particleMerger.rst

Particle Merger

Merges macro particles that are close in phase space to reduce computational load.

.param file

In particleMerging.param <usage-params-plugins> is currently one compile-time parameter:

Compile-Time Option	Description
MAX_VORONOI_CELLS	Maximum number of active Voronoi cells per supercell. If the number of active Voronoi cells reaches this limit merging events are dropped.

.cfg file

PIConGPU command line option	Description
--<species>_merger.period	The ouput periodicity of the plugin. A value of 100 would mean an output at simulation time step 0, 100, 200, ....
--<species>_merger.minParticlesToMerge	minimal number of macroparticles needed to merge the macroparticle collection into a single macroparticle.
--<species>_merger.posSpreadThreshold	Below this threshold of spread in position macroparticles can be merged [unit: cell edge length].
--<species>_merger.absMomSpreadThreshold	Below this absolute threshold of spread in momentum macroparticles can be merged [unit: me− ⋅ c]. Disabled for -1 (default).
--<species>_merger.relMomSpreadThreshold	Below this relative (to mean momentum) threshold of spread in momentum macroparticles can be merged [unit: none]. Disabled for -1 (default).
--<species>_merger.minMeanEnergy	minimal mean kinetic energy needed to merge the macroparticle collection into a single macroparticle [unit: keV].

Notes

• absMomSpreadThreshold and relMomSpreadThreshold are mutually exclusive
• absMomSpreadThreshold is always given in [electron mass * speed of light]!

Memory Complexity

Accelerator

no extra allocations, but requires an extra particle attribute per species, voronoiCellId.

Host

no extra allocations.

Reference

The particle merger implements a macro particle merging algorithm based on:

Luu, P. T., Tueckmantel, T., & Pukhov, A. (2016). Voronoi particle merging algorithm for PIC codes. Computer Physics Communications, 202, 165-174.