The OPAL Discussion Forum

["Dragos Constantin" <dragos.constantin AT gmail.com>]

Hi Andreas,
:) I was trying to do something similar. Unfortunately nothing worked.

My approach was to set a collimator in zero or at a small positive z
coordinate with a very small aperture and generate the macroparticles after
the collimator. By the way, setting the aperture of a collimator to zero will
generate an error at runtime. Also not specifying the length of a collimator
will not include the collimator in the beamline. My approach did not work, as
an emitted beam will not shift the beam emission position from zero. The
ZSTART attribute of the TRACK command has no effect on the reference particle
starting point. The reference particle will always start at zero regardless
the ZSTART value. Also, the SORCE command has no effect on the beam. I am not
sure of its purpose.

Your proposed approch did not work either. ECOL and RCOL are not included in
the simulation if their Z<0.

The only think left to try is to switch from an emitted distribution to an
injected one. It is not clear if ZSTART attribute will work in that case
either.

I am using OPAL v 2.2.1 (I have compiled the sources in this case) and the
binary OPAL v 2022.1.0 which I have downloaded form PSI AMAS website. Both
versions run on Linux.

I am not sure what is the easiest: enable collimators at negative axial
positions or debug the ZSTART attribute.

I'll let you know if ZSTART approach works with an injected beam.

Thanks,
Dragos