controlled by the last generate block (see Matter Loading). There can only be one cold fluid module in a simulation. Electron, ion, and neutral density are tracked in this one module. Any profiles installed for the fluid refer to a gas with constant fractional ionization.

new fluid <name> { <directives> }
Parameters:

  • name (str) – assigns a name to the fluid

  • directives (block) –

    The following directives are supported:

    Installable tools: PhotoIonization

    charge = q
    Parameters:

    q (float) – charge of the fluid constituent, usually electrons

    mass = m
    Parameters:

    m (float) – mass of the fluid constituent, usually electrons

    neutral cross section = sigma
    Parameters:

    sigma (float) – electron-neutral collision cross section

    coulomb collisions = cc
    Parameters:

    cc (bool) – if true, add collision frequency based on Coulomb cross section to neutral collision frequency

    Note

    the ion species and electron species variables (see PhotoIonization) have no meaning here

SPARC Hydro Modules

new hydrodynamics [<name>] { <directives> }

This is the top level SPARC module. Internally it contains and manages all other SPARC modules.

Parameters:

  • name (str) – name given to the hydro manager

  • directives (block) –

    The following directives are supported:

    Installable tools: Particle Movers

    epsilon factor = eps
    Parameters:

    eps (float) – error tolerance for adaptive time step

    background density = n0
    Parameters:

    n0 (float) – automatically create a uniform background density n0 for every chemical species. Charged species are automatically weighted such that neutrality is maintained. Defaults to zero, in which case the user is responsible for explicitly loading every chemical species.

    background temperature = T0
    Parameters:

    T0 (float) – temperature to use for the background fluid. If the background density is nonzero this must be set to a positive value.

    radiation model = rad
    Parameters:

    rad (enum) – takes values thick, thin, none

    laser model = las
    Parameters:

    las (enum) – takes values vacuum, isotropic

    plasma model = plas
    Parameters:

    plas (enum) – takes values neutral, quasineutral

    electrostatic heating = esh
    Parameters:

    esh (bool) – If on, electrons are heated by self-consistent electrostatic fields. Default is off.

    dipole center = Dx Dy Dz

    Reference point for dipole moment diagnostic

new chemical [<name>] [for <name>] { <directives> }

The chemical module uses automatic attachment, i.e., if a chemical is created at the root level without the for clause a new equilibrium group module is created for it automatically. As a result, chemical modules should never be attached using get statements.

Parameters:

  • name (str) – name given to the chemical species

  • directives (block) –

    The following directives are supported:

    Installable tools: PhotoIonization, Equation of State Tools

    mass = m0
    Parameters:

    m0 (float) – mass of the constituent particles, default = 1.0

    charge = q0
    Parameters:

    q0 (float) – charge of the constituent particles, default = -1.0

    cv = cv0
    Parameters:

    cv0 (float) – normalized specific heat at constant volume, mc_v/k_B, a typical value is 1.5 for species with no internal degrees of freedom.

    vibrational energy = epsv
    Parameters:

    epsv (float) – energy between vibrational levels, default = 0 = no vibrations

    implicit = tst
    Parameters:

    tst (bool) – whether to use implicit electron advance for this species

    thermometric conductivity = k
    Parameters:

    k (float) – Thermometric conductivity. Thermometric conductivity is K/\rho c_p, where K = heat conductivity. For air, k = 2e-5 m^2/s = 0.2 cm^2/s, and K = 2.5e-4 W/(cm*K). SPARC solves the heat equation \rho c_v dT/dt - \nabla\cdot (K \nabla T) = 0. For electrons the Braginskii conductivity is used.

    kinematic viscosity = x
    Parameters:

    x (float) – Kinematic viscosity. Kinematic viscosity is X/\rho, where X = dynamic viscosity. For air, kinematic viscosity is about 0.15 cm^2/s. SPARC solves the momentum diffusion equation \rho dv/dt - \nabla\cdot (X \nabla v) = 0.

    effective mass = meff
    Parameters:

    meff (float) – effective mass for density >> 1.0 for electrons moving through this chemical

    permittivity = (epsr,epsi)
    Parameters:

    • epsr (float) – real part of permittivity relative to free space permittivity

    • epsi (float) – imaginary part of permittivity relative to free space permittivity

new group [<name>] [for <name>] { directives }

Create an equilibrium group module. This is a container for chemical species that are assumed to be in equilibrium with one another, and therefore have a common temperature and velocity. All chemicals are part of a group.

The group module uses automatic attachment, i.e., if created at the root level without the for clause it is automatically attached to hydrodynamics. The hydrodynamics module is automatically created, if necessary.

Parameters:

  • name (str) – name given to the group

  • directives (block) –

    The following directives are supported:

    mobile = tst
    Parameters:

    tst (bool) – whether chemicals in this group are mobile or immobile

SPARC Collision Directives

SPARC collisions broadly include elastic and inelastic collisions, as well as chemical reactions. All such processes have to explicitly resolved. These directives are special in that they use a compact, ordered declaration (without the usual parameter block), and use dimensional numbers in CGS-eV units. This is due to the potentially large number of such constructs that may appear in an input file. Dimensional numbers should not be used.

SPARC collision directives should appear at the root level in the input file. They find their parent modules automatically. This makes it more straightforward to #include reaction data from separate files.

new collision = sp1 <-> sp2 , cross section = sigma
Parameters:

  • sp1 (str) – name of chemical species 1 in two-body collision

  • sp2 (str) – name of chemical species 2 in two-body collision

  • sigma (float) – cross section in square centimeters

new collision = sp1 <-> sp1 , coulomb

Uses the Coulomb collision cross section, derived from local conditions.

Parameters:

  • sp1 (str) – name of chemical species 1 in two-body collision

  • sp2 (str) – name of chemical species 2 in two-body collision

new collision = sp1 <-> sp1 , metallic , ks = ks0 , fermi_energy_ev = ef , ref_density = nref

Uses the harmonic mean of electron-phonon and coulomb collision rates

Parameters:

  • ks0 (float) – dimensionless, see K. Eidmann et al., Phys. Rev. E 62, 1202 (2000)

  • ef (float) – the Fermi energy in eV

  • nref (float) – the density at which the formula directly applies in particles per cubic centimeter

new reaction = { eq1 : eq2 : eq3 : ... } rate = c0 c1 c2 cat(range)

Sets up a chemical reaction between arbitrary species using a modified Arrhenius rate

{\cal R} = c_0 T^{c_1} \exp(-c_2/T)

over a range of temperatures. Piecewise rate constructions can be created by using multiple reactions which have the same equation but different rates and different temperature ranges.

Parameters:

  • eq1 (str) – chemical equation, or subreaction, in the form r1 + r2 + ... -> p1 + p2 + ... + eps, where r1 etc. are replaced by names of reactants, p1 etc. are replaced by names of products, and eps is a heat of reaction in eV. Breaking the reaction into subreactions can be used to control the flow of energy from reactants to products. The heat of reaction, if negative, is taken from the equilibrium group of the last reactant listed. If positive, it is added to the equilibrium group of the last product listed.

  • c0 (float) – rate coefficient in cm^(3(N-1))/s, where N is the number of reactants

  • c1 (float) – dimensionless exponent in rate law

  • c2 (float) – temperature reference appearing in rate law in eV

  • cat (str) – name of the chemical to be considered the catalyst, i.e., the one whose temperature affects the rate

  • range (numpy_range) – range of temperatures specified as in numpy, i.e., T1:T2, where T1 and T2 are floating point literals, given in eV. Also as in numpy, :T2 means 0-T2, while T1: means T1-infinity.

new reaction = { eq1 : eq2 : eq3 : ... } janev_rate = c0 c1 c2 c3 c4 c5 c6 c7 c8 cat(range)

Alternative way of specifying the reaction rate:

\ln {\cal R} = \sum_{n=0}^{8} c_n (\ln T)^n

new excitation = sp1 -> sp2 level = n rate = c0 c1 c2

Vibrational excitation of one species by another. If level = n the transition is between ground and level n. If level = 0 the transition is between adjacent levels, where it is assumed the rate for transitions from n to n+1 is the same for all n.

new excitation = sp1 -> sp2 level = n janev_rate = c0 c1 c2 c3 c4 c5 c6 c7 c8

Alternative way of specifying the excitation rate.