I'm trying to benchmark the pyORBIT3 gap model against that of TraceWin for the ESS SCL cavities. In the process, I've found a behaviour in TraceWin that we do not fully understand.
The image below shows the energy gain of particles at a transverse offset (x) compared to that of the particle on axis, as a function of the phase set for the field map, so W(x)-W(x=0 mm) as function of phi. While all other properties, for example angular kick (see tracewin_transverse_xpr.png), show a periodicity with phase, the energy gain seems to depend on something more like the square of cos(phi). The difference is overall very small but seems systematic.
- tracewin_transverse_dE.png (68.7 KiB) Viewed 5 times
The plot is obtained using the attached project:
- Distribution contains a randomly chosen Gaussian distribution + the first ten particles at x = 0 cm .. 10 mm, with all else 0 / nominal.
- Run the project changing the phase parameter of the FIELD_MAP. I'm running from the command line with tracemac64 ("Ele[1][3]=${i}"), but get the same results when running from the GUI.
- Take the first 10 particles from the output distribution and plot the difference of the energy of the particle at 10 mm minus that of the particle at 0 mm, as function of phase.
I'm running Tracewin 2.24.1.1 on an M2 Mac.
Thanks,
Daniel
