Probe block

This block contains information about particle probes used for output. See EPOCH input deck for more information on the input deck.

Sometimes it is useful to consider all the properties of particle which pass through a point/line/plane (depending on dimension) in the simulation. To allow this, it is possible to specify one or more Particle Probe blocks in the input deck. These record copies of all particles which cross a point/line/plane in a given direction which meet minimum and maximum kinetic energy criteria and output the particle properties into the normal output files. Each output file only contains properties for particles which have passed the probe since the previous output, and not all particles which have passed the probe since the start of the simulation.

Particle probes record the positions, momenta and weight of all particles passing through the plane. If the code is compiled with -DPARTICLE_ID or -DPARTICLE_ID4, the code also outputs the ID of passing particles. If the code is compiled with -DPROBE_TIME, the time at which the particle touches the probe surface is also output.

To use particle probes, the code must not have been compiled with the -DNO_PARTICLE_PROBES compiler option. This is a fairly heavyweight diagnostic since each particle position must be tested from within the particle push. The code will run faster if it is not compiled in.

The probe is specified in terms of a point in the plane and the normal vector to the plane which is to be monitored. Particles are only recorded if they cross the plane in the direction given by the normal vector. If you want to record particles travelling in both directions then use two particle probes, one with an opposite signed normal vector to the other.

begin:probe
   name = electron_back_probe

   point = (50.0e-6, -50.0e-6)
   normal = (1.0, 0.0)

   ek_min = 0.0
   ek_max = -1.0
   include_species : s1

   dumpmask = always
end:probe

• name - The name that the probe should have in output dumps. Output variables are then named this as a prefix. For example, the block shown above will result in the name electron_back_probe_px for the x momentum. The particle positions would just be called electron_back_probe.
• point - An arbitrary point in the plane of the probe.
• normal - A vector normal to the plane of the probe, in the direction of crossings you wish to monitor.
• include_species - The species to which this probe should be applied. To probe several species, use several probe blocks in the input deck. “probe_species” is accepted as a synonym.
• ek_min - The minimum kinetic energy of particles to store information about. Set to 0 for no minimum kinetic energy.
• ek_max - The maximum kinetic energy of particles to store information about. Set to -1 for no maximum kinetic energy.
• dumpmask - The dump code for this particle probe. This is the same as that for the main output controls in input.deck. Note that the code has to store copies of particles which pass through the probe until a dump occurs. This means that the code’s memory requirements can increase drastically if this code only dumps probe information infrequently. If this is set to never then the code effectively never uses the probe.