Dear PIConGPU-Users,

# Scope

In case you are using the alternative current solver "ZigZag" in
PIConGPU, which is *not* the default setting but an *alternative* solver
that is optimized for speed, this bug affects you.

The bug affects all releases, both 3D3V and 2D3V and the development
branch `dev`.


# Problem

The implementation of the *alternative* current depositions scheme
"ZigZag" is broken in terms of charge conservation.

Simulations using "ZigZag" will result in unphysical/undefined results.


# Mitigation

Please stay with the *default* implementation "Esirkepov". A working
alternative if you are only using 2nd order particle schemes is "VillaBune".


# Verification

You can control your setups by looking for the line in
  species.param

of your simulation "case"'s include/simulation_defines/param/
  http://git.io/vnoOz


# Following Updates

At the time of writing, we did not yet roll out a testable fix for "ZigZag".

We will provide a patch as soon as we are sure the results are physical,
you can follow the issue on GitHub to stay tuned.

  https://github.com/ComputationalRadiationPhysics/picongpu/issues/1128


Again as a reminder: if you stay with the default current implementation
which is "Esirkepov" all is save and sound.

Please excuse the inconveniences.

Best regards,
Axel Huebl
--

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