Dear PIConGPU Users,


Heiko Burau found a bug today with the calculation of a derived
"particle energy density" in our file output.

In case you enable a so called "FieldTmp output" in "fileOutput.param",
which maps particles to cell-wise scalar quantities, the
"EnergyDensityOperation" calculates wrong values. In ADIOS and HDF5
files you see those named as "fields/<species>_energyDensity".

As a workaround, just use the "EnergyOperation"
(fields/<species>_particleEnergy") instead, which is the cell-wise total
kinetic particle energy of a species, and divide the resulting field by
cell volume.

- CreateEnergyOperation: sum of kinetic particle energy per cell with
                         respect to shape
- CreateEnergyDensityOperation: average kinetic particle energy per
                                cell times the particle density
    note: this is the same as the sum of kinetic particle energy
          divided by a constant for the cell volume


Note that both operations are the same but for a constant (cell volume).

Thanks to Heiko for spotting & fixing it!


Best,
Axel

P.S.: Relevant FieldTmp operations now also work for massless particles
in `dev`. Yeay!

P.P.S.: We fix the "EnergyDensity" in dev [1] via #1750 and consider to
deprecate the less physically relevant "Energy" in the future, so people
do not accidentally calculate the same quantity twice.

[1] https://github.com/ComputationalRadiationPhysics/picongpu/pull/1750
--

Axel Huebl
Phone +49 351 260 3582
https://www.hzdr.de/crp
Computational Radiation Physics
Laser Particle Acceleration Division
Helmholtz-Zentrum Dresden - Rossendorf e.V.

Bautzner Landstrasse 400, 01328 Dresden
POB 510119, D-01314 Dresden
Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey
          Prof. Dr.Dr.h.c. P. Joehnk
VR 1693 beim Amtsgericht Dresden