Visualization issue

[sweber04]

Dear All,

I prepared an electron beam and studying its evolution in vacuum before coupling with other beamline elements. The electron has to travel 2 meters in vacuum. I used the following command to see the beam at 2 meter:

# add beam diagnostics
monitor = elements.BeamMonitor("monitor", backend="h5")

sim.lattice.extend([ monitor,
                     elements.Drift(name="drift", ds=2.0),
                     monitor])

# run simulation
sim.track_particles()

For visualization, I used the attached python file. I noticed that the figure always giving me the initial electron beam and not after 2 meters.

Any suggestions will be highly appreciated.

Thank you.

visualize.txt

[ax3l]

hi @sweber04,

Thanks for your question and the script demonstrating it.

When you use the same monitor name multiple times in a beamline, we will store the beam according to its "simulation step" in that monitor file. In other words, the line above will have a monitor output with two steps.

Looking at your script:

beam_series = io.Series("diags/openPMD/monitor.h5", io.Access.read_only)
beam_steps = list(beam_series.iterations)

if I print beam_steps I get:

[1, 3]

Thus, the next lines of your script visualize the first (initial output) and not the last one:

# ...
step = 1
beam_at_step = beam_series.iterations[step].particles["beam"].to_df()

If you want the final step, do:

step_final = beam_steps[-1]
beam_final = beam_series.iterations[step_final].particles["beam"].to_df()

[sweber04]

Hi @ax3l,

Thank you. I will do it again and will come back to you if there is any other issue.

Cheers,
Stefan