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Re: [Opal] OPAL Dispersion Issues

Chronological Thread 
  • From: Christof Metzger-Kraus <christof.j.kraus AT>
  • To: Ryan Roussel <roussel AT>
  • Cc: opal AT
  • Subject: Re: [Opal] OPAL Dispersion Issues
  • Date: Mon, 16 Apr 2018 20:58:33 +0200
  • Authentication-results: localhost; dmarc=pass

Hi Ryan,

you can use the generated python file to create a
- a VTK file (which can be viewed with e. g. ParaView [] or VisIt []),
- a file that can be viewed with Firefox (the other browsers unfortunately don't work) or
- a projection of the lattice that can be plotted using gnuplot (and possibly other plotting tools as well).

I almost exclusively use the last option. Visualizations of the projection of the lattice combined with the reference trajectory helps a lot to debug the input files.


On Mon, Apr 16, 2018 at 8:47 PM, Ryan Roussel <roussel AT> wrote:
Thank you for your help. I ran your input file and the final distribution looks correct but the dispersion function calculated by OPAL-T is still incorrect. Its not a big issue as of right now, but its worth looking into. Do you have a recommended linux program for viewing the .vtk files created by the python code you mentioned?

On Sun, Apr 15, 2018 at 4:23 AM Christof Metzger-Kraus <christof.j.kraus AT> wrote:
Hi Ryan,

a first general remark when modeling fringe fields with a hard-edge model: you wont get any edge focusing and odd effects can occur (as with any element whose length is shorter than X * dt * beta and/or whose fields aren't smooth).

I don't think that the orientation of the second dipole is what you wanted it to be, see the plot in the attachment (file: 'lattice.png'. The data for this plot can be produced using the python file data/<inputfn> where in your case <inputfn> is CSR. The path of the reference particle in lab coordinates is in the file <inputfn>.stat (columns 18-20)).

I've corrected the lattice (although with hard-coded bend radius), see attachment (plot: 'lattice_corrected.png', input: '') and ran the simulation with 1e4 particles. The final particle distribution is also in the attachment ('CSR_end.dat.gz').


On Tue, Apr 10, 2018 at 11:43 PM, Ryan Roussel <roussel AT> wrote:
Hello all,
I am having difficulty obtaining correct physical results with OPAL-T involving dipole magnets. I have attached the relevant files.

The beamline is a single dogleg with two equal strength bend magnets. The issue I am seeing is in the calculation of the dispersion function and the final particle distribution. The dispersion contribution from the first dipole magnet is orders of magnitude lower than what it should be, while the second dipole contributes something reasonable. On the other hand the particle phase space distribution between the dipoles looks correct for a dispersion section but the final particle distribution after the second dipole looks incorrect as it is not symmetrical. 

Note: My graph x-axes have been cut off for some reason both labels are z(m).

Any help on this issue would be greatly appreciated.
Ryan Roussel

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