Composition tracking in phantom
This file documents how to track chemical abundances and mixing in phantom.
Composition tracking with fixed abundances
Tracking the chemical composition of the gas in phantom with fixed abundances is straightforward, since phantom is a Lagrangian code and the particle identifiers are preserved throughout the simulation.
In the non-MPI code without particle injection, the particles are always written to the dump files in the same order, so the particle id is simply the particle index in the dump file. In the MPI code, the particle id is stored in the ‘iorig’ array in the dump file.
Hence composition tracking can done as a post-processing step.
Writing a .comp file
In practice, the composition of the gas can be tracked by writing a .comp file either once for the entire simulation, or one per dump file. The .comp file is a simple ascii file with one row per particle, where the columns are the abundances. You should also give the first line a header with labels for each element:
# h1, he3, he4, c12, n14, o16, ne20, mg24, si28, s32, ar36, ca40, ti44, cr48, fe52, ni56
7.1119142075E-01 9.3180507858E-05 2.7341075111E-01 ...
7.1119141814E-01 9.3180815248E-05 2.7341075311E-01 ...
7.0179434509E-01 3.6580185766E-06 2.8264795926E-01 ...
...
If the phantom dump is called foo_0000, the .comp file should be called foo_0000.comp or simply foo.comp if the composition is constant on each particle.
This file is automatically read by splash and used to create extra columns in the visualisation.