sddsanalyzebeam Twiss parameters
Posted: 18 Oct 2022, 09:02
Hello,
I am looking into how slice Twiss parameters evolve through a bunch compressor. I do this by slicing the beam and assigning each particle to a slice, then I use sddsanalyzebeam on each slice to get the slice beta and alpha along the bunch compressor. Typically I do this with a 2,000,000 macro-particles and have used 20-600 longitudinal slices. I've noticed the slice Twiss parameters were larger than the whole beam Twiss parameters from twiss_output. I assigned the particles to a single slice to check whether the sddsanalyzebeam Twiss match that of twiss_output, in case there problem was the number of slices, but I still found the Twiss parameters from sddsanalyzebeam were much larger than from twiss_output. I find that more slices I use the larger the slice parameters get. The corrected geometric emittance and sigma beam size from sddsanalyzebeam match the sigma output file.
I have attached plots of beta, ecx and Sx along the bunch compressor using *twiss and *sigma output files, and using the equivalent single 'slice' beta, ecx and Sx from sddsanalyzebeam at each watch file. Also attached the *ele and *lte and initial bunch.
Do you understand why the beta from *twiss output and sddsanalyzebeam are different here?
I am looking into how slice Twiss parameters evolve through a bunch compressor. I do this by slicing the beam and assigning each particle to a slice, then I use sddsanalyzebeam on each slice to get the slice beta and alpha along the bunch compressor. Typically I do this with a 2,000,000 macro-particles and have used 20-600 longitudinal slices. I've noticed the slice Twiss parameters were larger than the whole beam Twiss parameters from twiss_output. I assigned the particles to a single slice to check whether the sddsanalyzebeam Twiss match that of twiss_output, in case there problem was the number of slices, but I still found the Twiss parameters from sddsanalyzebeam were much larger than from twiss_output. I find that more slices I use the larger the slice parameters get. The corrected geometric emittance and sigma beam size from sddsanalyzebeam match the sigma output file.
I have attached plots of beta, ecx and Sx along the bunch compressor using *twiss and *sigma output files, and using the equivalent single 'slice' beta, ecx and Sx from sddsanalyzebeam at each watch file. Also attached the *ele and *lte and initial bunch.
Do you understand why the beta from *twiss output and sddsanalyzebeam are different here?