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Current Distribution
Posted: 13 Jul 2010, 13:28
by tennant
Hello,
Was reading Michael's PRST-AB on modeling microbunch instability and see lots of figures showing the current distribution (current vs time). Is this column generated in a particular output file or did you compute this using sdds tools?
Thanks,
chris
Re: Current Distribution
Posted: 13 Jul 2010, 21:43
by michael_borland
Chris,
I think you are referring to the output from CSRCSBEND. Use the OUTPUT_FILE parameter to specify a filename, and you should see what you are looking for.
--Michael
Re: Current Distribution
Posted: 14 Jul 2010, 08:24
by tennant
Michael,
Okay, thanks - it's the linear density. I see it now.
As I was reading through your paper I'm able to follow until you describe the numerous steps you take to obtain the gain curve (p. 5). In particular, I am not familiar with NAFF. Any suggestions/help/examples you could provide to understand better what is involved with this analysis?
Thanks,
chris
Re: Current Distribution
Posted: 14 Jul 2010, 09:21
by tennant
I should've looked at the SDDS Toolkit manual first! I see a sddsnaff now. I don't suppose you have an example for all the steps you discuss in your paper (e.g. make histogram, remove ends, polynomial fit, naff, etc...)?
Re: Current Distribution
Posted: 14 Jul 2010, 09:30
by michael_borland
Chris,
I don't have the link for the original paper, but this paper describes the algorithm (see page 5) and gives references
cdsweb.cern.ch/record/301630/files/p183.pdf
The attached script is the one I used to perform the analysis. It expects a set of histogram files (produced with the HISTOGRAM element) with the run parameters encoded in the file rootname. See the comments for explanations.
--Michael
Re: Current Distribution
Posted: 17 Nov 2014, 16:15
by headdoggy64
Hello,
Just wondering if this procedure is valid.
1)
Code: Select all
elegant2genesis bunch.out test.out -slices=200 -totalCharge=20e-12
2)
Code: Select all
sddsfft test.out test.tmp -columns=s,current
to get FFT of current
3)
Code: Select all
sddsfft test.out test2.tmp -columns=s,gamma
to obtain FFT of modulations in energy
Also, why does the current after sddsfft still have the units of Amp?
Thanks,
Alex.
Re: Current Distribution
Posted: 18 Nov 2014, 19:52
by michael_borland
Alex,
What you are doing is valid, at least mathematically, since the spacing of the s points is uniform.
I'm not sure why it is surprising that the FFT of I(s) has units of Amps. Unlike a continuous Fourier transform, the discrete Fourier transform is just a sum of the samples times some exponentials. There's no change of units.
--Michael