Tracer Particles

Section author: Axel Huebl

Tracer particles are like probe particles, but interact self-consistenly with the simulation. They are usually used to visualize representative particle trajectories of a larger distribution.

In PIConGPU each species can be a tracer particle species, which allows tracking fields along the particle trajectory.

Workflow

  • speciesDefinition.param:

Add the particle attribute particleId to your species to give each particle a unique id. The id is optional and only required if the particle should be tracked over time. Adding probeE creates a tracer species stores the interpolated electric field seen by the tracer particle.

using ParticleFlagsTracerElectrons = MakeSeq_t<
    particlePusher< particles::pusher::Boris >,
    shape< UsedParticleShape >,
    interpolation< UsedField2Particle >,
    currentSolver::Esirkepov<UsedParticleCurrentSolver>
>;

using TracerElectron = Particles<
    PMACC_CSTRING( "e_tracer" ),
    ParticleFlagsTracerElectrons,
    MakeSeq_t<
        position< position_pic >,
        momentum,
        weighting,
        particleId,
        probeE
    >
>;

and add it to VectorAllSpecies:

using VectorAllSpecies = MakeSeq_t<
    TracerElectron,
    // ...
>;

  • create tracer particles by either

    • speciesInitialization.param: initializing a low percentage of your initial density inside this species or

    • speciesInitialization.param: assigning the target (electron) species of an ion’s ionization routine to the tracer species or

    • speciesInitialization.param: moving some particles of an already initialized species to the tracer species (upcoming)

  • fileOutput.param: make sure the the tracer particles are part of FileOutputParticles

// either all via VectorAllSpecies or just select
using FileOutputParticles = MakeSeq_t< TracerElectron >;

The electron tracer species is equivalent to normal electrons, the initial density distribution can be configured in speciesInitialization.param.

Known Limitations

  • currently, only the electric field \(\vec E\) and the magnetic field \(\vec B\) can be recorded

  • we currently do not support time averaging