# Radiation Parameters¶

## Background Radiation Parameters¶

`RadiationFieldType`(external)- This integer parameter specifies the type of radiation field that is to be used. Except for
`RadiationFieldType`= 9, which should be used with`MultiSpecies`= 2, UV backgrounds can currently only be used with`MultiSpecies`= 1 (i.e. no molecular H support). The following values are used. Default: 01 - Haardt & Madau spectrum with q_alpha = 1.5 2 - Haardt & Madau spectrum with q_alpha = 1.8 3 - Modified Haardt & Madau spectrum to match observations (Kirkman & Tytler 2005). 4 - Haardt & Madau spectrum with q_alpha = 1.5 supplemented with an X-ray Compton heating background from Madau & Efstathiou (see astro-ph/9902080) 9 - Constant molecular H2 photo-dissociation rate 10 - Internally computed radiation field using the algorithm of Cen & Ostriker 11 - Same as previous, but with very, very simple optical shielding fudge 12 - Haardt & Madau spectrum with q_alpha = 1.57 15 - Haardt & Madau 2012. See Table 3 in '2012ApJ...746..125H <http://adsabs.harvard.edu/abs/2012ApJ...746..125H />'_

`RadiationFieldLevelRecompute`(external)- This integer parameter is used only if the previous parameter is set to 10 or 11. It controls how often (i.e. the level at which) the internal radiation field is recomputed. Default: 0
`RadiationSpectrumNormalization`(external)- This parameter was initially used to normalize the photo-ionization
and photo-heating rates computed in the function
`RadiationFieldCalculateRates()`and then passed on to the`calc_photo_rates()`,`calc_rad()`and`calc_rates()`routines. Later, the normalization as a separate input parameter was dropped for all cases by using the rates computed in`RadiationFieldCalculateRates()`with one exception: The molecular hydrogen (H2) dissociation rate. There a normalization is performed on the rate by multiplying it with`RadiationSpectrumNormalization`. Default: 1e-21 `RadiationShield`(external)- This parameter specifies whether the user wants to employ
approximate radiative-shielding. This parameter will be
automatically turned on when RadiationFieldType is set to 11. See
`calc_photo_rates.src`. Default: 0 `RadiationFieldRedshift`(external)- This parameter specifies the redshift at which the radiation field is calculated. Default: 0
`RadiationRedshiftOn`(external)- The redshift at which the UV background turns on. Default: 7.0.
`RadiationRedshiftFullOn`(external)- The redshift at which the UV
background is at full strength. Between z =
`RadiationRedshiftOn`and z =`RadiationRedshiftFullOn`, the background is gradually ramped up to full strength. Default: 6.0. `RadiationRedshiftDropOff`(external)- The redshift at which the
strength of the UV background is begins to gradually reduce,
reaching zero by
`RadiationRedshiftOff`. Default: 0.0. `RadiationRedshiftOff`(external)- The redshift at which the UV background is fully off. Default: 0.0.
`TabulatedLWBackground`(external)- When on, the amplitude of the Lyman-Werner background is read from the file LW_J21.in as a function of redshift. Each line should have the redshift and LW background in units of 1e-21 erg/cm^3/s/Hz/sr. Default: 0
`AdjustUVBackground`(external)- Add description. Default: 1.
`AdjustUVBackgroundHighRedshift`(external)- Add description. Default: 0.
`SetUVAmplitude`(external)- Add description. Default: 1.0.
`SetHeIIHeatingScale`(external)- Add description. Default: 1.8.
`RadiationSpectrumSlope`(external)- Add description. Default: 1.5.

## Radiative Transfer (Ray Tracing) Parameters¶

`RadiativeTransfer`(external)- Set to 1 to turn on the adaptive ray tracing following Abel, Wise &
Bryan 2007. Note that Enzo must be first recompiled after setting
`make photon-yes`. Default: 0. `RadiativeTransferRadiationPressure`(external)- Set to 1 to turn on radiation pressure created from absorbed photon packages. Default: 0
`RadiativeTransferInitialHEALPixLevel`(external)- Chooses how many rays are emitted from radiation sources. The
number of rays in Healpix are given through # =
12x4
^{level}. Default: 3. `RadiativeTransferRaysPerCell`(external)- Determines the accuracy of the scheme by giving the minimum number of rays to cross cells. The more the better (slower). Default: 5.1.
`RadiativeTransferSourceRadius`(external)- The radius at which the photons originate from the radiation source. A positive value results in a radiating sphere. Default: 0.
`RadiativeTransferPropagationRadius`(external)- The maximum distance a photon package can travel in one timestep. Currently unused. Default: 0.
`RadiativeTransferPropagationSpeed`(external)- The fraction of the speed of light at which the photons travel. Default: 1.
`RadiativeTransferCoupledRateSolver`(external)- Set to 1 to calculate the new ionization fractions and gas energies after every radiative transfer timestep. This option is highly recommended to be kept on. If not, ionization fronts will propagate too slowly. Default: 1.
`RadiativeTransferOpticallyThinH2`(external)- Set to 1 to include an optically-thin H_2 dissociating
(Lyman-Werner) radiation field. Only used if
`MultiSpecies`> 1. If`MultiSpecies`> 1 and this option is off, the Lyman-Werner radiation field will be calculated with ray tracing. Default: 1. `RadiativeTransferSplitPhotonPackage`(external)- Once photons are past this radius, they can no longer split. In
units of kpc. If this value is negative (by default), photons can
always split. Default:
`FLOAT_UNDEFINED`. `RadiativeTransferPhotonEscapeRadius`(external)- The number of photons that pass this distance from its source are
summed into the global variable
`EscapedPhotonCount[]`. This variable also keeps track of the number of photons passing this radius multiplied by 0.5, 1, and 2. Units are in kpc. Not used if set to 0. Default: 0. `RadiativeTransferSourceClustering`(external)- Set to 1 to turn on ray merging from combined virtual sources on a binary tree. Default: 0.
`RadiativeTransferPhotonMergeRadius`(external)- The radius at which the rays will merge from their SuperSource, which is the luminosity weighted center of two sources. This radius is in units of the separation of two sources associated with one SuperSource. If set too small, there will be angular artifacts in the radiation field. Default: 2.5
`RadiativeTransferSourceBeamAngle`(external)- Rays will be emitted within this angle in degrees of the poles from sources with “Beamed” types. Default: 30
`RadiativeTransferPeriodicBoundary`(external)- Set to 1 to turn on periodic boundary conditions for photon packages. Default: 0.
`RadiativeTransferTimestepVelocityLimit`(external)- Limits the radiative transfer timestep to a minimum value that is determined by the cell width at the finest level divided by this velocity. Units are in km/s. Default: 100.
`RadiativeTransferHIIRestrictedTimestep`(external)- Adaptive ray tracing timesteps will be restricted by a maximum change of 10% in neutral fraction if this parameter is set to 1. If set to 2, then the incident flux can change by a maximum of 0.5 between cells. See Wise & Abel (2011) in Sections 3.4.1 and 3.4.4 for more details. Default: 0
`RadiativeTransferAdaptiveTimestep`(external)- Must be 1 when RadiativeTransferHIIRestrictedTimestep is non-zero. When RadiativeTransferHIIRestrictedTimestep is 0, then the radiative transfer timestep is set to the timestep of the finest AMR level. Default: 0
`RadiativeTransferLoadBalance`(external)- When turned on, the grids are load balanced based on the number of ray segments traced. The grids are moved to different processors only for the radiative transfer solver. Default: 0
`RadiativeTransferHydrogenOnly`(external)- When turned on, the photo-ionization fields are only created for hydrogen. Default: 0
`RadiationXRaySecondaryIon`(external)- Set to 1 to turn on secondary ionizations and reduce heating from X-ray radiation (Shull & van Steenberg 1985). Currently only BH and MBH particles emit X-rays. Default: 0.
`RadiationXRayComptonHeating`(external)- Set to 1 to turn on Compton heating on electrons from X-ray radiation (Ciotti & Ostriker 2001). Currently only BH and MBH particles emit X-rays. Default: 0.
`RadiativeTransferInterpolateField`(obsolete)- A failed experiment in which we evaluate the density at the midpoint of the ray segment in each cell to calculate the optical depth. To interpolate, we need to calculate the vertex interpolated density fields. Default: 0.
`SimpleQ`(external)- Ionizing photon luminosity of a “simple radiating source” that is independent of mass. In units of photons per second. Default: 1e50
`SimpleRampTime`(external)- Time to exponential ramp up the luminosity of a simple radiating source. In units of 1e6 years. Default: 0.1
`RadiativeTransferTraceSpectrum`(reserved)- reserved for future experimentation. Default: 0.
`RadiativeTransferTraceSpectrumTable`(reserved)- reserved for future experimentation. Default:
`spectrum_table.dat`

## Radiative Transfer (FLD) Parameters¶

`RadiativeTransferFLD`(external)Set to 2 to turn on the fld-based radiation solvers following Reynolds, Hayes, Paschos & Norman, 2009. Note that you also have to compile the source using

`make photon-yes`and a`make hypre-yes`. Note that if FLD is turned on, it will force`RadiativeCooling = 0`,`GadgetEquilibriumCooling = 0`, and`RadiationFieldType = 0`to prevent conflicts. Default: 0.*IMPORTANT*: Set`RadiativeTransfer = 0`to avoid conflicts with the ray tracing solver above. Set`RadiativeTransferOpticallyThinH2 = 0`to avoid conflicts with the built-in optically-thin H_2 dissociating field from the ray-tracing solver.`ImplicitProblem`(external)- Set to 1 to turn on the implicit FLD solver, or 3 to turn on the split FLD solver. Default: 0.
`RadHydroParamfile`(external)- Names the (possibly-different) input parameter file containing
solver options for the FLD-based solvers. These are described in
the relevant User Guides, located in
`doc/implicit_fld`and`doc/split_fld`. Default: NULL. `RadiativeTransferFLDCallOnLevel`(reserved)- The level in the static AMR hierarchy where the unigrid FLD solver should be called. Currently only works for 0 (the root grid). Default: 0.
`StarMakerEmissivityField`(external)- When compiled with the FLD radiation transfer >make emissivity-yes; make hypre-yes, setting this to 1 turns on the emissivity field to source the gray radiation. Default: 0
`uv_param`(external)- When using the FLD radiation transfer and StarMakerEmissivityFIeld = 1, this is the efficiency of mass to UV light ratio. Default: 0

## Radiative Transfer (FLD) Implicit Solver Parameters¶

These parameters should be placed within the file named inRadHydroParamfilein the main parameter file. All are described in detail in the User Guide indoc/implicit_fld.

`RadHydroESpectrum`(external)- Type of assumed radiation spectrum for radiation field, Default: 1.
-1 - monochromatic spectrum at frequency h nu_{HI} = 13.6 eV 0 - power law spectrum, (nu / nu_{HI} )^(-1.5) 1 - T = 1e5 blackbody spectrum

`RadHydroChemistry`(external)- Use of hydrogen chemistry in ionization model, set to 1 to turn on the hydrogen chemistry, 0 otherwise. Default: 1.
`RadHydroHFraction`(external)- Fraction of baryonic matter comprised of hydrogen. Default: 1.0.
`RadHydroModel`(external)- Determines which set of equations to use within the solver. Default: 1.
1 - chemistry-dependent model, with case-B hydrogen II recombination coefficient. 2 - chemistry-dependent model, with case-A hydrogen II recombination coefficient. 4 - chemistry-dependent model, with case-A hydrogen II recombination coefficient, but assumes an isothermal gas energy. 10 - no chemistry, instead uses a model of local thermodynamic equilibrium to couple radiation to gas energy.

`RadHydroMaxDt`(external)- maximum time step to use in the FLD solver. Default: 1e20 (no limit).
`RadHydroMinDt`(external)- minimum time step to use in the FLD solver. Default: 0.0 (no limit).
`RadHydroInitDt`(external)- initial time step to use in the FLD solver. Default: 1e20 (uses hydro time step).
`RadHydroDtNorm`(external)- type of p-norm to use in estimating time-accuracy for predicting next time step. Default: 2.0.
0 - use the max-norm. >0 - use the specified p-norm. <0 - illegal.

`RadHydroDtRadFac`(external)- Desired time accuracy tolerance for the radiation field. Default: 1e20 (unused).
`RadHydroDtGasFac`(external)- Desired time accuracy tolerance for the gas energy field. Default: 1e20 (unused).
`RadHydroDtChemFac`(external)- Desired time accuracy tolerance for the hydrogen I number density. Default: 1e20 (unused).
`RadiationScaling`(external)- Scaling factor for the radiation field, in case standard non-dimensionalization fails. Default: 1.0.
`EnergyCorrectionScaling`(external)- Scaling factor for the gas energy correction, in case standard non-dimensionalization fails. Default: 1.0.
`ChemistryScaling`(external)- Scaling factor for the hydrogen I number density, in case standard non-dimensionalization fails. Default: 1.0.
`RadiationBoundaryX0Faces`(external)- Boundary condition types to use on the x0 faces of the radiation field. Default: [0 0].
0 - Periodic. 1 - Dirichlet. 2 - Neumann.

`RadiationBoundaryX1Faces`(external)- Boundary condition types to use on the x1 faces of the radiation field. Default: [0 0].
`RadiationBoundaryX2Faces`(external)- Boundary condition types to use on the x2 faces of the radiation field. Default: [0 0].
`RadHydroLimiterType`(external)- Type of flux limiter to use in the FLD approximation. Default: 4.
0 - original Levermore-Pomraning limiter, à la Levermore & Pomraning, 1981 and Levermore, 1984. 1 - rational approximation to LP limiter. 2 - new approximation to LP limiter (to reduce floating-point cancellation error). 3 - no limiter. 4 - ZEUS limiter (limiter 2, but with no "effective albedo").

`RadHydroTheta`(external)- Time-discretization parameter to use, 0 gives explicit Euler, 1 gives implicit Euler, 0.5 gives trapezoidal. Default: 1.0.
`RadHydroAnalyticChem`(external)- Type of time approximation to use on gas energy and chemistry equations. Default: 1 (if possible for model).
0 - use a standard theta-method. 1 - use an implicit quasi-steady state (IQSS) approximation.

`RadHydroInitialGuess`(external)- Type of algorithm to use in computing the initial guess for the time-evolved solution. Default: 0.
0 - use the solution from the previous time step (safest). 1 - use explicit Euler with only spatially-local physics (heating & cooling). 2 - use explicit Euler with all physics. 5 - use an analytic predictor based on IQSS approximation of spatially-local physics.

`RadHydroNewtTolerance`(external)- Desired accuracy for solution to satisfy nonlinear residual (measured in the RMS norm). Default: 1e-6.
`RadHydroNewtIters`(external)- Allowed number of Inexact Newton iterations to achieve tolerance before returning with FAIL. Default: 20.
`RadHydroINConst`(external)- Inexact Newton constant used in specifying tolerances for inner linear solver. Default: 1e-8.
`RadHydroMaxMGIters`(external)- Allowed number of iterations for the inner linear solver (geometric multigrid). Default: 50.
`RadHydroMGRelaxType`(external)Relaxation method used by the multigrid solver. Default: 1.

:: 1 - Jacobi. 2 - Weighted Jacobi. 3 - Red/Black Gauss-Seidel (symmetric). 4 - Red/Black Gauss-Seidel (non-symmetric).

`RadHydroMGPreRelax`(external)- Number of pre-relaxation sweeps used by the multigrid solver. Default: 1.
`RadHydroMGPostRelax`(external)- Number of post-relaxation sweeps used by the multigrid solver. Default: 1.
`EnergyOpacityC0`,`EnergyOpacityC1`,`EnergyOpacityC2`,`EnergyOpacityC3`,`EnergyOpacityC4`(external)- Parameters used in defining the energy-mean opacity used with
`RadHydroModel`10. Default: [1 1 0 1 0]. `PlanckOpacityC0`,`PlanckOpacityC1`,`PlanckOpacityC2`,`PlanckOpacityC3`,`PlanckOpacityC4`(external)- Parameters used in defining the Planck-mean opacity used with
`RadHydroModel`10. Default: [1 1 0 1 0].

## Radiative Transfer (FLD) Split Solver Parameters¶

These parameters should be placed within the file named inRadHydroParamfilein the main parameter file. All are described in detail in the User Guide indoc/split_fld.

`RadHydroESpectrum`(external)- Type of assumed radiation spectrum for radiation field, Default: 1.
1 - T=1e5 blackbody spectrum 0 - power law spectrum, ( nu / nu_{HI})^(-1.5)` -1 - monochromatic spectrum at frequency h nu_{HI}= 13.6 eV -2 - monochromatic spectrum at frequency h nu_{HeI}= 24.6 eV -3 - monochromatic spectrum at frequency h nu_{HeII}= 54.4 eV

`RadHydroChemistry`(external)- Use of primordial chemistry in computing opacities and photo-heating/photo-ionization. Default: 1.
0 no chemistry 1 hydrogen chemistry 3 hydrogen and helium chemistry

`RadHydroHFraction`(external)- Fraction of baryonic matter comprised of hydrogen. Default: 1.0.
`RadHydroModel`(external)- Determines which set of equations to use within the solver. Default: 1.
1 - chemistry-dependent model, with case-B hydrogen II recombination coefficient. 4 - chemistry-dependent model, with case-A hydrogen II recombination coefficient, but assumes an isothermal gas energy. 10 - no chemistry, instead uses a model of local thermodynamic equilibrium to couple radiation to gas energy.

`RadHydroMaxDt`(external)- maximum time step to use in the FLD solver. Default: 1e20 (no limit).
`RadHydroMinDt`(external)- minimum time step to use in the FLD solver. Default: 0.0 (no limit).
`RadHydroInitDt`(external)- initial time step to use in the FLD solver. Default: 1e20 (uses hydro time step).
`RadHydroMaxSubcycles`(external)- desired number of FLD time steps per hydrodynamics time step (must be greater than or equal to 1). This is only recommended if the FLD solver is performing chemistry and heating internally, since it will only synchronize with the ionization state at each hydrodynamic time step. When using Enzo’s chemistry and cooling solvers this parameter should be set to 1 to avoid overly decoupling radiation and chemistry. Default: 1.0.
`RadHydroMaxChemSubcycles`(external)- desired number of chemistry time steps per FLD time step. This only applies if the FLD solver is performing chemistry and heating internally, instead of using Enzo’s built-in routines for this task. Default: 1.0.
`RadHydroDtNorm`(external)- type of p-norm to use in estimating time-accuracy for predicting next time step. Default: 2.0.
0 - use the max-norm. >0 - use the specified p-norm. <0 - illegal.

`RadHydroDtGrowth`(external)- Maximum growth factor in the FLD time step between successive iterations. Default: 1.1 (10% growth).
`RadHydroDtRadFac`(external)- Desired time accuracy tolerance for the radiation field. Default: 1e20 (unused).
`RadHydroDtGasFac`(external)- Desired time accuracy tolerance for the gas energy field. Only used if the FLD solver is performing heating internally. Default: 1e20 (unused).
`RadHydroDtChemFac`(external)- Desired time accuracy tolerance for the hydrogen I number density. Only used if the FLD solver is performing chemistry internally. Default: 1e20 (unused).
`RadiationScaling`(external)- Scaling factor for the radiation field, in case standard non-dimensionalization fails. Default: 1.0.
`EnergyCorrectionScaling`(external)- Scaling factor for the gas energy correction, in case standard non-dimensionalization fails. Default: 1.0.
`ChemistryScaling`(external)- Scaling factor for the hydrogen I number density, in case standard non-dimensionalization fails. Default: 1.0.
`AutomaticScaling`(external)- Enables an heuristic approach in the FLD solver to update the above scaling factors internally. Works well for reioniztaion calculations, but is not recommended for problems in which the optimal unit scaling factor is known a-priori. Default: 1.0.
`RadiationBoundaryX0Faces`(external)Boundary condition types to use on the x0 faces of the radiation field. Default: [0 0].

0 - Periodic. 1 - Dirichlet. 2 - Neumann.

`RadiationBoundaryX1Faces`(external)- Boundary condition types to use on the x1 faces of the radiation field. Default: [0 0].
`RadiationBoundaryX2Faces`(external)- Boundary condition types to use on the x2 faces of the radiation field. Default: [0 0].
`RadHydroTheta`(external)- Time-discretization parameter to use, 0 gives explicit Euler, 1 gives implicit Euler, 0.5 gives trapezoidal. Default: 1.0.
`RadHydroKrylovMethod`(external)Desired outer linear solver algorithm to use. Default: 1.

0 - Preconditioned Conjugate Gradient (PCG) 1 - Stabilized Bi-Conjugate Gradient (BiCGStab) 2 - Generalized Minimum Residual (GMRES)

`RadHydroSolTolerance`(external)- Desired accuracy for solution to satisfy linear residual (measured in the 2-norm). Default: 1e-8.
`RadHydroMaxMGIters`(external)- Allowed number of iterations for the inner linear solver (geometric multigrid). Default: 50.
`RadHydroMGRelaxType`(external)Relaxation method used by the multigrid solver. Default: 1.

0 - Jacobi 1 - Weighted Jacobi 2 - Red/Black Gauss-Seidel (symmetric) 3 - Red/Black Gauss-Seidel (non-symmetric)

`RadHydroMGPreRelax`(external)- Number of pre-relaxation sweeps used by the multigrid solver. Default: 1.
`RadHydroMGPostRelax`(external)- Number of post-relaxation sweeps used by the multigrid solver. Default: 1.
`EnergyOpacityC0`,`EnergyOpacityC1`,`EnergyOpacityC2`(external)- Parameters used in defining the energy-mean opacity used with RadHydroModel 10. Default: [1 1 0].