(gocode)¶

GO+CODE refers to the coupled fluid-kinetic framework consisting of the fluid code GO [1] [2], which is used to solve for the toroidal electric field evolution, and the kinetic solver CODE [3] [4] [5], which solves the spatially homogeneous Fokker–Planck equation for electrons. The framework calculates the electron distribution function with one spatial dimension and two momentum dimensions.

[1]	Smith et al., 2006 “Runaway electrons and the evolution of the plasma current in tokamak disruptions”. Physics of Plasmas 13, 102502 doi:10.1063/1.2358110.

[2]	Papp et al., 2013 “The effect of ITER-like wall on runaway electron generation in JET”. Nuclear Fusion 53 (12), 123017 doi:10.1088/0029-5515/53/12/123017.

[3]	Landreman et al., 2014 “Numerical calculation of the runaway electron distribution function and associated synchrotron emission”. Computer Physics Communications 185 (3), 847-855 doi:10.1016/j.cpc.2013.12.004.

[4]	Stahl et al., 2016 “Kinetic modelling of runaway electrons in dynamic scenarios”, Nuclear Fusion 56 (11), 112009 doi:10.1088/0029-5515/56/11/112009.

[5]	http://ft.nephy.chalmers.se/retools/code/

Summary of options¶

Option	Description
`gocode interptype`	Interpolation method to use when interpolating in the distribution function.
`gocode name`	Name of file containing distribution function.
`gocode time`	Index of distribution function time slice to use for simulation.

Example configuration¶

The following example shows how to load a GO+CODE distribution function and use the final time step of the simulation:

distribution_function = ourDistribution;

@DistributionFunction ourDistribution (gocode) {
    name    = "/path/to/gocode/distribution.mat";
    time    = -1;         # -1 = last time step
}

File layout¶

In contrast to pure CODE and LUKE distribution functions, a GO+CODE cannot be directly saved to a MAT file. Instead, the output must be converted into a special format, consisting of two levels of structs.

In the root path of the file, the following variables must be set:

Variable	Description
`r`	Radial grid on which the distribution is defined (corresponding to the dimensionful `r` variable in GO).
`t`	List of times at which the distribution is available.
`nt`	Number of elements in `t`.
`tX`	Struct, containing the distribution functions at time index `X` (i.e. `X` is an integer, ranging from `0` to `nt-1`.

Each struct tX (t0, t1 etc.) in turn contains several variables rY, with Y an integer ranging from 0 to nr-1, where nr is the number of elements in r. Finally, each rY contains a momentum distribution which has the format described on the page for the CODE distribution function: (code). We repeat it here for convenience:

Variable	Description
`delta`	Normalization of momentum. Defined such that \(p = y\delta\), where \(p\) is momentum normalized to the electron rest mass \(m_e c\).
`f`	Distribution function matrix. Must be of size \(n_t\times n_y n_\xi\).
`Nxi`	Number of Legendre modes used in the CODE calculation to resolve the angular dependence.
`nref`	Reference density (used for un-normalising the distribution function).
`Tref`	Reference temperature (used for un-normalising the distribution function).
`y`	Momentum grid, given in thermal units.

All options¶

interptype¶

Default value:	`cspline`
Allowed values:	`akima`, `akima_periodic`, `cspline`, `cspline_periodic`, `linear`, `polynomial`, `steffen`

Determines which interpolation method to use for interpolating in the momentum dimension.

name¶

Default value:	None
Allowed values:	String

Specifies the name of the file containing the GO+CODE distribution function to load.

time¶

Default value:	`-1` (last timestep)
Allowed values:	Any integer with absolute value less than the number of time points in the distribution function

Selects the index of the time step to take the distribution function from. Negative indices count from the back of the array, so that -1 corresponds to the last timestep, -2 to the next-to-last etc.