Initial conditions#

A default parameter file for each model can be created with:

struphy params MODEL

Assume a model features the fluid species mhd with three variables n3 (density as 3-form), u2 (velocity as 2-form) amd p0 (pressure as 0-form). In the parameter file, the section for setting the corresponding initial conditions reads as follows:

fluid:
    mhd:
        background:
            n3:
                BACKGR_NAME_1:
                    BACKGR_PARAMS_1
                BACKGR_NAME_2:
                    BACKGR_PARAMS_2
            u2:
                BACKGR_NAME_1:
                    BACKGR_PARAMS_1
                BACKGR_NAME_2:
                    BACKGR_PARAMS_2
            p0:
                BACKGR_NAME_1:
                    BACKGR_PARAMS_1
                BACKGR_NAME_2:
                    BACKGR_PARAMS_2
        perturbation:
            n3:
                PERT_NAME_1:
                    PERT_PARAMS_1
                PERT_NAME_2:
                    PERT_PARAMS_2
            u2:
                PERT_NAME_1:
                    PERT_PARAMS_1
                PERT_NAME_2:
                    PERT_PARAMS_2
            p0:
                PERT_NAME_1:
                    PERT_PARAMS_1
                PERT_NAME_2:
                    PERT_PARAMS_2

Available BACKR_NAMES along with their available BACKGR_PARAMS are listed in Available fluid equilibria. Available PERT_NAMES along with their available PERT_PARAMS are listed in Perturbations. Note the following:

  • If a variable (e.g. p0) is removed from the dictionary it will be initialized as zero.

  • The initial condition of each appearing variable is the sum of all backgrounds and all perturbations listed under its name.

  • If the same (!) BACKR_NAME appears multiple times under one varaible one must append _1, _2 to differentiate them in the code.

  • One or both of the sections background and perturbation can be removed.

A valid example of the above structure reads as follows:

fluid:
    mhd:
        perturbation:
            n3:
                ModesCos:
                    given_in_basis: '0'
                    ls: [0, 1, 2, 4]

Here, only the variable n3 is initialized with a pertubration composed of cosines with the mode numbers 0, 1, 2, and 4 in the first direction, given as a 0-form.

A typical example of a kinetic initialization looks as follows:

background : # at least one background is mandatory for kinetic species
    Maxwellian3D_1 :
        n  : 0.5
        u1 : 3.0
    Maxwellian3D_2 :
        n  : 0.5
        u1 : -3.0
perturbation :
    n :
        TorusModesCos :
            given_in_basis : '0'
            ms : [1, 3] # two poloidal modes for the density

  • Available kinetic backgrounds can be found in kinetic_backgrounds

  • Available perturbations can be found in Perturbations

For kinetic species, the background is mandatory. The moments of maxwellians can be initialized with fluid equilibrium quantities. For this, the value of the respective moment must be set to fluid_background. For example:

background :
    Maxwellian3D :
        n  : 0.05
        u1 : fluid_background
        u2 : 2.5
        vth1 : fluid_background

In the above case, the first component of the mean- and thermal velocity are initialized with fluid background quantities. The fluid_background specified in the parameter file is then taken for initialization of the respective Maxwellian moment.

The moments of maxwellians can be also initialized with functions defined in moment_functions. In this case the value of the respective moment must be a dictionary with the function parameters, for instance:

background :
    Maxwellian3D :
        n  :
            ITPA_density :
                given_in_basis : '0'
                n0 : 0.00720655
                c : [0.491230, 0.298228, 0.198739, 0.521298]

Multiple background and perturbation types can be given as in the above fluid case.

Check out the Maxwellian3D source code for more details.

Check out this unit test for more information.

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